Coherence properties and diagnostics of betatron radiation emitted by an externally-injected electron beam propagating in a plasma channel

B Paroli,E Chiadroni,M Ferrario,A Mostacci,V Petrillo,M.A.C Potenza,A.R Rossi,L Serafini

doi:10.1016/j.nimb.2015.03.070

Abstract

A 3-dimensional time-domain simulation of X-ray produced by a laser wakefield accelerated electron beam was performed in order to know its properties like intensity, spectrum, divergence and coherence. Particular attention was paid to the coherence around the acceleration axis. The broad spectrum of betatron radiation (1–10keV) leads to a short coherence length. Nevertheless we observe that under particular detection condition the spatial coherence has a characteristic enlargement. We give a simplified interpretation of this effect in terms of phase shift of the electric field on a virtual detector. Moreover we describe a near field scattering technique to characterize the betatron radiation. This diagnostics will be used to map the transverse spatio-temporal coherence of X-ray radiation in the laser wakefield accelerator under development at Frascati National Laboratories (LNF).

Highlights

Laser wakefield acceleration has recently been exploited to produce femtosecond X-ray bursts with low divergence and high brightness [1,2]
In this work we present recent results about a 3-dimensional time-domain simulation of the radiation emitted by a low emittance (2.7 mm mrad) 14 pC electron beam with 3.5 lm size and 78 MeV initial energy
We describe the diagnostics under development at the University of Milan to measure the coherence of radiation emitted by laser wakefield acceleration

Summary

Introduction

Laser wakefield acceleration has recently been exploited to produce femtosecond X-ray bursts with low divergence and high brightness [1,2]. L0 is the distance between the bunch and an arbitrary off-axis point of the detector, while L is the bunch-detector distance along the acceleration axis In such condition an enlargement of the coherence area is significantly observed. This phenomenon can be interpreted studying the phase shift of the simulated electric field on the curved detector as a function of the observation angle. We discuss about the optical diagnostics under development at the University of Milan in collaboration with Frascati National Laboratories to detect the X-ray radiation emitted by electron during acceleration.

Simulation method and results

Near field scattering diagnostics

Conclusions