Investigation on robustness of Nanosized-Scandia Doped Dispenser Cathodes

Abstract

In order for practical applications in Vacuum Electron Devices (VEDs), the robustness of Scandia Doped Dispenser (SDD) cathodes has been widely concerned. Machinability, emission performance from machined surface, recovery of emission after poisoning; air exposure and ion bombardment have, thereby, been studied. The investigation demonstrated that the cathodes can be successfully machined by normal lathing to the required diameters and curvature radius. A life test with DC loads of up to 40 A/cm ² at 970 °C _b has been completed more than 5000 hours to date for a cathode with machined surface. A full restoring of emission has been proved after the cathodes were exposed to air and reactivated for a short time. This performance allows the cathodes to be pre-heated before assembling into the electron guns. Poisoning experiment evinces that in comparison with that of a 311-XM cathode, which was reported to be less affected by gas poisoning than other M cathode, the poisoning thresholds of residual gases for the SDD cathodes are more than one order of magnitude higher at equivalent temperatures but with higher emission level. The emission and surface behaviour, when an activated cathode encounters ion bombardment at its operating condition, has also been investigated and discussed.