Instabilities in foil implosions and the effect on radiation output

Abstract

One of the aims of the Athena program at the Los Alamos National Laboratory is the generation of a high fluence of soft X-rays from the thermalization of a radially imploding foil. In experiments in the Athena program, a large axial current is passed through a cylindrical aluminum foil. Under the action of the Lorentz force, the resulting plasma accelerates toward the axis, thermalizes, and produces a fast soft X-ray pulse with a blackbody temperature up to several hundred electron volts. We present visible light images and X-ray data designed to study the effects of foil mass, current, and initial perturbations on the instability growth during foil implosion. Representative data is presented from several experiments using the Pegasus capacitor bank system and the explosively driven Procyon system. These experiments are labeled Peg 25 and Peg 33 for the Pegasus experiments and PDD1, PDD2 and PRFO for the Procyon experiments. In these experiments, all foils had radii of 5 cm but varied in mass and initial conditions. Experimental data from several shots were compared with each other and to a radiation magnetohydrodynamic (RMHD) computation. The data obtained from these experiments and the analysis has given us understanding of the physical mechanisms involved and insight for future experiments and has lead us to propose methods for minimizing the instability growth and maximizing the radiation output. In particular, we observed that wrinkles and other physical anomalies in the initial shape of foil do not appear to contribute to the growth of the instabilities.