Publications (5)14.35 Total impact
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Article: Suppression of edge localized modes in high-confinement KSTAR plasmas by nonaxisymmetric magnetic perturbations.
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ABSTRACT: Edge localized modes (ELMs) in high-confinement mode plasmas were completely suppressed in KSTAR by applying n=1 nonaxisymmetric magnetic perturbations. Initially, the ELMs were intensified with a reduction of frequency, but completely suppressed later. The electron density had an initial 10% decrease followed by a gradual increase as ELMs were suppressed. Interesting phenomena such as a saturated evolution of edge T(e) and broadband changes of magnetic fluctuations were observed, suggesting the change of edge transport by the applied magnetic perturbations.Physical Review Letters 07/2012; 109(3):035004. · 7.37 Impact Factor -
Article: Characteristics of the first H-mode discharges in KSTAR
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ABSTRACT: Typical ELMy H-mode discharges have been obtained in the KSTAR tokamak with the combined auxiliary heating of neutral beam injection (NBI) and electron cyclotron resonant heating (ECRH). The minimum external heating power required for the L–H transition is about 0.9 MW for a line-averaged density of ~2.0 × 1019 m−3. There is a clear indication of the increase in the L–H threshold power with decreasing density for densities lower than ~2 × 1019 m−3. The L–H transitions typically occurred shortly after the beginning of plasma current flattop (Ip = 0.6 MA) period and after the fast shaping to a highly elongated double-null divertor configuration. The maximum heating power available was marginal for the L–H transition, which is also implied by the relatively slow transition time (>10 ms) and the synchronization of the transition with large sawtooth crashes. The initial analysis of thermal energy confinement time (τE) indicates that τE is higher than the prediction of multi-machine scaling laws by 10–20%. A clear increase in electron and ion temperature in the pedestal is observed in the H-mode phase but the core temperature does not change significantly. On the other hand, the toroidal rotation velocity increased over the whole radial range in the H-mode phase. The measured ELM frequency was around 10–30 Hz for the large ELM bursts and 50–100 Hz for the smaller ones. In addition, very small and high frequency (200–300 Hz) ELMs appeared between large ELM spikes when the ECRH is added to the NBI-heated H-mode plasmas. The drop of total stored energy during a large ELM is up to 5% in most cases.Nuclear Fusion 10/2011; 51(11):113009. · 4.09 Impact Factor -
Conference Proceeding: Key features in the operation of KSTAR
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ABSTRACT: The Korean Superconducting Tokamak Advanced Research (KSTAR) device is aimed at advanced tokamak (AT) research. Three years have passed since it achieved its first plasma in 2008. Because it is a superconducting machine and is pursuing AT research, it has unique features in terms of the machine engineering and operation. The toroidal field (TF) magnet coils are made of Nb<sub>3</sub>Sn, which provide high toroidal fields up to 3.5 T, and have been fully tested. The poloidal field (PF) magnet coils, consisting of both Nb3Sn and NbTi, which have a maximum current of 25 kA in their design, were tested up to 15 kA. A thermal hydraulic analysis is being conducted for PF magnet coil operation. All plasma facing components (PFCs) are equipped with water cooled graphite tiles and have the capability of being baked up to 350 °C. A startup scenario, which considered both the effect of the ferromagnetic material in the cable in conduit conductor (CICC) jacket in the magnet coils as well as a non-ferromagnetic up-down asymmetry in the cryostat structure, was developed and demonstrated its effectiveness by the last two year's reliable operations. Passive stabilizers and In-Vessel Control Coils (IVCC) are key components to realize AT Operation in KSTAR. The segmented IVCC coils were connected to form circular coils for internal vertical control in 2010 and diverted plasmas with high elongation (κ~1.8, δ>;0.6) were achieved. A neutral beam injection (NBI) system was developed aiming at 2 MW, 300 s per ion source which meets the long-pulse requirement of KSTAR. An NBI ion source with a power of 1.7 MW at 100 kV has been commissioned. Finally, ELMy H-modes were successfully produced with 1.3 MW NBI power at a plasma current of 0.6 MA in the 2010 campaign. The first H-mode discharge (#4200) in KSTAR was achieved one year earlier than officially planned and it was done at B<sub>T</sub>=2.0 T with Ip=0.6 MA in a well-balanced double null configuration after- - boronization on the PFC. Successful operations in the early days of KSTAR including H-mode experiments revealed the capability of advanced and steady-state operation which is essential for the International Thermonuclear Experimental Reactor (ITER) and future fusion reactors.Fusion Engineering (SOFE), 2011 IEEE/NPSS 24th Symposium on; 07/2011 -
Article: Diagnostics for first plasma and development plan on KSTAR
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ABSTRACT: The first plasma with target values of the plasma current and the pulse duration was finally achieved on June 13, 2008 in the Korea Superconducting Tokamak Advanced Research (KSTAR). The diagnostic systems played an important role in achieving successful first plasma operation for the KSTAR tokamak. The employed plasma diagnostic systems for the KSTAR first plasma including the magnetic diagnostics, millimeter-wave interferometer, inspection illuminator, Hα, visible spectrometer, filterscope, and electron cyclotron emission (ECE) radiometer have provided the main plasma parameters, which are essential for the plasma generation, control, and physics understanding. Improvements to the first diagnostic systems and additional diagnostics including an x-ray imaging crystal spectrometer, reflectometer, ECE radiometer, resistive bolometer, and soft x-ray array are scheduled to be added for the next KSTAR experimental campaign in 2009.Review of Scientific Instruments 06/2010; 81(6):063502-063502-6. · 1.37 Impact Factor -
Article: Descriptions of a linear device developed for research on advanced plasma imaging and dynamics.
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ABSTRACT: The research on advanced plasma imaging and dynamics (RAPID) device is a newly developed linear electron cyclotron resonance (ECR) plasma device. It has a variety of axial magnetic field profiles provided by eight water-cooled magnetic coils and two dc power supplies. The positions of the magnetic coils are freely adjustable along the axial direction and the power supplies can be operated with many combinations of electrical wiring to the coils. A 6 kW 2.45 GHz magnetron is used to produce steady-state ECR plasmas with central magnetic fields of 875 and/or 437.5 G (second harmonic). The cylindrical stainless steel vacuum chamber is 300 mm in diameter and 750 mm in length and has eight radial and ten axial ports including 6-in. and 8-in. viewing windows for heating and diagnostics. Experimental observation of ECR plasma heating has been recently carried out during the initial plasma operation. The main diagnostic systems including a 94 GHz heterodyne interferometer, a high-resolution 25 channel one-dimensional array spectrometer, a single channel survey spectrometer, and an electric probe have been also prepared. The RAPID device is a flexible simulator for the understanding of tokamak edge plasma physics and new diagnostic system development. In this work, we describe the RAPID device and initial operation results.The Review of scientific instruments 10/2009; 80(10):103503. · 1.52 Impact Factor
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2011
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National Fusion Research Institute
Taiden, Daejeon, South Korea
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