Investigation of shell stability in imploding cylindrical targets

As part of a program to determine the feasibility of inertial confinement fusion (ICF), the physics of implosion stability is being studied. Ablatively-driven double-shell cylinders with and without initial periodic perturbations on the outer edge of the pusher were imploded using a single electron beam. Four-pulse holographic shadowgraphy yielded spatially and temporally resolved images of the implosions. The experiments are in a regime where fluidlike behavior is expected to dominate. A comparison of experimental data on the free-surface motion with two-dimensional, planar-geometry numerical calculations which include materials effects indicates shock-accelerated unstable growth of fabrication irregularities at the perturbed material interface. Peak pressures of 0.26 TPa (2.6 Mbars) are inferred in the high-density pusher material. Both the experiment and the calculation show a decrease in the amplitude of the free-surface perturbations at late time. In the experiment this decrease in amplitude begins earlier and the amount of the decrease is larger because of the enhanced interaction of adjacent perturbations due to convergence. The complex nonlinear development of both intentional and nonintentional target perturbations are demonstrated in the experiments.