NEOCLASSICAL KINETIC-THEORY NEAR AN X-POINT - PLATEAU REGIME

Traditionally, neoclassical transport calculations ignore poloidal var iation of the poloidal magnetic field. Near an X point of the confinin g field of a diverted plasma, the poloidal field is small, causing gui ding centers to linger at that poloidal position. A study of how neocl assical transport is affected by this differential shaping is presente d. The problem is solved in general in the plateau regime, and a model poloidal flux function with an X point is utilized as an analytic exa mple to show that the plateau diffusion coefficient can change conside rably (factor of 2 reduction). Ion poloidal rotation is proportional t o the local value of B(pol) but otherwise it is not strongly affected by shaping. The usual favorable scaling of neoclassical confinement ti me with plasma current is unaffected by the X point.