Multi-objective optimization of the matching beamline for external injection into a laser-driven plasma accelerator

E Panofski,E N Svystun,R W Assmann

doi:10.1088/1742-6596/1596/1/012041

Abstract

Accelerators based on laser plasma wakefield acceleration are of great interest for a new generation of compact machines. External injection of an electron beam from an RF injector into a plasma accelerating stage has the advantage that a well-controlled and fully characterized beam can be used. The matching of the electron bunches into an accelerating plasma wakefield places high demands on the electron beam quality. The electron beam size must be extremely small to match the field structure inside the plasma wake. The short period of the accelerating field in the plasma requires a bunch length in the (sub-)fs range. These electron beam properties result in a high electron density and strongly space charge dominated bunches. The beamline upstream of the plasma must be able to control the significant effect of space charge on the bunch and to transversely match the beam to the focusing fields of the plasma. Further constraints to the beamline design are given by the in-coupling of the high-power drive laser and the implementation of diagnostic tools. Choosing suitable settings for the beamline elements in order to match the beam thus poses a great challenge. Using multi-objective optimization, suitable settings for the beamline elements can be extracted from Pareto optimum solutions. The development of a universal multi-objective optimization algorithm for beamline matching as well as first optimization results are presented.

Highlights

Summary and Outlook This paper presents a newly developed optimization tool based on a multi-objective genetic algorithm
The program finds stable settings for a focusing system to transversally match an electron beam into a plasma accelerator. It allows to map out the physical limits of the matching area and the focusing system
Since the calculation of the electron beam parameters is done with a standard particle tracking tool, different focusing strategies can be tested and optimized with the introduced optimizer

Summary

Introduction

The beamline upstream of the plasma must be able to control the significant effect of space charge on the bunch and to transversely match the beam to the focusing fields of the plasma. Strong transverse focusing elements are required to externally match the beam into the plasma. Because of the ultrashort bunch length and resulting space charge (SC) forces, its focusing is limited to β-functions at the plasma entrance of more than one magnitude larger than the matched value.

Results

Conclusion