Performance of a High Efficiency High Power UHF Klystron

A 500 kW CW klystron has been designed for the PEP storage ring at SLAC. The tube operates at 353.2 MHz, 62 kV, a microperveance of 0.75, and a gain of approximately 50 dB. Stable operation is required for a VSWR as high as 2:1 at any phase angle. The design efficiency is 70 percent. To obtain this value of efficiency a second harmonic cavity is used in order to produce a very tightly bunched beam in the output gap. At the present time it is planned to install 12 such klystrons in PEP. A tube with a reduced size collector was operated at 4 percent duty at 500 kW. An efficiency of 63 percent was observed. The same tube was operated up to 200 kW CW for PEP accelerator cavity tests. A full-scale CW tube reached 500 kW at 65 kV with an efficiency of 55 percent. In addition to power and phase measurements into a matched load, some data at various load mismatches are presented.