Counterstreaming ions at the inner pole of a magnetically shielded Hall thruster

Abstract

During development testing of a 12.5 kW magnetically shielded Hall thruster, direct evidence of counterstreaming ions eroding the pole covers was found. One stream of ions appears to originate from the discharge channel while the other stream appears to originate from the centrally mounted cathode. Velocity distribution measurement indicates that each stream impacts the poles of the thruster at high oblique angles of incidence. While the average energy of each stream was in the tens of eV, the energy distributions contained high-energy tails that can be a major contributor to erosion. Starting with the physical picture of high oblique angle bombardment, predictions of change in erosion behavior over time are in good agreement with pole cover erosion measurements taken during wear testing. The new evidence points to a need to study these ions that are traditionally considered "low-energy"ions and the role they play in the erosion of the poles of magnetically shielded Hall thrusters.