Research Needs for Magnetic Fusion Energy Sciences - US Burning ...

plaSMa FaciNg coMpoNENtS
The ReneW PFc panel has reviewed the status of high heat-flux removal development, which indicates
the difficulties of designing for a maximum heat flux of 10 mW/m 2 (see doerner 2 ) while
maintaining the ability to withstand a high-power elm energy flux of 0.5 mJ/m 2 (see Ritz 3 ) when
helium is used as the coolant. For the latter case, due to the potential damage from cyclic stresses,
the best approach is to avoid pulse loads from high-energy density elms. The avoidance of disruptions
is mandatory. an important transition is the evolution from mostly inertially cooled tokamak
experiments to iteR, where the pulse length will be increased from a few seconds to the
range of 400-3000 s, the structural material will be stainless steel, and components will have to
be actively water-cooled copper and maintained remotely. For a successful development of PFcs,
the following research is required to advance to demo.
• identification and qualification of materials that can take the heat loads, survive damage
from edge alphas, neutron flux and fluence at operating surface temperature while
maintaining acceptable erosion rates and core plasma contamination levels.
• Properties of low activation solid materials, joining technologies and cooling strategies
sufficient to design robust first-wall and divertor components in a high heat flux, steadystate
nuclear environment and with adequate design margin.
• characterization of welds, brazes or other joining techniques that can carry high heat
fluxes in the presence of high-edge alphas and neutron flux and fluence.
• strategies for heat removal with gas coolant at high temperatures while maintaining
structural integrity, especially with respect to temperature excursions or other off-normal
events.
• characterization of tritium effects including permeation, embrittlement, retention and
migration.
• strategies for handling dust migration and inventories.
• strategies for remote maintenance for high machine availability.
innoVaTiVe design of The solid surfaCe pfCs
Can innovative solid surface components be developed for DEMO?
iteR will operate with an integrated neutron fluence of 0.3 mW-yr/m 2 , and the plasma facing material
will consist of a combination of be, carbon fiber composite (cFc) and tungsten (W). Fusion
machines beyond iteR will require the development of robust helium-cooled solid surface PFcs
for the first wall to withstand steady-state maximum surface loading of ~ 1 mW/m 2 , the divertor
2 R. Doerner, “PMI issues beyond ITER” Presentation at the International HHFC Workshop on
Readiness to proceed from near-term fusion systems to power plants, San Diego, CA, USA Dec 10-12,
2008.
3 G. Ritz, T. Hirai, J. Linke et al., “Post-examination of helium-cooled tungsten components exposed to
DEMO specific cyclic thermal loads,” To be published in Fusion Engineering and Design, 2009.
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