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For the first time, large general audiences
are witnessing actual demonstrations of controlled nuclear fusion,
a scientific development of major significance in man's quest
of new energy sources. Each demonstration -- there is one very
six minute -- is a full scientific experiment in which fusion
reactions are achieved by the same techniques which have been
used for studying these processes at the General Electric Research
Laboratory.
What is Nuclear Fusion?
It is a process in which the cores (nuclei)
of two or more atoms collide and combine in such a way that,
in accordance with Einstein's basic equation, a portion of their
matter is changed into energy. Fusion reactions are the source
of the tremendous heat of the sun and stars.
During each demonstration, such as the one
you saw, a plasma of deuterium gas is created with a quartz tube,
around which is placed an electrical coil that produces an intense
magnetic field (sometimes called a "magnetic bottle").
A high bank of capacitors is charged to 60,000 volts. As the
countdown reaches "0", an automatic control discharges
the capacitors, releasing a tremendous electrical current of
a million amperes into the coil around the tube. Within the tube,
the current "squeezes" and heats the plasma, producing
large numbers of deuterons (deuterium nuclei) having energies
equivalent to those which would exist at a temperature of 100,000,000
degrees Fahrenheit. As the capacitor bank is suddenly discharged
with a bright flash and loud "bang," the deuterium
nuclei inside the quartz tube collide and "fuse" producing
energy measured by the output of neutrons. The fusion reactions
take place during about six millionths of a second.
Evidence of the fusion reactions is demonstrated
on large oscilloscope screens, and electronic digital-counters
record the actual number of neutrons released during each experiment.
The Promise
Fusion promises humanity -- in the distant
future -- the benefits of a virtually unlimited supply of energy.
Predictions are that it may fulfill man's power needs by using
the most common of all natural resources: water. Thus, it has
the promise of unlimited power, for an unlimited amount of time,
with minimal "fuel" costs.
The fusion process demonstrated in this experiment
uses deuterium, a special form of hydrogen found in water. There
is enough deuterium in one gallon of water to produce, through
controlled fusion, energy equal to that of 350 gallons of gasoline.
Extraction of deuterium from ordinary water is an inexpensive
process.
Fission / Fusion
The fusion process releases energy
by joining together two very light atomic nuclei, such
as those of deuterium. Fission, by contrast, involves
splitting a very large, heavy nucleus, such as uranium.
Fission is the process by which modern nuclear-powered ships
and atomic electric-generating plants derive the heat that powers
their turbines.
Why Not Now?
The problems involved with fusion reactions,
compared with fission reactions, are far more taxing to man's
scientific knowledge. Nuclear fission was first demonstrated
in 1938, and the first working reactor was activated in 1942.
By contrast, nuclear fusion was first discovered in 1932 and
still remains a "laboratory phenomenon." The reason
for this slow pace of development is that the fusion reaction
must take place for a sustained period of time under extreme
physical conditions of high pressure and high temperature.
To contain the heated plasma in the demonstration
experiment, the magnetic field produces an equivalent pressure
of 1500 pounds per square inch (100 atmospheres). The plasma
pressure is somewhat lower than this, with the high energy portion
being approximately 150 lbs/sq. inch. As has been indicated,
this portion of the deuterium plasma has an energy equivalent
to tens of millions of degrees.
While these deuteron energies and pressures
are close to those required for an ultimate practical fusion
power plant, the efficiency of heating the deuterium and the
time of containment, or reaction time, must both be significantly
increased.
What is Efficient?
Let's explain it this way. In the G-E World's
Fair display, you witnessed a fusion reaction in which over a
million pairs of atomic nuclei collided and combined. Each one
of these "fusions" released several hundred times the
energy required to make the particles react, but for every deuteron
taking part in such a fusion, over a billion deuterons did not.
In other words, even though you witnessed true nuclear fusion,
the energy input required to perform the experiment far exceeded
the energy output that the fusion reactions produce. Hopefully,
future scientific breakthroughs will make it possible to increase
the fraction of deuterium nuclei which actively undergo nuclear
fusion to the point where more energy is released than is required
to heat and contain the plasma.
You saw an experiment in which the reaction
period was six millionths of a second (six microseconds). For
an efficient fusion process, at pressures which have been achieved,
the reaction period will have to be extended to more than a hundredth
of a second, and the efficiency of heating the plasma will have
to be substantially improved. Reaching these extremes will probably
still require years of intensive research.
GE's Role
Research in nuclear fusion has been under
way at G.E.'s Research Laboratory, Schenectady, N.Y., for over
seven years. The Company has thus far invested several million
dollars toward development of this future power source. The General
Electric program is one of only two large fusion research programs
being financed by private industry. Research in fusion is also
being pursued in several other U.S. laboratories, principally
operated by the U.S. Atomic Energy Commission. Internationally,
all the major countries have active fusion research programs.
Are the Reactions Real?
Yes. The fact that fusion reactions occur
is unequivocally demonstrated by the production of neutrons.
Neutrons released in the fusion reactions leave the reaction
vessel and activate silver foils in the counters placed close
to the quartz tubes. Neutrons are the only particles which can
activate the silver in this manner.
The number of neutrons produced and the variation
of the production rate with time tell the scientists about the
pressure of the high-energy portion of the deuterium plasma and
also about the efficiency of plasma heating.
What Kind of Experiment?
This apparatus is called a theta-pinch fusion
device, so-called because the current in the plasma flows in
the azimuthal, or theta direction, with respect to the compressing
magnetic field. Other experimental devices of this type are also
being studied in this country at Los Alamos and at the Naval
Research Laboratory and in laboratories in several other countries.
Theta-pinch type experiments are of particular
interest since they provide an energetic plasma having a high
energy portion with pressure a hundred to a million times greater
than that now obtainable from other types of fusion devices.
Therefore, whether or not these theta-pinch
devices find ultimate application as fusion reactors, it is certainly
true that they are at this time contributing significantly to
our scientific knowledge regarding the behavior of fusion plasmas.
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