Publications

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Dense z-pinches produced by 100 ns implosions of wire arrays or gas puffs produce substantial soft X-ray power. One class of z-pinch radiation sources includes low- to moderate-atomic-number K-shell radiators, such as aluminum and iron. These loads are designed for 1-10 keV K-shell X-ray generation, and offer opportunities for crystal spectroscopy that can reveal fundamental properties of the plasma when studied using plasma spectroscopic modeling. Typically these plasmas are characterized by ion densities of ∼1020 cm-3, diameters of 1-5 mm, electron temperatures up to several keV, and a range of opacities of the K-shell lines. Measurements from wire arrays on Sandia's 20 MA Z accelerator are presented along with collisional radiative and hydrodynamic simulations. The impact of opacity and 3D structure on non-LTE, non-diffusive radiation transport and X-ray production is discussed. © 2005 Elsevier Ltd. All rights reserved.

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The study of implosion dynamics and spectroscopy of X-pinches and wire arrays with Al wires alloyed or coated with other near-Z or higher-Z materials is discussed. In particular, X-pinches from two combined Al 5056 and Mo wires and composed from four identical Al 5056 (5%Mg) wires and Cu clad Al (90% Al and 10%Cu) are studied. In addition, wire arrays with Alumel wires (95% Ni and 5% Al) and with Al 5056 wires (uncoated) and coated with 5% NaF are investigated. Spatially-resolved and integrated x-ray spectral data and time integrated and time-gated pinhole x-ray images accumulated in these X-pinch and wire array experiments on the UNR 1MA Zebra generator are analyzed. Modeling of K-shell radiation from Mg provides K-shell plasma parameters for all Al 5056 wire experiments, whereas modeling of L-shell radiation from Ni, Cu, and Mo provide parameters for L-shell plasmas. The importance of using different materials or dopants for understanding of implosion dynamics of different wire materials is illustrated. © 2006 American Institute of Physics.

Implosion of wire arrays was investigated at the 1 MA Zebra accelerator by multiframe laser probing and gated x-ray self-emission diagnostics. Different regimes of implosion were observed in Al and Cu wire arrays. Implosion of Al loads with masses of 33-37 μgcm produces a dense pinch 1-1.5 mm in diameter. Strong instabilities are observed in the Z pinch at the time of stagnation. Implosion of "overmassed" loads produces a plasma column 3-4 mm in diameter with a core. The plasma column does not collapse during the x-ray pulse. The core of the plasma column is not subjected to the kink instability and transforms to a chain of dense spots in the later stage. Different regimes of implosion were observed in Al 8×15 μm loads presumably due to variations in the current pulse and load conditions. Observed regimes are compared to three-dimensional hybrid simulation of ideal and nonideal magnetohydrodynamics modes of implosion. © 2006 American Institute of Physics.

Experimental results of studies of the 1 MA X-pinch X-ray source in a wide spectral region are overviewed. Implosion dynamics and radiative properties of various X-pinches were studied by spatially and time-resolved X-ray and optical diagnostics. In particular, dynamics of spatial and temporal developments of the structure of X-ray emitting regions (1-5 keV), temporal characteristics of X-ray pulses, X-ray radiation outputs and electron beam characteristics from symmetric and asymmetric Mo, Cu, and combined asymmetric Mo/W X-pinches with two or four wires were studied. The mechanisms of X-ray multiburst generation are discussed. The future applications of the high-current X-pinch as a 5-10 kJ sub-keV-10 keV radiation driver are considered. © 2005 Elsevier Ltd. All rights reserved.

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Controlled seeding of perturbations is employed to study the evolution of wire array z-pinch implosion instabilities which strongly impact x-ray production when the 3D plasma stagnates on axis. Wires modulated in radius exhibit locally enhanced magnetic field and imploding bubble formation at discontinuities in wire radius due to the perturbed current path. Wires coated with localized spectroscopic dopants are used to track turbulent material flow. Experiments and MHD modeling offer insight into the behavior of z-pinch instabilities.

Experiments to study the implosion dynamics and radiation characteristics of copper z-pinches have been fielded at the 1 MA Zebra facility and the 20 MA Z facility. The impact of initial load mass, initial load diameter, and nesting of wire arrays on the precursor and the stagnated plasma has been evaluated through spectroscopy, shadowgraphy, and fluence measurements. Plasma parameters extracted from modeling of the time-integrated L-shell spectra indicate the presence of more than one plasma source contributing to the radiation, likely due to non-uniform hot spot x-ray emission or temporal gradients.

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Three-dimensional hybrid simulation of a plasma current-carrying column reveal two different regimes of sausage and kink instability development. In the first regime, with small Hall parameter, development of instabilities leads to the appearance of large-scale axial perturbations and eventually to bending of the plasma column. In the second regime, with a four-times-larger Hall parameter, small-scale perturbations dominate and no bending of the plasma column is observed. Simulation results are compared with laser probing experimental data obtained during wire array implosions on the Zebra pulse power generator at the Nevada Terawatt Facility.