Very long pulse high power klystrons for FEL and their generating conditions

Abstract

High power RF sources for major scientific machines (accelerators, plasma heating) are often either short pulse devices with very high peak power levels (e.g. 30-40 MW peak, 5μs pulses in S-band) or CW devices (e.g. 500 kW in S-band). Free electron lasers, on the other hand, require klystrons operating in a long-pulse mode (100 μs and 10 ms). In this case, the technology used in the two other cases (short pulse, CW) is not necessarily appropriate. When the peak power levels are very high in nearly-CW operation, new problems are encountered, for example thermal cycling and HV breakdown modes. The most critical parts are the output cavity, output window and the electron gun. We will discuss a family of 1·3 GHz klystrons as an example: 35-40 MW/10μs; 10-15 MW/200 μs and a few MW/1-10ms