Almost four stories high, framed in steel beams and tangled in pipes, conduits, cables, and coils, the Joint European Torus (JET) claims to be the largest fusion power experiment in the world. Located near Oxford, England, JET is a monument to big science, its donut-shaped containment vessel dwarfing maintenance workers who enter it in protective suits. Here in this gleaming nuclear cauldron, deuterium gas is energized with 7 million amperes and heated to 300 million degrees Celsius – more than 10 times hotter than the center of the sun. Under these extreme conditions atomic nuclei collide and fuse, liberating energy that could provide virtually limitless power.