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

• employ energetic particle beams, plasma waves, particle control, and core fueling
techniques to maintain the current and control the plasma profiles.
• develop normally conducting radiation-tolerant magnets for low-a applications.
• extend the st to near-burning plasma conditions in a new or further upgraded device.
a strongly integrated plasma theory and modeling effort, validated against experiment, is required
to enable an optimal st design for a component test facility. This Thrust will also benefit
from, and contribute to, the understanding of the conventional aspect ratio tokamak.
The spherical torus is a low aspect ratio tokamak offering unique physical properties due to very
strong magnetic curvature and compact geometry. it has potential advantages in size, cost, maintenance,
and magnet simplicity. it produces high plasma pressure relative to the external confining
magnetic pressure, and promises high neutron wall loading with reduced tritium consumption.
The st program has made substantial progress since its inception, and is now ready to develop
the knowledge base to confidently construct and operate an st-based Fnst component testing
device, and to aggressively pursue improvements to advance the st for energy production. This
knowledge base is embodied in the Thrust elements below that describe: (1) plasma startup and
ramp-up, (2) plasma-material interface (Pmi), (3) transport, (4) plasma stability and control, (5)
current sustainment, (6) magnets, and (7) next-step st facilities.
Thrust 16 Elements:
1. exploit and understand magnetic turbulence, electromagnetic waves, and energetic particles for
megampere plasma current formation and ramp-up.
low-a tokamak designs reduce or eliminate the available transformer flux for plasma current
initiation and ramp-up to reduce device size and aspect ratio. near-term startup research should
continue to focus on developing the understanding of magnetic helicity injection, radiofrequency
wave-based startup, and novel inductive startup schemes. noninductive ramp-up to full operating
current requires additional effort beyond the capabilities of present sts. Physics-based modeling
of plasma current ramp-up must be validated against existing and upgraded st experiments,
and be extended to include the effects of energetic particle instabilities on fast-particle transport.
These validated models are needed to specify the required noninductive current drive capability
of future st experiments.
actions:
• develop helicity-injection-based startup to a current level sufficient to provide a target
for radiofrequency or neutral beam (nb) ramp-up in present and upgraded facilities.
• Perform, in present or upgraded facilities, startup and initial buildup of a discharge using
radiofrequency in the electron cyclotron frequency range to a similar level. cost-effective
collaborative experiments on the diii-d tokamak device should be explored.
• if needed, conduct mechanical and thermal testing of neutron-tolerant inductive systems
for startup assist, including small iron core and mineral-insulated solenoid approaches.
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