Study on hollow cathode discharge mode with high flow rate

Hall and ion propulsion systems at power levels of ten kilowatts or higher are in development or application stages in recent years, yet research on the operational characteristics of corresponding hollow cathodes remains incomplete. This study conducts experimental research using a hollow cathode with a rated condition of 15 sccm of krypton gas and 10 A of current. By supplying a larger flow rate, the study expands the range of discharge currents to investigate changes in the discharge modes. The plume plasma characteristics and spatial distributions under various conditions were measured using a Langmuir single probe mounted on a planar two-dimensional displacement platform. The experimental results indicate that at krypton flow rates of 25 sccm and 30 sccm, as the current increases, the anode voltage and discharge oscillations increase at first but decrease later. The discharge mode transitions from low-current spot mode to plume mode, and then back to spot mode at high current. The increase in anode voltage and oscillations during the first transition phase is gradual and continuous, while the decrease during the second transition phase is abrupt. Conditions of 10 A, 12.5 A, and 20 A were selected to represent these three modes for single-probe plume spatial diagnostics. The results indicate that in the high-current spot mode, the axial potential gradient is significantly reduced compared to the radial gradient, and the cathode plasma plume is more collimated. This study shows that at high flow rates, hollow cathodes may exhibit nonlinear impedance and undergo multiple discharge mode transitions, with each transition phase displaying distinct characteristics.