Choongki Sung
Korea Advanced Institute of Science & Technology (KAIST), Daejeon
Seminar Information
Engineering Building Unit 2 (EBU2)
Room 479
Seminar Recording Available: Please contact seminar coordinator, Jake Blair at (j1blair@ucsd.edu)
Fast ions, generated through fusion reactions and external heating, play a critical role in fusion energy production, making fast-ion physics a key area of research in fusion science. Recently, increasing attention has been given to the potential of fast ions to enhance performance through turbulence suppression. In this context, the FIRE (Fast Ion Regulated Enhancement) mode, an internal transport barrier (ITB) discharge with high fast ion fraction, has been identified in KSTAR. This study employed gyrokinetic simulations to investigate the impact of fast ions on turbulence inside the ITB region of the FIRE mode discharge, depending on the scale of turbulence. Our analysis revealed that the turbulence energy flux was significantly reduced with the addition of fast ions in both ion and electron scale simulations, qualitatively consistent with experimental observations. Notably, the physical mechanisms driving this reduction differed between scales. In ion-scale simulations, the reduction in energy flux was primarily attributed to dilution effects caused by fast ions. Conversely, in electron-scale simulations, the enhanced Shafranov shift due to fast ions played the dominant role. In addition, we observed a long-wavelength mode destabilized by the addition of fast ions. While this mode did not significantly contribute to the reduction in energy flux, it generated significant zonal flow, suggesting a potential role in turbulence suppression. This presentation will provide an in-depth analysis of gyrokinetic simulations, elucidating the mechanisms by which fast ions influence turbulence and their implications for performance enhancement in the FIRE mode discharge.
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 turbulence and transport 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.