Confinement and Local Transport in the National Spherical Torus Experiment NSTX

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NSTX operates at low aspect ratio (R/a~1.3) and high beta (up to 40%), allowing tests of global confinement and local transport properties that have been established from higher aspect ratio devices. NSTX plasmas are heated by up to 7 MW of deuterium neutral beams with preferential electron heating as expected for ITER. Confinement scaling studies indicate a strong ΒΤ dependence, with a current dependence that is weaker than that observed at higher aspect ratio. Dimensionless scaling experiments indicate a strong increase of confinement with decreasing collisionality and a weak degradation with beta. The increase of confinement with ΒΤ is due ... continued below

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Kaye, S M; Stutman, D; Tritz, K; Yuh, H; Bell, M G; Bell, R E et al. March 15, 2007.

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NSTX operates at low aspect ratio (R/a~1.3) and high beta (up to 40%), allowing tests of global confinement and local transport properties that have been established from higher aspect ratio devices. NSTX plasmas are heated by up to 7 MW of deuterium neutral beams with preferential electron heating as expected for ITER. Confinement scaling studies indicate a strong ΒΤ dependence, with a current dependence that is weaker than that observed at higher aspect ratio. Dimensionless scaling experiments indicate a strong increase of confinement with decreasing collisionality and a weak degradation with beta. The increase of confinement with ΒΤ is due to reduced transport in the electron channel, while the improvement with plasma current is due to reduced transport in the ion channel related to the decrease in the neoclassical transport level. Improved electron confinement has been observed in plasmas with strong reversed magnetic shear, showing the existence of an electron internal transport barrier (eITB). The development of the eITB may be associated with a reduction in the growth of microtearing modes in the plasma core. Perturbative studies show that while L-mode plasmas with reversed magnetic shear and an eITB exhibit slow changes of LΤe across the profile after the pellet injection, H-mode plasmas with a monotonic q-profile and no eITB show no change in this parameter after pellet injection, indicating the existence of a critical gradient that may be related to the q-profile. Both linear and non-linear simulations indicate the potential importance of ETG modes at the lowest ΒΤ. Localized measurements of high-κ fluctuations exhibit a sharp decrease in signal amplitude levels across the L-H transition, associated with a decrease in both ion and electron transport, and a decrease in calculated linear microinstability growth rates across a wide κ-range, from the ITG/TEM regime up to the ETG regime.

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  • 21st IAEA Fisopm Emergu Cpmferemce, 16-22 October, 2006, Chengdu, China

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  • Report No.: PPPL-4238
  • Grant Number: DE-ACO2-76CHO3073
  • Office of Scientific & Technical Information Report Number: 963555
  • Archival Resource Key: ark:/67531/metadc935137

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  • March 15, 2007

Added to The UNT Digital Library

  • Nov. 13, 2016, 7:26 p.m.

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  • Dec. 12, 2016, 8:48 p.m.

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Kaye, S M; Stutman, D; Tritz, K; Yuh, H; Bell, M G; Bell, R E et al. Confinement and Local Transport in the National Spherical Torus Experiment NSTX, article, March 15, 2007; Princeton, New Jersey. (digital.library.unt.edu/ark:/67531/metadc935137/: accessed July 16, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.