Speaker: Dr. Choongki Sung, KAIST
Title: Experimental Investigation of Internal Reconnection Events in Versatile Experiment Spherical Torus
Abstract:
An Internal Reconnection Event (IRE) is a disruption-like phenomenon observed in spherical tokamaks, characterized by a sudden change in plasma current and internal magnetic structure, yet allowing the plasma to recover without an abrupt termination [1]. IREs are believed to be associated with internal plasma instabilities, such as the excitation and coupling of magnetohydrodynamic (MHD) modes [2,3]. Interestingly, previous studies have also reported correlations between edge plasma blobs and IRE dynamics [4]; however, the detailed nature of this interaction has not been thoroughly investigated. In this work, we have examined IREs observed in the Versatile Experimental Spherical Torus (VEST) using a newly installed soft X-ray (SXR) diagnostic system, magnetic probes, and a fast camera. Two dominant MHD modes and their synchronization were identified prior to the IRE onset inside the plasma. Furthermore, we found that the core SXR channels became synchronized with edge blob signals, showing a propagation from the edge toward the core. Notably, this synchronization begins at nearly the same time as the core mode synchronization event. These observations suggest the possible role of core–edge coupling in the onset of IRE. Details of the analysis will be presented, along with an introduction to other research activities in the Fusion and Plasma Dynamics Laboratory at KAIST.
[1] A. Sykes et al., Nucl. Fusion 32 694 (1992).
[2] S. Chai et al., Phys. Plasmas 24 032503 (2017).
[3] Naoki Mizuguchi et al., Phys. Plasmas 7 940-949 (2000).
[4] E. C. Jung et al., Nucl. Fusion 62 126029 (2022).
Bio: Choongki Sung is an associate professor in the Department of Nuclear and Quantum Engineering at KAIST. Before joining KAIST in 2020, he worked at Lam Research Corp. as a process engineer from 2018-2020, where he developed etching processes for semiconductor manufacturing. He also worked at UCLA as a postdoctoral researcher from 2015 to 2018. During this time, he developed a diagnostic for turbulence measurements in magnetized high-temperature plasmas relevant to nuclear fusion, i.e., fusion plasmas, and studied the effects of turbulence on the confinement of the fusion plasmas. He received his B.S. and M. S. degrees from Seoul National University in 2008 and 2010, respectively, and his Ph.D. degree from MIT in 2015. His main research focus involved instabilities in fusion plasmas. He has concentrated on plasma physics research for fusion energy production, particularly in studying turbulence behavior and its effects on macroscopic instability and overall fusion plasma performance through measurements, data analysis, and modeling studies using simulations. He has also explored alternative fusion concepts to find a shorter pathway to a commercial fusion reactor compared to conventional fusion reactor concepts. Furthermore, he is expanding his research portfolio from fusion to other plasma applications, such as plasma processing for semiconductor manufacturing and neutron source development.