Re: Linnax railguns?

On Sun, Jan 26, 2003, Roger Burton West wrote:

>On Sun, Jan 26, 2003 at 03:52:43AM -0600, Mark & Staci Drake wrote:
>
>>In the first chapter the aliens (Ubenfrarr) land on the planet surface

>>and are trying to knock out the main planetary defense which is a 
>>linnax railgun........can anyone give me a description of what this 
>>weapon is ?  I have a rough idea,but want to make sure.
>>Also what material is linnax? I have heard it used before at work but 
>>do not know what it is.....
>
>I haven't read the book, but it sounds like a corruption of "linear
>accelerator" rather than a type of material. Since I'm not aware of any
>shades of railgun which are _not_ linear accelerators, it seems a bit
>superfluous, but perhaps technology has changed by then. Apart from
>details of implementation, this is basically the same thing as a gauss
>gun, magnetic accelerator, etc.; something which uses a series of
>magnetic fields to accelerate a projectile, thus avoiding the
>inconvenient speed limit imposed by gunpowder's combustion velocity.

    In general you're correct, but not quite. The thing that separates a
railgun from a gauss gun / magnetic accelerator / coil gun is that the
railgun (surprise) features rails.
    In the railgun, the projectile is in contact with two parallel
rails,
forming the bridge between them and completing a circut. As such, it
feels a force and accelerates, remaining in contact with the rails. This
has obvious problems in that, for high velocities, you have a good
chance
of things melting due to friction, or needing really high power levels.
It has the advantage that we can build them now. Often in SF, the term
"railgun" is mistakenly used when another term (I use "linear
accelerator", but "coilgun" is another possibility) should have been
used
instead.
    A coilgun consists of a series of rings of some magnetic material
(or
some material that becomes magnetic with the introduction of an electric
field -- you want an induced dipole rather than a permanent dipole. The
projectile is fired down the middle of these rings by magnetic
acceleration. You could, in theory, probably also use a solenoid for
this, but I'm not sure how that would work in practice. Since there's no
actual contact, the coilgun removes some of the friction problems, but
adds others (if you *get* contact, what you really have is a very high
speed collision, and things will probably not go well for you).

    -Brian

-- 
Brian Quirt (brianq@ncf.ca)
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