Europe finishes its part of the ITER fusion reactor

Building a machine meant to recreate the power of the sun takes a very long time. On Monday, the final piece of Europe's share crossed the finish line. It was the last of five huge curved steel sections that form ITER's vacuum vessel. That's the sealed chamber where the actual fusion reaction happens. It just arrived at the ITER site in southern France after a 15-year manufacturing effort.

ITER's vacuum vessel needs nine of these sections welded together: five built in Europe, four in South Korea. With Europe's last piece delivered, every sector the project needs has now reached the site. Manufacturers Ansaldo Nucleare, Westinghouse, and Walter Tosto built each one. It's a genuine industrial achievement. It is not the same as ITER working. The sectors still need to be welded together and the rest of the reactor built around them.

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When does ITER actually produce its first plasma? That date has already slipped multiple times since the project began in 2006. Finishing the vacuum vessel's parts doesn't guarantee the next steps go faster. Fusion megaprojects like this one get judged less by any single delivery. They're judged more by whether the whole machine ever actually turns on.