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Beta limits in long-pulse tokamak discharges

Research output: Contribution to journalArticle


  • O Sauter
  • R J LaHaye
  • Z Chang
  • D A Gates
  • Y Kamada
  • H Zohm
  • A Bondeson
  • D Boucher
  • J D Callen
  • M S Chu
  • T A Gianakon
  • O Gruber
  • R W Harvey
  • C C Hegna
  • L L Lao
  • D A Monticello
  • F Perkins
  • A Pletzer
  • A H Reiman
  • M Rosenbluth
  • E J Strait
  • T S Taylor
  • A D Turnbull
  • F Waelbroeck
  • J C Wesley
  • R Yoshino


Publication details

JournalPhysics of Plasmas
DatePublished - May 1997
Issue number5
Number of pages11
Pages (from-to)1654-1664
Original languageEnglish


The maximum normalized beta achieved in long-pulse tokamak discharges at low collisionality falls significantly below both that observed in short pulse discharges and that predicted by the ideal MHD theory. Recent long-pulse experiments, in particular those simulating the International Thermonuclear Experimental Reactor (ITER) [M. Rosenbluth et al., Plasma Physics and Controlled Nuclear Fusion (International Atomic Energy Agency, Vienna, 1995), Vol. 2, p. 517] scenarios with low collisionality nu(e)*, are often limited by low-m/n nonideal magnetohydrodynamic (MHD) modes. The effect of saturated MHD modes is a reduction of the confinement time by 10%-20%, depending on the island size and location, and can lead to a disruption. Recent theories on neoclassical destabilization of tearing modes, including the effects of a perturbed helical bootstrap current, are successful in explaining the qualitative behavior of the resistive modes and recent results are consistent with the size of the saturated islands. Also, a strong correlation is observed between the onset of these low-m/n modes with sawteeth, edge localized modes (ELM), or fishbone events. consistent with the seed island required by the theory. We will focus on a quantitative comparison between both the conventional resistive and neoclassical theories, and the experimental results of several machines, which have all observed these low-min nonideal modes. This enables us to single out the key issues in projecting the long-pulse beta limits of ITER-size tokamaks and also to discuss possible plasma control methods that can increase the soft beta limit, decrease the seed perturbations, and/or diminish the effects on confinement. (C) 1997 American Institute of Physics.

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