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Development program of a 60 kA high temperature superconductor current lead for the ITER toroidal field coils
Fusion Engineering and Design 58 – 59 (2001) 105– 109 www.elsevier.com/locate/fusengdes
Development program of a 60 kA high temperature superconductor current lead for the ITER toroidal field coils R. Heller a,*, G. Friesinger a, A.M. Fuchs b, P. Komarek a, T. Mito c, S. Satoh c, K. Takahata c, M. Tasca a, A. Ulbricht a, G. Ve´csey b, M. Vogel b a
Forschungszentrum Karlsruhe, Institut fu¨r Technische Physik, P.O. Box 3640, 76021 Karlsruhe, Germany b Centre de Recherches en Physique des Plasmas (CRPP), Villigen, Switzerland c National Institute for Fusion Science (NIFS), Toki City, Gifu Prefecture, Japan
Abstract A high temperature superconducting current lead for application in fusion magnets was developed in collaboration of three laboratories. Bi-2223 Ag/Au tapes were selected to be used in the current lead and two industrial fabricated 10 kA modules were extensively tested. Both modules were used in the 20 kA current lead which was successfully tested in continous operation at 20 kA and over short time up to 40 kA. © 2001 Elsevier Science B.V. All rights reserved. Keywords: ITER toroidal field coils; High temperature superconductors (HTS); Current lead
1. Introduction The aim of the task is to develop a 60 kA current lead for the ITER Toroidal Field Coil system using high temperature superconductors (HTS) in the temperature range between 4.5 and 70 K to reduce the steady state heat load at the 4 K level [1]. The task is being done in collaboration with the Fusion Technology Division of the Centre de Recherches en Physique des Plasmas of the E´cole Polytechnique Fe´de´rale de Lausanne (CRPP-EPFL). * Corresponding author. Tel.: + 49-7247-82-2701; fax: + 49-7247-82-2849. E-mail address: [email protected] (R. Heller).
The development program is subdivided into four stages: A-1: Test of different materials and concepts in 1 kA modules for selection, i.e. Bi-2212 bulk material (tubes) and Bi-2223 tapes with Ag/Au matrix in a straight stacked configuration. A-2: Test of a 10 kA HTS current lead using the material selected in stage A-1. B: Design and test of a 20 kA HTS current lead to prove the modularity and scaleability of the design. C: After completion of stage B, a 60 kA current lead could be designed to replace an existing 80 kA current lead in the TOSKA facility. This stage
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is still under discussion and a decision about it will be made after completion of stage B.
In the meantime, also AgAu cladded Bi-2212 tubes have been developed by Alcatel (former Hoechst/Aventis).
2. Results of stage A-1 (material selection) A description of the different materials and concepts and a detailed presentation of the results is given in [1,2]. Here, the main results and conclusions are summarized. Comparing the three tested configurations, i.e. Bi-2212 tubes fabricated by Hoechst AG, Bi-2223 tapes manufactured by American Superconductor Corp. (ASC), and Bi-2223 tapes fabricated by the Forschungszentrum Karlsruhe [3], there is no difference in the 60 K He mass flow rate which is adjusted thus to fix the temperature of the upper end of the HTS module to 70 K. Looking to the heat load at 4.5 K, the bulk material has a much lower value than the stabilized tapes, i.e. about a factor of 4. The contact resistances are however comparable. Comparing the transient behaviour, there is a clear distinction between bulk and stabilized tape material. Important for the safety margin during quench is the time duration between 10 mV (detection level) and 90 mV (voltage at current switch off) which is more than one order of magnitude larger for the tapes. The stabilized tapes are safer than the bulk material. According to the achieved results it was decided to order one 10 kA module from industry (ASC). For stage B (20 kA lead), later on a second 10 kA module was ordered from ASC. The use of bulk material would need further research for optimization of an electrical by-pass.
3. Results of stage A-2 (construction and test of a 10 kA lead) The design of the modules as follows: an appropriate number of Bi-2223 tapes, sintered together, form so-called stacks which are soldered on the outer surface of a stainless steel support tube. At both ends, copper end caps are placed for current transfer to adapt the HTS module into the apparatus of the customer. The support structure also serves as an additional heat sink in case of a quench. In our case, the safety requirement is such that the module has to withstand the full current of 10 kA for 10 s in case of loss of active cooling of the copper heat exchanger, which is part of the lead, without reaching room temperature. At the beginning of September 1998, both HTS modules were delivered from ASC. One of them was tested in the test facility at CRPP in spring 1999, and the other one was tested in October 1999. Fig. 1 shows a picture of the 10 kA HTS module. The test results of both 10 kA HTS modules were presented in [4] and can be summarized as follows. The operation up to steady-state currents of 10 kA was successful. No problems occurred during various tests. The test results were reproducible. Both modules have quite similar contact resistances at 70 K (25 nV) and quite low ones at 4.5 K (2 nV).
Fig. 1. The 10 kA HTSC module manufactured by American Superconductor.
R. Heller et al. / Fusion Engineering and Design 58–59 (2001) 105–109
The conduction losses of the HTS modules at 4.5 K for zero current and 70 K were measured to be about 1.5 W. The quench currents of both HTS modules at 70 K could only be measured at a higher temperature of the upper end of the HTS part. Extrapolating the measured quench currents to 70 K by using the temperature dependence of the tapes as given by the manufacturer, results in a quench current of about 18 kA at 70 K, and no degradation of the critical current has been found. For the determination of the current flowing in each stack, Hall sensors were positioned on the outer surface of the module measuring the azimuthal component of magnetic field generated by the stacks. The measurement results of the Hall probes show that there is a rather inhomogeneous current distribution between the stacks for module 1 and a more homogeneous one for module 2 which is independent on the transport current and determined by the contact resistances. Running the HTS module in the current sharing regime a current redistribution takes place between the stacks resulting in a smaller scattering. The safety margin of the HTS module was measured by looking at the behaviour of the current lead during a switch off of the 60 K helium mass flow rate of the copper heat exchanger while the transport current of 10 kA was kept constant. The transition of the upper end of the HTS module to the normal conducting state could only be observed at a start temperature of the warm end of about 90 K. Even in this case, the time difference between stopping the helium mass flow and the switching off the transport current, which was done at a resistive voltage of about 0.4 mV, was measured to be more than 70 s. Comparing this to the requirements of the discharge scenario of the ITER TF coil system, i.e. a time delay of 2 s until an exponential discharge of 15 s will be initiated, there is a high margin available. In summary, the design of the 10 kA HTS current lead is robust and could be used in coil experiments without any problems. Therefore, the stage A-2 was concluded with the test of two 10 kA modules fabricated by ASC, which were then available for stage B.
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Fig. 2. The 20 kA HTS module including the Cu adapters and clamp contact.
4. Results of stage B (test of the 20 kA HTS current lead) The 20 kA HTS current lead consists of the conventional heat exchanger of the Forschungszentrum Karlsruhe current lead type [5], whereas the 20 kA HTS module is constructed such to connect the two tested 10 kA modules in parallel. Fig. 2 shows the completed HTS module including the copper adapters and the clamp contact. The test has been performed within a new collaboration at the National Institute for Fusion Science, NIFS (within the LIME project). There, a test cryostat constructed for testing model coils for the PF coils of the Large Helical Device, LHD, was used. One of the existing 30 kA vapour cooled current leads was replaced by the 20 kA HTS current lead, and both leads were connected by a superconducting bus bar manufactured with a W 7-X prototype conductor. The first cooling and excitation tests were done for 2 weeks from the end of May 2000. Here the main results are given. More details are presented in [6]. The steady state operation up to 20 kA, using different inlet temperatures and mass flow rates for the helium cooling of the conventional heat exchanger, shows that there were no problems for the HTS part as well as for the conventional heat exchanger. The losses agree very well with the expectations. For the evaluation of the quench current of the HTS part, the temperature at the upper end of the module had to be increased to about 83 K. The measured quench current at 85 K is about 30 kA, twice as high as expected from the single tape, which is mainly due to the different (and much
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lower) voltage level criterion used in this experiment. Helium mass flow stop tests were done at 20 kA and 70 K and for different quench detection levels (up to 100 mV) for the quench detector to evaluate the safety margin of the current lead. The critical temperature measured in this test is about 90 K and agrees well with the results obtained in the quench current test. It took about 15 min to quench the HTS after the He mass flow rate was stopped. The time delay between a resistive voltage signal of 50 and 100 mV is about 8 s, between 10 and 100 mV even 12 s. Comparing this to the ITER scenarios, the measured time delay is well above these requirements. Special tests were done at the end of the experiment, i.e. ramp rate tests up to 20, 30 and 40 kA with 10 s flat top. It could be demonstrated that at about 60 K, the HTS current lead could be excited to 40 kA for 10 s without any problem neither in the HTS part nor in the conventional heat exchanger. For the determination of the current flowing in each of the 14 stacks, Hall sensors were positioned on the outer surface of each HTS module. It turned out that the current distribution is less homogeneous than measured at CRPP on the single modules. This indicates that the current transfer from the heat exchanger to the two HTS modules is responsible for this imbalance and not the contact resistances between the individual stacks and the copper endcaps. The connection between the copper conductor of the heat exchanger and the copper adapter in which the two HTS modules are soldered is done via a screw contact. The measured current distribution results in a current imbalance between the two modules of about 8200 A (module 1) and about 11 800 A (module 2) at a total current of 20 kA. This ratio is rather independent on the transport current. If the critical current of the HTS modules is reached, there is a current redistribution which is more pronounced in case of the quench tests than of the loss of mass flow tests. It is interesting that the redistribution takes place mainly between the two modules and not
within the modules although the current imbalance in the modules is much larger than between them. In summary, the robustness of the HTS current lead was demonstrated. Obviously, some modifications of the design have to be done if going up to 60 kA.
5. Design of a 60 kA HTS current lead Because the tests of both individual 10 kA HTS modules as well as of the 20 kA current lead were very successful, it was decided to use their basic layout and design parameters as a reference for the 60 kA HTS module, such as critical current density, contact resistances, modular arrangement of the HTS tapes in stacks and use of stainless steel as support structure. Three different arrangements of the stacks have been considered and were presented in [7]. Here only the main aspects are summarized. The first layout is an extrapolation of the 20 kA HTS module: five HTS modules of the same layout as for the 10 kA ones are arranged cylindrically resulting in 35 HTS stacks. This solution could be advantageous from the manufacturer’s point of view because it minimizes the risk of failure of the whole HTS module during fabrication. The second solution consists of two concentric rings of cylindrically arranged HTS stacks which form a very compact module. Due to the different stack numbers and maximum BÞ in the inner and outer rings, the current distribution could be a problem even in steady state. This has to be considered during the design of the connectors between the HTS module and the conventional parts of the current lead. In the third solution, 26 stacks are cylindrically arranged. The advantages of this design are the following: the relatively simple manufacturing, the small angle between two adjacent stacks allowing a smaller BÞ than in the other designs, the particular geometrical symmetry. It is planned to develop a more detailed design, as soon as the programme has been approved.
R. Heller et al. / Fusion Engineering and Design 58–59 (2001) 105–109
6. Design of a 10 kA HTS module using Bi-2212 tubes As an extension to the development programme, an alternative design of a 10 kA current lead using Bi-2212 tubes cladded with AgAu sheath is being investigated. This option was not available yet at the begining of the task but has the advantage of being much cheaper than the tape option. Presently, two 5 kA tubes are being connected in parallel to form a 10 kA HTS module and will be tested at CRPP in October 2000. During the test, two questions have to be answered, i.e. what is the safety margin in case of a quench (this was the main reason to use the tape option in the stages A-2 and B of the development programme), and what is the current unbalance between the two tubes in both steady state and transient operation.
7. Conclusions It has been demonstrated that it is possible to operate a HTS current lead for nominal currents up to 20 kA using commercially available Bi2223/AgAu tapes in a safe and reliable way. Due to the very robust design, it is possible to fullfill all requirements needed for the operation of the
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ITER TF coils. An alternative design using cladded bulk material, which could be much cheaper, is being investigated. The results will be available by the end of 2000. It is planned to start afterwards with the construction of a 60 kA HTS current lead (stage C of the programme), as soon as an approval has been obtained. References [1] R. Heller, et al., Development program of a 60 kA current lead using high temperature superconductors, IEEE Trans. Magn. 7 (2) (1996) 692 –695. [2] R. Heller, et al., Status of the development program of a 60 kA HTSC current lead for the ITER toroidal field coils, IEEE Trans. Appl. Supercond. 9 (2) (1999) 507 – 510. [3] W. Goldacker et al., Properties of Bi(2223)/AgAu multifilamentary tapes for current leads, Inst. Phys. Conf. Ser. No. 158 (1997) 1223 – 1226. [4] R. Heller, et al., Test results of a 10 kA current lead using Ag/Au stabilized Bi-2223 tapes, IEEE Trans. Appl. Supercond. 10 (1) (2000) 1470 – 1473. [5] G. Friesinger, et al., Test of a forced-flow cooled 30 kA current lead for the POLO model coil, IEEE Trans. Magn. 30 (4) (1994) 2387 – 2390. [6] R. Heller et al., Test results of a 20 kA current lead using Ag/Au stabilized Bi-2223 tapes, IEEE Trans. Appl. Supercond. 11 (82) (2001) 2603 – 2606. [7] M. Tasca et al., Design of a 60 kA HTS current lead for the ITER toroidal field coils, presented at 6th Advanced Studies on Superconducting Engineering (ASSE 2000), Eger, Hungary, July 1 – 9, 2000.
Development program of a 60 kA high temperature superconductor current lead for the ITER toroidal field coils R. Heller a,*, G. Friesinger a, A.M. Fuchs b, P. Komarek a, T. Mito c, S. Satoh c, K. Takahata c, M. Tasca a, A. Ulbricht a, G. Ve´csey b, M. Vogel b a
Forschungszentrum Karlsruhe, Institut fu¨r Technische Physik, P.O. Box 3640, 76021 Karlsruhe, Germany b Centre de Recherches en Physique des Plasmas (CRPP), Villigen, Switzerland c National Institute for Fusion Science (NIFS), Toki City, Gifu Prefecture, Japan
Abstract A high temperature superconducting current lead for application in fusion magnets was developed in collaboration of three laboratories. Bi-2223 Ag/Au tapes were selected to be used in the current lead and two industrial fabricated 10 kA modules were extensively tested. Both modules were used in the 20 kA current lead which was successfully tested in continous operation at 20 kA and over short time up to 40 kA. © 2001 Elsevier Science B.V. All rights reserved. Keywords: ITER toroidal field coils; High temperature superconductors (HTS); Current lead
1. Introduction The aim of the task is to develop a 60 kA current lead for the ITER Toroidal Field Coil system using high temperature superconductors (HTS) in the temperature range between 4.5 and 70 K to reduce the steady state heat load at the 4 K level [1]. The task is being done in collaboration with the Fusion Technology Division of the Centre de Recherches en Physique des Plasmas of the E´cole Polytechnique Fe´de´rale de Lausanne (CRPP-EPFL). * Corresponding author. Tel.: + 49-7247-82-2701; fax: + 49-7247-82-2849. E-mail address: [email protected] (R. Heller).
The development program is subdivided into four stages: A-1: Test of different materials and concepts in 1 kA modules for selection, i.e. Bi-2212 bulk material (tubes) and Bi-2223 tapes with Ag/Au matrix in a straight stacked configuration. A-2: Test of a 10 kA HTS current lead using the material selected in stage A-1. B: Design and test of a 20 kA HTS current lead to prove the modularity and scaleability of the design. C: After completion of stage B, a 60 kA current lead could be designed to replace an existing 80 kA current lead in the TOSKA facility. This stage
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is still under discussion and a decision about it will be made after completion of stage B.
In the meantime, also AgAu cladded Bi-2212 tubes have been developed by Alcatel (former Hoechst/Aventis).
2. Results of stage A-1 (material selection) A description of the different materials and concepts and a detailed presentation of the results is given in [1,2]. Here, the main results and conclusions are summarized. Comparing the three tested configurations, i.e. Bi-2212 tubes fabricated by Hoechst AG, Bi-2223 tapes manufactured by American Superconductor Corp. (ASC), and Bi-2223 tapes fabricated by the Forschungszentrum Karlsruhe [3], there is no difference in the 60 K He mass flow rate which is adjusted thus to fix the temperature of the upper end of the HTS module to 70 K. Looking to the heat load at 4.5 K, the bulk material has a much lower value than the stabilized tapes, i.e. about a factor of 4. The contact resistances are however comparable. Comparing the transient behaviour, there is a clear distinction between bulk and stabilized tape material. Important for the safety margin during quench is the time duration between 10 mV (detection level) and 90 mV (voltage at current switch off) which is more than one order of magnitude larger for the tapes. The stabilized tapes are safer than the bulk material. According to the achieved results it was decided to order one 10 kA module from industry (ASC). For stage B (20 kA lead), later on a second 10 kA module was ordered from ASC. The use of bulk material would need further research for optimization of an electrical by-pass.
3. Results of stage A-2 (construction and test of a 10 kA lead) The design of the modules as follows: an appropriate number of Bi-2223 tapes, sintered together, form so-called stacks which are soldered on the outer surface of a stainless steel support tube. At both ends, copper end caps are placed for current transfer to adapt the HTS module into the apparatus of the customer. The support structure also serves as an additional heat sink in case of a quench. In our case, the safety requirement is such that the module has to withstand the full current of 10 kA for 10 s in case of loss of active cooling of the copper heat exchanger, which is part of the lead, without reaching room temperature. At the beginning of September 1998, both HTS modules were delivered from ASC. One of them was tested in the test facility at CRPP in spring 1999, and the other one was tested in October 1999. Fig. 1 shows a picture of the 10 kA HTS module. The test results of both 10 kA HTS modules were presented in [4] and can be summarized as follows. The operation up to steady-state currents of 10 kA was successful. No problems occurred during various tests. The test results were reproducible. Both modules have quite similar contact resistances at 70 K (25 nV) and quite low ones at 4.5 K (2 nV).
Fig. 1. The 10 kA HTSC module manufactured by American Superconductor.
R. Heller et al. / Fusion Engineering and Design 58–59 (2001) 105–109
The conduction losses of the HTS modules at 4.5 K for zero current and 70 K were measured to be about 1.5 W. The quench currents of both HTS modules at 70 K could only be measured at a higher temperature of the upper end of the HTS part. Extrapolating the measured quench currents to 70 K by using the temperature dependence of the tapes as given by the manufacturer, results in a quench current of about 18 kA at 70 K, and no degradation of the critical current has been found. For the determination of the current flowing in each stack, Hall sensors were positioned on the outer surface of the module measuring the azimuthal component of magnetic field generated by the stacks. The measurement results of the Hall probes show that there is a rather inhomogeneous current distribution between the stacks for module 1 and a more homogeneous one for module 2 which is independent on the transport current and determined by the contact resistances. Running the HTS module in the current sharing regime a current redistribution takes place between the stacks resulting in a smaller scattering. The safety margin of the HTS module was measured by looking at the behaviour of the current lead during a switch off of the 60 K helium mass flow rate of the copper heat exchanger while the transport current of 10 kA was kept constant. The transition of the upper end of the HTS module to the normal conducting state could only be observed at a start temperature of the warm end of about 90 K. Even in this case, the time difference between stopping the helium mass flow and the switching off the transport current, which was done at a resistive voltage of about 0.4 mV, was measured to be more than 70 s. Comparing this to the requirements of the discharge scenario of the ITER TF coil system, i.e. a time delay of 2 s until an exponential discharge of 15 s will be initiated, there is a high margin available. In summary, the design of the 10 kA HTS current lead is robust and could be used in coil experiments without any problems. Therefore, the stage A-2 was concluded with the test of two 10 kA modules fabricated by ASC, which were then available for stage B.
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Fig. 2. The 20 kA HTS module including the Cu adapters and clamp contact.
4. Results of stage B (test of the 20 kA HTS current lead) The 20 kA HTS current lead consists of the conventional heat exchanger of the Forschungszentrum Karlsruhe current lead type [5], whereas the 20 kA HTS module is constructed such to connect the two tested 10 kA modules in parallel. Fig. 2 shows the completed HTS module including the copper adapters and the clamp contact. The test has been performed within a new collaboration at the National Institute for Fusion Science, NIFS (within the LIME project). There, a test cryostat constructed for testing model coils for the PF coils of the Large Helical Device, LHD, was used. One of the existing 30 kA vapour cooled current leads was replaced by the 20 kA HTS current lead, and both leads were connected by a superconducting bus bar manufactured with a W 7-X prototype conductor. The first cooling and excitation tests were done for 2 weeks from the end of May 2000. Here the main results are given. More details are presented in [6]. The steady state operation up to 20 kA, using different inlet temperatures and mass flow rates for the helium cooling of the conventional heat exchanger, shows that there were no problems for the HTS part as well as for the conventional heat exchanger. The losses agree very well with the expectations. For the evaluation of the quench current of the HTS part, the temperature at the upper end of the module had to be increased to about 83 K. The measured quench current at 85 K is about 30 kA, twice as high as expected from the single tape, which is mainly due to the different (and much
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R. Heller et al. / Fusion Engineering and Design 58–59 (2001) 105–109
lower) voltage level criterion used in this experiment. Helium mass flow stop tests were done at 20 kA and 70 K and for different quench detection levels (up to 100 mV) for the quench detector to evaluate the safety margin of the current lead. The critical temperature measured in this test is about 90 K and agrees well with the results obtained in the quench current test. It took about 15 min to quench the HTS after the He mass flow rate was stopped. The time delay between a resistive voltage signal of 50 and 100 mV is about 8 s, between 10 and 100 mV even 12 s. Comparing this to the ITER scenarios, the measured time delay is well above these requirements. Special tests were done at the end of the experiment, i.e. ramp rate tests up to 20, 30 and 40 kA with 10 s flat top. It could be demonstrated that at about 60 K, the HTS current lead could be excited to 40 kA for 10 s without any problem neither in the HTS part nor in the conventional heat exchanger. For the determination of the current flowing in each of the 14 stacks, Hall sensors were positioned on the outer surface of each HTS module. It turned out that the current distribution is less homogeneous than measured at CRPP on the single modules. This indicates that the current transfer from the heat exchanger to the two HTS modules is responsible for this imbalance and not the contact resistances between the individual stacks and the copper endcaps. The connection between the copper conductor of the heat exchanger and the copper adapter in which the two HTS modules are soldered is done via a screw contact. The measured current distribution results in a current imbalance between the two modules of about 8200 A (module 1) and about 11 800 A (module 2) at a total current of 20 kA. This ratio is rather independent on the transport current. If the critical current of the HTS modules is reached, there is a current redistribution which is more pronounced in case of the quench tests than of the loss of mass flow tests. It is interesting that the redistribution takes place mainly between the two modules and not
within the modules although the current imbalance in the modules is much larger than between them. In summary, the robustness of the HTS current lead was demonstrated. Obviously, some modifications of the design have to be done if going up to 60 kA.
5. Design of a 60 kA HTS current lead Because the tests of both individual 10 kA HTS modules as well as of the 20 kA current lead were very successful, it was decided to use their basic layout and design parameters as a reference for the 60 kA HTS module, such as critical current density, contact resistances, modular arrangement of the HTS tapes in stacks and use of stainless steel as support structure. Three different arrangements of the stacks have been considered and were presented in [7]. Here only the main aspects are summarized. The first layout is an extrapolation of the 20 kA HTS module: five HTS modules of the same layout as for the 10 kA ones are arranged cylindrically resulting in 35 HTS stacks. This solution could be advantageous from the manufacturer’s point of view because it minimizes the risk of failure of the whole HTS module during fabrication. The second solution consists of two concentric rings of cylindrically arranged HTS stacks which form a very compact module. Due to the different stack numbers and maximum BÞ in the inner and outer rings, the current distribution could be a problem even in steady state. This has to be considered during the design of the connectors between the HTS module and the conventional parts of the current lead. In the third solution, 26 stacks are cylindrically arranged. The advantages of this design are the following: the relatively simple manufacturing, the small angle between two adjacent stacks allowing a smaller BÞ than in the other designs, the particular geometrical symmetry. It is planned to develop a more detailed design, as soon as the programme has been approved.
R. Heller et al. / Fusion Engineering and Design 58–59 (2001) 105–109
6. Design of a 10 kA HTS module using Bi-2212 tubes As an extension to the development programme, an alternative design of a 10 kA current lead using Bi-2212 tubes cladded with AgAu sheath is being investigated. This option was not available yet at the begining of the task but has the advantage of being much cheaper than the tape option. Presently, two 5 kA tubes are being connected in parallel to form a 10 kA HTS module and will be tested at CRPP in October 2000. During the test, two questions have to be answered, i.e. what is the safety margin in case of a quench (this was the main reason to use the tape option in the stages A-2 and B of the development programme), and what is the current unbalance between the two tubes in both steady state and transient operation.
7. Conclusions It has been demonstrated that it is possible to operate a HTS current lead for nominal currents up to 20 kA using commercially available Bi2223/AgAu tapes in a safe and reliable way. Due to the very robust design, it is possible to fullfill all requirements needed for the operation of the
109
ITER TF coils. An alternative design using cladded bulk material, which could be much cheaper, is being investigated. The results will be available by the end of 2000. It is planned to start afterwards with the construction of a 60 kA HTS current lead (stage C of the programme), as soon as an approval has been obtained. References [1] R. Heller, et al., Development program of a 60 kA current lead using high temperature superconductors, IEEE Trans. Magn. 7 (2) (1996) 692 –695. [2] R. Heller, et al., Status of the development program of a 60 kA HTSC current lead for the ITER toroidal field coils, IEEE Trans. Appl. Supercond. 9 (2) (1999) 507 – 510. [3] W. Goldacker et al., Properties of Bi(2223)/AgAu multifilamentary tapes for current leads, Inst. Phys. Conf. Ser. No. 158 (1997) 1223 – 1226. [4] R. Heller, et al., Test results of a 10 kA current lead using Ag/Au stabilized Bi-2223 tapes, IEEE Trans. Appl. Supercond. 10 (1) (2000) 1470 – 1473. [5] G. Friesinger, et al., Test of a forced-flow cooled 30 kA current lead for the POLO model coil, IEEE Trans. Magn. 30 (4) (1994) 2387 – 2390. [6] R. Heller et al., Test results of a 20 kA current lead using Ag/Au stabilized Bi-2223 tapes, IEEE Trans. Appl. Supercond. 11 (82) (2001) 2603 – 2606. [7] M. Tasca et al., Design of a 60 kA HTS current lead for the ITER toroidal field coils, presented at 6th Advanced Studies on Superconducting Engineering (ASSE 2000), Eger, Hungary, July 1 – 9, 2000.