Dispersion based beam tilt correction

TL;DR

This paper proposes a dispersion-based correction method for beam tilt in Free Electron Lasers, utilizing sextupole, quadrupole, and skew quadrupole magnets to improve FEL performance by reducing slice misalignments.

Contribution

It introduces a novel correction scheme using magnetic elements in dispersive sections to mitigate slice misalignments in FELs, validated through simulations and measurements.

Findings

Effective correction of slice misalignments demonstrated

Simulation and experimental results confirm scheme viability

Improved FEL performance potential

Abstract

In Free Electron Lasers (FEL), a transverse centroid misalignment of longitudinal slices in an electron bunch reduces the effective overlap between radiation field and electron bunch and therefore the FEL performance. The dominant sources of slice misalignments for FELs are the incoherent and coherent synchrotron radiation within bunch compressors as well as transverse wake fields in the accelerating cavities. This is of particular importance for over-compression which is required for one of the key operation modes for the SwissFEL planned at the Paul Scherrer Institute. The centroid shift is corrected using corrector magnets in dispersive sections, e.g. the bunch compressors. First and second order corrections are achieved by pairs of sextupole and quadrupole magnets in the horizontal plane while skew quadrupoles correct to first order in the vertical plane. Simulations and measurements at the SwissFEL Injector Test Facility are done to investigate the proposed correction scheme for SwissFEL. This paper presents the methods and results obtained.