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Bleeding Edge

The E-Bomb

by Cyrus Ance
Jun 11,2003


The E-Bomb

As I write the attack on Iraq rages on. One weapon that had some thought about being used is the so called Electromagnetic Bomb, or E-Bomb. (1) The history of this mode of attack goes back to the development of atomic weapons. Some of the developers of the original atomic bomb had theorized that the atomic blast would produce an intense pulse of electromagnetic radiation, but did not have hard data on exactly how large the effect would be. In the 50's most of the study was devoted to blast and radiation effects and the electromagnetic pulse (EMP) was ignored. In 1962 the United States was conducting a series of high-altitude atmospheric tests, code named "Fishbowl." One of the goals of this series of tests was to measure the electromagnetic effects of a nuclear explosion in the atmosphere to see if it was disruptive to nearby nuclear war heads. This had both defensive, the US was developing nuclear tipped interceptors at the time, and offensive, seeing how much protection needed to be added to US warheads to make sure that they were not disrupted by the nearby explosion of their brother warheads, implications. The test named "Starfish Prime," which was detonated in the Pacific Ocean 800 miles from Hawaii, caused an EMP that disrupted radio stations and electrical equipment throughout Hawaii. (2) This was one of the drivers behind the 1963 Atmospheric Test Ban Treaty between the United States and the Soviet Union signed to limit the threat posed by EMPs.

The electromagnetic shock wave of EMP can be strong enough to produce transient voltages of thousands of Volts on exposed electrical conductors and particularly within semiconductor chips. These are particularly difficult to shield as their internal circuitry is very dense thus not a great deal of energy is required to damage such chips. Thus computers, other data processing devices, and telecommunications equipment are very vulnerable to EMP. The US military is especially exercised about such a threat as it is the most dependent on data processing. The US is also, probably, furthest along versus this threat as the danger has been clear since the Starfish Prime shot.

Thus the impetus today is to find non-nuclear means of generating an EMP that would knock out enemy electronic devices as part of a decapitating attack. All of the devices under consideration have neat names or acronyms: explosively pumped Flux Compression Generators (FCG); explosive or propellant driven Magneto-Hydrodynamic (MHD) generators; and various High Power Microwave (HPM) devices one of which is the Virtual Cathode Oscillator or Vircator. The Vircator, I think, wins the prize for the coolest name. There is lots of information in the public domain on each of these sorts of devices as there are non-weapon uses for these devices. A web search on any of these names will turn up a flood of information. They all have the feature that the pulse they generate is small compared to what can be generated by a nuclear explosion and thus the range of the damaging EMP is small, hundreds of yards as compared to hundreds of miles. Thus the idea is to place these in bombs or warheads that would be delivered on target by planes or missiles.

The explosively pumped FCG is the furthest along of these technologies. Working ones were demonstrated at Los Alamos in the late 50's by Clarence Fowler. The basic idea is to store a large amount of electric charge in a bank of capacitors. This is released to make a strong magnetic field confined in a metal tube. A carefully controlled explosion starts at one end of the tube compressing the magnetic field and pushing the compressed field towards the other end of the tube. At the end the highly compressed field has concentrated all the power stored by the magnetic field and the explosion into an EMP that floods out as the tube disintegrates. There are a great many technical hurdles. The magnetic field must peak at exactly the same moment as the explosion starts compressing the tube. The tube is under tremendous stress as the field and explosion travel down it and has to be wrapped in something very strong to prevent it from disintegrating and releasing the EMP prematurely at reduced strength. Also the output of an FCG cannot be focused into a beam thus the range is always going to be limited. It seems quite likely that the US has tested such a device as a warhead for a cruise missile. It is not at all clear if it is in the arsenal today. The FCG is pretty simple, and a crude one could be easily constructed by just about any nation and probably a determined smaller entity.

The MHD is still in the R&D phase. The idea is that a conductor passing through a magnetic field will have an electric current induced in it. The size of the current depends on the rate of change of the magnetic field within the conductor. Thus if the conducter is a plasma resulting from an explosion driven through an intense magnetic field a very large current can be generated. This current can be used to generate a magnetic field for an FCG, the beam for a Vircator, or to directly generate an EMP. It has the virtue of being reusable and thus one can imagine an EMP cannon that is loaded just as a conventional artillery piece. A major problem is generating the intense magnetic field with a device that occupies a reasonable amount of space and does not weigh tons.

HPM devices have the advantage that their output can be focused into a beam and thus can have much longer ranges that FCGs. There are many options including Relativistic Klystrons, Magnetrons, Slow Wave Devices, Reflex triodes, and Spark Gap Devices. At the moment most effort is focused on the Vircator as it is mechanically simple and can produce very high power output. Vircators are more complicated to explain than the previous devices. They begin with a high current electron beam which feeds a pool of charge trapped in a conducting cavity by a real anode and a virtual cathode. This cavity can constructed such that it resonates at microwave frequencies and microwave power extracted. By carefully matching the conditions of the incoming electron beam with the resonant cavity a large amount of power can be stored and then extracted in a burst. Typically the power output of such a burst is limited by the melting of the resonant cavity. Other problems include maintaining the resonance frequency as the stored power builds up and extracting the power burst without catastrophic losses when forming the microwave beam.

Even if a practical EMP generator can be built the problem of damaging targets is non-trivial. The foreseeable EMP weapons are likely to be of limited range, a few hundred yards. Thus they will need to be delivered in precision guided mode. Straight forward defense versus EMP are available for critical electronics including enclosure in a conducting cage and ways to isolate critical items from external signal and power inputs. Nevertheless any defense may have holes and the possibility for non-lethal decapitation attacks are quite attractive. Especially vulnerable would be sensors, such as radar, and communication devices. Thus the plan is to use EMP to blind and isolate defenses in advance of a full scale attack.

As of this writing there have been no reports of use of an E-Bomb in the attack on Iraq. It seems that the US and its allies are doing just fine destroying sensors and communications with precision guided munitions, dumb bombs, artillery, tank shells, etc. The Hussein regime it would seem would have a large incentive to develop an E-Bomb to use versus the electronics heavy US forces, but there is no evidence that they have any precision guided munitions to deliver such a weapon, and a non-lethal weapon is probably not high on their priority list. If an E-Bomb is used during this attack by either side the US military is going to try very hard to keep it a secret since they are the most dependent on electronics. They would be the last ones to let the world know that an E-Bomb can be an effective weapon.

1 - A very complete analysis of E-Bombs by Carlo Kopp can be found at the rather frightening abovetopsecret.com. Another useful site with some good links is Electromagnetic Weapons at Northwestern.

2 - See this site for nuclear test film clips. This site has a bunch of raw data on nuclear tests, but seems to have not been maintained in some time. Here< /a> are pictures of the aftermath of the Starfish Prime explosion. There is lots of useful information on nuclear tests at this site.

Roleplaying Ideas

  • A hole in space: A new E-Bomb is under test at a secret military base in the desert southwest. It worked way better than expected and the intense electromagnetic wave blows a hole in the fabric of space time. Would the characters like to investigate what is in the hole? It could be another time, another place, another universe, or something else entirely.
  • Miniature EMP: Someone is using a small EMP generator, like a large handgun, to disable electronic equipment to commit crimes. To be somewhat realistic it should have limitations, such as needing cartridges that have to be reloaded, have to be recharged, or have its batteries drained after a small number of shots. Certainly it should have a short range meaning the criminals have to be clever to get close to targets before using the weapon. Also they would probably try to conceal their use of an EMP weapon. This could make for quite a story line starting with the investigation into a string of impossible crimes, the growing realization that a super science gadget is involved, and the pursuit of and struggle with the group behind it all.
  • Check that report: Someone approaches the characters with evidence that an E-Bomb of some sort was used in the Iraq attack. They will pay handsomely for the characters to go in during the midst of the fight to confirm the report, gather evidence on exactly what sort of device was used, and how effective it is. Too bad that US military and US intelligence are determined that no one finds out anything about an E-Bomb used in combat. Who besides the US military would be interested enough to pay for such an investigation?
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What do you think?

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