Hollow cathode testing of Y2O3, La2O3-doped tungsten and LaB6 emitters with krypton and iodine

In iodine electric propulsion the remaining challenge is an iodine fed hollow cathode to enable single propellant subsystems for higher power levels. In this pursuit novel hollow cathode emitter materials such as Y2O3 and La2O3-doped tungsten have been tested both with krypton and iodine and are compared to LaB6 as conventional emitter. LaB6 and Y2O3 failed to ignite with iodine, whereas the La2O3-doped tungsten degraded to be unusable within only 2.4 h through erosion and depletion. For krypton operation, the doped tungsten performed similar to LaB6 requiring keeper currents of 1.2 A to extract 0.3 A at the anode in spot-mode at flow rates below 1 sccm. The Y2O3 showed promising performance, allowing lower flow rates and power consumption. Degradation occurred however after 600 h testing and the emitter was destroyed by subsequent exposure to air. To characterize the materials, the thermionic emission properties of the three emitters have been determined by measuring current temperature relations. Although the two evaluated emitter materials did operate satisfactory on krypton, they show only limited lifetime and performance compared to conventional emitters and are not iodine compatible.