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 10⁴-10⁵ levels in order to maintain the required energy spread.