A nuclear weapon deriving most of its power from the nuclear fusion of hydrogen isotopes, also called H-bomb or thermonuclear bomb. Unlike a nuclear fission device, the hydrogen bomb functions by the fusion of lighter elements into heavier elements. The end product weighs less than its components, the difference being released as energy.
The first thermonuclear device was developed by the United States and tested as Operation Ivy on November 1 1952 on Elugelab Island in the Enewetak (or Eniwetok) Atoll of the Marshall Islands, code-named Mike it yielded 10.4MT, over 450 times the power of the bomb that fell on Nagasaki. Mike used liquid deuterium as the fusion fuel and had a 92 point ignition system. It was 20ft high, 6ft 8 in wide, and weighing 140,000 lb (164,000lb including attached refrigeration and measuring equipment). The detonation obliterated Elugelab, leaving an underwater crater 6240ft wide and 164ft deep where an island had once been. The largest pure fission bomb (King at 500KT) was tested in the Enewetak atoll two weeks later on November 15, 1952.
The USSR exploded its first device on August 12 1953. Great Britain (May 15 1957. Operation Grapple, test off Malden Island), France (February 13 1960), and China (October 16 1964) have also exploded thermonuclear weapons.
The structure and physics of a hydrogen bomb can be found under nuclear weapon.
Since the fusion reaction produces mostly neutrons and very little that is radioactive compard to an atomic bomb, the concept of a 'clean bomb' has developed - one having a small atomic trigger, a less fissionable shell, and therefore less fallout. The neutron bomb is another development, with a minimum trigger and a nonfissionable shell the blast effects would be reduced but a hail of neutrons would be generated causing minimal physical damage to buildings but killing most living things. A contrary development uses Cobalt in the shell, the neutrons convert the Cobalt into Cobalt 60, a powerful emitter of Gamma rays with the aim of creating extremely radioactive fallout.
Rhodes, Richard. Dark Sun: The Making of the Hydrogen Bomb. Simon & Schuster, New York, 1995. This book is less about the hydrogen bomb than it is about the years from 1945 to 1954, when the hydrogen bomb was debated and then achieved. It includes a detailed look at Soviet espionage in the Manhattan Project and at the Oppenheimer security clearance hearings.