Deflecting RF cavity design for a Recirculating Linac based facility for Ultrafast X-ray Science (LUX)

We report on superconducting deflecting RF cavity designs for a Recirculating Linac Based Facility for Ultrafast X-ray Science (LUX) at Lawrence Berkeley National Laboratory. The deflecting cavities operate in the lowest dipole mode and are required to produce a temporal correlation within flat electron bunches, as needed for X-ray compression in crystal optics. Deflecting voltage of up to 8.5 MV is required at 3.9 GHz. We present a 7-cell cavity design in this paper. Seven such cavities are required to generate the 8.5 MV deflecting voltage. Longitudinal and transverse impedance from LOM's (lower order mode) and HOM's (higher order mode) are simulated using the MAFIA code. Short-range and long-range wakefields excited through these impedances are calculated. Beam loading effects of the deflecting mode and parasitic modes are estimated. Q values of the LOM monopole modes in the cavity need to be damped to be below 10/sup 4/-10/sup 5/ levels in order to maintain the required energy spread.