2023
High current MgB2 joints made by IMD process
Superconducting joints between single-core MgB2/Ni and MgB2/Nb wires made by the Internal Magnesium Diffusion (IMD) process have been manufactured in a “scarf joints” architecture. Joints with an angle of 15 degrees have reached the current carrying capacity of only 6.7% of critical current measured for MgB2/Ni wire. The superconducting connection of MgB2/Ni wires is difficult to prepare due to interaction of Mg particles with Ni sheath and penetration of Mg-Ni between the joined wires, which resulted in no superconducting current path. It was found that addition of boron powder between the joined wires allows creation of sufficient superconducting current path. It was shown that usage of inert metallic sheath, optimized pressing mode and sufficient amount of added boron are decisive for well-connected superconducting wires made by “scarf joints” architecture. Joined MgB2/Nb wires have large transport currents up to 60 % of critical current of used wire. Consequently, this technique can be applied for MgB2 coils working in persistent mode.
- I. Hušek, P. Kováč, T. Melišek and M. Hain, Transport currents and micro-structure of superconducting joint between MgB2/Ni and MgB2/Nb wires made by IMD process, Ceramics International, Volume 49 issue 7 (2023) 11178-11183.
AC losses in superconducting round cables with alternating and coinciding winding directions
Traditionally, the HTS tapes in round cables are wound following an alternating sense of helicity. Then, the tape edges are raised due to the Poisson effect, causing local surface irregularity and pressing into subsequent layers. We have found recently that this effect is less deteriorating in the case of coinciding lay angles because then the tape edges create imprints that are parallel to the tape length. However, it was not clear how such arrangement will influence the AC loss. The investigations by experimental testing of small laboratory models and numerical modelling revealed that the impact of geometry is found only in low AC magnetic fields. There, the lowest AC loss was found for the cable consisting of pairs of stacked tapes. On the other hand, at the conditions expected in the winding of a coil generating magnetic field the AC loss of different arrangements approached the same values.
In the preparatory work for experimental verifications it was necessary to study in detail the limits of mechanical loads inevitably experienced by tapes during the cabling process, and the role of non-uniformities as sources of excessive degradation of critical current.
- Ries, R., Hlaváč, D., Solovyov, M., and Gömöry, F.: Induced delamination in REBCO coated-conductor tape by a scratch line and bending, Physica C 613 (2023) 1354358.
- Mošať, M., Šouc, J., Ries, R., and Gömöry, F.: Longitudinal critical current profiles in coated conductors examined by transport and magnetization measurements, IEEE Trans. Applied Supercond. 33 (2023) 6602205.
- Gömöry, F., Šouc, J., Godár, M., Hintze, C., and Grosse, V.: Analysis of critical current fluctuations as a means of checking the quality of high-temperature superconductor tape slitting, Supercond. Sci Technol. 36 (2023) 054001.
- Kujovič, T., Ries, R., Mošať, M., and Gömöry, F.: The critical current of REBCO coated conductors subjected to a mechanical loading at varying angles, IEEE Trans. Applied Supercond. 33 (2023) 6601004.
- Solovyov, M., Šouc, J., Kujovič, T., Frolek, L., and Gömöry, F.: Magnetization AC losses in multilayer superconducting round cables with coinciding and opposite lay angles, Supercond. Sci Technol. 36 (2023) 034001.
- Ries, R., Gömöry, F., Mošať, M., Kujovič, T., Hintze, C., and Gil, P.: Effect of off-axis bending on microstructural and transport properties of coated conductor tape, Supercond. Sci Technol. 36 (2023) 014006.