Ändra sökning
Avgränsa sökresultatet
1234567 101 - 150 av 834
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Träffar per sida
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
Markera
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 101. Cherigier-Kovacic, L.
    et al.
    Ström, Petter
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Lejeune, A.
    Doveil, F.
    Electric field induced Lyman-alpha emission of a hydrogen beam for electric field measurements2015Ingår i: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 86, nr 6, artikel-id 063504Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Electric field induced Lyman-alpha emission is a new way of measuring weak electric fields in vacuum and in a plasma. It is based on the emission of Lyman-alpha radiation (121.6 nm) by a low-energy metastable H atom beam due to Stark-quenching of the 2s level induced by the field. In this paper, we describe the technique in detail. Test measurements have been performed in vacuum between two plates polarized at a controlled voltage. The intensity of emitted radiation, proportional to the square of the field modulus, has been recorded by a lock-in technique, which gives an excellent signal to noise ratio. These measurements provide an in situ calibration that can be used to obtain the absolute value of the electric field. A diagnostic of this type can help to address a long standing challenge in plasma physics, namely, the problem of measuring electric fields without disturbing the equilibrium of the system that is being studied.

  • 102. Chérigier-Kovacic, L.
    et al.
    Ström, Petter
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Doveil, F.
    Electric field induced lyman-α Emission (EFILE) diagnostic for electric field measurements2015Ingår i: Proceedings of Science, Proceedings of Science (PoS) , 2015Konferensbidrag (Refereegranskat)
    Abstract [en]

    When a metastable hydrogen test beam is exposed to a constant or oscillating electric field, Lyman-A (121.6 nm) emission occurs. This results from the Stark quenching of the metastable 2s level, induced by the field. The intensity of the radiation is proportional to the square of the electric field amplitude and it is recorded by a lock-in technique, which gives an excellent signal to noise ratio. This provides us with a very sensitive and non intrusive method to measure the electric field value, called EFILE (Electric Field Induced Lyman-A emission). Sensitivity is as good as 0.1 V/cm in the case of an oscillatory field resonant with the Lamb shift frequency ≈ 1 GHz. Hydrogen ions are produced in a magnetic multicusp source by a thermo-electronic discharge. The ions are extracted from the source, focused by a series of electrostatic lenses and accelerated to 500 eV. The beam interacts with cesium vapor which produces atoms in the metastable 2s1=2 state. In the diagnosed volume, the beam passes between a pair of plane electrodes separated by 5 cm. One of them is grounded, the other one is polarized to generate an electric field. The diagnosed volume can be kept under vacuum or exposed to an argon plasma. Lyman-A emission from the beam passing between the plates is measured as a function of the polarized plate voltage. A saturation of the signal is observed at large field amplitudes, which is explained through oscillatory and geometrical mechanisms. A function that takes this saturation into account is used as a calibration for the subsequent electric field profile measurements in the case of a constant voltage applied between the plates in vacuum. We find a good agreement between our results and a finite element method calculation of the profile.

  • 103. Citrin, J.
    et al.
    Garcia, J.
    Görier, T.
    Jenko, F.
    Mantica, P.
    Told, D.
    Bourdelle, C.
    Hatch, D. R.
    Hogeweij, G. M. D.
    Johnson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Pueschel, M. J.
    Schneider, M.
    Electromagnetic stabilization of tokamak microturbulence in a high-β regime2014Ingår i: 41st EPS Conference on Plasma Physics, EPS 2014, European Physical Society (EPS) , 2014Konferensbidrag (Refereegranskat)
    Abstract [en]

    The impact of electromagnetic stabilization and flow shear stabilization on ITG turbulence is investigated. Analysis of a low-β JET L-mode discharge illustrates the relation between ITG stabilization, and proximity to the electromagnetic instability threshold. This threshold is reduced by suprathermal pressure gradients, highlighting the effectiveness of fast ions in ITG stabilization. Extensive linear and nonlinear gyrokinetic simulations are then carried out for the high-β JET hybrid discharge 75225, at two separate locations at inner and outer radii. It is found that at the inner radius, nonlinear electromagnetic stabilization is dominant, and is critical for achieving simulated heat fluxes in agreement with the experiment. The enhancement of this effect by suprathermal pressure also remains significant. It is also found that flow shear stabilization is not effective at the inner radii. However, at outer radii the situation is reversed. Electromagnetic stabilization is negligible while the flow shear stabilization is significant. These results constitute the high-β generalization of comparable observations found at low-β at JET. This is encouraging for the extrapolation of electromagnetic ITG stabilization to future devices. An estimation of the impact of this effect on the ITER hybrid scenario leads to a 20% fusion power improvement.

  • 104. Citrin, J.
    et al.
    Garcia, J.
    Görler, T.
    Jenko, F.
    Mantica, P.
    Told, D.
    Bourdelle, C.
    Hatch, D. R.
    Hogeweij, G. M. D.
    Johnson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Pueschel, M. J.
    Schneider, M.
    Electromagnetic stabilization of tokamak microturbulence in a high-beta regime2015Ingår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 57, nr 1, s. 014032-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The impact of electromagnetic stabilization and flow shear stabilization on ITG turbulence is investigated. Analysis of a low-beta JET L-mode discharge illustrates the relation between ITG stabilization and proximity to the electromagnetic instability threshold. This threshold is reduced by suprathermal pressure gradients, highlighting the effectiveness of fast ions in ITG stabilization. Extensive linear and nonlinear gyrokinetic simulations are then carried out for the high-beta JET hybrid discharge 75225, at two separate locations at inner and outer radii. It is found that at the inner radius, nonlinear electromagnetic stabilization is dominant and is critical for achieving simulated heat fluxes in agreement with the experiment. The enhancement of this effect by suprathermal pressure also remains significant. It is also found that flow shear stabilization is not effective at the inner radii. However, at outer radii the situation is reversed. Electromagnetic stabilization is negligible while the flow shear stabilization is significant. These results constitute the high-beta generalization of comparable observations found at low-beta at JET. This is encouraging for the extrapolation of electromagnetic ITG stabilization to future devices. An estimation of the impact of this effect on the ITER hybrid scenario leads to a 20% fusion power improvement.

  • 105. Citrin, J.
    et al.
    Jenko, F.
    Mantica, P.
    Told, D.
    Bourdelle, C.
    Dumont, R.
    Garcia, J.
    Haverkort, J. W.
    Hogeweij, G. M. D.
    Johnson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Pueschel, M. J.
    Ion temperature profile stiffness: non-linear gyrokinetic simulations and comparison with experiment2014Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 54, nr 2, s. 023008-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Recent experimental observations at JET show evidence of reduced ion temperature profile stiffness. An extensive set of nonlinear gyrokinetic simulations are performed based on the experimental discharges, investigating the physical mechanism behind the observations. The impact on the ion heat flux of various parameters that differ within the data-set are explored. These parameters include the safety factor, magnetic shear, toroidal flow shear, effect of rotation on the magnetohydrodynamic equilibrium, R/L-n, beta(e), Z(eff), T-e/T-i, and the fast-particle content. While previously hypothesized to be an important factor in the stiffness reduction, the combined effect of toroidal flow shear and low magnetic shear is not predicted by the simulations to lead to a significant reduction in ion heat flux, due both to an insufficient magnitude of flow shear and significant parallel velocity gradient destabilization. It is however found that nonlinear electromagnetic effects due to both thermal and fast-particle pressure gradients, even at low beta(e), can significantly reduce the ion heat flux, and is a key factor in explaining the experimental observations. A total of four discharges are examined, at both inner and outer radii. For all cases studied, the simulated and experimental ion heat flux values agree within reasonable variations of input parameters around the experimental uncertainties.

  • 106. Citrin, J.
    et al.
    Jenko, F.
    Mantica, P.
    Told, D.
    Bourdelle, C.
    Garcia, J.
    Haverkort, J. W.
    Hogeweij, G. M. D.
    Johnson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Pueschel, M. J.
    Nonlinear stabilization of tokamak microturbulence by fast ions2013Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 111, nr 15, s. 155001-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Nonlinear electromagnetic stabilization by suprathermal pressure gradients found in specific regimes is shown to be a key factor in reducing tokamak microturbulence, augmenting significantly the thermal pressure electromagnetic stabilization. Based on nonlinear gyrokinetic simulations investigating a set of ion heat transport experiments on the JET tokamak, described by Mantica et al., this result explains the experimentally observed ion heat flux and stiffness reduction. These findings are expected to improve the extrapolation of advanced tokamak scenarios to reactor relevant regimes.

  • 107. Coad, J. P.
    et al.
    Alves, E.
    Barradas, N. P.
    Baron-Wiechec, A.
    Catarino, N.
    Heinola, K.
    Likonen, J.
    Mayer, M.
    Matthews, G. F.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Widdowson, A.
    Surface analysis of tiles and samples exposed to the first JET campaigns with the ITER-like wall2014Ingår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T159, s. 014012-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper reports on the first post-mortem analyses of tiles removed from JET after the first campaigns with the ITER-like wall (ILW) during 2011-12 [1]. Tiles from the divertor have been analysed by ion beam analysis techniques and by secondary ion mass spectrometry to determine the amount of beryllium deposition and deuterium retention in the tiles exposed to the scrape-off layer. Films 10-20 mu m thick were present at the top of tile 1, but only very thin films (<1 mu m) were found in the shadowed areas and on other divertor tiles. The total amount of Be found in the divertor following the ILW campaign was a factor of similar to 9 less than the material deposited in the 2007-09 carbon campaign, after allowing for the longer operations in 2007-09.

  • 108. Coad, J. P.
    et al.
    Andrew, P.
    Erents, S. K.
    Hole, D. E.
    Likonen, J.
    Mayer, M.
    Pitts, R.
    Rubel, Marek J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Strachan, J. D.
    Vainonen-Ahlgren, E.
    Widdowson, A.
    Erosion and deposition in the JET MkII-SRP divertor2007Ingår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 363, s. 287-293Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Carbon-13 labelled methane was injected into the outer divertor during a series of H-mode discharges on the last day of operations with the JET MkII-SRP divertor. Tiles from around the vessel were removed during the subsequent shutdown and surface deposits were analysed by IBA techniques and SIMS. First attempts to model the pattern of 13 C deposition using EDGE2D are reported. Erosion of W markers at the outer divertor was observed, with implications for the ITER-like wall experiment planned for JET, whilst thin film growth in the same region has been followed by the effect on infrared measurements. The composition of thick films deposited at the inner divertor during the MkII-SRP campaign, and the migration to the inner corner of the divertor observed by a quartz micro-balance, provide further information on divertor transport. Crown

  • 109. Coad, J. P.
    et al.
    Esser, H. -G
    Likonen, J.
    Mayer, M.
    Neill, G.
    Philipps, V.
    Rubel, Marek J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Vince, J.
    Diagnostics for studying deposition and erosion processes in JET2005Ingår i: Fusion engineering and design, ISSN 0920-3796, E-ISSN 1873-7196, Vol. 74, nr 1-4, s. 745-749Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Estimates of erosion, deposition and H-isotope retention in JET from previous divertor campaigns have relied on analysis of in-vessel components removed at shutdowns. The components analysed have also provided an incomplete coverage of the vessel. In 2004, new diagnostics are being installed to give a more complete picture (such as smart tiles) and to provide some time resolution. The latter includes further quartz microbalances (QMB), following the successful operation of a prototype in 2002-2004 [H.-G. Esser, G. Neill, P. Coad, G.F. Matthews, D. Jolovic, D. Wilson, M. Freisinger, V. Philipps, Quartz microbalance: a time-resolved diagnostic to measure material deposition in JET, Fusion Eng. Des. 66-68 (2003) 855-860; H.-G. Esser, V. Philipps, M. Freisinger, G.F. Matthews, J.P. Coad, G.F. Neill, JET EFDA Contributors, Effect of plasma configuration on carbon migration measured in the inner divertor of JET using quartz microbalance, J. Nucl. Mater. 337-339 (2005) 84-87], which will also have temperature control. Other diagnostics include rotating collectors and deposition monitors [M. Mayer, V. Rohde, P. Coad, P. Wienhold, ASDEX Upgrade Team, JET EFDA Contributors, Carbon erosion and migration in fusion devices, Phys. Scr. T111 (2004) 55-59]. Units are also being installed to provide information on mirrors for ITER.

  • 110. Coad, J. P.
    et al.
    Gruenhagen, S.
    Hole, D. E.
    Hakola, A.
    Koivuranta, S.
    Likonen, J.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Widdowson, A.
    Overview of JET post-mortem results following the 2007-9 operational period, and comparisons with previous campaigns2011Ingår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T145, s. 014003-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In 2010, all the plasma-facing components were removed from JET so that the carbon-based surfaces could be replaced with beryllium (Be) or tungsten as part of the ITER-like wall (ILW) project. This gives unprecedented opportunities for post-mortem analyses of these plasma-facing surfaces; this paper reviews the data obtained so far and relates the information to studies of tiles removed during previous JET shutdowns. The general pattern of erosion/deposition at the JET divertor has been maintained, with deposition of impurities in the scrape-off layer (SOL) at the inner divertor and preferential removal of carbon and transport into the corner. However, the remaining films in the SOL contain very high Be/C ratios at the surface. The first measurements of erosion using a tile profiler have been completed, with up to 200 microns erosion being recorded at points on the inner wall guard limiters.

  • 111. Coad, J. P.
    et al.
    Hole, D. E.
    Rubel, Marek J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Widdowson, A.
    Vince, J.
    Deposition results from rotating collector diagnostics in JET2009Ingår i: Physica scripta. T, ISSN 0281-1847, Vol. T138, s. 014023-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Rotating collectors (RC) were installed in JET during the period 2005-2007, each providing a time-resolved deposition pattern on the surface of a rotating silicon disc, which could be analysed once retrieved from the vessel. This paper reports results from the silicon disc removed from the RC located under the load-bearing septum replacement plate in JET in 2007. Nuclear reaction analysis results of the deposits on the disc have been correlated directly with the pattern of erosion and deposition observed by the quartz microbalance (QMB) located in an equivalent position. The thickest film in the time-resolved region (i.e. deposited in similar to 60 pulses) was similar to 250 nm, and the Be/C ratio was generally found to be 0.1 or lower, with two regions where the ratio rose to 0.2. The deposition observed with the QMB appears to be about a factor of four less.

  • 112. Coad, J. P.
    et al.
    Likonen, J.
    Rubel, Marek J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Vainonen-Ahlgren, E.
    Hole, D. E.
    Sajavaara, T.
    Renvall, T.
    Matthews, G. F.
    Overview of material re-deposition and fuel retention studies at JET with the Gas Box divertor2006Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 46, nr 2, s. 350-366Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    in the period 1998-2001 the JET tokamak was operated with the MkII Gas Box divertor. On two occasions during that period a number of limiter and divertor tiles were retrieved from the torus and then examined ex situ with surface sensitive techniques. Erosion and deposition patterns were determined in order to assess the material erosion, material migration and fuel inventory on plasma facing components. Tracer techniques, e.g. injection of C-13 labelled methane and tiles coated with a low-Z and high-Z marker layer, were used to enhance the volume of information on the material transport. The results show significant asymmetry in the distribution of fuel and plasma impurity species between the inner (net deposition area) and the outer (net erosion) divertor channels. No significant formation of highly hydrogenated carbon films has been found in the Gas Box structure. The important processes for material migration, and the influence of operation scenarios on the morphology of the deposits are discussed. Comparison is also made with results obtained following previous divertor campaigns.

  • 113. Coad, J. P.
    et al.
    Rubel, Marek J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Bekris, N.
    Brennan, D.
    Hole, D.
    Likonen, J.
    Vainonen-Ahlgren, E.
    Distribution of hydrogen isotopes, carbon and beryllium on in-vessel surfaces in the various jet divertors2005Ingår i: Fusion science and technology, ISSN 1536-1055, E-ISSN 1943-7641, Vol. 48, nr 1, s. 551-556Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    JET has operated with divertors of differing geometries since 1994. Impurities accumulated in the inner leg of all the divertors, and operation of the first (Mk I) divertor with beryllium tiles demonstrated that most are eroded from the main chamber walls and swept along the scrape-off layer to the inner divertor. Carbon deposited at the inner divertor is then locally transported to shadowed regions such as the inner louvres, where, for example, most of the tritium was trapped during the deuterium-tritium experiment (DTE1). Factors affecting these transport processes (e.g. temperature) are important for ITER, but are not well understood.

  • 114.
    Coad, J. P.
    et al.
    Culham Sci Ctr, Culham Ctr Fus Energy, Abingdon OX14 3DB, Oxon, England..
    Rubel, Marek
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Likonen, J.
    VTT Tech Res Ctr Finland, POB 1000, FIN-02044 Espoo, Finland..
    Bekris, N.
    Karlsruhe Inst Technol, D-76021 Karlsruhe, Germany..
    Brezinsek, S.
    Forschungszentrum Juelich, Inst Energieforsch Plasmaphys, D-52425 Julich, Germany..
    Matthew, G. F.
    Culham Sci Ctr, Culham Ctr Fus Energy, Abingdon OX14 3DB, Oxon, England..
    Mayer, M.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Widdowson, A. M.
    Culham Sci Ctr, Culham Ctr Fus Energy, Abingdon OX14 3DB, Oxon, England..
    Material migration and fuel retention studies during the JET carbon divertor campaigns2019Ingår i: Fusion engineering and design, ISSN 0920-3796, E-ISSN 1873-7196, Vol. 138, s. 78-108Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The first divertor was installed in the JET machine between 1992 and 1994 and was operated with carbon tiles and then beryllium tiles in 1994-5. Post-mortem studies after these first experiments demonstrated that most of the impurities deposited in the divertor originate in the main chamber, and that asymmetric deposition patterns generally favouring the inner divertor region result from drift in the scrape-off layer. A new monolithic divertor structure was installed in 1996 which produced heavy deposition at shadowed areas in the inner divertor corner, which is where the majority of the tritium was trapped by co-deposition during the deuterium-tritium experiment in 1997. Different divertor geometries have been tested since such as the Gas-Box and High-Delta divertors; a principle objective has been to predict plasma behaviour, transport and tritium retention in ITER. Transport modelling experiments were carried out at the end of four campaigns by puffing C-13-labelled methane, and a range of diagnostics such as quartz-microbalance and rotating collectors have been installed to add time resolution to the post-mortem analyses. The study of material migration after D-D and D-T campaigns clearly revealed important consequences of fuel retention in the presence of carbon walls. They gave a strong impulse to make a fundamental change of wall materials. In 2010 the carbon divertor and wall tiles were removed and replaced with tiles with Be or W surfaces for the ITER-Like Wall Project.

  • 115. Coda, S.
    et al.
    Ahn, J.
    Albanese, R.
    Alberti, S.
    Alessi, E.
    Allan, S.
    Anand, H.
    Anastassiou, G.
    Andrèbe, Y.
    Angioni, C.
    Ariola, M.
    Bernert, M.
    Beurskens, M.
    Bin, W.
    Blanchard, P.
    Blanken, T. C.
    Boedo, J. A.
    Bolzonella, T.
    Bouquey, F.
    Braunmüller, F. H.
    Bufferand, H.
    Buratti, P.
    Calabró, G.
    Camenen, Y.
    Carnevale, D.
    Carpanese, F.
    Causa, F.
    Cesario, R.
    Chapman, I. T.
    Chellai, O.
    Choi, D.
    Cianfarani, C.
    Ciraolo, G.
    Citrin, J.
    Costea, S.
    Crisanti, F.
    Cruz, N.
    Czarnecka, A.
    Decker, J.
    De Masi, G.
    De Tommasi, G.
    Douai, D.
    Dunne, M.
    Duval, B. P.
    Eich, T.
    Elmore, S.
    Esposito, B.
    Faitsch, M.
    Fasoli, A.
    Fedorczak, N.
    Felici, F.
    Février, O.
    Ficker, O.
    Fietz, S.
    Fontana, M.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Furno, I.
    Galeani, S.
    Gallo, A.
    Galperti, C.
    Garavaglia, S.
    Garrido, I.
    Geiger, B.
    Giovannozzi, E.
    Gobbin, M.
    Goodman, T. P.
    Gorini, G.
    Gospodarczyk, M.
    Granucci, G.
    Graves, J. P.
    Guirlet, R.
    Hakola, A.
    Ham, C.
    Harrison, J.
    Hawke, J.
    Hennequin, P.
    Hnat, B.
    Hogeweij, D.
    Hogge, J. -P
    Honoré, C.
    Hopf, C.
    Horáček, J.
    Huang, Z.
    Igochine, V.
    Innocente, P.
    Ionita Schrittwieser, C.
    Isliker, H.
    Jacquier, R.
    Jardin, A.
    Kamleitner, J.
    Karpushov, A.
    Keeling, D. L.
    Kirneva, N.
    Kong, M.
    Koubiti, M.
    Kovacic, J.
    Krämer-Flecken, A.
    Krawczyk, N.
    Kudlacek, O.
    Labit, B.
    Lazzaro, E.
    Le, H. B.
    Lipschultz, B.
    Llobet, X.
    Lomanowski, B.
    Loschiavo, V. P.
    Lunt, T.
    Maget, P.
    Maljaars, E.
    Malygin, A.
    Maraschek, M.
    Marini, C.
    Martin, P.
    Martin, Y.
    Mastrostefano, S.
    Maurizio, R.
    Mavridis, M.
    Mazon, D.
    McAdams, R.
    McDermott, R.
    Merle, A.
    Meyer, H.
    Militello, F.
    Miron, I. G.
    Molina Cabrera, P. A.
    Moret, J. -M
    Moro, A.
    Moulton, D.
    Naulin, V.
    Nespoli, F.
    Nielsen, A. H.
    Nocente, M.
    Nouailletas, R.
    Nowak, S.
    Odstrčil, T.
    Papp, G.
    Papřok, R.
    Pau, A.
    Pautasso, G.
    Pericoli Ridolfini, V.
    Piovesan, P.
    Piron, C.
    Pisokas, T.
    Porte, L.
    Preynas, M.
    Ramogida, G.
    Rapson, C.
    Juul Rasmussen, J.
    Reich, M.
    Reimerdes, H.
    Reux, C.
    Ricci, P.
    Rittich, D.
    Riva, F.
    Robinson, T.
    Saarelma, S.
    Saint-Laurent, F.
    Sauter, O.
    Scannell, R.
    Schlatter, C.
    Schneider, B.
    Schneider, P.
    Schrittwieser, R.
    Sciortino, F.
    Sertoli, M.
    Sheikh, U.
    Sieglin, B.
    Silva, M.
    Sinha, J.
    Sozzi, C.
    Spolaore, M.
    Stange, T.
    Stoltzfus-Dueck, T.
    Tamain, P.
    Teplukhina, A.
    Testa, D.
    Theiler, C.
    Thornton, A.
    Tophøj, L.
    Tran, M. Q.
    Tsironis, C.
    Tsui, C.
    Uccello, A.
    Vartanian, S.
    Verdoolaege, G.
    Verhaegh, K.
    Vermare, L.
    Vianello, N.
    Vijvers, W. A. J.
    Vlahos, L.
    Vu, N. M. T.
    Walkden, N.
    Wauters, T.
    Weisen, H.
    Wischmeier, M.
    Zestanakis, P.
    Zuin, M.
    Overview of the TCV tokamak program: Scientific progress and facility upgrades2017Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 57, nr 10, artikel-id 102011Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The TCV tokamak is augmenting its unique historical capabilities (strong shaping, strong electron heating) with ion heating, additional electron heating compatible with high densities, and variable divertor geometry, in a multifaceted upgrade program designed to broaden its operational range without sacrificing its fundamental flexibility. The TCV program is rooted in a three-pronged approach aimed at ITER support, explorations towards DEMO, and fundamental research. A 1 MW, tangential neutral beam injector (NBI) was recently installed and promptly extended the TCV parameter range, with record ion temperatures and toroidal rotation velocities and measurable neutral-beam current drive. ITER-relevant scenario development has received particular attention, with strategies aimed at maximizing performance through optimized discharge trajectories to avoid MHD instabilities, such as peeling-ballooning and neoclassical tearing modes. Experiments on exhaust physics have focused particularly on detachment, a necessary step to a DEMO reactor, in a comprehensive set of conventional and advanced divertor concepts. The specific theoretical prediction of an enhanced radiation region between the two X-points in the low-field-side snowflake-minus configuration was experimentally confirmed. Fundamental investigations of the power decay length in the scrape-off layer (SOL) are progressing rapidly, again in widely varying configurations and in both D and He plasmas; in particular, the double decay length in L-mode limited plasmas was found to be replaced by a single length at high SOL resistivity. Experiments on disruption mitigation by massive gas injection and electron-cyclotron resonance heating (ECRH) have begun in earnest, in parallel with studies of runaway electron generation and control, in both stable and disruptive conditions; a quiescent runaway beam carrying the entire electrical current appears to develop in some cases. Developments in plasma control have benefited from progress in individual controller design and have evolved steadily towards controller integration, mostly within an environment supervised by a tokamak profile control simulator. TCV has demonstrated effective wall conditioning with ECRH in He in support of the preparations for JT-60SA operation.

  • 116. Coda, S.
    et al.
    Eriksson, L. -G
    Lennholm, M.
    Graves, J.
    Johnson, Thomas J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Brzozowski, Jerzy H.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    DeBaar, M.
    Howell, D. F.
    Jachmich, S.
    Kiptily, V.
    Koslowski, R.
    Mayoral, M. -L
    Mueck, A.
    Pinches, S.
    Saibene, G.
    Santala, M. I. K.
    Stamp, M. F.
    Valisa, M.
    NTM prevention by ICCD control of fast-ion-stabilised sawteeth2007Ingår i: 34th EPS Conference on Plasma Physics 2007, EPS 2007 - Europhysics Conference Abstracts, 2007, nr 3, s. 2138-2141Konferensbidrag (Refereegranskat)
  • 117.
    Coda, S.
    et al.
    Ecole Polytech Fed Lausanne, Swiss Plasma Ctr, CH-1015 Lausanne, Switzerland..
    Frassinetti, Lorenzo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Zuin, M.
    Consorzio RFX, Corso Stati Uniti 4, I-35127 Padua, Italy..
    et al.,
    Physics research on the TCV tokamak facility: from conventional to alternative scenarios and beyond2019Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 59, nr 11, artikel-id 112023Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The research program of the TCV tokamak ranges from conventional to advanced-tokamak scenarios and alternative divertor configurations, to exploratory plasmas driven by theoretical insight, exploiting the device's unique shaping capabilities. Disruption avoidance by real-time locked mode prevention or unlocking with electron-cyclotron resonance heating (ECRH) was thoroughly documented, using magnetic and radiation triggers. Runaway generation with high-Z noble-gas injection and runaway dissipation by subsequent Ne or Ar injection were studied for model validation. The new 1 MW neutral beam injector has expanded the parameter range, now encompassing ELMy H-modes in an ITER-like shape and nearly noninductive II-mode discharges sustained by electron cyclotron and neutral beam current drive. In the H-mode, the pedestal pressure increases modestly with nitrogen seeding while fueling moves the density pedestal outwards, but the plasma stored energy is largely uncorrelated to either seeding or fueling. High fueling at high triangularity is key to accessing the attractive small edge-localized mode (type-II) regime. Turbulence is reduced in the core at negative triangularity, consistent with increased confinement and in accord with global gyrokinetic simulations. The geodesic acoustic mode, possibly coupled with avalanche events, has been linked with particle flow to the wall in diverted plasmas. Detachment, scrape-off layer transport, and turbulence were studied in L- and H-modes in both standard and alternative configurations (snowflake, super-X, and beyond). The detachment process is caused by power `starvation' reducing the ionization source, with volume recombination playing only a minor role. Partial detachment in the H-mode is obtained with impurity seeding and has shown little dependence on flux expansion in standard single-null geometry. In the attached 1,-mode phase, increasing the outer connection length reduces the in-out heat-flow asymmetry. A doublet plasma, featuring an internal X-point, was achieved successfully, and a transport barrier was observed in the mantle just outside the internal separatrix. In the near future variableconfiguration baffles and possibly divertor ptunping will be introduced to investigate the effect of divertor closure on exhaust and performance, and 3.5 MW ECR and 1 MW neutral beam injection heating will be added.

  • 118. Coenen, J. W.
    et al.
    Arnoux, G.
    Bazylev, B.
    Matthews, G. F.
    Autricque, A.
    Balboa, I.
    Clever, M.
    Dejarnac, R.
    Coffey, I.
    Corre, Y.
    Devaux, S.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Gauthier, E.
    Horacek, J.
    Jachmich, S.
    Komm, M.
    Knaup, M.
    Krieger, K.
    Marsen, S.
    Meigs, A.
    Mertens, Ph.
    Pitts, R. A.
    Puetterich, T.
    Rack, M.
    Stamp, M.
    Sergienko, G.
    Tamain, P.
    Thompson, V.
    ELM-induced transient tungsten melting in the JET divertor2015Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 55, nr 2, artikel-id 023010Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The original goals of the JET ITER-like wall included the study of the impact of an all W divertor on plasma operation (Coenen et al 2013 Nucl. Fusion 53 073043) and fuel retention (Brezinsek et al 2013 Nucl. Fusion 53 083023). ITER has recently decided to install a full-tungsten (W) divertor from the start of operations. One of the key inputs required in support of this decision was the study of the possibility of W melting and melt splashing during transients. Damage of this type can lead to modifications of surface topology which could lead to higher disruption frequency or compromise subsequent plasma operation. Although every effort will be made to avoid leading edges, ITER plasma stored energies are sufficient that transients can drive shallow melting on the top surfaces of components. JET is able to produce ELMs large enough to allow access to transient melting in a regime of relevance to ITER. Transient W melt experiments were performed in JET using a dedicated divertor module and a sequence of I-P = 3.0 MA/B-T = 2.9 T H-mode pulses with an input power of P-IN = 23 MW, a stored energy of similar to 6 MJ and regular type I ELMs at Delta W-ELM = 0.3 MJ and f(ELM) similar to 30 Hz. By moving the outer strike point onto a dedicated leading edge in the W divertor the base temperature was raised within similar to 1 s to a level allowing transient, ELM-driven melting during the subsequent 0.5 s. Such ELMs (delta W similar to 300 kJ per ELM) are comparable to mitigated ELMs expected in ITER (Pitts et al 2011 J. Nucl. Mater. 415 (Suppl.) S957-64). Although significant material losses in terms of ejections into the plasma were not observed, there is indirect evidence that some small droplets (similar to 80 mu m) were released. Almost 1 mm (similar to 6 mm(3)) of W was moved by similar to 150 ELMs within 7 subsequent discharges. The impact on the main plasma parameters was minor and no disruptions occurred. The W-melt gradually moved along the leading edge towards the high-field side, driven by j x B forces. The evaporation rate determined from spectroscopy is 100 times less than expected from steady state melting and is thus consistent only with transient melting during the individual ELMs. Analysis of IR data and spectroscopy together with modelling using the MEMOS code Bazylev et al 2009 J. Nucl. Mater. 390-391 810-13 point to transient melting as the main process. 3D MEMOS simulations on the consequences of multiple ELMs on damage of tungsten castellated armour have been performed. These experiments provide the first experimental evidence for the absence of significant melt splashing at transient events resembling mitigated ELMs on ITER and establish a key experimental benchmark for the MEMOS code.

  • 119. Coenen, J. W.
    et al.
    Arnoux, G.
    Bazylev, B.
    Matthews, G. F.
    Jachmich, S.
    Balboa, I.
    Clever, M.
    Dejarnac, R.
    Coffey, I.
    Corre, Y.
    Devaux, S.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Gauthier, E.
    Horacek, J.
    Knaup, M.
    Komm, M.
    Krieger, K.
    Marsen, S.
    Meigs, A.
    Mertens, Ph.
    Pitts, R. A.
    Puetterich, T.
    Rack, M.
    Stamp, M.
    Sergienko, G.
    Tamain, P.
    Thompson, V.
    ELM induced tungsten melting and its impact on tokamak operation2015Ingår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 463, s. 78-84Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In JET-ILW dedicated melt exposures were performed using a sequence of 3MA/2.9T H-Mode JET pulses with an input power of P-IN = 23 MW, a stored energy of similar to 6 MJ and regular type I ELMs at Delta W-ELM = 0.3 MJ and f(ELM) similar to 30 Hz. In order to assess the risk of starting ITER operations with a full W divertor, one of the task was to measure the consequences of W transients melting due to ELMs. JET is the only tokamak able to produce transients/ ELMs large enough (>300 kJ per ELM) to facilitate melting of tungsten. Such ELMs are comparable to mitigated ELMs expected in ITER. By moving the outer strike point (OSP) onto a dedicated leading edge the base temperature was raised within similar to 1 s to allow transient ELM-driven melting during the subsequent 0.5 s. Almost 1 mm (similar to 6 mm(3)) of W was moved by similar to 150 ELMs within 5 subsequent discharges. Significant material losses in terms of ejections into the plasma were not observed. There is indirect evidence that some small droplets (similar to 80 mu m) were ejected. The impact on the main plasma parameters is minor and no disruptions occurred. The W-melt gradually moved along the lamella edge towards the high field side, driven by j x B forces. The evaporation rate determined is 100 times less than expected from steady state melting and thus only consistent with transient melting during individual ELMs. IR data, spectroscopy, as well as melt modeling point to transient melting. Although the type of damage studied in these JET experiments is unlikely to be experienced in ITER, the results do strongly support the design strategy to avoid exposed edges in the ITER divertor. The JET experiments required a surface at normal incidence and considerable pre-heating to produce tungsten melting. They provide unique experimental evidence for the absence of significant melt splashing at events resembling mitigated ELMs on ITER and establish a unique experimental benchmark for the simulations being used to study transient shallow melting on ITER W divertor PFUs.

  • 120. Coenen, J. W.
    et al.
    Matthews, G. F.
    Krieger, K.
    Iglesias, D.
    Bunting, P.
    Corre, Y.
    Silburn, S.
    Balboa, I.
    Bazylevs, B.
    Conway, N.
    Coffey, I.
    Dejarnac, R.
    Gauthier, E.
    Gaspar, J.
    Jachmich, S.
    Jepu, I.
    Makepeace, C.
    Scannell, R.
    Stamp, M.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Pitts, R. A.
    Wiesen, S.
    Widdowson, A.
    Heinola, K.
    Baron-Wiechec, A.
    Transient induced tungsten melting at the Joint European Torus (JET)2017Ingår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T170, artikel-id 014013Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Melting is one of the major risks associated with tungsten (W) plasma-facing components (PFCs) in tokamaks like JET or ITER. These components are designed such that leading edges and hence excessive plasma heat loads deposited at near normal incidence are avoided. Due to the high stored energies in ITER discharges, shallow surface melting can occur under insufficiently mitigated plasma disruption and so-called edge localised modes-power load transients. A dedicated program was carried out at the JET to study the physics and consequences of W transient melting. Following initial exposures in 2013 (ILW-1) of a W-lamella with leading edge, new experiments have been performed on a sloped surface (15 degrees slope) during the 2015/2016 (ILW-3) campaign. This new experiment allows significantly improved infrared thermography measurements and thus resolved important issue of power loading in the context of the previous leading edge exposures. The new lamella was monitored by local diagnostics: spectroscopy, thermography and high-resolution photography in between discharges. No impact on the main plasma was observed despite a strong increase of the local W source consistent with evaporation. In contrast to the earlier exposure, no droplet emission was observed from the sloped surface. Topological modifications resulting from the melting are clearly visible between discharges on the photographic images. Melt damage can be clearly linked to the infrared measurements: the emissivity drops in zones where melting occurs. In comparison with the previous leading edge experiment, no runaway melt motion is observed, consistent with the hypothesis that the escape of thermionic electrons emitted from the melt zone is largely suppressed in this geometry, where the magnetic field intersects the surface at lower angles than in the case of perpendicular impact on a leading edge. Utilising both exposures allows us to further test the model of the forces driving melt motion that successfully reproduced the findings from the original leading edge exposure. Since the ILW-1 experiments, the exposed misaligned lamella has now been retrieved from the JET machine and post mortem analysis has been performed. No obvious mass loss is observed. Profilometry of the ILW-1 lamella shows the structure of the melt damage which is in line with the modell predictions thus allowing further model validation. Nuclear reaction analysis shows a tenfold reduction in surface deuterium concentration in the molten surface in comparison to the non-molten part of the lamella.

  • 121. Coenen, J. W.
    et al.
    Sertoli, M.
    Brezinsek, S.
    Coffey, I.
    Dux, R.
    Giroud, C.
    Groth, M.
    Huber, A.
    Ivanova, Darya
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Krieger, K.
    Lawson, K.
    Marsen, S.
    Meigs, A.
    Neu, R.
    Puetterich, T.
    van Rooij, G. J.
    Stamp, M. F.
    Long-term evolution of the impurity composition and impurity events with the ITER-like wall at JET2013Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 53, nr 7, s. 073043-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper covers aspects of long-term evolution of intrinsic impurities in the JET tokamak with respect to the newly installed ITER-like wall (ILW). At first the changes related to the change over from the JET-C to the JET-ILW with beryllium (Be) as the main wall material and tungsten (W) in the divertor are discussed. The evolution of impurity fluxes in the newly installed W divertor with respect to studying material migration is described. In addition, a statistical analysis of transient impurity events causing significant plasma contamination and radiation losses is shown. The main findings comprise a drop in carbon content (x20) (see also Brezinsek et al (2013 J. Nucl. Mater. 438 S303)), low oxygen content (x10) due to the Be first wall (Douai et al 2013 J. Nucl. Mater. 438 S1172-6) as well as the evolution of the material mix in the divertor. Initially, a short period of repetitive ohmic plasmas was carried out to study material migration (Krieger et al 2013 J. Nucl. Mater. 438 S262). After the initial 1600 plasma seconds the material surface composition is, however, still evolving. With operational time, the levels of recycled C are increasing slightly by 20% while the Be levels in the deposition-dominated inner divertor are dropping, hinting at changes in the surface layer material mix made of Be, C and W. A steady number of transient impurity events, consisting of W and constituents of inconel, is observed despite the increase in variation in machine operation and changes in magnetic configuration as well as the auxiliary power increase.

  • 122. Coenen, J. W.
    et al.
    Van Rooij, G. J.
    Aho-Mantila, L.
    Brezinsek, S.
    Clever, M.
    Dux, R.
    Groth, M.
    Ivanova, Darya
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Krieger, K.
    Marsen, S.
    Meigs, A.
    Müller, H. W.
    Neu, R.
    Potzel, S.
    Stamp, M. F.
    Tungsten erosion in the all-metal tokamaks JET and ASDEX Upgrade2012Ingår i: 39th EPS Conference on Plasma Physics 2012, EPS 2012 and the 16th International Congress on Plasma Physics: Volume 1, 2012, 2012, s. 253-256Konferensbidrag (Refereegranskat)
    Abstract [en]

    The tungsten source in the all W outer divertor and Be main wall configuration has been quantified mainly during L-mode plasmas and compared to AUG Data both gained from local spectroscopy. Results so far show differences between AUG and JET based on impurities in the plasma changing the sputter behavior. This stresses the need for detailed analysis of the divertor impurity composition and detailed molding in the future analysis. The H-Mode examples indicate at ELM dominated sputtering and a rather low averaged sputtering yield in general. Nitrogen seeding can change the divertor conditions significantly either increasing W sputtering or suppressing it due to local cooling, JET and AUG behave similarly. All together it is clear that by having low divertor temperature or a beneficial impurity composition sputtering can be controlled and is rather low as expected in an all metal environment.

  • 123. Counsell, G.
    et al.
    Coad, P.
    Grisola, C.
    Hopf, C.
    Jacob, W.
    Kirschner, A.
    Kreter, A.
    Krieger, K.
    Likonen, J.
    Philipps, V.
    Roth, J.
    Rubel, Marek J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Salancon, E.
    Semerok, A.
    Tabares, F. L.
    Widdowson, A.
    Tritium retention in next step devices and the requirements for mitigation and removal techniques2006Ingår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 48, nr 12B, s. B189-B199Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Mechanisms underlying the retention of fuel species in tokamaks with carbon plasma-facing components are presented, together with estimates for the corresponding retention of tritium in ITER. The consequential requirement for new and improved schemes to reduce the tritium inventory is highlighted and the results of ongoing studies into a range of techniques are presented, together with estimates of the tritium removal rate in ITER in each case. Finally, an approach involving the integration of many tritium removal techniques into the ITER operational schedule is proposed as a means to extend the period of operations before major intervention is required.

  • 124.
    Dahlin, Jon-Erik
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Scheffel, Jan
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Advanced Reversed-field Pinch Scaling Laws2005Ingår i: 32nd EPS Conference on Plasma Physics, Tarragona, Spain 27 June-1 July, P-1.118, 2005, 2005Konferensbidrag (Refereegranskat)
    Abstract [en]

    A series of resistive magnetohydrodynamic numerical simulations are performed to generate scaling laws for energy confinement time τE and poloidal beta βp for the advanced reversed field-pinch (RFP). Strongly improved scaling with basic initial parameters is obtained as compared to the conventional RFP. Early results indicate an improved scaling of τE with plasma current I and line density N compared to the conventional RFP. The improved behaviour of the advanced RFP as compared to the conventional, uncontrolled RFP stems from the introduction of current profile control (CPC). In the present numerical simulations, CPC is performed by implementation of a parameter free automatic feedback algorithm, optimised to reduce the fluctuation caused v × B electric field. The scheme introduces an ad-hoc electric field within the plasma volume, automatically adjusted to dynamically control the plasma into more quiescent behaviour by eliminating current driven tearing mode instabilities and reducing resistive interchange modes.

  • 125.
    Dahlin, Jon-Erik
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Scheffel, Jan
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Improved Computer Simulations of Energy Confinement in the Advanced Reversed-field Pinch2006Ingår i: 33rd EPS Conference on Plasma Phys, 2006Konferensbidrag (Refereegranskat)
    Abstract [en]

    A revised algorithm for numerical simulations of the advanced reversed-field pinch (RFP) is presented. The results show improved scalings of magnetic fluctuations, energy confinement time τE and poloidal beta βθ with basic initial parameters as compared to what has been presented by the authors in earlier studies of the advanced RFP. The improved behaviour of the advanced RFP stems from the introduction of current profile control (CPC), implemented through a scheme of active feedback of the electric dynamo field. The work, which has an optimistic approach and sweeps over a large parameter domain reaching into the reactor relevant region, is theoretical and claims to answer the question of how far CPC can bring the RFP concept in principle. Experimental implementation is thus a later concern. With this scheme, a state with strongly suppressed tearing mode activity is achieved, which allows for a theoretical study of pressure driven resistive g-modes. This is a task that has been very hard to perform in the past, since tearing modes have always dominated the RFP dynamics. Thus it is now possible, for the first time, to investigate whether pressure driven modes, which are persistent in the RFP, are fatal for the confinement of a high-beta RFP configuration or if they can be accepted in a future reactor.

  • 126.
    Dahlin, Jon-Erik
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Scheffel, Jan
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Scaling Laws of Confinement Parameters for the Advanced Reversed-field Pinch2005Ingår i: 47th APS Division of Plasma Physics Meeting, Denver, Colorado, 24-28 October, 2005, 2005Konferensbidrag (Refereegranskat)
  • 127. de la Luna, E
    et al.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Lomas, P
    Maggi, C
    Brezinsek, S
    Challis, C
    Nunes, I
    Rimini, F
    Type I ELM characterization in JET with the ITER-like wall2015Ingår i: 15th International Workshop on H-mode Physics and Transport Barriers, 19-21 October 2015. Garching, Germany, 2015Konferensbidrag (Övrigt vetenskapligt)
  • 128. de la Luna, E
    et al.
    Rimini, F
    Lomas, P
    Sips, A
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Amicucci, L
    Drewelow, P
    Flanagan, J
    Nunes, I
    Saarelma, S
    Recent Results on High-Triangularity H-Mode Studies in JET-ILW2016Ingår i: 26th IAEA Fusion Energy Conference, 17-22 October 2016, 2016Konferensbidrag (Refereegranskat)
  • 129. De Temmerman, G.
    et al.
    Rubel, Marek J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Coad, J. P.
    Pitts, R. A.
    Drake, James Robert
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Mirror test for ITER: Optical characterisation of metal mirrors in divertor tokamaks2005Ingår i: 32nd EPS Conference on Plasma Physics 2005, EPS 2005, Held with the 8th International Workshop on Fast Ignition of Fusion Targets: Europhysics Conference Abstracts, 2005, s. 586-589Konferensbidrag (Refereegranskat)
  • 130. de Vries, P. C.
    et al.
    Joffrin, E.
    Hawkes, N. C.
    Litaudon, X.
    Challis, C. D.
    Andrew, Y.
    Beurskens, M.
    Brix, M.
    Brzozowski, Jerzy H.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Crombe, K.
    Giroud, C.
    Hobirk, J.
    Johnson, T.
    Lonnroth, J.
    Salmi, A.
    Tala, T.
    Yavorskij, V.
    Zastrow, K. D.
    Effect of toroidal field ripple on the formation of internal transport barriers2008Ingår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 50, nr 6Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The effect of a toroidal field (TF) ripple on the formation and performance of internal transport barriers (ITBs) has been studied in JET. It was found that the TF ripple had a profound effect on the toroidal plasma rotation. An increased TF ripple up to delta = 1% led to a lower rotation and reduced the rotational shear in the region where the ITBs were formed. ITB triggering events were observed in all cases and it is thought that the rotational shear may be less important for this process than, for example, the q-profile. However, the increase in the pressure gradient following the ITB trigger was reduced in discharges with a larger TF ripple and consequently a lower rotational shear. This suggests that toroidal rotation and its shear play a role in the growth of the ITB once it has been triggered.

  • 131. de Vries, P. C.
    et al.
    Salmi, A.
    Parail, V.
    Giroud, C.
    Andrew, Y.
    Biewer, T. M.
    Crombe, K.
    Jenkins, I.
    Johnson, Thomas J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Kiptily, V.
    Loarte, A.
    Lonnroth, J.
    Meigs, A.
    Oyama, N.
    Sartori, R.
    Saibene, G.
    Urano, H.
    Zastrow, K. D.
    Effect of toroidal field ripple on plasma rotation in JET2008Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 48, nr 3Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Dedicated experiments on TF ripple effects on the performance of tokamak plasmas have been carried out at JET. The TF ripple was found to have a profound effect on the plasma rotation. The central Mach number, M, defined as the ratio of the rotation velocity and the thermal velocity, was found to drop as a function of TF ripple amplitude (3) from an average value of M = 0.40-0.55 for operations at the standard JET ripple of 6 = 0.08% to M = 0.25-0.40 for 6 = 0.5% and M = 0.1-0.3 for delta = 1%. TF ripple effects should be considered when estimating the plasma rotation in ITER. With standard co-current injection of neutral beam injection (NBI), plasmas were found to rotate in the co-current direction. However, for higher TF ripple amplitudes (delta similar to 1%) an area of counter rotation developed at the edge of the plasma, while the core kept its co-rotation. The edge counter rotation was found to depend, besides on the TF ripple amplitude, on the edge temperature. The observed reduction of toroidal plasma rotation with increasing TF ripple could partly be explained by TF ripple induced losses of energetic ions, injected by NBI. However, the calculated torque due to these losses was insufficient to explain the observed counter rotation and its scaling with edge parameters. It is suggested that additional TF ripple induced losses of thermal ions contribute to this effect.

  • 132. De Vries, P. C.
    et al.
    Salmi, A.
    Parail, V.
    Giroud, C.
    Andrew, Y.
    Biewer, T. M.
    Crombé, K.
    Jenkins, I.
    Johnson, Thomas J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Kiptily, V.
    Loarte, A.
    Lönnroth, J.
    Meigs, A.
    Oyama, N.
    Sartori, R.
    Saibene, G.
    Urano, H.
    Zastrow, K. -D
    Effect of toroidal field ripple on plasma rotation in JET2007Ingår i: 34th EPS Conference on Plasma Physics 2007, EPS 2007 - Europhysics Conference Abstracts, 2007, nr 1, s. 603-606Konferensbidrag (Refereegranskat)
  • 133. Dejarnac, R.
    et al.
    Podolnik, A.
    Komm, M.
    Arnoux, G.
    Coenen, J. W.
    Devaux, S.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Gunn, J. P.
    Matthews, G. F.
    Pitts, R. A.
    Numerical evaluation of heat flux and surface temperature on a misaligned JET divertor W lamella during ELMs2014Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 54, nr 12, s. 123011-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A series of experiments has been performed on JET to investigate the dynamics of transient melting due to edge localized modes (ELMs). The experiment employs a deliberately misaligned lamella in one module of the JET bulk tungsten outer divertor, allowing the combination of stationary power flux and ELMs to transiently melt the misaligned edge. During the design of the experiment a number of calculations were performed using 2D particle-in-cell simulations and a heat transfer code to investigate the influence on the deposited power flux of finite Larmor radius effects associated with the energetic ELM ions. This has been performed using parameter scans inside a range of pedestal temperatures and densities to scope different experimentally expected ELM energies. On the one hand, we observe optimistic results, with smoothing of the heat flux due to the Larmor gyration on the protruding side of the lamella which sees the direct parallel flux-the deposited power tends to be lower than the nominal value expected from geometric magnetic field line impact over a distance smaller than 2 Larmor radii, a finding which is always valid during ELMs for such a geometry. On the other hand, the fraction of the flux not reaching the directly wetted side is transferred and spread to the top surface of the lamella. The hottest point of the lamella (corner side/top) does not always benefit from the gain from the Larmor smoothing effect because of an enhanced power deposition from the second contribution.

  • 134. Di Siena, A.
    et al.
    Görier, T.
    Doerk, H.
    Citrin, J.
    Johnson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Schneider, M.
    Poli, E.
    Non-Maxwellian background effects in gyrokinetic simulations with GENE2016Ingår i: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 775, nr 1, artikel-id 012003Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The interaction between fast particles and core turbulence has been established as a central issue for a tokamak reactor. Recent results predict significant enhancement of electromagnetic stabilisation of ITG turbulence in the presence of fast ions. However, most of these simulations were performed with the assumption of equivalent Maxwellian distributed particles, whereas to rigorously model fast ions, a non-Maxwellian background distribution function is needed. To this aim, the underlying equations in the gyrokinetic code GENE have been re-derived and implemented for a completely general background distribution function. After verification studies, a previous investigation on a particular JET plasma has been revised with linear simulations. The plasma is composed by Deuterium, electron, Carbon impurities, NBI fast Deuterium and ICRH 3He. Fast particle distributions have been modelled with a number of different analytic choices in order to study the impact of non-Maxwellian distributions on the plasma turbulence: slowing down and anisotropic Maxwellian. Linear growth rates are studied as a function of the wave number and compared with those obtained using an equivalent Maxwellian. Generally, the choice of the 3He distribution seems to have a stronger impact on the microinstabilities than that of the fast Deuterium.

  • 135. Di Siena, A.
    et al.
    Görler, T.
    Doerk, H.
    Bilato, R.
    Citrin, J.
    Johnson, Thomas
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Schneider, M.
    Poli, E.
    Impact of realistic fast ion distribution function in gyrokinetic GENE simulations2017Ingår i: 44th EPS Conference on Plasma Physics, EPS 2017, European Physical Society (EPS) , 2017Konferensbidrag (Refereegranskat)
    Abstract [en]

    Understanding the stabilising mechanism of fast particles on plasma turbulence is an essential task for a fusion reactor, where the energetic particles can constitute a significant fraction of the main ions. While the consideration of equivalent Maxwellian distributed fast ions in the simulations has greatly improved the agreement with experiments, fast ion electromagnetic stabilization seems to be somewhat over-estimated. Power balance is usually reached only with increased plasma gradients. However, it is well known that to rigorously model highly non thermalised particles, a non-Maxwellian background distribution function is needed. To this aim, a previous study on a particular JET plasma has been revised and analysed with the gyrokinetic code GENE. Fast particles have been modelled with a number of different analytic and numerical distributions. The latter have been imported from the modelling tools NEMO/SPOT and SELFO. 

  • 136. Doveil, F.
    et al.
    Cherigier-Kovacic, L.
    Ström, Petter
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Lamb-shift and electric field measurements in plasmas2017Ingår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 59, nr 1, artikel-id 014020Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The electric field is a quantity of particular relevance in plasma physics. Indeed, its fluctuations are responsible for different macroscopic phenomena such as anomalous transport in fusion plasmas. Answering a long-standing challenge, we offer a new method to locally and non-intrusively measure weak electric fields and their fluctuations in plasmas, by means of a beam of hydrogen ions or atoms. We present measurements of the electric field in vacuum and in a plasma where Debye shielding is measured. For the first time, we have used the Lamb-shift resonance to measure oscillating electric fields around 1 GHz and observed the strong enhancement of the Lyman-alpha signal. The measurement is both direct and non-intrusive. This method provides sensitivity (mV cm(-1)) and temporal resolution (ns) that are three orders higher compared to current diagnostics. It thus allows measuring fluctuations of the electric field at scales not previously reached experimentally.

  • 137. Drake, J. R.
    et al.
    Scheffel, Jan
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Calculations of Toroidal Extrap Equilibria for Different Toroidal Ring-Current Configurations1985Rapport (Övrigt vetenskapligt)
  • 138.
    Drake, James Robert
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Bolzonella, T.
    Olofsson, Erik
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Baruzzo, T. M.
    Brunsell, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Guo, S. C.
    Igochine, V.
    Liu, Y. Q.
    Marchiori, G.
    Paccagnella, R.
    Rubinacci, G.
    Soppelsa, A.
    Villone, F.
    Yadikin, D.
    Martin, P.
    Zohm, H.
    Reversed-Field Pinch Contributions to Resistive Wall Mode Physics and Control2008Konferensbidrag (Refereegranskat)
    Abstract [en]

    Optimal feedback control of resistive-wall modes (RWM) is of common interest for toroidal fusionconcepts that use conducting walls for stabilization of ideal MHD modes. From the RWM control point of view,the RFP situation is in many respects similar to the advanced tokamak situation in the presence of very lowplasma rotation, where the most effective stabilizing mechanism is the feedback action of a set of active coils.Results from EXTRAP T2R (Sweden) and RFX-mod (Italy) RFP experiments have shown that full feedbackcontrol of multiple RWMs is possible and their deleterious effects can be completely suppressed. However it isnow important to optimize the RWM control systems both for the RFP and tokamak configuration for futureimplementation. Important aspects of optimization are effective mode identification and tracking capability,avoidance of the harmful effects of sideband modes (aliasing) in the control spectrum, minimized powerrequirements and robust controller stability. The paper describes collaborative work carried out on the two RFPexperiments. Controller models based on the mode harmonic control concept and on a state-space multipleinputmultiple-output intelligent shell concept are studied. Progress in development of optimal control schemesare presented both through experimental studies and simulations.

  • 139.
    Drake, James Robert
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Brunsell, Per R.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Yadikin, Dmitriy
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Bergsåker, Henric
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Cecconello, Marco
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hedqvist, Anders
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Kuldkepp, Mattias
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Menmuir, Sheena
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Rachlew, Elisabeth
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Experiments on feedback control of multiple resistive wall modes comparing different active coil arrays and sensor types2006Ingår i: IAEA-F1-CN-149, 2006, s. Paper EX/P8-11-Konferensbidrag (Refereegranskat)
  • 140.
    Dumont, R. J.
    et al.
    CEA, IRFM, F-13108 St Paul Les Durance, France..
    Mailloux, J.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Aslanyan, V
    MIT, PSFC, 175 Albany St, Cambridge, MA 02039 USA..
    Baruzzo, M.
    Consorzio RFX, Corso Stati Uniti 4, I-35127 Padua, Italy..
    Challis, C. D.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Coffey, I
    Queens Univ, Dept Pure & Appl Phys, Belfast BT7 1NN, Antrim, North Ireland..
    Czarnecka, A.
    Inst Plasma Phys & Laser Microfus, Hery St 23, PL-00908 Warsaw, Poland..
    Delabie, E.
    Oak Ridge Natl Lab, Oak Ridge, TN USA..
    Eriksson, J.
    Uppsala Univ, Dept Phys & Astron, SE-75119 Uppsala, Sweden..
    Faustin, J.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Ferreira, J.
    Univ Lisbon, IST, Inst Plasmas & Fusao Nucl, Lisbon, Portugal..
    Fitzgerald, M.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Garcia, J.
    CEA, IRFM, F-13108 St Paul Les Durance, France..
    Giacomelli, L.
    Univ Milano Bicocca, Piazza Sci 3, I-20126 Milan, Italy..
    Giroud, C.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Hawkes, N.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Jacquet, Ph
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Joffrin, E.
    CEA, IRFM, F-13108 St Paul Les Durance, France..
    Johnson, Thomas
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Keeling, D.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    King, D.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Kiptily, V
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Lomanowski, B.
    Aalto Univ, POB 14100, FIN-00076 Aalto, Finland..
    Lerche, E.
    Ass EUROFUS Belgian State, LPP ERM KMS, TEC Partner, Brussels, Belgium..
    Mantsinen, M.
    Barcelona Supercomp Ctr, Barcelona, Spain.;ICREA, Barcelona, Spain..
    Meneses, L.
    Univ Lisbon, IST, Inst Plasmas & Fusao Nucl, Lisbon, Portugal..
    Menmuir, S.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    McClements, K.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Moradi, S.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Nabais, F.
    Univ Lisbon, IST, Inst Plasmas & Fusao Nucl, Lisbon, Portugal..
    Nocente, M.
    Univ Milano Bicocca, Piazza Sci 3, I-20126 Milan, Italy..
    Patel, A.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Patten, H.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Puglia, P.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Scannell, R.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Sharapov, S.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Solano, E. R.
    CIEMAT, Lab Nacl Fus, Madrid, Spain..
    Tsalas, M.
    FOM Inst DIFFER, NL-3430 BE Nieuwegein, Netherlands.;ITER Org, Route Vinon Sur Verdon, F-13067 St Paul Les Durance, France..
    Vallejos, Pablo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Weisen, H.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Scenario development for the observation of alpha-driven instabilities in JET DT plasmas2018Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 58, nr 8, artikel-id 082005Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In DT plasmas, toroidal Alfven eigenmodes (TAEs) can be made unstable by the alpha particles resulting from fusion reactions, and may induce a significant redistribution of fast ions. Recent experiments have been conducted in JET deuterium plasmas in order to prepare scenarios aimed at observing alpha-driven TAEs in a future JET DT campaign. Discharges at low density, large core temperatures associated with the presence of internal transport barriers and characterised by good energetic ion confinement have been performed. ICRH has been used in the hydrogen minority heating regime to probe the TAE stability. The consequent presence of MeV ions has resulted in the observation of TAEs in many instances. The impact of several key parameters on TAE stability could therefore be studied experimentally. Modeling taking into account NBI and ICRH fast ions shows good agreement with the measured neutron rates, and has allowed predictions for DT plasmas to be performed.

  • 141. Dunne, M
    et al.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Poetzel, S
    Reimold, F
    Wischmeier, M
    Wolfrum, E
    Bernerdt, M
    The Role of the Density Profile Location on Pedestal Stability in ASDEX-Upgrade2016Ingår i: 26th IAEA Fusion Energy Conference, 17-22 October 2016, 2016Konferensbidrag (Refereegranskat)
  • 142. Dunne, M. G.
    et al.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Beurskens, M.
    Cavedon, M.
    Fischer, R.
    Huijsmans, G. T. A.
    Laggner, F. M.
    McDermott, R. M.
    Tardini, G.
    Viezzer, E.
    Wolfrum, E.
    Impact of nitrogen seeding on the AUG pedestal: Experiments and modelling2015Ingår i: 42nd European Physical Society Conference on Plasma Physics, EPS 2015, European Physical Society (EPS) , 2015Konferensbidrag (Refereegranskat)
  • 143. Dunne, M. G.
    et al.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Beurskens, M. N. A.
    Cavedon, M.
    Fietz, S.
    Fischer, R.
    Giannone, L.
    Huijsmans, G. T. A.
    Kurzan, B.
    Laggner, F.
    McCarthy, P. J.
    McDermott, R. M.
    Tardini, G.
    Viezzer, E.
    Willensdorfer, M.
    Wolfrum, E.
    Global performance enhancements via pedestal optimisation on ASDEX Upgrade2017Ingår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 59, nr 2, artikel-id 025010Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Results of experimental scans of heating power, plasma shape, and nitrogen content are presented, with a focus on global performance and pedestal alteration. In detailed scans at low triangularity, it is shown that the increase in stored energy due to nitrogen seeding stems from the pedestal. It is also shown that the confinement increase is driven through the temperature pedestal at the three heating power levels studied. In a triangularity scan, an orthogonal effect of shaping and seeding is observed, where increased plasma triangularity increases the pedestal density, while impurity seeding (carbon and nitrogen) increases the pedestal temperature in addition to this effect. Modelling of these effects was also undertaken, with interpretive and predictive models being employed. The interpretive analysis shows a general agreement of the experimental pedestals in separate power, shaping, and seeding scans with peeling-ballooning theory. Predictive analysis was used to isolate the individual effects, showing that the trends of additional heating power and increased triangularity can be recoverd. However, a simple change of the effective charge in the plasma cannot explain the observed levels of confinement improvement in the present models.

  • 144. Dunne, M. G.
    et al.
    Potzel, S.
    Reimold, F.
    Wischmeier, M.
    Wolfrum, E.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Beurskens, M.
    Bilkova, P.
    Cavedon, M.
    Fischer, R.
    Kurzan, B.
    Laggner, F. M.
    McDermott, R. M.
    Tardini, G.
    Trier, E.
    Viezzer, E.
    Willensdorfer, M.
    The role of the density profile in the ASDEX-Upgrade pedestal structure2017Ingår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 59, nr 1, artikel-id 014017Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Experimental evidence for the impact of a region of high density localised in the high-field side scrape-off layer (the HFSHD) on plasma confinement is shown in various dedicated experiments on ASDEX Upgrade (AUG). Increasing main ion fuelling is shown to increase the separatrix density and shift the density profile outwards. Predictive pedestal modelling of this shift indicates a 25% decrease in the attainable pedestal top pressure, which compares well with experimental observations in the gas scan. Since the HFSHD can be mitigated by applying nitrogen seeding, a combined scan in fuelling rate, heating power, and nitrogen seeding is presented. Significant increases in the achievable pedestal top pressure are observed with seeding, in particular at high heating powers, and are correlated with inward shifted density profiles and a reduction of the HFSHD and separatrix density. Interpretive linear stability analysis also confirms the impact of a radially shifted pressure profile on peeling-ballooning stability, with an inward shift allowing access to higher pressure gradients and pedestal widths.

  • 145. Dunne, M
    et al.
    Poetzel, S
    Wischmeier, M
    Wolfrum, E
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Reimold, F
    Predictive  modelling  of  the  impact  of  a  radiative  divertor  on pedestal  con nement  on  ASDEX  Upgrade2015Ingår i: 57rd Meeting of the APS Division of Plasma Physics, November 2015, Savannah, USA, 2015Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    In future devices, tailoring of the edge density profile and radiation profile for power exhaust control via a deuterium gas puff and extrinsic impurity seeding will be necessary. It has been observed on present day machines that high D fuelling can reduce the plasma stored energy while adding impurity seeding can act to improve confinement by up to 40{\%}. This study presents a combination of observations and modelling completed on AUG with the aim of determining the mechanisms behind the confinement degradation with a gas puff and improvement with impurity seeding. In particular, predictive modelling, based on the EPED pedestal model, has been extensively used. Alterations of the temperature and density at the separatrix are found to have large impacts on pedestal stability. Measured changes in divertor properties are used to inform the direction and magnitude of these alterations, with experimentally relevant confinement changes being recovered via pressure profile shifts.

  • 146. Dunne, M
    et al.
    Potzel, S
    Remold, F
    Viezzer, E
    Wischmeier, M
    Wolfrum, E
    Bernerdt, M