Development and operation study of gas-free cathode-compensator as part of the static plasma thruster

Preliminary studies on using a thermionic gas-free cathode as a compensating cathode (CC) in a static plasma thruster (SPT) are presented. The study is due to the need to develop CC for SPT running on iodine propellant. Properties of various emission materials are discussed. Boride and metal-alloy cathodes are proposed to be used as a gas-free CC. A design procedure for wire type gas-free CC is presented, including the CC location, dimensions and filament current. An experimental setup for testing SPT with a gas-free CC is described. Fire test results of SPT-70 thruster with a gas-free CC are presented. Possibility of SPT with gas-free CC stable operation is generally verified. It is noted that the cathode potential drop happened to be higher than the design value and amounted to 47 V.