100s Mbar equation of state measurements on the National Ignition Facility - Equation of state data analysis

Experiments at the National Ignition Facility can give pressure-density relations for materials at extreme pressures. An experimental platform on which such measurements have been taken over the last few years consists of a physics package mounted on the side of a hohlraum. X-rays produced in the holhraum are absorbed by an ablator in the physics package, producing a planar high-pressure drive. This drive propagates through materials mounted on the package, and VISAR measures shock velocities via break-out times. The relative shock-velocities measured in the samples are used to make relative equation of state measurements. In January this year, a platform development shot was fired to explore the possibility of using a new, smaller holhraum design on this existing platform to extend the accessible pressure range.

 

For this platform development shot, sample tiles of 50um thickness gold and molybdenum were mounted on a base of molybdenum, driven by a stack of diamond and gold, which served as an ablator and a pre-heat shield. VISAR measures average shock velocity in gold and molybdenum samples and tracks the steadiness of the shock through a quartz witness. Precise metrology of the physics package and high-quality VISAR measurements were required to gather high-precision shock-velocity data. This talk will detail the velocity and equation of state data analysis.