A general equation for the radial current due to the ion-neutral friction and neoclassical viscosity is given. The equation models the effect of a possible poloidal non-uniformity of the neutral friction, and is valid in an arbitrary toroidally symmetric geometry. A strong dependence on the poloidal distribution of the neutral friction is found. With the help of Monte Carlo simulations the neutral friction in ASDEX Upgrade has been calculated. A large poloidal asymmetry in the neutral density exists, and for the studied shot the neutral friction in the edge is not large enough to compete with the neoclassical viscosity.
Toroidal and poloidal momentum transport studies in JET