Bunch compressor and de-compressor in the FEL for satellite power beaming

A FEL of average power 200 kW is being designed at the LBNL for satellite power beaming. It utilizes the radiation of ~100 MeV electrons with ~200 A peak current. In order to obtain the desired peak current, the 5 mm long electron bunches delivered by a linear accelerator are compressed to 1 mm. Furthermore, it is important for the FEL operations that the compressed bunches have a uniform longitudinal density distribution over the entire bunch length. After the FEL, the electron beam is returned to the linear accelerator for deceleration. Since the electron beam acquires approximately 6% energy spread during radiation in the FEL, bunch de-compressor is used between the FEL and the linac to expand the electron bunches back to its original length and to reduce the energy spread. In the paper we present the design and analysis of the bunch compressor and the bunch de-compressor that perform the needed functions