ANOMALOUS TRANSPORT DUE TO THE ION-ACOUSTIC DRIFT MODE IN TOKAMAKS

In toroidal geometry, the ion Landau resonance is suppressed by the io n magnetic drift for modes propagating in the electron diamagnetic dri ft, and long wavelength modes with (k(perpendicular to) rho)(2) simila r or equal to O(0.01) remain unstable. Coupling to the ion acoustic tr ansit mode becomes predominant in such long wavelength regime allowing the mode frequency to exceed the diamagnetic drift frequency by a lar ge margin. Finite beta has a destabilizing influence on the toroidal i on acoustic mode particularly in the long wavelength regime. The quasi linear electron and ion thermal fluxes both increase with beta partly through finite beta modification of the mode frequency and/or growth r ate, and partly through magnetic fluctuations. Even the trapped electr on thermal flux exhibits an increase with beta. In strong turbulence r egime, the thermal diffusivity scales as Bohm corrected for finite bet a, chi proportional to (r/R)(2)(cT/eB)q(2) beta.