Naked Science Forum
On the Lighter Side => That CAN'T be true! => Topic started by: Chase on 05/06/2006 15:33:13
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CAN SOMEONE PLEASE TELL ME HOW TO MAKE A VERY SIMPLE< CRUDE< HOMEMADE ELECTROMAGNETIC PULSE? (a weak one at that)
Chase Smith
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What you need is a high power source (such as a massive bank of capacitors) and a spark gap switch.
http://home.earthlink.net/~jimlux/hv/hvtrigsg.htm
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Triggered Spark Gaps
Triggered spark gaps are very popular as fast high current switches. With proper design, a triggered spark gap can switch megawatts of power in a few microseconds, with jitters of less than a nanosecond. These devices make use of the very low impedance of an arc once the arc is established. Two electrodes are separated by sufficient distance that the gap doesn't spontaneously break down. The breakdown is initiated by a variety of means: UV irradiation from another spark or a laser, an overvoltage pulse, or reducing the gas pressure in the gap.
There is a lot of similarity to a xenon flash tube here. In a triggered spark gap, the idea is to switch a lot of current at high voltage, so the arc characteristics are optimized for that. In a flash tube, the idea is to generate light, so the design is optimized for that (i.e. use xenon (high lumens/watt), a long path (limit watts/volume), etc).
Some triggered gaps operate in a vacuum, for instance the GPV series sold by EG&G (now part of Perkin-Elmer). Others use a gas filling which breaks down, as in those sold by Maxwell Labs (and others sold by EG&G, and others). Both sealed and unsealed gaps are made.
Triggered spark gaps should be distinguished from other arc conduction devices in that they are bidirectional. Other devices like thyratrons and ignitrons have a preferred direction of current flow.
Trigger mechanisms used in triggered sparkgaps
Field distortion - The voltage on an auxiliary electrode (typically between the main gap electrodes) causes a local increase in the E field strength above the breakdown field. This technique is often combined with the swinging cascade design.
Swinging Cascade -
Irradiation - A spark across an auxiliary spark gap near (or within) the main gap produces UV light which ionizes the air in the gap or causes the emission of photoelectrons from the main gap electrodes, either of which reduces the breakdown voltage below the impressed voltage. Laser triggered spark gaps use a pulsed laser instead of the auxiliary spark gap. The "Trigatron" developed by Meek, et. al., is an implementation of this technique.
Overvoltage - The voltage across the gap is momentarily raised above the breakdown voltage. This method is used in triggering high power xenon flash lamps by the "series" technique. A not so obvious approach to overvoltaging a gap is by reducing the pressure of the gas in the gap.
http://www.amazing1.com/sparkgap.htm has some prices for off the shelf spark gap switches.
The other way would be to generate a massive energy storage in a homopolar generator, and then release the stored energy across a very large air gap.
http://en.wikipedia.org/wiki/Homopolar_generator
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One of the larger homopolar generators that was produced by Parker Kinetic Designs via the collaboration of Richard Marshall, William Weldon, and Herb Woodson. Parker Kinetic Designs have produced devices which can produce five mega-amperes. Another large homopolar generator was built by Sir Mark Oliphant at the Research School of Physical Sciences and Engineering, Australian National University. It produced 500 mega-joules and was used as an extremely high-current source for experimentation from 1962. It was disassembled in 1986. Oliphant's construction was capable of supplying currents of up to 2 mega-amperes.
The huge current from a homo polar generator will create an EMP in the surrounding area, whereas simply using a spark gap switch will merely allow you create a massive pulse within the circuit itself, which you can direct where you like (but not back into the local mains electricity supply, unless you want some very angry people chasing you). Whatever you do, do make sure that all of your equipment is electrically isolated, even if you do not believe there is any risk of a pulse going back up the circuit the wrong way, you could get it wrong, at at very least all of your domestic electronic equipment could be trashed.
George