Ponderomotive Acceleration by Relativistic Waves

TL;DR

This paper explores how ponderomotive acceleration dominates electron energy gain in extremely high-intensity electromagnetic waves in plasma, especially when the wave's vector potential far exceeds unity, with implications for cosmic ray and laser acceleration.

Contribution

It demonstrates that in the extreme high intensity regime, ponderomotive acceleration surpasses wakefield acceleration, with energy gain proportional to the square of the vector potential, extending understanding of plasma acceleration mechanisms.

Findings

Energy gain scales with a_0^2 in extreme regimes

PA can dominate WA at very high intensities

Signature features depend on mass ratio and spectral properties

Abstract

In the extreme high intensity regime of electromagnetic (EM) waves in plasma, the acceleration process is found to be dominated by the ponderomotive acceleration (PA). While the wakefields driven by the ponderomotive force of the relativistic intensity EM waves are important, they may be overtaken by the PA itself in the extreme high intensity regime when the dimensionless vector potential $a_0$ of the EM waves far exceeds unity. The energy gain by this regime (in 1D) is shown to be (approximately) proportional to $a_0^2$. Before reaching this extreme regime, the coexistence of the PA and the wakefield acceleration (WA) is observed where the wave structures driven by the wakefields show the phenomenon of multiple and folded wave-breakings. Investigated are various signatures of the acceleration processes such as the dependence on the mass ratio for the energy gain as well as the energy spectral features. The relevance to high energy cosmic ray acceleration and to the relativistic laser acceleration is considered.