Scandate Cathode Performance in Xenon Discharge

Performance data on scandate cathodes in noble gas discharges is presented. These devices are used for ionization and neutralization in electric space propulsion. Two geometries were tested., one device was a 4 A plasma cathode for small satellite thrusters. The other device was a > 100 A plasma cathode for moving heavy payloads in space. The first device employed a 0.080-inch planar scandate cathode as electron source and was loaded to over 100 A/cm, The second employed a hollow scandate cathode with inside diameter 0.160-inch and length 0.5-inch and was loaded at 62 A/cm, It was found that the devices with scandate cathodes outperformed all other thermionic cathodes tested both in temperature efficiency (emission/cathode temperature) and electron efficiency (emission current/watts of input power). In one case a hollow scandate cathode delivered 100 A at 1059° Cb, at an anode voltage of less than 23 volts for an electron efficiency of 43.5 mA/watt. By contrast a hollow reservoir cathode with osmium/tungsten insert required 87 anode volts to extract 100 A of discharge current.