DIII-D Research to Address Key Challenges for ITER and Fusion Energy
IAEA Fusion Energy Conference
Saint Petersburg, Russia, October 13-18, 2014
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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.