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Dive into the research topics where Dong-Woo Ha is active.

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Featured researches published by Dong-Woo Ha.


Journal of Applied Physics | 2008

Residual and fracture strains of Bi2223 filaments and their relation to critical current under applied bending and tensile strains in Bi2223/Ag/Ag alloy composite superconductor

S. Ochiai; J.K. Shin; Sohei Iwamoto; Hiroshi Okuda; Sang-Soo Oh; Dong-Woo Ha; M. Sato

Mechanical and electromagnetic stresses are exerted on Bi2223∕Ag∕Ag alloy superconducting composite tapes during fabrication∕winding and operation, which cause reduction in critical current when the Bi2223 filaments are damaged. In the damage process, the thermally induced residual strain and fracture strain of the Bi2223 filaments play a dominant role. The aim of the present work was to propose a comprehensive method for estimation of these strain values and a quantitative description method of the relation of critical current to the applied bending∕tensile strain, and to examine the accuracy of the method in comparison with the experimental results. The residual strain of Bi2223 filaments in the composite tape was measured by the x-ray diffraction method. The measured residual strain value was used for analysis of the load-strain curve, from which the intrinsic fracture strain of filaments was estimated. The relation of critical current to applied bending∕tensile strain was predicted by the proposed cal...


IEEE Transactions on Applied Superconductivity | 2007

Critical Current Degradation Behavior in YBCO Coated Conductors Under Torsional Strain

Hyung-Seop Shin; John Ryan C. Dizon; Tae-Hyung Kim; Dong-Woo Ha; Sang-Soo Oh

The Ic degradation behaviors of a YBCO coated conductor (CC) tape (RABiTS/MOD) was investigated using a sample holder which gives torsional angles to HTS tapes. The Ic degradation in YBCO CC tape under torsional strains occurred gradually which is a characteristic feature under torsion. Uniform torsional deformation was induced in the YBCO CC tape evident from the consistent Ic degradation behavior at each subsection along the longitudinal direction of the tape. Similar with the tension case, the reversible behavior of Ic under torsional loading was found. The irreversible strain, epsivirr.t., was ~0.6%. The critical strain defined by the 95% Ic retention criterion was 1.4% which was located within the irreversible limit. The n-value-thetas behavior in the YBCO CC tape was similar to the Ic/Ic0-thetas behavior.


Superconductor Science and Technology | 2005

A Monte Carlo–shear lag simulation of tensile fracture behaviour of Bi2223 filament

Shojiro Ochiai; T Ishida; D. Doko; Kohei Morishita; Hiroshi Okuda; Sang-Soo Oh; Dong-Woo Ha; Masaki Hojo; Mototsugu Tanaka; Michinaka Sugano; Kozo Osamura

The damage evolution in Bi2223 filaments and its influence on critical current was described by a Monte Carlo–shear lag simulation method. The experimentally observed zigzag crack propagation across aligned Bi2223 grains under tensile strain was effectively modelled by including transverse and longitudinal failure modes for individual grains. From the simulated stress–strain curve, the survival parameter (slope of the stress–strain curve normalized with respect to the original Youngs modulus) was estimated with increasing applied strain. With this parameter combined with the strain sensitivity of the critical current, the measured change of critical current of the composite tape with applied strain could be described well.


IEEE Transactions on Applied Superconductivity | 2008

Effect of Filament Configuration on Critical Current Density of Bi2212/Ag Wires With Low Ag Ratio

Sang-Cheol Kim; Dong-Woo Ha; Sang-Soo Oh; Il-Yong Han; Jae-Geun Oh; Ho-Sang Sohn

Effect of filament configuration and heat treatment of Bi2212/Ag round wire with low Ag ratio on the engineering critical current density (J<sub>e</sub>) was reported. We have fabricated 557, 85 7, and 121 7 wires with different Ag ratio and evaluated at various wire diameters. We have also changed the parameters of heat treatment. The effects of maximum process temperature (T<sub>max</sub>)and soaking time at T<sub>max</sub> and average filament diameter on the J<sub>e</sub> were also studied. 121 7 wire of 0.95 mm diameter heat-treated at showed J<sub>e</sub> of 858mm<sup>2</sup> at 4.2K, 0 T.


IEEE Transactions on Applied Superconductivity | 2010

Nondestructive Measurement of Critical Current Distribution of SmBCO Coated Conductor Using Hall Probe

Ho-Sup Kim; Sang-Soo Oh; Nam-Jin Lee; Seung-Kyu Baik; Dong-Woo Ha; Rock-Kil Ko; Hong-Soo Ha; Tae-Hyung Kim; Dojun Youm; Seung-Hyun Moon; Chan Park

The Hall probe measurement system was used to measure the critical current distribution of superconducting coated conductor. The system consists of reel to reel moving apparatus, 7 array Hall probe, a rotary encoder and permanent magnet. The magnetic field profile across the width of superconducting coated conductor using Beans critical state model was calculated. The effect of various parameters of the formulas on the magnetic field distribution and the effect of shape and size of artificial defects, which were formed on the surface of SmBa2Cu3O7-d(SmBCO) coated conductor using laser marking system, on the Hall probe magnetic field signal of the Hall probe measurement system was investigated.


IEEE Transactions on Applied Superconductivity | 2010

Purification of the Coolant for Hot Roller by Superconducting Magnetic Separation

Tae-Hyung Kim; Dong-Woo Ha; Jun-Mo Kwon; Myung-Hwan Sohn; Seung-Kyu Baik; Sang-Soo Oh; Rock-Kil Ko; Ho-Sup Kim; Young-Hun Kim; Seong-Kuk Park

It is important to recycle industrial wastewater in the aspect of energy saving and minimizing the environment damage. Steel manufacture factories make an effort to purify and recycle wastewater from the manufacturing processes. A steel manufactory in Korea, POSCO (POhang iron and Steel COmpany) has also concerned about the treatment of wastewater for long time. The coolant of hot roller at steel making factory includes suspended solid (SS) like steel fines, iron oxide and emulsified oil. A laboratory-scale conduction cooled high temperature superconducting (HTS) magnet was used for high gradient magnetic separation (HGMS) systems. It consists of eight double-pancake sub-coils, two HTS current leads, a GM cryo-cooler and a cryostat without a radiation shield vessel. Sub coils were wound with 1 G HTS tapes of Sumitomo Electric Industries by wet-winding method. A Cryo-cooled high temperature superconducting magnet system with 70 mm room temperature bore and 250 mm of height was prepared. This magnet was used for batch type HGMS system. Superconducting HGMS system that had a purpose to purify the wastewater was assembled. Various magnetic seeding reactions were investigated to increase the reactivity of coagulation.


IEEE Transactions on Applied Superconductivity | 2010

Purification of Wastewater From Paper Factory by Superconducting Magnetic Separation

Dong-Woo Ha; Tae-Hyung Kim; Myung-Hwan Sohn; Jun-Mo Kwon; Seung-Kyu Baik; Rock-Kil Ko; Sang-Soo Oh; Hong-Soo Ha; Ho-Sup Kim; Young-Hun Kim; Tae-Wook Ha

It is environmentally important to recycle the wastewater, since paper factories use a large amount of water and equivalent amount of wastewater is generated. Conventional water treatment facilities like precipitation process need large-scale equipment and wide space to purify the wastewater of paper factory. In case of massive waste water, high gradient magnetic separation (HGMS) parts are more effective to purify it rapidly and to occupy relatively small space, since large voids at filter with HGMS are adopted. In this respect, we prepared two types of superconducting magnets in order to apply HGMS parts for wastewater purification process. We made cryo-cooled Bi-2223 (HTS) superconducting magnet parts with room temperature bore in diameter of 70 mm and 200 mm in height. Also, cryo-cooled Nb-Ti superconducting magnet with room temperature bore in diameter of 100 mm and 600 mm in height was used for magnetic separator. Magnetic filters were designed by the analysis of magnetic field distribution at superconducting magnets. The faster wastewaters flow rate was, the worse the degree of clarity in treated water was. The ability of wastewater treatment in the case of magnetic separation used with 10 of magnetite particles was better than that in the case of 5 of magnetite particles.


Superconductor Science and Technology | 2006

Distribution of local critical current along sample length and its relation to overall current in a long Bi2223/Ag superconducting composite tape

S. Ochiai; D. Doko; Hiroshi Okuda; Sang-Soo Oh; Dong-Woo Ha

The distribution of the local critical current and the n-value along the sample length and its relation to the overall critical current were studied experimentally and analytically for the bent multifilamentary Bi2223/Ag/Ag–Mg alloy superconducting composite tape. Then, based on the results, it was attempted to simulate on a computer the dependence of the critical current on the sample length. The main results are summarized as follows. The experimentally observed relation of the distributed local critical current and n-value to the overall critical current was described comprehensively with a simple voltage summation model, in which the sample was regarded as a one-dimensional series circuit. The sample length dependence of the critical current was reproduced on the computer by a Monte Carlo simulation incorporating the voltage summation model and the regression analysis results for the local critical current distribution and the relation of the n-value to the critical current.


IEEE Transactions on Applied Superconductivity | 2015

Separation of Steel Slag From Landfill Waste for the Purpose of Decontamination Using a Superconducting Magnetic Separation System

Jee-Eun Kim; Dong-Woo Ha; Young-Hun Kim

Superconducting magnetic separation has been applied on a soil remediation. Huge amount of steel slag has been dumped into a landfill site and mixed with covering soil. The soil-steel slag mixture is hazardous material and needs to be treated because steel slag has heavy metals, which can be leached out. Two types of soil sample from the landfill site, i.e., plain soil and soil sample after the soil-washing process, have been sampled and tested with the superconducting magnetic separation system. Variable magnetic force (0.5-4 T) was applied, and the separated portion was increased as the magnetic field increased. The separated and passed through soil was analyzed for iron and heavy metal species. The concentration of these species was obtained by the magnetic separation, and the concentration was 1.1-2.2 times depending on the metal species, and the concentrating effect were higher in the soil sample pretreated with the soil-washing process. In comparing the concentration effect of the analyzed metal species by the magnetic separation, the concentration factor is in order of Fe ≥ Zn ≥ Cu ≥ Pb.


IEEE Transactions on Applied Superconductivity | 2007

Influence of Filament Number on Workability and Critical Current Density of Bi-2212/Ag Superconducting Wires

Dong-Woo Ha; Sang-Cheol Kim; Jae-Gun Oh; Hong-Soo Ha; Nam-Jin Lee; K.J. Song; Tae-Hyung Kim; Rock-Kil Ko; Ho-Sup Kim; Seong-Kuk Park; Sang-Kil Lee; Yu-Mi Roh; Sang-Soo Oh

The important merit of Bi-2212/Ag high Tc superconducting wire is to apply cable as round wire geometry. Bi-2212/Ag wires were fabricated in order to develop Rutherford cable for SMES near the future. Various Ag ratio and various numbers of filaments for PIT (powder-in-tube) process were applied to investigate the workability during drawing and to improve critical current property of the wires. In order to find proper working process, we investigated the variation of drawing stress during working. Post-annealing of Bi-2212/Ag wires at various atmospheres was carried out after main heat-treatment in order to increase critical current density. The results of post-annealing in nitrogen were better than that of post-annealing in oxygen. Jc of Bi-2212/Ag wire was increased as increased maximum temperature,Tm , for partial melting until 890degC, and highest Jc was over than 2000 A/mm2. The shape of grain was observed by SEM to investigate Bi-2212 phase formation in filaments. The critical current density increased in proportion to the increase of Bi-2212/Ag wires filaments number.

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Rock-Kil Ko

Korea Electrotechnology Research Institute

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Sang-Soo Oh

Korea Electrotechnology Research Institute

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Ho-Sup Kim

University of Wollongong

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Hong-Soo Ha

Korea Electrotechnology Research Institute

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Myung-Hwan Sohn

Korea Electrotechnology Research Institute

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Nam-Jin Lee

Korea Electrotechnology Research Institute

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Young-Hun Kim

Andong National University

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Seung-Kyu Baik

Korea Electrotechnology Research Institute

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Chan Park

Seoul National University

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