Exploding ULIire Disruption Suuitch (High-Pouuer, High – Frequency Pulse)

This is where the stored energy in the circuit induc­tance is released as an explosion of electromagnetic energy at broadband proportions. The released energy is a function of LI2 where I is the current rise in the spark gap switch at the moment the wire explodes and L is the inductance. The actual power lost in the spark switch is but a fraction of that emit­ted in the explosion of the wire.

Selection of the wire size must take into considera­tion the elcctrical circuit parameters for the proper timing of the optimum release of energy. We experi­mented with a .I-millimeter (.004 inch) to.3-miIlime – ter (.012 inch) diameter of brass and aluminum wire about 50 centimeters in length. The wire is attached by a sandwiching action between two flat brass wash­ers as shown. Note that a longer wire will tend to pro­duce more of a magnetic pulse, whereas a shorter will produce more of an electric pulse.

Charger

The charger for the system can be any current – limited source with an open-circuit voltage in excess of 50 Kv. The charging current rate will determine the amount of time necessary to reach a firing level and need not be that fast for this experimental system. A single charging cycle produces approximately 500 joules per shot and requires reloading of the wire for an exploding disrupter switch. A 2-milIiampere cur­rent source will charge the.5 mfd capacitor to 50 Kv in approximately 5 seconds. This is shown mathemati­cally by t = cv/i(.5)(10e — 6)(5 X 10,000/.002). This rate is more than ample and there is no advantage to a higher-current system unless you are planning to do a multiple discharge system using a spark gap-driven radiator or wire-dispensing scheme.

The ion supply described in Chapter 1 can supply an open-circuit voltage of 50 Kv by easily adding four more capacitors and high-voltage diodes to the multi­plier section. Everything else can remain the same.

Exploding ULIire Disruption Suuitch (High-Pouuer, High - Frequency Pulse)

Rssembly

RFC1 Radio Frequency Choke

This component is necessary to keep the fast current pulse rise isolated from the charger multiplier diodes that could be avalanched by the rapid dv/dt. The sug­gested value is around.2 mh with.3 Uh tertiary coils. The assembly can be a single-layer close wound winding of 150 turns for the.2 mh section. Wind three turns spaced over 1 inch for the.3 Uh section. Use #28 magnet wire on a 1 Ч2- X 12-inch PVC plastic tube.

R1 Resistor

Intended as a safety precaution, this resistor provides a high impedance should a short occur in the output stage of the current driver. Use approximately 50 to 100K with at least 100 watts.

Our lab pulser is shown constructed using materials and parts available from any hardware store. The structure uses a combination of 3/<j-inch schedule 40 PVC tubing for the pillars and flat-faced end caps for the retainers (see Figure 25-4). Partitions are made from nonconductive material of structural integrity for the application. We used 3/s-inch, clear, acrylic plate stock. Figure 25-3 shows the scheme we used to attach these sections to the flat-faced end caps. The sections are secured by drilling clearance holes and plastic tie wraps keep them together. PVC cement is obviously stronger but prevents disassembly unless you destroy the support structure.

The pillar and cap assemblies are attached to the partition plates using 1-inch X */4-20 bolts and nuts. A cradle assembly fabricated from wood or plastic secures the capacitor Cl to the bottom partition. This scheme stabilizes the bottom of the capacitor.

The metal plate sections extend the terminal con­nections of the capacitor. These attach to the termi­nals connecting to the exploding wire cavity section

Exploding ULIire Disruption Suuitch (High-Pouuer, High - Frequency Pulse)

Figure 25-4 Side view of EMP pulser

via brass-threaded rods sleeved into pieces of -’/4-inch made adjustable by adjusting the bottom nut on the

PVC pillar tubing. The bottom spark gap electrode is extended rod.

You will note the four longer pillars are positioned at the corners of the bottom and middle partition plates. The shorter pillars, however, are positioned at the midsections of the middle and top partition plates. This layout is shown in figure 25-5. Figure 25-6 illustrates the final view of the pulser and Figure 25-7 shows the spark switch setup for coupling to the antenna.

Exploding ULIire Disruption Suuitch (High-Pouuer, High - Frequency Pulse)

Exploding ULIire Disruption Suuitch (High-Pouuer, High - Frequency Pulse)

Figure 25-5 Top view of middle partition plate, showing the x-ray view of capacitor placement and mounting holes

Exploding ULIire Disruption Suuitch (High-Pouuer, High - Frequency Pulse)

Event action occurs along the wire that explodes. The foci point of the dish is not exact for all points of the explosion event Expenment for best results

Our low-cost open-air spark switch is shown Serious experimenters may want to consider our triggered enclosed devices as on cover sheet

Charging

resistor

Figure 25-6 Final view of pulser, showing conic antenna

Exploding ULIire Disruption Suuitch (High-Pouuer, High - Frequency Pulse)

Rpplication

This system is intended for research into the suscepti­bility of sensitive electronic equipment to an EMP The system can be scaled down for portable field use and operate on rechargeable batteries. It can be

scaled up to produce kilojoule pulses at the user’s own risk. No attempt to construct or use this device should be considered unless thoroughly experienced in the use of high-pulse energy systems.

The electromagnetic energy pulse can be focused or made parallel by use of a parabolic reflector. Experimental targets can be any sensitive electronic

Exploding ULIire Disruption Suuitch (High-Pouuer, High - Frequency Pulse)

Form coil from 3 turns o! J" ID coppertube 3” diameter Adjust to 3 to 6" length to obtain required inductance

}■’ threaded rod is sleeved into ID of copper tubing and soldered with a propane torch Rod is retained in position by shaft collars

Exploding ULIire Disruption Suuitch (High-Pouuer, High - Frequency Pulse)

Figure 25-7 Spark switch setup and layout for low-frequency coupling to antenna

equipment or even a gas-discharge lamp. Hie acousti­cal spark energy can produce a sonic shockwave of high sound pressure at the focal length of the para­bolic antenna.

Sources

High-voltage chargers, transformers, capacitors, gas – filled and isotope doped spark switches, MARX impulse generators up to 2 megavolts, and EMP gen­erators are all available at www. amazingl. com.

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