In an unassuming industrial park 30 miles outside Boston, engineers are building a futuristic machine to replicate the energy of the stars. If all goes to plan, it could be the key to producing virtually unlimited, clean electricity in the United States in about a decade.

The donut-shaped machine Commonwealth Fusion Systems is assembling to generate this energy is simultaneously the hottest and coldest place in the entire solar system, according to the scientists who are building it.

It is inside that extreme environment in the so-called tokamak that they smash atoms together in 100-million-degree plasma. The nuclear fusion reaction is surrounded by a magnetic field more than 400,000 times more powerful than the Earth’s and chilled with cryogenic gases close to absolute zero.