NEUTRAL DIFFUSION AND ANOMALOUS EFFECTS ON COLLISIONAL ION FLOW SHEARIN TOKAMAKS

Ion plasma flow and flow shear just inside the last closed flux surfac e of a tokamak can be strongly altered by neutral atoms and anomalous effects. For a collisional edge, neutrals modify the standard Pfirsch- Schluter expression for the parallel ion flow through the strong coupl ing provided by ion-neutral collisions. Even for rather small neutral to plasma density ratios, the large diffusivity of the neutrals in com bination with the ion-neutral coupling can directly modify the ion dis tribution function as well as cause neutral diffusion modifications to the parallel momentum constraint that determines the parallel ion flo w. Direct modification of the ion distribution function only dominates at order unity aspect ratios, and was unimportant in an earlier plate au evaluation of the effects of neutrals on ion flow. Like the earlier work, anomalous effects are retained to maintain a steady state and d emonstrate that large anomalous transport can alter neoclassical colli sional ion flows. (C) 1998 American Institute of Physics. [S1070-664X( 98)1511-0].