Flux Dynamics and Thermal Behavior of a GdBaCuO Bulk Magnetized by Single- and Double-Pulse Techniques Using a Split-Type Coil

We have investigated the electromagnetic and thermal properties of a REBaCuO ring bulk with an inhomogeneous critical current density, J c, profile during pulsed field magnetization (PFM) using a numerical simulation and compared those to a bulk with a homogeneous J c profile. A notch was introduced in the bulk periphery, which was assumed as a crack existing in the actual bulk material. A sudden flux penetration (flux jump) took place through the notch area and as a result, a large temperature rise also took place around this notch. Consequently, the final trapped field profile was simulated to be a ‘C-shaped profile’, which qualitatively reproduced our previous experimental results. The size and position dependences of the notch on the flux penetration behaviour were also simulated, in which a larger and outer notch promotes the flux jump phenomenon easily. On the other hand, in the homogeneous model, under the same conditions, no flux jump phenomenon was observed. These results suggest that the imperfection in the bulk can be a possible starting point of the flux jump. The electromagnetic and thermal hoop stresses were also simulated in the ring bulk during PFM, in which the electromagnetic stress and the thermal stress were both observed to be lower than the fracture strength of the bulk material. This provides good evidence that the experimentally observed ‘C-shaped profile’ results from the flux jump rather than the fracture of the bulk.

Section: Electromagnetic and Thermal Hoop Stresses During Pfmsupporting

confidence: 82%

Numerical simulation of flux jump behavior in REBaCuO ring bulks with an inhomogeneous J_c profile during pulsed-field magnetization

Hirano

Fujishiro

Naito

et al. 2020

“…On the other hand, MgB 2 bulk superconductors have also promising potential as TFMs, such as being rare-earth-free, lightweight and presenting a homogeneous trapped field distribution [9], which are in clear contrast with REBaCuO bulks. The better and larger MgB 2 polycrystalline TFMs can be realized because of their long coherence length, ξ, below T c = 39 K [10].…”

Section: Introductionmentioning

confidence: 99%

A record-high trapped field of 1.61 T in MgB₂ bulk comprised of copper plates and soft iron yoke cylinder using pulsed-field magnetization

Hirano

Takahashi

Namba

et al. 2020

A trapped field of B T = 1.61 T was experimentally achieved at the central surface of an MgB 2 bulk composite (60 mm in diameter and 20 mm in height) at 20 K by double pulsed-field magnetization (PFM) using a split-type coil. The composite bulks consisted of two MgB 2 ring bulks sandwiched by thin copper ring plates, which were then stacked, and a soft iron yoke cylinder was inserted in the central bore of the rings. The copper ring plates delayed the rise time and duration of the magnetic pulse due to eddy currents. The inserted soft iron yoke attracted the magnetic flux and enhanced the trapped field strength mainly due to its large permeability. As a result, the trapped field was enhanced from B T = 0.34 T for the single MgB 2 ring bulk without the copper plates and soft iron yoke to B T = 1.00 T for the composite with both copper plates and the soft iron yoke. The inserted soft iron yoke can be exploited to enhance the trapped field because the intrinsic B T of the single MgB 2 ring bulk was smaller than the saturation field of the yoke (∼2 T). Using an optimized second pulse application after suitable flux trapping from the first pulse application, the trapped field was enhanced considerably to B T (2nd) = 1.61 T, which is a record-high trapped field for an MgB 2 bulk by PFM to date. The combination of the longer magnetic pulse application by the copper plates, the enhancement of the effective applied field by the inserted soft iron yoke, and the double pulse application using split-type coil is an effective technique to enhance the trapped field in the MgB 2 bulk using PFM.

“…Unlike traditional methods that can trap magnetic fields up to 10 Tesla, PFM can only trap magnetic fields of several Tesla. Since the external magnetic field is applied for a few milliseconds during PFM, fast movement of the flux will generate a significant amount heat, which reduces the trapped field [9,10]. By using a modified multi-pulse technique combined with stepwise cooling, Fujishiro et al realized a trapped field up to 5.2 T in the GdBaCuO bulk superconductor, which is the largest trapped field for PFM so far [11].…”

Section: Introductionmentioning

confidence: 99%

Analysis of mechanical behavior in inhomogeneous high-temperature superconductors under pulsed field magnetization

Yong

Zhou

2020

Melt-textured large, single-grain REBCO (RE: rare earth element or Y) bulk superconductors have growth sector boundaries (GSBs) and growth sector regions (GSRs). The critical current density is dependent on the GSBs and the GSRs, which will influence the electromagnetic field and the temperature field distributions. REBCO bulk superconductors are brittle materials and during the manufacturing process, cracks and inclusions may exist, therefore it is necessary to analyze the mechanical response during the magnetization process. In this paper, the mechanical response of an inhomogeneous cylinder superconductor under electromagnetic stress and the thermal stress during the pulsed field magnetization process is studied. By solving the coupled magnetic and heat diffusion equations in association with a modified E − J power-law relationship, we can obtain the electromagnetic field and the temperature field distributions; then, the mechanical response of the bulk can be determined. The trend shown by our numerical simulation is consistent with the experimental results. Then we study the mechanical behavior of inhomogeneous high-temperature superconductors with and without a flux jump. The case without or with the SUS 304 ring is also analyzed.