Generation of high-charge electron beam in a subcritical-density plasma through laser pulse self-trapping

TL;DR

This paper demonstrates how to generate high-charge electron beams in subcritical plasmas by optimizing laser pulse parameters to achieve self-trapping, supported by 3D PIC simulations and analytic theory, enabling high-yield particle production.

Contribution

It provides a validated method for producing high-charge electron beams via laser self-trapping in subcritical plasmas, combining simulation and analytic theory.

Findings

High-charge electron beams (multi-nC) achieved in subcritical plasma.

Optimal pulse length and parameters for self-trapping confirmed.

Potential for high-yield gamma, positron, and photonuclear particle production.

Abstract

To maximize the charge of a high-energy electron beam accelerated by an ultra-intense laser pulse propagating in a subcritical plasma, the pulse length should be longer than both the plasma wavelength and the laser pulse width, which is quite different from the standard bubble regime. In addition, the laser--plasma parameters should be chosen to produce the self-trapping regime of relativistic channeling, where the diffraction divergence is balanced by the relativistic nonlinearity such that the laser beam radius is unchanged during pulse propagation in a plasma over many Rayleigh lengths. The condition for such a self-trapping regime is the same as what was empirically found in several previous simulation studies in the form of the pulse width matching condition. Here, we prove these findings for a subcritical plasma, where the total charge of high-energy electrons reaches the multi-nC level, by optimization in a 3D PIC simulation study and compare the results with an analytic theory of relativistic self-focusing. A very efficient explicitly demonstrated generation of high-charge electron beams opens a way to a high-yield production of gammas, positrons, and photonuclear particles.