The influence of magnetic field curvature on intermittency in drift-wave turbulence in the stellarator TJ-K

Abstract

The influence of magnetic field curvature on the intermittency in density and potential fluctuations in drift-wave turbulence has been investigated in the stellarator TJ-K in the framework of an extended Hasegawa–Wakatani model. A structure function analysis was used to estimate the intermittency level of poloidally resolved drift-wave turbulence measurements of a deuterium plasma in TJ-K. Potential fluctuations were found to be broadly self-similar, whereas density fluctuations were found to be more intermittent in the region with negative normal and positive geodesic curvatures. This behavior could be understood by comparing the data to two-dimensional extended Hasegawa–Wakatani simulations that retain gradients in the magnetic field strength, giving rise to curvature effects. The model is able to reproduce the trends in the experimental data if both normal and geodesic curvature effects are accounted for, as well as the local anisotropy of turbulent length scales. The analysis indicates the importance of local magnetic geometry as a factor in the decoupling of density and potential fluctuations, leading to intermittency in drift-wave turbulence.