Short wavelength ion temperature gradient instability in toroidal plasmas

Series of ion temperature gradient (ITG or eta(i)) driven modes in the short wavelength region, parallel tok(perpendicular to)rho(i)parallel to>1, are investigated with a gyrokinetic integral equation code in toroidal plasmas. These instabilities exist even if electrons are assumed adiabatic. However, nonadiabatic electron response can influence these short wavelength ITG (SWITG) modes, especially the fundamental l=0 mode. At typical parameters, excitation of the l=0 mode requires that both eta(i) and eta(e) exceed thresholds, while the l=1 and l=2 modes with higher harmonic eigenfunctions persist unstable even at eta(e)=0. Dependence of the SWITG modes on other parameters is also investigated. The l=1 mode with an odd potential eigenfunction grows faster than the l=0 mode and may be dominant in low eta(e), high beta, weak positive magnetic shear, and/or weak toroidicity regions. (C) 2005 American Institute of Physics.