Shock Ignition Laser-Plasma Interactions in Ignition-Scale Plasmas

We use a subignition scale laser, the 30 kJ Omega, and novel shallow-cone target to study laser-plasma interactions at ablation-plasma density lengths laser intensities anticipated for direct drive shock-ignition implosions National Ignition Facility scale. Our results show that, under these conditions, dominant instability is convective stimulated Raman scatter with experimental evidence of two plasmon decay (TPD) only when length reduced. Particle-in-cell simulations indicate this due TPD being shifted lower densities, removing back-scatter signature reducing hot-electron temperature. The energy-coupling hot electrons was found be 1%--2.5%, electron temperatures between 35 45 keV. Radiation-hydrodynamics employing characteristics that they should not preheat fuel in MJ-scale shock ignition experiments.