Electron properties of an emissive cathode: analysis with incoherent thomson scattering, fluid simulations and Langmuir probe measurements

Emissive cathodes serve a key function as the electron source for Hall plasma thrusters. Development of reliable numerical models for their operation and information on plasma behavior requires the use of sensitive and accurate diagnostics. This paper discusses results from a combined experimental and numerical study of the plasma regimes and properties of a 5 A LaB6 pellet emitter cathode. Electron properties across a range of currents (2-16 A) are determined for the first time using incoherent Thomson scattering. A 2D axisymmetric fluid code is adapted to the study of the electron properties of this cathode and the nature of regime transitions. Similar trends in the numerical and experimental results are found, such as transitions to plume-like behavior with increasing current; quantitative agreement would require the use of a combined thermal-plasma model for the cathode under study. Comparisons of results from non-invasive Thomson scattering to Langmuir probe measurements reveal limitations of the latter diagnostic for plasma characterization.