April 15-17

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Author: Plamen G. Ivanov
Requested Type: Poster
Submitted: 2019-03-05 09:22:34

Co-authors: A.A.Schekochihin, A.R.Field

Contact Info:
University of Oxford
Clarendon Laboratory, Parks Rd
Oxford, OX1 3JP,   00000
United Kingdom

Abstract Text:
Numerical simulations have shown that turbulence in tokamaks is regulated by the interaction of zonal flows (ZF) and drift-waves (DW) [1][2]. The latter are wave-like fluctuations in the plasma, driven by gradients in the equilibrium plasma parameters. Zonal flows are Larmor-scale shear flows in the poloidal direction, which are generated nonlinearly by the drift-wave turbulence itself.

Starting from the gyrokinetic equation [3] for ions, we derive equations for a 2D 2-fluid system of ion density and ion temperature perturbations of an equilibrium of fixed magnetic curvature and constant background temperature gradient. These equations are numerically integrated to explore the turbulent state of the model. We report results on the interplay of zonal and nonzonal perturbations in saturated turbulence. The transition from a saturated, low-transport state (“Dimits regime”) to a strongly turbulent regime with stiff transport is controlled by the ratio of normalised background temperature gradient and collisionality. These results are discussed in the context of ZF-DW behaviour and saturation in similar 2D models [4].

[1] A.M. Dimits et al, Nuclear Fusion 40, 3Y (2000)
[2] BN Rogers, W Dorland, M Kotschenreuther, Physical Review Letters 85, 25 (2000)
[3] IG Abel et al, Multiscale gyrokinetics for rotating tokamak plasmas: fluctuations, transport and energy flows. Reports on Progress in Physics, 76(11):116201, 2013.
[4] DA St-Onge. On non-local energy transfer via zonal flow in the Dimits shift. Journal of
Plasma Physics, 83(5), 2017

PGI is funded through an EU H2020 grant, agreement No 3000207035. 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.The views and opinions expressed herein do not necessarily reflect those of the European Commission.

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