The role of magnetic islands in modifying long range temporal correlations of density fluctuations and local heat transport

TL;DR

This study investigates how magnetic islands influence long-range correlations in density fluctuations and heat transport in a stellarator, revealing that magnetic islands enhance both correlations and heat transport, supported by experimental and simulation data.

Contribution

It demonstrates the impact of magnetic islands on long-range correlations and heat transport, combining experimental measurements with turbulence simulations.

Findings

Enhanced Hurst coefficient inside the magnetic island

Increased heat transport associated with long-range correlations

Simulation results support experimental observations

Abstract

This work explores the relation between magnetic islands, long range temporal correlations and heat transport. A low order rational surface ($\iota/2\pi = 3/2$) was purposely scanned outward through an Electron Cyclotron Resonance Heated (ECRH) plasma in the TJ-II stellarator. Density turbulence and the poloidal flow velocity (or radial electric field) were characterized using a two channel Doppler Reflectometer. Simultaneously, the ECRH power was modulated to characterize heat transport, using measurements from a 12 channel Electron Cyclotron Emission diagnostic. A systematic variation of the poloidal velocity was found to be associated with the stationary $\iota/2\pi = 3/2$ magnetic island. Inside from the rational surface, the Hurst coefficient, quantifying the nature of long-range correlations, was found to be significantly enhanced. Simultaneously, heat transport was enhanced as well, establishing a clear link between density fluctuations and anomalous heat transport. The variation of the Hurst coefficient was consistent with a magnetohydrodynamic turbulence simulation.