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The hordes of normal, glowing stars like the sun are a much more
common sight in the sky than such extreme displays. In the stars'
central cores, the plasma is so hot that light nuclei within it
can overcome their mutual repulsion and fuse into heavier nuclei,
emitting energetic particles in the process and ultimately driving
the stars' luminous output. Since the fuel for such reactions
is plentiful on Earth, plasma physicists have labored for decades
to stably confine hot thermonuclear plasmas in laboratory devices,
with the goal of using them as large power plants to replace those
based on nonrenewable fossil fuels. This power production method
would produce no greenhouse gases and its radioactive by-products
would have much shorter life times than those created in fission
reactors. On the downside, because of a hot plasma's furious and
infuriating ability to squirm through any cage that is put around
it, no net-power-generating plasma has yet been demonstrated.
Thus the feasibility of a practical fusion power plant is still
to be proved.
Still, many plasma physicists remain optimistic. They point out
that the overall amounts of power produced by real fusion devices
have increased by a factor of a trillion over the past two and
a half decades. Researchers have scored a number of recent successes
in donut-shaped devices called tokamaks, which use twisting magnetic
field lines to confine hot plasmas. In laboratories in the United
States and around the world, researchers believe they may have
gained crucial insights into how to confine such plasmas without
inducing the deleterious instabilities arising from spontaneously
generated waves that usually spring leaks in the confinement.
The potential payoff of such research is enormous.
Yet another concept for making fusion power plants ignores magnetic
fields for confining the plasma and instead zaps a pellet of fuel
from all directions with intense laser or ion beams. This compresses
and heats the pellet, briefly creating the proper conditions for
fusion to take place. While the potential of this method as a
practical energy source will likely be the subject of research
for some time to come, such research enjoys strong governmental
support because of its utility for weapons research. The conditions
within a compressed fusion pellet are similar to those in a nuclear
bomb. Therefore these studies can be used to ensure the safety
and efficacy of nuclear weapons without actually detonating them.
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COPIOUS AMOUNTS OF FUSION POWER has been observed
in the Tokamak Fusion Test Reactor (TFTR). The toroidal region
in which the plasma is contained is shown in (a). On the outside,
shown in (b), the toroidal structure is surrounded by magnetic
field coils, neutral beam injectors, and the vast array of diagnostics
necessary to study ultra-hot plasmas. [Courtesy of Princeton Plasma
Physics Laboratory]
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