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

introduction
Thrust 11 addresses the fundamental engineering science and the technology required to develop
components that can handle the higher heat fluxes in a power-producing fusion reactor. much of
this technology is useful in alternate concepts as well as conventional toroidal devices. Plasma facing
components such as those in the first wall and divertor, and internal components (ics) such as
radiofrequency launchers, Faraday shields and electron cyclotron resonance heating (ecRh) mirrors,
will need to operate at higher temperatures and handle particle and heat loads much higher
than iteR. First wall and blanket components may consist of refractory alloys, vanadium alloys,
reduced activation ferritic martinsitic steel (RaFms), oxide dispersion strengthened ferritic steel,
and silicon carbide composite. Power conversion systems for demo will require heat sinks for plasma
facing components that can operate at high temperatures as part of a highly efficient closed
brayton cycle. Plasma facing components could endure peak heat fluxes in excess of 10 mW/m 2
at the divertor and localized peak heat fluxes as high as 0.5-2 mW/m 2 on the first wall and internal
components. since these components are an integral part of the power conversion system, this
work must connect closely to Thrust 13 to ensure careful integration with blanket requirements.
The technologies and components developed in this Thrust feed directly into Thrust 12, and likewise
benefit from the integrated testing in Thrust 12’s toroidal confinement facility. in addition,
the activities in Thrust 11 focus on the bulk PFc properties and complement the basic plasma-surface
interaction research of the first few micrometers described in Thrust 10.
a close coupling must exist between the PFc materials research focused on the development of
more ductile refractories and improved joining techniques in Thrust 14 with PFc development in
Thrust 11. both free-surface liquid metal PFcs and ducted liquid metal and gas coolants in solid
PFcs are under consideration. currently, the technology Readiness level (tRl) (mankins, 1995)
for helium-cooled components is approximately 3 and that for liquid metal PFcs is about 4. more
fundamental research is required to assess the temperature limits of free-surface liquid metal PFcs
and devise efficient power conversion systems that address this limitation. certainly, further development
is required to reach the technology readiness level required for demo (9-10). Progress is
stymied by a lack of investment in high-temperature materials and liquid metal research, and the
limited capabilities of our present test loops and equipment to operate at the required high temperatures
and pressures. Unless the community addresses this need in a timely manner, we will
not have the actively cooled components required for high-temperature applications like demo, or
even the intermediate facilities needed to fulfill the goals described in Thrusts 12 and 13.
advanced Cooling technologies for Solid PFCs
helium cooling has many advantages in a nuclear system due to its inherently safe, inert chemical
properties; lack of corrosion; vacuum compatibility; single-phase heat transfer without the possibility
of a critical heat flux (chF) excursion; lack of neutron activation; and easy separation from
tritium. most importantly for demo, helium is the fluid of choice for a highly efficient, high-temperature
brayton cycle exhibiting minimal wear and corrosion of gas turbines, and the closed cycle
helps contain any tritium reaching the coolant.
one key disadvantage of helium is its low thermal mass, rc p , that is less than 1% of water. This
necessitates the use of high mass flow rates and greatly enhanced heat transfer area and turbulence
promoters for efficient heat transfer. tremendous progress occurred in this regard during
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