Plasma flow, turbulence and magnetic islands in TJ-II. (15th January 2016)

• Record Type: Journal Article
• Authors: Estrada, T.; Ascasíbar, E.; Blanco, E.; Cappa, A.; Hidalgo, C.; Ida, K.; López-Fraguas, A.; van Milligen, B.Ph
• Is Part Of: Nuclear fusion. Volume 56:Number 2(2016:Feb.)
• Publication Date: 2016-01-15
• Subjects: magnetic island -- plasma turbulence -- plasma flows -- Doppler reflectometry -- stellarators; Nuclear fusion -- Periodicals; 621.48405
• DOI: 10.1088/0029-5515/56/2/026011
• Languages: English
• ISSNs: 0029-5515

Abstract

Abstract: The effect of magnetic islands on plasma flow and turbulence has been experimentally investigated in ohmically induced magnetic configuration scans at the stellarator TJ-II. This operational mode allows sweeping the radial position of a low order rational surface from the plasma core towards the edge in a controlled way, what reveals effects that are difficult to notice in scans performed on a shot to shot basis. The main diagnostic used in the present work is a two-channel Doppler reflectometer that allows the measurement of the perpendicular rotation velocity of the turbulence and density fluctuations with good spatial and temporal resolution. A characteristic signature of the n / m = 3/2 magnetic island as it crosses the measurement position is clearly detected: the perpendicular flow reverses at the center of the magnetic island and a flow shear develops at the island boundaries. Fluctuations of the perpendicular flow and density have been also measured along the 3/2 magnetic island. An increase in the low frequency flow oscillations is measured at the magnetic island boundaries together with a reduction in the density fluctuation level; the later being more pronounced at the inner island boundary. These observations could explain the link between magnetic islands and transport barriers observed in a number of fusion devices.