Using beam phasing and pointing to control indirect drive implosion symmetry*

Implosions using inertial confinement fusion must be symmetric to achieve ignition on the NIF. This requires precise control of the drive symmetry incident on the ignition capsule. We performed two studies, using either beam pointing, or power imbalance [phasing] of three cones from the OMEGA laser to affect the symmetry of an imploded capsule. For pointing we used a NIF 0.7 scale vacuum-hohlraum and D$_{2}$-filled 1400 $\mu $m CH capsules to verify the technique. We captured images at different times for different pointings of the inner and middle laser cones, verifying the technique and demonstrating symmetry tuning. For phasing, a 1/4 scale NIF vacuum-hohlraum was used to drive a 475 $\mu $m diameter D$_{2}-^{3}$He-filled capsule. Imaging of the imploded core was used to measure the implosion symmetry and to verify its control. We also show that propagation of the inner beam cone is important, even in a vacuum hohlraum, and has the largest effect on the hohlraum energetics.