Re: Fusion energy

Hi,

I have been following fusion research as a hobby for over a decade.

On Friday, February 8, 2002, at 02:25 AM, KH.Ranitzsch@t-online.de
wrote:
[snip]

> There are several paths towards building a fusion reactor that are
> being explored. The two that look most promising are plasma
confinement
> and Laser Implosion fusion. And all use the Deuterium isotope of
> Hydrogen instead of plain Hydrogen, because Deuterium is easier to
fuse
> that hydrogen.

Another approach that looks promising is termed the z-pinch. A brief
synopsis can be found at
http://www.sciam.com/1998/0898issue/0898yonas.html
One of the really cool features of this technology is that it may
scale quite well. Another really cool feature is the lightning
storm it creates ;)

> For plasma confinement, Deuterium gas is heated to extremely high
> temperatures and compressed by electromagnetic fields to a high
> pressure to simulate conditions inside a star.
>
> For Laser implusion fusion, you take a small hydrogen pellet and hit
it
> from all sides with Laser beams. The pellet implodes to produce a
> micro-hydrogen-bomb.
>
> None of the methods being explored has, AFAIK yet achieved energy
> break-even. That is, there have been fusion reactions, but so few that
> the energy pumped in far heating etc. has been rather higher than the
> energy from the reactions.

Break-even was first achieved in the mid-90s. The ratio of energy out to
energy in is called "Q". Break-even has Q = 1, but for a commercial 
reactor,
they are looking for Q > 50. So far, the tokamak design has reached the
highest Q. The current problem is that plasma instabilities quickly
halt the fusion process. Very recently, computer models have shown that
it may be possible lengthen the stable regime through magnetic field
feedback. Basically, as instabilities occur, the confinement field is
adjusted to wipe them out. Only recently has computer power reached the
speeds necessary to make this possible. There are currently several
tokamak's undergoing refit to test this approach.

[snip]

> At our current stage of fusion development, how did they
>> (the science boys) figure a little hydrogen will go a long way?
>
> Because the basic fusion reactions have been well studied in nuclear
> accelerator experiments. You shoot protons (Hydrogen atoms' nuclei) at
> liquid hydrogen targets and observe the results. So we know pretty
well
> at which speeds hydrogen will fuse and what kind of energy and
> particles will get out. From this and the laws of thermodynamics, it
is
> fairly easy to calculate the energy output of a hydrogen cloud under
> any conditions.
>
> Unfortunately, the accelerator method doesn't scale well to produce
> worthwhile amounts of energy (thouhg I think there have been
> experiments in that direction).

Linear accelerators, cyclotrons and synchrotrons require a huge amount
of energy to accelerate a very small number of particles. However, a
tokamak still accelerates the particles in the plasma to fusion
energies.
It just does it in bulk with a much wider energy spectrum.

The goal of most modern accelerators is to break nuclear matter into its
constituent "fundamental" particles. The energies required are far
beyond
those required to initiate fusion, and you pay for that with remarkable
inefficiency. I think that that technology would be better utilised as
a weapon technology.

[snip]

> Greetings
> Karl Heinz
>
>
Cheer,