How does a hydrogen fusion bomb work?

Answer 1

A Fusion Bomb (also called a Hydrogen Bomb, H-bomb, or Thermonuclear Bomb) is one of two main types of nuclear weapons. The fusion bomb relies on the fusion of light isotopes (usually of hydrogen and sometimes helium) to create a large amount of its energy. This is different from fission bombs, that release energy by inducing a neutron chain reaction to split large atoms in metals like Uranium 235 and Plutonium 329. The fusion bomb was invented in the decade after the first nuclear weapons were designed in the early 1940's.

The fusion bombs in use today all rely on a fission bomb first stage (called a "primary") to compress and heat a second fusion stage (called a "secondary"). The second stage has a thick shell of dense metal (which can be a fissionable metal, but need not be) on the outside and is filled with fusion fuel (hydrogen isotopes, or more usually a lithium-hydrogen compound [LiD]). It is usually round. In the center of the fusion fuel is another piece of fissile metal (usually Plutonium 239) called a "spark plug." These two stages are placed inside a case of dense metal, usually shaped like a peanut, with one stage at each end.

When the fission primary goes off, x-ray radiation floods down around the fusion secondary instantly heating its metal shell and causing it to implode inwards as it outer layers explode away. This is called "radiation implosion." As the shell of the secondary implodes, it compresses both the fusion fuel and the "spark plug." The "spark plug" quickly is crushed to such a density that it is supercritical and it fissions and explodes against the fusion fuel which is still being crushed inward by the radiation implosion. The effect is that the fission primary is pushing inward on the secondary while the spark plug (basically another fission bomb) explodes outward--the fusion fuel is caught between. That fuel is heated and compressed (and any lithium transmuted) to such a degree that fusion can finally occur. The lite isotopes fuse and some mass it converted into huge amounts of energy. A large number of fast neutrons are also produced. if the casing of the bomb or the metal shell of the secondary are made of uranium of a similar fissionable metal, these neutrons will fission the metal producing even more energy (this can almost double the yield in designs that use such metals as well as increasing fallout dramatically.) It is possible to add additional fusion stages, (which has been done in practice), though any number of additional ever-larger stages is possible.

Thus, theoretically, a fusion bomb of unlimited size can be build. While most nuclear weapons existing today are fusion designs, most of them are no larger than the largest fission bomb (500kt), since military needs actually favor smaller weapons over big yields.

All of the biggest nuclear bombs ever built have been fusion bombs. The largest bomb detonated was a fusion bomb that was equivalent to 50 million tons of TNT. The largest fission bomb tested was only one 100th as powerful, yielding 500 kilotons (half a million tons of TNT), which is still more than 20 times more powerful than the weapon dropped on Nagasaki.