Partial beam stalling as an alternative source of intercepted current in ionic-liquid electrospray thrusters

The standard interpretation of intercepted current in electrospray thrusters is direct impingement of the plume on any downstream electrodes as the plume leaves the thruster. In this paper, we propose and analyze partial beam stalling as an alternative source of intercepted current in ionic-liquid electrospray thrusters. We show in simulation that low-energy ions created by the dissociation of heavy ion clusters are reflected by a potential barrier downstream of the thruster created due to the lack of explicit plume neutralization. These reflected ions impact the downstream surface of the extractor grid and are recorded as intercepted current, but may not contribute to key life-limiting mechanisms such as emitter–extractor propellant bridging. Simulation predictions of the intercepted current under this mechanism are consistent with trends in prior laboratory testing, which suggests that partial beam stalling may provide an alternative mechanism for the measured intercepted current in ionic-liquid electrospray thrusters.