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Confinement degradation by Alfvén-eigenmode induced fast-ion transport in steady-state scenario discharges

  • Author(s): Heidbrink, WW
  • Ferron, JR
  • Holcomb, CT
  • Van Zeeland, MA
  • Chen, X
  • Collins, CM
  • Garofalo, A
  • Gong, X
  • Grierson, BA
  • Podestà, M
  • Stagner, L
  • Zhu, Y
  • et al.
Abstract

Analysis of neutron and fast-ion D data from the DIII-D tokamak shows that Alfvén eigenmode activity degrades fast-ion confinement in many high β , high q , steady-state scenario discharges. (β is the normalized plasma pressure and q is the minimum value of the plasma safety factor.) Fast-ion diagnostics that are sensitive to the co-passing population exhibit the largest reduction relative to classical predictions. The increased fast-ion transport in discharges with strong AE activity accounts for the previously observed reduction in global confinement with increasing q ; however, not all high q discharges show appreciable degradation. Two relatively simple empirical quantities provide convenient monitors of these effects: (1) an 'AE amplitude' signal based on interferometer measurements and (2) the ratio of the neutron rate to a zero-dimensional classical prediction. © 2014 IOP Publishing Ltd. α N min N min min min

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