Demonstration of passive plasma lensing of a laser wakefield accelerated electron bunch

S Kuschel,B Hidding,M Zepf,M Yeung,A Knetsch,O Karger,D Hollatz,M Leier,Alexander Sävert ,Alexander Blinne ,D J Corvan ,Stefan Karsch ,M B Schwab ,Thomas Heinemann ,Daniel Ullmann ,Christian Rödel ,Hao Ding ,Malte C Kaluza ,Thomas Kurz ,Andreas Seidel

doi:10.1103/physrevaccelbeams.19.071301

Abstract

We report on the first demonstration of passive all-optical plasma lensing using a two-stage setup. An intense femtosecond laser accelerates electrons in a laser wakefield accelerator (LWFA) to 100 MeV over millimeter length scales. By adding a second gas target behind the initial LWFA stage we introduce a robust and independently tunable plasma lens. We observe a density dependent reduction of the LWFA electron beam divergence from an initial value of 2.3 mrad, down to 1.4 mrad (rms), when the plasma lens is in operation. Such a plasma lens provides a simple and compact approach for divergence reduction well matched to the mm-scale length of the LWFA accelerator. The focusing forces are provided solely by the plasma and driven by the bunch itself only, making this a highly useful and conceptually new approach to electron beam focusing. Possible applications of this lens are not limited to laser plasma accelerators. Since no active driver is needed the passive plasma lens is also suited for high repetition rate focusing of electron bunches. Its understanding is also required for modeling the evolution of the driving particle bunch in particle driven wake field acceleration.

Highlights

Linear accelerators reaching energies in the range of hundreds of MeV to GeV are typically large devices, their size determined by accelerating fields in the range of tens of MeV=m
We observe a density dependent reduction of the laser wakefield accelerator (LWFA) electron beam divergence from an initial value of 2.3 mrad, down to 1.4 mrad, when the plasma lens is in operation
We report the first demonstration of passive plasma focusing of a laser wakefield accelerated electron bunch resulting in an ultracompact, all-optical setup

Summary

INTRODUCTION

Linear accelerators reaching energies in the range of hundreds of MeV to GeV are typically large devices, their size determined by accelerating fields in the range of tens of MeV=m Focusing optics for these devices have been developed to high standards and operate on commensurate length scales. Plasma lenses have attracted notable interest in the literature because of their ability to provide compact beam collimation/focusing devices for energetic electron beams [7,8,9] These are of particular interest for the rapidly developing field of laser plasma accelerators. LWFA beams depart significantly from the parameter range where these devices have previously been considered Possible applications of such a compact collimating device include beam shaping for transport or injecting an electron beam into a conventional undulator structure [10,11,12]. Others include the generation of dense, 2469-9888=16=19(7)=071301(9)

Published by the American Physical Society

Δn n

Findings

CONCLUSION