Plume particle energy analysis of an ionic liquid electrospray ion source with high emission density

Abstract

A retarding potential analyser was used to characterise the energy distribution of the plume particles from an electrospray source. The electrospray device uses an ionic liquid, operates at bipolar and relatively high voltages from ±1800 to ±3500 V, and demonstrated ionic emissions with relatively high emission density of more than ±30 µA per emission tip. Electrostatic simulations were used to study the effects of electric field distortion near the grids in the retarding potential analyser, and a correction factor of 93% was used to regulate the deceleration voltage in the energy analysis, from which the voltage losses between the applied voltage of the electrospray source and the actual acceleration voltage of the charged particles were calculated, demonstrating non-kinetic efficiency from 85.8% at -2100 V to 79.6% at 2600 V. The plume particle energy analysis shows evidence of fragmentation of heavier particles, mostly from dimer ions to monomer ions, and detailed energy analysis was used to estimate the position where the fragmentation occurs. The results suggest that about 45% to 55% of the particle fragmentation occurred in the field-free region, 20% to 30% occurred in the acceleration region with an intense electric field, with the rest of the plume containing unfragmented ions.

Energy properties and spatial plume profile of ionic liquid ion sources based on an array of porous metal strips

“…As the sweeping voltage of the retarding grid increases from zero to the acceleration voltage, the normalized collected current first holds steady, then experiences three stages of decline, and finally decreases to zero in both polarities. The overall RPA curves are generally consistent with some other RPA studies of ILISs [25,29,30].…”

“…Correspondingly, the energy efficiency versus the applied acceleration voltage is decreased, though the decrease is relatively slight due to the simultaneous increase of the applied acceleration voltage. A similar trend was mentioned in references [30], though the material of the emitter is different. The voltage loss is probably due to the resistance of the propellant liquid or circuit.…”

Simulation of electrospray emission processes for low to moderate conductivity liquids

“…36,37 In experiment, droplets could fragment or undergo downstream influences such that droplets reaching the detector may not be those emitted off the jet. 38,39 Note in Fig. 8(b), the total current by modeling lying between those by the experiment 30 and scaling law proportional to a half-power of the flow rate in Eq.…”

Molecular Dynamics Simulations of Ion Extraction from Nanodroplets for Ionic Liquid Electrospray Thrusters

“…1 Schematic of the electrospray thruster potential analyzer (RPA) experiments have shown that variations in initial ion emission energy can influence the spacing between the cation-anion pairs. Past a certain energy threshold, the cation and anion molecules may overcome their attractive Coulomb forces, resulting in ion cluster dissociation or fragmentation of downstream solvated ion clusters [24,25]. Furthermore, Gamero-Castaño [26] implemented an Eulerian electrospray beam model based on the line-of-point-charges approach and demonstrated a strong dependence of charged droplet trajectories on their initial velocities.…”