SUPPRESSION OF TEARING MODES BY MEANS OF LOCALIZED ELECTRON CYCLOTRON CURRENT DRIVE IN THE DIII-D TOKAMAK

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The onset of tearing modes and the resulting negative effects on plasma performance set significant limits on the operational domain of tokamaks. Modes with toroidal mode number (n) larger than two cause only a minor reduction in energy confinement (<10%). Modes which have a dominant poloidal mode number (m) of three and n=2 lead to a significant reduction in confinement (<30%) at fixed power. The plasma pressure {beta} (normalized to the magnetic field pressure) can be raised further, albeit with very small incremental confinement. Pushing to higher {beta} often destabilizes the m=2/n=1 tearing mode which can lock to the wall ... continued below

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LUCE, T.C.; LaHAYE, R.J.; D.A.HUMPHREYS; PETTY, C.C.; PRATER, R.; AUSTIN, M.E. et al. July 1, 2002.

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The onset of tearing modes and the resulting negative effects on plasma performance set significant limits on the operational domain of tokamaks. Modes with toroidal mode number (n) larger than two cause only a minor reduction in energy confinement (<10%). Modes which have a dominant poloidal mode number (m) of three and n=2 lead to a significant reduction in confinement (<30%) at fixed power. The plasma pressure {beta} (normalized to the magnetic field pressure) can be raised further, albeit with very small incremental confinement. Pushing to higher {beta} often destabilizes the m=2/n=1 tearing mode which can lock to the wall and lead to a complete and rapid disruption of the plasma with potentially serious consequences for the tokamak. The {beta} values at which these modes usually appear in conventional tokamak discharges are well below the limits calculated using ideal MHD theory. Therefore, the tearing modes can set effective upper limits on energy confinement and pressure. Significant progress has been made in stabilizing these modes by local current generation using electron cyclotron waves. The tearing mode is essentially a deficit in current flowing helically, resonant with the spatial structure of the local magnetic field. This forms an ''island'' where the magnetic flux is no longer monotonic. It was predicted theoretically [1,2] that replacement of this ''missing'' current would return the plasma to the state prior to the instability. Experiments on the ASDEX-Upgrade [3], JT-60U [4], and DIII-D [5] tokamaks have demonstrated stabilization of m=3/n=2 modes using electron cyclotron current drive (ECCD) to replace the current in the island. Following these initial experiments, recent work on the DIII-D tokamak has demonstrated two significant advances in application of this technique--extending the operational domain stable to m=3/n=2 modes to higher {beta} and the first suppression of the more dangerous m=2/n=1 mode.

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Oakland Operations Office, Oakland, CA (US); INIS

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  • 29th European Physical Society Conference on Plasma Physics and Controlled Fusion, Montreux (CH), 06/17/2002--06/21/2002; Other Information: THIS IS A PREPRINT OF A PAPER PRESENTED AT THE 29TH EUROPEAN PHYSICAL SOCIETY CONFERENCE ON PLASMA PHYSICS AND CONTROLLED FUSION, JUNE 17-21,2002, IN MONTREUX, SWITZERLAND, AND TO BE PUBLISHED IN THE ''PROCEEDINGS''

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  • Report No.: NONE
  • Grant Number: AC03-99ER54463
  • Office of Scientific & Technical Information Report Number: 804707
  • Archival Resource Key: ark:/67531/metadc738951

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  • July 1, 2002

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  • Oct. 18, 2015, 6:40 p.m.

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  • Jan. 3, 2017, 1:35 p.m.

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LUCE, T.C.; LaHAYE, R.J.; D.A.HUMPHREYS; PETTY, C.C.; PRATER, R.; AUSTIN, M.E. et al. SUPPRESSION OF TEARING MODES BY MEANS OF LOCALIZED ELECTRON CYCLOTRON CURRENT DRIVE IN THE DIII-D TOKAMAK, article, July 1, 2002; United States. (digital.library.unt.edu/ark:/67531/metadc738951/: accessed October 19, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.