Flexible multi-bunch-length operation for continuous-wave x-ray free-electron lasers

TL;DR

This paper introduces a novel dipole-kicker method to vary electron bunch lengths in continuous-wave XFELs, enabling simultaneous multi-mode operation tailored to different undulator requirements.

Contribution

It proposes a new technique combining dipole-kickers with bunch compressors to optimize electron bunch length for diverse XFEL operation modes.

Findings

Feasibility demonstrated through start-to-end simulations.

Enables simultaneous self-amplified spontaneous emission and seeded FEL.

Optimizes electron bunch compression for different undulator lines.

Abstract

The X-ray free-electron lasers (XFELs) are cutting-edge instruments pivotal in a broad range of fields, providing high-power X-ray pulses with durations spanning from femtoseconds to attoseconds. One of the critical challenges in XFEL facilities is the simultaneous accommodation of diverse requirements for XFEL operation modes and photon properties across different undulator lines. This paper proposes a dipole-kicker combination in the bunch compressors to vary the electron bunch length for the continuous-wave XFEL facilities driven by a superconducting linac. This method enables optimization of the electron bunch length on a per-bunch basis, tailored to each specific needs of each undulator. Through start-to-end simulations based on the parameters of the Shanghai high-repetition-rate XFEL and extreme light facility, we demonstrate the feasibility of this technique. The results show its effectiveness in enabling simultaneous operations of self-amplified spontaneous emission and externally seeded FEL across different undulator lines, ensuring optimal electron bunch compression for each undulator line.