Modeling of possible hot-hohlraum targets for use in high-energy density experiments at the NIF

Abstract

The development of a hot-hohlraum platform to facilitate the experimental study of matter in extreme states is important for future high-energy density physics (HEDP) at the National Ignition facility (NIF). Specifically, HEDP experiments can be used to test the accuracy of current models and databases for the equation of state (EOS) and X-ray opacity of materials. In the past, both laser and Z-pinch experiments have been used to perform shock driven tests of EOS (in the 100 GPa to 1 TPa regime), and for radiation transparency experiments at conditions relevant to Inertial Confinement Fusion (ICF) and astrophysics. This work evaluates the use of the NIF laser for generating a thermal X-ray source for backlit opacity experiments. Using NIF, it should be feasible to generate radiation temperatures greater than currently possible. For comparison, one can consider recent opacity experiments performed at Sandia National Laboratory's Z facility. Here, a dynamic Z-pinch hohlraum initially produces radiations temperatures of ~200 eV that pre-heat an opacity sample. Later in time, the collapse of the Z-pinch on axis generates a ~300 eV source, which is used as a broadband X-ray backlighter. On NIF, two independent laser-heated half-hohlraums (or halfraums) can be used to obtain two independent source temperatures, equivalent to the Z temporal sources. Results from Lasnex simulations of the hotter halfraum (the continuous wavelength X-ray backlighter) will be described. Radiation temperatures of ~370 eV have been calculated assuming 200 kJ of laser energy deposited into a 1.6 mm diameter by 1 mm long halfraum. These temperatures require the smallest laser spot size available, which increases the possibility of laser-plasma interactions (LPI). These interactions may be the limiting factor in achieving the maximum halfraum temperatures. Estimates of the possible effect of LPI on this experiment, including comparisons with recent experiments at the Omega laser will be described.