Examining the molecular origins of anomalously high HO generation at oxide-passivated metal surfaces for plasma applications.

Elucidating the mechanisms responsible for sub-microsecond desorption of water and other impurities from electrode surfaces at high heating rates is crucial for understanding pulsed-power behavior and optimizing its efficiency. Ionization of desorbed impurities in the vacuum regions may create parallel loads and current loss. Devising methods to limit desorption during the short time duration of pulsed-power will significantly improve the power output.

A fiber-coupled dispersion interferometer for density measurements of pulsed power transmission line electron sheaths on Sandia's Z machine.

A fiber-coupled Dispersion Interferometer (DI) is being developed to measure the electron density of plasmas formed in power flow regions, such as magnetically insulated transmission lines, on Sandia National Laboratories (SNL's) Z machine [D. B. Sinars et al.

Water desorption from rapidly-heated metal oxide surfaces-first principles, molecular dynamics, and the Temkin isotherm.

Quantitative understanding and control of water and impurity desorption from steel surfaces are crucial for high-voltage, pulsed power, vacuum technology, catalysis, and environmental applications. We apply a suite of modeling techniques, ranging from electronic density functional theory, to classical molecular dynamics (MD) and grand canonical Monte Carlo (GCMC) methods to study the thermodynamics and kinetics of fast water desorption from different surfaces of hematite FeO and CrO. Water binding energies on chromium oxide are found to be higher than iron oxide at zero temperature.

Electrothermal instability mitigation by using thick dielectric coatings on magnetically imploded conductors.

Recent experiments on Sandia's Z facility have confirmed simulation predictions of dramatically reduced instability growth in solid metallic rods when thick dielectric coatings are used to mitigate density perturbations arising from an electrothermal instability. These results provide further evidence that the inherent surface roughness as a result of target fabrication is not the dominant seed for the growth of magneto-Rayleigh-Taylor instabilities in liners with carefully machined smooth surfaces, but rather electrothermal instabilities that form early in the electrical current pulse as Joule heating melts and vaporizes the liner surface. These results suggest a new technique for substantially reducing the integral magneto-Rayleigh-Taylor instability growth in magnetically driven implosions, such as cylindrical dynamic material experiments and inertial confinement fusion concepts.

X-ray emission current scaling experiments for compact single-tungsten-wire arrays at 80-nanosecond implosion times.

We report the results of a series of current scaling experiments with the Z accelerator for the compact, single, 20-mm diameter, 10-mm long, tungsten-wire arrays employed for the double-ended hohlraum ICF concept [M. E. Cuneo, Plasma Phys.

Profiled bar transmission gratings: soft-x-ray calibration of new Kirchoff solutions.

A new analytical model, derived rigorously from scalar diffraction theory, accurately fits soft-x-ray measurements of symmetrical profile gold transmission gratings in all diffracted orders. The calibration system selects numerous photon energies by use of a high-resolution grazing-incidence monochromator and a dc e-beam source. Fine-period free-standing gratings exhibit limited performance and require such testing to determine parameters of and select acceptable gratings for use in time-resolved (0.

Evaluation of bent-crystal x-ray backlighting and microscopy techniques for the Sandia Z machine.

X-ray backlighting and microscopy systems for the 1-10-keV range based on spherically or toroidally bent crystals are discussed. These systems are ideal for use on the Sandia Z machine, a megajoule-class x-ray facility. Near-normal-incidence crystal microscopy systems have been shown to be more efficient than pinhole cameras with the same spatial resolution and magnification [Appl.