Practical Applications of Fusion Power

(Created prior to 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?
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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
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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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