Experimental measurement of planarity of a 1 TPa shock on exit from a shock amplification system

First Light Fusion uses one sided projectile impact to produce fusion within a target cavity. Projectile impact velocities and pressures are of order 10 km/s and 100 GPa respectively. An intermediate shock amplification stage amplifies the pressure incident on the fuel cavity by ~10 times.

The planarity, velocity and temperature of the shock exiting the amplifier are essential knowledge for validation of amplifier simulations and optimisation of fusion targets. By observing spatially and temporally resolved intensity of optical emission as the shock exiting the amplifier breaks out of a metal foil, the planarity of the shock can be measured. Nanosecond time resolution is required to capture the event lasting < 10 ns. If the emissivity of the metal foil is known, and the imaging system is absolutely calibrated, a temperature measurement of the shock front can be obtained and the amplifier output pressure inferred.

We present data from experiments on the large light gas gun at First Light Fusion, which fires a 32 mm diameter, 100 g projectile at the amplifier. Measured shock profiles are in excellent agreement with simulations performed using in-house codes. In some experiments the release profile is tilted, which is believed to be caused by input projectile tilt.