Electron properties comparison of microwave cathode and hollow cathode by incoherent laser Thomson scattering

We report a measurement of electron properties at the plume region of a microwave cathode and a hollow cathode by incoherent laser Thomson scattering (incoherent LTS). Compared to probe measurements, incoherent LTS can directly measure electron velocity distribution function(EVDF) with less disturbance. In addition, it is suitable to measure non-Maxwellian EVDF. However, measuring plasma around electric propulsion systems is generally difficult, whose typical electron density is 10^16~10^18 m^-3 and whose typical electron temperature is 1-10eV. In this work, to realize the measurement, laser stray light noise is drastically reduced using a triple monochromator with a notch slit. Then, to improve the signal-to-noise ratio (S/N), a photon-counting technique is applied. We succeed in measuring the electron number density of 10^17 m^-3 ~10^18 m^-3 at the plume region of microwave cathode and Hollow cathode. The results provide the difference in electron properties such as electron temperature and bulk velocity between these cathodes.