Mitigation of breathing oscillations and focusing of the plume in a segmented electrode wall-less Hall thruster

In the absence of the channel walls bounding the plasma, a wall-less Hall thruster is a promising configuration with a potentially longer lifetime and easier scalability than conventional Hall thrusters. Because the ion acceleration takes place in the fringing magnetic field with a strong axial component, the operation of a typical wall-less thruster is characterized by a large beam divergence of the plasma flow, which reduces the thrust. In this work, the addition of a biased segmented electrode to the wall-less thruster is shown to significantly narrow the plasma plume and suppress large amplitude breathing oscillations of the discharge current commonly associated with ionization instability. Both effects result in improvements to the thruster performance. Physical mechanisms responsible for these effects are unclear, but they are apparently associated with the reduction of the electron cross field transport to the anode and a transition in the breathing mode frequency.