The Christofilos effect, sometimes known as the Argus effect, refers to the entrapment of electrons from nuclear weapons in the Earth's magnetic field. It was first predicted in 1957 by Nicholas Christofilos, who suggested the effect had defensive potential in a nuclear war, with so many beta particles becoming trapped that warheads flying through the region would experience huge electrical currents that would destroy their trigger electronics. The concept that a few friendly warheads could disrupt an enemy attack was so promising that a series of new nuclear tests was rushed into the US schedule before a testing moratorium came into effect in late 1958. These tests demonstrated that the effect was not nearly as strong as predicted, and not enough to damage a warhead. However, the effect is strong enough to be used to black out radar systems and disable satellites.
Concept Electrons from nuclear explosions Among the types of energy released by a nuclear explosion are a large number of beta particles, or high energy electrons. These are primarily the result of beta decay within the debris from the fission portions of the bomb, which, in most designs, represents about 50% of the total yield.
Because electrons are electrically charged, they induce electrical currents in surrounding atoms as they pass them at high speed. This causes the atoms to ionize while also causing the beta particles to slow down. In the lower atmosphere, this reaction is so powerful that the beta particles slow to thermal speeds within a few tens of meters at most. This is well within a typical nuclear explosion fireball, so the effect is too small to be seen.
At high altitudes, the much less-dense atmosphere means the electrons are free to travel long distances. They have enough energy that they will not be recaptured by the proton that is created in the beta decay, so they can, in theory, last indefinitely.
Mirror effect
In 1951, as part of the first wave of research into fusion energy, University of California Radiation Laboratory at Livermore ("Livermore") researcher Richard F. Post introduced the magnetic mirror concept. The mirror is a deceptively simple device, consisting largely of a cylindrical vacuum chamber that holds the fusion fuel and an electromagnet wound around it to form a modified solenoid.
A solenoid normally generates a linear magnetic field along the center of its axis, in this case down the middle of the vacuum chamber. When charged particles are placed in a magnetic field, they orbit around the field lines, which, in this case, stops them from moving sideways and hitting the walls of the chamber. In a normal solenoid, they would still be free to move along the lines and thus escape out the ends. Post's insight was to wind the electromagnet in such a way that the field was stronger at the ends than in the center of the chamber. As particles flow towards the ends, these stronger fields force the lines together, and the resulting curved field causes particles to "reflect" back, thus leading to the name mirror.
In a perfect magnetic mirror, the particles of fuel would bounce back and forth, never reaching the ends nor touching the sides of the cylinder. However, even in theory, no mirror is perfect; there is always a population of particles with the right energy and trajectory that allow them to flow out of the ends through the "loss cone". This makes magnetic mirrors inherently leaky systems, although initial calculations suggested the rate of leakage was low enough that one could still use it to produce a fusion reactor.
Christofilos effect
The shape of the Earth's magnetic field, or geomagnetic field, is similar to that of a magnetic mirror. The field balloons outward over the equator, and then necks down as it approaches the poles. Such a field would thus reflect charged particles in the same fashion as Post's mirrors. This was not a new revelation; it was already long understood to be the underlying basis for the formation of aurora. In the case of the aurora, particles of the solar wind begin orbiting around the field lines, bouncing back and forth between the poles. With every pass, some of the particles leak past the mirror points and interact with the atmosphere, ionizing the air and causing the light.
Electrons released by fission events are generally in the range of . Initially, these would be subject to mirroring high in the atmosphere, where they are unlikely to react with atmospheric atoms and might reflect back and forth for some time. When one considers a complete "orbit" from north pole to south and back again, the electrons naturally spend more time in the mirror regions because this is where they are slowing down and reversing. This leads to increased electron density at the mirror points. The magnetic field created by the moving electrons in this region interacts with the geomagnetic field in a way that causes the mirror points to be forced down into the atmosphere. Here, the electrons undergo more interactions as the density of the atmosphere increases rapidly. These interactions slow the electrons so they produce less magnetic field, resulting in an equilibrium point being reached in the upper atmosphere about in altitude.
Using this as the average altitude as the basis for the air density calculation allowed the interaction rate with the atmosphere to be calculated. Running the numbers, it appeared that the average lifetime of an electron would be of the order of 2.8 days.
Example
As an illustration, Christofilos considered the explosion of a bomb. This would produce 10 fission events, which in turn produce four electrons per fission. For the mirror points being considered, almost any beta particle traveling roughly upward or downward would be captured, which he estimated to be about half of them, leaving 2×10 electrons trapped in the field. Because of the shape of the Earth's field, and the results of the right-hand rule, the electrons would drift eastward and eventually create a shell around the entire Earth.
Assuming the electrons were evenly spread, a density of 0.2 electrons per cubic centimeter would be produced. Because the electrons are moving rapidly, any object within the field would be subjected to impacts of about 1.5×10 electrons per second per square centimeter. These impacts cause the electrons to slow down, which, through bremsstrahlung, releases radiation into the object. The rate of bremsstrahlung depends on the relative atomic mass, or Z, of the material. For an object with an average Z of 10, the resulting flux is about 100 roentgen/hour, compared to the median lethal dose of about 450 roentgen. Christofilos noted that this would be a significant risk to space travelers and their electronic equipment.
As reentry vehicles (RVs) from ICBMs approach their targets, they travel at about , or around . An RV traveling through the mirror layer, where the electrons are at their densest, would thus be in the midst of the electric field for about ten seconds. Because of a warhead's high speed, the apparent voltage spike would induce an enormous current in any of its metal components. This might be so high as to melt the airframe, but more realistically, could destroy the trigger or guidance mechanisms.
The density of the field is greatest at the mirror points, of which there are always two for a given explosion, the so-called magnetic conjugates. The explosion can take place at either of these two points, and the magnetic field will cause them to concentrate at the other point as well. Christofilos noted that the conjugate point for most of the continental United States is in the South Pacific, far west of Chile, where such explosions would not be noticed. Thus, if one were to explode a series of such bombs in these locations, a massive radiation belt would form over the US, which might disable the warheads of a Soviet attack.
Of additional interest to military planners was the possibility of using this effect as an offensive weapon. In the case of an attack by US forces on the Soviet Union, the southern conjugate locations are generally in the Indian Ocean, where they would not be seen by Soviet early warning radar. A series of explosions would cause a massive radar blackout over Russia, degrading its anti-ballistic missile (ABM) system without warning. Since these effects were expected to endure for up to five minutes, about the amount of time that a line-of-sight radar in Russia would have to see the warheads, careful timing of the attack could render the ABM system useless.
History Background Christofilos began his career in physics while reading journal articles at an elevator company during the Axis occupation of Greece when he had little else to do. In the post-war era, he started an elevator repair service, during which time he began to develop the concept today known as strong focusing, a key development in the history of particle accelerators. In 1949, he sent a letter describing the idea to the Berkeley Lab but they rejected it after finding a minor error. In 1952, the idea was developed independently at the Brookhaven National Laboratory, which published on the topic. Convinced they had stolen the idea, Christofilos traveled to the US where he managed to win a job at Brookhaven.
Christofilos soon became more interested in nuclear fusion efforts than particle accelerator design. At the time there were three primary designs being actively worked on in the US program, the magnetic mirror, the stellarator, and the z-pinch. The mirror was often viewed unfavorably due to its inherent leakiness, a side effect of its open field lines. Christofilos developed a new concept to address this problem, known as the Astron. This consisted of a mirror with an associated particle accelerator that injected electrons outside the traditional mirror area. Their rapid movement formed a second magnetic field which mixed with that of the electromagnet and caused the resulting net field to "close", fixing the mirror's biggest problem.
Sputnik and Explorer During the same period, plans were being made by the US to test the presence of the expected charged layer directly using the Explorer 1 satellite as part of the International Geophysical Year (IGY). Before Explorer launched, the Soviets surprised everyone by launching Sputnik 1 in October 1957. This event caused near-panic in US defense circles, where many concluded the Soviets had achieved an insurmountable scientific lead.
Among those worried about the Soviet advances was Christofilos, who published his idea in an internal memo that same month. When Explorer launched in January 1958, it confirmed the existence of what became known as the Van Allen radiation belts. This led to new panic within the defense establishment when some concluded that the Van Allen belts were not due to the Sun's particles, but secret Soviet high-altitude nuclear tests of the Christofilos concept.
Planning begins Christofilos' idea immediately sparked intense interest; if the concept worked in practice, the US would have a "magic bullet" that might render the Soviet ICBM fleet useless. In February 1958, James Rhyne Killian, chairman of the recently formed President's Science Advisory Committee (PSAC), convened a working group at Livermore to explore the concept. The group agreed that the basic concept was sound, but many practical issues could only be solved by direct testing with explosions at high altitudes.