From: fernee@newton.physics.uq.oz.au (Mark Fernee)
Subject: Re: capacitor discharge initiation
Keywords: capacitor discharge initiation
Organization: Physics Dept. The University of Queensland
Date: Thu, 19 Nov 1992 08:32:27 GMT

In article <u926135.722091269@tasman>, u926135@tasman.cc.utas.edu.au (Adrian Hassall Lewis) writes:
|> >	Because PE is soo dangerous, it is not used in application where an 
|> >	accident would be catastrophic, such as for nuclear weapons. Instead 
|> >	high energy capacitor discharge initiation of a secondary explosive 
|> >	is employed (in these applications timing of the initiation is also
|> >	highly critical).
|> >
|> >	Please be careful if using any high explosive,
|> >
|> >	Mark.
|> 
|> As I'm not sure who "Mark" is, I'm asking the net -
|> 	Exactly what are capacity discharge detonators?
|> 	How do they work?
|> 	Can anyone point me to any refrences?
|> 
|> Any help greatly appreciated.
|> 
|> 		ajax
|> 

High energy capacitor initiators are used in applications where the high
sensitivity of primary explosives is not desireable. It is based on an
exploding wire technique. Basically a high energy storeage capacitor is
used to discharge across a resistive wire imbedded in a secondary explosive.
Such secondary explosives are primarily shock sensitive and are far more stable
than primary explosives. Secondary explosives do not undergo the deflagration
to detonation transition (DDT), as do primary explosives, and are at least
an order of magnitude less sensitive to shock initiation. 

The principle of the exploding wire is that a current is delivered to the
wire via a discharging capacitor such that the subsequent ohmic heating
causes a rapid vaporization of the wire (ie the wire explodes). This 
requires a very rapid discharge of the capacitor such that sufficient
energy is delivered to the explosive. To fascilitate such a rapid energy
delivery the capacitor must have a negligible resistance and a very small
inductance. Infact the inductance of the circuit must be kept to a minimum
to enable an efficient high frequency response (this will give a very 
sharp pulse shape required for the rapid delivery of the energy).

Apparently nuclear weapons use capacitor discharge initiation to vastly
increase the safety of such devices. The geometry of the initiation points
is such that the timing of the initiation is critical for a successful
nuclear reaction. Nukes are designed such that if the explosive charge was
accidently initiated, the total effect would be no more than a couple of
kilograms of HE, rather than hundreds of kilotonnes of HE. There has been
a report of such an accident onboard a US navy vessel, with non-catasrophic
effects. I have also heard of an unarmed nuke being accidentilly dropped from
a plane, again with no serious effect. 

I also believe that these capacitors are the things that Mr Hussein was trying
to get his hot little hands on. 

I have never tried direct capacitor discharge initiation. It may be feasable
if PETN were used as the explosive due to its great succeptability to shock.
However, high voltage/ low inductance discharge capacitors are quite expensive.

Sorry, but I haven't had time to chase up any references.

I hope this helps,

Mark.