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

integrated effort that includes fundamental improvements in modeling coupled with experimental
validation of the models on both dedicated test stands and confinement devices.
other challenges concern the antenna straps, Faraday shield or front grill of launchers and additional
nearby structure and surfaces. Radiofrequency breakdown/arcing is one of the main power
limiting issues with operating the antenna in a plasma environment and is poorly understood.
The anticipated large outer gap on demo (and iteR) and the resulting impact on loading will likely
push operating voltages to at least as high as the iteR design limit of 45 kv. The interaction of
the antenna surfaces with the plasma (including elms) and the role of the resulting particles and
local gas load on breakdown and loading are issues that need improved understanding.
The antenna structure and Faraday shield will likely be constructed from layered or coated materials.
launcher materials require good conductivity and high heat resistance. The behavior of
these structures in a nuclear environment and the survivability in long-term operations is a concern.
The exposed antenna or launcher surfaces must be resistive to high heat (1-10 mW/m 2 ) and
neutron fluxes with acceptable levels of impurity production. launcher windows and antenna insulators
must retain their function in high-radiation environments. also, issues that result from
operating at ~600 °c, as required by demo, need to be addressed.
For remotely maintained d-t experiments, the performance criteria for radiofrequency antennas
and launchers become more demanding, as replacement or repair becomes complicated. shadowing
components may be required in some cases where extensive particle deposition can impede
function.
in present-day ech launchers, a final mirror is used to direct the microwave power toroidally and
poloidally to achieve optimal coupling to the plasma. The final mirror must have a highly reflecting
surface to reduce the heat load on the mirror itself. The obvious concern is that this surface
will not last for many years when exposed to the burning plasma.
inTernal Coils
Can the severity of off-normal events be lessened or eliminated by using 3-D internal coil systems?
Can insulating and conductive materials be developed with specific materials, coatings, and heat sinks
suitable for internal coil components for the fusion environment, resulting in components that are robust
and tolerant of plasma conditions?
There are fundamental gaps in our understanding of internal control coils in future confinement
devices as fusion research proceeds toward demo. Reliable and predictable cancellation of error
fields, suppression of resistive wall modes, RmPs, and elms, and control of vertical stability cannot
be achieved unless these gaps are closed. integration of fully 3-d mhd codes with realistic
control coil geometry is needed to understand how the coils affect the plasma and how the different
coil sets interact with each other. Three-dimensional fields could have an impact on the sol
and possibly the divertor, and could result in toroidally asymmetric heat and particle loads on the
PFcs. This could be beneficial by spreading the heat flux, or deleterious, by increasing the peak
heat flux. The impact of these effects has not been considered for iteR or demo. to address these
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