PRELIMINARY OSCILLATING FLUXES CURRENT DRIVE EXPERIMENT IN DIII-D TOKAMAK

A preliminary oscillating flux helicity injection experiment was done on DIII-D tokamak. The toroidal flux was modulated by programming the plasma elongation. Instead of programming the surface voltage directly , the plasma current was programmed with a periodic modulation at some phase shift. The theoretical basis of this modulation is discussed in terms of the helicity injection and also introduced by cross-field mo tion of the modulated plasma. Because the primary winding is well coup led with the plasma current and the power supply is strong, the plasma current behaves as programmed. However, as the plasma shape is not co upled strongly with the shaping and equilibrium coils, the elongation amplitude and phase are affected by the change of plasma current and d o not behave as programmed. Because of this, the voltage induced by th e helicity injection is low, and the experiment did not test the princ iple of helicity injection. The injection powers of helicity and energ y, and the electric field intensity of the helicity injection model an d the cross-field motion of plasma are compared with each other experi mentally. The improvement necessary to do the experiment is also propo sed.