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Manufacturing design and development of the current feeders and coil terminal boxes for JT-60SA
Fusion Engineering and Design 98–99 (2015) 1094–1097
Contents lists available at ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Manufacturing design and development of the current feeders and coil terminal boxes for JT-60SA Kaname Kizu a,∗ , Haruyuki Murakami a , Kyohei Natsume a , Katsuhiko Tsuchiya a , Yoshihiko Koide a , Kiyoshi Yoshida a , Tetsuhiro Obana b , Shinji Hamaguchi b , Kazuya Takahata b a b
Japan Atomic Energy Agency, Naka, Ibaraki 311-0193, Japan National Institute for Fusion Science, Toki, Gifu 509-5292, Japan
h i g h l i g h t s • • • •
Key components for current feeding system for JT-60SA were developed and tested. The joint resistance of feeder joint sample was 1.7 n at 2 T, 20 kA. Trial manufacturing of crank shaped feeder showed the max. dimensional error of 3 mm. Feeder insulation samples showed >60 MPa in shear strength at 77 K.
a r t i c l e
i n f o
Article history: Received 17 September 2014 Received in revised form 24 March 2015 Accepted 8 April 2015 Available online 30 April 2015 Keywords: Coil terminal box Current feeder Electrical joint JT-60SA NbTi
a b s t r a c t Feeders and coil terminal boxes (CTBs) of the superconducting magnets for JT-60SA have been designed. A small tool which can connect soldering joint with vertical direction in the cryostat has been developed. The joint resistance of the sample showed 1.7 n at 2 T, 4.2 K, 20 kA which is within the requirement of <5 n. A prototype feeder in CTB with crank shape was manufactured. The maximum dimensional error was 3 mm being within the requirement of ±10 mm. Feeder insulation samples showed a shear strength >60 MPa which is much higher than the requirement of 10 MPa as derived from analysis. Since all the manufacturing processes concerned have been proof-tested, the production of feeders and CTBs has been released. © 2015 Elsevier B.V. All rights reserved.
1. Introduction The superconducting coil system for JT-60SA consists of 18 Toroidal Field (TF) coils and 10 Poloidal Field (PF) coils [1]. PF coils include a Central Solenoid (CS) with 4 modules, and 6 Equilibrium Field (EF) coils. The current of TF and PF coils are 25.7 and 20 kA, respectively. The current feeding system consists of in-cryostat feeders and Coil Terminal Boxes (CTBs) [2,3]. CTBs contain feeders and High Temperature Superconductor Current Leads (HTS CLs) [4]. Because of the available space in torus building, five CTBs (CT0105) are spread around the main cryostat as shown in Fig. 1. CTBs, in-cryostat feeders and superconductor for PF feeders [5] are procured by Japan. HTS CLs and superconductor for TF feeder [6] are procured by Europe.
∗ Corresponding author. E-mail address: [email protected] (K. Kizu). http://dx.doi.org/10.1016/j.fusengdes.2015.04.030 0920-3796/© 2015 Elsevier B.V. All rights reserved.
There were several concerns for the production of feeder components. The first was the manufacturability of electrical joint in the narrow space in the cryostat after the coil installation. The second was the manufacturability of bent feeder to reduce the reaction force of HTS CL by thermal contraction. In this paper, the trial manufacturing and test results of feeder components are described. 2. Design of CTB and feeder Fig. 2 shows the structure of CTB. Normal conducting busbars from power supply are connected to HTS CLs. Feeders consisting of superconductors are connected to the cold ends of HTS CLs, and are routed to main cryostat. Feeders in CTB are connected to the incryostat feeders through mid joints in the vicinity of cryostat wall. The in-cryostat feeders are connected to the terminal joints of coils. Since the maximum (max.) allowable magnetic field of HTS CL is 33 mT, HTS CLs are 12 m away from the torus center. The max. allowable horizontal force of HTS CL that is perpendicular to the axis
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Fig. 3. The cross section of feeder conductors. Fig. 1. The current feeding system of JT-60SA. Several TF and EF coils are invisible in this figure.
of HTS CL is 560 N. In order to reduce the horizontal force of HTS CL by the thermal shrinkage of feeder by cooling down, octagonal rings fixing feeders with four supports from room temperature are adopted. The positive and negative conductors of feeders are clamped to withstand the repulsive force. Feeders in CTB are bent shaped to reduce the thermal stress of octagonal rings. Because of the limitation of the space for CTB vessel, large loops of feeder inside CTB vessel could not be adopted. Fig. 3 shows the cross section of conductors. TF and PF feeders are manufactured from TF coil conductor and EF coil conductor, respectively. Table 1 shows the major parameters of conductors. The conductor in feeder is insulated by Glass/Kapton/Glass (GKG) tapes with epoxy resin. 3. Confirmation of terminal joint Terminal joints of PF coils and mid joints of TF and PF feeders are the lap type joints connected by solder. The joint is surrounded by stainless steel can. He from one conductor flows out in the can, then flows into another conductor. The design is based on the pancake joint of EF coils [1]. The void fraction and pressing force of cable during soldering are 25% and 140 kN, respectively. However, because the direction of terminal joint is vertical, it was required to confirm that the solder connection can be done appropriately. In the case of EF coil joint, the press is conducted by hydraulic pressure. On the
Fig. 2. The structure of CTB.
Table 1 Major parameters of feeder conductors.
Type of strand Max. Current (kA) Number of NbTi strands Number of Cu wires Central spiral (id × od) (mm) Cable dimensions (mm)
TF
PF
NbTi 25.7 324 162 NA 22.0 × 18.0
NbTi 20.0 216 108 7×9 19.1 × 19.1
other hand, in order to reduce the size of tool for terminal joint, the developed connecting tool equips bolts (M12 × 8) to press the joint and sheath heaters embedded to melt solder (50 Pb/50 Sn). Fig. 4(a) shows the photograph of the tool during the connection work. Fig. 4(b) shows the manufactured joint. A terminal joint sample connected by the tool was fabricated in order to confirm the resistance of joint at operational condition at 2 T, 4.2 K and 20 kA. Fig. 5 shows the schematic drawing of sample. The PF feeder cable and EF coil cable were connected. After removing the nickel coating of NbTi strands and copper (Cu) wires, PF feeder cable, Cu saddle and EF coil cable were soldered and clamped by SS clamp with bolts. The connecting length was 160 mm which is equal to the final twist pitch of cables. This sample was installed in the superconducting coil at National Institute for Fusion Science (NIFS) [7] to apply the external magnetic field. The sample was cooled to 4.2 K. The joint resistance was derived from the electric current and voltage between voltage taps installed at both ends of joint.
Fig. 4. (a) The connecting tool and (b) the manufactured joint.
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Fig. 5. Schematic drawing of terminal joint sample.
Fig. 6 shows the external magnetic field dependence of joint resistance at 5, 10, 15 and 20 kA. The resistance at 2 T, 20 kA was 1.7 n which is below the allowable value of 5 n. This means that the developed tool can be used for assembly. Three lap type joint samples (two pancake joints [1] and one terminal joint of this work) have been manufactured. The resistances at 2 T, 20 kA were 1.8, 2.1 and 1.7 n indicating sufficient repeatability. The open triangles in Fig. 6 show the resistance of the joint sample connected at the horizontal position [1]. The resistance of sample of this work connected vertically shows slightly smaller resistance than the horizontally connected sample. The one possible reason is the thickness of solder sheet. The solder sheet used for vertical sample was 0.20 mm. On the other hand, that for horizontal sample was 0.15 mm. The variation of resistance at 10–20 kA, 1–3 T was within 5%. However, the resistance at 5 kA, 0 T was 30% smaller than that at 10–20 kA. This phenomenon was also observed for the horizontal sample. The solid line in Fig. 6 shows the fitting curve in which the magnetic field dependence of resistance is dominated by the magneto resistive effect of Cu (RRR = 100). The smaller resistance at 5 kA, 0 T cannot be explained only by Cu. The resistance is probably influenced by the resistivity of solder. Fast et al. [8] measured 50 Pb/50 Sn solder resistivity as a function of magnetic
Fig. 7. The distribution of self field.
field. The resistivity was rapidly decreased below 0.3 T. Fig. 7 shows the distribution of self field in joint. The region below 0.3 T is spread over solder region in the case of 5 kA. 4. Development of feeder 4.1. Bending shape of feeder In order to connect the feeder with octagonal rings and with in-cryostat feeder at mid joint, the target value of max. dimensional error was set at ±10 mm. Trial manufacturing of feeder in CTB was performed using superconductor for PF feeder as shown in Fig. 8. The length and curvature radius at crank part were 7.8 m and 150 mm, respectively. The critical current of the conductor sample with curvature radius of 150 mm was measured [5]. The critical current was almost agree with the expected values from the strand performance indicating that the no degradation was observed by bending. The dimension of manufactured feeder was measured and compared with CAD data. The max. error was 3 mm which satisfies the allowable value of ±10 mm. 4.2. Insulation of feeder conductor In order to evaluate the requirement of bonding strength between jacket of feeder conductor and insulation, the FEM structure analysis was conducted using the CAD model (see Fig. 2). The max. Tresca stress in insulation was found at the octagonal ring. Then, the normal () and shear stress () in insulation of the adhesive surface at the octagonal ring was evaluated along the conductor jacket perimeter like Fig. 9(b). The solid line in Fig. 9(a) shows the evaluated and . The dashed line in Fig. 9(a) shows the fracture criterion curve of the insulation in Mohr–Coulomb theory which is given by Eq. (1). 2 + 2 =1 0 0
Fig. 6. The external magnetic field dependence of joint resistance.
(1)
where 0 = 38 MPa and 0 = 27 MPa [9]. The analyzed stress was below 10 MPa which is within the criterion. The insulation material of feeder in factory is pre-impregnated Glass/Kapton/Glass (GKG) tapes with epoxy resin which is also used for the turn insulation of EF coils [1]. The curing temperature, time and pressure for a pancake of EF coils were 150 ◦ C, 8 h and 0.2 MPa, respectively. Because
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Fig. 10. The shear strength of feeder insulation samples.
Fig. 8. The manufactured PF feeder in CTB on trial.
the angle of 45◦ , then pressed by compression testing machine to apply both the shear and normal force. The measurements were conducted at 77 K because strength at 4 K becomes higher than at 77 K. Fig. 10 shows the measured shear strength. The influence of surface roughness was not clear. The lowest shear strength of GKG configuration with 0.016 MPa applied pressure was 60 MPa which was 40% smaller than GKG configuration with 0.2 MPa applied pressure. Stycast glued glass configuration showed the lowest shear strength of 93 MPa. Because the shear strength of GKG configuration with 0.016 MPa applied pressure and Stycast glued glass configuration was much higher than 10 MPa, these materials can be applied for the manufacturing of feeder insulation of JT-60SA. The shear strength measurement of GKG with Stycast 1266 is planned as future work. 5. Summary Key components for current feeding system were developed and tested. The joint resistance of terminal joint sample was 1.7 n at 2 T, 20 kA. Trial manufacturing of crank shaped feeder showed the max. dimensional error of 3 mm. Feeder insulation samples showed >60 MPa in shear strength at 77 K. Since all the manufacturing processes concerned were proof-tested, the production of CTBs and feeders can be started.
Fig. 9. (a) The evaluated normal and shear stress in insulation along the jacket perimeter and (b) schematic drawing of the evaluation line.
References
of the different shape and length of the feeders from that for EF coils, the adoption of press and curing device applied for EF coils is difficult. Thus, the following curing method was adopted for feeder. After winding pre-impregnated tapes on feeder conductor, thermal shrinkage tape is wound on insulation. Then, flexible sheet heater is wound on the thermal shrinkage tape to heat it up. It was concerned that the pressure to be applied by thermal shrinkage tape is only 0.016 MPa, which is much smaller than 0.2 MPa. There was another concern for the insulation around joint. After connecting feeders with coils, feeders around joints have to be insulated inside cryostat. It is difficult to press and heat up to 150 ◦ C because of the complicated shape of the joint. Thus, Stycast 1266 with the curing temperature of 80–90 ◦ C, pressure of 0.005 MPa and time of 24 h is applied for bonding material. Samples to measure the shear strength of insulation were fabricated. The insulation material was sandwiched by two SS discs with 12.7 mm in diameter. Samples of Stycast 1266 consist of Stycast glued glass tape. The disc surface was roughened by sand paper of #40 or sand blast of #200 or belt sander to confirm the influence of surface roughness. Each sample was installed on the test tool with
[1] K. Yoshida, K. Kizu, K. Tsuchiya, H. Murakami, K. Kamiya, M. Peyrot, The manufacturing of the superconducting magnet system for the JT-60SA, IEEE Trans. Appl. Supercond. 22 (3) (2012) 4200304. [2] K. Yoshida, K. Kizu, H. Murakami, K. Kamiya, A. Honda, Y. Ohnishi, et al., Feeder components and instrumentation for the JT-60SA magnet system, Fusion Eng. Des. 88 (2013) 1499–1504. [3] Y. Song, P. Bauer, Y. Bi, Y. Chen, A. Devred, F. Rodriguez-Mateos, Design of the ITER TF magnet feeder systems, IEEE Trans. Appl. Supercond. 20 (3) (2010) 1710–1713. [4] W.H. Fietz, R. Heller, A. Kienzler, R. Lietzow, High temperature superconductor current leads for WENDELSTEIN 7-X and JT-60SA, IEEE Trans. Appl. Supercond. 19 (3) (2009) 2202–2205. [5] K. Kizu, Y. Kashiwa, H. Murakami, T. Obana, K. Takahata, T. Tsuchiya, et al., Fabrication and tests of EF conductors for JT-60SA, Fusion Eng. Des. 86 (2011) 1432–1435. [6] L. Zani, P. Barabaschi, E. Di Pietro, Status of European manufacture of toroidal field conductor and strand for JT-60SA project, Fusion Eng. Des. 88 (2013) 555–558. [7] T. Obana, K. Takahata, T. Mito, S. Imagawa, K. Kizu, H. Murakami, Magnetic field measurements on a shake-hands lap joint sample of cable-in-conduit conductors for JT-60SA EF coil, IEEE Trans. Appl. Supercond. 20 (3) (2010) 1471–1474. [8] R.W. Fast, W.W. Craddock, M. Kobayashi, M.T. Mruzek, Electrical and mechanical properties of lead/tin solders and splices for superconducting cables, Cryogenics 28 (1988) 7–9. [9] K. Kitamura, T. Yamamoto, T. Uchida, H. Moriyama, J. Yamamoto, A. Nishimura, Cryogenic shear fracture tests of interlaminar organic insulation for a forcedflow superconducting coil, IEEE Trans. Magn. 30 (4) (1994) 1879–1882.
Contents lists available at ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Manufacturing design and development of the current feeders and coil terminal boxes for JT-60SA Kaname Kizu a,∗ , Haruyuki Murakami a , Kyohei Natsume a , Katsuhiko Tsuchiya a , Yoshihiko Koide a , Kiyoshi Yoshida a , Tetsuhiro Obana b , Shinji Hamaguchi b , Kazuya Takahata b a b
Japan Atomic Energy Agency, Naka, Ibaraki 311-0193, Japan National Institute for Fusion Science, Toki, Gifu 509-5292, Japan
h i g h l i g h t s • • • •
Key components for current feeding system for JT-60SA were developed and tested. The joint resistance of feeder joint sample was 1.7 n at 2 T, 20 kA. Trial manufacturing of crank shaped feeder showed the max. dimensional error of 3 mm. Feeder insulation samples showed >60 MPa in shear strength at 77 K.
a r t i c l e
i n f o
Article history: Received 17 September 2014 Received in revised form 24 March 2015 Accepted 8 April 2015 Available online 30 April 2015 Keywords: Coil terminal box Current feeder Electrical joint JT-60SA NbTi
a b s t r a c t Feeders and coil terminal boxes (CTBs) of the superconducting magnets for JT-60SA have been designed. A small tool which can connect soldering joint with vertical direction in the cryostat has been developed. The joint resistance of the sample showed 1.7 n at 2 T, 4.2 K, 20 kA which is within the requirement of <5 n. A prototype feeder in CTB with crank shape was manufactured. The maximum dimensional error was 3 mm being within the requirement of ±10 mm. Feeder insulation samples showed a shear strength >60 MPa which is much higher than the requirement of 10 MPa as derived from analysis. Since all the manufacturing processes concerned have been proof-tested, the production of feeders and CTBs has been released. © 2015 Elsevier B.V. All rights reserved.
1. Introduction The superconducting coil system for JT-60SA consists of 18 Toroidal Field (TF) coils and 10 Poloidal Field (PF) coils [1]. PF coils include a Central Solenoid (CS) with 4 modules, and 6 Equilibrium Field (EF) coils. The current of TF and PF coils are 25.7 and 20 kA, respectively. The current feeding system consists of in-cryostat feeders and Coil Terminal Boxes (CTBs) [2,3]. CTBs contain feeders and High Temperature Superconductor Current Leads (HTS CLs) [4]. Because of the available space in torus building, five CTBs (CT0105) are spread around the main cryostat as shown in Fig. 1. CTBs, in-cryostat feeders and superconductor for PF feeders [5] are procured by Japan. HTS CLs and superconductor for TF feeder [6] are procured by Europe.
∗ Corresponding author. E-mail address: [email protected] (K. Kizu). http://dx.doi.org/10.1016/j.fusengdes.2015.04.030 0920-3796/© 2015 Elsevier B.V. All rights reserved.
There were several concerns for the production of feeder components. The first was the manufacturability of electrical joint in the narrow space in the cryostat after the coil installation. The second was the manufacturability of bent feeder to reduce the reaction force of HTS CL by thermal contraction. In this paper, the trial manufacturing and test results of feeder components are described. 2. Design of CTB and feeder Fig. 2 shows the structure of CTB. Normal conducting busbars from power supply are connected to HTS CLs. Feeders consisting of superconductors are connected to the cold ends of HTS CLs, and are routed to main cryostat. Feeders in CTB are connected to the incryostat feeders through mid joints in the vicinity of cryostat wall. The in-cryostat feeders are connected to the terminal joints of coils. Since the maximum (max.) allowable magnetic field of HTS CL is 33 mT, HTS CLs are 12 m away from the torus center. The max. allowable horizontal force of HTS CL that is perpendicular to the axis
K. Kizu et al. / Fusion Engineering and Design 98–99 (2015) 1094–1097
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Fig. 3. The cross section of feeder conductors. Fig. 1. The current feeding system of JT-60SA. Several TF and EF coils are invisible in this figure.
of HTS CL is 560 N. In order to reduce the horizontal force of HTS CL by the thermal shrinkage of feeder by cooling down, octagonal rings fixing feeders with four supports from room temperature are adopted. The positive and negative conductors of feeders are clamped to withstand the repulsive force. Feeders in CTB are bent shaped to reduce the thermal stress of octagonal rings. Because of the limitation of the space for CTB vessel, large loops of feeder inside CTB vessel could not be adopted. Fig. 3 shows the cross section of conductors. TF and PF feeders are manufactured from TF coil conductor and EF coil conductor, respectively. Table 1 shows the major parameters of conductors. The conductor in feeder is insulated by Glass/Kapton/Glass (GKG) tapes with epoxy resin. 3. Confirmation of terminal joint Terminal joints of PF coils and mid joints of TF and PF feeders are the lap type joints connected by solder. The joint is surrounded by stainless steel can. He from one conductor flows out in the can, then flows into another conductor. The design is based on the pancake joint of EF coils [1]. The void fraction and pressing force of cable during soldering are 25% and 140 kN, respectively. However, because the direction of terminal joint is vertical, it was required to confirm that the solder connection can be done appropriately. In the case of EF coil joint, the press is conducted by hydraulic pressure. On the
Fig. 2. The structure of CTB.
Table 1 Major parameters of feeder conductors.
Type of strand Max. Current (kA) Number of NbTi strands Number of Cu wires Central spiral (id × od) (mm) Cable dimensions (mm)
TF
PF
NbTi 25.7 324 162 NA 22.0 × 18.0
NbTi 20.0 216 108 7×9 19.1 × 19.1
other hand, in order to reduce the size of tool for terminal joint, the developed connecting tool equips bolts (M12 × 8) to press the joint and sheath heaters embedded to melt solder (50 Pb/50 Sn). Fig. 4(a) shows the photograph of the tool during the connection work. Fig. 4(b) shows the manufactured joint. A terminal joint sample connected by the tool was fabricated in order to confirm the resistance of joint at operational condition at 2 T, 4.2 K and 20 kA. Fig. 5 shows the schematic drawing of sample. The PF feeder cable and EF coil cable were connected. After removing the nickel coating of NbTi strands and copper (Cu) wires, PF feeder cable, Cu saddle and EF coil cable were soldered and clamped by SS clamp with bolts. The connecting length was 160 mm which is equal to the final twist pitch of cables. This sample was installed in the superconducting coil at National Institute for Fusion Science (NIFS) [7] to apply the external magnetic field. The sample was cooled to 4.2 K. The joint resistance was derived from the electric current and voltage between voltage taps installed at both ends of joint.
Fig. 4. (a) The connecting tool and (b) the manufactured joint.
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Fig. 5. Schematic drawing of terminal joint sample.
Fig. 6 shows the external magnetic field dependence of joint resistance at 5, 10, 15 and 20 kA. The resistance at 2 T, 20 kA was 1.7 n which is below the allowable value of 5 n. This means that the developed tool can be used for assembly. Three lap type joint samples (two pancake joints [1] and one terminal joint of this work) have been manufactured. The resistances at 2 T, 20 kA were 1.8, 2.1 and 1.7 n indicating sufficient repeatability. The open triangles in Fig. 6 show the resistance of the joint sample connected at the horizontal position [1]. The resistance of sample of this work connected vertically shows slightly smaller resistance than the horizontally connected sample. The one possible reason is the thickness of solder sheet. The solder sheet used for vertical sample was 0.20 mm. On the other hand, that for horizontal sample was 0.15 mm. The variation of resistance at 10–20 kA, 1–3 T was within 5%. However, the resistance at 5 kA, 0 T was 30% smaller than that at 10–20 kA. This phenomenon was also observed for the horizontal sample. The solid line in Fig. 6 shows the fitting curve in which the magnetic field dependence of resistance is dominated by the magneto resistive effect of Cu (RRR = 100). The smaller resistance at 5 kA, 0 T cannot be explained only by Cu. The resistance is probably influenced by the resistivity of solder. Fast et al. [8] measured 50 Pb/50 Sn solder resistivity as a function of magnetic
Fig. 7. The distribution of self field.
field. The resistivity was rapidly decreased below 0.3 T. Fig. 7 shows the distribution of self field in joint. The region below 0.3 T is spread over solder region in the case of 5 kA. 4. Development of feeder 4.1. Bending shape of feeder In order to connect the feeder with octagonal rings and with in-cryostat feeder at mid joint, the target value of max. dimensional error was set at ±10 mm. Trial manufacturing of feeder in CTB was performed using superconductor for PF feeder as shown in Fig. 8. The length and curvature radius at crank part were 7.8 m and 150 mm, respectively. The critical current of the conductor sample with curvature radius of 150 mm was measured [5]. The critical current was almost agree with the expected values from the strand performance indicating that the no degradation was observed by bending. The dimension of manufactured feeder was measured and compared with CAD data. The max. error was 3 mm which satisfies the allowable value of ±10 mm. 4.2. Insulation of feeder conductor In order to evaluate the requirement of bonding strength between jacket of feeder conductor and insulation, the FEM structure analysis was conducted using the CAD model (see Fig. 2). The max. Tresca stress in insulation was found at the octagonal ring. Then, the normal () and shear stress () in insulation of the adhesive surface at the octagonal ring was evaluated along the conductor jacket perimeter like Fig. 9(b). The solid line in Fig. 9(a) shows the evaluated and . The dashed line in Fig. 9(a) shows the fracture criterion curve of the insulation in Mohr–Coulomb theory which is given by Eq. (1). 2 + 2 =1 0 0
Fig. 6. The external magnetic field dependence of joint resistance.
(1)
where 0 = 38 MPa and 0 = 27 MPa [9]. The analyzed stress was below 10 MPa which is within the criterion. The insulation material of feeder in factory is pre-impregnated Glass/Kapton/Glass (GKG) tapes with epoxy resin which is also used for the turn insulation of EF coils [1]. The curing temperature, time and pressure for a pancake of EF coils were 150 ◦ C, 8 h and 0.2 MPa, respectively. Because
K. Kizu et al. / Fusion Engineering and Design 98–99 (2015) 1094–1097
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Fig. 10. The shear strength of feeder insulation samples.
Fig. 8. The manufactured PF feeder in CTB on trial.
the angle of 45◦ , then pressed by compression testing machine to apply both the shear and normal force. The measurements were conducted at 77 K because strength at 4 K becomes higher than at 77 K. Fig. 10 shows the measured shear strength. The influence of surface roughness was not clear. The lowest shear strength of GKG configuration with 0.016 MPa applied pressure was 60 MPa which was 40% smaller than GKG configuration with 0.2 MPa applied pressure. Stycast glued glass configuration showed the lowest shear strength of 93 MPa. Because the shear strength of GKG configuration with 0.016 MPa applied pressure and Stycast glued glass configuration was much higher than 10 MPa, these materials can be applied for the manufacturing of feeder insulation of JT-60SA. The shear strength measurement of GKG with Stycast 1266 is planned as future work. 5. Summary Key components for current feeding system were developed and tested. The joint resistance of terminal joint sample was 1.7 n at 2 T, 20 kA. Trial manufacturing of crank shaped feeder showed the max. dimensional error of 3 mm. Feeder insulation samples showed >60 MPa in shear strength at 77 K. Since all the manufacturing processes concerned were proof-tested, the production of CTBs and feeders can be started.
Fig. 9. (a) The evaluated normal and shear stress in insulation along the jacket perimeter and (b) schematic drawing of the evaluation line.
References
of the different shape and length of the feeders from that for EF coils, the adoption of press and curing device applied for EF coils is difficult. Thus, the following curing method was adopted for feeder. After winding pre-impregnated tapes on feeder conductor, thermal shrinkage tape is wound on insulation. Then, flexible sheet heater is wound on the thermal shrinkage tape to heat it up. It was concerned that the pressure to be applied by thermal shrinkage tape is only 0.016 MPa, which is much smaller than 0.2 MPa. There was another concern for the insulation around joint. After connecting feeders with coils, feeders around joints have to be insulated inside cryostat. It is difficult to press and heat up to 150 ◦ C because of the complicated shape of the joint. Thus, Stycast 1266 with the curing temperature of 80–90 ◦ C, pressure of 0.005 MPa and time of 24 h is applied for bonding material. Samples to measure the shear strength of insulation were fabricated. The insulation material was sandwiched by two SS discs with 12.7 mm in diameter. Samples of Stycast 1266 consist of Stycast glued glass tape. The disc surface was roughened by sand paper of #40 or sand blast of #200 or belt sander to confirm the influence of surface roughness. Each sample was installed on the test tool with
[1] K. Yoshida, K. Kizu, K. Tsuchiya, H. Murakami, K. Kamiya, M. Peyrot, The manufacturing of the superconducting magnet system for the JT-60SA, IEEE Trans. Appl. Supercond. 22 (3) (2012) 4200304. [2] K. Yoshida, K. Kizu, H. Murakami, K. Kamiya, A. Honda, Y. Ohnishi, et al., Feeder components and instrumentation for the JT-60SA magnet system, Fusion Eng. Des. 88 (2013) 1499–1504. [3] Y. Song, P. Bauer, Y. Bi, Y. Chen, A. Devred, F. Rodriguez-Mateos, Design of the ITER TF magnet feeder systems, IEEE Trans. Appl. Supercond. 20 (3) (2010) 1710–1713. [4] W.H. Fietz, R. Heller, A. Kienzler, R. Lietzow, High temperature superconductor current leads for WENDELSTEIN 7-X and JT-60SA, IEEE Trans. Appl. Supercond. 19 (3) (2009) 2202–2205. [5] K. Kizu, Y. Kashiwa, H. Murakami, T. Obana, K. Takahata, T. Tsuchiya, et al., Fabrication and tests of EF conductors for JT-60SA, Fusion Eng. Des. 86 (2011) 1432–1435. [6] L. Zani, P. Barabaschi, E. Di Pietro, Status of European manufacture of toroidal field conductor and strand for JT-60SA project, Fusion Eng. Des. 88 (2013) 555–558. [7] T. Obana, K. Takahata, T. Mito, S. Imagawa, K. Kizu, H. Murakami, Magnetic field measurements on a shake-hands lap joint sample of cable-in-conduit conductors for JT-60SA EF coil, IEEE Trans. Appl. Supercond. 20 (3) (2010) 1471–1474. [8] R.W. Fast, W.W. Craddock, M. Kobayashi, M.T. Mruzek, Electrical and mechanical properties of lead/tin solders and splices for superconducting cables, Cryogenics 28 (1988) 7–9. [9] K. Kitamura, T. Yamamoto, T. Uchida, H. Moriyama, J. Yamamoto, A. Nishimura, Cryogenic shear fracture tests of interlaminar organic insulation for a forcedflow superconducting coil, IEEE Trans. Magn. 30 (4) (1994) 1879–1882.