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Title: High internal inductance for steady-state operation in ITER and a reactor

Increased confinement and ideal stability limits at relatively high values of the internal inductance ($${{\ell}_{i}}$$ ) have enabled an attractive scenario for steady-state tokamak operation to be demonstrated in DIII-D. Normalized plasma pressure in the range appropriate for a reactor has been achieved in high elongation and triangularity double-null divertor discharges with $${{\beta}_{\text{N}}}\approx 5$$ at $${{\ell}_{i}}\approx 1.3$$ , near the ideal $n=1$ kink stability limit calculated without the effect of a stabilizing vacuum vessel wall, with the ideal-wall limit still higher at $${{\beta}_{\text{N}}}>5.5$$ . Confinement is above the H-mode level with $${{H}_{98\left(\text{y},2\right)}}\approx 1.8$$ . At $${{q}_{95}}\approx 7.5$$ , the current is overdriven, with bootstrap current fraction $${{f}_{\text{BS}}}\approx 0.8$$ , noninductive current fraction $${{f}_{\text{NI}}}>1$$ and negative surface voltage. For ITER (which has a single-null divertor shape), operation at $${{\ell}_{i}}\approx 1$$ is a promising option with $${{f}_{\text{BS}}}\approx 0.5$$ and the remaining current driven externally near the axis where the electron cyclotron current drive efficiency is high. This scenario has been tested in the ITER shape in DIII-D at $${{q}_{95}}=4.8$$ , so far reaching $${{f}_{\text{NI}}}=0.7$$ and $${{f}_{\text{BS}}}=0.4$$ at $${{\beta}_{\text{N}}}\approx 3.5$$ with performance appropriate for the ITER Q=5 mission, $${{H}_{89}}{{\beta}_{\text{N}}}/q_{95}^{2}\approx 0.3$$ . Modeling studies explored how increased current drive power for DIII-D could be applied to maintain a stationary, fully noninductive high $${{\ell}_{i}}$$ discharge. Lastly, stable solutions in the double-null shape are found without the vacuum vessel wall at $${{\beta}_{\text{N}}}=4$$ , $${{\ell}_{i}}=1.07$$ and $${{f}_{\text{BS}}}=0.5$$ , and at $${{\beta}_{\text{N}}}=5$$ with the vacuum vessel wall.
Authors:
 [1] ;  [2] ;  [1] ;  [3] ;  [4] ;  [1] ;  [4] ;  [5]
  1. General Atomics, San Diego, CA (United States)
  2. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  4. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  5. Columbia Univ., New York, NY (United States)
Publication Date:
OSTI Identifier:
1371747
Grant/Contract Number:
FC02-04ER54698; AC52-07NA27344; AC05-00OR22725; AC02-09CH11466; FG02-04ER54761
Type:
Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 55; Journal Issue: 7; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Research Org:
General Atomics, San Diego, CA (United States)
Sponsoring Org:
USDOE Advanced Research Projects Agency - Energy (ARPA-E); USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; internal inductance; steady-state; tokamak operation