Ignition mechanism of a dual trigger electrode hollow cathode

Hollow cathodes serve as the electron source for thrusters and are critical elements of the electric propulsion system. To overcome the limitations of the small orifice blockage in the discharge path of the conventional hollow cathode on the ignition performance, a dual trigger electrode heater-based cathode with a sub-millimeter columnar bias electrode inserted into the emitter cavity is proposed. Both experiments and simulations indicate that the dual trigger electrode cathode provides faster ignition time and self-healing ability from poisoning. A coupled plasma-Thermal model reveals the ignition mechanism from the discharge process, power deposition, and ion sputtering. The electric field penetration induced by the inner electrode enhances the energy injection of emitted electrons and internal ohmic heating to establish an efficient discharge from upstream to downstream. Primary ignition of the inner electrode enhances the power deposition on the emitter with ion bombardment dominated, raising the emitter temperature rapidly by 150 K from 1173 K in the preheating phase to accelerate the electrode switching. Energetic ions during the primary ignition perform explosive scanning sputtering of the emitter, uniformly cleaning the tungstate layer from the emitter surface and allowing the cathode to self-heal from poisoning, as verified by destructive environmental tests.