# Multi-beam-energy operation for the continuous-wave x-ray free electron laser

## TL;DR

This paper proposes a delay system with kickers for multi-beam-energy operation in continuous-wave XFELs, enabling flexible energy control of electron beams to improve facility efficiency.

## Contribution

A novel delay system design using four double bend achromats combined with kickers for energy modulation in continuous-wave XFELs.

## Key findings

- Able to control electron beam energy from 1.48 to 8.74 GeV
- Demonstrated flexible energy control via start-to-end simulations
- Enhances multi-beam operation efficiency in high-repetition-rate XFELs

## Abstract

The parallel operation of multiple undulator lines with a wide spectral range is an important way to increase the efficiency of x-ray free electron laser (XFEL) facilities, especially for machines with high-repetition-rate. In this paper, a delay system based on four double bend achromats is proposed to delay electron beams, thereby changing the arrival time of those delayed electron beams in the accelerating structure behind the system. Combined with kickers, the delay system can be used to generate bunch-to-bunch energy changed electron beams in a continuous wave XFEL facility. Start-to-end simulations based on the Shanghai high-repetition-rate XFEL and extreme light facility parameters are performed to demonstrate that the delay system can flexibly control electron beam energy from 1.48 to 8.74 GeV at the end of the linac.