Ponderomotive acceleration by relativistic waves

C K Lau,O Luk,P C Yeh,T Ebisuzaki,T Tajima,J Mcclenaghan

doi:10.1103/physrevstab.18.024401

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.

Highlights

Extreme high energy cosmic rays ([1] extending beyond 1020 eV and certainly beyond the Greisen-ZatsepinKuzmin cutoff [2,3]) attract contemporary interest, because these high energy particles continue to arrive and, the genesis of them remains a puzzle
While the wakefields driven by the ponderomotive force of the relativistic intensity EM waves are important, they may be overtaken by the ponderomotive acceleration (PA) itself in the extreme high intensity regime when the dimensionless vector potential a0 of the EM waves far exceeds unity
We have demonstrated the robust mechanism of particle acceleration in the regime of very high intensity (a0 ≫ 1)

Summary

INTRODUCTION

Extreme high energy cosmic rays ([1] extending beyond 1020 eV and certainly beyond the Greisen-ZatsepinKuzmin cutoff [2,3]) attract contemporary interest, because these high energy particles continue to arrive and, the genesis of them remains a puzzle. Ebisuzaki and Tajima revisited such philosophy and developed new insight into large energy releasing astrophysical phenomena [8] These studies are based on better understood energy release mechanisms in astrophysical objects such as accretion disks of BH and active galactic nuclei [13]. Such an energy release of a large amount in a very short period of time is amenable to the process of wakefield excitations, as considered by Refs. Ebisuzaki and Tajima [8] identified the most important process as the ponderomotive acceleration Based on this, they built a theory for the extreme high energy cosmic ray acceleration and some observational correlations. We shall describe the simulation approach and its characteristics results in detail

Description of simulation

SCALING LAWS OF ENERGY GAIN

ENERGY SPECTRA AND THEIR IMPLICATIONS

CONCLUSION