Radio-frequency inductively coupled plasma discharges for electric propulsion applications

Radio-Frequency (RF) Inductively Coupled Plasmas (ICPs) are an attractive technology that has a wide range of applications: including as electrodeless plasma sources for several electric propulsion devices such as gridded ion thrusters, ambipolar thrusters, and RF neutralizers. While the discharge pressure in these systems is typical less than 1 Pa, ICPs can also be used to generate high-pressure (10-100 kPa or higher) plasmas and have been proposed as novel electrothermal plasma thrusters capable of generating high thrust-to-power ratios. In these thrusters, an inductive plasma is used to superheat a propellant gas which is then expanded and accelerated through a physical supersonic nozzle to generate thrust, without requiring a neutralizer or an applied magnetic field. Here, we present the basic operation of these thrusters and review the current state-of-the art. We also discuss recent advances associated with bidirectional vortex gas injection – inspired by vortex chemical rocket engines – and how this can significantly reduce heat losses and enhance thruster performance. We also highlight how this versatile technology can be used for many ground-based applications including materials processing, gas conversion, and aerothermodynamics testing.