Issue
EPL
Volume 84, Number 6, December 2008
Article Number 65001
Number of page(s) 5
Section Physics of Gases, Plasmas and Electric Discharges
DOI http://dx.doi.org/10.1209/0295-5075/84/65001
Published online 03 December 2008
EPL, 84 (2008) 65001
DOI: 10.1209/0295-5075/84/65001

First experimental observation of a two-step process in the development of the edge velocity shear layer in a fusion plasma

T. Happel, T. Estrada and C. Hidalgo

Laboratorio Nacional de Fusión, Asociación Euratom-CIEMAT - Madrid, Spain, EU

tim.happel@ciemat.es

received 19 November 2008; accepted in final form 21 November 2008; published December 2008
published online 3 December 2008

Abstract
The radial origin and the process of formation of the velocity shear layer (VSL) in the stellarator TJ-II have been investigated. Results show that the VSL starts its formation in the region of maximum density gradient and then expands radially outwards, until it is fully established and shows the universal properties of edge sheared flows observed in fusion plasmas. A two-step process in the edge shear formation is proposed: 1) a seeding mechanism linked to plasma gradients and 2) an amplification process in which edge shearing rates and fluctuations are self-organized near marginal stability.

PACS
52.35.Ra - Plasma turbulence.
52.25.Xz - Magnetized plasmas.
52.70.Gw - Radio-frequency and microwave measurements.

© EPLA 2008