Designers and engineers at the ITER Organization, at the Chinese Domestic Agency (responsible for the procurement), and at the Southwestern Institute of Physics, SWIP (tasked with manufacturing the 20-tonne components) faced a
major challenge that required many years of prototyping, load analysis and qualification testing.
In order to support the dead weight of the magnetic system*, the gravity supports needed to be extremely strong. But they also needed to be relatively elastic to absorb the loads generated by the machine's wobbling during operations and the possible accelerations generated by a seismic event.
After a lot of design optimization, the potential for flexibility was achieved by creating a structure made of ITER-grade stainless steel plates, arranged vertically and strongly bolted together at the top and bottom of the component to assure structural integrity. Each gravity support is made of twenty-one 30-millimetre-thick plates.
The challenge however was not about structure only. The design of the gravity supports had to take into account the huge difference in temperature between the top of the component, where it interfaces with the toroidal field coil operating at 4K (minus 269 °C), and the bottom that rests on the ring pedestal of the cryostat base at approximately room temperature.
At the foot of the 2.65-metre-tall component it will be like mild winter morning in Provence; at the top it will be colder than night-time on Pluto ...
This temperature gradient across the component has two main consequences. One is that "heat" from the cryostat base, if not intercepted, could raise the temperature of the coil winding packs through conduction. Also, if not smoothly distributed throughout the component, the 290 °C difference between head and toe would influence its flexibility.
Protruding from the upper part of the component, a set of pipes and manifolds forms the visible part of a gaseous helium cooling circuit that acts as a thermal buffer to intercept the "heat load" coming from the cryostat base and heading to the magnets. Circulating in two parallel sets of welded pipes for redundancy, the 80 K (minus 193 °C) gaseous flux also cools the component's plates, thus smoothing the temperature gradient of the component.