Ändra sökning
Avgränsa sökresultatet
3456789 251 - 300 av 837
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.
  • 251. Gasior, P.
    et al.
    Irrek, F.
    Petersson, P.
    Penkalla, Hj.
    Rubel, Marek J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Schweer, B.
    Sundelin, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Wessel, E.
    Linke, J.
    Philipps, V.
    Emmoth, Birger
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT.
    Wolowski, J.
    Hirai, T.
    Laser-induced removal of co-deposits from graphitic plasma-facing components: Characterization of irradiated surfaces and dust particles2009Ingår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 390-91, s. 585-588Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Laser-induced fuel desorption and ablation of co-deposited layers on limiter plates from the TEXTOR tokamak have been studied. Gas phase composition was monitored in situ, whereas the ex situ studies have been focused on the examination of irradiated surfaces and broad analysis of dust generated by ablation of co-deposits. The size of the dust grains is in the range of few nanometers to hundreds of micrometers. These are fuel-rich dust particles, as determined by nuclear reaction analysis. The presence of deuterium in dust indicates that not all fuel species are transferred to the gas phase during irradiation. This also suggests that photonic removal of fuel and the ablation of co-deposit from plasma-facing components may lead to the redistribution of fuel-containing dust to surrounding areas.

  • 252. Giacomelli, L.
    et al.
    Hjalmarsson, A.
    Hellesen, C.
    Gatu Johnson, M.
    Källne, J.
    Weiszflog, M.
    Sharapov, S.
    Andersson Sundén, E.
    Conroy, S.
    Ericsson, G.
    Ronchi, E.
    Sjöstrand, H.
    Gorini, G.
    Tardocchi, M.
    Popovichev, S.
    Johnson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Neutron emission spectroscopy diagnosis of fast ions in RF D( 3He) heated plasmas at JET2007Ingår i: 34th EPS Conference on Plasma Physics 2007, EPS 2007 - Europhysics Conference Abstracts, 2007, nr 2, s. 1158-1161Konferensbidrag (Refereegranskat)
  • 253. Giroud, C
    et al.
    Aiba, N
    Brezinsek, S
    Chankin, J
    Delabie, E
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Lupelli, I
    Moulton, J
    Simpson, J
    Drewelow, P
    On the recovery of pedestal temperature of JET-ILW plasmas with injection of low-Z impurities2016Ingår i: 58th Annual Meeting of the APS Division of Plasma Physics, 31-oct / 4Nov 2016, 2016Konferensbidrag (Övrigt vetenskapligt)
  • 254. Giroud, C
    et al.
    Aiba, N
    Brezinsek, S
    Chankin, S
    Delabie, E
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hillesheim, J
    Pamela, S
    Saarelma, S
    Wiesen, H
    Maggi, C
    Urano, H
    Drewelow, P
    Leyland, M
    Progress in Understanding the Role of Low-Z Impurity in the Confinement in JET-ILW and in JET-C Plasmas2016Ingår i: 26th IAEA Fusion Energy Conference, 17-22 October 2016, 2016Konferensbidrag (Refereegranskat)
  • 255. Giroud, C
    et al.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Leyland, M
    Maggi, C
    Saarelma, S
    Urano, H
    Effect of nitrogen and neon seeding in confinement and pedestal structure in JET with carbon and Be/W wall2015Ingår i: 15th International Workshop on H-mode Physics and Transport Barriers, 19-21 October 2015. Garching, Germany., 2015Konferensbidrag (Övrigt vetenskapligt)
  • 256. Giroud, C.
    et al.
    Jachmich, S.
    Jacquet, P.
    Jarvinen, A.
    Lerche, E.
    Rimini, F.
    Aho-Mantila, L.
    Aiba, N.
    Balboa, I.
    Belo, P.
    Angioni, C.
    Beurskens, M.
    Brezinsek, S.
    Casson, F. J.
    Coffey, I.
    Cunningham, G.
    Delabie, E.
    Devaux, S.
    Drewelow, P.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Figueiredo, A.
    Huber, A.
    Hillesheim, J.
    Garzotti, L.
    Goniche, M.
    Groth, M.
    Kim, Hyun-Tae
    Leyland, M.
    Lomas, P.
    Maddison, G.
    Marsen, S.
    Matthews, G.
    Meigs, A.
    Menmuir, S.
    Puetterich, T.
    van Rooij, G.
    Saarelma, S.
    Stamp, M.
    Urano, H.
    Webster, A.
    Progress at JET in integrating ITER-relevant core and edge plasmas within the constraints of an ITER-like wall2015Ingår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 57, nr 3, artikel-id 035004Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper reports the progress made at JET-ILW on integrating the requirements of the reference ITER baseline scenario with normalized confinement factor of 1, at a normalized pressure of 1.8 together with partially detached divertor whilst maintaining these conditions over many energy confinement times. The 2.5 MA high triangularity ELMy H-modes are studied with two different divertor configurations with D-gas injection and nitrogen seeding. The power load reduction with N seeding is reported. The relationship between an increase in energy confinement and pedestal pressure with triangularity is investigated. The operational space of both plasma configurations is studied together with the ELM energy losses and stability of the pedestal of unseeded and seeded plasmas. The achievement of stationary plasma conditions over many energy confinement times is also reported.

  • 257. Giroud, C.
    et al.
    Maddison, G.
    McCormick, K.
    Beurskens, M. N. A.
    Brezinsek, S.
    Devaux, S.
    Eich, T.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Fundamenski, W.
    Groth, M.
    Huber, A.
    Jachmich, S.
    Jarvinen, A.
    Kallenbach, A.
    Krieger, K.
    Moulton, D.
    Saarelma, S.
    Thomsen, H.
    Wiesen, S.
    Alonso, A.
    Alper, B.
    Arnoux, G.
    Belo, P.
    Boboc, A.
    Brett, A.
    Brix, M.
    Coffey, I.
    de la Luna, E.
    Dodt, D.
    De Vries, P.
    Felton, R.
    Giovanozzi, E.
    Harling, J.
    Harting, D.
    Hawkes, N.
    Hobirk, J.
    Jenkins, I.
    Joffrin, E.
    Kempenaars, M.
    Lehnen, M.
    Loarer, T.
    Lomas, P.
    Mailloux, J.
    McDonald, D.
    Meigs, A.
    Morgan, P.
    Nunes, I.
    van Thun, C. Perez
    Riccardo, V.
    Rimini, F.
    Sirinnelli, A.
    Stamp, M.
    Voitsekhovitch, I.
    Integration of a radiative divertor for heat load control into JET high triangularity ELMy H-mode plasmas2012Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 52, nr 6, s. 063022-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Experiments on JET with a carbon-fibre composite wall have explored the reduction of steady-state power load in an ELMy H-mode scenario at high Greenwald fraction similar to 0.8, constant power and close to the L to H transition. This paper reports a systematic study of power load reduction due to the effect of fuelling in combination with seeding over a wide range of pedestal density ((4-8) x 10(19) m(-3)) with detailed documentation of divertor, pedestal and main plasma conditions, as well as a comparative study of two extrinsic impurity nitrogen and neon. It also reports the impact of steady-state power load reduction on the overall plasma behaviour, as well as possible control parameters to increase fuel purity. Conditions from attached to fully detached divertor were obtained during this study. These experiments provide reference plasmas for comparison with a future JET Be first wall and an all W divertor where the power load reduction is mandatory for operation.

  • 258. Giroud, C.
    et al.
    Maddison, G. P.
    Jachmich, S.
    Rimini, F.
    Beurskens, M. N. A.
    Balboa, I.
    Brezinsek, S.
    Coelho, R.
    Coenen, J. W.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Joffrin, E.
    Oberkofler, M.
    Lehnen, M.
    Liu, Y.
    Marsen, S.
    McCormick, K.
    Meigs, A.
    Neu, R.
    Sieglin, B.
    van Rooij, G.
    Arnoux, G.
    Belo, P.
    Brix, M.
    Clever, M.
    Coffey, I.
    Devaux, S.
    Douai, D.
    Eich, T.
    Flanagan, J.
    Gruenhagen, S.
    Huber, A.
    Kempenaars, M.
    Kruezi, U.
    Lawson, K.
    Lomas, P.
    Lowry, C.
    Nunes, I.
    Sirinnelli, A.
    Sips, A. C. C.
    Stamp, M.
    Wiesen, S.
    Impact of nitrogen seeding on confinement and power load control of a high-triangularity JET ELMy H-mode plasma with a metal wall2013Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 53, nr 11, s. 113025-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper reports the impact on confinement and power load of the high-shape 2.5MA ELMy H-mode scenario at JET of a change from all carbon plasma-facing components to an all metal wall. In preparation to this change, systematic studies of power load reduction and impact on confinement as a result of fuelling in combination with nitrogen seeding were carried out in JET-C and are compared with their counterpart in JET with a metallic wall. An unexpected and significant change is reported on the decrease in the pedestal confinement but is partially recovered with the injection of nitrogen.

  • 259. Giroud, C
    et al.
    Oberkofler, M
    Douai, H
    Maddison, G
    Beurskens, M
    Brezinsek, S
    Coenen, J
    Dittmar, T
    Drenik, A
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Grunhagen, A
    Jachmick, S
    Joffrin, E
    Mc Kormick, G
    Neu, R
    Rimini, F
    van Rooij, J
    Sips, A
    Tabares, F
    de Vries, P
    Nitrogen Seeding for Heat Load Control in JET ELMy H-mode Plasmas and its Compatibility with ILW Materials2012Ingår i: 24th IAEA Fusion Energy Conference: 24th IAEA Fusion Energy Conference, 2012, s. EX/P5-30-Konferensbidrag (Refereegranskat)
  • 260. Graves, J. P.
    et al.
    Chapman, I.
    Coda, S.
    Crombe, K.
    Eriksson, L. -G
    Johnson, Thomas Joe
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Koslowski, R.
    Lennholm, M.
    Mayoral, M. -L
    Nunes, I.
    Sawtooth control mechanism on JET using off-axis toroidally propagating ICRF waves2009Ingår i: 36th EPS Conference on Plasma Physics 2009, EPS 2009 - Europhysics Conference Abstracts, 2009, s. 1511-1514Konferensbidrag (Refereegranskat)
  • 261. Graves, J. P.
    et al.
    Chapman, I.
    Coda, S.
    Eriksson, L. G.
    Johnson, Thomas J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Sawtooth-Control Mechanism using Toroidally Propagating Ion-Cyclotron-Resonance Waves in Tokamaks2009Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 102, nr 6Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The sawtooth control mechanism in plasmas employing off-axis toroidally propagating ion cyclotron resonance waves in tokamaks is reinvestigated. The radial drift excursion of energetic passing ions distributed asymmetrically in the velocity parallel to the magnetic field determines stability when the rational q=1 surface resides within a narrow region centered about the shifted fundamental cyclotron resonance.

  • 262. Graves, J. P.
    et al.
    Chapman, I.
    Coda, S.
    Eriksson, L. -G
    Johnson, Thomas Joe
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Sawtooth control mechanism using counter current propagating ICRH in JET2008Ingår i: EPS Conf. Plasma Phys., EPS - Europhys. Conf. Abstr., 2008, nr 3, s. 2010-2013Konferensbidrag (Refereegranskat)
    Abstract [en]

    The sawtooth control mechanism in plasmas employing off-axis ICCD is reinvestigated. In particular, for counter propagating waves on the high field side, asymmetrically distributed energetic passing ions destabilise the ideal internal kink mode when the q=1 surface resides within a narrow region centred about the shifted fundamental cyclotron resonance.

  • 263. Graves, J. P.
    et al.
    Chapman, I. T.
    Coda, S.
    Johnson, Thomas J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Lennholm, M.
    A new sawtooth control mechanism relying on toroidally propagating ion cyclotron resonance frequency waves: Theory and Joint European Torus tokamak experimental evidence2010Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 17, nr 5, s. 056118-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The sawtooth control mechanism in plasmas employing toroidally propagating ion cyclotron resonance waves is extended. The asymmetrically distributed energetic passing ions are shown to modify the ideal internal kink mode when the position of the minority ion cyclotron resonance resides within a narrow region close to the q=1 surface. An analytical treatment of the internal kink mode in the presence of model distribution function with parallel velocity asymmetry is developed. The fast ion mechanism explains the strong sensitivity of sawteeth to resonance position, and moreover is consistent with dedicated Joint European Torus [F. Romanelli, Nucl. Fusion 49, 104006 (2009)] experiments which controlled sawteeth despite negligible current drive. [doi:10.1063/1.3363201]

  • 264. Graves, J. P.
    et al.
    Chapman, I. T.
    Coda, S.
    Johnson, Thomas J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Lennholm, M.
    Paley, J. I.
    Sauter, O.
    RECENT ADVANCES IN SAWTOOTH CONTROL2011Ingår i: Fusion science and technology, ISSN 1536-1055, E-ISSN 1943-7641, Vol. 59, nr 3, s. 539-548Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Important advances have been made recently in the invention and application of experimental methods to control the sawtooth instability in tokamak plasmas. The primary means of control involves the application of either ion cyclotron resonance heating (ICRH), or electron cyclotron heating, with resonance very close to the q = 1 radius in the plasma core. Reported here are experiments that have successfully applied these methods to either shorten or lengthen the sawteeth deliberately, in a variety of plasma conditions, in three tokamaks: Joint European Torus (JET), TCV, and Tore Supra. It is shown that despite the sensitivity of the sawtooth period to the resonance position, sawteeth can be controlled using either real-time control of the electron cyclotron deposition, or in the case of ion cyclotron heating, very careful adjustment of the magnetic field strength and minority ion concentration. The latter technique has been guided by theoretical advances that have enabled the control of sawteeth in JET with ITER-relevant ICRH scenarios.

  • 265. Graves, J. P.
    et al.
    Chapman, I. T.
    Coda, S.
    Johnson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Lennholm, M.
    Alper, B.
    de Baar, M.
    Crombe, K.
    Eriksson, L. -G
    Felton, R.
    Howell, D.
    Kiptily, V.
    Koslowski, H. R.
    Mayoral, M. -L
    Monakhov, I.
    Nunes, I.
    Pinches, S. D.
    Experimental verification of sawtooth control by energetic particles in ion cyclotron resonance heated JET tokamak plasmas2010Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 50, nr 5, s. 052002-Artikel i tidskrift (Övrigt vetenskapligt)
    Abstract [en]

    Experimental evidence from the JET tokamak is presented supporting the predictions of a recent theory (Graves et al 2009 Phys. Rev. Lett. 102 065005) on sawtooth instability control by toroidally propagating ion cyclotron resonance waves. Novel experimental conditions minimized a possible alternate effect of magnetic shear modification by ion cyclotron current drive, and enabled the dependence of the new energetic ion mechanism to be tested over key variables. The results have favourable implications on sawtooth control by ion cyclotron resonance waves in a fusion reactor.

  • 266. Graves, J. P.
    et al.
    Chapman, I. T.
    Coda, S.
    Johnson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Lennholm, M.
    Alper, B.
    de Baar, M.
    Crombe, K.
    Eriksson, L.-G.
    Felton, R.
    Howell, D.
    Kiptily, V.
    Koslowski, H. R.
    Mayoral, M.-L.
    Monakov, I.
    Nunes, I.
    Pinches, S. D.
    Sawtooth Control Relying on Toroidally Propagating ICRF Waves2010Konferensbidrag (Övrigt vetenskapligt)
  • 267. Graves, J. P.
    et al.
    Cooper, W. A.
    Coda, S.
    Eriksson, L. -G
    Johnson, Thomas J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Modelling ICCD experiments for sawtooth control in JET2006Ingår i: Theory of Fusion Plasmas , 2006, Vol. 871, s. 350-355Konferensbidrag (Refereegranskat)
  • 268. Graves, J. P.
    et al.
    Lennholm, M.
    Chapman, I. T.
    Lerche, E.
    Reich, M.
    Alper, B.
    Bobkov, V.
    Dumont, R.
    Faustin, J. M.
    Jacquet, P.
    Jaulmes, F.
    Johnson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Keeling, D. L.
    Liu, Y.
    Nicolas, T.
    Tholerus, Simon
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Blackman, T.
    Carvalho, I. S.
    Coelho, R.
    Van Eester, D.
    Felton, R.
    Goniche, M.
    Kiptily, V.
    Monakhov, I.
    Nave, M. F. F.
    Von Thun, C. P.
    Sabot, R.
    Sozzi, C.
    Tsalas, M.
    Sawtooth control in JET with ITER relevant low field side resonance ICRH and ITER like wall2014Ingår i: 41st EPS Conference on Plasma Physics, EPS 2014, European Physical Society (EPS) , 2014Konferensbidrag (Refereegranskat)
    Abstract [en]

    New experiments at JET with the ITER like wall show for the first time that ITER-relevant low field side resonance first harmonic ICRH with can be used to control sawteeth that have been initially lengthened by fast particles. In contrast to previous [J. P. Graves et al, Nature Communs 3, 624 (2012)] high field side resonance sawtooth control experiments undertaken at JET, it is found that the sawteeth of L-mode plasmas can be controlled with less accurate alignment between the resonance layer and the sawtooth inversion radius. This advantage, as well as the discovery that sawteeth can be shortened with various antenna phasings, including dipole, indicates that ICRH is a particularly effective and versatile tool that can be used in future fusion machines for controlling sawteeth. Without sawtooth control, NTMs and locked modes were triggered at very low normalised beta. High power H-mode experiments show the extent to which ICRH can be tuned to control sawteeth and NTMs while simultaneously providing effective electron heating with improved flushing of high Z core impurities. Dedicated ICRH simulations using SELFO, SCENIC and EVE, including wide drift orbit effects, explain why sawtooth control is effective with various antenna phasings, and show that the sawtooth control mechanism cannot be explained by enhancement of the magnetic shear. Hybrid kinetic-MHD stability calculations using MISHKA and HAGIS unravel the optimal sawtooth control regimes in these ITER relevant plasma conditions.

  • 269. Graves, J. P.
    et al.
    Lennholm, M.
    Chapman, I. T.
    Lerche, E.
    Reich, M.
    Alper, B.
    Bobkov, V.
    Dumont, R.
    Faustin, J. M.
    Jacquet, P.
    Jaulmes, F.
    Johnson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Keeling, D. L.
    Liu, Yueqiang
    Nicolas, T.
    Tholerus, Simon
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Blackman, T.
    Carvalho, I. S.
    Coelho, R.
    Van Eester, D.
    Felton, R.
    Goniche, M.
    Kiptily, V.
    Monakhov, I.
    Nave, M. F. F.
    von Thun, C. Perez
    Sabot, R.
    Sozzi, C.
    Tsalas, M.
    Sawtooth control in JET with ITER relevant low field side resonance ion cyclotron resonance heating and ITER-like wall2015Ingår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 57, nr 1, s. 014033-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    New experiments at JET with the ITER-like wall show for the first time that ITER-relevant low field side resonance first harmonic ion cyclotron resonance heating (ICRH) can be used to control sawteeth that have been initially lengthened by fast particles. In contrast to previous (Graves et al 2012 Nat. Commun. 3 624) high field side resonance sawtooth control experiments undertaken at JET, it is found that the sawteeth of L-mode plasmas can be controlled with less accurate alignment between the resonance layer and the sawtooth inversion radius. This advantage, as well as the discovery that sawteeth can be shortened with various antenna phasings, including dipole, indicates that ICRH is a particularly effective and versatile tool that can be used in future fusion machines for controlling sawteeth. Without sawtooth control, neoclassical tearing modes (NTMs) and locked modes were triggered at very low normalised beta. High power H-mode experiments show the extent to which ICRH can be tuned to control sawteeth and NTMs while simultaneously providing effective electron heating with improved flushing of high Z core impurities. Dedicated ICRH simulations using SELFO, SCENIC and EVE, including wide drift orbit effects, explain why sawtooth control is effective with various antenna phasings and show that the sawtooth control mechanism cannot be explained by enhancement of the magnetic shear. Hybrid kinetic-magnetohydrodynamic stability calculations using MISHKA and HAGIS unravel the optimal sawtooth control regimes in these ITER relevant plasma conditions.

  • 270. Gregoratto, D.
    et al.
    Drake, James R.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Yadikin, D.
    Liu, Y. Q.
    Paccagnella, R.
    Brunsell, Per R.
    Bolzonella, T.
    Marchiori, G.
    Cecconello, Marco
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Studies on the response of resistive-wall modes to applied magnetic perturbations in the EXTRAP T2R reversed field pinch2005Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 12, nr 9Artikel i tidskrift (Refereegranskat)
  • 271.
    Grigore, E.
    et al.
    Euratom MEdC Assoc, Natl Inst Laser Plasma & Radiat Phys, Bucharest, Romania..
    Gherendi, M.
    Euratom MEdC Assoc, Natl Inst Laser Plasma & Radiat Phys, Bucharest, Romania..
    Baiasu, F.
    Euratom MEdC Assoc, Natl Inst Laser Plasma & Radiat Phys, Bucharest, Romania..
    Firdaouss, M.
    IRFM CEA Cadarache, F-13108 St Paul Les Durance, France..
    Hernandez, C.
    IRFM CEA Cadarache, F-13108 St Paul Les Durance, France..
    Weckmann, Armin
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik. KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Hakola, A.
    VTT Tech Res Ctr Finland Ltd, POB 1000, FI-02044 Espoo, Finland..
    The influence of N on the D retention within W coatings for fusion applications2019Ingår i: Fusion engineering and design, ISSN 0920-3796, E-ISSN 1873-7196, Vol. 146, s. 1959-1962Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Plasma facing components (PFC) in a fusion device are subjected to a harsh operating environment involving high heat fluxes and exposure to high fluxes of hydrogen isotopes. This exposure can lead to high fuel retention that can raise serious concern from the safety point of view. One of the reasons for the use of W as a material for the construction of the first wall is to reduce fuel retention compared to carbon wall. Nitrogen seeding, used during the operation of fusion reactors, represents a method to cool the divertor plasma and to reduce the W source in the divertor due to ELMS. However an exposure of the PFC to a combination of hydrogen isotopes and nitrogen can lead to changes in properties of exposed surfaces or to unexpected material behavior. In this work, the influence of nitrogen on the deuterium content within tungsten coatings produced by reactive high power impulse magnetron sputtering (HIPIMS) was investigated. The deposition process of W coatings in a nitrogen deuterium environment leads to a significant retention of deuterium. Coatings with a deuterium content up to 54 at% were obtained in the presence of nitrogen compared with a deuterium content of 25 at% measured for the coatings produced in absence of nitrogen from the deposition atmosphere.

  • 272. Grisolia, C.
    et al.
    Counsell, G.
    Dinescu, G.
    Semerok, A.
    Bekris, N.
    Coad, P.
    Hopf, C.
    Roth, J.
    Rubel, Marek J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Widdowson, A.
    Tsitrone, E.
    Treatment of ITER plasma facing components: Current status and remaining open issues before ITER implementation2007Ingår i: Fusion engineering and design, ISSN 0920-3796, E-ISSN 1873-7196, Vol. 82, nr 15-24, s. 2390-2398Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The in-vessel tritium inventory control is one of the most ITER challenging issues which has to be resolved to fulfil safety requirements. This is due mainly to the presence of carbon as a constituent of plasma facing components (PFCs) which leads to a high fuel permanent retention. For several years now, physics studies and technological developments have been undertaken worldwide in order to develop reliable techniques which could be used in ITER severe environment (magnetic field, vacuum, high temperature) for in situ tritium recovery. The scope of this contribution is to review the present status of these achievements and define the remaining work to be done in order to propose a dedicated work program. Different treatment techniques (chemical treatments, photonic cleaning) will be reviewed. In the frame of ITER, they will be compared in terms of fuel removal rate as well as surface accessibility, type of production (gas or particulates), ability to clean mixed material. And lastly, consequences of bulk trapping observed in tokamak on the techniques currently under development will be addressed.

  • 273. Grisolia, C.
    et al.
    Rosanvallon, S.
    Coad, P.
    Bekris, N.
    Braet, J.
    Brennan, D.
    Brichard, B.
    Counsell, G.
    Day, C.
    Likonen, J.
    Piazza, G.
    Poletiko, C.
    Rubel, Marek J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Semerok, A.
    JET contributions to ITER technology issues2006Ingår i: Fusion engineering and design, ISSN 0920-3796, E-ISSN 1873-7196, Vol. 81, nr 07-jan, s. 149-154Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Joint European Torus (JET) fusion machine is the only device capable of operation with tritium and of handling Be and therefore is best suited to the study of tritium and fusion-related issues. A large variety of activities are performed within the JET fusion technology task force (FT-TF). In this paper, some topics such as erosion/deposition and material transport, characterisation of flakes and detritiation techniques are highlighted. Recent examples of results obtained on waste management studies are also given. Data on some ITER-relevant components that have been tested at JET, such as a pumping cryopanel and hardened optics fibers, are presented. In all fields, the work to be addressed in future JET work programmes is discussed.

  • 274. Haines, M. G.
    et al.
    Dangor, A. E.
    Coppins, M.
    Choi, P.
    Mitchell, I. H.
    Chittenden, J. P.
    Bayley, J. M.
    Aliaga-Rossel, R. F.
    Arber, T. D.
    Beg, F.
    Bell, A. R.
    Scheffel, Jan
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Decker, G.
    Russell, P.
    Worley, J. F.
    Fiber Z-pinch Experiments and Calculations in the Finite Larmor Radius Regime1996Ingår i: Laser and particle beams (Print), ISSN 0263-0346, E-ISSN 1469-803X, Vol. 14, s. 261-271Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The dense Z-pinch project at Imperial College is aimed at achieving radiative collapse to high density in a hydrogen plasma, and also to study plasmas close to controlled fusion conditions. To this end, the MAGPIE generator (2.4 MV, 1.25, and 200 ns) has been built and tested, and is now giving preliminary experimental data at 60% of full voltage for carbon and CD2 fibers. These discharges are characterized by an initial radial expansion followed by the occurrence of m = 0 structures with transient X-ray emission from bright spots. Late in the discharge a disruption can occur, accompanied by hard X-ray emission from the anode due to an energetic electron beam and, in the case of CD2 fibers, a neutron burst. Concomitant theoretical studies have solved the linear stability problem for a Z-pinch with large ion Larmor radii, showing that a reduction in growth rate of m = 0 and m = 1 modes to about 20% of the magnetohydrodynamic (MHD) value can occur for a parabolic density profile when the Larmor radius is optimally 20% of the pinch radius. Two dimensional MHD simulations of Z-pinches in two extremes of focussed short-pulse laserplasma interactions and of galactic jets reveal a nonlinear stabilizing effect in the presence of sheared flow. One-dimensional simulations show that at low line density the lower hybrid drift instability can lead to coronal radial expansion of a Z-pinch plasma.

  • 275. Hakola, A.
    et al.
    Airila, M. I.
    Björkas, C.
    Borodin, D.
    Brezinsek, S.
    Coad, J. P.
    Groth, M.
    Järvinen, A.
    Kirschner, A.
    Koivuranta, S.
    Krieger, K.
    Kurki-Suonio, T.
    Likonen, J.
    Lindholm, V.
    Makkonen, T.
    Mayer, M.
    Miettunen, J.
    Mueller, H. W.
    Neu, R.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Rohde, V.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Widdowson, A.
    Global migration of impurities in tokamaks2013Ingår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 55, nr 12Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The migration of impurities in tokamaks has been studied with the help of tracer-injection (C-13 and N-15) experiments in JET and ASDEX Upgrade since 2001. We have identified a common pattern for the migrating particles: scrape-off layer flows drive impurities from the low-field side towards the high-field side of the vessel. Migration is also sensitive to the density and magnetic configuration of the plasma, and strong local variations in the resulting deposition patterns require 3D treatment of the migration process. Moreover, re-erosion of the deposited particles has to be taken into account to properly describe the migration process during steady-state operation of the tokamak.

  • 276. Hakola, A.
    et al.
    Brezinsek, S.
    Douai, D.
    Balden, M.
    Bobkov, V.
    Carralero, D.
    Greuner, H.
    Elgeti, S.
    Kallenbach, A.
    Krieger, K.
    Meisl, G.
    Oberkofler, M.
    Rohde, V.
    Schneider, P.
    Schwarz-Selinger, T.
    Lahtinen, A.
    De Temmerman, G.
    Caniello, R.
    Ghezzi, F.
    Wauters, T.
    Garcia Carrasco, Alvaro
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Radovic, I. Bogdanovic
    Siketic, Z.
    Plasma-wall interaction studies in the full-W ASDEX upgrade during helium plasma discharges2017Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 57, nr 6, artikel-id 066015Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Plasma-wall interactions have been studied in the full-W ASDEX Upgrade during its dedicated helium campaign. Relatively clean plasmas with a He content of > 80% could be obtained by applying ion cyclotron wall conditioning (ICWC) discharges upon changeover from D to He. However, co-deposited layers with significant amounts of He and D were measured on W samples exposed to ICWC plasmas at the low-field side (outer) midplane. This is a sign of local migration and accumulation of materials and residual fuel in regions shadowed from direct plasma exposure albeit globally D was removed from the vessel. When exposing W samples to ELMy H-mode helium plasmas in the outer strike-point region, no net erosion was observed but the surfaces had been covered with co-deposited layers mainly consisting of W, B, C, and D and being the thickest on rough and modified surfaces. This is different from the typical erosion-deposition patterns in D plasmas, where usually sharp net-erosion peaks surrounded by prominent net-deposition maxima for W are observed close to the strike point. Moreover, no clear signs of W nanostructure growth or destruction could be seen. The growth of deposited layers may impact the operation of future fusion reactors and is attributed to strong sources in the main chamber that under suitable conditions may switch the balance from net erosion into net deposition, even close to the strike points. In addition, the absence of noticeable chemical erosion in helium plasmas may have affected the thickness of the deposited layers. Retention of He, for its part, remained small and uniform throughout the strike-point region although our results indicate that samples with smooth surfaces can contain an order of magnitude less He than their rough counterparts.

  • 277. Hakola, A.
    et al.
    Koivuranta, S.
    Likonen, J.
    Groth, M.
    Kurki-Suonio, T.
    Lindholm, V.
    Miettunen, J.
    Krieger, K.
    Mayer, M.
    Müller, H. W.
    Neu, R.
    Rohde, V.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Global migration of C-13 impurities in high-density L-mode plasmas in ASDEX Upgrade2013Ingår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 438, nr Suppl., s. S694-S697Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have studied the migration of 13C in ASDEX Upgrade after a global impurity injection experiment in 2011. The main chamber was observed to be the largest deposition region for carbon: almost 35% of the injected atoms end up there. Moreover, gaps between wall tiles account for surface densities which are comparable to those on the plasma-facing surfaces. SOLPS modeling of the experiment produced a set of background plasmas and poloidal flow profiles for simulating the transport of 13C with ASCOT; a match with measured deposition, however, required using an imposed flow profile. ASCOT reproduced the observed localized deposition at the outer midplane but work is needed to explain the measured deposition at the inner side of the torus and at the top of the vessel.

  • 278.
    Hannan, Abdul
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Modelling Ion Cyclotron Resonance Heating and Fast Wave Current Drive in Tokamaks2013Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Fast magnetosonic waves in the ion cyclotron range of frequencies have the potential to heat plasma and drive current in a thermonuclear fusion reactor. A code, SELFO-light, has been developed to study the physics of ion cyclotron resonantheating and current drive in thermonuclear fusion reactors. It uses a global full wave solver LION and a new 1D Fokker-Planck solver for the self-consistent calculations of the wave field and the distribution function of ions.In present day tokamak experiments like DIII-D and JET, fast wave damping by ions at higher harmonic cyclotron frequencies is weak compared to future thermonuclear tokamak reactors like DEMO. The strong damping by deuterium, tritium and thermonuclear alpha-particles and the large Doppler width of fast alpha-particles in DEMO makes it difficult to drive the current when harmonic resonance layers of these ionspecies are located at low field side of the magnetic axis. At higher harmonic frequencies the possibility of fast wave current drive diminishes due to the overlapping of alpha-particle harmonic resonance layers. Narrow frequency bands suitable for the fast wave current drive in DEMO have been identified at lower harmonics of the alpha-particles. For these frequencies the effect of formation of high-energy tails in the distribution function of majority and minority ion species on the current drive have been studied. Some of these frequencies are found to provide efficient ion heating in the start up phase of DEMO. The spectrum where efficient current drive can be obtained is restricted due to weak electron damping at lower toroidal mode numbers and strong trapped electron damping at higher toroidal mode numbers. The width of toroidal mode spectra for which efficient current drive can be obtained have been identified, which has important implications for the antenna design.

  • 279.
    Hannan, Abdul
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hellsten, Torbjörn
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Johnson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    A Fokker-Planck Code for Fast Self-Consistent Calculations of ICRH2010Ingår i: 37th EPS Conference on Plasma Physics, 2010Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Modeling of ion cyclotron resonant heating, ICRH, requires self-consistent modeling of the distribution function of the resonant ion species and the wave field. A method has been devised for fast self-consistent calculation of the distribution function and the wave field for ICRH modeling. The distribution function is obtained by solving a pitch angle averaged 1D time dependent Fokker Planck equation that includes the Coulomb collision and quasi-linear operators. The quasi-linear operators describing the wave-particle interactions are obtained from the LION code [1]. The time dependent 1D Fokker-Planck equation solved with a cubic finite element method will be presented in this report. The modifications of the susceptibility tensors of the resonant ion species due to changes of the distribution functions caused by heating are calculated by the Fokker-Planck solver and then used in the LION code for calculating the modified wave field

  • 280.
    Hannan, Abdul
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hellsten, Torbjörn
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Johnson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Fast wave current drive scenarios for DEMO2013Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 53, nr 4, s. 043005-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Scenarios for non-inductive current drive using the fast magnetosonic wave in the ion cyclotron range of frequencies in DEMO have been studied. The strong ion cyclotron damping and large Doppler broadening of the alpha particles are shown to limit the possible current drive scenarios to four frequency bands. However, these scenarios may be compromised in the presence of impurities with unfavourable charge to mass ratio. For each frequency the current drive efficiency is optimized with respect to the parallel wave number. The optimized current drive efficiencies are comparable to that from neutral beam injection and electron cyclotron heating, and thus the ion cyclotron range of frequencies should remain a candidate for driving the non-inductive current in DEMO.

  • 281.
    Hannan, Abdul
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hellsten, Torbjörn
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Johnson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    On fast wave current drive at higher cyclotron harmonics2011Ingår i: 38th EPS Conference on Plasma Physics 2011, EPS 2011 - Europhysics Conference Abstracts: Volume 35 1, 2011, s. 889-892Konferensbidrag (Övrigt vetenskapligt)
  • 282.
    Hannan, Abdul
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hellsten, Torbjörn
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Johnson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Self-consistent Ion Cyclotron Resonant Heating and Fast Wave Current Drive for DEMOArtikel i tidskrift (Övrigt vetenskapligt)
  • 283. Hawkes, N. C.
    et al.
    Esposito, B.
    Andrew, Y.
    Biewer, T. M.
    Brzozowski, Jerzy H.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Brix, M.
    Cardinali, A.
    Crisanti, F.
    Crombé, K.
    Van Eester, D.
    Felton, R.
    Giroud, C.
    Johnson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Lerche, E.
    Meigs, A.
    Parail, V.
    Sharapov, S.
    Sozzi, C.
    Voitsekhovitch, I.
    Zastrow, K. -D
    Ion transport barrier formation with low injected torque in JET2007Ingår i: 34th EPS Conference on Plasma Physics 2007, EPS 2007 - Europhysics Conference Abstracts, 2007, nr 1, s. 504-507Konferensbidrag (Refereegranskat)
    Abstract [en]

    Ion temperature ITB trigger events have been provoked on JET with very low levels of injected torque using a 3He minority ion heating scheme. The evidence indicates that E x B shear driven by toroidal rotation is not important in these ITB triggers, however the ITBs which form are weak and short lived. Evidence from other experiments [4], suggests that higher torque is necessary to establish and maintain strong ITBs. Future experiments with the increased RF power of the new JET ICRH antenna will be made to explore whether 'strong' ITBs can be created at high power and low applied torque.

  • 284. Heinola, K.
    et al.
    Widdowson, A.
    Likonen, J.
    Alves, E.
    Baron-Wiechec, A.
    Barradas, N.
    Brezinsek, S.
    Catarino, N.
    Coad, P.
    Koivuranta, S.
    Krat, S.
    Matthews, G. F.
    Mayer, M.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. EUROfusion Consortium, Culham Science Centre, JET, Abingdon, United Kingdom.
    Contributors, J.
    Long-term fuel retention in JET ITER-like wall2016Ingår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T167, artikel-id 014075Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Post-mortem studies with ion beam analysis, thermal desorption, and secondary ion mass spectrometry have been applied for investigating the long-term fuel retention in the JET ITERlike wall components. The retention takes place via implantation and co-deposition, and the highest retention values were found to correlate with the thickness of the deposited impurity layers. From the total amount of retained D fuel over half was detected in the divertor region. The majority of the retained D is on the top surface of the inner divertor, whereas the least retention was measured in the main chamber on the mid-plane of the inner wall limiter. The recessed areas of the inner wall showed significant contribution to the main chamber total retention. Thermal desorption spectroscopy analysis revealed the energetic T from DD reactions being implanted in the divertor. The total T inventory was assessed to be >0.3 mg.

  • 285. Heinola, K.
    et al.
    Widdowson, A.
    Likonen, J.
    Alves, E.
    Baron-Wiechec, A.
    Barradas, N.
    Brezinsek, S.
    Catarino, N.
    Coad, P.
    Koivuranta, S.
    Matthews, G. F.
    Mayer, M.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Fuel retention in JET ITER-Like Wall from post-mortem analysis2015Ingår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 463, s. 961-965Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Selected Ion Beam Analysis techniques applicable for detecting deuterium and heavier impurities have been used in the post-mortem analyses of tiles removed after the first JET ITER-Like Wall (JET-ILW) campaign. Over half of the retained fuel was measured in the divertor region. The highest figures for fuel retention were obtained from regions with the thickest deposited layers, i.e. in the inner divertor on top of tile 1 and on the High Field Gap Closure tile, which resides deep in the plasma scrape-off layer. Least retention was found in the main chamber high erosion regions, i.e. in the mid-plane of Inner Wall Guard Limiter. The fuel retention values found typically varied with deposition layer thicknesses. The reported retention values support the observed decrease in fuel retention obtained with gas balance experiments of JET-ILW.

  • 286. Hellesen, C.
    et al.
    Johnson, M. G.
    Sunden, E. A.
    Conroy, S.
    Ericsson, G.
    Ronchi, E.
    Sjostrand, H.
    Weiszflog, M.
    Gorini, G.
    Tardocchi, M.
    Johnson, Thomas J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Kiptily, V. G.
    Pinches, S. D.
    Sharapov, S. E.
    Johnson, M. Gatu
    Anderson-Sunden, E.
    Neutron emission generated by fast deuterons accelerated with ion cyclotron heating at JET2010Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 50, nr 2Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    For the first time, the neutron emission from JET plasmas heated with combined deuterium neutral beam injection and third harmonic ion cyclotron radio frequency heating have been studied with neutron emission spectroscopy (NES). Very high DD neutron rates were observed with only modest external heating powers, which was attributed to acceleration of deuterium beam ions to energies of about 2-3 MeV, where the DD reactivity is on a par of that of the DT reaction. Fast deuterium energy distributions were derived from analysis of NES data and confirm acceleration of deuterium beam ions up to energies around 3 MeV, in agreement with theoretical predictions. The high neutron rates allowed for observations of changes in the fast deuterium populations on a time scale of 50 ms. Correlations were seen between fast deuterium ions at different energies and magnetohydrodynamic activities, such as monster sawtooth crashes and toroidal Alfven eigenmodes.

  • 287. Hellesen, C.
    et al.
    Johnson, M. Gatu
    Sunden, E. Andersson
    Conroy, S.
    Ericsson, G.
    Eriksson, J.
    Gorini, G.
    Johnson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Kiptily, V. G.
    Pinches, S. D.
    Sharapov, S. E.
    Sjostrand, H.
    Nocente, M.
    Tardocchi, M.
    Weiszflog, M.
    Measurements of fast ions and their interactions with MHD activity using neutron emission spectroscopy2010Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 50, nr 8, s. 084006-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Ion cyclotron radio frequency (ICRF) heating can produce fast ion populations with energies reaching up to several megaelectronvolts. Here, we present unique measurements of fast ion distributions from an experiment with 3rd harmonic ICRF heating on deuterium beams using neutron emission spectroscopy (NES). From the experiment, very high DD neutron rates were observed, using only modest external heating powers. This was attributed to acceleration of deuterium beam ions to energies up to about 2-3 MeV, where the DD reactivity is on a par with that of the DT reaction. The high neutron rates allowed for observations of changes in the fast deuterium energy distribution on a time scale of 50 ms. Clear correlations were seen between fast deuterium ions in different energy ranges and magnetohydrodynamic activities, such as monster sawteeth and toroidal Alfven eigen modes (TAE). Specifically, NES data showed that the number of deuterons in the region between 1 and 1.5 MeV were decaying significantly during strong TAE activity, while ions with lower energies around 500 keV were not affected. This was attributed to resonances with the TAE modes.

  • 288. Hellesen, C.
    et al.
    Johnson, M. Gatu
    Sundén, E. Andersson
    Conroy, S.
    Ericsson, G.
    Eriksson, J.
    Sjöstrand, H.
    Weiszflog, M.
    Johnson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Gorini, G.
    Nocente, M.
    Tardocchi, M.
    Kiptily, V. G.
    Pinches, S. D.
    Sharapov, S. E.
    Fast-ion distributions from third harmonic ICRF heating studied with neutron emission spectroscopy2013Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 53, nr 11, s. 113009-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The fast-ion distribution from third harmonic ion cyclotron resonance frequency (ICRF) heating on the Joint European Torus is studied using neutron emission spectroscopy with the time-of-flight spectrometer TOFOR. The energy dependence of the fast deuteron distribution function is inferred from the measured spectrum of neutrons born in DD fusion reactions, and the inferred distribution is compared with theoretical models for ICRF heating. Good agreements between modelling and measurements are seen with clear features in the fast-ion distribution function, that are due to the finite Larmor radius of the resonating ions, replicated. Strong synergetic effects between ICRF and neutral beam injection heating were also seen. The total energy content of the fast-ion population derived from TOFOR data was in good agreement with magnetic measurements for values below 350 kJ.

  • 289.
    Hellsten, Torbjörn
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    A statistical model of the wave field in a bounded domain2017Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 24, nr 2, artikel-id 022122Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Numerical simulations of plasma heating with radiofrequency waves often require repetitive calculations of wave fields as the plasma evolves. To enable effective simulations, bench marked formulas of the power deposition have been developed. Here, a statistical model applicable to waves with short wavelengths is presented, which gives the expected amplitude of the wave field as a superposition of four wave fields with weight coefficients depending on the single pass damping, as. The weight coefficient for the wave field coherent with that calculated in the absence of reflection agrees with the coefficient for strong single pass damping of an earlier developed heuristic model, for which the weight coefficients were obtained empirically using a full wave code to calculate the wave field and power deposition. Antennas launching electromagnetic waves into bounded domains are often designed to produce localised wave fields and power depositions in the limit of strong single pass damping. The reflection of the waves changes the coupling that partly destroys the localisation of the wave field, which explains the apparent paradox arising from the earlier developed heuristic formula that only a fraction a(s)(2)(2-a(s)) and not as of the power is absorbed with a profile corresponding to the power deposition for the first pass of the rays. A method to account for the change in the coupling spectrum caused by reflection for modelling the wave field with ray tracing in bounded media is proposed, which should be applicable to wave propagation in non-uniform media in more general geometries.

  • 290.
    Hellsten, Torbjörn
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Integrated Modelling of Heating, Current Drive and Fast Particle Physics2007Ingår i: IAEA Technical Meeting on Fast Particles, 2007Konferensbidrag (Övrigt vetenskapligt)
  • 291.
    Hellsten, Torbjörn
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Momentum transport by wave-particle interaction2011Ingår i: PLASMA PHYS CONTROL FUSION, 2011, Vol. 53, nr 5, s. 054007-Konferensbidrag (Refereegranskat)
    Abstract [en]

    Energy and momentum can be transported across the plasma by waves emitted at one place and absorbed at another. Exchange of momentum and energy between the particles and the waves change the drift orbits, which may give rise to a non-ambipolar particle transport. The main effect of the non-ambipolar transport and quasi-neutrality is a toroidal precession of the trapped particles, which together with the changes in the parallel velocities of the passing resonant particles conserve the toroidal momentum. Non-resonant interactions can give rise to a net change of the local wave number in spatial inhomogeneous plasmas with a resulting force on the medium. Both resonant and non-resonant interactions have to be taken into account in order to have a consistent description of the momentum transported by the waves. The momentum transfer is, in particular, important for waves with short wave length and low frequency, and may explain the enhanced rotation seen in some mode conversion experiments, when the fast magnetosonic wave is converted to an ion-cyclotron wave. The apparent contradiction that the wave momentum may change due to non-resonant wave-particle interactions without changing the energy in geometric optics is explained.

  • 292.
    Hellsten, Torbjörn
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    On self-consistent modelling of energetic particles generated by auxiliary heating and associated instabilities2006Konferensbidrag (Övrigt vetenskapligt)
  • 293.
    Hellsten, Torbjörn
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Rotation Driven by Rectified RF-sheath Potentials and Spatial Dispersion2009Ingår i: RADIO FREQUENCY POWER IN PLASMAS, 2009, Vol. 1187, s. 625-628Konferensbidrag (Refereegranskat)
    Abstract [en]

    Plasma rotation is of interest for improving confinement and stabilising plasma. Effects from fast particles with broad orbits can only partly explain the changes in the rotation profiles during ICRH. The effect on wave-particle interaction of a finite poloidal mode number is discussed and two new RF-mechanisms are proposed: Co-current torque caused by sputtering by rectified RF-sheath potentials and transport of momentum due to spatial dispersion. The latter effect affects the RF-current drive, in particular, in conjunction with mode conversion.

  • 294.
    Hellsten, Torbjörn A. K.
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Holmström, Kerstin
    KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Johnson, Thomas J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Bergkvist, Tommy
    KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Laxåback, Martin
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    On ion cyclotron emission in toroidal plasmas2006Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 46, nr 7, s. S442-S454Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A detailed study of ion cyclotron interactions in a toroidal plasma has been carried out in order to elucidate the role of toroidal effects on ion cyclotron emission. It is well known that non-relaxed distribution functions can give rise to excitation of magnetosonic waves by ion cyclotron interactions when the distribution function increases with respect to the perpendicular velocity. We have extended and clarified the conditions under which even collisionally relaxed distribution function can destabilize magnetosonic eigenmodes. In a toroidal plasma, cyclotron interactions at the plasma boundary with ions having barely co-current passing orbits and marginally trapped orbits can cause destabilisation by the strong inversion of the distribution function along the characteristics of cyclotron interaction by neo-classical effects. The unstable interactions can further be enhanced by tangential interactions, which can also prevent the interactions from reaching the stable part of the characteristics, where they interact with trapped orbits. Conditions on the localization of the magnetosonic eigenmodes for unstable excitation are analysed by studying the anti-Hermitian part of the susceptibility tensor of thermonuclear alpha-particles. The pattern of positive and negative regions of the anti-Hermitian part of the susceptibility tensor of thermonuclear alpha-particles is, in general, consistent with the excitation of edge localized magnetosonic eigenmodes, even though the eigenmodes are usually not localized in the major radius and for distribution functions that have relaxed to steady state.

  • 295.
    Hellsten, Torbjörn
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Bergkvist, Tommy
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Johnson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Laxåback, Martin
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Effects of Finite Orbit Width and RF-Induced Spatial Diffusion on Ion Cyclotron Emission2005Ingår i: Radio Frequency Power in Plasmas: 16th Topical Conference on Radio Frequency Power in Plasmas / [ed] S. J. Wukitch and P. T. Bonoli, Melville, New York: AIP Conference Proceedings , 2005, s. 50-53Konferensbidrag (Refereegranskat)
    Abstract [en]

    The theory of ion cyclotron emission, ICE, in tokamak plasmas has been revised by including the effects of finite orbit width and RF-induced spatial transport in the wave-particle interactions. Two mechanisms for excitation of edge localised magnetosonic modes are discussed. An inverted distribution function of suprathermal ions near the plasma edge is driving the modes. Counter current propagating waves can be excited by interacting with barely co passing ions. Co current propagating waves interacting at the inner leg only can drive the modes unstable by throwing the fast ions out of the plasma.

  • 296.
    Hellsten, Torbjörn
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Bergkvist, Tommy
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Johnson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Laxåback, Martin
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Integrated Modelling of ICRH and AE Dynamics2005Ingår i: IEA Burning Plasma Workshop, 2005Konferensbidrag (Övrigt vetenskapligt)
  • 297.
    Hellsten, Torbjörn
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hannan, Abdul
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Johnson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Eriksson, L. -G
    Höök, Josef
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Villard, L.
    On Self-Consistent ICRH ModellingArtikel i tidskrift (Övrigt vetenskapligt)
  • 298.
    Hellsten, Torbjörn
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hannan, Abdul
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Johnson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Eriksson, L. -G
    Höök, Josef
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Villard, L.
    Self-consistent ICRH modelling2012Ingår i: 39th EPS Conference on Plasma Physics 2012, EPS 2012 and the 16th International Congress on Plasma Physics: Volume 2, 2012, 2012, s. 1106-1109Konferensbidrag (Refereegranskat)
  • 299.
    Hellsten, Torbjörn
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hannan, Abdul
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Johnson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Eriksson, L. -G
    Höök, Josef
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Villard, L.
    Self-Consistent ICRH Modelling2011Ingår i: RADIO FREQUENCY POWER IN PLASMAS: PROCEEDINGS OF THE 19TH TOPICAL CONFERENCE, 2011, s. 365-368Konferensbidrag (Refereegranskat)
    Abstract [en]

    A new code for self-consistent modelling of ion cyclotron heating suitable for routine calculations has been developed.

  • 300.
    Hellsten, Torbjörn
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hannan, Abdul
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Johnson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Eriksson, L-G
    Höök, Lars Josef
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Villard, L.
    A model for self-consistent simulation of ICRH suitable for integrating modelling2013Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 53, nr 9, s. 093004-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A self-consistent modelling of ion cyclotron resonance heating (ICRH) is reviewed with the aim of obtaining a fast robust scheme suitable for routine simulation for transport codes and data analysis. Due to the complexity of calculating the wave field and the distribution function self-consistently simplifications are necessary. To improve modelling of the wave field, methods are developed to include higher order finite Larmor radius terms, up-and downshifts of the parallel wave number and to improve calculations of damping due to the transit time magnetic pumping in finite element wave codes without decomposing the wave locally into planar waves. A new code, SELFO-light, for self-consistent modelling of ion cyclotron heating suitable for routine calculations is developed. The code is based on coupling the global wave code LION with a simple one-dimensional time-dependent Fokker-Planck code. Both the wave and the Fokker-Planck codes use finite element representations. The importance of self-consistent modelling of ion cyclotron heating is illustrated by studying the effect on the power partition for a fast wave current drive scenario at lower harmonic resonances in a deuterium plasma. It is found that the fraction of the power absorbed on the deuterium and the time to reach the steady state vary strongly depending on the position of the resonances. It is found that the deuterium absorption becomes strongly localized to regions where the resonances are tangential to the magnetic flux surfaces.