The spatio-temporal evolution of turbulence and plasma flows has been studied experimentally by means of Doppler reflectometry during the back-transition from the high to low confinement mode in the TJ-II stellarator. Signatures of spatial spreading of the turbulence are found inside the radial position of the sheared E × B flow as the H–L back-transition is approached. The results point to the possible role of radial spreading of turbulence in determining the width of transport barriers.
Role of isotope mass and evidence of fluctuating zonal flows during the L–H transition in the TJ-II stellarator