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Sanket Gadgil

Position: 4th Year PhD Student

Supervisor: Dr. Bogdan Hnat

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

Background: MSci Theoretical Physics, University of Birmingham(2016)

Project Outline:
The main interest in turbulence for this project lies in a phenomenon where turbulent fluctuations can organise into zonal flows-poloidally elongated structures. Curvature effects introduced in reactors due to their toroidal geometry can cause the zonal flows to oscillate. In particular a mode known as the Geodesic Acoustic Mode(GAM) is of interest to this project as it oscillates at a real frequency which can be observed. An aim is to understand how drift-waves can take energy from zonal flows and how GAMs factor into(and are influenced by) this interaction. This is being investigated both analytically, by employing averaging techniques to obtain a spatially-independent dispersion relation and obtaining a value for the growth of drift waves as they gain energy from zonal flows, and validating this numerically via slab geometry Hasegawa-Wakatani model. An example of the numerical simulation used to validate the drift-wave growth rate is shown in the video below. The simulation shows an initial zonal flow(vertical) structure decaying to a drift-wave(horizontal) dominated structure. To investigate GAMs in further detail a separate 3rd-party simulation is being used(Hermes based on the BOUT++ framework). This simulation is far more detailed and is a cold-ion reduced drift model with additional options not found in BOUT++. The ISTTOK test case included in Hermes is being used currently to investigate if and how GAMs appear and behave.