Observation of the heteroclinic tangles in the heat flux pattern of the ergodic divertor at TEXTOR

A fine structure of open chaotic field lines, namely, a heteroclinic tangle, in the ergodic divertor has been observed by measurements of heat deposition pattern on the divertor plates at TEXTOR. Calculations show that magnetic footprints on the divertor plates are formed by open field lines coming from the plasma along narrow stripe regions called fingers. The latter are determined by the structure of stable and unstable manifolds of the outermost resonant magnetic island. This fact is confirmed by observations of the bifurcations of the heat flux pattern on the divertor plates with changing edge safety factor.