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Power Plays
The devil, as always, is
in the details as UCLA scientists and engineers participate in an international
effort to harness the power of the sun
By Bruce Schecter
“Nuclear fusion,” Mohamed Abdou, codirector of UCLA’s Institute of Plasma
and Fusion Research, likes to point out, “was discovered long before fission.”
Walk out on a sunny day, he observes, and you are basking in the warmth
and light created by fusion taking place in our home star. In contrast
with nuclear fission, however, whose energy scientists were harnessing
within a decade of its discovery in the late 1930s, fusion energy, which
will essentially use seawater as fuel, is still a dream -- a dream that
scientists around the world, including several from UCLA, are energetically
pursuing.
The urgency of the scientists’ pursuit is driven by their awareness
of our planet’s rapidly dwindling stockpile of fossil fuel. Estimates of
how long coal and oil will continue to serve as the world’s principal sources
of energy vary widely. An increasing world population, accelerating rates
of energy consumption and our high tolerance for the damage to the environment
caused by the burning of fossil fuels are some of the variables that must
be taken into account. A good ballpark estimate is that in something like
100 years we will have burned up our prehistoric energy legacy.
Renewable resources such as solar, wind and wave power will help compensate
for the loss, but with a world population estimated at 11 billion by the
year 2100, such sources will not supply nearly enough energy to satisfy
demand. Fission power plants, with their susceptibility to catastrophic
accidents, their hazardous, long lived wastes and their dependence on a
finite stockpile of uranium, will inevitably multiply. That is, until safe,
commercial fusion power plants begin to supply the world with affordable,
virtually inexhaustible energy -- perhaps in the early decades of the next
century.
Nuclear fusion is the purest realization of Albert Einstein’s equation
of mass and energy. In a fusion power plant, nuclei of deuterium and tritium
(two isotopes of hydrogen that may be extracted from seawater) fuse to
make helium. The combined weight of a deuterium nucleus and a tritium nucleus
exceeds the weight of the resulting nucleus of helium. The difference in
mass, as predicted by Einstein’s famous equation, is converted into energy
-- the energy that powers the sun and the stars, the energy of a hydrogen
bomb, the energy scientists have been trying to domesticate for more than
four decades.
Thermonuclear fusion has been difficult to achieve and control because
its fuel must burn at tremendously high temperatures. The deuterium and
tritium in a power plant must be heated to 100 million degrees Celsius
(10 times the temperature of the sun’s interior) if they are to fuse. The
sun burns a different fuel, a mixture of hydrogen and helium, that gives
off energy at a rate of only about two watts of power per ton -- far too
low to be useful as an energy source on Earth. (A ton of hamsters running
on treadmills generates far more energy.) The sun makes up for this paltry
output by its sheer mass, an attribute that researchers on Earth cannot
imitate.
At the temperatures required for fusion, the electrons that orbit atomic
nuclei are stripped away. The result is a new state of matter, called a
plasma, a swirling, overheated mass of negatively charged electrons and
positively charged nuclei. The challenge of fusion energy is to find a
way to hold this astronomically hot plasma as it burns, to find a bottle
that can hold a star.
No material bottle will work, of course. And even if a material could
be found that did not vaporize under such intense heat, the plasma would
cool as it came into contact with the bottle walls, quickly dousing the
fusion reaction. One possible solution, pursued by researchers for more
than 40 years, is to build a bottle without walls, or at least not walls
made from matter. Such a container would take advantage of the fact that
a plasma consists of electrically charged particles, and that electrically
charged particles can be manipulated by a magnetic field. The weaving of
such bottles out of magnetic fields (called magnetic confinement) has proven
to be an extremely challenging scientific and technological problem.
The most promising approach has been a device known as a tokamak, in
which the plasma is confined to a donut shaped (torroidal, in the jargon
of topology) magnetic field.
With the aid of tokamaks, scientists discovered that plasmas are far
more difficult to handle than they ever imagined. (A plasma confined in
a tokamak writhes and bends in the magnetic field, becomes as turbulent
as white water rapids and soon splashes out of the bottle.) Nevertheless,
after decades of research at laboratories around the world, enough progress
has been made that scientists are now confident that tokamak fusion reactors
will someday work.
Scientists and engineers from Europe, Japan, Russia and the United States
have embarked on an unprecedented international collaboration to investigate
how such breakthroughs in fusion technology can be translated into a working
power plant. The project, known as the International Thermonuclear Experimental
Reactor (ITER), is planned for completion in 2010 at a cost of around $10
billion, hence the need for international cooperation. UCLA scientists
are deeply involved in the planning of this massive project.
Finally, after years of speculation and research, scientists are confident
that they will be able to achieve and control the release of fusion energy.
Exactly when the first economically feasible fusion plants will go on-line
is still an open question. Meanwhile, an assortment of scientists and engineers
at UCLA are hard at work to ensure that the power of fusion will be available
when we need it.
Power Plays...
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