Measurements of wake-induced electron beam deflection in a dechirper at the Linac Coherent Light Source

TL;DR

This paper presents the first systematic measurements of wake-induced electron beam deflections in a dechirper at LCLS, comparing experimental data with analytical models, and exploring transverse wakefield effects for beam diagnostics.

Contribution

It provides the first detailed measurements of transverse wakefields in a dechirper with high-energy, short-pulse electron beams, validating analytical models.

Findings

Good agreement between measurements and analytical formulas.

Transverse wakefields depend on beam offset and proximity to a single plate.

Results enable improved beam diagnostics using wakefield effects.

Abstract

The RadiaBeam/SLAC dechirper, a structure consisting of pairs of flat, metallic, corrugated plates, %a corrugated structure in flat geometry, has been installed just upstream of the undulators in the Linac Coherent Light Source (LCLS). As a dechirper, with the beam passing between the plates on axis, longitudinal wakefields are induced that can remove unwanted energy chirp in the beam. However, with the beam passing off axis, strong transverse wakes are also induced. This mode of operation has already been used for the production of intense, multi-color photon beams using the Fresh-Slice technique, and is being used to develop a diagnostic for attosecond bunch length measurements. Here we measure, as function of offset, the strength of the transverse wakefields that are excited between the two plates, and also for the case of the beam passing near to a single plate. We compare with analytical formulas from the literature, and find good agreement. This report presents the first systematic measurements of the transverse wake strength in a dechirper, one that has been excited by a bunch with the short pulse duration and high energy found in an X-ray free electron laser.