High Current Density Cathode Evaluation

Summary form only given. Reliable, high current density cathodes are an enabling technology for the development of vacuum tubes operating at higher frequencies, e.g. millimeter wave devices. High perveance amplifiers such as the multi-beam klystron (MBK) also require high current density cathodes, particularly when operating in the high-R/Q fundamental pillbox cavity mode required for large bandwidth applications. Single beam devices will also benefit from higher emission densities and the ability to operate at lower cathode temperatures, and therefore, extended life. Cathodes that can operate for over 50,000 hours at current densities greater than 5 A/cm² are highly desired. The SLAC 5045 klystron, with an MTBF greater than 60,000 hours, uses a scandate cathode at a loading of 7 A/cm². However, the pulse width is only a few microseconds, whereas for accelerator MBK applications, millisecond pulse widths are required. L-3 Communications has obtained scandate cathodes and M-coated scandate cathodes from Spectra-Mat. The cathodes will be tested in the L-3 Communications L5822 klystron, which has a 9 microsecond pulse, and a loading of 4 A/cm² , and the L4869 klystron which operates CW, with a loading of 2.5 A/cm². The scandate cathodes will be compared to the M-type tungsten dispenser cathodes currently in use in these devices. Miram curves for both types of cathodes will be presented. Life studies are in progress