Casing potential oscillations and radially diverging plume ions in a 5 kW Hall thruster

Studies on the lifetime and stability of Hall thrusters are generally more concerned with the interior of the acceleration chamber, or at most the surface of magnetic poles, but the flanking or back side of the thruster is rarely considered. We found severe ion erosion on the flanking area of a 5 kW dual-mode Hall thruster (in its initial stage of development), and then measured the thruster casing potential and plume ion energy in the radial direction. The results showed that the floating potential of the casing had a large amplitude oscillation of −20 V to +175 V, accompanied by 50‒300 eV radial ion energy. Analysis suggested that this thruster’s externally loaded magnetic field might have facilitated ion divergence, thereby activating a neutralization pathway that was not noticeable in the past; the pathway ran from the cathode to the external magnetic mirror and then to the casing, which created a visibly intense glow in the outer magnetic mirror on the side of the thruster. Since the coupling area was clearly unstable in this case, further optimization is needed to suppress the problem. It is also recommended to assess the coupling situations of similar Hall thrusters in addition to the normal tests.