Instability growth in magnetically imploded high-conductivity cylindrical liners with material strength

Magnetically imploded cylindrical metal shells (z-pinch liners) are attractive drivers for experiments exploring hydrodynamics and properties of materials at extreme conditions. As in all z-pinches, the outer surface of a liner is unstable to magneto Rayleigh-Taylor (RT) modes during acceleration, and large-scale distortion arising from RT modes could make such liners unuseable. On the other hand, material strength in the liner should, from first principles, reduce the growth rate of RT modes, and material strength can render some combinations of wavelength and amplitude analytically stable. A series of experiments has been conducted in which high-conductivity, soft, cylindrical aluminum liners were accelerated with 6-MA, 7-/spl mu/s rise-time driving currents. Small perturbations were machined into the outer surface of the liner and perturbation growth monitored. Two-dimensional magneto-hydrodynamic (2-D-MHD) calculations of the growth of the initial perturbations were in good agreement with experimentally observed perturbation growth through the entire course of the implosions. In general, for high-conductivity and soft materials, theory and simulation adequately predicted the behavior of magneto-RT modes in liners where elastic-plastic behavior applies. This is the first direct verification of the growth of magneto-RT in solids with strength known to the authors.

I. Introduction

Imploding cylindrical metal shells (liners) can be used as precise, reproducible sources of kinetic energy (drivers) for a wide variety of experiments exploring hydrodynamics and material properties. When the mechanism imploding the liner is the magnetic pressure derived from very large electrical currents, implosion velocities of 10–30 km/s can be achieved at the inner surface of the liner, while most of the liner remains at or above solid density and a significant fraction of the liner material remains below ambient melt temperature [1]. If liners can be imploded with good cylindrical symmetry and with good axial uniformity, pulsed-power machines delivering 50- to 100-MA currents can produce shock pressures of 10–100 Mbar in centimeter-scale experimental assemblies located inside the liner. Such conditions make possible unprecedented high-energy density experiments.