Mechanisms of Unexpected Electrical Breakdown Initiation in Ion Optics System: A 2D PIC/MCC Study

Ion thrusters are widely used in satellite operations due to their high specific impulse, efficiency, and precise thrust control. However, unexpected electrical breakdowns in ion optics severely limit the performance and reliability of ion thrusters. To investigate the initiation mechanisms of such breakdowns, a two-step 2D Particle-in-Cell/Monte Carlo Collision (PIC/MCC) simulation model is developed, integrating ion beam extraction with inter-grid breakdown processes. The accuracy of the model is validated by comparison with the experimental data. Simulation results reveal that the breakdown initiation evolves through three distinct stages: the formation of a neutral gas region, the development of cathode plasma, and a rapid surge in gap current. The point at which ion and electron densities near micro-protrusions become equal is identified as a key indicator of the breakdown onset, triggering the final breakdown stage. Breakdown initiation is strongly influenced by the electric field, background gas pressure, and micro-protrusion geometry, while the influence of ion beam extraction is negligible due to its limited effect on the inter-grid field and metal evaporation. Strategies such as increasing the gap voltage while widening the gap spacing and minimizing high-energy particle impacts are shown to effectively enhance thruster performance and suppress breakdown risk. These findings provide valuable insights for optimizing ion optics design and improving the operational reliability of electric propulsion systems.