Study on influence of propellant flow rate on ECR ion source beam current

The electron cyclotron resonance (ECR) ion source with grid inlet has the characteristics of low propellant supply pressure and no cathode required for operation, so it has the potential for application in atmosphere breathing electric propulsion. The flow rate has a significant impact on the beam current of the ion source. When the flow rate exceeds the critical flow rate, the increase of the ion beam is suppressed. To clarify the determining factors that limit the increase of ion beam flow, this paper conducted Langmuir probe diagnostic experiments on ECR ion sources with grid inlet driven by nitrogen gas at different flow rates, and calculated the distribution of ordinary (O) wave cutoff region and electron energy acquisition indicators based on the diagnostic results. The research results indicate that when the flow rate is below the critical flow rate, the ion density rapidly increases with the increase of flow rate, and the main factor limiting the increase of ion beam is the neutral gas density. When the flow rate exceeds the critical flow rate, the O wave cutoff zone almost covers the entire main plasma production aera, which leads to a decrease of one order of magnitude in the efficiency of electron energy acquisition. At this moment, the main factor limiting the increase of ion beams shifts to electron temperature.