Directed Energy Weapons: Particle Beam Weapons

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This articles focuses on new class of weapons known as directed energy weapons (DEWs) along with with the exception of particle beam weapons (PBWs) and laser-induced plasma channel (LIPC) weapons that generate streams of electromagnetic energy that can be precisely directed over long distances to disable or destroy intended targets.

Laser is no longer confined to premises of prominent research centres like Bell laboratories, Hughes Research Laboratories and major academic institutes like Columbia University, USA, as it was in its early stages of development and evolution. In the last five decades, after Theodore Maiman demonstrated the first laser in May 1960 at Hughes Research Laboratories, there has been explosive growth in industrial, medical, scientific and military applications of lasers. Application areas are continuing to grow with every passing day.

Lasers have been used in various military applications since the early days of development that followed their invention. There has been large-scale proliferation of lasers and optronic devices and systems for applications like range finding, target designation, target acquisition and tracking, precision-guided munitions and so on during 1970s and 1980s.

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These devices continue to improve in performance and find increased acceptance and usage in contemporary battlefield weaponry. Technological advances in optics, optoelectronics and electronics leading to more rugged, reliable, compact and efficient laser devices are largely responsible for making these indispensable in modern warfare.

Last one decade or so has also seen emergence of a new class of weapons known as directed energy weapons (DEWs) leading to enhanced global interest from scientists and engineers in DEWs’ development. Lasers, high-power microwaves and high-energy particle beams have been exploited for DEW development. These weapons, with the exception of particle beam weapons (PBWs) and laser-induced plasma channel (LIPC) weapons, generate streams of electromagnetic energy that can be precisely directed over long distances to disable or destroy intended targets.

After decades of research and development, directed energy weapons (DEWs) are now becoming an operational reality. This has been possible due to their unique characteristics that potentially enable new concepts of military operation and also because there has been considerable progress over the past two decades in developing relevant technologies such as power sources, beam-control concepts and pointing and tracking techniques. For these applications, lethal energy from a high-power laser or a source of high-power microwaves or high-energy particle beam is delivered to the targets for causing either neutralisation of electro-optic sensors onboard the target platform or structural damage to the target itself.

Directed Energy Weapons (DEWs)

A directed energy weapons (DEW) system, with the exception of LIPC weapons, primarily uses directed energy in the form of concentrated beam of electromagnetic energy, or atomic or subatomic particles in the targeted direction to cause intended damage to the enemy’s equipment, facilities and personnel. Intended damage could be lethal or non-lethal.

Ever since H.G. Wells published War of the Worlds in 1898, directed energy weapons (DEWs)directed energy weapons have been a recurring theme in science fiction literature. Idea of a death ray, which can instantly destroy or burn a target at a distance, in fact, dates back to a belief that Archimedes used a burning glass to set afire Roman ships during the siege of Syracuse in 212 B.C. Although many images of the death ray depict Archimedes with a parabolic mirror, use of a set of individual flat mirrors appropriately positioned seemed to be a more practical implementation of the concept (Fig. 1).

Though the story has long been dismissed as a myth, interest generated by it has led to a number of experiments being conducted to verify the technical feasibility of such an event. Experiments conducted by Comte de Buffon and Dr Ioannis Sakkas, and more recently by students of Massachusetts Institute of Technology (MIT), USA, have established the feasibility of such an occurrence.

Buffon assembled 168 mirrors, 20.3cm x 25.4cm (8-inch x 10 inch) each, adjusted to produce the smallest image 45.7m (150-feet) away. The array turned out to be a formidable weapon. With this elaborate setup, he performed several experiments. He demonstrated igniting a creosoted plank at 20.1m (66-feet) distance using only 40 mirrors. 128 mirrors could ignite a pine plank instantly and, in another experiment, 45 mirrors melted 2.7kg (six pounds) of tin at 6.1m (20-feet).

In an another effort, Dr Sakkas lined up nearly 60 Greek sailors, each holding an oblong mirror tipped to catch the Sun’s rays and directed these at a wooden ship 48.7m (160-feet) away. The ship caught fire at once.

As recently as 2009, MIT students carried out an experiment with 11.7sqm (127-sqft) mirrors focusing solar radiation on to a boat 30.5m (100-feet) away, causing a sustained flame and confirming technical feasibility of what Archimedes might have achieved with his death ray (Fig. 2).

Directed Energy Weapons (DEWs) versus Kinetic energy weapons (KEWs)

At the most fundamental level, directed energy weapons (DEWs) share the concept of delivering a large amount of stored energy from the weapon to the target to produce structural and incendiary damage effects. Kinetic energy weapons (KEWs) deliver this effect at subsonic or supersonic speeds while directed energy weapons (DEWs) do so at the speed of light.

Both kinetic energy weapons (KEWs) and directed energy weapons (DEWs) need to address two fundamental issues. The first major concern is related to travel or propagation through the atmosphere and hitting the target. In the case of KEWs, it is getting the projectile to successfully travel through the atmosphere and hit the target. In the case of directed energy weapons (DEWs), it is the propagation of high-energy beams such as high-power electromagnetic radiation or high-energy particle beams through the atmosphere and directing these to hit the target.

The second major concern is to produce sufficient damage to the intended target. This is where interaction of high energy with matter comes into play. This implies that, having a high-power laser or a HPM emitter alone does not make a directed energy weapons directed energy weapons (DEW).

Three important constituents of directed energy weapons (DEW) therefore are the high-energy sources influencing operational range, target-tracking and beam-pointing technology determining probability of target hit and interaction of high-energy beams with matter that determines lethality.

Types of directed energy weapons (DEWs)

Four major categories of DEWs are:
1. PBWs
2. Microwave based DEWs
3. Laser based DEWs
4. LIPC weapons

A PBW uses a high-energy beam of atomic or subatomic particles to inflict intended damage to the target by disrupting its atomic and/or molecular structure. It is the least mature of the four directed energy weapons (DEW) technologies and receives by far the least amount of research effort. It is not a true DEW. Unlike high-energy laser weapons and high-power microwaves that direct electromagnetic energy towards the target, it delivers kinetic energy into the target’s atomic structure and is only a hard-kill weapon.

A microwave based directed energy weapons (DEW) system is designed to produce the equivalent of electromagnetic interference to damage enemy’s electronics systems. Due to concerns regarding unintended side effects on the host platform, it is usually preferred to put such weapons only on unmanned combat air vehicles. Also under consideration is use of high-power microwaves as a weapon to attack underground and deeply-buried targets that are resistant to high explosives.

At the core of the laser based DEW is a high-power laser that has enough power in the case of continuous wave laser, or sufficient pulse energy in the case of pulsed laser, to inflict physical damage to the target. Though the lasers intended for already-established applications such as range finding, target designation for munitions guidance and more will continue to improve as newer technologies evolve and develop, it is the use of lasers as weapon that is going to rewrite the military balance in the next 15 to 20 years.

Introduction of laser based directed energy weapons (DEWs) is set to dramatically alter the war-fighting capabilities of nations by making possible execution of missions that would be extremely complex, if not impossible, to realise with conventional KEWs. These include ground based laser systems for disabling low Earth orbit satellites and destroying missiles, airborne laser systems for destroying ballistic missiles and space based laser systems for neutralising theatre and inter-continental ballistic missiles.

A large number of experiments with laser based directed energy weapons (DEWs) to demonstrate these or similar capabilities have been carried out in different parts of the world. Realisability of these weapons has been established beyond doubt, and these weapons have been projected by strategists as the weapons of the 21st century.

LIPC weapons are hybrid weapons that use a laser to ionise a path of molecules to the target, via which an electric charge can be delivered into the target to cause damaging effects. These can be used to destroy anything that conducts electricity better than the air or ground surrounding it. This works as follows:

A high-intensity train of picosecond laser pulses is used to create a powerful electromagnetic pulse around itself that strips electrons from air molecules, thereby creating a plasma channel through the air. Since the air is composed of neutral particles that act as insulators, LIPC is relatively a good conductor. A high-voltage current discharge is sent down this conducting filament to the target rather than arcing unpredictably through the air—a phenomenon similar to lightening that finds its way from clouds to ground via the path of least resistance.

Of these four categories, high-energy laser weapons have the greatest potential in the near term to become worthy of a potent weapon system.

High-power microwave technology, too has similar potential, but has not been funded as generously as high-energy laser weapon development programmes. LIPC has significant potential especially as a non-lethal weapon. PBWs at this time are apt to remain in the science fiction domain, as the weight and cost as yet do not justify achievable military effect.

Though technology needed for PBWs exists and seems feasible, it is too impractical for miniaturisation and operational deployment. There are no known operational PBWs and, as of now, such weapons exist only in science fiction and artists’ imagination (Figs 3 and 4). Fig. 5 shows yet another PBW called Disruptor known in science fiction.

PBWs

A PBW is a form of directed energy weapons (DEW that uses atomic or subatomic particles accelerated to the speed of light or near speed of light with the help of powerful electric and magnetic fields in a particle accelerator. The particles are directed to deliver a fraction of their kinetic energy to the intended target, thereby causing severe damage due to disruption of its atomic structure. It is characterised by beam energy in electron-volts, beam current in amperes and beam power in watts.

PBWs come in two primary types: charged-particle weapons and neutral-particle weapons. When it comes to military application of these different types of PBWs, charged-particle weapons are endo-atmospheric, while neutral-particle weapons are exo-atmospheric.

At the core of a PBW is the particle accelerator. It is also the most complex part of the beam weapon and is built using a linear electric field to accelerate charged particles similar to Gauss or coil gun or an induction linear accelerator system.

Induction linear accelerator consists of a simple non-resonant structure where drive voltage is applied to an axially symmetric gap that encloses a toroidal ferromagnetic material. Change in flux in the magnetic core induces an axial electric field that provides particle acceleration.

Characteristic parameters

A particle beam consists of protons, electrons or neutral atoms flowing with real or imaginary current. It is characterised by beam energy, current and power. Beam energy is expressed in mega electron-volts (MeV). One eV is the kinetic energy of an electron that has been accelerated by an electric potential of one volt. Particle beam energy is characterised by the energy of a typical particle of the beam as all particles in a beam will have been accelerated to the same velocity. A PBW capable of inflicting serious damage to a target 1000km away in space would typically require beam energy of 1GeV.

An estimate of the number of charged particles in the beam can be made from the magnitude of beam current. It is possible to assign a current to the particle beam, assuming that each particle has a charge quantum equal to that of an electron even if the charged particle was the neutral atom. Beam current for the possible beam weapon described above would typically be 1000 amperes.

Power of a particle beam is the rate at which beam energy is transported, which is also indicative of the rate at which it can deposit energy into a target. As an analogy to electric circuits, the particle beam in watts is equal to the product of energy in electron-volts and the beam current in amperes.

Types of PBWs

There are two broad categories of PBWs, namely, charged-particle beam (CPB) and neutral-particle beam (NPB) weapons. CPB weapons have a set of technological characteristics that are entirely different from NPB weapons. While characteristics of the former make these suitable for use within the atmosphere, the latter are better suited for use in space.

Both endo-atmospheric (used within atmosphere) and exo-atmospheric (used in space) beam weapons have their own technological hurdles to overcome. A particle beam propagating through atmosphere requires having extremely-high power and precisely-defined beam characteristics.

Technologies required for the development of a suitable power supply and particle accelerators with sufficient power and appropriately-shaped pulses for endo-atmospheric weapons are very complex and involve high risk.

On the other hand, the greatest challenge in the case of exo-atmospheric beam weapons is in the area of beam control. The PBW should not only be able to produce a high-intensity low-divergence particle beam at the exit of the accelerator, it should also have the necessary beam-control mechanism for aiming and beaming at the target, and the ability to detect pointing errors in the beam for applying correction, if required.

Because of these two different sets of demands, endo- and exo-atmospheric devices represent two different types of weapon systems in appearance and operation. Nevertheless, there are certain fundamental areas of development that are common to both types of PBWs.

Charged PBWs. A CPB consists of electrons accelerated to the required energy level in a particle accelerator using a combination of electric and magnetic fields. To be able to destroy the target, particle energy should be high, and so should be the beam current. As an example, a practical electron beam weapon would need to hit a target 1000km away with a 1000-ampere beam with energy of 1GeV for 0.1 millisecond to destroy it.

Particles in the beam have kinetic energies equal to their rest-mass energies, with the result that these would travel with nearly the speed of light. Particle accelerators researched for high-energy physics have high energies and pulsing rates but low beam currents.

On the other hand, particle accelerators related to fusion research generate high beam currents but at low energies and pulsing rates. Particle accelerators suitable for producing beam weapons need to generate high-intensity and high-energy particle beams.

CPBs are of little use in space. The combined effects of emittance and Coulomb’s force of repulsion between like-charged particles broaden the beam. As an example, a 1GeV, 1000-ampere CPB would spread from 1cm to 5m over 1000 km.

Further, the beam is deflected by Earth’s magnetic field. By the same study, the 1GeV, 1000-ampere beam would deflect by 1000km over 1000km distance due to Earth’s magnetic field. CPBs though can be made to propagate satisfactorily over a few kilometres through an air channel evacuated by heating air in a straight line. Thus, a CPB weapon could be employed for ballistic missile defence. The system could be installed in a few ground based sites in conjunction with either Earth-borne or space-borne radar systems to identify and track incoming ballistic missile warheads.

The CPB weapon could be rapidly pointed at the incoming missile to destroy it. For an interception in air at 10km, an electron beam weapon would typically require 500MeV beam energy and 10,000 amperes of beam current. However, large fixed installations required for CPB weapons, as per current status of technology, may render these vulnerable to sabotage or other forms of attack by an adversary.

Neutral PBWs. A NPB weapon consists of neutral atomic particles accelerated to a high kinetic energy level in a particle accelerator. The process of generation of high-energy NPB is as follows:

Hydrogen or deuterium gas is subjected to an enormous electrical charge. The electrical charge produces negatively-charged ions that are accelerated through a long vacuum tunnel by an electrical potential in the hundreds-of-megavolt range. After the negatively-charged ions have been accelerated, at the end of the tunnel, electrons are stripped from the negative ions, thereby forming the high-speed NPB.

Weapons-class NPB weapons also require energies in hundreds of MeV and beam powers in tens of megawatts. Modern devices have not yet reached this level. Given the state of the art in accelerator technology, achieving the required beam energy and power levels would require hundreds of tons of accelerator hardware and enormous power sources to operate. Due to size, weight, power constraints and inherent complexity, it does not appear feasible that a NPB weapon would see the light of the day before 2025.

NPBs travel in a straight line once these have been accelerated and magnetically pointed just before neutralisation in the accelerator.

Also, an NPB is strongly affected by passage through the atmosphere. It gets attenuated and diffused as it passes through dense gas or suspended aerosols, which makes it far more suitable as compared to a CPB for applications in space against high-flying airborne or space borne targets.

Damage assessment of the target could be possible. When the beam penetrates a target, the target’s atomic and subatomic structure produce characteristic emissions that could be used to determine the target’s mass or assess the extent of damage to the target.

The major disadvantage of a NPB weapon even in space is that it is extremely difficult to sense, which complicates the problem of beam control and direction.

In the next part, we will learn more about PBWs. In subsequent parts, we will look at high-power microwaves, less-lethal weapons and high-energy laser weapons.

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Dr Anil Kumar Maini is former director, Laser Science and Technology Centre, a premier laser and optoelectronics research and development laboratory of Defence Research and Development Organisation of Ministry of Defence