DIII-D research advancing the physics basis for optimizing the tokamak approach to fusion energy
M. Fenstermacher, (E. Schuster), et al. (Collaboration Paper)
Nuclear Fusion 62 (2022) 042024 (22pp).
Abstract
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DIII-D physics research addresses critical challenges for the operation
of ITER and the next generation of fusion energy devices. This is done
through a focus on innovations to provide solutions for high performance
long pulse operation, coupled with fundamental plasma physics understanding
and model validation, to drive scenario development by integrating high
performance core and boundary plasmas. Substantial increases in off-axis
current drive efficiency from an innovative top launch system for EC power,
and in pressure broadening for Alfven eigenmode control from a co-/counter-Ip s
teerable off-axis neutral beam, all improve the prospects for optimization
of future long pulse/steady state high performance tokamak operation.
Fundamental studies into the modes that drive the evolution of the pedestal
pressure profile and electron vs ion heat flux validate predictive models
of pedestal recovery after ELMs. Understanding the physics mechanisms of
ELM control and density pumpout by 3D magnetic perturbation fields leads
to confident predictions for ITER and future devices. Validated modeling
of high-Z shattered pellet injection for disruption mitigation, runaway
electron dissipation, and techniques for disruption prediction and avoidance
including machine learning, give confidence in handling disruptivity for
future devices. For the non-nuclear phase of ITER, two actuators are
identified to lower the L–H threshold power in hydrogen plasmas. With
this physics understanding and suite of capabilities, a high poloidal
beta optimized-core scenario with an internal transport barrier that
projects nearly to Q = 10 in ITER at ∼8 MA was coupled to a detached
divertor, and a near super H-mode optimized-pedestal scenario with co-Ip
beam injection was coupled to a radiative divertor. The hybrid core
scenario was achieved directly, without the need for anomalous current
diffusion, using off-axis current drive actuators. Also, a controller
to assess proximity to stability limits and regulate βN in the ITER
baseline scenario, based on plasma response to probing 3D fields, was
demonstrated. Finally, innovative tokamak operation using a negative
triangularity shape showed many attractive features for future pilot
plant operation.