Demonstration of 200-Mbar Ablation Pressure for Shock Ignition

The shock-ignition concept in inertial confinement fusion uses a high-power spike at the end of an assembly laser pulse, launching a strong shock wave with an ablation pressure of $\sim $0.3 Gbar that increases in strength as it converges in the imploding shell. A key milestone for shock ignition to be a credible path to ignition is to demonstrate the generation of a seed shock pressure 0.3 Gbar at laser intensities greater than $5\times 10^{15}$ W/cm$^{2}$. We demonstrate shock pressures close to 0.2 Gbar at $\sim 4\times 10^{15}$ W/cm$^{2}$ in OMEGA experiments with $\sim $500-$\mu $m-diam solid plastic ball targets doped with a small percentage of titanium. The strong shock wave converges in the center of the solid target and heats a small volume of $\sim 10^{3} \mu$m$^{3}$ to temperatures of several hundred eV, creating a short x-ray flash of titanium line emission. The emerging x-ray flash was measured with spatial and temporal resolution, allowing for the laser drive conditions to be inferred by comparison with hydrodynamic simulations. Hot-electron generation was also characterized by the measurement of K$_{\alpha }$ emission and hard x-ray emission. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.