Experimental study on beam focusing of ionic liquid electrospray thruster with focus structure

The application of Ionic Liquid Electrospray Thrusters (ILETs) in micro/nanosatellites is very promising. However, the divergent beam of ILETs significantly affects their performance, including thrust, specific impulse, lifetime, propulsion efficiency, and more. Therefore, in order to improve the performance of ILETs, it is essential to optimize the beam. In this study, a focus structure was designed and fabricated. A series of beam focusing experiments were performed using a conical porous tungsten emitter and the ionic liquid EMI-BF₄ as a propellant. The operational state of ILETs was demonstrated, with over 95 % of the beam composed of ions. After configuring the focus structure, the electric field in the emission region is weakened by the focus electrode, which has a certain negative effect on the starting voltage and emission current. Analysis of the beam focusing results showed that the focus structure reduced the beam divergence half-angle (half-angle) from 40° to 11° and concentrated the beam current within a half-angle of 7.3°. By estimating the thrust and specific impulse of the thruster, it was found that the focus structure could maximize the specific impulse by up to 22.4 % at the same voltage and increase it by approximately 23 % at the same power-to-thrust ratio. This focus structure demonstrated excellent focusing effect on a single conical emitter, making this research valuable as a reference for designing a focus structure for other types of emitters.