Heaterless LaB6 Lollipop Hollow Cathode for Center-Mounting in Hall Thrusters

Hollow cathodes are a critical component of Hall thrusters, providing electrons for both plasma generation and beam neutralization. A new 10-kW-class thruster, named the H10, has been developed at JPL and demonstrated >3000 s Isp and over 70 % efficiency in steady state operation at up to 15 kW. The cathode for the H10 thruster is a heaterless lanthanum hexaboride (LaB6) hollow cathode designed in a “lollipop” configuration and center-mounted in the Hall thruster. This shape features a short, compact cathode body that contains the LaB6 thermionic insert, graphite keeper and alumina insulators. The cathode assembly then necks down to a small diameter gas feed tube that acts as the cathode electrical conductor, and a separately insulated keeper lead. This geometry is ideally suited for magnetically shielded Hall thrusters because it minimizes the amount of magnetic material that must be removed from the inner magnetic core to fit in the centrally-mounted cathode, thus enabling higher magnetic fields by reducing saturation of the inner core. The heaterless cathode starts in only 3 min using less than 100 W of keeper discharge power, and has demonstrated operation in the thruster at discharge currents of 2–50 A. The design, performance and life of the cathode and heater are described.