Thermonuclear weapons, also known as hydrogen bombs, are nuclear weapons that use energy released by a burning plasma's fusion reactions to produce part of their explosive yield. This is in contrast to pure-fission weapons, which produce all of their yield from a neutronic nuclear fission reaction. The first thermonuclear explosion, and thus the first man-made burning plasma, was the Ivy Mike test carried out by the United States in 1952. All high-yield nuclear weapons today are thermonuclear weapons.