Coupling Effects in Multistage Laser Wake-field Acceleration of Electrons

Zhan Jin,Naveen Pathak,Hirotaka Nakamura,Alexei Zhidkov,Ryosuke Kodama,Tomonao Hosokai,Keiichi Sueda,Yasuo Sakai

doi:10.1038/s41598-019-56654-x

Abstract

Staging laser wake-field acceleration is considered to be a necessary technique for developing full-optical jitter-free high energy electron accelerators. Splitting of the acceleration length into several technical parts and with independent laser drivers allows not only the generation of stable, reproducible acceleration fields but also overcoming the dephasing length while maintaining an overall high acceleration gradient and a compact footprint. Temporal and spatial coupling of pre-accelerated electron bunches for their injection in the acceleration phase of a successive laser pulse wake field is the key part of the staging laser-driven acceleration. Here, characterization of the coupling is performed with a dense, stable, narrow energy band of <3% and energy-selectable electron beams with a charge of ~1.6 pC and energy of ~10 MeV generated from a laser plasma cathode. Cumulative focusing of electron bunches in a low-density preplasma, exhibiting the Budker–Bennett effect, is shown to result in the efficient injection of electrons, even with a long distance between the injector and the booster in the laser pulse wake. The measured characteristics of electron beams modified by the booster wake field agree well with those obtained by multidimensional particle-in-cell simulations.

Highlights

The laser wake-field acceleration (LWFA) of electrons is one of the rapidly developing scientific fields of the last decade[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17]
The transverse size of a laser wake field is limited by the value of a0, which is necessary for efficient acceleration and implies an upper limit on the value of the laser pulse waist, w0
The longitudinal size of the acceleration field is determined by the plasma electron density: the smaller the electron density is, the longer the wave of the laser pulse wake

Summary

Introduction

The laser wake-field acceleration (LWFA) of electrons is one of the rapidly developing scientific fields of the last decade[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17]. It is clear that if the bunch transverse size exceeds the laser pulse diameter in the focus spot, an essential part of the injected electron cannot be accelerated. The injection efficiency of an electron bunch with a diameter of ~1 mm into a wake generated by a laser pulse with a focus spot of ~20 μm is only 0.04% or almost zero. This coupling cannot be estimated using only the geometrical emittance of bunches. To understand the details of the effects, we perform multidimensional particle-in-cell simulations for both temporal coupling and electron focusing in various plasmas

Methods

Results

Conclusion