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Saturday, February 9, 2019

Directed-energy weapon

From Wikipedia, the free encyclopedia

A directed-energy weapon (DEW) is a ranged weapon that damages its target with highly focused energy, including laser, microwaves and particle beams. Potential applications of this technology include weapons that target personnel, missiles, vehicles, and optical devices.

In the United States, the Pentagon, DARPA, the Air Force Research Laboratory, United States Army Armament Research Development and Engineering Center, and the Naval Research Laboratory are researching directed-energy weapons and railguns to counter ballistic missiles, hypersonic cruise missiles, and hypersonic glide vehicles. These systems of missile defense are expected to come online no sooner than the mid to late-2020s.

Russia, China, India, and the United Kingdom are also developing directed-energy weapons. 

After decades of research, directed-energy weapons are still at the experimental stage and it remains to be seen if or when they will be deployed as practical, high-performance military weapons.

Operational advantages

Directed energy weapons could have several main advantages over conventional weaponry:
  • Direct energy weapons can be used discreetly; radiation above and below the visible spectrum is invisible and does not generate sound.
  • Light is only very slightly altered by gravity, giving it an almost perfectly flat trajectory. It is also practically immune (in anything resembling normal planetary conditions) to both windage and Coriolis force. This makes aim much more precise and extends the range to line-of-sight, limited only by beam diffraction and spread (which dilute the power and weaken the effect), and absorption or scattering by intervening atmospheric contents.
  • Lasers travel at light-speed and have near infinite range and therefore, are suitable for use in space warfare.

Microwave weapons

Although some devices are labelled as microwave weapons, the microwave range is commonly defined as being between 300 MHz and 300 GHz which is within the RF range—these frequencies having wavelengths of 1–1000 micrometers. Some examples of weapons which have been publicized by the military are as follows:
  • Active Denial System is a millimeter wave source that heats the water in a human target's skin and thus causes incapacitating pain. It was developed by the U.S. Air Force Research Laboratory and Raytheon for riot-control duty. Though intended to cause severe pain while leaving no lasting damage, concern has been voiced as to whether the system could cause irreversible damage to the eyes. There has yet to be testing for long-term side effects of exposure to the microwave beam. It can also destroy unshielded electronics. The device comes in various sizes including attached to a humvee.
  • Vigilant Eagle is a proposed airport defense system that directs high-frequency microwaves towards any projectile that is fired at an aircraft. The system consists of a missile-detecting and tracking subsystem (MDT), a command and control system, and a scanning array. The MDT is a fixed grid of passive infrared (IR) cameras. The command and control system determines the missile launch point. The scanning array projects microwaves that disrupt the surface-to-air missile's guidance system, deflecting it from the aircraft.
  • Bofors HPM Blackout is a high-powered microwave weapon that is said to be able to destroy at short distance a wide variety of commercial off-the-shelf (COTS) electronic equipment. It is said to be not lethal to humans.
  • The effective radiated power (ERP) of the EL/M-2080 Green Pine radar makes it a hypothetical candidate for conversion into a directed-energy weapon, by focusing pulses of radar energy on target missiles. The energy spikes are tailored to enter missiles through antennas or sensor apertures where they can fool guidance systems, scramble computer memories or even burn out sensitive electronic components.
  • AESA radars mounted on fighter aircraft have been slated as directed energy weapons against missiles, however, a senior US Air Force officer noted: "they aren't particularly suited to create weapons effects on missiles because of limited antenna size, power and field of view". Potentially lethal effects are produced only inside 100 meters range, and disruptive effects at distances on the order of one kilometer. Moreover, cheap countermeasures can be applied to existing missiles.
  • Counter-electronics High Power Microwave Advanced Missile Project

Laser weapons

Electrolaser

An electrolaser first ionizes its target path, and then sends a powerful electric current down the conducting track of ionized plasma, somewhat like lightning. It functions as a giant, high-energy, long-distance version of the Taser or stun gun.

Pulsed energy projectile

Pulsed Energy Projectile or PEP systems emit an infrared laser pulse which creates rapidly expanding plasma at the target. The resulting sound, shock and electromagnetic waves stun the target and cause pain and temporary paralysis. The weapon is under development and is intended as a non-lethal weapon in crowd control though it can also be used as a lethal weapon.

Dazzler

A dazzler is a directed-energy weapon intended to temporarily blind or disorient its target with intense directed radiation. Targets can include sensors or human vision. Dazzlers emit infrared or invisible light against various electronic sensors, and visible light against humans, when they are intended to cause no long-term damage to eyes. The emitters are usually lasers, making what is termed a laser dazzler. Most of the contemporary systems are man-portable, and operate in either the red (a laser diode) or green (a diode-pumped solid-state laser, DPSS) areas of the electromagnetic spectrum. 

Initially developed for military use, non-military products are becoming available for use in law enforcement and security.

PHASR Rifle

The personnel halting and stimulation response rifle (PHASR) is a prototype non-lethal laser dazzler developed by the Air Force Research Laboratory's Directed Energy Directorate, U.S. Department of Defense. Its purpose is to temporarily disorient and blind a target. Blinding laser weapons have been tested in the past, but were banned under the 1995 United Nations Protocol on Blinding Laser Weapons, which the United States acceded to on 21 January 2009. The PHASR rifle, a low-intensity laser, is not prohibited under this regulation, as the blinding effect is intended to be temporary. It also uses a two-wavelength laser. The PHASR was tested at Kirtland Air Force Base, part of the Air Force Research Laboratory Directed Energy Directorate in New Mexico.

Laser weapon examples

Most of these projects have been cancelled, discontinued, never went beyond the prototype or experimental stage, or are only used in niche applications. Effective, high performance laser weapons seem to be difficult to achieve using current or near-future technology.

Problems with laser weapons

Blooming

Laser beams begin to cause plasma breakdown in the atmosphere at energy densities of around one megajoule per cubic centimeter. This effect, called "blooming," causes the laser to defocus and disperse energy into the surrounding air. Blooming can be more severe if there is fog, smoke, or dust in the air. 

Techniques that may reduce these effects include:
  • Spreading the beam across a large, curved mirror that focuses the power on the target, to keep energy density en route too low for blooming to happen. This requires a large, very precise, fragile mirror, mounted somewhat like a searchlight, requiring bulky machinery to slew the mirror to aim the laser.
  • Using a phased array. For typical laser wavelengths, this method would require billions of micrometre-size antennae. There is currently no known way to implement these, though carbon nanotubes have been proposed. Phased arrays could theoretically also perform phase-conjugate amplification. Phased arrays do not require mirrors or lenses, and can be made flat and thus do not require a turret-like system (as in "spread beam") to be aimed, though range will suffer if the target is at extreme angles to the surface of the phased array.
  • Using a phase-conjugate laser system. This method employs a "finder" or "guide" laser illuminating the target. Any mirror-like ("specular") points on the target reflect light that is sensed by the weapon's primary amplifier. The weapon then amplifies inverted waves, in a positive feedback loop, destroying the target, with shockwaves as the specular regions evaporate. This avoids blooming because the waves from the target pass through the blooming, and therefore show the most conductive optical path; this automatically corrects for the distortions caused by blooming. Experimental systems using this method usually use special chemicals to form a "phase-conjugate mirror". In most systems, the mirror overheats dramatically at weapon-useful power levels.
  • Using a very short pulse that finishes before blooming interferes.
  • Focusing multiple lasers of relatively low power on a single target.

Countermeasures

The Chinese People's Liberation Army has invested in the development of coatings that can deflect beams fired by U.S. military lasers. Laser light can be deflected, reflected, or absorbed by manipulating physical and chemical properties of materials. Artificial coatings can counter certain specific types of lasers, but a different type of laser may match the coating's absorption spectrum enough to transfer damaging amounts of energy. The coatings are made of several different substances, including low-cost metals, rare earths, carbon fiber, silver, and diamonds that have been processed to fine sheens and tailored against specific laser weapons. China is developing anti-laser defenses because protection against them is considered far cheaper than creating competing laser weapons themselves. Apart from creating countermeasures, China has also created a direct-energy weapon called the Silent Hunter that can burn through 5mm of steel at 1000m.

Dielectric mirrors, inexpensive ablative coatings, thermal transport delay and obscurants are also being studied as countermeasures. In not a few operational situations, even simple, passive countermeasures like rapid rotation (which spreads the heat and doesn't allow a fixed targeting point) or higher acceleration (which increases the distance and changes the angle quickly) can defeat or help to defeat non-highly pulsed, high energy laser weapons.

Particle-beam weapons

Particle-beam weapons can use charged or neutral particles, and can be either endoatmospheric or exoatmospheric. Particle beams as beam weapons are theoretically possible, but practical weapons have not been demonstrated yet. Certain types of particle beams have the advantage of being self-focusing in the atmosphere. 

Blooming is also a problem in particle-beam weapons. Energy that would otherwise be focused on the target spreads out; the beam becomes less effective:
  • Thermal blooming occurs in both charged and neutral particle beams, and occurs when particles bump into one another under the effects of thermal vibration, or bump into air molecules.
  • Electrical blooming occurs only in charged particle beams, as ions of like charge repel one another.

Plasma weapons

Plasma weapons fire a beam, bolt, or stream of plasma, which is an excited state of matter consisting of atomic electrons & nuclei and free electrons if ionized, or other particles if pinched. 

The MARAUDER (Magnetically Accelerated Ring to Achieve Ultra-high Directed-Energy and Radiation) used the Shiva Star project (a high energy capacitor bank which provided the means to test weapons and other devices requiring brief and extremely large amounts of energy) to accelerate a toroid of plasma at a significant percentage of the speed of light.

The Russian Federation is developing plasma weapons.

Sonic weapons

Tests performed on mice show the threshold for both lung and liver damage occurs at about 184 dB. Damage increases rapidly as intensity is increased. Noise-induced neurological disturbances in humans exposed to continuous low frequency tones for durations longer than 15 minutes involved development of immediate and long-term problems affecting brain tissue. The symptoms resembled those of individuals who had suffered minor head injuries. One theory for a causal mechanism is that the prolonged sound exposure resulted in enough mechanical strain to brain tissue to induce an encephalopathy.

Long Range Acoustic Device (LRAD)

The LRAD is the round black device on top of the New York City police Hummer.
 
The Long Range Acoustic Device (LRAD) is an acoustic hailing device developed by LRAD Corporation to send messages and warning tones over longer distances or at higher volume than normal loudspeakers. LRAD systems are used for long range communications in a variety of applications including as a means of non-lethal, non-kinetic crowd control. 

According to the manufacturer's specifications, the systems weigh from 15 to 320 pounds (6.8 to 145.1 kg) and can emit sound in a 30°- 60° beam at 2.5 kHz.

History

Mirrors of Archimedes

Archimedes may have used mirrors acting collectively as a parabolic reflector to burn ships attacking Syracuse.

According to a legend, Archimedes created a mirror with an adjustable focal length (or more likely, a series of mirrors focused on a common point) to focus sunlight on ships of the Roman fleet as they invaded Syracuse, setting them on fire. Historians point out that the earliest accounts of the battle did not mention a "burning mirror", but merely stated that Archimedes's ingenuity combined with a way to hurl fire were relevant to the victory. Some attempts to replicate this feat have had some success; in particular, an experiment by students at MIT showed that a mirror-based weapon was at least possible, if not necessarily practical.

Robert Watson-Watt

In 1935, the British Air Ministry asked Robert Watson-Watt of the Radio Research Station whether a "death ray" was possible. He and colleague Arnold Wilkins quickly concluded that it was not feasible, but as a consequence suggested using radio for the detection of aircraft and this started the development of radar in Britain.

The fictional "engine-stopping ray"

Stories in the 1930s and World War Two gave rise to the idea of an "engine-stopping ray". They seemed to have arisen from the testing of the television transmitter in Feldberg, Germany. Because electrical noise from car engines would interfere with field strength measurements, sentries would stop all traffic in the vicinity for the twenty minutes or so needed for a test. Reversing the order of events in retelling the story created a "tale" where tourists car engine stopped first and then were approached by a German soldier who told them that they had to wait. The soldier returned a short time later to say that the engine would now work and the tourists drove off. Such stories were circulating in Britain around 1938 and during the war British Intelligence relaunched the myth as a "British engine-stopping ray", trying to spoof the Germans into researching what the British had supposedly invented in an attempt to tie up German scientific resources.

German World War II experimental weapons

During the early 1940s Axis engineers developed a sonic cannon that could cause fatal vibrations in its target body. A methane gas combustion chamber leading to two parabolic dishes pulse-detonated at roughly 44 Hz. This sound, magnified by the dish reflectors, caused vertigo and nausea at 200–400 metres (220–440 yd) by vibrating the middle ear bones and shaking the cochlear fluid within the inner ear. At distances of 50–200 meters (160–660 ft), the sound waves could act on organ tissues and fluids by repeatedly compressing and releasing compressive resistant organs such as the kidneys, spleen, and liver. (It had little detectable effect on malleable organs such as the heart, stomach and intestines.) Lung tissue was affected at only the closest ranges as atmospheric air is highly compressible and only the blood rich alveoli resist compression. In practice, the weapon was highly vulnerable to enemy fire. Rifle, bazooka and mortar rounds easily deformed the parabolic reflectors, rendering the wave amplification ineffective.

In the later phases of World War II, Nazi Germany increasingly put its hopes on research into technologically revolutionary secret weapons, the Wunderwaffen. 

Among the directed-energy weapons the Nazis investigated were X-ray beam weapons developed under Heinz Schmellenmeier, Richard Gans and Fritz Houtermans. They built an electron accelerator called Rheotron (invented by Max Steenbeck at Siemens-Schuckert in the 1930s, these were later called Betatrons by the Americans) to generate hard X-ray synchrotron beams for the Reichsluftfahrtministerium (RLM). The intent was to pre-ionize ignition in aircraft engines and hence serve as anti-aircraft DEW and bring planes down into the reach of the FLAK. The Rheotron was captured by the Americans in Burggrub on April 14, 1945.

Another approach was Ernst Schiebolds 'Röntgenkanone' developed from 1943 in Großostheim near Aschaffenburg. The Company Richert Seifert & Co from Hamburg delivered parts.

Reported use in Sino-Soviet conflicts

The Central Intelligence Agency informed Secretary Henry Kissinger that it had twelve reports of Soviet forces using laser-based weapons against Chinese forces during the 1969 Sino-Soviet border clashes, though William Colby doubted that they had actually been employed.

Strategic Defense Initiative

In the 1980s, U.S. President Ronald Reagan proposed the Strategic Defense Initiative (SDI) program, which was nicknamed Star Wars. It suggested that lasers, perhaps space-based X-ray lasers, could destroy ICBMs in flight. Panel discussions on the role of high-power lasers in SDI took place at various laser conferences, during the 1980s, with the participation of noted physicists including Edward Teller.

Though the strategic missile defense concept has continued to the present under the Missile Defense Agency, most of the directed-energy weapon concepts were shelved. However, Boeing has been somewhat successful with the Boeing YAL-1 and Boeing NC-135, the first of which destroyed two missiles in February 2010. Funding has been cut to both of the programs.

Iraq War

During the Iraq War, electromagnetic weapons, including high power microwaves, were used by the U.S. military to disrupt and destroy Iraqi electronic systems and may have been used for crowd control. Types and magnitudes of exposure to electromagnetic fields are unknown.

Alleged tracking of Space Shuttle Challenger

The Soviet Union invested some effort in the development of ruby and carbon dioxide lasers as anti-ballistic missile systems, and later as a tracking and anti-satellite system. There are reports that the Terra-3 complex at Sary Shagan was used on several occasions to temporarily "blind" US spy satellites in the IR range. 

It has been claimed (and proven false) that the USSR made use of the lasers at the Terra-3 site to target the Space Shuttle Challenger in 1984. At the time, the Soviet Union were concerned that the shuttle was being used as a reconnaissance platform. On 10 October 1984 (STS-41-G), the Terra-3 tracking laser was allegedly aimed at Challenger as it passed over the facility. Early reports claimed that this was responsible for causing "malfunctions on the space shuttle and distress to the crew", and that the United States filed a diplomatic protest about the incident. However, this story is comprehensively denied by the crew members of STS-41-G and knowledgeable members of the US intelligence community.

Planetary defense

In the United States, the Directed Energy Solar Targeting of Asteroids and exploRation (DE-STAR) Project was considered for non-military use to protect Earth from asteroids.

Non-lethal weapons

The TECOM Technology Symposium in 1997 concluded on non-lethal weapons, "determining the target effects on personnel is the greatest challenge to the testing community", primarily because "the potential of injury and death severely limits human tests".

Also, "directed energy weapons that target the central nervous system and cause neurophysiological disorders may violate the Certain Conventional Weapons Convention of 1980. Weapons that go beyond non-lethal intentions and cause "superfluous injury or unnecessary suffering" may also violate the Protocol I to the Geneva Conventions of 1977."

Some common bio-effects of non-lethal electromagnetic weapons include:
Interference with breathing poses the most significant, potentially lethal results. 

Light and repetitive visual signals can induce epileptic seizures. Vection and motion sickness can also occur. 

Cruise ships are known to use sonic weapons (such as LRAD) to drive off pirates.

Russia has been reportedly using blinding laser weapons during its military intervention in Donbass.
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Electromagnetic pulse

From Wikipedia, the free encyclopedia
 
An electromagnetic pulse (EMP), also sometimes called a transient electromagnetic disturbance, is a short burst of electromagnetic energy. Such a pulse's origination may be a natural occurrence or man-made and can occur as a radiated, electric, or magnetic field or a conducted electric current, depending on the source.

EMP interference is generally disruptive or damaging to electronic equipment, and at higher energy levels a powerful EMP event such as a lightning strike can damage physical objects such as buildings and aircraft structures. The management of EMP effects is an important branch of electromagnetic compatibility (EMC) engineering.

Weapons have been developed to deliver the damaging effects of high-energy EMP.

General characteristics

An electromagnetic pulse is a short burst of electromagnetic energy. Its short duration means that it will be spread over a range of frequencies. Pulses are typically characterized by:
  • The type of energy (radiated, electric, magnetic or conducted).
  • The range or spectrum of frequencies present.
  • Pulse waveform: shape, duration and amplitude.
The last two of these, the frequency spectrum and the pulse waveform, are interrelated via the Fourier transform and may be seen as two different ways of describing the same pulse.

Types of energy

EMP energy may be transferred in any of four forms:
  1. Electric field
  2. Magnetic field
  3. Electromagnetic radiation
  4. Electrical conduction
Due to Maxwell's equations, a pulse of any one form of electromagnetic energy will always be accompanied by the other forms, however in a typical pulse one form will dominate. 

In general, only radiation acts over long distances, with the others acting over short distances. There are a few exceptions, such as a solar magnetic flare.

Frequency ranges

A pulse of electromagnetic energy typically comprises many frequencies from DC (zero Hz) to some upper limit depending on the source. The range defined as EMP, sometimes referred to as "DC to daylight", excludes the highest frequencies comprising the optical (infrared, visible, ultraviolet) and ionizing (X and gamma rays) ranges. 

Some types of EMP events can leave an optical trail, such as lightning and sparks, but these are side effects of the current flow through the air and are not part of the EMP itself.

Pulse waveforms

The waveform of a pulse describes how its instantaneous amplitude (field strength or current) changes over time. Real pulses tend to be quite complicated, so simplified models are often used. Such a model is typically described either in a diagram or as a mathematical equation. 

" "
Rectangular Pulse



" "
Double exponential pulse

Most electromagnetic pulses have a very sharp leading edge, building up quickly to their maximum level. The classic model is a double-exponential curve which climbs steeply, quickly reaches a peak and then decays more slowly. However, pulses from a controlled switching circuit often approximate the form of a rectangular or "square" pulse. 

EMP events usually induce a corresponding signal in the surrounding environment or material. Coupling usually occurs most strongly over a relatively narrow frequency band, leading to a characteristic damped sine wave. Visually it is shown as a high frequency sine wave growing and decaying within the longer-lived envelope of the double-exponential curve. A damped sinewave typically has much lower energy and a narrower frequency spread than the original pulse, due to the transfer characteristic of the coupling mode. In practice, EMP test equipment often injects these damped sinewaves directly rather than attempting to recreate the high-energy threat pulses. 

In a pulse train, such as from a digital clock circuit, the waveform is repeated at regular intervals. A single complete pulse cycle is sufficient to characterise such a regular, repetitive train.

Types

An EMP arises where the source emits a short-duration pulse of energy. The energy is usually broadband by nature, although it often excites a relatively narrow-band damped sine wave response in the surrounding environment. Some types are generated as repetitive and regular pulse trains.

Different types of EMP arise from natural, man-made, and weapons effects. 

Types of natural EMP event includes:
  • Lightning electromagnetic pulse (LEMP). The discharge is typically an initial huge current flow, at least mega-amps, followed by a train of pulses of decreasing energy.
  • Electrostatic discharge (ESD), as a result of two charged objects coming into close proximity or even contact.
  • Meteoric EMP. The discharge of electromagnetic energy resulting from either the impact of a meteoroid with a spacecraft or the explosive breakup of a meteoroid passing through the Earth's atmosphere.
  • Coronal mass ejection (CME). A burst of plasma and accompanying magnetic field, ejected from the solar corona and released into the solar wind. Sometimes referred to as a Solar EMP.
Types of (civil) man-made EMP event include:
  • Switching action of electrical circuitry, whether isolated or repetitive (as a pulse train).
  • Electric motors can create a train of pulses as the internal electrical contacts make and break connections as the armature rotates.
  • Gasoline engine ignition systems can create a train of pulses as the spark plugs are energized or fired.
  • Continual switching actions of digital electronic circuitry.
  • Power line surges. These can be up to several kilovolts, enough to damage electronic equipment that is insufficiently protected.
Types of military EMP include:
  • Nuclear electromagnetic pulse (NEMP), as a result of a nuclear explosion. A variant of this is the high altitude nuclear EMP (HEMP), which produces a secondary pulse due to particle interactions with the Earth's atmosphere and magnetic field.
  • Non-nuclear electromagnetic pulse (NNEMP) weapons.

Lightning

Lightning is unusual in that it typically has a preliminary "leader" discharge of low energy building up to the main pulse, which in turn may be followed at intervals by several smaller bursts.

Electrostatic discharge (ESD)

ESD events are characterised by high voltages of many kV but small currents and sometimes cause visible sparks. ESD is treated as a small, localised phenomenon, although technically a lightning flash is a very large ESD event. ESD can also be man-made, as in the shock received from a Van de Graaff generator. 

An ESD event can damage electronic circuitry by injecting a high-voltage pulse, besides giving people an unpleasant shock. Such an ESD event can also create sparks, which may in turn ignite fires or fuel-vapour explosions. For this reason, before refueling an aircraft or exposing any fuel vapor to the air, the fuel nozzle is first connected to the aircraft to safely discharge any static.

Switching pulses

The switching action of an electrical circuit creates a sharp change in the flow of electricity. This sharp change is a form of EMP. 

Simple electrical sources include inductive loads such as relays, solenoids, and the brush contacts in electric motors. Typically these send a pulse down any electrical connections present, as well as radiating a pulse of energy. The amplitude is usually small and the signal may be treated as "noise" or "interference". The switching off or "opening" of a circuit causes an abrupt change in the current flowing. This can in turn cause a large pulse in the electric field across the open contacts, causing arcing and damage. It is often necessary to incorporate design features to limit such effects. 

Electronic devices such as vacuum tubes or valves, transistors and diodes can also switch on and off very quickly, causing similar issues. One-off pulses may be caused by solid-state switches and other devices used only occasionally. However, the many millions of transistors in a modern computer may switch repeatedly at frequencies above 1 GHz, causing interference which appears to be continuous.

Nuclear electromagnetic pulse (NEMP)

A nuclear electromagnetic pulse is the abrupt pulse of electromagnetic radiation resulting from a nuclear explosion. The resulting rapidly changing electric fields and magnetic fields may couple with electrical/electronic systems to produce damaging current and voltage surges.

The intense gamma radiation emitted can also ionize the surrounding air, creating a secondary EMP as the atoms of air first lose their electrons and then regain them.

NEMP weapons are designed to maximize such EMP effects as the primary damage mechanism, and some are capable of destroying susceptible electronic equipment over a wide area.

A high-altitude electromagnetic pulse (HEMP) weapon is a NEMP warhead designed to be detonated far above the Earth's surface. The explosion releases a blast of gamma rays into the mid-stratosphere, which ionizes as a secondary effect and the resultant energetic free electrons interact with the Earth's magnetic field to produce a much stronger EMP than is normally produced in the denser air at lower altitudes.

Non-nuclear electromagnetic pulse (NNEMP)

Non-nuclear electromagnetic pulse (NNEMP) is a weapon-generated electromagnetic pulse without use of nuclear technology. Devices that can achieve this objective include a large low-inductance capacitor bank discharged into a single-loop antenna, a microwave generator, and an explosively pumped flux compression generator. To achieve the frequency characteristics of the pulse needed for optimal coupling into the target, wave-shaping circuits or microwave generators are added between the pulse source and the antenna. Vircators are vacuum tubes that are particularly suitable for microwave conversion of high-energy pulses.

NNEMP generators can be carried as a payload of bombs, cruise missiles (such as the CHAMP missile) and drones, with diminished mechanical, thermal and ionizing radiation effects, but without the consequences of deploying nuclear weapons.

The range of NNEMP weapons is much less than nuclear EMP. Nearly all NNEMP devices used as weapons require chemical explosives as their initial energy source, producing only 10−6 (one millionth) the energy of nuclear explosives of similar weight. The electromagnetic pulse from NNEMP weapons must come from within the weapon, while nuclear weapons generate EMP as a secondary effect. These facts limit the range of NNEMP weapons, but allow finer target discrimination. The effect of small e-bombs has proven to be sufficient for certain terrorist or military operations. Examples of such operations include the destruction of electronic control systems critical to the operation of many ground vehicles and aircraft.

The concept of the explosively pumped flux compression generator for generating a non-nuclear electromagnetic pulse was conceived as early as 1951 by Andrei Sakharov in the Soviet Union, but nations kept work on non-nuclear EMP classified until similar ideas emerged in other nations.

Electromagnetic forming

The large forces generated by electromagnetic pulses can be used to shape or form objects as part of their manufacturing process.

Effects

Minor EMP events, and especially pulse trains, cause low levels of electrical noise or interference which can affect the operation of susceptible devices. For example, a common problem in the mid-twentieth century was interference emitted by the ignition systems of gasoline engines, which caused radio sets to crackle and TV sets to show stripes on the screen. Laws were introduced to make vehicle manufacturers fit interference suppressors. 

At a high voltage level an EMP can induce a spark, for example from an electrostatic discharge when fueling a gasoline engine vehicle. Such sparks have been known to cause fuel-air explosions and precautions must be taken to prevent them.

A large and energetic EMP can induce high currents and voltages in the victim unit, temporarily disrupting its function or even permanently damaging it. 

A powerful EMP can also directly affect magnetic materials and corrupt the data stored on media such as magnetic tape and computer hard drives. Hard drives are usually shielded by heavy metal casings. Some IT asset disposition service providers and computer recyclers use a controlled EMP to wipe such magnetic media.

A very large EMP event such as a lightning strike is also capable of damaging objects such as trees, buildings and aircraft directly, either through heating effects or the disruptive effects of the very large magnetic field generated by the current. An indirect effect can be electrical fires caused by heating. Most engineered structures and systems require some form of protection against lightning to be designed in. 

The damaging effects of high-energy EMP have led to the introduction of EMP weapons, from tactical missiles with a small radius of effect to nuclear bombs tailored for maximum EMP effect over a wide area.

Control

EMP simulator HAGII-C testing a Boeing E-4 aircraft.
 
EMPRESS I (antennas along shoreline) with USS Estocin (FFG-15) moored in the foreground for testing.

Like any electromagnetic interference, the threat from EMP is subject to control measures. This is true whether the threat is natural or man-made.

Therefore, most control measures focus on the susceptibility of equipment to EMP effects, and hardening or protecting it from harm. Man-made sources, other than weapons, are also subject to control measures in order to limit the amount of pulse energy emitted.

The discipline of ensuring correct equipment operation in the presence of EMP and other RF threats is known as electromagnetic compatibility (EMC).

Test simulation

To test the effects of EMP on engineered systems and equipment, an EMP simulator may be used.

Induced pulse simulation

Induced pulses are of much lower energy than threat pulses and so are more practicable to create, but they are less predictable. A common test technique is to use a current clamp in reverse, to inject a range of damped sine wave signals into a cable connected to the equipment under test. The damped sine wave generator is able to reproduce the range of induced signals likely to occur.

Threat pulse simulation

Sometimes the threat pulse itself is simulated in a repeatable way. The pulse may be reproduced at low energy in order to characterize the victim's response prior to damped sinewave injection, or at high energy to recreate the actual threat conditions. 

A small-scale ESD simulator may be hand-held.

Bench- or room-sized simulators come in a range of designs, depending on the type and level of threat to be generated.

At the top end of the scale, large outdoor test facilities incorporating high-energy EMP simulators have been built by several countries. The largest facilities are able to test whole vehicles including ships and aircraft for their susceptibility to EMP. Nearly all of these large EMP simulators used a specialized version of a Marx generator.

Examples include the huge wooden-structured ATLAS-I simulator (also known as TRESTLE) at Sandia National Labs, New Mexico, which was at one time the world's largest EMP simulator. Papers on this and other large EMP simulators used by the United States during the latter part of the Cold War, along with more general information about electromagnetic pulses, are now in the care of the SUMMA Foundation, which is hosted at the University of New Mexico. The US Navy also has a large facility called the Electro Magnetic Pulse Radiation Environmental Simulator for Ships I (EMPRESS I).

Safety

High-level EMP signals can pose a threat to human safety. In such circumstances, direct contact with a live electrical conductor should be avoided. Where this occurs, such as when touching a Van de Graaf generator or other highly-charged object, care must be taken to release the object and then discharge the body through a high resistance, in order to avoid the risk of a harmful shock pulse when stepping away. 

Very high electric field strengths can cause breakdown of the air and a potentially lethal arc current similar to lightning to flow, however electric field strengths of up to 200 kV/m (Kilovolts per metre) are regarded as safe.

Magnetic pulses are generally safe, although extremely high pulse levels can affect brain activity, as in transcranial magnetic stimulation.

In popular culture

The popular media often depict EMP effects incorrectly, causing misunderstandings among the public and even professionals. Official efforts have been made in the U.S. to disprove these misconceptions.
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This spud’s for you: A breeding revolution could unleash the potential of potato

Diverse potatoes, such as these from Peru, will help breeders create resilient new varieties.
JIM RICHARDSON/NATIONAL GEOGRAPHIC
 

THE SACRED VALLEY OF THE INCAS IN PERU—On a bleak, brown hill here, David Ellis examines a test plot of potato plants and shakes his head. "They're dead, dead, dead," he says. Pests and lack of rain have laid waste to all 17 varieties that researchers had planted.

It is a worrying sign for Ellis, the now-retired director of the gene bank at the International Potato Center (CIP) in Lima. People have grown potatoes in this rugged stretch of the Andes for thousands of years. In recent years, that task has gotten tougher, in part because of climate change. Drought and frost are striking more often. The rains come later, shortening the growing season. And warmer temperatures have allowed moths and weevils to encroach from lower elevations.

To find potatoes that can cope with those challenges, researchers and Peruvian farmers are testing dozens of the 4350 locally cultivated varieties, or landraces, kept in CIP's refrigerated storage. The plants in this plot fell short. "Native land races evolved over time," Ellis says. But, he says, climate change is happening "too fast for these varieties to adapt."

In Peru and around the world, enhancing the potato has become a high priority. It is the most important food crop after wheat and rice. Potatoes are already a staple for 1.3 billion people, and the nutritious tubers are becoming increasingly popular in the developing world. Keeping up with the demand means adapting the potato to various soils and climates. It must also resist new threats from pests, disease, heat, and drought.

Unlike other major crops, however, the potato has not had a breeding breakthrough of the kind that helped dramatically boost yields during the Green Revolution of the 1950s and 1960s. The reason is that creating a new potato variety is slow and difficult, even by the patient standards of plant breeders. Commercial varieties carry four copies of each chromosome, which forces breeders to create and test hundreds of thousands of seedlings to find just one with the desired combination of traits. Readying a new variety for farm fields can take a decade or more.

Many countries continue to plant popular potato varieties that have remained essentially unchanged for decades. But new approaches, including genetic engineering, promise to add more options. Potato breeders are particularly excited about a radical new way of creating better varieties. This system, called hybrid diploid breeding, could cut the time required by more than half, make it easier to combine traits in one variety, and allow farmers to plant seeds instead of bulky chunks of tuber. "It will change the world tremendously," says Paul Struik, an agronomist at Wageningen University in the Netherlands.

To breed a better potato, it helps to have plenty of genetic raw material on hand. But the world's gene banks aren't fully stocked with the richest source of valuable genes: the 107 potato species that grow in the wild. Habitat loss threatens many populations of those plants. In a bid to preserve that wild diversity before it vanishes, collectors have made their biggest push ever, part of a $50 million program coordinated by the Crop Trust, a charity based in Bonn, Germany.

The collectors and breeders are racing against warming, drying, and the proliferation of pests. "Because of climate change," says Nigel Maxted, a conservation biologist at the University of Birmingham in the United Kingdom, "we require higher levels of diversity than ever before."

Climate change threatens yields in Potato Park, a farming association near Cuzco, Peru.
JIM RICHARDSON/NATIONAL GEOGRAPHIC

The closest ancestors of cultivated potatoes evolved in the Andes, where people domesticated the plant at least 7000 years ago. After the Spanish brought the tuber to Europe in the 16th century, it remained a botanical curiosity and was mostly fed to livestock. Europeans began to eat potatoes in earnest only in the 1800s, during the famines of the Napoleonic Wars.

Once the potato caught on, there was no turning back. The plant can grow in cold climates and poor soil, and in some places yields several crops per season. Once harvested, the energy-rich tubers, packed with vitamin C, can be stored for months and cooked in many ways. A hectare of potatoes can provide up to four times the calories of a grain crop.

Like rice and wheat, the potato was a target for improvement during the Green Revolution. Yields increased thanks to fertilizer and improved farming techniques, but they didn't skyrocket. Potato breeders achieved no genetic gains such as the one that produced wheat with short, sturdy stalks that can bear more grain.

Still, global potato production has steadily grown. China has doubled its harvests over the past 20 years. It now grows more than twice as many potatoes as India, the next-biggest producer. Uzbekistan and Bangladesh, among other nations, have come to depend on the potato for food security. In 2005, developing countries for the first time grew more potatoes than the developed world. Many African countries are aiming to boost production.

To reap bigger harvests, farmers will have to manage many risks, including disease. The potato's greatest scourge is the funguslike pathogen Phytophthora infestans, which causes a disease called late blight. The pathogen unleashed the Irish potato famine in the mid–19th century, and plant breeders have struggled ever since to rein it in. "Phytophthora is always evolving and overcoming resistance," says Jadwiga Śliwka of the Plant Breeding and Acclimatization Institute in Młochów, Poland. Rich countries use fungicides to minimize the devastating losses from late blight. But in developing countries, 15% to 30% of the crop is ruined.

Then there is heat and drought, which climate change is exacerbating. In some parts of the world, farmers are planting their crop earlier so that it matures before the nights get too hot, which prevents tubers from forming. But eventually farmers will need hardier plants. "We focus on developing a robust potato that will perform better in a stressful environment," says Thiago Mendes, a potato breeder with CIP's regional office in Nairobi. "Our target is food security."

The key to that robust potato may be waiting in the wild species that grow from southwestern North America through Central and South America. Wild potatoes from Mexico, for example, evolved in the presence of P. infestans and can resist many strains. Many other wild species have yet to be thoroughly collected or studied.

Growing appetite

In June 2018, beside a cattle pasture in southern Brazil, botanist Gustavo Heiden strode along an embankment, his eyes fixed on the long grass. Then, he dropped to his knees and jabbed a trowel into the soil. "Aha! Look at this," said Heiden, who works with the Brazilian Agricultural Research Corporation (EMBRAPA) in Pelotas. He pulled up a short plant with small tubers dangling from its roots. It was Solanum commersonii, one of three wild relatives of the potato known in Brazil.

Brazil is far from the potato's center of origin in the Andes. But the ranges of wild relatives extend into the state of Rio Grande do Sul, where the climate shifts from temperate to tropical. Plants in this transition zone have evolved to survive occasionally harsh winters and hot, dry summers. "The wild potatoes here are probably pretty adapted to the extreme weather that will be happening more frequently with climate change," Heiden says.

Heiden's collecting trip was just one element of the Crop Trust's effort to collect, conserve, and breed the wild relatives of 29 crops, which began in 2011. Plant collectors used to travel the world on such expeditions. But they became much less frequent after governments began to adopt the Convention on Biological Diversity in the 1990s. Intended to prevent unfair exploitation of biodiversity, the convention made it harder to get collecting permits and to exchange plant material. An international seed treaty established in 2004 eased swaps for crops and wild relatives, but collecting remained stagnant because of lack of funding and expertise. "We didn't have any experience on how to collect wild potatoes or how to conserve them," says Cinthya Zorrilla, subdirector of genetic resources at the National Institute of Agricultural Innovation in Lima.

The Crop Trust has provided grants and training to collectors around the world. The effort on wild potatoes, which wraps up this month, has yielded a collection representing 39 species from six nations: Peru, Brazil, Ecuador, Guatemala, Costa Rica, and Chile. Zorrilla's team alone found 31 species in Peru, including one for which no seeds had ever been collected. They plan to continue to search for four other species still missing from gene banks. "We will not stop," she says. The plants are being stored in each nation's gene bank, CIP, and the Millennium Seed Bank at the Royal Botanic Gardens, Kew, in the United Kingdom. The stored seeds will be available to potato breeders worldwide.

The hardest part comes next: getting desirable genes from wild species into cultivated potatoes. In the past, breeders acquired traits such as disease resistance from a dozen wild species. Those victories were hard-won, some taking decades to achieve. That's largely because wild relatives also carry many unwanted traits, which combine with those of cultivated potatoes and vastly lower a breeder's chances of finding a good variety.

Even without wild species, potato breeding is a crapshoot. Because breeding lines have four copies of their 12 chromosomes, the traits of the two parents show up in the next generation in largely unpredictable combinations. As experts say, the current varieties don't breed true, which is why farmers plant bits of "seed tuber," which yield genetically identical plants, rather than seeds. Compounding the headache, breeders select for many traits at once, further lowering the probability of finding a winner. "The numbers get really hard, really fast," says Laura Shannon, a potato breeder at the University of Minnesota in St. Paul.

Genetic markers linked to specific genes have sped up the process. To find out whether seedlings have inherited a trait such as disease resistance, breeders can quickly test for the marker rather than wait for the plants to mature and then expose them to the disease. Even with this tool, a potato breeder must screen up to 100,000 offspring per year. It can take 15 years or longer to find one with the right traits, fully test it, and generate enough seed tubers to distribute to farmers.

Another frustration is that potato breeders can't easily improve existing varieties. Once a potato variety is established, introducing new traits while retaining all of its favored characteristics is practically impossible. That's why classic, widely grown varieties, such as the russet burbank, still dominate the market many decades after their debuts.

Patient breeders using traditional methods can nevertheless achieve impressive results. In 2017, for example, CIP released four new varieties in Kenya, the result of crosses from established breeding lines. In field trials, the new potato plants maintained yields with 20% less rainfall and temperatures higher by 3°C.

Such success shows there is still genetic diversity to be tapped in existing breeding lines. But researchers fear that gene pool may not be deep enough to adapt the potato to future climates or enable other improvements. Wild potatoes, however, hold valuable, untapped genetic diversity. One trait from those wild plants, Mendes says, "could save our life."

Wild species have traits that could improve cultivated potatoes. Alberto Salas of the International Potato Center in Lima prepares a sample of Solanum contumazaense (above); its hairs defend against insects.
SARA FAJARDO/CIP

The search for vital traits is already underway. Last year, at an EMBRAPA research station near Pelotas, technicians in lab coats leaned over the wild species Heiden had collected. They gently daubed their faintly purple flowers with yellow powder from a plastic tube, fertilizing them with pollen from domesticated potatoes.

In a nearby greenhouse, tables were lined with the offspring of previous crosses. Researchers have evaluated thousands of those seedlings for health and yield, among other traits. They screened older plants for drought resistance by limiting the water in plastic-lined troughs. In a temperature-controlled walk-in chamber, researchers tested the ability of other plants to withstand heat; the yellowed plants appeared to be sweltering.

Such expansive testing is aimed at moving wild genes into traditional breeding programs as quickly as possible. It's part of EMBRAPA's larger effort to help Brazil expand production of potato, the country's most important vegetable crop.

In Lima, the Crop Trust has funded CIP to test wild varieties for promising traits even before any breeding begins. In 2013, center researchers started to characterize 12 wild species collected 30 years ago. Records suggested those species might tolerate drought and resist diseases such as bacterial wilt, a serious problem for developing countries. Merideth Bonierbale and colleagues planted seeds and have tested the plants in greenhouses at CIP's main facility. Mendes is now expanding the work to Kenya.

Other researchers are skirting the limitations of traditional breeding by using genetic engineering. CIP's Marc Ghislain and colleagues, for example, have directly added genes to already successful potato varieties without altering the plants in any other way—an approach not possible with traditional breeding. They took three genes for resistance to late blight from wild relatives and added them to varieties of potato popular in East Africa. The engineered varieties have proved successful in 3 years of field tests in Uganda and are undergoing final studies for regulators. Transgenic potatoes that resist late blight have already been commercialized in the United States and Canada.

Biotech approaches have their own limits. They have succeeded with traits controlled by single genes, such as disease resistance and tolerance of bruising. But improving complex physiological traits governed by many genes, such as water-use efficiency, requires traditional breeding, however cumbersome.
[Hybrid breeding] could be a real game changer. It will definitely make breeding more agile.
Glenn Bryan, James Hutton Institute
In Wageningen, Pim Lindhout has been plotting a revolution that would do away with much of that tedium and complexity. As head of Research and Development for Solynta, a startup company founded in 2006, he and his colleagues have been developing a new way to breed potatoes: creating hybrid offspring from true-breeding parent lines. "Everyone was convinced it's impossible," he says. "Many people thought I was crazy."

Hybrid breeding revolutionized maize production in the 20th century. It enabled breeders to quickly create high-yielding varieties that have what's known as hybrid vigor. The first step is to make inbred parent lines, which have identical alleles on all chromosome copies; the offspring of those true-breeding parents then inherit a predictable set of traits. Making the inbred lines requires repeated self-pollination over many generations. That process tends to impair the health of the plants, but when breeders cross two inbred lines, the first-generation offspring are healthy and have beneficial traits from both parents.

Potato breeders doubted the approach was possible for tubers. "I was trained to believe that potatoes can't be inbred," says Shelley Jansky, a potato breeder with the U.S. Department of Agriculture in Madison. One big obstacle is that many potato species cannot fertilize themselves. In 1998, researchers discovered a gene that somehow allows one wild species of potato to self-fertilize. When that gene is bred into other species, it lets them self-fertilize as well. But the resulting plants are frail and produce puny tubers.

The next step is to inbreed those weaklings by self-fertilizing them, generation after generation. Don't bother trying it at home: Success with cultivated potatoes would likely take decades because of the small odds of getting the same allele on all four copies of their chromosomes. Breeders reduce the complexity either by using species with only two sets of chromosomes (known as diploids) or by manipulating domesticated potatoes to cut the number of chromosomes in half. With persistence, diploid potatoes can be inbred. In 2011, Lindhout published the first report of inbred diploid lines that are vigorous and productive. More recently, Jansky and colleagues also created inbred diploid lines.

Such diploid inbred plants are at the heart of Solynta's strategy to revolutionize potato breeding. They will make it possible to combine traits in commercial varieties with unprecedented certainty, ease, and speed. And the plants will simplify efforts to add desirable traits directly from wild relatives while eliminating their many drawbacks, such as small tubers or poor flavor. Undesirable traits can be bred out of the descendants of a diploid cross through a standard technique called backcrossing.

In 2016, Solynta conducted its first field trials of hybrid seedlings in the Democratic Republic of the Congo and in 17 locations across Europe. The plants did well, yielding large tubers over a typical growing season. The company has not yet commercialized a variety. Within a few years, it hopes to create customized potatoes for European and African markets. Other firms, including large seed companies, are also working to develop hybrid potatoes. HZPC in Joure, the Netherlands, has begun field trials in Tanzania and in several countries in Asia.

Hybrid breeding "could be a real game changer," says geneticist Glenn Bryan, head of the Potato Genetics and Breeding group at the James Hutton Institute in Dundee, U.K. "It will definitely make breeding more agile."

Basic research could benefit from the work. "Having diploid potatoes will drastically increase our understanding of the potato genome," Shannon says. Although firms typically keep their inbred plants secret, Solynta plans to release a line, dubbed Solynthus, so that scientists can study its genetics. Jansky, for one, hopes further research could reveal genes that control yield, which might then be tapped to boost harvests.

Hybrids could also change how potatoes are planted, giving farmers the option of sowing fields with true seeds, because these are genetically identical in hybrids. Another benefit is logistical; planting 10 hectares, for instance, takes just 200 grams of easily transported seeds, compared with 25 tons of bulky tubers. In the developing world, where quality seed tubers are rare, seeds could also make obtaining superior plants easier for farmers. And in perhaps the biggest advantage over tubers for poor farmers, seeds transmit no major diseases.

Hybrid potato seeds aren't a panacea. Young plants grow more quickly and vigorously from tubers than from seeds, putting seeds at a disadvantage in some climates. And depending on how complete the inbreeding, hybrid potatoes could have less uniformly shaped tubers than those of traditional plants, a problem for farmers who supply food-processing companies. Such complexities have prompted the Dutch government to commission a study of the potential socioeconomic impacts of hybrid potatoes.

With collectors amassing genetic diversity and new techniques promising to overcome the complexities of the potato genome, researchers are optimistic that they can make significant improvements. "That's what gets me up in the morning," Jansky says. "There's no better time to be a breeder—and especially a potato breeder."

Until hybrid breeding and other strategies produce more resilient potatoes, farmers will have to work with the resources at hand. Here in Peru's Sacred Valley, Ellis and others from CIP have teamed with small-scale farmers who belong to an association known as Potato Park, which is dedicated to preserving hundreds of local potato varieties. The group has been planting those colorful potatoes in test plots.

Some succumb to pests or drought, like those that Ellis found dead, whereas others survive. In May 2018, as part of their search for more resilient tubers, Potato Park farmers neatly piled red, yellow, and brown tubers harvested from some of Ellis's experimental plots on rows of sacks, scoring each variety for yield and health. Local farmers had abandoned many of those landraces generations ago, as villages faded and exchange fewer plants.

Bringing some of that ancient diversity back into cultivation could hedge against environmental change. In Potato Park, farmers have already tried to escape the pests and disease that thrive in warmer temperatures by moving their cultivation 200 meters higher over the past 30 years. But René Gomez, CIP's curator of cultivated potatoes, warns that arable land is scarcer at higher elevations.

Pedro Condori Quispe, one of the park's growers, is optimistic that the communities will find a way to keep growing potatoes here. Potato farmers, he says with a smile, "are used to challenges."
 
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doi:10.1126/science.aaw9287

Erik Stokstad

Erik is a reporter at Science, covering environmental issues and UK research.
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