Experimental Study on Electron Extraction Characteristics of an RF Plasma Bridge Neutralizer in an Ion-Plume Environment

Systematic experimental characterization of the electron extraction characteristics of a radio-frequency plasma bridge neutralizer (RPN) in the actual ion-plume environment of a radio-frequency ion thruster (RIT) remains limited, particularly regarding the effects of ion-beam conditions and the relative configuration between the RIT and RPN. In this study, an experiment consisting of an RIT-13 and an RPN-2.5 was established, in which the RIT-13 operated with an Xe + N2 + O2 mixed propellant and the RPN-2.5 operated with Xe. Experimental investigations were conducted to systematically examine the effects of collector bias voltage, ion beam current, screen-grid voltage, RPN installation angle, and spatial position on electron extraction. The results show that the collector bias voltage is the primary parameter governing the electron extraction state, and two distinct jumps occur as the magnitude of the negative collector bias voltage increases, while the ion beam current mainly modulates the electron extraction state near the threshold of the first jump. The 60° and 90° configurations generally exhibit stronger electron extraction capability than the 0° and 30° configurations and require smaller magnitudes of negative collector bias voltage to reach the high-current electron extraction state. A pronounced spatial dependence is also observed. At an ion beam current of approximately 440 mA and a screen-grid voltage of 1200 V, the region of X = −10 mm and Y = 20–40 mm exhibits favorable electron extraction characteristics. Among the investigated configurations, the 90° configuration at (−10, 40) mm requires the smallest magnitude of collector bias voltage, approximately 13.5–14 V, for the RPN electron extraction current to match the RIT ion beam current. This current-matching bias is defined in the present study as the equivalent floating potential Ueq. These results provide an experimental basis for the matching design and spatial configuration of RITs and RPNs in an air-breathing electric propulsion system.