Speaker
Description
See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O2.112.pdf
Turbulent transport and its impact on ITER performance is investigated with the global flux-driven gyrokinetic code GYSELA. In that framework, a heat source, balanced by turbulent cross-field transport, determines the temperature profile. It is expected that the heat sink at the boundary and turbulence in the edge may interplay with the core conditions. Consistently with such a global property, an immersed outer boundary with axisymmetric limiter and toroidally and poloidally symmetric first wall geometry has been implemented in the code. These regions are penalized towards a cold temperature and act as a heat sink. The Scrape-Off Layer is identified in the ensemble of magnetic field lines intercepting the poloidally asymmetric limiter. There, the flux surface averaged potential is modified to take into account the sheath effect in the case of adiabatic electrons, affordable in terms of numerical cost. The geometry of the immersed boundary can be varied through the definition of several masks. Also the limiter can be biased with respect to the wall.
A staged verification of the physics and first global results are reported here. First, the parallel propagation of heat in the SOL has been investigated. A cold front propagation is recovered matching the analytical modelling [Caschera, JPCS, 2018]. Second, a reversal of the radial electric field is recovered at the interface between the SOL and core plasma. Third, the drift velocity governed by the magnetic field inhomogeneity drives plasma polarization which is enhanced by the limiter. Indeed, the latter intercepts the parallel currents, and a strong shear region of the poloidal velocity develops close to the separatrix. High amplitude zonal flows and large scale ExB convection yield poloidally inhomogeneous shearing. The strong electric field modifies the density pattern which, together with the enhanced shear, yields opposite effects: on the one hand the shear layer and large radial density gradient tend to stabilize ITG turbulence, and, on the other hand the shear layer can become Kelvin-Helmholtz unstable favoring the spreading of turbulence both inward towards the core and outwards in the SOL. Qualitative agreement has been observed with the edge turbulence fluid code TOKAM3X and will be further investigated.
