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Thermal analysis of the cryocooled superconducting magnet for the liquid helium-free hybrid magnet
Physica C 470 (2010) S1027–S1029
Contents lists available at ScienceDirect
Physica C journal homepage: www.elsevier.com/locate/physc
Thermal analysis of the cryocooled superconducting magnet for the liquid helium-free hybrid magnet Masayuki Ishizuka a,b,*, Takataro Hamajima a, Tomoyuki Itou c, Junji Sakuraba b, Gen Nishijima d, Satoshi Awaji d, Kazuo Watanabe d a
Graduate School of Engineering, Tohoku University, 6-6 Aramaki Aza Aoba, Aoba-ku, Sendai 980-8579, Japan Research and Development Center, Sumitomo Heavy Industries, Ltd., 19 Natsushima-chou, Yokosuka, Kanagawa 237-8555, Japan Ehime Works, Sumitomo Heavy Industries, Ltd., 5-2 Soubiraki-cho, Niihama, Ehime 792-8588, Japan d Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan b c
a r t i c l e
i n f o
Article history: Accepted 9 November 2009 Available online 12 November 2009 Keywords: Cryocooled superconducting magnet Hybrid magnet Magneto-science High magnetic field High-strength Nb3Sn wire
a b s t r a c t The liquid helium-free hybrid magnet, which consists of an outer large bore cryocooled superconducting magnet and an inner water-cooled resistive magnet, was developed for magneto-science in high fields. The characteristic features of the cryogen-free outsert superconducting magnet are described in detail in this paper. The superconducting magnet cooled by Gifford–McMahon cryocoolers, which has a 360 mm room temperature bore in diameter, was designed to generate high magnetic fields up to 10 T. The hybrid magnet has generated the magnetic field of 27.5 T by combining 8.5 T generation of the cryogen-free superconducting magnet with 19 T generation of the water-cooled resistive magnet. The superconducting magnet was composed of inner Nb3 Sn coils and outer NbTi coils. In particular, inner Nb3 Sn coils were wound using high-strength CuNi—NbTi=Nb3 Sn wires in consideration of large hoop stress. Although the cryocooled outsert superconducting magnet achieved 9.5 T, we found that the outsert magnet has a thermal problem to generate the designed maximum field of 10 T in the hybrid magnet operation. This problem is associated with unexpected AC losses in Nb3 Sn wires. Ó 2009 Elsevier B.V. All rights reserved.
Since continuously stable high magnetic fields were required for magneto-science, a liquid helium-free hybrid magnet was very useful for it. We have, therefore, designed and developed a 10 T cryocooled superconducting magnet with a /360 mm room temperature bore for the liquid helium-free hybrid magnet [1,2]. The developed cryocooled superconducting magnet could generate the field of 8.5 T in a hybrid magnet operation. As the result, the hybrid magnet has generated the resultant field of 27.5 T by adding 19 T from an inner water-resistive magnet. Although this result has already reported [3,4], causes that the cryocooled superconducting magnet was limited to generate the magnetic field of 8.5 T have not been described in detail yet. In this paper, we discuss about problems of unattained magnetic field against the designed one. The outline specification of the superconducting magnet is shown in Table 1. The superconducting coils were composed of inner Nb3 Sn coils and outer NbTi coils. Nb3 Sn coils were adopted reinforced Nb3 Sn wires for considering large hoop stress. A performance * Corresponding author. Address: Graduate School of Engineering, Tohoku University, 6-6 Aramaki Aza Aoba, Aoba-ku, Sendai 980-8579, Japan. E-mail address: [email protected] (M. Ishizuka). 0921-4534/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2009.11.066
of the cryocooled superconducting magnet was greatly influenced by thermal conditions of each component in a cryostat, because superconducting coils were cooled by a solid state thermal conduction in vacuum atmosphere. The heat load estimation is listed in Table 2. Estimated heat of 79.4 W was loaded into the 1st-stage of the GM-cryocooler and that of 4.5 W was loaded into the 2nd-stage during energizing. GM-cryocooler which had a cooling capacity of 35 W at 50 K on the 1st-stage and 1.5 W at 4.2 K on the 2nd-stage was applied for the cryocooled superconducting magnet. Moreover, since it was necessary to cool down below 4.2 K for the superconducting coils, four GM-cryocoolers were adopted as shown in Fig. 1. The energizing result of the hybrid magnet is shown in Fig. 2. Although the resultant field of 27.5 T could be generated by adding 8.5 T from the superconducting magnet to 19 T from the water-cooled resistive magnet, it was difficult for the superconducting magnet to generate 10 T of the designed maximum field by a temperature rise of the Nb3 Sn coil. When the superconducting magnet was energized in single operation, the inner surface temperature of the Nb3 Sn coil bobbin rose to 8 K at the beginning of the energizing in spite of rising to 5 K in other parts temperature. Further, the temperature of the Nb3 Sn coil inside was estimated to be higher than that of the Nb3 Sn coil
S1028
M. Ishizuka et al. / Physica C 470 (2010) S1027–S1029
Table 1 The outline specification of the superconducting magnet. Items
Inner coil
Outer coil
Section A Superconducting wire Wire diameter (mm) Coil inner diameter (mm) Coil outer diameter (mm) Coil height (mm) Operating current (A) Critical temperature (K) Maximum magnetic field (T) Central field generation (T) Total magnetic field (T) Stored energy (MJ) Hoop stress (MPa)
Section B
Section C
Section D
High-strength CuNi–NbTi/ Nb3 Sn 1.85 1.80
2.00
1.60
400
495
605
670
480
580
665
755
450
500
400
NbTi
246
550 350
8.5
9.5
6.5
7.5
11.5
8.5
5.5
2.6
2.3
2.4
2.1
3.2
155
130
10 6.5 161
155
Table 2 The heat load estimation.
26.0 38.2 0.4 8.5 6.3
Total
54.0
79.4
0.1 0.2 0 0.5 0 0.2
0.1 0.2 0.9 0.5 2.8 0.2
Total (W)
0.9
4.5
bobbin. This result indicated that the temperature distribution existed in the cryocooled superconducting coils. It was also found that the 3 K temperature difference between the superconducting coil electrode and the coil bobbin was caused by a decrease of thermal conductive passes due to exfoliation from the coil bobbin of the coil itself. Moreover, the temperature rise of the Nb3 Sn coil was due to a large hysteresis loss by a thick Nb3 Sn layer formed on Nb-barrier component in high-strength Nb3 Sn wire. Two Nb-barrier layers existed in each reinforced Nb3 Sn wire as shown in Fig. 3. The Nb3 Sn layer on Nb-barrier indicated a thickness of about 2 lm which was thicker than expected thickness of 1 lm. In order to reduce hysteresis loss, adopting a Ta-barrier is effective as the barrier material compared with the Nb-barrier because no Nb3 Sn layer is formed on the Ta-barrier. In summary, it was discussed that problems of unattained magnetic field were due to the temperature rise of the Nb3 Sn coil. This
water-cooled resistive coil 15 kA 348 A 340 A
20 kA
400
NbTi coil
15
300 200
176 A
202 A
222 A
10
Nb3Sn coil
100
5 0
0 9 8
25 20
inner surface of the Nb3Sn coil bobbin the top of the thermal shield Nb3Sn coil electrode
7 6
NbTi coil electrode
the bottom of the thermal shield
55 50 45 40
5
35
4
30
3
25
the bottom of the Nb3Sn coil bobbin
2
20
30
23.1 T
27.5 T
25
Thermal shield temperature [K]
2nd-stage Radiation (W) Measuring wires (W) Joule heating (W) Support structures (W) AC losses Bi-2223 current leads (W)
500
Coil temperature [K]
26.0 21.3 0.4 0 6.3
Fig. 1. The liquid helium-free hybrid magnet.
Superconducting coil curernt [A]
Full energized
Magnetic field [T]
No operating current
1st-stage (W) Radiation Copper current leads Measuring wires Joule heating Support structures
Water-cooled resistive coil current [kA]
Heat load
9.5 T
20 8.5 T
15 10 5 0
0
100
200
300
400
500
600
Time [min] Fig. 2. The enerziging result of the hybrid magnet.
temperature rise was caused by the decrease of thermal conductive passes by exfoliation from the coil bobbin of the coil itself and the
M. Ishizuka et al. / Physica C 470 (2010) S1027–S1029
large hysteresis loss by the thick Nb3 Sn layer formed on Nb-barrier component in Nb3 Sn wires.
Cu Outer Nb-barrier Nb3Sn and bronze
References
Inner Nb-barrier CuNi-NbTi
1.85 mm
S1029
1.80 mm
Fig. 3. Cross-sectional view of high-strength Nb3 Sn wires.
[1] T. Hasebe, S. Okada, M. Ishizuka, T. Tsurudome, T. Ito, H. Ookuba, J. Sakuraba, K. Watanabe, S. Awaji, K. Koyama, G. Nishijima, K. Takahashi, IEEE Trans. Appl. Supercond. 14 (2) (2004) 368–371. [2] K. Watanabe, G. Nishijima, S. Awaji, K. Takahashi, K. Koyama, M. Motokawa, M. Ishizuka, T. Hasebe, J. Sakuraba, IEEE Trans. Appl. Supercond. 14 (2) (2004) 388– 392. [3] K. Watanabe, G. Nishijima, S. Awaji, K. Takahashi, K. Koyama, N. Kobayashi, M. Ishizuka, T. Itou, T. Tsurudome, J. Sakuraba, IEEE Trans. Appl. Supercond. 16 (2) (2006) 934–939. [4] T. Ito, M. Ishizuka, T. Tsurudome, H. Ookubo, J. Sakuraba, S. Awaji, G. Nishijima, K. Koyama, K. Takahashi, K. Watanabe, Adv. Cryogenic. Eng. 51 (2006) 1743– 1748.
Contents lists available at ScienceDirect
Physica C journal homepage: www.elsevier.com/locate/physc
Thermal analysis of the cryocooled superconducting magnet for the liquid helium-free hybrid magnet Masayuki Ishizuka a,b,*, Takataro Hamajima a, Tomoyuki Itou c, Junji Sakuraba b, Gen Nishijima d, Satoshi Awaji d, Kazuo Watanabe d a
Graduate School of Engineering, Tohoku University, 6-6 Aramaki Aza Aoba, Aoba-ku, Sendai 980-8579, Japan Research and Development Center, Sumitomo Heavy Industries, Ltd., 19 Natsushima-chou, Yokosuka, Kanagawa 237-8555, Japan Ehime Works, Sumitomo Heavy Industries, Ltd., 5-2 Soubiraki-cho, Niihama, Ehime 792-8588, Japan d Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan b c
a r t i c l e
i n f o
Article history: Accepted 9 November 2009 Available online 12 November 2009 Keywords: Cryocooled superconducting magnet Hybrid magnet Magneto-science High magnetic field High-strength Nb3Sn wire
a b s t r a c t The liquid helium-free hybrid magnet, which consists of an outer large bore cryocooled superconducting magnet and an inner water-cooled resistive magnet, was developed for magneto-science in high fields. The characteristic features of the cryogen-free outsert superconducting magnet are described in detail in this paper. The superconducting magnet cooled by Gifford–McMahon cryocoolers, which has a 360 mm room temperature bore in diameter, was designed to generate high magnetic fields up to 10 T. The hybrid magnet has generated the magnetic field of 27.5 T by combining 8.5 T generation of the cryogen-free superconducting magnet with 19 T generation of the water-cooled resistive magnet. The superconducting magnet was composed of inner Nb3 Sn coils and outer NbTi coils. In particular, inner Nb3 Sn coils were wound using high-strength CuNi—NbTi=Nb3 Sn wires in consideration of large hoop stress. Although the cryocooled outsert superconducting magnet achieved 9.5 T, we found that the outsert magnet has a thermal problem to generate the designed maximum field of 10 T in the hybrid magnet operation. This problem is associated with unexpected AC losses in Nb3 Sn wires. Ó 2009 Elsevier B.V. All rights reserved.
Since continuously stable high magnetic fields were required for magneto-science, a liquid helium-free hybrid magnet was very useful for it. We have, therefore, designed and developed a 10 T cryocooled superconducting magnet with a /360 mm room temperature bore for the liquid helium-free hybrid magnet [1,2]. The developed cryocooled superconducting magnet could generate the field of 8.5 T in a hybrid magnet operation. As the result, the hybrid magnet has generated the resultant field of 27.5 T by adding 19 T from an inner water-resistive magnet. Although this result has already reported [3,4], causes that the cryocooled superconducting magnet was limited to generate the magnetic field of 8.5 T have not been described in detail yet. In this paper, we discuss about problems of unattained magnetic field against the designed one. The outline specification of the superconducting magnet is shown in Table 1. The superconducting coils were composed of inner Nb3 Sn coils and outer NbTi coils. Nb3 Sn coils were adopted reinforced Nb3 Sn wires for considering large hoop stress. A performance * Corresponding author. Address: Graduate School of Engineering, Tohoku University, 6-6 Aramaki Aza Aoba, Aoba-ku, Sendai 980-8579, Japan. E-mail address: [email protected] (M. Ishizuka). 0921-4534/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2009.11.066
of the cryocooled superconducting magnet was greatly influenced by thermal conditions of each component in a cryostat, because superconducting coils were cooled by a solid state thermal conduction in vacuum atmosphere. The heat load estimation is listed in Table 2. Estimated heat of 79.4 W was loaded into the 1st-stage of the GM-cryocooler and that of 4.5 W was loaded into the 2nd-stage during energizing. GM-cryocooler which had a cooling capacity of 35 W at 50 K on the 1st-stage and 1.5 W at 4.2 K on the 2nd-stage was applied for the cryocooled superconducting magnet. Moreover, since it was necessary to cool down below 4.2 K for the superconducting coils, four GM-cryocoolers were adopted as shown in Fig. 1. The energizing result of the hybrid magnet is shown in Fig. 2. Although the resultant field of 27.5 T could be generated by adding 8.5 T from the superconducting magnet to 19 T from the water-cooled resistive magnet, it was difficult for the superconducting magnet to generate 10 T of the designed maximum field by a temperature rise of the Nb3 Sn coil. When the superconducting magnet was energized in single operation, the inner surface temperature of the Nb3 Sn coil bobbin rose to 8 K at the beginning of the energizing in spite of rising to 5 K in other parts temperature. Further, the temperature of the Nb3 Sn coil inside was estimated to be higher than that of the Nb3 Sn coil
S1028
M. Ishizuka et al. / Physica C 470 (2010) S1027–S1029
Table 1 The outline specification of the superconducting magnet. Items
Inner coil
Outer coil
Section A Superconducting wire Wire diameter (mm) Coil inner diameter (mm) Coil outer diameter (mm) Coil height (mm) Operating current (A) Critical temperature (K) Maximum magnetic field (T) Central field generation (T) Total magnetic field (T) Stored energy (MJ) Hoop stress (MPa)
Section B
Section C
Section D
High-strength CuNi–NbTi/ Nb3 Sn 1.85 1.80
2.00
1.60
400
495
605
670
480
580
665
755
450
500
400
NbTi
246
550 350
8.5
9.5
6.5
7.5
11.5
8.5
5.5
2.6
2.3
2.4
2.1
3.2
155
130
10 6.5 161
155
Table 2 The heat load estimation.
26.0 38.2 0.4 8.5 6.3
Total
54.0
79.4
0.1 0.2 0 0.5 0 0.2
0.1 0.2 0.9 0.5 2.8 0.2
Total (W)
0.9
4.5
bobbin. This result indicated that the temperature distribution existed in the cryocooled superconducting coils. It was also found that the 3 K temperature difference between the superconducting coil electrode and the coil bobbin was caused by a decrease of thermal conductive passes due to exfoliation from the coil bobbin of the coil itself. Moreover, the temperature rise of the Nb3 Sn coil was due to a large hysteresis loss by a thick Nb3 Sn layer formed on Nb-barrier component in high-strength Nb3 Sn wire. Two Nb-barrier layers existed in each reinforced Nb3 Sn wire as shown in Fig. 3. The Nb3 Sn layer on Nb-barrier indicated a thickness of about 2 lm which was thicker than expected thickness of 1 lm. In order to reduce hysteresis loss, adopting a Ta-barrier is effective as the barrier material compared with the Nb-barrier because no Nb3 Sn layer is formed on the Ta-barrier. In summary, it was discussed that problems of unattained magnetic field were due to the temperature rise of the Nb3 Sn coil. This
water-cooled resistive coil 15 kA 348 A 340 A
20 kA
400
NbTi coil
15
300 200
176 A
202 A
222 A
10
Nb3Sn coil
100
5 0
0 9 8
25 20
inner surface of the Nb3Sn coil bobbin the top of the thermal shield Nb3Sn coil electrode
7 6
NbTi coil electrode
the bottom of the thermal shield
55 50 45 40
5
35
4
30
3
25
the bottom of the Nb3Sn coil bobbin
2
20
30
23.1 T
27.5 T
25
Thermal shield temperature [K]
2nd-stage Radiation (W) Measuring wires (W) Joule heating (W) Support structures (W) AC losses Bi-2223 current leads (W)
500
Coil temperature [K]
26.0 21.3 0.4 0 6.3
Fig. 1. The liquid helium-free hybrid magnet.
Superconducting coil curernt [A]
Full energized
Magnetic field [T]
No operating current
1st-stage (W) Radiation Copper current leads Measuring wires Joule heating Support structures
Water-cooled resistive coil current [kA]
Heat load
9.5 T
20 8.5 T
15 10 5 0
0
100
200
300
400
500
600
Time [min] Fig. 2. The enerziging result of the hybrid magnet.
temperature rise was caused by the decrease of thermal conductive passes by exfoliation from the coil bobbin of the coil itself and the
M. Ishizuka et al. / Physica C 470 (2010) S1027–S1029
large hysteresis loss by the thick Nb3 Sn layer formed on Nb-barrier component in Nb3 Sn wires.
Cu Outer Nb-barrier Nb3Sn and bronze
References
Inner Nb-barrier CuNi-NbTi
1.85 mm
S1029
1.80 mm
Fig. 3. Cross-sectional view of high-strength Nb3 Sn wires.
[1] T. Hasebe, S. Okada, M. Ishizuka, T. Tsurudome, T. Ito, H. Ookuba, J. Sakuraba, K. Watanabe, S. Awaji, K. Koyama, G. Nishijima, K. Takahashi, IEEE Trans. Appl. Supercond. 14 (2) (2004) 368–371. [2] K. Watanabe, G. Nishijima, S. Awaji, K. Takahashi, K. Koyama, M. Motokawa, M. Ishizuka, T. Hasebe, J. Sakuraba, IEEE Trans. Appl. Supercond. 14 (2) (2004) 388– 392. [3] K. Watanabe, G. Nishijima, S. Awaji, K. Takahashi, K. Koyama, N. Kobayashi, M. Ishizuka, T. Itou, T. Tsurudome, J. Sakuraba, IEEE Trans. Appl. Supercond. 16 (2) (2006) 934–939. [4] T. Ito, M. Ishizuka, T. Tsurudome, H. Ookubo, J. Sakuraba, S. Awaji, G. Nishijima, K. Koyama, K. Takahashi, K. Watanabe, Adv. Cryogenic. Eng. 51 (2006) 1743– 1748.