From an observation deck on the side, the surgically-clean, hospital-white room feels both like a cathedral and yet somehow too tiny for its lofty purpose. Commonwealth Fusion Systems, the company building it, says the room will soon hold a tokamak, the central donut-shaped device necessary for one approach to nuclear fusion. In the tokamak, scientists will heat up deuterium and tritium to 100 million degrees Celsius and fuse them together—producing heat that can be converted to electricity in the process.

But as impressive as Tokamak Hall may be, I left the company's campus more taken by the factory floor in the building next door. There, employees are hard at work manufacturing the company's key innovation: giant magnets made of high-temperature, superconducting tape to be used in the tokamak. The magnets keep the superheated fuel in place and stable enough for the fusion process to occur. In the facility, they're churning out magnets for the pilot project—and, eventually, to build a fleet of fusion power plants. It's a testament not just to fusion's technological potential but the commercial possibilities as well.