Shock Ignition - an alternative concept for laser fusion

Shock-ignition (SI) [R. Betti et al., PRL 98, 155001 (2007)] is an advanced concept in inertial confinement fusion, which promises relaxed ignition conditions compared to the conventional hot-spot concept. SI is based on a two-step scheme, which separates the fuel compression from the ignition phase by applying a shaped laser pulse. The laser pulse with duration of several nanoseconds is formed in such a way that at the end an intense spike launches a strong shock wave into the imploding capsule, which leads to ignition. A critical component is the seed pressure that is generated by the spike with intensity ~5×1015-1016 W/cm2, which depends on the energy coupling into the target. The laser-energy coupling is currently not well understood at high spike intensities. This presentation discusses experiments on the OMEGA laser studying the produced seed pressures and the effect of supra-thermal electrons in planar and spherical geometries at SI relevant laser intensities. We demonstrate ablation pressures >370 Mbar with absorbed intensity of 3×1015 W/cm2 that surpass the 300-Mbar requirement for shock ignition. The spherical target experiments produce a large quantity of hot electrons which augment the shock.