Most STARTUPS need time to prove that they can be trusted with investors’ money, let alone dangerous technologies. But not Fusion Energy Tech, a Chinese company in the city of Hefei that was carved out two years ago from a nuclear-research lab. In July it announced that it would be commercialising a plasma technology derived from fusing the nuclei of atoms, which produces a reaction much hotter than the sun. It has already developed a security-screening device using related technology that is popping up in local metro stations. Commuters walk past them every day.