Measurements of the early time symmetry of delayed two shock pulse shapes relevant to double shell implosions

Recent double shell experiments at the National Ignition Facility have utilized a two shock laser pulse shape. In contrast to the single shock pulse shapes typically used for double shell implosions, two shock laser pulses can potentially offer improved symmetry as well as better mitigation of the joint where the two outer shell hemispheres are joined. In addition to pulse shape tuning, beam repointings and wavelength shifts between the four NIF laser cones will be needed to adequately control backscatter and symmetry during these implosions. Here, we discuss the first set of two shock laser pulse, outer shell only, two-axis keyhole experiments. These experiments are able to measure the first shock breakout timings and speed, as well as the shock merger time, along two axes. Outer cone beam repointings, quad splitting, and wavelength shifts between the four NIF laser cones were used to control backscatter and symmetry. We will discuss the measured shock symmetry and backscatter, as well as comparisons to simulation.