Transport Current Measurement of $I_{c}(T, B,\theta)$ and $n(T, B,\theta)$ for a Bulk REBCO Superconductor

Ba1-xKxFe2As2 superconductors have strong potential for magnet applications through their very high upper critical field, relatively high superconducting transition temperature and manufacturability through the powder-in-tube (PIT) route. However, the critical current density in PIT tapes is still low compared to the incumbent technologies, so a greater understanding of the limiting factors is required. We have measured in-field critical currents (Ic) of stainless steel and silver double-sheathed monofilament Ba0.6K0.4Fe2As2 superconductor tapes at elevated temperatures from 15 K to 35 K. At 20 K the critical current density is up to 140 kA/cm2 in low (optimal) field and 22 kA/cm2 in 8 T. In the low-field region we observe an anomalous and sharp suppression of Ic centred at zero field. This feature is non-hysteretic for lower temperatures and perpendicular field, but becomes hysteretic for higher temperatures in perpendicular field and all temperatures in parallel field. The low-field suppression is reflected also in the n-values which can otherwise be very high, in excess of 100, in optimal field. Magnetic-field hysteresis of Ic is generally attributed to flux exclusion / flux trapping in granular superconductors and this is likely to be the case also in the present conductors. The low-field Ic anomaly also likely has its origin in the planar granularity, while magnetic phases in grains or grain boundaries may also play a role.

Section: Hysteresis and Low-field Anomalymentioning

confidence: 99%

Low field anomaly in the critical current of Ba₁₋ _x K _x Fe₂As₂ tapes

Strickland,

Chong,

Dong

et al. 2024

“…where E 0 = 1 µV cm −1 and J is the local current density. J c is the critical current density obtained from interpolations of experimental measurements, as described in the supplementary material [24][25][26][27][28][29].…”

Section: Fe Modelmentioning

confidence: 99%

A proof-of-concept Bitter-like HTS electromagnet fabricated from a silver-infiltrated (RE)BCO ceramic bulk

Taylor,

Weijers,

Ainslie

et al. 2024

Self Cite

A novel concept for a compact high-field magnet coil is introduced. This is based on stacking slit annular discs cut from bulk (RE)BCO ceramic in a Bitter-like architecture. Finite-element modelling shows that a small 20-turn stack (with a total coil volume of <20 cm3) is capable of generating a central bore magnetic field of >2 T at 77 K and >20 T at 30 K. Unlike resistive Bitter magnets, the HTS Bitter stack exhibits significant non-linear field behaviour during current ramping, caused by current filling proceeding from the inner radius outwards in each HTS layer. Practical proof-of-concept for this architecture was then demonstrated through fabricating an uninsulated 4-turn prototype coil stack and operating this at 77 K. A maximum central field of 0.382 T was measured at 1.2 kA, with an accompanying 6.1 W of internal heat dissipation within the coil. Strong magnetic hysteresis behaviour was observed within the prototype coil, with ≈30% of the maximum central field still remaining trapped 45 min after the current had been removed. The coil was thermally stable during a 15 min hold at 1 kA, and survived thermal cycling to room temperature without noticeable deterioration in performance. A final test-to-destruction of the coil showed that the limiting weak point in the stack was growth-sector boundaries present in the original (RE)BCO bulk.

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.