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

The improved confinement from quasi-symmetry has been demonstrated in a university-scale
device, and 3-d theory and modeling continues to develop the range of Qs confinement possibilities.
This Thrust calls for new experiments combined with advances in 3-d theory, to build
Qs stellarators that operate at higher temperature and plasma pressure. The goal of this effort
is to develop sufficient scientific understanding to assess the feasibility of a burning plasma device
based on the Qs stellarator. if successful, the approach could obviate the need for most of the
plasma control sensors and actuators used or proposed for tokamak operation, and largely avoid
the risks associated with operating fusion plasmas at or beyond their stability boundaries.
Research Elements
Progress on stellarator experiments in Japan and Germany over the past two decades leaves little
doubt that high-performance, sustained, disruption-free plasmas are attainable in 3-d configurations.
This Thrust delineates activities to advance our understanding of Qs stellarators to realize
this level of performance. elements of the Thrust also address the unique challenges of constructing
the magnets of 3-d devices, including the implementation of 3-d divertors. lastly, even
tokamaks and other nominally axisymmetric toroidal systems increasingly exhibit nonsymmetric
equilibria, and could benefit from varying degrees of 3-d shaping guided by analytic and numerical
tools drawn from stellarator research.
The Thrust actions are organized into four elements:
• new Qs stellarator experiments for improved confinement in high-performance plasmas.
• design and construction of 3-d coil systems.
• divertors for 3-d configurations.
• Three-dimensional shaping for improved operation of other toroidal systems.
action 1: new QS stellarators for improved confinement in high-performance plasmas
Promising results obtained from the exploratory quasi-symmetric hsX device, coupled with the
scientific benefits of quasi-symmetry, motivate pursuing Qs confinement at a larger scale. The
extensive knowledge base from larger (non-Qs) stellarators gives confidence that a research program
in quasi-symmetric 3-d confinement could be successfully addressed on an experiment at
the performance extension (Pe) scale — an integrated investigation of sustained, stable plasmas
with hot ions, high pressure, and good confinement — as a precursor to a Qs burning plasma device
that could follow iteR. This Thrust as a whole outlines the key research steps to be taken
in preparing for such a performance extension device. in addition to expanded efforts in theory
and international collaborations, these include two intermediate-scale proof-of-principle experiments
that will provide the span of scientific and technical knowledge required for the penultimate
step to a burning Qs stellarator plasma.
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