EFFECT OF TEARING MODES ON TEMPERATURE AND DENSITY PROFILES AND ON THE PERPENDICULAR TRANSPORT IN THE W-VII-A STELLARATOR

In the ohmically heated W VII-A stellarator, the behavior of which is similar to that of a medium sized tokamak, the additional shearless external rotational transform t0 (Δt0/t0 0&le0.15. The two-dimensional shapes of the profiles found experimentally can be attributed to the magnetic islands predicted by tearing mode theory. These shapes are further used to define an effective, locally enhanced radial transport coefficient κ⊥,e in a one-dimensional heat transport code. The transport model is used to investigate the explicit dependence of κ⊥,e on the plasma current and to study the importance of plasma current driven instabilities for the energy confinement in the W VII-A stellarator as well as in tokamaks.