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Practical Applications of Fusion Power
Name: Unknown
Status: N/A
Age: N/A
Location: N/A
Country: N/A
Date: Around 1993
Question:
World's only operational fusion reactor is the sun. Probably the
most practical application of fusion energy is converting photons to electrons
using photo cells, or converting infrared into hot water using roof-top
collectors. Why have you guys not figured this out yet?
Replies:
Well, That is a good point. However, there are actually 10^24 or
so other "operational fusion reactors" out there besides the sun... The
universe is pretty big, and maybe our perspectives are all too narrow! The
biggest problem with solar power is it is practically impossible to
concentrate - it needs to be collected over huge areas, preferably sunny
areas. Actually, the easiest use of solar power is hydroelectric (how did the
water get up there in the first place?) and as you probably are aware, this
already accounts for quite a substantial portion of electrical generation, but
huge hydro power projects (the most efficient way of using it) tend to cause
huge environmental catastrophes, which people are no longer willing to accept.
Would other solar schemes be less environmentally unfriendly? What about all
the chemicals used in semiconductor manufacture to make all those solar cells?
How long do those things last, anyway? And I had a friend with a house near
New York who had one of those roof-top collectors. You want to buy a house
that only has hot water in the summer? Fossil fuel use also uses "old" solar
power - energy sent by the sun millions of years ago (unless Thomas Gold is
right about where oil comes from). The only truly non-solar power sources on
the earth are geothermal, tide-based, and nuclear (fission or fusion), and
only the nuclear ones are likely to produce a substantial amount of power -
anyway, I also think solar energy will eventually be our best source.
A. Smith
The major hurdle in inducing fusion is getting the fuel nuclei
sufficiently close to each other so that the nuclear strong force, which binds
the protons and neutrons in a nucleus, can kick in. As you know, nuclei have
positive charges so they repel each other. A number of strategies have been
suggested: (1) Heat the fuel (usually some isotope of hydrogen) to a very
high temperature so that the nuclei will be moving very fast; this enhances
the probability that the colliding nuclei will get close enough to fuse (that
is how the sun works). The problem is confining the heated fuel. The sun
does it with its gravity, a feat we cannot accomplish on earth. Nor can we
use a material "bottle"; when the hot fuel touches the walls of the container,
it cools the fuel. So there have been attempts to contain the fuel with a
magnetic "bottle", but this has also had a lot of technical difficulties. (2)
Blast solid tritium "pellets" with intense laser light. The heating takes
place so rapidly that there is not a need to confine the fuel. This would
produce bursts of fusion, instead of a continuous fusion reaction So far, the
energy needed to induce the fusion exceeds the energy produced. (3) "Cold
fusion". This uses the ability of certain materials such as palladium to
absorb hydrogen. The palladium electrons partially shield the hydrogen nuclei
from each others' positive charges, and it was believed that the nuclei could
be caused to get close enough for fusion to take place. So far, this appears
to be a dead end. (4) Perhaps the most exotic idea: induce the replacement
of electrons in hydrogen atoms by muons. This is referred to as muon-
catalyzed fusion, and sometimes is also called cold fusion. Because the muon
is much heavier than the electron, it orbits at a much smaller distance from a
hydrogen nucleus, providing the same sort of shielding as in (3). Then the
two nuclei in the hydrogen molecule can, in theory, get close enough for
fusion to occur. The problem here is that muons are unstable; they decay
about 2 microseconds after being produced. So they would have to be produced
in large quantities then efficiently directed into the fuel to induce fusion
before they decayed.
R.C. Winther
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