Linac coherent light source (LCLS) at 2-4 nm using the SLAC linac

We describe the possible use of the SLAC linac to drive a unique, powerful, short wavelength Linac Coherent Light Source. Using the FEL principle, lasing is achieved in a single pass of a high peak current electron beam through a long undulator by self-amplified-spontaneous- emission (SASE). The main components are a high-brightness electron RF gun with a photocathode, two electron bunch length compressors, the existing SLAC linac, beam diagnostics, and a long undulator combined with a FODO quadrupole focusing system. The RF gun, to be installed about 1 km from the end of the SLAC linac, would produce a single bunch of 6 X 109 electrons with an invariant emittance of about 3 mm-mrad and a bunch length of about 500 micrometers . That bunch is then accelerated to 100 MeV and compressed to a length of about 200 micrometers . The main SLAC linac accelerates the bunch to 2 GeV where a second bunch compressor reduces the length to 30 - 40 micrometers and produces a peak current of 2 - 3 kA. The bunch is then accelerated to 7 - 8 GeV and transported to a 50 - 70 m long undulator. Using electrons below 8 GeV, the undulator could operate at wavelengths down to 2 nm, producing about 10 GW peak power in sub-ps light pulses.