Plasma diagnosis of an unclosed E × B drift thruster with a visible ionization zone

Abstract

The traditional annular closed-loop E × B drifting Hall thruster is limited by its compact structure. Two-dimensional (2D) distribution of the plasma parameters inside the discharge channel cannot be accurately measured, thus directly hindering further understanding of the discharge process. In this paper, we propose to employ an unclosed E × B drift thruster with a visible (UDTv) ionization zone to conduct research into the effects of the crossed electric field and magnetic field on the plasma distribution inside the discharge channel. Experiments showed that the UDTv presented discharge similar to a Hall thruster, especially the low-frequency oscillation related to the discharge voltage. A 2D symmetrically crescent-shaped distribution of plasma inside the channel with a hollow zone located near the maximum of the magnetic field was clearly captured by optical imaging and an emission spectrometer. Correlation between the location of the maximal magnetic gradient and the 2D ionization zone configuration was verified. A decreased magnetic mirror effect at the location of the maximum magnetic field enhanced the electron–wall interaction, inducing near-wall conduction and secondary electron emission. The electron temperature presented a canyon distribution, resulting in a bimodal configuration of the plasma density. Increased flowrate lowered the ionization inside the channel and transformed the plasma distribution into a unimodal structure because of enhanced electron conduction and the lower electron temperature. Generally, the ability to capture the correlation between 2D plasma distribution and the magnetic field inside the discharge channel was successfully demonstrated, thus proposing new ideas for further research into the internal plasma of Hall thrusters.