In the heart of the National Ignition Facility (NIF), a technician inspects the optics assembly where 192 powerful laser beams will zap a pellet filled with deuterium and tritium, two heavy forms of hydrogen. The pellet will immediately implode, reaching a temperature of more than 100 million degrees at a pressure 100 billion times that of Earth’s atmosphere. Under those conditions the hydrogen will fuse into helium, releasing a vast amount of energy and creating the kinds of nuclear processes that occur deep inside the sun. The NIF, dedicated in May in Livermore, California, will also mimic the detonation of nuclear weapons and will perform astrophysics experiments. Research at the facility could speed the development of abundant, clean fusion power.