Predictive control of plasma kinetics: Time-resolved measurements of inert gas mixing in a hollow cathode discharge
Improved Hall-effect Thruster (HET) efficiency would enable more extensive cost-capped, Discovery class NASA missions such as robotic missions to Mars and near-Earth asteroids to perform round trip sample-returns. HET efficiency would be further improved if electrons with energies that contribute to ionization are increased, and those involved in transient processes are reduced. Therefore, control of the Electron Energy Distribution Functions (EEDFs) is needed. Inert gas mixing is proposed to be an effective method for tuning electron temperature and density. An initial assessment of this method for EEDF control in HETs shows that when 1% of the total gas flow in a hollow cathode's argon plasma is substituted with nitrogen gas, the electron temperature increases from 3.2 eV to 3.8 eV and the number density decreased from 5×10 17 m -3 to 2.2 ×10 17 m -3. The EEDF for the case with nitrogen gas mixing showed more distinct plateaus and peaks compared to the case with a pure argon plasma. This analysis will be used to guide further investigation into using a gas-mixing method to demonstrate predictive electron energy control in HETs. The end goal is to develop schemes to predictably tailor the EEDF in order to increase HET efficiency. Copyright ©2011 by the International Astronautical Federation. All rights reserved.
