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Vacuum vessel

First sector safely docked

12 Apr 2021

It was 8:00 p.m. on Tuesday 6 April and something quite unusual happened in the ITER Assembly Hall: applause spontaneously erupted from the teams that had been at work since early afternoon. Specialists do not usually clap for their own accomplishments but this was a unique circumstance: the lifting of the 440-tonne vacuum vessel sector and its positioning in the sector sub-assembly tool was a masterpiece of coordination and precision. Concluding five hours of tension, the applause was both an expression of relief and a tribute to the teams' competence.

VVS6_inSSAT2_06.jpg
Delivered to ITER on 7 August 2020, equipped and tested during the eight months that followed, vacuum vessel sector #6 is now safely docked on one of the sector sub-assembly tools. It is the first element of the Tokamak's core to be ready for pre-assembly.
Over the past 11 months, there have been both heavier and larger loads. The cryostat base, lower cylinder and lower cryostat thermal shield are without contest spectacular components, but none of them is part of the torus-shaped core of the machine; rather, they are large, sophisticated steel structures designed to envelop and insulate the machine. Vacuum vessel sector #6 is something else: it is the first element of the tokamak itself, a 40-degree segment of the vast toroidal chamber hosting the burning plasma— a state of matter that only exists at the core of the stars.

Steps to transfer a 440-tonne vacuum vessel sector from its horizontal orientation on the shop floor to the V-shaped sector sub-assembly tool:

  • The upending tool is used to raise the sector from horizontal to vertical. (See this article.) 
  • Because the overhead travelling cranes cannot "grasp" these major vertical loads directly, several layers of attachment are installed between crane and component. These adaptive devices are brought together before the lift operation. (Next bullet.)
  • The 90-tonne dual crane heavy lifting beam (attaches to the four hooks of the double crane to allow the cranes to work in tandem) is connected to the sector lifting tool (equipped with a balance control system that can be activated to perform horizontal-plane load adjustments along the X and Y axis), and a radial beam (which will remain attached to the vacuum vessel sector through to its final position in the assembly pit).
  • The assembled lift attachments are brought above the vacuum vessel sector in its vertical position.
  • The support and alignment units of the sector lifting tool are connected to two lifting hooks on the vacuum vessel sector. This is a tricky step due to the position and angle of the lifting hooks, which have been welded to the sector.
  • Through controllers and actuators, the sector lift tool adjusts its balancing cross beam to match the calculated centre of gravity of the vacuum vessel sector. The sector is lifted to verify that the pre-set centre of gravity is satisfactorily aligned, and that the pins in the upending tool line up with the "guiding pins" on the vacuum vessel sector.
  • If alignment is confirmed, the pins slowly disengage and the vacuum vessel sector is fully lifted and transported in front of the sector sub-assembly tool.
  • The dual crane heavy lifting beam rotates the load 90° for mounting on the V-shaped tool.
  • The load is raised more than 20 metres above the shop floor and brought above the sector sub-assembly tool.
  • The load is lowered into the tool. From the top, the sector is supported by the radial beam, which is braced on the tool. At the bottom, a temporary pillar supports the lower port extension. Two hydraulic jacks in the pillar help to adjust the vertical angle of the sector through a "push and pull" movement until the required position is achieved.
  • The sector lifting tool performs a final balancing adjustment operation before disengaging from the radial beam.
  • The sector sub-assembly operation can proceed: panels of thermal shielding and two toroidal field coils are rotated in to the sector and assembled.
On 20 March, sector #6 was transferred from the laydown area to upending tool. On 26 March, bolted and strapped in the upending tool, the component was lifted and tilted from horizontal to vertical. Ten days later, it was time to perform the third stage of the operation and position it inside the sector sub-assembly tool.

This was the culmination of an eight-month preparatory campaign since the arrival of sector #6 at ITER. Following site acceptances tests (including a leak test in September), months were spent fully instrumenting the component, first by welding bosses and other attachments onto its outer shell, then by welding magnetic sensors and other instrumentation onto the bosses.

On Tuesday 6 April, attached to a complex rigging system (see box below) and delicately pulled out of its berth, vacuum vessel sector #6 travelled a few dozen metres to face sub-assembly tool #2 and made a right angle turn.

The last phase of the operation was the most spectacular: lifted by the double overhead crane, the component rose above the 20-metre high sub-assembly tool, before slowly descending through the tool's V-shaped opening to eventually settle, hanging from the radial beam that finds a home on supporting blocks at the top of the tool.

The central and most massive element of the first pre-assembly is now in place. In the coming months, it will be encased in thermal shield panels and associated to two toroidal field coils. Before the end of the year, the 1,200-tonne pre-assembly will be lowered into the pit, marking the first step in creating the tokamak's toroidal chamber.

Watch a time-lapse video of the transfer operation here.

The lifting of the 440-tonne vacuum vessel sector and its positioning in the sector sub-assembly tool was a masterpiece of coordination and precision. A team's work, deserving of the round of applause that erupted at the operation's conclusion.
As the vacuum vessel sector slowly descends into the sub-assembly tool, the operator in white coveralls provides an indication of size. In total, the tokamak's toroidal chamber is comprised of nine vacuum vessel sectors.
Supported by the radial beam, which is docked on supporting blocks in the sub-assembly tool, the vacuum vessel sector is in place.
Procured by Korea, vacuum vessel sector #6 was close to ten years in the making. It is the first element of the Tokamak core to be ready for pre-assembly.
The component is now ready to pass over the tool (at right). Hundreds of small diagnostics devices, as well as cable looms, are visible on its outer surface.
The vacuum vessel sector has been disengaged from the upending tool and has travelled to sector sub-assembly tool #2. The component has to be lifted 20 metres to enter the V-shaped tool from above.
Three layers of rigging (a dual crane heavy lifting beam in yellow, a sector lifting tool, and a radial beam) are installed between the overhead travelling crane and the component.
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