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357 results on '"Fujishiro, Hiroyuki"'

8. Field-cooled magnetization of Y-Ba-Cu-O superconducting bulk pair reinforced by full metal encapsulation under high magnetic fields up to 22 T.

Author

Naito, Tomoyuki, Fujishiro, Hiroyuki, and Awaji, Satoshi

Subjects
*MAGNETIC fields, *MAGNETIZATION, *MAGNETIC traps, *THERMAL instability, *STRESS concentration
Abstract

We report on the field-cooled magnetization (FCM) process under magnetic fields of up to 22 T for the stacked Y-Ba-Cu-O (YBCO) bulk pair reinforced by a stainless steel (SUS316) container. On the basis of the numerically simulated mechanical stress in a bulk during FCM, the SUS316 container was designed by the numerical simulation to offer the sufficient hoop stress tolerance to the bulk trapping the magnetic field of 20 T. As a result, we obtained successfully the trapped field, B T , of 15.1 T by FCM from 18 T at 28 K at the center of the YBCO bulk pair. However, the extremely large-scale vortex jumps and large temperature rise occurred suddenly during FCM from a higher field of 22 T at a lower temperature of 23 K, and then a small crack was confirmed at the periphery of "both" YBCO bulks from the distorted contour maps of B T . The simultaneous break of both YBCO bulks probably in spite of sufficient mechanical reinforcement led us to conclude that the thermal instability triggered off the large-scale vortex jumps and large heat generation. The stress concentration induced thermally at the hot spot brought about the cracking. [ABSTRACT FROM AUTHOR]

Published
2019
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15. A conceptual study of a high gradient trapped field magnet (HG-TFM) toward providing a quasi-zero gravity space on Earth

Author

Takahashi, Keita, Fujishiro, Hiroyuki, Ainslie, Mark D, Takahashi, K [0000-0002-8278-2688], Fujishiro, H [0000-0003-1483-835X], Ainslie, Mark [0000-0003-0466-3680], Apollo - University of Cambridge Repository, Takahashi, Keita [0000-0002-8278-2688], Fujishiro, Hiroyuki [0000-0003-1483-835X], Ainslie, Mark D [0000-0003-0466-3680], and Ainslie, MD [0000-0003-0466-3680]

Subjects
Paper, quasi-zero gravity, high gradient magnets, magnetic levitation, Materials science, Field (physics), finite element method, Metals and Alloys, Condensed Matter Physics, Space (mathematics), Conceptual study, Finite element method, trapped field magnets, Magnet, Quantum electrodynamics, Materials Chemistry, Ceramics and Composites, bulk superconductors, Zero gravity, Electrical and Electronic Engineering, Earth (classical element), Magnetic levitation
Abstract

In this work, we propose a new concept of a high gradient trapped field magnet (HG-TFM). The HG-TFM is made from (RE)BaCuO bulk superconductors, in which slit ring bulks (slit-TFMs) are tightly stacked with TFM cylinders (full-TFMs), and state-of-the-art numerical simulations were used to investigate the magnetic and mechanical properties in detail during and after magnetization. A maximum value of the magnetic field gradient product of B z ��� d B z / d z = 6040 T2 m���1 was obtained after conventional field cooled magnetization (FCM) with an applied field, B app, of 10 T of the HG-TFM with 60 mm in outer diameter and 10 mm in inner diameter. This value may be the highest value ever reported compared to any other magnetic sources. The B z ��� d B z / d z value increased with decreasing inner diameter of the HG-TFM and with increasing B app during FCM. The electromagnetic stress in the HG-TFM during the FCM process mainly results from the hoop stress along the circumferential direction. The simulations suggested that there is no fracture risk of the bulk components during FCM from 10 T in a proposed realistic configuration of the HG-TFM where both TFM parts are mounted in Al-alloy rings and the whole HG-TFM is encapsulated in a steel capsule. A quasi-zero gravity space can be realized in the HG-TFM with a high B z ��� d B z / d z value in an open space outside the vacuum chamber. The HG-TFM device can act as a compact and cryogen-free desktop-type magnetic source to provide a large magnetic force and could be useful in a number of life/medical science applications, such as protein crystallization and cell culture., JSPS KAKENHI Grant No. 19K05240 Adaptable and Seamless Technology transfer Program through Target-driven R&D (A-STEP) from Japan Science and Technology Agency (JST), Grant Nos. VP30218088419 and JPMJTM20AK

Published
2021

16. Trapped Field Properties of Large Disk MgB<inline-formula><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula> Bulks Fabricated by an In-situ Infiltration and Reaction Method Using an Amorphous B Preform Containing Dilute Mg

Author

Takahashi, Yuhei, Naito, Tomoyuki, and Fujishiro, Hiroyuki

Abstract

An in-situ infiltration and reaction (IR) method is one of the most promising methods for the mass production of dense MgB$_{2}$ with a filling factor of over 90%. This is because it does not require an apparatus that applies physical pressure during synthesis, in contrast to the hot isostatic pressing, hot pressing, and spark plasma sintering methods. To promote the infiltration of Mg melt into the B preform, a low-reactivity crystalline B has usually been used to create MgB$_{2}$ bulks with centimetric dimensions. In this paper, we attempted to fabricate large MgB$_{2}$ bulks by the IR method using highly reactive amorphous B, which should result in a high critical current, as reported in the literature. To promote the intrusion of Mg melt, we mixed a small amount of Mg into the amorphous B preform, which is expected to give a similar effect to the so-called premix method. We successfully produced IR-processed MgB$_{2}$ disk bulks, of 20 mm diameter and 5 mm thickness, at a reaction temperature of 700 °C with a holding time of 9 or 24 h. A trapped field $B_\mathrm{T}$ of 1.85 T at 20 K was obtained at the surface centers of the MgB$_{2}$ bulks, which is comparable with the $B_\mathrm{T}$ values of dense MgB$_{2}$ bulks prepared by the hot isostatic pressing, hot pressing, and spark plasma sintering methods. Therefore, we can conclude that the Mg premixing method is an effective way of preparing dense MgB$_{2}$ bulks with a high $B_\mathrm{T}$ by the IR process using amorphous B.

Published
2023
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20. Numerical simulation of flux jump behavior in REBaCuO ring bulks with an inhomogeneous Jc profile during pulsed-field magnetization

Author

Hirano, Tatsuya, Fujishiro, Hiroyuki, Naito, Tomoyuki, Ainslie, Mark D, Ainslie, Mark [0000-0003-0466-3680], Apollo - University of Cambridge Repository, Hirano, Tatsuya [0000-0003-1658-914X], Fujishiro, Hiroyuki [0000-0003-1483-835X], Naito, Tomoyuki [0000-0001-7594-3466], and Ainslie, Mark D [0000-0003-0466-3680]

Subjects
Paper, inhomogeneous Jc profile, pulsed field magnetization, Focus on Processing and Application of Superconducting Bulk Materials 2019, numerical simulation, flux jump, mechanical stress, bulk superconductor
Abstract

Funder: Japan Agency for Medical Research and Development; doi: https://doi.org/10.13039/100009619, We have investigated the electromagnetic and thermal properties of a REBaCuO ring bulk with an inhomogeneous critical current density, Jc, profile during pulsed field magnetization (PFM) using a numerical simulation and compared those to a bulk with a homogeneous Jc 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.

Published
2020

21. Modelling the record trapped field by pulsed field magnetisation of a composite bulk MgB2 superconducting ring

Author

Cientanni, Vito, Ainslie, Mark, Fujishiro, Hiroyuki, Takahashi, Keita, Engineering Department, University of Cambridge [UK] (CAM), and Université de Lorraine

Subjects
FEM, MgB2, [SPI.NRJ]Engineering Sciences [physics]/Electric power, PFM, Bulk superconductor
Abstract

International audience; The recent results of Hirano et al. [1] produced a record breaking trapped field of 1.61 T in a composite MgB2 ring, comprising copper plates and a soft iron yoke. Inspired by these results, a systematic numerical study was conducted to investigate the key parameters leading to the success of Hirano et al. [1]. Leveraging a finite-element method modelling framework in a commercial software package (COMSOL Multiphysics), we accurately repli- cated their experimental results [1]. Excellent quantitative agreement with the experimental data was achieved by making novel assumptions to the thermal physics, namely to that of the heat flow within the sample. The models are extended to investigate open & remaining questions; such as the influence of the iron yoke and the copper plates, and their interaction with the applied field. The results of the study illustrate how composite MgB2 rings may be optimised to trap even higher fields, and how the physics of their operation affect the trapped field distribution and magnitude. This submission disseminates the physics and modelling techniques used in detail, illustrating the novel modelling methods adopted to accurately simulate bulk composite MgB2 rings acting as trapped field magnets

Published
2021

23. Oxidation states and thermoelectric properties of BiCuSeO bulks fabricated under Bi or Se deficiencies in the nominal composition.

Author

Ishizawa, Mamoru, Yasuzato, Yuki, Fujishiro, Hiroyuki, Naito, Tomoyuki, Katsui, Hirokazu, and Goto, Takashi

Subjects
OXIDATION states, THERMOELECTRIC effects, BISMUTH, SELENIUM deficiency, ELECTRICAL resistivity, X-ray photoelectron spectroscopy
Abstract

We have fabricated the BiCuSeO bulks using raw materials with Bi or Se deficiencies in the nominal composition and investigated crystallographic, chemical compositional, and thermoelectric properties. Owing to the Bi or Se deficiencies in the starting composition, excessive elements and related compounds were deposited as impurity phases and the matrix phase is nearly the stoichiometric BiCuSeO phase. The electrical resistivity, ρ(T), of the bulks decreases and thermoelectric power, S(T), also decreases with increasing the contents of Bi or Se deficiencies in the starting composition in spite of the stoichiometric matrix phase. These results strongly suggest that, from the X-ray photoelectron spectroscopy measurements, the actual oxidation states of Bi and Cu deviate from the formal valences of stoichiometric Bi3+Cu1+Se2−O2−. The introduction of a small amount of Bi and Se vacancies is also suggested. As a result, mobile carriers are introduced and the ρ and S values are changed. The maximum thermoelectric dimensionless figure of merit of ZT = 0.60 was achieved at 773 K for the Bi1-xCuSeO samples (x =0.025 and 0.05) in the starting composition. These results are in clear contrast with the reported results for the Cu deficiency bulks. Using these results, we propose charge valence equations and the origin of the carriers in the present BiCuSeO bulks and discuss the influence of created carriers on the thermoelectric properties. [ABSTRACT FROM AUTHOR]

Published
2018
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24. Complex pulse magnetization process and mechanical properties of spark plasma sintered bulk MgB2

Author

MIRYALA, Muralidhar, ARVAPALLI, Sai Srikanth, SAKAI, Naomichi, MURAKAMI, Masato, MOCHIZUKI, Hidehiko, NAITO, Tomoyuki, FUJISHIRO, Hiroyuki, JIRSA, Milos, MURAKAMI, Akira, NOUDEM, Jacques, MIRYALA, Muralidhar, ARVAPALLI, Sai Srikanth, SAKAI, Naomichi, MURAKAMI, Masato, MOCHIZUKI, Hidehiko, NAITO, Tomoyuki, FUJISHIRO, Hiroyuki, JIRSA, Milos, MURAKAMI, Akira, and NOUDEM, Jacques

Abstract

High-density MgB2 bulks with superior mechanical and superconducting properties were fabricated using spark plasma sintering (SPS). The sharp superconducting transition at 37.5 K proved high quality of the superconductors. Critical current density significantly exceeded that of conventionally sintered bulks. Flux pinning diagrams indicated dominance of grain boundary pinning, with peak position at 0.2. SPS bulks showed improved mechanical properties with 8-times higher bending strength compared to dense hot isostatic pressed bulks. Trapped field was measured at 14 K and 20 K, 1 mm above the bulk’s surface, with applied pulse field up to 2 T. A local overheating together with a complex trapped field formation in the MgB2 bulks during pulse-field magnetization were studied to elucidate limitations of Pulse Field Magnetization.

Published
2021

26. Numerical evaluation of pulsed field magnetization in a bulk superconductor using energy minimization technique

Author

Kajikawa, Kazuhiro, Yokoo, Ryosuke, Tomachi, Kyohei, Enpuku, Keiji, Funaki, Kazuo, Hayashi, Hidemi, and Fujishiro, Hiroyuki

Subjects
Magnetic fields -- Analysis, Magnetization -- Analysis, Superconducting magnets -- Design and construction, Superconducting magnets -- Electric properties, Business, Electronics, Electronics and electrical industries
Abstract

The properties of pulsed field magnetization in the cylindrical superconductors are evaluated from the electromagnetic point of view. The effects of the histories of flux penetration and the aspect ratios of cross section on final trapped magnetic fields are examined toward an optimal design of a bulk superconductor magnet.

Published
2008

29. Flux motion studies by means of temperature measurement in magnetizing processes for HTSC bulks

Author

Fujishiro, Hiroyuki, Oka, Tetso, Yokoyama, Kazuya, Kaneyama, Masahiko, and Noto, Koshichi

Subjects
Magnetic fields -- Analysis, High temperature superconductors -- Thermal properties, Business, Electronics, Electronics and electrical industries
Abstract

The temperature rises deltaT(t) of cryo-cooled SmBaCuO bulk superconductor is measured by applying the pulse magnetic field from b(sub ex) = 3.01 to 5.42 T for various initial stage temperatures. The conclusion states that the maximum temperature rise delta(sub max) decreases with increasing T(sub s) under the identical B(sub ex).

Published
2004

33. Thermal conductivity, thermal diffusivity and thermoelectric power of Sm-based bulk superconductors

Author

Fujishiro, Hiroyuki and Kohayashi, Shuichi

Subjects
Superconducting magnets -- Research, Electrical equipment and supplies industry -- Research, Superconductors -- Thermal properties, Phonons -- Scattering, Thermal diffusivity -- Research, High temperature superconductors -- Research, Electrical engineering, Business, Electronics, Electronics and electrical industries, European Organization for Nuclear Research -- Conferences, meetings and seminars
Abstract

The ab-plane thermal conductivity, diffusivity and thermoelectric power of Sm-based bulk superconductors are measured. Results are summarized and discussed.

Published
2002

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