Time-varying non-classical electron resistivity in a hollow cathode plume
An investigation is performed into the time-dependent correlation between the local electron resitivity in a hollow cathode plume and the enhanced electron drag induced by wave-driven turbulence. Emissive, floating, and ion saturation current probes are applied to the plume of a 20-A class LaB6 hollow cathode to characterize the density, potential, and electron temperature. Emissive probes are employed to characterize the energy in ion acoustic turbulent modes near the cathode exit plane. The actual electron resistivity in the cathode plume is measured through a solution of the generalized Ohm’s law with the measured plasma properties. The energy in the ion acoustic turbulence is related to an enhanced resistivity on the electrons through a quasilinear formulation. A phase-averaging technique is applied to both sets of measurements to generate spatially resolved maps of the total resistivity and wave-driven contribution on the time scale of the 45 kHz, large-scale plume mode oscillation in the cathode plasma. The time-averaged values of the plasma properties show that, as is consistent with previous numerical simulations, the electron resistivity in the cathode plume is greater than two orders of magnitude higher than electron resistance and can be explained entirely by the wave-driven turbulence. The wave-driven drag similarly is the dominant contributor to electron resistance on the timescale of the 45 kHz oscillations in the near-field of the cathode. These results suggest that the quasilinear form for the turbulence driven transport is correct for both the time-averaged and time-resolved dynamics in the plume. These results are discussed in the context of the relationship between the ion acoustic turbulence and the onset of the plume mode oscillation.
