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Cryostat

Home stretch for base and lower cylinder

17 Dec 2018
See more detail in the gallery below. 
Cryostat_Base_1.jpg
The components of the cryostat base—the 20-metre-in-diameter bottom disk, side shells, and 30-metre-in-diameter pedestal ring—are positioned for final assembly in the Cryostat Workshop. After welding, tests and final machining, site acceptance tests will be carried out in April 2019.

On large steel frames at either end of the Cryostat Workshop ITER's largest component—and the world's largest stainless steel high-vacuum pressure chamber—is taking shape. The 29 x 29 metre cryostat has two important functions in the ITER machine: it provides a vacuum environment to critical "cold" components (the magnets operating at 4.5 K and thermal shield operating at 80 K); and it has a structural role in supporting the mass of the Tokamak and transferring horizontal and rotational forces to the radial walls.

The assembly of the cryostat has been underway since September 2016, when teams of welding specialists began assembling the pie-slice-shaped segments of tier one of the base. Work began in 2017 on the lower cylinder and today, the fabrication of both lower sections has advanced to the final activity stage under Indian contractor Larsen & Toubro (manufacturing design, fabrication and assembly) and sub-contractor MAN Energy Solutions (welding).

The last seam welds are underway now on the lower cylinder, while the three parts of the base—lower sandwich, upper pedestal, and vertical shells—have been aligned for final welding and assembly.

See more detail in the gallery below. 

Final assembly in progress
The team in the Cryostat Workshop is now fitting and aligning the six side shells of the base on the completed bottom sandwich structure. Up above is the thick pedestal ring—the part of the cryostat base that will be supported by the concrete crown in the Tokamak Pit, and that will in turn support the upper sections of the cryostat.
Back in August, the vertical shells had already been trial fitted on the bottom sandwich structure, inspected, and then disassembled for adjustment. One by one, the six segments are being re-positioned for final assembly.
Lift #1
The completed cryostat base will weigh 1,250 tonnes—the heaviest single component to be lowered by the overhead cranes into the machine assembly well in the Tokamak Building. This operation will be the first major lift of ITER assembly in March 2020.
In total, the Indian Domestic Agency estimates that one kilometre of full penetration weld joints will have to be carried out to exacting standards on the four sections of the cryostat in the site workshop, followed by several hundred metres of weld joints to assemble the cryostat sections in the Tokamak Pit. The cryostat chamber must be completely leak free in order to achieve high vacuum within its large volume (8,500 m³).
Lower cylinder: ready in March
The lower cylinder of the cryostat is well advanced. The last seam welds should be completed in one month, and site acceptance tests are scheduled for March.
A generous volume
The ITER Tokamak and superconducting magents will all be contained within the generous volume of the cryostat. The lower cylinder is a ten-metre-tall component that will sit on the cryostat base. The upper cylinder will in turn fit perfectly on the lower cylinder and the entire assembly will be topped off with a lid.
Upon its completion the lower cylinder will be moved out of the Cryostat Workshop to protected storage on site. That will free the assembly platform for the next activity—the assembly of the upper cylinder from steel segments shipped by India.
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