This American Scientific Affiliation Science Brief was published in the
ASA Newsletter, Vol. 37, No. 5, Sep/Oct 1995.
The Search for a New Source of Energy from Nuclear Fusion
The Energy Problem
Our energy comes mainly from fossil fuels and nuclear fission. Both have
undesirable consequences. Nuclear fission is leaving us with an accumulating
supply of depleted nuclear fuel rods, which will remain radioactive for
centuries. And though well-designed nuclear reactors are inherently safe,
a nuclear accident as happened at Chernobyl can be disastrous. Fossil fuels‹oil,
gas, and coal‹power our cars and electric generating plants, polluting
the air with COX and sulfur emissions. Sulfur dioxide combines with atmospheric
oxygen to form sulfur trioxide, which reacts with water vapor to form sulfuric
acid. The result is acid rain, which some scientists think could be causing
damage to northeastern Canadian and American hardwood forests.
Other energy sources, such as solar (heating and photovoltaic), wind, ocean
wave, and geothermal are under development, but none of these will be able
to supply the large amounts required in the foreseeable future. More efficient
electrical devices and building insulation (conservation) can reduce the
rate of increase of demand but cannot generate energy. All our energy comes
from the sun. Our problem is to convert enough of it to useful forms.
A Solution: Energy from Matter
Our best hope for an abundant energy source here on earth is nuclear
fusion. While it is nuclear (involving the nuclei of atoms) it
is quite different from the presently-used nuclear fission. Fission starts
with a heavy element that has large atoms, such as uranium. Uranium nuclei,
orbited by clouds of electrons, are so large that they are unable to remain
in one piece and tend to lose fragments. These emitted fragments dissipate
their energy as heat, but they are still radioactive and continue to break
down into smaller atoms in time. This is the fission process, and
these radioactive fragments create a serious waste disposal problem.
Nuclear fusion begins instead with atoms of the lightest element,
hydrogen, abundant in water. Fuel cost is negligible. Instead of breaking
them apart, hydrogen nuclei are fused together to form non-radioactive helium
and neutrons as by-products. Fusion is not easy to achieve, though it happens
naturally in stars because gravity causes large amounts of gaseous matter
in space to collapse in upon itself. The hydrogen bomb works on fusion,
but the energy release is uncontrolled.
The central problem for physicists and engineers working on controlled nuclear
fusion is due to the electrical nature of matter. Nuclei consist of positively
charged protons and neutral neutrons, and are surrounded by negatively charged
electrons. From basic electricity, like charges repel while opposite charges
attract. As two nuclei are brought together, the force of repulsion becomes
immense. This keeps matter from collapsing but makes fusion difficult. Large
amounts of energy are needed to force nuclei together. When nuclei are close
enough, another basic force (the "strong force") within the nucleus
itself causes them to attract, overcoming the electric (or electtromagnetic)
force, and they fuse into a heavier element. In fusing, some mass is converted
to energy according to Einstein's famous formula: E = mc2.
What are some ways nuclei can be fused? Building a star is impractical because
the amount of matter required for gravitational confinement far exceeds
that available on earth. Another approach is to converge high-energy laser
beams on a glass microsphere containing hydrogen. The rapid, uniform heating
then causes the desired conditions for fusion. This inertial confinement
approach has similarities to hydrogen bomb technology and much of this work
remains confidential.
The Princeton Plasma Physics Lab
Another way to cause fusion is to heat hydrogen to such a high temperature
that the nuclei and their surrounding electrons are free to separate and
travel randomly as charged particles. When this ionized gas, or plasma,
is heated to 100 million degrees Celsius (over six times the sun's interior)
sufficient fusion occurs to provide a practical energy source. High temperature
is needed for fusion because at the atomic scale, temperature is related
to how fast gas molecules or ions are moving around. As ions collide at
these high speeds, their kinetic (motion) energy is sufficient to overcome
electric repulsion.
The Plasma Physics Laboratory (PPL) at Princeton University is funded by
the U.S. Dept. of Energy and is leading research on this approach. No material
container can withstand fusion temperatures. Instead, PPL's Tokamak reactors
are hollow, doughnut-shaped toruses circled by electromagnets. The
resulting magnetic fields confine the plasma, keeping it away from the reactor
walls. And what if the magnets were to fail? Would the unconfined plasma
become a hydrogen bomb? Just the opposite would happen. Magnetic confinement
is necessary to keep the plasma from colliding with the walls and cooling
off, causing fusion to cease. Hydrogen ions fuse into helium nuclei, or
alpha particles, and give off a neutron. The alpha particles further heat
the plasma, and escaping neutrons will be used to heat water to power steam
turbines. The long-lasting radiation found in fission reactors is not produced.
The plasma, with its fast-moving electrons and ions, is a conductor that
heats itself through electric resistance (Ohmic) heating. Because
the plasma is a gas, it can also be heated by compressing it. Other heating
methods involve injection of high-energy uncharged (neutral beam) atoms
into the plasma, or with radio waves, like a microwave oven.
Princeton's Tokamak Fusion Test Reactor (TFTR), one of the three largest
in the world, produced its first plasma Christmas Eve, 1982, and has recently
set the world record in momentarily producing 10.7 million watts of power,
enough electricity for 3,000 homes. With this long-sought achievement, power
coming out approaches the amount put in to sustain fusion; this milestone
of energy breakeven is now within reach. A smaller, new-generation reactor,
the Princeton Beta Experiment-Modification (PBX-M), is a refined design,
with more control of plasma current and cross-sectional shape, needed for
operation in a new mode of stability required by high-pressure plasmas.
Considering the importance of plasma current density, temperature, or pressure,
how do researchers measure these quantities in a 100 million degree plasma?
Thermometers and pressure gauges are definitely out! What helps make such
research challenging is that scientists must also devise new diagnostic
tools to make these measurements.
One physicist who is working on a special probe for measuring the plasma
current-density profile in the PBX-M is Robert Kaita, who has been
at the PPL for 18 years and is the head of the diagnostic effort on the
PBX-M. Bob's device injects an electrically-neutral beam of atoms into the
plasma. As they move through the plasma, they are excited by collisions
they experience. Their electrons jump to a higher energy state and release
the extra energy as light, polarized in the direction of the magnetic field.
The local field strength is related to the field generated by the plasma
current, and varies with the density of the current. By sensing the polarization
of the light, the plasma current distribution can be determined at specific
locations across the plasma.
Bob's perspective on his scientific work is wider than the details of fusion.
He has given talks on science, noting its historic foundations laid by the
earliest scientists. They shared a view that the "book of nature"
reveals the same Creator as spoken of in the Bible, and that, like the laws
given in it, the universe must also reflect its rational order. Science,
for them, became the search for these laws.
What are these laws? To use physicist Richard Feynman's example, scientific
research is like learning chess by watching it being played. The rules of
science, like those of chess, are assumed to be comprehensible, so that
it is possible for us to discover them. The physical constants of our universe‹the
starting position of the game‹are also "just right" so that
life could exist. Tiny changes in the nuclear (strong) or electromagnetic
force constants would have resulted in a universe without the chemical elements
needed for life. Minuscule variations in the density of the universe just
after the Big Bang would have led to a universe that would have expanded
only briefly and then collapsed, so that stars and planets would not have
formed.
Games like chess make sense to us because they are obviously designed, with
starting positions, consistent rules, and a goal. The universe also seems
game-like in significant ways. This analogy suggests that it too has a designer,
and it makes scientific research‹the search for the rules established
by that designer‹a rational activity.
A well-established method of science is to test promising assumptions, or
hypotheses. A hypothesis for science itself is that the Creator gave
us laws of nature that we can discover. Three centuries of scientific progress
support this assumption; the laws do exist and few scientists today deny
their "incredible elegance, simplicity, and beauty" (Paul Davies,
Superforce). But what to make of this result varies. One possible
response is the Anthropic Cosmological Principle, as Stephen Hawking writes
about in his book, A Brief History of Time: "We see the universe
the way it is because we exist ..." For Hawking, the universe just
happened to turn out such that we are here. Alternatively, as Bob points
out, we are here because of the Creator and the narrow range of possibilities
for our being here are not coincidental. This second response is consistent
with the views held by the originators of science.
Bob concludes by pointing out that regardless of which of these alternatives
we choose, our goal for science is to put it to good use, but not worship
it, for science itself has more basic foundations.
In a recent interview, Bob reflected on the rapidly changing state of physics
in relation to views common in some other scientific fields. "It's
the physicists and astronomers who are constantly in these crises, trying
to figure out why the oldest stars look older than the universe and what-not.
So you could make some rather simple conclusions that physicists are in
a much worse state in their discipline than other scientists because their
theoretical basis is [in crisis]." But, Bob followed, "To be in
crisis is not a bad thing. I think its great that we have problems
that are really tough to solve. This is what makes the field fun‹as
opposed to: `Ho hum. Yet another finding that fits neatly into a sequence.'
That just doesn't seem to have the [same] kind of excitement."
Dr. Kaita concluded the comparison by applying this perspective to the on-going
debate in biology over origins and development of life: "If there are
legitimate questions, why then do many people do the attacks [against alternative
proposals to Darwinism] on metaphysical levels without addressing the data,
whereas we should simply say, `Hey, we have to explain x and y
and z, and we admit this is a problem if the prevailing theories
are inadequate.'"
Bob is a member of the American Scientific Affiliation, a fellowship of
about 2,500 Christians in science. If you are interested in more information
about the relationship of science to wider issues, please write or call
the ASA office at:
American Scientific Affiliation
P.O. Box 668
Ipswich, MA 01938-0668
voice: (508) 356-5656
fax: (508) 356-4375
e-mail: asa@newl.com
About the ASA
Science has brought about enormous changes in our world. Christians have
often reacted as though science threatened the very foundations of Christian
faith. ASA`s unique mission is to integrate, communicate, and facilitate
properly researched science and biblical theology in service to the Church
and the scientific community. ASA members have confidence that such integration
is not only possible but necessary to an adequate understanding of God and
his creation. Our total allegiance is to our Creator. We acknowledge our
debt to him for the whole natural order and for the development of science
as a way of knowing that order in detail. We also acknowledge our debt to
him for the Scriptures, which give us "the wisdom that leads to salvation
through faith in Jesus Christ." We believe that honest and open study
of God's dual revelation, in nature and in the Bible, must eventually lead
to understanding of its inherent harmony.
The ASA is also committed to the equally important task of providing advice
and direction to the Church and society in how best to use the results of
science and technology while preserving the integrity of God's creation.
It is the only organization where scientists, social scientists, philosophers,
and theologians can interact together and help shape Christian views of
science. The vision of the ASA is to have science and theology interacting
and affecting one another in a positive light.
Anyone interested in the objectives of the Affiliation may have a part in
the ASA.
The ASA publishes a quarterly journal, Perspectives in Science and Christian
Faith, and a bimonthly newsletter. The journal has become the outstanding
forum for discussion of key issues at the interface of science and Christian
thought. It also contains news of current trends in science and reviews
of important books on science/faith issues. ASA also has distributed over
100,000 copies of Teaching Science in a Climate of Controversy, written
primarily for high-school biology teachers, offering advise on how to handle
controversy over creation/evolution issues in the classroom. These and other
resources are available by contacting ASA at the above address or telephone
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