Hong-Soo Ha

Ultra-High Performance, High-Temperature Superconducting Wires via Cost-effective, Scalable, Co-evaporation Process

Long-length, high-temperature superconducting (HTS) wires capable of carrying high critical current, Ic, are required for a wide range of applications. Here, we report extremely high performance HTS wires based on 5 μm thick SmBa2Cu3O7 − δ (SmBCO) single layer films on textured metallic templates. SmBCO layer wires over 20 meters long were deposited by a cost-effective, scalable co-evaporation process using a batch-type drum in a dual chamber. All deposition parameters influencing the composition, phase, and texture of the films were optimized via a unique combinatorial method that is broadly applicable for co-evaporation of other promising complex materials containing several cations. Thick SmBCO layers deposited under optimized conditions exhibit excellent cube-on-cube epitaxy. Such excellent structural epitaxy over the entire thickness results in exceptionally high Ic performance, with average Ic over 1,000 A/cm-width for the entire 22 meter long wire and maximum Ic over 1,500 A/cm-width for a short 12 cm long tape. The Ic values reported in this work are the highest values ever reported from any lengths of cuprate-based HTS wire or conductor.

Use of SrTiO/sub 3/ as a single buffer layer for RABiTS YBCO coated conductor

SrTiO/sub 3/ (STO) films were epitaxially deposited by PLD on textured Ni-3wt%W (Ni-3W) substrates. The STO film was deposited in two steps-reducing atmosphere first, and then oxidizing atmosphere-to prevent the oxidation of the metal surface from hindering the epitaxial relationship between the film and the substrate. The deposited STO films exhibited sharp biaxial texture and dense surface. YBCO films were epitaxially deposited on STO/Ni-3W and showed J/sub c/(77K, self field)=1.2MA/cm/sup 2/ and T/sub c/(onset)=88 K. Auger electron spectrometry depth profile analyses show that the STO film can block the diffusion of the metal from the substrate. This work has shown that STO films epitaxially deposited on textured Ni-3W substrate can be used as a single buffer layer of the high current carrying YBCO coated conductor.

De-Lamination Characteristics of Coated Conductor for Conduction Cooled HTS Coil

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 from 18 MPa to 53 MPa. Through the FEM analysis for multi-layered structure of the HTS tape, concept design for HTS tape of enhanced c-axis strength is suggested.

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.

Ic degradation behavior in Bi-2223 superconducting tapes under torsional deformation

Abstract In this study, the I c degradation behavior in HTS tapes due to torsional deformation was investigated. Three kinds of commercially available Bi-2223 tapes were used. The sample holder for torsion test of HTS tapes was newly devised. Utilizing it, the influence of the torsion angle on the critical current ( I c ) and n -value in Ag alloy/Bi-2223 tapes was investigated at 77 K. The I c began to degrade when the torsion angle exceeded 150°, after which, it showed a gradual decrease with an increase in torsion angle. Superconducting tapes with larger number of filaments showed more significant I c degradation compared to tapes with smaller number of filaments. The n -value also showed a similar behavior to the I c ( θ ) behavior. Eventually, it was found that the torsion strain did not significantly reduce the critical currents of Bi-2223 tapes, when compared with cases of other loading types such as bending or tension.

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

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.

Thick SmBCO/IBAD-MgO Coated Conductor for High Current Carrying Power Applications

Long-length (Sm_1+xB_2-xC₃O_7-y) coated conductor was fabricated using ion beam assisted deposition (IBAD)-MgO template (LaMnO₃/IBAD - MgO/Y₂O₃/Al₂O₃/Hastelloy) by the reactive co-evaporation method for electric power applications. SmBCO superconducting layers with thicknesses from 1 to 3 ¿m were deposited to investigate the effect of SmBCO thickness on the in-plane texture, surface morphology and superconducting properties. In this study, the optimal deposition conditions were examined to make thick SmBCO coated conductor without degradation of critical current density. The oxygen partial pressure and temperature were controlled in the range of 1~20 mTorr and 600 ~ 800°C, respectively. SmBCO/IBAD-MgO coated conductors showed high critical current densities over 2.0 MA/cm² with small amount of degradation by increasing the thickness of superconducting layer up to 3 ¿m. The critical current of 637.5 A/cm-w (J_C = 2.12 MA/cm²) at 77 K in self- field was obtained in 3 ¿m-thick and 1 m long coated conductor. This is the highest critical current reported so far of the coated conductor with SmBCO superconducting layer deposited by co-evaporation.

Purification of Wastewater From Paper Factory by Superconducting Magnetic Separation

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.

Single-filament composite MgB2/stainless-steel ribbons by powder-in-tube process

Abstract We report the successful fabrication of single-filament composite MgB 2 /stainless-steel ribbons, as an ultrarobust conductor type. The transport critical current of the non-sintered MgB 2 /stainless-steel ribbons is remarkably high, as an unexpected result. Transport critical currents I c ∼316 A at T =4.2 K and I c ∼82 A at T =20 K were observed at self-field for the non-sintered composite MgB 2 /stainless-steel ribbons. The I c value of 316 A is the higher than any other value reported so far. In addition, the persistent current density, that was estimated by Bean formula, of the sintered composite MgB 2 /stainless-steel ribbons was more than J p ∼6×10 5 A/cm 2 at T =5 K with H =0 G, and J p ∼1.1×10 5 A/cm 2 at T =30 K with H =0 G.