Microbunch rotation for hard x-ray beam multiplexing∗

Electron bunches in an undulator develop periodic density modulations, or microbunches, which enable the exponential gain of X-ray power in a SASE FEL. Many FEL applications could ����from the ability to preserve microbunching through a dipole kick. For example, X-ray beam multiplexing can be achieved if electron bunches are kicked into separate beamlines and allowed to lase in a ���undulator. The microbunches developed in upstream undulators, if properly rotated, will lase � axis, producing radiation at an angle ���from the initial beam axis. Microbunch rotation with soft X-rays was previously published and demonstrated experimentally [1], multiplexing LCLS into three X-ray beams. Additional 2018 data demonstrated multiplexing of hard X-rays. Here we describe ��� ts to reproduce these hard X-ray experiments using an analytical model and Genesis simulations. Our goal is to apply microbunch rotation to outcoupling from a cavity-based XFEL, (RAFEL/XFELO) [2].