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Re: starship-design: Fusion

Timothy van der Linden wrote:
>Hello Isaac,
>This is the rest of the previously "abandoned" letter about a pellet track.
>>>Why is it easier?

>>In a traditional continuous fusion rocket design, you need magnetic
>>confinement, but you can't use superconductors because the field

Oops, I neglected the electric field confinement concept.  I can't
plead ignorance, because I did read up on it before.  I just forgot
about it for no good reason.

>But what about these 1 second sustained fusion reports we've heard about?
>Did they fail because they are too leaky?

Calling magnetic field confinement "leaky" is actually a gross
oversimplification of the problem.  The annoying thing about
plasma is that it conducts electricity, and like any normal
conductor magnetic field lines tend to get "pulled" along
with them.  Thus, what started as a nice magnetic torus or
bottle neatly containing the plasma can get bent out of shape
with deformations in the plasma, which reinforce those same
deformations (like the way a bend in a river gets bigger).

There has been a lot of research into trying to develop ways
to stabalize those deformations, including helical magnetic
fields and studying chaos theory and such, but it may simply
turn out to be intractable.

Anyway, these deformations aren't instantaneous, so you can
actually contain the plasma for a significant amount of
time before they get too bad.

>But if a super conducting magnet is strong enough for pulsed fusion, why
>isn't it strong enough for sustained fusion?

The stronger the magnetic field, the less tendency they will have
to be "pulled" by the moving plasma.  The problem with the
deformations is practically irrelevant to pulsed fusion.
    _____     Isaac Kuo kuo@bit.csc.lsu.edu http://www.csc.lsu.edu/~kuo
/___________\ "Mari-san...  Yokatta...
\=\)-----(/=/  ...Yokatta go-buji de..." - Karigari Hiroshi