ION-TEMPERATURE-GRADIENT-DRIVEN TURBULENCE AND TRANSPORT IN A SHEARED MAGNETIC-FIELD

An analytical and numerical investigation has been completed of the nonlinear growth and saturation of long-wavelength ion-temperature-gradient-driven turbulence in a sheared magnetic field for the case of an isolated rational surface. The radial correlation length of the turbulence is found to be of order rho(i)L(s)/L(t), with rho-i the ion Larmor radius, L(s) the magnetic shear length, and L(T) the temperature scale length. The scaling of the resulting anomalous cross-field diffusivity is chi-perpendicular-to proportional g(eta-i)(rho-i2/L(T)L(y))(L(s)/L(T))2-rho-i-upsilon-ti, where g(eta-i) is obtained from the numerical results. In the poloidal direction, the spectrum collapses to the longest wavelength, L(y), available. Explicit results for the function g(eta-i) are presented for values of eta-i ranging from just above marginal stability eta-ic to eta-i = infinity. Although the quasilinear temperature profile is held fixed, the transport rates are very small as a result of local flattening of the temperature profile near the rational surface. The implications of these results for understanding anomalous transport in tokamaks are discussed.