Performance at High Current Densities of a Magnetically-Shielded Hall Thruster

Hall thrusters are a type of electric propulsion device with decades of heritage. With the advent of magnetic shielding, a technology that shapes the magnetic field lines in the thruster channel such that the erosion of channel walls by energetic ions is greatly reduced, Hall thruster lifetimes and mission spaces have been greatly expanded. One key remaining challenge is scaling to high powers in the 100-kW range, which is critical for the use of these thrusters for human exploration of the solar system. Historically, there have been issues associated with high-power, high-current density operation on unshielded thrusters. The need is then apparent for an investigation of performance of high current densities on a magnetically-shielded Hall thruster.

In this work, we operate the H9, a 9-kW magnetically-shielded Hall thruster, in the Large Vacuum Test Facility at the University of Michigan. Keeping voltage constant at 300 V, we vary the current from nominal operating values of 15 and 20 A up in 5 A increments to 40 A. We used a null-type inverted pendulum thrust stand to measure thrust, and a probe suite to measure various plasma parameters used to inform an efficiency model that breaks down the anode efficiency into various contributions. Our results show that we are able to run safely and stably up to 12 kW at 300 V, 40 A, achieving a maximum thrust of 700.1 mN and 65.8% anode efficiency here. Additionally, the thrust, specific impulse, and efficiency of the thruster increases monotonically with current, although we do observe dimimishing returns in efficiency as we approach 40 A. Our probe analyses indicate that the mass utilization efficiency is primarily responsible for the increase in efficiency, with most other efficiencies decreasing with rising current density. We then speculate that our efficiency is maxed out at 40 A as the mass utilization approaches unity. We discuss these results in context of scaling single-channel Hall thrusters to the 100-kW range.