Artists concept view of the interior of the ITER reaction vessel. Nuclear fusion involves creating a plasma of superheated gas to temperatures of more than 200 million degrees C, conditions hot enough to force deuterium and tritium atoms to fuse together and release energy. Fusion takes place inside a 'Tokamak' torus within a giant magnetic field, the only way to contain the heat generated. The ITER reactor is designed to produce 500 MW, 10 times more energy than it consumes. Nuclear fusion is the joining (fusing) of light elements to form heavier elements, which releases large amounts of energy. It is hoped that fusion will be a clean, renewable energy source for the future. Nuclear fusion is the joining (fusing) of light elements to form heavier elements, which releases large amounts of energy. It is hoped that fusion will be a clean, renewable energy source for the future.