Poloidal mode structure of long-distance correlation of fluctuations under strong E×B shear in the torsatron TJ-K

Abstract

Long-distance correlations of density and potential fluctuations are investigated on the poloidal circumference of flux surface in the TJ-K plasmas. Shear flow as induced by biasing causes a strong increase in the long-distance correlation of potential and density fluctuations. In the potential fluctuations, zonal-flow-like modes are excited. The density long-distance correlation is dominated by an m=3 mode. As a new feature a coherency analysis reveals also the existence of m=0 density fluctuations. As an explanation, background profile fluctuations or a turbulent zonal density drive are proposed.