Laser coupling and window mixing in NIF MagLIF gas pipe experiments

Recent MagLIF gas pipe experiments at the NIF have continued to investigate laser energy coupling into the target gas fill. One of the most significant uncertainties in the coupling is the energy deposition into the window material, which is predicted in simulations to be or order \textasciitilde few kJ but which is difficult to measure directly. By employing the NIF Visar system to measure the shock strength when the heated plasma reaches the wall of the target, the total energy deposited into the gas can be accurately determined. Additionally, in some experiments the target entrance window has had a mid-Z tracer added to track the depth of window material propagation into the target, allowing for assessments of window mixing with the gas fill. Preliminary data indicate that the window material does not propagate further than \textasciitilde 2 mm into the target, and that the mixing depth is dependent on the initial gas pressure inside the pipe.$\backslash $This work was performed under the auspices of the U.S. Department of Energy by LLNL under Contract DE-AC52-07NA27344.