Computational studies of multi-shock pulse shapes for double shell implosions with considerations for symmetry and engineering feature control

Inertial Confinement Fusion Double Shell implosions rely on the efficient transfer of kinetic energy from an outer (ablator) shell to an inner shell to compress and heat its central DT fuel. Maintaining adequate low-mode symmetry and controlling growth of interfacial mix and engineering features are essential to maintaining the flow of energy from radiation drive to fusion fuel. The time-dependent shape of the radiation drive applied to the ablator shell from a laser-driven hohlraum plays a central role in controlling the behavior of each of these processes. Very few studies of this type, however, have been performed for double shells.

For current double shell experiments at the National Ignition Facility, a single shock pulse shape is used to drive the implosion. Peak laser power is reached while the shock is only midway through the ablator shell and under these conditions shock symmetry cannot be maintained. To improve shock symmetry significant changes must be made to the pulse shape, such as utilizing a multi-shock pulse. Our recent simulations using the LANL xRAGE code have also shown that significant reductions in growth of the outer shell assembly joint can be made with a particular type of 2-shock pulse. In this presentation we will discuss the status of our computational findings with multi-shock-driven double shell implosions and our plans for upcoming experimental tests of these designs.