Stabilization of Low-Frequency Fluctuations by Radial Potential-Profile Control in an ECR-Produced Plasma

Low-frequency fluctuations related with a radial electric field are investigated in a magnetized plasma column produced by the electron cyclotron resonance. Various radial profiles of space potential are formed by biasing a segmented endplate. Radial electric field and its shear are obtained by fitting the 6th order polynomials to the potential profiles measured. Two types of fluctuations are observed in this experiment. The flute mode fluctuations which are strongly excited in a range of large electric-field shear are considered to be a Kelvin-Helmholtz instability. The drift-wave mode is stabilized with an increase in the radial electric field regardless of its sign, which also tends to be stabilized by the E×B drift velocity shear.