Investigation of edge pedestal structure in DIII-D

Abstract

A calculation based on the requirements of particle, momentum and energy conservation, conductive heat transport, and atomic physics resulting from a recycling and fueling neutral influx was employed to investigate the experimental density, temperature, rotation velocities, and radial electric field profiles in the edge of three DIII-D [J. Luxon, Nucl. Fusion 42, 614 (2002)] high-confinement-mode plasmas. The calculation indicated that the cause of the pedestal structure in the density was a momentum balance requirement for a steep negative pressure gradient to balance the forces associated with an edge peaking in the inward pinch velocity (caused by the observed edge peaking in the radial electric field and rotation velocity profiles) and, to a lesser extent, in the outward radial particle flux (caused by the ionization of recycling neutrals). Thermal and angular momentum transport coefficients were inferred from experiment and compared with theoretical predictions, indicating that thermal transport coefficients were of the magnitude predicted by neoclassical and ion-temperature-gradient theories (ions) and electron-temperature-gradient theory (electrons), but that neoclassical gyroviscous theory plus atomic physics effects combined were not sufficient to explain the inferred angular momentum transfer rate throughout the edge region.