Date: Thursday, May 1st
Presenter: Prof. Brian Wirth, Governors Chair Professor of Computational Nuclear Engineering, Department of Nuclear Engineering, University of Tennessee
The plasma facing components, first wall and blanket systems of future tokamak-based fusion power plants arguably represent the single greatest materials engineering challenge of all time. Indeed, the United States National Academy of Engineering has recently ranked the quest for fusion as one of the top grand challenges for engineering in the 21st Century. These challenges are even more pronounced by the lack of experimental testing facilities that replicate the extreme operating environment involving simultaneous high heat and particle fluxes, large time varying stresses, corrosive chemical environments, and large fluxes of 14-MeV peaked fusion neutrons. Fortunately, recent innovations in computational modeling techniques, increasingly powerful high performance and massively parallel computing platforms, and improved analytical experimental characterization tools provide the means to develop self-consistent, experimentally validated models of materials performance and degradation in the fusion energy environment.
This presentation will describe the challenges associated with modeling the performance of plasma facing component and structural materials in a fusion materials environment, the opportunities to utilize high performance computing and then focus on an example of recent progress to investigate the dramatic surface evolution of tungsten exposed to low-energy He and H plasmas. More specifically, multiscale modeling results will be presented to identify the mechanisms of tungsten surface morphology changes when exposed to 100 eV He plasma conditions as a function of temperature and initial tungsten microstructure. The results demonstrate that during the bubble formation process, He clusters create self-interstitial defect clusters in W by a trap mutation process, followed by the migration of these defects to the surface that leads to the formation of layers of adatom islands on the tungsten surface. As the helium clusters grow into nanometer sized bubbles, their proximity to the surface and extremely high gas pressures leads them to rupture the surface thus enabling helium release. Helium bubble bursting induces additional surface damage and tungsten mass loss which varies depending on the nature of the surface.
Brian Wirth is Governors Chair Professor of Computational Nuclear Engineering in the Department of Nuclear Engineering at the University of Tennessee, Knoxville and Oak Ridge National Laboratory, which he joined in July 2010. Brian received a BS in nuclear engineering from the Georgia Institute of Technology in 1992 and a PhD in mechanical engineering from the University of California, Santa Barbara in 1998, where he was a Department of Energy Nuclear Engineering Graduate Fellow. Dr. Wirth spent four years in the High Performance Computational Materials Science Group at Lawrence Livermore National Laboratory, where he lead efforts to investigate the microstructural stability of structural materials in nuclear environments. In 2002 he joined the faculty at the University of California, Berkeley as an Assistant Professor of Nuclear Engineering and was promoted to Associate Professor in 2006. He has received a number of awards, including the 2011 Hochreiter Distinghuished Lecture in the Department of Mechanical and Nuclear Engineering at the Pennsylvania State University, the 2007 Fusion Power Associates David J. Rose Excellence in Fusion Engineering Award and the 2003 Presidential Early Career Award for Scientists and Engineers (PECASE).