Electron polytropic exponent in the plasma plume of a high power Hall thruster firing with xenon and krypton

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2025年7月1日

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Stéphane Mazouffre,
Vincent Delbosq

摘要

Langmuir probe measurements were performed in the downstream region of the plasma plume of a high power Hall thruster fired with both xenon and krypton as propellant for input powers from 3 kW up to 6 kW. Our analysis shows that the measured electron energy distribution function is well fitted with a Druyvesteyn distribution, especially for large electron energies. Angular profiles of the electron density and temperature have been determined for many operating conditions. The electron density is larger for xenon while the electron temperature is larger for krypton, as a consequence of the ionization energy difference. Combining density and temperature data, the electron polytropic exponent $\gamma _e$ $γ_{e}$ was computed. In the far-field, the value of the exponent is below the value of an adiabatic expansion (5/3) in agreement with previous works. The exponent is larger for krypton than for xenon. Surprisingly, the value of the exponent remains independent of the angular position in spite of significant variations in electron density and temperature with the angle.