Laser-Driven Double Cylinder Experiments Studying Classically Unstable Interfaces

The double shell design for inertial confinement fusion uses a high-Z inner shell containing deuterium-tritium fuel nested inside of an indirectly driven low-Z outer shell. The collision between the shells drives the inner shell inwards, compressing and heating the fuel volumetrically. However, this inward acceleration is classically Rayleigh-Taylor unstable, and the large density of the high-Z shell results in considerable hydrodynamic instability growth during this phase. Understanding and mitigating this growth is crucial to improving double shell performance. We are leveraging a cylindrical implosion platform with two concentric cylinders in order to directly measure instability growth by imaging down the cylinder axis, enabling quantification of proposed mitigation schemes. Crucially, the axial non-uniformity of the inner cylinder must be minimized during the implosion in order to directly measure the instability growth at the outer surface. We present design simulations testing various methods of limiting the axial non-uniformity, and we compare these to the first experimental results obtained on the National Ignition Facility. We also discuss next steps for the platform testing gradient-density layers as a means for mitigating instability growth on the inner cylinder.