Enhancing Neutral Propellant Flow Uniformity in Hall Thrusters via Anode Design

Abstract

The uniformity of propellant gas flow in the discharge channel of Hall thrusters is a crucialfactor for thruster performance. Uneven particle flux to the ionization region results in asymmetric thrust vectors, diminished propellant ionization, and decreased total efficiency. In this work, the gas density profiles within the ACME Hall thruster discharge channel were characterized for four unique anode designs with a modified fast ionization gauge. Additive manufacturing was used to develop anode models with complex internal baffles that aimed to increase flow uniformity and decrease axial flow velocity. Normalized, fine resolution azimuthal measurements were made at 4-5 axial locations, and empirical fits were generated to quantify the evolution of pressure uniformity as a function of axial distance from the anode. Results were compared to the NASA standard acceptance criteria of ≤ 5% absolute deviation (α) and ≤ 10% peak-to-peak deviation (μ) from the mean pressure at the axial midpoint between the anode and thruster exit plane. The original ACME anode met the NASA acceptance criteria, despite observed asymmetries in erosion and plasma density, with α = 2.57% and μ = 4.23%. Two novel anode designs improved flow uniformity with fit functions predicting α = 0.47% and α = 0.87% at the criteria location. Upcoming ACME performance testing will quantify the effect that these gains in neutral azimuthal uniformity have on thruster efficiency.