Analysis of multibunch free electron laser operation

TL;DR

This paper investigates the intra-bunch-train transverse dynamics in multibunch free electron lasers at FLASH and European XFEL, analyzing how cavity operation impacts trajectory stability and FEL performance.

Contribution

It provides a detailed analysis of the relationship between superconducting RF cavity operation and intra-bunch-train trajectory variations in multibunch FELs.

Findings

Trajectory variation during multibunch operation is linked to RF intra-bunch-train variations.

Intra-bunch-train stability is crucial for FEL performance.

Analysis informs improvements in cavity operation for better FEL stability.

Abstract

At the SASE-FEL user facilities FLASH and European XFEL, superconducting TESLA type cavities are used for acceleration of the driving electron bunches. The high achievable duty cycle allows for operating with long bunch trains, hence considerably increasing the efficiency of the machine. However, multibunch free electron lasers (FEL) operation requires longitudinal and transverse stability within the bunch train. The purpose of this work is to investigate the intra-bunch-train transverse dynamics at FLASH and European XFEL. Key relationships of superconducting rf cavity operation and the resulting impact on the intrabunch-train trajectory variation are described. The observed trajectory variation during multibunch user runs at FLASH is analyzed and related to both, intrabunch-train variations of the rf and the following impact on the multibunch FEL performance.