Oscillatory zonal flows and their interaction with turbulence in magnetically confined plasmas

Lead Research Organisation: University of Warwick
Department Name: Physics


Nuclear Fusion
Magnetically confined plasmas are out of equilibrium driven systems in which micro-instabilities extract energy from temperature and density gradients, driving turbulent fluctuations. Turbulent transport strongly impacts on global plasma confinement properties and thus is in the core of any future reactor design. Under certain conditions turbulent fluctuations can organise into large-scale zonal flows, as shown in the figure below. These flows can regulate turbulence by shearing and are believed to be a key factor in plasma transition to high-confinement mode (H-mode), currently the main operating scenario for the ITER reactor.
Pure zonal flows have no frequency and are difficult to observe in the laboratory. The toroidal curvature of a tokamak induces additional compressional mode of zonal flows known as the Geodesic Acoustic Mode (GAM). This mode oscillates with real frequency and can give an insight into the non-linear interactions and feedback between the turbulence and zonal flows. The GAM frequency is dependent on the ion and electron temperatures, rotation and shaping of the plasma.
This proposal addresses interaction between turbulence, GAMs and non-oscillatory zonal flows. Main areas of interest for this project include radial structure of GAM, understanding how electron transport along the magnetic field lines influences dissipation of GAMs and what is the impact of fast plasma rotation on this mode. Practical aspects will explore a possibility of using observed GAM features to infer the ratio of electron and ion temperature, which are not available on MAST with current diagnostics. Close collaboration with CCFE MAST team is essential for the project.
The project combines exciting physics of nuclear fusion with practical skills such as advanced data analysis and the use of high performance computational resources for numerical simulations. The mathematical techniques used to describe zonal flows are very rich and generic, with the same equations governing flows in the Jupiters atmosphere, ocean currents and in tokamak plasmas.


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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/N509796/1 01/10/2016 30/09/2021
1781587 Studentship EP/N509796/1 03/10/2016 31/03/2020 Sanket Gadgil
Description Results from an analytical and numerical study of zonal flow-drift wave interactions in the Hasegawa-Wakatani show a boost in drift-wave growth in the presence of zonal flows via resonant coupling. Furthermore CENTORI simulations of MAST(Mega-Ampere-Spherical-Tokamak) show a presence of GAM(Geodesic Acoustic Mode) oscillations in the simulations and results from the analysis of linear aspects of GAM have been obtained.
Exploitation Route Comparison to experimental data of the zonal flow-drift wave interaction may allow for a better understanding of energy transfer between different scales in a tokamak plasma. The same analysis used for CENTORI-MAST case can be applied to simulations of different tokamaks and may elucidate further details about the behaviour of GAMs.
Sectors Energy