Evaluation of abrupt energy transfer among turbulent plasma structures using singular value decomposition

Evaluation of abrupt energy transfer among turbulent plasma structures using singular value decomposition

Evaluation of abrupt energy transfer among turbulent plasma structures using singular value decomposition 150 150 UKAEA Opendata
UKAEA-CCFE-PR(20)101

Evaluation of abrupt energy transfer among turbulent plasma structures using singular value decomposition

A method to quantify the energy transfer among turbulent structures
using singular value decomposition (SVD) is presented. We apply the method to numerical turbulence data obtained from a global plasma simulation using the Hasegawa-Wakatani fluid model, in which the Kelvin-Helmholtz instability plays a dominant role. Using the SVD method, the electrostatic potential is decomposed into a background potential deformation, a zonal flow, a coherent mode and an intermittent structure. Thus there are four key structures, as distinct from the three found in conventional theory. The kinetic energy of each structure is evaluated, and the limit cycle among them is obtained. In the limit cycle, an abrupt change of the background is found to be synchronised with the period of the zonal flow. The energy transfer function of each turbulence structure, which is defined on the basis of a vorticity equation, is evaluated. This then provides physical understanding of how the limit cycle is sustained by dynamical changes in the energy transfer among structures over its period. In addition, it is shown that the abrupt deformation of the background is caused by the nonlinear coupling between the coherent mode and the intermittent structure.

Collection:
Journals
Journal:
Plasma Physics and Controlled Fusion
Publisher:
IOP (Institute of Physics)
Published date:
12/08/2020
The published version of this paper is currently under embargo and will be available on 08/12/2021