DIII-D Research Towards Establishing the Scientific Basis for Future Fusion Reactors
C.C. Petty, (E. Schuster) et al. (Collaboration Paper)
Nuclear Fusion 59 (2019) 112002 (16pp)
Abstract
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DIII-D research is addressing critical challenges in preparation for
ITER and the next generation of fusion devices through focusing on
plasma physics fundamentals that underpin key fusion goals, understanding
he interaction of disparate core and boundary plasma physics, and
developing integrated scenarios for achieving high performance fusion
regimes. Fundamental investigations into fusion energy science find that
anomalous dissipation of runaway electrons (RE) that arise following a
disruption is likely due to interactions with RE-driven kinetic
instabilities, some of which have been directly observed, opening a new
avenue for RE energy dissipation using naturally excited waves.
Dimensionless parameter scaling of intrinsic rotation and gyrokinetic
simulations give a predicted ITER rotation profile with significant
turbulence stabilization. Coherence imaging spectroscopy confirms near
sonic flow throughout the divertor towards the target, which may account
for the convection- dominated parallel heat flux. Core-boundary integration
studies show that the small angle slot divertor achieves detachment at
lower density and extends plasma cooling across the divertor target plate,
which is essential for controlling heat flux and erosion. The Super H-mode
regime has been extended to high plasma current (2.0 MA) and density to
achieve very high pedestal pressures (~30 kPa) and stored energy (3.2 MJ)
with H98y2 ≈ 1.6–2.4. In scenario work, the ITER baseline Q = 10 scenario
with zero injected torque is found to have a fusion gain metric βτE
independent of current between q95 = 2.8–3.7, and a lower limit of
pedestal rotation for RMP ELM suppression has been found. In the wide
pedestal QH-mode regime that exhibits improved performance and no ELMs,
the start-up counter torque has been eliminated so that the entire
discharge uses ≈0 injected torque and the operating space is more
ITER-relevant. Finally, the high-βN (⩽3.8) hybrid scenario has been
extended to the high-density levels necessary for radiating divertor
operation, achieving ~40% divertor heat flux reduction using either
argon or neon with Ptot up to 15 MW.