Linking Theory to Practice in the Workplace

No abstract available

A new concept of a hybrid trapped field magnet lens

In this paper, a new concept of a hybrid trapped field magnet lens (HTFML) is proposed. The HTMFL exploits the “vortex pinning effect” of an outer superconducting bulk cylinder, which is magnetized as a trapped field magnet (TFM) using field-cooled magnetization (FCM), and the “diamagnetic shielding effect” of an inner bulk magnetic lens to generate a concentrated magnetic field higher than the trapped field from the TFM in the bore of the magnetic lens. This requires that, during the FCM process, the outer cylinder is in the normal state (T > superconducting transition temperature, Tc) and the inner lens is in the superconducting state (T < Tc) when the external magnetizing field is applied, followed by cooling to an appropriate operating temperature, then removing the external field. This is explored for two potential cases: 1) exploiting the difference in Tc of two different bulk materials (“case-1”), e.g. MgB2 (Tc = 39 K) and GdBaCuO (Tc = 92 K) or 2) using the same material for the whole HTFML, e.g., GdBaCuO, but utilizing individually-controlled cryostats, the same cryostat with different cooling loops or coolants, or heaters that keep the outer bulk cylinder at a temperature above Tc to achieve the same desired effect. The HTFML is verified using numerical simulations for “case-1” using an MgB2 cylinder and GdBaCuO lens pair and for “case-2” using a GdBaCuO cylinder and GdBaCuO lens pair. As a result, the HTFML could reliably generate a concentrated magnetic field Bc = 4.73 T with the external magnetizing field Bapp = 3 T in the “case-1, and a higher Bc = 13.49 T with higher Bapp = 10 T in the “case-2,” respectively. This could, for example, be used to enhance the magnetic field in the bore of a bulk superconducting NMR/MRI system to improve its resolution

Simulation study for magnetic levitation in pure water exploiting the ultra-high magnetic field gradient product of a hybrid trapped field magnet lens (HTFML)

A hybrid trapped field magnet lens (HTFML) is a promising device that is able to concentrate a magnetic field higher than the applied field continuously, even after removing an external field, which was conceptually proposed by the authors in 2018. In this study, we propose a new additional advantage of the HTFML, which could be applicable for magnetic levitation and separation. The HTFML device consisting of a GdBaCuO bulk cylinder and a GdBaCuO magnetic lens, after the magnetization process from an applied field, Bapp = 10 T, can generate a maximum trapped field, Bc = 11.4 T, as well as an ultra-high magnetic field gradient product, Bz⋅dBz/dz, over ±3000 T2/m at Ts = 20 K, which is higher than that of existing superconducting magnets and large-scale hybrid magnets. Through detailed numerical simulations, the HTFML device is considered for the magnetic separation of a mixture of precious metal particles (Pt, Au, Ag, and Cu) dispersed in pure water, by exploiting the magneto-Archimedes effect. The HTFML can be realized as a compact and mobile desktop-type superconducting bulk magnet system, and there are a wide range of potential industrial applications, such as in the food and medical industries.Adaptable and Seamless Technology Transfer Program through Target-driven R&D (A-STEP), Japan Science and Technology Agency (JST), Grant No. VP30218088419 JSPS KAKENHI Grant No. 19K0524

Pulsed-Field Magnetizing Characteristics of Rectangular-Shaped Gd-Ba-Cu-O Bulk Using Split- and Solenoid-Type Coils

We have investigated the trapped-held characteristics of a rectangular-shaped Gd-Ba-Cu-O bulk (33 × 33 × 15 mm$^3$) magnetized by pulsed-field magnetization (PFM) using split- and solenoid-type coils. A soft iron yoke was set below the bulk for the solenoid coil and two yokes are inserted in the bores of the split coil. The maximum trapped held B$_{Zmax}$ at the center of the bulk surface was 1.73 T at 40 K in the case of the solenoid coil, with a distorted profile. On the other hand B$_{Zmax}$ was enhanced to 3.05 T at 40 K for the split coil with two yokes for which a symmetric trapped-held profile was observed. The behavior of the magnetic flux motion indicated two conditions for the enhancement of the trapped held: that the magnetic flux intrudes easily into the bulk even for lower applied fields and then saturates with minimal flux creep. We have also investigated the electromagnetic and thermal properties of the bulk during PFM using a numerical simulation in which the magnetic flux tended to align along the z-axis due to the presence of the soft iron yoke. The use of the split coil with two yokes is effective in enhancing the trapped held for the rectangular-shaped bulks.This work was supported by Open Partnership Joint Projects of Japan Society for the Promotion of Science (JSPS) Bilateral Joint Research Projects, and JSPS KAKENHI grant number 23560002 and 15K04646. Dr. Mark Ainslie would like to acknowledge the support of a Royal Academy of Engineering Research Fellowship

Trapped Field Enhancement of a Thin, High-Jc MgB2 Bulk without Flux Jumps using Pulsed Field Magnetization with a Split-type Coil with a Soft Iron Yoke

We have investigated the suppression of flux jumps and the enhancement of trapped field on a thin, high-J$_{c}$ MgB₂ bulk (30 mm in diameter and 7 mm in thickness) for the pulsed field magnetization (PFM) using a split-type coil with a soft iron yoke, and compared the results to those magnetized using the split-type coil without a yoke and a solenoid-type coil with a yoke. A maximum-trapped field, B$_{z}$, of 0.71 T at 14 K was achieved on the bulk surface without flux jumps by using the split coil with yoke. On the other hand, low B$_{z}$ values with flux jumps were observed for the cases using the split-type coil without a soft iron yoke, and the solenoid-type coil with a yoke. These results reproduce previous ones for a thick, high-J$_{c}$ MgB₂ bulk (22 mm in diameter and 15 mm in thickness), for which the trapped field was enhanced to a record high value of B$_{z}$=1.10 T at 13 K by PFM using the split-type coil with a yoke

Influence of Jc(B, T) Characteristics on the Pulsed Field Magnetization of REBaCuO Disk Bulks

The trapped field properties during pulsed-field magnetization (PFM) have been investigated numerically using three different assumptions relating to the Jc(B, T) characteristics (Jirsa, Kim and Bean models) and compared with experimental results. The trapped field properties using the Jirsa model with the so-called ‘peak effect’, in which a realistic Jc(B, T) is assumed, rather than the Kim model, result in a more realistic numerical simulation. The trapped field properties using a Kim model with a monotonically decreasing Jc(B) also show similar results to those using the Jirsa model. The trapped field properties using a Bean model, for which Jc is independent of magnetic field, are not necessarily enhanced because of a larger temperature rise. The numerical results suggest it is necessary to fabricate REBaCuO bulks with Jc(B, T) characteristics with moderate magnetic field and temperature dependences to enhance the trapped field by PFM

Fast and efficient critical state modelling of field-cooled bulk high-temperature superconductors using a backward computation method

Abstract: A backward computation method has been developed to accelerate modelling of the critical state magnetization current in a staggered-array bulk high-temperature superconducting (HTS) undulator. The key concept is as follows: (i) a large magnetization current is first generated on the surface of the HTS bulks after rapid field-cooling (FC) magnetization; (ii) the magnetization current then relaxes inwards step-by-step obeying the critical state model; (iii) after tens of backward iterations the magnetization current reaches a steady state. The simulation results show excellent agreement with the H -formulation method for both the electromagnetic and electromagnetic-mechanical coupled analyses, but with significantly faster computation speed. The simulation results using the backward computation method are further validated by the recent experimental results of a five-period Gd–Ba–Cu–O (GdBCO) bulk undulator. Solving the finite element analysis (FEA) model with 1.8 million degrees of freedom (DOFs), the backward computation method takes less than 1.4 h, an order of magnitude or higher faster than other state-of-the-art numerical methods. Finally, the models are used to investigate the influence of the mechanical stress on the distribution of the critical state magnetization current and the undulator field along the central axis

Design Optimization of a Hybrid Trapped Field Magnet Lens (HTFML)

The concept of a hybrid trapped field magnet lens (HTFML) was recently proposed by the authors, which consists of a trapped field magnet (TFM) cylinder exploiting the “vortex pinning effect,” combined with a superconducting bulk magnetic lens exploiting the “diamagnetic shielding effect.” This HTFML can generate, within its bore, a magnetic field higher than the applied magnetic field, even after external field decreases to zero. In this paper, a design optimization of the inner GdBaCuO magnetic lens within the GdBaCuO TFM cylinder was carried out using numerical simulations based on the finite element method, in order to maximize the concentrated magnetic field. The HTFML with an optimized shape and size achieved a concentrated magnetic field of Bc = 5.6 and 12.8 T at the center of the lens for applied magnetic fields of Bapp = 3 and 10 T, respectively. A maximum tensile stress of +135 MPa exists in the outer GdBaCuO TFM cylinder during the magnetizing process for Bapp = 10 T, which exceeds the fracture strength of the bulk. This result suggests that mechanical reinforcement is necessary to avoid mechanical fracture under such high magnetic field conditions

Influence of inner diameter and height of ring-shaped REBaCuO bulks on trapped field and mechanical stress during field-cooled magnetization

In this paper, the trapped field, Bz, thermal hoop stress, σθcool, by cooling from 300 to 50 K and electromagnetic hoop stress, σθFCM, during field cooled magnetization (FCM) from Bapp = 6.3 and 9.4 T are investigated numerically for ring-shaped REBaCuO bulks with various inner diameters (I.D.) and heights (H) and reinforced by an Al alloy ring. For simplicity, an identical critical current density, Jc(B), which is a typical value at 50 K, is assumed in the simulation. The Bz value at the center of the ring bulk changes depending on the I.D. and H values of the ring bulk, which results from the different distribution of the superconducting current. As a result, the total hoop stress, σθtotal, (= σθcool + σθFCM) also changes for each ring bulk and for each Bapp due to the variation of the σθcool and σθFCM values. The maximum σθ total value, which affects the bulk fracture at Bapp = 9.4 T, increases with decreasing the height of ring bulk. These results can present guidelines for designing a trapped-field magnet using ring bulks