Current pathways model for hall thruster plumes in ground-based vacuum test facilities: measurements and observations

Area of Science:

• Plasma physics
• Electric propulsion

Background:

• A prior study introduced a current pathways model for Hall effect thruster (HET) electrical coupling.
• Understanding the vacuum test facility's role in HET operation is crucial for accurate performance characterization.

Purpose of the Study:

• Quantify Hall effect thruster (HET) current pathways model aspects.
• Characterize the influence of metal vacuum chambers on the HET discharge circuit.
• Investigate the impact of discharge current on these interactions.

Main Methods:

• Operated a 7-kW class HET on krypton at specified power and current levels.
• Measured far-field ion and electron saturation currents using planar electrodes.
• Obtained plasma properties using Langmuir probes at multiple facility locations.

Main Results:

• Thruster beam ions neutralized with electrons from the metallic chamber wall, not cathode electrons.
• Charge-exchange (CEX) ion current constituted approximately 23% of the total ion current.
• Plasma sheath near walls exhibited non-uniformity with capacitance ranging from 0.45 µF to 1.79 µF.
• Plasma sheath behaved as a parallel RC circuit, potentially masking HET AC characteristics.
• Inductive effects, with inductances from 76.5 nH to 101.4 nH, were observed due to plasma oscillations.

Conclusions:

• Metallic vacuum chambers are essential for neutralizing HET ion populations.
• The vacuum test facility introduces capacitive and inductive effects that influence HET discharge dynamics.
• The current pathways model needs to account for facility-induced electrical characteristics.