High Current Density Long Life Cathodes for High POwer RF Sources

The power that can be produced by klystrons and other RF devices is often limited by the current emission density that can be extracted from the cathode. Operation of existing cathodes at high current density leads to dramatically reduced lifetime. Long life cathodes operating at high current density will allow development of higher power RF sources with improved performance. Control of barium diffusion reduces lifetime limitations due to arcing. Calabazas Creek Research, Inc. proposes to extend the capability of controlled porosity, reservoir cathodes to high power klystrons. Currently, these cathode are only available in diameters less than 0.25 inches. This research will develop techniques to generate cathodes to 2.0 inch diameter. Research will also be performed to lower the work function using alternative materials in the cathode reservoir. Cathodes were built and tested, resulting in improvements in the fabrication and assembly techniques. Cathode material was fabricated allowing larger diameter cathodes with increased mechanical stability. Design formulations were refined to increase mechanical strength and control barium diffusion rates. Designs were generated for magnetron injection guns and Pierce cathodes to two inch diameter. Cathodes will be built and tested with diameters up to two inches, including installation in a high power klystron. Research will continue to refine design calculations, investigate new material, and increase understanding of emission mechanisms by building an emission microscope. A design procedure will be developed and distributed to potential users. Commercial Applications and Other Benefits: High power RF sources are in demand for the next generation of high energy accelerators and colliders. High current density, long life cathodes would be applicable to almost all future linear beam devices, including single beam and multiple beam klystrons, traveling wave tubes, backward wave oscillators, and gyrotrons. They would also be applicable to accelerator injectors.