After 81 weeks, we have reached the formal end of the JET shutdown. The final items were removed from the torus on Monday afternoon, and on Tuesday the port doors were closed and sealed by members of the vacuum group. That is a milestone in itself, but it is also a pre-requisite for the next stage. Last Tuesday it was formally declared that JET is in an operational state called “Intervention”.
From a practical point of view you might ask why this nomenclature is important. JET is operated under the terms of a document called the ’Safety Case’, which has been extensively revised and updated while the machine has been ‘asleep’. The safety case defines the conditions required for different activities. In order to work inside the machine we must be in ‘shutdown’ and one of the requirements is that all power supplies to the machine must be isolated. Now that we are back into ‘intervention’ we can start to switch the power back on. There are nearly 2,000 control cubicles in total. Every single one had to be checked for electrical safety in the last 18 months. During the next week the first 150 of them will be turned on ready for ‘pumpdown’ when we start to remove the air from the torus and work towards the clean vacuum conditions that we need.
Of course there is still a lot of work to do before the machine re-starts. Hundreds of vital pieces of equipment and their protection systems have to be formally re-commissioned in a phase known as ‘restart’ before we can return to plasma operations.
This weekly update now draws to a close. Indeed the ‘Shutdown Weekly’ is being shut down. Hopefully they have given our regular readers an insight into the day-to-day activities at JET when the machine is not operational.