Characterization of Electron Mach Number in a Hollow Cathode with Thomson Scattering

Abstract

Electron flow is measured non-perturbatively via the incoherent scattering of laser light from electrons in a hollow cathode plume. The scattered spectrum is used to infer the moments of the electron velocity distribution along the axial dimension throughout the expanding cathode plume. Statistical fits of the spectra are employed to compute 1D fluid moments including temperature and mean velocity with uncertainty quantification under assumptions of thermodynamic equilibrium. It is found that electron temperatures range from 4 to 12 eV, flow velocities range from 600 to 1300 km/s, and electron Mach number ranges from 0.3 to 0.8. These results are discussed in the context of previous probe-based estimates for Mach number and in the context of the growth of drift-driven ion acoustic turbulence in the cathode plume.