An exact formula for the thermal and particle diffusivities based on the diffusive transport model in tokamak plasmas

An exact solution for the thermal (X^e) or particle (D) diffusivities is derived (up to a constant factor) for the diffusive model in terms of the Fourier coefficients of the perturbed T^e (or n^e) signals. The common assumptions of constant n^e and X^e (or D) generally used in the standard analytical or semi-analytical solutions are not required, since their radial dependences are taken explicitly into account. The effect of a damping (sink) term in the heat equation can also be implemented easily.