Laser--Plasma Coupling Near Critical Density in Direct-Drive ICF Plasmas

Laser--plasma coupling near the critical density has a major effect on absorption and heat transport in direct-drive inertial confinement fusion (ICF) plasmas. The characteristic features of the near-critical-density region are steep gradients of plasma density and temperature. This region also includes turning points for laser beams, and laser--plasma coupling is influenced by interference between multiple incident and reflected beams. Modeling with the laser--plasma interaction code\footnote{ A. V. Maximov \textit{et al}., Phys. Plasmas \textbf{11}, 2994 (2004).} for nonlinear beam propagation near the beam turning points allows us to study the generation of magnetic fields caused by crossing gradients of temperature and laser-driven density perturbations, and also the structure of $p$-polarized laser fields that affect the resonance absorption. The modification of transport by laser-driven magnetic fields together with the effect of the laser field on the electron-distribution function are implemented in the hydrodynamic modeling. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-92SF19460.