• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.11
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• pp.23-30
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• 2017

Most superconducting magnets which generate more than 20 T consist of nested magnets. A combination of LTS and HTS magnets is conventionally used, but high field magnets which use only HTS magnets have been developed recently. As HTS wires have very strong magnetic anisotropy, appropriate techniques should be used to consider this effect properly. The load line method has been conventionally used to design nested magnets for high field generation. Because this method considers only parallel and perpendicular magnetic fields, the effect of their orientation is not taken into account. In this paper, the actual orientation of the magnetic fields from 0 to 90 degrees is considered. The critical currents of the two kinds of high field nested magnets designed using the proposed method are calculated. The finite element method is used to calculate the distribution of the magnetic fields and the evolution strategy is used to find the critical current which maximizes the central magnetic field.

• Journal of Electrical Engineering and Technology
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• v.4 no.1
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• pp.98-105
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• 2009

This paper presents the characteristics of soil ionization for different water contents, and the parameters associated with the dynamic properties of a simple model grounding system subject to lightning impulse currents. The laboratory experiments for this study were carried out based on factors affecting the soil resistivities. The soil resistivities are adjusted with water contents in the range from 2 to 8% by weight. A test cell with a spherical electrode buried in the middle of the hemispherical container was used. As a result, the electric field intensity $E_c$ initiating ionization is decreased with the reduction of soil resistivities. Also, as the water content increased, the pre-ionization resistance $R_1$ and the post-ionization resistance $R_2$ became lower with increasing current amplitude. The time-lag to ionization $t_1$ and the time-lag to the second current peak $t_2$ at high applied voltages were significantly shorter than those of low applied voltages. It was found that the soil ionization behaviors are highly dependent on the water content and the applied voltage amplitude.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.3 no.2
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• pp.71-79
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• 1998

Fish larvae and environmental variables were collected in the sea around Cheju Island of Korea in November, 1986. Fish larvae were found at the 43 of 44 stations. Abundance of fish larvae rangεd from 3 to 259 indiv./$10^3\;m^3$ (average 50 indiv./$10^3\;m^3$) Dominant species were Engraulis japonicus, Champsodon snyderi, Gobiidae, Sebastiscus marmoratus, and Synagrops philippinensis, which comprised 56.6% of total fish larvae abundance. 43 stations were c1assified into two groups by c1uster analysis based on the abundance of fish taxa. Most stations of Group I were located in the middle reach of Tsushima Current and had higher number of species and abundance than the sites of Group II which cover the marginal areas of Tsushima Current, Korean Coastal Waters, and coastal water of China. The dominant taxa in the sites of the Group I were E. japonicus, Gobiidae, S. philippinensis, Aulops japonicus, Bregmaceros spp., Benthosema pterotum, Lampanctus spp., etc., all of which are typical warm-water species. Therefore, Tsushima Current seems to be the most critical factor regulating the structure of fish larvae community in the study area. The discriminant analysis using the environmenta1 variables (temperature, salinity, and dissolved oxygen) produced result with a difference only of 11.6% from that of c1uster analysis using the taxa composition and abundance data. Consequently, the structural type of fish larvae community can be used for predicting the changes of environmental conditions in the study area.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2003.02a
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• pp.109-112
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• 2003

The high temperature superconducting YBCO films were deposited on the SrTiO$_3$(100) single crystals to find out the proper deposition conditions of YBCO on biaxially-textured metal substrates. Different sets of the substrate temperature, oxygen partial pressure and laser fluence were used to investigate the effect of deposition conditions on the superconducting properties. The new apparatuses for measuring critical temperature (Tc) and critical current (Ic) were designed and manufactured, which were used to obtain Tc's and Ic's of the deposited films. The accuracy of the new apparatus was confirmed by comparing the results with those from SQUID magnetometer. The results on the YBCO films deposited on single crystal substrates which will be used to get the optimum deposition conditions of YBCO films in the coated conductor, are summarized in this report.

• Progress in Superconductivity and Cryogenics
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• v.18 no.4
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• pp.21-24
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• 2016

The mechanical properties of REBCO coated conductor (CC) wires under uniaxial tension are largely determined by the thick component layers in the architecture, namely, the substrate and the stabilizer or even the reinforcement layer. Depending on device applications of the CC tapes, it is necessary to reinforce thin metallic foils externally to one-side or both sides of the CC tapes. Due to the external reinforcement of brass foils, it was found that this could increase the reversible strain limit from the Cu-stabilized CC tapes. In this study, the effects of differently hardened brass foil laminate on the electromechanical property of CC tapes were investigated under uniaxial tension loading. The tensile strain dependence of the critical current ($I_c$) was measured at 77 K and self-field. Depending on whether the $I_c$ of CC tapes were measured during loading or after unloading, a reversible strain (or stress) limit could be determined, respectively. The both-sides of the Cu-stabilized CC tapes were laminated with brass foils with different hardness, namely 1/4H, 1H and EH. From the obtained results, it showed that the yield strength of the brass laminated CC tapes with EH brass foil laminate was comparable to the one of the Cu-stabilized CC tape due to its large yield strength even though its large volume fraction. It was found that the brass foil with different hardness was mainly sensitive on the stress dependence of $I_c$, but not on the strain sensitivity due to the residual strain induced in the laminated CC tapes during unloading.

• 한국초전도학회:학술대회논문집
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• v.14
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• pp.81-81
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• 2004

• 한국초전도학회:학술대회논문집
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• v.14
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• pp.40-40
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• 2004

• Progress in Superconductivity and Cryogenics
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• v.14 no.2
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• pp.8-11
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• 2012

In order to recognize the allowable bending diameter in coils, the strain as function of diameters is evaluated. The irreversible strain limits of $I_c$ in the easy and hard bending modes were measured. Strains were calculated at the coating film in the easy bending and at outer edge or inner edge in the hard bending of the CC tape, respectively. The tape geometry subjected to bending procedures is considered from the current industrial spool winding operation. Through the linear superposition of strain induced in different bending modes regarding the expressions, the appropriate design for critical bending diameter is suggested. Results proved that the existence of buckling resulting from bending in hard direction when applied strain exceeded 0.6% is possible. The depicted results showed that the strain limit as a viable parameter should be considered for future purposes.

• 한국초전도학회:학술대회논문집
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• 2008.08a
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• pp.24-24
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• 2008

• Proceedings of the KIEE Conference
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• 1997.07d
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• pp.1494-1496
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• 1997

The MRI Magnet is a most practical application of NbTi superconductor. In this paper, we present the main research results on superconducting wires for MRI magnet which we have developed. Cu/NbTi superconducting wires were fabricated by repeat of cold working and heat-treating process after that billets were extruded. We investigated the relation of superconductivities of wires and heat treatment condition. The correlation between cross section shape of wires and work inhomogeneity of NbTi rods was investigated by microscopic observation. The more repeatation number of cold working and heat-treating process, the higher critical current is achieved.