Pre-compression rings
An iron fist - in reverse
10 Sep 2018
Knowing that the large electromagnetic forces at work during machine operation would cause stress over time to ITER's largest magnet set, engineers devised a compression system to "push back." The resilience of the solution—large composite "pre-compression" rings that will encircle the tips of the toroidal field coil cases at top and bottom—is about to be tested at a dedicated facility.
This unusual test bench has 36 actuators exerting a force of 1,000 tonnes each. They will operate simultaneously to subject the toroidal field coil magnet system's pre-compression rings to ITER-like forces in order to test their resistance and durability.
At a brand-new facility at CNIM (La Seyne-sur-Mer, France) everything is ready for the arrival of an exceptional test bench, capable of applying stresses similar to those of ITER operation to the toroidal field coil pre-compression rings and measuring millimetric deformation.
The tool, developed by Douce Hydro (France) in collaboration with CNIM, will subject the rings to a combined circumferential force of 36,000 tonnes while maintaining a positional accuracy of 0.1 mm. The test on each ring will last a few hours and will be supplemented by other tests to confirm creep and fatigue performance.
The ITER Organization is procuring the test facility and tooling through a contract awarded to the CNIM/Douce Hydro consortium, while the European Domestic Agency has developed the conceptual design of the test facility and is responsible for technical progress.
Neil Mitchell, ITER Magnet Division head, cites the collaboration as "an excellent example of ITER Organization and the European Domestic Agency working as a single team to construct the facility within budget and to schedule."
At a newly created facility at CNIM, representatives of ITER, the European Domestic Agency, manufacturer Douce Hydro and host CNIM stand before the test bench where nine pre-compression rings will be tested (three upper, three lower and three spare).
The European Domestic Agency is responsible for the fabrication of nine pre-compression rings (three top, three bottom and three spare). Weighing roughly 3 tonnes each, with an inner diameter of 5 metres, they are made of a fiberglass composite that consists of more than one billion minuscule glass fibres glued together using epoxy resin. This material—the result of an in-depth R&D program—has proved to be the best material for withstanding high loads and avoiding the circulation of current.
The first full-scale prototype should be delivered to the test facility by the European Domestic Agency before the end of the year. Eventually all nine of the pre-compression rings will be proof tested before installation.
The first full-scale prototype should be delivered to the test facility by the European Domestic Agency before the end of the year. Eventually all nine of the pre-compression rings will be proof tested before installation.