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(TH1/2) Discontinuity Model for Internal Transport Barrier Formation in Reversed Magnetic Shear Plasmas

Y. Kishimoto, J-Y. Kim¹, W. Horton², T. Tajima², M. J. LeBrun²

Japan Atomic Energy Research Institute, Naka Fusion Research Establishment, Naka, Ibaraki, 311-01 Japan
¹ Korea Basic Science Institute, 52 Yeoeundong, Yusung, Korea
² Institute for Fusion Studies, The University ofTexas at Austin, Austin, Texas, 78712 USA

Abstract.  To aid in understanding the internal transport barrier (ITB) being formed in reversed magnetic shear experiments, in addition to the well known shear flow effect, we point out an important nonlocal effect and/or finite size effect which comes from the complex behavior of the nonlocal mode over a finite radial region around the minimum q(safety factor)-surface. The nonlocal mode changes its structure depending on the sign of the magnetic shear and due to this fact, the nonlocal modes are weakly excited across the q_min-surface. This leads to a discontinuity or gap which disconnects the phase relation in the global wave structure across the q_min-surface. Once such a discontinuity (or gap) is formed, transport suppression occurs and therefore a transport barrier can be expected near the q_min-surface. We confirm the existence of this discontinuity using a toroidal particle simulation.

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