Examination of liner stability during magnetic implosion using experiments and simulations

Los Alamos has been conducting a number experiments to examine dynamic properties of materials using high-energy pulse power generator systems. These experiments are conducted in a Z-pinch configuration typically with an outer aluminum liner to carry the current, develop the acting force, and act as the driving element. The peak magnetic fields produced by these systems have ranged from 0.5 to 1.7 mega gauss. The onset of what has been called Magneto-Raleigh-Taylor (MRT) instabilities in the outer aluminum liner, when excessive current is applied, has been considered a limitation on the design of these liners. However, in several cases where the material of the liner was calculated to be completely melted the outside liner surface remained stable. Analysis of the data from this and several other experiments and comparison to 1D MHD simulations has already permitted us to examine how the drive conditions on this aluminum layer appear to effect the likelihood of onset of these instabilities. Additionally, careful variations of drive conditions, initial liner surface conditions, and EOS properties (including conductivity) suggest two phenomenons that appear to cause onset of instability. First, while the nature of the instability may still be fundamentally driven by the acceleration of a fluid interface, the effect may be drastically accentuated by the onset of liquid to vapor phase change if the material is allowed to approach too closely to the saturated liquid line. Furthermore, several observed cases which remained stable even after melting suggest that there may be drive conditions which maintain the aluminum at densities and temperatures above the saturated liquid line and significantly delay the onset of MRT instabilities. Second, the gradient of distribution of forces within the melted liner may also impact the growth of instabilities. We will also present the results of 2D simulations of these conditions and examine in greater detail the apparent mechanisms by which these instabilities grow.