Trapped field of 1.1 T without flux jumps in an MgB<sub>2</sub>bulk during pulsed field magnetization using a split coil with a soft iron yoke

Physica C: Superconductivity and its Applications

et al. 2017

We have investigated, both experimentally and numerically, the trapped field characteristics of a standard Y-Ba-Cu-O bulk of 30 mm in diameter and 14 mm in thickness magnetized by pulsed field magnetization (PFM) using a split coil, in which three kinds of iron yoke are inserted in the bore of the coil: soft iron with a flat surface, soft iron with a taper, and permendur (50Fe+50Co alloy) with a flat surface. The highest trapped field, B Tmax , of 2.93 T was achieved at 40 K in the case of the permendur yoke, which was slightly higher than that obtained for the flat soft iron or the tapered soft iron yokes, and was much higher than 2.20 T in the case without the yoke. The insertion effect of the yoke on the trapped field characteristics was also investigated using numerical simulations. The results suggest that the saturation magnetic flux density, B sat , of the yoke acts to reduce the flux flow due to its hysteretic magnetization curve and the higher electrical conductivity, ,of the yoke material also acts to suppress the flux increase rate. A flux jump (or flux leap) can be reproduced in the ascending stage of PFM using numerical simulation, using an assumption of relatively high J c (T, B) characteristics. The insertion effect of the yoke with high B sat and is discussed to enhance the final trapped field from both electromagnetic and thermal points of view.

Section: Introductionmentioning

confidence: 88%

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

Physica C: Superconductivity and its Applications

et al. 2017

“…1(a) and 1(b) and in ref. [19]. For the split-type coil, the MgB 2 disk was fastened in a copper sample holder around the bulk periphery and was connected to the cold stage of a Gifford-McMahon (GM) cycle, helium refrigerator in the vacuum chamber.…”

Section: Methodsmentioning

confidence: 99%

“…We have also analyzed the electromagnetic and thermal instability of a high-J c MgB 2 bulk using conventional parameters, such as the critical thickness, d c , and the minimum propagation zone (MPZ) length, l m [18]. Recently, we have achieved a trapped field of B z = 1.1 T on a thick, high-J c MgB 2 bulk at 13 K without flux jumps using a split-type coil with a soft iron yoke, which is a record high trapped field by PFM for bulk MgB 2 to date [19].…”

mentioning

confidence: 99%

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

IEEE Trans. Appl. Supercond.

et al. 2017

We have investigated the suppression of flux jumps and the enhancement of trapped field on a thin, high-J c MgB 2 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 MgB 2 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. Index Terms-MgB 2 bulk, pulsed field magnetization, split coil, flux jump, soft iron yoke. I. INTRODUCTION GB 2 superconducting polycrystalline bulks as trapped field magnets (TFMs) have been intensively investigated due to their merits of being rare-earth-free, lightweight , presenting a symmetric trapped field distribution and their long coherence length [1, 2], which are in clear contrast with REBaCuO bulk magnets (RE: rare earth elements and Y) [3]. MgB 2 polycrystalline bulks with high critical current density, J c , have been fabricated by various methods and activated by field-cooled magnetization (FCM) [4, 5, 6]. A record-high trapped field of B z = 5.4 T has been attained at 12 K on a single MgB 2 bulk disk 20 mm in diameter [7]. To magnetize superconducting bulks, pulsed-field magnetization (PFM) has been also investigated intensively,

“…An overview of the split coil PFM experimental setup is described in [11], [12]. The sample was fastened in a copper holder with thin indium foil (0.2 mm in thickness) and connected to the cold stage of a Gifford-McMahon cycle, helium refrigerator in the vacuum chamber.…”

Section: A Split Coil Pulsed Field Magnetizationmentioning

confidence: 99%

“…The split coil has an inner diameter of 72 mm, an outer diameter of 124 mm and a height of 35 mm, and is submerged in liquid nitrogen outside the vacuum chamber. A pair of soft iron, Ni-plated yokes (60 mm in diameter and 65 mm in height) can be inserted in the central bores of the coil, which was shown to enhance the trapped field in bulk high-temperature superconductors [11], as well as bulk MgB 2 [12]. The initial temperature of the bulk was set to T s = 65, 40 and 20 K, and magnetic pulses, B ex , up to around 6 T, with a rise time of t r = 18 ms and duration of approximately t d = 200 ms were applied via a pulse current in the coil.…”

Section: A Split Coil Pulsed Field Magnetizationmentioning

confidence: 99%

Pulsed Field Magnetization of Bridge-Seeded Bulk YBCO Using Solenoid and Split Coils

IEEE Trans. Appl. Supercond.

et al. 2017

The multi-seeding process has the potential to enlarge the sample size of (RE)BCO (where RE = rare earth or Y) single-grain, bulk superconductors with improved fabrication speed, and in previous studies on multi-seeding, a significant improvement was made in the alignment of the seeds in such samples using a novel bridge-seeding technique. In this paper, we report the experimental measurements of the pulsed field magnetization (PFM) of a 0°-0° bridge-seeded Y-Ba-Cu-O (YBCO) sample. The PFM is carried out using a solenoid coil, as well as a split coil arrangement with an iron yoke, at temperature of 65, 40 and 20 K, and the resultant trapped fields and magnetic flux dynamics for these two PFM techniques are compared. It is shown that such bridge-seeded bulk YBCO can be fabricated that performs as a bulk magnet with trapped fields comparable to or better than standard, single-seeded high-J c samples, with the potential of enlarging the sample size. Furthermore, the split coil arrangement with an iron yoke is useful to enhance the trapped field and has a positive effect on the maximum temperature rise in the sample, which increases at lower temperatures and seriously impacts the achievable trapped field from PFM.  Index Terms-Bulk superconductors, high-temperature superconductors, magnetic flux penetration, magnetization processes, multi-seeding, pulsed field magnetization, trapped field magnets.