Superconductor Science and Technology

VIEWPOINT • OPEN ACCESSNew type of hybrid magnetic lens for practical applications of HTS bulk
superconductors
To cite this article: Shinya Nariki 2021 Supercond. Sci. Technol. 34 030501

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Superconductor Science and Technology
Supercond. Sci. Technol. 34 (2021) 030501 (3pp)

https://doi.org/10.1088/1361-6668/abcb47

Viewpoint

New type of hybrid magnetic lensfor practical applications of HTS bulk
superconductors
This is a viewpoint on the letter by S Namba et al 2019 (Supercond. Sci. Technol.
32 12LT03).
Advanced Technology ResearchHigh-T c bulk superconductors such as RE-Ba-Cu-O (RE: a rare earth element)
Laboratory, Nippon Steeland MgB2 can trap high magnetic fields at low temperatures. The magnetizedCorporation, 20-1 Sintomi,
bulk superconductors can be used as a compact, high strength trapped field
Futtsu-shi, Chiba 293-8511, Japanmagnet (TFM) for many practical applications.
E-mail:nariki.qy2.shinya@jp.nipponsteel.com
However, the trapped field is limited experimentally by the poor mechanicalstrength of the brittle ceramic material. A large Lorentz force is developed in thebulk during the magnetization process, which sometimes results in crack
formation and propagation, leading to eventual mechanical failure. Remarkableprogress has been made in increasing trapped fields with mechanicalreinforcement using epoxy resin or shrink-fit stainless steel. Up to now, trappedmagnetic fields over 17 T are achieved in RE-Ba-Cu-O disk pairs throughfield-cooling magnetization (FCM) [1, 2]. The group of Iwate University andUniversity of Cambridge has been working on the magnetization techniques ofbulk superconductors. Recently, Fujishiro et al [3] suggested the possibility toachieve a trapped field over 20 T in the RE-Ba-Cu-O disk pair by FCM method
using numerical simulation. However, FCM requires a high applied fieldgenerated by a superconducting magnet, which has limitations for practicalapplications. Pulsed-field magnetization (PFM) is the most practical method tomagnetize bulk superconductors since it is a faster magnetizing process thanFCM and is an inexpensive and mobile experimental setup using a copper pulsed
magnet. A trapped field of 5.2 T by PFM is reported in an HTS bulk [4]. A flux
jump assisted multi-pulse magnetization has recently been reported led to atrapped field of 5.3 T in Gd-Ba-Cu-O bulk [5]. However, the maximum trappedfield by PFM is still significantly lower than that achieved by FCM.
The magnetic lens was reported by Matsumoto et al for the first time in 2003
[6]. In this device, magnetic flux concentration was carried out by using hollow
cylinders made of low- and high-temperatures superconductors. It is important todevelop compact high magnetic field systems. A magnetic lens made of a
Gd-Ba-Cu-O bulk was placed in a superconducting magnet. An external field of
2 T was amplified to 5.65 T at the center of the lens, demonstrating magnetic flux
concentration by a Gd-Ba-Cu-O magnetic lens [7]. A concentrated field ofBc = 12.42 T has been obtained at 20 K for a background field of 8 T using a
Gd-Ba-Cu-O bulk magnetic lens, and Bc = 30.35 T at 4.2 K achieved for abackground field of 28.3 T [8].
Shinya Nariki

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Supercond. Sci. Technol. 34 (2021) 030501

Viewpoint

Since the magnetic lens effect vanishes after the applied field decreased tozero, the external magnet must be operated continuously, which consumes energy
and is not environmentally friendly. In 2018, the new concept of a hybrid trappedfield magnet lens (HTFML) was reported [9]. This consists of a TFM cylinder
exploiting the ‘vortex pinning effect’, combined with a bulk magnetic lens
exploiting the ‘diamagnetic shielding effect’. The HTFML can reliably generate aconcentrated magnetic field in the central bore of the magnetic lens that is higher
than both the trapped field in the single cylindrical bulk TFM and the external
magnetizing field, even after the externally applied field decreases to zero. In thisletter, the first experimental realization using HTFML device was presented.
In the HTFML consisting of a Gd-Ba-Cu-O bulk lens and a MgB2 bulk TMF
cylinder, a maximum concentrated magnetic field of Bc = 3.55 T was achieved at
the central bore after removing the applied field of 2.0 T at 20 K. Although, theexperimental value of Bc = 3.55 T is lower than the value predicted fromnumerical simulation, the concentrated field will be enhanced with the designoptimization of HTFML.
A ring-shaped RE-Ba-Cu-O bulk superconductor is a strong candidate for
NMR and MRI systems [10]. An Eu-Ba-Cu-O bulk is suitable for a compact
NMR magnet because of its low relative magnetic permeability. The HTFML
using a RE-Ba-Cu-O bulk TFM cylinder and a RE-Ba-Cu-O lens pair can be
expected to achieve higher HTFM effect compared to that using a MgB2 bulk
TFM cylinder [9, 11, 12]. Most recently, the performance of HTFML consistingof an Eu-Ba-Cu-O bulk TFM cylinder and a Gd-Ba-Cu-O lens was reported [13].
At 77 K, a concentrated magnetic field of Bc = 0.8 T was experimentallyconfirmed after removing an applied magnetic field of 0.5 T. The concentrated
magnetic field will be enhanced with lowering the operating temperature. In thisletter, the authors mentioned that the goal of a concentrated magnetic field is over
10 T (e.g. Bc = 13.5 T) when an applied field is 10 T. It is extremely effective for
an improvement in the resolution of a compact NMR. The realization of themagnetic field over 10 T in an open space using the HTML system will accelerate
practical applications of bulk superconductors.
ORCID iD

Shinya Nariki  https://orcid.org/0000-0001-6691-8437
References[1] Tomita M and Murakami M 2003 High-temperature superconductor bulk magnets that can
trap magnetic fields of over 17 tesla at 29 K Nature 421 517–20[2] Durrell J H et al 2014 A trapped field of 17.6 T in melt-processed, bulk Gd-Ba-Cu-O
reinforced with shrink-fit steel Supercond. Sci. Technol. 27 082001[3] Fujishiro H, Naito T and Awaji S 2019 Proposal of an effective mechanical reinforcement
structure for a REBaCuO disk bulk pair by full metal encapsulation to achieve a higher
trapped field over 20 T Supercond. Sci. Technol. 32 045005[4] Fujishiro H, Tateiwa T, Fujiwara A, Oka T and Hayashi H 2006 Higher trapped field over 5 T
on HTSC bulk by modified pulse field magnetizing Physica C 334–8 445–8[5] Zhou D, Ainslie M D, Srpčič J, Huang K, Shi Y, Dennis A R, Cardwell D A, Durrell J H,Boll M and Filipenko M 2018 Exploiting flux jumps for pulsed field magnetization
Supercond. Sci. Technol. 31 105005[6] Matsumoto S, Kiyoshi T, Asano T, Ozaki O, Koyanagi K, Fujihira J and Wada H 2003
Magnetic flux concentration and magnetic force enhancement using YBCO cylinders IEEE
Trans. Appl. Supercond. 13 1652–5[7] Kiyoshi T, Choi S, Matsumoto S, Asano T and Uglietti D 2009 Magnetic flux concentrator
using Gd-Ba-Cu-O bulk superconductors IEEE Trans. Appl. Supercond. 19 2174–7[8] Choi S, Yoon J-H, Lee B-S, Won M-S, Ok J-W, Zhang Z-Y, Kiyoshi T, Matsumoto S andLee S-H 2012 Magnetic lens effect using Gd-Ba-Cu-O bulk superconductor in very highmagnetic field J. Appl. Phys. 111 07E728
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Supercond. Sci. Technol. 34 (2021) 030501

Viewpoint[9] Takahashi K, Fujishiro H and Ainslie M D 2018 A new concept of a hybrid trapped fieldmagnet lens Supercond. Sci. Technol. 31 044005[10] Nakamura T, Tamada D, Yanagi Y, Itoh Y, Nemoto T, Utumi H and Kose K 2015 Developmentof a superconducting bulk magnet for NMR and MRI J. Magn. Reson. 259 68–75[11] Namba S, Fujishiro H, Ainslie M D, Takahashi K, Namburi D K, Zhou D and Naito T 2019
Design optimization of a hybrid trapped field magnet lens (HTFML) IEEE Trans. Appl.
Supercond. 29 6801605[12] Shinden M, Namba S, Hirano T, Fujishiro H, Naito T and Ainslie M D 2000 Numericalsimulation of a hybrid trapped field magnet lens (HTFML) magnetized by pulsed fields J.
Phys.: Conf. Ser. 1590 012048[13] Namba S, Fujishiro H, Naito T, Ainslie M D and Zhou D 2000 Realisation of hybrid trappedfield magnetic lens (HTFML) consisting of REBCO bulk lens and REBCO bulk cylinder at
77 K J. Phys.: Conf. Ser. 1559 012079

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