Rayleigh-Taylor instability growth enigma: liner studies on Pegasus

Abstract

The goal of the RTMIX series on Pegasus is to study Rayleigh-Taylor instability growth and mixing in a convergent geometry, at a metal-foam interface, as a function of material strength and initial perturbation amplitude. Results of three experiments are presented. The first experiment, reported in the previous Pulsed Power Conference, involved a solid Z-pinch liner driven by a Pegasus current of /spl sim/5.5 MA onto a high-density foam target. The inside diameter of the liner was smooth for the first experiment. No instability growth or mixing was observed at the resolution limit of the diagnostics, as expected. In the second experiment, azimuthally symmetric sine-wave perturbations were machined onto the inner diameter with a wavelength of 1.0 mm and amplitudes of 12.5 /spl mu/m and 50 /spl mu/m. Growth of the large amplitude perturbations was predicted, but growth of the small amplitude perturbations was expected to be inhibited by the material strength of the Cu. Neither amplitude perturbation grew. The third experiment was a repeat of the second with a low-strength Sn/In alloy (in place of the Cu) that should have melted early in the implosion. The Sn/In layer was mass-matched to the Cu layer that it replaced. Since the Sn/In layer was expected to be liquid during the unstable deceleration phase, no material strength stabilization should have occurred, and both amplitude perturbations should have shown dramatic growth. Preliminary inspection of radiographs from this experiment indicates no Rayleigh-Taylor instability growth.