Measurement of XeI and XeII velocity in the near exit plane of a low-power Hall effect thruster by light induced fluorescence spectroscopy

Near exit plane non-resonant light induced fluorescence spectroscopy is performed in a Hall effect low-power Xenon thruster at discharge voltage of 250~V and anode flow rate of 0.7~mg/sec. Measurement of the axial and radial velocity components are performed, exciting the $6s~^2[3/2]^o_2\rightarrow6p~^2[3/2]_2$ transition at $823.16$~nm in XeI and the $5d~[4]_{7/2}\rightarrow6p~[3]^o_{5/2}$ transition at $834.724$~nm in XeII. No significant deviation from the thermal velocity is observed for XeI. Two most probable ion velocities are registered at a given position with respect to the thruster axis, which are mainly attributed to different areas of creation of ions inside the acceleration channel. The spatial resolution of the set-up is limited by the laser beam size (radius of the order of $0.5$~mm) and the fluorescence collection optics, which have a view spot diameter of $8$~mm.