Total Electrode Fall Measurement in a Parallel-Plate Magnetoplasmadynamic Thruster

*† ‡ § ** †† The total electrode fall voltage in a channel of Magnetoplasmadynamic thruster was determined by using "zero-limit approximating method", which is one of the classical methods widely used in welding society. 5ch parallel-plate MPD was newly designed and operated in quasi-steady mode. Changing its electrode gap from 4mm to 1mm, an electrode gap vs. discharge voltage characteristics was obtained and the intercept of the extrapolated line was 18V, which was considered to be the total electrode fall. The electrode fall voltage did not depend on the discharge current unless the discharge current did not exceed onset threshold. It is considered that most of the electrode fall lies on the cathode side since the space potential at the mid point between both electrodes was almost closed to the anode potential.