Experimental Characterization of the Near-Wall Region in Hall Thrusters andits Implications on Performance and Lifetime.

Electric Propulsion;Hall Thrusters;Plasma-wall Interactions;Aerospace Engineering;Engineering;Aerospace Engineering

Shastry, RohitHofer, Richard R. ;

University of Michigan

关键词: Electric Propulsion;    Hall Thrusters;    Plasma-wall Interactions;    Aerospace Engineering;    Engineering;    Aerospace Engineering;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/84654/rshastry_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Hall thruster lifetime codes presently under development at NASA aim to provide predictive tools that can substantially reduce the need for expensive lifetime testing to qualify flight articles.The ability to accurately predict Hall thruster channel wear requires extensive knowledge of the interaction between the plasma and dielectric walls.While significant advances have been made in understanding these interactions, there is a noticeable lack of experimental validation.To this end, five flush-mounted Langmuir probes were placed along each channel wall near the exit plane of a 6-kW Hall thruster in order to characterize the near-wall plasma and measure properties relevant to Hall thruster performance and lifetime.Studies were first performed to improve the fidelity of analysis techniques for flush-mounted Langmuir probes.Comparison of resulting data to prior internal measurements shows that the plasma accelerates further upstream close to the wall, creating de-focusing electric fields that can force ions towards the channel walls.Large radial plasma density gradients were found to be the cause of these de-focusing electric fields.Calculations of the ion power deposition to the channel walls showed increased incident power at voltages below 200 V and above 400 V.Alarge beam divergence as well as higher sheath energies was found to be the cause of the increased power at low discharge voltages, while an increase in ion current to the wall due to plasma recession as well as higher beam energies was found to be the cause of increased power at high discharge voltage.Estimates of the required sputter yield to reproduce observed erosion profiles indicate an energy-dependent yield that resembles the model proposed by Bohdanksy, with a threshold energy of at least 25 eV.The secondary electron emission properties of the channel wall were found to significantly affect the calculated electron power to the wall as well as resulting sheath voltages.Further study is recommended to determine the exact role of secondary electrons in the plasma discharge and its effects on performance and lifetime.