Exploring a small sawtooth regime in Joint European Torus plasmas with counterinjected neutral beams

Nave, M. F. F.; Coda, J. W.; Stamp, M.; Giroud, C.; Buttery, R.; Graves, J.; de Vries, P.; Challis, C.; Koslowski, H. R.

doi:10.1063/1.2162528

Journal Article

Exploring a small sawtooth regime in Joint European Torus plasmas with counterinjected neutral beams

Nave, M. F. F. ; Koslowski, H. R.FZJ* ; Coda, J. W. ; Graves, J. ; Buttery, R. ; Challis, C. ; Giroud, C. ; Stamp, M. ; de Vries, P.

2006
American Institute of Physics [S.l.]

Physics of plasmas 13, 014503 (2006) [10.1063/1.2162528]

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Please use a persistent id in citations: http://hdl.handle.net/2128/1846 doi:10.1063/1.2162528

Abstract: During a recent reversed toroidal field (B-T) campaign at the Joint European Torus (JET), experiments were performed to investigate the effect on sawteeth of neutral beam injection (NBI)-driven toroidal plasma rotation counter to the direction of the toroidal plasma current and B-T. A power scan at constant density has permitted analytical continuation, into the reversed B-T domain, of previous experiments with forward field and hence corotation. Earlier JET results were confirmed, indicating that counter-NBI results in sawtooth periods shorter than in the Ohmic regime. This study has demonstrated that, whereas with co-NBI the sawtooth period increases with power, with counter-NBI the sawtooth period initially decreases with power passing through a minimum at 4 MW. Clearly this trend also manifests itself in terms of the toroidal plasma rotation, for which a minimum is observed for counter-rotation frequency similar to 3 kHz. Sawteeth smaller than Ohmic sawteeth are found to be easier to obtain with perpendicular counter-NBI, for which heating penetrates deeper into the core. The sign and magnitude of the toroidal rotation, the penetration of heating to the electrons, and the peaking of the fast-ion pressure profile in the core may all play an important role in modifying the sawtooh period. (c) 2006 American Institute of Physics.

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