High power klystrons and lasertrons

Recent developments on high power sources at SLAC are described. High power klystrons have been under development for many years. The two most recent tubes are a 150 MW klystron operating at an RF pulse length of 1 microsec and a 50 MW klystron operating at 5 microsec. The latter is the tube used for the SLAC linear collider. All work discussed in this paper was done at a frequency of 2856 MHz, the linear accelerator frequency. Design criteria and operating experience for both of these tubes are described. Several computer codes exist for calculating the performance of proposed designs. Problem areas encountered were with high voltage breakdown in the 300 to 500 KV range, window failures and RF instabilities. Window R and D has concentrated on dual output windows, BeO and multipactor suppressing coatings. The tubes must operate with fewer than four high voltage breakdowns in an eight-hour shift and with as few missing RF pulses as possible (less than 10/Hour is desirable). Current status on these criteria is described. Efficiencies achieved with these tubes are in the 45 to 50 percent range. Approaches to improve this performance are described