Enhancement of high-energy electron generation through suppression of Raman backscattering

Abstract

The effect of Raman backscattering (RBS) on high-energy electron generation in laser-plasma interaction has been investigated for laser intensities well above the wave breaking and electron trapping threshold. One-dimensional particle-in-cell simulations show that suppression of RBS increases the high-energy electron yield in this regime. RBS-induced heating causes heavy beam loading and damping of the laser wake. Its suppression leads to higher wake amplitudes and higher particle energies. RBS suppression through direct stimulation of Raman forward scatter is demonstrated. The implications for high-energy electron production through laser-plasma interaction are discussed.Introduction. -Several recent experiments (see [1,2] and references therein) on the interaction of intense laser pulses with underdense plasmas have demonstrated the production of energetic electrons in the self-modulated regime of the laser wakefield accelerator (LWFA) with accelerating gradients in excess of 100 GV/m. The resulting electron bunches are characterized by high charge (up to 10 nC), sub-ps duration, and an exponential energy distribution which extends out to hundreds of MeV. Applications of these bunches include injectors to secondary accelerators [3], short-pulse radiation sources [4], short-lived radio-isotope production [5], and fast-ignition fusion [6].Raman forward (RFS) and backward (RBS) scattering are laser-plasma instabilities that govern the self-trapping and acceleration dynamics in the self-modulated LWFA. According to basic Raman scattering theory [7], RBS is a three-wave interaction, in which the incoming laser light (carrier frequency ω 0 , wave number k 0 , peak amplitude E 0 = (m e ω 0 c/e)a 0 ) decays into a backscattered electromagnetic (EM) wave (ω 0 − ω p , −(k 0 − k p )) and a slow Langmuir wave (ω p , 2k 0 − k p ). Here, ω p = n 0 e 2 /(ε 0 m e ), k p = ω p /c, and n 0 is the unperturbed plasma electron density. The Langmuir wave phase velocity is approximately ω p c/(2ω 0 ) c for an

On the effect of laser and plasma parameters on stimulated Raman scattering and fast-electron generation

“…In this paper, we investigate the role of Raman backscattering (RBS) in highenergy electron production and the interplay between RBS and Raman forwardscattering (RFS) in the high-intensity regime of a self-modulated LWFA [13]. In previous work [5,[14][15][16][17][18][19], it has been demonstrated that the presence of RBS leads to the production of mildly energetic electrons.…”