Cold cathodes for CFAs

Summary form only given. Application of cold cathode technology for use in crossed-field amplifiers (CFAs) has been limited by the characteristics of the materials, usually platinum (Pt) or beryllium (Be/BeO), used as the emitter. A case in point is the L-4717, used as the second stage amplifier (baby Amplitron) in the SPS-48-C/E transmitters. This tube, which uses a thermionic emitter, is characterized by short life and high noise. Attempts to use a platinum emitter were not successful because of unacceptable mode boundary separation at rated drive. Similarly, beryllium was found to be unsuitable because the emitter was too active, causing lower mode boundary interference at the rated operating current. A metal alloy cathode (MAC) material, palladium/ barium (Pd/Ba), was evaluated for use in an experimental L-4717 CFA. This tube, using a standard body, and Pd/Ba material developed at Istok, Moscow, Russia, is designated L-4870. Test results are very encouraging. Two tubes demonstrated satisfactory operation in the SPS-48-C and SPS-48-E test beds at ITT Gilfillan, Van Nuys, CA. One of these is currently under evaluation in the SPS-48-E transmitter at Dam Neck, VA. A third tube has been used as an in-plant driver in the Litton SPS-48-E test set. The Pd/Ba material has been evaluated in other experimental tubes to determine whether it is a suitable replacement for beryllium, again with promising results. Both the L-4806 (TPS-63) and the L-4808 (AN/SPY I-B/D) were equipped with Pd/Ba emitters and showed satisfactory operating characteristics. This paper presents test results and gives a description of Pd/Ba emitter assembly techniques.