Scandate Dispenser Cathodes With Sharp Transition and Their Application in Microwave Tubes

We report on a new cathode which is based on die-pressed matrices made from scandia-doped tungsten powder using the liquid-solid doping technique. Transition temperatures from space charge to temperature limited emission are as low as 840 °C_b(W) for emission of 5 A/cm². Transitions are sharper than previously published scandate cathodes and compare favorably with M and ternary alloy cathodes. We present emission curves on several cathodes, show comparisons with other types of cathodes, and offer tentative explanations for the improvement. We discuss their suitability in microwave tubes at loadings of 5-10 A/cm².