The impact of rational surfaces on radial heat transport in TJ-II Articles uri icon

authors

  • VAN MILLIGEN, B.PH.
  • HERNANDEZ NICOLAU, JAVIER
  • GARCIA GONZALO, LUIS
  • CARRERAS VERDAGUER, BENJAMIN ANDRES
  • HIDALGO, C.

publication date

  • May 2017

start page

  • 056028(1)

end page

  • 056028(18)

issue

  • 5

volume

  • 57

International Standard Serial Number (ISSN)

  • 0029-5515

Electronic International Standard Serial Number (EISSN)

  • 1741-4326

abstract

  • In this work, we study the outward propagation of temperature perturbations. For this purpose, we apply an advanced analysis technique, transfer entropy, to ECE measurements performed in ECR heated discharges at the low-shear stellarator TJ-II. We observe that the propagation of these perturbations is not smooth, but is slowed down at specific radial positions, near 'trapping zones' characterized by long time lags with respect to the perturbation origin. We also detect instances of rapid or instantaneous (non-local) propagation, in which perturbations appear to 'jump over' specific radial regions. The analysis of perturbations introduced in a resistive magneto-hydrodynamic model of the plasma leads to similar results. The radial regions corresponding to slow radial transport are identified with maxima of the flow shear associated with rational surfaces (mini-transport barriers). The non-local interactions are ascribed to MHD mode coupling effects.

keywords

  • turbulence; transport; stellarator; electron thermal transport; thomson scattering; plasmas; barriers; stellarator; tokamaks; turbulence; physics; rtp