Effect of the axial magnetic field on the ionization region and ion kinetics in Hall thruster plasmas

Abstract

Hall thruster is a plasma device that utilizes Hall current generated by rotating electrons around an axis by forming an axial electric field and a radial magnetic field. The magnetic field has a great influence on plasma characteristics and performance because it controls electron transport. In this study, the effect of the axial magnetic field on the ionization region and ion motion in Hall thruster plasma was studied by establishing the magnetic field shape as the main variable. In the axially dominant magnetic field region, there was no clear relationship between the magnitude of magnetic field and the ionization and acceleration regions. The ionization region was distant from the discharge channel exit approximately 2/3 times the discharge channel length in the upstream direction, and the length scale of the ion acceleration region was formed over a region 3.5 times the discharge channel length. As the radial component of the magnetic field increased and became comparable to the axial component, the ionization region and the maximum electric field location moved toward the maximum radial magnetic field position, and the length of the ion acceleration region decreased. A significant population of high velocity ions was observed in the region where the axially dominant magnetic field is formed, and this is interpreted as originating from ion-driven plasma instabilities that occur over a wide acceleration region in the axial direction.