Monte Carlo diffusion operator for anomalous radial transport in tokamaks

We have revised the numerical model for anomalous diffusion across the magnetic surfaces in tokamaks, originally derived in the cylindrical limit, i.e., at very large aspect ratio values, and assuming circular flux surfaces. The new model removes these restrictions and properly accounts for the toroidal geometry even in the limit of very tight aspect ratio, and is applicable with flux surfaces of arbitrary shape. Copyright (C) EPLA, 2012