Transient non-classical transport in the hollow cathode plume I: measurements of time-varying electron collision frequency

Abstract

Electrostatic probes are employed to measure the time-variations in electron collision frequency due to a large-scale, low-frequency, plasma instability in a high-current hollow cathode plasma discharge (plume mode oscillation). Time-resolved measurements of ion acoustic turbulence are used to infer the effective collision frequency on the timescale of this underlying wave. Through a direct comparison, it is shown that the observed variation in the electron collision frequency cannot be described by classical collisional processes, i.e. Coulomb and neutral collisions, but rather is well represented by the changes in the anomalous collision frequency due to the turbulence.