Sauter, O.LaHaye, R. J.Chang, Z.Gates, D. A.Kamada, Y.Zohm, H.Bondeson, A.Boucher, D.Callen, J. D.Chu, M. S.Gianakon, T. A.Gruber, O.Harvey, R. W.Hegna, C. C.Lao, L. L.Monticello, D. A.Perkins, F.Pletzer, A.Reiman, A. H.Rosenbluth, M.Strait, E. J.Taylor, T. S.Turnbull, A. D.Waelbroeck, F.Wesley, J. C.Wilson, H. R.Yoshino, R.2008-04-162008-04-162008-04-16199710.1063/1.872270https://infoscience.epfl.ch/handle/20.500.14299/21418WOS:A1997WY64700020The 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.ITERtext::journal::journal article::research article