“It’s not a question I get very often,” says Michl Binderbauer, CEO of TAE Technologies, when asked about the economics of his company’s design. People are more likely to query how he plans to get plasma in his reactor heated to 1 billion degrees Celsius, up from the 75 million the company has demonstrated so far. But the questions are intertwined, he says.

That extreme temperature is required because TAE uses boron as fuel, alongside hydrogen, which Binderbauer thinks will ultimately simplify the fusion reactor and result in a power plant…