Femtosecond X-ray Pulses from a Spatially Chirped Electron Bunch in a SASE FEL

We propose a simple method to produce short x-ray pulses using a spatially chirped electron bunch in a SASE FEL. The spatial chirp is generated using an rf deflector which produces a transverse offset (in y and/or y′) correlated with the longitudinal bunch position. Since the FEL gain is very sensitive to an initial offset in the transverse phase space at the entrance of the undulator, only a small portion of the electron bunch with relatively small transverse offset will interact significantly with the radiation, resulting in an x-ray pulse length much shorter than the electron bunch length. The x-ray pulse is also naturally phase locked to the rf deflector and so allows high precision timing synchronization. We discuss the generation and transport of such a spatially chirped electron beam and show that tens of femotsecond long pulse can be generated for the linac coherent light source (LCLS). Contributed to 25th International FEL Conference and 10th FEL Users Workshop Tsukuba, Ibaraki, Japan September 8 – September 12, 2003 * Work supported by Department of Energy contract DE–AC03–76SF00515. Femtosecond X-ray Pulses from a Spatially Chirped Electron Bunch in a SASE FEL P. Emma and Z. Huang* Stanford Linear Accelerator Center, Stanford University, CA 94309, USA