Non-linear incompressible poloidal viscosity is an important ingredient in understanding the L-H transition in both tokamaks and stellarators. Usually two or more local maxima in poloidal viscosity corresponding to this transition may appear in stellarator/heliotron devices. Depending on the relative magnitudes of the toroidal and helical components of the magnetic spectrum, the local maxima can occur at a poloidal E*B Mach number Mp somewhat larger than mod m-nq mod /m, where E (B) is the electric (magnetic) field strength, m(n) is the poloidal (toroidal) mode number of the components of the mod B mod spectrum and q is the safety factor. Non-linear incompressible viscosities for the plateau Pfirsch-Schluter regime are calculated for present and next generation stellarator/heliotron devices (Heliotron-E, CHS, LHD, W7-AS and W7-X) by using a magnetic spectrum near the edge region under the assumption of negligibly small parallel flow. The possibility of the occurrence of the L-H transition and the limitation due to the effect of the charge exchange momentum loss are discussed. When the ion-ion collision frequency and neutrals are reduced sufficiently, all these devices show a local maximum of poloidal viscosity at Mp approximately 1. However, the reduction of the poloidal viscosity in the region beyond this maximum is not large compared with the tokamak case
Poloidal plasma rotation and its effect on fluctuations in a toroidal plasma