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It sounds like a kind of gothic torture—being put in a large bucket and lowered into a 9m-deep hole at the centre of a huge machine. But it's all in a day's work for JET's inspection team as part of maintenance of JET's central magnet, the P1 solenoid.

 

The solenoid itself is made up of 1,440 turns of copper, separated into 14 "pancakes"—sections of coils stacked on top of each other. During the course of experiments these carry up to 60,000 amps and are subjected to huge magnetic forces, which cause them to shift around slightly. A set of spring-loaded keys pull the pancakes back into alignment, but over the course of thousands of plasma pulses you would expect these to wear and lose their precision.