Multi-scale self-organisation of edge plasma turbulent transport in 3D global simulations

Abstract

The 3D global edge turbulence code TOKAM3X is used to study the properties of edge particle turbulent transport in circular limited plasmas, including both closed and open flux surfaces. Turbulence is driven by an incoming particle flux from the core plasma and no scale separation between the equilibrium and the fluctuations is assumed. Simulations show the existence of a complex self-organization of turbulence transport coupling scales ranging from a few Larmor radii up to the machine scale. Particle transport is largely dominated by small scale turbulence with fluctuations forming quasi field-aligned filaments. Radial particle transport is intermittent and associated with the propagation of coherent structures on long distances via avalanches. Long range correlations are also found in the poloidal and toroidal direction. The statistical properties of fluctuations vary with the radial and poloidal directions, with larger fluctuation levels and intermittency found in the outboard scrape-off layer (SOL). Radial turbulent transport is strongly ballooned, with 90% of the flux at the separatrix flowing through the low-field side. One of the main consequences is the existence of quasi-sonic asymmetric parallel flows driving a net rotation of the plasma. Simulations also show the spontaneous onset of an intermittent E × B rotation characterized by a larger shear at the separatrix. Strong correlation is found between the turbulent particle flux and the E × B flow shear in a phenomenology reminiscent of H-mode physics. The poloidal position of the limiter is a key player in the observed dynamics.

Turbulent heat transport in TOKAM3X edge plasma simulations

“…They propagate intermittently through the SOL as coherent structures over long distances via an avalanche process. Note that these structures present the same general features as those described for previous Tokam3X results in the isothermal version , …”

Plasma shaping effects on tokamak scrape-off layer turbulence

“…In the past decade, several computational models were developed and implemented into numerical codes, that are used to investigate the tokamak SOL dynamics [7][8][9][10][11][12][13][14][15][16]. The main instabilities driving the SOL turbulence were characterized in the simplest SOL configuration (i.e.…”

The GBS code for tokamak scrape-off layer simulations

“…However, 3D effects such as drift-wave turbulence and magnetic fluctuations can have a strong impact on edge turbulence [9]. Advances in computer hardware and algorithms have now enabled the study of SOL dynamics in 3D using codes such as GEMR [9,10], BOUT++ [11], TOKAM3D/3X [12,13], and GBS [14].…”