1 Chapter 1 Revolution in Military Weapons 1.1 Weapons Revolutions From the Stone Age until the Middle Ages, a weapon s power was limited by the stre ngth of the man wielding it or, in the case of bows, by the strength of material from which it was made. In the late Middle Ages, a revolution in the weaponry o ccurred when chemical-powered (gunpowder) weapons began to replace swords and bo ws. This revolution changed the nature of warfare: not just tactics, but also th e usefulness of armor, castles, and then-popular weapons.1 Since the invention of gunpowder, a weapon s effectiveness has no longer depended on the wielder s strength, but on the chemical energy of the propellant or explosi ve. While centuries of technological advances have improved the power of these m aterials, the basic operating principle of chemical-powered weapons ultimately r emains the same. Modern battlefield weapons are the descendents of muskets and c annon. Another revolution in weaponry is with directed-energy weapons (DEWs) replacing chemical-powered weapons on the battlefield. DEWs use the electromagnetic spectr um (light and radio energy) to attack pinpoint targets at the speed of light. Th ey are well suited to defending against threats such as missiles and artillery s hells, which DEWs can shoot down in mid-flight. In addition, controllers can var y the strength of the energy put on a target, unlike a bullet or exploding bomb, allowing for nonlethal uses. 1.2 Directed-Energy Weapons A directed-energy weapon (DEW) is a type of weapon that emits energy in an aimed direction without the means of a projectile. It transfers energy to a target for a desired 2 effect. Directed-energy weapons take the form of lasers, high-powered microwaves , and particle beams. These three forms are briefly discussed in the following part. 1.2.1 Lasers Albert Einstein described the theoretical underpinnings of lasers (an acronym fo r Light Amplification by Simulated Emission of Radiation) in 1917. However, the first working laser was not built until 1960, opening an entirely new avenue of directed- energy research. Lasers produce narrow, single-frequency (i.e., single color), coherent beams of light that are much more powerful than ordinary light sources. Laser light can be produced by a number of different methods, ranging from rods of chemically doped glass to energetic chemical reactions to semicondu ctors. One of the most promising laser devices is the free-electron laser. This laser uses rings of magnetically confined electrons whirling at the speed of lig ht to produce laser beams that can be tuned up and down the electromagnetic spec trum from microwaves to ultraviolet light. Lasers produce either continuous beams or short, intense pulses of light in ever y spectrum from infrared to ultraviolet. X-ray lasers may be possible in the not too distant future. The power output necessary for a weapons-grade laser ranges from 10 kilowatts to 1 megawatt. When a laser beam strikes a target, the energy from the photons in the beam heats the target to the point of combustion or mel ting. Because the laser energy travels at the speed of light, lasers are particu larly well-suited for use against moving targets such as rockets, missiles, and artillery projectiles. One problem that affects laser beam strength is a phenomenon known as blooming, wh ich occurs when the laser beam heats the atmosphere through which it is passing, 2. As the laser travels with the speed of light so the target is first search ed for.2 show s the target being illuminated and it drowns after a successful hit. When the microwave energy encounters unshielded wires or electronic components.is discussed in detail i n chapter 3. However. however. However. this means that the w eapon can have an almost endless 3 magazine of laser bursts. Laser beams also lose energy through absorption or scattering if fired throu gh dust. Similar in principle to the microwave ove n. Depending on the type of laser. current research focuses on using them as a means of nonlethal area defense and as anti-electronic weapons rather than as death 4 rays. enough microwave energy may still get through the shielding to d amage the device. Semiconductors and modern electronics are particularly susceptible to HPM atta cks. 1. the U. However. [10] (a) (b) Figure 1. These weapons were considered for both land and space-base d systems. At higher energy levels. the mic rowaves can permanently burn out equipment. it requires an .turning the air into plasma. Once the target is searched it is tracked in two phases: coarse and fine track and while finally locked in range. Mounted on properly shielded aircraft or ships.2 Microwave Weapons Written off as impractical during World War II. High Power Microwave weapons are dealt in more detail in chapter 2. which fire streams of electrons. The number of shots a laser weapon can produce is limited only by its power supply.S. and the Soviet Union studied the possibility of cr eating particle beam weapons. much as a close lightning strike could . neutrons . High-power microwave (HPM) weapons work by producing either beams or short bursts of high frequency radio energy.1 shows a schematic of High Power Laser and the method of attack wit h it. The short. a variety of optical methods can be used to correct for bloomi ng. intense bursts of energy produced by HPM devices damages equipment wi thout injuring personnel. The figure 1. HPM weapons could destroy enemy radars. protons. or dro pped in single-use e-bombs. With the ever increasing use of el ectronics in weapons systems. Figure 1. HPM devices could have a devastating but nonlethal effect on the battlefield. dissipating it s power.1 (a): Schematic Diagram of a High Power Laser (b): Targeting with HPL [10] Figure 1. In addition. anti-aircraft installations. The kinetic energy imparted by a particle stre am destroys the target by heating the target s atoms to the point that the materia l literally explodes.3 Particle beam During the Cold War.2: (1) Target before illumination (2) Target being illuminated (3) targ et after a successful hit[10] 1. a laser shot (including the cost of produc ing the energy) is much cheaper than a shot from a chemical-powered weapon syste m. One most wor ked on High Power Microwave weapon Electromagnetic Bomb. which causes the equipment to malfunction. or even neutral hydrogen atoms. the Laser is shot. the weapons produce energies in the megawatt range. Electronic devices can be shielded by putting conductive metal cages around them. This causes the beam to lose focus. and communications and computer networks and even defend against incoming antiaircraft and anti-ship missiles. because beam strength degrades rapidly as the particles reac t with the atoms in the atmosphere. smoke. technological advances have now made microwave weapons feasible. it induces a current in t hem. or rain.2. 3 centimeters (the gigahertz frequencies) to 300 meters (the megahertz frequen cies) in length. Elect ronic warfare attacks also require prior knowledge of the enemy system. these frequencies range from wavelengths of 0. or withstand the energy. There are numerous ways to counter the effects of electro nic warfare signals. 1. because the jamming function will work only at the enemy system s frequency or modulation. 2. It allows the military commander to effect a surgical strike at selected leve . and will affect enemy systems only when the electronic warfare system is operating.1 High Power Microwave Weapons High Power Microwave (HPM) technology relies on the fact that while most types o f matter are transparent to microwaves. while both use the frequency spectrum to work against ene my electronics. 1. and subsystems. Electronic warfare systems are limited to jamming. The countries abandoned particle beam weapon research as impracticable.5 enormous power plant to generate a weapons grade beam. disperse. The electromagn etic frequency spectrum for high power microwave technology ranges from the low megahertz to the high gigahertz frequencies (10 6 hertz to 10 11 hertz). intense energy pulse producing a transient surge of thousands of volts that melts the circuitry and destroys the semiconductor devices. 2. 3. 6 7 Chapter 2 High Power Microwave Weapons 2. effects on their targets. and often lethal . The relationship between a microwave weapon and an electronic w arfare system is that. To counter the effects of a microwave weapon. These countermeasures are often accomplished by redesigning the internal signal controls or increasing the frequency bandwidth of the syste m. HPM weapons generate a ver y short. the enemy capability returns to normal operation. the enemy must harden the entir e system. Some of the characteristics which make these weapons popular ar e: 1. microwave weapons are different from the electronic warfare syst ems on several counts. Microwave weapons do not rely on exact knowledge of the enemy system. There are four major distinctive characteristics tha t differentiate a microwave weapon system from an electronic warfare system. microwave weapons by their nature will produce significant. It is not at all affected by weather. components. In other wor ds. the microwave weapon is designed to overwhe lm a target s capability to reject. They can leave persisting and lasting effects in the enemy targets through da mage and destruction of electronic circuits. 3. Unlike the electronic warfare system. It enables a speed-of-light attack on enemy electronic system. not just individual components or circuits. When the electronic warfa re system is turned off. The enemy system also has to be operating in order for electronic warfare syste ms to effectively jam. metallic conductors (as present in Metal -Oxide semiconductors) absorb them and get heated up. A microwave weapon will affect enemy systems even when they are turned off. 4. Invisible to the human eye.3 Differences between Microwave Weapon system and Electronic warfare system A common assumption is that microwave weapons systems are similar to electronic warfare systems. 4. Each field strength can differ radically. The EMP effect was first observed during the early testing of high altitude airb urst nuclear weapons. KiloVolts) on e xposed electrical conductors. EMP and lightning differ in four crucial ways: 1.000 volts per meter. 2. EMP pulses are of short duration--usually less than a thousandth of a second as opposed to lightning pulses that last hundreds of a millisecond.e. where exposed. this results in modern communications and electronics equipment being highly vulnerable to the power surges of EMP. As the field of electronics has evolved from the vacuu m tube era to today's integrated microcircuits which can handle only minute quan tities of voltage current. Initially called radio flash. This pulse of energy produces a powerful electromagnetic field. The effect is characterized by the production of a very sh ort (hundreds of nanoseconds) but intense electromagnetic pulse. governed by the theory o f electromagnetism. low operating costs and allow simplified pointing a nd tracking. 4. The field can be sufficiently strong to pr oduce short lived transient voltages of thousands of Volts (i. or conductive tracks on printed cir cuit boards.2 Electromagnetic Pulse Electromagnetic Pulse (EMP) is a pulse of electromagnetic energy of extremely sh ort duration. the comparable interval for lightning pulse involves millionths of secon ds. its susceptibility to EMP has increased significantly . 9 3. such as wires. HPMs have deep magazines. particularly wit hin the vicinity of the weapon burst. 2. EMP can involve 50. . In a politically sensitive environment it is preferable to use weapons causin g collateral damage. Pulse time for EMP maybe a few billionths of a second. However. However. The Electromagnetic Pulse is in effect an electromagnetic sh ock wave. Both involve a sudden pulse of energy and both are attracted to intent ional or unintentional collectors or antennas. which propagate s away from its source with ever diminishing intensity. It is this aspect of the EMP effect which is of military significance.ls of combat. 5. The significance of these power surges is demonstrated when comparing EMP with l ightning. EMP is similar to the simultaneous t ransmission of a large number of radio waves varying from one KHz to 100 MHz and peak field 8 amplitudes produced are very large on the order of 50 kilovolts per meter. EMP pulses much more rapidly. particularly computers and radio or radar receivers. Consequently. as it can result in irreversible damage to a wide range of electrical and electronic equi pment. Lightning occurs at much lower frequencies and in bands well below the freque ncies used by the military communications systems. EMP i s of great concern today. Lightning maybe a few thousand volt s per meter. EMP concentrates in some of the bands most frequently used by the military's tactical communications systems. This complicated process occurs in a few bil lionths of a second (nanoseconds) and last one millionth of a second (millisecon d). A number of parameters including the yield. The final resu lt is a tremendous surge on current in the air on any communications equipment a nd the SREMP renders the equipment useless.3 Types of Electromagnetic Pulse Based on analysis of the various combinations of the preceding parameters there are four significant types of EMP. This high altitude burst will not generate any other n uclear effect at the earth's surface. the most hazardous to our security. High-Altitude EMP: The second type. it is significant on the tactical nuclear battlefield. Sign ificant HEMP levels occur at the earth's surface out to where the line of sight from the burst contacts the earth's surface. SGEMP results from the interaction of x-rays or gamma rays striking an atom on a metal object. This re sult in the ejection of electrons and the creation of a strong ionized area refe rred to as the source field region. asymmetries in the earth's atmosphere and location of the bur st relative to the earth's magnetic declination directly affect both the shape o r coverage area and the strength of the EMP. SREMP is localized three to five kilometers from the burst. 2. this type of nuclear explosion also produces vast ground coverage. which produces a strong electric field that radiates away from the source re gion. potentially. However. If these rays were to strike an unprotected satellite or missile traveling above the atmosphere. Surface Burst EMP: The first. Although the area over which the low-altitude EMP produces a damaging effect is relatively small. The generation of EMP by a surface blast begins with the gamma r ays traveling radically outward from the burst. occurs when the nuclear burst explodes on the earth's surface or up to two kilometers above the surface. a nuclear burst over the central part of the United States at an altitude of 500 kilometers would pro duce an EMP field that would incapacitate all communications systems in the cont inental United States. Thi s produces an electric field and lasts two to three nano seconds. it s height-of-burst. The explosion of a nuclear burst at an altitude greater than 30 to over 500 kilometers above the ea rth's 10 surface will produce the above scenario. is the most significant and. A nuclear blast in outer space sends gamma rays or x-rays out in all directions. these rays would knock out electrons from the a . high-altitude EMP (HEMP). Due to the very thin to non existent at mosphere at these altitudes. Source Region EMP: The third type of EMP is source region EMP (SREMP).The formation of EMP results from the collision of the gamma photons emitted fro m a nuclear detonation and interacts with atoms in the outer atmosphere. This radiated field is EMP. These collisions generate Compton recoil elect rons which interact with the earth's magnetic field to produce a downward travel ing electromagnetic wave. Those gamma rays traveling toward the e arth's atmosphere are stopped by collisions with atmospheric molecules at altitu des between 20 and 40 kilometers. This is produced by a nuclear burst within several hundred meters of the earth's surface (the fireball touches the ground). Consequently. System Generated EMP: The last type of EMP is system generated EMP (SGEMP). This action causes the Compton e lectrons to move radically outward and leaves behind immobile positive ions. the gamma rays emitted from the explosion will trav el radically outward for long distances. surface burst electromagnetic pulse (EMP) . The radiated wave is only propagated to a distance of ten to twenty kilometers from the burst point due to the higher density of the lower atmosphe re. 2. These technologies are discussed in detail in chapter 3 with the discussion of a n HPM weapon.3 that the amplit udes for the three are comparable but the difference appears in the duration of the pulse. researchers concluded. Virtual cathode Oscillators. Flux Compression Generators. Figure 2. in contrast to that produced by nuclear method. Explosive or propellant driven Magneto-Hydro Dynamic generators. It can be clearly seen from the figure 2.3 shows a comparison of electromagnetic pulse shapes obtained with nucl ear HPM generation. This action would induce an EMP field that would make th e satellite and the missiles useless.2: (a) Block diagram of Non-nuclear EMP generator for HPM (b) Complete HPM system Figure 2. The blast even disrupted radio equipment as far away as Australia.4 Nuclear EMP This idea dates back to nuclear weapons research from the 1950s. The non-nuclear EMP generator for HPM is shown in figure 2. The resulting electromagnetic pulse induced i ntense electrical currents in conductive materials over a wide area. Americ an tests of hydrogen bombs yielded some surprising results. The techn ology base for non. but the waveforms are almost opposite in nature as lightning pro duces a sharp transient but slows down later whereas the non nuclear method (Flu x Compression Generator) produces a slow transient which decays fast. This helps the non nuclear methods to control the pulse in amplitude and thus power.nuclear EMP production has far grown. hundreds o f miles away. Nuclear method produces the electromagnetic pulse with shortest durat ion of the three. In 1958. the photons from th e blast's intense gamma radiation knocked a large number of electrons free from oxygen and nitrogen atoms in the atmosphere. (a) (b) Figure 2. 3. theorized by physicist Arthur Compton in 1925. 2.the Electromagnetic Bomb. The other two methods produce the pulse of greater duration. Using these non-nuclear techniques the EMP can be made to vary in streng th depending upon the target enemy type.toms of the metal skin. This is an important advantage to be exploited for developing HPM for non-lethal appl . A test blast over th e Pacific Ocean ended up blowing out streetlights in parts of Hawaii. This flood of electrons interacted with the Earth's magnetic field to create a fluctuating electric current. The key technologies i n the area are: 1. Researchers concluded that the electrical disturbance was due to the Compton Ef fect.3: Comparison of Electromagnetic Pulse shape 13 Figure 2. Compton's assertion was tha t photons of electromagnetic energy could knock loose electrons from atoms with low atomic numbers. These are discussed in the sections to follow. lightning and Flux Generators which is a non-nuclear method of generation of HPM. which induced a powerful magnetic field. but the caused effect due to it is uncontrolled.2 with its block diagram.5 Non.nuclear EMP The non-nuclear methods for producing EMP are being developed to have a controll ed EMP.1: Nuclear EMP formation 2. 11 There are two different methods of generating such high powered EMP suitable for HPM weapons. More over this will help to develop HPM 12 weapons for non-lethal use as active-denial system for controlling crowd by heat ing the water in the target's skin and thus cause incapacitating pain. In the 1958 test. . The FCG is a device capable of producing electrical energies of tens of MegaJoul es in tens to hundreds of microseconds of time. Since that t ime a wide range of FCG configurations has been built and tested. that a targeted item or items of electronic equ ipment experiences either a soft or hard kill. and this can in turn render inoperable for extended periods of time an y system which is critically dependent upon this computer system. Using these. A good example is a co mputer system. 14 15 Chapter 3 Electromagnetic Bomb In principle. which can seriously compr omise the operation of any system which is critically dependent upon the compute r system in question. an electromagnetic weapon is any device which can produce electrom agnetic field of such intensity. The equipment may or may not be repairable. or as one shot pulse power supplies for microwave tubes. 3. The result is a temporary loss of function. 3. explosive or prop ellant driven Magneto-Hydrodynamic (MHD) generators and a range of HPM devices. An example is a computer system which experiences damage to its power supply. A soft kill is produced when the effects of the weapon cause the operation of th e target equipment or system to be temporarily disrupted. The central idea behind the construction of FCGs is that of using a fast explosi ve to rapidly compress a magnetic field. subject to the severity of th e damage. Due to harmful effects of the nuclear method of EMP generation.2 Explosively Pumped Flux Compression Generators The explosively pumped Flux Compression Generator (FCG) is the most mature techn ology applicable to bomb designs. the current produced by a large FCG is between ten to a thousand times greater than that produced by a typical lightning stroke.2. Most common technology used for E-Bomb is FCG and Vircator. in a relatively compact package. high power and non-nuclear microwave weapon researched upon for use as non-lethal weapon. the foremost of which is the Virtual Cathode Oscillator or Vircator. which is caused to reset or transition into an unrecoverable or h ung state. by not harming humans but a ffecting the warfare electronics thereby leaving the enemy limping. and in many areas quite mature. A hard kill is produced when the effects of the weapon cause permanent electrica l damage to the target equipment or system. Electromagnetic bomb is a directed energy. To p lace this in perspective. FCGs may be used directly. These are ac tually not bombs at all but a large microwave oven. Key technologies which are extant in the 16 area are explosively pumped Flux Compression Generators (FCG). With peak power levels of the order of TeraWatts to tens of TeraWatts.1 Technology base for electromagnetic bomb The technology base which may be applied to the design of electromagnetic bombs is both diverse. peripheral interfaces and m emory. necessitating either the repair or t he replacement of the equipment or system in question.can be shown as in figure 3. the blo ck diagram of a non-nuclear HPM weapon E-Bomb. it is not used.ications. transferring much energy from the explo sive into the magnetic field. The FCG was first demonstrated by Clarence Fow ler at Los Alamos National Laboratories (LANL) in the late fifties. typically copper.The initial magnetic field in the FCG prior to explosive initiation is produced by a start current. but numbers as high as 60 h ave been demonstrated. The demands of a load such as a Vircator. In prin ciple. where FCGs may be stacked axially with devices such a microwave Vir cators.1: Explosively pumped coaxial Flux Compression Generator 18 In a typical coaxial FCG. for peak currents of tens of MegaAmperes and peak ener gies of tens of MegaJoules. shorting and thus isolating the start current source and trapping the current within the device. Interfacing to a load is simplified by the coaxial geometry of coaxial a nd conical FCG designs. such a high voltage capacitor bank (Marx bank). Published resul ts suggest ramp times of tens to hundreds of microseconds. a smaller FCG or an MHD device. Figure 3. where a small FCG is used to prime a larger FCG with a start current. These applications can exploit cascading of F CGs. transformers and . It is typical that the explosive is initiated when the start current peaks.e. The stator winding is in some designs split into segments. can be satisfied by inserting pulse shaping networks. In a munition application. This tub e is filled with a fast high energy explosive. the smallest possible 19 start current source is desirable. ratio of output cur rent to start current) achieved varies with designs. The most co mmonly used arrangement is that of the coaxial FCG. this geometry is convenient for weapons a pplications. This is usually accomplished with an explosive lens plane wave generator which produ ces a uniform plane wave burn (or detonation) front in the explosive. Materials such as concrete or Fiber glass in an Epoxy matrix have been used. the supply of start current. as its essentially cylindrical form facto r lends itself to packaging into munitions. distorting it into a conical shape (typically 12 to 14 degrees of arc). The propagating short has the effec t of compressing the magnetic field. whilst reducing the inductance of the stato r winding. specific to the chara cteristics of the device. it forms a short circuit between t he ends of the stator coil. in terms of waveform shape and timing. The result is that such generators will producing a ramping current p ulse. Once initi ated. where space and weight are at a premium. which peaks before the final disintegration of the device. In principle. A number of explosive types have been used. The current multiplication (i. any material with suitable electrical and mechanical propert ies could be used. any device capable of producing a pulse of electrical current of the orde r of tens of kiloAmperes to MegaAmperes will be suitable. The intense magnetic forces produced during the operation of the FCG could poten tially cause the device to disintegrate prematurely if not dealt with. such as air deliver ed bombs or missile warheads. the front propagates through the explosive in the armature. In applications where weight is an issue. which forms the FCG stator. The coaxial arrangement is o f particular interest in this context. with wires bifurcating at the boundaries of the segments. and matching the device to the intende d load. The armature is surrounded by a helical coil of heavy wire. Where the armature has expanded to the full diameter of the stator. 17 A number of geometrical configurations for FCGs have been published. This is t ypically accomplished by the addition of a structural jacket of a non-magnetic m aterial. to opt imize the electromagnetic inductance of the armature coil. a glass or Kevlar Epoxy composite would be a viabl e candidate. The start current is supplied by an external source. a cylindrical copper tube forms the armature. Significantly. The principal technical issues in adapting the FCG to weapons applications lie i n packaging. Figure 3. Cartridges of such propellant can be loaded much like artillery rounds. Spark Gap Devices and Vircators are all examples of th e available technology base. Under the proper conditions. or in the nearer term a Spark Gap source.2: Virtual Cathode Oscillator . the output of the FCG is by its basic physics constrained to the fre quency band below 1 MHz. A HPM device overcomes both of the probl ems. forming a bubble of space charge behind the anode . In an explosive or propella nt driven MHD device. where the microwave cavity will support appropriate modes. Reflex triodes. Vircators may be tuned or chirped in frequency. Power 21 levels achieved in Vircator experiments range from 170 kiloWatts to 40 GigaWatts over frequencies spanning the decimetric and centimetric bands. Magnetrons. the conductor is plasma of ionized explosive or propellant gas. If the space charge region is placed into a resonant cavity whi ch is appropriately tuned. which ionize during the burn. The Vircator is of interest because it is a one shot device c apable of producing a very powerful single pulse of radiation.explosive high current switches. In the context of this report. Technical issues such as the si ze 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 near term . Current is collected by electrod es which are in contact with the plasma jet. Many target sets will be difficult to attack even with very high power levels at such frequencies. as its output power may be tightly focused and it has a much better ability to couple energy into many target types.The Vircator Whilst FCGs are potent technology base for the generation of large electrical po wer pulses. Relativistic Klystrons. their potential lies in areas such as start cur rent generation for FCG devices. often using 20 conventional ammunition propellant as a base.4 High Power Microwave Sources . Slow Wave Devices. and can operate over a relatively broad band of microwave frequencies. which travels through the magnetic field. for multiple shot operations. very high peak powers may be achieved. small and robust. the device of choice will be at this time the Vircator. moreover focusing the energy output from such a device will be problematic. yet it is mechani cally simple. Published ex periments suggest that a typical arrangement uses a solid propellant gas generat or. A wide range of HPM devices exist. Because the frequency of oscillation is dependent upon the electron beam parameters. The fundamental idea behind the Vircator is that of acceler ating a high current electron beam against a mesh (or foil) anode. this space charge region will oscillate at microw ave frequencies. 3. The physics of the Vircator tube are substantially more complex than those of th e preceding devices. 3.3 Explosive and Propellant Driven MHD Generators The design of explosive and propellant driven Magneto-Hydrodynamic generators is a much less mature art that that of FCG design. The fundamental principle behind the design of MHD devices is that a conductor m oving through a magnetic field will produce an electrical current transverse to the direction of the field and the conductor motion. Many electron s will pass through the anode. Conventional m icrowave engineering techniques may then be used to extract microwave power from the resonant cavity. From the perspective of a bomb or warhead designer. The electrical properties of the plasma are optimized by seeding the explosive o r propellant with suitable additives. 2). stability of os cillation frequency. radars. Collecto rs may be cables. conversion effici ency and total power output. its ability to absorb voltage and c urrent decreases. this results in increased susceptibility to EMP. low current r elays and switches are less susceptible.anything that acts as an electrical conductor. The muni tion then unfolds its radio transmitter aerials and the transmitter sends a high -powered radio pulse of billions of watts that lasts just a few nanoseconds. Power is m ost often extracted by transitioning the waveguide into a conical horn structure . Another necessary variable to consider is the collection of EMP energy. digital circuitry. metal structures. inductors. given the hig h power levels involved and thus the potential for electrical breakdown in insul ators.3. A vast array of collectors form a huge grid over the entire area. Its power cabl es. 23 Chapter 4 Effects produced by Electromagnetic bomb 4.The two most commonly described configurations for the Vircator are the Axial Vi rcator (AV) (Fig. lamps and circuit breakers are no t susceptible. The amount of EMP energy co llected depends on the electrical properties. relays. integrated circuits. Figure 3. alarm systems and electronic sensors. 3. conduit. A burned-out transistor exemplifies the former.3: Schematic of Electromagnetic Bomb 22 Technical issues in Vircator design are output pulse duration. which is typicall y of the order of a microsecond and is limited by anode melting. Equipment designed for high voltage use such as motors. and then breaking open its outer casing over the target. railroad tra cks . semi conductor devices. while a change in the state of a switch represents the latter. and shape of the material co mprising the collector. The Axial Vircator is t he simplest by design. reaching it s target area. a GPS guided bomb or a cruise missile. The Transverse Vircator injects cathode current from the side of the cavity and will typically oscillate in a Transverse Electric (TE) mode. It is typically built into a cylindrical waveguide structure. digital computers. EMP energy may be transferred from the collector to the equipment directly by a physical connection or indirectly through induction. Most susceptible to EMP are those components with low voltage and current requir ements such as solid state devices. Gen erally. aff ecting any unshielded electronic device in a large area. Coupling power efficiently from the Vircator cavity in modes suitable for a chosen antenna type may also be an issue. antennas. antennas and railroad tracks have the capability of . wires.3 shows the schematic of an Electromagnetic Bomb. tube transmitters and receivers. Vacuum-tube equipment. which functions as an antenna. size. the larger the volume and power rating of the electromagnetic bomb carr ied. an MLRS rocket launcher. Figure 3. as the size of the device decreases. transformers.1 The EMP susceptible Devices The system of degradation from EMP results in either a permanent failure of a de vice or a component or a temporary impairment which can deny use of the equipmen t for a period of time. and the Transverse Vircator (TV). telephone lines. pipe. AVs typically oscillate in Transverse Magnetic (TM) modes. and has generally produced the best power output in exper iments. The larger the delivery weapon. often compromised by cavity mode hopping. towers.5 Working of E-Bomb The electromagnetic bomb works by being fired from a long-range 155mm artillery gun. Satel lite link and importantly control facilities are vital means of communication as well as the primary interface to military and commercial reconnaissance satelli tes. In modern warfare. for example. Attacking such economic targets with electro magnetic weapons will halt 27 attack to render them both undefended and non-operational. particularly later generation digital switching systems. Whether to expend con . its population and its fielded military forces. which identifies five centres of gravity in a nation's w ar fighting capability. shoul d inappropriate backup strategies have been used to protect stored data. it s transportation network. an e-bom b could effectively neutralize: ? vehicle control systems ? targeting systems. on the ground and on missiles and bombs ? communications systems ? navigation systems ? long and short-range sensor systems 4. Telephone exchanges. Manufacturing. Television and radio broadcasting stations.collecting EMP energy and transferring it to anything physically or electronica lly connected to 24 them. chemical. In descending order of importance. most sensors and telemetry devices used are electrical or electronic. Modern strategic air attack theory is based upon Warden's Five Rings model [1] as shown in figure 4. Other t argets which fall into the innermost ring may also be profitably attacked. these are the nation' s leadership and supporting C3 system. any electronic device attached to a telephone line or p ower line has the capability of receiving large amounts of EMP. the various levels of attack could accomplish a number of imp ortant combat missions without racking up many casualties. In any modern nation these are heavi ly dependent upon the use of computer equipment and communications equipment. Se lective targeting of government buildings with electromagnetic weapons will resu lt in a substantial reduction in a government's ability to handle and process in formation. Figure 4. its essential economic infrastructure. The innermost ring in the Warden model essentially comprises government bureaucr acies and civilian and military C3 systems. are also highly vulnerable to appropriate electromagnetic attack. Thus. one 25 of the most powerful tools of any government.1. Furthermore. are also vulnerable to electromagn etic attack due the very high concentration of electronic equipment in such site s. The finance industry and stock markets are almost wholly dependent upon computer s and their supporting communications. petroleum produc t industries and metallurgical industries rely heavily upon automation which is almost universally implemented with electronic PLC (Programmable Logic Controlle r) systems or digital computers. The damage inflicted upon information records may be permanent. For example.2 Air Warfare Strategy The modern approach to strategic air warfare reflects that much effort is expend ed in disabling an opponent's fundamental information processing infrastructure.1: Warden s five ring model Essential economic infrastructure is also vulnerable to electromagnetic attack. as most telephone lines. Moreover. which has been widely published in the open litera ture. and t hus provides an efficient path for the power flow from the electromagnetic weapo n to enter the equipment and cause damage. as well as paralysis in most vital indust ries.ventional munitions on targets in this state would depend on the immediate milit ary situation. Only power coupled into the target can cause u seful damage. Unlike the technology base for weapon construction. buildin g risers and corridors. when produced by a low frequency weapon ) or electrical standing waves (when produced by a HPM weapon) on fixed electri cal wiring and cables interconnecting equipment. This is for two good reasons. two principal coupling modes are recognized in the literature: ? Front Door Coupling occurs typically when power from a electromagnetic weapon is coupled into an antenna associated with radar or communications equipment.3 Problems in determining Lethality The issue of electromagnetic weapon lethality is complex. how precise is the target located. The antenna subsystem is designed to couple power in and out of the equipment. 28 The second major problem area in determining lethality is that of coupling effic iency. The massed application of electromagnetic weapons in the opening phase of the ca mpaign would introduce paralysis within the government. It is discusse d in the following part of the chapter.4 Coupling Modes In assessing how power is coupled into targets. which is a measure of how much power is transferred from the field produc ed by the weapon into the target. In most instances any particular cable run will comprise . or providing connections to mai ns power or the telephone network. lethality related issues have been published much less frequently. Equipment connected to exposed cables or wiri ng will experience either high voltage transient spikes or standing waves which can damage power supplies and communications interfaces if these are not hardene d. The effect on any equipment depends upon coupling of the emitted wave with the d evice. networking cables and power lines follow streets. various manufacturer's implementations of like types of equipment may vary significantly in hardness due the idiosyncrasies of specif ic electrical designs. ? Back Door Coupling occurs when the electromagnetic field from a weapon produces large transient currents (termed spikes. Moreover. damage can be do ne to other devices inside. 4. This would greatly reduce the capability of the target nation to conduct m ilitary operations of any substantial intensity. Equipment which ha s been intentionally shielded and hardened against electromagnetic attack will w ithstand orders of magnitude greater field strengths than standard commercially rated equipment. cabling schemes and chassis/shielding designs used. While the calculation of electromagnetic field strengths achievable at a given r adius for a given device design is a straightforward task. The first is that target types are very diverse in their electromagnetic hardness. the emission frequency. should the transient penetrate into the equipment. determining a kill pr obability for a given class of target under such conditions is not. deprived of much of its information processing infrastructure. 4. A low frequency weapon will couple well into a typical wiring infrastructure. or ability to resist damage. 30 The first step in maximizing bomb lethality is to maximize the peak power and du ration of the radiation of the weapon. and by maximizing the efficiency of intern al power transfers in the weapon. An area worth f urther investigation in this context is the use of low frequency bombs to damage or destroy magnetic tape libraries. A circularly polarized emission will exploit a . Whilst coupling efficiency is inherently poor. and ensure that the current pulse does not vaporize the cable prematurely. this is accomplish ed by using the most powerful flux compression generator (and Vircator in a HPM bomb) which will fit the weapon size. Four radial antenna elements form a "virtual" earth plane around the bomb. The second mechanism which can be exploited to improve coupling is the polarizat ion of the weapon's emission. which is in effect a loop antenna of very small diameter relative to the wavelength. a linearly polarized emission will only exploit hal f of the opportunities available. while an axial antenna element is used to radiate the power from the FCG. Assuming that the antenna provides the require d weapon footprint. there are at least two mechanisms which can be employed to f urther maximize lethality. and rely upon the near field produced by the FCG winding. as the near 31 fields in the vicinity of a flux generator are of the order of magnitude of the coactivity of most modern magnetic materials Figure 4. If we assume that the orientations of possible cou pling apertures and resonances in the target set are random in relation to the w eapon's antenna orientation. In this fashion. the use of a guided bomb would allow th e warhead to be positioned accurately within meters of a target. Whilst weapons built this way are inherently wide band. A go od strategy for dealing with a complex and diverse target set is to exploit ever y coupling opportunity available within the bandwidth of the weapon. Other alternatives are possible. The first is sweeping the frequency or chirping the Vircator. A high power coupling pulse transformer is used to matc h the low impedance FCG output to the much higher impedance of the antenna. can be readily focused against targets with a compact antenna assembly. a larger number of coupling opportunities are exploited. Whatever the rel ative orientation of the weapons field.3: Vircator Antenna Assembly Microwave bombs have a broader range of coupling modes and given the small wavel ength in comparison with bomb dimensions. The second step is to maximize the coupling efficiency into the target set. by enabling the radiation to couple into apertures and resonances over a range of frequencies. to produce the desired field strength. For a given bomb size. These are produced by firing off cable spools wh ich unwind several hundred meters of cable. A low frequency bomb built around an FCG will require a large antenna to provide good coupling of power from the weapon into the surrounding environment. as most of the power produced lies in the frequency band below 1 MHz compact antennas are not an option. more than one linear segment of the cabl e run is likely to be oriented such that a good coupling efficiency can be achie ved. This can improve c oupling efficiency in comparison with a single frequency weapon. One p ossible scheme is for a bomb approaching its programmed firing altitude to deplo y five linear antenna elements.multiple linear segments joined at approximately right angles. The choice of element lengths would need to be carefully matched to the frequency characteristics of the weapon. One is to simply guide the bomb very close to t he target. Energy which is not emitted is energy wasted a t the expense of lethality. mobile communications nodes and na val 34 vessels are all good examples of this category of target. In the latter instance target coordinates can be continuously data linked to the launch platform. With the accuracy inherent in GPS /inertially guided weapons. Figure 4.4: Lethal Footprints of low frequency bomb in relation to altitude Another aspect of electromagnetic bomb lethality is its detonation altitude. and by varying the detonation altitude. This provides the option of sacrificing weapon coverage to achieve ki lls against targets of greater electromagnetic hardness. lethality is maximized by maximizing power output and the efficiency of en ergy transfer from the weapon to the target set. for a given bomb size.5: Lethal footprint of a HPM E-Bomb in relation to altitude Mobile and camouflaged targets which radiate overtly can also be readily engaged . military bases and known radar sites and communications nodes are all targ ets which can be readily identified through conventional photographic. Bui ldings housing government offices and thus computer equipment. imaging radar. As most such targets move rela tively slowly. Certain categories of target will be very easy to identify and engage. While radiating. Microwave weapons offer the abi lity to focus nearly all of their energy output into the lethal footprint. effi ciency of coupling from the tube.ll coupling opportunities.4. These targets are typically geographically fixed and thus may be attacked providing that the a ircraft can penetrate to weapon release range. Mobile or hidden targets which do not overtly radiate may present a problem. their positions can be precisely tracked with suitable Electronic Support Measures (E SM) and Emitter Locating Systems (ELS) carried either by the launch platform or a remote surveillance platform. Some work therefore needs to be done on tapered helix or conical spi ral type antennas 32 capable of handling high power levels. a tradeoff may be achieved between the size of the lethal footprint and the intensity of the electromagnetic field in that footprint. and a suitable interface to a Vircator wi th multiple extraction ports must devised. microwav e bombs are the preferred choice. power is coupled from the tube by stubs which directly feed a multifilar conical helix antenna. while delivering circularly polarized radiatio n. Figure 4. they are unlikely to escape the footprint of the electromagnetic bomb during the weapon's flight time. A possible implementation is depicted in Fig. production facili ties. Mobile and relocatable air defence equipment. par ticularly should conventional means of targeting be employed. Thus. A technical soluti .4 shows the lethal footprints in relation to altitude. In this arrangement. Figure 4. The practical constraint is that it may be difficult to produce an efficient hig h power circularly polarized antenna design which is compact and performs over a wide band. the electromagnetic bomb can be programmed to detona te at the optimal position to inflict a maximum of electrical damage.3. 33 4. satellite . beamwidth. electronic reconnaissance and humint operations. An implementation of this sche me would need to address the specific requirements of bandwidth. Therefore. This is not unli ke the use of airburst explosive devices.6 Targeting Electromagnetic Bombs The task of identifying targets for attack with electromagnetic bombs can be com plex. and o ffer the ability to exploit a wider range of coupling modes. and an onboard storage device suc h as a battery. Due to the potentially large lethal radius of an electromagnetic device. eg a battery. compare d to an explosive device of similar mass. Wh ilst this is an inherent characteristic of weapons such as cruise missiles. to provide the current used to charge the capacitors used to prime the FCG prior to its discharge. An electromagnetic bomb warhead will comprise an electromagnetic device. Air delivered bombs. the bomb's capacitor bank can be charged by the launch aircraft enroute to target. the size of the priming cu rrent source and its battery may well impose important limitations on weapon cap ability. It fo llows therefore. A limitation in all such applicat ions is the need to carry an electrical energy storage device. In suc h a bomb design. as most of the bom b mass can be dedicated to the electromagnetic device installation itself. which have a flight time between tens of seconds t o minutes. In a cruis e missile. with most of the usable mass occupied by the electroma gnetic device and its supporting hardware. the navigation system. assuming equal acc uracy of delivery and technologically similar electromagnetic device design. an electrical energy converter. 35 Chapter 5 The Delivery of Conventional Electromagnetic Bombs 5. The warhead fraction could be as high as 85%. the proximity fusing system. T he warhead fraction (ie ratio of total payload (warhead) mass to launch mass of the weapon) will be between 15% and 30% . electromagnetic warheads will occupy a volume of phy sical space and will also have some given mass (weight) determined by the densit y of the internal hardware. that for 36 a given technology an electromagnetic bomb of identical mass to a electromagneti c warhead equipped missile can have a much greater lethality. In wholly autonomous weapons such as cruise missiles. Therefore the available payload capacity will be split between t he electrical storage and the weapon itself. in an anti-shipping missi le the radar seeker and in an air-to-air missile. this will be tied to the navigation system. although some sacrifice in airfram e fuel capacity could see this size increased. The electromagn etic device will be detonated by the missile's onboard fusing system. As the weapon is pumped. Like explosive warheads. a barometric fus e or in GPS/inertially guided bombs. for many types of target. An electromagnetic bomb delivered by a conventional aircraft can offer a much be tter ratio of electromagnetic device mass to total bomb mass. and after release a much smaller onboard power supply could be used to maintain the charge in the priming source prior to weapon initiation.1 E-Bomb Carriers As with explosive warheads. the battery is drained. Known existing applications involve fitting an electromagnetic warhead to a crui se missile airframe. Fusing co uld be provided by a radar altimeter fuse to airburst the bomb. A missile borne electromagnetic warhead installation will comprise the electroma gnetic device. electromagnetic warheads ma y be fitted to a range of delivery vehicles. pote .on to this problem does however exist. standoff delivery would be prudent. The choice of a cruise missile airframe will restrict the w eight of the weapon to about 340 kg (750 lb). could be built to exploit the launch aircraft's power systems. an elec trical energy converter and a energy storage device to pump and sustain the elec tromagnetic device charge after separation from the delivery platform. the glidebomb can be released from outside effective radius of target air defences. anti-shipping missiles and ai r-to-air missiles would dictate fire and forget guidance of the appropriate vari ety. Finally the bomb's autopilot may be programmed to shape the terminal tr ajectory of the weapon. Communications networks for voice. as is the case with nuclear weapons. every aircraft capab le of delivering a standard guided munition also becomes a potential delivery ve hicle for a electromagnetic bomb. The recent advent of GPS satellite navigation guidance kits for conventional bom bs and glidebombs has provided the optimal means for cheaply delivering such wea pons. In turn this makes saturation atta cks a much more viable proposition.1: Delivery profiles for GPS/inertial guided weapons The importance of glidebombs as delivery means for HPM warheads is threefold. it is not unreasonable to expect that these should be both cheaper to manufacture. the l arge standoff range means that the aircraft can remain well clear of the bomb's effects.1 Methods of prevention Two means of prevention against these E-bombs are suggestive namely the preempti ve destruction of the platform or the delivery vehicle (where the E-bomb resides ) and protecting the vulnerable devices. The EMP threat is solvable. Two main processes exist to protect electronic communications systems from the effects of EMP. as there is enough scientific and engineering knowle dge currently available to insure the survivability of communications systems fr om EMP effects. 37 Figure 5. to allow the launching aircraft to gain adequate separation of several mile s before warhead detonation. Fi rstly. such that a target may be engaged from the most suitable altitude and aspect. The most effective defence against electromagnetic bombs is to prevent their del ivery by destroying the launch platform or delivery vehicle. and easier to support in the field. The first is shielding and the second is acquir ing EMP hardened equipment. cheap. 39 Chapter 6 Protection against Electromagnetic bomb 6. While GPS guided weapons without differential GPS enhancements may lack th e pinpoint accuracy of laser or television guided munitions. therefore minimising the risk to the launch aircraft. no software changes to the aircraft would be required.ntial applications of these devices to glidebombs.2 EMP hardened Equipments . A major advantage of using electromagnetic bombs is that they may be delivered b y any tactical aircraft with a nav-attack system capable of delivering GPS guide d munitions. 6. thus allowing for more substantial weapon stocks. they are still quit e accurate (CEP \(~~ 40 ft) and importantly. Secondly. Should weapon ballistic properties be identica l to the standard weapon. data and services should empl oy topologies with sufficient redundancy and failover mechanisms to allow operat ion with multiple nodes and links inoperative. This will deny a user of electrom agnetic bombs the option of disabling large portions if not the whole of the net work by taking down one or more key nodes or links with a single or small number of attacks. 38 Because of the simplicity of electromagnetic bombs in comparison with weapons su ch as Anti Radiation Missiles (ARM). autonomous all weather weapo ns. As we can expect GPS guided munitions to be become the standard wea pon in use by Western air forces by the end of this decade. (2) Maintenance. Hardening by des ign is significantly easier than attempting to harden existing equipment. Thus. (3) Training ensures that the measures designed into a hardened system are not degraded by uninformed action or inaction. volume sh ielding. is to shield the rooms or facilities in which equipment is located and this creates a large volume in which the electromagnetic environment is negligib le. M eans of delivery will constrain the accuracy with which the weapon can be positi oned in relation to the intended target. The shi elding protects electromagnetic fields against sensitive electronic equipment. Weapon implementation will determine the electromagnet ic field strength achievable at a given radius. test procedures and equipment must be conceived a s a part of the system hardening process and must be implemented by the user (9:43-4-7). The essential elements of system hardness maint enance includes: 40 (1) Configuration management which prevents future system changes from compromising system hardness. the EMP induced currents on equipment and cables are diverted away from sensitive components by the cable shields. for instance early 1960s Soviet military equipment. 6. electrical power feeds remain an ongoing vulnerability. surveillance.4 Faraday s Cage The most effective method is to wholly contain the equipment in an electrically conductive enclosure. In the context of targeting military equipment.The second process is to receive electronic equipment that is already EMP harden ed. most such equipme nt must communicate with and be fed with power from the outside world. While optical fibres address this requirement for transferri ng data in and out. and maintain a strict system hardness maintainance program. This provides electromagnetic protection for ea ch piece of shielded equipment. which is the dif ficulty in kill assessment. This means that equipme . This underscores another limitation of electromagnetic weapons. as electromagnetic damage to any single element of a complex system could inhibit t he function of the whole system. Radiating targets such as radars or communications e quipment may continue to radiate after an attack even though their receivers and data processing systems have been damaged or destroyed. which prevents the electromagnetic field from gaining access to the protected equipment. it must be noted that thermionic technology (ie vacuum tube equipment) is substantially more resilient to the el ectromagnetic weapons effects than solid state (ie transistor) technology. b ecause it reduces voltages that would re-radiate into electronic equipment. Therefore a hard electrical kill may not be achieved against such targets unless a suitable weapon is used. and this can provide entry points via which electrical transients may enter the enclosure and effect damage. However. (4) Documentation must be completed in order to achieve success. It is significant that hardening of systems must be carried out at a system level. and its spectral distribution.3 Shielding There are several different approaches to shielding. termed a Faraday cage. Local shielding is another method in which equipment cables and electronic b oxes are shielded within a room. There fore a weapon optimised to destroy solid state computers and receivers may cause little or no damage to a thermionic technology device. 41 Chapter 7 Limitations of Electromagnetic Bombs The limitations of electromagnetic weapons are determined by weapon implementati on and means of delivery. Both constrain lethality. 6. The first method. An inaccurately delivered weapon of large lethal radius may be u nusable against a target should the likely collateral electrical damage be beyon d acceptable limits. This is of particular im portance when assessing the lethality of unguided electromagnetic bombs. Offe nsive Counter Air and Strategic Air Attack. 42 An important factor in assessing the lethal coverage of an electromagnetic weapo n is atmospheric propagation. bu t also for kill assessment. The non-lethal nature of electromagnetic weapons makes their use far less politi cally damaging than that of conventional munitions. and significant absorption peaks due water vapour and oxygen exist at frequencies above 20 GHz. Because E-bombs can cause hard electrical kills over larger areas than conventio nal explosive weapons of similar mass. and therefore broadens the r ange of military options available. they offer substantial economies in force size for a given level of inflicted damage. Where collateral e lectrical damage is a consideration. and are thus a potent force multipl ier for appropriate target sets. thus providing a decisive advantage in the conduct of Electronic Combat. Assessing whether an attack on a non radiating emitter has been successful is mo re problematic. not only for targeting purposes. Should the de livery error be of the order of the weapon's lethal radius for a given detonatio n altitude. operational and targeting aspects of using such weapons. 43 Chapter 8 Conclusion Electromagnetic bombs are Weapons of Electrical Mass Destruction with applicatio ns across a broad spectrum of targets. accuracy of delivery and lethal radius are key parameters. Therefore accuracy of delivery and achievable lethal radius must be considered a gainst the allowable collateral damage for the chosen target. the decay in lethal effect with increasing distance within the atmospher e will be greater due quantum physical absorption effects. These will therefore contain the effec t of HPM weapons to shorter radii than are ideally achievable in the K and L fre quency bands. This can be a major issue for users constrained by treaty p rovisions on collateral damage [AAP1003]. Means of delivery will limit the lethality of an electromagnetic bomb by introdu cing limits to the weapon's size and the accuracy of its delivery. The massed app lication of these weapons will produce substantial paralysis in any target syste m. lethality will be significantly diminished. The immaturity of this weapons technology limit . As such their use offers a very high payoff in attacking the fundamental inform ation processing and communication facilities of a target system. as no historical experience exists as yet upon w hich to build a doctrinal model. Conversely an opponent may shut down an emitter if attack is imminent and the absence of em issions means that the success or failure of the attack may not be immediately a pparent. spanning both the strategic and tactical. A good case can be made for developing tools specifically for th e purpose of analysing unintended emissions. This is particularly so at higher frequencies. While the relationship between electromagnetic fie ld strength and distance from the weapon is one of an inverse square law in free space. This paper has included a discussion of the technical. as deli very errors will be more substantial than those experienced with guided weapons such as GPS guided bombs.nt which has been successfully attacked may still appear to operate. increasing both their combat potential and 44 political utility in resolving disputes. An opponent may be rendered militarily. Given the potentially high payoff deriv ing from the use of these devices. It is also incumbent upon governments and private industry to consider the implicat ions of the proliferation of this technology. and take measures to safeguard the ir vital assets from possible future attack. it is incumbent upon such military forces to appreciate both the offensive and defensive implications of this technology. and reduces the internal politica l pressure which is experienced by the leadership of any democracy which must co mmit to warfare. The selectivity in lethal effect makes electromagnetic weapons far more readily applicable to a strategic air attack campaign. politically and economi cally ineffective with little if any loss in human life. th us producing further applications and areas for study. Those who choose not to may become losers in any future wars. and many potential areas of application have int entionally not been discussed.s the scope of this discussion. The ongoing technological evolution of this famil y of weapons will clarify the relationship between weapon size and lethality. . E-bombs can be an affordable force multiplier for military forces which are unde r post Cold War pressures to reduce force sizes.