Intermittence and turbulence in fusion devices

In this work, we explore the response of the intermittence parameter C(1) to the magnetic topology of confined fusion plasmas, as well as to spontaneously generated zonal flows. To achieve this, we make extensive use of resistive Magneto-Hydrodynamic calculations. First, we explore single helicity calculations, where we observed clearly that the intermittence is due to the mixing between turbulence and (poloidal) flow fluctuations. The minima of C(1) were correlated with maxima of the mean transfer entropy, , noting that the latter have been identified with 'trapping zones' for radial transport in previous work. Thus, these 'trapping zones' are closer to monofractality than the surrounding plasma. In more realistic multiple helicity calculations, these results were confirmed, although somewhat less clear, as the mutual interaction between helicities now also contributed to the intermittence. We applied these techniques to experimental Electron Cyclotron Emission data from the W7-X stellarator and found that these observations also appear to hold in an experimental situation. Thus, we conclude that the intermittence parameter C(1) may provide valuable indirect information about the interaction between fluctuations, zonal flows, and the magnetic topology of fusion plasmas.

Intermittence and turbulence in fusion devices Articles