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ISSN: 2772-8307
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cited:7
Phase evolution mechanism study and fabrication of PbMo6S8 superconducting materials with two-step sintering process
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Article Number:Article 100038
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Corresponding email:snzhang@c-nin.com
PbMo6S8 superconducting materials are considered to have great potential for practical applications at low temperatures and high fields due to their high upper critical field, low anisotropy, and low preparation cost. In this work, PbMo6S8 bulks were prepared through a solid-state sintering process using PbS, Mo, and MoS2 as raw materials. The phase evolution mechanism during the sintering of PbMo6S8 was studied in detail. It was found that during sintering at 750 °C for 24 h, both the S and Pb atoms diffuse into the Mo and MoS2 particles, leading to the formation of the PbMo6S8 phase. After sintering at 950 °C for 72 h, a high superconducting phase content was obtained in the bulk; however, numerous pores remained. Therefore, in order to obtain a higher density for the bulk, a two-step sintering process was developed. Based on this technique, PbMo6S8 bulks with a higher bulk density and a higher superconducting phase content were obtained. This study provides an effective method for the fabrication of high-quality precursor powders, which can be the foundation for the future fabrication of PbMo6S8 superconducting long wires or tapes for practical applications.
cited:30
Electromagnetic analysis and AC losses of triaxial cables with multiple 2G-HTS layers per phase
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Article Number:Article 100039
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Corresponding email:mlc42@leicester.ac.uk
For an accurate estimation of the AC losses of superconducting triaxial cables, in this paper we present a two-dimensional model capable to provide a global assessment of multi-layer triaxial cables, validated against the reported AC-losses measurements on single-phase cables provided by the Russian Scientific and Research Institute of the Cable Industry (VNIIKP). Four models are presented, the first being a single-phase cable of 50 tapes and the others being three triaxial cables made of up to 135 coated conductors distributed in up to 9 layers. A systematic study is devised, where the number of layers per phase increases from 1 to 3, with at least 14 tapes distributed across each layer of the first (innermost) phase, 15 in the secondary (middle) phase, and 16 in the third (outermost) phase, respectively. Remarkably, our results reveal that the simple strategy of considering an unbalanced distribution for the amplitudes of the applied current, can generally balance the magnetic field between the three phases even for the bilayer and trilayer cables, resulting in negligible magnetic leaks in all situations. Besides, our high-resolution simulations allow to see for the first time how the transport and magnetization currents distribute across the thickness of all the superconducting tapes, from which we have found that the AC-losses of the 2nd phase is generally higher than at the other phases at low to moderate transport currents, , being the critical current of the corresponding tapes. Nevertheless, depending on whether the of the SC tapes at the 3rd phase layers is lower than the one at the 2nd phase, the layers at the third phase can exhibit a considerable increment on the AC losses. This is result of the considered magneto angular anisotropy of the superconducting tapes, which lead to intriguing electromagnetic features that suggest a practical threshold for the applied transport current, being it . Likewise, the relative change in the AC-losses per adding layers, per phase, and as a function of the entire range of applied transport current is disclosed.
cited:4
The impact of magnetic field periodicity on the hysteresis loss in superconducting magnetic bearings
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Article Number:Article 100040
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Corresponding email:mohammad.siamaki@vuw.ac.nz
Since the discovery of high-temperature superconductors (HTS), superconducting magnetic bearings (SMB) have attracted much attention for practical applications such as flywheel energy storage systems, electrical machines, gyroscopes, etc., because of their ability to provide passive stable levitation under high-load conditions. Despite providing contactless linear and rotational motion, SMBs gradually decelerate by AC losses mainly generated by magnetic field inhomogeneity. The main component of AC losses at low rotational speeds is hysteresis loss, which is said to be independent of rotational speed, intrinsic to HTS, and proportional to the cube of magnetic field inhomogeneity. Although the state-of-the-art analytical expression of hysteresis loss in SMBs captures the general physics of the loss mechanism, it ignores the periodicity of the magnetic field in one complete rotation of the bearing. In this paper, the analytical expression of hysteresis loss is modified, taking into account the impact of magnetic field periodicity and the distribution of loss over the bearing surface. The new expression is tested by performing spin-down experiments with magnets of different levels of inhomogeneity in an actual SMB environment. The impact of magnetic field inhomogeneity on the dynamic behaviour of the bearing is also investigated. The results show consistency between modified analytical calculations and experimental data.
cited:12
Pulsed field magnetization of multiple bulks used as field pole of a high-temperature superconducting rotating machine
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Article Number:Article 100041
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Corresponding email:acau001@kaiyodai.ac.jp
An array of three GdBa2Cu3O7-δ bulk high-temperature superconductors (HTS) that mimic the field pole of a high-power superconducting motor had been magnetized by pulsed field magnetization (PFM) while cooled by liquid nitrogen. The bulk array was magnetized by a passive PFM technique using three vortex-type coils placed over each individual bulk and connected in series. The trapped magnetic flux density distribution was comparable to the distribution obtained with more traditional quasi-static magnetization such as field-cooling. This suggests that the use of PFM technique on arrays of HTS bulks is possible. PFM has also been performed using each coil individually, to magnetize each bulk sequentially. The magnetization sequences showed a maximum reduction of the peak trapped magnetic flux density of 12% due to the demagnetization effect of the magnetization sequence, while the trapped magnetization distribution was improved.
cited:31
Mechanical characterization of a 10-MJ HTS SMES magnet wound by quasi-isotropic strands and directly stacked tape conductors
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Article Number:Article 100042
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Corresponding email:yswang@ncepu.edu.cn
A 10-MJ-class superconducting magnetic energy storage (SMES) magnet is designed and optimized in this study using quasi-isotropic strands and stacked-tape conductors. In order to ensure the stable operation of SMES systems, it is necessary to evaluate the mechanical properties risk caused by the Lorentz force. Therefore, in this study, the magnetic stress caused by the Lorentz force is analyzed using the finite element method. The results show that the tapes near the inner diameter of the magnet are subjected to a higher stress and require considerable support. Although the maximum stress is increased by two times due to the presence of the screening current, it is within the safety range. The screening current does not vanish after the discharge process. After discharge, the coil is still subjected to a stress on the other of a few MPa.
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