F4E and Alsymex ready to manufacture ITER Inner Vertical Targets

A second European contractor will be taking the Divertor Inner Vertical Targets (IVTs) to the factory line. This May, Alsymex received confirmation that the successful completion of their prototype paves the way series manufacturing. It’s a first-of-a-kind piece of equipment that will intercept the super-hot plasma particles driven by the powerful magnetic field. Fusion for Energy (F4E) signed a contract with the French company this summer for the production of 13 IVTs by 2028. In parallel, in Europe 13 other units are underway, produced by Research Instruments (RI).

In total, F4E is providing to ITER the 54 IVTs (plus 4 spares) that will sustain the heat loads coming from the plasma as part of the divertor. Located at the bottom of the vacuum chamber, the divertor is acting as an “ashtray” to receive the plasma ashes and impurities. It is made up of 54 cassettes aligned in a doughnut shape. Each of these 10-tonne components consists of a stainless-steel structure holding three plasma-facing ‘targets’: the dome, procured by Russia; the outer target, by Japan; and the IVT, part of Europe’s contribution together with the cassette body.

The journey to a fully tested prototype was no walk in the park for Alsymex or RI. “There were no precedents for an IVT with the scale and specifications of ITER. We had to create our own facilities, tools, even our own process standards”, recounts Thierry Hovsepian, Programme Managing Director at Alsymex. The collaboration with F4E started in 2015. The first stage of the contract required the validation of fabrication technologies and small mock-ups. Then, they advanced to manufacturing real-scale models, weighing half a tonne and measuring 1.5 m.

The IVTs are protected from the fierce plasma heat by a silvery coat of 1.104 blocks of tungsten, the metal with the highest melting point (3400 °C). They are meticulously arranged in eight rows to distribute the load evenly. To measure the tight spaces between them, metrology engineers used ‘Gap Gun’, a precise laser measurement system.

But for a component that will be exposed to irradiation and temperatures of up to 2000 °C, the make-or-break moment came last year with the high-flux tests. As the drills bombarded the IVTs with hot electrons, most eyes were on the joints between the blocks and the cooling pipes below them. After thousands of firing rounds, the joints proved their resistance: the final boxes were ticked and the qualified prototype travelled back to Alsymex for final integration and tests.

For F4E, it ratifies the success of a procurement strategy that involved several companies in a competition by stages. The goal was to spread expertise and mitigate risks in the development of a technology with little benchmark. F4E In-Vessel Project Manager, Pierre Gavila worked closely with Alsymex and RI to orient them and convince them manufacturing was achievable. “With patience and perseverance we managed to keep the momentum. Now, upscaling the IVT production opens a new chapter, and our partners showed they were ready”, insists Gavila. After the first batches by each contractor, the call will be re-opened for the fabrication of the remaining units.