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

ing edge plasma models, a new high-plasma heat-flux tokamak facility will be needed. once the
underlying edge/sol instabilities are identified, a key need is to develop an edge/sol transport
model for the intermittent blob/elm plasma filaments. Furthermore, this intermittent transport
likely causes inward convection of impurities that must be understood.
Code deVelopmenT
Can simulation codes be developed with improved coupling among plasma components (neutral, plasma,
and impurity transport) and overall material response to yield predictive capability?
as discussed, these are extensive gaps in existing plasma-material interaction theory, modeling/
code efforts and experimental validation. Gaining understanding and predictive capabilities in
this critical area will require addressing simultaneously complex and diverse physics occurring
over a wide range of lengths (angstroms to meters) and times (femtoseconds to days). This will
require further development of detailed physics models and computational strategies at each of
these scales, as well as algorithms and methods to strongly couple them in a way that can be robustly
validated. While present research, combining at most a few of these scales, already pushes
the state-of-the-art in technique and available computational power, simulations spanning the
multiple scales needed for iteR and demo will require extreme-scale computing platforms and
integrated physics and computer science advances.
The goal is to develop comprehensive computational models for predictive, self-consistent, validated,
and time-dependent plasma-material interactions. This would first encompass modeling
of the edge and scrape-off layer plasma, including treatment of turbulent transport, and full coupling
of plasma ions and electrons, neutrals, photons, and electromagnetic fields. next, plasma
contamination from near-surface transport of sputtered or vaporized material, and quantification
of PFc particle and photon fluxes (and prediction of instability regimes) would be included. a
critical related issue is to predict the near-surface material response to the extreme plasma fluxes
of photons and particles, both under normal and transient operation. This involves modeling of
sputtering erosion and redeposition and other time-integrated PFc processes (e.g., dust formation
and transport, helium, and d-t induced microstructure formation and flaking) and the resultant
impurity transport, core plasma contamination, mixed-material formation, and tritium
co-deposition in redeposited materials. The material and edge plasma response to transient processes
such as high-powered elms, vertical displacement events (vdes), plasma disruptions,
and runaway electrons would be an important component of this effort.
innoVaTiVe diVerTors
Can innovative divertor configurations be developed to control the plasma heat flux problem?
large, localized plasma heat exhaust is a critical problem for the development of tokamak fusion
reactors. excessive heat flux erodes and melts plasma facing materials, thereby dramatically
shortening their lifetime and increasing the impurity contamination of the core plasma. a detailed
assessment of the iteR divertor has revealed substantial limitations on the plasma operational
space imposed by the divertor performance. For a commercial fusion reactor the problem
becomes worse in that the divertor must accommodate 20% of the total fusion power (less any
broadly radiated loss), while not allowing excessive impurity production or tritium co-deposition
and retention. This is a challenging set of problems that must be solved for fusion to succeed as a
power source; it calls for a substantial research investment.
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