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  • Pre-compression ring facility | Ready to exert serious pressure

    The tool is ready; the first prototypes are on their way. Soon, a specialized test bench at CNIM (France) will enter into service to verify the resistance of th [...]

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  • Internal auditor | A partner in identifying solutions

    ITER's new internal auditor Friedrich Lincke goes where his expertise is needed to make a difference. Armed with valuable experience from many years of service [...]

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  • Sub-assembly tools | A 12-tonne beam, a crane and a little push

    There is nothing remarkable about lifting a 12-tonne beam. Except when it happens in the spectacular setting of the ITER Assembly Hall, and the beam needs to be [...]

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  • Hiring | Skilled candidates wanted

    In 2018 the number of staff members employed by the ITER Organization increased to 858, as skilled and qualified candidates joined from each of the seven ITER M [...]

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  • Toroidal field coils | First ITER magnet arrives this year

    A major milepost is projected for 2019 as the first of ITER's powerful, high-field magnets is scheduled to arrive from Japan. Let's take a look behind the scene [...]

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Of Interest

See archived entries

The fellowship of the composite rings

Juan Knaster, ITER Magnet Division

At the Italian laboratory ENEA, Juan assesses the failure mode of one of the ten mock-up rings tested to rupture. (Click to view larger version...)
At the Italian laboratory ENEA, Juan assesses the failure mode of one of the ten mock-up rings tested to rupture.
The pre-compression rings will be one of the most challenging composite structures ever manufactured. Weighing more than 3 tonnes each, they will tightly hold the ITER toroidal field coils from the top and bottom with a radial load of 7,000 tonnes per coil and withstanding hoop stress of 350 MPa per ring.

Ten years of successful R&D performed by the Italian laboratory ENEA near Frascati, under Task Agreements with the European Fusion Development Agency (EFDA), the European Domestic Agency, and direct contracts with the ITER Organization, have recently been brought to a close. The work performed at ENEA by the team of Paolo Rossi identified two suitable fabrication processes for the rings, and developed applicable non-destructive examination methods by x-ray and ultrasound. The Italian team further completed the full mechanical characterization of the glass-fibre/epoxy composite at room and operating temperatures, allowing a final optimization of the ring design, and determined the ultimate tensile stress (UTS) of six mock-up rings (in average over 1500 MPa) in a purpose-designed machine that, with 18 independent hydraulic pullers, simulates the configuration of the 18 toroidal field coils (see related article).

The last challenge was to achieve the prediction of the long-term performance of the mock-up rings: this challenge has also been met. Tests on specimens at different constant loads during long periods had allowed the definition of the creep behaviour, however the correlation with long-term tests on the mock-up rings was pending. Early last year a ring was loaded at 950 MPa (65 percent of UTS) with no measurable degradation rate after 210 days maintained at such stress. A new ring was loaded last month at 1100 MPa (77 percent of UTS) and maintained under constant load until rupturing after 140 hours, right between the breaking times of two specimens loaded equivalently.

This accomplishment occurred concurrently with the end of the European Domestic Agency call for tender for the pre-compression rings. It enables our Division to wrap up the technical understanding of the rings' performance before industry enters in the game. The expertise and the purpose-design equipment available at ENEA will continue to play an essential role for industry in the years to come.


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