- Email: [email protected]
Measurement of the magnetic field of resin-impregnated bulk superconductor annuli
Physica C 470 (2010) S33–S34
Contents lists available at ScienceDirect
Physica C journal homepage: www.elsevier.com/locate/physc
Measurement of the magnetic field of resin-impregnated bulk superconductor annuli Masaru Tomita a,*, Yusuke Fukumoto b, Kenji Suzuki a, Yukikazu Iwasa b a b
Railway Technical Research Institute/Applied Superconductivity Laboratory, 2-8-38 Hikari-Cho Kokubunji-Shi, Tokyo 185-8540, Japan Massachusetts Institute of Technology/Francis Bitter Magnet Laboratory, 170 Albany Street, Cambridge, MA 02139-4307, USA
a r t i c l e
i n f o
Article history: Accepted 8 January 2010 Available online 13 January 2010 Keywords: Bulk superconductor Mechanical property Epoxy resins Field trapping Field homogeneity NMR magnet
a b s t r a c t Large single-grain bulk RE–Ba–Cu–O (RE: rare earth elements) superconductors can trap large fields exceeding several teslas and thus can function as very strong quasi-permanent magnets. We have found that the resin can penetrate into a bulk superconductor, when the sample was immersed in molten resin. Hence, resin impregnation was effective in improving mechanical properties. Three bulk superconductors‘ annuli with resin impregnation, each 50-mm i.d. and 80-mm o.d. was built and energized, by a field-cool method, to generate, in a bath of liquid nitrogen, a persistent trapped field of 1.62 T. Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental
Recent advancement in the fabrication techniques has allowed the production of large single-grain bulk RE–Ba–Cu–O (RE: rare earth elements) superconductors with large critical current density (Jc) values. Today, the technique is poised to expand and accelerate the application of the bulk to many areas, including those heretofore considered unfeasible. One such promising area of applications is a compact, high-field magnet suitable for NMR microspectroscopy, a tool used extensively in the pharmaceutical industry for drug discovery and development [1]. A systematic study to identify crack mechanisms in high-temperature bulk superconductor caused chiefly by cooling and electromagnetic forces, has resulted in a successful technique to produce high-performance bulks applicable in a high magnetic field. The technique infiltrates cracks with epoxy resin; impregnation with a low-melting metal improves thermal stability, enabling the bulks to trap a field of 17.24 T, the highest field ever trapped by a bulk superconductor [2]. To complete a uniform magnetic field, we measured the trapping field that depended on number of resin-impregnated bulk superconductor annuli. The results of field trapping measurements on such bulk superconductors will be reported.
Resin-impregnated bulk superconductor annuli is shown in Fig. 1. Bulk Gd–Ba–Cu–O was immersed in the molten epoxy resin at 70 °C and held for 30 min–1 h, during which period the gas was evacuated with a rotary pump to impregnate resin into the bulk. Finally, resin-impregnated bulk samples were heated 80 °C for 6 h and at 120 °C for 2 h under ambient at pressure. Epoxy resin used in the present experiment was composed of phenol–formaldehyde and polyamideimide, added as hardening material. These compounds were mixed in a weight ratio of 100:32. Specification of bulk superconductor is as shown in Table 1. The size of the bulk is within resin layer on the surface. The field trapping experiments were conducted by magnetizing the samples using a 3 T superconducting solenoid. For characterization at 77 K, the samples were cooled by liquid nitrogen in 3 T. After reducing the external field to zero, the axial component of the trapped magnetic flux density at the center of bulk annuli was measured using hall sensors.
* Corresponding author. Tel.: +81 42 573 7297; fax: +81 42 573 7360. E-mail address: [email protected] (M. Tomita). 0921-4534/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2010.01.020
3. Result and discussion The magnetic field distribution of bulk surface is as shown in Fig. 2. The result, which plotted the height axially (h) direction, is as shown in Fig. 3, and the result, which plotted the radius (r) direction of the central part, is as shown in Fig. 4. Each result shows that a magnetic field distribution also changes with the number of bulks. The magnetic field at the center
S34
M. Tomita et al. / Physica C 470 (2010) S33–S34
Fig. 1. Resin-impregnated bulk superconductor annuli.
Fig. 3. Magnetic field in height axially (h) direction (h = 0:center).
Table 1 Specification of bulk superconductor annuli. Inner diameter (except resin layer) Outer diameter (except resin layer) Height (except resin layer)
47 mm (50 mm) 87 mm (80 mm) 22 mm (20 mm)
Fig. 4. Magnetic field in radius (r) direction.
tral portion rises, and becomes flatter. In addition, uniformity in a radial magnetic field improves. An expanded version of this method, with many large-bore bulk superconductors, can potentially lead to a constant-field magnet having a high spatial homogeneity with many useful applications. Fig. 2. Magnetic field on surface of bulk annuli.
References of bulk annuli was 0.75 T. However, the magnetic field at the center improves to 1.62 T if three bulks annuli are piled up. When the number of layers of bulks increases, the magnetic field in the cen-
[1] Y. Iwasa, S. Hahn, M. Tomita, H. Lee, J. Bascunan A, IEEE Transactions on Applied Superconductivity 15 (2005) 2352. [2] M. Tomita, M. Murakami, Nature 421 (2003) 517.
Contents lists available at ScienceDirect
Physica C journal homepage: www.elsevier.com/locate/physc
Measurement of the magnetic field of resin-impregnated bulk superconductor annuli Masaru Tomita a,*, Yusuke Fukumoto b, Kenji Suzuki a, Yukikazu Iwasa b a b
Railway Technical Research Institute/Applied Superconductivity Laboratory, 2-8-38 Hikari-Cho Kokubunji-Shi, Tokyo 185-8540, Japan Massachusetts Institute of Technology/Francis Bitter Magnet Laboratory, 170 Albany Street, Cambridge, MA 02139-4307, USA
a r t i c l e
i n f o
Article history: Accepted 8 January 2010 Available online 13 January 2010 Keywords: Bulk superconductor Mechanical property Epoxy resins Field trapping Field homogeneity NMR magnet
a b s t r a c t Large single-grain bulk RE–Ba–Cu–O (RE: rare earth elements) superconductors can trap large fields exceeding several teslas and thus can function as very strong quasi-permanent magnets. We have found that the resin can penetrate into a bulk superconductor, when the sample was immersed in molten resin. Hence, resin impregnation was effective in improving mechanical properties. Three bulk superconductors‘ annuli with resin impregnation, each 50-mm i.d. and 80-mm o.d. was built and energized, by a field-cool method, to generate, in a bath of liquid nitrogen, a persistent trapped field of 1.62 T. Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental
Recent advancement in the fabrication techniques has allowed the production of large single-grain bulk RE–Ba–Cu–O (RE: rare earth elements) superconductors with large critical current density (Jc) values. Today, the technique is poised to expand and accelerate the application of the bulk to many areas, including those heretofore considered unfeasible. One such promising area of applications is a compact, high-field magnet suitable for NMR microspectroscopy, a tool used extensively in the pharmaceutical industry for drug discovery and development [1]. A systematic study to identify crack mechanisms in high-temperature bulk superconductor caused chiefly by cooling and electromagnetic forces, has resulted in a successful technique to produce high-performance bulks applicable in a high magnetic field. The technique infiltrates cracks with epoxy resin; impregnation with a low-melting metal improves thermal stability, enabling the bulks to trap a field of 17.24 T, the highest field ever trapped by a bulk superconductor [2]. To complete a uniform magnetic field, we measured the trapping field that depended on number of resin-impregnated bulk superconductor annuli. The results of field trapping measurements on such bulk superconductors will be reported.
Resin-impregnated bulk superconductor annuli is shown in Fig. 1. Bulk Gd–Ba–Cu–O was immersed in the molten epoxy resin at 70 °C and held for 30 min–1 h, during which period the gas was evacuated with a rotary pump to impregnate resin into the bulk. Finally, resin-impregnated bulk samples were heated 80 °C for 6 h and at 120 °C for 2 h under ambient at pressure. Epoxy resin used in the present experiment was composed of phenol–formaldehyde and polyamideimide, added as hardening material. These compounds were mixed in a weight ratio of 100:32. Specification of bulk superconductor is as shown in Table 1. The size of the bulk is within resin layer on the surface. The field trapping experiments were conducted by magnetizing the samples using a 3 T superconducting solenoid. For characterization at 77 K, the samples were cooled by liquid nitrogen in 3 T. After reducing the external field to zero, the axial component of the trapped magnetic flux density at the center of bulk annuli was measured using hall sensors.
* Corresponding author. Tel.: +81 42 573 7297; fax: +81 42 573 7360. E-mail address: [email protected] (M. Tomita). 0921-4534/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2010.01.020
3. Result and discussion The magnetic field distribution of bulk surface is as shown in Fig. 2. The result, which plotted the height axially (h) direction, is as shown in Fig. 3, and the result, which plotted the radius (r) direction of the central part, is as shown in Fig. 4. Each result shows that a magnetic field distribution also changes with the number of bulks. The magnetic field at the center
S34
M. Tomita et al. / Physica C 470 (2010) S33–S34
Fig. 1. Resin-impregnated bulk superconductor annuli.
Fig. 3. Magnetic field in height axially (h) direction (h = 0:center).
Table 1 Specification of bulk superconductor annuli. Inner diameter (except resin layer) Outer diameter (except resin layer) Height (except resin layer)
47 mm (50 mm) 87 mm (80 mm) 22 mm (20 mm)
Fig. 4. Magnetic field in radius (r) direction.
tral portion rises, and becomes flatter. In addition, uniformity in a radial magnetic field improves. An expanded version of this method, with many large-bore bulk superconductors, can potentially lead to a constant-field magnet having a high spatial homogeneity with many useful applications. Fig. 2. Magnetic field on surface of bulk annuli.
References of bulk annuli was 0.75 T. However, the magnetic field at the center improves to 1.62 T if three bulks annuli are piled up. When the number of layers of bulks increases, the magnetic field in the cen-
[1] Y. Iwasa, S. Hahn, M. Tomita, H. Lee, J. Bascunan A, IEEE Transactions on Applied Superconductivity 15 (2005) 2352. [2] M. Tomita, M. Murakami, Nature 421 (2003) 517.