Carbon nanotube-based cathodes for microwave tubes

Summary form only given. In this paper we describe the approach and apparatus for realizing and testing field emission cathodes based on carbon nanotubes for microwave tubes. These are intended to replace thermionic cathodes, avoiding their cost and fabricational difficulties while producing pulse current densities at least 10 A/cm. The carbon nanotubes are grown on molybdenum substrates such that the tubes are oriented normal to the surface. The tubes are roughly 10 nm in diameter and 1 micron in height, with a spacing chosen for maximum current density. Cathodes with areas up to 10 cm/sup 2/ will be fabricated and tested in a Pierce-gun geometry using a 1 microsecond pulse, 100 A @ 100 kV pulser. Results of measurements of the current and current uniformity as a function of tube density, height and voltage will be presented.