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

An exact solution for the thermal (χe) or particle (D) diffusivities is derived (up to a constant factor) for the diffusive model in terms of the Fourier coefficients of the perturbed Te (or ne) signals. The common assumptions of constant ne and χe (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. (author)