Gyrokinetic Theory of Drift Waves in Negative Shear Tokamaks
Yasuhiro IDOMURA, Shinji TOKUDA, Yasuaki KISHIMOTO
Naka Fusion Research Establishment, Japan Atomic Energy Research Institute, Naka, Ibaraki, 311-0193, Japan
Masahiro WAKATANI
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 qmin-surface region of negative shear tokamaks are studied, where qmin 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 qmin-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 ErxB 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 ErxB 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 ErxB zonal flows arising from the ETG turbulence have a strong stabilizing effect on the slab ITG mode.