Except for a few plywood stairs and dust that remained, the complex appeared to be almost finished. There’s a huge glass wall in the front of the building, a feature meant to show that the company is open with the community about what’s going on inside, as my tour guide, marketing director Joe Paluska, put it.

Four main buildings surround the central hall of the tokamak. These domestic support equipment were necessary to cool the magnets, heat the plasma, and measure conditions in the reactor. Most of these large industrial systems that support SPARC are either close to being ready to turn on or are actively being installed, explained Alex Creely, director of operations at tokamak, in a call after my tour.

When it finally came time to see the tokamak room that will house SPARC, we had to take a winding route to get there. A maze of concrete walls led us to the entrance and I lost track of my left and right turns. Called a labyrinth, it is a safety feature designed to prevent stray neutrons from escaping the room once the reactor is operational. (Neutrons are a form of radiation and sufficient exposure can be dangerous to humans.)

Finally, we entered a cavernous space. From our elevated vantage point on a metal walkway, we look into a room with gleaming white floors and equipment scattered around the perimeter. In the center was a hole, covered with a tarp and surrounded by bright yellow railings. That empty space is where the star of the show, SPARC, will eventually settle.

COMMONWEALTH FUSION SYSTEMS

While there is still very little tokamak in the tokamak room right now, Commonwealth has an ambitious timeline planned: The goal is to have SPARC up and running and the first plasma in the reactor by 2026. The company plans to demonstrate that it can produce more power in the reactor needed to power it (a milestone known as Q>1 in the fusion world) by 2027.

When we published our 2022 story on Commonwealth, the plan was to power up the reactor and reach the Q>1 milestone by 2025, so the schedule has been pushed back. It is not uncommon for large projects in virtually every industry to take longer than expected. But there is an especially long and complicated period. story of promises and missed milestones in fusion.

Commonwealth has certainly made progress in recent years, and it’s becoming easier to imagine the company firing up a reactor and meeting milestones the field has been working toward for decades. But there’s still a tokamak-shaped hole in suburban Massachusetts waiting to be filled.

Related reading

Read our 2022 article on Commonwealth Fusion Systems and their path to commercializing fusion energy. here.