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 ͑1͒ the pinch implosion time, ͑2͒ time-resolved pinhole pictures that give sizes of the K-shell emission region, ͑3͒ timeresolved K-series spectra that give the relative amounts of hydrogenlike to heliumlike to continuum emission, ͑4͒ the total and the K-shell x-ray power outputs, and ͑5͒ time-resolved photoconducting diode measurements from which continuum slopes and time-resolved electron temperatures can be inferred. Time-resolved Ly-␣ and Ly-␤ 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. ͓S1063-651X͑97͒06609-9͔

Benchmarking multilevel, 2-D cylindrical radiation transport in a high energy density plasma environment

“…These conditions are within the range of those attained in the Saturn Z pinches analyzed in Ref. [18]. Al ion temperatures ranging up to w30 keV were measured on Saturn Z-pinch experiments by Sanford et al [21].…”

“…The relevant literature is too extensive to fully cite here; for examples see Ref. [18], which analyzed 14 spectra from Al pinches on the Saturn generator at Sandia National Laboratories, and Ref. [19], which summarizes and extracts trends from Ar Z-pinch data collected since 1991 from 7 different drivers.…”

Effective statistical weights of bound states in plasmas

“…For K ≈ 1 (low n), the empirical factor 2 in reference [18] amends partially for the inaccuracy introduced there by the simplifying approximation of the uniformity of the NN-ion field. Taking E bind given by (2), and Z 0 = Z i , we find R crit.unif = 4n 2 a 0 /Z 0 , R crit.peak = 6n 2 a 0 /Z 0 . Thus, we find that the use of the factor of 1.5 3 = 3.375 restores the ideal-plasma NN-approximation result for hydrogen.…”

“…Refs. [1][2][3][4][5][6][7][8]). However, the theoretical interpretation of experimental data, as well as the analysis of collisional-radiative kinetics in general, is still based on rather simplified treatments of plasma density effects.…”

I. First-order calculation of the pressure tensor for cylindrical, Z-pinch plasmas

“…Recent experiments have shown that compressional heating can be fairly non-uniform, leading to hot plasma cores and much cooler surrounding shells. [4][5][6] In strongly driven Z-pinch or inertial confinement fusion ͑ICF͒ plasmas, shock waves and/or sharp gradients in temperature and density can form. During the passage of a shock front, the plasma undergoes large, rapid, but predictable jumps in electron and ion temperature.…”