Experimental Investigation on Ionization Length Required for Efficient Operation of Argon Hall Thrusters

Highlights • Measurement of discharge parameters under various magnetic field configurations. • Estimation of ionization zone length using Langmuir probe diagnostics and current-voltage characteristics. • Comparison with xenon-based operation to understand differences in propellant behavior. • Discussion on scaling laws and implications for efficient argon propulsion system design.

Abstract: The propellant utilization efficiency of RAIJIN-66, a 2-kW class Hall thruster with anode layer, was investigated with varying anode temperature to evaluate ionization length, which is the length of the ionization region determined by the channel and magnetic field design. During RAIJIN-66’s thermally transient operation from the ignition, the ion beam current was monitored as a function of anode temperature using an ion collector plate biased negatively at 40 V. Two magnetic field profiles were examined with and without trim yokes. From the measured correlation between the propellant utilization efficiency and anode temperature, the ionization length was evaluated. As a result, the ionization length was 5.6 mm without the yokes, and 2.5 mm with the yokes. The ionization length of 2.5 mm was enough to achieve high propellant utilization efficiency with xenon, while it is too short to operate with argon because argon ionization mean free path is notably longer than xenon. This measured length was experimentally confirmed to be almost independent of discharge voltage and electron temperature. In conclusion, to achieve the high performance with argon propellant equivalent to that with xenon propellant, the ionization length as long as 14.5 mm is required in RAIJIN-66 size thrusters.

Recommended citation: Satpathy D, Sekine H, Barth N, Kawashima R, Komurasaki K, Koizumi H. Experimental investigation on ionization length required for efficient operation of argon Hall thrusters. Transactions of the Japan society for aeronautical and space sciences, 68(1), 12-18. 2025.
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