Sources of nonadiabaticity in tokamak turbulence

The two-fluid equations governing the nonlinear evolution and saturation of drift wave-like turbulence and transport in tokamaks under quasi-neutral conditions in periodic cylinder geometry are investigated. Using experiment as guide and employing appropriate orderings, two non-adiabaticity parameters, Υes and Υem are derived as functions of the reduced frequency ωa/vthi and wave number ρi kr characteristic of the turbulent fluctuation spectrum. These parameters correspond respectively to the electrostatic limit and the general electromagnetic case. It is shown that they must be O(1) if significant particle and ion energy transport are to be expected from the turbulence. In other words, they are measures of the departure from neo-classical particle and ion energy transport due to the turbulence. These analytic results are complementary to, and serve as guidelines for, any future direct numerical simulations of the set of seven nonlinear partial differential equations which must be solved with suitable sources of particles, momentum and energy to determine the turbulence evolution and resultant saturated power spectra of density, pressure, electrostatic potential and magnetic field. The nonadiabaticity parameters discussed suggest possible qualitative explanations of the isotope effect and reduction of anomalous transport noted in H-mode tokamak discharges.