Image of the week
The lighthouse in the pit
6 Sep 2021
Like a lighthouse (without a beacon) the central column rises more than 20 metres above the floor of the assembly pit. The massive structure does not belong to the tokamak, however: once connected to an array of nine radial beams it will form the backbone of a 600-tonne temporary tool that will support, align, and stabilize the vacuum vessel sub-assemblies as they are joined and welded. The tool is designed to support a total nominal weight of 5,400 tonnes.
The central column rises more than 20 metres above the floor of the assembly pit. It is one of the most massive tools used in the assembly process.
On 27 March 2021, the first and sturdiest segment of the central column (the 70-tonne bottom cylinder) was lowered into the assembly pit and carefully inserted into the circular opening at the bottom of the cryostat base. Metrology confirmed that the structure was placed within 2 millimetres of its nominal position inside of the Tokamak Global Coordinate System (TGCS).
Five months later, on 20 August, the remaining four sections were successively installed and assembled, bringing the column to its full height.
Each of the nine radial beams will be supported by the central column on one side and the concrete bioshield on the other through brackets embedded in the L2 level of the bioshield wall. On 30 August, the first of these brackets, called a radial beam support, was successfully installed in port cell #12.
The port cells are numbered at the top of the assembly pit (photo). Once all nine vacuum vessel sub-assemblies are in place, the central column will be removed. In its place, operators will install the central solenoid.
Everything is in place for a first "insertion" test. Later this week, the overhead cranes will lift a test radial beam (without its load) and insert it into the Tokamak pit in order to confirm the alignment between the central column and the radial beam support. This is one of the 27 steps leading to the installation of the first 1,200-tonne vacuum vessel sub-assembly, planned for late October.