Nuclear fusion, the process that fuels the sun, might offer the kind of clean, abundant energy we need—if only scientists can figure it out. The heart of the experiment is a 23,000-ton cylinder where intense superconducting magnets will try to keep a 150-million-degree-Celsius plasma contained long enough for fusion to occur. WORLD’S LARGEST: The tokamak chamber, seen from the top (top) and middle (bottom), is a cylinder that will hold the ITER experiment. DEEP FREEZE: The superconducting magnets in the reactor can work only at supercold temperatures near absolute zero, which will be maintained by liquid helium circulating through cryogenic pumps. The finished cryogenic plant, built by contractor Air Liquide (bottom), will be the world’s largest helium-refrigeration unit.