High-flux helium and hydrogen plasma exposure of materials for magnetic fusion




MON, 02/06/2017 - 4:00PM TO 5:00PM
Spring 2017 Colloquium Series

It is widely recognized that the science of plasma-material interactions (PMI) is central to the realization of magnetic fusion as an energy source. Predicting how materials behave in the extreme environments characteristic of fusion devices remains among the most daunting and complex technical challenges in materials science. Surfaces directly exposed to intense plasmas will be reconstituted many times over their designed operational lifetime. This surface evolution governs not only how materials degrade, but is also intimately coupled to the effect of neutral and impurity recycling and edge turbulence on the core plasma.

This talk will focus on one of the most challenging aspects of the PMI problem: how the intense fluxes of low-energy species (e.g. shallowly implanted hydrogen and helium) affect the structure of solid plasma-facing components. I will emphasize our recent experimental work to decipher the mechanisms that underlie this surface modification, including surface-to-bulk transport, defect nucleation, nanostructure growth, and stresses induced in materials during plasma exposure. A key component of our experimental program at Sandia/CA involves a collaboration using the tritium plasma experiment (TPE), a linear plasma device located at Idaho National Laboratory capable of exposing materials to high-flux tritium plasmas and handling neutron-damaged metals. Our recent work focuses on understanding insoluble gas precipitation in plasma-exposed tungsten and how different microstructures (including advanced ultra-fine grained materials) affect bubble growth. Given the tremendous capacity of near-surface bubbles to trap diffusing atomic species, precipitation will have significant implications for tritium inventory in large magnetic fusion experiments, including ITER. At a more fundamental level, we have also studied hydrogen adsorption on surfaces using low energy ion scattering, a form of low-energy ion beam analysis. Because of its high surface-sensitivity, LEIS can be used to detect the presence of hydrogen adatoms on surfaces precisely, providing insight into surface binding energies. I will present some of our recent results aimed at understanding recombination and exchange on tungsten and beryllium surfaces. I will conclude with a short summary of plans for upcoming diagnostic development.

About the Speaker:

Robert Kolasinski is a Principal Member of the Technical Staff in the Energy Innovation Department at Sandia National Laboratories, in Livermore, CA. While at Sandia, Rob’s research efforts have focused on plasma-material interactions for magnetic fusion energy, hydrogen storage, and infrastructure for fuel cell electric vehicles. Rob received M.S. (2001) and Ph.D. (2007) degrees from the California Institute of Technology in mechanical engineering following undergraduate study at Rutgers University. While at Caltech, he studied ion-surface interactions in plasma propulsion systems as part of an extensive collaboration with the Advanced Propulsion Group at the NASA Jet Propulsion Laboratory. In 2016, Rob was selected for Department of Energy Office of Science Early Career Award.

Sandia National Laboratories is a multi-mission laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.