Novel approach for manufacture of single‐grain EuBCO/Ag bulk superconductors via modified single‐direction melt growth

In this work, we demonstrate experimentally the remarkable DC magnetic screening ability of hybrid superconducting screens. The configurations under investigation combine a 30 mm-diameter disk-shaped superconducting bulk, or another with a 10 mm-diameter hole, with different closed superconducting loops made from coated conductors. The loops are placed coaxially with the bulk. The bulk superconductors and the closed-loop coated conductors are made of GdBa2Cu3O7 and the experiments are performed in liquid nitrogen (77 K). The DC and inhomogeneous field to be screened is produced by a bespoke coil and reaches around 100 mT at the location of the superconducting bulk, which is much less than its full-penetration field. By mapping the magnitude of the flux density using a 3-axis cryogenic Hall probe, we show that such a hybrid superconducting screen allows the maximum shielding factor SF above the bulk to be almost doubled. For the best investigated hybrid configuration, the SF reaches ~45 at 2.7 mm above the bulk. In addition, the area of the spatial region for which less than half of the applied field remains (SF > 2) is roughly multiplied by 4 when compared to a situation involving only a disk-shaped bulk. In this work, this region corresponds to a 60 mm-diameter circle. The choice of the loop diameter is found to result from a trade-off between maximum SF and extension of the screened region. Finally, we detail why these hybrid configurations bring such improvements: the key point is that the flux lines generated by the source coil are diverted by the bulk towards a region where the closed-loop coated conductors can oppose the best to them.

Section: Experimental Set-upmentioning

confidence: 99%

Improving the screening ability of high-temperature superconductors by combining disk-shaped bulks and closed-loop coated conductors

Rotheudt,

Brialmont,

Fagnard

et al. 2024

Excellent field–trapping properties of large ring–shaped REBCO melt–textured bulks fabricated by the single–direction melt growth (SDMG) method

Motoki,

Shimoyama

2024

Ring-shaped homogeneous YBCO and DyBCO bulks were successfully fabricated using the Single-Direction Melt Growth (SDMG) method. The bulks were directly grown from ring-shaped compacted powder using ring-shaped molds with an outer diameter of 50 mm and inner diameters of 15, 20, and 25 mm. The ring-shaped bulks exhibited high trapped fields inside the rings up to 1.2 T at 77 K. Analyses of trapped field distributions revealed uniform current density distributions along the orbital direction. Stacked ring bulks demonstrated even higher trapped fields, reaching 2.0 T at 77 K. It was confirmed for the stacked bulks that time-independent uniform trapped fields can be achieved by magnetizing at lower fields than fully magnetizing conditions. Observed paramagnetic magnetization of the SDMG-processed YBCO bulk was negligibly small below the detection limit, which is considered to be more suitable for bulk NMR/MRI applications than DyBCO. Additionally, we proposed a method to quantitatively evaluate trapped fields of superconducting bulks with various diameters and thicknesses, where the estimated average current densities from the maximum trapped fields for all the obtained ring-shaped bulks were above 104 A/cm2 at 77 K. These results indicate that SDMG is an effective method for fabricating high-quality, large-scale ring-shaped bulks with superior field-trapping properties.

Review on high-temperature superconducting trapped field magnets

Wang,

Zhang,

Hao

et al. 2024

Superconducting (SC) magnets can generate exceptionally high magnetic fields and can be employed in various applications to enhance system power density. In contrast to conventional coil-based SC magnets, high-temperature superconducting (HTS) trapped field magnets (TFMs), namely HTS trapped field bulks (TFBs) and trapped field stacks (TFSs), can eliminate the need for continuous power supply or current leads during operation and thus can function as super permanent magnets. TFMs can potentially trap very high magnetic fields, with the highest recorded trapped field reaching 17.89 T, achieved by TFSs. TFMs find application across diverse fields, including rotating machinery, magnetic bearings, energy storage flywheels, and magnetic resonance imaging (MRI). However, a systematic review of the advancement of TFMs over the last decade remains lacking, which is urgently needed by industry, especially in response to the global net zero target. This paper provides a comprehensive overview of various aspects of TFMs, including simulation methods, experimental studies, fabrication techniques, magnetisation processes, applications, and demagnetisation issues. Several respects have been elucidated in detail to enhance the understanding of TFMs, encompassing the formation of HTS bulk composites and TFSs, trapped field patterns, enhancement of trapped field strength through pulsed field magnetisation (PFM), as well as their applications such as SC rotating machines, levitation, and Halbach arrays. Challenges such as demagnetisation, mechanical failure, and thermal instability have been illuminated, along with proposed mitigation measures. The different roles of ferromagnetic materials in improving the trapped field during magnetisation and in reducing demagnetisation have also been summarised. It is believed that this review article can provide a useful reference for the theoretical analysis, manufacturing, and applications of TFMs within various domains such as materials science, power engineering, and clean energy conversion.