How the self-interaction mechanism affects zonal flow drive and convergence of turbulent transport simulations with system size
Abstract
We use gyrokinetic flux-tube simulations to report a decrease in the shearing rate of ExB zonal flows with increasing system size measured by 1/ ρ* =a/ρi, where a is the tokamak minor radius and ρi is the ion Larmor radius. This is done in practice by decreasing ky,minρi ( ρ*), where ky,minis the minimum wavenumber along the direction y, bi-normal to the magnetic field. The corresponding gyro-Bohm normalised heat and particle fluxes also increase with decreasing ky,min. We find that this results from the non-adiabatic passing electron dynamics and corresponding fine structures at mode rational surfaces associated to each ky mode. The related strong self-interaction mechanism disrupts resonant 3-wave interactions involving the zonal modes. As a consequence, the different ky contributions to Reynolds Stress driving the zonal flows tend to get decorrelated, which results in the shearing rate level developing a statistical dependence on ky,min. In adiabatic electron simulations, the scaling is not as severe, owing to a weaker self-interaction mechanism at play.
This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 and 2019-2020 under Grant agreement No 633053. Computations were performed on Piz Daint, CSCS (CH) and Marconi, CINECA (Italy).- Publication:
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APS Division of Plasma Physics Meeting Abstracts
- Pub Date:
- 2019
- Bibcode:
- 2019APS..DPPU10014C