The implosion dynamics and emission characteristics of Al liner-on-wire implosions

Abstract

Previous experiments at 0.1 TW level have shown that stability and X-ray emission of fast Z-pinch could be significantly improved by imploding an Al vapor jet onto a very thin coaxial wire (Wessel et al., 1992). Here we present the first results of an Al Z-pinch using a similar liner but at mega-ampere level. The pinch is driven by AMBIORIX facility, a 2 TW, 0.5 Ω, 2 MA, and a 50-ns pulse-line generator. We study the effect of an Al wire and its diameter (20–50 μm) on the implosion dynamics, on X-ray yield, on-axis magnetohydrodynamics (MHD) stability, and on Rayleigh–Taylor instability of the column at stagnation. Analysis of an Al jet on Al wire shots demonstrates that X-ray yield due to emission processes in the H- and He-like ionization stages (i.e., the K-shell) is enhanced, relative to the ones with Al jet only. The wire leads also to a better symmetrization of the implosion, and to better reproducibility of the shots. X-ray signals exhibit two similar pulses, 10-ns-wide and separated by 15 ns. To discern spectrally the origin of each pulse, further experiments have been performed with stainless steel wire (25 μm in diameter). Results show that liner and wire radiate simultaneously and contribute to both pulses. Full analysis of a typical Al jet on Al wire shot, using detailed collisional-radiative equilibrium (CRE) model is given in this paper. A sketch of the pinch at stagnation, with a cold dense core embedded in a hot low density corona, reproduces well all features of X-ray emission.