Abstract Body

MgB₂ wire is a superconducting wire that can be used at a liquid hydrogen temperature of 20K, and it is expected to be utilized in both static magnetic field applications and variable magnetic field applications. The main issue in the development of wire for variable magnetic field applications is the suppression of AC losses, which consist of hysteresis losses and coupling losses. In recent years, we have been studying the reduction of AC losses in MgB₂ wire [1][2]. Figure 1 shows an example of a cross-section of a wire with a diameter of 0.31mm and 51 filaments. In this symposium, we will report on the filament diameter dependence of the critical current characteristics of the MgB₂ wire for low AC loss.

References

[1] H Tanaka, et al. : Abstracts of CSSJ Conference Vol.103 (2022) p.61
[2] H Tanaka, et al. : Abstracts of CSSJ Conference Vol.104 (2022) p.75

Figure 1. Cross-sections of 0.31 mm 51-filaments MgB₂ wire.

Keywords: MgB₂, AC Loss, Critical current, filament diameter

Abstract Body

Work presents the progress at National Institute of Materials Physics, Romania in processing and characterization of bulk MgB₂ superconductor. Samples are pristine or with selected additives, (001) textured or randomly oriented, machinable by chipping or brittle and hard. Materials were obtained by ex situ spark plasma sintering (SPS) or by combining slip casting under elevated magnetic fields (12 T) and SPS. Structural, microstructural and superconducting characteristics were investigated. Some peculiar profiles in the shape of the pinning force curves with magnetic field were noted and it was not possible to fit these curves with the universal scaling procedure. Therefore, a new model sensitive to dissipation generated by the presence of slightly non-stoichiometric phases, defects, homogeneity, anisotropy, and texture within the Dew-Hughes scaling law predictions for a grain boundary pinning mechanism was proposed. In this model a connecting factor is used. This factor was found to be expressed through a connecting function that takes the form of a single or double peaked function, Gaussian or LogNormal.

In the second part of the presentation, the potential of MgB₂ as a sustainable material will be examined based on our results and literature data. MgB₂ emerges as a remarkable case study and reference when looking to materials from the viewpoint of their level of integration into nature cycles. Our analysis suggests that MgB₂ has the ability to become a game-changing key material needed for the progress in the future sustainable economy.

Acknowledgment

Author acknowledges support from MCI-UEFISCDI Romania through Core Program PC2-PN23080202.

Keywords: MgB₂ bulk, material processing, superconductivity, sustainability

Abstract Body

We are promoting the R&D of ultrafine superconducting wires with a much smaller diameter than human hair.  In principle, the bending strain decreases with decreasing the wire diameter, therefore, we may expect that the brittle compound or brittle oxide superconducting wires become flexible through the wire diameter reduction.  This is a big advantage of applying the React and Wind method for magnet fabrication, and it would minimize the fabrication cost and improve the magnetic field quality.  So far, we have already reported for the bronze-processed Nb₃Sn wire with 20-50 microns in diameter [1], the Jelly roll processed Nb₃Al wires with 17-50 microns in diameter [2], and the powder-in-tube processed MgB₂ wire with 15-50 microns in diameter [3].  Recently, we demonstrated a fabrication of the Silver sheathed Bi2212 mono-core wire with 50 microns in diameter.  SC filament size is about 10 microns.  In addition, we have fabricated a 50-micron Nb47Ti multifilamentary wire that had 55 Nb47Ti filaments as well.  A filament size is about 4 microns.  NbTi is well known as a ductile alloy, but NbTi wire is still generally a little hard. However, the present fine NbTi multifilamentary wire shows an extremely flexible and very easy to handle compared to general ones.  In this paper, recent progress of the development of NbTi, Nb₃Sn, Nb₃Al, MgB₂, and Bi2212 ultrafine superconducting wires and some of those flexible cables will be reported.

References

[1] Akihiro Kikuchi, Yasuo Iijima, Masaru Yamamoto, Masatoshi Kawano and Masato Otsubo, “The Bronze Processed Nb3Sn Ultra-Thin Superconducting Wires”, IEEE Transaction on Applied Superconductivity, Vol. 32, No. 4, 6000104 (2022) DOI: 10.1109/TASC.2022.3145286.

[2] Akihiro Kikuchi, Yasuo Iijima, Shigeki Nimori, Masaru Yamamoto, Masahiko Kawano, Motoyoshi Kimura, Jun Nagamatsu, Masato Otsubo, Ataru Ichinose and Kiyosumi Tsuchiya, “Ultra-Fine Nb3Al Mono-Core Wires and Cables”, IEEE Transaction on Applied Superconductivity, Vol. 31, No. 5, 6000105 (2021) DOI: 10.1109/TASC.2021.3057323.

[3] Akihiro Kikuchi, Yasuo Iijima, Hiroaki Kumakura, Masaru Yamamoto, Masatoshi Kawano, and Masato Otsubo, “Development of the Ultrafine MgB₂ Superconducting Wires and Flexible Cables”, IEEE Transaction on Applied Superconductivity, Vol. 34, No. 3 6200104 (2024) DOI: 10.1109/TASC.2023.3335881

Acknowledgment

A part of this study was financially supported by the mid-term research project at NIMS, JSPS KAKENHI Grant Number 19K05088, 21H04477, 23K25130, 24H00234, a project, JPNP16006, commissioned by the New Energy and Industrial Technology Development Organization (NEDO), and U.S.-Japan Science and Technology Cooperation Program in High Energy Physics operated by KEK in Japan and DOE in U.S.

Keywords:fine superconducting wire, flexible cable, Nb₃Al, Nb₃Sn, MgB₂, Bi2212, NbTi

Abstract Body

Iron-based superconductors (IBS) are highly promising candidates for high-field magnet applications due to their ultrahigh upper critical fields and very small anisotropy. Recently, significant progress has been made in enhancing the critical current density (J_c) of IBS wires and tapes based on the powder-in-tube technique. For instance, a high transport J_c above 2×10⁵ A/cm²(4.2 K, 10 T) has been achieved in IBS short tape samples, and the J_c of multi-filament 100-m long tapes was continuously improved, reaching 6×10⁴ A/cm² at 4.2 K, 10 T. These results demonstrate great potential of IBS wires and tapes for high-field applications. In this presentation, I will introduce our new findings on the formation and modulation mechanisms in melting-processed Ba-Fe-Co-As IBS, as well as the phase formation and reaction kinetics of Ba-K-Fe-As system. These insights provide valuable information for the impurity control and future J_c improvement for Ba-122 IBS. Then I will present some new strategies and methods developed for fabricating Cu/Ag and SS/Ag composite sheathed IBS tapes, in which the grain texture, grain boundaries and pinning landscape were well engineered to achieve new record-high J_c values. Finally, I will highlight some remarkable recent advances relevant to practical applications, including long-length wires, joints, pancake & racetrack coils, and cables. The prospects of IBS materials for future applications will also be discussed.

Keywords: iron-based superconductors, superconducting wires, critical current density, flux pinning

Abstract Body

The 122-type iron-based superconductors (IBSs) [1] show a higher superconducting transition temperature (T_c) and upper critical field (H_c2) than commercially used superconductors such as NbTi and Nb₃Sn. The superconducting wires and tapes of 122-type IBSs are fabricated using the powder-in-tube (PIT) method, which is beneficial for reducing production costs. Therefore, 122-type IBSs are expected to be used in superconducting wires and tapes for superconducting magnets that generate magnetic fields in liquid He or H₂. The widely accepted threshold for transport critical current density (J_c) in superconducting wires and tapes for practical use is 100 kA/cm² under 100 kOe and at 4.2 K [2]. The record-high transport J_c value for IBS round wires under these conditions is 71 kA/cm² in the (Ba,Na)Fe₂As₂ round wire [3]. The highest transport J_c value under the same conditions for the (Ba,K)Fe₂As₂ round wires is 49 kA/cm² [4]. Meanwhile, the highest transport J_c value for IBS tapes under the same conditions reached 150 kA/cm² in the (Ba,K)Fe₂As₂ tape [5]. The highest value of transport J_c (100 kOe, 4.2 K) for the (Ba,Na)Fe₂As₂ round wires is 44 kA/cm² [6] where there is room for improvements. In this study, we fabricated Ag-sheathed (Ba,Na)Fe₂As₂ tapes by the PIT method, incorporating cold pressing. Figure 1 shows the X-ray diffraction (XRD) pattern of the tape. We assessed c-axis texturing by measuring the texturing parameter (r = I(002) / I(103)) in the XRD pattern. The r value is ~1.2, which is relatively high for (Ba,Na)Fe₂As₂ tapes. We will discuss the fabrication process and measurement results for the transport properties. We will also report the results on (Ba,Na)Fe₂As₂ tapes using harder sheath materials such as Ag-Sn alloy.

References

[1] M. Rotter et al., Phys. Rev. B 101, 107006 (2008).
[2] H. Hosono et al., Mater. Today 21, 278 (2018).
[3] S. Pyon et al., Physica C 613, 1354354 (2023).
[4] S. Pyon et al., J. Phys. Conf. Ser. 2323, 012020 (2022).
[5] H. Huang et al., Supercond. Sci. Technol. 31, 015017 (2018).
[6] T. Tamegai et al., IEEE Trans. Appl. Supercon. 31, 7300505 (2021).

Figure 1. X-ray diffraction (XRD) pattern for Ag-sheathed (Ba,Na)Fe₂As₂ tape with Bragg-Brentano geometry. The longitudinal direction of the tape was set parallel to the X-ray. We subtracted the background.

Keywords: iron-based superconductor, superconducting tapes, X-ray computed tomography