Symmetry breaking in MAST plasma turbulence due to toroidal flow shear

Abstract

The flow shear associated with the differential toroidal rotation of tokamak plasmas breaks an underlying symmetry of the turbulent fluctuations imposed by the up-down symmetry of the magnetic equilibrium. Using experimental Beam-Emission-Spectroscopy (BES) measurements and gyrokinetic simulations, this symmetry breaking in ion-scale turbulence in MAST is shown to manifest itself as a tilt of the spatial correlation function and a finite skew in the distribution of the fluctuating density field. The tilt is a statistical expression of the "shearing" of the turbulent structures by the mean flow. The skewness of the distribution is related to the emergence of long-lived density structures in sheared, near-marginal plasma turbulence. The extent to which these effects are pronounced is argued (with the aid of the simulations) to depend on the distance from the nonlinear stability threshold. Away from the threshold, the symmetry is effectively restored.

References in corpus (2)

• Modifications of turbulence and turbulent transport associated with a bias-induced confinement transition in LAPD
• Transition to subcritical turbulence in a tokamak plasma

Cited by in corpus (4)

• Interpreting Radial Correlation Doppler Reflectometry using Gyrokinetic Simulations
• Dimits transition in three-dimensional ion-temperature-gradient turbulence
• Bistable turbulence in strongly magnetised plasmas with a sheared mean flow
• Suppression of temperature-gradient-driven turbulence by sheared flows in fusion plasmas