Quench Detection of the KSTAR CS Coil by Considering Plasma Current Effect

Kim, Jinsub,Jeon, Young Mu,Yonekawa, Hirofumi,Kim, Yeong-ok,Kim, Kwang Pyo,Park, K. R.,Chu, Yong Institute of Electrical and Electronics Engineers 2019 IEEE transactions on applied superconductivity Vol.29 No.5

<P>The plasma-driven inductive voltages were not negligible and should be taken into account for the reliable operation of the voltage-based quench detection of the KSTAR CS coil. For the active compensation of such plasma-induced voltage noise, plasma parameters should be measured in real-time and applied to the quench detection system. The selection of plasma parameters by considering their contribution to the noise is of primary importance. A code, which can estimate the induced coil voltage driven by plasma, is developed by using a simplified plasma response modeling. The numerical analysis has showed that there is an apparent influence from the plasma, while the influence from eddy currents induced in passive structures is negligible. The change of plasma current is the primary noise source and the radial and vertical motions of plasma have an effect, although they are small. The performance of the quench detector is developed and tested during the 2017 KSTAR campaign. The noise rejection performance is discussed with various experimental results and numerical estimations.</P>

Fabrication of hybrid composites based on biomineralization of phosphorylated poly(ethylene glycol) hydrogels

Kim, Chan Woo,Kim, Sung Eun,Kim, Yong Woo,Lee, Hong Jae,Choi, Hyung Woo,Chang, Jeong Ho,Choi, Jinsub,Kim, Kyung Ja,Shim, Kwang Bo,Jeong, Young-Keun,Lee, Sang Cheon Cambridge University Press (Materials Research Soc 2009 Journal of materials research Vol.24 No.1

<P>A novel route to organic-inorganic composites was described based on biomineralization of poly(ethylene glycol) (PEG)-based hydrogels. The 3-dimensional hydrogels were synthesized by radical crosslinking polymerization of poly(ethylene glycol fumarate) (PEGF) in the presence of ethylene glycol methacrylate phosphate (EGMP) as an apatite-nuclating monomer, acrylamide (AAm) as a composition-modulating comonomer, and potassium persulfate (PPS) as a radical initiator. We used the urea-mediated solution precipitation technique for biomineralization of hydrogels. The apatite grown on the surface and interior of the hydrogel was similar to biological apatites in the composition and crystalline structure. Powder x-ray diffraction (XRD) showed that the calcium phosphate crystalline platelets on hydrogels are preferentially aligned along the crystallographic c-axis direction. Inductively-coupled plasma mass spectroscopy (ICP-MS) analysis showed that the Ca/P molar ratio of apatites grown on the hydrogel template was found to be 1.60, which is identical to that of natural bones. In vitro cell experiments showed that the cell adhesion/proliferation on the mineralized hydrogel was more pronounced than on the pure polymer hydrogel.</P>

이종(異種) 차량간 운행시험 방안 연구

김대식(Daesik Kim),김주원(Juwon Kim),소진섭(JinSub So),김진우(Jinwoo Kim),정형일(Hyeongil Jeong),이성준(Seoungjun Lee),김용한(Yonghan Kim) 한국철도학회 2014 한국철도학회 학술발표대회논문집 Vol.2014 No.5

철도운영의 효율화와 최적의 유지보수를 위해서는 KTK, KTX-산천, 전동차와 같이 고정 편성으로 동일한 차종으로 구성하여 운행하는 것이 가장 효율적이며, 이런 이유로 국내는 물론 세계적으로 동종의 차량으로 열차 운행 다이아를 설정하고 있으며, 화물열차도 최대한 동일 사양으로 묶어 운행을 하고 있다. 본 연구는 국가R&D 사업으로 개발하고 있는 2층 고속열차, 고속화물열차 및 여객/화물 복합열차의 종합편성시험을 위한 안전 및 인터페이스 측면에서 고려되어야 할 사항에 대하여 연구하고 분석하였다. In light of operational efficiency and maintenance effectiveness, it is the most effective way that a train is composed of same cars such as KTX, KTX-Sancheon and Electric Multiple Unit. Therefore, world trend of a train formation is toward the same kind of cars’ and even a freight train often run with the same kind of cars. This study is aimed at analysis of essential elements about safety and interface of a developing high speed train which is composed of duplex passenger cars and passenger/freight complex cars.

Electrochemical Characteristics of Solid Polymer Electrode Fabricated with Low IrO₂ Loading for Water Electrolysis

Ban, Hee-Jung,Kim, Min Young,Kim, Dahye,Lim, Jinsub,Kim, Tae Won,Jeong, Chaehwan,Kim, Yoong-Ahm,Kim, Ho-Sung The Korean Electrochemical Society 2019 Journal of electrochemical science and technology Vol.10 No.1

To maximize the oxygen evolution reaction (OER) in the electrolysis of water, nano-grade $IrO_2$ powder with a low specific surface was prepared as a catalyst for a solid polymer electrolyte (SPE) system, and a membrane electrode assembly (MEA) was prepared with a catalyst loading as low as $2mg\;cm^{-2}$ or less. The $IrO_2$ catalyst was composed of heterogeneous particles with particle sizes ranging from 20 to 70 nm, having a specific surface area of $3.8m^2g^{-1}$. The anode catalyst layer of about $5{\mu}m$ thickness was coated on the membrane (Nafion 117) for the MEA by the decal method. Scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS) confirmed strong adhesion at the interface between the membrane and the catalyst electrode. Although the loading of the $IrO_2$ catalyst was as low as $1.1-1.7mg\;cm^{-2}$, the SPE cell delivered a voltage of 1.88-1.93 V at a current density of $1A\;cm^{-2}$ and operating temperature of $80^{\circ}C$. That is, it was observed that the over-potential of the cell for the oxygen evolution reaction (OER) decreased with increasing $IrO_2$ catalyst loading. The electrochemical stability of the MEA was investigated in the electrolysis of water at a current density of $1A\;cm^{-2}$ for a short time. A voltage of ~2.0 V was maintained without any remarkable deterioration of the MEA characteristics.

Structural Behavior of KSTAR CS Magnet During Plasma Operation

Ahn, Hee-Jae,Park, Hyun-Ki,Kim, Jinsub,Kim, YoungOk,Kim, Kwang Pyo,Chu, Yong,Kim, Hyun-Seok,Park, Kaprai,Oh, Yeong-Kook,Lee, Sudo,Kim, Yong Hwan Institute of Electrical and Electronics Engineers 2018 IEEE transactions on applied superconductivity Vol.28 No.3

<P>The finite element model of KSTAR central solenoid (CS) magnet has been developed with new smeared orthotropic material properties of CS coils and the effective coefficient of thermal expansion of the magnet structures. The accuracy of structural analysis for assembly and cool-down processes is higher than in previous studies. Electromagnetic analysis was performed to evaluate Lorentz forces of poloidal field (PF) coils during a long pulse discharge. The analyzed structural behavior of the CS magnet was clearly consistent with the measured data and calculated Electromagnetic (EM) forces during the plasma operation. The current of PF4 coil had a significant effect on axial compression and the minimum preloading was maintained at 2.0 MN in the end of plasma. Equivalent EM force can easily predict the axial compression of CS magnet without complicated structural analysis. The study on the structural behavior of CS magnet is expected to provide the optimal combination of PF coil current limits for large plasma current and long pulse discharges.</P>

Effects of AC Disturbance on Cowinding HTS Coils According to the Inserted Materials

Jinsub Kim,Young Jin Hwang,Woo Seung Lee,Tae Sung Lee,Jeyull Lee,Tae Kuk Ko Institute of Electrical and Electronics Engineers 2015 IEEE transactions on applied superconductivity Vol.25 No.3

<P>Alternating field causes energy loss due to induced back electromotive force (EMF) to high-temperature superconducting (HTS) coils in the superconducting electric machines. Therefore, a method of reducing the effects of the alternating fields on the HTS coils in superconducting machines according to the winding insulation conditions has been investigated. In addition, the HTS coils cowound with turn-to-turn inserted materials to control the time constant has been proposed. The charge-discharge delay can be determined with the time constant, also the time constant is related to the radial directional resistance of the no-insulation coil. The variation of the radial resistance would affect the reduction effect of ac disturbance on the no-insulation coil. Therefore, trade-off between the reduction effect of the alternating disturbance and charge-discharge delay could be considered. In this paper, we evaluated the effects of alternating magnetic fields on the HTS coils according to the varying radial resistance caused by cowinding method with metal tapes in liquid nitrogen. Four types of the HTS coils are: 1) no-insulation coil, 2) cowound coil with copper tape, 3) cowound coil with stainless steel tape and 4) insulation coil which have different radial resistance respectively. The experimental result shows that the co-winding method can be applicable in the superconducting electric machines.</P>

Experimental Study on Thermal Behavior of HTS Coils With Quasi-Insulation Winding Method at Overcurrent Operation

Jinsub Kim,Hyungjun Kim,Jeyull Lee,Tae Kuk Ko Institute of Electrical and Electronics Engineers 2016 IEEE transactions on applied superconductivity Vol.26 No.4

<P>Recently, superconducting power applications by using the high-temperature superconducting (HTS) tape have been widely researched due to the development of the HTS tape. In particular, the HTS coils cowound with insulation materials have been dominantly used for the power applications. However, the insulated HTS coil has low thermal stability at overcurrent operation, which causes much likely to be damaged. To relieve this issue, other insulation methods such as insulation-free or partial insulation have been investigated. These methods have good thermal stability; however, they have weaknesses such as magnetic field saturation and charge-discharge delay as well. In particular, charge-discharge delay is a significant obstacle for superconducting magnetic energy storage due to a frequently variable current operation. Therefore, a quasi-insulation (QI) coil that compensates the disadvantages has been proposed. In this paper, two QI coils according to the width of the insulation tape were fabricated since the performance of this winding method is affected by the exposure area to the coolant. In addition, insulation-free coil and partial insulation coil were fabricated and tested as the control group. The terminal coil voltage and center magnetic field were measured to compare the characteristics of each coil. The experimental result shows the QI coil has good thermal stability at overcurrent operation without magnetic field saturation and degradation. In addition, cooling effect is proportional to the exposed area to the coolant and adjustable with a different width of insulation tape.</P>

Designing a highly bioactive 3D bone-regenerative scaffold by surface immobilization of nano-hydroxyapatite

Kim, Sung Eun,Choi, Hyung Woo,Lee, Hong Jae,Chang, Jeong Ho,Choi, Jinsub,Kim, Kyung Ja,Lim, Hee Jin,Jun, Young Joon,Lee, Sang Cheon Royal Society of Chemistry 2008 Journal of materials chemistry Vol.18 No.41

<P>A novel approach to the fabrication of porous scaffolds with surface-immobilized nano-hydroxyapatite (N-HAp) is developed for effective bone tissue engineering. The discrete nano-level anchoring of N-HAp on the pore surface of chitosan scaffolds is achieved using surface-repellent stable colloidal N-HAp with surface phosphate functionality. Field-emission scanning electron microscopy (FE-SEM) and X-ray photoelectron spectroscopy (XPS) confirm pronounced exposure of N-HAp on the surfaces of chitosan scaffolds at the nano-level, which can not be accomplished with the conventional polymer/N-HAp composite scaffolds. This rational surface engineering enables surface-anchored N-HAp to express its overall intrinsic bioactivity, since N-HAp is not phase-mixed with the polymers. The porous chitosan scaffolds with surface-immobilized N-HAp provide more favorable environments than conventional bulk phase-mixed chitosan/N-HAp scaffolds in terms of cellular interaction and growth. <I>In vitro</I> biological evaluation using alkaline phosphatase activity assay supports that immobilized N-HAp on pore surfaces of chitosan scaffolds contributed to the more enhanced <I>in vitro</I> osteogenic potential. In addition, scaffolds with surface-exposed N-HAp provide favorable environments for enhanced <I>in vivo</I> bone tissue growth, estimated by characteristic biomarkers of bone formation such as collagen. The results suggest that the newly developed hybrid scaffolds with surface-immobilized N-HAp may serve as useful 3D substrates with pore surfaces featuring excellent bone tissue-regenerative properties.</P> <P>Graphic Abstract</P><P>Rational surface engineering through immobilization of nano-hydroxyapatite (N-HAp) on the pore surfaces of 3D polymer scaffolds can provide a novel hybrid scaffold featuring excellent bone tissue-regenerative properties. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=b810328c'> </P>

Bi-functional anodic TiO₂ oxide: Nanotubes for wettability control and barrier oxide for uniform coloring

Kim, Sunkyu,Jung, Minkyeong,Kim, Moonsu,Choi, Jinsub Elsevier 2017 APPLIED SURFACE SCIENCE - Vol.407 No.-

<P><B>Abstract</B></P> <P>A uniformly colored TiO<SUB>2</SUB>, on which the surface is functionalized with nanotubes to control wettability, was prepared by a two-step anodization; the first anodization was carried out to prepare nanotubes for a super-hydrophilic or -hydrophobic surface and the second anodization was performed to fabricate a thin film barrier oxide to ensure uniform coloring. The effect of the nanotubes on barrier oxide coloring was examined by spectrophotometry and UV-vis-IR spectroscopy. We found four different regimes governing the color changes in terms of anodization voltage, indicating that the color of the duplex TiO<SUB>2</SUB> was primarily determined by the thickness of the barrier oxide layer formed during the second anodization step. The surface wettability, as confirmed by the water contact angle, revealed that the single barrier TiO<SUB>2</SUB> yielded 74.6°±2.1, whereas the nanotubes on the barrier oxide imparted super-hydrophilic properties as a result of increasing surface roughness as well as imparting a higher hydrophobicity after organic acid treatment.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Controllable colored TiO<SUB>2</SUB> with different wettability is produced by two-consecutive anodization. </LI> <LI> Uniform color is primarily determined by the thickness of the barrier oxide. </LI> <LI> Controllable wettability is mainly influenced by the roughness of nanotubes. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Study on Quench Detection of the KSTAR PF Coils Using Numerical Compensation of Inductive Voltages With Genetic Algorithm

Jinsub Kim,Seok Chan An,Yojong Choi,Tae Kuk Ko,Yong Chu IEEE 2017 IEEE transactions on applied superconductivity Vol.27 No.4

<P>A quench detection system for Korea Superconducting Tokamak Advanced Research (KSTAR) Poloidal Field (PF) coils is indispensable against the occurrence of a normal zone due to frequently variable current operation and an enormous amount of stored energy. The co-wound conductive strips and Wheatstone bridges have been adopted in KSTAR to detect abnormal voltage signal caused from quench. Those voltage detection methods have sufficient capability to detect quench occurrence, but additional cancelling out of mutual induction by adjacent coils would improve stability and reliability of quench detection system. A new voltage detection concept, using central difference averaging (CDA) and mutual inductance compensation (MIK) simultaneously, as an advanced technique to compensate the mutual inductive voltage, has been suggested and studied for this study. The CDA and MIK methods were practically adapted to the KSTAR PF 1 coil for the feasibility study. Test results show that the inductance matrix calculated by the FEM tool should be revised because of a revealed discrepancy between measured CDA voltage and calculated MIK voltage. In this study, the inductance matrix was revised by using the “Genetic algorithm” optimization method to reduce the discrepancy between CDA and MIK effectively. The adoption of the MIK revised inductance matrix was consistent with CDA voltage; mutual inductive voltage was expected to be successfully eliminated.</P>