Anomalous transport due to the ion acoustic drift mode in tokamaks

Abstract

In toroidal geometry, the ion Landau resonance is suppressed by the ion magnetic drift for modes propagating in the electron diamagnetic drift, and long wavelength modes with (k⊥ρ)2 ≃ \U0001d4aa(0.01) remain unstable. Coupling to the ion acoustic transit mode becomes predominant in such long wavelength regime allowing the mode frequency to exceed the diamagnetic drift frequency by a large margin. Finite β has a destabilizing influence on the toroidal ion acoustic mode particularly in the long wavelength regime. The quasilinear electron and ion thermal fluxes both increase with β partly through finite β modification of the mode frequency and/or growth rate, and partly through magnetic fluctuations. Even the trapped electron thermal flux exhibits an increase with β. In strong turbulence regime, the thermal diffusivity scales as Bohm corrected for finite β, χ ∝ (r/R)2(cT/eB)q2β.