The first successful man-made fusion device was the boosted fission weapon tested in 1951 in the Greenhouse Item test . This was followed by true fusion weapons in 1952 's Ivy Mike , and the first practical examples in 1954 's Castle Bravo . This was uncontrolled fusion . In these devices , the energy released by the fission explosion is used to compress and heat fusion fuel , starting a fusion reaction . Fusion releases neutrons . These neutrons hit the surrounding fission fuel , causing the atoms to split apart much faster than normal fission processes — almost instantly by comparison . This increases the effectiveness of bombs : normal fission weapons blow themselves apart before all their fuel is used ; fusion/fission weapons do not have this practical upper limit
Castle Bravo
Castle Bravo
Fusion power