Bonded grid electron gun for 95 GHz extended interaction amplifier (EIA)

A high-convergence (250:1) bonded-grid-electron gun for use in 95 GHz, extended-interaction-amplifier klystrons has been designed and built at Varian Associates. Non-intercepting-gridded guns for this application require very close tolerances in grid-cathode spacings. Present shadow-grid guns cannot provide these tolerances; therefore, the bonded grid approach is a promising solution. The bonded grid consists of a metal-insulator-metal sandwich attached directly to an impregnated tungsten cathode. The metallic top surface is the control grid and the metallic surface on the bottom is the focusing grid. The bottom metallic surface provides a diffusion barrier as well as optimization control of cell beam laminarity. The major advantage of this design approach is that the close tolerances required in cathode-grid spacings for millimeter-wave applications can be easily obtained. The superiority of a bonded-grid design over present shadow-grid guns for use in high-power millimeter-wave tubes was demonstrated. A bonded-grid gun was fabricated and successfully tested in a beam tester.