Ho-Sup Kim

Development of long-length SmBCO coated conductors using a batch-type reactive co-evaporation method

In order to fabricate long-length high temperature superconducting coated conductors, we have employed a batch-type reactive co-evaporation process for the deposition of a SmBCO layer on the IBAD-MgO substrate of LaMnO3/epi-MgO/IBAD-MgO/Y2O3/Al2O3/Hastelloy. Critical current densities (Jc) of SmBCO coated conductors were investigated with respect to their composition ratios. Higher Jc was obtained in the Sm-rich, Ba-poor and Cu-rich composition region, compared to the stoichiometric region. The highest critical transition temperature (Tc) of the SmBCO coated conductor was ~94xa0K with a narrower transition width of about 0.5xa0K. A 93xa0m long SmBCO layer was deposited on a 4xa0mm wide IBAD-MgO substrate for 90xa0min. Although some differences in the appearance of pores and Cu oxide precipitates between both ends of the deposited tape exist, the deposited SmBCO layer was dense and biaxially textured. The growth of a highly textured SmBCO layer was maintained up to the thickness of 2.2xa0µm. A minimum Ic of 305xa0A/cm-w was achieved at the 27xa0m section of the 93xa0m long SmBCO coated conductor at 77xa0K in self-field.

Deposition of Y2O3 film on textured metal substrates for a single buffer layer of a YBCO coated conductor

A study regarding the epitaxial growth of Y2O3 film on textured metal substrate and its use as a single buffer layer of a YBCO coated conductor is reported. Different deposition conditions were employed and compared in order to obtain good epitaxial Y2O3 film followed by deposition of YBCO superconducting films. The YBCO film deposited by PLD on top of the Y2O3 films has good microstructure and superconducting properties. The effect of the thickness of Y2O3 film on the texture of Y2O3 film and the critical current density (Jc) of YBCO film deposited on top of that were analysed. The Jc of YBCO films on Y2O3/Ni and Y2O3/NiW were 1.0 × 106xa0Axa0cm−2 and 1.1 × 106xa0Axa0cm−2 at 77xa0K and self-field respectively, which indicated that Y2O3 is a suitable candidate as a single buffer layer for the fabrication of a YBCO coated conductor.

Electro-Mechanical Property Investigation of Striated REBCO Coated Conductor Tapes in Pure Torsion Mode

In superconducting cable applications using the HTS tapes, striation of ReBCO coated conductor (CC) is being considered to reduce ac loss. The striation of ReBCO coating film with laser patterned filaments has been tried. In practical applications, the striated ReBCO CC tapes should also exhibit acceptable tolerance to mechanical stress/strains. However, reports on the electromechanical properties of striated CC tapes in bending or torsion mode are limited. In this study, the critical current degradation behavior of the striated Cu stabilized SmBCO CC tapes in pure torsion mode was investigated using a sample holder which gives torsional deformation to CC tapes. The CC tape has been laser scribed to produce multi-filaments. The Ic/Ic0 and n-value-torsional angle (θ) behaviors in the striated SmBCO CC tapes were examined and compared with the case of non-striated ones. According to the location of the coating film strip striated within the cross-section, there existed some difference in the Icf degradation behavior indicating that a non-uniform deformation was induced on each striated strip.

YBCO coated conductor using biaxially textured clad composite Ni–Mn/Ni–Cr substrate

A new biaxially textured composite tape of Ni?4.5%?Mn/Ni?1.5%?Cr was used as a substrate for a YBCO coated conductor through the RABiTS approach. Multi-layer CeO2/YSZ/Y2O3 buffer layers and YBCO film were deposited on the substrate by pulsed laser deposition. The deposition conditions of the buffer layers and the YBCO were studied and compared. Good biaxial textures have been obtained for buffer layers on composite Ni?4.5%?Mn/Ni?1.5%?Cr substrates. Scanning electron microscopy on sample cross-sections was used to examine the interface and diffusion of oxygen. The uniform formation of an Ni?Mn?O layer between NiO and the Ni?4.5%?Mn layer was observed, and the Ni?Mn?O layer restricted the further growth of NiO layer, which was thin and not continuous, within the coated conductor during YBCO deposition at higher temperature and higher oxygen pressure. The Jc of YBCO films on these metal substrates was 1.5 ? 106?A?cm?2 at 77?K, 0?T.

The effect of nano-powder additions on the superconducting properties of MgB/sub 2/

To investigate the effect of Ag or SiC nano-powder additions on the superconducting properties of MgB/sub 2/, a series of superconducting (Ag)/sub (x)wt.-%/(MgB/sub 2/)/sub (100-x)wt.-%/(Ag/sub x/-MgB/sub 2/) and (SiC)/sub (x)wt.-%/(MgB/sub 2/)/sub (100-x)wt.-%/((SiC)/sub x/-MgB/sub 2/)(0/spl les/x/spl les/20), containing Ag and SiC nano-powders, respectively, of different diameters (30 nm and 130 nm), were prepared by a simple solid-state reaction route, cold-pressed into a pellet form and investigated. To maintain the same environment of MgB/sub 2//stainless-steel tapes/wires, Ag/sub x/-MgB/sub 2/ and (SiC)/sub x/-MgB/sub 2/ pellets made out of the mixed powders were put inside stainless steel tubes and then sintered at 900/spl deg/C for two hours in Ar atmosphere. Characterization performed included both X-ray diffraction and magnetization. No impurity phase was identified for as-rolled samples. However, both the Ag/sub x/-MgB/sub 2/ and (SiC)/sub x/-MgB/sub 2/ composite pellets, when sintered, contain various impurity phases. The isothermal magnetizations M(H) of a series of samples were measured at temperatures between 5 and 50 K in fields up to 5 T, using a PPMS-9 (Quantum Design). The optimal amounts of Ag and SiC nano-powder in Ag/sub x/-MgB/sub 2/ and (SiC)/sub x/-MgB/sub 2/ to obtain the largest flux pinning effect are /spl sim/8 and /spl sim/4 wt.-%, respectively. The two-step structures in ZFC M(T) curves of (SiC)/sub x/-MgB/sub 2/ were more developed than Ag/sub x/-MgB/sub 2/. The best flux pinning centers can be created by adding a suitable size and amount of SiC nano-powder, not too large to increase the decoupling between the MgB/sub 2/ grains.

Characteristics Measurements of HTS Tape with Parallel HTS Tapes

Many high temperature superconducting (HTS) tape manufactures make an effort to reduce the transport current loss of HTS tapes. The knowledge of critical current and self-field in an HTS tape is very useful to compute the transport current losses. The spatial distribution and magnitude of self-field are variable due to the neighboring materials. In this paper, the critical currents and the transport current losses of BSCCO and YBCO tapes with paralleled magnetic material (Ni tape) and/or diamagnetic material (BSCCO tape) are experimentally investigated to improve the AC loss properties. The critical currents of HTS tapes with paralleled Ni tape are slightly decreased and the transport current losses are markedly increased. However, the critical currents and transport current losses of HTS tapes with paralleled BSCCO tape have not current carrying are more improved than single HTS tape