Near-Infrared Collisional Radiative Model for Xe Plasma Electrostatic Thrusters: The Role of Metastable Atoms
AIR FORCE RESEARCH LAB HANSCOM AFB MA SPACE VEHICLES DIRECTORATE
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Metastable Xe atoms play an important role in the collisional radiative processes of dense xenon plasmas, including those of electric thrusters for space vehicles. Recent measurements and calculations of electron-excitation processes out of the metastable state have allowed for the development of a collisional radiative model for Xe near-infrared NIR emissions based on the population of the metastable level through radiative transitions, and based on depopulation through electron-impact excitation. A modified plasma radiative model incorporating newly computed electron-impact excitation cross sections using both relativistic distorted wave and semi-relativistic Breit-Pauli B-Spline R-matrix methods is presented. The model applies to optically thin, low-density regions of the thruster plasma and is most accurate at electron temperatures below 10 eV. The model is tested on laboratory spectral measurements of the D55 TAL and BHT-200 Hall thruster plasma NIR radiation. The metastable neutral fraction is determined to rise from 0.1 to slightly above. The electron temperature increases from 2 to 10 eV, reaching a maximum around 15 eV. Electron temperatures derived with the modified model are approximately 20 lower than a previous version of the model that used an approximate approach to account for metastable population and line intensity enhancement.
- Inorganic Chemistry
- Infrared Detection and Detectors
- Particle Accelerators
- Unmanned Spacecraft