Study and Development of Alloy-film Dispenser Cathodes

In this paper, the developmental work on alloy-coated cathode and thermionic emission microscope (THEM) is presented. The cathode is incorporated with potted heater assembly. A contra-wound helix filament is used to minimize inductance. The heater is potted using non-shrinkable alumina powder at elevated temperature. To minimize thermal and mechanical stresses at the heater lead, a spring (micro-helix) is incorporated which slide fits into the lead wire that is partially buried into the potting region. The above alloy of 20s:2Re:1W is chosen on the basis of work carried out at Cambridge, using auger electron spectroscopy (AES) in conjunction with THEM.