Design of an S-band parallel-coupled transverse deflecting cavity with variable polarization for multi-dimensional phase space diagnostics in photoinjectors

Beam quality from photoinjectors is crucial for lasing in Free Electron Laser (FEL) facilities. While phase space measurement are usually limited to 2D with conventional methods, the recently-developed transverse deflecting cavities (TDCs) with variable polarization provide the capability to measure multi-dimensional phase space information. Such information could guide the improvement of beamline setup for optimal lasing performance. We therefore propose an S-band parallel-coupled TDC, in which two chains that deflect beam horizontally and vertically are independently fed by waveguides and variable polarization can be obtained by adjusting their relative amplitude and phase. This design offers several advantages, including tunability, single-frequency operation, compactness, and high shunt impedance. In this manuscript, physical and mechanical design of this TDC as well as the planned proof-of-principle experiment will be presented in detail.