Measurement and control of turbulence spreading in the Scrape-Off Layer of TJ-II

Abstract

In this paper, we report measurements of turbulence drive and spreading in the edge region and scrape-off layer (SOL) of the TJ-II stellarator for plasmas heated by ECRH and NBI. In addition, we show how these and various other relevant quantities can be modulated actively via edge biasing, i.e. by establishing an edge flow shear layer. When the edge ExB shear reaches values close to the inverse of the turbulence correlation time, turbulence spreading and edge-SOL coupling are reduced significantly. The resulting control of SOL spreading via the edge shear is important in view of the issue of understanding and controlling the SOL width in fusion-relevant devices.