500-A LaB6 Hollow Cathode for High Power Electric Thrusters

NASA continues to develop higher power ion and Hall thrusters for deep space human and robotic missions that require higher thrust and specific impulse than available in current thrusters. The NASA NextSTEP program produced a successful demonstration the XR-100 nested Hall thruster system operating at 100 kW of power; driven by a JPL LaB6 hollow cathode operating at 250 A of discharge current. This X3 hollow cathode represents the state-of-the-art in high current thruster cathodes and has been operated at 25-350A of discharge current in the JPL cathode test facility. The next generation of this LaB6 hollow cathode has been designed and built at JPL and tested at up to 500 A of discharge current. Extending the current to this high a level was challenging, with iterations in the design necessary to provide adequate thermal isolation of the insert to lower the heater power required to ignite, to achieve sufficient keeper discharge current to aid in the startup, and to maintain the cathode orifice plate at acceptable temperatures during very high current operation. The cathode configuration that achieved 500 A discharge current operation is described, along with discussions about energetic ion suppression, plasma penetration into the insert region, and cathode life.