A superconducting linac driver for the Wisconsin free electron laser

We present an initial design of the driver for the Wisconsin VUV/Soft Xray FEL facility, which will provide high intensity coherent photons from 5 eV to 0.9 keV. It uses a 2.2 GeV, L-band CW superconducting linac with a 1.7 GeV tap-off to feed the lower energy FELs. In order to support multiple high rep-rate FELs, the average design current is 1 mA. Sub-nanocoulomb bunches with normalized transverse emittances of order 1 mum are generated in a photoinjector for beamlines operating at repetition rates from kHz to MHz. Multistage bunch compression provides 1 kA peak current to the FELs, with low energy spread and a suitable current profile. Compressed bunch lengths of order 100 fs will allow generation of photon pulses in the range 10 to 30 fs using seeded FELs. Consideration has been given to removing the residual energy chirp from the beam, and minimizing the effects of space charge, coherent synchrotron radiation, and microbunching instabilities. A beam switchyard using RF separators and fast kickers delivers the desired electron bunches to each of the FELs. Details of the design are presented, including those areas requiring the most development work.