Developing a Shock-Ramp Laser Drive to Extend the Pressure Ranges of the NIF Gbar Platform Single-Shot Hugoniot Measurements

Recent Gbar experiments at the National Ignition Facility (NIF) utilize spherically converging shock waves to reach high pressures (>300 Mbar) inside hydrocarbon capsules. Equation of State (EOS) measurements are made as the propagating shock wave drives the hydrocarbon sample along its principal Hugoniot. Further improvements to the Gbar experimental platform are proposed by utilizing a new shock-ramp drive, where the sample is initially shocked then driven with a strong ramp increasing the shock pressure faster than a spherically converging single shock. The goal of the shock-ramp drive is to reach higher pressures within the material sample and increase the ranges of pressures provided in a single experiment. The impacts of the shock-ramp drive would extend the range in which the EOS models can be validated and reduce the number of shots needed to collect Hugoniot data. The shock-ramp drive was designed by modeling the hydrocarbon capsules in the ALE radiation-hydrodynamic code HYDRA. Capsule parameters accounting for the geometry, materials, and laser drive were included in the HYDRA modeling. We present the parameter scan results to illustrate the possible pressure ranges achievable with the shock-ramp drive on the NIF Gbar platform. These findings will be used in upcoming experiments to improve Hugoniot measurements of CH at extreme pressures.