ELECTROSTATIC ION-CYCLOTRON WAVES DRIVEN BY A RADIAL ELECTRIC-FIELD

An experiment was conducted in a single-ended Q-machine in which a voltage was applied to an electrode of variable diameter. For electrode diameters D < 10-rho(i), field-aligned current-driven ion cyclotron waves were destabilized. If the electrode diameter was increased, a higher-frequency, lower-amplitude ion cyclotron wave was observed. The dispersion, mode amplitude and propagation characteristics of this mode were measured. The mode, which propagates azimuthally, was found to be driven by the radial electric field which exists at the edge of the current channel created by the biased electrode.