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(EX4/3) Long-Pulse High-Performance Discharges in the DIII-D Tokamak

T. C. Luce¹⁾, M. R. Wade²⁾, P. A. Politzer¹⁾, S. L. Allen³⁾, M. E. Austin⁴⁾, D. R. Baker¹⁾, B. Bray¹⁾, D. P. Brennen⁵⁾¹⁾, K. H. Burrell¹⁾, T. A. Casper³⁾, M. S. Chu¹⁾, J. C. DeBoo¹⁾, E. J. Doyle⁶⁾, J. R. Ferron¹⁾, A. M. Garofalo⁷⁾, P. Gohil¹⁾, I. A. Gorelov⁸⁾, C. M. Greenfield¹⁾, R. J. Groebner¹⁾, W. W. Heidbrink⁹⁾, C.-L. Hsieh¹⁾, A. W. Hyatt¹⁾, R. Jayakumar³⁾, J. E. Kinsey¹⁰⁾, R. J. La Haye¹⁾, L. L. Lao¹⁾, C. J. Lasnier³⁾, E. Lazarus²⁾, A. W. Leonard¹⁾, Y. R. Lin-Liu¹⁾, J. Lohr¹⁾, M. A. Mahdavi¹⁾, M. A. Makowski³⁾, M. Murakami²⁾, C. C. Petty¹⁾, R. I. Pinsker¹⁾, R. Prater¹⁾, C. L. Rettig⁶⁾, T. L. Rhodes⁶⁾, B. W. Rice³⁾, E. J. Strait¹⁾, T. S. Taylor¹⁾, D. M. Thomas¹⁾, A. D. Turnbull¹⁾, J. G. Watkins¹¹⁾, W. P. West¹⁾, and K. L. Wong^8)
 
1) General Atomics, P.O. Box 85608, San Diego, California USA
²⁾ Oak Ridge National Laboratory, Oak Ridge, Tennessee USA
³⁾ Lawrence Livermore National Laboratory, Livermore, California USA
⁴⁾ University of Texas-Austin, Austin, Texas USA
⁵⁾ ORISE, Oak Ridge, Tennessee USA
⁶⁾ University of California-Los Angeles, California USA
⁷⁾ Columbia University, New York, New York USA
⁸⁾ Princeton Plasma Physics Laboratory, Princeton, New Jersey USA
⁹⁾ University of California, Irvine, California USA
¹⁰⁾ Lehigh University, Bethlehem, Pennsylvania USA
¹¹⁾ Sandia National Laboratories, Albuquerque, New Mexico USA

Abstract.  Significant progress in obtaining high performance discharges for many energy confinement times in the DIII-D tokamak has been realized since the previous IAEA meeting. In relation to previous discharges, normalized performance $\sim$ 10 has been sustained for > 5$\tau_{\mathrm{E}}^{}$ with q_min > 1.5. (The normalized performance is measured by the product $\beta_{\mathrm{N}}^{}$H₈₉ indicating the proximity to the conventional $\beta$ limits and energy confinement quality, respectively.) These H-mode discharges have an ELMing edge and $\beta$ $\lesssim$ 5%. The limit to increasing $\beta$ is a resistive wall mode, rather than the tearing modes previously observed. Confinement remains good despite the increase in q. The global parameters were chosen to optimize the potential for fully non-inductive current sustainment at high performance, which is a key program goal for the DIII-D facility in the next two years. Measurement of the current density and loop voltage profiles indicate $\sim$ 75% of the current in the present discharges is sustained non-inductively. The remaining ohmic current is localized near the half radius. The electron cyclotron heating system is being upgraded to replace this remaining current with ECCD. Density and $\beta$ control, which are essential for operating advanced tokamak discharges, were demonstrated in ELMing H-mode discharges with $\beta_{\mathrm{N}}^{}$H₈₉ $\sim$ 7 for up to 6.3 s or $\sim$ 34$\tau_{\mathrm{E}}^{}$. These discharges appear to be in resistive equilibrium with q_min $\sim$ 1.05, in agreement with the current profile relaxation time of 1.8 s.

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