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Title: The high-β{sub N} hybrid scenario for ITER and FNSF steady-state missions

New experiments on DIII-D have demonstrated the steady-state potential of the hybrid scenario, with 1 MA of plasma current driven fully non-inductively and β{sub N} up to 3.7 sustained for ∼3 s (∼1.5 current diffusion time, τ{sub R}, in DIII-D), providing the basis for an attractive option for steady-state operation in ITER and FNSF. Excellent confinement is achieved (H{sub 98y2} ∼ 1.6) without performance limiting tearing modes. The hybrid regime overcomes the need for off-axis current drive efficiency, taking advantage of poloidal magnetic flux pumping that is believed to be the result of a saturated 3/2 tearing mode. This allows for efficient current drive close to the axis, without deleterious sawtooth instabilities. In these experiments, the edge surface loop voltage is driven down to zero for >1 τ{sub R} when the poloidal β is increased above 1.9 at a plasma current of 1.0 MA and the ECH power is increased to 3.2 MW. Stationary operation of hybrid plasmas with all on-axis current drive is sustained at pressures slightly above the ideal no-wall limit, while the calculated ideal with-wall MHD limit is β{sub N} ∼ 4–4.5. Off-axis Neutral Beam Injection (NBI) power has been used to broaden the pressure and current profiles in this scenario, seeking tomore » take advantage of higher predicted kink stability limits and lower values of the tearing stability index Δ′, as calculated by the DCON and PEST3 codes. Results based on measured profiles predict ideal limits at β{sub N} > 4.5, 10% higher than the cases with on-axis NBI. A 0-D model, based on the present confinement, β{sub N} and shape values of the DIII-D hybrid scenario, shows that these plasmas are consistent with the ITER 9 MA, Q = 5 mission and the FNSF 6.7 MA scenario with Q = 3.5. With collisionality and edge safety factor values comparable to those envisioned for ITER and FNSF, the high-β{sub N} hybrid represents an attractive high performance option for the steady-state missions of these devices.« less
Authors:
 [1] ; ; ; ; ;  [2] ;  [3] ;  [4] ;  [5] ;  [6]
  1. Columbia University, New York, New York 10027 (United States)
  2. General Atomics, P.O. Box 85608, San Diego, California 92186-5608 (United States)
  3. University of California, Irvine, Irvine, California 92697 (United States)
  4. Dipartimento di Energia, Politecnico di Milano, via Ponzio 34/3, I-20133 Milano (Italy)
  5. Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States)
  6. Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)
Publication Date:
OSTI Identifier:
22410393
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 22; Journal Issue: 5; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; BEAM INJECTION; BETA RATIO; COMPUTER CODES; DIFFUSION; DOUBLET-3 DEVICE; ECR HEATING; ELECTRIC CURRENTS; ELECTRIC POTENTIAL; FIRST WALL; ITER TOKAMAK; KINK INSTABILITY; MAGNETIC FLUX; MAGNETOHYDRODYNAMICS; PLASMA; PLASMA CONFINEMENT; SAWTOOTH OSCILLATIONS; STEADY-STATE CONDITIONS; TEARING INSTABILITY