Electromagnetic Pulse - Clarification of Common Misconceptions

Clarification of Common Misconceptions

In non-technical writings about nuclear EMP, both in print and on the Internet, some common misconceptions about EMP are nearly always found. These widely-repeated misconceptions have led to a very considerable amount of confusion about the subject. In 2010, a technical report written for the US government's Oak Ridge National Laboratory even included a brief section addressing some of those EMP myths. Here are some further clarifications on common areas of confusion that have already been discussed (with references) in the above sections of this article:

1. Most nuclear weapons effects vary greatly depending upon the altitude of the detonation. This is especially true of nuclear EMP. The standard reference text on nuclear weapon effects published by the U.S. Department of Defense discusses this relationship extensively in the first two chapters, and provides mutually-exclusive definitions for phrases such as "air burst" and "high-altitude burst." As explained in above sections of this article, nuclear detonations at all altitudes within the Earth's magnetic field will produce an electromagnetic pulse; but the magnitude of the EMP and area that is affected by the EMP are strongly affected by many factors, and is especially strongly dependent upon the altitude of the detonation. (See the discussion above in the "Weapon altitude" and "Weapon distance" sections.) A nuclear explosion in deep space and not in a strong planetary magnetic field would be ineffective at generating EMP.
2. EMP is not a new kind of weapon effect. As stated in the "History" section above, nuclear EMP from a nuclear air burst has been known since 1945. The unique characteristics of high-altitude nuclear EMP have been known since at least 1962. Non-nuclear EMP has been known since at least 1951. Electromagnetic pulse is a prompt secondary effect of a nuclear explosion, and nearly all of the nuclear EMP is produced outside of the weapon. All nuclear weapons can produce EMP as a secondary effect, but the effect can be enhanced by special weapon design.
3. The E3 component of nuclear EMP that produces geomagnetically induced currents in very long electrical conductors is roughly proportional to the total energy yield of the weapon. The other components of nuclear EMP are less likely to be dependent on total energy yield of the weapon. The E1 component, in particular, is proportional to prompt gamma ray output; but EMP levels can be strongly affected if more than one burst of gamma rays occurs in a short time period. Large thermonuclear weapons produce large energy yields through a multi-stage process. This multi-stage process is completed within a small fraction of a second, but it nevertheless requires a finite length of time. The first fission reaction is usually of relatively small yield, and the gamma rays produced by the first stage pre-ionize atmospheric molecules in the stratosphere. This pre-ionization causes the gamma ray emission from the high-energy final stage of the thermonuclear weapon (a fraction of a second later) to be relatively ineffective at producing a large E1 pulse. (See the blue pre-ionization curve in the "Peak Electric Field at Ground Zero" graph above.)
4. It has long been known that there are many ways to protect against nuclear EMP (or to quickly begin repairs where protection is not practical); but the United States EMP Commission determined that such protections are almost completely absent in the civilian infrastructure of the United States, and that even large sectors of the United States military services were no longer protected against EMP to the level that they were during the Cold War. The public statements of the physicists and engineers working in the EMP field tend to emphasize the importance of making electronic equipment and electrical components resistant to EMP — and of keeping adequate spare parts on hand, and in the proper location, to enable prompt repairs to be made. The United States EMP Commission did not look at the civilian infrastructures of other nations.