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In this report, we present a simulation study of dielectric beam energy dechirper designed for the proposed NSRRC EUV FEL facility. As revealed from ELEGANT simulation of the high brightness driver linac system, a residual energy chirp of about 42 keV/m is left after bunch compression. It can be corrected by a capacitive dechirper structure when the bunch is slightly over-compressed. We successfully used a 1-m long corrugated pipe to remove the residual energy chirp in such simulation. However, in order to save space and for a simplified mechanical design, we consider also the usage of two orthogonally oriented planar dielectric-lined waveguide (DLW) structures to remove residual energy chirp after bunch compression. Wake fields due to this DLW dechirper has been calculated by CST code and the deduced wake function will be used in particle tracking using ELEGANT.

S.Y. Teng(1,2), S.H. Chen(1), W.Y. Chiang(2), M.C. Chou(2), H.P. Hsueh(2), W.K. Lau(2), A.P. Lee(2), P.T. Lin(3) 1 Department of Physics, NCU, Taoyuan, Taiwan 2 NSRRC, Hsinchu, Taiwan 3 Department of Engineering and System Science, NTHU, Hsinchu, Taiwan. Intense coherent THz radiation has been generated from an 18-period, hybrid-type U100 planar undulator as it is driven by short relativistic electron pulses produced from the NSRRC photoinjector. However, it is observed that the number of output optical pulse cycles is much less than the number of undulator periods and therefore the radiation spectral bandwidth has been broadened. It is found that the dispersion of undulator with excessive energy spread is responsible for this undesired broadening of THz radiation spectrum. In this study, instead of using rectilinear rf bunch compression (i.e. velocity bunching) in photoinjector linac, we investigate the feasibility of using nonlinear magnetic bunch compression for spectral bandwidth control of coherent THz undulator radiation.