Publications

Results 76–100 of 109
Skip to search filters

Fundamental hydrogen interactions with beryllium : a magnetic fusion perspective

Kolasinski, Robert K.; Bartelt, Norman C.; Whaley, Josh A.; Felter, Thomas E.; Wampler, William R.

Increasingly, basic models such as density functional theory and molecular dynamics are being used to simulate different aspects of hydrogen recycling from plasma facing materials. These models provide valuable insight into hydrogen diffusion, trapping, and recombination from surfaces, but their validation relies on knowledge of the detailed behavior of hydrogen at an atomic scale. Despite being the first wall material for ITER, basic single crystal beryllium surfaces have been studied only sparsely from an experimental standpoint. In prior cases researchers used electron spectroscopy to examine surface reconstruction or adsorption kinetics during exposure to a hydrogen atmosphere. While valuable, these approaches lack the ability to directly detect the positioning of hydrogen on the surface. Ion beam techniques, such as low energy ion scattering (LEIS) and direct recoil spectroscopy (DRS), are two of the only experimental approaches capable of providing this information. In this study, we applied both LEIS and DRS to examine how hydrogen binds to the Be(0001) surface. Our measurements were performed using an angle-resolved ion energy spectrometer (ARIES) to probe the surface with low energy ions (500 eV - 3 keV He{sup +} and Ne{sup +}). We were able to obtain a 'scattering maps' of the crystal surface, providing insight on how low energy ions are focused along open surface channels. Once we completed a characterization of the clean surface, we dosed the sample with atomic hydrogen using a heated tungsten capillary. A distinct signal associated with adsorbed hydrogen emerged that was consistent with hydrogen residing between atom rows. To aid in the interpretation of the experimental results, we developed a computational model to simulate ion scattering at grazing incidence. For this purpose, we incorporated a simplified surface model into the Kalypso molecular dynamics code. This approach allowed us to understand how the incident ions interacted with the surface hydrogen, providing confirmation of the preferred binding site.

More Details
TYPE SAND Report YEAR 2012
OSTIDOI

Deuterium retention in tungsten at elevated temperatures

Journal of Nuclear Materials

Causey, Rion A.; Cowgill, D.F.; Doerner, R.; Kolasinski, Robert K.; Mills, B.; Morse, D.; Smugeresky, J.E.; Wampler, W.R.; Wampler, William R.; Huber, D.

The tungsten ITER divertor will be operated at temperatures above 1000 K. Most of the laboratory experiments on hydrogen isotope retention in tungsten have been performed at lower temperatures where the hydrogen is retained as both atoms and molecules. At higher temperatures, atomic trapping plays a smaller role. The purpose of this paper is to see if hydrogen is trapped at internal voids at elevated temperatures, and to see if gas-filled cavities can be formed at high fluences. Additionally, this paper examines the effect of helium bubbles and radiation damage on trapping. © 2010 Elsevier B.V. All rights reserved.

More Details
TYPE Conference YEAR 2011
ScopusOSTI

A continuum-scale model of hydrogen precipitate growth in tungsten plasma-facing materials

Journal of Nuclear Materials

Kolasinski, Robert K.; Cowgill, D.F.; Causey, Rion A.

The low solubility of hydrogen in tungsten leads to the growth of near-surface hydrogen precipitates during high-flux plasma exposure, strongly affecting migration and trapping in the material. We have developed a continuum-scale model of precipitate growth that leverages existing techniques for simulating the evolution of 3He gas bubbles in metal tritides. The present approach focuses on bubble growth by dislocation loop punching, assuming a diffusing flux to nucleation sites that arises from ion implantation. The bubble size is dictated by internal hydrogen pressure, the mechanical properties of the material, as well as local stresses. In this article, we investigate the conditions required for bubble growth. Recent focused ion beam (FIB) profiling studies that reveal the sub-surface damage structure provide an experimental database for comparison with the modeling results. © 2010 Elsevier B.V. All rights reserved.

More Details
TYPE Conference YEAR 2011
ScopusOSTI
Results 76–100 of 109
Results 76–100 of 109