Plasma diagnosis inside the discharge channel of a low-power Hall thruster working on Xe/Kr mixtures

In this paper, optical diagnostics for the internal plasma of a low-power Hall thruster working on Xe/Kr mixtures is carried out. The emission spectroscopy results show that the atomic and ionic spectral lines reach the maximum at 5 mm and 3 mm upstream of the channel exit, respectively, indicating a spatial separation between atom excitation and ionization. The krypton atomic spectral intensity obtains the maximum closer to the channel exit than xenon. Presence of xenon is demonstrated to substantially increase the density of krypton atoms in metastable state and promote the ionization of krypton atoms. Both the enhanced mixture flowrate and Kr fraction push the ionization zone downstream. Increases in discharge voltage and discharge channel length shift the ionization zone upstream. For the overall performance, a longer discharge channel improves the thrust efficiency. It is mainly attributed to a more focused plume, an increase in the current efficiency from 80% to 84%, and a reduction in the electron current of about 28.57%. Therefore, under the condition of further optimized channel erosion issue, an extended discharge channel is recommended in the practical tests of Xe/Kr mixtures to compensate for the inefficiencies caused by krypton atoms.