Control of electron beam current, charge and energy spread using density downramp injection in laser wakefield accelerators

TL;DR

This paper demonstrates that by fine-tuning plasma density parameters in laser wakefield accelerators, it is possible to generate high-charge, low-energy-spread electron beams, advancing the control over beam quality and charge.

Contribution

The study reveals the direct correlation between plasma density transition parameters and the injected electron beam profile, enabling improved control of beam charge and energy spread.

Findings

High-charge electron beams up to several hundreds of pC achieved.

Low energy spread around 1% FWHM demonstrated.

Beam quality can be optimized through plasma density parameter tuning.

Abstract

Density dowmramp injection has been demonstrated to be an elegant and efficient approach for generating high quality electron beams in laser wakefield accelerators. Yet, the charge of the produced beam is tens of pC per Joule of laser energy, still limiting its use for a wider range of applications. The possibility of generating high charge beam while keeping a good beam quality, stays to be explored. Moreover, despite previous studies focused on separate physical processes such as beam loading which affects the uniformity of the acceleration field and thus the energy spread of the trapped electrons, repulsive force from the rear spike of the bubble which reduces the transverse momentum $p_\perp$ of the trapped electrons and results in small beam emmittance, and the laser evolution when travelling in plasma. A more general investigation of the plasma density parameters on the final beam properties is required. In this work, we demonstrate that the current profile of the injected electron beam is directly correlated with the density transition parameters, which further affects the beam charge and energy spread. By fine-tuning the plasma density parameters, high-charge (up to several hundreds of pC) and low-energy-spread (around 1\% FWHM) electron beams can be obtained. All these results are supported by large-scale three-dimensional particle-in-cell simulations.