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WHAT
IS FUSION?
Fusion
is the process
that powers the sun and the stars. It is the reaction in which two atoms
of hydrogen combine together, or fuse, to form an atom of helium. In
the
process some of the mass of the hydrogen is converted into energy. The
easiest fusion reaction to make happen is combining deuterium (or heavy
hydrogen) with tritium (or heavy-heavy hydrogen) to make
helium and a neutron. Deuterium is plentifully available in ordinary
water. Tritium
can be produced by combining the fusion neutron with the abundant light
metal lithium. Thus fusion has the potential to be an inexhaustible source
of energy.
To make fusion
happen, the atoms of hydrogen must be heated to very high temperatures
(100 million degrees) so they are ionized (forming a plasma) and have
sufficient energy to fuse, and then be held together i.e. confined, long
enough for fusion to occur. The sun and stars do this by gravity. More
practical approaches on earth are magnetic confinement, where a strong
magnetic field holds the ionized atoms together while they are heated
by microwaves or other energy sources, and inertial confinement, where
a tiny pellet of frozen hydrogen is compressed and heated by an intense
energy beam, such as a laser, so quickly that fusion occurs before the
atoms can fly apart.
Who cares? Scientists have sought to make fusion work on
earth for over 40 years. If we are successful, we will have an energy
source that is inexhaustible. One out of every 6,500 atoms of hydrogen
in ordinary water is deuterium, giving a gallon of water the energy content
of 300 gallons of gasoline. In addition, fusion would be environmentally
friendly, producing no combustion products or greenhouse gases. While
fusion is a nuclear process, the products of the fusion reaction (helium
and a neutron) are not radioactive, and with proper design a fusion power
plant would be passively safe, and would produce no long-lived radioactive
waste. Design studies show that electricity from fusion should be about
the same cost as present day sources.
Were getting close!
While fusion sounds simple, the details are difficult and exacting. Heating,
compressing and confining hydrogen plasmas at 100 million degrees is a
significant challenge. It has taken a lot of science and engineering research to get fusion developments to where they are today. Both magnetic and inertial fusion programs are conducting experiments to develop a commercial application.
If all goes well, commercial application should be possible by about 2020,
providing humankind a safe, clean, inexhaustible energy source for the
future.
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