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

esearch requirements
• evaluate the physics targets for device optimization and the sensitivity of the designs
to these targets. identify the level of quasi-symmetry needed as reactor conditions are
approached.
• identify the most deleterious field errors and how to correct with trim coils.
• determine optimal aspect ratios and divertor solutions for Qs stellarators; this may
depend on the type of quasi-symmetry employed.
• examine the use of magnetic materials for field shaping and coil simplification.
• investigate how 3-d fields can be used to improve performance in axisymmetric devices.
PREDiCtiVE CaPabiLity
improved predictive capability is a key element across all of toroidal confinement and is the basis
for Thrust 6. Three-dimensional equilibrium effects are central to stellarator optimization. There is
a need to further develop major theory and computational efforts that have the ability to describe
plasma physics in 3-d configurations without well-formed magnetic surfaces. equilibrium determination
and finite-beta magnetic field structure are overlapping issues for all toroidal configurations.
This is especially true given that stability limits in stellarators appear to manifest themselves
as degradation in transport and not virulent behavior. it would be highly desirable for major
simulation codes in the Us fusion program to have the capability to handle 3-d configurations.
research requirements
• Predictive tools that credibly describe 3-d equilibria including the effects of magnetic
islands, plasma flow, stochasticity, and energetic particle modes.
• clear understanding with experimental confirmation of stability limits in stellarators.
• Three-dimensional equilibrium reconstruction capability.
• integration of 3-d effects into the Fusion simulation Program (FsP) in the Us.
DiVERtORS
a key element for any fusion device is an effective divertor to remove heat and helium “ash,” and
to restrict impurity atoms from entering the core plasma. divertors have been essential in achieving
present stellarator results, and led to record hour-long discharges in lhd, limited only by divertor
power handling. a radiative divertor with a more uniform power deposition is plausible in
advanced stellarators because they can operate with high-edge densities. nonetheless, divertor development
for stellarators trails that for tokamaks, and is furthermore complicated by the 3-d geometry.
much of the work on stellarator divertors makes use of the island divertor concept, which
depends on edge resonances in the rotational transform. This introduces a need to control the edge
magnetic geometry, and the interaction region is undesirably close to the confinement region.
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