National Centralized Tokamak Project
JT-60 Machine and Database
Following the completion of 340° vacuum vessel thermal shield (VVTS) assembly, the assembly of the toroidal field coils began. The TF coils are the most important components for the torus type plasma confinement device.
The first coil (TFC-10) was erected with a dedicated standing jig to measure the deformation by its own weight. Such deformation causes the error magnetic field which deteriorates plasma performance. In the TF coil assembly, the coils will be installed while such deformation is measured with a laser tracker and modified by precise positioning with jacks.
The TFC-10 was successfully inserted from the 20° VVTS opening and finally transported to the appropriate position (opposite to the 20° opening).
The JT-60SA superconducting coils will be cooled down to cryogenic temperature (4K) during the operations. In order to maintain such a cryogenic state, it is necessary to reduce the heat intrusion from the surrounding components.
The JT-60SA has the thermal shields (TSs), consists of double stainless panels, with a thickness of 3 mm, with cooling pipes located in between. In the JT-60SA operation, 80 K gaseous Helium is circulated through the pipes to cool the TSs and supress the heat intrusion to the superconducting coils.
The vacuum vessel thermal shields (VVTSs) mainly shield the radiation from the VV (at room temperature in operation). The VVTS assembly, which began in January 2015, finished this month except the final 20° sector. The final sector is necessary to be unmounted for the later toroidal field coil assembly. The final sector was temporarily inserted into the 20° opening and its connection with the both 340° sector ends was checked as well.
In the JT-60SA project, Europe manufactures 18 superconducting toroidal field (TF) coils, and Japan produces 6 superconducting equilibrium field (EF) coils and 1 superconducting central solenoid. 3 EF coils to be positioned at the lower side of tokamak (EF4, EF5 and EF6) have already been completed and temporarily installed to the bottom of the 340° vacuum vessel (VV) in the JT-60 torus hall. This month, the remaining 3 EF coils to be mounted to the upper side (EF1, EF2 and EF3) were completed.
The EF1 (an outer diameter of 12.0 m and a weight of 27 t), EF2 (an outer diameter of 9.6 m and a weight of 27 t), and EF3 (an outer diameter of 4.4 m and a weight of 21 t) had been manufactured in the superconducting coil winding building of the Naka institute since July 2014. Especially, the EF1 is the largest among all of the JT-60SA coils. Those large superconducting coils were produced with excellent high precision of ±0.2 mm. The coils are scheduled to be transported to the JT-60 assembly hall and mounted to the tokamak, after the TF coil assembly is finished and the final 20° VV sector is inserted and jointed.
The JT-60SA construction is progressing steadily at Naka Fusion Institute. The delivery of the superconducting toroidal field (TF) coils, procured by Europe, to the Naka institute started this month.
JT-60SA has a total of 18 TF coils, whose conductors are made from Niobium Titanium (NbTi) that enables continuous energization. Those coils are manufactured by Europe (9 each by France and Italy) and mounted to the tokamak by Japan. This month, the initial and second delivery of the coils, manufactured by France, arrived at the port of Hitachi in Japan via marine transport. And then, they were delivered to the Naka institute on July 20 and August 25, 2016. European colleagues has decided to give a female name to each coil at the shipment from Europe. The first and second coils were named ANNIE and BRIGITTE, respectively.
On July 26 2016 (soon after the initial TF coil delivery), "Celebration of Steady Progress of Delivery, Installation and Commissioning of JT-60SA Component Procured by France" was held at the Naka institute. The participants from France and Japan celebrated the start of the TF coil delivery.
The systems and components, which Europe procures for JT-60SA, have been delivered steadily. The superconducting magnet power supplies (SCMPSs) procured by France were delivered to the Naka Fusion Institute at the end of June 2016.
The PSs delivered this time were a total of 5 thyristor DC PSs to be connected to the toroidal field (TF) coils and 4 poloidal field (PF) coils. The TF coil PS continuously supplies a unipolar output of 80V/25.7A at maximum. The PF coil PSs supply the bipolar output of 1kV/20kA at maximum for 220 seconds every 30 minutes. These PSs will be connected to each superconducting coils via a quench protection circuit. In addition, a switching network unit or the booster PSs, which provide a high voltage at the plasma start-up, will be connected to the PF coils.
Following the SCMPS delivery, various tests toward their installation and final acceptance at the site will be performed from now on.
The 340° vacuum vessel (VV) torus, whose assembly began in May 2014, has been completed, and the assembly of the vacuum vessel thermal shields (VVTSs) has been started. Accordingly, a facility tour was offered to the press at the Naka Fusion Institute on 3 February 2016.
The TSs surround the superconducting coils: 18 toroidal field coils, 6 equilibrium field coils, and 1 central solenoid. The VVTSs, whose assembly has recently begun, will be mounted around the VV.
The superconducting coils are cooled down to cryogenic temperature (4K) during the operation. In order to maintain such a cryogenic state, it is required to reduce the heat transfer from the room temperature side. The TS has a double wall, made of 3 mm thick stainless steel. Furthermore, a long cooling pipe to circulate 80K helium throughout the TS is sandwiched between the walls, and cools the TS itself during the operation. Such a structure reduces the heat to the superconducting coils. The VVTSs shield the thermal radiation mainly from the VV, which is at room temperature during the operation.
In addition to the VVTS assembly, the press had a look inside of the VV after the constraint jigs were removed. They seemed to be interested and took many photos of the spacious VV interior.
This facility tour was reported on 6 media afterward.
The assembly of the 340° vacuum vessel (VV) torus began in May 2014 and finished in August 2015. The final 20° VV sector has not been integrated yet, because the vacuum vessel thermal shields (VVTSs) and toroidal field (TF) coils will be inserted through the 20° gap to be mounted around the VV.
In December 2015, the final 20° sector was temporarily inserted into the gap between the 340° torus ends to measure the complete VV position.
In the JT-60SA tokamak assembly, 17 TF coils, out of 18 in total, will be mounted around the 340° VV at first. Then, the 18th VVTS and TF coil will be assembled onto the final 20° sector. Finally, such an integrated sector will be incorporated with the 340° torus. The final sector will be jointed to the torus by welding with the splice plates which are 70 - 110 mm wide. Their shapes will be customised according to the measurements obtained this time.
Although the final sector had not been integrated permanently, the entire 360° VV torus appeared for a moment. It was a rare and valuable opportunity to see the 360° VV torus only, as it will be hidden by the TF coils as the assembly goes on.
The assembly of the 340° vacuum vessel (VV) torus began in May 2014 and finished in August 2015.
In October 2015, a rotary crane was mounted on the support structure surrounding the torus. The crane will be used to assemble the vacuum vessel thermal shields (VVTSs) and toroidal field (TF) coils. The VVTSs and TF coils will be inserted through the 20° gap of the torus, where the final 20° sector has not been installed yet, and then threaded over the VV into their designated positions.
The rated load of the crane is 30 t. It rotates 360° toroidally and moves along the girders horizontally, while pulling up the cargo. Thanks to it, the VVTSs and TF coils will be assembled efficiently.
After the 340° VV torus was completed, the constraint jigs mounted inside of the VV sectors were removed. The jigs had supported the sectors from the inside, and restrained them from deforming when they were set up or jointed by welding.
The jigs were disassembled, while the amount of the VV deformation was carefully checked. All of the jigs, except ones at both ends of the 340° torus, were removed, and a spacious room appeared inside of the VV. It shows how large the JT-60SA plasma will be.
Because the power supplies at room temperature feed the superconducting coils of the JT-60SA device, the thermal interface between the components in room and cryogenic (4.5 K) temperature is required. In the JT-60SA, the coil current with a maximum value of about 26 kA is supplied through a high temperature superconductor (HTS) current lead, made from Bi-2233/AgAu and cooled down to 50 K.
The HTS current leads are procured by Europe. The Karlsruhe Institute of Technology in Germany is responsible for the development and manufacturing of them.
One pair of the HTS current leads for the toroidal field (TF) coils, out of 3 pairs in total, had been delivered before, and the balance (2 pairs) was transported to the Naka Fusion Institute this time. Therefore, all of the 6 current leads (3 pairs) for the TF coils have arrived already.
Hereafter, these HTS current leads will be provided to the manufacturer of TF coil terminal boxes. Then, 10 pairs (a total of 20 current leads) for the poloidal field coils will be delivered to the Naka Fusion Institute in 2016.
The assembly of the 340° vacuum vessel (VV) torus began in May 2014 and finished in August 2015.
The VV has a double walled structure made of thin (18 mm) and low cobalt stainless steel (316L). It is composed of 10 sectors assembled (or to be assembled) on the cryostat base: seven 40°, two 30° and one 20° sectors. The 340° of the entire VV has been completed so far. (The last 20° sector will be incorporated after the other components, such as the vacuum vessel thermal shields (VVTSs) and toroidal field coils, are inserted from the 20° gap and mounted around the VV.)
Firstly, two 110° (40° × 2, 30° × 1) and one 120° (40° × 3) sectors were integrated by welding directly or with the splice plates. Then, these 3 sectors were jointed to each other by welding with the splice plates.
The splice plates are approximately 70 - 100 mm wide. Each plate was customised to adjust a margin in the gap between the sectors so as to accommodate the gaps exceeded the specified tolerances and the thermal deformation by welding, and to maintain the perfect circularity of the VV in the toroidal direction.
The 340° VV torus was fully integrated now. The VVTSs are planned to be assembled hereafter.
The JT-60SA device employs the superconducting coils to generate and maintain required magnetic fields for a long time. Accordingly, it also has the cryogenic system, procured by Europe, to cool down the superconducting coils.
The helium (He) refrigerator, which is one of the world’s largest, was delivered from France and installed at the Naka site in April 2015. Then, 6 gaseous He storage vessels were delivered and installed in May. A single vessel has a length of 22 m, a diameter of 4 m and a weight of about 70 t.
The vessels were carried by sea from Europe, discharged at Hitachi port in Japan, and one by one transported to the Naka Fusion Institute on the public road while controlling traffics in the midnight hours. At the Naka site, the vessels were lifted and unloaded from a heavy truck and positioned onto the vessel foundations with a 550 t crane. The large-scale and difficult transportation in Japan and installation at the site were completed within about 2 weeks.
On 20 April 2015, JAEA held a "Celebration of the delivery of main components and start of their on-site installation by EU, and completion of the initial assembly of the vacuum vessel of the JT-60SA tokamak". More than 200 guests from Europe and Japan, such as Mr. Viorel Isticioaia-Budura (Ambassadors of the European Union to Japan) and Mr. Motoyuki Fujii (State Minister of MEXT, Japan), attended the ceremony and a site tour.
The European contributors, as well as Japanese ones, are responsible for delivery and installation of the JT-60SA components. Recently, the Italian contributor delivered the first lot of the magnet power supply and the French did the main components of the Helium cryogenic system which is one of the world´s largest for nuclear fusion device use. Italian and French engineers have already begun installation on site. The first pair of high temperature superconductor current leads, to provide power for the superconducting coils, also arrived from Germany. This means that the contributors of all European countries concerned have started components delivery, including the Spanish contributors who delivered the cryostat base in January 2013. In the meantime, a Japanese vacuum vessel manufacture finished their initial assembly phase, the 340° structure installation on the cryostat base.
JAEA shared such project status with the guests and received their congratulations and expectations. The ceremony successfully came to a close.
The vacuum vessel (VV) assembly, which started in May 2014, has been progressed steadily in the torus hall. Nine VV sectors forming 340° structure in the toroidal direction were installed on the cryostat base in January 2015. A space on which the last 20° VV sector will be installed is kept empty pending placement of the VV thermal shield, which cuts out thermal radiation between the cryo-cooled superconducting coils and the room-temperature VV wall, and insertion of 18 toloidal field coils procured by Europe. After the completion of the welding between the installed VV sectors, the VV thermal shield insertion work will start in autumn 2015.
Seventh VV 40° sector installed
The vacuum vessel (VV) assembly, which started in May 2014, has been progressed steadily. 10 completely manufactured VV sectors are installed sequentially on the cryostat base to be welded each other. In November 2014, the seventh VV 40° sector was installed and seven VV 40° sectors (280°) were lined up on the cryostat base. The VV sector assembly will be continued until it becomes the 340° structure, and after that, the toroidal field coils (TFCs), manufactured in Europe, will be inserted from the empty space in which the very last VV 20° sector is installed. Finally, the last VV sector together with the last TFC will be installed to complete the 360° structure.
QPC components delivered to Naka
In parallel with the VV assembly, the quench protection circuit (QPC) components were delivered from Genoa, Italy to Naka, Japan in September 2014. When a quench occurs in the superconducting coils, the magnetic energy stored in the coils needs to be released while stopping the plasma discharge. The QPC safely converts the magnetic energy stored in the superconducting coils into thermal energy by leading the coil current to damp resistors. The QPC will be connected in series with the toroidal field coils and poloidal field coils in future.
The assembly of the superconducting tokamak JT-60SA has been fully in progress at the Naka Fusion Institute. In May 2014, the assembly of the vacuum vessel (VV), which confines plasma, has started in the JT-60 torus hall.
In JT-60SA, plasma is confined inside the VV, which is kept under ultrahigh vacuum condition. The VV is a doughnut-shaped double-walled structure made of stainless steel (316L) with an outer diameter of 10 m and a thickness of 18 mm, and its cross-section is D-shaped with a transverse diameter of 3.5 m and a longitudinal diameter of 6.5 m. It consists of 10 parts (sectors): one 20° sector, two 30° sectors and seven 40° sectors, which complete the 360°structure. Since the VV is an extremely large device with a total weight of 150 t, each sector is manufactured and assembled one by one at the VV sector assembly building. The assembly work started in April 2011 and was completed in April 2014. These sectors will be joined and installed using the latest welding technology. The two out of ten sectors were installed on the cryostat base and it was opened to the press on 4 June 2014. In future, the remaining eight sectors will be installed sequentially, and after installing and joining the ninth sector (340°), leaving aside the final (tenth) 20° sector, the assembly of the toroidal field coils, procured by Europe will start.
The assembly work of the superconducting tokamak JT-60SA has been fully in progress at the Naka Fusion Institute. The lower equilibrium field (EF) coils, which control the plasma position and shape, were delivered to the torus hall and temporarily installed on the cryostat base in the middle of January 2014.
JT-60SA has six EF coils in total and three of them are lower EF coils, EF4 (outer diameter: 4.4 m, weight: 30 t), EF5 (outer diameter: 8.2 m, weight: 23 t) and EF6 (outer diameter: 10.5 m, weight: 33 t) completely manufactured by the end of December 2013. The EF5 and EF6 were manufactured in the PF coil manufacturing building constructed at the Naka Fusion Institute due to their huge size. The completed three EF coils were delivered in three days (15, 18 and 22 January 2014) to the torus hall and then temporarily installed on the cryostat base. Since the EF5 and EF6 are the world´s largest class superconducting coils, they were stood upright and transported through the newly constructed delivery entrance on the wall of torus hall using the transport jig and rails. On 22 January 2014, the EF coil delivery and installation were performed as journalists watched, and successfully completed. In FY2014, the vacuum vessel assembly, whose 10 parts (sectors) have already completed, will start.
At the Naka Fusion Institute, modification of the JT-60U to a full superconducting tokamak, JT-60SA, has been progressed under the Satellite Tokamak Programme jointly implemented by Europe and Japan, and under the National Centralized Tokamak Programme. The cryostat base, the first major component made in Europe, arrived at the Naka Fusion Institute. On 25 March 2013, the "Celebration of the delivery of the first component from EU and start of assembly of the JT-60SA tokamak" was held.
About 100 guests from home and abroad, including Mr. Teru Fukui, Senior Vice-Minister of MEXT, Japan, Mr. Enrique. Asorey, Deputy Head of Mission, Ambassador of Spain to Japan (on behalf of Ms. Carmen Vela, Secretary of State for Research, Development and Innovation of the Spanish Ministry for Economy and Competitiveness), Mr. Shinichi Sakaki, Deputy Governor of Ibaraki prefecture, and Mr. Toru Umino, Mayor of Naka city, attended the ceremony. In the JT-60 torus hall, where the cryostat base is installed, the bolt tightening ceremony was performed by the representatives with the guests and attendees watching it.
At the Naka Fusion Institute, the modification of the JT-60U to a full superconducting tokamak, JT-60SA, has been progressed under the Satellite Tokamak Programme jointly implemented by Europe and Japan, and under the National Centralized Tokamak Programme. The related devices for JT-60SA have been designed and manufactured by Europe and Japan since 2007. The cryostat base, the first major component made in Europe, arrived at the Naka Fusion Institute and the tokamak assembly started.
The cryostat base, a large-scale structure (diameter: 12 m, height: 3 m, weight: 250 t) made of stainless steel, was divided into seven sectors and transported by ship from Spain to Japan. The ground transportation from the port of Hitachi to the Naka Fusion Institute was conducted in seven stages, each time requiring the road to be closed before dawn due to the maximum sector width of 6.5 m. Finally, on 28 January 2013, the tokamak assembly started as many journalists watched. The assembly will take six years to be completed and the operation of JT-60SA will start in 2018.