Pedestal and edge electrostatic turbulence characteristics from an XGC1 gyrokinetic simulation

Abstract

Abstract. Understanding the multi-scale neoclassical and turbulence physics in the edge region (pedestal + scrape-off layer) is required in order to reliably predict performance in future fusion devices. We explore turbulent characteristics in the edge region from a multiscale 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 δne/ne ∼ 0.18. Blobs are observed, born around the magnetic separatrix surface and propagate radially outward with velocities generally less than 1 km/s. Strong poloidal motion of the blobs is also present, near 20 km/s, consistent with E × B rotation. The electron density fluctuations show a negative skewness in the closed field line pedestal regions, 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 blobgeneration mechanism, can remain important in the steep H-mode pedestal and SOL. Qualitative comparisons will be made to experimental observations.

A fast low-to-high confinement mode bifurcation dynamics in the boundary-plasma gyrokinetic code XGC1

“…Detailed statistical properties of this boundary turbulence have been reported elsewhere. 57 In this subsection, we only present essential figures that have not yet been published, including Figs. 3 and 4.…”

Blob velocity scaling in diverted tokamaks: A comparison between theory and simulation

“…The results of a full 3D turbulent simulation with the XGC1 gyrokinetic code of a DIII-D H-mode discharge have been used to carry out an initial investigation of the blob properties. 30 In the present work, we extend the use of the pattern recognition algorithm introduced in Ref. 25 to analyse the blob motion in a full SOL turbulent simulation in a double-null configuration.…”

Full-f gyrokinetic simulation of turbulence in a helical open-field-line plasma

“…Effects connected to B v ∼ B p ∼ I plasma are explored by changing the magnetic-field-line incidence angle, since sin θ = B v /B z . We have performed simulations at three values of magnetic-field-line pitches B v /B z = (0.2, 0.3, 0.6), which correspond to L z = (12,8,4) m and θ = (20.14 • , 30.47 • , 64.4 • ). We scale the source appropriately in each simulation to keep the volumetric source rate the same.…”

“…Additionally, the turbulence in this helical open-field-line geometry with parameters appropriate for a tokamak SOL has not been previously studied using a gyrokinetic PIC approach, either. We do acknowledge, however, that gyrokinetic PIC codes that have the necessary capabilities for the problem described in this paper have already been developed, 12,13 and it should be straightforward for these codes to implement this simple helical geometry for cross-code comparisons.…”