High Current Density Scandate Cathodes For Future Vacuum Electronics Applications

All RF vacuum electron sources require a high quality electron beam for efficient operation. Research on improved cathodes is constantly exploring new alternatives to produce high current density, uniform electron beams with long life. Typical thermionic cathodes consists of a tungsten matrix impregnated with a mixture of barium calcium aluminates that reduces the work function surface. Recent tests confirmed that emission densities approaching 100 A/cm2 could be achieved with thermionic cathodes containing scandium. Calabazas Creek Research, Inc. and the Massachusetts Institute of Technology propose to incorporate scandium in sintered tungsten wire cathodes currently being developed for the U.S. Department of Energy. The proposed approach addresses issues related to deterioration of current scandate cathodes due to ion bombardments, which is common in RF sources. Facilities for fabricating these cathodes are available domestically. This program also proposes to integrate a scandate-based, reservoir cathode into a baked and sealed RF source and operate the device under typical source environments. The Phase I program will design the RF source, and the fabrication and testing will be performed in Phase II.