The effect of fast electron scattering on determining the laser-induced electron divergence

Summary form only given. Characterization of the divergence of fast electrons accelerated by the interaction of an intense, ultrafast laser and an over-dense plasma is essential to the development of fast ignition. Numerical calculations using the hybrid-PIC code LSP and the Monte-Carlo code MCNP have been performed to determine which physical processes dominate the divergence of fast electron beams propagating in solid targets. The divergence is influenced by the electron acceleration mechanism, the pre-plasma that forms in front of the target and the self-generated fields associated with the electron beam. A canonical way to measure the electron beam divergence is by imaging the electron-stimulated K-alpha emission from buried fluorescent layers located at different depths within the target. Scattering of the electrons results in a transverse expansion of the electron distribution and consequently an increase in the diameter of the x-ray spot. We are conducting numerical calculations to establish the role of scattering on the fast electron distribution and x-ray emission, especially the effect on the angular deviation from collisions with ions. A source of electrons, based on the prescription of Debayle et al., is launched into the target and the subsequent density of the x-ray production and the electron energy deposition versus transverse distance is calculated at various depths. LSP indicates that the electron distribution is influenced by scattering, leading us to infer that other analyses that do not include fast electron scattering could be misleading. The angular divergence induced by scattering of electrons from different sources is estimated according to MCNP results.