Multi-scale modeling of ionic electrospray emission

Abstract

The physics of ionic electrospray propulsion spans multiple length scales. This paper combines a molecular dynamics model, a particle-particle model, and a particle-in-cell model to investigate the physics of ionic electrospray propulsion over 9 orders of magnitude in length scale. The combined models are applied to simulate beam emission for an ionic electrospray propulsion system with porous emitter tips and 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid propellant from the emission site to the downstream plume. Additionally, the impact of multiple emission sites from a single emitter tip is analyzed with regard to extractor grid interception and overall beam neutralization for bipolar thruster pairs. Results show that beams consisting of species of different masses (i.e., monomer and dimer species) are affected by particle-particle forces during acceleration and should not be treated as a superposition of independently accelerated species in macro-scale plume models. The activation of multiple emission sites also causes a noticeable increase in the beam's spread, leading to increased intercepted current but relatively little adverse effects in the downstream plume region.