Scandate cathode with sharp transition

We report on a new cathode which is based on die-pressed matrices made from scandia-doped tungsten powder. Transition temperatures from space charge to temperature limited emission are as low as 840° Cb(W) for emission of 5 Amps/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 to other types of cathodes, and offer tentative explanations for the improvement. We discuss their suitability in microwave tubes at loadings of 5-10 Amps/cm².