Emission characteristics of hybrid emitter ionic liquid electrospray under an alternating electric field

Ionic liquid electrospray thrusters are simple, high-specific-impulse devices suited to microsatellites and typically use alternating voltage for plume self-neutralization. However, experiments have observed over-emission during polarity switching that enlarges beam divergence. The mechanism underlying this phenomenon remains unclear. To this end, molecular dynamics simulations of a hybrid emitter electrospray under alternating electric fields are performed and compared with vacuum chamber experiments to elucidate the emission characteristics. Two operating modes are investigated: the externally-wetted mode and the capillary mode. The results show that both modes exhibit a similar transient: after a polarity step the Taylor cone elongates then retracts, producing a current spike followed by a trough and gradual recovery, with the capillary mode recovering more quickly. The re-stabilization time (110–120 ps) is consistent with the liquid's charge-relaxation time. Further analysis of the charge distribution indicates that the current spike originates from rapid discharge of excess charge accumulated near the emitter head prior to reversal. Besides, the spike widens the beam divergence from ≈10° (steady) to ≈28°. Optimizing the voltage waveform mitigates this: a piecewise-linear waveform reduces the divergence peak to ≈15°. These results provide a reference for the polarity-switching mechanism and offer practical guidance for stable, long-life operation of alternating-voltage electrospray thrusters.