THE LONG-WAVELENGTH LIMIT OF THE ION-TEMPERATURE GRADIENT MODE IN TOKAMAK PLASMAS

The stability of the ion-temperature gradient (inverted-open-triangle T(i)) mode in tokamak geometries is examined in the limit of long wavelength and flat density, retaining the nonadiabatic electron response. The existence of three unstable branches is shown. The toroidicity-induced inverted-open-triangle T(i) branch tends to be stabilized for increasing wavelength by the finite epsilon-T(i)(epsilon-T(i) = L(T)(i)/R) corrections. Meanwhile, the slablike inverted-open-triangle T(i) branch remains unstable and is little affected by the electron dynamics. The third branch corresponds to toroidicity-induced inverted-open-triangle T(i) eigenmodes propagating, however, in the electron diamagnetic direction, which are destabilized by the nonadiabatic electron dynamics. At shorter wavelengths, the toroidicity-induced inverted-open-triangle T(i) branch remains strongly unstable, while the other two branches become stabilized.