Localized explosive magnetic reconnection in magnetized plasmas

Abstract

Hydrodynamic instabilities in magnetized high-temperature plasmas are often terminated by explosive crash events such as solar flares in space and sawtooth crash in fusion plasmas. The rapidness of such crash events implies the existence of an efficient dissipation channel of magnetic energy other than resistive heating. On the KSTAR tokamak, a suite of passive radiation diagnostics has been developed to study the entire evolution process of MHD instabilities in Alfvenic (~μs) time resolution, including electron cyclotron emission (ECE) imaging system (~100 GHz), fast RF spectrometer (< ~1 GHz), and fast hard X-ray (HXR) spectrometer (10--300 keV). These diagnostics revealed several important features of the sawtooth crash: (1) convective heat transport through a poloidally and toroidally localized channel, (2) rotation braking, (3) non-thermal ECE burst near inversion, and (4) long-lasting HXR burst after crash. These observations are compared with a model for fast magnetic reconnection accelerated by generation of Alfven/whistler waves (and rapid Landau damping on electrons) [Bellan, Phys. Plasma 5 (1998)], which may explain the rapid transport of heat during the crash.*Work supported by the National Research Foundation of Korea (grant Nos. NRF- 2014M1A7A1A03029881, NRF-2013M1A7A1A02043921, and BK21+ program) and Asia-Pacific Center for Theoretical Physics.