High-Speed Camera Imaging of the Ignition Process in a Heaterless Hollow Cathode

The plasma discharge inside a heaterless hollow cathode (HHC) is studied during its ignition process. A partly transparent HHC device is developed for this purpose. The temporal evolution images of the plasma in the cathode are obtained by a high-speed camera imaging method. It is observed that the ignition process is started with a gas breakdown that originates between the cathode plate and the keeper plate. After that the plasma discharge spreads out of the keeper through the orifice on the keeper plate. Then, the discharge moves back into the emitter region through the orifice on the cathode plate. It is seen that an arc discharge is formed as the plasma propagates from the downstream end of the emitter to its upstream region. Because of this process, part of the emitter (that next to the cathode plate) is heated gradually to the steady-state operating temperature. The HHC achieves thermal electron emission after the ignition process.