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Re: starship-design: Plasma power

Hiya Ben,

> Johnny Thunderbird wrote:
> >
> > Folks are too worried about making a static sort of fusion reaction,
> > contained in a can so they know just where it's happening. The number
> > fact about space is that there's plenty of room. That means you can use
> > accelerators to produce fusion, which is easy, rather than try to
> > contain and confine an energetic plasma, which is hard. Using particle
> > accelerators is the only way we know that these reactions happen, and
> > fusions have been done in detail, decades ago, in the energetic beams of
> > accelerators. Fusion research on Earth is concentrated on making it
> > in a can, and that's hard. To use fusion for space drives, we can use
> > well-known accelerator research, because we don't mind if our entire
> > reaction is going thataway real fast, because that is just what we want
> > do: our entire purpose is to make it go thataway real fast.
> You still have to contain the reaction on earth or in space.
> Note you could have a hole at one end in a space reactor for direct
> thrust but you need to have the plasma still burn.

The _magnetic bottle_ , Ben. Take the can away from the outside, we're in a
fine high vacuum in space. Magnetic fields don't mean heavy steel magnets.
If we're really, really good at this kind of design, magnetic fields might
not even mean copper wire coils, they might not not even mean
superconductive ceramic wire coils, they might just mean dynamically
confined orbits of charged particles.

> Why is  deuterium a red herring, I think some devices fusion only needs
> a factor of 100x improvement to be practical. Note fusion web sites have
> rather outdated for a while.

I started looking at designs for fusion power in 1966, and I haven't had to
refresh my reading of the primary design concepts very much since. Still the
front runner, the tokamak hasn't had much change over the last 34 years.
That's boring science. Only the maverick designs have any interest to them
at all.

> > How long can a linac (linear accelerator) be in space? There's plenty of
> > room, right?
> >
>   Ummm 16 feet ... thats all the room I have in my garage to build the
sucker :)
>   I think a linac needs to 1/3 of a mile long, but that information is
>   memory from a Scientific American in the 70's? Linacs I think use heavy
> magnets
>   too.

No, gotcha there, Ben. You're thinking cyclotrons, synchrotrons, or their
descendants the storage rings. The linac itself is an electrostatic device.
Well, not exactly static, because it uses alternating currents (preferably
in a resonance setup) to build high voltage gradients, synchronized with the
straight line time of flight of the particles. No magnets there at all. It
is built of conducting sleeve segments, which increase in length toward the
business end, where the particles get fastest. It's good for space design,
because conductive sleeves can be made very lightweight, and because long
linear structures can be conveniently deployed as extensible devices.

The Best fusion reactor is the Electro static confinement devices for
> space
>   like the ones designed at "starships-design" home page or at
>   http://www.songs.com/philo/fusion/index.html

I _like_ Philo Farnsworth's approach to fusion in a vacuum tube. I looked
over his published work on the subject, that I could find, a year or so ago.
Once again, take away the tube, when you're working in space. Farnsworth's
ideas about dynamic confinement, and particularly his electrostatic
shielding using a cloud of electrons, deserve a lot more investigation. Some
of the snobs working in computational fluid dynamics really need to get a
clue on this, but they're all so busy getting paid to work on meaningless

For working in space, take away the can, take away the tube, take away the
heavy magnets, even take away the wire, when you can get a beam of electrons
to conduct your current. Space construction puts the premium on minimalist
design, and also on huge structures. Have fun, enjoy, and be extreme.

Johnny Thunderbird