Instability and transport driven by electron temperature gradient close to critical

Electron temperature gradient (ETG) driven instability and turbulent transport in toroidal plasmas is studied with gyrokinetic theory. The full electron kinetics including finite Larmor radius effects, toroidal (curvature and magnetic gradient) drift motion is considered. The upgraded numerical scheme for solving the integral eigenvalue equations allows the study of both growing and damping modes, and thus direct calculation of critical gradient. A systematic parameter study is carried out for low beta(= plasma pressure/magnetic pressure) circular flux surface equilibria. The behaviors of the modes and the transport in the parameter regimes close to the threshold of the instability are emphasized. The scaling of the critical gradient with respect to plasma parameters such as toroidicity and ratio of electron temperature over ion temperature is given. Possible correlation between the unstable modes and experiments is discussed. (author)