Bright betatron radiation from direct-laser-accelerated electrons at moderate relativistic laser intensity

O N Rosmej,M Gyrdymov,N E Andreev,F Barbato,N G Borisenko,L Antonelli,S Zähter,M M Günther,X F Shen,A Pukhov,V S Popov

doi:10.1063/5.0042315

Abstract

Direct laser acceleration (DLA) of electrons in a plasma of near-critical electron density (NCD) and the associated synchrotron-like radiation are discussed for moderate relativistic laser intensity (normalized laser amplitude a0 ≤ 4.3) and ps length pulse. This regime is typical of kJ PW-class laser facilities designed for high-energy-density (HED) research. In experiments at the PHELIX facility, it has been demonstrated that interaction of a 1019 W/cm2 sub-ps laser pulse with a sub-mm length NCD plasma results in the generation of high-current well-directed super-ponderomotive electrons with an effective temperature ten times higher than the ponderomotive potential [Rosmej et al., Plasma Phys. Controlled Fusion 62, 115024 (2020)]. Three-dimensional particle-in-cell simulations provide good agreement with the measured electron energy distribution and are used in the current work to study synchrotron radiation from the DLA-accelerated electrons. The resulting x-ray spectrum with a critical energy of 5 keV reveals an ultrahigh photon number of 7 × 1011 in the 1–30 keV photon energy range at the focused laser energy of 20 J. Numerical simulations of betatron x-ray phase contrast imaging based on the DLA process for the parameters of a PHELIX laser are presented. The results are of interest for applications in HED experiments, which require a ps x-ray pulse and a high photon flux.

Highlights

Synchrotron-like radiation generated by electrons during laserplasma acceleration is characterized by a broadband x-ray spectrum with a small divergence and a high brilliance
Direct laser acceleration (DLA) of electrons in a plasma of near-critical electron density (NCD) and the associated synchrotron-like radiation are discussed for moderate relativistic laser intensity and ps length pulse
An ultrahigh x-ray photon number of ∼7 3 1011 is predicted by numerical simulations performed for the laser and target parameters used in the experiment [Elas ≃ 80 J (EFWHM ≃ 20 J), 0.7 ps, a0 4.2, and a target consisting of a 300 μm long NCD layer with electron density 6.5 3 1020 cm−3]

Summary

INTRODUCTION

Scitation.org/journal/mre and divergence angle, depend on the mechanism of electron acceleration, the electron energy distribution, and the charge carried by electrons. Electrons confined in the focusing phase of the plasma wake experience transverse betatron oscillations, emitting highly collimated synchrotron x-rays In such experiments, the charge carried by electrons is far below the nC level, and the number of photons around the critical energy Ec of some keV does not exceed 109. NCD plasma at moderate relativistic laser intensity, for parameters typical of kJ PW-class laser facilities currently in operation, and demonstrate the feasibility of a direct laser acceleration (DLA)-based betatron source that promises an ultrahigh number of x-ray photons for applications in high-energy-density (HED) research.

DLA IN PLASMA OF NEAR-CRITICAL DENSITY

PIC SIMULATIONS OF BETATRON RADIATION

22 Current work

X-RAY PHASE CONTRAST IMAGING SIMULATIONS FOR PHELIX

CONCLUSION