In the closed town of Sarov, roughly 350 kilometers east of Moscow, scientists are busy working on a project to help keep Russia’s nuclear weapons operational long into the future. Inside a huge facility, 10 storeys high and covering the area of two football fields, they are building what’s officially known as UFL-2M—or, as the Russian media has dubbed it, the “Tsar Laser.” If completed, it will be the highest-energy laser in the world.