Analysis of Alternative Propellants on the Dynamic and Turbulent Behavior of a Cathode Plasma

Hall effect thrusters (HETs) have commonly used xenon gas as a propellant because of its low first ionization energy and comparably heavy atomic mass. [1] It has recently become advantageous to seek alternative propellants, such as argon or krypton, due to the rising costs of xenon. Recent studies have demonstrated that krypton can result in comparable thruster performance to xenon, particularly at higher power. [2], [3] However, it is unclear how the change of gas effects the dynamic and turbulent behavior in the plume. If the generated krypton plasma enhances the turbulence, then it is likely the thruster would experience greater erosion rates. This study used a LaB₆ hollow cathode with a magnetic field simulator and cylindrical anode operated on krypton and argon. For both propellants, the cathode was operated at two discharge currents, two flow rates, and the magnetic field was swept from 0 G to 133 G. A wave probe constructed of two Langmuir probes held in ion saturation was used to map wave propagation in the plume. High speed discharge current, discharge voltage, and floating keeper voltage were captured simultaneously with the wave probe measurements. The first Wasserstein metric was used to qualitatively compare the cathode operation for the separate gas types. The data indicated that a significantly higher mass flow rate of argon was required to match the behavior of the krypton plasma. This mass dependency suggests the thruster will require more mass flow for lighter propellants to mitigate the instabilities dependent on the particle mass.



[1] D. M. Goebel and I. Katz, Fundamentals of Electric Propulsion: Ion and Hall Thrusters. 2008.

[2] L. L. Su et al., “Operation and Performance of a Magnetically Shielded Hall Thruster at Ultrahigh Current Densities,” pp. 1–32, 2023, doi: 10.2514/6.2023-0842.

[3] G. C. Potrivitu and S. Xu, “Phenomenological plasma model for open-end emitter with orificed keeper hollow cathodes,” Acta Astronaut., vol. 191, no. November 2021, pp. 293–316, 2022, doi: 10.1016/j.actaastro.2021.11.005.