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

Abstract

We have investigated the trapped field characteristics of a rectangular-shaped Gd-Ba-Cu-O bulk (33 x 33 x 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 field, 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 field profile was observed. The behavior of the magnetic flux motion indicated two conditions for the enhancement of the trapped field: that the magnetic flux intrudes easily into the bulk even for lower applied fields and then saturates with minimal flux creep. We also have 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 field for the rectangular-shaped bulks.  Index Terms-(RE) BaCuO bulk, pulsed field magnetization, numerical simulation, trapped field, soft iron yoke I. INTRODUCTION ULSED FIELD MAGNETIZATION (PFM) of (RE)BaCuO bulks (RE: rare earth element or Y) has been investigated intensively for practical applications as a substitute for fieldcooled magnetization (FCM) because PFM is an inexpensive and mobile experimental setup with no need for a superconducting magnet. However, the trapped field, B Z , by PFM is generally lower than that by FCM, where B Z values over 17 T have been achieved [1], because of the large temperature rise caused by the dynamical motion of the magnetic flux [2]. To enhance B Z by PFM, multi-pulse techniques using a solenoid coil are usually effective due to the reduction of temperature rise [3-6]. Using a new multipulse techniquethe so-called modified multi-pulse technique with stepwise cooling (MMPSC)we successfully achieved a highest trapped field of B Z = 5.20 T on a 45 mm Gd-Ba-Cu-O bulk disk at 30 K, which is a record-high value to date [7]. In addition, the use of new types of coils, such as a split coil

Trapped field properties of a Y–Ba–Cu–O bulk by pulsed field magnetization using a split coil inserted by iron yokes with various geometries and electromagnetic properties

“…It is clear that a higher trapped field with a conical profile can be obtained in the cases with a flat yoke (b2 and d2), compared to the tapered soft iron (c2). even after the whole process of magnetization (t > 300 ms) [15]. The contribution of the yoke insertion during PFM exists mainly in the descending stage.…”

“…Several studies using the numerical simulation have been reported for PFM [17][18][19][20][21][22][23]. We have previously confirmed the advantage of the insertion of a soft iron yoke with a flat surface in the split coil numerically, and compared this to the case without the yoke [14,15].…”

“…In recent years, a ferromagnetic yoke has been inserted in the magnetizing fixture to increase the trapped magnetic field [12,13], in which permendur (50Fe+50Co alloy) and soft iron were used experimentally as a yoke material. We have also achieved a trapped field of over 3 T at 40 K on Gd-Ba-Cu-O disk bulk by PFM, employing a split coil with a pair of soft iron yokes [14], in which a symmetric trapped field profile can be also realized [15]. In addition, for the MgB 2 bulk, we achieved over 1 T at 13 K by PFM without any flux jumps on a high-J c MgB 2 disk bulk using the split coil with soft iron yoke, which is a record-high trapped field by PFM for the MgB 2 bulk to date [16].…”

Numerical modelling of mechanical stresses in bulk superconductor magnets with and without mechanical reinforcement

“…differences in J c between growth sector boundaries (GSBs) and growth sector regions (GSRs) [19], and for shapes without cylindrical symmetry, Comparison of the Lorentz force in the radial direction, F L,r , and hoop stress, σ j , distributions throughout the cross-section of the bulk at the end of the FCM process (t=1250 s), for the 2D and 3D models. such as rectangular-shaped bulks [20]. It can also be useful to exploit symmetry, where possible, in a 3D model by applying appropriate boundary conditions to model, for example, one half (2D or 3D) or one quarter of the bulk.…”

“…In this section, the 3D model is used to investigate an example of the influence of inhomogeneous material properties around the ab-plane, such as those that occur during the growth process of c-axis seeded, single grain (RE)BCO bulk superconductors [19]. The 3D model is also useful for shapes without cylindrical symmetry, such as rectangular-shaped bulks [20].…”