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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 Dα data from the DIII-D tokamak shows that Alfvén eigenmode activity degrades fast-ion confinement in many high βN, high qmin, steady-state scenario discharges. (βN is the normalized plasma pressure and qmin 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 qmin; however, not all high qmin 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.

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