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17–22 Oct 2016
Kyoto International Conference Center
Japan timezone

Edge-localized modes on KSTAR: global structure and distinct evolution stages involving quasi-steady state and phase transitions

21 Oct 2016, 17:20
20m
Kyoto International Conference Center

Kyoto International Conference Center

Takaragaike, Sakyo-ku, Kyoto 606-0001 Japan
Oral EXD - Magnetic Confinement Experiments: Plasma–material interactions; divertors; limiters; scrape-off layer (SOL) ELMs Suppression & Dynamics

Speaker

Prof. Gunsu YUN (Pohang University of Science and Technology)

Description

Edge-localized modes (ELMs) in the KSTAR tokamak appear substantially different from the conventional picture of ELMs as an explosive transport event in the plasma edge triggered by exponentially growing ballooning and external kink modes on the low field side of the plasma. The 2-D images of ELMs visualized by an advanced imaging diagnostics^1 with microsecond time resolution revealed that the modes evolve in three distinctive stages: (1) quasi-steady (saturated) filamentary mode^2 with long life time (up to ~100 ms), (2) abrupt structural transformation near the onset of crash into irregular-shaped filaments^2 or in the middle of the inter-crash period^3, (3) and multiple filament bursts during the crash phase^2. Perhaps the most astonishing finding is the clear existence of filamentary modes exist on the high field side as well as on the low field side^4, suggesting that the ELM dynamics in the KSTAR involve other driving forces such as d’Angelo instability besides ballooning and external kink. In addition, we demonstrate that the ELM evolution stages are associated with distinct changes of RF emission spectra^5 (100—1000 MHz), suggesting the RF signal as a better alternative to the conventional D-alpha signal which represents only the aftermath of the collapse of the edge confinement. *Work supported by the NRF of Korea under grant No. NRF-2014M1A7A1A03029881, BK+ program, and A3 Foresight program. References: 1.G.S. Yun et al., Rev. Sci. Instrum. 85, 11D820 (2014) 2.G.S Yun et al., Phys. Rev. Lett. 107, 045004 (2011) 3.J.E. Lee et al., Nucl. Fusion 55, 113035 (2015) 4.J. Lee et al., submitted. 5.S. Thatipamula et al., submitted.
Country or International Organization Republic of Korea
Paper Number EX/10-3

Primary author

Prof. Gunsu YUN (Pohang University of Science and Technology)

Co-authors

Prof. Hyeon K. Park (UNIST) Dr Jaehyun Lee (Ulsan National Institute of Science and Technology) Mrs Jieun Lee (Pohang University of Science and Technology) Mr Minho Kim (Pohang University of Science and Technology) Dr Minjun J. Choi (National Fusion Research Institute) Dr Shekar Thatipamula (Pohang University of Science and Technology) Dr Woochang Lee (UNIST)

Presentation materials