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Mechanical analysis of the PF1 feeder for ITER
Fusion Engineering and Design 87 (2012) 728–731
Contents lists available at SciVerse ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Mechanical analysis of the PF1 feeder for ITER Mingzhun Lei ∗ , Yuntao Song, Zhongwei Wang, Kun Lu, Yong Cheng, Sumei Liu, Songke Wang Institute of Plasma Physics, Chinese Academy of Science, Hefei 230031, China
a r t i c l e
i n f o
Article history: Available online 8 March 2012 Keywords: PF1 feeder ITER Finite element analysis Tokamak
a b s t r a c t The ITER experimental device contains very powerful superconducting magnets operated at cryogenic temperatures to generate and control the deuterium–tritium plasma for thermo-nuclear fusion. The function of the feeders is to convey the cryogenic supply and electrical power through the warm-cold barrier to ITER magnets. Due to the complexity of the structure and working conditions, a global mechanical analysis is required to have simulation information to check the structural reliability of the design. Electromagnetic force analysis of PF1 feeder for further mechanical analysis was calculated under the worst scenarios with the maximum working current in every coil. Mechanical analysis model was built using the finite element software ANSYS. The structural performance of the PF1 feeder was analyzed. The numerical simulation results show that the design of the PF1 feeder is feasible. © 2012 Elsevier B.V. All rights reserved.
1. Introduction The ITER experimental device contains very powerful magnets which can generate, stabilize and control the deuterium–tritium plasma for nuclear fusion. These magnets and associated structures require electrical power, cryogenic temperature and instrumentation cables. The components which provide these functions are the so-called feeders. The ITER feeder system, one of important subsystem of the ITER magnet, connects the ITER magnet systems. The main function of the feeders is to convey the cryogenic supply and electrical power to the magnet system, and provides the instrumentation channel for monitoring the superconducting coil operation [1]. The feeder system consists of 31 feeders, 9 for the toroidal field (TF) magnet system, 6 for the poloidal field (PF) magnet system, 6 for the central solenoid (CS) modules, 5 for the correction coil (CC) system, 3 reserved exclusively for the supply of cryogens to the TF coil structure cooling system, and 2 for coil instrumentation. The PF1 feeder consists of In-Cryostat-Feeder (ICF), CryostatFeeder-Through (CFT), S-Bend-Box (SBB), Coil-Terminal-Box (CTB) and Dry-Box (DB), as shown in Fig. 1. The ICF components are located inside cryostat, enclosed by the cryostat thermal shield cooled at 80 K. The DB, CTB, SBB and part of the CFT are placed outside the cryostat. Thermal contraction of the PF1 feeder and the magnet system should be taken into account at the design stage. Meanwhile, electromagnetic (EM) forces on the PF1 feeder busbars should also be considered. Due to the complexity of the PF1 feeder structure and working conditions, the numerical simulation was carried out to check the
∗ Corresponding author. Tel.: +86 5515595029. E-mail address: [email protected] (M. Lei). 0920-3796/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.fusengdes.2012.02.019
design. With EM analysis, the EM force of PF1 busbar was calculated under the worst scenarios with the maximum working current in every coil and used for further busbar supports design, as well as for the globe model mechanical analysis. 2. PF1 design description The detailed design of the PF1 feeder is introduced below, as shown in Figs. 1 and 2. In-Cryostat-Feeder. The ICF connects to the end of the CFT and locates at the in-cryostat joints. It consists of a containment duct that prevents spilling out molten metal in the event of an electric arc between the busbars [2]. The containment duct also carries the feed and return helium lines and instrumentation cables. Cryostat-Feeder-Through. The CFT have interfaces with the ICF and SBB. Its assembly composed of the containment duct, the busbars, the cryo-pipes, the instrumentation pipes, the internal supports, the cold mass supports, the separator plate, the vacuum barrier, the cryostat extension duct, and the gravity supports [3]. S-Bend Box. The SBB contains S-shaped bends in the busbars and the cryo-pipes. The function of the S-bends is accommodating differential thermal contraction between the cryogenic feeder components and the warm feeder components. The SBB also includes most of the coil instrumentation feed-through [4]. Coil Terminal Box. The CTB is designed for easy access its components. Because most importantly the physical interfaces between the magnet and cryo-systems are located in the CTB and many feeder components require maintenance, such as cryo-control valves, HTS current leads, feeder instrumentation [4]. Dry Box. The main function of the DB is housing and protecting the feeder to power system interface and the connection between the feeder current leads and the power supply of the busbars. It is
M. Lei et al. / Fusion Engineering and Design 87 (2012) 728–731
729
Fig. 1. ITER PF1 feeder.
Fig. 3. Electromagnetic analysis model.
and can be considered as a guideline of the support design. The SOURC36 code, which is a primitive used to supply current source data to magnetic field problems, represents a distribution of current in a model. So SOURC36 is used to model magnet coils and plasma. SOLID5 has a 3-D magnetic, thermal, electric, piezoelectric and structural field capability with limited coupling between the fields. So the busbar was built with SOLID5 and meshed with 50 mm long elements. The EM model was shown in Fig. 3. EM analysis was performed to calculate Lorentz forces and magnetic field of PF1 feeder busbars under the worst scenarios with the maximum working current in every coil. The maximum magnetic flux density is 1.74 T. The EM force on busbar nodes in X Y Z direction is shown in Fig. 4. The EM force has some small fluctuation because of self field induced by neighbouring busbars. 4. Mechanical analysis 4.1. FE model The FE model of PF1 feeder is established for mechanical analysis, as shown in Fig. 5. In order to improve modeling efficiency, most of the PF1 feeder components were simulated by shell and beam elements. Due to the complexity of the model, a simplification is made to fit computer capacity. The busbar consists of parts, namely, superconducting cable, stainless steel jacket and insulation layer. Because the superconducting cable is much softer than the other two parts, it can be ignored in this analysis. The busbar and cryo-pipe support is much stiffness than
Fig. 2. The detailed CATIA model of PF1 feeder.
also to prevent the building-up of ice on the coil terminals, thus reducing the risk of arcing between the terminals [5]. 3. Magnetic analysis 3.1. EM analysis model The busbar which carries very large current will suffer from high Lorentz force due to the background magnetic field generated by the magnetic coils and the self field. This analysis aims at the magnetic field and Lorentz force on the busbar in the worst scenarios with the maximum working current in every coil. The busbar support distance can be also obtained from this analysis,
Fig. 4. Lorenz forces on busbar nodes (N).
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M. Lei et al. / Fusion Engineering and Design 87 (2012) 728–731
Fig. 5. The FE model of PF1 feeder.
the busbar and cryo-pipe itself, so an Mpc184 element (rigid beam) is chosen to connect the busbar to the separate plate as a support [6]. Meanwhile, the interface between the busbar and support was represented by CONTA178 elements, which can define the contact stiffness, gap and friction in the contact interface. Mass21 element is employed to simulate the weight of the components ignored. In the model, a total element number of 8550 is adopted [7].
Fig. 6. Displacements of PF1 structure for case 3 (m).
4.2. Loading and boundary conditions The thermal loading on the PF1 feeder is the reduction in temperature from 292 K to 4 K during cool-down. The gravity, coil displacements and electromagnetic loads also affect the mechanical characteristics of the PF1 feeder. Vertical acceleration of −9.81 m/s was applied over the whole model as gravity acceleration. Displacement of the PF1 coils occurs due to thermal contraction and deflection of the tokamak during operation [8]. The Lorentz force was used to the further structural analysis, as shown in Fig. 4. Following load cases were analyzed for checking the PF1 feeder design. Case 1: Cooldown Case 2: Deadweight + Lorentz forces + Coil displacements Case 3: Deadweight + Cooldown + Lorentz forces + Coil displacements 4.3. Stress design criterion Allowable stresses for the PF1 feeder structure are assessed in accordance with reference [9,10]. For stainless steel 316L, the value for the design stress intensity (Sm ) is the lowest value of 2/3Sy (Yield strength = 700 MPa) in ASME at 4 K. Primary general membrane stress (Pm ) and primary bending stress (Pb ), calculated by elastic analysis for the design conditions should satisfy the following Eq. (1) and Eq. (2). The thermal stress is defined as the secondary stress (Q) due to self-balancing characteristics, and the sum of Pm , Pb and Q should satisfy Eq. 3. Pm ≤ Sm = 467 MPa
(1)
Pm + Pb ≤ 1.3Sm = 607 MPa
(2)
PL + Pb + Q ≤ 1.5Sm = 700 MPa
(3)
Fig. 7. Stress intensity of busbars and cryopipes for case 3 (Pa).
from the supporting structures and the Lorenz forces on the busbars. The stresses in the busbars and cryopipes are shown in Fig. 7. The maximum stress is 321 MPa and occurs at S-bend region. Fig. 8 shows that the maximum stresses in containment duct and separator plate is 250 MPa at ICF region. Because the busbars withstand bigger load than other components of the feeder, the assessment of the busbars was done through comparing the simulation results with criteria. Figs. 9 and 10 give the stresses of two busbars. It can be seen that the stresses (Pm , Pm + Pb and PL + Pb + Q) are all lower than the allowable stresses. The maximum stresses obtained are for two busbars in the SBB. The stress is very low at the busbar joints, because the cross-sectional area is greater than other place.
4.4. Numerical simulation The detailed FE model of the PF1 feeder was analyzed for the three load cases described above. Considering the complexity of the load cases, the analysis results of the load case 3 are extracted. Fig. 6 gives the displacement of the PF1 feeder, and it can be seen that the maximum displacement is 70.0 mm at the gimbal joints. The reason is the fact that the gimbal joints allow for articulation of the feeder when the joints is subjected to the displacements imposed
Fig. 8. Stress intensity of containment duct and separator plate for case 3 (Pa).
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5. Summary Mechanical analysis of the PF1 feeder was performed with ANSYS. During the worst combined load case, the maximum stresses are below the limit stress and the displacements are acceptable. A stresses assessment was carried out based on the criteria of ASME. It is proved that the design of the PF1 feeder can satisfied the design requirements. Acknowledgments The authors would like to thank the ITER feeder design and analysis team for their excellent design and simulation work. References
Fig. 9. The stresses of the Busbar 1.
Fig. 10. The stresses of the Busbar 2.
[1] P. Bauer, A.K., Sahu, N. Sato, The ITER Magnet Feeder Systems Functional Specification and Interface Document, ITER doc. ITER D 2EH9YM. [2] Cheng Wang, PF In-Cryostat-Feeder Design Report, ITER doc. ITER D 3U8GYJ v1.0, September 2010. [3] Lu Kun, PF&CS Feeder Cryostat Feed through Design Report, ITER doc. ITER D 3TDXJS, September 2010. [4] Junsong Shen, Kun Lu, Design of the CTB&SBB for the ITER Coil Feeders, ITER doc. ITER D 3QN7RE, September 2010. [5] Joakim Baker, CS1U Feeder, Detailed Global Model, ITER doc. ITER D 42JRUJ v1.0, November 2010. [6] Lei Mingzhun, Song Yuntao, Liu Sumei, Lu Kun, Wang Zhongwei, Primary design and analysis of feeder for ITER poloidal field, Plasma Science and Technology 13 (October (5)) (2011). [7] P. Lorrière, PF5 Global Model Analysis, ITER doc. ITER D 3SA8E8 v1.1, September 2010. [8] ITER Feeder Analysis Team, Coil Displacements for Feeder Design, ITER xls. ITER D 3TDBQY, 2010. [9] C.H. Lee, Design Review Procedure, ITER doc. ITER 2832CF, December 2009. [10] American Society of Mechanical Engineers, ASME Boiler and Pressure Vessel Code Section III, American Society of Mechanical Engineers, 1993.
Contents lists available at SciVerse ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Mechanical analysis of the PF1 feeder for ITER Mingzhun Lei ∗ , Yuntao Song, Zhongwei Wang, Kun Lu, Yong Cheng, Sumei Liu, Songke Wang Institute of Plasma Physics, Chinese Academy of Science, Hefei 230031, China
a r t i c l e
i n f o
Article history: Available online 8 March 2012 Keywords: PF1 feeder ITER Finite element analysis Tokamak
a b s t r a c t The ITER experimental device contains very powerful superconducting magnets operated at cryogenic temperatures to generate and control the deuterium–tritium plasma for thermo-nuclear fusion. The function of the feeders is to convey the cryogenic supply and electrical power through the warm-cold barrier to ITER magnets. Due to the complexity of the structure and working conditions, a global mechanical analysis is required to have simulation information to check the structural reliability of the design. Electromagnetic force analysis of PF1 feeder for further mechanical analysis was calculated under the worst scenarios with the maximum working current in every coil. Mechanical analysis model was built using the finite element software ANSYS. The structural performance of the PF1 feeder was analyzed. The numerical simulation results show that the design of the PF1 feeder is feasible. © 2012 Elsevier B.V. All rights reserved.
1. Introduction The ITER experimental device contains very powerful magnets which can generate, stabilize and control the deuterium–tritium plasma for nuclear fusion. These magnets and associated structures require electrical power, cryogenic temperature and instrumentation cables. The components which provide these functions are the so-called feeders. The ITER feeder system, one of important subsystem of the ITER magnet, connects the ITER magnet systems. The main function of the feeders is to convey the cryogenic supply and electrical power to the magnet system, and provides the instrumentation channel for monitoring the superconducting coil operation [1]. The feeder system consists of 31 feeders, 9 for the toroidal field (TF) magnet system, 6 for the poloidal field (PF) magnet system, 6 for the central solenoid (CS) modules, 5 for the correction coil (CC) system, 3 reserved exclusively for the supply of cryogens to the TF coil structure cooling system, and 2 for coil instrumentation. The PF1 feeder consists of In-Cryostat-Feeder (ICF), CryostatFeeder-Through (CFT), S-Bend-Box (SBB), Coil-Terminal-Box (CTB) and Dry-Box (DB), as shown in Fig. 1. The ICF components are located inside cryostat, enclosed by the cryostat thermal shield cooled at 80 K. The DB, CTB, SBB and part of the CFT are placed outside the cryostat. Thermal contraction of the PF1 feeder and the magnet system should be taken into account at the design stage. Meanwhile, electromagnetic (EM) forces on the PF1 feeder busbars should also be considered. Due to the complexity of the PF1 feeder structure and working conditions, the numerical simulation was carried out to check the
∗ Corresponding author. Tel.: +86 5515595029. E-mail address: [email protected] (M. Lei). 0920-3796/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.fusengdes.2012.02.019
design. With EM analysis, the EM force of PF1 busbar was calculated under the worst scenarios with the maximum working current in every coil and used for further busbar supports design, as well as for the globe model mechanical analysis. 2. PF1 design description The detailed design of the PF1 feeder is introduced below, as shown in Figs. 1 and 2. In-Cryostat-Feeder. The ICF connects to the end of the CFT and locates at the in-cryostat joints. It consists of a containment duct that prevents spilling out molten metal in the event of an electric arc between the busbars [2]. The containment duct also carries the feed and return helium lines and instrumentation cables. Cryostat-Feeder-Through. The CFT have interfaces with the ICF and SBB. Its assembly composed of the containment duct, the busbars, the cryo-pipes, the instrumentation pipes, the internal supports, the cold mass supports, the separator plate, the vacuum barrier, the cryostat extension duct, and the gravity supports [3]. S-Bend Box. The SBB contains S-shaped bends in the busbars and the cryo-pipes. The function of the S-bends is accommodating differential thermal contraction between the cryogenic feeder components and the warm feeder components. The SBB also includes most of the coil instrumentation feed-through [4]. Coil Terminal Box. The CTB is designed for easy access its components. Because most importantly the physical interfaces between the magnet and cryo-systems are located in the CTB and many feeder components require maintenance, such as cryo-control valves, HTS current leads, feeder instrumentation [4]. Dry Box. The main function of the DB is housing and protecting the feeder to power system interface and the connection between the feeder current leads and the power supply of the busbars. It is
M. Lei et al. / Fusion Engineering and Design 87 (2012) 728–731
729
Fig. 1. ITER PF1 feeder.
Fig. 3. Electromagnetic analysis model.
and can be considered as a guideline of the support design. The SOURC36 code, which is a primitive used to supply current source data to magnetic field problems, represents a distribution of current in a model. So SOURC36 is used to model magnet coils and plasma. SOLID5 has a 3-D magnetic, thermal, electric, piezoelectric and structural field capability with limited coupling between the fields. So the busbar was built with SOLID5 and meshed with 50 mm long elements. The EM model was shown in Fig. 3. EM analysis was performed to calculate Lorentz forces and magnetic field of PF1 feeder busbars under the worst scenarios with the maximum working current in every coil. The maximum magnetic flux density is 1.74 T. The EM force on busbar nodes in X Y Z direction is shown in Fig. 4. The EM force has some small fluctuation because of self field induced by neighbouring busbars. 4. Mechanical analysis 4.1. FE model The FE model of PF1 feeder is established for mechanical analysis, as shown in Fig. 5. In order to improve modeling efficiency, most of the PF1 feeder components were simulated by shell and beam elements. Due to the complexity of the model, a simplification is made to fit computer capacity. The busbar consists of parts, namely, superconducting cable, stainless steel jacket and insulation layer. Because the superconducting cable is much softer than the other two parts, it can be ignored in this analysis. The busbar and cryo-pipe support is much stiffness than
Fig. 2. The detailed CATIA model of PF1 feeder.
also to prevent the building-up of ice on the coil terminals, thus reducing the risk of arcing between the terminals [5]. 3. Magnetic analysis 3.1. EM analysis model The busbar which carries very large current will suffer from high Lorentz force due to the background magnetic field generated by the magnetic coils and the self field. This analysis aims at the magnetic field and Lorentz force on the busbar in the worst scenarios with the maximum working current in every coil. The busbar support distance can be also obtained from this analysis,
Fig. 4. Lorenz forces on busbar nodes (N).
730
M. Lei et al. / Fusion Engineering and Design 87 (2012) 728–731
Fig. 5. The FE model of PF1 feeder.
the busbar and cryo-pipe itself, so an Mpc184 element (rigid beam) is chosen to connect the busbar to the separate plate as a support [6]. Meanwhile, the interface between the busbar and support was represented by CONTA178 elements, which can define the contact stiffness, gap and friction in the contact interface. Mass21 element is employed to simulate the weight of the components ignored. In the model, a total element number of 8550 is adopted [7].
Fig. 6. Displacements of PF1 structure for case 3 (m).
4.2. Loading and boundary conditions The thermal loading on the PF1 feeder is the reduction in temperature from 292 K to 4 K during cool-down. The gravity, coil displacements and electromagnetic loads also affect the mechanical characteristics of the PF1 feeder. Vertical acceleration of −9.81 m/s was applied over the whole model as gravity acceleration. Displacement of the PF1 coils occurs due to thermal contraction and deflection of the tokamak during operation [8]. The Lorentz force was used to the further structural analysis, as shown in Fig. 4. Following load cases were analyzed for checking the PF1 feeder design. Case 1: Cooldown Case 2: Deadweight + Lorentz forces + Coil displacements Case 3: Deadweight + Cooldown + Lorentz forces + Coil displacements 4.3. Stress design criterion Allowable stresses for the PF1 feeder structure are assessed in accordance with reference [9,10]. For stainless steel 316L, the value for the design stress intensity (Sm ) is the lowest value of 2/3Sy (Yield strength = 700 MPa) in ASME at 4 K. Primary general membrane stress (Pm ) and primary bending stress (Pb ), calculated by elastic analysis for the design conditions should satisfy the following Eq. (1) and Eq. (2). The thermal stress is defined as the secondary stress (Q) due to self-balancing characteristics, and the sum of Pm , Pb and Q should satisfy Eq. 3. Pm ≤ Sm = 467 MPa
(1)
Pm + Pb ≤ 1.3Sm = 607 MPa
(2)
PL + Pb + Q ≤ 1.5Sm = 700 MPa
(3)
Fig. 7. Stress intensity of busbars and cryopipes for case 3 (Pa).
from the supporting structures and the Lorenz forces on the busbars. The stresses in the busbars and cryopipes are shown in Fig. 7. The maximum stress is 321 MPa and occurs at S-bend region. Fig. 8 shows that the maximum stresses in containment duct and separator plate is 250 MPa at ICF region. Because the busbars withstand bigger load than other components of the feeder, the assessment of the busbars was done through comparing the simulation results with criteria. Figs. 9 and 10 give the stresses of two busbars. It can be seen that the stresses (Pm , Pm + Pb and PL + Pb + Q) are all lower than the allowable stresses. The maximum stresses obtained are for two busbars in the SBB. The stress is very low at the busbar joints, because the cross-sectional area is greater than other place.
4.4. Numerical simulation The detailed FE model of the PF1 feeder was analyzed for the three load cases described above. Considering the complexity of the load cases, the analysis results of the load case 3 are extracted. Fig. 6 gives the displacement of the PF1 feeder, and it can be seen that the maximum displacement is 70.0 mm at the gimbal joints. The reason is the fact that the gimbal joints allow for articulation of the feeder when the joints is subjected to the displacements imposed
Fig. 8. Stress intensity of containment duct and separator plate for case 3 (Pa).
M. Lei et al. / Fusion Engineering and Design 87 (2012) 728–731
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5. Summary Mechanical analysis of the PF1 feeder was performed with ANSYS. During the worst combined load case, the maximum stresses are below the limit stress and the displacements are acceptable. A stresses assessment was carried out based on the criteria of ASME. It is proved that the design of the PF1 feeder can satisfied the design requirements. Acknowledgments The authors would like to thank the ITER feeder design and analysis team for their excellent design and simulation work. References
Fig. 9. The stresses of the Busbar 1.
Fig. 10. The stresses of the Busbar 2.
[1] P. Bauer, A.K., Sahu, N. Sato, The ITER Magnet Feeder Systems Functional Specification and Interface Document, ITER doc. ITER D 2EH9YM. [2] Cheng Wang, PF In-Cryostat-Feeder Design Report, ITER doc. ITER D 3U8GYJ v1.0, September 2010. [3] Lu Kun, PF&CS Feeder Cryostat Feed through Design Report, ITER doc. ITER D 3TDXJS, September 2010. [4] Junsong Shen, Kun Lu, Design of the CTB&SBB for the ITER Coil Feeders, ITER doc. ITER D 3QN7RE, September 2010. [5] Joakim Baker, CS1U Feeder, Detailed Global Model, ITER doc. ITER D 42JRUJ v1.0, November 2010. [6] Lei Mingzhun, Song Yuntao, Liu Sumei, Lu Kun, Wang Zhongwei, Primary design and analysis of feeder for ITER poloidal field, Plasma Science and Technology 13 (October (5)) (2011). [7] P. Lorrière, PF5 Global Model Analysis, ITER doc. ITER D 3SA8E8 v1.1, September 2010. [8] ITER Feeder Analysis Team, Coil Displacements for Feeder Design, ITER xls. ITER D 3TDBQY, 2010. [9] C.H. Lee, Design Review Procedure, ITER doc. ITER 2832CF, December 2009. [10] American Society of Mechanical Engineers, ASME Boiler and Pressure Vessel Code Section III, American Society of Mechanical Engineers, 1993.