Poloidal flow damping inside transport barriers in a tokamak

The poloidal flow in a tokamak is damped by collisions. Thus, the poloidal damping can be described by the neoclassical theory. The effective poloidal Mach number, M_p, can be of the order of one or higher inside transport barriers in a tokamak. It is found that the poloidal damping rate decreases exponentially as the effective poloidal Mach number increases. The poloidal damping rate is reduced by one order of magnitude in the presence of sonic M_p. We also found that the ion plasma viscosity becomes negligible compared with the electron plasma viscosity when M p > 1.5. In this case, the poloidal flow is damped by electron collisions rather than ion collisions.