Heat diffusion coefficients in a stochastic magnetic field are determined in the case of frequently interrupted regime of neoclassical tearing modes and of incomplete sawtooth reconnection in the ASDEX Upgrade tokamak. Here the experimentally measured perturbations and profiles are used and the mapping technique is applied. With the derived diffusion coefficients the nonstationary diffusion equation is solved, making it possible to study time evolution of fast MHD phenomena in ASDEX Upgrade. The proposed phenomenological approach relies heavily on experimental information and requires very moderate computing resources.
The effect of magnetic surface destruction on test particle diffusion in the Wendelstein VII-A stellarator