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On an overcast day in early October, I picked up a rental car and drove to Devens, Massachusetts, to visit a hole in the ground.

Commonwealth Fusion Systems has raised over $2 billion in funding since it spun out of MIT in 2018, all in service of building the first commercial fusion reactor. The company has ambitions to build power plants, but currently the goal is to finish putting together its first demonstration system, the SPARC reactor. The plan is to have it operating by 2026.

I visited the company’s site recently to check in on progress. Things are starting to come together around the hole in the floor where SPARC will eventually be installed. Looking around the site, I found it becoming easier to imagine a future that could actually include fusion energy. But there’s still a lot of work left to do. 

Fusion power has been a dream for decades. The idea is simple: Slam atoms together and use the energy that’s released to power the world. The systems would require small amounts of abundant fuel and wouldn’t produce dangerous waste. The problem is, executing this vision has been much slower than many had hoped.

Commonwealth is one of the leaders in commercial fusion. My colleague James Temple wrote a feature story, published in early 2022, about the company’s attempts to bring the technology to reality. At the time, the Devens location was still a muddy construction site, with the steel and concrete just starting to go into the ground.

Things are much more polished now—when I visited earlier this month, I pulled into one of the designated visitor parking spots and checked in at a reception desk in a bustling office building before beginning my tour. There were two main things to see: the working magnet factory and the cluster of buildings that will house and support the SPARC reactor.

We started in the magnet factory. SPARC is a tokamak, a device relying on powerful magnets to contain the plasma where fusion reactions take place. There will be three different types of magnets in SPARC, all arranged to keep the plasma in position and moving around in the right way.

The company is making its own magnets powered with tape made from a high-temperature superconductor, which generates a magnetic field when an electric current runs through it. SPARC will contain thousands of miles’ worth of this tape in its magnets. In the factory, specialized equipment winds up the tape and tucks it into metal cases, which are then stacked together and welded into protective shells.  

After our quick loop around the magnet factory, I donned a helmet, neon vest, and safety glasses and got a short safety talk that included a stern warning to not stare directly at any welding. Then we walked across a patio and down a gravel driveway to the main complex of buildings that will house the SPARC reactor.

Except for some remaining plywood stairs and dust, the complex appeared to be nearly completed. There’s a huge wall of glass on the front of the building—a feature intended to show that the company is open with the community about the goings-on inside, as my tour guide, chief marketing officer Joe Paluska, put it.  

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

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

Finally, we stepped into a cavernous space. From our elevated vantage point on a metal walkway, we peered down into a room with gleaming white floors and equipment scattered around the perimeter. At the center was a hole, covered with a tarp and surrounded by bright-yellow railings. That empty slot is where the star of the show, SPARC, will eventually be installed.

While there’s still very little tokamak in the tokamak hall right now, Commonwealth has an ambitious timeline planned: The goal is to have SPARC running and the first plasma in the reactor by 2026. The company plans to demonstrate that it can produce more energy in the reactor than is 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 flip on the reactor and reach the Q>1 milestone by 2025, so the timeline has slipped. It’s not uncommon for big projects in virtually every industry to take longer than expected. But there’s an especially long and fraught history of promises and missed milestones in fusion. 

Commonwealth has certainly made progress over the past few years, and it’s getting easier to imagine the company actually turning on a reactor and meeting the milestones the field has been working toward for decades. But there’s still a tokamak-shaped hole in suburban Massachusetts waiting to be filled. 

Now read the rest of The Spark

Related reading

Read our 2022 feature on Commonwealth Fusion Systems and its path to commercializing fusion energy here. 

In late 2022, a reactor at a national lab in the US generated more energy than was put in, a first for the industry. Here’s what meeting that milestone actually means for clean energy. 

There’s still a lot of research to be done in fusion—here’s what’s coming next. 

Another company called Helion says its first fusion power plant is five years away. Experts are skeptical, to say the least.

Another thing

Generative AI will add to our growing e-waste problem. A new study estimates that AI could add up to 5 million tons of e-waste by 2030. 

It’s a small fraction of the total, but there’s still good reason to think carefully about how we handle discarded servers and high-performance computing equipment, according to experts. Read more in my latest story. 

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