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  • Thursday, February 26, 2009

    More information on EMP from high altitude tests, plus the threat from very low yield terrorist weapons with massively enhanced EMP output

    Above: Dr. Michael P. Bernardin of Los Alamos headed the Joint DoD/DOE Phase 2 Feasibility Study of a High Power Radio Frequency (HPRF) Weapon, which focused on the feasibility and effectiveness of developing an HPRF (i.e. enhanced EMP) weapon for offensive purposes. Consequently, the U.S. has designed low yield nuclear weapons with massively enhanced EMP output. (See also the reports on that project linked here, here, here, here, here, here, here, here, here, here, here, here, here, here, here, and here.) The STARFISH nuclear test (the EMP effects of which are described below in detail, with original newspaper cuttings) only emitted 0.1% of its energy as the prompt gamma rays that cause the peak EMP when hitting the atmosphere. However, that 1.4 megaton device was a particularly inefficient design from the point of view of maximising prompt gamma ray emission. Prompt gamma rays result from fission and from neutron collisions with suitable tamper materials. It is possible to design nuclear weapons to minimise the shielding of the fissile core in a preferential direction (say downwards) by the use of cylindrical or linear implosion techniques. This enhances the fraction of the prompt gamma rays that can escape from the core in those directions, optimising EMP effects.

    Honolulu Advertiser newspaper article dated 9 July 1962 (local time):

    'The street lights on Ferdinand Street in Manoa and Kawainui Street in Kailua went out at the instant the bomb went off, according to several persons who called police last night.'

    New York Herald Tribune (European Edition), 10 July 1962, page 2:

    'Electrical Troubles in Hawaii

    'In Hawaii, burglar alarms and air-raid sirens went off at the time of the blast. A few street lights were extinguished and others lighted. There was no immediate explanation for the electrical malfunctions.'

    A 'Quick Look' at the Technical Results of Starfish Prime, August 1962, p. A1-27:

    'The time interval detectors used on Maui went off scale, probably due to an unexpectedly large electromagnetic signal ...'

    J. Robertson, 'US Seeks Answers to A-blast Oddity', Electronic News, 30 October 1967, page 22:

    'WASHINGTON. - The quiet predawn in Honolulu ... was shattered by the simultaneous pealing of hundreds of burglar alarms. At the same instant, circuit breakers on the power lines started blowing like popcorn.'

    U.S. Defense Civil Preparedness Agency (DCPA), DCPA Attack Environment Manual, Chapter 4, What the Planner Needs to Know about Electromagnetic Pulse, U.S. Department of Defense, report CPG 2-1A4, June 1973, panels 2 and 5:

    'Few people have ever heard of EMP or 'radioflash'. It might be called the 'forgotten' nuclear weapon effect. It was not mentioned in either the 1950 'Effects of Atomic Weapons' or the 1957 'Effects of Nuclear Weapons'. EMP was first mentioned in a chapter on radio and radar effects in the 1962 version of the 'Effects of Nuclear Weapons' but the description was brief and no hint was given as to its damaging effects. ... Anyone who has hooked up an old radio to a bedspring knows that almost any metallic object can collect energy from radio waves. Any long wire can pick up the energy in the electromagnetic field and then deliver it in the form of current and voltage pulses to the attached equipment. The larger or longer the conductor, the greater the amount of energy collected. ... Typical collectors of EMP energy include long exposed cable runs, piping or conduit, large antennas, metallic guy wires, power and telephone lines, and even shallow-buried pipes and cables, long runs of electrical wiring in building, and the like. ... The failure of approximately 30 strings of street lights on Oahu at the time of the Starfish detonation about 750 miles away over Johnston Island was the most publicized effect during the weapons test series Operation FISHBOWL in 1962.'

    Dr John Malik, page 31, Chapter 7 of H. Hoerlin's US high-altitude test experiences, Los Alamos Scientific Laboratory, report LA-6405 (1976):

    Starfish produced the largest fields of the high-altitude detonations; they caused outages of the series-connected street-lighting systems of Oahu (Hawaii), probable failure of a microwave repeating station on Kauai, failure of the input stages of ionospheric sounders and damage to rectifiers in communication receivers. ... The failures observed were generally in the unprotected input stages of receivers or in rectifiers of electronic equipment; transients on the power line probably caused the rectifier failures. There was one failure in the unprotected part of an electronic system of the LASL Optical Station on top of Mount Haleakala on Maui Island. With the increase of solid-state circuitry over the vacuum-tube technology of 1962, the susceptibility of electronic equipment will be higher, and the probability of more problems for future detonations will be greater.’

    Samuel Glasstone and Philip J. Dolan, The Effects of Nuclear Weapons, 3rd ed., 1977, pp. 522-4:

    'A number of failures in civilian electrical systems were reported to have been caused by the EMP from the high-altitude test explosions conducted in the Johnston Island area of the Pacific Ocean in 1962. One of the best authenticated cases was the simultaneous failure of 30 strings (series-connected loops) of street lights at various locations on the Hawaiian island of Oahu, at a distance of some 800 miles from ground zero. The failures occurred in devices called "fuses" which are installed across the secondaries of transformers serving these strings; the purpose of the fuses is to prevent damage to the lighting system by sudden current surges. Similar fuses associated with individual street lights were not affected. It was also reported that "hundreds" of burglar alarms in Honolulu began ringing and that many circuit breakers in power lines were opened. These occurrences probably resulted from the coupling of EMP energy to the lines to which the equipment was connected and not to failure of the devices themselves. No serious damage occurred since these items are among the least susceptible to the EMP. ... Tests with EMP simulators have shown that a very short pulse of about 10-7 joule may be sufficient to damage a microwave semiconductor diode, roughly 5 x 10-2 will damage an audio transistor, but 1 joule would be required for vacuum tube damage. Systems using vacuum tubes only would thus be much less sensitive to the EMP than those employing solid-state components.'

    Dr Anthony Trippe, 'The Threat of Electromagnetic Pulse,' National Defense, December 1984:

    'With every new generation of electronics, more components are packed into smaller spaces ... This high device-packing density inhibits the ability of the circuit to conduct away the heat which results from the typically intense, short voltage and current flows generated by an EMP.'

    Charles N. Vittitoe, Did high-altitude EMP (electromagnetic pulse) cause the Hawaiian streetlight incident?, Sandia National Labs., Albuquerque, NM, report SAND-88-0043C; conference CONF-880852-1 (1988), page 3:

    'Several damage effects have been attributed to the high-altitude EMP. Tesche notes the input-circuit troubles in radio receivers during the Starfish [1.4 Mt, 400 km altitude] and Checkmate [7 kt, 147 km altitude] bursts; the triggering of surge arresters on an airplane with a trailing-wire antenna during Starfish, Checkmate, and Bluegill [410 kt, 48 km altitude] ...' (The EMP affected aircraft were about 300 kilometers away from the detonations.)

    Dr Lowell Wood, Senior Staff Member, Lawrence Livermore National Laboratory, testimony on pages 6-16 of U.S. Congressional Field Hearings, ELECTROMAGNETIC PULSE (EMP): SHOULD THIS BE A PROBLEM OF NATIONAL CONCERN TO PRIVATE ENTERPRISE, BUSINESSES SMALL AND LARGE, AS WELL AS GOVERNMENT?, JUNE 1, 1999:

    'This EMP also shut down radio stations and street lighting systems, turned off cars, burned out telephone systems, and wreaked other mischief throughout the Hawaiian Islands, nearly 1000 miles distant from ground zero. ...

    'However, it should be realized that it is also possible to do that with specially designed weapons whose yield would be much, much, much less than a megaton. ... the EMP yield of a nuclear weapon is not at all well correlated necessarily with its explosive yield. You can get much larger yields with a specially designed 10 kiloton device, you can get much larger electromagnetic pulses with a specially designed kiloton device than you can with a crudely designed 10 megaton device. The EMP output of a device, its EMP consequences, are very poorly related to its total explosive yield. ... in general, for a given class of device, as you increase the yield, the EMP consequences of it will increase, but the point that I am trying to make is that if you hop from class to class of nuclear weaponry, you can find classes in which the EMP yield can be very, very large, even though the explosive yield is very modest indeed.'

    (In his written testimony on page 70 of those 1999 hearings, Dr Lowell Wood states: 'During the '70s, I served on the Defense Nuclear Agency's Scientific Advisory Group on Effects (SAGE), the DoD's senior technical review group concerned with nuclear electromagnetic pulse, as well as all other military nuclear issues having a technical character. In the late '70s and early '80s, I worked on 'Third Generation' nuclear weaponry, a major component of which was nuclear explosive-driven generators of electromagnetic pulses of potentially greatly increased efficiency and military effectiveness ...')

    At 11 pm on 8 July 1962 (local time, Hawaii), 300 streetlights in 30 series connected loops (strings) were fused by the EMP from the Starfish nuclear test, detonated 800 miles away and 248 miles above Johnston Island. (A previous blog post with photographs of the Starfish test seen both through cloud from Hawaii and also from the observation KC-135 aircraft above the cloud, is linked here.) This is estimated to be only 1-3% of the total number of streetlights on Oahu, because the peak EMP of 5,600 volts/metre at 800 miles from Starfish was only just enough to burn out the heavy-duty fuses used in the streetlights (even intense local lightning storms on Hawaii only caused the failure of typically 4 strings of streetlights, so the failure of 30 strings indicated exceptionally intense EMP-induced currents).

    In a much earlier blog post (linked here), the 1962 EMP damage effects from high altitude explosions (including three Russian high altitude tests of 300 kt each with differing altitudes of burst) were examined in as much detail as possible.

    Then, in a more recent blog post (linked here), freshly released information from Dr Carl Baum's EMP notes series was given and discussed, including Dr Conrad Longmire's investigation (Note 353 of March 1985, EMP on Honolulu from the Starfish Event) which assessed the EMP field strength at Hawaii, which peaked after 100 nanoseconds at 5,600 volts/metre. (It is curious that this report was not published back in 1985, when there was no data publically available correlating peak field strength with nuclear test yield and burst altitude! The EMP was only just entering public attention in 1985, e.g., in that year's James Bond movie A View to a Kill, which features Roger Moore as 007 who is sent on a mission to find who leaked the secret blueprint of a totally fictional EMP-proof microchip to the enemy. The year before, in 1984, Whitley Strieber and James Kunetka had penned the first fictional EMP disaster story, War Day published by Holt, Rinehart and Winston, New York, in which the U.S.S.R. launches a pre-emptive EMP attack on the U.S. in response to a U.S. decision to build a defensive anti-ballistic missile system: '... in less than a second a silent and invisible EMP burst had plunged people from the twentieth century to the Middle Ages ... they knew absolutely nothing of what was happening beyond the borders of their own towns.' Civil defense writer Dr Bruce Clayton also in 1984 warned of the risk of a subversive EMP attack in his book Thinking About Survival, Paladin Press, Colorado: 'An orbiting Soviet "weather" satellite built around a 20 Mt warhead could explode over us with literally zero warning time.' In May 1971 the U.S. Office of Civil Defense issued report TR-61-A, EMP Protection for Emergency Operating Centres. However, nearly fifteen years later, in February 1986, only 110 out of 3,000 U.S. civil defence Emergency Operating Centres had been protected against EMP, i.e. 3.7%, and only 125 out of 2,771 U.S. Emergency Broadcast System radio stations had been similarly protected, i.e. 4.5%.)

    Longmire stated on page 12 of his report:

    'We see that the amplitude of the EMP incident on Honolulu [which blew the sturdy electric fuses in 1-3% of the streetlamps on the island] from the Starfish event was considerably smaller than could be produced over the northern U.S. ... Therefore one cannot conclude from what electrical and electronic damage did not occur in Honolulu that high-altitude EMP is not a serious threat. In addition, modern electronics is much more sensitive than that in common use in 1962. Strings of series-connected street lights did go out in Honolulu ... sensitive semiconductor components can easily be burned out by the EMP itself, 10-7 Joules being reportedly sufficient.'

    This 5,600 v/m figure allows definite correlations to be made between the observed effects and the size of the EMP field, which is a massive leap forward for quantitative civil defence assessments of the probable effects of EMP.

    Above: USSR Test ‘184’ on 22 October 1962, ‘Operation K’ (ABM System A proof tests) 300-kt burst at 290-km altitude near Dzhezkazgan. Prompt gamma ray-produced EMP induced a current of 2,500 amps measured by spark gaps in a 570-km stretch of 500 ohm impedance overhead telephone line to Zharyq, blowing all the protective fuses. The late-time MHD-EMP was of low enough frequency to enable it to penetrate the 90 cm into the ground, overloading a shallow buried lead and steel tape-protected 1,000-km long power cable between Aqmola and Almaty, firing circuit breakers and setting the Karaganda power plant on fire.


    Because EMP is a pulse typically a million times more intense than the typical 10 mV/m strength of radio transmissions at similar frequencies, a person in contact with an ungrounded sizable metallic object during EMP can receive a severe electric shock (Glasstone and Dolan, discussion on page 521 and illustration on page 530). A study of direct biological EMP effects cited by Glasstone and Dolan, called 'Absence of electromagnetic pulse effects on monkeys and dogs' (written by F. G. Hirsch and A. Bruner and published in the Journal of Occupational Medicine, vol. 14, 1972, issue 5, pp. 380-6), notes that monkeys and dogs were unaffected by EMP but that the rodents they exposed (not mentioned in the title) were seriously startled each time an EMP radiated. Hirsch and Bruner observed direct effects of EMP on 2 monkeys, 4 dogs, and 7 rats with repeated exposures to nanosecond rise-time pulsed fields of 300-600 kV/m. One of the monkeys had been previously trained to press buttons and the rats had been trained to correctly find their way around a maze. The animals were all carefully observed, and the trained monkey and rats were intelligence-tested using the buttons and maze. No prompt or delayed medical or intelligence effects occurred in the monkeys or dogs, but the rats were startled and stopped for 5-16 seconds after each 600 kV/m EMP, and 30 minutes after exposure they had hesitancy at decision points in the maze, and made errors. They completely recovered their maze-solving skill a day later. Hirsch and Bruner did not offer an explanation.

    But the effects on the rats was apparently because migratory animals, including rodents and birds, appear to use the tiny magnetite crystals in their brains to enable them to sense or 'see' the direction of magnetic field lines, which is the mechanism by which birds can navigate successfully during migration over vast distances of empty ocean when there is cloud cover to prevent the direction of the sun being available. The magnetite crystals may be temporarily upset by the magnetic field component of an intense EMP, which is a mechanism of interest since a human being contains 'a minimum of 5 million single-domain crystals [of magnetite, Fe3O4] per gram for most tissues in the brain', according to the paper by J. L. Kirschvink et al., 'Magnetite biomineralization in the human brain', Proceedings of the National Academy of Sciences, vol. 89 (1992), issue 16, pp. 7683-7. More data is linked here, here, here, here, here and here. A 1990 review of EMP health effects is here, and there is also a paper on relatively long-term EMP effects in dogs by C. U. I. Yufang et al., published in the Chinese Medical Journal (vol. 114, 2001, issue 10, pp. 1019-21), 'Effect and mechanism of EMP on peripheral lymphocytes in dogs' which finds that EMP can damage lymphocytes in dogs for up to 120 days after exposure, and also mentions other Chinese studies which indicate that EMP effects on the brains of mice may affect their learning and memory functions.

    Induced currents in animal and human nerves from EMP are insignificant, but a strong pulsed magnetic field rotates the many very small magnetite crystals actually found in animal and human brains, that can be used by animals for sensing direction changes relative to the earth’s magnetic field. Monkeys and dogs rely on smell, sight, and memory for navigation, but seasonally migrating birds, turtles, and even dolphins and whales travel large distances across oceans and may use earth’s magnetic field for guidance. Rats are small in comparison to wild grass and brush, so they may have used the magnetic field for long-distance seasonal navigation on land. On average, the earth’s magnetic field poles reverse once every 220,000 years, so animals with short generation times, and hence more evolution since the last reversal, will be able to use the earth’s magnetic field more accurately for migration than larger animals with longer generation times (whales often get lost, unlike birds).

    Above: This diagram plots typical peak radiated EMP signals from 1 kt and 1 Mt bombs as a function of burst altitude for an observer at a fixed distance of 100 km from ground zero. If we ignore the weak-field late-time MHD-EMP mechanism (which takes seconds to minutes to peak and has extremely low frequencies, but is important for very long buried cables, because low frequencies penetrate more deeply into the ground than higher frequencies as we shall see later) there are two EMP mechanisms determining the peak radiated EMP as a function of burst altitude: 'electric dipole' EMP and 'magnetic dipole' EMP. For very low burst altitudes, the major cause of EMP radiation is the asymmetry due to the Earth's surface (there is net upward Compton current, due to the ground absorbing downward-directed gamma rays). This is like the vertical 'electric dipole' radio transmitter antenna radiating radio waves horizontally (at right angles to the direction of the time-varying current) when the vertical current supplied to the antenna is varied in time. Dolan's DNA-EM-1 states that a 1 Mt surface burst radiates a peak EMP of 1,650 v/m at 7.2 km distance (which falls off inversely with distance for greater distances). As the burst altitude is increased above about 1 km or so, this ground asymmetry mechanism becomes less important because the gamma rays take 1 microsecond to travel 300 metres and don't reach the ground with much intensity; in any case by that time the EMP has been emitted by another 'electric dipole' mechanism of asymmetry, the fall in air density with increasing altitude, which is particularly important for bursts of 1-10 km altitude.

    Finally, detonations above 10 km altitude send gamma rays into air of low density, so that the Compton electrons have the chance (before hitting air molecules!) to be deflected immensely by the Earth's magnetic field; this 'magnetic dipole' deflection makes them emit synchrotronic radiation which is the massive EMP hazard from space bursts whose theory was discovered by Dr Conrad Longmire only after the Starfish test on 9 July 1962. After the intense Starfish 'magnetic dipole' EMP waveform was measured by Richard Wakefield in an aircraft, the Americans started looking for the weaker version of the 'magnetic dipole' EMP from normal megaton air bursts dropped from B-52 aircraft (at a few km altitude to prevent local fallout) in the final Pacific testing series of 1962 before the test ban treaty. But in fact, the intense, high frequency, fast-rising 'magnetic dipole' EMP had already been measured from the 1.7 kt balloon-lofted 99 kg W-25 air defense warhead test Hardtack-Yucca 26 km altitude burst on 28 April 1958, and specifically commented upon in detail in 1959 on page 347 of Interim Test Report ITR-1660-(SAN):

    'Shot Yucca ... [EMP] field strength at Kusaie indicated that deflection at Wotho would have been some five times the scope limits... The wave form was radically different from that expected. The initial pulse was positive, instead of the usual negative. The signal consisted mostly of high frequencies of the order of 4 Mc, instead of the primary lower-frequency component [electric dipole EMP] normally received ...'.

    Yet despite this prescient report discussing the massive high-frequency EMP from a mere 1.7 kt burst at 26 km altitude, it was simply ignored as an 'anomaly'.

    Above: the severe high frequency EMP (five-times the close-in oscilloscope limits, as shown by extrapolation from measurments recorded at vast distances) from the mere 1.7 kilotons high-altitude (26 km) balloon-carried Yucca shot in April 1958 produced the first clear evidence that should have suggested the 'magnetic dipole' EMP mechanism, but the waveform warning - despite attracting attention in the secret 'Interim Test Report' ITR-1660 - went unheeded and the truth only dawned more than four years later when Wakefield in an aircraft measured the intense 'magnetic dipole' EMP signal from Starfish.

    Until Wakefield's measurement at Starfish they usually measured EMP from air bursts using oscilloscopes set to measure EMP with durations of tens of microseconds. (In fact, this was common at Starfish, where most of the measurements failed or gave vertical spikes which went off scale on oscilloscopes set to excessively high sensitivity and slow sweep speed.) By increasing the sweep speed to sub-microsecond times (nanoseconds), they were then finally able to see the positive pulse of 'magnetic dipole' EMP even in sea level air bursts at relatively low altitude, typically peaking at 18 v/m at 70 nanoseconds for 20 km distance as in the following nuclear test measurement from 1962 in 1963 Los Alamos report LA-2808:

    Above: the long-duration, weak field electric-dipole EMP waveform due to vertical asymmetry from a typical air burst, measured 4,700 km from the Chinese 200 kt shot on 8 May 1966.

    Note 353 of March 1985 by Dr Conrad L. Longmire, 'EMP on Honolulu from the Starfish Event' states that: 'the transverse component of the geomagnetic field, to which the EMP amplitude is approximately proportional, was only 0.23 Gauss. Over the northern U.S., for some rays, the transverse geomagnetic field is 2.5 times larger.' (In note 354, page 18, he and others state that the magnetic field at the burst point for a nuclear explosion over the central United States is 0.56 Gauss with a dip angle of 70 degrees from the horizontal.) For Starfish shot, Longmire uses 400 km burst altitude, 1.4 Mt total yield and 1.4 kt (i.e. 0.1%) prompt gamma ray yield with a mean gamma ray energy of 2 MeV. Honolulu, Hawaii (which was 1,450 km from the Starfish bomb detonation point 400 km above Johnston Island) had a magnetic azimuth of 54.3 degrees East and a geomagnetic field strength in the source region of 0.35 gauss (the transverse component of this was 0.23 Gauss).

    Hence for the Starfish nuclear test shot of 1.4 megatons at 400 km altitude nearly directly over Johnston Island, the maximum peak EMP (which occurred near ground zero because the burst was nearly over the magnetic equator) was on the order 14,000 v/m, the peak EMP at Honolulu (1,300 km or 800 miles from ground zero) was 5,600 v/m and the peak EMP at the horizon radius of 2,200 km (1,400 statute miles) was on the order of 3,500 v/m. EMP of low frequencies extended past the horizon, but high frequencies were cutoff beyond the horizon. The Starfish EMP was recorded 13,000 km away in England by the Atomic Weapons Establishment for example, but the signal was grossly altered at such a distance, and at much lower frequencies and intensity than the close-in EMP within the horizon radius. VHF and UHF frequencies are line-of-sight dependent because the upward component gets absorbed by the ionosphere or at UHF escapes through the ionosphere into outer space. Only the lower frequencies scatter back off the ionosphere and are returned to earth, extending EMP and other radio frequency signal transmission beyond the horizon. Below are the prompt EMP waveforms measured in California, 5,400 km away from Starfish (1.4 Mt, 400 km altitude) and Kingfish (410 kt, 95 km altitude) space shots above Johnston Island in 1962:

    In an earlier blog post I analyzed the declassified curve of Richard L. Wakefield's originally secret measurement of the Starfish EMP in a C-130 aircraft 1,400 km East-South-East of the detonation, and it is surprising to find that on 11 January 1963, the American journal Electronics Vol. 36, Issue No. 2, had openly published the distant MHD-EMP waveforms from all five 1962 American high altitude detonations Starfish, Bluegill, Kingfish, Checkmate, and Tightrope: 'Recordings made during the high-altitude nuclear explosions over Johnston Island, from July to November 1962, shed new light on the electromagnetic waves associated with nuclear blasts. Hydrodynamic wave theory is used to explain the main part of the signal from a scope. The results recorded for five blasts are described briefly. The scopes were triggered about 30 micro-seconds before the arrival of the main spike of the electromagnefic pulse.' As explained in a previous blog post on EMP damage from low altitude nuclear tests, EMP or 'radioflash' as it was called was still widely regarded as a curiosity with no importance except as a means to detect and locate high altitude bursts in 1963, when most electronics in use were still based on the hardy high-voltage, high-current triode vacuum tube and could therefore survive 1-2 Joules of EMP energy, which is a million times what the silicon microchip (invented in the late 1950s and only widely used from the 1970s) can take. EMP also became more of a problem when it was finally recognised that long overhead power cables, longer than existed on the Hawaiian islands, could couple immense currents and burn up large transformers.

    For the same Starfish bomb detonated over the centre of the United States, due to the fact that the earth's magnetic field is stronger there than over Johnston Island, the peak EMP due to the deflection of Compton electrons by the earth's magnetic field would be about 2.4 times stronger than in the case of the Starfish test. I.e. the maximum peak EMP near the detonation would be 34,000 v/m and the peak EMP at the horizon radius of 2,200 km (1,400 statute miles) would be 8,400 v/m. This radius, for a burst over Topeka in the centre of the United States, would cover both the East and the West coast of America (see map from DNA-EM-1 chapter 7 below).

    In testimony to U.S. Congress, it has been published that for computer equipment which is not connected to mains power or other long conductors (i.e., wireless laptops using battery power, or turned off) a low frequency direct EMP signal will cause an increasing risk of temporary disruption (see the calculator video on U-tube, above) for peak field strengths of 3,000–8,000 v/m (improbable at 3,000 v/m; probable at 8,000 v/m) and damage at 7,000–20,000 v/m (improbable at 7,000 v/m; probable at 20,000 v/m) as confirmed by testing of computer equipment in September 1998.

    These data do not include damage for equipment connected to mains power supply or other long conductors which pick up massive surges. Much smaller EMP fields damage those! It seems that these damage figures apply to low frequency EMP, not the highest frequency: see the U.S. Congressional Hearing before the Military Research and Development Subcommittee of the Committee on Armed Services, House of Representatives, Electromagnetic Pulse Threats to U.S. Military and Civilian Infrastructure, 7 October 1999, Curt Weldon, Chairman. Stanley Jakubiak, the Deputy Chief of the Command Centre’s Division, Joint Chiefs of Staff, presented data on the effects of EMP on commercial off-the-shelf computers: ‘When the field strengths get above 8,000 V/m, the risk that there will be upset is more probable [than at 3,000 v/m]. In the range of 7,000-20,000 V/m, there is a possibility that some equipment will be damaged. Above the 20,000 V/m range, the damage is most likely probable, although some equipment will even perform above that level ...’ However, another expert witness argued: ‘the studies, and in particular the Army study to which Mr Jakubiak made extensive reference, has in its notes an indication that cables were not connected ... If you don’t have cables connected during EMP testing, you really haven’t tested under circumstances which are at all realistic ...the study notes also indicated that the equipment was sometimes powered up and sometimes was not ... reverse breakdown of semiconductors depends very strongly in ... the equipment being powered up ... if the equipment is powered up, it is the power supply itself whose energy tends to destroy the compromised semiconductors ... the most striking thing about these tests was that they used only the lowest frequency component of the EMP threat spectrum ... They did not use ... the high frequency component that tends to be especially penetrating of enclosures, especially unforgiving of cracks ... and what, in tests conducted by the Defense Nuclear Agency over the decades, has been the most damaging to the most types of electronic equipment.’

    'An EMP attack will certainly immediately disable a portion of the 130 million cars and 90 million trucks in operation in the United States. ... Our test results show that traffic light controllers will begin to malfunction following exposure to EMP fields as low as a few kV/m, thereby causing traffic congestion. Approximately 10 percent of the vehicles on the road will stop, at least temporarily, thereby possibly triggering accidents, as well as congestion, at field levels above 25 kV/m.' - EMP Commission report, 'Critical National Infrastructures', 2008, page 116.

    ‘The ARTCCs [air route traffic control centers] are composed, in part, of computer networks based on commercial components. Similar components have been EMP tested and have manifested latching upsets (requiring manual intervention to restore function) beginning in the 4 kV/m peak field range. Permanent damage has been observed in the 8 kV/m range but is more prevalent above 15 kV/m. Based on similarity, it is anticipated that ARTCCs will begin to manifest loss of function following EMP exposure to peak fields as low as 4 kV/m; but functions will not be seriously degraded unless exposed to peak fields in excess of 15 kV/m.’ – EMP Commission, report on ‘Critical National Infrastructures’, 2008, page 126.
    Robert H. Vandre, Janis Klebers, Frederick M. Tesche and Janie P. Blanchard, Minimising the Effects of Electromagnetic Pulse (EMP) on Field Medical Equipment (published in Military Medicine, vol. 1584, 1993, pp. 233-6) states:
    'Electromagnetic Pulse (EMP) simulator testing and computer simulations show that a field commander can expect approximately 65% of his unprotected electronic medical equipment to be damaged by a single nuclear detonation as far as 2,200 km away. ... The principal effect of EMP is to deposit damaging energy into circuit components sufficient to cause semiconductor burnout. That is, a critical junction in a transistor or an integrated circuit literally melts and is permanently damaged. Thus, service provided by equipment with affected components stops instantly. Measurements of the response of a 100 metre power cable when exposed to a simulated EMP coupling with calculations of the electromagnetic response of a typical field medical treatment facility's power grid indicate that one can expect currents and voltages as great as 120 amps and 12,000 volts, respectively to pass through equipment that is plugged into the power cable.'
    These predictions don't apply to the national power grid which has very long conductors and powerlines high off the ground, that pick up massive power surges. These predictions are instead just for short (100 metre long) power cables from a diesel generator on a military field hospital to the medical ward. Far worse effects would in general occur to the civilian medical infrastructure than to the short cables used for military field medical equipment power supplies. The report notes that the worst effects from prompt early-time EMP (it ignores late time MHD-EMP altogether, which is very serious for ground and even buried cables) occur for cables on overhead powerlines, since a powerline at 13 feet above the ground will pick up almost 20 times as much EMP as one laid on the ground. In addition, it notes that the geomagnetic field alignment means that East-West aligned power cables pick up 2.4 times more EMP energy than those aligned North-South.

    Starfish streetlights investigation

    Dr Baum (who has an important and interesting overview of EMP here, although it misses out some early important pieces of the secret history of EMP in the table of historical developments) has made available the report by Charles N. Vittitoe, 'Did high-altitude EMP (electromagnetic pulse) cause the Hawaiian streetlight incident?', Sandia National Labs., Albuquerque, NM, report SAND-88-0043C; conference CONF-880852-1 (1988).

    Vittitoe on page 3 states:


    This refers to the KC-135 aircraft that filmed the tests from above the clouds, approximately 300 kilometers away from the detonations. (C-130 aircraft were also used for EMP measurements. E.g., the only decent measurement of the Starfishh early-time EMP curve was from a C-130 aircraft at a distance of 1,400 from ground zero, South of the Hawaiian islands, by Richard Wakefield of Los Alamos National Laboratory.)

    The reference Vittitoe gives is:

    'G. S. Parks, Jr., T. I. Dayharsh, and A. L. Whitson, A Survey of EMP Effects During Operation Fishbowl, DASA [U.S. Department of Defense's Defense Atomic Support Agency, now the DTRA] Report DASA-2415, May 1970 (Secret - Restricted Data).'

    Vittitoe then quotes Glasstone and Dolan's statement in The Effects of Nuclear Weapons:

    'One of the best authenticated cases was the simultaneous failure of 30 strings (series-connected loops) of street lights at various locations on the Hawaiian island of Oahu, at a distance of 800 miles from ground zero.'
    The detonation occurred at 11pm 8 July 1962 (local time) for Hawaii, so the flash was seen across the night sky and the failure of some street lights was observed. Vittitoe usefully on page 5 quotes the vital newspaper reports of the EMP damage, the first of which is the most important since it was published the very next day following the explosion:


    - Honolulu Advertiser newspaper article dated 9 July 1962 (local time; this amazing Starfish EMP effects article was reprinted in the Tuesday 21 February 1984 edition, celebrating the 15th anniversary of Hawaiian statehood to the U.S.A.).

    A technical investigation was then done by the streetlights department into the causes of the 300 streetlight failures, and then on 28 July 1962, the Honolulu Star-Bulletin newspaper article 'What Happened on the Night of July 8?' by Robert Scott (a professor at Hawaii University) reported that a Honolulu streetlight department official attributed the failure of the streetlights in nine separate areas to blown fuses, due to the energy released by the bomb test being coupled into the power supply line circuits (see illustration above; the street lamps were attached to regular overhead power line poles, allowing EMP energy to be coupled into the circuit).

    On 8 April 1967, Honolulu Star-Bulletin newspaper published an article by Cornelius Downes about the blown fuses: 'small black plastic rings with two discs of lead separated by thin, clear-plastic washers.'

    Vittitoe reports that the streetlight officials found that: 'The failure of 30 strings was well beyond any expectations for severe [electrical lightning] storms (where ~4 failures were typical).'

    Vittitoe then gives a full analysis of the physics of how the EMP calculated by Longmire turned off the streetlights, and confirms that the EMP was responsible for the fuse failures.

    Interestingly, Vittitoe co-authoried the 2003 paper Radiative Reactions and Coherence Modeling in the High-Altitude Electromagnetic Pulse with Dr Mario Rabinowitz, who has kindly corresponded with me by email on the subjects of EMP and also particle physics (although Dr Rabinowitz did not mention this EMP paper he co-authored with Vittitoe!).

    Above: EMP Commission reports give these diagrams of the EMP effects of prompt (fast pulse) EMP and MHD-EMP (slow pulse).
    Above: map of areas covered by EMP from nuclear detonations at various heights of burst (HOB's) over the United States of America, taken from the previously secret Capabilities of Nuclear Weapons, DNA-EM-1, Chapter 7.

    Above: K. D. Leuthauser's A Complete EMP Environment Generated by High-Altitude Nuclear Bursts, Note 363, October 1992, gives this EMP pattern for a 10 kt prompt gamma ray yield (which would be emitted by a typical thermonuclear weapon yield of about 10 megatons) at 200 km altitude for 50 degrees north latitude (67 degrees magnetic dip angle, 0.47 Gauss magnetic field strength). Peak electric fields on the Earth's surface span from 56,000 v/m some 300 km south of the detonation to 26,000 v/m at the horizon radius some 1,600 km away. Increasing the burst altitude makes the EMP field strengths weaker, but a larger area is covered so there is a trade-off involved. (However, for very long power-lines, there is little difference in end effect because the weaker EMP field over a bigger area will enable a similar amount to be picked up as a strong field over a more limited area of the Earth's surface.) Another controversy is the effect of nuclear yield on the EMP, because to get a fixed peak EMP on the ground, you would generally need to increase the bomb yield if you increase the burst altitude. However, this is not true for the prompt gamma rays that cause the intense peak EMP, since prompt gamma rays carry off 3.5% of the energy of nuclear fission but the Starfish bomb released only 0.1% of its yield as prompt gamma rays into space! A low yield bomb with a very thin casing (or a cylindrical-implosion device like Greenhouse-George, with the end of the fissile cylinder exposed and facing downwards) could in principle release up to 3.5%/0.1% = 35 times more prompt gamma rays per kiloton of total yield in a preferred direction (say downwards) than than resulting from the Teller-Ulam Starfish device! I.e., a 40-kt pure fission cylindrical-implosion bomb could, in principle, produce an identical early-time EMP from the 1.4 Mt Starfish test at 400 km altitude in 1962 (and if the burst was over America, the EMP fields would be 2.4 times those from Starfish due to the increased strength of the Earth's magnetic field at northern latitudes, closer to the pole). Furthermore, in addition to using cylindrical or linear implosion to avoid shielding the prompt gamma rays from the core with a lot of TNT in spherical implosion, there are obviously other things you can do to further enhance the initial gamma ray pulse, such as selecting tamper materials around the core that will emit gamma rays when struck by neutrons (this happens with most tampers, but when you specifically set out to maximise this effect with the optimum geometry and scattering materials, you can cause a massive enhancement of gammas from case-scattered neutrons):

    '... the point is that the EMP yield of a nuclear weapon is not at all well correlated necessarily with its explosive yield. You can get much larger yields with a specially designed 10 kiloton device, you can get much larger electromagnetic pulses with a specially designed kiloton device than you can with a crudely designed 10 megaton device. The EMP output of a device, its EMP consequences, are very poorly related to its total explosive yield. ... the point that I am trying to make is that if you hop from class to class of nuclear weaponry, you can find classes in which the EMP yield can be very, very large, even though the explosive yield is very modest indeed.' - Dr Lowell Wood, Senior Staff Member, Lawrence Livermore National Laboratory, testimony on page 16 of U.S. Congressional Field hearings, ELECTROMAGNETIC PULSE (EMP): SHOULD THIS BE A PROBLEM OF NATIONAL CONCERN TO PRIVATE ENTERPRISE, BUSINESSES SMALL AND LARGE, AS WELL AS GOVERNMENT?, JUNE 1, 1999.

    Sandia nuclear weapons physicist Dr Wood isn't talking out of his hat, because he has actually seen how easy it is to design directed EMP nuclear weapons of very low yield which work. On page 70 of those 1999 hearings, Dr Lowell Wood states: 'In the late '70s and early '80s, I worked on 'Third Generation' nuclear weaponry, a major component of which was nuclear explosive-driven generators of electromagnetic pulses of potentially greatly increased efficiency and military effectiveness ...'

    During the U.S. Congressional Hearing before the Military Research and Development Subcommittee of the Committee on Armed Services, House of Representatives, Electromagnetic Pulse Threats to U.S. Military and Civilian Infrastructure, 7 October 1999 (Curt Weldon, Chairman), Dr Michael Bernardin of Los Alamos National Laboratory testified that the X-ray emissions by the primary stage in some two-stage thermonuclear weapons cause a pre-ionisation of the air below the detonation, which quickly shorts out (via the free electron conduction current, possible only in conductive, ionized air) the subsequent Compton current due to gamma rays emitted by the secondary stage in the weapon, thereby reducing the maximum EMP to only 25,000 V/m. This X-ray effect is dependent on nuclear weapon design, since the X-rays are not very penetrating and can be shielded to create 'shadows' by weapon components or by the missile delivery system. Let's consider the physics of magnetic dipole EMP generation in detail.

    Above: notice that the direction of the prompt gamma rays (travelling at the velocity of light) is the same as the direction of the radiated EMP that are created (also travelling at the velocity of light). This fact means that the high altitude EMP can be treated very simply, because the production of EMP occurs in-step with the shell of prompt gamma rays travelling through the deposition layer from 20-40 km altitude: successive deflections by the earth's magnetic field of Compton electrons (produced by the light-velocity gamma rays hitting air molecules) cause successive EMP energy emissions, which add up coherently, limited only by the conduction current of electrons returning to charges (which absorbs EMP energy when the air conductivity is high, in strong radiation environments).

    Longmire's EMP theory discovery boils down to his famous equation for the outgoing EMP wave, dE/dr = -(Z/2)(J + sE) v/m2, which can be derived in a simple way considering the conservation of energy in terms of the peak electric field, E volts/metre, of the electromagnetic pulse (see Longmire's report, Justification and verification of High-Altitude EMP Theory, Part 1, Mission Research Corporation, June 1986, pages 28-9):

    (1) From classical electromagnetism, the power density in the EMP (or any electromagnetic wave) is simply E2/Z W/m2 where Z is the impedance of free space, 377 ohms.

    (2) the derivative of this power density with respect to radial distance r, d(E2/Z)/dr, is the increase in power density per metre that the EMP wavefront progresses (d(E2/Z)/dr is in units of W/m3, not W/m2).

    (3) This increase in power density of the EMP derived above must be equal to the loss in power density of the electric current which supplies energy to the EMP by the successive deflection of Compton electrons in the earth's magnetic field. The total electric current density is J + sE A/m2 where J is the transverse component of the Compton current density (i.e., that with a vector pointed at 90 degrees to the ray from the bomb to the observer) which is proportional to both the gamma emission rate from the bomb (which produces Compton electrons) and to the component of the Earth's magnetic field strength which is transverse to the ray from bomb to observer, and which therefore deflects the Compton electrons, thus radiating EMP. The term sE is the conduction current density resulting from secondary electrons knocked off atoms by the Compton electrons as they slow down; on average it takes 34 eV of energy to knock an electron off an atom and a 2 MeV typical prompt gamma ray produces a 1 MeV typical Compton electron, so the Compton electron knocks some 29,000 secondary electrons from atoms which increases the air's electrical conductivity, eventually short-circuiting out the Compton current itself in strong radiation fields (s is the air conductivity in S/m or mho/m using old units which is the same thing as the reciprocal of resistance divided by distance r, so for air conductivity s, Ohm's law V = IR tells us simply: I = V/R = E/(R/r) = Es). Since electric power is the product of potential difference (volts) and current (amps), the current density J + sE A/m2 needs to be multiplied by E to get power density, E(J + sE) W/m3. Since E(J + sE) W/m3 represents a loss of power, it has a negative sign in the equivalence to the power gained by the EMP found in step (2) above:

    d(E2/Z)/dr = -E(J + sE)

    which simplifies to


    which is Dr Longmire's celebrated 'outgoing wave equation' of the EMP theory, first derived in his Los Alamos National Laboratory report LAMS-3073 of April 1964 (see pages 28-29 of Longmire's Justification and verification of High-Altitude EMP Theory, Part 1, Mission Research Corporation, June 1986). (Notice the factor of 2 is dropped by Longmire when quoting the formula without deriving it, on page 2 of his report EMP on Honolulu from the Starfish Event, EMP Theoretical Note 353, March 1985. On equation 43 on printed page 30 or PDF page 66 of the online version of book EMP Interaction gives the outgoing wave equation correctly including the factor of 2.)

    The dependence of the EMP on the earth's magnetic field strength and direction are not included here; these factors come into the expression for the transverse Compton current, J, which is the fraction of the radial Compton current that gets deflected sideways by the Earth's magnetic field for the ray in question, travelling in a straight line from bomb to observer. Because of the way the Earth's magnetic field lines curve and dip, these straight line rays from bomb to observers in different positions on the ground will have Compton electrons which undergo differing amounts of magnetic field deflection, producing some variations in the transverse (deflected) Compton current and therefore in the peak EMP at different points around the bomb. E.g., for a 200 km altitude burst at 50 degrees North the maximum prompt EMP occurs 300 km south of the detonation and you get a "smiley face" intensity contour, when the peak EMP intensities are plotted as iso-field strength lines on maps.

    To solve this outgoing wave equation, dE/dr = -(Z/2)(J + sE) v/m2, and predict EMP, the transverse Compton current J needs to be computed from the time-dependent prompt gamma ray (and other radiation, for later times) output striking air molecules, knocking off electrons and producing a current which is partially deflected sideways by the Earth's magnetic field, while the air conductivity s needs to be calculated from the production of secondary electrons caused by Compton electrons striking molecules, allowing for the time-dependent reattachment of secondary electrons to their ions and to neutral molecules. This step-wise solution requires numerical integration using a computer code. But there is an interesting analytical solution to this equation for the simple case of J = 0 (i.e. no Compton current), which is useful once the EMP has been generated and the EMP is propagating through air with a certain electrical conductivity due to either natural ionization at high altitudes (the ionosphere) or air which has been "pre-ionized" by radiation from either the primary fission stage of the same weapon (which detonates and emits prompt gamma rays and X-rays before the main pulse from the thermonuclear secondary stage in a Teller-Ulam design) or from a previous nuclear explosion:

    Er = E0*exp(-Zsr/2)

    where the exponential factor is an attenuation term, indicating the loss of EMP efficiency due to the effect of the air conductivity (the conduction current uses up some of the EMP energy by powering the return of electrons to separated charges, which becomes relatively important in limiting the increase of strong EMP fields where the air conductivity s is high due to strong air ionization caused by the high gamma ray intensity).

    This exponential term is important for the simplified theoretical caculation of the maximum peak EMP strengths you can get. See the earlier post linked here for a discussion of the role of the exponential "saturation" of the EMP as a limitation to the maximum possible field strengths that can occur, due to the reversed conduction current which increasingly begins to offset the Compton current where the air conductivity is high, as in the highly ionized atmosphere due to very intense radiation, either from a very powerful pulse of prompt gamma rays or due to "pre-ionization" of the atmosphere by either the X-rays and gamma rays from the fission primary stage which detonates before the main secondary stage in a 2-stage thermonuclear weapon, or from a previous detonation. Hence, the role of the conduction current, by rapidly opposing and partially cancelling out the Compton current in an already ionized atmosphere, tells us one piece of good news about the whole EMP threat: it has limits and can't exceed those limits. Increasing the bomb yield beyond a certain point doesn't increase the EMP, because the increase in the conduction current would immediately short out most of the extra Compton current, stopping extra EMP emission.

    In particular, because the atmosphere gets ionized very quickly by X-rays and prompt gamma rays (travelling at the velocity of light), you cannot even detonate two EMP weapons simultaneously to increase damage: even with atomic clocks to ensure they both detonated at the same time to within a fraction of a microsecond, the expanding shells of radiation from each detonation would immediately interfere with each other as soon as they started to overlap, so that - instead of getting a stronger EMP - the combination would weaken the EMP, because in the overlap zone each radiation front will be travelling through pre-ionized air caused by the other detonation. The actual amount of time taken for the air conductivity to fall after a nuclear explosion (allowing another one without degradation of the EMP) is governed by the reattachment rate of electrons to ions and neutral molecules.

    Professor Charles J. Bridgman produces a calculation of this effect on pages 477-8 of his book Introduction to the Physics of Nuclear Weapons Effects, U.S. Defense Threat Reduction Agency, Virginia, July 2001. The half-life of the electrons, i.e. the time for 50% of electrons to become attached to ions or molecules (reducing the electrical conductivity of air) is 0.7 milliseconds at 40 km altitude which is where the magnetic dipole EMP generation really begins, 0.1 second at 60 km altitude, and 30 seconds at 80 km altitude. (Attachment rates fall exponentially with increasing altitude due to the reduction in air density with increasing altitude, because the fewer air molecules and charged ions per cubic metre reduces the probability of one approaching and capturing a free electron. Thus, at altitudes of many hundreds of kilometres, electron belts can last for decades.)

    One simple way to calculate EMP is to start by looking at how energy is used in causing EMP:

    (a) about 50% of the prompt gamma ray energy is transferred to the Compton electron (the rest becomes the energy of the scattered gamma ray).

    (b) some of the Compton electrons can't radiate EMP, because they collide with air molecules before they have time to be deflected significantly by earth's magnetic field (this loss of energy due to collisions of Compton electrons with air molecules is particularly important where air density is high at low altitudes, and it produces "secondary electrons" which increase the air conductivity, limiting the EMP)

    (c) conduction current of secondary electrons and highly scattered Compton electrons returns to charges, a process which is powered by absorbing EMP field energy

    (d) in the calculation you need to allow for the fact that Compton electrons lose kinetic energy in order to radiate EMP (i.e., Compton electrons are slowed down by the act of emitting EMP energy)

    The report by Conrad L. Longmire, Robert M. Hamilton and Jane M. Hahn, A Nominal Set of High-Altitude EMP Environments (EMP Theoretical Note 354 of January 1987) on page 24 states that the efficiency of conversion of prompt gamma rays to EMP is only 6.0% for the case of a 2,200 km ground range horizon radius from a burst with a prompt gamma ray yield of 10 kt, emitting 2 MeV gamma rays at 400 km altitude in a geomagnetic field of 0.56 gauss. It adds that for lower prompt gamma ray yields, the efficiency is much higher because of the lower air conductivity in the source (or gamma ray deposition) region, causing less opposition by conduction electrons to the Compton electron current! The bigger the bomb, the less efficiently it radiates EMP, because of the greater air conductivity you get with the bigger gamma ray yield! This is one of the reasons why small nuclear bombs are so efficient for EMP, but there is another reason which also needs to be explained clearly so that the civil defence implications are widely recognised.

    Longmire also points out that Glasstone and Dolan's Effects of Nuclear Weapons pages 495 and 534 gives the fraction of bomb energy radiated in prompt gamma rays as 0.3%. However, this figure is apparently just the average of the 0.1% to 0.5% range stated by Philip J. Dolan in Capabilities of Nuclear Weapons, Chapter 7, Electromagnetic Pulse (EMP) Phenomena, page 7-1 (Change 1, 1978 update):

    'Briefly, the prompt gammas arise from the fission or fusion reactions taking place in the bomb and from the inelastic collisions of neutrons with the weapon materials. The fraction of the total weapon energy that may be contained in the prompt gammas will vary nominally from about 0.1% for high yield weapons to about 0.5% for low yield weapons, depending on weapon design and size. Special designs might increase the gamma fraction, whereas massive, inefficient designs would decrease it.'

    Page 12 of The Effects of Nuclear Weapons 3rd ed., 1977, states that 7 MeV of the 200 MeV released in nuclear fission, i.e. 3.5% of the energy of nuclear fission, appears in the prompt gamma rays. Additional prompt gamma ray energy is produced by the inelastic collision of neutrons (which come from both fission and fusion processes) with the bomb casing and debris. However, the amount of prompt gamma ray energy escaping from the weapon is reduced due to shielding (absorption of the prompt gamma rays by the weapon casing and other debris from the missile delivery system, etc.). Longmire stated that the Starfish prompt gamma ray release was just 0.1% of the total yield, so it is clear that much higher prompt gamma ray yields can be produced if the weapon casing thickness is reduced to minimise shielding. This is why, as Dolan states in the quotation above, low yield weapons yield a greater fraction of their yield in prompt gamma rays than high yield weapons.

    It is simply the neutron bomb mechanism at work: the outer casing thickness for a nuclear bomb to hold it together long enough for reasonable efficiency is proportional to the cube root of the total yield. Therefore, a 1 Mt bomb requires a casing thickness 10 times that for a 1 kt bomb, and this effect of yield on casing thickness for megaton bombs means that in megaton weapons the prompt gamma rays and neutrons are mostly absorbed by the thick casing you need at high yields to hold the bomb together while x-rays from the fission primary stage reflect from the casing on to the massive fusion secondary stage to heat it and compress it by the recoil from ablation, but in low-yield kiloton weapons the casing needs to reflect less energy and for a shorter period of time, so that in kiloton weapons the prompt gamma rays and neutrons can mostly escape. This is what limits the usefulness of megaton weapons as either neutron bombs or EMP weapons. But for kiloton bombs, you get a massive enhancement of prompt radiation outputs simply because at lower yields for equal efficiency you are containing less energy for a shorter nuclear reaction process, so you can use thinner bomb casing. For this reason, a low yield terrorist nuclear bomb would produce a far more efficient output of prompt gamma rays than a megaton bomb produces, so that the prompt EMP effects could be similar!

    To give an example of the simple and ancient technology involved, back on May 9, 1951, at Eberiru island in the Eniwetok Atoll, America tested a cylindrical-implosion nuclear bomb, the Greenhouse-George 225 kt device (so-named after its designer, the Los Alamos consultant Dr George Gamow) which used a hollow cylinder of TNT (8 feet in diameter and 2 feet thick) to compress a cylinder of oralloy (Oak Ridge alloy, highly enriched uranium-235) in the middle. This was done to expose the bare ends of the uranium cylinder to get unshielded radiation from it, without the intervening TNT-shielding you would get if you compressed a sphere of plutonium using a sphere of TNT around it. Although the unshielded radiation from the fissioning core was used for experimenting with nuclear fusion in the Greenhouse-George test, such systems also obviously maximise prompt gamma ray output in a preferred direction as an efficient 'directed-energy' EMP weapon.

    Above: illustration of a tactical U-235 spherical-implosion 1 kt enhanced-EMP weapon which would be detonated at 500 m altitude like a neutron bomb, preventing collateral damage because there is no fallout danger for that yield and altitude in the absence of rain, and the blast even at ground zero would be only 6 psi peak overpressure with 5 cal/cm2 which is enough for burns to bare skin, but falling to only 1 psi and negligible thermal effects at 2 km, so 'duck and cover' action against flying glass would protect people nearby. This works by producing a directed beam of prompt gamma rays. It was published in my November 1994 article, 'The Weapon of Peace' (Electronics World, November 1994, pp. 959-60).

    When I wrote the article in 1994, the question was how to stop nuclear proliferation. An enhanced-EMP bomb with little blast and shielded nuclear radiation but lots of EMP to burn out electronics over a Korean or Iranian nuclear reactor would put it out of action without ill effects (the peak overpressure even at ground zero, 500 metres below a 1 kt bomb, would not even rupture anybody's eardrum).

    The technical appendix to the article wasn't published. It shows that the fraction of prompt gamma rays escaping from the aperture in the casing in the spherical-implosion design shown (surface area of circular aperture)/(surface area of U-238 radiation shield) is about 1/6 for 110 degrees aperture angle as illustrated. The article states on page 960:

    'blast, fallout and thermal effects are virtually negligible on the ground. ... the EMP weapon is basically a simple pure fission device maximising the relative yield of prompt gamma rays.'

    It notes that the successful Nevada Ming Blade underground nuclear test of 1974 was set up to produce strong EMP fields, testing EMP theory, that the Nevada Dining Car underground nuclear test of 1975 subjected military hardware to intense EMP, and adds:

    'Experience in 1962 on Hawaii, 1,300 km from the 1.4 megaton Starfish Prime nuclear test (detonated over Johnston Island) showed that an EMP of just a few kV/m can cause marked effects even on old electronic systems. For example, 300 street lights were fused in 30 series connected loops, dozens of burglar alarms were set off, and circuit breakers initiated power cuts in different circuits. Except for fuses [and a microwave diode in the microwave link of the telephone system between the islands] electronic equipment was not permanently affected since it takes about 1 to 2 J to burn out a valve. However, microelectronics are a crucial component of nuclear reactors and modern weaponry, and they are thousands to millions of times more vulnerable than [1940s, 1950s and 1960s electronics] valve technology. For example, an MC17 silicon chip (data input gate) is burned out, according to the previously secret Capabilities of Nuclear Weapons [Chapter 9, Introduction to Damage Criteria, ADA955393, 187 pages; see also paragraph 11.31 on page 524 of The Effects of Nuclear Weapons], by an EMP of just 0.08 mJ. ... various kinds of explosive detonators are fired off by an EMP of between 0.02 and 0.6 mJ.'

    Above: my November 1994 Electronics World article, inspired by Sir Winston Churchill's suggestion in 1925 that:
    "It might have been hoped that the electromagnetic waves would in certain scales have been found capable of detonating explosives of all kinds from a great distance."

    Churchill's 1925 article about the amazing future of military science doesn't just forecast directed EMP weapons, but also nuclear weapons and guided missiles themselves:
    "Might not a bomb no bigger than an orange be found to possess a secret power - nay, to concentrate the force of a thousand tons of cordite and blast a township at a stroke?"


    Churchill's 1925 article is reprinted in his book "Thoughts and Adventures" (Butterworth, 1932).

    Above: the late-time magnetohydrodynamic EMP (MHD-EMP) measured by the change in the natural magnetic field flux density as a function of time after American tests Starfish (1.4 Mt, 400 km burst altitude), Checkmate (7 kt, 147 km burst altitude) and Kingfish (410 kt, 95 km burst altitude) at Johnston Island, below the detonations. The first (positive) pulse in each case is due to the ionized (diamagnetic) fireball expanding and pushing out the earth's magnetic field, which cannot penetrate into a conductive cavity such as an ionized fireball. Consequently, the pushed-out magnetic field lines become bunched up outside the fireball, which means that the magnetic field intensity increases (the magnetic field intensity can be defined by the concentration of the magnetic field lines in space). Under the fireball - as in the case of the data above, measured at Johnston Island, which was effectively below the fireball in each case - there is a patch of ionized air caused by X-rays being absorbed from the explosion, and this patch shields in part the first pulse of MHD-EMP (i.e., that from the expansion of the fireball which pushes out the earth's magnetic field). The second (negative) pulse of the late-time EMP is bigger in the case of the Starfish test, because it is unshielded: this large negative pulse is simply due to the auroral effect of the ionized fireball rising and moving along the earth's magnetic field lines. This motion of ionized fission product debris constitutes a large varying electric current for a high yield burst like Starfish, and as a result of this varying current, the accelerating charges radiate an EMP signal which can peak at a minute or so after detonation.

    Above: the measured late-time MHD-EMP at Hawaii, 1,500 km from the Starfish test, was stronger than at Johnston Island (directly below the burst!) because of the ionized X-ray patch of conductive air below the bomb, which shielded Johnston Island. The locations of these patches of ionized air below bursts at various altitudes are discussed in the earlier blog post linked here.
    Above: correlation of global measurements of the Starfish MHD-EMP late signal which peaked 3-5 seconds after detonation.

    The 3-stages of MHD-EMP:

    1. Expansion of ionized, electrically conducting fireball excludes and so pushes out Earth’s magnetic field lines, causing an EMP. This peaks within 10 seconds. However, the air directly below the detonation is ionized and heated by X-rays so that it is electrically conducting and thus partly shields the ground directly below the burst from the late-time low-frequency EMP.
    2. A MHD-EMP wave then propagates between the ionosphere’s F - layer and the ground, right around the planet.
    3. The final stage of the late-time EMP is due to the aurora effect of charged particles and fission products physically moving along the Earth’s magnetic field lines towards the opposite pole. This motion of charge constitutes a large time-varying electric current which emits the final pulse of EMP, which travels around the world.

    MHD-EMP has serious effects for long conductors because its extremely low frequencies (ELF) can penetrate a lot further into the ground than higher frequencies can, as proved by its effect on a long buried power line during the nuclear test of a 300 kt warhead at 290 km altitude on 22 October 1962 near Dzhezkazgan in Kazakhstan (as part of some Russian ABM system proof tests). In this test, prompt gamma ray-produced EMP induced a current of 2,500 amps measured by spark gaps in a 570-km stretch of overhead telephone line out to Zharyq, blowing all the protective fuses. But the late-time MHD-EMP was of special interest because it was of low enough frequency to enable it to penetrate the 90 cm into the ground, overloading a shallow buried lead and steel tape-protected 1,000-km long power cable between Aqmola and Almaty, firing circuit breakers and setting the Karaganda power plant on fire. The Russian 300 kt test on 22 October 1962 at 290 km altitude (44,84º N, 66,05º E) produced an MHD-EMP magnetic field of 1025 nT measured at ground zero, 420 nT at 433 km, and 240 nT at 574 km distance. Along ground of conductivity 10-3 S/m, 400 v was induced in a cable 80 km long, implying an MHD-EMP of 5 v/km. (See the map of these effects in a previous post, linked here.)

    Above: the incendiary effects of a relatively weak but natural MHD-EMP from the geomagnetic solar storm of 13 March 1989 in saturating the core of a transformer in the Hydro-Quebec electric power grid. Hydro-Quebec lost electric power, cutting the supply of electricity to 6 million people for several hours, and it took 9 hours to restore 83% (21.5 GW) of the power supply (1 million people were still without electric power then). Two 400/275 kV autotransformers were also damaged in England:

    'In addition, at the Salem nuclear power plant in New Jersey, a 1200 MVA, 500 kV transformer was damaged beyond repair when portions of its structure failed due to thermal stress. The failure was caused by stray magnetic flux impinging on the transformer core. Fortunately, a replacement transformer was readily available; otherwise the plant would have been down for a year, which is the normal delivery time for larger power transformers. The two autotransformers in southern England were also damaged from stray flux that produced hot spots, which caused significant gassing from the breakdown of the insulating oil.' - EMP Commission report, 'Critical National Infrastructures', 2008, page 42.

    A study of these effects is linked here. Similar effects from the Russian 300 kt nuclear test at 290 km altitude over Dzhezkazgan in Kazakhstan on 22 October 1962 induced enough current in a 1,000 km long protected underground cable to burn the Karaganda power plant to the ground. Dr Lowell Wood testified on 8 March 2005 during Senate Hearings 109-30 that these MHD-EMP effects are: 'the type of damage which is seen with transformers in the core of geomagnetic storms. The geomagnetic storm, in turn, is a very tepid, weak flavor of the so-called slow component of EMP. So when those transformers are subjected to the slow component of the EMP, they basically burn, not due to the EMP itself but due to the interaction of the EMP and normal power system operation. Transformers burn, and when they burn, sir, they go and they are not repairable, and they get replaced, as you very aptly pointed out, from only foreign sources. The United States, as part of its comparative advantage, no longer makes big power transformers anywhere at all. They are all sourced from abroad. And when you want a new one, you order it and it is delivered - it is, first of all, manufactured. They don't stockpile them. There is no inventory. It is manufactured, it is shipped, and then it is delivered by very complex and tedious means within the U.S. because they are very large and very massive objects. They come in slowly and painfully. Typical sort of delays from the time that you order until the time that you have a transformer in service are one to 2 years, and that is with everything working great. If the United States was already out of power and it suddenly needed a few hundred new transformers because of burnout, you could understand why we found not that it would take a year or two to recover, it might take decades, because you burn down the national plant, you have no way of fixing it and really no way of reconstituting it other than waiting for slow-moving foreign manufacturers to very slowly reconstitute an entire continent's worth of burned down power plant.'


    Dr William R. Graham (an engineer and physicist who was director of the Office of Science and Technology Policy and science adviser to President Reagan) on 2 September 2008 wrote an article on EMP threats, 'Invisible nuclear threat', for The Washington Times newspaper:

    'Our nation and the Department of Homeland Security are rightly concerned about the threat from nuclear terrorism. Extraordinary efforts are under way to detect and prevent a terrorist operation from smuggling a nuclear weapon into a U.S. city or seaport. New technologies, such as muon tomography, are being developed to scan the interior of containers and other objects for nuclear weapon materials.

    'Yet there is another nuclear threat to the U.S. homeland that could be posed by terrorists that is much less well-known - to our collective peril. This other nuclear threat is just as plausible and equally credible when compared to the threat of a weapon smuggled into the United States. Compared to a smuggled nuclear weapon detonated in New York, D.C. or Los Angeles, this other nuclear threat is potentially far more catastrophic: instead of a single city, it could threaten the entire nation's survival.

    'But the DHS and their institutional advisers are so fixated on the "conventional wisdom" of the threat from a nuclear bomb smuggled in that they are doing far too little to detect and prevent nuclear terrorists and their state sponsors from executing an electromagnetic pulse (EMP) attack on the United States.

    'A high-altitude EMP results from the detonation of a nuclear warhead at altitudes above 25 miles over the Earth's surface, and covers the area within line-of-sight from the bomb. The immediate effects of EMP are disruption of, and damage to, electronic systems that are indispensable to the operation of critical national infrastructures - the electric power grid, wired and cell telephone systems, fuel handling, land and air transportation, government operations, banking and finance, food storage and distribution, and water treatment and supply - that sustain our economy, military power and civilian population.

    'Our vulnerability to EMP attack is increasing daily as our dependence on electronics continues to grow. The impact of EMP is asymmetric in relation to potential antagonists who are less dependent on modern electronics. ...

    'A determined adversary could carry out an EMP attack without having the high level of technical sophistication of a major nation.

    'One scenario of special concern is an EMP attack against the United States launched from an ordinary freighter off the U.S. coast using a short- or medium-range missile to loft a nuclear warhead to high-altitude (such missiles are readily available on the world armaments black market).

    'Terrorists sponsored by a hostile state could try to launch such an attack without revealing the sponsors' identity. Iran, the world's leading sponsor of international terrorism, has practiced launching a mobile ballistic missile from a vessel in the Caspian Sea. Iran has also tested high-altitude explosions of its Shahab-III ballistic missile, a test mode consistent with EMP attack. Iranian military writings explicitly discuss a nuclear EMP attack that would destroy the United States. Connecting the dots is not difficult.

    'Designs for missile-launched nuclear weapons may have been illicitly trafficked for at least a quarter-century. Recently, as reported in the press, United Nations investigators found the design for an advanced nuclear weapon, miniaturized to fit ballistic missiles currently in the inventory of Iran, North Korea and other potentially hostile states, was in the possession of Swiss nationals affiliated with the A. Q. Khan nuclear proliferation network.

    'This suggests that additional nuclear weapon designs may also be in the possession of hostile states and of states that sponsor terrorism. However, even a primitive, low-yield modern day "entry-level" nuclear weapon could be used to conduct an EMP attack.

    'Why is the Department of Homeland Security moving aggressively to protect America's cities and seaports from nuclear terrorists smuggling in a nuclear weapon but overlooking the possibility of EMP attack? Their assumption is that if terrorists acquire a nuclear weapon, they would certainly prefer to detonate it in a major metropolitan area, rather than attack an entire seaboard or even the whole nation with EMP.

    'The assumption that a nuclear weapon would be used against us in only one way is unwarranted, as an EMP attack offers some significant advantages over smuggling. Smuggling a nuclear weapon into a U.S. city is risky, and becoming increasingly so, as homeland security measures improve. Significant investments are being made in measures to defeat such attempts. In contrast, an EMP attack using a missile launched from a ship outside U.S.-controlled waters eliminates most of the operational hazards of smuggling a nuclear weapon into a U.S. port or city. Moreover, it offers less opportunity for detection, less risk of weapon seizure, less risk of crewmember defection, greater difficulty for the United States in conducting forensic analysis to determine who sponsored the attack, less certainty of prompt retaliation and greater long-term, potentially catastrophic consequences for the nation.

    'Indeed, EMP attack is the only nuclear option where one or two nuclear weapons could gravely damage the entire United States, and give terrorism a large-scale victory from attacking the U.S.

    'While an EMP attack on our critical national infrastructures is one of the most serious terrorist and hostile state threats facing our nation, the United States need not be vulnerable to the catastrophic consequences of such an attack. The nation owes the recent progress made toward addressing EMP to the leadership of Rep. Roscoe G. Bartlett, Maryland Republican, and one of the few scientists in Congress, whose concern led him to initiate legislation that established the commission that I chair to address the EMP threat. ...'

    Dr Graham is Chair of the Commission to Assess the Threat to the United States from Electromagnetic Pulse (EMP) Attack (the 'EMP Commission'), which was:


    The Commission has released a Critical National Infrastructures Report (PDF, 7MB) and testified before the House Armed Services Committee (July 10, 2008) - Written Testimony (PDF, 76KB). Volume 3: Critical National Infrastructures (PDF, 4.6MB).

    The Critical National Infrastructures report contains the following set of nuclear test photographs and also contains a good analysis of the range of damaging effects caused by various peak electric field strengths in volts/metre for a wide range of electronic and electrical systems, industries and equipment.

    Below: the EMP Commission 'Critical National Infrastructures' 2008 report states on pages 158-162 that space systems were vulnerable to U.S. nuclear tests in 1958 and 1962: '... primary threats to the physical integrity of satellites: (1) direct, line-of-sight exposure to nuclear radiation pulses (e.g., X-ray, ultraviolet, gamma-ray, and neutron pulses) and (2) chronic exposure to enhanced high-energy electrons durably trapped in the Earth’s magnetic field. These effects can jeopardize satellites in orbit, as data from U.S. and Soviet high-altitude nuclear tests of 1958 and 1962 attest. ... Each detonation produced copious X-ray fluxes and trapped energetic electron radiation in space. When the United States detonated the 1.4-megaton STARFISH device on July 9, 1962, at 400 km altitude, a total of 21 satellites were in orbit or were launched in weeks following. Eight suffered radiation damage that compromised or terminated their missions. Information concerning the fate of the remaining 13 satellites is not publicly available. ... Natural radiation to an electronic part in LEO [Low Earth Orbit; 200-2,000 km altitude], such as the National Oceanic and Atmospheric Administration (NOAA) satellite, in polar orbit behind a 2.54 mm semi-infinite aluminum slab is, on long-term average, about 620 rads per year, while some satellites with the same shielding might receive 50 kilorads per year. Electronics must be shielded in accordance with the intended orbit to limit the dose received to a tolerable level.'

    Executive Report (PDF, 578KB)

    Critical National Infrastructures Report - High Resolution version (PDF, 53MB)

    Critical National Infrastructures Report (PDF, 7MB)

    EMP Commission Website:

    In addition, the Critical National Infrastructures report finishes with an assessment of the problem of premature satellite failure due to the pumping of the Van Allen belts (transversed by satellites) with extra electrons released by the beta decay of the fission product debris of a high altitude nuclear detonation. I've already summarised the effects of such radiation belts from Starfish as calculated using a Monte Carlo simulation by the British Atomic Weapons Establishment (which has since removed the useful internet pages), here:

    For further EMP information, see:

    Link to PDF download of DNA-EM-1 “Capabilities of Nuclear Weapons” Chapter 5
    “Nuclear Radiation Phenomena” (152 page, 4.6 MB)

    “Electromagnetic Pulse (EMP) Phenomena” (40 page, 1.3 MB)

    “Phenomena Affecting Electromagnetic propagation” (94 page, 3.6 MB)

    On 24 November 2008, the The Wall Street Journal published an article by Brian T. Kennedy (president of the Claremont Institute and a member of the Independent Working Group on Missile Defense), titled ‘What a Single Nuclear Warhead Could Do; Why the U.S. needs a space-based missile defense against an EMP attack’:







    Because of the economic influence of America, this would help protect the world, for example in Europe, whose markets and economic systems are affected on a day to day basis by the situation in America. This is because - as has been known since the market crash way back in 1929 - economic crises stemming from America spread world wide. Therefore, although an American ABM system will not directly protect the rest of the world, it will have major indirect benefits of ensuring continued worldwide economic stability in the event of terrorist attacks! But ignorant and cynical critics point out that nobody takes threats seriously without strong, clear, articulate, unambiguous, convincing scientific evidence:

    The Next Fake Threat by Nick Schwellenbach, AlterNet, Posted September 21, 2005:

    'A congressionally-mandated commission with ties to the defense industry is pushing a fake threat - electromagnetic pulse attacks - when the Pentagon can hardly conduct one itself. Cars won't start. The electricity and phone lines go out. Electronic devices have their circuits fried. ... The members of the Commission to Assess the Threat to the United States from Electromagnetic Pulse Attack (EMP Commission) have impressive credentials, yet they are also deeply tangled up with pro-missile defense organizations and the defense industry. Given their conflicts of interest and the controversial assumptions behind their report, questions about their credibility arise. Is the EMP Commission's scenario realistic or is it scare mongering to rally support for a pro-missile defense agenda? ... Perhaps the most controversial of the EMP Commission's claims is their insistence that a Hiroshima-sized nuclear detonation (10-20 kilotons) could produce enough EMP to fry circuits across a continent. ... A 1.4 megaton thermonuclear weapon detonated 250 miles above Johnston Island in the Pacific affected street lamps, circuit breakers, cars and radio stations in Hawaiian, 800 miles to the north. Still, even there the effect was far from comprehensive. ... But Starfish Prime was a thermonuclear device with a yield over a hundred times that of the bomb dropped on Hiroshima. Experts [‘Science is the organized skepticism in the reliability of expert opinion.’ - R. P. Feynman (quoted by Smolin, The Trouble with Physics, 2006, p. 307)] including [Richard] Garwin and Philip Coyle, former Pentagon director of operational test and evaluation, have expressed skepticism about the EMP Commission's claim that a 10-20 kiloton nuclear device could produce EMP on par with that of a thermonuclear weapon. ... In a world where anything can be a threat, and where only limited resources are available to us, the public needs its government to provide assessments and actions unclouded by parochial interests.'

    Plausibility of EMP Threat Classified, Expert Says by David Ruppe, Global Security Newswire, Friday, September 24, 2004 issue:

    'WASHINGTON — Questions about the plausibility of an alleged special electromagnetic pulse nuclear weapon that could to someday wipe out modern U.S. society by damaging or destroy its electrical system cannot be publicly addressed because the answers are classified, a U.S. expert said Wednesday. ... Philip Coyle, who was the assistant secretary of defense and Pentagon director of operational test and evaluation during the Clinton administration ... questioned the certainty of the report’s conclusion that smaller, kiloton-scale nuclear weapons could be developed to produce the catastrophic consequences described by the report. ... When asked following his presentation whether U.S. scientists have developed and tested a kilotons-scale weapon to demonstrate its EMP capability, [Dr Lowell] Wood said he could not comment. ... The commission’s five volumes on the subject were: an unclassified executive summary released in July; a classified threat assessment; an unclassified critical infrastructure assessment; a volume on military topics; and an assessment of potential threats.'

    'The growth of the city is perhaps the distinguishing characteristic of modern civilization. It is the expression of its power and its vulnerability. In a primitive society the basic unit is the family which is largely self-sufficient, producing its own food supply and containing the skills required for its survival. ... The modern city, on the other hand, is made possible by specialization. ...

    'The entire economic life of the city is dependent on the uninterrupted supply of energy ... Above all, a city is held together by an intangible quality: the confidence of its inhabitants that the highly articulated mechanism will continue to function; the conviction of the individual that the machine will serve and not destroy him. ... The penalty of a loss of confidence is illustrated by the depression of 1929. The physical plant of our society did not shrink, the skills of the people did not grow less, yet production fell by more than 40 per cent and millions were unemployed.'

    - Dr Henry A. Kissinger, Nuclear Weapons and Foreign Policy, Harper & Brothers, New York, 1957, pp. 65-6.

    '[There is] a tendency in our planning to confuse the unfamiliar with the improbable. The contingency we have not considered looks strange; what looks strange is therefore improbable; what seems improbable need not be considered seriously.'

    — Thomas C. Schelling, in Roberta Wohlstetter, Pearl Harbor: Warning and Decision, Stanford University Press, 1962, p. vii.

    Praemonitus praemunitus - forewarned is forearmed. Civil defence, to be taken seriously, requires the publication of solid facts about believable threats. Secrecy over the effects of nuclear weapons tests hinders civil defence planning against threats; it does not hinder plutonium and missile production by rogue states.