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  • 151. Leyland, M. J.
    et al.
    Beurskens, M. N. A.
    Flanagan, J. C.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Gibson, K. J.
    Kempenaars, M.
    Maslov, M.
    Scannell, R.
    Edge profile analysis of Joint European Torus (JET) Thomson scattering data: Quantifying the systematic error due to edge localised mode synchronisation2016In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 87, no 1, article id 013507Article in journal (Refereed)
    Abstract [en]

    The Joint European Torus (JET) high resolution Thomson scattering (HRTS) system measures radial electron temperature and density profiles. One of the key capabilities of this diagnostic is measuring the steep pressure gradient, termed the pedestal, at the edge of JET plasmas. The pedestal is susceptible to limiting instabilities, such as Edge Localised Modes (ELMs), characterised by a periodic collapse of the steep gradient region. A common method to extract the pedestal width, gradient, and height, used on numerous machines, is by performing a modified hyperbolic tangent (mtanh) fit to overlaid profiles selected from the same region of the ELM cycle. This process of overlaying profiles, termed ELM synchronisation, maximises the number of data points defining the pedestal region for a given phase of the ELM cycle. When fitting to HRTS profiles, it is necessary to incorporate the diagnostic radial instrument function, particularly important when considering the pedestal width. A deconvolved fit is determined by a forward convolution method requiring knowledge of only the instrument function and profiles. The systematic error due to the deconvolution technique incorporated into the JET pedestal fitting tool has been documented by Frassinetti et al. [Rev. Sci. Instrum. 83, 013506 (2012)]. This paper seeks to understand and quantify the systematic error introduced to the pedestal width due to ELM synchronisation. Synthetic profiles, generated with error bars and point-to-point variation characteristic of real HRTS profiles, are used to evaluate the deviation from the underlying pedestal width. We find on JET that the ELM synchronisation systematic error is negligible in comparison to the statistical error when assuming ten overlaid profiles (typical for a pre-ELM fit to HRTS profiles). This confirms that fitting a mtanh to ELM synchronised profiles is a robust and practical technique for extracting the pedestal structure.

  • 152. Leyland, M. J.
    et al.
    Beurskens, M. N. A.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    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 wall2015In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 55, no 1, article id 013019Article in journal (Refereed)
    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.

  • 153. Leyland, M. J.
    et al.
    Beurskens, M. N. A.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    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 wall2013In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 53, no 8, p. 083028-Article in journal (Refereed)
    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.

  • 154. Liang, Y
    et al.
    Lomas, P
    Nunes, I
    Gryaznevich, M
    Beurskens, M
    Brezinsek, S
    Coenen, J
    Derren, P
    Eich, T
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Gerasimov, S
    Harting, D
    Jachmich, S
    Meigs, A
    Pearson, P
    Rach, J
    Samuli, S
    Siegelin, S
    Yang, Y
    Mitigation of Type-I ELMs with n =2 Fields on JET2012In: 24th IAEA Fusion Energy Conference, 8-13 October 2012, 2012, p. EX/P4-23-Conference paper (Refereed)
    Abstract [en]

    Recently, strong mitigation of Type-I Edge Localized Modes (ELMs) has been observed with application of the n = 2 field in high collisionality (nu^*_e=2.0) H-mode plasma on JET tokamak with ITER-like wall. In this experiment, the EFCC power supply system has been enhanced with a coil current up to 88kAt (twice than before). With an n = 2 field, the large type-I ELMs with frequency of ~ 45 Hz was replaced by the high frequency (few hundreds Hz) small ELMs. No density pump-out was observed during an application of the n = 2 field. The influence of the n = 2 field on the core and the pedestal electron pressure profiles is within the error bar and it can be neglected. During the normal type-I ELM H-mode phase, the maximal surface temperature (Tmax) on the outer divertor plate was overall increasing and associated with large periodical variation due to the type-I ELMs. However, during an application of the n = 2 field, Tmax was saturated and has only small variation in few degrees due to the small mitigated ELMs. Splitting of the outer strike point has been observed during the strong mitigation of the type-I ELMs.

  • 155. 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, School of Electrical Engineering (EES), Fusion Plasma Physics.
    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 wall2013In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 53, no 7, p. 073036-Article in journal (Refereed)
    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.

  • 156. Lituadon, Xavier
    et al.
    Bergsåker, Henric
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Bykov, Igor
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Garcia-Carrasco, Alvaro
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Jonsson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Petersson, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Rubel, Marek
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Stefániková, Estera
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Tholerus, Emmi
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Vallejos Olivares, Pablo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Weckmann, Armin
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Zhou, Yushan
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Ström, Petter
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    et al.,
    Overview of the JET results in support to ITER2017In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 57, no 10, article id 102001Article in journal (Refereed)
    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.

  • 157. 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, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Plasma density and temperature evolution following the H-mode transition at JET and implications for ITER2013In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 53, no 8, p. 083031-Article in journal (Refereed)
    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.

  • 158. Loarte, A.
    et al.
    Leyland, M.
    Mier, J.A.
    Beurskens, M.N.A.
    Nunes, I.
    Parail, V.
    Lomas, P.
    Saibene, G.
    Sartori, R.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Plasma density evolution following the H-mode transition at JET and implications for ITER2012In: 39th EPS Conference on Plasma Physics 2012, EPS 2012 and the 16th International Congress on Plasma Physics, 2012, p. 686-689Conference paper (Refereed)
  • 159. 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, School of Electrical Engineering (EES), Fusion Plasma Physics.
    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 JET2014In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 54, no 7, p. 073016-Article in journal (Refereed)
    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.

  • 160. Maggi, C. F.
    et al.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    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 wall2017In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 57, no 11, article id 116012Article in journal (Refereed)
    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.

  • 161. Maggi, C. F.
    et al.
    Saarelma, S.
    Casson, F. J.
    Challis, C.
    de la Luna, E.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    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-modes2015In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 55, no 11, article id 113031Article in journal (Refereed)
    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.

  • 162. Maggi, C
    et al.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Saarelma, S
    Delabie, E
    Horvath, L
    Lunnis, A
    Lupelli, I
    Casson, F
    Leyland, M
    Pamela, S
    Urano, H
    Wilson, H
    Studies of the Pedestal Structure in JET with the ITER-Like Wall2016In: 26th IAEA Fusion Energy Conference, 17-22 October 2016, 2016Conference paper (Refereed)
  • 163. Mantica, P.
    et al.
    Angioni, C.
    Baiocchi, B.
    Baruzzo, M.
    Beurskens, M. N. A.
    Bizarro, J. P. S.
    Budny, R. V.
    Buratti, P.
    Casati, A.
    Challis, C.
    Citrin, J.
    Colyer, G.
    Crisanti, F.
    Figueiredo, A. C. A.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Giroud, C.
    Hawkes, N.
    Hobirk, J.
    Joffrin, E.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Lerche, E.
    Migliano, P.
    Naulin, V.
    Peeters, A. G.
    Rewoldt, G.
    Ryter, F.
    Salmi, A.
    Sartori, R.
    Sozzi, C.
    Staebler, G.
    Strintzi, D.
    Tala, T.
    Tsalas, M.
    Van Eester, D.
    Versloot, T.
    de Vries, P. C.
    Weiland, J.
    Ion heat transport studies in JET2011In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 53, no 12, p. 124033-Article in journal (Refereed)
    Abstract [en]

    Detailed experimental studies of ion heat transport have been carried out in JET exploiting the upgrade of active charge exchange spectroscopy and the availability of multi-frequency ion cyclotron resonance heating with (3)He minority. The determination of ion temperature gradient (ITG) threshold and ion stiffness offers unique opportunities for validation of the well-established theory of ITG driven modes. Ion stiffness is observed to decrease strongly in the presence of toroidal rotation when the magnetic shear is sufficiently low. This effect is dominant with respect to the well-known omega(ExB) threshold up-shift and plays a major role in enhancing core confinement in hybrid regimes and ion internal transport barriers. The effects of T(e)/T(i) and s/q on ion threshold are found rather weak in the domain explored. Quasi-linear fluid/gyro-fluid and linear/non-linear gyro-kinetic simulations have been carried out. Whilst threshold predictions show good match with experimental observations, some significant discrepancies are found on the stiffness behaviour.

  • 164. Mantica, P
    et al.
    Angioni, C
    Baiocchi, B
    Challis, C
    Citrin, J
    Colyer, G
    Figueiredo, A
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Joffrin, E
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Versloot, T.W.
    et, al
    Key to Improved Ion Core Confinement in the JET Tokamak: Ion Stiffness Mitigation due to Combined Plasma Rotation and Low Magnetic Shear2010Conference paper (Other academic)
    Abstract [en]

    New experimental evidence indicates that ion stiffness mitigation in the core of rotating plasmas, observed previously in JET, results from the combined effect of high rotational shear and low magnetic shear. Ionstiffness in the outer plasma region is found to remain very high irrespective of rotation. Dedicated experimentsin plasmas with different q profiles and rotation levels point to a larger effect of rotation in reducing stiffnesswhen the core q profile is made flatter. The results have implications for the understanding of improved ion coreconfinement in hybrid plasmas or Internal Transport Barriers, both characterized by high rotation and low magnetic shear. Experimental evidence in these scenarios is discussed. Simulations indicate that the physics behindthese results may lie in the ITG/TEM turbulence behavior at the transition between fully developed turbulenceand zonal flows quenching. These findings point to the need for future devices of achieving sufficient rotationalshear and capability of q profile manipulation to reach improved ion core confinement, which is an essentialfeature of Advanced Tokamak operation.

  • 165. Mantica, P.
    et al.
    Angioni, C.
    Challis, C.
    Colyer, G.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hawkes, N.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Tsalas, M.
    deVries, P. C.
    Weiland, J.
    Baiocchi, B.
    Beurskens, M. N. A.
    Figueiredo, A. C. A.
    Giroud, C.
    Hobirk, J.
    Joffrin, E.
    Lerche, E.
    Naulin, V.
    Peeters, A. G.
    Salmi, A.
    Sozzi, C.
    Strintzi, D.
    Staebler, G.
    Tala, T.
    Van Eester, D.
    Versloot, T.
    A Key to Improved Ion Core Confinement in the JET Tokamak: Ion Stiffness Mitigation due to Combined Plasma Rotation and Low Magnetic Shear2011In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 107, no 13, p. 135004-Article in journal (Refereed)
    Abstract [en]

    New transport experiments on JET indicate that ion stiffness mitigation in the core of a rotating plasma, as described by Mantica et al. [Phys. Rev. Lett. 102, 175002 (2009)] results from the combined effect of high rotational shear and low magnetic shear. The observations have important implications for the understanding of improved ion core confinement in advanced tokamak scenarios. Simulations using quasilinear fluid and gyrofluid models show features of stiffness mitigation, while nonlinear gyrokinetic simulations do not. The JET experiments indicate that advanced tokamak scenarios in future devices will require sufficient rotational shear and the capability of q profile manipulation.

  • 166. Mantica, P
    et al.
    Angioni, C
    Valisa, M
    Baruzzo, M
    Belo, P
    Beurskens, M
    Challis, C
    De l'Abie, E
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Giroud, C
    Hawkes, N
    Hobirk, J
    Joffrin, E
    Transport analysis of Tungsten and Beryllium in JET Hybrid Plasmas with the ITER like wall2013In: 40th European Physical Society (EPS) Conference on Plasma Physics: July 1 – July 5, 2013,  Aalto, Finland, 2013Conference paper (Refereed)
  • 167.
    Marco, Aitor
    et al.
    IDOM, Adv Design & Anal Dept, Bilbao, Spain..
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Zuin, M.
    Consorzio RFX, Corso Stati Uniti 4, I-35127 Padua, Italy..
    et al.,
    Sliding Surface Based Schemes for the Tokamak a Configuration Variable2018In: 2018 WORLD AUTOMATION CONGRESS (WAC), IEEE , 2018, p. 253-258Conference paper (Refereed)
    Abstract [en]

    Fusion power may be seen as the energy of the future in the sense that it composes a potentially clean, cheap and unlimited power source that would reduce the worldwide dependency on non-renewable energies. Nevertheless, while nowadays the fusion reaction process itself has been achieved, significant net power has not yet been obtained, since the generated plasma needs to remain in particular pressure and temperature conditions. For this purpose, the plasma has to be confined. To do so, one of the solutions is to use a fusion reactor device that creates magnetic fields in a toroidal chamber, called Tokamak reactor. The main issue of Tokamak reactors is the presence of plasma instabilities, which provoke the fusion reaction decay and, in consequence, a reduction in the pulse duration. To maintain this pulse duration as long as possible, the use of robust and fast controllers is mandatory due to the unpredictability and the small time constant of the plasma behavior. In this context, this article focuses on improving the controllability of the plasma current, a relevant control variable, crucial during the plasma heating and confinement processes. In particular, two new robust control schemes based on sliding surfaces, namely, a Sliding Mode Controller (SMC) and a Supertwisting Controller (STC) are presented and applied to the plasma current control problem. In order to test the validity and goodness of the proposed controllers, their behavior is compared to that of the traditional PID schemes applied in these systems, using the RZIp model for the TCV (Tokamak a Configuration Variable) reactor. The obtained results are very promising, leading to consider these controllers as strong candidates to improve the performance of the PID-based controllers usually employed in this kind of systems.

  • 168.
    Marco, Aitor
    et al.
    IDOM, Adv Design & Anal Dept, Bilbao, Spain..
    Garrido, Aitor J.
    Univ Basque Country, UPV EHU, Inst Res & Dev Proc, ACG,IIDP,Automat Control & Syst Engn Dept, Bilbao, Spain..
    Coda, Stefano
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Garrido, Izaskun
    Univ Basque Country, UPV EHU, Inst Res & Dev Proc, ACG,IIDP,Automat Control & Syst Engn Dept, Bilbao, Spain..
    Ahn, J.
    Albanese, R.
    Alberti, S.
    Alessi, E.
    CNR, IFP, Via R Cozzi 53, I-20125 Milan, Italy..
    Allan, S.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Anand, H.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Anastassiou, G.
    Natl Tech Univ Athens, Athens, Greece..
    Andrebe, Y.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Angioni, C.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Ariola, M.
    Univ Napoli Parthenope, Consorzio CREATE, Via Claudio 21, I-80125 Naples, Italy..
    Bernert, M.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Beurskens, M.
    Max Planck Inst Plasma Phys, Teilinst Greifswald, D-17491 Greifswald, Germany..
    Bin, W.
    CNR, IFP, Via R Cozzi 53, I-20125 Milan, Italy..
    Blanchard, P.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Blanken, T. C.
    Eindhoven Univ Technol, POB 513, NL-5600 MB Eindhoven, Netherlands..
    Boedo, J. A.
    Univ Calif San Diego, Energy Res Ctr, La Jolla, CA 92093 USA..
    Bolzonella, T.
    Consorzio RFX, Corso Stati Uniti 4, I-35127 Padua, Italy..
    Bouquey, F.
    IRFM, CEA, F-13108 St Paul Les Durance, France..
    Braunmueller, F. H.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Bufferand, H.
    IRFM, CEA, F-13108 St Paul Les Durance, France..
    Buratti, P.
    ENEA CR Frascati, Unita Tecn Fus, Via E Fermi 45, I-00044 Rome, Italy..
    Calabro, G.
    ENEA CR Frascati, Unita Tecn Fus, Via E Fermi 45, I-00044 Rome, Italy..
    Camenen, Y.
    Aix Marseille Univ, CNRS, PIIM, F-13013 Marseille, France..
    Carnevale, D.
    Univ Roma Tor Vergata, Via Politecn 1, I-00133 Rome, Italy..
    Carpanese, F.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Causa, F.
    ENEA CR Frascati, Unita Tecn Fus, Via E Fermi 45, I-00044 Rome, Italy..
    Cesario, R.
    ENEA CR Frascati, Unita Tecn Fus, Via E Fermi 45, I-00044 Rome, Italy..
    Chapman, I. T.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Chellai, O.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Choi, D.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Cianfarani, C.
    ENEA CR Frascati, Unita Tecn Fus, Via E Fermi 45, I-00044 Rome, Italy..
    Ciraolo, G.
    IRFM, CEA, F-13108 St Paul Les Durance, France..
    Citrin, J.
    FOM Inst DIFFER Dutch Inst Fundamental Energy Res, Eindhoven, Netherlands..
    Costea, S.
    Univ Innsbruck, Inst Ionen & Angew Phys, Tech Str 25, A-6020 Innsbruck, Austria..
    Crisanti, F.
    ENEA CR Frascati, Unita Tecn Fus, Via E Fermi 45, I-00044 Rome, Italy..
    Cruz, N.
    Univ Lisbon, Inst Super Tecn, Inst Plasmas & Fusao Nucl, Lisbon, Portugal..
    Czarnecka, A.
    Inst Plasma Phys & Laser Microfus, Hery 23, PL-01497 Warsaw, Poland..
    Decker, J.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    De Masi, G.
    Consorzio RFX, Corso Stati Uniti 4, I-35127 Padua, Italy..
    De Tommasi, G.
    Univ Napoli Federico II, Consorzio CREATE, Via Claudio 21, I-80125 Naples, Italy..
    Douai, D.
    IRFM, CEA, F-13108 St Paul Les Durance, France..
    Dunne, M.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Duval, B. P.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Eich, T.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Elmore, S.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Esposito, B.
    ENEA CR Frascati, Unita Tecn Fus, Via E Fermi 45, I-00044 Rome, Italy..
    Faitsch, M.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Fasoli, A.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Fedorczak, N.
    IRFM, CEA, F-13108 St Paul Les Durance, France..
    Felici, F.
    Eindhoven Univ Technol, POB 513, NL-5600 MB Eindhoven, Netherlands..
    Fevrier, O.
    IRFM, CEA, F-13108 St Paul Les Durance, France..
    Ficker, O.
    Inst Plasma Phys AS CR, Za Slovankou 1782-3, Prague 18200, Czech Republic..
    Fietz, S.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Fontana, M.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Furno, I.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Galeani, S.
    Univ Roma Tor Vergata, Via Politecn 1, I-00133 Rome, Italy..
    Gallo, A.
    IRFM, CEA, F-13108 St Paul Les Durance, France..
    Galperti, C.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Garavaglia, S.
    CNR, IFP, Via R Cozzi 53, I-20125 Milan, Italy..
    Garrido, I.
    Univ Basque Country, UPV EHU, Fac Engn, Paseo RafaelMoreno 3, Bilbao 48013, Spain..
    Geiger, B.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany.;Max Planck Inst Plasma Phys, Teilinst Greifswald, D-17491 Greifswald, Germany..
    Giovannozzi, E.
    ENEA CR Frascati, Unita Tecn Fus, Via E Fermi 45, I-00044 Rome, Italy..
    Gobbin, M.
    Consorzio RFX, Corso Stati Uniti 4, I-35127 Padua, Italy..
    Goodman, T. P.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Gorini, G.
    Univ Milano Bicocca, Dept Phys G Occhialini, Piazza Sci 3, I-20126 Milan, Italy..
    Gospodarczyk, M.
    Univ Roma Tor Vergata, Via Politecn 1, I-00133 Rome, Italy..
    Granucci, G.
    CNR, IFP, Via R Cozzi 53, I-20125 Milan, Italy..
    Graves, J. P.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Guirlet, R.
    IRFM, CEA, F-13108 St Paul Les Durance, France..
    Hakola, A.
    VTT Tech Res Ctr Finland Ltd, POB 1000, FI-02044 Espoo, Finland..
    Ham, C.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Harrison, J.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Hawke, J.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Hennequin, P.
    Ecole Polytech, CNRS, UMR7648, Lab Phys Plasmas, F-91128 Palaiseau, France..
    Hnat, B.
    Univ Oxford, Rudolf Peierls Ctr Theoret Phys, Oxford, England.;Culham Ctr Fus Energy, Abingdon, Oxon, England..
    Hogeweij, D.
    FOM Inst DIFFER Dutch Inst Fundamental Energy Res, Eindhoven, Netherlands..
    Hogge, J. -Ph.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Honore, C.
    Ecole Polytech, CNRS, UMR7648, Lab Phys Plasmas, F-91128 Palaiseau, France..
    Hopf, C.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Horacek, J.
    Inst Plasma Phys AS CR, Za Slovankou 1782-3, Prague 18200, Czech Republic..
    Huang, Z.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Igochine, V.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Innocente, P.
    Consorzio RFX, Corso Stati Uniti 4, I-35127 Padua, Italy..
    Schrittwieser, C. Ionita
    Univ Innsbruck, Inst Ionen & Angew Phys, Tech Str 25, A-6020 Innsbruck, Austria..
    Isliker, H.
    Aristotle Univ Thessaloniki, Thessaloniki, Greece..
    Jacquier, R.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Jardin, A.
    IRFM, CEA, F-13108 St Paul Les Durance, France..
    Kamleitner, J.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Karpushov, A.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Keeling, D. L.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Kirneva, N.
    Kurchatov Inst, Natl Res Ctr, Inst Phys Tokamaks, Kurchatov Sq 1, Moscow 123182, Russia.;Natl Res Nucl Univ MEPhI, Moscow Engn Phys Inst, Kashirskoe Sh 31, Moscow 115409, Russia..
    Kong, M.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Koubiti, M.
    Aix Marseille Univ, CNRS, PIIM, F-13013 Marseille, France..
    Kovacic, J.
    Jozef Stefan Inst, Jamova 39, SI-1000 Ljubljana, Slovenia..
    Kramer-Flecken, A.
    Forschungszentrum Julich, Inst Energie & Klimaforsch, Plasmaphys, D-52425 Julich, Germany..
    Krawczyk, N.
    Inst Plasma Phys & Laser Microfus, Hery 23, PL-01497 Warsaw, Poland..
    Kudlacek, O.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany.;Consorzio RFX, Corso Stati Uniti 4, I-35127 Padua, Italy..
    Labit, B.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Lazzaro, E.
    CNR, IFP, Via R Cozzi 53, I-20125 Milan, Italy..
    Le, H. B.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Lipschultz, B.
    Univ York, York Plasma Inst, Dept Phys, York YO10 5DD, N Yorkshire, England..
    Llobet, X.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Lomanowski, B.
    Univ Durham, Dept Phys, Durham DH1 3LE, England..
    Loschiavo, V. P.
    Univ Napoli Federico II, Consorzio CREATE, Via Claudio 21, I-80125 Naples, Italy..
    Lunt, T.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Maget, P.
    IRFM, CEA, F-13108 St Paul Les Durance, France..
    Maljaars, E.
    Eindhoven Univ Technol, POB 513, NL-5600 MB Eindhoven, Netherlands..
    Malygin, A.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Maraschek, M.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Marini, C.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Martin, P.
    Consorzio RFX, Corso Stati Uniti 4, I-35127 Padua, Italy..
    Martin, Y.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Mastrostefano, S.
    Univ Napoli Parthenope, Consorzio CREATE, Via Claudio 21, I-80125 Naples, Italy..
    Maurizio, R.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Mavridis, M.
    Aristotle Univ Thessaloniki, Thessaloniki, Greece..
    Mazon, D.
    IRFM, CEA, F-13108 St Paul Les Durance, France..
    McAdams, R.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    McDermott, R.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Merle, A.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Meyer, H.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Militello, F.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Miron, I. G.
    Natl Inst Laser Plasma & Radiat Phys, POB MG-36, Bucharest, Romania..
    Cabrera, P. A. Molina
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Moret, J. -M
    Moro, A.
    CNR, IFP, Via R Cozzi 53, I-20125 Milan, Italy..
    Moulton, D.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Naulin, V.
    Tech Univ Denmark, Dept Phys, Bldg 309, DK-2800 Lyngby, Denmark..
    Nespoli, F.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Nielsen, A. H.
    Tech Univ Denmark, Dept Phys, Bldg 309, DK-2800 Lyngby, Denmark..
    Nocente, M.
    Univ Milano Bicocca, Dept Phys G Occhialini, Piazza Sci 3, I-20126 Milan, Italy..
    Nouailletas, R.
    IRFM, CEA, F-13108 St Paul Les Durance, France..
    Nowak, S.
    CNR, IFP, Via R Cozzi 53, I-20125 Milan, Italy..
    Odstrcil, T.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Papp, G.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Paprok, R.
    Inst Plasma Phys AS CR, Za Slovankou 1782-3, Prague 18200, Czech Republic..
    Pau, A.
    Univ Cagliari, Dept Elect & Elect Engn, Piazza Armi, I-09123 Cagliari, Italy..
    Pautasso, G.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Ridolfini, V. Pericoli
    Univ Napoli Parthenope, Consorzio CREATE, Via Claudio 21, I-80125 Naples, Italy..
    Piovesan, P.
    Consorzio RFX, Corso Stati Uniti 4, I-35127 Padua, Italy..
    Piron, C.
    Consorzio RFX, Corso Stati Uniti 4, I-35127 Padua, Italy..
    Pisokas, T.
    Aristotle Univ Thessaloniki, Thessaloniki, Greece..
    Porte, L.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Preynas, M.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Ramogida, G.
    ENEA CR Frascati, Unita Tecn Fus, Via E Fermi 45, I-00044 Rome, Italy..
    Rapson, C.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Rasmussen, J. Juul
    Tech Univ Denmark, Dept Phys, Bldg 309, DK-2800 Lyngby, Denmark..
    Reich, M.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Reimerdes, H.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Reux, C.
    IRFM, CEA, F-13108 St Paul Les Durance, France..
    Ricci, P.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Rittich, D.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Riva, F.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Robinson, T.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Saarelma, S.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Saint-Laurent, F.
    IRFM, CEA, F-13108 St Paul Les Durance, France..
    Sauter, O.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Scannell, R.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Schlatter, Ch.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Schneider, B.
    Univ Innsbruck, Inst Ionen & Angew Phys, Tech Str 25, A-6020 Innsbruck, Austria..
    Schneider, P.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Schrittwieser, R.
    Univ Innsbruck, Inst Ionen & Angew Phys, Tech Str 25, A-6020 Innsbruck, Austria..
    Sciortino, F.
    MIT, Plasma Sci & Fusion Ctr, 77 Massachusetts Ave, Cambridge, MA 02139 USA..
    Sertoli, M.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Sheikh, U.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Sieglin, B.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Silva, M.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Sinha, J.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Sozzi, C.
    CNR, IFP, Via R Cozzi 53, I-20125 Milan, Italy..
    Spolaore, M.
    Consorzio RFX, Corso Stati Uniti 4, I-35127 Padua, Italy..
    Stange, T.
    Max Planck Inst Plasma Phys, Teilinst Greifswald, D-17491 Greifswald, Germany..
    Stoltzfus-Dueck, T.
    Princeton Univ, Princeton, NJ 08544 USA..
    Tamain, P.
    IRFM, CEA, F-13108 St Paul Les Durance, France..
    Teplukhina, A.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Testa, D.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Theiler, C.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Thornton, A.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Tophoj, L.
    Tech Univ Denmark, Dept Phys, Bldg 309, DK-2800 Lyngby, Denmark..
    Tran, M. Q.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Tsironis, C.
    Natl Tech Univ Athens, Athens, Greece..
    Tsui, C.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland.;Univ Calif San Diego, Energy Res Ctr, La Jolla, CA 92093 USA..
    Uccello, A.
    CNR, IFP, Via R Cozzi 53, I-20125 Milan, Italy..
    Vartanian, S.
    IRFM, CEA, F-13108 St Paul Les Durance, France..
    Verdoolaege, G.
    UG Ghent Univ, Dept Appl Phys, St Pietersnieuwstraat 41, B-9000 Ghent, Belgium..
    Verhaegh, K.
    Univ York, York Plasma Inst, Dept Phys, York YO10 5DD, N Yorkshire, England..
    Vermare, L.
    Ecole Polytech, CNRS, UMR7648, Lab Phys Plasmas, F-91128 Palaiseau, France..
    Vianello, N.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland.;Consorzio RFX, Corso Stati Uniti 4, I-35127 Padua, Italy..
    Vijvers, W. A. J.
    FOM Inst DIFFER Dutch Inst Fundamental Energy Res, Eindhoven, Netherlands..
    Vlahos, L.
    Aristotle Univ Thessaloniki, Thessaloniki, Greece..
    Vu, N. M. T.
    Inst Polytech Grenoble, Lab Concept & Integrat Syst, BP54, F-26902 Valence 09, France..
    Walkden, N.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Wauters, T.
    Ecole Royale Mil, Koninklijke Mil Sch, Lab Plasma Phys, Renaissancelaan 30 Ave Renaissance, B-1000 Brussels, Belgium..
    Weisen, H.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Wischmeier, M.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Zestanakis, P.
    Natl Tech Univ Athens, Athens, Greece..
    Zuin, M.
    Consorzio RFX, Corso Stati Uniti 4, I-35127 Padua, Italy..
    A Variable Structure Control Scheme Proposal for the Tokamak a Configuration Variable2019In: Complexity, ISSN 1076-2787, E-ISSN 1099-0526, article id 2319560Article in journal (Refereed)
    Abstract [en]

    Fusion power is the most significant prospects in the long-term future of energy in the sense that it composes a potentially clean, cheap, and unlimited power source that would substitute the widespread traditional nonrenewable energies, reducing the geographical dependence on their sources as well as avoiding collateral environmental impacts. Although the nuclear fusion research started in the earlier part of 20th century and the fusion reactors have been developed since the 1950s, the fusion reaction processes achieved have not yet obtained net power, since the generated plasma requires more energy to achieve and remain in necessary particular pressure and temperature conditions than the produced profitable energy. For this purpose, the plasma has to be confined inside a vacuum vessel, as it is the case of the Tokamak reactor, which consists of a device that generates magnetic fields within a toroidal chamber, being one of the most promising solutions nowadays. However, the Tokamak reactors still have several issues such as the presence of plasma instabilities that provokes a decay of the fusion reaction and, consequently, a reduction in the pulse duration. In this sense, since long pulse reactions are the key to produce net power, the use of robust and fast controllers arises as a useful tool to deal with the unpredictability and the small time constant of the plasma behavior. In this context, this article focuses on the application of robust control laws to improve the controllability of the plasma current, a crucial parameter during the plasma heating and confinement processes. In particular, a variable structure control scheme based on sliding surfaces, namely, a sliding mode controller (SMC) is presented and applied to the plasma current control problem. In order to test the validity and goodness of the proposed controller, its behavior is compared to that of the traditional PID schemes applied in these systems, using the RZIp model for the Tokamak a Configuration Variable (TCV) reactor. The obtained results are very promising, leading to consider this controller as a strong candidate to enhance the performance of the PID-based controllers usually employed in this kind of systems.

  • 169. Marrelli, L.
    et al.
    Frassinetti, Lorenzo
    Consorzio RFX.
    Martin, P.
    Sarff, J.S.
    Reduced intermittency in the magnetic turbulence of reversed field pinch plasmas2005In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 12, no 3, p. 030701-Article in journal (Refereed)
    Abstract [en]

    The statistical temporal properties of broadband magnetic turbulence in the edge of reversed field pinch (RFP) plasmas are significantly altered when global magnetohydrodynamic tearing modes and magnetic relaxation are reduced. Standard RFP plasmas, having relatively large tearing fluctuations, exhibit broadband intermittent bursts of magnetic fluctuations in the bandwidth f < 1.5 MHz. When the global tearing is reduced via parallel current drive in the edge region, the magnetic turbulence is much less intermittent and has statistical behavior typical of self-similar turbulence (like that expected in self-organized criticality systems). A connection between intermittency and long wavelength plasma instabilities is therefore implied.

  • 170. Martin, P.
    et al.
    Marrelli, L.
    Alfier, A.
    Bonomo, F.
    Escande, D.
    Franz, P.
    Frassinetti, Lorenzo
    Consorzio RFX.
    Gobbin, M.
    Pasqualotto, R.
    Piovesan, P.
    Terranova, D.
    A new paradigm for RFP magnetic self-organization: results and challenges2007In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 49, no 5A, p. A177-A193Article in journal (Refereed)
    Abstract [en]

    This paper reports the most recent experimental results on quasi-single helicity (QSH) reversed field pinch (RFP) plasmas. QSH is considered a key element towards the full experimental realization of the theoretically predicted single helicity (SH) RFP. The SH RFP, where an individual resistive kink mode and its harmonics drive the dynamo electric field, is predicted to have superior confinement performance with respect to the standard multiple helicity (MH) state. Magnetic chaos is in fact strongly reduced in the SH RFP, which therefore retains all the positive features of the RFP configuration without the problems connected with the magnetic turbulence typical of the MH scenario. Data from the RFX-mod device, presented here, provide a more complete description of QSH states, indicate a positive synergy between the growth of the dominant resistive mode and the decrease in the secondary modes (with reduction of magnetic chaos and hints of confinement improvement outside the helical domain), and showa promising scaling with plasma current. Initial experiments on active control of QSH states in RFX-mod are presented.

  • 171. 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, Superseded Departments, Alfvén Laboratory.
    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 pinches2003In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 43, no 12, p. 1855-1862Article in journal (Refereed)
  • 172. 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, School of Electrical Engineering (EES), Fusion Plasma Physics.
    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, School of Electrical Engineering (EES), Fusion Plasma Physics.
    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 programme2013In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 53, no 10, p. 104018-Article, review/survey (Refereed)
    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 &lt; 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.

  • 173.
    Menmuir, Sheena
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics. EURATOM-VR Association, Denmark .
    Bergsåker, Henric
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics. EURATOM-VR Association, Denmark .
    Brunsell, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics. EURATOM-VR Association, Denmark .
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics. EURATOM-VR Association, Denmark .
    Drake, James Robert
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics. EURATOM-VR Association, Denmark .
    Particle flux and surface interaction in EXTRAP T2R2007In: 34th EPS Conference on Plasma Physics 2007, EPS 2007 - Europhysics Conference Abstracts, European Physical Society , 2007, p. 347-350Conference paper (Refereed)
  • 174.
    Menmuir, Sheena
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Brunsell, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Khan, Muhammad Waqas Mehmood
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Olofsson, Erik
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Drake, James Robert
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Response of EXTRAP T2R plasma velocity and ion temperature profiles to varying plasma conditions2011In: 38th EPS Conference on Plasma Physics 2011, EPS 2011 - Europhysics Conference Abstracts, 2011, p. 1216-1219Conference paper (Refereed)
  • 175.
    Menmuir, Sheena
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Hedqvist, Anders
    KTH, School of Engineering Sciences (SCI), Physics.
    Kuldkepp, Mattias
    KTH, School of Engineering Sciences (SCI), Physics.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics.
    Brunsell, Per R.
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Drake, James Robert
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Large periodic fluctuations of plasma signals in EXTRAP T2R2007In: Proceedings of the 34th European Physical Society Conference on Plasma Physics, 2007Conference paper (Refereed)
  • 176. Meyer, H.
    et al.
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    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.
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    Brezinsek, S.
    Brida, D.
    Brochard, F.
    Buchanan, J.
    Bufferand, H.
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    Calabro, G.
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    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.
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    Dimitrova, M.
    D'Inca, R.
    Doric, V.
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    Dudson, B.
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    Easy, L.
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    Figueiredo, A.
    Fil, A.
    Fishpool, G.
    Fitzgerald, M.
    Fontana, M.
    Ford, O.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Fridstr, R.
    Frigione, D.
    Fuchert, G.
    Fuchs, C.
    Palumbo, M. Furno
    Futatani, S.
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    Gallo, A.
    Galperti, C.
    Gao, Y.
    Garavaglia, S.
    Garcia, J.
    Garcia-Carrasco, Alvaro
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Garcia-Lopez, J.
    Garcia-Munoz, M.
    Gardarein, J. -L
    Garzotti, L.
    Gaspar, J.
    Gauthier, E.
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    Gleason Gonzalez, C.
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    Gorini, G.
    Gospodarczyk, M.
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    Ham, C.
    Happel, T.
    Harrison, J.
    Harting, D.
    Hauer, V.
    Havlickova, E.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Helou, W.
    Henderson, S.
    Hennequin, P.
    Heyn, M.
    Hnat, B.
    Holzl, M.
    Hogeweij, D.
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    Ivanova-Stanik, I.
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    Jardin, A.
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    Jenko, F.
    Jensen, T.
    Busk, O. Jeppe Miki
    Jessen, M.
    Joffrin, E.
    Jones, O.
    Jonsson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Kallenbach, A.
    Kallinikos, N.
    Kalvin, S.
    Kappatou, A.
    Karhunen, J.
    Karpushov, A.
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    Leyland, M.
    Li, L.
    Liang, Y.
    Lipschultz, B.
    Liu, Y. Q.
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    Loarte, A.
    Loewenhoff, T.
    Lomanowski, B.
    Loschiavo, V. P.
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    Lyssoivan, A.
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    Maggiora, R.
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    Mantica, P.
    Mantsinen, M.
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    Parra, I.
    Pau, A.
    Pautasso, G.
    Pehkonen, S. -P
    Pereira, A.
    Cippo, E. Perelli
    Ridolfini, V. Pericoli
    Peterka, M.
    Petersson, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    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, School of Electrical Engineering (EES), Fusion Plasma Physics.
    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, School of Electrical Engineering (EES), Space and Plasma Physics.
    Tophoj, L.
    Treutterer, W.
    Trevisan, G. L.
    Tripsky, M.
    Tsironis, C.
    Tsui, C.
    Tudisco, O.
    Uccello, A.
    Urban, J.
    Valisa, M.
    Vallejos, Pablo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    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 solution2017In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 57, no 10, article id 102014Article in journal (Refereed)
    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.

  • 177. Meyer, H.
    et al.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Garcia Carrasco, Alvaro
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Ratynskaia, Svetlana V.
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Rubel, Marek
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Thorén, Emil
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Zohm, H.
    et al.,
    Overview of physics studies on ASDEX Upgrade2019In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 59, no 11, article id 112014Article in journal (Refereed)
    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.

  • 178. Neu, R.
    et al.
    Arnoux, G.
    Beurskens, M.
    Bobkov, V.
    Brezinsek, S.
    Bucalossi, J.
    Calabro, G.
    Challis, C.
    Coenen, J. W.
    De La Luna, E.
    De Vries, P. C.
    Dux, R.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Giroud, C.
    Groth, M.
    Hobirk, J.
    Joffrin, E.
    Lang, P.
    Lehnen, M.
    Lerche, E.
    Loarer, T.
    Lomas, P.
    Maddison, G.
    Maggi, C.
    Matthews, G.
    Marsen, S.
    Mayoral, M. -L
    Meigs, A.
    Mertens, P.
    Nunes, I.
    Philipps, V.
    Pütterich, T.
    Rimini, F.
    Sertoli, M.
    Sieglin, B.
    Sips, A. C. C.
    Van Eester, D.
    Van Rooij, G.
    First operation with the JET International Thermonuclear Experimental Reactor-like wall2013In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 20, no 5, p. 056111-1-056111-13Article in journal (Refereed)
    Abstract [en]

    To consolidate International Thermonuclear Experimental Reactor (ITER) design choices and prepare for its operation, Joint European Torus (JET) has implemented ITER's plasma facing materials, namely, Be for the main wall and W in the divertor. In addition, protection systems, diagnostics, and the vertical stability control were upgraded and the heating capability of the neutral beams was increased to over 30 MW. First results confirm the expected benefits and the limitations of all metal plasma facing components (PFCs) but also yield understanding of operational issues directly relating to ITER. H-retention is lower by at least a factor of 10 in all operational scenarios compared to that with C PFCs. The lower C content (≈ factor 10) has led to much lower radiation during the plasma burn-through phase eliminating breakdown failures. Similarly, the intrinsic radiation observed during disruptions is very low, leading to high power loads and to a slow current quench. Massive gas injection using a D2/Ar mixture restores levels of radiation and vessel forces similar to those of mitigated disruptions with the C wall. Dedicated L-H transition experiments indicate a 30% power threshold reduction, a distinct minimum density, and a pronounced shape dependence. The L-mode density limit was found to be up to 30% higher than for C allowing stable detached divertor operation over a larger density range. Stable H-modes as well as the hybrid scenario could be re-established only when using gas puff levels of a few 1021 es-1. On average, the confinement is lower with the new PFCs, but nevertheless, H factors up to 1 (H-Mode) and 1.3 (at β N ≈ 3, hybrids) have been achieved with W concentrations well below the maximum acceptable level.

  • 179.
    Olofsson, K. Erik J.
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Brunsell, Per R.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Drake, James Robert
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    A first attempt at few coils and low-coverage resistive wall mode stabilization of EXTRAP T2R2012In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 54, no 9, p. 094005-Article in journal (Refereed)
    Abstract [en]

    The reversed-field pinch features resistive-shell-type instabilities at any (vanishing and finite) plasma pressure. An attempt to stabilize the full spectrum of these modes using both (i) incomplete coverage and (ii) few coils is presented. Two empirically derived model-based control algorithms are compared with a baseline guaranteed suboptimal intelligent-shell-type (IS) feedback. Experimental stabilization could not be achieved for the coil array subset sizes considered by this first study. But the model-based controllers appear to significantly outperform the decentralized IS method.

  • 180. Osborne, T. H.
    et al.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Zabeo, L.
    et. al.,
    Scaling of H-Mode Pedestal and ELM Characteristics in the JET and DIII-D Tokamaks2010Conference paper (Refereed)
    Abstract [en]

    The dependence of the H-mode edge pedestal width and Type I edge localized mode (ELM) characteristics on ion gyro-radius, ρ*=ρ/a, was studied in experiments combining data from the JET and DIII-D tokamaks to achieve a factor of 4 variation in ρ* [M.N.A. Beurskens, et al., Plasma Phys. Control. Fusion (2010)]. No change was found in the radial or poloidal correlation lengths of density fluctuations in the ETB as a function of ρ*. The ELM energy loss normalized to the pedestal energy increased with ρ* on DIII-D to twice the value expected from an established scaling with collisionality; however, this trend was reversed on JET where the ΔWELM/WPED instead decreased weakly with increasing ρ*. The ELM size was also correlated with the proximity of the density to the value at which the power for transition from L- to H-mode is a minimum.

  • 181. Pamela, S
    et al.
    Eich, T
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Sieglin, B
    Saarelma, S
    Non-linear MHD simulations of ELMs in JET and quantitative comparisons to experiments2016In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 58, p. 014026-Article in journal (Refereed)
    Abstract [en]

    A subset of JET ITER-like wall (ILW) discharges, combining electron density and temperature as well as divertor heat flux measurements, has been collected for the validation of non-linear magnetohydrodynamic (MHD) simulations of edge-localised-modes (ELMs). This permits a quantitative comparison of simulation results against experiments, which is required for the validation of predicted ELM energy losses and divertor heat fluxes in future tokamaks like ITER. This paper presents the first results of such a quantitative comparison, and gives a perspective of what will be necessary to achieve full validation of non-linear codes like JOREK. In particular, the present study highlights the importance of pre-ELM equilibria and parallel energy transport models in MHD simulations, which form the underlying basis of ELM physics.

  • 182. Pamela, S
    et al.
    Hujisman, G
    Hoezl, M
    Giroud, C
    Saarelma, S
    Futatani, S
    Urano, H
    Bevoulet, M
    Lupelli, I
    Maggi, C
    Roach, C
    Chapman, I
    Kirk, A
    Harrison, J
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Dickinson, D
    Aiba, N
    Eich, T
    Lessig, F
    Orain, F
    Multimachine Modelling of ELMs and Pedestal Confinement: From Validation to Prediction2016In: 26th IAEA Fusion Energy Conference, 17-22 October 2016, 2016Conference paper (Refereed)
  • 183. Pamela, S. J. P.
    et al.
    Huijsmans, G. T. A.
    Eich, T.
    Saarelma, S.
    Lupelli, I.
    Maggi, C. F.
    Giroud, C.
    Chapman, I. T.
    Smith, S. F.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. EUROfus Consortium, England.
    Becoulet, M.
    Hoelzl, M.
    Orain, F.
    Futatani, S.
    Recent progress in the quantitative validation of JOREK simulations of ELMs in JET2017In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 57, no 7, article id 076006Article in journal (Refereed)
    Abstract [en]

    Future devices like JT-60SA, ITER and DEMO require quantitative predictions of pedestal density and temperature levels, as well as inter-ELM and ELM divertor heat fluxes, in order to improve global confinement capabilities while preventing divertor erosion/melting in the planning of future experiments. Such predictions can be obtained from dedicated pedestal models like EPED, and from non-linear MHD codes like JOREK, for which systematic validation against current experiments is necessary. In this paper, we show progress in the quantitative validation of the JOREK code using JET simulations. Results analyse the impact of diamagnetic terms on the dynamics and size of the ELMs, and evidence is provided that the onset of type-I ELMs is not governed by linear MHD stability alone, but that a nonlinear threshold could be responsible for large MHD events at the plasma edge.

  • 184. Pamela, S. J. P.
    et al.
    Huysmans, G. T. A.
    Beurskens, M. N. A.
    Arnoux, G.
    Kirk, A.
    Eich, T.
    Devaux, S.
    Benkadda, S.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Simulation of ELMs in JET2010In: 37th EPS Conference on Plasma Physics 2010, EPS 2010: Volume 1, 2010, p. 53-56Conference paper (Refereed)
  • 185. Perez von Thun, C
    et al.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Beurskens, M
    Pedestal MHD stability at JET – an experimentalist’s view2015In: 15th International Workshop on H-mode Physics and Transport Barriers, 19-21 October 2015. Garching, Germany, 2015Conference paper (Other academic)
  • 186. Puiatti, M E
    et al.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Zuin, M.
    Olofsson, Erik
    KTH.
    Overview of the RFX-mod contribution to the international Fusion Science Program2015In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 55, no 10, article id 104012Article in journal (Refereed)
    Abstract [en]

    The RFX-mod device is operated both as a reversed field pinch (RFP), where advanced regimes featuring helical shape develop, and as a tokamak. Due to its flexibility, RFX-mod is contributing to the solution of key issues in the roadmap to ITER and DEMO, including MHD instability control, internal transport barriers, edge transport and turbulence, isotopic effect, high density limit and three-dimensional (3D) non-linear MHD modelling. This paper reports recent advancements in the understanding of the self-organized helical states, featuring a strong electron transport barrier, in the RFP configuration; the physical mechanism driving the residual transport at the barrier has been investigated. Following the first experiments with deuterium as the filling gas, new results concerning the isotope effect in the RFP are discussed. Studies on the high density limit show that in the RFP it is related to a toroidal particle accumulation due to the onset of a convective cell. In the tokamak configuration, q(a) regimes down to q(a) = 1.2 have been pioneered, with (2,1) tearing mode (TM) mitigated and (2,1) resistive wall mode (RWM) stabilized: the control of such modes can be obtained both by poloidal and radial sensors. Progress has been made in the avoidance of disruptions due to the (2,1) TM by applying q(a) control, and on the general issue of error field control. The effect of externally applied 3D fields on plasma flow and edge turbulence, sawtooth control and runaway electron decorrelation has been analysed. The experimental program is supported by substantial theoretical activity: 3D non-linear visco-resistive MHD and non-local transport modelling have been advanced; RWMs have been studied by a toroidal MHD kinetic hybrid stability code.

  • 187. Romanelli, F.
    et al.
    Bergsåker, Henric
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Brzozowski, Jerzy
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Chernyshova, M.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Drake, James Robert
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Elevant, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Emmoth, Birger
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Ivanova, Darya
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Johnson, Thomas J.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Laxåback, Martin
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Menmuir, Sheena
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Rubel, Marek
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Overview of the JET results with the ITER-like wall2013In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 53, no 10, p. 104002-Article in journal (Refereed)
    Abstract [en]

    Following the completion in May 2011 of the shutdown for the installation of the beryllium wall and the tungsten divertor, the first set of JET campaigns have addressed the investigation of the retention properties and the development of operational scenarios with the new plasma-facing materials. The large reduction in the carbon content (more than a factor ten) led to a much lower Z(eff) (1.2-1.4) during L- and H-mode plasmas, and radiation during the burn-through phase of the plasma initiation with the consequence that breakdown failures are almost absent. Gas balance experiments have shown that the fuel retention rate with the new wall is substantially reduced with respect to the C wall. The re-establishment of the baseline H-mode and hybrid scenarios compatible with the new wall has required an optimization of the control of metallic impurity sources and heat loads. Stable type-I ELMy H-mode regimes with H-98,H-y2 close to 1 and beta(N) similar to 1.6 have been achieved using gas injection. ELM frequency is a key factor for the control of the metallic impurity accumulation. Pedestal temperatures tend to be lower with the new wall, leading to reduced confinement, but nitrogen seeding restores high pedestal temperatures and confinement. Compared with the carbon wall, major disruptions with the new wall show a lower radiated power and a slower current quench. The higher heat loads on Be wall plasma-facing components due to lower radiation made the routine use of massive gas injection for disruption mitigation essential.

  • 188. Saarelma, A.
    et al.
    Alfier, A.
    Liang, Y.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Beurskens, M.
    Jachmich, S.
    Koslowski, H.R.
    Lang, P.
    Pasqualotto, R.
    Sun, Y.
    Wiegmann, C.
    Zhang, T.
    Density pump-out compensation during type-I edge localized mode control experiments with n = 1 perturbation fields on JET2011In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 53, no 8Article in journal (Refereed)
    Abstract [en]

    Experiments to balance the density pump-out effect during edge localized mode (ELM) control through the application of an n = 1 magnetic perturbation in type-I H-mode plasmas at JET are presented, describing the effect on T e, ne and pe profiles. Reference discharges during H-mode with and without resonant magnetic perturbation are first considered, and compared with results obtained in previous work. Pellet and gas injection are the two applied techniques; on the basis of previous experience, various particle fuelling rates have been tested on two different divertor configurations, finding those for which the compensation takes place. In terms of plasma confinement, while core pressure is found to be almost unvaried with the particle fuelling, the edge pressure pedestal improves towards the value obtained during the H-mode without the application of the magnetic perturbation. The edge stability analysis shows that the mitigated edge plasma even with the addition of particle fuelling is in the stable region against the type-I ELM triggering peeling-ballooning modes.

  • 189. Saarelma, S
    et al.
    Beurskens, M
    Bottino, F
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Giroud, C
    Kirk, A
    Leyland, M
    Global Ideal MHD and Gyrokinetic Pedestal Stability of JET with a Carbon and Metal wall and a Comparison with MAST H-mode Plasmas2013Conference paper (Other academic)
  • 190. Saarelma, S
    et al.
    Beurskens, M
    Casper, A
    Chapman, I
    Dickinson, T
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Huijsman, G
    Kirk, A
    Kwon, O
    Leyland, M
    Lee, Y
    Loarte, A
    Na, Y
    Roach, CM
    Wilson, F
    Pedestal Modelling Based on Ideal MHD And Gyrokinetic Stability Analyses on JET And ITER Plasmas2012In: 24th IAEA Fusion Energy Conference, 2012, p. TH/P3-10-Conference paper (Other academic)
  • 191. Saarelma, S.
    et al.
    Beurskens, M. N. A.
    Dickinson, D.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Leyland, M. J.
    Roach, C. M.
    MHD and gyro-kinetic stability of JET pedestals2013In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 53, no 12, p. 123012-Article in journal (Refereed)
    Abstract [en]

    The pedestal profile measurements in high triangularity JET plasmas show that with low fuelling the pedestal width decreases during the ELM cycle and with high fuelling it stays constant. In the low fuelling case the pedestal pressure gradient keeps increasing until the ELM crash and in the high fuelling case it initially increases then saturates during the ELM cycle. Stability analysis reveals that both JET plasmas become unstable to finite-n ideal MHD peeling-ballooning modes at the end of the ELM cycle. During the ELM cycle, n = infinity ideal MHD ballooning modes and kinetic ballooning modes are found to be locally stable in most of the steep pressure gradient region of the pedestal owing to the large bootstrap current, but to be locally unstable in a narrow region of plasma at the extreme edge. Unstable micro-tearing modes are found at the JET pedestal top, but they are sub-dominant to ion temperature gradient modes. They are insensitive to collisionality and stabilized by increasing density gradient.

  • 192. Saarelma, S.
    et al.
    Challis, C. D.
    Garzotti, L.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Maggi, C. F.
    Romanelli, M.
    Stokes, C.
    Integrated modelling of H-mode pedestal and confinement in JET-ILW2018In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 60, no 1, article id 014042Article in journal (Refereed)
    Abstract [en]

    A pedestal prediction model Europed is built on the existing EPED1 model by coupling it with core transport simulation using a Bohm-gyroBohm transport model to self-consistently predict JET-ILW power scan for hybrid plasmas that display weaker power degradation than the IPB98(y, 2) scaling of the energy confinement time. The weak power degradation is reproduced in the coupled core-pedestal simulation. The coupled core-pedestal model is further tested for a 3.0 MA plasma with the highest stored energy achieved in JET-ILW so far, giving a prediction of the stored plasma energy within the error margins of the measured experimental value. A pedestal density prediction model based on the neutral penetration is tested on a JET-ILW database giving a prediction with an average error of 17% from the experimental data when a parameter taking into account the fuelling rate is added into the model. However the model fails to reproduce the power dependence of the pedestal density implying missing transport physics in the model. The future JET-ILW deuterium campaign with increased heating power is predicted to reach plasma energy of 11 MJ, which would correspond to 11-13 MW of fusion power in equivalent deuterium-tritium plasma but with isotope effects on pedestal stability and core transport ignored.

  • 193. Saarelma, S.
    et al.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Bilkova, P.
    Challis, C. D.
    Chankin, A.
    Fridström, Richard
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Garzotti, L.
    Horvath, L.
    Maggi, C. F.
    Contributors, J E T
    Self-consistent pedestal prediction for JET-ILW in preparation of the DT campaign2019In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 26, no 7, article id 072501Article in journal (Refereed)
    Abstract [en]

    The self-consistent core-pedestal prediction model of a combination of EPED1 type pedestal prediction and a simple stiff core transport model is able to predict Type I ELMy (edge localized mode) pedestals of a large JET-ILW (ITER-like wall) database at the similar accuracy as is obtained when the experimental global plasma β is used as input. The neutral penetration model [R. J. Groebner et al., Phys. Plasmas 9, 2134 (2002)] with corrections that take into account variations due to gas fueling and plasma triangularity is able to predict the pedestal density with an average error of 15%. The prediction of the pedestal pressure in hydrogen plasma that has higher core heat diffusivity compared to a deuterium plasma with similar heating and fueling agrees with the experiment when the isotope effect on the stability, the increased diffusivity, and outward radial shift of the pedestal are included in the prediction. However, the neutral penetration model that successfully predicts the deuterium pedestal densities fails to predict the isotope effect on the pedestal density in hydrogen plasmas.

  • 194. Saarelma, S.
    et al.
    Järvinen, A.
    Beurskens, M.
    Challis, C.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Giroud, C.
    Groth, M.
    Leyland, M.
    Maggi, C.
    Simpson, J.
    The effects of impurities and core pressure on pedestal stability in Joint European Torus (JET)2015In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 22, no 5, article id 056115Article in journal (Refereed)
    Abstract [en]

    The H-mode pedestal plays an important role in determining global confinement in tokamaks. In high triangularity H-mode experiments in Joint European Torus with the ITER-like wall (JET-ILW), significantly higher pedestal temperature and global confinement have been achieved with nitrogen seeding. The experimentally observed increase in pedestal height is inconsistent with the stability calculations using the experimental profiles. Numerically, we find that the consistency with stability improvement can be restored if we assume a shift of the pedestal inwards and increased ion dilution due to the impurity seeding. Significantly better confinement and pedestal height have been observed in JET-ILW plasmas when the core pressure is increased. The enhanced pedestal height can be linked to an improvement in edge stability arising from an increase in the Shafranov-shift, higher edge current, and pedestal widening in flux space.

  • 195. Schweinzer, J.
    et al.
    Beurskens, M.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Joffrin, E.
    Bobkov, V.
    Dux, R.
    Fischer, R.
    Fuchs, C.
    Kallenbach, A.
    Hopf, C.
    Lang, P. T.
    Mlynek, A.
    Pütterich, T.
    Ryter, F.
    Stober, J.
    Tardini, G.
    Wolfrum, E.
    Zohm, H.
    Development of the Q = 10 scenario for ITER on ASDEX Upgrade (AUG)2016In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 56, no 10, article id 106007Article in journal (Refereed)
    Abstract [en]

    The development of the baseline H-mode scenario foreseen for ITER on the ASDEX Upgrade tokamak, i.e. discharges at q 95 = 3, relatively low β N ∼ 1.8, high normalized density n/n GW ∼ 0.85 and high triangularity δ = 0.4, focused on the integration of elements foreseen for ITER and available on ASDEX Upgrade, such as ELM mitigation techniques and impurity seeding in combination with a metallic wall. Values for density and energy confinement simultaneously came close to the requirements of the ITER baseline scenario as long as β N stayed above 2. At lower heating power and thus lower β N normalized energy confinement H 98y2 ∼ 0.85 is obtained. It has been found that stationary discharges are not easily achieved under these conditions due to the low natural ELM frequency occurring at the low q 95/high δ operational point. Up until now the ELM parameters were uncontrollable with the tools developed in other scenarios. Therefore studies on an alternative operational point at higher β N and q 95 have been conducted. In order to prepare for the ITER first non-activation operational phase, Helium operation has been investigated as well.

  • 196.
    Setiadi, A. C.
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Brunsell, Per R.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Villone, F.
    Mastrostefano, S.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Gray-box modeling of resistive wall modes with vacuum-plasma separation and optimal control design for EXTRAP T2R2017In: Fusion engineering and design, ISSN 0920-3796, E-ISSN 1873-7196, Vol. 121, p. 245-255Article in journal (Refereed)
    Abstract [en]

    This paper presents a graybox methodology to model the resistive wall mode instability by combining first principle approach and system identification technique. In particular we propose a separate vacuum and plasma modeling with cascade interconnection. The shell is modeled using CARIDDI code which solves the 3D integral formulation of eddy current problem, whereas the plasma response is obtained empirically by system identification. Furthermore the resulting model is used to design an optimal feedback control. The model and feedback control is validated experimentally in EXTRAP T2R reversed-field pinch, where RWMs stabilization and non-axisymmetric mode sustainment is considered. 

  • 197.
    Setiadi, Agung Chris
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Brunsell, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Fabio, Villone
    DIEI, Università di Cassino e del Lazio Meridionale, Italy.
    Stefano, Mastrostefano
    DIEI, Università di Cassino e del Lazio Meridionale, Italy.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Graybox Modelling of EXTRAP T2R with Vacuum-Plasma Separation and Optimal Control Design of Resistive Wall ModesArticle in journal (Refereed)
    Abstract [en]

    This paper presents a graybox methodology to model the Resistive Wall Mode instability by combining first principle approach and system identification technique. In particular we propose a separate vacuum and plasma modeling with cascade interconnection. The shell is modeled using CARIDDI code which solves the 3D integral formulation of eddy current problem, whereas the plasma response is obtained empirically by system identification. Furthermore the resulting model is used to design an optimal feedback control. The model and feedback control is validated experimentally in EXTRAP T2R reversed-field pinch, where RWMs stabilization and non-axisymmetric mode sustainment is considered.

  • 198.
    Setiadi, Agung Chris
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Brunsell, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Design and operation of fast model predictive controller for stabilization of magnetohydrodynamic mode in a fusion deviceManuscript (preprint) (Other academic)
  • 199.
    Setiadi, Agung Chris
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Brunsell, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Implementation of model predictive control for resistive wall mode stabilization on EXTRAP T2R2015In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 57, no 10, article id 104005Article in journal (Refereed)
    Abstract [en]

    A model predictive control (MPC) method for stabilization of the resistive wall mode (RWM) in the EXTRAP T2R reversed-field pinch is presented. The system identification technique is used to obtain a linearized empirical model of EXTRAP T2R. MPC employs the model for prediction and computes optimal control inputs that satisfy performance criterion. The use of a linearized form of the model allows for compact formulation of MPC, implemented on a millisecond timescale, that can be used for real-time control. The design allows the user to arbitrarily suppress any selected Fourier mode. The experimental results from EXTRAP T2R show that the designed and implemented MPC successfully stabilizes the RWM.

  • 200.
    Setiadi, Agung Chris
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Brunsell, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Improved model predictive control of resistive wall modes by error field estimator in EXTRAP T2R2016In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 58, no 12, article id 124002Article in journal (Refereed)
    Abstract [en]

    Many implementations of a model-based approach for toroidal plasma have shown better control performance compared to the conventional type of feedback controller. One prerequisite of model-based control is the availability of a control oriented model. This model can be obtained empirically through a systematic procedure called system identification. Such a model is used in this work to design a model predictive controller to stabilize multiple resistive wall modes in EXTRAP T2R reversed-field pinch. Model predictive control is an advanced control method that can optimize the future behaviour of a system. Furthermore, this paper will discuss an additional use of the empirical model which is to estimate the error field in EXTRAP T2R. Two potential methods are discussed that can estimate the error field. The error field estimator is then combined with the model predictive control and yields better radial magnetic field suppression.

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