Drive of parallel flows by turbulence and large-scale E × B transverse transport in divertor geometry

Abstract

The poloidal asymmetries of parallel flows in edge plasmas are investigated by the 3D fluid turbulence code TOKAM3X. A diverted COMPASS-like magnetic equilibrium is used for the simulations. The measurements and simulations of parallel Mach numbers are compared, and exhibit good qualitative agreement. Small-scale turbulent transport is observed to dominate near the low field side midplane, even though it co-exists with significant large-scale cross-field fluxes. Despite the turbulent nature of the plasma in the divertor region, simulations show the low effectiveness of turbulence for the cross-field transport towards the private flux region. Nevertheless, a complex pattern of fluxes associated with the average field components are found to cross the separatrix in the divertor region. Large-scale and small-scale turbulent transport, along with the drift, drive the asymmetries in parallel flows. A semi-analytical model based on mass and parallel momentum balances allows the poloidal drift effects on the asymmetry pattern to be evaluated. As in the experiments, a reversed B T simulation provides a way of self-consistently separating the effects of turbulent transport and large-scale flows, which must be reversed for a reversed field. The large-scale contribution is found to be responsible for typically 50% of the effect on the Mach number, evaluated at the top of the machine. The presented picture shows the complex interplay between drifts and turbulence, underlining the necessity of a global approach to edge plasma modelling, including a self-consistent description of the turbulence.

Turbulent heat transport in TOKAM3X edge plasma simulations

“…This limited geometry has been chosen to understand the basic properties of turbulence and transport in the anisothermal model. The studies on divertor geometry are out of the scope of this paper and should be discussed in future work to complement those already done with an isothermal model . The physical domain simulated extends from the closed flux surface r min / a = 0.8 to the open flux surfaces r max / a = 1.2.…”

Impact of the plasma geometry on divertor power exhaust: experimental evidence from TCV and simulations with SolEdge2D and TOKAM3X

“…An alternative approach to modelling edge and SOL is to abandon the simplified diffusive picture and to take into account the turbulent nature of transport. This can be done with TOKAM3X, a 3D fluid turbulent code solving a set of drift-reduced conservation equations for mass, parallel momentum, electric charge and energy for electrons and ions, in an electrostatic approximation [22,23]. TOKAM3X gives a multi-scale description of turbulence in plasma edge and SOL.…”

Development of Extended Two-Point Model for Asymmetric Scrape-Off Layer

“…The divertor is one of the most important components of the reactor and may be exposed to excessive heat and particle fluxes. While the complex magnetic configuration in tokamaks and the peculiar transport in the SOL give rise to the asymmetry in the high field and low field energy fluxes [11,12], this issue should be properly addressed in SYCOMORE for quick and reliable predictions. In this work, the SOL-DIV code which is a scrape-off-layer and divertor module in SYCOMORE has been used to investigate this asymmetry problem based on an extended two-point model.…”