Arc-Like Variable Bunch Compressors

TL;DR

This paper introduces an innovative approach to electron bunch compression using arc-like variable bunch compressors, allowing adjustable longitudinal compression without significant chromatic degradation, beneficial for free-electron laser upgrades.

Contribution

It extends arc compressor utility to enable variable longitudinal compression independently in momentum deviation, using additional dipoles for minimal chromatic impact.

Findings

Variable compression achieved without significant chromatic degradation

Comparison shows dipole-based approach is advantageous over quadrupole methods

Application to MAX IV linac upgrade for soft X-ray FELs

Abstract

Electron bunch compressors formed of achromat arcs have a natural advantage over the more commonly used chicane compressors in that linearisation of the longitudinal phase space is of the correct sign to compensate for the curvature imprinted by rf acceleration. Here we extend the utility of arc compressors to enable variation of the longitudinal compaction within a fixed footprint. We also show that this variability can be achieved independently order-by-order in momentum deviation. The technique we employ consists of additional dipoles, leading to the advantageous property that variability can be achieved without incurring significant penalty in terms of chromatic degradation. We show this by comparison to an alternative system where additional quadrupoles are utilised to enable variation of momentum compaction. Each of these alternative approaches are being considered in the context of an upgrade of the MAX IV linac, Sweden, to enable a soft X-ray free-electron laser (FEL) in addition to its existing functions.