Pedestal and edge electrostatic turbulence characteristics from an XGC1 gyrokinetic simulation. (30th August 2017) - Churchill, R M
Abstract: Understanding the multi-scale neoclassical and turbulence physics in the edge region (pedestal + scrape-off layer (SOL)) is required in order to reliably predict performance in future fusion devices. We explore turbulent characteristics in the edge region from a multi-scale neoclassical and turbulent XGC1 gyrokinetic simulation in a DIII-D like tokamak geometry, here excluding neutrals and collisions. For an H-mode type plasma with steep pedestal, it is found that the electron density fluctuations increase towards the separatrix, and stay high well into the SOL, reaching a maximum value of δ n e / n ̄ e ∼ 0.18 . Blobs are observed, born around the magnetic separatrix surface and propagate radially outward with velocities generally less than 1 km s −1 . Strong poloidal motion of the blobs is also present, near 20 km s −1, consistent with E × B rotation. The electron density fluctuations show a negative skewness in the closed field-line pedestal region, consistent with the presence of 'holes', followed by a transition to strong positive skewness across the separatrix and into the SOL. These simulations indicate that not only neoclassical phenomena, but also turbulence, including the blob-generation mechanism, can remain important in the steep H-mode pedestal and SOL. Qualitative comparisons will be made to experimental observations.