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Anseong, South Korea

Lee J.B.,Korea Polytechnic University | Park S.K.,Korea Polytechnic University | Kim B.J.,Korea Polytechnic University | Lee H.J.,Korea Polytechnic University | And 4 more authors.
Physica C: Superconductivity and its Applications | Year: 2011

CeO2 has been used as a buffer layer of a coated conductor because of good chemical and structural compatibility with YBCO. But cracks were often observed at the surface for films thicker than 100 nm deposited at a high temperature because of a large difference in a thermal expansion coefficient between metal and CeO2. The deposition rate was limited to be slow for getting good epitaxy. In order to increase the film deposition rate, while maintaining the epitaxy till a final thickness, two-step deposition process was tested. The thin seed layer with a thickness less than 10 nm was deposited with a deposition rate of 3 /s, and the homo-epitaxial layer at a thickness more than 240 nm was deposited at a deposition rate of 30 /s. The resulting CeO 2 films deposited at 600 °C showed a good texture with a Δ of 5.3°, Δω of 4.2° and Ra of 2.2 nm. The two-step process may be option for a low cost buffer layer for Ni-3%W metal substrates for the coated conductor. © 2011 Elsevier B.V. All rights reserved. Source

Jeong H.,Changwon National University | Park H.,Changwon National University | Kim S.,Changwon National University | Park M.,Changwon National University | And 7 more authors.
IEEE Transactions on Applied Superconductivity | Year: 2012

According to the continuous development of coated conductors and compact cryocoolers, research and development efforts for High Temperature Superconducting (HTS) magnets are increasing using conduction cooling method. To increase the cooling efficiency and thermal stability of the HTS magnet, the coated conductor is wound by wet-winding or epoxy impregnating in vacuum after dry-winding. Due to the large Lorentz force and thermal contraction, stress analysis of the composite material, which is composed of HTS conductor, insulation layer and epoxy layer, is necessary to assure the mechanical stability of the HTS magnets.Mechanical strength for a/b axis, which is parallel to the conductor surface, is usually strong enough to endure the large tensile stress due to the tough substrate material. However, c-axis strength, which is perpendicular to the conductor surface, is not strong enough to ensure the large Lorentz force. The de-lamination of the multi-layered HTS tape in a coil structure can occur and the results were previously reported. Therefore, the test data for allowable c-axis strength is necessary to design the mechanical stability of the HTS coil. This paper describes the experimental results for the c-axis tensile strength of various coated conductors. The results show the wide divergence of the c-axis tension force from18MPa to 53MPa. Through the FEM analysis for multi-layered structure of the HTS tape, concept design for HTS tape of enhanced c-axis strength is suggested. © 2011 IEEE. Source

Jung H.S.,Konkuk University | Lee J.H.,Konkuk University | Lee J.H.,SuNAM Co. | Han H.K.,Konkuk University | And 2 more authors.
Electronic Materials Letters | Year: 2016

Thicknesses of Pt films ranging from 60 to 950 nm are measured noninvasively using a TE011-mode dielectric resonator with the resonant frequency of 8.5 - 9.8 GHz at temperatures of 77 K and 293 K. A cylindrical rutile rod is used as the dielectric, with a high-TC superconductive YBa2Cu3O7−δ film used as the bottom endplate of the resonator for measurements at 77 K. This method is based on two facts: i) Due to the electromagnetic interferences of incoming and reflected waves at the surface of the metal film surface, the effective surface resistance varies with the film thickness, and ii) the intrinsic surface resistance of normal metals is equal to the intrinsic surface reactance in the local limit. The measured thicknesses using the rutile resonator appear to be comparable with those obtained using a profilometer. [Figure not available: see fulltext.] © 2016, The Korean Institute of Metals and Materials and Springer Science+Business Media Dordrecht. Source

Park H.,Changwon National University | Jung H.,Changwon National University | Kim S.,Changwon National University | Park M.,Changwon National University | And 4 more authors.
IEEE Transactions on Applied Superconductivity | Year: 2013

For the conduction cooling of HTS magnets using coated conductor, the coils are either wet-wound or vacuum impregnated by cryogenic epoxy after dry winding. It is known that the magnet can be degraded after cool down due to delamination of the conductor. There have been several experimental investigations on the weak c-axis strength of the coated conductor. The structural delamination characteristics of the stacked conductor are also important for the design of mechanically stable conductively cooled HTS coil such as HTS generators, HTS motors, and SMES. C-axis tension experiments were performed with narrow soldering anvils to investigate the different delamination strengths at the edge and center of the conductor. FEM analysis was carried out to investigate the thermal stress caused by the different thermal expansion coefficients of several components of HTS coil for conduction cooling. The results of our analysis suggest possible coil configuration changes to avoid excess tensile stress at the edge of the conductor © 2002-2011 IEEE. Source

Sunam Co. and Snu R&Db Foundation | Date: 2012-10-08

Provided is a method of forming a superconducting body. The method includes providing amorphous rare-earth-copper-barium oxide and performing a heat treatment on the amorphous rare-earth-copper-barium oxide to form a superconductor containing distributed rare-earth oxide grains.

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