From: dpe@inel.gov (Don Palmrose)
Subject: Re: Questions on EMP
Organization: INEL EG&G Idaho
Date: Tue, 13 Oct 1992 16:33:30 GMT


From dpe@inel.gov (Don Palmrose)


From dpe@inel.gov (Don Palmrose)

In article <BvvsrE.FAA@law7.DaytonOH.NCR.COM>, andrewh@panix.com (Andrew Huie) writes:
> 
> 
> From andrewh@panix.com (Andrew Huie)
> 
> 1. Does anyone know at what altitude a nuclear device would have to explode in
> order to create an EMP that would severely disrupt New York City (esp. the
> commercial and business districts) without causing serious collateral damage 
> due to radiation, shockwave, etc.?
> 
> 2. How powerful would the bomb have to be?
> 
> 3. What effect would this have on communications, electronics, and magnetic
> storage media?
> 
> 4. Is there a way (theoretically) to create an EMP to disable an area of about
> 1 mile radius without using a nuclear device?  It was mentioned in this group 
> earlier that the British(?) were attempting to build such a device.  How large
> would it be?
> 
> Any answers will be appreciated.  Thanks!
> 
> 
> 

Lots of questions that would require some rough calculations based on infor-
mation that is not public domain, but I will try to answer in a general
fashion.

But let's cover some basic information on EMP for those not familiar with it:  

EMP is caused by a lot of charged particles very suddenly being created high 
in the atmosphere so that they can travel along the earth's magnetic field 
lines.  It has to occur above the atmosphere because a burst of charged 
particles in the air would be quickly neutralized by interaction with the 
surrounding air molecules.  

A nuclear explosion yields mega-amounts of charge particles due
to the gamma rays stripping electrons off the molecules in the upper 
atmosphere.  By moving along the magnetic field lines, you now have a moving 
charges => moving charges create their own magnetic field which is felt on
the earth's surface.  Now because the charged particles were created in a 
burst, their "current" is not constant so the induced magnetic field they
create builds up, peaks, and rapidly decreases.  This is felt on the earth's
surface.  A changing magnetic field through a conductor creates an induced 
voltage so every electrical conductor below the burst will see a voltage
spike.  

For most equipment, this voltage spike is not very big.  However, the miles
and miles of transmission lines in the area see this voltage spike for several
miles.  The end result is a massive voltage spike gets sent down the 
transmission lines to fry all of the circuits.

Now for your questions:

1.  The altitude would be in the upper fringes of our atmosphere.  Basically,
for it to cause EMP, only the flash will hurt people on the ground.

2. The size of the nuclear explosion only determines the size of the EMP.
I do not know of any equations that will give you an EMP size to kiloton
yield (they may be listed in some physics journal, but I have not read any)

3.  The results of EMP would be the equivalent of a lighting bolt hitting
nearby your computer.  The surge would fry your circuits and hard drive.
I am not clear whether the induced EMP voltage on the circuit boards and 
storage media would be enough to damage them directly.  My educated guess is
it would screw up the silicon chips but not damage the storage media.  All
electrical fuses and circuit breakers will blow or open and could cause
arching damage in the circuit breakers.  BTW how quickly can you switch ALL 
fuses in a city of 3 million if they all go out at once?

4.  There are devices that could create a small EMP pulse on the ground.  I
am not familiar with the exact process but it has to do with explosively
compressing an electrical conductor with a current.  Whether it could produce
an EMP pulse to damage equipment in a 1 mile radius, your guess is as good as
mine.  Again, you ask a question requiring technical details that I do not
think is available to most of us.

Well, that's my $0.02 worth.  I hope it helps.
P.S. this is from my memory, if you have a good reference handy with technical
details, please quote the reference for my information also.

Don Palmrose
"I'd rather not serve on a ship designed to sink...."





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