Development of In-Situ Erosion Diagnostics for Hall Thrusters with a Long-Distance Microscope*

Plasma-induced erosion of Hall Thruster channel walls limits thruster lifetimes. Diagnostics of thruster wall surface evolution due to sputtering and deposition will aid in understanding erosion and help develop accelerated erosion tests to eliminate the need for costly life tests required prior to space missions [1]. The aim of this work is to develop in-situ erosion diagnostics of Hall Thruster channel walls which can be used without interrupting plasma operation. For that purpose, a diagnostic setup based on a Long-Distance Microscope (LDM) [2] was developed.  In the described experiments, samples made from boron nitride ceramic and other materials were exposed to a neutralized argon ion beam generated by a 3-cm gridded ion source. Geometries and placement of these samples with respect to the beam were designed by applying a simplified model [4] to enhance the erosion rate. Erosion rates for different materials were measured in situ using LDM and applying the Shape from Focus image processing technique [3]. Results of the LDM measurements and their comparison with an independent determination of erosion rates by measurements of the weight of the eroded material [5] will be presented.

References:

[1]: N.P. Brown and M.L.R. Walker. Applied Sciences 10, 3775 (2020).

[2]: A. Ottaviano et. al. Rev. Sci. Instrum. 92, (2021).

[3]: M. Chen, et. al.  IEEE Trans. Plasma Sci. 26, 1713, (1998).

[4]: S.K. Nayar and Y. Nakagawa. IEEE PAMI 16, 824, (1994).

[5]: Y. Garnier, et. al. J. Vac. Sci. Technol. A. 17, 3264 (1999).