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

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to handle 10 mW/m 2 , and elms with a pulsed energy density of ≤ 0.5 mJ/m 2 . <strong>Research</strong> should<br />

include heat flux removal enhancement techniques, e.g., internal roughening, swirl tape, microjets<br />

and porous media. design margin enhancement should also be included. innovative magnetic<br />

configurations <strong>for</strong> high heat flux reduction, like the super X and snowflake divertor configurations,<br />

will require development of PFcs compatible with the unique magnetic geometry and possible<br />

differences in plasma transport.<br />

development of solid surface PFc designs that are tolerant to a few off-normal events should continue.<br />

This should include low-z material loaded tungsten surfaces and low-z material alloying<br />

of tungsten-surface materials. These concepts rely on the vapor shielding effects from the low-z<br />

material to protect the tungsten surfaces and be able to withstand a few disruptions. Real time<br />

replenishment of the low-z surface materials will be needed <strong>for</strong> this option.<br />

innovative refractory materials with high thermal conductivity compatible with the design of<br />

he coolant or liquid surfaces must be developed <strong>for</strong> neutron fluence up to 15 mW-yr/m 2 . Joining<br />

techniques compatible with he or liquid metal coolants are needed <strong>for</strong> the solid surface option<br />

to be viable. tungsten or tungsten alloys are the leading candidates <strong>for</strong> such material because of<br />

their high thermal conductivity, low erosion rate, and high melting point. however, neutron embrittlement<br />

is a serious issue the innovative alloys must address.<br />

TesTing requiremenTs To ValidaTe design issues<br />

Can testing scenarios be developed <strong>for</strong> new plasma facing component designs on new or existing laboratory<br />

and fusion facilities?<br />

helium-cooled heat sinks (including fabrication methods) <strong>for</strong> high heat flux removal capacity refractory<br />

material PFcs need to be developed and validated through rigorous testing. The joint between<br />

the plasma facing material and the heat sink is typically a few microns thick and composed<br />

of intermetallics. (These intermetallics have uncertain properties <strong>for</strong> which there are no measurements<br />

after neutron irradiation.) extensive heat flux testing of new designs must be conducted on<br />

test stands and the designs applied to long pulse fusion devices be<strong>for</strong>e they can be considered <strong>for</strong><br />

demo. This development should include different nondestructive inspection techniques. neutron<br />

irradiation typically hardens materials while decreasing ductility and fracture toughness.<br />

development of a database on nuclear irradiation effects on the above advanced and innovative<br />

PFc concepts is required to address issues, including cyclic fatigue, thermal creep, fracture<br />

toughness, and fracture mechanics at interfaces.<br />

Results from linear machines have shown that with the impingement of edge alphas, blisters can<br />

be created at the first-wall chamber owing to trapping of the impinging helium ions, and generation<br />

of W-fuzz on the divertor surfaces. no explanation <strong>for</strong> the cause of the generation of the Wfuzz<br />

is available. in general, the damage effects from edge alphas have not been systematically<br />

studied. to address the synergistic effects, new and upgraded facilities that can allow flexibility<br />

in the testing of PFc surface materials with the combination of simulated neutron, alphas and<br />

plasma environment at high temperature, and operate in pulsed and steady-state modes, will be<br />

needed.<br />

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