Transport-driven toroidal rotation in the tokamak edge.

The interaction of passing-ion drift orbits with spatially inhomogeneous but purely diffusive radial transport is demonstrated to cause spontaneous toroidal spin-up in a simple model of the tokamak edge. Physically, major-radial orbit shifts cause orbit-averaged diffusivities to depend on v(∥), including its sign, leading to residual stress. The resulting pedestal-top intrinsic rotation scales with T(i)/B(θ), resembling typical experimental scalings. Additionally, an inboard (outboard) X point enhances co- (counter)current rotation.