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  • 151. Leyland, M. J.
    et al.
    Beurskens, M. N. A.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Giroud, C.
    Saarelma, S.
    Snyder, P. B.
    Flanagan, J.
    Jachmich, S.
    Kempenaars, M.
    Lomas, P.
    Maddison, G.
    Neu, R.
    Nunes, I.
    Gibson, K. J.
    The H-mode pedestal structure and its role on confinement in JET with a carbon and metal wall2015Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 55, nr 1, artikel-id 013019Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present the pedestal structure, as determined from the high-resolution Thomson scattering measurements, for a database of low and high triangularity (δ ≈ 0.22-0.39) 2.5 MA, type I ELMy H-mode JET plasmas after the installation of the new ITER-like wall (JET-ILW). The database explores the effect of increasing deuterium fuelling and nitrogen seeding with a view to explain the observed changes in performance (edge and global). The low triangularity JET-ILW plasmas show no significant change in performance and pedestal structure with increasing gas dosing. These results are in good agreement with EPED1 predictions. At high triangularity, for pure deuterium fuelled JET-ILW plasmas, there is a 20-30% reduction in global performance and pressure pedestal height in comparison to JET-C plasmas. This reduction in performance is primarily due to a degradation of the temperature pedestal height. The global performance and pressure pedestal height of JET-ILW plasmas can be partially recovered to that of JET-C plasmas with additional nitrogen seeding (Giroud et al 2013 Nucl. Fusion 53 113025). This observed improvement in performance is predominately due to a significant increase in density pedestal height as well as a small increase in the temperature pedestal height. A key result with increasing deuterium fuelling for JET-ILW plasmas is there is no improvement in pressure pedestal height however the pedestal still widens which is inconsistent with the Δ = 0.076√βpol,ped scaling. Furthermore, a key result with increasing nitrogen seeding is the pressure pedestal widening is due to an increase in the temperature pedestal width whilst the density pedestal shows no clear trend. The comparison of EPED1 predictions with the measurements at high triangularity is complex as, for example, for pure deuterium fuelled plasmas there is very good agreement for the pedestal height but not the width. In addition, current EPED1 runs under-predict the pedestal height and width at high nitrogen seeding for JET-ILW plasmas however further work is required to determine the significance of these deviations. Understanding these deviations is essential as provides an insight to the physical mechanisms governing the pedestal structure and edge performance.

  • 152. Leyland, M. J.
    et al.
    Beurskens, M. N. A.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Osborne, T.
    Snyder, P. B.
    Giroud, C.
    Jachmich, S.
    Maddison, G.
    Lomas, P.
    von Thun, C. Perez
    Saarelma, S.
    Saibene, G.
    Gibson, K. J.
    Pedestal study across a deuterium fuelling scan for high delta ELMy H-mode plasmas on JET with the carbon wall2013Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 53, nr 8, s. 083028-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present the results from a new fuelling scan database consisting of 14 high triangularity (delta similar to 0.41), type I ELMy H-mode JET plasmas. As the fuelling level is increased from low, (Gamma(D) similar to 0.2 x 10(22) el s(-1), n(e),(ped)/n(GW) = 0.7), to high dosing (Gamma(D) similar to 2.6 x 10(22) el s(-1), n(e, ped)/n(GW) = 1.0) the variation in ELM behaviour is consistent with a transition from 'pure type I' to 'mixed type I/II' ELMs (Saibene et al 2002 Plasma Phys. Control. Fusion 44 1769). However, the pulses in this new database are better diagnosed in comparison to previous studies and most notable have pedestal measurements provided by the JET high resolution Thomson scattering (HRTS) system. We continue by presenting, for the first time, the role of pedestal structure, as quantified by a least squares mtanh fit to the HRTS profiles, on the performance across the fuelling scan. A key result is that the pedestal width narrows and peak pressure gradient increases during the ELM cycle for low fuelling plasmas, whereas at high fuelling the pedestal width and peak pressure gradient saturates towards the latter half of the ELM cycle. An ideal MHD stability analysis shows that both low and high fuelling plasmas move from stable to unstable approaching the ideal ballooning limit of the finite peeling-ballooning stability boundary. Comparison to EPED predictions show on average good agreement with experimental measurements for both pedestal height and width however when presented as a function of pedestal density, experiment and model show opposing trends. The measured pre-ELM pressure pedestal height increases by similar to 20% whereas EPED predicts a decrease of 25% from low to high fuelling. Similarly the measured pressure pedestal width widens by similar to 55%, in poloidal flux space, whereas EPED predicts a decrease of 20% from low to high fuelling. We give two possible explanations for the disagreement. First, it may be that EPED under predicts the critical density, which marks the transition from kink-peeling to ballooning-limited plasmas. Second, the stronger broadening of the experimental pedestal width than predicted by EPED is an indication that other transport related processes contribute to defining the pedestal width such as enhanced inter-ELM transport as observed at high fuelling, for mixed type I/II ELMy pulses.

  • 153. Liang, Y.
    et al.
    Lomas, P.
    Nunes, I.
    Gryaznevich, M.
    Beurskens, M. N. A.
    Brezinsek, S.
    Coenen, J. W.
    Denner, P.
    Eich, Th
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Gerasimov, S.
    Harting, D.
    Jachmich, S.
    Meigs, A.
    Pearson, J.
    Rack, M.
    Saarelma, S.
    Sieglin, B.
    Yang, Y.
    Zeng, L.
    Mitigation of type-I ELMs with n=2 fields on JET with ITER-like wall2013Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 53, nr 7, s. 073036-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Mitigation of type-I edge-localized modes (ELMs) was observed with the application of an n = 2 field in H-mode plasmas on the JET tokamak with the ITER-like wall (ILW). Several new findings with the ILW were identified and contrasted to the previous carbon wall (C-wall) results for comparable conditions. Previous results for high collisionality plasmas (nu*(e,ped) similar to 2.0) with the C-wall saw little or no influence of either n = 1 or n = 2 fields on the ELMs. However, recent observations with the ILW show large type-I ELMs with a frequency of similar to 45 Hz were replaced by high-frequency (similar to 200 Hz) small ELMs during the application of the n = 2 field. With the ILW, splitting of the outer strike point was observed for the first time during the strong mitigation of the type-I ELMs. The maximal surface temperature (T-max) on the outer divertor plate reached a stationary state and has only small variations of a few degrees due to the small mitigated ELMs. In moderate collisionality (nu*(e,ped) similar to 0.8) H-mode plasmas, similar to previous results with the C-wall, both an increase in the ELM frequency and density pump-out were observed during the application of the n = 2 field. There are two new observations compared with the C-wall results. Firstly, the effect of ELM mitigation with the n = 2 field was seen to saturate so that the ELM frequency did not further increase above a certain level of n = 2 magnetic perturbations. Secondly splitting of the outer strike point during the ELM crash was seen, resulting in mitigation of the maximal ELM peak heat fluxes on the divertor region.

  • 154. Litaudon, X.
    et al.
    Becoulet, A.
    Crisanti, F.
    Wolf, R. C.
    Hellsten, T.
    Rachlew, Elisabeth
    KTH, Tidigare Institutioner                               , Fysik.
    et al,
    Progress towards steady-state operation and real-time control of internal transport barriers in JET2003Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 43, nr 7, s. 565-572Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In JET, advanced tokamak research mainly focuses on plasmas with internal transport barriers (ITBs) that are strongly influenced by the current density profile. A previously developed optimized shear regime with low magnetic shear in the plasma centre has been extended to deeply negative magnetic shear configurations. High fusion performance with wide ITBs has been obtained transiently with negative central magnetic shear configuration: H-IPB98(y,H-2) similar to 1.9, beta(N) = 2.4 at I-p = 2.5 MA. At somewhat reduced performance, electron and ion ITBs have been sustained in full current drive operation with 1 MA of bootstrap current: H-IPB98(y,H-2) similar to 1, beta(N) = 1.7 at I-p = 2.0 MA. The ITBs were maintained for up to 11 s for the latter case. This duration, much larger than the energy confinement time (37 times larger), is already approaching a current resistive time. New real-time measurements and feedback control algorithms have been developed and implemented in JET for successfully controlling the ITB dynamics and the current density profile in the highly non-inductive current regime.

  • 155. Litaudon, X.
    et al.
    Bizarro, J. P. S.
    Challis, C. D.
    Crisanti, F.
    De Vries, P. C.
    Lomas, P.
    Rimini, F. G.
    Tala, T. J. J.
    Akers, R.
    Andrew, Y.
    Arnoux, G.
    Artaud, J. F.
    Baranov, Yu F.
    Beurskens, M.
    Brix, M.
    Cesario, R.
    De La Luna, E.
    Fundamenski, W.
    Giroud, C.
    Hawkes, N. C.
    Huber, A.
    Joffrin, E.
    Pitts, R. A.
    Rachlew, Elisabeth
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Atom- och molekylfysik.
    Reyes-Cortes, S. D. A.
    Sharapov, S. E.
    Zastrow, K. D.
    Zimmermann, O.
    Jet Efda contributors,
    Prospects for steady-state scenarios on JET2007Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 47, nr 9, s. 1285-1292Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the 2006 experimental campaign, progress has been made on JET to operate non-inductive scenarios at higher applied powers (31 MW) and density (n(1) similar to 4 x 10(19) m(-3)), with ITER-relevant safety factor (q(95) similar to 5) and plasma shaping, taking advantage of the new divertor capabilities. The extrapolation of the performance using transport modelling benchmarked on the experimental database indicates that the foreseen power upgrade (similar to 45 MW) will allow the development of non-inductive scenarios where the bootstrap current is maximized together with the fusion yield and not, as in present-day experiments, at its expense. The tools for the long-term JET programme are the new ITER-like ICRH antenna (similar to 15 MW), an upgrade of the NB power (35 MW/20s or 17.5 MW/40s), a new ITER-like first wall, a new pellet injector for edge localized mode control together with improved diagnostic and control capability. Operation with the new wall will set new constraints on non-inductive scenarios that are already addressed experimentally and in the modelling. The fusion performance and driven current that could be reached at high density and power have been estimated using either 0D or 1-1/2D validated transport models. In the high power case (45 MW), the calculations indicate the potential for the operational space of the non-inductive regime to be extended in terms of current (similar to 2.5 MA) and density (n(1) > 5 x 10(19) m(-3)), with high beta(N) (beta(N) > 3.0) and a fraction of the bootstrap current within 60-70% at high toroidal field (similar to 3.5 T).

  • 156.
    Litnovsky, A.
    et al.
    Forschungszentrum Julich, Inst Energie & Klimaforsch Plasmaphys, D-52425 Julich, Germany..
    Voitsenya, V. S.
    NSC Kharkov Inst Phys & Technol, IPP, UA-61008 Kharkov, Ukraine..
    Reichle, R.
    ITER Org, Route Vinon Sur Verdon,CS 90 046, F-13067 Saint Paul Lez Durance, France..
    Walsh, M.
    ITER Org, Route Vinon Sur Verdon,CS 90 046, F-13067 Saint Paul Lez Durance, France..
    Razdobarin, A.
    Ioffe Physictech Inst, Polytech Skaya 26, St Petersburg 194021, Russia..
    Dmitriev, A.
    Ioffe Physictech Inst, Polytech Skaya 26, St Petersburg 194021, Russia..
    Babinov, N.
    Ioffe Physictech Inst, Polytech Skaya 26, St Petersburg 194021, Russia..
    Marot, L.
    Univ Basel, Klingelbergstr 82, CH-4056 Basel, Switzerland..
    Moser, L.
    Univ Basel, Klingelbergstr 82, CH-4056 Basel, Switzerland..
    Yan, R.
    Chinese Acad Sci, Inst Plasma Phys, Hefei 230031, Anhui, Peoples R China..
    Rubel, Marek
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Widdowson, A.
    CCFE EURATOM Fus Assoc, Culham Sci Ctr, Abingdon OX14 3DB, Oxon, England..
    Moon, Sunwoo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Oh, S. G.
    Ajou Univ, Suwon 16499, South Korea..
    An, Y.
    Natl Fus Res Inst, Daejeon 34133, South Korea..
    Shigin, P.
    ITER Org, Route Vinon Sur Verdon,CS 90 046, F-13067 Saint Paul Lez Durance, France..
    Orlovskiy, I
    Natl Res Ctr Kurchatov Inst, Moscow 123098, Russia..
    Vukolov, K. Yu
    Natl Res Ctr Kurchatov Inst, Moscow 123098, Russia..
    Andreenko, E.
    Natl Res Ctr Kurchatov Inst, Moscow 123098, Russia..
    Krimmer, A.
    Forschungszentrum Julich, Inst Energie & Klimaforsch Plasmaphys, D-52425 Julich, Germany..
    Kotov, V
    Forschungszentrum Julich, Inst Energie & Klimaforsch Plasmaphys, D-52425 Julich, Germany..
    Mertens, Ph
    Forschungszentrum Julich, Inst Energie & Klimaforsch Plasmaphys, D-52425 Julich, Germany..
    Diagnostic mirrors for ITER: research in the frame of International Tokamak Physics Activity2019Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 59, nr 6, artikel-id 066029Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Mirrors will be used as first plasma-viewing elements in optical and laser-based diagnostics in ITER. Deterioration of the mirror performance due to e.g. sputtering of the mirror surface by plasma particles or deposition of impurities will hamper the entire performance of the affected diagnostic and thus affect ITER operation. The Specialists Working Group on First Mirrors (FM SWG) in the Topical Group on Diagnostics of the International Tokamak Physics Activity (ITPA) plays an important role in finding solutions for diagnostic first mirrors. Sound progress in research and development of diagnostic mirrors in ITER was achieved since the last overview in 2009. Single crystal (SC) rhodium (Rh) mirrors became available. SC rhodium and molybdenum (Mo) mirrors survived in conditions corresponding to similar to 200 cleaning cycles with a negligible degradation of reflectivity. These results are important for a mirror cleaning system which is presently under development. The cleaning system is based on sputtering of contaminants by plasma. Repetitive cleaning was tested on several mirror materials. Experiments comprised contamination/cleaning cycles. The reflectivity SC Mo and Rh mirrors has changed insignificantly after 80 cycles. First in situ cleaning using radiofrequency (RF) plasma was conducted in EAST tokamak with a mock-up plate of ITER edge Thomson Scattering (ETS) with five inserted mirrors. Contaminants from the mirrors were removed. Physics of cleaning discharge was studied both experimentally and by modeling. Mirror contamination can also be mitigated by protecting diagnostic ducts. A deposition mitigation (DeMi) duct system was exposed in KSTAR. The real-time measurement of deposition in the diagnostic duct was pioneered during this experiment. Results evidenced the dominating effect of the wall conditioning and baking on contamination inside the duct. A baffled cassette with mirrors was exposed at the main wall of JET for 23,6 plasma hours. No significant degradation of reflectivity was measured on mirrors located in the ducts. Predictive modeling was further advanced. A model for the particle transport, deposition and erosion at the port-plug was used in selecting an optical layout of several ITER diagnostics. These achievements contributed to the focusing of the first mirror research thus accelerating the diagnostic development. Modeling requires more efforts. Remaining crucial issues will be in a focus of the future work of the FM SWG.

  • 157. Lituadon, Xavier
    et al.
    Bergsåker, Henric
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Bykov, Igor
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Garcia-Carrasco, Alvaro
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hellsten, Torbjörn
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Jonsson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Stefániková, Estera
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Tholerus, Emmi
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Vallejos Olivares, Pablo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Weckmann, Armin
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Zhou, Yushan
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Ström, Petter
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    et al.,
    Overview of the JET results in support to ITER2017Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 57, nr 10, artikel-id 102001Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The 2014–2016 JET results are reviewed in the light of their significance for optimising the ITER research plan for the active and non-active operation. More than 60 h of plasma operation with ITER first wall materials successfully took place since its installation in 2011. New multi-machine scaling of the type I-ELM divertor energy flux density to ITER is supported by first principle modelling. ITER relevant disruption experiments and first principle modelling are reported with a set of three disruption mitigation valves mimicking the ITER setup. Insights of the L–H power threshold in Deuterium and Hydrogen are given, stressing the importance of the magnetic configurations and the recent measurements of fine-scale structures in the edge radial electric. Dimensionless scans of the core and pedestal confinement provide new information to elucidate the importance of the first wall material on the fusion performance. H-mode plasmas at ITER triangularity (H  =  1 at β N ~ 1.8 and n/n GW ~ 0.6) have been sustained at 2 MA during 5 s. The ITER neutronics codes have been validated on high performance experiments. Prospects for the coming D–T campaign and 14 MeV neutron calibration strategy are reviewed.

  • 158. Lloyd, B.
    et al.
    Akers, R. J.
    Alladio, F.
    Andrew, Y.
    Appel, L. C.
    Applegate, D.
    Axon, K. B.
    Ben Ayed, N.
    Bunting, C.
    Buttery, R. J.
    Carolan, P. G.
    Chapman, I.
    Ciric, D.
    Connor, J. W.
    Conway, N. J.
    Cox, M.
    Counsell, G. F.
    Cunningham, G.
    Darke, A.
    Delchambre, E.
    Dendy, R. O.
    Dowling, J.
    Dudson, B.
    Dunstan, M.
    Field, A. R.
    Foster, A.
    Gee, S.
    Garzotti, L.
    Gryaznevich, M. P.
    Gurchenko, A.
    Gusakov, E.
    Hawkes, N. C.
    Helander, P.
    Hender, T. C.
    Hnat, B.
    Howell, D. F.
    Joiner, N.
    Keeling, D.
    Kirk, A.
    Koch, B.
    Kuldkepp, Mattias
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Atom- och molekylfysik.
    Lisgo, S.
    Lott, F.
    Maddison, G. P.
    Maingi, R.
    Mancuso, A.
    Manhood, S. J.
    Martin, R.
    McArdle, G. J.
    McCone, J.
    Meyer, H.
    Micozzi, P.
    Morris, A. W.
    Muir, D. G.
    Nelson, M.
    O'Brien, M. R.
    Patel, A.
    Pinches, S.
    Preinhaelter, J.
    Price, M. N.
    Rachlew, Elisabeth
    Roach, C. M.
    Rozhansky, V.
    Saarelma, S.
    Saveliev, A.
    Scannell, R.
    Sharapov, S. E.
    Shevchenko, V.
    Shibaev, S.
    Stammers, K.
    Storrs, J.
    Surkov, A.
    Sykes, A.
    Tallents, S.
    Taylor, D.
    Thomas-Davies, N.
    Turnyanskiy, M. R.
    Urban, J.
    Valovic, M.
    Vann, R. G. L.
    Volpe, F.
    Voss, G.
    Walsh, M. J.
    Warder, S. E. V.
    Watkins, R.
    Wilson, H. R.
    Wisse, M.
    Overview of physics results from MAST2007Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 47, nr 10, s. S658-S667Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Substantial advances have been made on the Mega AmpÚre Spherical Tokamak (MAST). The parameter range of the MAST confinement database has been extended and it now also includes pellet-fuelled discharges. Good pellet retention has been observed in H-mode discharges without triggering an ELM or an H/L transition during peripheral ablation of low speed pellets. Co-ordinated studies on MAST and DIII-D demonstrate a strong link between the aspect ratio and the beta scaling of H-mode energy confinement, consistent with that obtained when MAST data were merged with a subset of the ITPA database. Electron and ion ITBs are readily formed and their evolution has been investigated. Electron and ion thermal diffusivities have been reduced to values close to the ion neoclassical level. Error field correction coils have been used to determine the locked mode threshold scaling which is comparable to that in conventional aspect ratio tokamaks. The impact of plasma rotation on sawteeth has been investigated and the results have been well-modelled using the MISHKA-F code. Alfvén cascades have been observed in discharges with reversed magnetic shear. Measurements during off-axis NBCD and heating are consistent with classical fast ion modelling and indicate efficient heating and significant driven current. Central electron Bernstein wave heating has been observed via the O-X-B mode conversion process in special magnetically compressed plasmas. Plasmas with low pedestal collisionality have been established and further insight has been gained into the characteristics of filamentary structures at the plasma edge. Complex behaviour of the divertor power loading during plasma disruptions has been revealed by high resolution infra-red measurements.

  • 159. Loarer, T.
    et al.
    Bergsåker, Henric
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Bykov, Igor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Elevant, Thomas
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Frassinetti, Lorenzo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Garcia-Carrasco, Alvaro
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hellsten, Torbjörn
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Ivanova, Darya
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Johnson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Menmuir, Sheena
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Rachlew, Elisabeth
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Ström, Petter
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Tholerus, Emmi
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Weckmann, Armin
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Zychor, I.
    et al.,
    Plasma isotopic changeover experiments in JET under carbon and ITER-like wall conditions2015Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 55, nr 4, artikel-id 043021Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In JET-ILWisotopic plasma wall changeover experiments have been carried out to determine the amount of particles accessible by changing the plasma from H to D and from D to H. The gas balance analysis integrated over the experimental sessions show that the total amount of H or D removed from the wall is in the range of (1-3) x 10(22)D. For both changeover experiments, the respective plasma isotopic ratio behaviour is exactly the same as a function of the pulse number. After only 80 s of plasma (4 pulses), the plasma isotopic ratio is lower than 10%, below 4.5% after 13 pulses and then saturates around similar to 2-3%. In these conditions, the removal efficiency through plasma operation becomes very poor. The saturation of the plasma isotopic ratio in the range of 10% is also observed for the JET-C configuration although the amount of tritium retained in the vessel after the DT pulses was more than one order of magnitude compared to the retention observed with the JET-ILW. This demonstrates that the amount of particle recovery through plasma changeover is independent from the long term retention. Since this long term reservoir results from codeposition, these experiments suggest that there is a limited access to these codeposited particles by plasma isotopic changeover. Finally, in ITER, change over from D/T to H at the end of the discharge for possibly reducing the long term retention does not appear as a good strategy.

  • 160. Loarer, T.
    et al.
    Brosset, C.
    Bucalossi, J.
    Coad, P.
    Esser, G.
    Hogan, J.
    Likonen, J.
    Mayer, M.
    Morgan, Ph
    Philipps, V.
    Rohde, V.
    Roth, J.
    Rubel, Marek J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Tsitrone, E.
    Widdowson, A.
    Gas balance and fuel retention in fusion devices2007Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 47, nr 9, s. 1112-1120Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The evaluation of hydrogenic retention in present tokamaks is of crucial importance to estimate the expected tritium (T) vessel inventory in ITER, limited from safety considerations to 350 g. In the framework of the European Task Force on Plasma Wall Interaction (EU TF on PWI) efforts are underway to investigate gas balance and fuel retention during discharges, and to compare the data obtained with those from post-mortem analysis of in-vessel components exposed over whole experimental campaigns. This paper summarizes the principal findings from coordinated studies on gas balance and fuel retention from a number of European tokamaks, namely, ASDEX-Upgrade (AUG), JET, TEXTOR and Tore Supra (TS). For most devices, the long-term retention fraction deduced from integrated particle balance is similar to 10-20%. This is larger than the similar to 3-4% deduced from post-mortem analysis of plasma facing components (PFCs). However, from the database available for tokamaks with their main PFCs made of carbon, the important conclusion is that the T inventory limit (set by the working guideline for operations) could be reached in ITER within fewer than 100 discharges. This, therefore, would seriously impact on operation of the device unless efficient T removal processes are developed.

  • 161. Loarte, A.
    et al.
    Leyland, M. J.
    Mier, J. A.
    Beurskens, M. N. A.
    Nunes, I.
    Parail, V.
    Lomas, P. J.
    Saibene, G. R.
    Sartori, R. I. A.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Plasma density and temperature evolution following the H-mode transition at JET and implications for ITER2013Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 53, nr 8, s. 083031-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The build-up of plasma parameters following the H-mode transition in JET has been analysed in view of its consequences for the alpha power evolution in the access to burning plasma conditions in ITER. JET experiments show that the build-up of plasma temperature both at the plasma core and the plasma edge occurs in timescales comparable to the energy confinement time. In contrast, the evolution of the edge and core densities differs strongly depending on the level of plasma current in the discharge and of the associated NBI penetration. For higher plasma current H-mode discharges (I-p > 2.0-2.5 MA, depending on plasma shape), with naturally higher plasma densities for which NBI penetration is poorer, the core density evolves in much longer timescales than the edge density leading to the formation of rather hollow density profiles. These hollow density profiles persist for timescales of several energy confinement times until they are usually terminated by a sawtooth. Modelling of the JET experiments with JETTO shows that the density build-up following the H-mode transition can be described with a purely diffusive model, despite the low collisionalities of high current H-mode plasmas at JET. The consequences of these JET experimental/modelling findings for the access to burning plasma conditions in the ITER Q(DT) = 10 scenario are presented.

  • 162. Lomanowski, B. A.
    et al.
    Bergsåker, Henric
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Bykov, Igor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Elevant, Thomas
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Frassinetti, Lorenzo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Garcia-Carrasco, Alvaro
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hellsten, Torbjörn
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Ivanova, Darya
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Johnson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Menmuir, Sheena
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Rachlew, Elisabeth
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Ström, Petter
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Tholerus, Emmi
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Weckmann, Armin
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Zychor, I.
    et al.,
    Inferring divertor plasma properties from hydrogen Balmer and Paschen series spectroscopy in JET-ILW2015Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 55, nr 12, artikel-id 123028Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A parametrised spectral line profile model is formulated to investigate the diagnostic scope for recovering plasma parameters from hydrogenic Balmer and Paschen series spectroscopy in the context of JET-ILW divertor plasmas. The separate treatment of Zeeman and Stark contributions in the line model is tested against the PPP-B code which accounts for their combined influence on the spectral line shape. The proposed simplified model does not fully reproduce the Stark-Zeeman features for the alpha and beta transitions, but good agreement is observed in the line width and wing profiles, especially for n > 5. The line model has been applied to infer radial density profiles in the JET-ILW divertor with generally good agreement between the D 5 -> 2, 5 -> 3, 6 -> 2, 7 -> 2 and 9 -> 2 lines for high recycling and detached conditions. In an L-mode detached plasma pulse the Langmuir probe measurements typically underestimated the density by a factor 2-3 and overestimated the electron temperature by a factor of 5-10 compared to spectroscopically derived values. The line model is further used to generate synthetic high-resolution spectra for low-n transitions to assess the potential for parameter recovery using a multi-parametric fitting technique. In cases with 4 parameter fits with a single Maxwellian neutral temperature component the D 4 -> 3 line yields the best results with parameter estimates within 10% of the input values. For cases with 9 parameter fits inclusive of a multi-component neutral velocity distribution function the quality of the fits is degraded. Simultaneous fitting of the D 3 -> 2 and 4 -> 3 profiles improves the fit quality significantly, highlighting the importance of complementary spectroscopic measurements for divertor plasma emission studies.

  • 163. Maddison, G. P.
    et al.
    Brix, M.
    Budny, R.
    Rachlew, Elisabeth
    KTH, Tidigare Institutioner                               , Fysik.
    Rapp, J.
    et al,
    Impurity-seeded plasma experiments on JET2003Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 43, nr 1, s. 49-62Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Scaling to larger tokamaks of high confinement plasmas with radiating edges, induced by impurities, is being studied through internationally collaborative experiments on JET. In campaigns till the end of 2000, three different regimes have been explored. A small number of limiter L-mode discharges seeded with neon have most closely repeated the approach used on TEXTOR-94, but different collisionality and particle transport in JET impede central peaking of the density associated with improved confinement. Divertor L-modes at intermediate density, again with neon injection, have pursued transiently enhanced states found on DIII-D. Confinement up to H-mode quality, together with radiation fractions of approximate to40%, have briefly been obtained, though central Z(eff) quickly increases. Most effectively, neon and argon seeding of higher density ELMy H-modes formed mainly at low triangularity on the septum of the MkIIGB divertor, resembling a pumped-limiter arrangement, have been examined. Good confinement has been sustained at densities close to the Greenwald level in 'afterpuff' (AP) phases following the end of main gas fuelling, for little change of central Z(eff) but up to approximate to60% radiation. Outstanding normalized properties up to H-97 = 0.99 at f(Gwd) = 0.94 have thus been achieved, above the conventional H-mode density limit for diverted plasmas. Stationarity of states has also been extended to many energy confinement times by including low, extra gas inputs in the 'AP', suggestive of an optimized fuelling scheme. Further development in 2001 is reported separately in [1]. Accompanying ELMs are generally reduced in frequency though not evidently in size, electron pedestal pressure being almost unchanged from unseeded behaviour. There are indications of the most favourable impurity species scaling with plasma parameters, performance, radiation and its concentration within a mantle all increasing with argon compared to neon in JET. These benefits in terms of integrated properties are just as required for long burning pulses in ITER, supporting its use of a radiating mantle to assist not only power exhaust but performance too. Impurity-seeded H-modes can therefore contribute directly to next-step scenario development.

  • 164. Maddison, G. P.
    et al.
    Giroud, C.
    Alper, B.
    Arnoux, G.
    Balboa, I.
    Beurskens, M. N. A.
    Boboc, A.
    Brezinsek, S.
    Brix, M.
    Clever, M.
    Coelho, R.
    Coenen, J. W.
    Coffey, I.
    da Silva Aresta Belo, P. C.
    Devaux, S.
    Devynck, P.
    Eich, T.
    Felton, R. C.
    Flanagan, J.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Garzotti, L.
    Groth, M.
    Jachmich, S.
    Jarvinen, A.
    Joffrin, E.
    Kempenaars, M. A. H.
    Kruezi, U.
    Lawson, K. D.
    Lehnen, M.
    Leyland, M. J.
    Liu, Y.
    Lomas, P. J.
    Lowry, C. G.
    Marsen, S.
    Matthews, G. F.
    McCormick, G. K.
    Meigs, A. G.
    Morris, A. W.
    Neu, R.
    Nunes, I. M.
    Oberkofler, M.
    Rimini, F. G.
    Saarelma, S.
    Sieglin, B.
    Sips, A. C. C.
    Sirinelli, A.
    Stamp, M. F.
    van Rooij, G. J.
    Ward, D. J.
    Wischmeier, M.
    Contrasting H-mode behaviour with deuterium fuelling and nitrogen seeding in the all-carbon and metallic versions of JET2014Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 54, nr 7, s. 073016-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The former all-carbon wall on JET has been replaced with beryllium in the main torus and tungsten in the divertor to mimic the surface materials envisaged for ITER. Comparisons are presented between type I H-mode characteristics in each design by examining respective scans over deuterium fuelling and impurity seeding, required to ameliorate exhaust loads both in JET at full capability and in ITER. Attention is focused upon a common high-triangularity, single-null divertor configuration at 2.5 MA, q(95) approximate to 3.5 yielding the most robust all-C performance. Contrasting results between the alternative linings are found firstly in unseeded plasmas, for which purity is improved and intrinsic radiation reduced in the ITER-like wall (ILW) but normalized energy confinement is approximate to 30% lower than in all-C counterparts, owing to a commensurately lower (electron) pedestal temperature. Divertor recycling is also radically altered, with slower, inboard-outboard asymmetric transients at ELMs and spontaneous oscillations in between them. Secondly, nitrogen seeding elicits opposite responses in the ILW to all-C experience, tending to raise plasma density, reduce ELM frequency, and above all to recover (electron) pedestal pressure, hence global confinement, almost back to previous levels. A hitherto unrecognized role of light impurities in pedestal stability and dynamics is consequently suggested. Thirdly, while heat loads on the divertor outboard target between ELMs are successfully reduced in proportion to the radiative cooling and ELM frequency effects of N in both wall environments, more surprisingly, average power ejected by ELMs also declines in the same proportion for the ILW. Detachment between transients is simultaneously promoted. Finally, inter-ELM W sources in the ILW divertor tend to fall with N input, although core accumulation possibly due to increased particle confinement still leads to significantly less steady conditions than in all-C plasmas. This limitation of ILW H-modes so far will be readdressed in future campaigns to continue progress towards a fully integrated scenario suitable for D-T experiments on JET and for 'baseline' operation on ITER. The diverse changes in behaviour between all-C and ILW contexts demonstrate essentially the strong impact which boundary conditions and intrinsic impurities can have on tokamak-plasma states.

  • 165. Maggi, C. F.
    et al.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Horvath, L.
    Lunniss, A.
    Saarelma, S.
    Wilson, H.
    Flanagan, J.
    Leyland, M.
    Lupelli, I.
    Pamela, S.
    Urano, H.
    Garzotti, L.
    Lerche, E.
    Nunes, I.
    Rimini, F.
    Studies of the pedestal structure and inter-ELM pedestal evolution in JET with the ITER-like wall2017Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 57, nr 11, artikel-id 116012Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The pedestal structure of type I ELMy H-modes has been analysed for JET with the ITER-like Wall (JET-ILW). The electron pressure pedestal width is independent of rho* and increases proportionally to root beta(pol,PED). Additional broadening of the width is observed, at constant beta(pol, PED), with increasing nu* and/ or neutral gas injection and the contribution of atomic physics effects in setting the pedestal width cannot as yet be ruled out. Neutral penetration alone does not determine the shape of the edge density profile in JET-ILW. The ratio of electron density to electron temperature scale lengths in the edge transport barrier region, eta(e), is of order 2-3 within experimental uncertainties. Existing understanding, represented in the stationary linear peeling-ballooning mode stability and the EPED pedestal structure models, is extended to the dynamic evolution between ELM crashes in JET-ILW, in order to test the assumptions underlying these two models. The inter-ELM temporal evolution of the pedestal structure in JET-ILW is not unique, but depends on discharge conditions, such as heating power and gas injection levels. The strong reduction in (pe,PED) with increasing D-2 gas injection at high power is primarily due to clamping of del T-e half way through the ELM cycle and is suggestive of turbulence limiting the T-e pedestal growth. The inter-ELM pedestal pressure evolution in JET-ILW is consistent with the EPED model assumptions at low gas rates and only at low beta at high gas rates. At higher beta and high gas rate the inter-ELM pedestal pressure evolution is qualitatively consistent with the kinetic ballooning mode (KBM) constraint but the peeling-ballooning (P-B) constraint is not satisfied and the ELM trigger mechanism remains as yet unexplained.

  • 166.
    Maggi, C. F.
    et al.
    EUROfus Consortium, Culham Sci Ctr, JET, Abingdon OX14 3DB, Oxon, England.;Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Menmuir, S.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Bergsåker, Henrik
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Bykov, Igor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Frassinetti, Lorenzo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Garcia Carrasco, Alvaro
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hellsten, Torbjörn
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Johnson, Thomas
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Maggi, C.
    CCFE Culham Sci Ctr, Abingdon OX14 3DB, Oxon, England..
    Petersson, P
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Rachlew, Elisabeth
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Ratynskaia, Svetlana
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Rymd- och plasmafysik.
    Rubel, Marek
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Stefániková, Estera
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Ström, Petter
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Tholerus, Emmi
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Tolias, Panagiotis
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Rymd- och plasmafysik.
    Olivares, Pablo Vallejos
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Weckmann, Armin
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Zhou, Y
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Zychor, I.
    Natl Ctr Nucl Res, PL-05400 Otwock, Poland..
    et al,
    Isotope identity experiments in JET-ILW with H and D L-mode plasmas2019Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 59, nr 7, artikel-id 076028Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    NBI-heated L-mode plasmas have been obtained in JET with the Be/W ITER-like wall (JET-ILW) in H and D, with matched profiles of the dimensionless plasma parameters, rho*, nu*, beta and q in the plasma core confinement region and same T-i/T-e and Z(eff). The achieved isotope identity indicates that the confinement scale invariance principle is satisfied in the core confinement region of these plasmas, where the dominant instabilities are Ion Temperature Gradient (ITG) modes. The dimensionless thermal energy confinement time, Omega(i) tau(E,th), and the scaled core plasma heat diffusivity, A chi(eff)/B-T, are identical in H and D within error bars, indicating lack of isotope mass dependence of the dimensionless L-mode thermal energy confinement time in JET-ILW. Predictive flux driven simulations with JETTO-TGLF of the H and D identity pair is in very good agreement with experiment for both isotopes: the stiff core heat transport, typical of JET-ILW NBI heated L-modes, overcomes the local gyro-Bohm scaling of gradient-driven TGLF, explaining the lack of isotope mass dependence in the confinement region of these plasmas. The effect of E x B shearing on the predicted heat and particle transport channels is found to be negligible for these low beta and low momentum input plasmas.

  • 167. Maggi, C. F.
    et al.
    Saarelma, S.
    Casson, F. J.
    Challis, C.
    de la Luna, E.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Giroud, C.
    Joffrin, E.
    Simpson, J.
    Beurskens, M.
    Chapman, I.
    Hobirk, J.
    Leyland, M.
    Lomas, P.
    Lowry, C.
    Nunes, I.
    Rimini, F.
    Sips, A. C. C.
    Urano, H.
    Pedestal confinement and stability in JET-ILW ELMy H-modes2015Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 55, nr 11, artikel-id 113031Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    New experiments in 2013-2014 have investigated the physics responsible for the decrease in H-mode pedestal confinement observed in the initial phase of JET-ILW operation (2012 Experimental Campaigns). The effects of plasma triangularity, global beta and neutrals on pedestal confinement and stability have been investigated systematically. The stability of JET-ILW pedestals is analysed in the framework of the peeling-ballooning model and the model assumptions of the pedestal predictive code EPED. Low D neutrals content in the plasma, achieved either by low D-2 gas injection rates or by divertor configurations with optimum pumping, and high beta are necessary conditions for good pedestal (and core) performance. In such conditions the pedestal stability is consistent with the peeling-ballooning paradigm. Moderate to high D-2 gas rates, required for W control and stable H-mode operation with the ILW, lead to increased D neutrals content in the plasma and additional physics in the pedestal models may be required to explain the onset of the ELM instability. The changes in H-mode performance associated with the change in JET wall composition from C to Be/W point to D neutrals and low-Z impurities playing a role in pedestal stability, elements which are not currently included in pedestal models. These aspects need to be addressed in order to progress towards full predictive capability of the pedestal height.

  • 168. Maier, H.
    et al.
    Hirai, T.
    Rubel, Marek J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Neu, R.
    Mertens, Ph
    Greuner, H.
    Hopf, Ch
    Matthews, G. F.
    Neubauer, O.
    Piazza, G.
    Gauthier, E.
    Likonen, J.
    Mitteau, R.
    Maddaluno, G.
    Riccardi, B.
    Philipps, V.
    Ruset, C.
    Lungu, C. P.
    Uytdenhouwen, I.
    Tungsten and beryllium armour development for the JET ITER-like wall project2007Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 47, nr 3, s. 222-227Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    For the ITER-like wall project at JET the present main chamber CFC tiles will be exchanged with Be tiles and in parallel a fully tungsten-clad divertor will be prepared. Therefore three R&D programmes were initiated: Be coatings on Inconel as well as Be erosion markers were developed for the first wall of the main chamber. High heat flux screening and cyclic loading tests carried out on the Be coatings on Inconel showed excellent performance, above the required power and energy density. For the divertor a conceptual design for a bulk W horizontal target plate was investigated, with the emphasis on minimizing electromagnetic forces. The design consisted of stacks of W lamellae of 6 mm width that were insulated in the toroidal direction. High heat flux tests of a test module were performed with an electron beam at an absorbed power density Up to 9 MW m(-2) for more than 150 pulses and finally with increasing power loads leading to surface temperatures in excess of 3000 degrees C. No macroscopic failure occurred during the test while SEM showed the development of micro-cracks on the loaded surface. For all other divertor parts R&D was performed to provide the technology to coat the 2-directional CFC material used at JET with thin tungsten coatings. The W-coated CFC tiles were subjected to heat loads with power densities ranging up to 23.5 MW m(-2) and exposed to cyclic heat loading for 200 pulses at 10.5 MW m(-2). All coatings developed cracks perpendicular to the CFC fibres due to the stronger contraction of the coating upon cool-down after the heat pulses.

  • 169. Mantsinen, M. J.
    et al.
    Eriksson, L. G.
    Gormezano, C.
    Hawkes, N. C.
    Hellsten, Torbjörn A. K.
    KTH, Tidigare Institutioner                               , Alfvénlaboratoriet.
    Litaudon, X.
    Rimini, F. G.
    Sharapov, S. E.
    Stratton, B. C.
    On the role of different phasings of the ICRF antennas in optimized shear discharges in JET2000Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 40, nr 10, s. 1773-1789Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In discharges with internal transport barriers produced by combined NBI and ICRF heating using the hydrogen minority scheme in JET, confinement and fusion performance are strongly affected by the direction of propagation of the ICRF waves. When the waves propagate along the plasma current, the formation of an internal transport barrier is prompter and the neutron yield is up to a factor of two higher than that for propagation against the current. An ICRF induced pinch of resonating trapped ions is put forward as a candidate for explaining the observations. Simulation results are presented which show that this effect is strong enough to provide a credible explanation for the experimental results.

  • 170. Mantsinen, M. J.
    et al.
    Mayoral, M. L.
    Van Eester, D.
    Alper, B.
    Barnsley, R.
    Beaumont, P.
    Bucalossi, J.
    Coffey, I.
    Conroy, S.
    de Baar, M.
    de Vries, P.
    Erents, K.
    Figueiredo, A.
    Gondhalekar, A.
    Gowers, C.
    Hellsten, Torbjörn A. K.
    KTH, Tidigare Institutioner                               , Alfvénlaboratoriet.
    Joffrin, E.
    Kiptily, V.
    Lamalle, P. U.
    Lawson, K.
    Lyssoivan, A.
    Mailloux, J.
    Mantica, P.
    Meo, F.
    Milani, F.
    Monakhov, I.
    Murari, A.
    Nguyen, F.
    Noterdaeme, J. M.
    Ongena, J.
    Petrov, Y.
    Rachlew, Elisabeth
    KTH, Tidigare Institutioner                               , Fysik.
    Riccardo, V.
    Righi, E.
    Rimini, F.
    Stamp, M.
    Tuccillo, A. A.
    Zastrow, K. D.
    Zerbini, M.
    Localized bulk electron heating with ICRF mode conversion in the JET tokamak2004Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 44, nr 1, s. 33-46Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Ion cyclotron resonance frequencies (ICRF) mode conversion has been developed for localized on-axis and off-axis bulk electron heating on the JET tokamak. The fast magnetosonic waves launched from the low-field side ICRF antennas are mode-converted to short-wavelength waves on the high-field side of the He-3 ion cyclotron resonance layer in D and He-4 plasmas and subsequently damped on the bulk electrons. The resulting electron power deposition, measured using ICRF power modulation, is narrow with a typical full-width at half-maximum of approximate to30 cm (i.e. about 30% of the minor radius) and the total deposited power to electrons comprises at least up to 80% of the applied ICRF power. The ICRF mode conversion power deposition has been kept constant using He-3 bleed throughout the ICRF phase with a typical duration of 4-6 s, i.e. 15-40 energy confinement times. Using waves propagating in the counter-current direction minimizes competing ion damping in the presence of co-injected deuterium beam ions.

  • 171.
    Martin, P.
    et al.
    Consorzio RFX.
    Adamek, J.
    Agostinetti, P.
    Agostini, M.
    Alfier, A.
    Angioni, C.
    Antoni, V.
    Apolloni, L.
    Auriemma, F.
    Barana, O.
    Barison, S.
    Baruzzo, M.
    Bettini, P.
    Boldrin, M.
    Bolzonella, T.
    Bonfiglio, D.
    Bonomo, F.
    Boozer, A. H.
    Brombin, M.
    Brotankova, J.
    Buffa, A.
    Canton, A.
    Cappello, S.
    Carraro, L.
    Cavazzana, R.
    Cavinato, M.
    Chacon, L.
    Chitarin, G.
    Cooper, W. A.
    Bello, S. D.
    Dalla Palma, M.
    Delogu, R.
    De Lorenzi, A.
    De Masi, G.
    Dong, J. Q.
    Drevlak, M.
    Escande, D. F.
    Fantini, F.
    Fassina, A.
    Fellin, F.
    Ferro, A.
    Fiameni, S.
    Fiorentin, A.
    Franz, P.
    Gaio, E.
    Garbet, X.
    Gazza, E.
    Giudicotti, L.
    Gnesotto, F.
    Gobbin, M.
    Grando, L.
    Guo, S. C.
    Hirano, Y.
    Hirshman, S. P.
    Ide, S.
    Igochine, V.
    In, Y.
    Innocente, P.
    Kiyama, S.
    Liu, S. F.
    Liu, Y. Q.
    Lòpez Bruna, D.
    Lorenzini, R.
    Luchetta, A.
    Manduchi, G.
    Mansfield, D. K.
    Marchiori, G.
    Marcuzzi, D.
    Marrelli, L.
    Martini, S.
    Matsunaga, G.
    Martines, E.
    Mazzitelli, G.
    McCollam, K.
    Menmuir, Sheena
    Assoc EURATOM ENEA Fus, Consorzio RFX, I-35137 Padua, Italy .
    Milani, F.
    Momo, B.
    Moresco, M.
    Munaretto, S.
    Novello, L.
    Okabayashi, M.
    Ortolani, S.
    Paccagnella, R.
    Pasqualotto, R.
    Pavei, M.
    Perverezev, G. V.
    Peruzzo, S.
    Piovan, R.
    Piovesan, P.
    Piron, L.
    Pizzimenti, A.
    Pomaro, N.
    Pomphrey, N.
    Predebon, I.
    Puiatti, M. E.
    Rigato, V.
    Rizzolo, A.
    Rostagni, G.
    Rubinacci, G.
    Ruzzon, A.
    Sakakita, H.
    Sanchez, R.
    Sarff, J. S.
    Sattin, F.
    Scaggion, A.
    Scarin, P.
    Schneider, W.
    Serianni, G.
    Sonato, P.
    Spada, E.
    Soppelsa, A.
    Spagnolo, S.
    Spolaore, M.
    Spong, D. A.
    Spizzo, G.
    Takechi, M.
    Taliercio, C.
    Terranova, D.
    Toigo, V.
    Valisa, M.
    Veranda, M.
    Vianello, N.
    Villone, F.
    Wang, Z.
    White, R. B.
    Yadikin, D.
    Zaccaria, P.
    Zamengo, A.
    Zanca, P.
    Zaniol, B.
    Zanotto, L.
    Zilli, E.
    Zollino, G.
    Zuin, M.
    Overview of the RFX fusion science program2011Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 51, nr 9, s. 094023-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper summarizes the main achievements of the RFX fusion science program in the period between the 2008 and 2010 IAEA Fusion Energy Conferences. RFX-mod is the largest reversed field pinch in the world, equipped with a system of 192 coils for active control of MHD stability. The discovery and understanding of helical states with electron internal transport barriers and core electron temperature >1.5 keV significantly advances the perspectives of the configuration. Optimized experiments with plasma current up to 1.8 MA have been realized, confirming positive scaling. The first evidence of edge transport barriers is presented. Progress has been made also in the control of first-wall properties and of density profiles, with initial first-wall lithization experiments. Micro-turbulence mechanisms such as ion temperature gradient and micro-tearing are discussed in the framework of understanding gradient-driven transport in low magnetic chaos helical regimes. Both tearing mode and resistive wall mode active control have been optimized and experimental data have been used to benchmark numerical codes. The RFX programme also provides important results for the fusion community and in particular for tokamaks and stellarators on feedback control of MHD stability and on three-dimensional physics. On the latter topic, the result of the application of stellarator codes to describe three-dimensional reversed field pinch physics will be presented.

  • 172. Martin, P.
    et al.
    Apolloni, L.
    Puiatti, M. E.
    Adamek, J.
    Agostini, M.
    Alfier, A.
    Annibaldi, Silvia Valeria
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Antoni, V.
    Auriemma, F.
    Barana, O.
    Baruzzo, M.
    Bettini, P.
    Bolzonella, T.
    Bonfiglio, D.
    Bonomo, F.
    Brombin, M.
    Brotankova, J.
    Buffa, A.
    Buratti, Paolo
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Canton, A.
    Cappello, S.
    Carraro, L.
    Cavazzana, R.
    Cavinato, M.
    Chapman, B. E.
    Chitarin, G.
    Dal Bello, S.
    De Lorenzi, A.
    De Masi, G.
    Escande, D. F.
    Fassina, A.
    Ferro, A.
    Franz, P.
    Gaio, E.
    Gazza, E.
    Giudicotti, L.
    Gnesotto, F.
    Gobbin, M.
    Grando, L.
    Guazzotto, L.
    Guo, S. C.
    Igochine, V.
    Innocente, P.
    Liu, Y. Q.
    Lorenzini, R.
    Luchetta, A.
    Manduchi, G.
    Marchiori, G.
    Marcuzzi, D.
    Marrelli, L.
    Martini, S.
    Martines, E.
    McCollam, K.
    Menmuir, S.
    Milani, F.
    Moresco, M.
    Novello, L.
    Ortolani, S.
    Paccagnella, R.
    Pasqualotto, R.
    Peruzzo, S.
    Piovan, R.
    Piovesan, P.
    Piron, L.
    Pizzimenti, A.
    Pomaro, N.
    Predebon, I.
    Reusch, J. A.
    Rostagni, G.
    Rubinacci, G.
    Sarff, J. S.
    Sattin, F.
    Scarin, P.
    Serianni, G.
    Sonato, P.
    Spada, E.
    Soppelsa, A.
    Spagnolo, S.
    Spolaore, M.
    Spizzo, G.
    Taliercio, C.
    Terranova, D.
    Toigo, V.
    Valisa, M.
    Vianello, N.
    Villone, F.
    White, R. B.
    Yadikin, D.
    Zaccaria, P.
    Zamengo, A.
    Zanca, P.
    Zaniol, B.
    Zanotto, L.
    Zilli, E.
    Zohm, H.
    Zuin, M.
    Overview of RFX-mod results2009Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 49, nr 10, s. 104019-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    With the exploration of the MA plasma current regime in up to 0.5 s long discharges, RFX-mod has opened new and very promising perspectives for the reversed field pinch (RFP) magnetic configuration, and has made significant progress in understanding and improving confinement and in controlling plasma stability. A big leap with respect to previous knowledge and expectations on RFP physics and performance has been made by RFX-mod since the last 2006 IAEA Fusion Energy Conference. A new self-organized helical equilibrium has been experimentally achieved ( the Single Helical Axis-SHAx-state), which is the preferred state at high current. Strong core electron transport barriers characterize this regime, with electron temperature gradients comparable to those achieved in tokamaks, and by a factor of 4 improvement in confinement time with respect to the standard RFP. RFX-mod is also providing leading edge results on real-time feedback control of MHD instabilities, of general interest for the fusion community.

  • 173. Martin, P.
    et al.
    Marrelli, L.
    Spizzo, G.
    Franz, P.
    Piovesan, P.
    Predebon, I.
    Bolzonella, T.
    Cappello, S.
    Cravotta, A.
    Escande, D. F.
    Frassinetti, L.
    Ortolani, S.
    Paccagnella, R.
    Terranova, D.
    Chapman, B. E.
    Craig, D.
    Prager, S. C.
    Sarff, J. S.
    Brunsell, P.
    Malmberg, J. A.
    Drake, James R.
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Yagi, Y.
    Koguchi, H.
    Hirano, Y.
    White, R. B.
    Sovinec, C.
    Xiao, C.
    Nebel, R. A.
    Schnack, D. D.
    Overview of quasi-single helicity experiments in reversed field pinches2003Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 43, nr 12, s. 1855-1862Artikel i tidskrift (Refereegranskat)
  • 174. Martin, P.
    et al.
    Puiatti, M. E.
    Agostinetti, P.
    Agostini, M.
    Alonso, J. A.
    Antoni, V.
    Apolloni, L.
    Auriemma, F.
    Avino, F.
    Barbalace, A.
    Barbisan, M.
    Barbui, T.
    Barison, S.
    Barp, M.
    Baruzzo, M.
    Bettini, P.
    Bigi, M.
    Bilel, R.
    Boldrin, M.
    Bolzonella, T.
    Bonfiglio, D.
    Bonomo, F.
    Brombin, M.
    Buffa, A.
    Bustreo, C.
    Canton, A.
    Cappello, S.
    Carralero, D.
    Carraro, L.
    Cavazzana, R.
    Chacon, L.
    Chapman, B.
    Chitarin, G.
    Ciaccio, G.
    Cooper, W. A.
    Dal Bello, S.
    Dalla Palma, M.
    Delogu, R.
    De Lorenzi, A.
    Delzanno, G. L.
    De Masi, G.
    De Muri, M.
    Dong, J. Q.
    Escande, D. F.
    Fantini, F.
    Fasoli, A.
    Fassina, A.
    Fellin, F.
    Ferro, A.
    Fiameni, S.
    Finn, J. M.
    Finotti, C.
    Fiorentin, A.
    Fonnesu, N.
    Framarin, J.
    Franz, P.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Furno, I.
    Furno Palumbo, M.
    Gaio, E.
    Gazza, E.
    Ghezzi, F.
    Giudicotti, L.
    Gnesotto, F.
    Gobbin, M.
    Gonzales, W. A.
    Grando, L.
    Guo, S. C.
    Hanson, J. D.
    Hidalgo, C.
    Hirano, Y.
    Hirshman, S. P.
    Ide, S.
    In, Y.
    Innocente, P.
    Jackson, G. L.
    Kiyama, S.
    Liu, S. F.
    Liu, Y. Q.
    Lòpez Bruna, D.
    Lorenzini, R.
    Luce, T. C.
    Luchetta, A.
    Maistrello, A.
    Manduchi, G.
    Mansfield, D. K.
    Marchiori, G.
    Marconato, N.
    Marcuzzi, D.
    Marrelli, L.
    Martini, S.
    Matsunaga, G.
    Martines, E.
    Mazzitelli, G.
    McCollam, K.
    Momo, B.
    Moresco, M.
    Munaretto, S.
    Novello, L.
    Okabayashi, M.
    Olofsson, Erik
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Paccagnella, R.
    Pasqualotto, R.
    Pavei, M.
    Peruzzo, S.
    Pesce, A.
    Pilan, N.
    Piovan, R.
    Piovesan, P.
    Piron, C.
    Piron, L.
    Pomaro, N.
    Predebon, I.
    Recchia, M.
    Rigato, V.
    Rizzolo, A.
    Roquemore, A. L.
    Rostagni, G.
    Ruzzon, A.
    Sakakita, H.
    Sanchez, R.
    Sarff, J. S.
    Sartori, E.
    Sattin, F.
    Scaggion, A.
    Scarin, P.
    Schneider, W.
    Serianni, G.
    Sonato, P.
    Spada, E.
    Soppelsa, A.
    Spagnolo, S.
    Spolaore, M.
    Spong, D. A.
    Spizzo, G.
    Takechi, M.
    Taliercio, C.
    Terranova, D.
    Theiler, C.
    Toigo, V.
    Trevisan, G. L.
    Valente, M.
    Valisa, M.
    Veltri, P.
    Veranda, M.
    Vianello, N.
    Villone, F.
    Wang, Z. R.
    White, R. B.
    Xu, X. Y.
    Zaccaria, P.
    Zamengo, A.
    Zanca, P.
    Zaniol, B.
    Zanotto, L.
    Zilli, E.
    Zollino, G.
    Zuin, M.
    Overview of the RFX-mod fusion science programme2013Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 53, nr 10, s. 104018-Artikel, forskningsöversikt (Refereegranskat)
    Abstract [en]

    This paper reports the highlights of the RFX-mod fusion science programme since the last 2010 IAEA Fusion Energy Conference. The RFX-mod fusion science programme focused on two main goals: exploring the fusion potential of the reversed field pinch (RFP) magnetic configuration and contributing to the solution of key science and technology problems in the roadmap to ITER. Active control of several plasma parameters has been a key tool in this endeavour. New upgrades on the system for active control of magnetohydrodynamic (MHD) stability are underway and will be presented in this paper. Unique among the existing fusion devices, RFX-mod has been operated both as an RFP and as a tokamak. The latter operation has allowed the exploration of edge safety factor q edge < 2 with active control of MHD stability and studies concerning basic energy and flow transport mechanisms. Strong interaction has continued with the stellarator community in particular on the physics of helical states and on three-dimensional codes.

  • 175.
    Maslov, M.
    et al.
    United Kingdom Atom Energy Author, Culham Ctr Fus Energy, Culham Sci Ctr, Abingdon OX14 3DB, Oxon, England.;CCFE Culham Sci Ctr, Abingdon OX14 3DB, Oxon, England..
    Bergsåker, Henric
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Bykov, Igor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Frassinetti, Lorenzo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Garcia-Carrasco, Alvaro
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hellsten, Torbjörn
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Johnson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Menmuir, Sheena
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Petersson, Per
    Rachlew, Elisabeth
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Ratynskaia, Svetlana
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Stefanikova, Estera
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Ström, Petter
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Tholerus, Emmi
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Tolias, Panagiotis
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Olivares, Pablo Vallejos
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Weckmann, Armin
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Zhou, Yushun
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Zychor, I.
    Natl Ctr Nucl Res, PL-05400 Otwock, Poland..
    et al.,
    Observation of enhanced ion particle transport in mixed H/D isotope plasmas on JET2018Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 58, nr 7, artikel-id 076022Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Particle transport in tokamak plasmas has been intensively studied in the past, particularly in relation to density peaking and the presence of anomalous inward particle convection in L-and H-modes. While in the L-mode case the presence of the anomalous inward pinch has previously been unambiguously demonstrated, particle transport in the H-mode was unclear. The main difficulty of such studies is that particle diffusion and convection could not be measured independently in steady-state conditions in the presence of a core particle flux. Therefore, it is usually not possible to separate the transport effect(inward convection), from the source effect (slow diffusion of particles introduced to the plasma core by neutral beam injection heating). In this work we describe experiments done on JET with mixtures of two hydrogenic isotopes: H and D. It is demonstrated that in the case of several ion species, convection and diffusion can be separated in a steady plasma without implementation of perturbative techniques such as gas puff modulation. Previous H-mode density peaking studies suggested that for this relatively high electron collisionality plasma scenario, the observed density gradient is mostly driven by particle source and low particle diffusivity D < 0.5 * chi(eff). Transport coefficients derived from observation of the isotope profiles in the new experiments far exceed that value-ion particle diffusion is found to be as high as D >= 2 * chi(eff), combined with a strong inward convection. Apparent disagreement with previous findings was explained by significantly faster transport of ion components with respect to the electrons, which could not be observed in a single main ion species plasma. This conclusion is confirmed by quasilinear gyrokinetic simulations.

  • 176. Mayoral, M. L.
    et al.
    Lamalle, P. U.
    Van Eester, D.
    Lerche, E. A.
    Beaumont, P.
    De La Luna, E.
    De Vries, P.
    Gowers, C.
    Felton, R.
    Harling, J.
    Kiptily, V.
    Lawson, K.
    Laxåback, Martin
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Lomas, P.
    Mantsinen, M. J.
    Meo, F.
    Noterdaeme, J. M.
    Nunes, I.
    Piazza, G.
    Santala, M.
    Hydrogen plasmas with ICRF inverted minority and mode conversion heating regimes in the JET tokamak2006Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 46, nr 7, s. S550-S563Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    During the initial operation of the International Thermonuclear Experimental Reactor (ITER), it is envisaged that activation will be minimized by using hydrogen (H) plasmas where the reference ion cyclotron resonance frequency (ICRF) heating scenarios rely on minority species such as helium (He-3) or deuterium (D). This paper firstly describes experiments dedicated to the study of He-3 heating in H plasmas with a sequence of discharges in which 5 MW of ICRF power was reliably coupled and the He-3 concentration, controlled in real-time, was varied from below 1% up to 10%. The minority heating (MH) regime was observed at low concentrations (up to 2%). Energetic tails in the He-3 ion distributions were observed with effective temperatures up to 300 keV and bulk electron temperatures up to 6 keV. At around 2%, a sudden transition was reproducibly observed to the mode conversion regime, in which the ICRF fast wave couples to short wavelength modes, leading to efficient direct electron heating and bulk electron temperatures up to 8 keV. Secondly, experiments performed to study D minority ion heating in H plasmas are presented. This MH scheme proved much more difficult since modest quantities of carbon

  • 177.
    McClements, K. G.
    et al.
    Culham Sci Ctr, JET, EUROfus Consortium, Abingdon OX14 3DB, Oxon, England.;Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England.;CCFE Culham Sci Ctr, Abingdon OX14 3DB, Oxon, England..
    Bergsåker, Henric
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Bykov, Igor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Frassinetti, Lorenzo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Garcia-Carrasco, Alvaro
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hellsten, Torbjörn
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Johnson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Menmuir, Sheena
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Rachlew, Elisabeth
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Ratynskaia, Svetlana
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Stefanikova, Estera
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Ström, Petter
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Tholerus, Emmi
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Tolias, Panagiotis
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Olivares, Pablo Vallejos
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Weckmann, Armin
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Zhou, Yushun
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Zychor, I.
    Natl Ctr Nucl Res, PL-05400 Otwock, Poland..
    Observations and modelling of ion cyclotron emission observed in JET plasmas using a sub-harmonic arc detection system during ion cyclotron resonance heating2018Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 58, nr 9, artikel-id 096020Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Measurements are reported of electromagnetic emission close to the cyclotron frequency of energetic ions in JET plasmas heated by waves in the ion cylotron range of frequencies (ICRF). Hydrogen was the majority ion species in all of these plasmas. The measurements were obtained using a sub-harmonic arc detection system in the transmission lines of one of the ICRF antennas. The measured ion cyclotron emission spectra were strongly filtered by the antenna system, and typically contained sub-structure, consisting of sets of peaks with a separation of a few kHz, suggesting the excitation of compressional Alfven eigenmodes closely spaced in frequency. In most cases the energetic ions can be clearly identified as ICRF wave-accelerated He-3 minority ions, although in two pulses the emission may have been produced by energetic He-4 ions, originating from third harmonic ICRF wave acceleration. It is proposed that the emission close to the He-3 cyclotron frequency was produced by energetic ions of this species undergoing drift orbit excursions to the outer midplane plasma edge. Particle-in-cell and hybrid (kinetic ion, fluid electron) simulations using plasma parameters corresponding to edge plasma conditions in these JET pulses, and energetic particle parameters inferred from the cyclotron resonance location, indicate strong excitation of waves at multiple He-3 cyclotron harmonics, including the fundamental, which is identified with the observed emission. These results underline the potential importance of ICE measurements as a method of studying confined fast particles that are strongly suprathermal but have insufficient energies or are not present in sufficient numbers to excite detectable levels of gamma-ray emission or other collective instabilities.

  • 178. Meyer, H.
    et al.
    Akers, R. J.
    Alladio, F.
    Appel, L. C.
    Axon, K. B.
    Ben Ayed, N.
    Boerner, P.
    Buttery, R. J.
    Carolan, P. G.
    Ciric, D.
    Challis, C. D.
    Chapman, I. T.
    Coyler, G.
    Connor, J. W.
    Conway, N. J.
    Cowley, S.
    Cox, M.
    Counsell, G. F.
    Cunningham, G.
    Darke, A.
    deBock, M.
    deTemmerman, G.
    Dendy, R. O.
    Dowling, J.
    Dnestrovskij, A. Yu
    Dnestrovskij, Yu. N.
    Dudson, B.
    Dunai, D.
    Dunstan, M.
    Field, A. R.
    Foster, A.
    Garzotti, L.
    Gibson, K.
    Gryaznevich, M. P.
    Guttenfelder, W.
    Hawkes, N. C.
    Harrison, J.
    Helander, P.
    Hender, T. C.
    Hnat, B.
    Hole, M. J.
    Howell, D. F.
    Hua, M. Duc
    Hubbard, A.
    Istenic, M.
    Joiner, N.
    Keeling, D.
    Kirk, A.
    Koslowski, H. R.
    Liang, Y.
    Lilley, M.
    Lisgo, S.
    Lloyd, B.
    Maddison, G. P.
    Maingi, R.
    Mancuso, A.
    Manhood, S. J.
    Martin, R.
    McArdle, G. J.
    McCone, J.
    Michael, C.
    Micozzi, P.
    Morgan, T.
    Morris, A. W.
    Muir, D. G.
    Nardon, E.
    Naylor, G.
    O'Brien, M. R.
    O'Gorman, T.
    Patel, A.
    Pinches, S. D.
    Preinhaelter, J.
    Price, M. N.
    Rachlew, Elisabeth
    Reiter, D.
    Roach, C. M.
    Rozhansky, V.
    Saarelma, S.
    Saveliev, A.
    Scannell, R.
    Sharapov, S. E.
    Shevchenko, V.
    Shibaev, S.
    Smith, H.
    Staebler, G. E.
    Stork, D.
    Storrs, J.
    Sykes, A.
    Tallents, S.
    Tamain, P.
    Taylor, D.
    Temple, D.
    Thomas-Davies, N.
    Thornton, A.
    Thyagaraja, A.
    Turnyanskiy, M. R.
    Urban, J.
    Valovic, M.
    Vann, R. G. L.
    Volpe, F.
    Voss, G.
    Walsh, M. J.
    Warder, S. E. V.
    Watkins, R.
    Wilson, H. R.
    Windridge, M.
    Wisse, M.
    Zabolotski, A.
    Zoletnik, S.
    Zolotukhin, O.
    Overview of physics results from MAST2009Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 49, nr 10, s. 104017-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Several improvements to the MAST plant and diagnostics have facilitated new studies advancing the physics basis for ITER and DEMO, as well as for future spherical tokamaks (STs). Using the increased heating capabilities P-NBI <= 3.8 MW H-mode at I-P = 1.2 MA was accessed showing that the energy confinement on MAST scales more weakly with I-P and more strongly with B-t than in the ITER IPB98(y, 2) scaling. Measurements of the fuel retention of shallow pellets extrapolate to an ITER particle throughput of 70% of its original designed total throughput capacity. The anomalous momentum diffusion, chi(phi), is linked to the ion diffusion, chi(i), with a Prandtl number close to P-phi approximate to chi(phi)/chi(i) approximate to 1, although chi(i) approaches neoclassical values. New high spatial resolution measurements of the edge radial electric field, E-r, show that the position of steepest gradients in electron pressure and E-r (i.e. shearing rate) are coincident, but their magnitudes are not linked. The T-e pedestal width on MAST scales with root beta(ped)(pol) rather than rho(pol). The edge localized mode (ELM) frequency for type-IV ELMs, new in MAST, was almost doubled using n = 2 resonant magnetic perturbations from a set of four external coils (n = 1, 2). A new internal 12 coil set (n <= 3) has been commissioned. The filaments in the inter-ELM and L-mode phase are different from ELM filaments, and the characteristics in L-mode agree well with turbulence calculations. A variety of fast particle driven instabilities were studied from 10 kHz saturated fishbone like activity up to 3.8 MHz compressional Alfven eigenmodes. Fast particle instabilities also affect the off-axis NBI current drive, leading to fast ion diffusion of the order of 0.5 m(2) s(-1) and a reduction in the driven current fraction from 40% to 30%. EBW current drive start-up is demonstrated for the first time in a ST generating plasma currents up to 55 kA. Many of these studies contributed to the physics basis of a planned upgrade to MAST.

  • 179. Meyer, H.
    et al.
    Eich, T.
    Beurskens, M.
    Coda, S.
    Hakola, A.
    Martin, P.
    Adamek, J.
    Agostini, M.
    Aguiam, D.
    Ahn, J.
    Aho-Mantila, L.
    Akers, R.
    Albanese, R.
    Aledda, R.
    Alessi, E.
    Allan, S.
    Alves, D.
    Ambrosino, R.
    Amicucci, L.
    Anand, H.
    Anastassiou, G.
    Andrebe, Y.
    Angioni, C.
    Apruzzese, G.
    Ariola, M.
    Arnichand, H.
    Arter, W.
    Baciero, A.
    Barnes, M.
    Barrera, L.
    Behn, R.
    Bencze, A.
    Bernardo, J.
    Bernert, M.
    Bettini, P.
    Bilkova, P.
    Bin, W.
    Birkenmeier, G.
    Bizarro, J. P. S.
    Blanchard, P.
    Blanken, T.
    Bluteau, M.
    Bobkov, V.
    Bogar, O.
    Boehm, P.
    Bolzonella, T.
    Boncagni, L.
    Botrugno, A.
    Bottereau, C.
    Bouquey, F.
    Bourdelle, C.
    Bremond, S.
    Brezinsek, S.
    Brida, D.
    Brochard, F.
    Buchanan, J.
    Bufferand, H.
    Buratti, P.
    Cahyna, P.
    Calabro, G.
    Camenen, Y.
    Caniello, R.
    Cannas, B.
    Canton, A.
    Cardinali, A.
    Carnevale, D.
    Carr, M.
    Carralero, D.
    Carvalho, P.
    Casali, L.
    Castaldo, C.
    Castejon, F.
    Castro, R.
    Causa, F.
    Cavazzana, R.
    Cavedon, M.
    Cecconello, M.
    Ceccuzzi, S.
    Cesario, R.
    Challis, C. D.
    Chapman, I. T.
    Chapman, S.
    Chernyshova, M.
    Choi, D.
    Cianfarani, C.
    Ciraolo, G.
    Citrin, J.
    Clairet, F.
    Classen, I.
    Coelho, R.
    Coenen, J. W.
    Colas, L.
    Conway, G.
    Corre, Y.
    Costea, S.
    Crisanti, F.
    Cruz, N.
    Cseh, G.
    Czarnecka, A.
    D'Arcangelo, O.
    De Angeli, M.
    De Masi, G.
    De Temmerman, G.
    De Tommasi, G.
    Decker, J.
    Delogu, R. S.
    Dendy, R.
    Denner, P.
    Di Troia, C.
    Dimitrova, M.
    D'Inca, R.
    Doric, V.
    Douai, D.
    Drenik, A.
    Dudson, B.
    Dunai, D.
    Dunne, M.
    Duval, B. P.
    Easy, L.
    Elmore, S.
    Erdos, B.
    Esposito, B.
    Fable, E.
    Faitsch, M.
    Fanni, A.
    Fedorczak, N.
    Felici, F.
    Ferreira, J.
    Fevrier, O.
    Ficker, O.
    Fietz, S.
    Figini, L.
    Figueiredo, A.
    Fil, A.
    Fishpool, G.
    Fitzgerald, M.
    Fontana, M.
    Ford, O.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Fridstr, R.
    Frigione, D.
    Fuchert, G.
    Fuchs, C.
    Palumbo, M. Furno
    Futatani, S.
    Gabellieri, L.
    Galazka, K.
    Galdon-Quiroga, J.
    Galeani, S.
    Gallart, D.
    Gallo, A.
    Galperti, C.
    Gao, Y.
    Garavaglia, S.
    Garcia, J.
    Garcia-Carrasco, Alvaro
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Garcia-Lopez, J.
    Garcia-Munoz, M.
    Gardarein, J. -L
    Garzotti, L.
    Gaspar, J.
    Gauthier, E.
    Geelen, P.
    Geiger, B.
    Ghendrih, P.
    Ghezzi, F.
    Giacomelli, L.
    Giannone, L.
    Giovannozzi, E.
    Giroud, C.
    Gleason Gonzalez, C.
    Gobbin, M.
    Goodman, T. P.
    Gorini, G.
    Gospodarczyk, M.
    Granucci, G.
    Gruber, M.
    Gude, A.
    Guimarais, L.
    Guirlet, R.
    Gunn, J.
    Hacek, P.
    Hacquin, S.
    Hall, S.
    Ham, C.
    Happel, T.
    Harrison, J.
    Harting, D.
    Hauer, V.
    Havlickova, E.
    Hellsten, Torbjörn
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Helou, W.
    Henderson, S.
    Hennequin, P.
    Heyn, M.
    Hnat, B.
    Holzl, M.
    Hogeweij, D.
    Honore, C.
    Hopf, C.
    Horacek, J.
    Hornung, G.
    Horvath, L.
    Huang, Z.
    Huber, A.
    Igitkhanov, J.
    Igochine, V.
    Imrisek, M.
    Innocente, P.
    Ionita-Schrittwieser, C.
    Isliker, H.
    Ivanova-Stanik, I.
    Jacobsen, A. S.
    Jacquet, P.
    Jakubowski, M.
    Jardin, A.
    Jaulmes, F.
    Jenko, F.
    Jensen, T.
    Busk, O. Jeppe Miki
    Jessen, M.
    Joffrin, E.
    Jones, O.
    Jonsson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Kallenbach, A.
    Kallinikos, N.
    Kalvin, S.
    Kappatou, A.
    Karhunen, J.
    Karpushov, A.
    Kasilov, S.
    Kasprowicz, G.
    Kendl, A.
    Kernbichler, W.
    Kim, D.
    Kirk, A.
    Kjer, S.
    Klimek, I.
    Kocsis, G.
    Kogut, D.
    Komm, M.
    Korsholm, S. B.
    Koslowski, H. R.
    Koubiti, M.
    Kovacic, J.
    Kovarik, K.
    Krawczyk, N.
    Krbec, J.
    Krieger, K.
    Krivska, A.
    Kube, R.
    Kudlacek, O.
    Kurki-Suonio, T.
    Labit, B.
    Laggner, F. M.
    Laguardia, L.
    Lahtinen, A.
    Lalousis, P.
    Lang, P.
    Lauber, P.
    Lazanyi, N.
    Lazaros, A.
    Le, H. B.
    Lebschy, A.
    Leddy, J.
    Lefevre, L.
    Lehnen, M.
    Leipold, F.
    Lessig, A.
    Leyland, M.
    Li, L.
    Liang, Y.
    Lipschultz, B.
    Liu, Y. Q.
    Loarer, T.
    Loarte, A.
    Loewenhoff, T.
    Lomanowski, B.
    Loschiavo, V. P.
    Lunt, T.
    Lupelli, I.
    Lux, H.
    Lyssoivan, A.
    Madsen, J.
    Maget, P.
    Maggi, C.
    Maggiora, R.
    Magnussen, M. L.
    Mailloux, J.
    Maljaars, B.
    Malygin, A.
    Mantica, P.
    Mantsinen, M.
    Maraschek, M.
    Marchand, B.
    Marconato, N.
    Marini, C.
    Marinucci, M.
    Markovic, T.
    Marocco, D.
    Marrelli, L.
    Martin, Y.
    Solis, J. R. Martin
    Martitsch, A.
    Mastrostefano, S.
    Mattei, M.
    Matthews, G.
    Mavridis, M.
    Mayoral, M. -L
    Mazon, D.
    McCarthy, P.
    McAdams, R.
    McArdle, G.
    McClements, K.
    McDermott, R.
    McMillan, B.
    Meisl, G.
    Merle, A.
    Meyer, O.
    Milanesio, D.
    Militello, F.
    Miron, I. G.
    Mitosinkova, K.
    Mlynar, J.
    Mlynek, A.
    Molina, D.
    Molina, P.
    Monakhov, I.
    Morales, J.
    Moreau, D.
    Morel, P.
    Moret, J. -M
    Moro, A.
    Moulton, D.
    Mueller, H. W.
    Nabais, F.
    Nardon, E.
    Naulin, V.
    Nemes-Czopf, A.
    Nespoli, F.
    Neu, R.
    Nielsen, A. H.
    Nielsen, S. K.
    Nikolaeva, V.
    Nimb, S.
    Nocente, M.
    Nouailletas, R.
    Nowak, S.
    Oberkofler, M.
    Oberparleiter, M.
    Ochoukov, R.
    Odstrcil, T.
    Olsen, J.
    Omotani, J.
    O'Mullane, M. G.
    Orain, F.
    Osterman, N.
    Paccagnella, R.
    Pamela, S.
    Pangione, L.
    Panjan, M.
    Papp, G.
    Paprok, R.
    Parail, V.
    Parra, I.
    Pau, A.
    Pautasso, G.
    Pehkonen, S. -P
    Pereira, A.
    Cippo, E. Perelli
    Ridolfini, V. Pericoli
    Peterka, M.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Petrzilka, V.
    Piovesan, P.
    Piron, C.
    Pironti, A.
    Pisano, F.
    Pisokas, T.
    Pitts, R.
    Ploumistakis, I.
    Plyusnin, V.
    Pokol, G.
    Poljak, D.
    Poloskei, P.
    Popovic, Z.
    Por, G.
    Porte, L.
    Potzel, S.
    Predebon, I.
    Preynas, M.
    Primc, G.
    Pucella, G.
    Puiatti, M. E.
    Putterich, T.
    Rack, M.
    Ramogida, G.
    Rapson, C.
    Rasmussen, J. Juul
    Rasmussen, J.
    Ratta, G. A.
    Ratynskaia, Svetlana
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Ravera, G.
    Refy, D.
    Reich, M.
    Reimerdes, H.
    Reimold, F.
    Reinke, M.
    Reiser, D.
    Resnik, M.
    Reux, C.
    Ripamonti, D.
    Rittich, D.
    Riva, G.
    Rodriguez-Ramos, M.
    Rohde, V.
    Rosato, J.
    Ryter, F.
    Saarelma, S.
    Sabot, R.
    Saint-Laurent, F.
    Salewski, M.
    Salmi, A.
    Samaddar, D.
    Sanchis-Sanchez, L.
    Santos, J.
    Sauter, O.
    Scannell, R.
    Scheffer, M.
    Schneider, M.
    Schneider, B.
    Schneider, P.
    Schneller, M.
    Schrittwieser, R.
    Schubert, M.
    Schweinzer, J.
    Seidl, J.
    Sertoli, M.
    Sesnic, S.
    Shabbir, A.
    Shalpegin, A.
    Shanahan, B.
    Sharapov, S.
    Sheikh, U.
    Sias, G.
    Sieglin, B.
    Silva, C.
    Silva, A.
    Fuglister, M. Silva
    Simpson, J.
    Snicker, A.
    Sommariva, C.
    Sozzi, C.
    Spagnolo, S.
    Spizzo, G.
    Spolaore, M.
    Stange, T.
    Pedersen, M. Stejner
    Stepanov, I.
    Stober, J.
    Strand, P.
    Susnjara, A.
    Suttrop, W.
    Szepesi, T.
    Tal, B.
    Tala, T.
    Tamain, P.
    Tardini, G.
    Tardocchi, M.
    Teplukhina, A.
    Terranova, D.
    Testa, D.
    Theiler, C.
    Thornton, A.
    Tolias, Panagiotis
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Tophoj, L.
    Treutterer, W.
    Trevisan, G. L.
    Tripsky, M.
    Tsironis, C.
    Tsui, C.
    Tudisco, O.
    Uccello, A.
    Urban, J.
    Valisa, M.
    Vallejos, Pablo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Valovic, M.
    Van den Brand, H.
    Vanovac, B.
    Varoutis, S.
    Vartanian, S.
    Vega, J.
    Verdoolaege, G.
    Verhaegh, K.
    Vermare, L.
    Vianello, N.
    Vicente, J.
    Viezzer, E.
    Vignitchouk, L.
    Vijvers, W. A. J.
    Villone, F.
    Viola, B.
    Vlahos, L.
    Voitsekhovitch, I.
    Vondracek, P.
    Vu, N. M. T.
    Wagner, D.
    Walkden, N.
    Wang, N.
    Wauters, T.
    Weiland, M.
    Weinzettl, V.
    Westerhof, E.
    Wiesenberger, M.
    Willensdorfer, M.
    Wischmeier, M.
    Wodniak, I.
    Wolfrum, E.
    Yadykin, D.
    Zagorski, R.
    Zammuto, I.
    Zanca, P.
    Zaplotnik, R.
    Zestanakis, P.
    Zhang, W.
    Zoletnik, S.
    Zuin, M.
    Overview of progress in European medium sized tokamaks towards an integrated plasma-edge/wall solution2017Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 57, nr 10, artikel-id 102014Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Integrating the plasma core performance with an edge and scrape-off layer (SOL) that leads to tolerable heat and particle loads on the wall is a major challenge. The new European medium size tokamak task force (EU-MST) coordinates research on ASDEX Upgrade (AUG), MAST and TCV. This multi-machine approach within EU-MST, covering a wide parameter range, is instrumental to progress in the field, as ITER and DEMO core/pedestal and SOL parameters are not achievable simultaneously in present day devices. A two prong approach is adopted. On the one hand, scenarios with tolerable transient heat and particle loads, including active edge localised mode (ELM) control are developed. On the other hand, divertor solutions including advanced magnetic configurations are studied. Considerable progress has been made on both approaches, in particular in the fields of: ELM control with resonant magnetic perturbations (RMP), small ELM regimes, detachment onset and control, as well as filamentary scrape-off-layer transport. For example full ELM suppression has now been achieved on AUG at low collisionality with n = 2 RMP maintaining good confinement H-H(98,H-y2) approximate to 0.95. Advances have been made with respect to detachment onset and control. Studies in advanced divertor configurations (Snowflake, Super-X and X-point target divertor) shed new light on SOL physics. Cross field filamentary transport has been characterised in a wide parameter regime on AUG, MAST and TCV progressing the theoretical and experimental understanding crucial for predicting first wall loads in ITER and DEMO. Conditions in the SOL also play a crucial role for ELM stability and access to small ELM regimes.

  • 180. Meyer, H.
    et al.
    Frassinetti, Lorenzo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Garcia Carrasco, Alvaro
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Ratynskaia, Svetlana V.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Rubel, Marek
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Thorén, Emil
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Tolias, Panagiotis
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Zohm, H.
    et al.,
    Overview of physics studies on ASDEX Upgrade2019Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 59, nr 11, artikel-id 112014Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The ASDEX Upgrade (AUG) programme, jointly run with the EUROfusion MST1 task force, continues to significantly enhance the physics base of ITER and DEMO. Here, the full tungsten wall is a key asset for extrapolating to future devices. The high overall heating power, flexible heating mix and comprehensive diagnostic set allows studies ranging from mimicking the scrape-off-layer and divertor conditions of ITER and DEMO at high density to fully non-inductive operation (q(95) = 5.5, beta(N) <= 2.8) at low density. Higher installed electron cyclotron resonance heating power <= 6 MW, new diagnostics and improved analysis techniques have further enhanced the capabilities of AUG. Stable high-density H-modes with P-sep/R <= 11 MW m(-1) with fully detached strike-points have been demonstrated. The ballooning instability close to the separatrix has been identified as a potential cause leading to the H-mode density limit and is also found to play an important role for the access to small edge-localized modes (ELMs). Density limit disruptions have been successfully avoided using a path-oriented approach to disruption handling and progress has been made in understanding the dissipation and avoidance of runaway electron beams. ELM suppression with resonant magnetic perturbations is now routinely achieved reaching transiently H-H98(y,H-2) <= 1.1. This gives new insight into the field penetration physics, in particular with respect to plasma flows. Modelling agrees well with plasma response measurements and a helically localised ballooning structure observed prior to the ELM is evidence for the changed edge stability due to the magnetic perturbations. The impact of 3D perturbations on heat load patterns and fast-ion losses have been further elaborated. Progress has also been made in understanding the ELM cycle itself. Here, new fast measurements of T-i and E-r allow for inter ELM transport analysis confirming that E-r is dominated by the diamagnetic term even for fast timescales. New analysis techniques allow detailed comparison of the ELM crash and are in good agreement with nonlinear MHD modelling. The observation of accelerated ions during the ELM crash can be seen as evidence for the reconnection during the ELM. As type-I ELMs (even mitigated) are likely not a viable operational regime in DEMO studies of 'natural' no ELM regimes have been extended. Stable I-modes up to n/n(GW) <= 0.7 have been characterised using beta-feedback. Core physics has been advanced by more detailed characterisation of the turbulence with new measurements such as the eddy tilt angle-measured for the first time-or the cross-phase angle of T-e and n(e) fluctuations. These new data put strong constraints on gyro-kinetic turbulence modelling. In addition, carefully executed studies in different main species (H, D and He) and with different heating mixes highlight the importance of the collisional energy exchange for interpreting energy confinement. A new regime with a hollow T-e profile now gives access to regimes mimicking aspects of burning plasma conditions and lead to nonlinear interactions of energetic particle modes despite the sub-Alfvenic beam energy. This will help to validate the fast-ion codes for predicting ITER and DEMO.

  • 181.
    MIrza, Ahmed Akram
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Scheffel, Jan
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Johnson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Effect of thermal conduction on pressure-driven modes in the reversed-field pinch2012Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 52, nr 12, s. 123012-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Classical linearized resistive magnetohydrodynamic (MHD) stability theory predicts unstable pressure-driven modes even at low plasma beta values for the reversed-field pinch (RFP) because of its unfavourable curvature and strong poloidal magnetic field. These resistive g-modes undermine energy confinement and are detrimental to the RFP reactor potential. In the analysis, one aspect is common, which is the usage of the adiabatic energy equation, ignoring the contribution due to thermal conduction effects. However, in recent analysis, stabilization of pressure-driven modes is demonstrated through inclusion of thermal conductivity. In this paper, we compare the results obtained from both classical and thermal conduction modified boundary layer stability analysis with those from a time-spectral resistive linearized MHD code. Ohmic heating and thermal conduction effects are included in the calculations. We have found that thermal conduction effects stabilize pressure-driven resistive g-modes only for very low values of plasma beta. In addition, analytical and numerical investigation of the equilibrium reveal that, for reactor relevant values of S-0 and tearing stable plasmas, the scaling gamma similar to S-0(-1/5) for the growth rate of these modes is weaker than that for the adiabatic case gamma similar to S-0(-1/3).

  • 182.
    Modestov, Mikhail
    et al.
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA. Dept. of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ 08544, United States of America.
    Kolemen, E.
    Fisher, A. E.
    Hvasta, M. G.
    Electromagnetic control of heat transport within a rectangular channel filled with flowing liquid metal2018Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 58, nr 1, artikel-id 016009Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The behavior of free-surface, liquid-metal flows exposed to both magnetic fields and an injected electric current is investigated via experiment and numerical simulations. The purpose of this paper is to provide an experimental and theoretical proof-of-concept for enhanced thermal mixing within fast-flowing, free-surface, liquid-metal plasma facing components that could be used in next-generation fusion reactors. The enhanced hydrodynamic and thermal mixing induced by non-uniform current density near the electrodes appears to improve heat transfer through the thickness of the flowing metal. Also, the outflow heat flux profile is strongly affected by the impact of the J x B forces on flow velocity. The experimental results are compared to COMSOL simulations in order to lay the groundwork for future liquid-metal research.

  • 183.
    Monakhov, I.
    et al.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England.;CCFE Culham Sci Ctr, Abingdon OX14 3DB, Oxon, England..
    Bergsåker, Henric
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Bykov, Igor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Frassinetti, Lorenzo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Garcia-Carrasco, Alvaro
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hellsten, Torbjörn
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Johnson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Menmuir, Sheena
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Rachlew, Elisabeth
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Ratynskaia, Svetlana
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Stefanikova, Estera
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Ström, Petter
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Tholerus, Emmi
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Tolias, Panagiotis
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Olivares, Pablo Vallejos
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Weckmann, Armin
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Zhou, Yushun
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Zychor, I.
    Natl Ctr Nucl Res, PL-05400 Otwock, Poland..
    et al.,
    ICRH antenna &ITS&IT-matrix measurements and plasma coupling characterisation at JET2018Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 58, nr 4, artikel-id 046012Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The paper is dedicated to the characterisation of multi-strap ICRH antenna coupling to plasma. Relevance of traditional concept of coupling resistance to antennas with mutually coupled straps is revised and the importance of antenna port excitation consistency for application of the concept is highlighted. A method of antenna S-matrix measurement in presence of plasma is discussed allowing deeper insight into the problem of antenna-plasma coupling. The method is based entirely on the RF plant hardware and control facilities available at JET and it involves application of variable phasing between the antenna straps during the RF plant operations at >100 kW. Unlike traditional techniques relying on low-power (similar to 10 mW) network analysers, the applied antenna voltage amplitudes are relevant to practical conditions of ICRH operations; crucially, they are high enough to minimise possible effects of antenna loading non-linearity due to the RF sheath effects and other phenomena which could affect low-power measurements. The method has been successfully applied at JET to conventional 4-port ICRH antennas energised at frequencies of 33 MHz, 42 MHz and 51 MHz during L.-mode plasma discharges while different gas injection modules (GIMs) were used to maintain comparable plasma densities during the pulses. The S-matrix assessment and its subsequent processing yielding 'global' antenna coupling resistances in conditions of equalised port maximum voltages allowed consistent description of antenna coupling to plasma at different strap phasing, operational frequencies and applied GIMs. Comprehensive experimental characterisation of mutually coupled antenna straps in presence of plasma also provided a unique opportunity for in-depth verification of TOPICA computer simulations.

  • 184. Monier-Garbet, P
    et al.
    Andrew, P
    Belo, P
    Bonheure, G
    Corre, Yann
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Atom- och molekylfysik.
    Crombe, K
    Dumortier, P
    Eich, T
    Felton, R
    Harling, J
    Hogan, J
    Huber, A
    Jaclunich, S
    Joffrin, E
    Koslowski, H R
    Kreter, A
    Maddison, G
    Matthews, G F
    Messiaen, A
    Nave, M F
    Ongena, J
    Parail, V
    Puiatti, M E
    Rapp, J
    Sartori, R
    Stober, J
    Tokar, M Z
    Unterberg, B
    Valisa, M
    Voitsekhovitch, I
    von Hellermann, M
    Impurity-seeded ELMy H-modes in JET, with high density and reduced heat load2005Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 45, nr 11, s. 1404-1410Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Experiments performed at JET during the past two years show that, in high triangularity H-mode plasmas with I-p = 2.5 MA, n(e)/n(Gr) approximate to 1.0, it is possible to radiate separately up to approximate to 40% of the total injected power on closed flux surfaces in the pedestal region (argon seeding) and up to approximate to 50% of the injected power in the divertor region (nitrogen seeding), while maintaining the confinement improvement factor at the value required for ITER, H98(y, 2) 1.0. The total radiated power fraction achieved in both cases (65-70%) is close to that required for ITER. However, Type I ELMS observed with impurity seeding have the same characteristics as that observed in reference pulses without seeding: decreasing plasma energy loss per ELM with increasing pedestal collisionality. One has to reach the Type III ELM regime to decrease the transient heat load to the divertor to acceptable values for ITER, although at the expense of confinement. The feasibility of an integrated scenario with Type-III ELMS, and q(95) = 2.6 to compensate for the low H factor, has been demonstrated on JET. This scenario would meet ITER requirements at 17 MA provided that the IPB98 scaling for energy content is accurate enough, and provided that a lower dilution is obtained when operating at higher absolute electron density.

  • 185. Moreau, D.
    et al.
    Mazon, D.
    Ariola, M.
    De Tommasi, G.
    Laborde, L.
    Piccolo, F.
    Sartori, F.
    Tala, T.
    Zabeo, L.
    Boboc, A.
    Bouvier, E.
    Brix, M.
    Brzozowski, Jerzy H.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Challis, C. D.
    Cocilovo, V.
    Cordoliani, V.
    Crisanti, F.
    De la Luna, E.
    Felton, R.
    Hawkes, N.
    King, R.
    Litaudon, X.
    Loarer, T.
    Mailloux, J.
    Mayoral, M.
    Nunes, I.
    Surrey, E.
    Zimmerman, O.
    A two-time-scale dynamic-model approach for magnetic and kinetic profile control in advanced tokamak scenarios on JET2008Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 48, nr 10Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Real-time simultaneous control of several radially distributed magnetic and kinetic plasma parameters is being investigated on JET, in view of developing integrated control of advanced tokamak scenarios. This paper describes the new model-based profile controller which has been implemented during the 2006-2007 experimental campaigns. The controller aims to use the combination of heating and current drive (H&CD) systems-and optionally the poloidal field (PF) system-in an optimal way to regulate the evolution of plasma parameter profiles such as the safety factor, q(x), and gyro-normalized temperature gradient,. rho*(Te)(x). In the first part of the paper, a technique for the experimental identification of a minimal dynamic plasma model is described, taking into account the physical structure and couplings of the transport equations, but making no quantitative assumptions on the transport coefficients or on their dependences. To cope with the high dimensionality of the state space and the large ratio between the time scales involved, the model identification procedure and the controller design both make use of the theory of singularly perturbed systems by means of a two-time-scale approximation. The second part of the paper provides the theoretical basis for the controller design. The profile controller is articulated around two composite feedback loops operating on the magnetic and kinetic time scales, respectively, and supplemented by a feedforward compensation of density variations. For any chosen set of target profiles, the closest self-consistent state achievable with the available actuators is uniquely defined. It is reached, with no steady state offset, through a near-optimal

  • 186.
    Moser, L.
    et al.
    Univ Basel, Dept Phys, Klingelbergstr 82, CH-4056 Basel, Switzerland.;Univ Basel, Dept Phys, Basel, Switzerland..
    Bergsåker, Henric
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Bykov, Igor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Frassinetti, Lorenzo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Garcia-Carrasco, Alvaro
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hellsten, Torbjörn
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Johnson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Menmuir, Sheena
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Rachlew, Elisabeth
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Ratynskaia, Svetlana
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Stefanikova, Estera
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Ström, Petter
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Tholerus, Emmi
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Tolias, Panagiotis
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Olivares, Pablo Vallejos
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Weckmann, Armin
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Zhou, Yushun
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik. KTH, Fusion Plasma Phys, EES, SE-10044 Stockholm, Sweden..
    Zychor, I.
    Natl Ctr Nucl Res, PL-05400 Otwock, Poland..
    et al.,
    Investigation and plasma cleaning of first mirrors coated with relevant ITER contaminants: beryllium and tungsten2017Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 57, nr 8, artikel-id 086019Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In order to extend the investigation of the plasma cleaning of ITER first mirrors, a set of molybdenum mirrors was coated in a laboratory with ITER-relevant contaminants, namely beryllium and tungsten. Different coating techniques as well as several contaminant compositions were used to ensure a large variety of films to clean, completing a previous study conducted on mirrors exposed in the JET ITER-like wall (tokamak deposits) [ 1]. Due to the toxicity of beryllium, the samples were treated in a vacuum chamber specially built for this purpose. The cleaning was performed using capacitively coupled RF plasma and evaluated by performing reflectivity measurements, scanning electron microscopy, x-ray photoelectron spectroscopy and ion beam analysis. The removal of all types of contaminants was achieved by using different plasma compositions (argon, helium and mixtures of the two) with various ion energies (from 200-600 eV) and in some cases the mirror's reflectivity was restored towards initial values. Pure helium discharges were capable of removing mixed beryllium/tungsten layers and oxidized molybdenum. In addition, no significant increase in the diffuse reflectivity of the mirrors was observed for the helium cleaning, though this was the case for some samples cleaned with argon. Helium is therefore appropriate for cleaning all mirrors in ITER leading to a possible cleaning regime where the entire vessel is filled with He and all mirrors are cleaned simultaneously without damaging their surfaces.

  • 187.
    Moulton, D.
    et al.
    Culham Sci Ctr, EUROfus Consortium, JET, Abingdon OX14 3DB, Oxon, England.;UKAEA, CCFE, Culham Sci Ctr, Abingdon OX14 3DB, Oxon, England.;Aalto Univ, POB 14100, FIN-00076 Aalto, Finland.;CCFE Culham Sci Ctr, Abingdon OX14 3DB, Oxon, England..
    Bergsåker, Henric
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Bykov, Igor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Frassinetti, Lorenzo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Garcia-Carrasco, Alvaro
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hellsten, Torbjörn
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Johnson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Menmuir, Sheena
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Rachlew, Elisabeth
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Ratynskaia, Svetlana
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Stefanikova, Estera
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Ström, Petter
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Tholerus, Emmi
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Tolias, Panagiotis
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Olivares, Pablo Vallejos
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Weckmann, Armin
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Zhou, Yushun
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Zychor, I.
    Natl Ctr Nucl Res, PL-05400 Otwock, Poland..
    et al.,
    Neutral pathways and heat flux widths in vertical- and horizontal-target EDGE2D-EIRENE simulations of JET2018Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 58, nr 9, artikel-id 096029Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper further analyses the EDGE2D-EIRENE simulations presented by Chankin et al (2017 Nucl. Mater. Energy 12 273), of L-mode JET plasmas in vertical-vertical (VV) and Vertical-horizontal (VH) divertor configurations. As expected, the simulated outer divertor ionisation source peaks near the separatrix in VV and radially further out in VH. We identify the reflections of recycled neutrals from lower divertor tiles as the primary mechanism by which ionisation is concentrated on the outer divertor separatrix in the VV configuration. These lower tile reflection pathways (of neutrals from the outer divertor, and to an even greater extent from the inner divertor) dominate the outer divertor separatrix ionisation. In contrast, the lower-tile-reflection pathways are much weaker in the VII simulation and its outer divertor ionisation is dominated by neutrals which do not reflect from any surfaces. Interestingly, these differences in neutral pathways give rise to strong differences in the heat flux density width lambda(q) at the outer divertor entrance: lambda(q) = 3.2 mm in VH compared to lambda(q) = 11.8 mm in VV. In VH, a narrow channel exists in the near scrape-off-layer (SOL) where the convected heat flux, driven by strong E-r x B flow and thermoelectric current, dominates over the conducted heat flux. The width of this channel sets lambda(q) and is determined by the radial distance between the separatrix and the ionisation peak in the outer divertor.

  • 188. Murari, A.
    et al.
    Bergsåker, Henric
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Bykov, Igor
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Elevant, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Garcia Carrasco, Alvaro
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hellsten, Torbjörn
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Ivanova, Darya
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Jonsson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Menmuir, Sheena
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Rachlew, Elisabeth
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Atom- och molekylfysik.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Ström, Petter
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Tholerus, Simon
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Weckmann, Armin
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Zychor, I.
    et al.,
    Application of transfer entropy to causality detection and synchronization experiments in tokamaks2016Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 56, nr 2, artikel-id 026006Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Determination of causal-effect relationships can be a difficult task even in the analysis of time series. This is particularly true in the case of complex, nonlinear systems affected by significant levels of noise. Causality can be modelled as a flow of information between systems, allowing to better predict the behaviour of a phenomenon on the basis of the knowledge of the one causing it. Therefore, information theoretic tools, such as the transfer entropy, have been used in various disciplines to quantify the causal relationship between events. In this paper, Transfer Entropy is applied to determining the information relationship between various phenomena in Tokamaks. The proposed approach provides unique insight about information causality in difficult situations, such as the link between sawteeth and ELMs and ELM pacing experiments. The application to the determination of disruption causes, and therefore to the classification of disruption types, looks also very promising. The obtained results indicate that the proposed method can provide a quantitative and statistically sound criterion to address the causal-effect relationships in various difficult and ambiguous situations if the data is of sufficient quality.

  • 189.
    Murari, A.
    et al.
    Culham Sci Ctr, JET, EUROfus Consortium, Abingdon OX14 3DB, Oxon, England.;Culham Sci Ctr, ITER Phys Dept, EUROfus Programme Management Unit, Abingdon OX14 3DB, Oxon, England.;Univ Padua, Consorzio RFX, Acciaierie Venete SpA, CNR,ENEA,INFN, Corso Stati Uniti 4, I-35127 Padua, Italy.;Consorzio RFX, I-35127 Padua, Italy..
    Bergsåker, Henric
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Bykov, Igor
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Elevant, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Garcia Carrasco, Alvaro
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hellsten, Torbjörn
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Ivanova, Darya
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Jonsson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Menmuir, Sheena
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Rachlew, Elisabeth
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Atom- och molekylfysik.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Ström, Petter
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Tholerus, Simon
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Weckmann, Armin
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Zychor, I.
    Inst Plasma Phys & Laser Microfus, PL-01497 Warsaw, Poland..
    et al.,
    Determining the prediction limits of models and classifiers with applications for disruption prediction in JET2017Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 57, nr 1, artikel-id 016024Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Understanding the many aspects of tokamak physics requires the development of quite sophisticated models. Moreover, in the operation of the devices, prediction of the future evolution of discharges can be of crucial importance, particularly in the case of the prediction of disruptions, which can cause serious damage to various parts of the machine. The determination of the limits of predictability is therefore an important issue for modelling, classifying and forecasting. In all these cases, once a certain level of performance has been reached, the question typically arises as to whether all the information available in the data has been exploited, or whether there are still margins for improvement of the tools being developed. In this paper, a theoretical information approach is proposed to address this issue. The excellent properties of the developed indicator, called the prediction factor (PF), have been proved with the help of a series of numerical tests. Its application to some typical behaviour relating to macroscopic instabilities in tokamaks has shown very positive results. The prediction factor has also been used to assess the performance of disruption predictors running in real time in the JET system, including the one systematically deployed in the feedback loop for mitigation purposes. The main conclusion is that the most advanced predictors basically exploit all the information contained in the locked mode signal on which they are based. Therefore, qualitative improvements in disruption prediction performance in JET would need the processing of additional signals, probably profiles.

  • 190. Murari, A.
    et al.
    Bergsåker, Henric
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Bykov, Igor
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Elevant, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Garcia Carrasco, Alvaro
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hellsten, Torbjörn
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Ivanova, Darya
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Jonsson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Menmuir, Sheena
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Rachlew, Elisabeth
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Atom- och molekylfysik.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Ström, Petter
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Tholerus, Simon
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Weckmann, Armin
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Zychor, I.
    et al.,
    How to assess the efficiency of synchronization experiments in tokamaks2016Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 56, nr 7, artikel-id 076008Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Control of instabilities such as ELMs and sawteeth is considered an important ingredient in the development of reactor-relevant scenarios. Various forms of ELM pacing have been tried in the past to influence their behavior using external perturbations. One of the main problems with these synchronization experiments resides in the fact that ELMs are periodic or quasi-periodic in nature. Therefore, after any pulsed perturbation, if one waits long enough, an ELM is always bound to occur. To evaluate the effectiveness of ELM pacing techniques, it is crucial to determine an appropriate interval over which they can have a real influence and an effective triggering capability. In this paper, three independent statistical methods are described to address this issue: Granger causality, transfer entropy and recurrence plots. The obtained results for JET with the ITER-like wall (ILW) indicate that the proposed techniques agree very well and provide much better estimates than the traditional heuristic criteria reported in the literature. Moreover, their combined use allows for the improvement of the time resolution of the assessment and determination of the efficiency of the pellet triggering in different phases of the same discharge. Therefore, the developed methods can be used to provide a quantitative and statistically robust estimate of the triggering efficiency of ELM pacing under realistic experimental conditions.

  • 191. Murari, A.
    et al.
    Gelfusa, M.
    Bergsåker, Henric
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Bykov, Igor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Frassinetti, Lorenzo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Garcia-Carrasco, Alvaro
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hellsten, Torbjörn
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Johnson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Menmuir, Sheena
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Rachlew, Elisabeth
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Ratynskaia, Svetlana
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Stefanikova, Estera
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Ström, Petter
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Tholerus, Emmi
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Tolias, Panagiotis
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Olivares, Pablo Vallejos
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Weckmann, Armin
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Zhou, Yushun
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Zychor, I.
    et al.,
    Adaptive predictors based on probabilistic SVM for real time disruption mitigation on JET2018Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 58, nr 5, artikel-id 056002Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Detecting disruptions with sufficient anticipation time is essential to undertake any form of remedial strategy, mitigation or avoidance. Traditional predictors based on machine learning techniques can be very performing, if properly optimised, but do not provide a natural estimate of the quality of their outputs and they typically age very quickly. In this paper a new set of tools, based on probabilistic extensions of support vector machines (SVM), are introduced and applied for the first time to JET data. The probabilistic output constitutes a natural qualification of the prediction quality and provides additional flexibility. An adaptive training strategy 'from scratch' has also been devised, which allows preserving the performance even when the experimental conditions change significantly. Large JET databases of disruptions, covering entire campaigns and thousands of discharges, have been analysed, both for the case of the graphite and the ITER Like Wall. Performance significantly better than any previous predictor using adaptive training has been achieved, satisfying even the requirements of the next generation of devices. The adaptive approach to the training has also provided unique information about the evolution of the operational space. The fact that the developed tools give the probability of disruption improves the interpretability of the results, provides an estimate of the predictor quality and gives new insights into the physics. Moreover, the probabilistic treatment permits to insert more easily these classifiers into general decision support and control systems.

  • 192.
    Murari, A.
    et al.
    EUROfus Consortium, JET, Culham Sci Ctr, Abingdon OX14 3DB, Oxon, England.;Univ Padua, Acciaierie Venete SpA, INFN, Consorzio RFX,CNR,ENEA, Corso Stati Uniti 4, I-35127 Padua, Italy.;JET, EUROfus Programme Management Unit, Culham, England.;Consorzio RFX, Corso Stati Uniti 4, I-35127 Padua, Italy.;Culham Sci Ctr, EUROfus Programme Management Unit, Culham OX14 3DB, England..
    Gelfusa, M.
    EUROfus Consortium, JET, Culham Sci Ctr, Abingdon OX14 3DB, Oxon, England.;Univ Roma Tor Vergata, Via Politecn 1, I-00133 Rome, Italy.;Univ Roma Tor Vergata, Via Politecn 1, Rome, Italy..
    Bergsåker, Henric
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Bykov, Igor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Frassinetti, Lorenzo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Garcia-Carrasco, Alvaro
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hellsten, Torbjörn
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Johnson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Menmuir, Sheena
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Rachlew, Elisabeth
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Ratynskaia, Svetlana
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Stefanikova, Estera
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Ström, Petter
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Tholerus, Emmi
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Tolias, Panagiotis
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Olivares, Pablo Vallejos
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Weckmann, Armin
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Zhou, Yushun
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik. KTH, Fusion Plasma Phys, EES, SE-10044 Stockholm, Sweden..
    Zychor, I.
    Natl Ctr Nucl Res, PL-05400 Otwock, Poland..
    et al.,
    On efficiency and interpretation of sawteeth pacing with on-axis ICRH modulation in JET2017Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 57, nr 12, artikel-id 126057Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In metallic machines ICRH heating is playing an increasingly important role. One of its most recent applications on the Joint Europena Torus (JET) is sawtooth control by ICRH modulation, for avoiding triggering dangerous neo-classical tearing modes (NTMs) and counteracting impurity accumulation. Some of the main difficulties of these experiments are the assessment of the synchronization efficiency and the understanding of the main physical mechanisms at play. In this paper, three independent classes of statistical indicators are introduced to address these issues: Recurrence Plots, Convergent Cross Mapping and Transfer Entropy. The application to JET experiments with the ILW shows that the proposed indicators agree quite well among themselves and provide sound estimates of the efficiency of the synchronisation scheme investigated. They also support, with a shot to shot basis analysis and an estimate of the uncertainties, the interpretation that the fast ions play a fundamental role in the stabilization of the sawteeth, in both L and H mode. Proposals for experiments to be carried out in the future to consolidate the interpretation of the results are discussed.

  • 193.
    Murari, A.
    et al.
    EUROfus Consortium, Culham Sci Ctr, JET, Abingdon OX14 3DB, Oxon, England.;Univ Padua, Acciaierie Venete SpA, Ist Nazl Fis Nucl, Consorzio RFX,CNR,ENEA, Corso Stati Uniti 4, I-35127 Padua, Italy.;EUROfus Consortium JET, Culham Sci Ctr, Abingdon OX14 3DB, Oxon, England.;Consorzio RFX, Corso Stati Uniti 4, I-35127 Padua, Italy.;Culham Sci Ctr, EUROfus Programme Management Unit, Culham OX14 3DB, England..
    Lungaroni, M.
    EUROfus Consortium, Culham Sci Ctr, JET, Abingdon OX14 3DB, Oxon, England.;Univ Roma Tor Vergata, Dept Ind Engn, Via Politecn 1, Rome, Italy.;EUROfus Consortium JET, Culham Sci Ctr, Abingdon OX14 3DB, Oxon, England.;Univ Roma Tor Vergata, Via Politecn 1, Rome, Italy..
    Bergsåker, Henrik
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Bykov, Igor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Frassinetti, Lorenzo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Fridström, Richard
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Garcia Carrasco, Alvaro
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hellsten, Torbjörn
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Johnson, Thomas
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Moon, Sunwoo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Petersson, P
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Rachlew, Elisabeth
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Ratynskaia, Svetlana
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Rymd- och plasmafysik.
    Rubel, Marek
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Stefániková, Estera
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Ström, Petter
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Tholerus, Emmi
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Tolias, Panagiotis
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Rymd- och plasmafysik.
    Olivares, Pablo Vallejos
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Weckmann, Armin
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Zhou, Y
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Zychor, I
    EUROfus Consortium JET, Culham Sci Ctr, Abingdon OX14 3DB, Oxon, England.;Natl Ctr Nucl Res NCBJ, PL-05400 Otwock, Poland..
    et al,
    Adaptive learning for disruption prediction in non-stationary conditions2019Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 59, nr 8, artikel-id 086037Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    For many years, machine learning tools have proved to be very powerful disruption predictors in tokamaks. On the other hand, the vast majority of the techniques deployed assume that the input data is independent and is sampled from exactly the same probability distribution for the training set, the test set and the final real time deployment. This hypothesis is certainly not verified in practice, since the experimental programmes evolve quite rapidly, resulting typically in ageing of the predictors and consequent suboptimal performance. This paper describes various adaptive training strategies that have been tested to maintain the performance of disruption predictors in non-stationary conditions. The proposed approaches have been implemented using new ensembles of classifiers, explicitly developed for the present application. The improvements in performance are unquestionable and, given the difficulties encountered so far in translating predictors from one device to another, the proposed adaptive methods from scratch can therefore be considered a useful option in the arsenal of alternatives envisaged for the next generation of devices, particularly at the very beginning of their operation.

  • 194.
    Myers, C. E.
    et al.
    Princeton Plasma Phys Lab, POB 451, Princeton, NJ 08543 USA..
    Bergsåker, Henric
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Bykov, Igor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Frassinetti, Lorenzo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Garcia-Carrasco, Alvaro
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hellsten, Torbjörn
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Johnson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Menmuir, Sheena
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Rachlew, Elisabeth
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Ratynskaia, Svetlana
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Stefanikova, Estera
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Ström, Petter
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Tholerus, Emmi
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Tolias, Panagiotis
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Olivares, Pablo Vallejos
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Weckmann, Armin
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Zhou, Yushun
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Zychor, I.
    Natl Ctr Nucl Res, PL-05400 Otwock, Poland..
    et al.,
    A multi-machine scaling of halo current rotation2018Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 58, nr 1, artikel-id 016050Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Halo currents generated during unmitigated tokamak disruptions are known to develop rotating asymmetric features that are of great concern to ITER because they can dynamically amplify the mechanical stresses on the machine. This paper presents a multi-machine analysis of these phenomena. More specifically, data from C-Mod, NSTX, ASDEX Upgrade, DIII-D, and JET are used to develop empirical scalings of three key quantities: (1) the machine-specific minimum current quench time, tau(CQ); (2) the halo current rotation duration, trot; and (3) the average halo current rotation frequency, < f(h)>. These data reveal that the normalized rotation duration, t(rot)/tau(CQ), and the average rotation velocity, < v(h)>, are surprisingly consistent from machine to machine. Furthermore, comparisons between carbon and metal wall machines show that metal walls have minimal impact on the behavior of rotating halo currents. Finally, upon projecting to ITER, the empirical scalings indicate that substantial halo current rotation above < f(h)> = 20 Hz is to be expected. More importantly, depending on the projected value of tau(CQ) in ITER, substantial rotation could also occur in the resonant frequency range of 6-20 Hz. As such, the possibility of damaging halo current rotation during unmitigated disruptions in ITER cannot be ruled out.

  • 195.
    Nabais, F.
    et al.
    EUROfus Consortium, JET, Culham Sci Ctr, Abingdon OX14 3DB, Oxon, England.;Univ Lisbon, Inst Super Tecn, Inst Plasmas & Fusao Nucl, P-1049001 Lisbon, Portugal.;Univ Lisbon, Inst Plasma & Fus Nucl, Inst Super Tecn, Lisbon, Portugal..
    Bergsåker, Henric
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Bykov, Igor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Frassinetti, Lorenzo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Garcia-Carrasco, Alvaro
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hellsten, Torbjörn
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Johnson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Menmuir, Sheena
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Rachlew, Elisabeth
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Ratynskaia, Svetlana
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Stefanikova, Estera
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Ström, Petter
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Tholerus, Emmi
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Tolias, Panagiotis
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Olivares, Pablo Vallejos
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Weckmann, Armin
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Zhou, Yushun
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Zychor, I.
    Natl Ctr Nucl Res, PL-05400 Otwock, Poland..
    et al.,
    TAE stability calculations compared to TAE antenna results in JET2018Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 58, nr 8, artikel-id 082007Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The excitation of modes in the toroidal Alfven eigenmodes (TAE) gap by an external antenna can be modelled by a driven damped harmonic oscillator. By performing a frequency scan it is possible to determine the damping rate of the mode through the quality factor. This method has been employed in recent Joint European Torus (JET) experiments dedicated to scenario development for the observation of alpha-driven instabilities in JET DT plasmas (i.e. plasmas composed by Deuterium and Tritium). However, the toroidal mode number n of the mode for which the measurements were performed could not be determined experimentally. The value of the damping obtained through experimental measurements for a selected time slice is then compared with those obtained from calculations performed by numerical codes for different modes with frequencies close to the experimental frequency of the antenna. This paper describes the modelling method and presents the numerical simulations carried out using a suite of codes to calculate the damping of TAE, which are compared with the value measured experimentally. The radial structures of these modes are first calculated with the ideal magnetohydrodynamic (MHD) code MISHKA. For each of these modes, the damping on thermal ions and thermal electrons and the contribution to the mode growth rate resulting from the resonant interaction with the ion cyclotron resonance heating (ICRH) accelerated ion population are calculated using the drift-kinetic code CASTOR-K. The radiative damping is calculated by using a complex resistivity in the resistive MHD code CASTOR code and the continuum damping is estimated using also the CASTOR code through the standard method of making the real part of the resistivity tend to zero. It was found the radiative damping is largely dominant over all other effects, except for the n = 3 TAE. The overall damping calculated numerically is consistent with the damping measured experimentally.

  • 196. Nabais, F.
    et al.
    Borba, D.
    Garcia-Munoz, M.
    Johnson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Kiptily, V. G.
    Reich, M.
    Nave, M. F. F.
    Pinches, S. D.
    Sharapov, S. E.
    Impact of strongly driven fishbones and Alfven Eigenmodes on fast ion losses2010Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 50, nr 11, s. 115006-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The instabilities responsible for ion cyclotron resonance heating (ICRH) accelerated fast ion losses in plasmas with monotonic profile of the safety factor and long period sawteeth, as well as the range of energies at which the losses occur, were identified on the JET tokamak. The temporal evolution of fast ion losses with resolution on energy and pitch angle was measured using the scintillator probe, which allows us to determine the orbits of the fast ions that reach the detector. On the other hand, the orbits of the fast ions in resonance with Alfvenic instabilities were identified using the CASTOR-K code, so it is possible to identify which instabilities were responsible for the losses collected in the detector. Two different phases of losses, with different characteristics, were identified. The first phase occurs just after a sawtooth crash, when toroidal Alfven eigenmodes (TAEs) and high frequency fishbones are unstable. In this phase, TAEs are responsible for most of the measured losses. Losses caused by fishbones, if any, are not significant. The second phase initiates when tornado modes (TAE inside the q = 1 radius) become unstable: the peak loss signal increases by a factor of 2 to 5, the average energy of the ions that reach the detector decreases and its pitch angle increases. In this phase, the strong drive of the tornado modes by the ICRH accelerated ions initiates the losses.

  • 197.
    Nardon, E.
    et al.
    CEA, IRFM, F-13108 St Paul Les Durance, France.;IRFM, CEA, F-13108 St Paul Les Durance, France..
    Bergsåker, Henric
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Bykov, Igor
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Elevant, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Garcia Carrasco, Alvaro
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hellsten, Torbjörn
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Ivanova, Darya
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Jonsson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Menmuir, Sheena
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Rachlew, Elisabeth
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Atom- och molekylfysik.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Ström, Petter
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Tholerus, Simon
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Weckmann, Armin
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Zychor, I.
    Inst Plasma Phys & Laser Microfus, PL-01497 Warsaw, Poland..
    et al.,
    On the mechanisms governing gas penetration into a tokamak plasma during a massive gas injection2017Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 57, nr 1, artikel-id 016027Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A new 1D radial fluid code, IMAGINE, is used to simulate the penetration of gas into a tokamak plasma during a massive gas injection (MGI). The main result is that the gas is in general strongly braked as it reaches the plasma, due to mechanisms related to charge exchange and (to a smaller extent) recombination. As a result, only a fraction of the gas penetrates into the plasma. Also, a shock wave is created in the gas which propagates away from the plasma, braking and compressing the incoming gas. Simulation results are quantitatively consistent, at least in terms of orders of magnitude, with experimental data for a D2 MGI into a JET Ohmic plasma. Simulations of MGI into the background plasma surrounding a runaway electron beam show that if the background electron density is too high, the gas may not penetrate, suggesting a possible explanation for the recent results of Reux et al in JET (2015 Nucl. Fusion 55 093013).

  • 198. Nave, M. F. F.
    et al.
    Kirov, K.
    Bernardo, J.
    Brix, M.
    Ferreira, J.
    Giroud, C.
    Hawkes, N.
    Hellsten, Torbjörn
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Jonsson, Tord
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Mailloux, J.
    Ongena, J.
    Parra, F.
    The effect of lower hybrid waves on JET plasma rotation2017Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 57, nr 3, artikel-id 034002Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper reports on observations of rotation in JET plasmas with lower hybrid current drive. Lower hybrid (LH) has a clear impact on rotation. The changes in core rotation can be either in the co- or counter-current directions. Experimental features that could determine the direction of rotation were investigated. Changes from co- to counter-rotation as the q-profile evolves from above unity to below unity suggests that magnetic shear could be important. However, LH can drive either co- or counter-rotation in discharges with similar magnetic shear and at the same plasma current. It is not clear if a slightly lower density is significant. A power scan at fixed density, shows a lower hybrid power threshold around 3 MW. For smaller LH powers, counter rotation increases with power, while for larger powers a trend towards co-rotation is found. The estimated counter-torque from the LH waves, would not explain the observed angular frequencies, neither would it explain the observation of co-rotation.

  • 199.
    Neverov, V. S.
    et al.
    EUROfus Consortium, JET, Culham Sci Ctr, Abingdon OX14 3DB, Oxon, England.;Natl Res Ctr Kurchatov Inst, Moscow 123182, Russia. Natl Res Nucl Univ MEPhI, Moscow 115409, Russia. Moscow Inst Phys & Technol, Dolgoprudnyi 141700, Moscow Region, Russia..
    Bergsåker, Henrik
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Bykov, Igor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Frassinetti, Lorenzo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Garcia Carrasco, Alvaro
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hellsten, Torbjörn
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Johnson, Thomas
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Menmuir, S.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Petersson, P
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Rachlew, Elisabeth
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Ratynskaia, Svetlana
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Rymd- och plasmafysik.
    Rubel, Marek
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Stefániková, Estera
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Ström, Petter
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Tholerus, Emmi
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Tolias, Panagiotis
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Rymd- och plasmafysik.
    Olivares, Pablo Vallejos
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Weckmann, Armin
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Zhou, Y
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Zychor, I
    Natl Ctr Nucl Res NCBJ, Otwock, Poland..
    et al,
    Determination of isotope ratio in the divertor of JET-ILW by high-resolution H alpha spectroscopy: H-D experiment and implications for D-T experiment2019Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 59, nr 4, artikel-id 046011Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The data of the H alpha high-resolution spectroscopy, collected on the multiple lines of sight, which cover the entire divertor space in poloidal cross-section, during the recent hydrogen-deuterium experiments in JET-ILW (ITER-like wall), are processed. A strong spatial inhomogeneity of the hydrogen concentration, H/(H + D), in divertor is found in many pulses. Namely, the H/(H + D) ratio may be lower in the inner divertor than that in the outer divertor by the values of 0.15-0.35, depending on the conditions of gas puffing and plasma heating. This effect suggests the necessity of spatially-resolved measurements of isotope ratio in the divertor in the upcoming deuterium-tritium experiments. Also, separation of the overlapped T alpha and D alpha spectral lines is shown to be a challenging task especially when the local Doppler-broadened (Gaussian) line shapes are noticeably distorted by the net inward flux of fast non-Maxwellian neutral atoms. We use the respective, formerly developed model of an asymmetric spectral line shape, while analysing the data of the first deuterium-tritium experiment in JET-C (carbon wall), and test the model via comparing the isotope ratio results with another diagnostic's measurements. This model is shown to increase the accuracy of tritium concentration measurements in the divertor.

  • 200. Noterdaeme, J. M.
    et al.
    Budny, R.
    Cardinali, A.
    Castaldo, C.
    Cesario, R.
    Crisanti, F.
    DeGrassie, J.
    D'Ippolito, D. A.
    Durodie, F.
    Ekedahl, A.
    Figueiredo, A.
    Ingesson, C.
    Joffrin, E.
    Hartmann, D.
    Heikkinen, J.
    Hellsten, Torbjörn A. K.
    KTH, Tidigare Institutioner                               , Alfvénlaboratoriet.
    Jones, T.
    Kiptily, V.
    Lamalle, P.
    Litaudon, X.
    Nguyen, F.
    Mailloux, J.
    Mantsinen, M.
    Mayoral, M.
    Mazon, D.
    Meo, F.
    Monakhov, I.
    Myra, J. R.
    Pamela, J.
    Pericoli, V.
    Petrov, Y.
    Sauter, O.
    Sarazin, Y.
    Sharapov, S. E.
    Tuccillo, A. A.
    Van Eester, D.
    Heating, current drive and energetic particle studies on JET in preparation of ITER operation2003Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 43, nr 3, s. 202-209Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper summarizes the recent work on JET in the three areas of heating, current drive and energetic particles. The achievements have extended the possibilities of JET, have a direct connection to ITER operation and provide new and interesting physics. Toroidal rotation profiles of plasmas heated far off axis with little or no refuelling or momentum input are hollow with only small differences on whether the power deposition is located on the low field side or on the high field side. With LH current drive the magnetic shear was varied from slightly positive to negative. The improved coupling (through the use of plasma shaping and CD4) allowed up to 3.4 MW of PLH in internal transport barrier (ITB) plasmas with more than 15 MW of combined NBI and ICRF heating. The q-profile with negative magnetic shear and the ITB could be maintained for the duration of the high heating pulse (8 s). Fast ions have been produced in JET with ICRF to simulate alpha particles: by using third harmonic He-4 heating, beam injected He-4 at 120 kV were accelerated to energies above 2 MeV taking advantage of the unique capability of JET to use NBI with 4 He and to confine MeV class ions. ICRF heating was used to replicate the dynamics of alpha heating and the control of an equivalent Q = 10 `burn' was simulated.

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