Demonstrating Control of Symmetry Capsule Implosions in Omega Experiments using NIF 0.7-Scale Hohlraums

We have demonstrated the ability to detect the weak x-ray emission from, and control the imploded core shape of, large weakly-driven plastic capsules in NIF 0.7-scale hohlraums at the Omega laser. The capsules are similar to those that can be used to diagnose hohlraum radiation drive symmetry during the early stages (``foot'') of the drive in eventual NIF ignition experiments. Because the foot drive temperature is so low ($\sim $90 eV), it had been doubtful that capsule x-ray emission would be detectable. Because the capsule shells must be thin, making them hydrodynamically unstable and subject to complete ionization (``burnthrough'') before peak compression, it had been doubtful that their shape would respond to variations in laser beam pointing. We have now put those doubts to rest. These experiments used 1400-$\mu $m diameter CH shells, of thickness 15-20 $\mu $m, filled with 1 atm D$_{2}$, in 6.38 mm x 3.56 mm gold hohlraums. No higher-Z dopant was necessary to make the x-ray emission detectable.