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Fusion: Overview |
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Fusion
is a nuclear process, where light nuclei are combined to form heavier
nuclei and a certain amount of released energy. Fusion reactors harness
these nuclear reactions to generate energy for useful applications such
as propulsion. In a simple fusion process two light nuclei in the
roiling hundred million degree Kelvin plasma combined to form a bigger
nucleus. However a change in binding energy means that it does not quite
exactly weigh the same as the components that were put together, there
is actually a mass deficit, where some of the mass has been converted to
free energy. This matter conversion is
responsible for the vast amount
of energy released, the same process is responsible for the stellar
fires that light our universe. There
are many different ‘types’ of fusion, though ‘types’ refers to
the reaction mixtures, some reactions can run on nothing but hydrogen,
some run on heavier isotopes of hydrogen, there are different advantages
to each reaction, some are easier to achieve, others ‘burn’ more
cleanly. Fusion
technology really began in the late 20th century, however no
real successful reactors were developed until 2040, and even then,
reactors only started to supercede other forms of power in 2060. Fusion
remains one of the principle sources of power many centuries later,
though other power sources have been increasingly exploited. The changes
that occur to society through the development of cheap clean power from
fusion is worth its own article. The
most common fusion reaction used by the federation, mimics the processes
that happens in stars, these reactions are preferred as they ‘burn’
relatively cleanly, and the feedstock is plentiful, indeed it is the
most common element in the universe, hydrogen. The
process that shall be described in the text below, but before all the
nuclear reactions can start, the atoms need to become ionized, e.g., all
the electrons have to be removed, this is done at high temperatures and
energies, and it is this process of ionization that forms the plasma in
the core of the reactor. First
two energetic protons (hydrogen ions) merge together, this forms a new
nucleus consisting of one proton and one neutron (one proton is changed
into a neutron), if this nucleus was not ionized it would form an atom
of deuterium, a hydrogen isotope, but as it is ionized, it is called a
deuteron. This deuteron is bombarded by another high-energy proton, and
forms one nucleus of helium 3, (2 protons, 1 neutron), two of these
nuclei combine in another reaction to form a stable helium isotope (2,2)
and two high energy protons, which go back to stage one. As mentioned above there are many different methods, and equations, early fusion reactions used deuterium and tritium, where the tritium was generated by neutron bombardment of the lithium coating of the reactor. From
its first days of development, one fusion reactor design has succeeded,
these are a type of reactor called a tokamak, these can be though of
toroidal containers containing a ring of plasma, these and a generation
of spherical tokamaks are the most commonly used designs, other designs
can be found, there are linear reactors used for propulsion, or
‘pumped’ multiple tokamaks, which are used to create heavy elements
and unusual isotopes. ___ Images: A Fusion Reactor |
