DIII-D Research Towards Establishing the Scientific Basis for Future Fusion Reactors
C.C. Petty, (E. Schuster), et al. (Collaboration Paper)
27th IAEA Fusion Energy Conference
Gandhinagar, India, October 22-27, 2018
Abstract
|
|
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
the 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 can 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. A rotating n=2 RMP combined with a stationary n=3 RMP has
demonstrated access to ELM suppression with lower 3D field strength,
while at the same time dynamically smoothing out the divertor heat and
particle flux. 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 to the pedestal rotation for RMP ELM
suppression has been found. In the wide pedestal QH-mode regime that
exhibits improved performance and no ELMs, the startup 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.