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VERSION:2.0
CALSCALE:GREGORIAN
PRODID:UW-Madison-Physics-Events
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SEQUENCE:1
UID:UW-Physics-Event-4646
DTSTART:20171120T180000Z
DTEND:20171120T190000Z
DTSTAMP:20240328T195957Z
LAST-MODIFIED:20171111T161854Z
LOCATION:Chamberlin 2241
SUMMARY:Multiscale computational modeling and materials research for n
ext-step devices after ITER \, Plasma Physics (Physics/ECE/NE 922) Sem
inar\, Prof. Brian D. Wirth\, University of Tennessee\, Knoxville
DESCRIPTION:The performance of plasma facing components (PFC) and stru
ctural materials is one of the main issues facing ITER and future magn
etic fusion reactors. Tungsten will be used in ITER as the PFC materia
l and is considered to be one of the primary candidates for future rea
ctors. However\, recent experiments that exposed tungsten to He plasma
exposure or He ion irradiation with ion energy less than about 100 eV
(well below the threshold energy for physical sputtering or Frenkel p
air production in tungsten) reveal significant surface modification\,
including the growth of nanometer-sized “fuzz”\, and formation of
a layer of nano-bubbles in the near-surface region [1\,2]. It is widel
y accepted that He atoms in tungsten\, like in other metals\, are inso
luble and tend to form small clusters\, which serve as the nucleating
event for the formation of larger gas bubbles. It is also clear from a
tomistic simulations [3\,4] that the processes of trap mutation produc
e W interstitial atoms that lead to surface morphology modification as
the interstitials diffuse to and annihilate at the surface\, in addit
ion to plastic flow and dislocation loop punching processes driven by
high compressive stresses caused by over-pressurized clusters\, or nan
ometer-sized bubbles\, and these processes can alter both the tungsten
surface morphology and the He clustering dynamics.
\n
\nOne o
f the challenges with describing these effects for the large-extrapola
tions in performance required for the PFCs in next-step devices beyond
ITER is the large span of spatial and temporal scales of the governin
g phenomena and\, therefore\, the theoretical and computational tools
that can be used. Fortunately\, recent innovations in computational mo
deling techniques\, increasingly powerful high performance and massive
ly parallel computing platforms\, and improved analytical experimental
characterization tools provide the means to develop self-consistent\,
experimentally validated models of plasma materials interactions that
govern the performance and degradation of the divertor and PFCs in th
e fusion energy environment. This presentation will describe the chall
enges associated with modeling the performance of divertor PFCs in a n
ext-step fusion materials environment\, the opportunities to utilize h
igh performance computing and present examples of recent progress to i
nvestigate the dramatic surface evolution of tungsten exposed to low-e
nergy He and H plasmas\, as well as the coupled He-defect evolutions i
n bulk structural materials exposed to high-energy He and neutron irra
diation before laying out a vision for developing a computational mate
rials modeling framework for fusion materials behavior.
\n
\n[
1] S. Takamura\, et al.\, Plasma Fusion Res. 051 (2006) 1
\n
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n[2] M. J. Baldwin and R. P. Doerner\, Nucl. Fusion 035001 (2008) 48
\n
\n[3] F. Sefta\, et al.\, Nucl. Fusion 073015 (2013) 53
\n
\n[4] A. Lasa\, et al.\, NIMB 156-161 (2013) 303
URL:https://www.physics.wisc.edu/events/?id=4646
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