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​An important milestone has been reached on the , with the re-installation of four of the largest magnetic coils inside the machine.

Many of the internal poloidal field magnetic coils are new, especially around the upper and lower parts of the device. Only four coils in MAST-Upgrade remain from the original MAST experiment — the large mid-plane P4 and P5 (upper and lower) coils.

But it was not as simple as just leaving them in the vessel — they were removed with all the other internal equipment to enable the interior to be fully stripped down and cleaned. The coils were also comprehensively cleaned, including a hydroblast pressure wash. The P5 coils were then fitted with new flux loops.

Prior to re-installation, a full spatial survey of the vessel and coil supports and indeed of the shape of the coils themselves was undertaken. All four cleaned and surveyed coils were re-installed a few weeks ahead of schedule, on new strengthened coil supports inside the MAST-U vessel. A final survey indicated they were within 0.5mm of their optimum position — minimizing any stray fields when operations commence.

Coil re-installation is an important step, marking in many ways the beginning of the rebuild of the tokamak.