Fusion

A fusion reaction is one in which two atomic nuclei merge
to form a heavier nucleus. This is the process that happens
in the stars. In average stars, like the sun, the process
of fusion is converting hydrogen nuclei (or protons) into
helium nuclei. There is an enormous amount of kinetic
energy and gamma rays released in this process that heat
the star's interior, and this release is what maintains it
at the extremely high temperatures (greater than 10 million
K) required to continue the fusion.
 
This process which has been making the stars go for
billions of years, has clear potential as a power source on
earth. Once we have started the reaction, fusion requires
no energy and releases energy in a great surplus. It also
has no environmental problems and causes no pollution
whatsoever.
 
The problems with fusion are the molecules of hydrogen,
that are supposed to be fused, electro-statically repel
each other at a great force. The only way to create the
conditions where it is possible to force these atoms
together and override their repulsion is through enormous
heat, this method is called thermonuclear.
 
Even though fusion research still needs a lot of time,
there has been some progress in discovering how we can use
this. The two fusion reactions that are the most promising,
both involve the heavier isotopes of hydrogen: 1) deuterium
(composed of one proton and one neutron) Deuterium occurs
naturally as a minor constituent in all hydrogen-containing
materials--such as water--in quantities sufficient to meet
all the energy needs of societies for many billions of
years. 2) tritium (composed of one proton and two neutrons).
 
Tritium can be bred from lithium by a neutron-induced
reaction in a blanket that could conceivably surround a
fusion reactor. The western United States contains large
lithium deposits in the salts of dry lake beds, and much
larger quantities are dissolved in the sea.
 
Scientists are trying different combinations of these
nuclei to make fusion. The reaction that occurs with the
greatest probability and at the lowest temperatures
involves the fusing of a deuterium nucleus with a tritium
nucleus to form a helium (He4) nucleus and a neutron. The
products contain 17.6 million electron volts of released
kinetic energy, this is great--except it's only in theory.
 
At this time, the problem facing scientists is how to get
the deuterium nucleus and the tritium nucleus to fuse. The
other objective is to create an energy source that can get
more energy out than is put in.
 
The first method tried was to use a charged particle
accelerator to bombard a solid or gaseous tritium target
with energetic deuterium nuclei. This technique consumes
power rather than producing it, however, because most of
the accelerated nuclei lose their energy traveling at this
speed.
 
Another idea proposed in 1990 involved Tritium within metal
bars that was put into a tank of deuterium in water. When
energy was put into this tank something in the tritium bars
forced deuterium out of the water and a chemical reaction
fused the materials. Unfortunately, that was again a net
energy loss, and only a small amount of extra heat was
produced.
 
Another approach to fusion, pursued since about 1974, is
termedinertial confinement. Its aim is to compress a solid
pellet of frozen deuterium and tritium to very high
temperatures and densities in a process analogous to what
occurs in a thermonuclear (hydrogen) bomb. The compression
is accomplished by bombarding the pellet from all sides,
simultaneously, with an intense pulse of LASER light, ions,
or electrons. In 1988 it was learned that the U.S.
government, which secretly had been using underground
nuclear tests in Nevada to study inertial -confinement
fusion, had achieved such fusion in 1986 by this means,
unfortunately it only lasted less than a second.
 
After trying these methods, most scientists now agree that
the only way there is a net energy gain obtained is by
mimicking the Sun, and producing starlike thermonuclear
conditions.
 
The goal of fusion--in effect, to make and hold a small
star--is so daunting as to be widely considered the supreme
technological challenge yet undertaken.
 
In addition to an almost inexhaustible fuel supply, fusion
has other attractive features: it is environmentally
benign; the resulting ash is harmless helium and hydrogen;
and the afterheat in the reactor structure would be much
less than in a fission reactor and would be distributed
through a greater thermal mass. In addition, because fusion
is not a chain reaction, it cannot run out of control, and
any tampering to the process would cause the plasma (the
energy involved in the process) to extinguish itself. It
would also be far more difficult to produce nuclear-weapons
materials surreptitiously at a fusion plant than at a
fission plant; because no fissionable material should
ordinarily be present at a fusion plant.
 
Present levels of support for research are aimed at
building the first demonstration fusion plant in about the
year 2024. This year is based on the amount necessary for
fusion research and the very small amount of money given to
fusion to this research by most governments.