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Media Corner
20 April 2018

Closing the circle: Final JT-60SA Toroidal Field coil is installed

The last TF coil installed in JT-60SA (Photo courtesy of QST).

The assembly of JT-60SA at its Naka site, Japan, has moved a step closer to completion with the installation of the eighteenth and last Toroidal Field (TF) coil. Pre-assembled together with the final sector of the vacuum vessel, which will contain the superheated plasma at the heart of the experiment, and its thermal shield, which will reduce the heat radiating to the cryogenically cooled coil, today, it was lifted high over the tokamak assembly frame and lowered into the waiting space on the cryostat base.

The installation of these "missing pieces" is a major milestone for the whole JT-60SA project. Now each part of the subassembly must be precisely located and joined to its neighbours. The thermal shield is challengingly flexible and access to connect it is very restricted. The welding of the vacuum vessel has had to be been carefully planned to allow for the slight change of shape that occurs when the welds cool.

The 340 degree JT-60SA tokamak assembly ready for the insertion of the final sector (Photo courtesy of QST).
The pre-assembled sector comprising TF coil, final vacuum vessel sector and its thermal shield being lifted for installation (Photo courtesy of QST).
The subassembly being placed within the JT-60SA tokamak assembly frame and lowered into the waiting space on the cryostat base (Photo courtesy of QST).

For F4E the connection of the last TF coil will be particularly significant  ̶  a testament not only to the care of the assembly contractor Toshiba but to years of preparation by F4E. "We engineered those coils so they would slot together like Lego, and the last one has to fit on both sides, so this is the final test", explains Sam Davis, F4E Technical Officer.

"The first 17 coils have been aligned with high accuracy and their positions have been 'frozen' by bolting and pinning them together. But only with all the coils acting together does the structure function as intended", says Valerio Tomarchio, who will provide expert on-site support during the positioning and the final connection.

After the TF magnet is complete, the attachment of the Poloidal Field coils will start – beginning with the 12 metre in diameter EF1, currently the world's largest pulsed superconducting coil – the next spectacular lifting operation!