Experimental Measurements of Late Time Wall Mix Occurring in >20 kJ laser Preheated MagLIF Relevant Gas Pipes at NIF

A core component of the ICF concept known as Magnetized Liner Inertial Fusion (MagLIF) is laser pre-heat. Here, the laser heats the DT fuel within the magnetized pipe, such that once the system thermalizes the fuel will be at the required adiabat for high fusion yield following the system’s subsequent cylindrical compression. However, the act of preheating the pipe creates plasma, which produces a shockwave and can ionize the gas pipe wall. After a little over 10 ns the shockwave reaches the wall and its rebound can carry the wall’s higher Z material with it, mixing it in the fusible fuel and degrading the fusion yield. This late time dynamic is studied at the National Ignition Facility at the scale (>20 kJ) needed for future higher yield (igniting) MagLIF facility. This is accomplished using higher Z tracing elements. 30-60 ns after the system is pre-heated laser driven backlighters are turned on, which are paired to be strongly absorbed by the wall tracer. The lateral movement of the tracer will appear as a shadow to the GXD, producing a radiograph. This has so far been investigated in unmagnetized room temperature neopentane filled targets using a Ti tracer paired to a Cr line emission backlighter and in 40 K deuterium filled targets using an Al tracing element paired to a continuum backlighter. These measurements are than compared to HYDRA simulation to inform MagLIF predictive capabilities.