Analyzing time-resolved spectroscopic data from an azimuthally symmetric, aluminum-wire array,z-pinch implosion

Abstract

A 90-wire, aluminum, $z$-pinch experiment was conducted on the Saturn accelerator at the Sandia National Laboratories that exhibited azimuthally symmetric implosions and two x-ray bursts, a main burst and a subsidiary one. These bursts correlated with two consecutive radial implosions and are consistent with predicted magnetohydrodynamics behavior. A variety of time-resolved, accurately timed, spectroscopic measurements were made in this experiment and are described in this paper. These measurements include (1) the pinch implosion time, (2) time-resolved pinhole pictures that give sizes of the $K$-shell emission region, (3) time-resolved $K$-series spectra that give the relative amounts of hydrogenlike to heliumlike to continuum emission, (4) the total and the $K$-shell x-ray power outputs, and (5) time-resolved photoconducting diode measurements from which continuum slopes and time-resolved electron temperatures can be inferred. Time-resolved Ly-\ensuremath{\alpha} and Ly-\ensuremath{\beta} linewidths are obtained from the spectra and inferences about time-resolved ion temperatures are also made. All of these data correlate well with one another. A method is then presented of analyzing this data that relies on the complete set of time-resolved measurements. This analysis utilizes one-dimensional radiative magnetohydrodynamic simulations of the experiments, which drive $z$-pinch implosions using the measured Saturn circuit parameters. These simulations are used to calculate the same x-ray quantities as were measured. Then, comparisons of the measured and calculated data are shown to define a process by which different dynamical assumptions can be invoked or rejected in an attempt to reproduce the ensemble of data. This process depends on the full data set and provides insight into the structure of the radial temperature and density gradients of the on-axis pinch. It implies that the first implosion is composed of a hot plasma core, from which the kilovolt emissions emanate, surrounded by a cooler, denser shell, and it provides details about the structure of the temperature and density gradients between the core and shell regions. These results are found to be broadly consistent with an earlier, less detailed, data analysis in which plasma gradients are ignored. However, the ability to reproduce the full spectroscopic data in the present analysis is found to be sensitively dependent on the radial gradients that are calculated.