Nuclear electromagnetic pulse
The term "electromagnetic pulse" generally excludes optical (infrared, visible, ultraviolet) and ionizing (such as X-ray and gamma radiation) ranges.
In military terminology, 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.
[1] During the first United States nuclear test on 16 July 1945, electronic equipment was shielded because Enrico Fermi expected the electromagnetic pulse.
[1][6][7] 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.
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.
[14] Although these weapons were much smaller (300 kiloton) than the Starfish Prime test, they were over a populated, large landmass and at a location where the Earth's magnetic field was greater.
[17][18] For one of 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.
[17] Published reports, including a 1998 IEEE article,[17] have stated that there were significant problems with ceramic insulators on overhead electrical power lines during the tests.
[9] Longmire gives numerical values for a typical case of E1 pulse produced by a second-generation nuclear weapon such as those of Operation Fishbowl.
[24] 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 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.
[30] Factors that control weapon effectiveness include altitude, yield, construction details, target distance, intervening geographical features, and local strength of the Earth's magnetic field.
In the Starfish Prime nuclear test, most damage was to the satellites' solar panels while passing through radiation belts created by the explosion.
[citation needed] 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 means that although a 10 kt (42 TJ) weapon has only 0.7% of the energy release of the 1.44 Mt (6.0 PJ) Starfish Prime test, the EMP will be at least 8% as powerful.
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.
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.
[39] These weapons capitalize on the E1 pulse component of a detonation involving gamma rays, creating an EMP yield of potentially up to 200,000 volts per meter.
While the United States also possesses nuclear weapons, the country has not experimented with super-EMPs and is hypothetically highly vulnerable to any future attacks by nations.
[40] Abroad, U.S. aircraft carriers stationed within a reasonable range of an exploding bomb could potentially be subject to complete destruction of missiles on board, as well as telecommunication systems that would allow them to communicate with nearby vessels and controllers on land.
This would call for detonations up to 100 kilometres (62 mi) above the Earth's surface, with the potential to disrupt the electronic systems of U.S. satellites suspended in orbit around the planet, many of which are vital for deterrence and alerting the country of possible incoming missiles.
Soviet Cold War-era military aircraft often had avionics based on vacuum tubes because solid-state capabilities were limited and vacuum-tube gear was believed to be more likely to survive.
[44] The earlier PRC-25, nearly identical except for a vacuum tube final amplification stage, was tested in EMP simulators, but was not certified to remain fully functional.
Therefore, airline authorities are creating high intensity radiated fields (HIRF) requirements for new airplanes to help prevent the chance of crashes caused by EMPs or electromagnetic interference (EMI).
A study found that exposure to 200–400 pulses of EMP caused the leaking of vessels in the brain,[47] leakage that has been linked to small problems with thinking and memory recollection.
In public statements, the Commission recommended making electronic equipment and electrical components resistant to EMP – and maintaining spare parts inventories that would enable prompt repairs.
[citation needed] In 2011, the Defense Science Board published a report about the ongoing efforts to defend critical military and civilian systems against EMP and other nuclear weapons effects.
[62][63] In 2018, the US Department of Homeland Security released the Strategy for Protecting and Preparing the Homeland against Threats from Electromagnetic Pulse (EMP) and Geomagnetic Disturbance (GMD), which was the department's first articulation of a holistic, long-term, partnership-based approach to protecting critical infrastructure and preparing to respond and recover from potentially catastrophic electromagnetic incidents.
The popular media often depict EMP effects incorrectly, causing misunderstandings among the public and even professionals, and official efforts have been made in the United States to set the record straight.
