Fusion materials modeling: Challenges and opportunities
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Introduction The performance demands on plasma facing components (PFCs), first wall, and blanket systems of future fusion power are beyond the capability of current materials, which is one of the reasons that the United States National Academy of Engineering has ranked the quest for fusion as one of the top grand challenges for engineering in the 21st century.1 The fusion plasma in the international tokamak experimental reactor (ITER) and projected future power plants will be at a temperature of roughly 100 million K (see the Raj et al. article in MRS Bulletin April 2008 issue), which corresponds to an average kinetic energy for the hydrogen isotopes of roughly 10 keV.2–4 Hence, particles escaping the plasma encounter the plasma facing materials and first wall structural materials, where they deposit their kinetic energy in the form of atomic displacements and deposited thermal energy. Moreover, the deuterium (D)–D and D–tritium (T) reactions produce neutrons, T, and He nuclei with energies up to 14 MeV. In tokamak plasma confinement, the plasma should be fully confined, but in practice, significant leakage of the plasma occurs in the divertor at the bottom of the reactor as well as on the edges.
The fusion energy plasma environment presents numerous inherently multiscale computational grand challenges at the extreme of high-performance computing. For example, consideration of the edge, or boundary region where the plasma meets the material surface, leads to the identification of three coupled spatial regions that involve critical scientific issues for fusion power. These regions consist of (1) the edge and scrape off layer region of the plasma, (2) the near-surface material response to extreme thermal and particle fluxes under the influence of, and feedback to, the plasma sheath, and (3) the structural materials response to an intense, 14 MeV peaked neutron spectrum, which produces very high concentrations of transmuted elements within the bulk of the material through nuclear (n,p) and (n,α) reactions in which neutrons (n) are absorbed and protons (p) or alpha (α) particles (e.g., helium nuclei) are emitted from the nucleus, which transmutes the nucleus to a different element containing one or two fewer protons, respectively. These interlinked, plasma-materials interactions (PMI) are critical scientific issues for fusion power and affect (1) the PFC lifetime due to erosion processes during both steady-state and transient operation, (2) bulk plasma performance through plasma
B.D. Wirth, University of Tennessee, Knoxville, TN 37996, USA; [email protected] K. Nordlund, University of Helsinki, Finland; kai.nordlund@helsinki.fi D.G. Whyte, MIT Plasma Science & Fusion Center, Cambridge, MA 02139, USA; [email protected] D. Xu, University of California, Berkeley, CA 94720-1730, USA; [email protected] DOI: 10.1557/mrs.2011.37
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MRS BULLETIN • VOLUME 36 • MARCH 2011 • www.mrs.org/bulletin
© 2011 Materials Research Society
FUSION MATERIALS MODELING: CHALLENGES AND OPPORTUNITIES
contamination by eroded materials, (3) tritiu
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