Poloidally and radially resolved parallel D{sup +} velocity measurements in the DIII-D boundary and comparison to neoclassical computations

• Published in: Physics of plasmas 2011-03, Vol.18 (3)
• Main Authors: Boedo, J. A., Hollmann, E., Rudakov, D. L., Groebner, R. J., Moyer, R. A., Porter, G. D., Muller, S., Tynan, G., Belli, E. A., Prater, R., Candy, J., Burrell, K. H., Grassie, J. S. de, Leonard, A. W., Brooks, N. H., Solomon, W. M., Watkins, J. G., Lasnier, C. J., Unterberg, E. A.
• Format: Article
• Language: English
• Subjects: 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; CHARGED PARTICLES; CLOSED PLASMA DEVICES; CONFINEMENT; DEUTERIUM IONS; DOUBLET-3 DEVICE; ELECTRIC DISCHARGES; IONS; L-MODE PLASMA CONFINEMENT; MAGNETIC CONFINEMENT; PLASMA CONFINEMENT; THERMONUCLEAR DEVICES; TOKAMAK DEVICES; VELOCITY
• ISSN: 1070-664X; 1089-7674
• DOI: 10.1063/1.3559492

First measurements of the D{sup +} parallel velocity, V{sub ||}{sup D+}, in L-mode discharges in the DIII-D [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] tokamak boundary region at two poloidal locations, {theta}{approx}0 deg. and {theta}{approx}255 deg., 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{sup 6+} toroidal velocity, V{sub {phi}}{sup C6+}, in the same location. The V{sub ||}{sup 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 {approx}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{sub ||}{sup D+} measurements are quantitatively consistent with a purely neoclassical computational modeling of V{sub ||}{sup D+} by the code NEO[E. A. Belli and J. Candy, Plasma Phys. Controlled Fusion 50, 095010 (2008)], using V{sub {phi}}{sup C6+} as input, for {rho}{approx}0.7-0.95 at the two poloidal locations, where V{sub ||}{sup D+} measurements exist. The midplane NEO-calculated V{sub ||}{sup D+} grows larger than V{sub ||}{sup C6+} in the steeper edge gradient region and trends to agreement with the probe-measured V{sub ||}{sup D+} data near {rho}{approx}1, where the local V{sub ||}{sup D+} velocity peak exists. The measurements and computations were made in OH and L-mode discharges on an upper single null, with ion {nabla}B{sub 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.