Electromagnetic Bombs

ABSTRACT
Electromagnetic Pulse generation technology has matured to the point where Electromagnetic bombs are becoming technically feasible, with uses warfare. The development of these weapons allows there use in a nonnuclear way.

INTRODUCTION
For a success full war against an industrialized or post-industrial opponent will require nonnuclear weapons. .These weapons will play an important role in crippling the enemy. The efficient execution of campaign against a modern industrial or post-industrial opponent will require the use of tools designed to destroy information systems. Electromagnetic bombs built for this purpose can provide a very effective tool for this purpose.

THE EMP EFFECT
The Electromagnetic Pulse (EMP) effect was first observed during the early testing of high altitude airburst nuclear weapons The effect is characterized by the production of a very short (hundreds of nanoseconds) but intense electromagnetic pulse, which propagates away from its source with ever diminishing intensity, governed by the theory of electromagnetism. The Electromagnetic Pulse is in effect an electromagnetic shock wave.

This pulse of energy produces a powerful electromagnetic field, particularly within the vicinity of the weapon burst. The field can be sufficiently strong to produce short transient voltages of thousands of Volts on exposed electrical conductors, such as wires, or conductive tracks on printed circuit boards, where exposed.

It is this aspect of the EMP effect which is of military significance, as it can result in irreversible damage to a wide range of electrical and electronic equipment, particularly computers and radio or radar receivers. Subject to the electromagnetic hardness of the electronics, a measure of the equipment’s resilience to this effect, and the intensity of the field produced by the weapon, the equipment can be irreversibly damaged or in effect electrically destroyed. The damage inflicted is not unlike that experienced through exposure to close proximity lightning strikes, and may require complete replacement of the equipment, or at least substantial portions thereof.

Commercial computer equipment is particularly vulnerable to EMP effects, as it is largely built up of high-density Metal Oxide Semiconductor devices, which are very sensitive to exposure to high voltage transients. What is significant about MOS devices is that very little energy is required to permanently wound or destroy them, any voltage is typically in excess of tens of Volts can produce an effect termed gate breakdown which effectively destroys the device. Even if the pulse is not powerful enough to produce thermal damage, the power supply in the equipment will readily supply enough energy to complete the destructive process. Wounded devices may still function, but their reliability will be seriously impaired. Shielding electronics by equipment chassis provides only limited protection, as any cables running in and out of the equipment will behave very much like antennae, in effect guiding the high voltage transients into the equipment.

Computers used in data processing systems, communications systems, displays, industrial control applications, including road and rail signaling, and those embedded in military equipment, such as signal processors, electronic flight controls and digital engine control systems, are all potentially vulnerable to the EMP effect.

Telecommunication equipment can be highly vulnerable, due to the presence of lengthy copper cables between devices. Receivers of all varieties are particularly sensitive to EMP, as the highly sensitive miniature high-frequency transistors and diodes in such equipment are easily destroyed by exposure to high voltage electrical transients. Therefore radar and electronic warfare equipment, satellite, microwave, UHF, VHF, HF, and low band communications equipment and television equipment are all potentially vulnerable to the EMP effect.

It is significant that modern military platforms are densely packed with electronic equipment, and unless these platforms are well hardened, an EMP device can substantially reduce their function.

THE TECHNOLOGY ELECTROMAGNETIC BOMBS
Key technologies which are used for making such weapons are Flux Compression Generators (FCG), or Magneto-Hydrodynamic (MHD) generators and a range of HPM devices, the foremost of which is the Virtual Cathode Oscillator. A range of experimental designs has been tested in these technology areas.

FLUX COMPRESSION GENERATORS
FCG is the most likely technology applicable to bomb designs. The FCG was first demonstrated by at Los Alamos National Laboratories in the late fifties. Since that time a wide range of FCG configurations has been built and tested, both in the US and the USSR. The FCG is a device capable of producing electrical energies of tens of MegaJoules in tens to hundreds of microseconds of time, in a relatively compact package. With peak power levels of the order of Terawatts to tens of Terawatts, FCGs may be used directly, or as one-shot pulse power supplies for microwave tubes. This means that the current produced by a large FCG is between ten to a thousand times greater than that produced by a typical lightning stroke. The central idea behind the construction of FCGs is that of using a fast explosive to rapidly compress a magnetic field, transferring much energy from the explosive into the magnetic field.

The initial magnetic field in the FCG prior to explosive initiation is produced by a start current. The start current is supplied by an external source, such a high voltage capacitor. In principle, any device capable of producing a pulse of electrical current of the order of tens of kilo Amperes to Mega Amperes will be suitable. The most commonly used arrangement is a coaxial FCG. It is essentially cylindrical form.

In a typical coaxial FCG , a cylindrical copper tube forms the armature. This tube is filled with fast high energy explosive. The armature is surrounded by a helical coil of heavy wire, typically copper, which forms the FCG stator. The stator winding is in some designs split into segments, with wires bifurcating at the boundaries of the segments, to optimize the electromagnetic inductance of the armature coil.

The intense magnetic forces produced during the operation of the FCG could potentially cause the device to disintegrate prematurely if not dealt with. This is typically accomplished by the addition of a structural jacket of a non-magnetic material. Materials such as concrete or Fiberglass in an Epoxy matrix have been used. In principle, any material with suitable electrical and mechanical properties could be used.

It is typical that the explosive is initiated when the start current peaks. This is usually accomplished with an explosive lens plane wave generator which produces a uniform plane wave detonation in the explosive. Once initiated, the front propagates through the explosive in the armature, distorting it into a conical shape Where the armature has expanded to the full diameter of the stator, it forms a short circuit between the ends of the stator coil, shorting and thus isolating the start current source and trapping the current within the device. The propagating short has the effect of compressing the magnetic field, whilst reducing the inductance of the stator winding. The result is that such generators will produce a ramping current pulse, which peaks before the final disintegration of the device.

The current multiplication (i.e. ratio of output current to start current) achieved varies with designs, but numbers as high as 60 have been demonstrated the smallest possible start current source is desirable. These applications can exploit cascading of FCGs, where a small FCG is used to prime a larger FCG with a start current. The principal technical issues in adapting the FCG to weapons applications lie in packaging, the supply of start current, and matching the device to the intended load. Interfacing to a load is simplified by the coaxial geometry of coaxial and conical FCG designs.

Significantly, this geometry is convenient for weapons applications, where FCGs may be stacked axially with devices such a microwave Vircators. The demands of a load such as a Vircator, in terms of waveform shape and timing, can be satisfied by inserting pulse shaping networks, transformers, and explosive high current switches.

MHD GENERATORS
The design of a Magneto-Hydrodynamic generator is a much less mature art than that of FCG design. Technical issues such as the size and weight of magnetic field generating devices required for the operation of MHD generators suggest that MHD devices will play a minor role in the future their potential, however, lies in areas such as starting current generation for FCG devices.

The fundamental principle behind the design of MHD devices is that a conductor moving through a magnetic field will produce an electrical current transverse to the direction of the field and the conductor motion. In an explosive or propellant driven MHD device, the conductor is plasma of ionized explosive or propellant gas, which travels through the magnetic field. Current is collected by electrodes which are in contact with the plasma jet. The electrical properties of the plasma are optimized by seeding the explosive or propellant with suitable additives, which ionize during the burn. Cartridges of the propellant can be loaded much like artillery rounds, for multiple shot operations.

THE POWER OF ELECTROMAGNETIC WARHEADS
The issue of electromagnetic weapon power is complex .hile the calculation of electromagnetic field strengths achievable at a given radius for a given device design is a straightforward task, determining a kill probability for a given class of target under such conditions is not.

This is for good reasons. The first is that target types are very diverse in their electromagnetic hardness, or ability to resist damage. Equipment which has been intentionally shielded and hardened against electromagnetic attack will withstand orders of magnitude greater field strengths than standard commercially rated equipment. Moreover, various manufacturer’s implementations of like types of equipment may vary significantly in hardness due to the idiosyncrasies of specific electrical designs, cabling schemes and chassis/shielding designs used.

The second major problem area in determining the killing power is that of coupling efficiency, which is a measure of how much power is transferred from the field produced by the weapon into the target. Only power coupled into the target can cause useful damage.

DEFENSE AGAINST ELECTROMAGNETIC BOMBS
Systems which can be expected to suffer exposure to the electromagnetic weapons effects must be electromagnetically hardened. The most effective method is to wholly contain the equipment in an electrically conductive enclosure, termed a Faraday cage, which prevents the electromagnetic field from gaining access to the protected equipment. However, most such equipment must communicate with and be fed with power from the outside world, and this can provide entry points via which electrical transients may enter the enclosure and effect damage. While optical fibers address this requirement for transferring data in and out, electrical power feeds remain an ongoing vulnerability.

Where an electrically conductive channel must enter the enclosure, electromagnetic arresting devices must be fitted. A range of devices exists, however, care must be taken in determining their parameters to ensure that they can deal with the rise time and strength of electrical transients produced by electromagnetic devices. it has been noticed that hardening measures attuned to the behavior of nuclear EMP bombs do not perform well when dealing with some conventional microwave electromagnetic device designs.

It is significant that the hardening of systems must be carried out at a system level, as electromagnetic damage to any single element of a complex system could inhibit the function of the whole system. Hardening new build equipment and systems will add a substantial cost burden. Older equipment and systems may be impossible to harden properly and may require complete replacement. In simple terms, hardening by design is significantly easier than attempting to harden existing equipment.

An interesting aspect of electrical damage to targets is the possibility of wounding semiconductor devices thereby causing equipment to suffer repetitive intermittent faults rather than complete failures. Such faults would tie down considerable maintenance resources while also diminishing the confidence of the operators in the equipment’s reliability. Intermittent faults may not be possible to repair economically, thereby causing equipment in this state to be removed from service permanently, with considerable loss in maintenance hours during damage diagnosis. This factor must also be considered when assessing the hardness of equipment against electromagnetic attack, as partial or incomplete hardening may in this fashion cause more difficulties than it would solve. Indeed, shielding which is incomplete may resonate when excited by radiation and thus contribute to damage inflicted upon the equipment contained within it.

Other than hardening against attack, facilities which are concealed should not radiate readily detectable emissions. Where radio frequency communications must be used, low probability of intercept (i.e. spread spectrum) techniques should be employed exclusively to preclude the use of site emissions for electromagnetic targeting purposes.
Communications networks for voice, data, and services should employ topologies with sufficient redundancy and failover mechanisms to allow operation with multiple nodes and links inoperative. This will deny a user of electromagnetic bombs the option of disabling the network.

LIMITATIONS OF ELECTROMAGNETIC BOMBS
The limitations of electromagnetic weapons are determined by weapon implementation and means of delivery. Weapon implementation will determine the electromagnetic field strength achievable at a given radius, and its spectral distribution. Means of delivery will constrain the accuracy with which the weapon can be positioned in relation to the intended target. Both constrain lethality.

In the context of targeting military equipment, it must be noted that vacuum tube equipment is substantially more resilient to the electromagnetic weapons effects than solid state (i.e. transistor) technology. Therefore a weapon optimized to destroy solid state computers and receivers may cause little or no damage to a vacuum tube technology device.

This underscores another limitation of electromagnetic weapons, which is the difficulty in kill assessment. Radiating targets such as radars or communications equipment may continue to radiate after an attack even though their receivers and data processing systems have been damaged or destroyed. This means that equipment which has been successfully attacked may still appear to operate. Conversely, an opponent may shut down an emitter if an attack is imminent and the absence of emissions means that the success or failure of the attack may not be immediately apparent.

An important factor in assessing the lethal coverage of an electromagnetic weapon is atmospheric propagation. While the relationship between electromagnetic field strength and distance from the weapon is one of an inverse square law in free space, the decay in lethal effect with increasing distance within the atmosphere will be greater due quantum physical absorption effects This is particularly so at higher frequencies, and significant absorption peaks due water vapor and oxygen exist at frequencies above 20 GHz. These will, therefore, contain the effect of HPM weapons to a shorter radius. Means of delivery will limit the lethality of an electromagnetic bomb by introducing limits to the weapon’s size and the accuracy of its delivery. Should the delivery error be of the order of the weapon’s lethal radius for a given detonation altitude, lethality will be significantly diminished. This is of particular importance when assessing the lethality of unguided electromagnetic bombs, as delivery errors will be more substantial than those experienced with guided weapons such as GPS guided bombs.

CONCLUSION
Electromagnetic bombs are Weapons of Electrical Mass Destruction with wide applications spanning both the strategic and tactical. As such their use offers a very high advantage in attacking the fundamental information processing and communication facilities of a target system. The massed application of these weapons will produce paralysis in any target system, thus providing a decisive advantage in the conduct of war. Because E-bombs can cause hard electrical kills over larger areas than conventional explosive weapons of similar mass, they offer a huge economic advantage as well.
The non-lethal nature of electromagnetic weapons makes their use far less politically damaging than that of conventional weapons and therefore broadens the range of military options available. Also if these weapons are used the can make a nuclear threat obsolete as well.

REFERENCES:-

http://www.tfd.chalmers.se/~valeri/EMP.html
http://www.geocities.com/CapeCanaveral/5971/emp.html
http://www.house.gov/hasc/testimony/106thcongress/99-10-07wood.htm
http://www.awe.co.uk/main_site/scientific_and_technical/featured_areas/dpd/computational_physics/nuclear_effects_group/electromagnetic_pulse/
http://www.fas.org/nuke/intro/nuke/emp.htm

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