There is something slightly bizarre in the prospect of the smallest fundamental particles of matter being employed to destroy the most powerful weapons which man can build. Modern physics has been a story akin to the opening of an endless series of Russian dolls. The discovery of the atomic nature of matter at the start of the last century was an immensely important achievement. John Dalton's experiments on the chemical composition of compounds revealed that there were atomic building blocks from which all substances derived. The ordering of the elements into a structured table by Mendeleyev in 1869, where properties could be predicted and missing elements identified, gave great confidence to scientists that they had discovered the true nature of matter. But the very predictability of the elements when tabulated by their atomic weight suggested some finer structure to their composition. This century the structure of the atom has been explored. Initially it seemed relatively simple. The less than a hundred elements could be explained by suitable combinations of smaller building blocks: electrons, protons and neutrons. In recent years the number of these sub-atomic particles, which have been identified, has grown until they are as numerous as the elements. The simple triad of particles has been joined by the neutrino, photon, muon, pion, kaon and many others. Just as the periodic table of the middle of the last century made it possible to predict undiscovered elements, so the start of attempts to classify the sub-atomic particles has led to prediction and discovery of previously unknown particles. This in turn has led to attempts to look for some fine structure to the elementary particles, and the search for quarks- the building blocks of subatomic particles.(1)

All this pure physics research has required higher and higher energy particle accelerators to investigate the fundamental nature of matter. Indeed, the term 'particle' is no more than a convenient label for the reader. The physicists are not investigating particles in the sense of grains of sand, but are measuring phenomena which can be identified by mass and energy level, and by effects on other 'particles'. In the search for simplicity of cause, atomic theory led to the identification of more than 100 elements, and many isotopes of those atoms. The simple structure underlying the atoms has grown more complex until there are more than 100 sub-atomic particles.

The investigations of physicists have identified four different types of force which control the interation of matter. Gravity is the one which affects us in the normal world, but it is remarkably weak compared to the three other fundamental forces. These are the electromagnetic force, the weak nuclear force and the strong nuclear force. Investigations into the nature of these forces, and how they may be related to each other, have also required bigger and bigger accelerators and the science of high energy physics is one of the major international areas of collaboration because of the high costs of the equipment involved. Research must be devoted into the design of the accelerators and into the power sources for them. Even with such collaboration, the rising cost of such pure research sets limits. At a late stage in the building of the 'Superconducting Super Collider' (an accelerator some 20 times more powerful than the largest existing machine), it was cancelled despite some $2 billion already spent.(2)

One major area for research into this field is in the search for fusion power. While current atomic energy is derived from the radioactive decay of atoms, this in nuclear terms releases only a small proportion of the energy locked in the nuclear structure. Our sun is able to burn for millions of years by fusing light atoms into heavier ones and releasing much greater amounts of fusion energy. In order to generate the necessary conditions for atomic fusion, a concentration of very high energy particles must be achieved. The necessary energy levels at sufficient concentrations are achieved in the middle of an atomic bomb. The atomic fission explosion provides the firelighter for the fusion process in thermonuclear weapons. A great deal of civil research effort is being expended on the search for a way to produce the necessary conditions in a more controlled way through accelerated particles confined in magnetic bottles. This line of civil energy research brings more expertise to bear on the problems of producing very high energy particle beams, and also the control of those beams to precise criteria . The research has been progressing for four decades and demonstrated the production of some 10 million watts of fusion power sustained for half a second in a 1994 experiment.(3)

One area of high energy physics research which has implications for the military use is that of laser research. The laser was initially an interesting demonstration of the discrete nature of energy states in matter. Changes from one energy state to another in an atom are accompanied by emission or absorption of radiation. The discreteness of the energy states is characterised by the associated radiation being of a single frequency. Just as a small sound picked up by a microphone near to a loudspeaker builds up to a loud squeal of feedback, so a small pulse of light reflected back into the laser material produces an amplification of the radiation through further emission, which produces in turn an intense 'squeal' of laser light. The light, or other radiation, produced has curious properties (4). It is coherent in nature. As a result of it being produced at a single frequency, with all the waves in step with one another, the beam spreads very little with distance, and can be focused to give intense energy concentrations. While initially a scientific novelty, the increasing power of lasers has made them important tools in investigating the nature of matter, as well as an increasing number of industrial applications. They are also being used in research into power from nuclear fusion.

In the military field, high energy particle beams and high energy lasers offer the prospect of a new class of firepower: Directed Energy Weapons. Science fiction writers have always been attracted to the prospect of instantaneous death rays. This does not mean that they necessarily offer any advantages over the more mundane methods of destruction. For directed energy to offer a useful avenue for military research, the advantages must be demonstrable given the costs of high energy physics research. Can directed energy weapons offer the prospect of changing the nature of warfare in the same sense as the repeating rifle, the aircraft, the submarine, or the atomic weapon?

In three areas the use of directed energy weapons appears to offer new opportunities:

(a) Speed of delivery. Laser radiation travels at the speed of light, and particle beams can be accelerated to significant fractions of the speed of light. Thus time of flight problems of more physical missiles are eliminated. Aiming at moving targets becomes much simpler. Damage can be assessed and if necessary the target re-engaged, where it might have passed beyond the operational range of missile or gun.

(b) Range. The range of a laser beam is theoretically infinite in a vacuum. Despite the coherence of the radiation it does diverge, and the power per unit area decreases with distance. The ability to focus the beam helps, and operational ranges of 1000 km in space are conceivable in the future. The effective range of particle beams is a complex issue, which is discussed further below.

(c) Logistics. At first inspection, the use of massless photons of light, or streams of protons, in place of heavy shells or missiles seems to solve the logistic supply problem of modern warfare at a stroke. Unfortunately, the energy requirements must be met from some fuel sources, and the overall logistic bill must be considered carefully in any proposed system.

These three factors are sufficiently important for serious consideration to be given to the role of directed energy weapons in future warfare. But before deciding on their deployment, the physical constraints on their operations must also be examined. Particle beams can be of two types: charged using electrons or protons; or neutral using neutrons or hydrogen atoms. An electron beam system is commonplace in the home today. The television cathode ray tube is a particle beam accelerator. Electrons are produced from a heated filament, are accelerated by high voltage plates, and manipulated by electric and magnetic fields to produce a focused beam on the surface of the television screen. Typically the electrons are accelerated through a voltage of a few thousand volts, and are equivalent to a current flow measured in microamps. The enormous research particle accelerators can achieve very high kinetic energies. Protons are accelerated to 500 thousand million electron volts (500 GeV) in the gigantic circular Fermi accelerator. The power of such a beam is the product of their energy and the number of particles produced per second. Just as a car light bulb operating at 12 volts and using 2 amps has a power of 2 x 12 = 24 watts, so our 1000 GeV accelerator with a current of 0.6 milliamps has a power of 600 Megawatts. Research into fusion reactors has produced high current particle beams but at much lower energies. The power of a useful beam weapon would require particles accelerated to the order of 1 GeV at currents of 1000 amps sustained for 0.1 of a millisecond. This represents a power of a million megawatts. No such accelerator is yet available.(5)

While the power requirements for particle beam weapons are daunting, the nature of the beam itself is also an area of uncertainty. Charged particles can be relatively easily accelerated and focused into a beam. However once in free flight, the repulsion between similar charged bodies causes the beam to disperse. An electron beam 1 cm wide as it leaves the accelerator has spread to some 15 metres across at a range of 1000 kms; and a similar proton beam would be 18 kms wide. Beam dispersion of that size makes the optimistic assumption that the path is in free space without an external magnetic field. A charged particle beam travelling in the atmosphere or in the earth's magnetic field would be dispersed or deflected to an extent which would make long range use impossible. The use of neutrally charged particle beams would overcome both the electrical and magnetic deflection effects, but brings with it new problems. The particles must start with an electrical charge, so that they can be accelerated and focused. Then the beam must be neutralised, which causes some spreading which continues to increase with distance. At a nominal 1000 km a neutral beam might be expected to have diverged to about 20 metres across, assuming that the source charged particle beam could be kept focused to an accuracy of 1 part in a million.

Our theoretical particle beam weapon would aim to produce sufficiently energetic particles at the target to penetrate its protective outer layer, and in sufficient concentration to damage the internal electronics or even detonate any high explosive warhead. The propagation difficulties are at their least in space, and so particle beam weapons seem to offer attractions for anti-ballistic missile and anti-satellite systems. However the sheer size of the accelerators, and the prodigious power requirements, coupled with the precise control needed in an unpredictable magnetic environment, makes the particle beam weapon in space based on current developments unlikely to be a productive avenue of research. In the atmosphere, propagation over relatively short distances may be possible by boring an evacuated channel in the air with a high power laser, before sending the particle beam down it. This might have applications for the short range interception of incoming missiles. It is comparable to firing a tank gun through a brick wall so that you can fire a bullet through the resulting hole. If a high power laser can produce such a controllable effect, then it can be used as the weapon itself.

At the current stage of research into accelerated particle beams, their application as weapons seems remote. They could provide destructive firepower, but at a considerably greater cost than more conventional means. There are also a number of relatively low cost counter measures which can be taken to disperse the beam before it strikes the target, or reduce the effect if it does strike home. This is not to say that at some stage in the future, particle beams may not have a role to play. Fortunately there are so many industrial and pure physics research projects driving the development of particle beam accelerators that work will continue apace without needing military prompting. If power requirements, focusing and control mechanisms, propagation characteristics and the physical size of the equipment change dramatically under civilian approach, then it will be time for military applications to be reviewed. Until then particle beam weapons offer little save novelty to defence.

The laser does not suffer from the magnetic and electric dispersion problems of particle beams. Widespread publicity has accompanied the testing of high energy lasers against drones. It is already possible to provide sufficient energy in a laser beam at short range to destroy a military target in clear atmospheric conditions. This does not necessarily mean that the laser is the best way to destroy such targets. A surface to air missile, or a radar laid anti aircraft gun can also do the job. Any laser weapon would be different in nature from other weapons. Its destructive power would be in the form of electromagnetic radiation. It would deliver its destruction at the speed of light, some 300 million metres per second or 100,000 times faster than a missile. It must also be aimed to strike the target, and held on the target for long enough to cause the necessary damage. In the atmosphere, the power of the laser beam is limited by the electrical breakdown of the air at high energy concentrations. It is also attenuated by dust, smoke, cloud or any medium which obscures radiation at that wavelength. While the classic demonstrations of lasers burning holes in razor blades suggest a mechanism for destruction of targets based on melting, this is unlikely to be the most efficient use. By pulsing the laser into high energy bursts of radiation, it is possible to cause damage to target aircraft or missiles by cracking. If the pulse rate is high enough, the thermal effect assists the fracturing process. This process is helped when the target material is already under stress, as it would be in a missile in flight. In the atmosphere the range would be limited both by the atmospheric conditions, and the power density limitations. In space, these limitations are relaxed while the necessary ranges are increased dramatically. Now the constraints become design problems for generating and focusing the laser power necessary.

The laser is already a useful military tool. Low power lasers are widely used on the battlefield. As a rangefinder, the laser provides instantaneous and accurate information for weapon aiming calculations. This task can be done by optical or radar sighting methods, but the laser gives much more precise measurements and is much less prone to enemy counter-measures. It is possible to conceive of further developments in this area leading towards a laser based radar system. A relatively low power laser with a scanning mirror, coupled to an electro-optical detection system could provide a precise three dimensional picture of target location, with far greater discrimination of detail than radar. It could be more difficult to detect and jam given the availability of tuneable lasers and filters. The overwhelming disadvantage of such a system would be the problems of propagation in obscured atmospheric conditions. However, developments in higher frequency lasers in the ultra-violet and beyond regions of the electromagnetic spectrum may bring new possibilities in this application.

One particular such application has already been considered. The oceans currently provide an excellent obscuring medium for military covert activities. The detection of submarines is still as much an art as a science. The oceans are vast hiding places, with the propagation of both sound and electromagnetic radiation subject to anomalies as the waves pass through the differing layers of water. Nevertheless, it has been reported that laser interferometry has been successfully used to detect submarines(6). Given the importance of strategic submarine detection to super-power nuclear retaliatory capability, this has been an area of intense research activity.

The laser is widely used today as a target designator for precision guided munitions. If a target can be illuminated by a beam of laser light, a missile or shell with a relatively low cost terminal guidance system can home on to the characteristic illuminated spot, and hit the target accurately. This has great attractions to the soldier. The difficulties in passing instructions from the front line to the close air support aircraft, or the fire support artillery battery are overcome. The general area of the target is sufficient, provided that the target is marked by the hand held laser. It can also be used by the weapon operator as an alternative means of guidance to control wire, radio beam, or radar. The system is well proven, and future development work is needed in improving the method of designation. Currently, the laser operator must be within line of sight of the target, which is by definition a somewhat vulnerable location, whether from the ground or in the air. It is likely that these target designation tasks will be possible from cheap unmanned Remotely Piloted Vehicles (RPVs) in the future. The operator can be located safely to the rear of the action, select targets from information relayed by the RPV, and lock the laser illuminator on target. Artillery, surface-to-surface or air-to-ground missiles can then home on the illuminated target. The advantages with such an approach are that the lowest cost items are placed at greatest risk, where the high cost men and machines have reduced exposure to the enemy, while the high kill rates of precision guided munitions are achieved.

Lasers are also in use as means of communication. The electromagnetic radiation in a laser beam is different from a radio wave only in being of higher frequency. The information capacity which a radio wave can carry depends on its frequency. The higher the frequency, the more information in the form of communication channels, which can be carried. The tight beam of a laser is also far more difficult to interfere with through jamming. While a piece of thin card placed between the beam would stop communication, placing the card is far more difficult than the blanket high power radio jamming which is possible. In the same way, there is no spillover of radiation which can be detected, used for intelligence or position finding. The disadvantages of modulated laser communication systems are those of the propagation of lasers in the atmosphere. This can be overcome by the use of fibre optics, which pipe the light with much less attenuation just as a wire can carry telephone communication. In looking at communication on the future battlefield, a system which was proof against the hostile electronic warfare environment would be a great asset. The technical problems of using lasers are considerable for mobile manpack systems. Yet low cost relay masts with automatic orientation might offer possibilities. At sea, data transmission by such means might offer advantages, and relay through satellite retransmission could offer great flexibility.

One other current offshoot of the laser will certainly have some military applications. The coherent predictable nature of laser light allows photographs to be taken, which can reconstruct the original waveforms when re-illuminated by a laser. The holograms produced are three dimensional pictures in a true sense, in that a photographed object can be viewed from different positions. While current applications seem more artistic than scientific, the possibility of much more realistic simulation, and instrumentation through holographic processes will bring the laser into another area of military development.

Moving away from the low powered laser and into more powerful offensive use of laser weapons, power levels for damage to the human eye and to optical sensors are relatively easy to achieve. Blinding the pilot of a modern aircraft through a laser eye damage weapon, would be an effective method of destroying the aircraft. However, it is not as simple as might at first be thought. The laser which is focused by the lens in the eye on to the retina, must be powerful enough to burn the retina over the time the beam is held on target. The target is remarkably small compared to the aircraft, and is obscured by the aircraft canopy and the pilot's visor. Given also the propagation problems of lasers in the smoke of the battlefield, the laser eye damage weapon is unlikely to be worth developing as a primary air defence system, even its use was considered permissible under the emerging views of the conduct of war. If an air defence gun is fitted with a laser rangefinder, then some states may consider it worth increasing the power levels so that eye damage becomes possible. This will force the opposition into taking protective measures which will degrade the overall mission effectiveness. The same line of argument holds for damaging sensor systems, particularly fitted to aircraft.

One class of sensors do offer opportunities for laser countermeasures. These are the reconnaissance satellites. Predictable targets free from the problems of the atmosphere, with extremely sensitive sensors are particularly vulnerable to laser damage. Such damage can be covert, as the satellite will continue to orbit while blinded. The offensive laser could be earth-based, aircraft-borne or deployed in space. Since the sensors are likely to be oriented towards the earth beneath, the target area for the reconnaissance is also the best area for deployment of the offensive laser. Use of a high flying aircraft with such a system allows considerable flexibility, and reduces the atmospheric absorption problems. Such systems would appear to have considerable potential.

Looking to yet higher powers for lasers, the target set is similar to that considered in the analysis of the prospects for particle beam weapons. Satellites, missiles and aircraft are the prime candidates for an operational laser weapon system. The problems of propagation in obscured atmospheric conditions would make the laser an unreliable weapon. If the weather has to be fine, and smoke can obscure not just vision but also killing power, then the laser is unlikely to become the ray gun of tomorrow's infantry. While the photons in the beam may be massless, the equipment necessary to generate the power, and the fuel to provide the energy, both have traditional logistic penalties. Basing laser weapons in space has great attractions in allowing long distance propagation with little attenuation. The power generation and fuel requirements become even more difficult to achieve. One analysis (7) concluded that it would take 125 years to deliver the fuel necessary for a laser weapon system designed to cope with the Soviet ICBM threat. The study pointed out that the laser power necessary was beyond technical possibility currently. A lesser problem would be a laser system to destroy satellites. Given that a space-based system would itself be vulnerable to a similar enemy system, an aircraft carried system would again have attractions. The copious writings (8) on complex laser weapons using enormous mirrors in space have yet to show them to be attractive options. While the problems of weight and size of power supplies, and the fuel requirements, could be overcome by a ground fixed laser site focused on a space mirror, the increasing number of critical points also increases the overall vulnerability of such a weapon system.

Looking to yet more powerful lasers of the future (9), research continues into higher frequency and greater power regions. Chemical lasers, using hydrogen or deuterium and fluorine as fuels, have been reported as achieving outputs greater than one megawatt, but that is likely to be the limit. Excimer krypton-fluoride lasers are higher frequency but still four orders of magnitude below power requirements for ballistic missile defence systems. Free electron lasers have the advantage of being tuneable so that the best frequency for propagation can be chosen, but the high powers come at the lower frequencies. This can be used to advantage as a high power radio frequency weapon, by using microwave energy to disrupt communications systems or cause local heating (10). The X-ray laser using a nuclear explosion as the source of energy is one possible avenue. While this might overcome some of the problems of sheer mass of fuel supplies in space, it introduces new difficulties. The large number of potential targets in any ballistic missile defence make a weapon, which self-destructs with a nuclear explosion each time it is fired, an expensive option. Indeed the precise aiming required might well be difficult to achieve under such circumstances.

Lasers offer less exciting prospects for future weapon systems than many would suggest. As components of various systems, they will be increasingly used for the unique characteristics which coherent radiation offers. They are already in use for communication, weapon aiming and target marking. For little extra development they could add eye damage and sensor damage capabilities. As high energy destructive weapons, the physical limitations associated with beam generation is likely to restrict them to relatively few target types. Satellites may be the most vulnerable laser weapon targets, and the weapon would be best operated from high flying aircraft. Just as civil research into particle beams will ensure that technological surprise is unlikely to be achieved by a potential enemy, so it is with laser research. The industrial and domestic use of lasers from the compact disc player to the laser fusion reactor will keep research going. More military applications will undoubtedly be found, but they as many will emerge from civil research projects rather than dedicated military research.

NOTES TO CHAPTER 5

1. For a review of the current thinking on the nature of matter see 'Elementary Particles and Forces' by C.Quigg, Scientific American, April 1985, pp64-75.

2. 'Particle Metaphysics' by J.Horgan, Scientific American February 1994. In 1985, the predicted total cost of the Superconducting Super Collider was $3 billion. On cancellation in October 1993, $2 billion had been spent and another £9 billion was estimated for completion.

3. 'Fusion' by H.P.Furth, Scientific American, September 1995, pp140-142.

4. 'Laser Light' by A.L.Schawlow, Scientific American, September 1968, pp120-136.

5. 'Particle Beam Weapons' by J.Parmentola & K.Tsipis, Scientific American, April 1979,pp38-49.

6. 'Advances in Antisubmarine Warfare' by J.S.Wit, Scientific American, February 1981,p30.

7. 'Laser Weapons' by K.Tsipis in Scientific American December 1981 pp39-40.

8. Report on Ballistic Missile Defence of North Atlantic Assembly Scientific and Technical Committee of November 1983 gives review of options.

9. For a review of the technical capabilities and requirements of laser weapons for ballistic missile defence see 'Strategic Defense and Directed-Energy Weapons' by C.Kumar, N.Patel & N.Bloembergen in Scientific American September 1987.

10. High power radio frequency weapons can also be produced from non-laser systems using microwave generators. The Soviet Union is reported to have achieved 500 Megawatts at a frequency of 3 GHz. For a report on progress in this area see B.Jasani, 'Space Weapons and International Security', SIPRI, Oxford University Press 1987, pp26-7.

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