Editing Nuclear electromagnetic pulse (section)

==Characteristics==
Nuclear EMP is a complex multi-pulse, usually described in terms of three components, as defined by the [[International Electrotechnical Commission]] (IEC).<ref name="iec.ch">{{cite report |date=1996-02-19 |language=en, fr, es |title=Electromagnetic compatibility (EMC) - Part 2: Environment - Section 9: Description of HEMP environment - Radiated disturbance. Basic EMC publication |docket=IEC 61000-2-9:1996 |publisher=[[International Electrotechnical Commission]] |df=dmy-all |url=https://webstore.iec.ch/publication/4141 |url-access=subscription}}</ref>

The three components of nuclear EMP, as defined by the IEC, are called "E1", "E2", and "E3".{{r|iec.ch}}{{r|empc}}

The three categories of high-altitude EMP are divided according to the time duration and occurrence of each pulse.  E1 is the fastest or "early time" high-altitude EMP. Traditionally, the term "EMP" often refers specifically to this E1 component of high-altitude electromagnetic pulse.<ref name="ORNL-2.4">{{cite report |last1=Savage |first1=Edward |last2=Gilbert |first2=James |last3=Radasky |first3=William |docket=Meta-R-320 |title=The Early-Time (E1) High-Altitude Electromagnetic Pulse (HEMP) and Its Impact on the U.S. Power Grid |section=Section 2.4 – (An Overview of E1 HEMP) - Other Types of EMP |date=January 2010 |publisher=Metatech Corporation for Oak Ridge National Laboratory|df=dmy-all |url=https://www.ferc.gov/industries/electric/indus-act/reliability/cybersecurity/ferc_meta-r-320.pdf |access-date=2017-09-08 |url-status=dead |archive-url=https://web.archive.org/web/20170520145500/https://www.ferc.gov/industries/electric/indus-act/reliability/cybersecurity/ferc_meta-r-320.pdf |archive-date=2017-05-20}}</ref>

The E2 and E3 pulses are often further subdivided into additional divisions according to causation.  E2 is a much lower intensity "intermediate time" EMP, which is further divided into E2A (scattered gamma EMP) and E2B (neutron gamma EMP).<ref name="ORNL-2.4"/>

E3 is a very long-duration "late time" pulse, which is extremely slow in rise and fall times compared to the other components of EMP.<ref name="ORNL-2.4"/>  E3 is further divided into E3A (blast wave) and E3B (heave).<ref name="ORNL-2.4"/>  E3 is also called [[magnetohydrodynamic]] EMP.<ref name="ORNL-2.4"/>

===E1===
The E1 pulse is a very fast component of nuclear EMP. E1 is a brief but intense electromagnetic field that induces high voltages in electrical conductors. E1 causes most of its damage by causing electrical [[breakdown voltage]]s to be exceeded. E1 can destroy computers and communications equipment and it changes too quickly (nanoseconds) for ordinary [[surge protector]]s to provide effective protection from it. Fast-acting surge protectors (such as those using [[surge protector#Transient voltage suppression diode|TVS diodes]]) will block the E1 pulse.

[[File:EMP mechanism.png|right|333px|thumb|The mechanism for a {{convert|400|km|mi ft|adj=mid|-high}} burst EMP: gamma rays hit the atmosphere between {{cvt|20-40|km|ft||}} altitude, ejecting electrons which are then deflected sideways by the Earth's magnetic field. This makes the electrons radiate EMP over a large area. Because of the curvature and downward tilt of Earth's magnetic field over the US, the maximum EMP occurs south of the detonation and the minimum occurs to the north.<ref>{{cite report |author=US Army Test and Evaluation Command |publisher=[[White Sands Missile Range|U.S. Army White Sands Missile Range]] |date=1994-04-15 |title=Test Operations Procedure (TOP) 1-2-612, Nuclear Environment Survivability |docket=ADA278230 |page=D-7 |via=[[Defense Technical Information Center]] |df=dmy-all |url=https://apps.dtic.mil/sti/pdfs/ADA278230.pdf |access-date=2022-08-11 |url-status=live |archive-url=https://web.archive.org/web/20210818180829/https://apps.dtic.mil/sti/pdfs/ADA278230.pdf |archive-date=2021-08-18}}</ref>]]

E1 is produced when [[gamma radiation]] from the nuclear detonation [[ionizes]] (strips electrons from) atoms in the upper atmosphere. This is known as the [[Compton effect]] and the resulting current is called the "Compton current". The electrons travel in a generally downward direction at [[relativistic speed]]s (more than 90 percent of the speed of light). In the absence of a magnetic field, this would produce a large, radial pulse of [[electric current]] propagating outward from the burst location confined to the source region (the region over which the gamma photons are attenuated). The Earth's magnetic field exerts a force on the electron flow at a right angle to both the field and the particles' original vector, which deflects the electrons and leads to [[synchrotron radiation]]. Because the outward traveling gamma pulse is propagating at the speed of light, the synchrotron radiation of the Compton electrons adds [[coherence (physics)|coherently]], leading to a radiated electromagnetic signal. This interaction produces a large, brief, pulse.<ref name="longmire">Longmire, Conrad L. LLNL-9323905, Lawrence Livermore National Laboratory. June 1986 "[https://ece-research.unm.edu/summa/notes/TheoreticalPDFs/TN368.pdf Justification and Verification of High-Altitude EMP Theory, Part 1]" (Retrieved 2010-15-12)</ref>

Several physicists worked on the problem of identifying the mechanism of the HEMP E1 pulse. The mechanism was finally identified by [[Conrad Longmire]] of [[Los Alamos National Laboratory]] in 1963.<ref name="nbcreport"/>

Longmire gives numerical values for a typical case of E1 pulse produced by a second-generation nuclear weapon such as those of [[Operation Fishbowl]]. The typical gamma rays given off by the weapon have an energy of about 2{{nbsp}}[[electron-volt|MeV]] ([[mega-|mega]] electron-volts). The gamma rays transfer about half of their energy to the ejected free electrons, giving an energy of about 1{{nbsp}}MeV.<ref name="longmire"/>

In a vacuum and absent a magnetic field, the electrons would travel with a [[current density]] of tens of [[ampere]]s per square metre.<ref name="longmire"/> Because of the downward tilt of the Earth's magnetic field at high [[latitude]]s, the area of peak field strength is a U-shaped region to the equatorial side of the detonation. As shown in the diagram, for nuclear detonations in the [[Northern Hemisphere]], this U-shaped region is south of the detonation point. Near the [[equator]], where the Earth's magnetic field is more nearly horizontal, the E1 field strength is more nearly symmetrical around the burst location.{{citation needed|date=August 2016}}

At geomagnetic field strengths typical of the mid-latitudes, these initial electrons spiral around the magnetic field lines with a typical radius of about {{convert|85|m|||round=5}}. These initial electrons are stopped by collisions with air molecules at an average distance of about {{convert|170|m|||}}. This means that most of the electrons are stopped by collisions with air molecules before completing a full spiral around the field lines.<ref name="longmire"/>

This interaction of the negatively charged electrons with the magnetic field radiates a pulse of electromagnetic energy. The pulse typically rises to its peak value in some five nanoseconds. Its magnitude typically decays by half within 200 nanoseconds. (By the IEC definition, this E1 pulse ends 1000 nanoseconds after it begins.) This process occurs simultaneously on about 10<sup>25</sup> electrons.<ref name="longmire"/>&nbsp; The simultaneous action of the electrons causes the resulting pulse from each electron to radiate coherently, adding to produce a single large-amplitude, short-duration, radiated pulse.<ref name="ORNL-2.12">{{cite report |last1=Savage |first1=Edward |last2=Gilbert |first2=James |last3=Radasky |first3=William |docket=Meta-R-320 |title=The Early-Time (E1) High-Altitude Electromagnetic Pulse (HEMP) and Its Impact on the U.S. Power Grid |section=Section 2.12 – (An Overview of E1 HEMP) - E1 HEMP: Instantaneous and Simultaneous  |date=January 2010 |publisher=Metatech Corporation for Oak Ridge National Laboratory|df=dmy-all |url=https://www.ferc.gov/industries/electric/indus-act/reliability/cybersecurity/ferc_meta-r-320.pdf |access-date=2017-09-08 |url-status=dead |archive-url=https://web.archive.org/web/20170520145500/https://www.ferc.gov/industries/electric/indus-act/reliability/cybersecurity/ferc_meta-r-320.pdf |archive-date=2017-05-20}}</ref>

Secondary collisions cause subsequent electrons to lose energy before they reach ground level. The electrons generated by these subsequent collisions have so little energy that they do not contribute significantly to the E1 pulse.<ref name="longmire"/>

These 2 MeV gamma rays typically produce an E1 pulse near ground level at moderately high latitudes that peaks at about 50,000 volts per metre. The ionization process in the mid-[[stratosphere]] causes this region to become an electrical conductor, a process that blocks the production of further electromagnetic signals and causes the field strength to saturate at about 50,000 volts per metre. The strength of the E1 pulse depends upon the number and intensity of the gamma rays and upon the rapidity of the gamma-ray burst. Strength is also somewhat dependent upon altitude.{{citation needed|date=August 2016}}

There are reports of "super-EMP" nuclear weapons that are able to exceed the 50,000 volts per metre limit by unspecified mechanisms. The reality and possible construction details of these weapons are classified and are, therefore, unconfirmed in the open scientific literature<ref name="pry">{{cite report |title=Foreign Views of Electromagnetic Pulse (EMP) Attack |date=2005-03-08 |last1=Pry |first1=Peter Vincent |publisher=[[United States Senate Committee on Homeland Security and Governmental Affairs|United States Senate Subcommittee on Terrorism, Technology and Homeland Security]] |df=dmy-all |url=http://kyl.senate.gov/legis_center/subdocs/030805_pry.pdf |access-date=2022-08-11 |url-status=dead |archive-url=https://web.archive.org/web/20121108204504/http://kyl.senate.gov/legis_center/subdocs/030805_pry.pdf |archive-date=2012-11-08}}</ref>{{rp|3}}

===E2===
The E2 component is generated by scattered gamma rays and inelastic gammas produced by [[neutron]]s. This E2 component is an "intermediate time" pulse that, by IEC definition, lasts from about one microsecond to one second after the explosion. E2 has many similarities to [[lightning]], although lightning-induced E2 may be considerably larger than a nuclear E2. Because of the similarities and the widespread use of lightning protection technology, E2 is generally considered to be the easiest to protect against.{{r|empc}}

According to the United States EMP Commission, the main problem with E2 is that it immediately follows E1, which may have damaged the devices that would normally protect against E2.

The EMP Commission Executive Report of 2004 states, "In general, it would not be an issue for critical infrastructure systems since they have existing protective measures for defense against occasional lightning strikes. The most significant risk is synergistic because the E2 component follows a small fraction of a second after the first component's insult, which has the ability to impair or destroy many protective and control features. The energy associated with the second component thus may be allowed to pass into and damage systems."<ref name="empc">{{cite report |title=Report of the Commission to Assess the Threat to the United States from Electromagnetic Pulse (EMP) Attack: Executive Report |volume=1 |date=2004 |last1=Foster, Jr. |first1=John S. |last2=Gjelde |first2=Earl |last3=Graham |first3=William R. |last4=Hermann |first4=Robert J. |last5=Kluepfel |first5=Henry (Hank) M. |last6=Lawson |first6=Richard L. |last7=Soper |first7=Gordon K. |last8=Wood, Jr. |first8=Lowell L. |last9=Woodard |first9=Joan B. |docket=ADA48449 |publisher=Electromagnetic Pulse (EMP) Commission |via=[[Defense Technical Information Center]] |df=dmy-all |url=https://apps.dtic.mil/sti/pdfs/ADA484497.pdf |url-status=live |archive-url=https://web.archive.org/web/20220427231453/https://apps.dtic.mil/sti/pdfs/ADA484497.pdf |archive-date=2022-04-27}}</ref>{{rp|page=6}}

===E3===
{{Main article|Geomagnetically induced current}}
{{See also|Geomagnetic storm}}

The E3 component is different from E1 and E2. E3 is a much slower pulse, lasting tens to hundreds of seconds. It is caused by the nuclear detonation's temporary distortion of the Earth's magnetic field. The E3 component has similarities to a [[geomagnetic storm]].<ref>[http://www.todaysengineer.org/2007/Sep/HEMP.asp High-Altitude Electromagnetic Pulse (HEMP): A Threat to Our Way of Life] {{Webarchive|url=https://web.archive.org/web/20140706143245/http://www.todaysengineer.org/2007/Sep/HEMP.asp |date=2014-07-06}}, 09.07, By William A. Radasky, PhD, P.E. – IEEE</ref>{{r|empc}} Like a geomagnetic storm, E3 can produce geomagnetically induced currents in long electrical conductors, damaging components such as power line [[transformer]]s.<ref>{{cite report |last1=Sanabria |first1=David E. |last2=Bowman |first2=Tyler |last3=Guttromson |first3=Ross |last4=Halligan |first4=Matthew |last5=Le |first5=Ken |last6=Lehr |first6=Jane|author6-link=Jane Lehr |docket=SAND2020-12133 |title=The Late-Time (E3) High-Altitude Electromagnetic Pulse (HEMP) and Its Impact on the U.S. Power Grid |date=November 2010 |publisher=[[Sandia National Laboratories]] |df=dmy-all |url=https://www.ferc.gov/industries/electric/indus-act/reliability/cybersecurity/ferc_meta-r-321.pdf |url-status=dead |archive-url=https://web.archive.org/web/20170507032644/https://www.ferc.gov/industries/electric/indus-act/reliability/cybersecurity/ferc_meta-r-321.pdf |archive-date=2017-05-07}}</ref>

Because of the similarity between solar-induced geomagnetic storms and nuclear E3, it has become common to refer to solar-induced geomagnetic storms as "Solar EMP".<ref name="empact">{{cite web |title=EMP Caused by Geomagnetic Storm |publisher=EMPACT America |date=n.d. |df=dmy-all |url=http://www.empactamerica.org/solar_emp.php |access-date=2022-08-10 |url-status=usurped |archive-url=https://web.archive.org/web/20110726030320/http://www.empactamerica.org/solar_emp.php |archive-date=2011-07-26}}</ref> "Solar EMP" does not include E1 or E2 components.<ref>{{cite news |title=E3 – ProtecTgrid |newspaper=ProtecTgrid |language=en-US |url=http://www.protectgrid.com/glossary/e3/ |access-date=2017-02-16}}{{Dead link|date=April 2020 |bot=InternetArchiveBot |fix-attempted=yes}}</ref>