Wakefields studies for the SXFEL user facility

TL;DR

This paper investigates the impact of undulator wakefields on beam energy and FEL performance at the SXFEL facility, proposing measurement methods and discussing compensation techniques to optimize laser output.

Contribution

It provides numerical analysis of wakefield-induced energy deviations and explores wakefield effects on FEL performance, including compensation strategies.

Findings

Beam energy deviation due to wakefields is quantified.

Wakefields degrade FEL pulse energy and spectrum.

Tapering the undulator field can mitigate wakefield effects.

Abstract

Besides the original seeded undulator line, in the Soft X-ray free-electron laser (SXFEL) user facility at Shanghai, a second undulator line based on self-amplified spontaneous emission is proposed to achieve 2 nm laser pulse with extremely high brightness. In this paper, the beam energy deviation induced by the undulator wakefields is numerically obtained, and it is verified to have a good agreement between 3D and 2D simulation results. The beam energy loss along the undulator degrades the expected FEL output performance. Impact of wakefields on pulse energy, radiation power and spectrum is discussed, as well as the benefits of compensation obtained with a taper in the undulator field. And using the planned SXFEL diagnostic, a longitudinal wakefields measurement experiment is proposed and simulated.