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

(up to 1000s) operation in iteR. Further challenges are presented when addressing the higher
power density, high-temperature wall, bulk (neutron) and surface (charged particle) accumulated
damage and near steady-state operational conditions necessary for a Fusion nuclear science Facility
(FnsF) or demo device.
PSi Research and the need for advanced test Facilities
Ultimately, the control of Psi must be demonstrated in a fully integrated confinement facility.
however, much of the understanding necessary to demonstrate control of Psi can be achieved
through the use of lower cost, more flexible, and partially integrated test facilities.
examples of the Psi knowledge gaps that can be addressed utilizing Psi test facilities are as follows:
• Erosion and redeposition — knowledge gaps remain in the basic processes that govern
erosion; an example is the impact of mixed materials on chemical sputtering. in addition,
the demo Psi will involve thick layers of redeposited material, whose interaction
properties are as yet unknown. The ability to predict the erosion and redeposition of
material, including the synergy of multi-species plasmas and mixed materials, is required.
• Tritium retention — tritium control and accounting will be crucial for the success of demo.
to achieve this, the processes that lead to retention of tritium in materials subjected to
high plasma particle flux, and the feedback of this saturated surface with the incident
plasma, need to be understood.
• Radiation transport — The conventional divertor scenario results in an optically
thick divertor at demo parameters. For prediction of divertor operation under these
conditions, plasma and neutrals models with radiation transport and trapping need to be
validated with high-quality data.
• Transient events — The survival of plasma facing materials to thermal transients will
set the limits on acceptable size and duration of the transient events. The damage to
materials caused by both rare, large events and frequent, smaller events must therefore
be well characterized.
• Testing of new materials and concepts — The extreme environment expected in demo
will require new material developments and concepts. exploration of materials and the
characterization of promising candidates need to be performed to test their possible
application to demo.
• Neutron irradiated materials — The high neutron fluence expected in demo will affect
erosion and tritium retention properties of materials in components. near-surface
material properties will be altered by the neutron damage. Thus, characterization of
neutron-damaged specimens and validation of performance are needed.
The scientific bases for filling the knowledge gaps in Psi technology can be accomplished by using
dedicated test facilities. at the simplest level, ion beam facilities allow measurements of the elementary
processes of chemical and physical sputtering, in an environment that allows full con-
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