Symmetry experiments in gas filled Hohlraums at Nova

Understanding drive symmetry in gas filled hohlraums is currently of interest because the baseline design of the indirect drive ignition target for the planned National Ignition Facility uses a gas filled hohlraum. We report on the results of a series of experiments performed at the Nova laser facility at Lawrence Livermore National Laboratory with the goal of understanding time dependent drive symmetry in gas filled hohlraums. Time dependent symmetry data from implosions in gas filled hohlraums will be discussed. The purpose of filling the hohlraum with gas is to tamp the motion of the high‐Z material ablating from the hohlraum walls, reducing the motion of the laser deposition regions and resultant temporal variations in drive symmetry. We have obtained time integrated and time resolved x‐ray images of the implosion of plastic deuterium filled capsules, neutron yields, implosion times and spectroscopy of argon emission from the imploded core. Preliminary results show that the gas is effective in impeding the motion of the wall blowoff material, and that the resulting implosion is in qualitative agreement with modeling. These experiments are relevant to those currently being planned for the National Ignition Facility.