Density Fluctuations in the Etude Stellarator

Abstract

Density fluctuations of the Ohmically heated plasma of the Étude stellarator can be resolved into azimuthally propagating waves by means of narrow-band correlation measurements. At frequencies below roughly 100 kHz, propagation velocities are comparable to macroscopic plasma velocities, but increase with frequency and azimuthal mode number. Kink or field degeneracy modes, such as those found on B-1, dominate the spectrum of azimuthal modes at appropriate plasma currents. At frequencies above 100 kHz, the wave propagation velocity tends to become constant at a value nearly an order of magnitude larger than either the ion diamagnetic drift or the mean column rotation velocity, but remains in the same direction.