L-H transition dynamics in fluid turbulence simulations with neoclassical force balance

Spontaneous transport barrier generation at the edge of a magnetically confined plasma is investigated. To this end, a model of electrostatic turbulence in three-dimensional geometry is extended to account for the impact of friction between trapped and passing particles on the radial electric field. Non-linear flux-driven simulations are carried out, and it is shown that considering the radial and temporal variations of the neoclassical friction coefficients allows for a transport barrier to be generated above a threshold of the input power

Improved boundary condition for full-f gyrokinetic simulations of circular-limited tokamak plasmas in ELMFIRE

| openaire: EC/H2020/633053/EU//EUROfusionWe report new results of full-torus gyrokinetic simulations of electrostatic turbulence with Elmfire spanning from the magnetic axis to the scrape-off layer (SOL). The new implementation presented here uses the logical boundary condition, which allows for improved stability and flexibility in terms of geometry. We simulate the full plasma of the FT-2 tokamak (Ioffe Institute, Saint-Petersburg, Russian Federation), with two poloidal limiters defining the SOL. We recover expected results in the SOL and find an improvement in our capacity to model the experimental particle and energy sinks in the SOL.Peer reviewe

Flux driven pedestal formation above a certain source Flux driven pedestal formation in tokamaks: Turbulence simulations validated against the isotope effect

International audienc

Flux driven pedestal formation above a certain source Flux driven pedestal formation in tokamaks: Turbulence simulations validated against the isotope effect

International audienc

Neoclassical and turbulent e × B flows in flux-driven gyrokinetic simulations of Ohmic tokamak plasmas

| openaire: EC/H2020/633053/EU//EUROfusionThe interplay of flows and turbulence in Ohmic FT-2 tokamak plasmas is analysed via gyrokinetic simulations with the flux-driven ELMFIRE code. The simulation predictions agree qualitatively with analytical estimates for the scaling of the neoclassical radial electric field as a function of collisionality for ad hoc parameters. For the experimental parameters, the global full-f modeling agrees well with the analytical estimates in a neoclassical setting, while including kinetic electrons and impurities has a small impact. Allowing turbulence to develop modifies the flow profile through relaxation of profiles caused by turbulent transport, non-adiabatic response of passing electrons around rational surfaces, and turbulent flow drive. Geodesic acoustic mode (GAM) is the main zonal flow component in the simulations, and its frequency and amplitude agree with theoretical predictions and experimental measurements. In the simulations, the non-linear energy transfer from the turbulence to the flows through the Reynolds force is balanced by the collisional flow dissipation. Temporal relationship between the oscillating flow, Reynolds force, and turbulent particle flux is consistent with the fundamental physics picture of GAM modulating turbulent transport on the time scale of the mode. Experimental evidence also suggests anti-correlation of GAM amplitude and turbulent fluctuations.Peer reviewe