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57-413: With the display unit mounted in a 3-foot-high (0.91 m) steel cabinet, the system used two sets of five photo-sensitive cells within the detection head to record the intense flash of light produced by the detonation of the weapon followed, within a second, by a second intense flash. This double flash is characteristic of a nuclear explosion and measurement of the short gap between the two flashes enabled

114-543: A current density of tens of amperes per square metre. Because of the downward tilt of the Earth's magnetic field at high latitudes , the area of peak field strength is a U-shaped region to the equatorial side of the detonation. As shown in the diagram, for nuclear detonations in the Northern Hemisphere , this U-shaped region is south of the detonation point. Near the equator , where the Earth's magnetic field

171-571: A geomagnetic storm . Like a geomagnetic storm, E3 can produce geomagnetically induced currents in long electrical conductors, damaging components such as power line transformers . Because of the similarity between solar-induced geomagnetic storms and nuclear E3, it has become common to refer to solar-induced geomagnetic storms as "Solar EMP". "Solar EMP" does not include E1 or E2 components. Factors that control weapon effectiveness include altitude, yield , construction details, target distance, intervening geographical features, and local strength of

228-447: A constant current will flow. Current from a discharging inductor is one example. For sensitive electronics , excessive current can flow if this voltage spike exceeds a material's breakdown voltage, or if it causes avalanche breakdown . In semiconductor junctions , excessive electric current may destroy or severely weaken that device. An avalanche diode , transient voltage suppression diode , varistor , overvoltage crowbar , or

285-487: A fission explosion is 3.5% of the yield, but in a 10 kt (42 TJ) detonation the triggering explosive around the bomb core absorbs about 85% of the prompt gamma rays, so the output is only about 0.5% of the yield. In the thermonuclear Starfish Prime the fission yield was less than 100% and the thicker outer casing absorbed about 95% of the prompt gamma rays from the pusher around the fusion stage. Thermonuclear weapons are also less efficient at producing EMP because

342-418: A large, radial pulse of electric current propagating outward from the burst location confined to the source region (the region over which the gamma photons are attenuated). The Earth's magnetic field exerts a force on the electron flow at a right angle to both the field and the particles' original vector, which deflects the electrons and leads to synchrotron radiation . Because the outward traveling gamma pulse

399-587: A lightning strike would not simultaneously register on two adjacent AWDREYs. The first two primary responsibilities of the United Kingdom Warning and Monitoring Organisation (UKWMO), for whom the ROC provided the field force were: AWDREY was the principal method by which the UKWMO would achieve its second responsibility. Simultaneous responses on two or more AWDREY units would identify the explosion as

456-524: A location where the Earth's magnetic field was greater. The damage caused by the resulting EMP was reportedly much greater than in Starfish Prime. The geomagnetic storm –like E3 pulse from Test 184 induced a current surge in a long underground power line that caused a fire in the power plant in the city of Karaganda . After the dissolution of the Soviet Union , the level of this damage

513-592: A nuclear explosion was known in the earliest days of nuclear weapons testing. The magnitude of the EMP and the significance of its effects were not immediately realized. During the first United States nuclear test on 16 July 1945, electronic equipment was shielded because Enrico Fermi expected the electromagnetic pulse. The official technical history for that first nuclear test states, "All signal lines were completely shielded, in many cases doubly shielded. In spite of this many records were lost because of spurious pickup at

570-689: A nuclear strike on the UK had been confirmed by the Director UKWMO (or his deputy), readings from AWDREY were ignored during subsequent nuclear bursts within the attack, and the readings from ROC posts became the main method of detecting and identifying any subsequent near ground bursts. The 12 ROC AWDREY units were located at the group controls in Exeter, Oxford, Horsham, Bristol, Colchester, Carmarthen, Coventry, Carlisle, York, Dundee, Inverness and Belfast. This siting pattern provided sufficient detectors that

627-536: A nuclear strike. ROC post bomb detection instruments (see Bomb Power Indicator ) operated by recording the peak overpressure of the blast wave from any nearby nuclear explosion. Any ultra-high-altitude nuclear explosion, designed to knock out the UK's communications and electronic equipment would not produce a detectable blast wave, and the AWDREY system was therefore the only method of identifying these bursts. The AWDREY installation consisted of three separate elements:

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684-463: A nuclear warhead detonated tens to hundreds of miles above the Earth's surface is known as a high-altitude electromagnetic pulse (HEMP) device. Effects of a HEMP device depend on factors including the altitude of the detonation, energy yield , gamma ray output, interactions with the Earth's magnetic field and electromagnetic shielding of targets. The fact that an electromagnetic pulse is produced by

741-483: A range of other overvoltage protective devices can divert ( shunt ) this transient current thereby minimizing voltage. Voltage spikes, also known as surges, may be created by a rapid buildup or decay of a magnetic field, which may induce energy into the associated circuit. However voltage spikes can also have more mundane causes such as a fault in a transformer or higher-voltage (primary circuit) power wires falling onto lower-voltage (secondary circuit) power wires as

798-577: A result of accident or storm damage. Voltage spikes may be longitudinal (common) mode or metallic (normal or differential) mode. Some equipment damage from surges and spikes can be prevented by use of surge protection equipment. Each type of spike requires selective use of protective equipment. For example, a common mode voltage spike may not even be detected by a protector installed for normal mode transients. Power increases or decreases which last multiple cycles are called swells or sags, respectively. An uninterrupted voltage increase that lasts more than

855-568: A short circuit on the line and some lines detaching from the poles and falling to the ground". Nuclear EMP is a complex multi-pulse, usually described in terms of three components, as defined by the International Electrotechnical Commission (IEC). The three components of nuclear EMP, as defined by the IEC, are called "E1", "E2", and "E3". The three categories of high-altitude EMP are divided according to

912-401: A surface burst, absorption of gamma rays by air would limit the range of gamma-ray deposition to approximately 16 kilometres (10 mi), while for a burst in the lower-density air at high altitudes, the range of deposition would be far greater. Typical nuclear weapon yields used during Cold War planning for EMP attacks were in the range of 1 to 10  Mt (4.2 to 41.8  PJ ). This

969-421: A typical case of E1 pulse produced by a second-generation nuclear weapon such as those of Operation Fishbowl . The typical gamma rays given off by the weapon have an energy of about 2   MeV ( mega electron-volts). The gamma rays transfer about half of their energy to the ejected free electrons, giving an energy of about 1   MeV. In a vacuum and absent a magnetic field, the electrons would travel with

1026-582: Is a burst of electromagnetic radiation created by a nuclear explosion . The resulting rapidly varying electric and magnetic fields may couple with electrical and electronic systems to produce damaging current and voltage surges . The specific characteristics of a particular nuclear EMP event vary according to a number of factors, the most important of which is the altitude of the detonation. The term "electromagnetic pulse" generally excludes optical (infrared, visible, ultraviolet) and ionizing (such as X-ray and gamma radiation) ranges. In military terminology,

1083-729: Is a very long-duration "late time" pulse, which is extremely slow in rise and fall times compared to the other components of EMP. E3 is further divided into E3A (blast wave) and E3B (heave). E3 is also called magnetohydrodynamic EMP. The E1 pulse is a very fast component of nuclear EMP. E1 is a brief but intense electromagnetic field that induces high voltages in electrical conductors. E1 causes most of its damage by causing electrical breakdown voltages to be exceeded. E1 can destroy computers and communications equipment and it changes too quickly (nanoseconds) for ordinary surge protectors to provide effective protection from it. Fast-acting surge protectors (such as those using TVS diodes ) will block

1140-405: Is more closely proportional to the total energy yield of the weapon. In nuclear EMP all of the components of the electromagnetic pulse are generated outside of the weapon. For high-altitude nuclear explosions , much of the EMP is generated far from the detonation (where the gamma radiation from the explosion hits the upper atmosphere). This electric field from the EMP is remarkably uniform over

1197-484: Is more nearly horizontal, the E1 field strength is more nearly symmetrical around the burst location. At geomagnetic field strengths typical of the mid-latitudes, these initial electrons spiral around the magnetic field lines with a typical radius of about 85 metres (280 ft). These initial electrons are stopped by collisions with air molecules at an average distance of about 170 metres (560 ft). This means that most of

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1254-549: Is propagating at the speed of light, the synchrotron radiation of the Compton electrons adds coherently , leading to a radiated electromagnetic signal. This interaction produces a large, brief, pulse. Several physicists worked on the problem of identifying the mechanism of the HEMP E1 pulse. The mechanism was finally identified by Conrad Longmire of Los Alamos National Laboratory in 1963. Longmire gives numerical values for

1311-493: Is roughly 50 to 500 times the size of the Hiroshima and Nagasaki bombs. Physicists have testified at United States Congressional hearings that weapons with yields of 10 kt (42 TJ) or less can produce a large EMP. The EMP at a fixed distance from an explosion increases at most as the square root of the yield (see the illustration to the right). This means that although a 10 kt (42 TJ) weapon has only 0.7% of

1368-546: The Starfish Prime nuclear test, most damage was to the satellites' solar panels while passing through radiation belts created by the explosion. For detonations within the atmosphere, the situation is more complex. Within the range of gamma ray deposition, simple laws no longer hold as the air is ionized and there are other EMP effects, such as a radial electric field due to the separation of Compton electrons from air molecules, together with other complex phenomena. For

1425-545: The electric potential of a circuit are typically caused by In the design of critical infrastructure and military hardware, one concern is of pulses produced by nuclear explosions , whose nuclear electromagnetic pulses distribute large energies in frequencies from 1 kHz into the gigahertz range through the atmosphere. The effect of a voltage spike is to produce a corresponding increase in current ( current spike ). However some voltage spikes may be created by current sources. Voltage would increase as necessary so that

1482-461: The 22 October (K-3) nuclear test (also known as Test 184) blew all of the fuses and destroyed all of the overvoltage protectors in all of the sub-lines. Published reports, including a 1998 IEEE article, have stated that there were significant problems with ceramic insulators on overhead electrical power lines during the tests. A 2010 technical report written for Oak Ridge National Laboratory stated that "Power line insulators were damaged, resulting in

1539-434: The 50,000 volts per metre limit by unspecified mechanisms. The reality and possible construction details of these weapons are classified and are, therefore, unconfirmed in the open scientific literature The E2 component is generated by scattered gamma rays and inelastic gammas produced by neutrons . This E2 component is an "intermediate time" pulse that, by IEC definition, lasts from about one microsecond to one second after

1596-478: The E1 pulse. E1 is produced when gamma radiation from the nuclear detonation ionizes (strips electrons from) atoms in the upper atmosphere. This is known as the Compton effect and the resulting current is called the "Compton current". The electrons travel in a generally downward direction at relativistic speeds (more than 90 percent of the speed of light). In the absence of a magnetic field, this would produce

1653-694: The Earth's magnetic field. According to an internet primer published by the Federation of American Scientists : Thus, for equipment to be affected, the weapon needs to be above the visual horizon . The altitude indicated above is greater than that of the International Space Station and many low Earth orbit satellites. Large weapons could have a dramatic impact on satellite operations and communications such as occurred during Operation Fishbowl. The damaging effects on orbiting satellites are usually due to factors other than EMP. In

1710-400: The K Project tests, Soviet scientists instrumented a 570-kilometer (350 mi) section of telephone line in the area that they expected to be affected by the pulse. The monitored telephone line was divided into sub-lines of 40 to 80 kilometres (25 to 50 mi) in length, separated by repeaters . Each sub-line was protected by fuses and by gas-filled overvoltage protectors. The EMP from

1767-416: The ability to impair or destroy many protective and control features. The energy associated with the second component thus may be allowed to pass into and damage systems." The E3 component is different from E1 and E2. E3 is a much slower pulse, lasting tens to hundreds of seconds. It is caused by the nuclear detonation's temporary distortion of the Earth's magnetic field. The E3 component has similarities to

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1824-473: The accelerating reliance on EMP-sensitive microelectronics, heightened awareness that EMP could be a significant problem. In 1962, the Soviet Union performed three EMP-producing nuclear tests in space over Kazakhstan, the last in the " Soviet Project K nuclear tests ". Although these weapons were much smaller (300 kiloton ) than the Starfish Prime test, they were over a populated, large landmass and at

1881-471: The devices that would normally protect against E2. The EMP Commission Executive Report of 2004 states, "In general, it would not be an issue for critical infrastructure systems since they have existing protective measures for defense against occasional lightning strikes. The most significant risk is synergistic because the E2 component follows a small fraction of a second after the first component's insult, which has

1938-510: The early days of EMP research, that the problem might not be significant. Later calculations showed that if the Starfish Prime warhead had been detonated over the northern continental United States, the magnitude of the EMP would have been much larger (22 to 30 kV/m) because of the greater strength of the Earth's magnetic field over the United States, as well as its different orientation at high latitudes. These calculations, combined with

1995-466: The electric field measurements from the 1.7 kiloton weapon exceeded the range to which the test instruments were adjusted and was estimated to be about five times the limits to which the oscilloscopes were set. The Yucca EMP was initially positive-going, whereas low-altitude bursts were negative-going pulses. Also, the polarization of the Yucca EMP signal was horizontal, whereas low-altitude nuclear EMP

2052-542: The electrons are stopped by collisions with air molecules before completing a full spiral around the field lines. This interaction of the negatively charged electrons with the magnetic field radiates a pulse of electromagnetic energy. The pulse typically rises to its peak value in some five nanoseconds. Its magnitude typically decays by half within 200 nanoseconds. (By the IEC definition, this E1 pulse ends 1000 nanoseconds after it begins.) This process occurs simultaneously on about 10 electrons.   The simultaneous action of

2109-565: The electrons causes the resulting pulse from each electron to radiate coherently, adding to produce a single large-amplitude, short-duration, radiated pulse. Secondary collisions cause subsequent electrons to lose energy before they reach ground level. The electrons generated by these subsequent collisions have so little energy that they do not contribute significantly to the E1 pulse. These 2 MeV gamma rays typically produce an E1 pulse near ground level at moderately high latitudes that peaks at about 50,000 volts per metre. The ionization process in

2166-497: The energy release of the 1.44 Mt (6.0 PJ) Starfish Prime test, the EMP will be at least 8% as powerful. Since the E1 component of nuclear EMP depends on the prompt gamma-ray output, which was only 0.1% of yield in Starfish Prime but can be 0.5% of yield in low-yield pure nuclear fission weapons, a 10 kt (42 TJ) bomb can easily be 5 * 8% = 40% as powerful as the 1.44 Mt (6.0 PJ) Starfish Prime at producing EMP. The total prompt gamma-ray energy in

2223-603: The entire UK was covered, but the units were far enough apart that a lightning storm would be unlikely to trigger simultaneous AWDREY responses at two sites. Royal Observer Corps reports following a reading on AWDREY were prefixed with the codeword "TOCSIN BANG" . The message would also include the three-letter group identifier, followed by the time and yield reading from the AWDREY printout. E.g. "TOCSIN BANG – CAR – 11.06 (hours) – 3 megatons" (with CAR relating to Carlisle control). Nuclear electromagnetic pulse A nuclear electromagnetic pulse ( nuclear EMP or NEMP )

2280-499: The explosion. E2 has many similarities to lightning , although lightning-induced E2 may be considerably larger than a nuclear E2. Because of the similarities and the widespread use of lightning protection technology, E2 is generally considered to be the easiest to protect against. According to the United States EMP Commission, the main problem with E2 is that it immediately follows E1, which may have damaged

2337-481: The field strength may be expected to be tens of kilovolts per metre over most of the area receiving the EMP radiation." The text also states that, "...   over most of the area affected by the EMP the electric field strength on the ground would exceed 0.5 E max . For yields of less than a few hundred kilotons, this would not necessarily be true because the field strength at the Earth's tangent could be substantially less than 0.5 E max ." ( E max refers to

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2394-409: The first stage can pre-ionize the air which becomes conductive and hence rapidly shorts out the Compton currents generated by the fusion stage. Hence, small pure fission weapons with thin cases are far more efficient at causing EMP than most megaton bombs. This analysis, however, only applies to the fast E1 and E2 components of nuclear EMP. The geomagnetic storm -like E3 component of nuclear EMP

2451-482: The high-altitude EMP phenomenon. The Bluegill Triple Prime and Kingfish high-altitude nuclear tests of October and November 1962 in Operation Fishbowl provided data that was clear enough to enable physicists to accurately identify the physical mechanisms behind the electromagnetic pulses. The EMP damage of the Starfish Prime test was quickly repaired due, in part, to the fact that the EMP over Hawaii

2508-417: The large area affected. According to the standard reference text on nuclear weapons effects published by the U.S. Department of Defense, "The peak electric field (and its amplitude) at the Earth's surface from a high-altitude burst will depend upon the explosion yield, the height of the burst, the location of the observer, and the orientation with respect to the geomagnetic field . As a general rule, however,

2565-610: The maximum electric field strength in the affected area.) In other words, the electric field strength in the entire area that is affected by the EMP will be fairly uniform for weapons with a large gamma-ray output. For smaller weapons, the electric field may fall at a faster rate as distance increases. Voltage surge In electrical engineering , spikes are fast, short duration electrical transients in voltage ( voltage spikes ), current ( current spikes ), or transferred energy ( energy spikes ) in an electrical circuit. Fast, short duration electrical transients ( overvoltages ) in

2622-481: The mid- stratosphere causes this region to become an electrical conductor, a process that blocks the production of further electromagnetic signals and causes the field strength to saturate at about 50,000 volts per metre. The strength of the E1 pulse depends upon the number and intensity of the gamma rays and upon the rapidity of the gamma-ray burst. Strength is also somewhat dependent upon altitude. There are reports of "super-EMP" nuclear weapons that are able to exceed

2679-478: The photograph above) could be mounted anywhere in the building – at ROC controls this was usually on the balcony adjacent to the Triangulation Team. The three elements of the installation were connected by EMP-shielded and heavy duty cabling. During the early phase of operations, a spare observer was required to stand next to the display unit and monitor it constantly to identify initial responses. Once

2736-458: The public by causing electrical damage in Hawaii , about 1,445 kilometres (898 mi) away from the detonation point, disabling approximately 300 streetlights, triggering numerous burglar alarms and damaging a microwave link. Starfish Prime was the first success in the series of United States high-altitude nuclear tests in 1962 known as Operation Fishbowl . Subsequent tests gathered more data on

2793-472: The sensor, the detection unit and the display cabinet (timer). The sensor was mounted on the roof of the building. The detection unit was installed in a special room that was enclosed inside a Faraday cage ; in the case of the Royal Observer Corps controls, this was the "Radio Room" that already protected the sensitive radio equipment from the effects of EMP. The display unit (timer) (shown in

2850-601: The significance of the EMP problem after a three-article series on nuclear EMP was published in 1981 by William J. Broad in Science . In July 1962, the US carried out the Starfish Prime test, exploding a 1.44  Mt (6.0  PJ ) bomb 400 kilometres (250 mi; 1,300,000 ft) above the mid-Pacific Ocean. This demonstrated that the effects of a high-altitude nuclear explosion were much larger than had been previously calculated. Starfish Prime made those effects known to

2907-467: The time duration and occurrence of each pulse. E1 is the fastest or "early time" high-altitude EMP. Traditionally, the term "EMP" often refers specifically to this E1 component of high-altitude electromagnetic pulse. The E2 and E3 pulses are often further subdivided into additional divisions according to causation. E2 is a much lower intensity "intermediate time" EMP, which is further divided into E2A (scattered gamma EMP) and E2B (neutron gamma EMP). E3

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2964-473: The time of the explosion that paralyzed the recording equipment." During British nuclear testing in 1952–53, instrumentation failures were attributed to " radioflash ", which was their term for EMP. The first openly reported observation of the unique aspects of high-altitude nuclear EMP occurred during the helium balloon -lofted Yucca nuclear test of the Hardtack I series on 28 April 1958. In that test,

3021-481: The weapon's power to be estimated, and the bearing to be indicated. It had a range of 150 miles (240 km) in good visibility. From 1974 AWDREY units were used together with a device known as DIADEM (Direction Indicator of Atomic Detonation by Electronic Means) which measured the electromagnetic pulse (EMP) generated by an explosion. The instruments were in constant operation (state of readiness) between 1968 and 1992 and tested daily by full-time ROC officers. AWDREY

3078-588: Was communicated informally to US scientists. For a few years US and Russian scientists collaborated on the HEMP phenomenon. Funding was secured to enable Russian scientists to report on some of the Soviet EMP results in international scientific journals. As a result, formal documentation of some of the EMP damage in Kazakhstan exists, although it is still sparse in the open-scientific literature. For one of

3135-519: Was designed, built and maintained by the Atomic Weapons Establishment at Aldermaston . The design was tested for performance and accuracy using real nuclear explosions at the 1957 Kiritimati (or Christmas Island) nuclear weapon trials, after being mounted on board a ship. Although a single AWDREY unit could not differentiate between a nuclear explosion and a lightning strike, the units were installed sufficiently far apart that

3192-563: Was relatively weak compared to what could be produced with a more intense pulse, and in part due to the relative ruggedness (compared to today) of Hawaii's electrical and electronic infrastructure in 1962. The relatively small magnitude of the Starfish Prime EMP in Hawaii (about 5.6 kilovolts/metre) and the relatively small amount of damage (for example, only 1% to 3% of streetlights extinguished) led some scientists to believe, in

3249-474: Was vertically polarized. In spite of these many differences, the unique EMP results were dismissed as a possible wave propagation anomaly. The high-altitude nuclear tests of 1962, as discussed below, confirmed the unique results of the Yucca high-altitude test and increased the awareness of high-altitude nuclear EMP beyond the original group of defense scientists. The larger scientific community became aware of

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