Effect of cross-field drifts and core rotation on flows in the main scrape-off layer of DIII-D L-mode plasmas

Deuteron flows measured in the scrape-off layer (SOL) measured in the region vertically opposite the divertor of low-confinement (L-mode) plasmas in DIII-D show a marked dependence on the direction of the ion ∇B direction with little sensitivity on core plasma rotation. In contrast, the parallel flow of low charge state carbon ions in the SOL was measured to be independent of both parameters, and thus appear to be de-coupled from the deuteron flow. Improved understanding of the SOL flows is required to reliably predict impurity transport in the SOL and pedestal regions, and material migration and fuel retention in future fusion devices, such as ITER. In single-null magnetic configurations, as the ion ∇B drift direction is changed, the deuteron flow parallel to the magnetic field ∇B toward the inner plate reduces in magnitude from M = 0.5 to M ∼ 0, while the magnitude of parallel carbon flow toward in the inner plate remains approximately the same. The poloidal flow of singly ionized carbon, on the other hand, increases roughly three-fold as the ion ∇B drift direction is reversed. These measurements suggests that the dynamics governing the deuteron flow in the SOL is a complex interaction of radial transport, and E x B and B x ∇B drifts in the SOL, and that the carbon SOL flow is not simply determined by entrainment in the deuteron flow. In L-mode plasmas with the ion ∇B direction away from the divertor x-point, reversing the core plasma rotation does not affect the flow of deuterons and low-charge state carbon ions in the SOL. Scrape-off layer transport simulations with the fluid edge code UEDGE for the L-mode plasma in the ion ∇B toward the divertor do not predict the measured deuteron flow at the crown. Low charge state carbon ions at the crown are predicted to flow in the direction of the outer divertor, opposite to the observation, while higher charge state carbon ions, carrying the bulk of the total carbon flow, are calculated to flow toward the high-field divertor. (author)