Simulation of plasma turbulence in scrape-off layer conditions: the GBS code, simulation results and code validation

Abstract

Based on the drift-reduced Braginskii equations, the Global Braginskii Solver, GBS, is able to model the scrape-off layer (SOL) plasma turbulence in terms of the interplay between the plasma outflow from the tokamak core, the turbulent transport, and the losses at the vessel. Model equations, the GBS numerical algorithm, and GBS simulation results are described. GBS has been first developed to model turbulence in basic plasma physics devices, such as linear and simple magnetized toroidal devices, which contain some of the main elements of SOL turbulence in a simplified setting. In this paper we summarize the findings obtained from the simulation carried out in these configurations and we report the first simulations of SOL turbulence. We also discuss the validation project that has been carried out together with the GBS development.

Aspect ratio effects on limited scrape-off layer plasma turbulence

“…23 At the top and at the bottom of the limiter, these are, in normalized units, The system of equations presented in this paper considers, with respect to the system of equations presented in Ref. 7, an arbitrary magnetic field configuration. The modulus of the magnetic field B, the divergence of the unitary magnetic field vector r Á b, the differential operators r k , r 2…”

“…Then, a flux-driven model is preferred over a fixed-gradient model because the former is closer to experimental conditions, where profiles result from a balance between sources and losses and are a-priori unknown, exhibiting richer physics such as the appearance of avalanches 6 and self-consistent interactions between the background and the fluctuations. Such fluid flux-driven simulations have emerged, [6][7][8][9] allowing to simulate SOL plasma turbulence and shedding light on the crucial physical phenomena at play in this region. In a recent publication, 10 it has been shown that the gradient-removal theory is able to predict relatively well the sustainable pressure gradient inside the SOL for 3D fluid simulations in limited geometry.…”

Ideal ballooning modes in the tokamak scrape-off layer

“…The model is described fully in Ref. 22. The use of a fluid model is justified by that fact that, in the tokamak scrape-off layer, collisions play an important role and kinetic effects, such as trapping, are less important.…”

“…In this section, we describe non-linear 3D electromagnetic simulations of scrape-off layer turbulence carried out with GBS, 22 an initial value, global 3D non-linear code which advances in time the five scalar fields in Eqs. (1)- (5).…”

“…In order to address the stability and turbulent dynamics of ideal ballooning modes in the scrape-off layer, we use a global, drift-reduced Braginskii fluid model 22 in combination with a proper set of boundary conditions at the magnetic pre-sheath entrance. 23 We carry out flux-driven, global 3D simulations inŝ À a geometry with a toroidal limiter on the equatorial plane at the high-field side.…”