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

ment, but also micro- and macro-instabilities – that is, turbulent transport and global stability.
The different approaches might also vary in optimal aspect ratio, how they simplify the coil structures,
or how they approach a 3-d divertor design.
The promise of stellarators is well recognized within the fusion community. stellarator research
is a mature field with many experiments worldwide including large performance extension facilities.
Recommendation 4 in the Fesac “Priorities, Gaps, and opportunities” report (PGo) urges
consideration of a major initiative (i-5) for an “advanced experiment in disruption-free concepts,”
of which the stellarator would be the most likely facility. The Fesac taP report states: “There is
little doubt that a stellarator configuration can confine plasma at the parameters necessary for
fusion burn” and that stellarator research “is likely to contribute significantly to the optimization
of tokamaks and perhaps to other confinement concepts.” This motivated the stellarator iteR-era
goal reported by the taP:
Develop and validate the scientific understanding necessary to assess the feasibility of a burning plasma
experiment based on the quasi-symmetric (QS) stellarator.
a critical gap exists in the worldwide stellarator program in that there are no moderate scale experiments
investigating quasi-symmetry. There is an immediate need to explore quasi-symmetry
with sufficient breadth and scale to achieve the iteR-era goal.
Scientific issues and Research Requirements
intEgRatED HigH PERFORManCE OF QuaSi-SyMMEtRiC OPtiMizED
StELLaRatORS
There is a need to study a plasma in a quasi-symmetric stellarator that has both high plasma pressure
and low ion collisionality. such a test of quasi-axisymmetry was to be performed on the national
compact stellarator experiment (ncsX), which was under construction until 2008. its cancellation
has left a gap in the worldwide program of exploring the science of quasi-symmetry and the
potential of the concept. as described earlier, quasi-symmetric stellarators may differ in how they
approach neoclassical and turbulent transport as well as macrostability. Therefore, there is a need
for multiple quasi-symmetric configurations to assess high-beta, low collisionality, t i ~ t e plasmas
with good confinement. because of the centrality of the issue of disruption control, one approach is
to differentiate the experiments based on the amount of bootstrap current present for a given set of
plasma parameters. The configurations will differ in other attributes such as divertors or impurity
control. based on the results of the multiple experiments, theory and modeling, information gained
from the international stellarator program, a performance extension (Pe) level quasi-symmetric
stellarator that extrapolates to burning plasma performance would be designed and constructed.
research requirements
The multiple quasi-symmetric stellarators would have a common set of research requirements.
These requirements serve as definitions of “integrated high performance.” implicit within these
requirements is sufficient operational flexibility of the magnetic geometry and plasma parameters
to test theory and modeling predictions.
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