Text 426, 62 rader
Skriven 2005-05-04 13:28:20 av Gerrit Kuehn (2:246/4020)
    Kommentar till text 423 av DAVID WILLIAMS (1:250/514)
Ärende: PNU 729
===============
Hello DAVID!

03 May 05 10:03, DAVID WILLIAMS wrote to MICHIEL VAN DER VLIST:


 DW> As far as I know, fusion reactors have passed the point of "physical" 
 DW> break-even, where the energy produced exceeds the energy required to 
 DW> fire the thing up, 

No, not quite... yet.
Apart from break-even there is another problem (well, of course there are
several, but this one is obvious): The most developed fusion devices operate on
the Tokamak principle. This involves (basically) a very large transformer coil
that induces a magnetic field to help confining and a current to heat the
plasma. Since a current is only induced by a changing magnetic field (and thus
a steadily increasing drive current) a Tokamak reactor has neccessarily to be
operated in pulsed mode. The length of the pulses is the limiting factor for
Asdex Upgrade right now, thus the plasma burns for only ~5s. For a power plant
you'll have to find a way to produce electricity in a continuous manner. But
you can probably solve this problem by making the pulse duration longer and by
building more than one device operating in different phases (like the cylinders
in a car's engine).
The other principle on which a fusion reactor can be built is the so-called
Stellarator. This would produce energy continuously by design, but it requires
a more sophisticated system of (supposedly super-conducting) coils and rather
complex magnetic fields. Thus research on stellarators is behind research on
tokamaks up to now, because tokamaks are easier to build.

People interested in research on fusion may like to visit the web pages of the
German experiments Asdex (Upgrade) (a Tokamak) and Wendelstein 7(X) (a
Stellarator) operated by the Max-Planck-Society, or JET (Joined European Torus
- the world's largest tokamak experiment up to now) and ITER (the
next-generation tokamak to be built hopefully soon):

<http://www.ipp.mpg.de/ippcms/eng/pr/index.html>
<http://www.jet.efda.org/>
<http://www.iter.org/>


I must admit that I know only a very few things about recent fusion experiments
outside Europe (especially in the USA). NIF (National Ignition Facility) that
worked on laser-based fusion seems to have turned more or less completely into
a military experiment to simulate H-bombs or something like that. Does anyone
here know what US fusion researchers are up to these days? Their politicians
seem still to be busy trying to get ITER built somewhere in the Nipponese
mountains instead of lovely France...

 DW> but have not yet reached "fiscal" break-even, 
 DW> where the value of the energy produced, in terms of money, exceeds the
cost 
 DW> of producing it. 
 DW> Money, of course, is a human fiction. 

Yep. And the "fiscal" break-even will depend heavily on the development of the
prices of energy produced in a different manner.


Regards,
Gerrit

--- Msged/BSD 6.0.0
 * Origin: America, America the western dream is gone (2:246/4020)