New Developments in RF Power Sources*

The most challenging rf source requirements for high-energy accelerators presently being studied or designed come from the various electron-positron linear collider studies. All of these studies except TESLA (the superconducting entry in the field) have specified rf sources with much higher peak powers than any existing tubes at comparable high frequencies. While circular machines do not, in general, require high peak power, the very high luminosity electron-positron rings presently being designed as B factories require prodigious total average rf power. In this age of energy conservation, this puts a high priority on high efficiency for the rf sources. Both modulating anodes and depressed collectors are being investigated in the quest for high efficiency at varying output powers. 1. L~~DUCTION Recent progress in radiofrequency (rf) sources has been evolutionary rather than revolutionary. There have been no great breakthroughs, no startling innovations, nothing comparable to the discovery of strong focusing or the invention of the FEL, that I am aware of. Rather, the period has been characterized by steady progress towards higher powers and higher efficiencies. UHF klystrons [I] for storage rings arc now available with 1.3 MW of CW power and an efficiency of 65%. Almost all tubes are designed with the aid of two- and/or three-dimensional PIC codes such as MASK, CONDOR, MAGIC, or FCI [2]. Klystrons intended for linear colliders have achieved peak powers on the order of 100 MW for short pulses at X-band and above. A microwave FEL has achieved 1 gigawatt at a 1 cm wavelength (quite a number of years ago). There is a lot of research activity at a number of universities and laboratories on various “gyro ” devices producing tens of megawatts at a number of frequencies above 10 GHz. I won’t discuss a number of ultra high power, high frequency rf sources like the vircator and the phase-locked relativistic magnetrons, which I view as having little or no chance of generating what I would call “accelerator grade rf. ” I hope this will not offend anyone. 2. CW AND LONG PULSE AMPLIFIER