Abstract
Magnetic islands (MIs), resulting from a magnetic field reconnection, are ubiquitous structures in magnetized plasmas. In tokamak plasmas, recent researches suggested that the interaction between an MI and ambient turbulence can be important for the nonlinear MI evolution, but a lack of detailed experimental observations and analyses has prevented further understanding. Here, we provide comprehensive observations such as turbulence spreading into an MI and turbulence enhancement at the reconnection site, elucidating intricate effects of plasma turbulence on the nonlinear MI evolution.
Highlights
Magnetic islands (MIs), resulting from a magnetic field reconnection, are ubiquitous structures in magnetized plasmas
While turbulence around an MI has been limitedly observed in other experiments, the Korea Superconducting Tokamak Advanced Research (KSTAR)[26] experiment[8] clearly demonstrates that the increase of the low-k Te turbulence can be localized in the inner region (r < rs where rs is an MI boundary) between the X-point and O-point poloidal angles
In the KSTAR experiments[8], the plasma was heated by the constant ~1 MW neutral beam and an m/n = 2/1 MI was driven by the external n = 1 magnetic field perturbation for accurate measurements and analyses of small Te fluctuations around the MI using the 2D local Te diagnostics. m and n are the poloidal and toroidal mode numbers, respectively
Summary
Magnetic islands (MIs), resulting from a magnetic field reconnection, are ubiquitous structures in magnetized plasmas. Magnetohydrodynamic instabilities[1,2] involving MIs are a serious concern since they destroy the nested structure of magnetic flux surfaces and lead to degradation of the plasma confinement The stability of those instabilities depends on the current[1] and pressure[2] profiles of the plasma which are affected by the turbulent transport. They include turbulence spreading into the MI and the turbulence enhancement at the reconnection site, either retarding or facilitating the magnetic reconnection, respectively These observations significantly extend our understanding of the nonlinear MI evolution in tokamak as well as provide general insights into the magnetic reconnection physics in magnetized plasmas
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