Density Measurements of the Inner Shell Release*

In inertial confinement fusion implosions, the release of plasma off the inner surface of the target shell after the shock breakout is an important parameter to the performance of the design. If the release has a higher density or longer scale length than that predicted by hydrodynamic simulations, the mass increase in the hot spot can decrease its compressibility and reduce performance compared to what is expected from the simulations. Experiments on OMEGA EP at the Laboratory for Laser Energetics were performed to measure the plasma expanding on the back side of a CH shell driven by two UV laser beams with a total of 6 kJ of energy in a 5-ns pulse focused to a 750-mm spot. The peak position of the driven shell was tracked using x-ray radiography streaked over 4 ns. The low-density plasma expanding off the undriven side of the shell after the shock breaks through was measured using the 4ω interferometer and angular filter refractometer. The experimental data will be presented and compared to the hydrodynamic simulations using 2-D radiation–hydrodynamic code DRACO.