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(OV1/3) Results from the DIII-D Scientific Research Program

T. S. Taylor for the DIII-D Team

DIII-D National Fusion Facility, General Atomics, San Diego, California 92186-5608

Abstract.  The DIII-D research program is aimed at developing the scientific basis for advanced modes of operation which can enhance the commercial attractiveness of the tokamak as an energy producing system. Features that improve the attractiveness of the tokamak as a fusion power plant include: high power density (which demands high $\beta$), high ignition margin (high energy confinement time), and steady state operation with low recirculating power (high bootstrap fraction), as well as adequate divertor heat removal, particle and impurity control. This set of requirements emphasizes that the approach to improved performance must be an integrated approach, optimizing the plasma from the core, through the plasma edge and into the divertor. We have produced high performance ELMing H-mode plasmas with $\beta_{\mathrm{N}}^{}$H_98y $\sim$ 6 for 5$\tau_{\mathrm{E}}^{}$( $\sim$ 1s) and demonstrated that core transport barriers can be sustained for the length of the 5-s neutral beam pulse in L-mode plasmas. We have demonstrated off-axis electron cyclotron current drive for the first time in a tokamak, discovering an efficiency above theoretical expectations. Edge stability studies have shown that the H-mode edge pressure gradient is not limited by ballooning modes; the self-consistent bootstrap provides second stable regime access. Divertor experiments have provided a new understanding of convection and recombination in radiative divertors and have produced enhanced divertor radiation with scrape off layer plasma flows and impurity enrichment.

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