High Efficiency, CW, High Power Klystrons for Storage Ring Applications

The 125 kW CW klystrons to be described in the first part of this paper were specifically designed for energy upgrading of the electron-positron storage ring, SPEAR II, at SLAC. Four tubes are required with an efficiency greater than 50 percent. The operating frequency is 358.54 MHz. The gain is approximately 50 dB, the operating voltage is 41 kV and the microperveance is 0.7. The klystron must be stable when working into an accelerator cavity VSWR as high as 2:1 at any phase angle. The calculated and experimental data to be presented include saturation and phase characteristics. A maximum efficiency of 57 percent was obtained and the highest output power was 160 kW CW at 42.5 kV. The second part of this paper deals with the design of a higher power version of this tube. The RF power is 500 kW CW at an efficiency exceeding 70 percent. The operating voltage and current are 62 kV and 11. 5 A, respectively. The higher efficiency is obtained by inserting an additional cavity to make use of second harmonic bunching. Eighteen such klystrons are to be used in the proposed PEP storage ring.