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Reports on the ionization and radiation dynamics of carbon ablation plasmas. Analysis of the interaction of a proton beam as it heats and ablates a carbon target; Overview of the ionization dynamics model; Ablation of a carbon target by a proton beam.

By varying current-loss circuit parameters, the Mach2-tabular collisional radiative equilibrium 2-D radiation magnetohydrodynamic model was tuned to reproduce the radiative and electrical properties of three recent argon gas-puff experiments (same initial conditions) performed on the Z machine at Sandia National Laboratories. The model indicates that there were current losses occurring near or within the diode region of the Z machine during the stagnation phase of the implosion. The “good” simulation reproduces the experimental K-shell powers, K-shell yields, total powers, percentage of emission radiated in $\alpha $ lines, size of the K-shell emission region, and the average electron temperature near the time-of-peak K-shell power. The calculated atomic populations, ion temperatures, and radial velocities are used as input to a detailed multifrequency ray-trace radiation transport model that includes the Doppler effect. This model is employed to construct time-, space-, and energy-resolved synthetic spectra. The role the Doppler effect likely plays in the experiments is demonstrated by comparing synthetic spectra generated with and without this effect. [ABSTRACT FROM PUBLISHER]

Two-dimensional (r, z) magnetohydrodynamic simulations with nonlocal thermodynamic equilibrium ionization and radiation transport are used to investigate the K-shell radiation output from doubly nested large-diameter (> 60 mm) stainless-steel arrays fielded on the refurbished Z pulsed-power generator. The effects of the initial density perturbations, wire ablation rate, and current loss near the load on the total power, K-shell power, and K-shell yield are examined. The broad mass distribution produced by wire ablation largely overcomes the deleterious impact on the K-shell power and yield of 2-D instability growth. On the other hand, the possible current losses in the final feed section lead to substantial reductions in K-shell yield. Following a survey of runs, the parameters for the perturbation level, ablation rate, and current loss are chosen to benchmark the simulations against existing 65-mm-diameter radiation data. The model is then used to predict the K-shell properties of larger diameter (70 mm) arrays to be imploded on the Z generator. [ABSTRACT FROM AUTHOR]

This paper presents theoretical extrapolations for the multi-keV X-ray radiation production capability of the 26-MA ZR accelerator at Sandia National Laboratories, which is scheduled to become available for experiments in 2007. These extrapolations are based on scaling models and ideas that have been developed over the years. These models and ideas have evolved and been refilled through the process of benchmarking one-dimensional nonlocal-thermodynamic equilibrium magnetohydrodynamic model results to experimental K-shell yields and powers as well as inferred temperatures and densities. For this ZR assessment, the models are first benchmarked to K-shell yields obtained from argon, titanium, stainless-steel, and .copper Z experiments and then they are applied to extrapolate yield predictions to the ZR machine. Extrapolations are based on 2-cm-length loads and similar wire configurations and nozzle designs as those employed in Z experiments. Projected K-shell yields for Ar (photon energy ∼3 keV), Ti (∼5 keV), stainless steel (∼7 keV), and Cu (∼8.6 keV) are 520, 300, 200, and 80 k J, respectively. In addition, the high-energy free-bound continuum emission above 10 keV is calculated to be 40 kJ on ZR. [ABSTRACT FROM AUTHOR]

In developing stainless-steel (SS) and copper wire-array X-ray sources on the Z machine, we consider the optimization of K-shell yield as a function of load height. Theory, numerical modeling, and experimental data suggest that an optimum exists corresponding to a tradeoff between the increase in radiating mass and the decrease in coupled current with increasing pinch height. A typical load height of 20 mm used on many previous Z wire-array X-ray sources is found to be near optimal for K-shell yield production in SS and copper implosions. Electrical data, pinhole imaging, and spectroscopy are used to study plasma conditions in wire-array z pinches corresponding to the variation in K-shell power and yield per unit length as the pinch height is changed from 12 to 24 mm. [ABSTRACT FROM PUBLISHER]

This paper presents explicit analytical formulas relating the X-ray yields in various energy bins of the free-bound recombination continuum to the mass, temperature, dimensions, and confinement time of the plasma participating in the K-shell emission. Estimates based on these formulas support the idea that K-shell recombination continuum radiation of argon, titanium, and iron can be a viable alternative to the K-shell line radiation of higher atomic number ions for advancing the operation of Z-pinch plasma radiation sources into the warm X-ray photon energy range of 10-20 keV. The potential of the refurbished Z accelerator for generating multikilojoule radiation yields in this energy range via recombination continuum is assessed. [ABSTRACT FROM AUTHOR]

Nested stainless steel wire array variations were investigated on the 20 MA Z machine [R. B. Spielman et al., Phys. Plasmas 5, 2105 (1998)]. In order to reach experimentally observed electron temperatures near 3.8 keV and excite the K shell, these ∼6.7 keV photon energy x-ray sources must be of large initial diameter (45–80 mm) which poses a concern for magnetic Rayleigh–Taylor instability growth. We discuss the implosion dynamics in these large diameter wire arrays, including an analysis of the ablation phase indicating that the prefill material is snowplowed at large radius. Nested array configurations with various mass and radius ratios are compared for instability mitigation and K-shell scaling. Degradation of the K-shell x-ray power and yield was observed for shots that did not have simultaneous implosion of the outer and inner wire arrays. Shots that were designed per this constraint exhibited K-shell yield scaling consistent with the model of J. W. Thornhill et al. [IEEE Trans. Plasma Sci. 34, 2377 (2006)] which had been benchmarked to single array results. This lends confidence to K-shell yield predictions using this model for future shots on the refurbished Z machine. Initial results employing a triple nested wire array to stabilize the large diameter implosion are also reported. [ABSTRACT FROM AUTHOR]

Experiments in the last few years at the 20-MA Z Accelerator have produced significant K-shell X-ray output from a variety of imtial load materials, including aluminum (1.7-keV photons, > 400-kJ yield), argon (3.1-keV photons, > 300-kJ yield), titanium (4.8-keV photons, 100-kJ yield), stainless steel (6.7-keV photons, > 50-kJ yield), and copper (8.4-keV photons, 20-kJ yield). K-shell scaling theories developed at the Naval Research Laboratory [K. G. Whitney et al., Phys. Rev. E 50, 2166 (1994)] in the 1990s were benchmarked against the Al K-shell emission data from < 10-MA facilities. The experiments at Z have not only led to a heuristic validation of this original theory but have also provided the data to fine tune the models for application to higher photon energies and for extension to higher current generators. The upgrade of the Z Accelerator to ZR, which will provide 26 MA to a Z-pinch load, should increase the radiated K-shell output for sources previously fielded at Z and will extend the range of photon energies where measurable radiation can be observed, which is likely up to 13 keV. A summary of the K-shell experiments at Z is presented, as well as an overview of the modified empirical-scaling theory. Proposed load configurations for ZR are discussed, as well as predictions for K-shell output. [ABSTRACT FROM AUTHOR]

We report an approximate energy distribution (coarse spectrum) over the range ∼0.1 to > 10 keV for the X-ray output of an argon Z-pinch. The tests, conducted at ∼15-MA peak current, utilized an 8-cm diameter double-shell nozzle. Sze et aL (2001) have previously described the performance of this Z.pinch with emphasis on the K-shell line emission at ∼3 keV. Additional measurements that address the non-K-line output of the Z-pinches are presented here. On the one hand, > 4-key photons due to the free-bound continuum constitute a significant fraction, almost 30%, of the nominal K-shell emission. On the other hand, the sub-3-keV L-shell lines and continuum show distinctive time histories and significant yields. These nonresonance-line emissions are important for a more complete understanding of the implosion physics, for proper analysis of diagnostic responses, and for their effects upon objects exposed to the Z-pinch's radiation. [ABSTRACT FROM AUTHOR]