• C. Pellegrini, J.B. Rosenzweig, G. Travish
  UCLA, Los Angeles, California
• V.A. Dolgashev, C.D. Nantista, S.G. Tantawi
  SLAC, Menlo Park, California

Funding: US Department of Energy

We describe a proposed high-gain FEL using an X-band microwave undulator and operating at a wavelength of about 0.5 μm. The FEL electron beam energy is 65 MeV. The beam is produced by the NLCTA X-band linac at SLAC, using an S-band high-brightness photoinjector. The undulator consists of a circular waveguide with an rf wave counter-propagating with respect to the electron beam. The undulator is powered with two high-power X-band klystrons and a dual-moded pulse compressor recently developed at SLAC. This system is capable of delivering flat-top rf pulses of up to 400 ns and a few hundred megawatts. The equivalent undulator period is 1.4 cm, the radius of the circular pipe is 1 cm, and the undulator parameter is about 0.4 for a helical undulator configuration, obtained using two cross-polarized TE modes, or larger for a planar configuration, using one rf polarization. The undulator is about four meters long. The FEL will reach saturation within this distance when operated in a SASE mode. We describe the FEL performance parameters, the undulator characteristics and tolerances. One main goal of the experiment is to demonstrate the feasibility of an rf undulator for high gain FELs.