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Re: Re: starship-design: Pellet track

KellySt@aol.com wrote:
>In a message dated 8/19/97 11:04:14 AM, kuo@bit.csc.lsu.edu (Isaac Kuo)
>>KellySt@aol.com wrote:
>>>In a message dated 8/18/97 9:17:14 AM, you wrote:
>>>>>>As for the efficacy of electric field containment for fusion power,
>>>>>>I'll admit I haven't read the reference articles on this compressions
>>>>>>system, but it seems very optimistic to assume it will even work well
>>>>>>enough to break even, much less provide power.

>>>>>I can't follow this.  Why do you assume its so dificult?

>>>>Because if it were so easy, it would already be giving us cheap
>>>>fusion power.

>>>That asumes theirs a market for it.  Specifically one big enough to pay for
>>>the R&D.  Comercial research in exotic power sources, especially ones
>>>invoving nuclear, died when the fuel crises evaporated.

>>At the very least, this means that there is a significant R&D cost
>>associated with it.  However, the potential profit is so great,
>>that the perceived risk must also be great for commercial concerns
>>to avoid it.  (The perceived risk being that even after all that
>>R&D it won't work.)

>You forget.  We are awash in cheap fuel, few new power plants of anykind are
>planed in the next 20+ years, and a fusion plant might mot be any cheaper
>then conventional.  Add to that the general expectation (and stated claims by
>them) that eco groups will attack Fusion plants as rabidly as nuclear plants
>(the power companies are still smarting over that), and you have some very
>reluctant investors.

Actually, a fusion plant only has to compete with fission plants to
acheive great profit potential.  The initial and running costs for
motive fission plants are so great that they're now restricted to
aircraft carriers and nuclear submarines.  The running costs for any
practical fusion plant would be much less than fission or conventional,
so that just leaves initial cost--including R&D.

For various reasons, naval power plant sales would be the first venue
for any "easy" fusion power plant.  Civilian power plants, bigger and
with more restrictions, would come later--but not very much later if
it were so easy.

>>I personally think magnetic target fusion offers the brightest
>>potential (it's a pulsed fusion concept), but even so the concept
>>is too new and the technology too immature to bank on it.  The
>>numbers look a _lot_ more acheivable than either magnetic
>>confinement or inertial confinement.

>Haven't heard of it.  Whats it like?

It is sort of a mix between traditional magnetic confinement fusion
and inertial confinement fusion.  For some reason, no one thought
of doing it until a couple years ago.

The idea is to start off with a magnetically contained bit of plasma,
like what we can acheive in magnetic confinement fusion reactors
today.  This bit of plasma is then compressed using a surge of
electricity through the magnetic coils.  This initiates a relatively
extended burst of inertial confinement fusion.

The temperature and density of the initial plasma obviously
doesn't have to be anywhere near what's needed for fusion, while
the compression is provided by a pulse of magnetic field (which
is easier to do than a pulse of lasers) over a period of time
longer than the laser pulse of ICF.  The products also fuse
over a longer period of time, making it easier to tap energy
from the products.

The fusion ramjet concept is similar to this, except that the
pulse of magnetic field is provided by the motion of the pellet
plasma into a fixed "bottleneck" of strong magnetic field.

>>>>There are difficulties in dealing with charged plasma, since
>>>>the more charged it is, the more it wants to fly apart (even
>>>>more).  The less charged it is, the more you need a stronger
>>>>electric potential difference.  Setting up that potential
>>>>difference in the right geometry is challenging as well.

>>>The geometry for this system is a hollow sphere by the way.  

>>Huh?  A conductive hollow sphere cannot generate an electric
>>potential gradient inside it.  You'd have to inject electrons
>>into the center in order to attract the (positively charged)
>>fuel particles to it, and rely on the charge of those electrons
>>alone to acheive compression.

>You charge the hollow sphere.  The ionized gas is repeled from it toward the
>center.  Which effectivly gets a oposite charge.  Fusion products blast
>outward, out of the potential well.

This does not work.  The ionized gas will _not_ be repelled from
the surface of the sphere.  Honest.  The net force on a charged
particle on the inside of an evenly charged hollow sphere is 0.

For the same reason, you would be weightless on the inside of a
"hollow Earth", and couldn't stand on it.  This has to do with
the fact that both gravity and electric force are inversely
proportional to the square of the distance.

Any second semester Physics course with Calculus uses this
example.  You know, you get a homework assignment where you
have to derive the electric field around various geometrically
shaped objects.
    _____     Isaac Kuo kuo@bit.csc.lsu.edu http://www.csc.lsu.edu/~kuo
/___________\ "Mari-san...  Yokatta...
\=\)-----(/=/  ...Yokatta go-buji de..." - Karigari Hiroshi