FLUCTUATION SUPPRESSION BY BIAS ELECTRODE INDUCED POLOIDAL FLOW AND FEEDBACK IN A TOROIDAL PLASMA

摘要

Results of an experimental study on the suppression of low frequency fluctuations in a currentless toroidal plasma by two methods: (i) bias electrode induced poloidal flow and (ii) phase sensitive feedback are presented. Poloidal plasma rotation at velocity v_θ and, concurrently, a reduction in the fluctuation level are observed with positive electrode biasing. At high v_θ, a new kind of fluctuation appears which is a coherent mode. Strong modification of the spectral characteristics of fluctuation and a change in fluctuation induced transport are found by feedback, using appropriate values of frequency dependent phase shifts. A theoretical model of the modified Simon-Hoh instability seems to explain the experimental characteristics of the observed fluctuations.