Massive cryopump installed in MITICA

Neutral Beam Heating is one of the key fusion technologies that ITER is taking to a new level. Europe will provide the two injectors that will operate in tandem to raise the temperature of the ITER plasma up to 150 million °C and sustain the fusion reaction. Basically, they will create a beam of neutralised particles and shoot it into the device. The accelerated ions will then collide with particles inside the plasma and transfer them their energy.

The Neutral Beam Injectors of ITER are among the most powerful of their kind. They will be 25 m long and will each deliver up to 16.5 MW of heating power. At such scale, the transition from the drawing board to their deployment in ITER needed an intermediate step. Europe, Japan, India and ITER Organization set up the Neutral Beam Test Facility, hosted by Consorzio RFX in Italy, to explore the physics and validate the technologies. There, MITICA, a full-size prototype of an injector, is being assembled with components provided by Fusion for Energy (F4E).

The latest piece in place is the cryopump, a sort of large cold hoover inside MITICA’s vessel. It is designed to create the pristine low-density vacuum for the accelerated ions to travel through the beam line undisturbed. The component consists of 192 panels (assembled in two separate frames), coated with a porous charcoal made from coconut shells. These panels will be cooled down to around 4K (–269 °C), near absolute zero, to trap even the tiniest residual gas molecules.

F4E worked with French companies SDMS and Ravanat to manufacture and deliver the cryopump. After passing site acceptance tests two years ago, the next step was its installation inside the steel vessel. It was no simple operation, given the unprecedented size (8 m long by 2.5 m tall per side) and a required tolerance of less than a millimetre. F4E and Consorzio RFX developed bespoke tools to move the cryopump and position it accurately. The last adjustments would then be made by hand to ensure a flawless fit on all supports and interfaces.

Before the actual transfer, the technicians simulated the process and metrology experts checked every detail through solutions like virtual models or photogrammetry.  After six months of preparation, the teams eventually installed the left cryopump section in just two hours and the right one in less than a day. It was a perfect landing: specialists tracked the whole move with laser technology and confirmed the success at the end.

“Our collaboration with Consorzio RFX and ITER Organisation made this complex operation a seamless one. We devised a sound plan and implemented it thanks to the broad skillset of our teams, from metrologists to mechanical engineers or assembly experts,” celebrates Daniel Dupuy, F4E Technical Officer.

The installation will be closed with dimensional controls and tests to ensure the component is leak-tight. After that, everything will be set for commissioning. The cryopumps will be cooled down with supercritical helium from MITICA’s cryoplant, built by Europe. “Testing their performance will give us essential feedback to confirm the design and minimise uncertainty ahead of the production of the actual ITER Neutral Beam cryopumps,” explains Josep Benet, F4E Programme Manager.