In this process, hydrogen-1 is converted into helium-4. Energy is freed up in the process.
a chain reaction
These are not chemical reactions but thermonuclear reactions.
fusion
Nuclear fusion is the process that powers stars, such as our sun.
The only place in the universe where nuclear fusion can occur on its own is in the interior of stars. After closely observing nature, and adapting its laws to fulfill human requirements, our advanced civilization has succeeded in creating nuclear fusion at will, on a small scale. Unfortunately, the only useful application successfully developed so far with our superior intellect is the construction of nuclear bombs and weapons.
There is no fire in the sun, that is a chemical process. The process in the core is thermonuclear fusion.
a chain reaction
fusion is called thermonuclear for a good reason: it needs a lot of heat to get started.
These are not chemical reactions but thermonuclear reactions.
There are several processes that happen in atomic bombs, the main ones are:Fission bombs - hydrodynamics, neutron chain reaction, fission.Fusion bombs - hydrodynamics, radiation transport, thermonuclear fusion, fission.Many other secondary processes occur also.
fusion
Nuclear fusion is the process that powers stars, such as our sun.
The temperatures are similar within about an order of magnitude, but the core of the sun is hotter. The thermonuclear bomb is at the temperature of DT fusion, the lowest temperature at which fusion can occur. The sun, in addition to fusing DT, is fusing HH, HD, DD, DHe-3, TT, He-3He-3, all of which ignite at various temperatures higher than DT.
A clump of matter must collapse under the attraction of its own gravity. The collapse must heat the matter up to form a plasma which undergoes thermonuclear fusion - of hydrogen into helium.
How can temperature either help fusion to occur or prevent fusion from occurring?
By thermonuclear fusion of hydrogen, producing helium. The same process that produces the energy in a hydrogen bomb (although the sun fuses far more hydrogen in the same period of time than the largest hydrogen bomb ever speculated would fuse during its entire explosion, thus producing more energy than such a bomb).
The only place in the universe where nuclear fusion can occur on its own is in the interior of stars. After closely observing nature, and adapting its laws to fulfill human requirements, our advanced civilization has succeeded in creating nuclear fusion at will, on a small scale. Unfortunately, the only useful application successfully developed so far with our superior intellect is the construction of nuclear bombs and weapons.