Effect of magnetic ergodicity on edge plasma structure and divertor distribution in LHD

In the heliotron type configuration there exists a relatively thick open ergodic region surrounding closed magnetic surfaces. Magnetic field lines there are connecting to the wall through intrinsic divertor legs with lengths of several hundred meters. Because of this ergodicity in the peripheral region, some characteristic edge plasma structure is formed according to the thickness or magnitude of the ergodicity, which are affected by the position of the magnetic axis or beta. In the experiments, not only various types of edge electron temperature or density profiles but the drastic change of the divertor flux distribution have been observed with various magnetic configurations in the Large Helical Device (LHD). In this paper the effect of the magnetic ergodicity on density/temperature profiles, divertor flux distribution and so on is discussed for different edge ergodicities estimating quantitatively by measure of Kolmogorov length, using a field line tracing code. Concerning the edge profiles, the effective last closed flux surface which may become important for equilibrium calculations is discussed taking the perpendicular electron heat conductivity into account. The variety of divertor flux distributions with various magnetic configurations is interesting. It is found that there exists strong ununiformity in both directions, and its property changes according to the magnetic axis position. These results agree well with those of experiments. Numerical calculation suggests that escaping paths of diverted particles are affected by the ergodicity. Results of precise analyses enriched by simulations for limiter and perturbation field experiments are presented at the conference. (orig.)