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Design and test program of a simplified divertor dummy coil structure for the WEST project
Fusion Engineering and Design 88 (2013) 3165–3168
Contents lists available at ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Design and test program of a simplified divertor dummy coil structure for the WEST project L. Doceul a,∗ , J. Bucalossi a , H. Dougnac a , F. Ferlay a , L. Gargiulo a , D. Keller a , S. Larroque a , M. Lipa a , A. Pilia a , C. Portafaix b , A. Saille a , M. Salami c , F. Samaille a , B. Soler a , D. Thouvenin a , J.M. Verger a , B. Zago a a
CEA, IRFM, Saint-Paul-Lez-Durance Cedex F-13108, France ITER Organization, Route de Vinon-sur-Verdon 13115, St. Paul-lez-Durance, France c AVANTIS Engineering Groupe, ZI de l’Aiguille 46100, Figeac, France b
h i g h l i g h t s • • • •
The mechanical design and integration of the divertor structure has been performed. The design of the casing and the winding-pack has been finalized. The coil assembly process has been validated. The realization of a coil mock-up scale one is in progress.
a r t i c l e
i n f o
Article history: Received 8 July 2013 Received in revised form 10 September 2013 Accepted 25 September 2013 Available online 28 October 2013 Keywords: Tore Supra Divertor Engineering Coil
a b s t r a c t In order to fully validate actively cooled tungsten plasma facing components (industrial fabrication, operation with long plasma duration), the implementation of a tungsten axisymmetric divertor structure in the tokamak Tore-Supra is studied. With this major upgrade, so-called WEST (Tungsten Environment in Steady state Tokamak), Tore-Supra will be able to address the problematic of long plasma discharges with a metallic divertor target. To do so, it is planned to install two symmetric divertor coils inside the vacuum vessel. This assembly, called divertor structure, is made up of two stainless steel casings containing a copper winding pack cooled by a pressurized hot water circuit (up to 180 ◦ C, 4 MPa) and is designed to perform steady state plasma operation (up to 1000 s). The divertor structure will be a complex assembly ring of 4 m diameter representing a total weight of around 20 tons. The technical challenge of this component will be the implementation of angular sectors inside the vacuum vessel environment (TIG welding of the coil casing, induction brazing and electrical insulation of the copper winding). Moreover, this complex assembly must sustain harsh environmental conditions in terms of ultra high vacuum conditions, electromagnetical loads and electrical isolation (13 kV ground voltage) under high temperature. In order to fully validate the assembly and the performance of this complex component, the production of a scale one dummy coil is in progress. The paper will illustrate, the technical developments performed in order to finalize the design for the call for tender for fabrication. The progress and the first results of the simplified dummy coils will be also addressed. © 2013 Published by Elsevier B.V.
1. Introduction In order to provide ITER relevant plasma conditions for the validation of a tungsten PFC (Plasma Facing Component) technology,
∗ Corresponding author. Tel.: +33 4 42 256 165; fax: +33 4 42 254 990. E-mail address: [email protected] (L. Doceul). 0920-3796/$ – see front matter © 2013 Published by Elsevier B.V. http://dx.doi.org/10.1016/j.fusengdes.2013.09.008
the creation of an X-point magnetic configuration in the upper and lower area of the Tore-Supra vacuum vessel has been proposed [1,2]. To do so, it is planned to install an axisymmetric divertor (coil in casing) covered with two sets of actively cooled PFCs (see Fig. 1) [3,4]. Technical developments have been performed in order to finalize the design for the call for tender phase of the Tore-Supra WEST divertor structure. Moreover, in order to fully validate the assembly
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L. Doceul et al. / Fusion Engineering and Design 88 (2013) 3165–3168
Fig. 3. Cross section of the lower casing.
Fig. 1. 3D view of the divertor implementation in Tore-Supra.
and the performance of this complex component, the production of a scale one dummy coil is in progress. 2. Design description of the divertor coils The divertor structure is made up of two stainless steel casings (4 m diameter) containing a copper winding pack cooled by hot pressurized water (180 ◦ C, 4 MPa). These two casings are located at the top and bottom of the vacuum vessel. Each stainless steel casing is composed of six U-shaped 60◦ sectors mechanically attached together by a bolting system and closed after coil insertion by six bolted 60◦ cover plates (see Fig. 2). Thus the windings are fitted closely in the casing. Vacuum tightness is performed by lip welding on the casing allowing us to operate the coil windings under atmospheric pressure (see Fig. 3). The conductor (copper–silver alloy) has a rectangular cross section of (32 mm × 30 mm) with a bore of 20 mm. The conductor turns are assembled from preformed pieces by induction brazing inside the vacuum vessel in order to form a coil of 4 m diameter and 8 turns. 3. Dummy coil description Due to the mechanical complexity of this component, a simplified divertor structure model (coil and casing) has been set up in order to validate the manufacturing and the assembly procedure especially for the upper coil setting. To be representative, this mock-up will represent a scale one assembly of three conductors
Fig. 2. View of the casing and the winding pack.
(4 m diameter). This coil will be connected to a representative cooling system. In parallel it will allow to carry out and will enable us to perform electrical tests. Fig. 4 represents the mockup on its assembly support. The associated tests are scheduled to be done during the second half of 2013. 4. Dummy coil test site The dummy coil support is constituted of eight vertical brackets maintaining the casing in a representative in-vessel position. This will allow assembling the conductors in a realistic vessel environment. The dummy casing is constituted of eight 45◦ stainless steel sector bolted on the dummy coil support. Eight bolted cover plates will close the U-shaped casing after the insertion of the conductors. In the bottom area of the dummy coil support eight vertical electric telescopic cylinders are positioned. All these cylinders are connected to a monitoring system. The 8 cylinders are controlled in position individually, in pairs or simultaneously. The flexibility of all these cylinders allows precise positioning of the pre-formed and ring-shaped conductors before the brazing operation and the insertion inside the casing structure. This insertion will be done thanks to a positioning tool situated at the extremity of each cylinder which takes into account the mechanical references of the casing (see Fig. 5). According to this process, during the assembly, the winding follows the geometric reference defined by the casing. This methodology allows us to produce a tight winding pack within the outer casing wall. Inside the casing, the conductors are individually put in place and pressed together thanks to dedicated tools. In the inner
Fig. 4. Divertor dummy coil.
L. Doceul et al. / Fusion Engineering and Design 88 (2013) 3165–3168
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Fig. 7. Metallographic examination. Fig. 5. Conductor positioning tools.
diameter area, the gap between the winding and the casing will be filled by means of epoxy shims avoiding relative movement caused by electromagnetic loads. Acceptance tests are performed (electrical, leak-tightness) along the assembly process. 5. Induction brazing process Several mocks up have been fabricated to validate the induction heating equipment. A 24 kW generator equipped with a rectangular shaped inductor (see Fig. 6) appears to be the best solution for our application. The braze temperature of 650 ◦ C (melting point of the brazing alloy) has been reached at conductor joint in 47 s and maintained during 5 s as required. At the same time a temperature of 250 ◦ C has been measured at a distance of 120 mm which is sufficient low to preserve the integrity of the Kapton layer (located at 210 mm). During this operation an axial force of 300 N is applied on the brazed area by means of a spring system implemented in the brazing tool. Before brazing, the conductor joint surface is prepared following a state of the art procedure: alcohol degreasing, acid pickling and water rinsing. The brazing material is a copper–phosphorus–silver
Fig. 6. Induction brazing tool and generator.
18% alloy self-fluxing on copper with a low melting point (645 ◦ C) and a very fast flow. This alloy is delivered with a ring shape (internal diameter 25 mm, diameter of the wire 2.16 mm). Each ring is fused between the two conductors using a Ø25 mm H7-f7 male/female centering assembly. After brazing, a mechanical deoxidation of the conductor surface is performed followed by an alcohol cleaning and degreasing. Helium testing of the brazed joint is required to validate the tightness of the assembly: in addition an ultrasonic test to check the homogeneity of the brazed surface could be envisioned (study in progress). After the completion of this brazing process, the application of the insulation layers (Kapton) on the joint area could be done followed by electrical tests. Metallographic examination of a brazed sample shows that wetting of the brazing material is satisfying. While a brazing factor of roughly 80% is reached. The braze failures (lack of brazing material of 20%) are mainly located in areas where the gap is the smallest (lower than 0.01 mm) and in edges with a 90◦ of angle (see Fig. 7). The variation of the gap seems to be related to non-perfect alignment between copper parts, this will be corrected for the next brazing operation. 6. Insulation of the conductors The reference solution for the electrical conductor insulation is adhesive Kapton (20 mm wide, 3 layers of 67 m, 50% overlapping) to be tested at a ground voltage level higher than 2U + 1000 V (U = 6 kV) without breakdown. An adhesive glass fabric layer (0.17 mm) is applied on the casing in order to protect mechanically the Kapton layer. An alternative solution using the same Kapton insulation layers surrounded by glass fabric layer (2 layers of 67 m, 50% overlapping) wrapped inside a Teflon thermal heat shrink tubing (0.5 mm thick) could be envisioned in case of insulation difficulty of the reference solution. In Fig. 8 is shown schematically the insulation area around the conductor joint before and after brazing. Several set ups of Kapton wrapping followed by high voltage tests have been performed on conductor samples showing that the reference solution is complying with the requirements (13 kV without break down). The straight conductors survived up to 18 kV (ultimate voltage of the test bed) without problem whereas the Sshape conductor insulation (transition part between 2 turns, see Fig. 9) failed at 15 kV which is nevertheless sufficient.
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7. Planned tests
Fig. 8. Schematic representation of the Kapton layer overlaping.
Fig. 9. S-shape conductor wrapped with Kapton.
First of all this dummy coil will permit to qualify the elementary assembly process (basic procedures, brazing sequences, acceptance tests). Then the dummy coil will be connected to a representative pressurized water loop in order to perform hydraulic and electric tests in representative condition. Several simulations have been performed in order to check the thermal response of the dummy coil showing that the model will heat up significantly (130 ◦ C, see Fig. 10) which presents a risk of burns for the operators. According to the safety rules, a protection device will be added: thermal insulation of the coil mock up, security perimeter. The hydraulic tests permit the evaluation of the pressure drop in the conductor circuit as a function coolant mass flow. The mechanical behavior of the assembly under the thermo hydraulic loads due to the cooling circuit conditions can be evaluated. Several cycling of water temperature from room temperature to 180 ◦ C (maximal acceptable temperature for the conductors’ Kapton wrapping) will be performed. The coil will be instrumented with 8 temperature probes on the casing, a water inlet-outlet temperature measurement system, a flow meter and associated pressure measurement sensors. On their side the electric tests will permit us to perform resistivity measurements of the coils in function of the temperature, to check the electrical insulation of the system at cold and hot temperature (T◦ operating coil 70 ◦ C to 120 ◦ C). High voltage (up to 13 kV) and current (up to 2 kA) tests will be also performed on the whole assembly in order to validate its electrical behavior. These performance tests will be followed by the total dismantling of the coil in order to perform a mechanical expertise of the assembly. During the expertise repairing tests could be proposed. 8. Conclusion The technical developments performed in order to produce a preliminary design of the Tore-Supra WEST divertor structure let to the conclusion that the implementation of this project is possible. The manufacturing and the very first assembly of the dummy coil confirm the technical choices. The brazing process and the electrical insulation are validated, the following results of the assembly and performance tests of this dummy coil will give confidence to go further in the manufacturing of this crucial component. References [1] J. Bucalossi, et al., Feasibility study of an actively cooled tungsten divertor in ToreSupra for ITER technology testing, Fusion Engineering and Design 86 (October 2011) 684–688. [2] A. Grosman, et al., The WEST programme: minimizing technology and operational risks of a full actively cooled tungsten divertor on ITER, Fusion Engineering and Design 88 (October 2013) 497–500. [3] L. Doceul, et al., Engineering studies for the installation of an axi-symmetric metallic divertor in Tore-Supra, Fusion Engineering and Design 86 (October 2011) 1660–1664. [4] L. Doceul, et al., Design, integration and feasibility studies of the Tore Supra West divertor structure, Fusion Engineering and Design 88 (October 2013) 814–817.
Fig. 10. Thermal response of the dummy coil.
Contents lists available at ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Design and test program of a simplified divertor dummy coil structure for the WEST project L. Doceul a,∗ , J. Bucalossi a , H. Dougnac a , F. Ferlay a , L. Gargiulo a , D. Keller a , S. Larroque a , M. Lipa a , A. Pilia a , C. Portafaix b , A. Saille a , M. Salami c , F. Samaille a , B. Soler a , D. Thouvenin a , J.M. Verger a , B. Zago a a
CEA, IRFM, Saint-Paul-Lez-Durance Cedex F-13108, France ITER Organization, Route de Vinon-sur-Verdon 13115, St. Paul-lez-Durance, France c AVANTIS Engineering Groupe, ZI de l’Aiguille 46100, Figeac, France b
h i g h l i g h t s • • • •
The mechanical design and integration of the divertor structure has been performed. The design of the casing and the winding-pack has been finalized. The coil assembly process has been validated. The realization of a coil mock-up scale one is in progress.
a r t i c l e
i n f o
Article history: Received 8 July 2013 Received in revised form 10 September 2013 Accepted 25 September 2013 Available online 28 October 2013 Keywords: Tore Supra Divertor Engineering Coil
a b s t r a c t In order to fully validate actively cooled tungsten plasma facing components (industrial fabrication, operation with long plasma duration), the implementation of a tungsten axisymmetric divertor structure in the tokamak Tore-Supra is studied. With this major upgrade, so-called WEST (Tungsten Environment in Steady state Tokamak), Tore-Supra will be able to address the problematic of long plasma discharges with a metallic divertor target. To do so, it is planned to install two symmetric divertor coils inside the vacuum vessel. This assembly, called divertor structure, is made up of two stainless steel casings containing a copper winding pack cooled by a pressurized hot water circuit (up to 180 ◦ C, 4 MPa) and is designed to perform steady state plasma operation (up to 1000 s). The divertor structure will be a complex assembly ring of 4 m diameter representing a total weight of around 20 tons. The technical challenge of this component will be the implementation of angular sectors inside the vacuum vessel environment (TIG welding of the coil casing, induction brazing and electrical insulation of the copper winding). Moreover, this complex assembly must sustain harsh environmental conditions in terms of ultra high vacuum conditions, electromagnetical loads and electrical isolation (13 kV ground voltage) under high temperature. In order to fully validate the assembly and the performance of this complex component, the production of a scale one dummy coil is in progress. The paper will illustrate, the technical developments performed in order to finalize the design for the call for tender for fabrication. The progress and the first results of the simplified dummy coils will be also addressed. © 2013 Published by Elsevier B.V.
1. Introduction In order to provide ITER relevant plasma conditions for the validation of a tungsten PFC (Plasma Facing Component) technology,
∗ Corresponding author. Tel.: +33 4 42 256 165; fax: +33 4 42 254 990. E-mail address: [email protected] (L. Doceul). 0920-3796/$ – see front matter © 2013 Published by Elsevier B.V. http://dx.doi.org/10.1016/j.fusengdes.2013.09.008
the creation of an X-point magnetic configuration in the upper and lower area of the Tore-Supra vacuum vessel has been proposed [1,2]. To do so, it is planned to install an axisymmetric divertor (coil in casing) covered with two sets of actively cooled PFCs (see Fig. 1) [3,4]. Technical developments have been performed in order to finalize the design for the call for tender phase of the Tore-Supra WEST divertor structure. Moreover, in order to fully validate the assembly
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L. Doceul et al. / Fusion Engineering and Design 88 (2013) 3165–3168
Fig. 3. Cross section of the lower casing.
Fig. 1. 3D view of the divertor implementation in Tore-Supra.
and the performance of this complex component, the production of a scale one dummy coil is in progress. 2. Design description of the divertor coils The divertor structure is made up of two stainless steel casings (4 m diameter) containing a copper winding pack cooled by hot pressurized water (180 ◦ C, 4 MPa). These two casings are located at the top and bottom of the vacuum vessel. Each stainless steel casing is composed of six U-shaped 60◦ sectors mechanically attached together by a bolting system and closed after coil insertion by six bolted 60◦ cover plates (see Fig. 2). Thus the windings are fitted closely in the casing. Vacuum tightness is performed by lip welding on the casing allowing us to operate the coil windings under atmospheric pressure (see Fig. 3). The conductor (copper–silver alloy) has a rectangular cross section of (32 mm × 30 mm) with a bore of 20 mm. The conductor turns are assembled from preformed pieces by induction brazing inside the vacuum vessel in order to form a coil of 4 m diameter and 8 turns. 3. Dummy coil description Due to the mechanical complexity of this component, a simplified divertor structure model (coil and casing) has been set up in order to validate the manufacturing and the assembly procedure especially for the upper coil setting. To be representative, this mock-up will represent a scale one assembly of three conductors
Fig. 2. View of the casing and the winding pack.
(4 m diameter). This coil will be connected to a representative cooling system. In parallel it will allow to carry out and will enable us to perform electrical tests. Fig. 4 represents the mockup on its assembly support. The associated tests are scheduled to be done during the second half of 2013. 4. Dummy coil test site The dummy coil support is constituted of eight vertical brackets maintaining the casing in a representative in-vessel position. This will allow assembling the conductors in a realistic vessel environment. The dummy casing is constituted of eight 45◦ stainless steel sector bolted on the dummy coil support. Eight bolted cover plates will close the U-shaped casing after the insertion of the conductors. In the bottom area of the dummy coil support eight vertical electric telescopic cylinders are positioned. All these cylinders are connected to a monitoring system. The 8 cylinders are controlled in position individually, in pairs or simultaneously. The flexibility of all these cylinders allows precise positioning of the pre-formed and ring-shaped conductors before the brazing operation and the insertion inside the casing structure. This insertion will be done thanks to a positioning tool situated at the extremity of each cylinder which takes into account the mechanical references of the casing (see Fig. 5). According to this process, during the assembly, the winding follows the geometric reference defined by the casing. This methodology allows us to produce a tight winding pack within the outer casing wall. Inside the casing, the conductors are individually put in place and pressed together thanks to dedicated tools. In the inner
Fig. 4. Divertor dummy coil.
L. Doceul et al. / Fusion Engineering and Design 88 (2013) 3165–3168
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Fig. 7. Metallographic examination. Fig. 5. Conductor positioning tools.
diameter area, the gap between the winding and the casing will be filled by means of epoxy shims avoiding relative movement caused by electromagnetic loads. Acceptance tests are performed (electrical, leak-tightness) along the assembly process. 5. Induction brazing process Several mocks up have been fabricated to validate the induction heating equipment. A 24 kW generator equipped with a rectangular shaped inductor (see Fig. 6) appears to be the best solution for our application. The braze temperature of 650 ◦ C (melting point of the brazing alloy) has been reached at conductor joint in 47 s and maintained during 5 s as required. At the same time a temperature of 250 ◦ C has been measured at a distance of 120 mm which is sufficient low to preserve the integrity of the Kapton layer (located at 210 mm). During this operation an axial force of 300 N is applied on the brazed area by means of a spring system implemented in the brazing tool. Before brazing, the conductor joint surface is prepared following a state of the art procedure: alcohol degreasing, acid pickling and water rinsing. The brazing material is a copper–phosphorus–silver
Fig. 6. Induction brazing tool and generator.
18% alloy self-fluxing on copper with a low melting point (645 ◦ C) and a very fast flow. This alloy is delivered with a ring shape (internal diameter 25 mm, diameter of the wire 2.16 mm). Each ring is fused between the two conductors using a Ø25 mm H7-f7 male/female centering assembly. After brazing, a mechanical deoxidation of the conductor surface is performed followed by an alcohol cleaning and degreasing. Helium testing of the brazed joint is required to validate the tightness of the assembly: in addition an ultrasonic test to check the homogeneity of the brazed surface could be envisioned (study in progress). After the completion of this brazing process, the application of the insulation layers (Kapton) on the joint area could be done followed by electrical tests. Metallographic examination of a brazed sample shows that wetting of the brazing material is satisfying. While a brazing factor of roughly 80% is reached. The braze failures (lack of brazing material of 20%) are mainly located in areas where the gap is the smallest (lower than 0.01 mm) and in edges with a 90◦ of angle (see Fig. 7). The variation of the gap seems to be related to non-perfect alignment between copper parts, this will be corrected for the next brazing operation. 6. Insulation of the conductors The reference solution for the electrical conductor insulation is adhesive Kapton (20 mm wide, 3 layers of 67 m, 50% overlapping) to be tested at a ground voltage level higher than 2U + 1000 V (U = 6 kV) without breakdown. An adhesive glass fabric layer (0.17 mm) is applied on the casing in order to protect mechanically the Kapton layer. An alternative solution using the same Kapton insulation layers surrounded by glass fabric layer (2 layers of 67 m, 50% overlapping) wrapped inside a Teflon thermal heat shrink tubing (0.5 mm thick) could be envisioned in case of insulation difficulty of the reference solution. In Fig. 8 is shown schematically the insulation area around the conductor joint before and after brazing. Several set ups of Kapton wrapping followed by high voltage tests have been performed on conductor samples showing that the reference solution is complying with the requirements (13 kV without break down). The straight conductors survived up to 18 kV (ultimate voltage of the test bed) without problem whereas the Sshape conductor insulation (transition part between 2 turns, see Fig. 9) failed at 15 kV which is nevertheless sufficient.
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7. Planned tests
Fig. 8. Schematic representation of the Kapton layer overlaping.
Fig. 9. S-shape conductor wrapped with Kapton.
First of all this dummy coil will permit to qualify the elementary assembly process (basic procedures, brazing sequences, acceptance tests). Then the dummy coil will be connected to a representative pressurized water loop in order to perform hydraulic and electric tests in representative condition. Several simulations have been performed in order to check the thermal response of the dummy coil showing that the model will heat up significantly (130 ◦ C, see Fig. 10) which presents a risk of burns for the operators. According to the safety rules, a protection device will be added: thermal insulation of the coil mock up, security perimeter. The hydraulic tests permit the evaluation of the pressure drop in the conductor circuit as a function coolant mass flow. The mechanical behavior of the assembly under the thermo hydraulic loads due to the cooling circuit conditions can be evaluated. Several cycling of water temperature from room temperature to 180 ◦ C (maximal acceptable temperature for the conductors’ Kapton wrapping) will be performed. The coil will be instrumented with 8 temperature probes on the casing, a water inlet-outlet temperature measurement system, a flow meter and associated pressure measurement sensors. On their side the electric tests will permit us to perform resistivity measurements of the coils in function of the temperature, to check the electrical insulation of the system at cold and hot temperature (T◦ operating coil 70 ◦ C to 120 ◦ C). High voltage (up to 13 kV) and current (up to 2 kA) tests will be also performed on the whole assembly in order to validate its electrical behavior. These performance tests will be followed by the total dismantling of the coil in order to perform a mechanical expertise of the assembly. During the expertise repairing tests could be proposed. 8. Conclusion The technical developments performed in order to produce a preliminary design of the Tore-Supra WEST divertor structure let to the conclusion that the implementation of this project is possible. The manufacturing and the very first assembly of the dummy coil confirm the technical choices. The brazing process and the electrical insulation are validated, the following results of the assembly and performance tests of this dummy coil will give confidence to go further in the manufacturing of this crucial component. References [1] J. Bucalossi, et al., Feasibility study of an actively cooled tungsten divertor in ToreSupra for ITER technology testing, Fusion Engineering and Design 86 (October 2011) 684–688. [2] A. Grosman, et al., The WEST programme: minimizing technology and operational risks of a full actively cooled tungsten divertor on ITER, Fusion Engineering and Design 88 (October 2013) 497–500. [3] L. Doceul, et al., Engineering studies for the installation of an axi-symmetric metallic divertor in Tore-Supra, Fusion Engineering and Design 86 (October 2011) 1660–1664. [4] L. Doceul, et al., Design, integration and feasibility studies of the Tore Supra West divertor structure, Fusion Engineering and Design 88 (October 2013) 814–817.
Fig. 10. Thermal response of the dummy coil.