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(TH2/6) Gyrokinetic Theory of Drift Waves in Negative Shear Tokamaks

Y. Idomura¹⁾, S. Tokuda¹⁾, Y. Kishimoto¹⁾, M. Wakatani^2)
 
1) Naka Fusion Research Establishment, Japan Atomic Energy Research Institute, Naka, Ibaraki, 311-0193, Japan
²⁾ Graduate School of Energy Science, Kyoto University, Uji, Kyoto, 611-0011, Japan

Abstract.  Linear and nonlinear properties of slab drift waves in the negative sheared slab configuration modeling the q_min-surface region of negative shear tokamaks are studied, where q_min is the minimum value of a safety factor q. Linear calculations show that both the slab ion temperature gradient driven (ITG) mode and the slab electron temperature gradient driven (ETG) mode become strongly unstable around the q_min-surface. Nonlinear simulations are performed for the ETG turbulence which evolves in a much faster time scale than the ITG turbulence. It is found that quasi-steady E_r×B zonal flows are generated by an inverse wave energy cascade process. Linear stability analyses of the electrostatic Kelvin-Helmholtz (K-H) mode show that the quasi-steady E_r×B zonal flow profile is closely related to the q-profile or the magnetic shear, which has a stabilizing effect on the K-H mode. It is shown that the microscopic quasi-steady E_r×B zonal flows arising from the ETG turbulence have a strong stabilizing effect on the slab ITG mode.

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