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Long pulse high performance discharges in the DIII-D tokamak

  • Author(s): Luce, TC;
  • Wade, MR;
  • Politzer, PA;
  • Allen, SL;
  • Austin, ME;
  • Baker, DR;
  • Bray, B;
  • Brennan, DP;
  • Burrell, KH;
  • Casper, TA;
  • Chu, MS;
  • DeBoo, JC;
  • Doyle, EJ;
  • Ferron, JR;
  • Garofalo, AM;
  • Gohil, P;
  • Gorelov, IA;
  • Greenfield, CM;
  • Groebner, RJ;
  • Heidbrink, WW;
  • Hsieh, CL;
  • Hyatt, AW;
  • Jayakumar, R;
  • Kinsey, JE;
  • La Haye, RJ;
  • Lao, LL;
  • Lasnier, CJ;
  • Lazarus, EA;
  • Leonard, AW;
  • Lin-Liu, YR;
  • Lohr, J;
  • Mahdavi, MA;
  • Makowski, MA;
  • Murakami, M;
  • Petty, CC;
  • Pinsker, RI;
  • Prater, R;
  • Rettig, CL;
  • Rhodes, TL;
  • Rice, BW;
  • Strait, EJ;
  • Taylor, TS;
  • Thomas, DM;
  • Turnbull, AD;
  • Watkins, JG;
  • West, WP;
  • Wong, KL
  • et al.
Abstract

Significant progress in obtaining high performance discharges lasting many energy confinement times in the DIII-D tokamak has been realized in recent experimental campaigns. Normalized performance ∼10 has been sustained for more than 5>E with qmin > 1.5. (The normalized performance is measured by the product βNH89, indicating the proximity to the conventional β limits and energy confinement quality, respectively.) These H mode discharges have an ELMing edge and β < 5%. The limit to increasing β is a resistive wall mode, rather than the tearing modes as previously observed. Confinement remains good despite qmin > 1. 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. Measurement of the current density and loop voltage profiles indicate that ≈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 β control, which are essential for operating advanced tokamak discharges, were demonstrated in ELMing H mode discharges with βNH89 ≈ 7 for up to 6.3 s or ≈34τE. These discharges appear to have stationary current profiles with qmin ≈ 1.05 in agreement with the current profile relaxation time ≈1.8 s.

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