Magnetohydrodynamic Activity During Limiter Biasing on the CT-6B Tokamak

Abstract

Magnetohydrodynamic phenomena in the CT-6B tokamak based on Mirnovoscillations have been investigated by applying the limiter biasingpotentials and changing the vacuum chamber gas pressure and plasmadisplacement. The results show that setting up a radial electric fieldat the plasma edge could drive electromagnetic instabilities in thetokamak plasma. Magnetic oscillation frequency upon application ofa positive bias decreases by about 10-15% and then after a delay time,τd = 2.5-3 ms, increases by about 20-25% with respect to their value withoutbiasing. In the negative bias regime, the oscillation frequency increases byabout 10% in 1 ms after the application of the bias pulse. The poloidalrotation velocity changes during two steps are related to its link withthe radial electric field and the timescale of the density gradient.The frequency of oscillations increases with the increasing chamber gaspressure and decreases with the increasing the outward plasma displacement.