The effect of inner-surface roughness of conical targets on the generation of fast electrons in the laser-cone interaction is investigated using particle-in-cell simulation. It is found that the surface roughness can reduce the fast-electron number （in the energy range E 〉 1 MeV） and energy, as compared to that from a cone with smooth inner wall. A scaling law for the laser reflectivity based on the vacuum-heating model is derived. Both theory and simulation indicate that laser reflection increases with the height-to-width ratio of the periodic inner surface structure and approaches that of a smooth cone as this ratio becomes zero.
A two-dimensional hybrid code is developed to model the transport of a high-current electron beam in a dense plasma target. The beam electrons are treated as particles and described by particle-in-cell simulation including collisions with the target plasma particles. The background target plasma is assumed to be a stationary fluid with temperature variations. The return current and the self-generated electric and magnetic fields are obtained by combining Amp^re＇s law without the displacement current, the resistive Ohm＇s law and Faraday＇s law. The equations are solved in two-dimensional cylindrical geometry with rotational symmetry on a regular grid, with centered spatial differencing and first-order implicit time differencing. The algorithms implemented in the code are described, and a numerical experiment is performed for an electron beam with Maxwellian distribution ejected into a uniform deuterium-tritium plasma target.
We discuss stimulated Raman scattering (SRS) and stimulated Brillouin scattering (SBS) under the convective instability condition with a one-dimensional three-wave interaction (3WI) model.Using linear theory,we deduce the temporal growth rate,gain exponent,and reflectivity of the backward scattered wave in a finite interaction region.We find that the growth rate is not only determined by the laser intensity and plasma density and temperature,but also related to the spatial gain.The length of the interaction region is important to the gain exponent and backscattering level.We simulate the developments and evolutions of SRS and SBS based on the 3WI equations.Our numerical results consist with the linear theory.
HAO LiangLIU ZhanJuZHENG ChunYangXIANG JiangFENG WuHU XiaoYanLI Bin
