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Dimensionless scaling of the critical beta for onset of a neoclassical tearing mode

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Author(s)

  • R J La Haye
  • R J Buttery
  • S Guenter
  • G T A Huysmans
  • M Maraschek
  • H R Wilson

Department/unit(s)

Publication details

JournalPhysics of Plasmas
DatePublished - Aug 2000
Issue number8
Volume7
Number of pages11
Pages (from-to)3349-3359
Original languageEnglish

Abstract

The islands from tearing modes driven unstable and sustained by the helically perturbed neoclassical bootstrap current often provide the practical limit to long-pulse, high confinement tokamak operation. The destabilization of such "metastable" plasmas depends on a "seed" island exceeding a threshold. A database from similar regimes [high confinement H-mode with periodic edge localized modes (ELMs) and periodic central sawteeth] was compiled from the tokamaks ASDEX Upgrade (AUG) [Plasma Phys. Controlled Fusion 41, 767 (1999)], DIII-D [Nucl. Fusion 38, 987 (1998)], and JET (Joint European Torus) [Plasma Phys. Controlled Fusion 41, B1 (1999)]. A comparison is made of the measured critical beta for onset of the m/n=3/2 mode (m and n being the poloidal and toroidal Fourier harmonics, respectively) to a model in terms of dimensionless parameters for the seed and threshold islands. This modeling is then used for extrapolation to a reactor-grade tokamak design such as ITER/FDR (International Thermonuclear Experimental Reactor/Final Design Report) [Nucl. Fusion 39, 2137 (1999)]; this indicates that the seed island from sawteeth could be too small to sufficiently disturb the metastable plasma and excite the m/n=3/2 neoclassical tearing mode. (C) 2000 American Institute of Physics. [S1070- 664X(00)02408-3].

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