Compton scattering in the ALS booster

Femtosecond X-ray pulses may be generated by 90° Compton side scattering of a short visible laser beam by a well-focused relativistic electron beam. A proof-of-principle experiment is underway using the ALS linac. From this experiment an X-ray pulse of 10⁵ photons with a duration of 230 fs in a bandwidth of 10% at 10 Hz is expected. In this paper we explore using the ALS booster instead to increase the average X-ray flux. To generate the small beam size we plan to radiation damp electrons by accelerating them to 600 MeV and decelerate quickly to 50 MeV before intra-beam scattering can increase the beam size. We can achieve a vertical emittance of <5x10^-9 m-rad. With a small modification of the booster lattice it is possible to focus the beam to a vertical beta function of β_y*=10 cm. By reflecting the incident laser pulse many times we expect to be able to obtain an increase of the average X-ray flux