- Email: [email protected]
Manufacturing of the full size prototype of the ion source for the ITER neutral beam injector – The SPIDER beam source
Fusion Engineering and Design 96–97 (2015) 319–324
Contents lists available at ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Manufacturing of the full size prototype of the ion source for the ITER neutral beam injector – The SPIDER beam source Mauro Pavei a,∗ , Deirdre Boilson e , Tullio Bonicelli g , Jacques Boury b , Michael Bush c , Andrea Ceracchi d , Diego Faso d , Joseph Graceffa e , Bernd Heinemann f , Ronald Hemsworth e , Christophe Lievin b , Diego Marcuzzi a , Antonio Masiello g , Bernd Sczepaniak c , Mahendrajit Singh e , Vanni Toigo a , Pierluigi Zaccaria a a
Consorzio RFX, C.so Stati Uniti 4, I-35127, Padova, Italy Thales Electron Devices, Velizy Villacoublay, France c Galvano-T GmbH, T, Raiffeisenstraße 8, 51570 Windeck, Germany d CECOM S.r.l., Via Tiburtina – Guidonia Montecelio, Roma, Italy e ITER Organization, Route de Vinon-sur-Verdon, CS 90 046, 13067 St. Paul Lez Durance Cedex, France f Max-Planck-Institut für Plasmaphysik, D-85740 Garching, Germany g Fusion for Energy, C/Joseph Pla 2, 08019 Barcelona, Spain b
h i g h l i g h t s • • • •
Negative ion sources are key components of neutral beam injectors for nuclear fusion. The SPIDER experiment aims to optimize the negative ion source of MITICA and HNB. The SPIDER Beam Source manufacturing is currently on-going. Manufacturing and assembling technological issues encountered are presented.
a r t i c l e
i n f o
Article history: Received 26 September 2014 Received in revised form 6 July 2015 Accepted 7 July 2015 Available online 18 July 2015 Keywords: Neutral beam injector Ion source RF source Manufacturing Prototypes
a b s t r a c t In ITER, each heating neutral beam injector (HNB) will deliver about 16.5 MW heating power by accelerating a 40 A deuterium negative ion beam up to the energy of 1 MeV. The ions are generated inside a caesiated negative ion source, where the injected H2 /D2 is ionized by a radio frequency electromagnetic field. The SPIDER test bed, currently being manufactured, is going to be the ion source test facility for the full size ion source of the HNBs and of the diagnostic neutral beam injector of ITER. The SPIDER beam source comprises an ion source with 8 radio-frequency drivers and a three-grid system, providing an overall acceleration up to energies of about 100 keV [1]. SPIDER represents a substantial step forward between the half ITER size ion source, which is currently being tested at the ELISE test bed in IPP-Garching, and the negative ion sources to be used on ITER, in terms of layout, dimensions and operating parameters. The SPIDER beam source will be housed inside a vacuum vessel which will be equipped with a beam dump and a graphite diagnostic calorimeter. The manufacturing design of the main parts of the SPIDER beam source has been completed and many of the tests on the prototypes have been successfully passed. The most complex parts, from the manufacturing point of view, of the ion source and the accelerator, developed by galvanic deposition of copper are being manufactured. The manufacturing phase will be completed within 2015, when the assembly of the device will start at the PRIMA site, in Padova (I).
∗ Corresponding author. E-mail address: [email protected] (M. Pavei). http://dx.doi.org/10.1016/j.fusengdes.2015.07.013 0920-3796/© 2015 Consorzio RFX. Published by Elsevier B.V. All rights reserved.
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M. Pavei et al. / Fusion Engineering and Design 96–97 (2015) 319–324
The paper describes the status of the procurement, the adaptations operated on the design of the beam source for the fabrication, with particular emphasis to the engineering development to enable the fulfillment of the tight requirements set in the technical specifications. Moreover the tests performed on the prototypes are reported. © 2015 Consorzio RFX. Published by Elsevier B.V. All rights reserved.
1. Introduction PRIMA (Padova Research Injector Megavolt Accelerated) is the name of the ITER Neutral Beam Test Facility currently under construction in Padova (Italy) [2]. PRIMA hosts two test-beds named respectively SPIDER (Source for Production of Ion of Deuterium Extracted from RF Plasma) [3], which is aimed to the development of the ion source, and MITICA (Megavolt ITER Injector Concept Advanced) [2,4] which is a full size prototype of the ITER heating neutral beam injector (HNB) [5]. The MITICA test-bed will accelerate negative ions up to an energy of 870 keV (for hydrogen) or 1000 keV (for deuterium) with a maximum beam current of 49 A or 40 A respectively. In SPIDER the acceleration voltage will be 100 kV with a maximum beam current of about 60 A. The SPIDER beam source manufacturing is started: the production of manufacturing drawings is being closed, most of the prototypes are manufactured and tested and the manufacturing of the most delicate components is well advanced.
2. Main characteristics of the SPIDER beam source The SPIDER beam source (BS) is about 3 m high, 2 m wide and 1.5 m deep; it is a complex assembly composed by more than 1000 parts, mainly of stainless steel (SS), copper and pure alumina (Fig. 1). A full description of the beam source and its main components, from requirements to design choices, analyses and verifications is reported in [6]. The whole BS operates in vacuum, at a main electric potential of −112 kV with respect to the vacuum vessel (VV), which is grounded [7,8]. However, inside the BS some components operate at different potential levels. Four cylindrical ceramic post insulators support the BS and guarantee its electrical insulation from the VV. Other smaller alumina cantilever insulators support the other components. The hydrogen or deuterium plasma is generated inside the 8 drivers by means of a radio frequency (RF) current at 1 MHz circulating in specific antennas, named RF coils, wound around the driver case [9]. Each driver is composed of a ceramic cylinder and a rear cover that closes the driver volume. The actively cooled Faraday Shield Lateral Wall (FSLW) and the Faraday Shield Back Plate (FSBP) define the plasma volume inside each driver and protect the driver walls. The plasma generated in the drivers flows into the expansion chamber. The chamber main dimensions are 1.8 m × 0.9 m × 0.2 m; its plasma facing components are the four Plasma Drivers Plate Quarters (PDPQs), closing the back of the source and the four lateral wall (LW) quarters, closing the sides of the chamber. In front of the source, negative ions (H− , D− ) are extracted from the plasma thanks to a difference of electric potential applied between the, the plasma grid (PG) and the extraction grid (EG). Finally, the negative ions are accelerated up to the required energy toward the grounded grid (GG), kept at ground potential. The bias plate (BP), aimed at reducing the extracted electron current, is made of 5 segments with large rectangular apertures; the PG, EG and GG are composed of 4 segments with 4 groups of 5 × 16 apertures each, for a total of 1280 apertures in each grid. The apertures of
Fig. 1. Exploded view of the beam source main components.
each grid segment have been designed with specific offsets from nominal positions, in order to compensate thermal expansion due to the different average equilibrium temperature of each grid and space charge effects [10]. The insulation between PG and EG (12 kV) and between EG and GG (100 kV) are guaranteed by pure alumina insulators. Downstream of the GG the electron dump intercepts the majority of the electrons passing through and exiting the accelerator. All the plasma facing components, the acceleration grids and the electron dump are actively cooled: 9 independent cooling circuits bring a total mass flow rate of about 60 kg/s of demineralized water at 20 bars through the BS. All the components that come in contact with the plasma are manufactured via electro-deposition of copper onto a copper baseplate with suitable cooling channels already machined into the baseplate. This process is widely used for nuclear fusion applications [1]. The ion source cooling water and the operating gas are fed through 2 electrically insulated bushings (called “hydraulic bushings”) on the VV, placed under the BS, dedicated to the water circuit feedthroughs. A third high voltage bushing (called “electrical bushing”) is placed over the BS for the feedthroughs of the electrical power connections required to feed the RF antennas and the electro-magnetic filter field circuits. Further low power feedthroughs are installed in the same bushing flange for BS circuits and diagnostics (electrostatic probes [11], temperature sensors [12], etc.) All these electrical connections are then linked to the Transmission Line (TL) [13] (Fig. 1).
M. Pavei et al. / Fusion Engineering and Design 96–97 (2015) 319–324
3. Manufacturing design review of the beam source In 2012 the contract for the supply of the SPIDER BS and VV was signed between F4E and a consortium of 4 companies: Thales Electronic Devices (F), as consortium leader, CECOM S.r.l. (I), Galvano-T GmbH (D) and Ettore Zanon S.p.A. (I). The extremely high complexity of the BS and VV made it necessary to group together different companies, with different know how and sound competences and experience in the production of complex parts by means of the most advanced technologies. This contract covers, as regards the BS: • the engineering design review, • the production of manufacturing drawings, • the construction of the prototypes and parts, their tests and assembly, • the tests at the factory of the whole BS, • the transport and installation in the VV at the PRIMA site and finally • the BS acceptance tests. In 2013 and 2014 the design review, the assembly check and the production of manufacturing drawings have been performed by Thales, CECOM and Galvano-T, together with the production of prototypes and of the first components of the BS. The first phase was the review of the design, aimed at defining the dimensional and geometrical tolerances of the various parts constituting the BS, in order to guarantee the correct assembly of the whole BS, optimizing the manufacturing, and verifying that the overall functional requirements defined in the technical specifications will be met. One of the issues encountered during the review was related to the demountable fittings of the cooling circuits: unlike in MITICA and the HNBs, where the cut-and-weld approach is mandatory for water pipes in vacuum, in SPIDER it was decided to keep higher maintenance flexibility by connecting the different parts of the cooling circuits by means of demountable fittings. During operation the BS is in vacuum, while inside the cooling pipes there will be water at 20 bars. In order to guarantee the absence of leaks, the cooling circuits must be individually tested with helium after installation and the maximum acceptable leak rate for the whole BS is set to 10−8 Pa m3 /s. Due to the large number of fittings (about 100 all over the BS), to the strict requirements for leak tightness and to the tight room available, it was necessary to customize specific demountable fittings featuring metallic gaskets, conceptually similar to the standard CF flanges, just less cumbersome, in collaboration with a sub-supplier. The 4 coaxial transmission lines that feed the RF current to the 8 RF coils also required additional investigations and analyses during the manufacturing design review phase. These lines were originally composed by standard 1–5/8 copper coaxial line components, allowing the use of off-the-shelf flexible elements necessary to recover possible adjustments of the BS with respect to the VV and to withstand thermal expansions during operations. A larger size of RF line would have implied customized components since off-the-shelf flexible elements were not available. As very few applications of high power RF lines in vacuum environment in steady state exist in the world, the supplier of the RF lines was unable to guarantee the functionality of the 1–5/8 coaxial line at the nominal operating parameters (200 kW for 1 h [9]). The operating limit for the RF line is set by the maximum allowable temperature for the components (about 150 ◦ C). Hence, several finite element thermal transient analyses of the RF lines during operations were performed at Consorzio RFX. Furthermore an R&D campaign on possible techniques to enhance the thermal emissivity of the RF conductors copper surfaces has been carried out. After discussion among the parties and the supplier of the RF components, it
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was decided to replace the 1–5/8 lines with the larger size 3–1/8 , renouncing the flexibility of the lines, but allowing the adjustments of the BS and the thermal expansions by a proper design of the four RF line paths and their supporting structures. Adopting the 3–1/8 lines, the power dissipated by the Joule effect is reduced by a factor 2 with respect to the 1–5/8 ones. Moreover the surface of the copper conductors is doubled, guaranteeing a substantial reduction of the operating temperature. 4. Criteria and sequence for the assembly of the grids In order to guarantee the negative ion beam optics, the grid apertures through which the ions are accelerated from −112 kV up to ground potential are required to be aligned with a maximum relative error of ±0.20 mm during operation. The segments of each grid are supported by a grid frame fixed to a mounting flange. Suitable calibrated dowels and holes and a proper assembly procedure are foreseen to guarantee the fulfillment of the apertures relative alignment. The apertures of each grid segment are precisely machined with reference to a calibrated hole that will be coupled with a correspondent supporting dowel on the grid frame. The segments are then fixed with screws allowing the free in-plane thermal expansion. Each obtained grid assembly is then installed on its mounting flange. The sequence of assembly and the check of relative alignment start with the PG that is fixed in position and kept as reference for the following alignment of EG and GG (Fig. 2). Due to the machining tolerance chain, the optimized positions of the grids will be identified by means of an algorithm that minimizes the overall misalignment of the 1280 sets of 3 apertures (PG + EG + GG). Once the actual position of each aperture is measured with respect to the segment dowel, plus the actual geometry of the frame, a simple algorithm developed in a worksheet allows to identify the best final position for each grid assembly (frame + segments) within the accelerator structure in order to minimize the aperture misalignment, in terms of sum of quadratic errors. Each grid will then be moved on its mounting flange to reach the required position. The EG and GG alignment process will be carried out with the accelerator placed in vertical position, in order to directly compensate any possible yielding caused by the dead weight of the system.
Fig. 2. Accelerator assembly sequence scheme.
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5. Manufacturing and testing of prototypes and first parts The design review of the more complex components like the grid segments, the FSLWs, FSBPs, PDPQs and LWs is completed and manufacturing drawings have been produced. The production of prototypes, required for the validation of the design, has also been carried out. Some prototypes of the heterogeneous joints between the SS pipes and the copper components have been produced, adapted to the various geometries and successfully pressure and leak tested. All these junctions are based on a male–female tight fitting between the SS and the copper parts, definitely sealed and joined by means of a galvanic deposition of copper over the joint. The prototypes for FSBP, PDPQ (designed and developed for the first time within the SPIDER project) and GG (adapted to the needs of SPIDER, starting from the solution described in [14]) are shown in Fig. 3. The production of some thermocouple and electrostatic probes prototypes is ongoing [11,12] (Fig. 4). Full scale prototypes of the ceramic insulators of the BS have been manufactured (Fig. 5); the electrical tests are still ongoing (Fig. 6) since some issues occurred before achieving the required insulation voltage. It was in fact difficult to reach the required voltage holding and several attempts were done changing the vacuum
Fig. 5. BS ceramic supports (112 kV) (a), PG–EG post insulators (12 kV) (b), EG–GG post insulators (100 kV) (c).
Fig. 3. Pictures of FSBP (a), PDPQ (b) and GG (c) heterogeneous joints prototypes.
Fig. 6. Picture of the 100 kV EG–GG post insulators installed in the high voltage insulation test stand.
Fig. 4. Pictures of one type of BP electrostatic probe prototypes installed on a mockup [11].
level, the surface finishing of the ceramic part and finally following a very delicate ramp-up of the applied voltage, during the tests. Mechanical tests will follow soon. Currently the manufacturing of the FSLWs, FSBPs, PDPQs, LWs, PG and GG segments, is proceeding. Some pictures of manufactured parts and mock-ups are shown in Figs. 7–10.
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Fig. 10. Pictures of one GG segment, during dimensional check (respectively of inner channels and of finished assembly).
6. Conclusions The construction of the SPIDER beam source components is in progress for the installation on PRIMA site in Padova (I). Specific requirements for manufacturing, assembly and testing drove some design changes and development of details. The manufacturing design review is finished; most of the required prototypes have been manufactured and successfully tested; the production of BS components is proceeding. All the pieces manufactured up to now have successfully passed the intermediate and final tests. The positive results so far obtained at the factory give confidence on correct assembly and tests on site around mid 2016. Fig. 7. FSBP mock-up during a manufacturing control (a) and of a FSBP during thermo-graphic test with infra-red camera (b).
F4E and ITER disclaimers The work leading to this publication has been funded partially by Fusion for Energy under the Contract F4E-OPE-081 and F4E-RFXPMS A-WP-2014. This publication reflects the views only of the authors, and Fusion for Energy cannot be held responsible for any use which may be made of the information contained therein. The views and opinions expressed herein do not necessarily reflect those of the ITER organization. References
Fig. 8. Picture of one of the four PG segments after the machining of the embedded cooling channels.
Fig. 9. Picture of one PDPQ during dimensional control, after machining of the embedded cooling channels.
[1] P. Franzen, B. Heinemann, U. Fantz, D. Wünderlich, W. Kraus, M. Fröschle, C. Martens, et al., Commissioning and first results of the ITER-relevant negative ion beam test facility ELISE, Fusion Eng. Des. 88 (2013) 3132–3140. [2] P. Sonato, b.V. Antoni, M. Bigi, G. Chitarin, A. Luchetta, D. Marcuzzi, R. Pasqualotto, et al., Status of PRIMA, the test facility For ITER neutral beam injectors, AIP Conf. Proc. 1515 (549) (2013), http://dx.doi.org/10.1063/1. 4792827 [3] P. Sonato, et al., The ITER full size plasma source device design, Fusion Eng. Des. 84 (2009) 269–274. [4] V. Antoni, P. Agostinetti, D. Aprile, M. Cavenago, G. Chitarin, N. Fonnesu, N. Marconato, Physics design of the injector source for ITER neutral beam injector, Rev. Sci. Instrum. 85 (February (2)) (2014) 02B128, http://dx.doi.org/ 10.1063/1.4857235 [5] R. Hemsworth, H. Decamps, J. Graceffa, B. Schunke, M. Tanaka, M. Dremel, A. Tanga, et al., Status of the ITER heating neutral beam system, Nucl. Fusion 49 (2009), http://dx.doi.org/10.1088/0029-5515/49/4/045006, 045006 (15 pp.). [6] D. Marcuzzi, P. Agostinetti, M. Dalla Palma, F. Degli Agostini, M. Pavei, A. Rizzolo, M. Tollin, et al., Detail design of the beam source for the SPIDER experiment, Fusion Eng. Des. 85 (December (10–12)) (2010) 1792–1797, http://dx.doi.org/10.1016/j.fusengdes.2010.05.039 [7] W. Rigato, et al., Design, interface development and structural analyses of SPIDER vacuum vessel, Fusion Eng. Des. 85 (December (10–12)) (2010) 2305–2311. [8] P. Zaccaria, et al., Manufacturing, assembly and tests of SPIDER vacuum vessel to develop and test a prototype of ITER neutral beam ion source, in: Proceedings of this Conference, 2015. [9] M. Bigi, et al., Design, manufacture and factory testing of the ion source and extraction power supplies for the SPIDER experiment, in: Presented at the SOFT, 2014. [10] P. Agostinetti, V. Antoni, N. Pilan, G. Serianni, Compensation of beamlet deflection by mechanical offset of the grids apertures in the SPIDER ion source, IEEE Trans Plasma Sci. 38 (7) (2010).
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[11] M. Spolaore, G. Serianni, A. Leorato, F. Degli Agostini, Design of a system of electrostatic probes for the RF negative ion source of the SPIDER experiment, J. Phys. D: Appl. Phys. 43 (12) (2010) 124018, http://dx.doi.org/10.1088/00223727/43/12/124018 [12] M. Dalla Palma, N. Pomaro, L. Trevisan, The thermal measurement system for the SPIDER beam source, Fusion Eng. Des. 86 (October (6–8)) (2011) 1328–1331, http://dx.doi.org/10.1016/j.fusengdes.2011.03.039
[13] M. Boldrin, et al., The transmission line for the SPIDER experiment, Fusion Eng. Des. 86 (October (6–8)) (2011) 754–758. [14] P. Agostinetti, M. Dalla Palma, F. Degli Agostini, D. Marcuzzi, A. Rizzolo, L. Romanato, F. Rossetto, P. Sonato, P. Zaccaria, Vacuum tight threaded junctions (VTTJ): a new solution for reliable heterogeneous junctions in ITER, in: Presented at the SOFT, 2014.
Contents lists available at ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Manufacturing of the full size prototype of the ion source for the ITER neutral beam injector – The SPIDER beam source Mauro Pavei a,∗ , Deirdre Boilson e , Tullio Bonicelli g , Jacques Boury b , Michael Bush c , Andrea Ceracchi d , Diego Faso d , Joseph Graceffa e , Bernd Heinemann f , Ronald Hemsworth e , Christophe Lievin b , Diego Marcuzzi a , Antonio Masiello g , Bernd Sczepaniak c , Mahendrajit Singh e , Vanni Toigo a , Pierluigi Zaccaria a a
Consorzio RFX, C.so Stati Uniti 4, I-35127, Padova, Italy Thales Electron Devices, Velizy Villacoublay, France c Galvano-T GmbH, T, Raiffeisenstraße 8, 51570 Windeck, Germany d CECOM S.r.l., Via Tiburtina – Guidonia Montecelio, Roma, Italy e ITER Organization, Route de Vinon-sur-Verdon, CS 90 046, 13067 St. Paul Lez Durance Cedex, France f Max-Planck-Institut für Plasmaphysik, D-85740 Garching, Germany g Fusion for Energy, C/Joseph Pla 2, 08019 Barcelona, Spain b
h i g h l i g h t s • • • •
Negative ion sources are key components of neutral beam injectors for nuclear fusion. The SPIDER experiment aims to optimize the negative ion source of MITICA and HNB. The SPIDER Beam Source manufacturing is currently on-going. Manufacturing and assembling technological issues encountered are presented.
a r t i c l e
i n f o
Article history: Received 26 September 2014 Received in revised form 6 July 2015 Accepted 7 July 2015 Available online 18 July 2015 Keywords: Neutral beam injector Ion source RF source Manufacturing Prototypes
a b s t r a c t In ITER, each heating neutral beam injector (HNB) will deliver about 16.5 MW heating power by accelerating a 40 A deuterium negative ion beam up to the energy of 1 MeV. The ions are generated inside a caesiated negative ion source, where the injected H2 /D2 is ionized by a radio frequency electromagnetic field. The SPIDER test bed, currently being manufactured, is going to be the ion source test facility for the full size ion source of the HNBs and of the diagnostic neutral beam injector of ITER. The SPIDER beam source comprises an ion source with 8 radio-frequency drivers and a three-grid system, providing an overall acceleration up to energies of about 100 keV [1]. SPIDER represents a substantial step forward between the half ITER size ion source, which is currently being tested at the ELISE test bed in IPP-Garching, and the negative ion sources to be used on ITER, in terms of layout, dimensions and operating parameters. The SPIDER beam source will be housed inside a vacuum vessel which will be equipped with a beam dump and a graphite diagnostic calorimeter. The manufacturing design of the main parts of the SPIDER beam source has been completed and many of the tests on the prototypes have been successfully passed. The most complex parts, from the manufacturing point of view, of the ion source and the accelerator, developed by galvanic deposition of copper are being manufactured. The manufacturing phase will be completed within 2015, when the assembly of the device will start at the PRIMA site, in Padova (I).
∗ Corresponding author. E-mail address: [email protected] (M. Pavei). http://dx.doi.org/10.1016/j.fusengdes.2015.07.013 0920-3796/© 2015 Consorzio RFX. Published by Elsevier B.V. All rights reserved.
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M. Pavei et al. / Fusion Engineering and Design 96–97 (2015) 319–324
The paper describes the status of the procurement, the adaptations operated on the design of the beam source for the fabrication, with particular emphasis to the engineering development to enable the fulfillment of the tight requirements set in the technical specifications. Moreover the tests performed on the prototypes are reported. © 2015 Consorzio RFX. Published by Elsevier B.V. All rights reserved.
1. Introduction PRIMA (Padova Research Injector Megavolt Accelerated) is the name of the ITER Neutral Beam Test Facility currently under construction in Padova (Italy) [2]. PRIMA hosts two test-beds named respectively SPIDER (Source for Production of Ion of Deuterium Extracted from RF Plasma) [3], which is aimed to the development of the ion source, and MITICA (Megavolt ITER Injector Concept Advanced) [2,4] which is a full size prototype of the ITER heating neutral beam injector (HNB) [5]. The MITICA test-bed will accelerate negative ions up to an energy of 870 keV (for hydrogen) or 1000 keV (for deuterium) with a maximum beam current of 49 A or 40 A respectively. In SPIDER the acceleration voltage will be 100 kV with a maximum beam current of about 60 A. The SPIDER beam source manufacturing is started: the production of manufacturing drawings is being closed, most of the prototypes are manufactured and tested and the manufacturing of the most delicate components is well advanced.
2. Main characteristics of the SPIDER beam source The SPIDER beam source (BS) is about 3 m high, 2 m wide and 1.5 m deep; it is a complex assembly composed by more than 1000 parts, mainly of stainless steel (SS), copper and pure alumina (Fig. 1). A full description of the beam source and its main components, from requirements to design choices, analyses and verifications is reported in [6]. The whole BS operates in vacuum, at a main electric potential of −112 kV with respect to the vacuum vessel (VV), which is grounded [7,8]. However, inside the BS some components operate at different potential levels. Four cylindrical ceramic post insulators support the BS and guarantee its electrical insulation from the VV. Other smaller alumina cantilever insulators support the other components. The hydrogen or deuterium plasma is generated inside the 8 drivers by means of a radio frequency (RF) current at 1 MHz circulating in specific antennas, named RF coils, wound around the driver case [9]. Each driver is composed of a ceramic cylinder and a rear cover that closes the driver volume. The actively cooled Faraday Shield Lateral Wall (FSLW) and the Faraday Shield Back Plate (FSBP) define the plasma volume inside each driver and protect the driver walls. The plasma generated in the drivers flows into the expansion chamber. The chamber main dimensions are 1.8 m × 0.9 m × 0.2 m; its plasma facing components are the four Plasma Drivers Plate Quarters (PDPQs), closing the back of the source and the four lateral wall (LW) quarters, closing the sides of the chamber. In front of the source, negative ions (H− , D− ) are extracted from the plasma thanks to a difference of electric potential applied between the, the plasma grid (PG) and the extraction grid (EG). Finally, the negative ions are accelerated up to the required energy toward the grounded grid (GG), kept at ground potential. The bias plate (BP), aimed at reducing the extracted electron current, is made of 5 segments with large rectangular apertures; the PG, EG and GG are composed of 4 segments with 4 groups of 5 × 16 apertures each, for a total of 1280 apertures in each grid. The apertures of
Fig. 1. Exploded view of the beam source main components.
each grid segment have been designed with specific offsets from nominal positions, in order to compensate thermal expansion due to the different average equilibrium temperature of each grid and space charge effects [10]. The insulation between PG and EG (12 kV) and between EG and GG (100 kV) are guaranteed by pure alumina insulators. Downstream of the GG the electron dump intercepts the majority of the electrons passing through and exiting the accelerator. All the plasma facing components, the acceleration grids and the electron dump are actively cooled: 9 independent cooling circuits bring a total mass flow rate of about 60 kg/s of demineralized water at 20 bars through the BS. All the components that come in contact with the plasma are manufactured via electro-deposition of copper onto a copper baseplate with suitable cooling channels already machined into the baseplate. This process is widely used for nuclear fusion applications [1]. The ion source cooling water and the operating gas are fed through 2 electrically insulated bushings (called “hydraulic bushings”) on the VV, placed under the BS, dedicated to the water circuit feedthroughs. A third high voltage bushing (called “electrical bushing”) is placed over the BS for the feedthroughs of the electrical power connections required to feed the RF antennas and the electro-magnetic filter field circuits. Further low power feedthroughs are installed in the same bushing flange for BS circuits and diagnostics (electrostatic probes [11], temperature sensors [12], etc.) All these electrical connections are then linked to the Transmission Line (TL) [13] (Fig. 1).
M. Pavei et al. / Fusion Engineering and Design 96–97 (2015) 319–324
3. Manufacturing design review of the beam source In 2012 the contract for the supply of the SPIDER BS and VV was signed between F4E and a consortium of 4 companies: Thales Electronic Devices (F), as consortium leader, CECOM S.r.l. (I), Galvano-T GmbH (D) and Ettore Zanon S.p.A. (I). The extremely high complexity of the BS and VV made it necessary to group together different companies, with different know how and sound competences and experience in the production of complex parts by means of the most advanced technologies. This contract covers, as regards the BS: • the engineering design review, • the production of manufacturing drawings, • the construction of the prototypes and parts, their tests and assembly, • the tests at the factory of the whole BS, • the transport and installation in the VV at the PRIMA site and finally • the BS acceptance tests. In 2013 and 2014 the design review, the assembly check and the production of manufacturing drawings have been performed by Thales, CECOM and Galvano-T, together with the production of prototypes and of the first components of the BS. The first phase was the review of the design, aimed at defining the dimensional and geometrical tolerances of the various parts constituting the BS, in order to guarantee the correct assembly of the whole BS, optimizing the manufacturing, and verifying that the overall functional requirements defined in the technical specifications will be met. One of the issues encountered during the review was related to the demountable fittings of the cooling circuits: unlike in MITICA and the HNBs, where the cut-and-weld approach is mandatory for water pipes in vacuum, in SPIDER it was decided to keep higher maintenance flexibility by connecting the different parts of the cooling circuits by means of demountable fittings. During operation the BS is in vacuum, while inside the cooling pipes there will be water at 20 bars. In order to guarantee the absence of leaks, the cooling circuits must be individually tested with helium after installation and the maximum acceptable leak rate for the whole BS is set to 10−8 Pa m3 /s. Due to the large number of fittings (about 100 all over the BS), to the strict requirements for leak tightness and to the tight room available, it was necessary to customize specific demountable fittings featuring metallic gaskets, conceptually similar to the standard CF flanges, just less cumbersome, in collaboration with a sub-supplier. The 4 coaxial transmission lines that feed the RF current to the 8 RF coils also required additional investigations and analyses during the manufacturing design review phase. These lines were originally composed by standard 1–5/8 copper coaxial line components, allowing the use of off-the-shelf flexible elements necessary to recover possible adjustments of the BS with respect to the VV and to withstand thermal expansions during operations. A larger size of RF line would have implied customized components since off-the-shelf flexible elements were not available. As very few applications of high power RF lines in vacuum environment in steady state exist in the world, the supplier of the RF lines was unable to guarantee the functionality of the 1–5/8 coaxial line at the nominal operating parameters (200 kW for 1 h [9]). The operating limit for the RF line is set by the maximum allowable temperature for the components (about 150 ◦ C). Hence, several finite element thermal transient analyses of the RF lines during operations were performed at Consorzio RFX. Furthermore an R&D campaign on possible techniques to enhance the thermal emissivity of the RF conductors copper surfaces has been carried out. After discussion among the parties and the supplier of the RF components, it
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was decided to replace the 1–5/8 lines with the larger size 3–1/8 , renouncing the flexibility of the lines, but allowing the adjustments of the BS and the thermal expansions by a proper design of the four RF line paths and their supporting structures. Adopting the 3–1/8 lines, the power dissipated by the Joule effect is reduced by a factor 2 with respect to the 1–5/8 ones. Moreover the surface of the copper conductors is doubled, guaranteeing a substantial reduction of the operating temperature. 4. Criteria and sequence for the assembly of the grids In order to guarantee the negative ion beam optics, the grid apertures through which the ions are accelerated from −112 kV up to ground potential are required to be aligned with a maximum relative error of ±0.20 mm during operation. The segments of each grid are supported by a grid frame fixed to a mounting flange. Suitable calibrated dowels and holes and a proper assembly procedure are foreseen to guarantee the fulfillment of the apertures relative alignment. The apertures of each grid segment are precisely machined with reference to a calibrated hole that will be coupled with a correspondent supporting dowel on the grid frame. The segments are then fixed with screws allowing the free in-plane thermal expansion. Each obtained grid assembly is then installed on its mounting flange. The sequence of assembly and the check of relative alignment start with the PG that is fixed in position and kept as reference for the following alignment of EG and GG (Fig. 2). Due to the machining tolerance chain, the optimized positions of the grids will be identified by means of an algorithm that minimizes the overall misalignment of the 1280 sets of 3 apertures (PG + EG + GG). Once the actual position of each aperture is measured with respect to the segment dowel, plus the actual geometry of the frame, a simple algorithm developed in a worksheet allows to identify the best final position for each grid assembly (frame + segments) within the accelerator structure in order to minimize the aperture misalignment, in terms of sum of quadratic errors. Each grid will then be moved on its mounting flange to reach the required position. The EG and GG alignment process will be carried out with the accelerator placed in vertical position, in order to directly compensate any possible yielding caused by the dead weight of the system.
Fig. 2. Accelerator assembly sequence scheme.
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5. Manufacturing and testing of prototypes and first parts The design review of the more complex components like the grid segments, the FSLWs, FSBPs, PDPQs and LWs is completed and manufacturing drawings have been produced. The production of prototypes, required for the validation of the design, has also been carried out. Some prototypes of the heterogeneous joints between the SS pipes and the copper components have been produced, adapted to the various geometries and successfully pressure and leak tested. All these junctions are based on a male–female tight fitting between the SS and the copper parts, definitely sealed and joined by means of a galvanic deposition of copper over the joint. The prototypes for FSBP, PDPQ (designed and developed for the first time within the SPIDER project) and GG (adapted to the needs of SPIDER, starting from the solution described in [14]) are shown in Fig. 3. The production of some thermocouple and electrostatic probes prototypes is ongoing [11,12] (Fig. 4). Full scale prototypes of the ceramic insulators of the BS have been manufactured (Fig. 5); the electrical tests are still ongoing (Fig. 6) since some issues occurred before achieving the required insulation voltage. It was in fact difficult to reach the required voltage holding and several attempts were done changing the vacuum
Fig. 5. BS ceramic supports (112 kV) (a), PG–EG post insulators (12 kV) (b), EG–GG post insulators (100 kV) (c).
Fig. 3. Pictures of FSBP (a), PDPQ (b) and GG (c) heterogeneous joints prototypes.
Fig. 6. Picture of the 100 kV EG–GG post insulators installed in the high voltage insulation test stand.
Fig. 4. Pictures of one type of BP electrostatic probe prototypes installed on a mockup [11].
level, the surface finishing of the ceramic part and finally following a very delicate ramp-up of the applied voltage, during the tests. Mechanical tests will follow soon. Currently the manufacturing of the FSLWs, FSBPs, PDPQs, LWs, PG and GG segments, is proceeding. Some pictures of manufactured parts and mock-ups are shown in Figs. 7–10.
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Fig. 10. Pictures of one GG segment, during dimensional check (respectively of inner channels and of finished assembly).
6. Conclusions The construction of the SPIDER beam source components is in progress for the installation on PRIMA site in Padova (I). Specific requirements for manufacturing, assembly and testing drove some design changes and development of details. The manufacturing design review is finished; most of the required prototypes have been manufactured and successfully tested; the production of BS components is proceeding. All the pieces manufactured up to now have successfully passed the intermediate and final tests. The positive results so far obtained at the factory give confidence on correct assembly and tests on site around mid 2016. Fig. 7. FSBP mock-up during a manufacturing control (a) and of a FSBP during thermo-graphic test with infra-red camera (b).
F4E and ITER disclaimers The work leading to this publication has been funded partially by Fusion for Energy under the Contract F4E-OPE-081 and F4E-RFXPMS A-WP-2014. This publication reflects the views only of the authors, and Fusion for Energy cannot be held responsible for any use which may be made of the information contained therein. The views and opinions expressed herein do not necessarily reflect those of the ITER organization. References
Fig. 8. Picture of one of the four PG segments after the machining of the embedded cooling channels.
Fig. 9. Picture of one PDPQ during dimensional control, after machining of the embedded cooling channels.
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