DIII-D Research to Address Key Challenges for ITER and Fusion Energy
R.J. Buttery, (E. Schuster), et al. (Collaboration Paper)
IAEA Fusion Energy Conference
Saint Petersburg, Russia, October 13-18, 2014
Abstract
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The DIII-D tokamak has addressed critical challenges in preparation
for ITER and the next generation of fusion devices. The robustness and
performance of ITER scenarios was expanded with edge localized mode
suppression demonstrated with a reduced coil set, disruption heat load
and runaway electron mitigation, extending the ITER baseline scenario
to low torque, and developing the promising QH mode to high Greenwald
fraction. Work with the ITER Test Blanket Module simulator has
developed error correction that reduces heat loads by 80% and recovers
most of the performance degradation. The path to fusion energy has been
advanced using DIII-D’s flexible heating systems to develop a high βP
steady state scenario at low neutral beam torque, a 1 MA fully
noninductive hybrid scenario, and sustain a high li regime to βN=5.
The compatibility of high performance regimes with edge solutions has
been demonstrated including: ELM suppression in fully non- inductive
plasmas and sustained high performance in radiative divertor conditions
and new divertor geometries such as the snowflake. A strong science
program identifies underlying physics mechanisms to guide new
developments and provide robust projection to future devices. Transport
studies show the approach to burning plasma conditions increases long
wavelength turbulence and thus thermal and particle transport. Pedestal
models predicted the path to a new super H-mode scenario, achieved with
doubled pedestal pressure, while kinetic models identify separate energy
and particle transport mechanisms near the separatrix. Lithium pellets
lead to a bifurcation to a wider, higher pedestal. The origin of
intrinsic rotation is explained by a kinetic loss-cone model, while the
bifurcation to H-mode is found triggered by turbulence driven rotational
shear and build up of ion diamagnetic flows. Detachment studies measuring
behavior to <1 eV with 2D Thomson scattering identify a radiation
shortfall in simulation models. Upgraded 3D magnetics validate linear
MHD predictions of plasma response. Energetic particle studies validate
fully nonlinear toroidicity-induced Alfvén eigenmode simulations, but
also point to a new paradigm critical gradient model to project behavior.
Future plans target key needs to anticipate burning plasma physics with
torque free electron heating, the path to steady state with increased
off axis currents, and a new divertor solution for future reactors.