MEASUREMENTS OF NON-AXISYMMETRICAL EFFECTS IN THE DIII-D DIVERTOR

Non-stationary toroidal asymmetries are observed in the DIII-D divertor heat flux and scrape-off layer (SOL) currents. Using the present DIII-D diagnostics, asymmetries are seen much less frequently in single-null H-modes (<5%) than in double-null H-modes (>50%). Divertor heat flux asymmetries are characterized by toroidal variations in the radial profile (i.e., multiple or bifurcated peaks) at some toroidal locations and single peaks at other toroidal locations while SOL currents sometimes have a strongly bipolar toroidal structure. SOL current asymmetries are particularly large during Edge Localized Modes (ELMs). The measurements reported here indicate that the asymmetries are best described by a model in which non-axisymmetric radial magnetic perturbations create magnetic islands in the plasma boundary and SOL which then cause toroidal variation in the divertor heat flux and the SOL currents.