Experimental evidence of fluctuation-induced inward transport linked to rational surfaces in the TJ-II stellarator

Radial profiles of electrostatic fluctuations and fluctuations-induced transport have been measured in the proximity of rational surfaces in the plasma boundary region of the TJ-II stellarator. Structures in plasma profiles linked to the location of low-order rational surfaces (n = 8/m = 5, n = 4/m = 2) have been observed. Local turbulent E×B driven fluxes are significantly modified in the proximity of rational surfaces. In the case of low-order rationals (n = 4/m = 2) turbulent transport reverses from radially outwards to radially inwards. These changes are due to a modification in the phase relation between density and electric field fluctuations.