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Kim, Doohyun,Han, Hyunsun,Kim, Ki Min,Park, Jong Kyu,Jeon, Young Mu,Na, Yong-Su,Hong, Sang Hee Published jointly by The Institute of Physics and 2010 Plasma physics and controlled fusion Vol.52 No.9
<P>Numerical simulations are carried out to investigate the applicability of resonant magnetic perturbation (RMP) to KSTAR plasmas for a possible control of edge localized mode (ELM) to suppress or mitigate its damages to divertor materials. For the verification of the feasibility of RMP application, magnetic island configurations, resonant normal fields, magnetic island widths and Chirikov parameters are calculated for two types of KSTAR operation scenarios: steady state and hybrid. Field error correction (FEC) coils in KSTAR are considered to produce externally perturbed magnetic fields for RMP, and the directions of coil currents determine the toroidal mode <I>n</I> and the parity (even or odd). The RMP configurations are described by vacuum superposition of the equilibrium magnetic fields and the perturbed ones induced by FEC coils. The numerical simulations for <I>n</I> = 2 toroidal mode in both operation scenarios show that when the pitches of the equilibrium and perturbed magnetic fields are well aligned, magnetic islands are formed for a series of <I>m</I> poloidal modes and the adjacent islands are overlapped to generate a stochastic layer in the edge region. Even parity turns out to be more effective in making the magnetic islands overlapped to become stochastic field lines in the steady-state operation, while odd parity in the hybrid operation. The formation of the stochastic layer is verified by the calculated Chirikov parameters, which also give basic information on the current requirement of FEC coils. Additionally, lobe structures of stochastic field lines are found in the edge region extended to the divertor plate in the hybrid scenario. Based on the standard vacuum criteria for RMP, the simulation results indicate that the FEC coils will be feasible for control of ELMs and mitigation of divertor heat load by RMP in both steady-state and hybrid operation scenarios.</P>
Suppression of edge localized mode crashes by multi-spectral non-axisymmetric fields in KSTAR
Kim, Jayhyun,Park, Gunyoung,Bae, Cheonho,Yoon, Siwoo,Han, Hyunsun,Yoo, Min-Gu,Park, Young-Seok,Ko, Won-Ha,Juhn, June-Woo,Na, Yong Su International Atomic Energy Agency 2017 Nuclear fusion Vol.57 No.2
<P>Among various edge localized mode (ELM) crash control methods, only non-axisymmetric magnetic perturbations (NAMPs) yield complete suppression of ELM crashes beyond their mitigation, and thus attract more attention than others. No other devices except KSTAR, DIII-D, and recently EAST have successfully achieved complete suppression with NAMPs. The underlying physics mechanisms of these successful ELM crash suppressions in a non-axisymmetric field environment, however, still remain uncertain. In this work, we investigate the ELM crash suppression characteristics of the KSTAR ELMy H-mode discharges in a controlled multi-spectral field environment, created by both <img ALIGN='MIDDLE' ALT='$n=2$ ' SRC='http://ej.iop.org/images/0029-5515/57/2/022001/nfaa3e05ieqn001.gif'/> middle reference and <img ALIGN='MIDDLE' ALT='$n=1$ ' SRC='http://ej.iop.org/images/0029-5515/57/2/022001/nfaa3e05ieqn002.gif'/> top/bottom proxy in-vessel control coils. Interestingly, the attempts have produced a set of contradictory findings, one expected (ELM crash suppression enhancement with the addition of <I>n</I> = 1 to the <I>n</I> = 2 field at relatively low heating discharges) and another unexpected (ELM crash suppression degradation at relatively high heating discharges) from the earlier findings in DIII-D. This contradiction indicates the dependence of the ELM crash suppression characteristics on the heating level and the associated kink-like plasma responses. Preliminary linear resistive MHD plasma response simulation shows the unexpected suppression performance degradation to be likely caused by the dominance of kink-like plasma responses over the island gap-filling effects.</P>
A call for action from workers, local residents, and consumers: a safe society from toxic chemicals
Kim, Shinbum,Im, Sanghyuk,Choi, Youngeun,Park, Soomi,Hyun, Jaesoon,Lee, Kyung Seok,Lee, Sunimm,Lee, Sung-nan,Seo, Jeongri,Kim, Ju Hee,Na, Hyunsun,Kim, Minsun,Korean Society for Environmental Health an The Korea Society of Environmental Toocicology 2016 환경독성보건학회지 Vol.31 No.-