Design of a Dogleg Bunch Compressor for Free Electron Lasers
Wai-Keung Lau1*, Nuan-Ya Huang1, Juhao Wu2, Chia-Hsiang Chen1
1National Synchrotron Radiation Research Center, Hsinchu, Taiwan
2SLAC National Accelerator Laboratory, Menlo Park, USA
* Presenter:Wai-Keung Lau,
A nonlinear bunch compressor is designed for the NSRRC 300 MeV S-band photoinjector linac system which will be used to drive a VUV seeded free electron laser. It is a double dog-leg configuration that provides a first order longitudinal dispersion function (i.e. R56) with a sign opposite to that of a conventional four-dipole chicane. Linearization optics is employed to correct the effects of nonlinear energy chirps on electron distribution in longitudinal phase space. The design strategy of this compressor is elaborated by analytical theory and verified by particle tracking simulation. Beam dynamics in the linac system including collective effects such as space charge, wake fields and coherent synchrotron radiation (CSR) are also studied. A large variation in the bunch length or the peak current for various operation conditions can be done by tuning R56. This can be realized by changing the longitudinal positions of the outside dipoles and adjusting the quadrupoles and sextupoles settings for desired bunch compression. Residual energy chirp left after bunch compression as revealed from ELEGANT simulation can be mitigated by a capacitive dechirper structure when the bunch is slightly over-compressed. Expected performance of the NSRRC VUV FEL with IU22 planar undulator predicted by GENESIS simulation will be presented. Tolerances of this bunch compressor due to jitters and fluctuations are also analyzed.

Keywords: high brightness electron beam, bunch compression, free electron lasers