Comparison of edge turbulence characteristics between DIII-D and C-Mod simulations with XGC1

Abstract

The physical processes taking place at the separatrix and scrape-off layer regions are crucial for the operation of tokamaks as they govern the interaction of hot plasma with the vessel walls. Numerical modeling of the edge with state-of-the-art codes attempts to elucidate the complex interactions between neoclassical drifts, turbulence, poloidal and parallel flows that control the physical set-up of the SOL region. Here, we present post-processing analysis of simulation results from the gyrokinetic code XGC1, comparing and contrasting edge turbulence characteristics from a simulation of the DIII-D tokamak against a simulation of the Alcator C-Mod tokamak. We find that the equilibrium E × B flux across the separatrix has a similar poloidal pattern in both discharges which can be explained by ∇B-drifts and trapped ion excursions. However, collisionality is noted to play a major role in the way that it prevents local charge accumulations from having more global effects in the C-Mod case. In both cases, turbulent electron heat flux is observed to be higher than the ion one. This seems to be a universal characteristic of the tokamak edge, possibly related to the need of electrons to maintain quasineutrality through the only channel available to them for exiting the confinement. By Fourier analysis, we identify turbulent frequencies and growth rates of the dominant mode in both simulations. In the case of C-Mod, these numbers point to the presence of a drift wave. In the DIII-D case, further linear simulations with the Gene code reveal a trapped electron mode. Furthermore, using a blob detection and tracking tool, we present the amplitude and size distributions of the blobs from both simulations. The amplitude distributions are in qualitative agreement with experimental observations while the size distributions are consistent with the fact that most of the blobs are not connecting to the divertor plates and suggest that they are generated by the shearing of the turbulent modes.

A hybrid full-wave Markov chain approach to calculating radio-frequency wave scattering from Scrape-off Layer filaments

“…Filament mean width a b is well bounded by gas-puff imaging (GPI) measurements as well as theory/simulation [1,33,34]. Langmuir probe and GPI measurements provide a rough lowerbound on the filament mean relative density n b /n 0 , though this value will vary significantly at different radial locations in the SOL [1,35].…”

A hybrid full-wave Markov chain approach to calculating radio-frequency wave scattering from scrape-off layer filaments

“…2002; Krasheninnikov, D'Ippolito & Myra 2008; Keramidas Charidakos et al. 2020). Langmuir probe and GPI measurements provide a rough lower bound on the filament mean relative density , though this value will vary significantly at different radial locations in the SOL (Zweben et al.…”