EMP device

[m4dn3s5.c0mb47]

Ok, in the coming weeks I'll be testing my first EMP "device" It will consist of what should principally be an EMP device. A high explosive charge in a pipe, with electrified copper wire wrapped around the outside. I'm going to place various electrical objects in the vicinity and check on them after the device goes off. I'll hopefully post a video and report my findings afterwards. For the main charge I need a HE compound, and was thinking either NG, or AP, which I already have. I'm hoping I won't need anything like RDX because that is a pain in the ass to synth and I've never done it before. If anyone has any experience with this type of thing, feel free to share your expertise.

[Marvin]

Experience, no, but for an EMP shouldnt you be *imploding* the coil as opposed to making a wire grenade with added glitch in next doors TV reception?

I would suggest from your description that making an EMP with good electronics and no HE at all would perform better than the current plan. My understanding is that a traditional EMP is done by having many turns of very thick copper wire round an air core, discharging a very big EHT capacitor into it and at the point of zero cap voltage/maximum coil current when the coil is trying to expand outward (turning electrical energy (contained in the magnetic field) into mechanical energy - small coils explode even if the heating isnt enough to melt anything) you squash it, turning mechanical energy (from the detonating explosive chemical energy) into more energy for the magnetic field which after destruction of the coil leaves the device as a pulse.

[nuclearattack]

There are various systems to make an EMP weapon, one method is with the wire around the HE charge. The capacitors discharge should be synchronized with the detonator, maybe that wiring the detonator with the capacitors trigger could work. Use NG because in this application you need a high vod, AP is too slow.
You will need also a good SCR able to handle very high current.
There is a file on EMule p2p network called "How to build an EMP bomb" maybe you will find it interesting.
I don't have experience but in the future i want to make some tests because EMP devices are very interesting.
This thread is in the wrong place it should be on improvised weapons section.

[mrcfitzgerald]

Check out this FCG patent- (4,370,576) as well as an improvement on its design(H148). These are, prehaps, the more complicated pulsed systems that are possible. Since you probably dont have these capabilities yet, several simpler systems can be made. One entails detonating HE inside a cylindrical magnet (which is positioned inside a coiled wire). This is probably the simplest device possible, and it doesnot need expensive or hard to make capcitor systems. I believe that the first patent has this referanced as prior work.

It is interesting to note that you could combine the magnetic system with the more conventional FCG so that you dont need to build any capacitor bank or (possibly) a quick switching device.

[Boomer]

As far as my understanding goes, you put a HEAVY copper wire (more like a rod) around a copper pipe full of HE. A cap bank is then discharged through the coil, and the HE is detonated from one end, so that the exploding/expanding pipe shorts one winding after the other until the whole pipe+coil are gone.

Say you have 100 turns: With E=1/2xIxIxL constant, the current in the last winding is 100 times the start current, then the magnetic energy will radiate outwards (since there is no more coil the current can run through in circles).

Problems:

1.Triggereing the det within microseconds

2. You need a gigawatt pulse for an effective range. Say a few 10 KV at a few 100 kA from the capacitors. The last turn will then conduct up to 50000000 Amps before being shorted! Needless to say, a camera flash will do shit.

I tried the non-explosive version, by skipping the pipe + HE. A 32 MW pulse (8000V at 4000A) through 50m of 10mm cable coiled up. I stood next to it and felt nothing - but a 300 buck multimeter on the same table (switched off + not connected) was destroyed (dont tell my boss :D ).

I guess the trick with the HE filled pipe is to completely turn all field energy to radiation, instead of having it oscillate between coil and capacitor until it is used up by the resistive losses.

[nuclearattack]

Your EMP test seems interesting and working Boomer. Can you give me more details on it's manufacture? How do you skip the pipe without using an HE?
I didn't understood well your experiment.
About the HE+wire+capacitors version i'm thinking if it is possible to directly energize the detonator with the same current from capacitors that energize the coiled wire. With this system you don't need to synchronize the capacitors discharge with the detonation. Is the huge current that ignite the detonator, you can connect the detonator and the coil in parallel but you will lose some power on the coil.
With such a big capacitor bank you will need a very big SCR, it is very expensive so i'm thinking that is possible to use a spark gap energized by a dedicated marx generator. When the marx discharge on the spark gap the air will be conductive and the capacitor current will pass.
An EMP bomb is one of my secret dreams but surely it will need a lot of work and tests...i'm young and i have time to do this!

[Marvin]

Expanding a metal tube looks a hell of a lot easier than imploding a coil, I like that design though conceptually its much harder to see why it works. An important point though, is the air gap. Its the copper tube expanding in the air gap that provides the power. Thats the dynamo, so to speak.

Its important to start the HE at the point of maximum current in the coil. This isnt coincident with the firing of the spark gap, you are 'charging up' the magnetic field and at the point of maximum current/zero cap voltage all of the energy has been transfered from the cap to the magnetic field around the coil (and importantly into the air gap). Depending on the configureation of the coil and cap, this could take a microsecond, or a millisecond after the spark gap fires.

"I guess the trick with the HE filled pipe is to completely turn all field energy to radiation"

Nonono, much more important. If you want to turn all that energy in the cap to EMP you only have to break the circuit very quickly. The trick here is that we dont want to rely on electronic energy for the pulse. Capacitors store tiny amount of energy compaired to chemicals. In a power station they dont use generators with fixed magnets, they use electromagnets becuase these are capable of much higher fields and thus a more compact generator. Typically a little dynamo (the exciter) powers the coils for the main generator. The same is true here, the cap discharges through the coil and dumps all its energy in the field - then the HE goes off. Before the field there is nothing to work against and expanding the copper pipe would do nothing. In the staged design the used stages short out so the later stages have a much bigger field to push against - the same energy in a smaller inductance.

The more I read on this subject the more sure I am simply wrapping a pipe in wire with a large current and detonating it would do nothing at all.

[CypherNinja]

Alright, I've heard a little bit about these things, so I'll just throw my 2 cents in.


As I understand it, these devices are refered to as 'flux compressors', and are a Transient Electrical Discharge (TED) Device. They are constructed by placing a metal, conductive tube inside a coil of wire with a small gap in between. The tube is filled with a HE of uniform density and high VOD. The tube must also be thin enough and elastic enough that when the HE is detonated from one side, the tube will expand in a 'wave' fashion following the detonation front as closely as possible. What you want to avoid is the tube building up pressure inside and expanding uniformly, like those super slow motion shots of pipe bombs going off.

Now, the coil is hooked up to a capacitor and an antenna or some type of emitter. The capacitor disharges into the coil and creates a strong magnetic field around it. When this field reaches its greatest magnitude the HE is detonated from the opposite side of the coil that the antenna is hooked up to. This means the coil has to have both leads on the same side (there are probably some creative coil winding methods that can be employed here). As the expanding tube contacts the coil (opposite end of the leads) it creates a rolling short which causes the coil to become shorter in length as the 'wave' moves toward the leads.

Now, I have no grasp of the electrical science behind this part, so please don't ask. ;) As I understand it, this rolling short causes causes the (now collapsing) magnetic field to be 'compressed', thus causing a huge power surge in the emitter, creating a very large transient electrical discharge. Essentially the device as a whole converts a certain amount of the potential energy of the chemical explosive into electrical energy. This is evident in the huge current surge in the coil and the resulting radiated discharge from the emitter.



There, thats my dictionary understanding of the device. Google could probably answer more questions.


EDIT: Here's a link to a short definition found on Google:
http://www.sew-lexicon.com/gloss_e.htm#EXPLOSIVE_MAGNETIC_FLUX_COMPRESSOR

And a quote from it:
"To conserve magnetic flux in the inductor, the inductor current increases as its area and inductance decreases. The result is a large pulse of current that can be employed in DIRECTED ENERGY WEAPONS"

[A2675770]

It really depends on how big of a radius, you wish to have.
I read up before that you can find a nice capacitor from the inside of an old Television, assuming noone's dumb enough to touch the +ve and -ve terminals.
Build up a timer circuit or find one with a High voltage/current Thyrisistor switch in it.
The rest is pretty basic, Copper wire, with a non-conducting container and a nice pure iron core.

Now I'm not exactly sure how that would turn out being that I have never attempted it, good luck anyway.

[FUTI]

No, it is not the energy of explosives that is converted into a EM pulse, but the energy stored inside (super)capacitors. And the EM wave generating device is harder to make as I seen it, since it should make directed flux of EM radiation in certain direction. But if we speak about diversion device to be planted inside some city to damage certain communication devices that is maybe easier to make.

[Jacks Complete]

If you want to cause a directional attack (which would be the wise way to do it) you need something that has gain, something like an antenna. A basic Yagi will have between 18 and 28 dB of gain, but this would be frequency dependant. A front surfaced dish would be better, as this would be a broader frequency gain curve, which would be better for the energy conversion.

You could go all the way to something like http://www.wifi-shootout.com/ use (but the link seems to be down)
(More details here-> http://www.bbwexchange.com/publications/newswires/page546-1086045.asp )

Needless to say, a 9ft dish is fairly obvious, but so will the explosion be! Aim it carefully if you use that much gain!
In other news,
"Then, German researcher Herfurt developed a program called Bluebug that could turn certain mobile phones into a bug to transmit conversations in the vicinity of the device to an attacker's phone.

The BlueSniper 'rifle,' created by John Hering and colleagues at Flexilis as a proof-of-concept device, resembles a rifle, she says, continuing:

"It has a vision scope and a yagi antenna with a cable that runs to a Bluetooth-enabled laptop or PDA in a backpack. Aiming the rifle from an 11th-floor window of the Aladdin hotel at a taxi stand across the street in Las Vegas, Hering and colleagues were able to collect phone books from 300 Bluetooth devices. They bested that distance and broke a record this week by attacking a Nokia 6310i phone 1.1 miles away and grabbing the phone book and text messages."

The BlueSniper rifle is probably something Chinese authorities could use
http://www.weblogsinc.com/common/images/8312965763230518.JPG?0.15513966423837589
Very simple, it is a rifle stock with an optical sight and a Yagi instead of a barrel. Your aim is to send the pulse back along the yagi to the system you have carefully scoped!

[Marvin]

FUTI,

"it is not the energy of explosives that is converted into a EM pulse"

Of course it is, thats the whole point of using explosives in the design. The amount of energy in the cap is tiny by comparison.

[Anthony]

How strange that a mobile phone would readily transmit its phonebook and text message inbox over its bluetooth facility. Surely a major design oversight? You wouldn't need a custom "rifle", just someone with a laptop in any large gathering (e.g lecture hall) could have a fun time.

[grandtheftauto]

I was thinking hypothetically, how much companies would buy this EMP weapons technology if it could give them an edge over their competition? Also it has the abilty to be made with reasonably easy technology (easier then finding explosives or guns), and hard to trace who let of the EMP.

I reckon in the near future this technology won't only be made for military uses, but for commercial uses.

[FUTI]

to Marvin: I had an impresion that only reason for use of explosive is the making that coil short circuit fast reducing its lenght. I'm maybe wrong...I will reseached that subject more...

[Boomer]

Sorry Marvin but I have the feeling Futi is right, the HE is just an easy way of creating the moving short-circuit fast enough.

Using explosives for a quarter century, and working as an EE for 15 years, I still have no idea how you want to convert heat + pressure into electromagnetic radiation.

I know the plasma of the det front is conductive, but how is it going to increase the field strength around it some magnitudes?

Do I overlook something? :confused:

[Marvin]

Dont be sorry, it just means I've failed to explain it well enough.

This will start to seem totally irralavent but bear with me. Superconductors float on magnets. The reason is that they repell magnetic fields by virtue of being very conductive. If you take an electromagnet repelling a superconductor and force the superconductor closer what happens? The current in the coil increases (at the expense of its inductance but we'll come back to this). Since it took energy to force the superconductor closer we have a gain in electrical energy of the coil. (In fact this is magnetic energy as all electrical energy in a current resides in the megnetic field, I digress).

Ok, why does this not happen with copper, it has a resistance, but it doesnt mean this doesnt happen at all, just that the effect is too small to be noticeable over the time frame humans view in. If you drop a copper plate on a magnet the same eddy currents are setup that cause the superconductor to float but they die away so quickly it only slows the decent slightly. A real superconductor wont carry a current for ever, but the resistance is so low that there is no noticable flux leakage through it during the time you press it against the coil (or for that matter over a human lifetime). If gravity was much stronger and our brains worked much much faster (or household magnets were much more powerful) the copper would seem to float for some time before slowly dropping onto the magnet. The key thing here is that the higher the resistance of the material the faster you need to do the experiment to get the same result.

Many people might have seen the experiment where a strong magnet slides down a copper pipe much more slowly than an unmagnetised weight of the same shape and size. You may have also been shown it from the top where the magnetic forces keep the magnet from touching the sides. Some also might have heard of magnetic braking, where magnetic fields are used as decelerators without contact friction. Copper does produce noticable forces at 'human' speeds they just arnt very strong in low magnetic fields.

The bottom line for copper in this application is that it takes time for a magnetic field to leak through it so if you can move a sheet very very quickly this leaking isnt noticable and you can 'push' flux around like you can with a superconductor.

Looking again at the EMP design and for the first part ignoring the shorting of the windings. We discharge a cap through the coil and this sets up quite a big field. Next the explosives are detonated and this starts to rapidly expand the copper. This wave of expanding copper is moving too quickly for the flux to pass through it, so the flux gets squashed towards the coil. This takes energy (and at high fields a *lot* of energy) and as a result a proportion of the energy in the explosive is transferred to the electrical pulse.

The inductance of the coil drops considerably and the current increases. This in magnetic terms is rather like the overused example of the iceskater. A spinning ice skater with their arms outstretched can be going quite quickly, but when they draw their arms in they spin much faster. Angular momentum is conserved, they've reduced the moment of inertia so they end up spinning faster. Though the inertia is less they do have more energy as bringing in the arms takes effort - working against a force - so the final state is of higher kinetic energy. In a similar way, total flux is conserved in the coil, and by squashing it against the edge we are reducing the inductance. Since we are putting in energy squashing the flux this results in more electrical power from the device.

Ok, end is in sight. Why the staged shortings. An explosive does not cause the whole of the copper to expand at once, it happens in a cone shape along the line. This can be used to an advantage. If we split up the single coil in our heads to several smaller coils all wired together in series without a shorting system I can explain more easily. When the first coil goes off its current increases as does the field in all the other coils, when the second charge goes off sometime after the first its explosive has a bigger field to push against because of the energy from the first coil. This makes more of the explosive energy become power. However *its* energy goes into the whole circuit which includes the coil thats allready fired. When the third one goes off it has a bigger field and so a furthur increase in conversion. Heres the thing - If the second coils energy had been directed only into the unfired coils the field in the 3rd coil would be bigger. Extra field put into the first coil is wasted and worse still leaving the coil in circuit risks that flux will leak back through the copper (which is only a matter of time anyway - the energy going into heating of the copper due to induced eddy currents which are all that stop the field leaking anyway). So if at the point of completion of each stage the copper liner shorts the coil, this inductance is taken out of the circuit and the flux/energy only goes into the coils that havnt fired yet and flux leaking through the copper cant drain power from the rest of the circuit.

In the same way when the copper has expanded in a given length of the coil to its maximum point that section of the device is shorted, when its stopped producing power its only a liability.

Its a very fast dynamo, not a switch. Switching can be done in nanoseconds with sparkgap circuits like marx ladders whereas an EMP needs more power than can feasably be put into a portable capacitor bank.

Addendum,

A few questions that might occur. Why cant we actually use superconductors, why cant we use perminant magnets and why cant we use ferromagnetic materials.

The reason is that all these materials have limits. Perminant magnets are typically limited to 2 or 3 kgauss, Iron as an example of a ferromagnetic material is limted to around 20 thousand gauss above which it saturates and superconductors have a critical field above which superconductivity collapses. A simple conducting surface however has no limits, its just a question of how rapidly you can move it and how quickly eddy currents alow flux to pass through it.

[Boomer]

I start to get the idea, thank you!

You convert the heat/pressure to electrical power via mechanical work done against a magnetic force. My F***ing bike dynamo does that all the time (sans the HE, I have to pedal). :)

I actually like these science riddles. Some more: If you hit the brake in your car, the kinetic energy is turned to heat in the brakes. But where does the impulse (momentum?) go? You actually spin the earth a little ;) faster beneath you!
This was a basic one, but 90% of high school kids cant answer it. Or this one: We dont care for efficiency or cost and cover all coasts with tidal generators. These then supply mankind with electricity for the next 100 million years. Where does the energy come from? :D

About the flux compressor: Do you have an idea about the efficiency? My *guess* would be you get about 10-100 times the power of the capacitors, by converting 1-10% of the explosion energy. Any closer values?

As a first figure I calculated the HE's power: HMX detonates at approx. 2 GW/cm^2. A 10cm ID pipe means 150 GW. CypherNinja's link mentions "several to several ten Terawatts OUTPUT". This requires a 10 square meter pipe if 10% is assumed for P/V -> H/B, and 100% is radiated. That is a truck load of HE. :(

This clearly shows that the energy first goes into the magnetic field, and at the end is given off at a much faster rate (like you described).

I would *really* like to build one! If my cap bank at 32 MW destroyed a voltmeter from close up, how much better would it perform if I put a copper pipe and some RDX inside the coil? I run short of voltmeters, but I think I will go buy some cheap watches today ... :D

[FUTI]

I'm still digesting the info you posted Marvin...thanks for being very thorough but I still have to say I have some doubts about it...I will have to dig my physics books to check out whole thing. All writen here sound logical...but I have trouble to start belive in it.

Why didn't they used plasma (explosive/thermite generated of course) in some kind of MHD generator for power source? I don't have idea what is the extent of energy and how fast it can be generated but is that possible?

[Jacks Complete]

Marvin, I concur. What a neatly written description!

A few additional points:
1: You could use a superconductor for the first stage, as they can sustain a field strength of ~7 Teslas. (The world record is now 23+T - see http://www.mext.go.jp/english/news/1999/06/990607.htm) Although this would increase complexity with LNitrogen or LHelium it would simplify the device somewhat. I don't know the field strength limits currently, but last time I looked, the low temperature superconductors were still far ahead in the maximum flux they could take.

2: You want the lowest resistance possible. Forget using a copper bar, you want to use braided copper, since over the very short timescales we are looking at, surface/skin effect will dominate. You could also use silver, which is, iirc, more conductive than copper. It also has the highest thermal conductivity of all the metals.

3: Injecting currents this high starts to get tricky. Make sure there are no loosely held wires, as they *will* jump when you test the circuit with a few thousand amps!

[nbk2000]

We dont care for efficiency or cost and cover all coasts with tidal generators. These then supply mankind with electricity for the next 100 million years. Where does the energy come from?


Tidal action from the moons rotation around the earth, though it gets weaker over time as the moons orbit is increasing and will eventually leave the earths orbit, at which time we'll have plenty of steam power because the sun will have swollen up into a red giant by that time, turning the oceans into giant steam boilers. :)

[CypherNinja]

Marvin: Thanks for that post man. :D You answered all the questions I didn't quite know enough to answer. So thanks for filling in that gigantic glaring hole in my post. ;) :D

[kingspaz]

A different method fo shorting the coil:

http://l2.espacenet.com/espacenet/viewer?PN=WO2004107524&CY=ch&LG=en&DB=EPD