E × B staircases and barrier permeability in magnetised plasmas

In-depth experimental characterisation of spontaneous shear flow patterning into a so-called E × B staircase-named after its planetary analogue-is shown in magnetised plasma turbulence, using ultrafast-sweeping reflectometry in the Tore Supra tokamak. Staircase signatures are found in a large variety of L-mode plasma conditions. Sensitivity to the dominant source of free energy is highlighted for the first time. A connection between staircase shear layer permeability and deviation from gyro-Bohm confinement scaling is strongly suggested, opening new routes to understanding confinement in drift-wave turbulence.