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

• experiments varying the magnitude of plasma current in plasmas of similar parameters
that would address relative susceptibility to macroscopic instabilities and requirements
for control. The Qa experiment would extrapolate the plasma characteristics of symmetric
tokamaks to 3-d systems.
• expansion of 3-d theory and modeling in the areas of turbulent transport, b-limits,
impurity transport, nonlinear effects, effects of stochastic magnetic fields, energetic
particle effects, effects of plasma rotation, and kinetic effects on equilibrium and stability
with 3-d fields.
• inclusion of 3-d theory and modeling in the effort to develop predictive simulation
capability for fusion plasmas (Thrust 6) applicable to both stellarators and tokamaks, in
which small asymmetries of order db/b ~ 10 -3 are known to affect the plasma behavior.
• targeted collaboration on the Pe-scale, nonsymmetric experiments lhd (Japan) and
W7-X (Germany). These activities will focus on steady-state 3-d divertor performance,
pressure-limiting mechanisms in stellarators (experimentally benign, but not yet well
understood), and integrated performance, e.g., confinement of high-temperature, highpressure
plasmas with low impurity content.
• implementation of research program to extend the knowledge of Qs plasma confinement
to near-burning conditions in a long-pulse, high-field Qs Pe-scale experiment. The
outcome will be a predictive understanding of the dependence of Qs confinement on
system size and plasma temperature that extrapolates to burning plasma performance.
The results of the other actions of this Thrust and further reactor studies will guide the
design of this experiment.
action 2: Design and construction of 3-D coil systems
The 3-d coil sets required to produce stellarator magnetic configuration are more complex than
those used in tokamaks. The goal is to reduce the technical risk and cost of constructing and
maintaining large-scale stellarators.
key research steps include:
• Reevaluation of the plasma parameters (maximum b, degree of quasi-symmetry, aspect
ratio, etc.) that drive the design of magnet coil. evolving knowledge from experiments,
theory, and engineering optimization will be folded into Qs magnet design.
• investigation through modeling of different coil geometries, e.g., continuous helical coils,
saddle coils, range of aspect ratios, to identify desirable Qs configurations with simpler
coils.
• Greater use of auxiliary trim coils to ease fabrication and assembly tolerances, and increase
flexibility in the magnetic configuration.
• innovative use of magnetic materials to simplify the shaping of the 3-d field.
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