Reassessing Jet Mode of Inertial Electrostatic Confinement Thruster for Space Propulsion Application

Inertial electrostatic confinement (IEC) utilizes strong electric fields to generate and confine plasma. It has been extensively used to conduct nuclear fusion reactions and commercially as a neutron source for activation analysis. This study investigates the two distinct discharge modes, "jet" mode and "spray" mode of an IEC thruster. This paper compares the discharge characteristics of an IEC system for various preliminary design options, such as cathode grid design and cathode grid dimensions. High resolution images are used to conduct intensity analysis at multiple operating points. A basic Faraday probe is used to qualitatively record the change in plasma current density. Results show that biasing the cathode at more negative potentials leads to an increase in current drawn by the grid and the visible intensity of the visible plasma. The current and light intensity increase is gradual until a mode transition from "jet" to "spray" occurs. In other words, the "jet" mode always precedes the "spray" mode. Additionally, background pressure and applied cathode potential are shown to be the two main operating variables for an IEC device. Finally, higher current densities were recorded when the device operated in "spray" mode, however, the ejected plasma was more collimated during "jet" mode.