Short wavelength electron temperature gradient instability in toroidal plasmas

The electron temperature gradient (ETG) driven mode in the very short wavelength region k(perpendicular to)rho(e)>1 is identified with a gyrokinetic integral equation code in toroidal plasmas. This "double-humped" growth rate of the conventional ETG and short wavelength ETG modes is attributed to the toroidal drift resonance mechanism and the nonmonotonic behavior of normalized real frequency as the poloidal wavelength varies. This instability provides a possibility existence of a kind of turbulence source with very small size of cells. However, the wavelength of the short wavelength ETG mode is too short and induced transport may be small unless there are inverse cascade effects. In addition, the critical threshold of electron temperature gradient (R/L-Te)(c) for the short wavelength ETG mode is higher than that for the conventional ETG mode. (C) 2005 American Institute of Physics.