Symmetry breaking in MAST plasma turbulence due to toroidal flow shear

M. F.J. Fox, F. Van Wyk, A. R. Field, Y. C. Ghim, F. I. Parra, A. A. Schekochihin

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14 Scopus citations


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 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.

Original languageEnglish (US)
Article number034002
JournalPlasma Physics and Controlled Fusion
Issue number3
StatePublished - Jan 27 2017
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Nuclear Energy and Engineering
  • Condensed Matter Physics


  • beam emission spectroscopy
  • flow shear
  • gyrokinetic simulations
  • tokamak turbulence


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