On the link between parallel flows, turbulence and electric fields in the edge of the TJ-II stellarator

Laboratorio Nacional de Fusión, EURATOM-CIEMAT Association - Av. Complutense 22, 28040 Madrid, Spain, EU

Corresponding author: arturo.alonso@ciemat.es

Received: 16 July 2008
Accepted: 15 December 2008

Abstract

The structure of turbulence and parallel and perpendicular EB flows have been investigated across the transition to improved confinement regimes induced by biasing. The radial electric field at the edge and the EB shear increase, while the level of edge fluctuations is reduced significantly during such improved confinement regimes in TJ-II. In addition, the parallel flow Mach number changes by in the plasma edge region which is in rough agreement with the expected change in the Pfirsch-Schlüter flow. In order to investigate the role of EB sheared flows and turbulence on parallel dynamics, the cross-correlation coefficient was computed in the presence of perpendicular flows induced by biasing. Although the level of turbulence decreases, the phase coherence increases and the resulting turbulent forces are shown to be high enough to affect parallel dynamics. These findings represent the first experimental evidence of the dual role of electric fields as a stabilizing mechanism of plasma turbulence and as an agent affecting the parallel momentum balance via turbulence modification.