Weld techniques for reservoir cathodes

We report on improvements in weld technology in support of our efforts to produce a commercial miniature reservoir cathode. These cathodes require that emissive material be sealed inside a pocket behind a so-called diffuser plug. Welds providing this seal must remain hermetic through the life of the cathode. Thus, the weld requirements are more exacting than for ordinary impregnated cathodes. Reservoir cathodes offer the possibility of significant improvement in current density and cathode life. Tests continue at the Naval Surface Warfare Center in Crane, Indiana. Such reservoir cathodes have demonstrated over 100,000 hours of stable operation at 2 and 4 Amps/cm/sup 2/. Our objective is a small, low power reservoir cathode capable of at least 100,000 hours at an emission current density greater than 5 Amps/cm/sup 2/. The diameter of our smallest cathode is 1.5 mm (0.060 inches).