WHAT IS FUSION?
F usion
is the
process that powers the sun and the stars. In one
type of this reaction, 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 combines
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.
Hydrogen
gas is
typically heated to very high temperatures
(100 million degrees or more) to give the atoms sufficient energy to fuse.
In the process the gas becomes ionized,
forming a plasma. If this plasma is
held together (i.e. confined) long enough, then
the sheer number of fusion reactions may produce more
energy than what's required to heat the gas,
generating excess energy that can be used for
other applications. The sun and stars do this with
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 intense radiation, such as a laser
beam, so quickly that fusion
occurs before the atoms can fly apart.
W ho
cares?
Scientists have sought to make fusion work on
earth for over 50 years. If we are successful, we
will have an energy source that is inexhaustible.
One out of every 6500 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
intrinsically radioactive. Short-lived
radioactivity may result from interactions of the
fusion products with the reactor walls, but 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
eventually be about the same cost as present day
sources.
W e’re
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. A lot of science and engineering had to
be learned to get fusion to where we are today.
Both magnetic and inertial fusion programs expect
to build their next experiments which will produce
more energy than they consume within the next 15
years. If all goes well, commercial application
should be possible by the middle of the 21st
century, providing humankind a safe, clean,
inexhaustible energy source for the future.
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