Pressure measurement of the amplified shock delivered to an FLF fusion target using VISAR

We report on an experiment designed to measure the output pressure of a First Light Fusion (FLF) amplifier target using VISAR. The amplifier increases the pressure of a projectile-driven planar input shock before it is delivered to the fusion target. Previous experiments at FLF have deduced the amplifier unload pressure within a transparent PMMA block by measuring the output shock position as a function of time using streaked optical shadowgraphy. These measurements are hampered by non-uniformities along the line-of-sight and the inherent noise introduced when differentiating the position-time data. This experiment used FLF's 38 mm two stage light gas gun and an amplifier target to produce a 300-400 GPa shock in water. These conditions are sufficient to transform the water into a metallic-like optical reflector, which has 40-50% reflectivity above 250 GPa. A velocity measurement was made using the shock front in water as a reflector for VISAR. This method is directly sensitive to the shock velocity and allows the pressure profile across the shock to be resolved. We present experimental results and comparisons to simulations performed using our in-house codes. Future improvements to the diagnostic are also discussed.