Abstract
First measurements of the D(+) parallel velocity, V(parallel to)(D+), in L-mode discharges in the DIII-D [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] tokamak boundary region at two poloidal locations, 0 similar to 0 degrees and 0 similar to 255 degrees, made using Mach probes, feature a peak with velocities of up to 80 km/s at the midplane last closed flux surface (LCFS), as high as ten times the charge exchange recombination C(6+) toroidal velocity, V(phi)(C6+), in the same location. The V(parallel to)(D+) profiles are very asymmetric poloidally, by a factor of 8-10, and feature a local peak at the midplane. This peak, 1-2 cm wide, is located at or just inside the LCFS, and it suggests a large source of momentum in that location. This momentum source is quantified at similar to 0.31 N m by using a simple momentum transport model. This is the most accurate measurement of the effects of so called "intrinsic" edge momentum source to date. The V(parallel to)(D+) measurements are quantitatively consistent with a purely neoclassical computational modeling of V(parallel to)(D+) by the code NEO [E. A. Belli and J. Candy, Plasma Phys. Controlled Fusion 50, 095010 (2008)], using V(phi)(C6+) as input, for rho similar to 0.7-0.95 at the two poloidal locations, where V(parallel to)(D+) measurements exist. The midplane NEO-calculated V(parallel to)(D+) grows larger than V(phi)(C6+) in the steeper edge gradient region and trends to agreement with the probe-measured V(parallel to)(D+) data near rho similar to 1, where the local V(parallel to)(D+) velocity peak exists. The measurements and computations were made in OH and L-mode discharges on an upper single null, with ion del B(T) drift away from the divertor. The rotating layer finding is similar in auxiliary heated discharges with and without external momentum input, except that at higher density the edge velocity weakens.
