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Joints for large superconducting conductors
Fusion Engineering and Design 58 – 59 (2001) 123– 127 www.elsevier.com/locate/fusengdes
Joints for large superconducting conductors P. Decool a,*, D. Ciazynski a, A. Nobili b, S. Parodi c, P. Pesenti c, A. Bourquard d, F. Beaudet d a
DRFC/STEP, Association Euratom – CEA Cadarache, F-13108 Saint Paul Lez Durance Cedex, France b Nobelclad, Ri6esaltes, France c Ansaldo, Genoa, Italy d Alstom, Belfort, France
Abstract Large fusion magnets call for high-current conductors (up to 60 kA). This has been achieved by the cable-in-conduit conductor concept. The connection of these conductors has to take into account several demanding boundary conditions: a large number of strands (around 1000), a low resistance at high current (1 – 2 nV), low losses in pulsed field operation, Nb3Sn heat treatment, helium tightness control, limited available space. A conceptual design was developed by the CEA, based on the connection of two separate twin boxes clamped together, according to the lap-joint concept. These boxes are machined out of an explosive bonding plate (jacket material/copper), and the electrical connection is achieved by tin–lead soldering of the facing copper soles. After qualification of the explosive bond and validation of the joint concept in the laboratory, the technology was transferred to the industry within the framework of the manufacture of the ITER Toroidal Field Model Coil (TFMC). In addition, three full-size joint samples (FSJS), relevant to different jacket materials and joining techniques, were manufactured by the industry and successfully tested in the SULTAN facility at CRPP, Villigen. The paper reports on the results of the laboratory tests, describes the transfer of technology to industry, and lastly presents some typical experimental results. © 2001 Elsevier Science B.V. All rights reserved.
1. Introduction Within the framework of NET contracts, CEA was in charge of designing the EU proposal of joints for the ITER coils. The retained solution was a lap joint using the twin-box concept associated with the explosive bonding technique for joint box manufacture [1]. Development tests were * Corresponding author. Tel.: + 33-4-4225-4350; fax: + 334-4225-2661. E-mail address: [email protected] (P. Decool).
carried out in the laboratory for mechanical qualification of copper –steel and copper –Incoloy explosively bonded materials. Parametric studies on sub-size joint samples were also performed by CEA for electrical qualification and optimisation of the design [2]. The design application was performed within the framework of ITER Toroidal Field Model Coil (TFMC) manufacture in industry [3]. In addition, three full-size prototype samples (FSJS) were designed and fabricated in the industry under technical monitoring by CEA [4]. Two sam-
0920-3796/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 0 - 3 7 9 6 ( 0 1 ) 0 0 4 0 8 - 2
P. Decool et al. / Fusion Engineering and Design 58–59 (2001) 123–127
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ples (SS-FSJS and TFMC-FSJS) are representative of the inner and outer joints of the TFMC using steel as conductor jacket material. The last sample (TF-FSJS) is representative of the original ITER –FDR TF coils using Incoloy as conductor jacket material. Complementary R&D was carried out in the industry on full-size samples for adapting the laboratory developments to real industrial constraints. The three FSJSs were then tested in the dedicated European test facility SULTAN (CRPP, Villigen, CH).
Fig. 2. Joint assembly cross-section.
2. Conceptual design The guidelines for the design of the joint [1] were the following: to reach a low resistance with acceptable a.c. losses, to keep as close as possible to the cable geometry in the joint region, to avoid any handling of the terminations after the reaction heat treatment, to allow tightness tests of each pancake (or layer) independently before the final winding assembly, and last but not least, to be easily transferred to the industry. These specifications led to the twin-box concept in which each termination is manufactured using a solid copper– steel or copper– Incoloy box made by explosive bonding (Fig. 1). Note that the joint boxes are machined in a pre-bent plate in order to allow the weld between the conductor jacket and the box at one end. The original sequence of fabrication was the following (Fig. 2): removal of the jacket and of the cable wrapping along one cable twist pitch length at the conductor end
removal of the sub-cable wrappings only on the area to be in contact with the copper sole removal of the chrome coating of the strands on the contact area (using sand blasting) cutting of strand ends to avoid tin leaks during heat treatment (cut with pinching) insertion of prepared conductor end inside the box welded onto the conductor jacket compaction of the cable by pressing the cover closure of the box by welding the cover without removing the pressure heat treatment of the Nb3Sn conductor with its terminations kept under pressure final assembly of the joint by insertion of a PbSn solder between the copper faces of the two boxes to be connected fixture of the joint position by an external clamping. This concept allows the manufacture of terminations at both ends of each length to be completed and vacuum-tested before heat treatment.
3. Mechanical characterisation of the bimetallic assembly
Fig. 1. Twin box.
One of the main technological characteristics of the joint design is the use of explosively bonded materials produced by the Nobelclad society. This bimetallic assembly used for the joint box manufacture was produced using 60 mm thick AISI 316L or Incoloy 908 plates as the base material bonded by the explosive technique against a 16 mm thick CuC1 copper plate. A mechanical test program was carried out to explore the mechanical capabilities of these explosive bonds.
P. Decool et al. / Fusion Engineering and Design 58–59 (2001) 123–127
First, tensile and shear samples, machined in an explosively bonded plate were tested until breakdown, at 300 and 4K, before and after a heat treatment at 650 °C under vacuum to simulate the Nb3Sn reaction heat treatment. The mechanical ultimate stress of the copper– steel as well as of the copper– Incoloy bimetallic assembly was found to be equal to that of copper and the breakdown indeed occurred every time in the copper material (Fig. 3). A second mechanical characterisation was undertaken on mock-ups of full-size joint boxes machined in both copper– steel and copper– Incoloy materials. These mock-ups reproduce the main geometrical specificity of the joint box such as the pre-bent part, a straight part and an inner hole for cable insertion. Initial geometrical checks as well as helium tightness tests were performed on every mock-up. The mock-ups were then heat treated at 650 °C for about 100 h under vacuum to simulate the Nb3Sn reaction heat treatment, before being subjected to several thermal shocks by immersion in a LN2 bath and warming up to 300 K. New geometrical checks and helium tightness tests were then performed. No leak was detected on all copper– steel and copper–Incoloy mock-ups. No deformation was recorded on copper –steel mock-ups while a general bending towards the copper sole with a radius of about 20 m due to the thermal differential contraction between copper and Incoloy was recorded on the copper –Incoloy mock-ups.
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4. Technology transfer to industry The application of the joint design described above and developed in the laboratory, including the final full-size validation of this concept, was passed to the industry within the framework of the ITER TFMC manufacture program. This work was performed under a contract between EFDA and the AGAN consortium (Noell, Accel, Ansaldo, Alstom). The TFMC winding pack is formed by the assembly of five double pancakes. Five inner joints and four outer joints linking the pancakes were manufactured on the basis of our conceptual design. The inner joints assembly was made as foreseen in the conceptual design by tin–lead soft soldering while the outer joint assembly was made by a specific method developed by Alstom, to take into account possible positioning errors between double pancakes to be connected, by using a set of copper pins inserted in between the two joint boxes which were electron beam (EB)-welded. A description of this joint is given in [3]. As a complementary program to this coil manufacture, three full-size joint samples were manufactured and tested for joint qualification in the dedicated European test facility at CRPP (Villigen, CH). The SS-FSJS is relevant to the inner joints with soft soldering assembly while the TFMC-FSJS is relevant to the outer joints of the TFMC with the EB-welded copper pins assembly. The third joint sample called the TF-FSJS is relevant to the original ITER–FDR TF joints with soft soldering assembly but using Incoloy material for both conductor jacket and joint boxes, instead of steel.
5. Complementary R&D in industry
Fig. 3. Shear samples.
Due to the scaling of the joint from the scaled version (developed in laboratory) to the full size, and taking into account the industrial constraints, some complementary R&D was needed to apply the joint concept to an industrial manufacture. The adjustments of the initial design can be summarised as follows:
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P. Decool et al. / Fusion Engineering and Design 58–59 (2001) 123–127
The compaction tests of the cable into the joint box on full-size mock-ups showed that the compaction force needed to reach the final cable void fraction (25%) was higher than the first estimation (up to 200 tons for a termination) and led to a buckling of the central spiral. Hence, a thick central tube (6 mm i.d. and 12 mm o.d.) was inserted in place of the spiral in the compacted region. The chrome removal on the strands in contact with the copper sole was performed in laboratory by sand blasting. Due to the difficulty in cleaning the residual sand in the conductor, the chrome removal operation was modified and performed by mechanical brushing of the strand surfaces. The closure of the strands’ extremity to avoid any tin leak during the heat was performed by nickel plating of the strand ends on the full-size conductors due to the high number of strands which have to be cut to the same length. The TFMC outer joints assembly was performed by a set of copper pins inserted in between the two terminations to be connected and welded by an EB instead of the soft soldering assembly foreseen in the initial joint design. This solution was developed by Alstom to take into account the misalignment errors during the stacking of the double pancakes and to limit strain in the free conductor lengths and insulation during joint soldering. Mechanical and welding tests were performed in the industry to assess this solution.
6. Problems encountered During the joint manufacture in industry, some problems were encountered which required some repairs or adjustments of the manufacturing sequence; they concern: Termination deformation: a general bending of the terminations was discovered after heat treatment and dismantling from the heat treatment tooling. This bending towards the cover with an average radius of about 20 m was due to residual stresses from the TIG weld of the cover on the box. Hence, the SS-FSJS assembly
was subsequently performed by using an adapted tapered copper wedge soft-soldered between the copper soles [4]. This deformation was anticipated on the TFMC-FSJS by an initial opposite inclination of the terminations before the heat treatment, while no compensation was needed on the TF-FSJS because of counter bending (same radius but in the opposite direction) due to the thermal contraction of the copper–Incoloy box. This problem was solved in the TFMC joints using the flexibility of the conductor between the radial plate exit and the joint. Cracks on the bimetallic explosive bond assembly: some cracks were detected at the copper– steel interface in the TFMC terminations. These cracks were checked and found to have a limited depth (B 2 mm) and had not affected the termination tightness. The main origin of these defects was the helium pipe weld at the termination end, which was too close to the interface. Some defects, also detected on one termination, were probably due to a base bimetallic piece not being taken from a sound area (i.e. too close to the plate edge). In future, a specific quality assurance procedure will have to be developed to avoid this risk. Electron Beam penetration: during the EB weld tests on mock-ups, it was discovered that the weld did not have a full penetration over the entire width of the termination sole. This phenomenon, combined with the reduction of the connected length due to the use of copper pins, was shown to reduce the connected area from 96% measured by X-ray control on a soft-soldered assembly (SS-FSJS) to 37% on the EBwelded pins assembly.
7. Performances The three joint samples were tested in the SULTAN test facility (CRPP, Villigen). Mainly, d.c. tests were performed with transport current up to 100 kA under a magnetic field up to 11 T. The joint d.c. resistances for the three samples, measured by the voltage drop and confirmed by calorimetric measurement, are plotted in Fig. 4 as
P. Decool et al. / Fusion Engineering and Design 58–59 (2001) 123–127
Fig. 4. Joint d.c. resistance.
functions of maximum magnetic field (i.e. applied field+self field). The results obtained on both SS-FSJS and TFFSJS are well in line with those expected for ITER joints from tests on sub-size joints, taking into account the number of superconducting strands in the cable (720 in the TF-FSJS against 1152 in the SS-FSJS) [5]. Only the TFMC-FSJS joint resistance appears too high (compared to the TF-FSJS), although remaining low enough for its use in the TFMC. This result, which has been confirmed on a sub-size joint, has been attributed to a degradation of the contact between the strands and the copper sole during the EB process, combined with a reduction of the intersole welded surface.
8. Conclusions Using laboratory developments on sub-size samples and copper–steel and copper– Incoloy explosive bond technique qualification, a joint de-
127
sign for large Nb3Sn superconducting conductors was developed. This joint design was applied as developed for the manufacture of the TFMC inner joints while a specific adaptation to the coil assembly constraint was required for the outer joints. In addition, three full-size joint samples representative of both the TFMC inner and outer joints and of the original ITER–FDR Toroidal Field coils (using Incoloy as reference material for the conductor jacket) were manufactured. Complementary developments were carried out by the involved industries for adapting the conceptual design to industrial constraints and for scaling up to full size. The excellent results obtained for the joint d.c. resistances have confirmed the validity of the CEA twin-box concept for the ITER TF coils, using the copper–steel or copper–Incoloy explosion-bonded joint box.
References [1] D. Ciazynski et al., Results of the European study on conductor joints for ITER coils, MT14, Tampere, Finland, 1995. [2] D. Ciazynski et al., Test results of the EU subsize conductor joints for ITER, 19th SOFT, Lisbon, Portugal, 1996. [3] P. Libeyre et al., B. Crepel, R. Kreutz, Development of joints in Europe for the ITER TFMC, MT15, Beijing, China, 1997. [4] D. Ciazynski et al., Fabrication of the first European full-size joint sample for ITER, ASC, Palm Desert, CA, USA, 1998. [5] D. Ciazynski et al., Test results and analysis of two European full-size conductor samples for ITER, MT16, Ponte Vedra Beach, FL, USA, 1999.
Joints for large superconducting conductors P. Decool a,*, D. Ciazynski a, A. Nobili b, S. Parodi c, P. Pesenti c, A. Bourquard d, F. Beaudet d a
DRFC/STEP, Association Euratom – CEA Cadarache, F-13108 Saint Paul Lez Durance Cedex, France b Nobelclad, Ri6esaltes, France c Ansaldo, Genoa, Italy d Alstom, Belfort, France
Abstract Large fusion magnets call for high-current conductors (up to 60 kA). This has been achieved by the cable-in-conduit conductor concept. The connection of these conductors has to take into account several demanding boundary conditions: a large number of strands (around 1000), a low resistance at high current (1 – 2 nV), low losses in pulsed field operation, Nb3Sn heat treatment, helium tightness control, limited available space. A conceptual design was developed by the CEA, based on the connection of two separate twin boxes clamped together, according to the lap-joint concept. These boxes are machined out of an explosive bonding plate (jacket material/copper), and the electrical connection is achieved by tin–lead soldering of the facing copper soles. After qualification of the explosive bond and validation of the joint concept in the laboratory, the technology was transferred to the industry within the framework of the manufacture of the ITER Toroidal Field Model Coil (TFMC). In addition, three full-size joint samples (FSJS), relevant to different jacket materials and joining techniques, were manufactured by the industry and successfully tested in the SULTAN facility at CRPP, Villigen. The paper reports on the results of the laboratory tests, describes the transfer of technology to industry, and lastly presents some typical experimental results. © 2001 Elsevier Science B.V. All rights reserved.
1. Introduction Within the framework of NET contracts, CEA was in charge of designing the EU proposal of joints for the ITER coils. The retained solution was a lap joint using the twin-box concept associated with the explosive bonding technique for joint box manufacture [1]. Development tests were * Corresponding author. Tel.: + 33-4-4225-4350; fax: + 334-4225-2661. E-mail address: [email protected] (P. Decool).
carried out in the laboratory for mechanical qualification of copper –steel and copper –Incoloy explosively bonded materials. Parametric studies on sub-size joint samples were also performed by CEA for electrical qualification and optimisation of the design [2]. The design application was performed within the framework of ITER Toroidal Field Model Coil (TFMC) manufacture in industry [3]. In addition, three full-size prototype samples (FSJS) were designed and fabricated in the industry under technical monitoring by CEA [4]. Two sam-
0920-3796/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 0 - 3 7 9 6 ( 0 1 ) 0 0 4 0 8 - 2
P. Decool et al. / Fusion Engineering and Design 58–59 (2001) 123–127
124
ples (SS-FSJS and TFMC-FSJS) are representative of the inner and outer joints of the TFMC using steel as conductor jacket material. The last sample (TF-FSJS) is representative of the original ITER –FDR TF coils using Incoloy as conductor jacket material. Complementary R&D was carried out in the industry on full-size samples for adapting the laboratory developments to real industrial constraints. The three FSJSs were then tested in the dedicated European test facility SULTAN (CRPP, Villigen, CH).
Fig. 2. Joint assembly cross-section.
2. Conceptual design The guidelines for the design of the joint [1] were the following: to reach a low resistance with acceptable a.c. losses, to keep as close as possible to the cable geometry in the joint region, to avoid any handling of the terminations after the reaction heat treatment, to allow tightness tests of each pancake (or layer) independently before the final winding assembly, and last but not least, to be easily transferred to the industry. These specifications led to the twin-box concept in which each termination is manufactured using a solid copper– steel or copper– Incoloy box made by explosive bonding (Fig. 1). Note that the joint boxes are machined in a pre-bent plate in order to allow the weld between the conductor jacket and the box at one end. The original sequence of fabrication was the following (Fig. 2): removal of the jacket and of the cable wrapping along one cable twist pitch length at the conductor end
removal of the sub-cable wrappings only on the area to be in contact with the copper sole removal of the chrome coating of the strands on the contact area (using sand blasting) cutting of strand ends to avoid tin leaks during heat treatment (cut with pinching) insertion of prepared conductor end inside the box welded onto the conductor jacket compaction of the cable by pressing the cover closure of the box by welding the cover without removing the pressure heat treatment of the Nb3Sn conductor with its terminations kept under pressure final assembly of the joint by insertion of a PbSn solder between the copper faces of the two boxes to be connected fixture of the joint position by an external clamping. This concept allows the manufacture of terminations at both ends of each length to be completed and vacuum-tested before heat treatment.
3. Mechanical characterisation of the bimetallic assembly
Fig. 1. Twin box.
One of the main technological characteristics of the joint design is the use of explosively bonded materials produced by the Nobelclad society. This bimetallic assembly used for the joint box manufacture was produced using 60 mm thick AISI 316L or Incoloy 908 plates as the base material bonded by the explosive technique against a 16 mm thick CuC1 copper plate. A mechanical test program was carried out to explore the mechanical capabilities of these explosive bonds.
P. Decool et al. / Fusion Engineering and Design 58–59 (2001) 123–127
First, tensile and shear samples, machined in an explosively bonded plate were tested until breakdown, at 300 and 4K, before and after a heat treatment at 650 °C under vacuum to simulate the Nb3Sn reaction heat treatment. The mechanical ultimate stress of the copper– steel as well as of the copper– Incoloy bimetallic assembly was found to be equal to that of copper and the breakdown indeed occurred every time in the copper material (Fig. 3). A second mechanical characterisation was undertaken on mock-ups of full-size joint boxes machined in both copper– steel and copper– Incoloy materials. These mock-ups reproduce the main geometrical specificity of the joint box such as the pre-bent part, a straight part and an inner hole for cable insertion. Initial geometrical checks as well as helium tightness tests were performed on every mock-up. The mock-ups were then heat treated at 650 °C for about 100 h under vacuum to simulate the Nb3Sn reaction heat treatment, before being subjected to several thermal shocks by immersion in a LN2 bath and warming up to 300 K. New geometrical checks and helium tightness tests were then performed. No leak was detected on all copper– steel and copper–Incoloy mock-ups. No deformation was recorded on copper –steel mock-ups while a general bending towards the copper sole with a radius of about 20 m due to the thermal differential contraction between copper and Incoloy was recorded on the copper –Incoloy mock-ups.
125
4. Technology transfer to industry The application of the joint design described above and developed in the laboratory, including the final full-size validation of this concept, was passed to the industry within the framework of the ITER TFMC manufacture program. This work was performed under a contract between EFDA and the AGAN consortium (Noell, Accel, Ansaldo, Alstom). The TFMC winding pack is formed by the assembly of five double pancakes. Five inner joints and four outer joints linking the pancakes were manufactured on the basis of our conceptual design. The inner joints assembly was made as foreseen in the conceptual design by tin–lead soft soldering while the outer joint assembly was made by a specific method developed by Alstom, to take into account possible positioning errors between double pancakes to be connected, by using a set of copper pins inserted in between the two joint boxes which were electron beam (EB)-welded. A description of this joint is given in [3]. As a complementary program to this coil manufacture, three full-size joint samples were manufactured and tested for joint qualification in the dedicated European test facility at CRPP (Villigen, CH). The SS-FSJS is relevant to the inner joints with soft soldering assembly while the TFMC-FSJS is relevant to the outer joints of the TFMC with the EB-welded copper pins assembly. The third joint sample called the TF-FSJS is relevant to the original ITER–FDR TF joints with soft soldering assembly but using Incoloy material for both conductor jacket and joint boxes, instead of steel.
5. Complementary R&D in industry
Fig. 3. Shear samples.
Due to the scaling of the joint from the scaled version (developed in laboratory) to the full size, and taking into account the industrial constraints, some complementary R&D was needed to apply the joint concept to an industrial manufacture. The adjustments of the initial design can be summarised as follows:
126
P. Decool et al. / Fusion Engineering and Design 58–59 (2001) 123–127
The compaction tests of the cable into the joint box on full-size mock-ups showed that the compaction force needed to reach the final cable void fraction (25%) was higher than the first estimation (up to 200 tons for a termination) and led to a buckling of the central spiral. Hence, a thick central tube (6 mm i.d. and 12 mm o.d.) was inserted in place of the spiral in the compacted region. The chrome removal on the strands in contact with the copper sole was performed in laboratory by sand blasting. Due to the difficulty in cleaning the residual sand in the conductor, the chrome removal operation was modified and performed by mechanical brushing of the strand surfaces. The closure of the strands’ extremity to avoid any tin leak during the heat was performed by nickel plating of the strand ends on the full-size conductors due to the high number of strands which have to be cut to the same length. The TFMC outer joints assembly was performed by a set of copper pins inserted in between the two terminations to be connected and welded by an EB instead of the soft soldering assembly foreseen in the initial joint design. This solution was developed by Alstom to take into account the misalignment errors during the stacking of the double pancakes and to limit strain in the free conductor lengths and insulation during joint soldering. Mechanical and welding tests were performed in the industry to assess this solution.
6. Problems encountered During the joint manufacture in industry, some problems were encountered which required some repairs or adjustments of the manufacturing sequence; they concern: Termination deformation: a general bending of the terminations was discovered after heat treatment and dismantling from the heat treatment tooling. This bending towards the cover with an average radius of about 20 m was due to residual stresses from the TIG weld of the cover on the box. Hence, the SS-FSJS assembly
was subsequently performed by using an adapted tapered copper wedge soft-soldered between the copper soles [4]. This deformation was anticipated on the TFMC-FSJS by an initial opposite inclination of the terminations before the heat treatment, while no compensation was needed on the TF-FSJS because of counter bending (same radius but in the opposite direction) due to the thermal contraction of the copper–Incoloy box. This problem was solved in the TFMC joints using the flexibility of the conductor between the radial plate exit and the joint. Cracks on the bimetallic explosive bond assembly: some cracks were detected at the copper– steel interface in the TFMC terminations. These cracks were checked and found to have a limited depth (B 2 mm) and had not affected the termination tightness. The main origin of these defects was the helium pipe weld at the termination end, which was too close to the interface. Some defects, also detected on one termination, were probably due to a base bimetallic piece not being taken from a sound area (i.e. too close to the plate edge). In future, a specific quality assurance procedure will have to be developed to avoid this risk. Electron Beam penetration: during the EB weld tests on mock-ups, it was discovered that the weld did not have a full penetration over the entire width of the termination sole. This phenomenon, combined with the reduction of the connected length due to the use of copper pins, was shown to reduce the connected area from 96% measured by X-ray control on a soft-soldered assembly (SS-FSJS) to 37% on the EBwelded pins assembly.
7. Performances The three joint samples were tested in the SULTAN test facility (CRPP, Villigen). Mainly, d.c. tests were performed with transport current up to 100 kA under a magnetic field up to 11 T. The joint d.c. resistances for the three samples, measured by the voltage drop and confirmed by calorimetric measurement, are plotted in Fig. 4 as
P. Decool et al. / Fusion Engineering and Design 58–59 (2001) 123–127
Fig. 4. Joint d.c. resistance.
functions of maximum magnetic field (i.e. applied field+self field). The results obtained on both SS-FSJS and TFFSJS are well in line with those expected for ITER joints from tests on sub-size joints, taking into account the number of superconducting strands in the cable (720 in the TF-FSJS against 1152 in the SS-FSJS) [5]. Only the TFMC-FSJS joint resistance appears too high (compared to the TF-FSJS), although remaining low enough for its use in the TFMC. This result, which has been confirmed on a sub-size joint, has been attributed to a degradation of the contact between the strands and the copper sole during the EB process, combined with a reduction of the intersole welded surface.
8. Conclusions Using laboratory developments on sub-size samples and copper–steel and copper– Incoloy explosive bond technique qualification, a joint de-
127
sign for large Nb3Sn superconducting conductors was developed. This joint design was applied as developed for the manufacture of the TFMC inner joints while a specific adaptation to the coil assembly constraint was required for the outer joints. In addition, three full-size joint samples representative of both the TFMC inner and outer joints and of the original ITER–FDR Toroidal Field coils (using Incoloy as reference material for the conductor jacket) were manufactured. Complementary developments were carried out by the involved industries for adapting the conceptual design to industrial constraints and for scaling up to full size. The excellent results obtained for the joint d.c. resistances have confirmed the validity of the CEA twin-box concept for the ITER TF coils, using the copper–steel or copper–Incoloy explosion-bonded joint box.
References [1] D. Ciazynski et al., Results of the European study on conductor joints for ITER coils, MT14, Tampere, Finland, 1995. [2] D. Ciazynski et al., Test results of the EU subsize conductor joints for ITER, 19th SOFT, Lisbon, Portugal, 1996. [3] P. Libeyre et al., B. Crepel, R. Kreutz, Development of joints in Europe for the ITER TFMC, MT15, Beijing, China, 1997. [4] D. Ciazynski et al., Fabrication of the first European full-size joint sample for ITER, ASC, Palm Desert, CA, USA, 1998. [5] D. Ciazynski et al., Test results and analysis of two European full-size conductor samples for ITER, MT16, Ponte Vedra Beach, FL, USA, 1999.