# Phase space dynamics of a plasma wakefield dechirper for energy spread reduction

## TL;DR

This paper demonstrates that a plasma wakefield dechirper can significantly reduce the energy spread of electron beams from linacs, achieving a tenfold decrease in energy spread through self wake effects.

## Contribution

The study introduces a plasma-based dechirper that effectively reduces energy spread in electron beams, with experimental and simulation validation showing substantial improvements.

## Key findings

- Reduced energy spread from 1.28% to 0.41% FWHM experimentally.
- Simulations indicate a final energy spread of about 0.13%.
- Achieved at least a threefold reduction in energy spread.

## Abstract

Plasma-based accelerators have made impressive progress in recent years. However, the beam energy spread obtained in these accelerators is still at ~ 1 % level, nearly one order of magnitude larger than what is needed for challenging applications like coherent light sources or colliders. In plasma accelerators, the beam energy spread is mainly dominated by its energy chirp (longitudinally correlated energy spread). Here we demonstrate that when an initially chirped electron beam from a linac with a proper current profile is sent through a low-density plasma structure, the self wake of the beam can significantly reduce its energy chirp and the overall energy spread. The resolution-limited energy spectrum measurements show at least a threefold reduction of the beam energy spread from 1.28 % to 0.41 % FWHM with a dechirping strength of ~ 1 (MV/m)/(mm pC). Refined time-resolved phase space measurements, combined with high-fidelity three-dimensional particle-in-cell simulations, further indicate the real energy spread after the dechirper is only about 0.13 % (FWHM), a factor of 10 reduction of the initial energy spread.