Ionization instability and turbulence in the plume of sub-ampere hollow cathodes depending on an applied magnetic field

When operated with a Hall effect thruster, either centrally or externally mounted, the hollow cathode discharge occurs in a magnetic field environment. Therefore, it is important to assess the influence of the magnetic field on the standalone operation of a hollow cathode to better predict device behavior when coupled with a Hall effect thruster. This study focuses on the influence of an applied axial magnetic field on the main oscillatory phenomena in the plume of a Kr-fed sub-ampere hollow cathode operated with an external disk anode. A probe array consisting of two cylindrical Langmuir probes and an emissive probe is used to assess changes in plasma parameters and collected ion saturation current as the magnetic field strength is varied up to 3 mT at the cathode’s location. The electron transport along the cathode–anode space is analyzed in terms of total electron collision frequency. It is shown that a higher magnetic field strength induces larger plasma densities and lower electron temperatures. Applying a magnetic field to the discharge of a cathode operating in plume mode causes a reduction in both the ionization instability and ion acoustic turbulence (IAT) energies. This suggests a dampening of the main oscillatory phenomena in the plume of the hollow cathode. Furthermore, the total electron collision frequency and its main contributor, the anomalous collision frequency due to high-frequency IAT, decrease at higher field strengths. The results included in this communication are, to the best of the authors’ knowledge, the first characterization of the response in low- and high-frequency wave content depending on a magnetic field in low-current hollow cathodes operating in standalone mode at <1 A.