Stochastic broadening of the divertor region using the standard map

Although perturbations give a stochastic region about a separatrix, it is not clear whether the image of the separatrix on the strike plate of a tokamak divertor is broadened or becomes a complicated curve. To address this issue the authors are using the standard map and a continuous analogy. When the parameter k of the map is close to unity, the topology of a double null divertor is faithfully reproduced. To lead trajectories into the separatrix region, they start in a region of good surfaces. But, in addition to the standard map they add a small diffusive term to the iterations. They are studying the width of the region intercepted by the field lines on the equivalent of the divertor strike plates in the limit as the diffusion coefficient goes to zero