Hydrodynamic instability and mix experiments at National Ignition Facility

Hydrodynamic growth and its effects on implosion performance and mix are being studied in hohlraum-driven implosions using gas-filled plastic shells at the National Ignition Facility (NIF). These experiments are motivated by observed elevated amounts of plastic mixed into the hot spot, degrading the performance of high-compression cryogenic DT layered implosions on NIF. Spherical shells with pre-imposed 2D modulations are being developed to measure Rayleigh-Taylor (RT) instability growth in the acceleration phase of implosions using in-flight x-ray radiography. Ablation-front RT growth measurements will be carried out for mode numbers ranging from 30 to 80 at drive conditions relevant to high-compression cryogenic implosions. In addition, implosion performance and mix are being studied at peak compression using plastic ``Symcap'' shells filled with tritium gas and imbedding localized CD diagnostic layer in various locations in the ablator. Neutron yield and ion temperature of the DT fusion reactions are used as a measure of shell-gas mix, while neutron yield of the TT fusion reaction is used as a measure of implosion performance. Experimental results and comparisons with 1D and 2D simulations, including mix models, will be presented.\\[4pt] This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.