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P: Plasmaphysik

P 13: Magnetic Confinement

P 13.2: Vortrag

Donnerstag, 20. März 2003, 11:50–12:10, FO1

Origin of fluctuations for helicity injection current drive in spheromaks and spherical tokamaks — •Philippa Browning¹, Dylan Brennan², and Ronald Van der Linden³ — ¹Dept of Physics, UMIST, PO box 88, Manchester M60 1QD, U.K. — ²Fusion Group, General Atomics, PO Box 85608,San Diego, CA 92186-5608, USA — ³Royal Observatory of Belgium, Ringlaan 3, B-1180 Brussel, Belgium

Helicity injection current drive is widely used in spherical tokamaks and spheromaks. This requires a relaxation mechanism to re-distribute current directly driven by external electrodes to the closed flux; fluctuations, usually with dominant toroidal mode number n = 1, play a key role. We model the onset of the instabilities whose saturation leads to these fluctuations, and hence the conditions under which current drive can operate, using a new linear ideal MHD stability code (SCOTS) which accounts for open flux, linking the helicity injection electrodes, as well as closed flux. Force-free equilibrium magnetic fields are considered with a high current on the open driven flux and a lower current on the closed flux. We investigate the stability of spheromak and spherical tokamaks and hence determine the operating space (in terms of the current profile) in which helicity injection is effective.