K Takahashi

Enhanced trapped field performance of bulk high-temperature superconductors using split coil, pulsed field magnetization with an iron yoke

Investigating and predicting the magnetization of bulk superconducting materials and developing practical magnetizing techniques is crucial to using them as trapped field magnets in engineering applications. The pulsed field magnetization (PFM) technique is considered to be a compact, mobile and relative inexpensive way to magnetize bulk samples, requiring shorter magnetization times (on the order of milliseconds) and a smaller and less complicated magnetization fixture; however, the trapped field produced by PFM is generally much smaller than that of slower zero field cooling or field cooling techniques, particularly at lower operating temperatures. In this paper, the PFM of two, standard Ag-containing Gd–Ba–Cu–O samples is carried out using two types of magnetizing coils: (1) a solenoid coil, and (2) a split coil, both of which make use of an iron yoke to enhance the trapped magnetic field. It is shown that a significantly higher trapped field can be achieved using a split coil with an iron yoke, and in order to explain these how this arrangement works in detail, numerical simulations using a 2D axisymmetric finite element method based on the H -formulation are carried to qualitatively reproduce and analyze the magnetization process from both electromagnetic and thermal points of view. It is observed that after the pulse peak significantly less flux exits the bulk when the iron core is present, resulting in a higher peak trapped field, as well as more overall trapped flux, after the magnetization process is complete. The results have important implications for practical applications of bulk superconductors as such a split coil arrangement with an iron yoke could be incorporated into the design of a portable, high magnetic field source/magnet to enhance the available magnetic field or in an axial gap-type bulk superconducting electric machine, where iron can be incorporated into the stator windings to (1) improve the trapped field from the magnetization process, and (2) increase the effective air-gap magnetic field.

Flux jump-assisted pulsed field magnetisation of high-

Investigating, predicting and optimising practical magnetisation techniques for charging bulk superconductors is a crucial prerequisite to their use as high performance ‘psuedo’ permanent magnets. The leading technique for such magnetisation is the pulsed field magnetisation (PFM) technique, in which a large magnetic field is applied via an external magnetic field pulse of duration of the order of milliseconds. Recently ‘giant field leaps’ have been observed during charging by PFM: this effect greatly aids magnetisation as flux jumps occur in the superconductor leading to magnetic flux suddenly intruding into the centre of the superconductor. This results in a large increase in the measured trapped field at the centre of the top surface of the bulk sample and full magnetisation. Due to the complex nature of the magnetic flux dynamics during the PFM process, simple analytical methods, such as those based on the Bean critical state model, are not applicable. Consequently, in order to successfully model this process, a multi-physical numerical model is required, including both electromagnetic and thermal considerations over short time scales. In this paper, we show that a standard numerical modelling technique, based on a 2D axisymmetric finite-element model implementing the

J_c

H

bulk high-temperature superconductors

-formulation, can model this behaviour. In order to reproduce the observed behaviour in our model all that is required is the insertion of a bulk sample of high critical current density,

Research data supporting [Towards Optimisation of Multi-Pulse, Pulsed Field Magnetisation of Bulk High-Temperature Superconductors]

J_c

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

. We further explore the consequences of this observation by examining the applicability of the model to a range of previously reported experimental results. Our key conclusion is that the ‘giant field leaps’ reported by Weinstein

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

\textit{et al}

Simulation studies of mechanical stresses in REBaCuO superconducting ring bulks with infinite and finite height reinforced by metal ring during field-cooled magnetization

and others need no new physical explanation in terms of the behaviour of bulk superconductors: it is clear the ‘giant field leap’ or flux jump-assisted magnetisation of bulk superconductors will be a key enabling technology for practical applications.

Fracture behavior analysis of EuBaCuO superconducting ring bulk reinforced by a stainless steel ring during field-cooled magnetization

Research data supporting [Towards Optimisation of Multi-Pulse, Pulsed Field Magnetisation of Bulk High-Temperature Superconductors]

A new concept of a hybrid trapped field magnet lens

We have investigated the trapped-held characteristics of a rectangular-shaped Gd-Ba-Cu-O bulk (33 × 33 × 15 mm3) 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 BZmax 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 BZmax 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.