The first large-scale application of thermonuclear energy was the so-called hydrogen bomb, or “H-bomb.” For a brief time an exploding fission bomb develops a temperature of hundreds of millions of degrees Fahrenheit, hot enough to cause some light nuclei to fuse. In the hydrogen bomb, light nuclei of deuterium and/or tritium are exposed to this temperature during such a fission explosion. The resulting fusion of these nuclei causes the explosion to be hundreds of times more powerful than that of the fission device alone. In 1952 the Atomic Energy Commission test-fired such a thermonuclear device at Eniwetok Atoll in the Pacific Ocean. The energy released by the highly efficient device produced an explosion that completely destroyed the coral islet where it was detonated. At such extreme temperatures all atoms are stripped of electrons; the resulting mixture of nuclei and free electrons is called a _plasma_. Several laboratories are now working on the problems connected with creating and containing plasma. Ordinary solid containers cannot be used. On contact with plasma they would instantly vaporize and would cool the plasma below the temperature necessary for fusion to occur. Fortunately, however, the particles that make up a plasma, being charged electrically, respond to forces in a magnetic field. A strong magnetic field of proper shape exerts a large confining pressure on a body of plasma in a high-vacuum chamber. Thus plasma can be contained in a small volume well removed from the walls of the chamber by surrounding the chamber with suitably designed large magnets or solenoids to create a “magnetic bottle.” In addition, a sudden increase in the intensity of the field can compress the plasma; this compression raises the temperature of the plasma to near that required for fusion. [Illustration: _This plasma is being pushed outward by an internal magnetic field as instabilities grow on its internal surface. The photo was taken by means of fast-shutter photography permitting photo sequences at intervals of 3 to 5 millionths of a second._ Courtesy General Atomic Division, General Dynamics Corporation] Fusion of light nuclei would be a much “cleaner” source of energy for peaceful purposes than fission of heavy ones, because the “ashes” of fission reactions are radioactive while those of fusion (helium atoms) are not. Great technical difficulties must be overcome, however, before a controlled thermonuclear reaction is possible. Fusionable material must be heated to a temperature of over 100 million degrees Fahrenheit and must be contained long enough for an appreciable amount of fusion to occur.