Following boronization, tokamak discharges in DIII-D have been obtained with confinement times up to a factor of 3.5 above the ITER89-P L-mode scaling and 1.8 times greater than the DIII-D/JET Hmode scaling relation. Very high confinement phases are characterized by relatively high central density with n e (0) ~ 1 xlO 20 m~3, and central ion temperatures up to 13.6 keV at moderate plasma currents (1.6 MA) and heating powers (12.5-15.3 MW). These discharges exhibit a low fraction of radiated power, F< 25%, Z e nr(0) close to unity, and lower impurity influxes than comparable DIII-D discharges before boronization.PACS numbers: 52.55.Fa, 52.25.Fi, 52.25.Vy In order to achieve ignition in proposed future fusion devices such as the Burning Plasma Experiment (BPX) and the International Thermonuclear Experimental Reactor (ITER), global energy confinement significantly better than the low-mode (L-mode) scaling relation is required in discharges with a low influx of impurities and low dilution of hydrogenic species [1]. Following boronization we have recently obtained discharges in the DIII-D tokamak with a very high confinement quiescent phase. These discharges have been repeated over many experimental days. We refer to this very high confinement phase as the VH mode. A number of tokamaks have obtained a high confinement mode (// mode) [2] with energy confinement times approximately a factor of 2 greater than for the L mode. In F/Z-mode discharges global energy confinement times are as much as a factor of 3.5 above ITER89-P [1] L-mode scaling and 1.8 times greater than the DIII-D/JET //-mode thermal confinement scaling relation [3]. This dramatic improvement in confinement quality is of great importance since the triple product noT,TE (related to the ratio of fusion power to heating power) in a tokamak fusion system increases as the square of the confinement enhancement factor over the L-mode scaling. Moreover, the VH phase of these discharges has shown less radiated power loss than is usually observed in comparable quiescent, i.e., ELM-free, //-mode discharges. [Edge-localized modes (ELMs) are transient phenomena which can occur in the outer plasma region and produce enhanced particle and energy transport, //-mode behavior is often described by the presence or absence (quiescent phase) of ELMs.] Temperature and density profiles show steep edge gradients extending further into the plasma than in the normal H mode, indicating a thicker edge transport barrier region.Boronization is a plasma-assisted chemical vapor deposition (CVD) process which deposits a thin, amorphous boron or boron-carbon film on all plasma facing components [4,5]. The boronization process was first implemented and later optimized in the TEXTOR tokamak at Forschungszentrum Julich GmbH [4]. Boronization in DIII-D (in collaboration with Julich) was accomplished using a glow discharge [6] in a helium-diborane gas mixture, 90% He and 10% B 2 D 6 , at a pressure of 5x10 ~3 mbar. A film of 100 nm average thickness was deposited. Depth profiles of a sample...

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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-I p steerable 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-I p 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 β N 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.

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