• Progress in Superconductivity and Cryogenics
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• v.24 no.4
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• pp.78-83
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• 2022

REBCO coated conductors are widely used for HTS power application, high magnetic field magnet application, and etc. A thermal stability of the REBCO conductor is essential for the operation of HTS-based device, and thermal conductivities of the conductor are relevant parameters for modeling cryogenic heat transfer. REBCO conductors consist of a REBCO layer, copper layers for electrical stabilization and a hastelloy substrate. At cryogenic temperature, thermal conductivity of copper and silver strongly depend on the purity of the material and the intensity of the magnetic field. In this study, thermal conductivities of the laminated composite structure of REBCO conductor are evaluated by using the thermal network model and the multidimensional heat conduction analysis. As a result, the thermal network model is applicable to REBCO conductors configured in series or parallel alone and multidimensional heat conduction analysis is necessary for complex cases of series and parallel configuration.

• Progress in Superconductivity and Cryogenics
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• v.24 no.1
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• pp.1-7
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• 2022

So far, large-scale scientific devices such as nuclear fusion tokamaks and high energy circular accelerators were constructed using high-current conductors made of metallic superconducting wires. Recently, as REBCO superconducting wires usable in high magnetic fields have been developed by several companies, researchesto apply high current cable type REBCO conductors to next-generation large superconducting magnets were also started. High critical currents of several kA or more in high magnetic fields have been successfully demonstrated on test samples of REBCO cable conductors by several research groups. In this review article, the main features and properties of the representative high current REBCO conductors such as CORC(Conductor On Round Core), TSTC(Twisted Stacked-Tape Cable) and RACC(Roebel-Assembled Coated Conductor), which are currently being developed at abroad are briefly introduced. Research activities of high-current density REBCO MHOS(Multi HTS layers on One Substrate) conductor at KERI, whose structure is different from other cable type REBCO conductors are also shortly introduced.

• Progress in Superconductivity and Cryogenics
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• v.24 no.4
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• pp.29-35
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• 2022

We fabricated MHOS (multi-HTS layers on one substrate) high-temperature superconducting (HTS) REBCO conductors using HTS REBCO coated conductor (CC) A-specimen, which induces an artificial magnetic flux pinning effect, and HTS REBCO CC B-specimen, that does not induce this effect. The superconducting magnetic properties of the fabricated MHOS conductors were examined by measuring their magnetic moment m(H) curves using a physical property measurement system (QD PPMS-14). The critical current density (J_c) characteristics of our four-layered MHOS HTS REBCO conductor specimens such as BAAB, BBBB, and AAAA were lower than those of their two-layered and three-layered counterparts. At a temperature T of 30 K the magnetic flux pinning physical indicator δ values (obtained from the relationship J_c ∝ H^-δ) of the three-layer ABA (δ = 0.35) and two-layer AB (δ = 0.43) specimens were found to be significantly lower than those of the four-layer ABBA (δ = 0.51), BAAB (δ = 0.60), AAAA (δ = 0.78) and BBBB (δ = 0.81) structures.

• Progress in Superconductivity and Cryogenics
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• v.20 no.1
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• pp.1-10
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• 2018

The improvement of critical current properties of $REBa_2Cu_3O_{7-x}$ (REBCO) coated conductors by introducing artificial pinning centers (APCs) is examined with respect to the field-angle anisotropy, high-field performance and relaxation property with time. Nano-rods along the c-axis introduced by PLD method and isotropic nano-particles introduced by TFA-MOD method are treated. The theoretical analysis is also shown to understand the effect of APCs quantitatively. The effects of superconducting layer thickness that influences the high-field performance and relaxation property are also discussed. It is shown that the upper critical field, which is another important factor to determine the high-field property, can be improved by introduction of APCs through electron scattering at interfaces with the superconducting matrix. The optimum critical current property can be obtained by properly designing the morphology and number density of APCs and the superconducting layer thickness.

• Progress in Superconductivity and Cryogenics
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• v.15 no.4
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• pp.1-5
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• 2013

This paper reviews recent progress in research and development (R&D) of reactive co-evaporation for high performance REBCO coated conductors in Korea. Two types of reactive co-evaporation methods were developed for the deposition of SmBCO and GdBCO superconducting layers respectively on the IBAD (Ion Beam Assisted Deposition)-MgO template in the Korean coated conductor project. Batch type reactive co-evaporation equipment and its processing were developed for SmBCO coated conductors at Korea Electrotechnology Research Institute (KERI) in conjunction with the Korea Advanced Institute of Science and Technology (KAIST), and a very high critical current exceeding 1,000 A/cm at 77 K in the self field was achieved through the optimization of deposition parameters. Reel-to-reel type reactive co-evaporation processing with a high conversion rate was also developed, while long length GdBCO coated conductors have been routinely produced by SuNAM Co. The minimum critical current of 422 A/cm-w at 77 K in self field was confirmed for 1 km-long GdBCO tape.

• Progress in Superconductivity and Cryogenics
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• v.20 no.4
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• pp.31-35
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• 2018

When REBCO coated conductors (CCs) are applied to superconducting devices such as coils and magnets, they are subjected to deformation in various modes such as compression/tension bending, uniaxial/transverse tension and torsion. Despite outstanding performances by REBCO CC tapes, their electromechanical properties have been evaluated primarily under uniaxial tension, therefore data about the critical current ($I_c$) response in the compressive strain region are lacking. In this study, the characteristic responses of $I_c$ in REBCO CC tapes under bending strains in the range from tensile to compressive were evaluated. The springboard bending beam was used, wherein the CC tape sample was soldered onto the surface of the springboard. A Goldacker-type bending test rig, which lacks a support holding the sample during testing, was used as a comparator. Degradation in $I_c$ behaviors, including strain sensitivity, in differently processed REBCO CC tapes were examined based on the test rig used.

• Progress in Superconductivity and Cryogenics
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• v.16 no.4
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• pp.7-16
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• 2014

Rare-earth barium copper oxide (REBCO) coated conductor (CC) tapes have already been commercialized but still possess some issues in terms of manufacturing cost, anisotropic in-field performance, $I_c$ response to mechanical loads such as delamination, homogeneity of current transport property, and production length. Development on improving its performance properties to meet the needs in practical device applications is underway and simplification of the tape's architecture and manufacturing process are also being considered to enhance the performance-cost ratio. As compared to low temperature superconductors (LTS), high temperature superconductor (HTS) REBCO CC tapes provide a much wider range of operating temperature and a higher critical current density at 4.2 K making it more attractive in magnet and coil applications. The superior properties of the REBCO CC tapes under magnetic field have led to the development of superconducting magnets capable of producing field way above 23.5 T. In order to achieve its optimum performance, the electromechanical properties under different deformation modes and magnetic field should be evaluated for practical device design. This paper gives an overview of the effects of mechanical stress/strain on $I_c$ in HTS CC tapes due to uniaxial tension, bending deformation, transverse load, and including the electrical performance of a CC tape joint which were performed by our group at ANU in the last decade.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.1307_1308
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• 2009

고온초전도체 REBCO(RE=rare earth) 선재는 높은 전류전송밀도를 가지고 있기 때문에 고용량의 전류가 요구되는 응용분야에 사용되어 전력기기 등의 성능을 높일 수 있을 것으로 기대되고 있다. 이전까지 대부분의 REBCO 선재 연구들은 GdBCO, NdBCO, YBCO 등 비교적 Tc값이 높은 고온초전도체에 집중되어 왔다. 반면에 TmBCO는 대부분의 REBCO 보다 Tc값이 낮기 때문에 선재 연구 분야에서 거의 주목받지 않았다. 하지만 본 연구 결과에 따르면 TmBCO 선재는 비교적 낮은 Tc(88K) 값에도 불구하고 우수한 전류전송밀도(Jc=2.3MA/$cm^2$) 특성을 나타내기 때문에 고온초전도 선재로서 활용이 가능하다. 또한 NdBCO 선재에 비해 낮은 기판온도에서 제조가 가능함으로써 공정상의 이점을 가질 수 있음을 확인하였다.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.11
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• pp.2209-2213
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• 2009

$REBa_{2}Cu_{3}O_{7-d}$(REBCO) coated conductors(REBCO CCs) have been studied for electric power applications which require high current density wires. As long as the critical transition temperature(Tc) is concerned, REBCO CCs with large $RE^{3+}$ ions have been expected to have better current transport properties than those with smaller $RE^{3+}$ ions. For this reason, REBCO's with large $RE^{3+}$ ions which include GdBCO, NdBCO and SmBCO have been mainly considered as the superconducting layer of CCs. On the other hand, REBCO's with smaller $RE^{3+}$ions are expected to have advantages in the fabrication process of CCs because of the lower melting temperature. But it has not yet been made clear which REBCO is the most suitable for the superconducting layer of CCs. In this study, we investigated the current transport properties of REBCO CCs with small $RE^{3+}$ ion and advantages of using that in the CC fabrication process. Thin films of TmBCO, which has smaller $RE^{3+}$ion than most other $RE^{3+}$ ions, were fabricated on buffered metal substrate as the superconducting layer of CC by PLD process. TmBCO CC shows critical current density (Jc (77 K, sf) = $2.3\;MA/cm^2$) high enough to be utilized for application in electric power devices. Compared with previous experiments using the same PLD system, deposition temperature was approximately $20^{\circ}C$ lower than NdBCO thin films on buffered metal substrates.

• Progress in Superconductivity and Cryogenics
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• v.14 no.4
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• pp.5-11
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• 2012

In this review article, we focus on various co-evaporation technologies developed for the fabrication of high performance $REBa_2Cu_3O_{7-{\delta}}$ (RE: Y and Rare earth elements, REBCO) superconducting films. Compared with other manufacturing technologies for REBCO films such as sputtering, pulsed laser deposition (PLD), metal-organic deposition (MOD), and metal organic chemical vapor deposition (MOCVD), the co-evaporation method has a strong advantage of higher deposition rate because metal sources can be used as precursor materials. After the first attempt to produce REBCO films by the co-evaporation method in 1987, various co-evaporation technologies for high performance REBCO films have been developed during last several decades. The key points of each co-evaporation technology are reviewed in this article, which enables us to have a good insight into a new high throughput process, called as a Reactive Co-Evaporation by Deposition and Reaction (RCE-DR).