High current RF accelerator for FEL applications

It is shown that the HCRF (high-current radio-frequency) concept promises to achieve an average gradient on the orders of 20 MV/m using standard conductors and low Q cavities. Therefore, relatively low technology, robust construction techniques can be used for the accelerator, and risk is reduced accordingly. Initial analysis of two critical issues, accelerator efficiency and beam quality, is presented. The concept uses high peak power (approximately 10-GW) microwaves to drive low-Q RF cavities. The cavities are designed to selectively damp modes that lead to transverse beam-breakup instabilities in the accelerator. The high power microwaves will be generated in external devices such as phase stable klystron amplifiers driven by relativistic electron beams. The HCRF accelerator will produce a 200-MeV FEL (free-electron laser) quality electron beam with 1500 2-kA, 50-ps micropulses contained in 50-A (average current), 3-μs macropulses that are repeated every 300 μs. Average electron beam power into the wiggler will be 100 MW, and the overall duty factor is 2.5×10^-4