Making Fusion Happen: Evaluating the Performance of Next Generation Plasma-Facing Materials

Speaker: Robert D. Kolasinski

Program Description
The science of plasma-material interactions (PMI) is fundamental 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 technical challenges in materials science. Surfaces directly exposed to intense plasmas will be continually reconfigured over their designed lifetime. The surface structure governs how materials degrade and is also closely coupled to the effects of neutral/impurity recycling and edge turbulence on the core plasma. Much of the work within our group at Sandia-Livermore focuses on experiments and modeling to better understand the effects of high-flux plasmas on materials. This presentation will highlight recent testing of advanced tungsten alloys, considered to be among the best candidate plasmafacing materials for fusion devices. These materials rely on dopants or dispersoids to stabilize the microstructure and to improve thermomechanical properties. However, there are significant gaps in our understanding of how this affects their response to high-flux plasma exposure, including factors such as erosion and redeposition, near-surface defect nucleation/growth, and tritium uptake. Our group has used a variety of methods to better characterize these aspects of their performance, using a wide range of in-situ and post-mortem diagnostics. One class of materials we have recently studied is tungsten containing small (100 nm diameter) metal-oxide and carbide-based dispersoids. Exposure to laboratory plasmas has yielded promising results, indicating improved resistance to recrystallization and formation of sub-surface defects, with only a modest increase in hydrogen isotope retention. This work motivated recent experiments at the DIII-D National Fusion Facility where we exposed several different tungsten microstructures to divertor plasmas. Post-test microscopy revealed that the dispersoid-strengthening dramatically improved the resilience of the surface against roughening and recrystallization, while also increasing its susceptibility to cracking. These tests serve as a pathway to testing more advanced materials, including nanostructured tungsten and ultra-high temperature ceramics. Forthcoming plans to investigate these materials in more detail will be discussed.

Bio
Robert Kolasinski is a Distinguished Member of the Technical Staff at Sandia National Laboratories - Livermore. His research activities focus on experiments related to plasma-surface interactions, materials for hydrogen storage and hydrogen energy infrastructure, and low energy ion scattering techniques for surface characterization. He is currently principal investigator for Sandia’s Department of Energy (DOE) Office of Science programs in Fusion Materials and Tritium Fuel Cycle R&D. In 2016 he received a 5-year DOE Early Career Award to support work on “Characterizing the dynamic response of surfaces to high-flux plasma exposure.” Rob joined Sandia in 2006 as a postdoc after receiving his undergraduate degree in Mechanical Engineering from Rutgers University, and his M.S. and Ph.D. degrees from the California Institute of Technology.