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Assembly preparation

Busy month ahead

1 Mar 2021
This year at ITER, the month of March will not only mark the coming of spring. It will also set into motion a series of spectacular operations in the assembly theatre—a space that extends from the entrance of the Assembly Hall to the depths of the Assembly Pit.
Ass_Hall_View_large_0a_small.jpg
March will be a busy month in the assembly theatre. In every corner of the vast Assembly Hall, teams are preparing for the upcoming operations.
In approximately two weeks the first 400-tonne vacuum sector (#6), now equipped with the sensors and cables that will feed data from the plasma to the diagnostic devices, will be "upended" and positioned on one of the giant sector sub-assembly tools in preparation for the first sub-assembly operation. In a months-long series of assembly steps, it will be paired with two toroidal field coils and thermal shield panels to form the first 1,200-tonne subunit of the central ITER vessel.

At around the same time the first component of the in-pit assembly tool—the central column—will be bolted to the massive embedded plate on the floor of the assembly pit. The 600-tonne temporary assembly tool must be in place in time to support the weight of the vacuum vessel subassemblies as they are progressively brought into the pit and welded. Drilling activities are underway now to prepare for the installation of this trunk-like colossus.

By end March, the lower pre-compression rings and spares will be pre-positioned in the pit prior to their final installation when the tokamak torus is complete. Six rings will help the toroidal field coils push back against the electromagnetic forces of the ITER machine in operation. Made of fiberglass laminate, the pre-compression rings have an inner diameter of 5 metres and weigh approximately 3 tonnes each.

Finally, a major operation—both symbolic and spectacular—is scheduled in April: the temporary positioning of the first ITER coil, poloidal field coil #6, at the bottom of the 30-metre-deep machine pit.

More information in the image gallery below.

A perfect alignment between two vacuum vessel thermal shield outboard panels was achieved during recent alignment tests. "Opaque" to electromagnetic radiation and positioned in the immediate vicinity of the magnetic system, the silver-coated vacuum vessel thermal shield, actively cooled by gaseous helium at 80 K (minus 193 °C), adds a final layer of protection against heat transfer to the ultra-cold superconducting coils.
The plasma inside the vacuum vessel is monitored in real-time by a vast array of magnetic sensors, thermocouples and accelerometers. Data, vital for machine operation, is transmitted by cables of the type that is seen here in a temporary "bundle." Once the vacuum vessel is in place inside the pit, the cables will be pulled through trays across the cryostat feedthroughs and connected to the corresponding diagnostic systems.
Pre-compression rings, made of fiberglass composite, will encircle the tips of the toroidal field coil cases at top and bottom and "push back" against the electromagnetic forces of the ITER machine, thus reducing the fatigue on the structures of the toroidal field magnets.
The lower part of the assembly pit is getting more crowded by the day. On the rim of the cryostat base (the "pedestal"), five toroidal gravity supports are now installed. At the bottom level, six temporary supports for poloidal field coil #6 are arranged in a perfect circle. In the middle, drilling is underway to prepare for the bolting of the 600-tonne "central column" on to a massive circular embedded plate.
Stub keys and flexible support housings dot the inner surface of vacuum vessel sector #6. Flexible support cartridges will lock into these housings and act as bolts securing the blanket modules to the vacuum vessel. This massive component is now ready to be upended and positioned on one of the twin giant sector sub-assembly tools.
Manufactured by the French company CNIM with fiberglass laminate developed by Exel Composites (Finland), the pre-compression coils were stress-tested under a pressure of 36,000 tonnes prior to delivery to ITER. Metrology operations are now being performed by Metromecanica France on the first six coils to be positioned inside the assembly pit at the end of the month (3 lower rings and 3 spares).
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