From: sdr57@cas.org ()
Subject: EMP - long (was Re: 21st Century Soldier)
Organization: Chemical Abstracts Service, Columbus, Ohio
Date: Tue, 15 Sep 1992 13:57:26 GMT

>In article <1992Sep14.134609.23335@cas.org> sdr57@cas.org () writes:
>}In article <BuH0JM.5E4@watdragon.uwaterloo.ca> jdnicoll@watyew.uwaterloo.ca (James Davis Nicoll) writes:
>}>
>}>       Hmmm. Anyone  know if EMP-enhanced weapons are available?
>}>A  non-nuclear EMP device might be very useful in a near-future war,
>}>as well. Only problem is that producing EMP weapons may require
>}>First World grade industry, in which case the Third World may find
>}>it hard to get their hands on them.
>}>
>}Generating an electromagnetic pulse can be done without a nuclear device.
>}It requires lots of power and an interesting array of wires. There is an
>}EMP setup big enough to put whole airplanes into at Kirtland Air Force
>}Base in New Mexico (it was, and presumably still is, used to evaluate
>}the vulnerability of aircraft electronics to emp - military electronics
>}are designed to survive with the possibility of exposure to EMP in mind).
>}It is big - not portable - and the aircraft has to be inside. Its use
>}did not disrupt electronics in Albuquerque, which is adjacent to the
>}site. In short, if you want to generate an EMP under battlefield conditions,
>}you will need a nuclear device
>
First, some background:

EMP = Electromagnetic Pulse - an effect resulting from the production of
an inhomogeneous electric field. In an earlier posting (above), I noted
that it took either a nuclear device or a big experimental setup to
generate an electromagnetic pulse. Strictly speaking, this is not true -
an electromagnetic pulse is generated any time an inhomogeneous field is
produced - when you rub two dissimilar materials together to build up
a static charge, you produce an electromagnetic pulse - and any time
a conventional explosive is set off, an electromagnetic pulse ison
produced - its just that the pulse produced is very small and can
therefore be ignored. Unlike conventional explosives, nuclear
explosives generate a significant EMP - (in atmospheres or on the
ground, mainly from Compton scattering interactions of gamma) in a
very short period of time.

Why worry about EMP? Well, it affects electronic devices because
the EMP fields cause electrons to move, producing a current. This
current depends (in very general terms) on where the device is in the
field and how "big" an antenna it acts as (bigger devices are exposed to
more field, producing more current - devices hooked up to long antennas
are going to get more current from the antenna than devices hooked
up to short antennas which in turn will get more current than devices
without antennas). Protection against EMP involves designing electronics
so that they aren't big (in terms of their size as antennas) and so
that they damp out pulses, shielding them, disconnecting them from
antennas when attack is imminent, and so on.

The military uses of EMP first became evident with the advent
of the A-bomb. It is now a part of nuclear war-fighting doctrine
that you set off a couple of bombs at high altitude first to
mess up as much of your enemy's electronics as you can, and it is
also part of doctrine to harden as much of your electronics against
EMP as you can.

There has been some consideration given to other ways of generating
EMP (these include sticking a cavity magnetron in a cruise missle
and imploding a superconducting magnet - neither of these has been
tried to the best of my knowledge, which comes completely from open
sources). Another method was mentioned by another poster:

In article <1992Sep14.175430.11621@linus.mitre.org> m23364@mwunix (James Meritt) writes:

>Nah.  A cesium seeded high temperature explosion can generate the electrical
>pulse through MHD to send the wave through trailing wires.  A use-it-once
>weapon, but most are.  Fits in a BIG artillery shell.

I wasn't aware of this, and Mr. Meritt hasn't yet had the time to respond
to my request for more information, but I have done some calculations
(back-of-the-envelope, using a lot of WAGs, and this isn't properly
my field, so figure at least one order of magnitude for error bars,
but it gives us a starting place to talk, so why not) which suggest
that a 16 inch shell could produce an EMP from plasma equivalent to
that produced by a 10 kiloton nuke. This makes it very much a tactical
weapon which would be unlikely to affect personal military electronics
(which have small antenna profiles) or the shielded electronics inside
tanks. It would be far from useless however, for certain specific roles:
Shoot one of these at an enemy equiped with counterbattery radar (for
tracking shells shot at you so you can figure out where they came from)
and you can at least force the radar to shut down briefly (EMP produced
by a chemical explosion would presumably be produced over a longer
period than that produced by a nuke, giving cutoffs a chance to
function to protect the electronics) since the radar antenna will
collect EMP nicely. This would complicate the counterbattery fire
and help your artillery survive longer. If your enemy is equipped
with a system for destroying incoming artillery shells a la "Hammer's
Slammers," this would let you screw that up so your barrage would
get through. It would also be a great weapon for use against civilian
targets in the "first world" by "third world" countries or terrorists -
relatively simple to make, doesn't kill anyone directly so that
retaliation becomes difficult (you can't bomb them just for screwing
up your electronics, and they don't have a lot of electronics for
you to screw up), and would be really damaging to civilian electronics
which are only minimally protected. I don't know if this is a real
device or just another thought experiment, but there is a lot
of potential for sf uses of it in either case:-)
******************************************************************************
Renegade academician. They're a dangerous breed when they go feral,
academics are...a chemist, too.
		    -(James P. Blaylock in "Lord Kelvin's Machine")

My organization hasn't agreed with any of my opinions so far, and
I doubt they'll start now.

Stanley "Ya nee speon" Roberts