Attempt of translation of (French) Magneto-Explosive Generator page 

Talk:Explosively Pumped Flux Compression Generators/Translation from french page

Explosively pumped flux compression generators generate high power electrical pulses by compressing magnetic flux using explosives.

The first work on these generators was conducted by the VNIIEF centre for nuclear research in Sarov at the beginning of the 1950's, and then, independently, by LANL in the USA.

 History 

At the start of the 1950's, the need for very short and powerful electrical pulses became evident to Soviet scientists  conducting nuclear fusion research. At that point in time, the Marx generator, which stores energy in capacitors, was the only device capable of producing such high power pulses. The prohibitive cost of the capacitors required to obtain the desired power motivated the search for a more economical device. The first Magneto-explosive generators, which followed from the ideas of Andreï Sakharov, were designed to fill this role. 
 
 Principles of Function  

''In the following text, we will use terms like 'compression' or 'confinement' of the magnetic field. Because of the similarity between certain properties of gases and magnetic fields, the conventional use of these terms can be extended by analogy to magnetic fields. Various uses of this similarity can be found in this article by J.-P. Petit..

Magneto-explosive generator use a technique called 'magentic flux compression', which will be described in detail later. The technique is made possible when the timescales over which the device operates are sufficiently brief that resistive current loss 
is negligible, and the magnetic flux on any surface surrounded by a conductor (copper wire, for example) remains constant, even though the size and shape of the surface may change. 

This flux conservation can be demonstrated from Maxwell's equations. The most intuitive explanation of this conservation of enclosed flux follows from the principle that any change in an electromagnetic system provokes an effect in order to oppose the change. For this reason, reducing the area of the surface enclosed by a conductor, which would reduce the magnetic flux, results in the induction of current in the electrical conductor, which tends to return the enclosed flux to its original value. In magneto-explosive generators, this phenomenon is obtained by various techniques which depend on powerful explosives.  Other techniques exist which do not depend on  explosives. Notably, see  : Flux compression scheme used at the Gramat centre of study, in doctoral thesis, Mathias Bavay, 8 july 2002.

The compression process allows the chemical energy of the explosives to be (partially) transformed into electrical energy, using the magnetic flux as an intermediary agent of energy storage. (Note that I didn't like the catalyser argument: the magnetic field is highly dynamic, and in a sense consumes the reactant (the initial kinetic energy), even though the flux is conserved, unlike most chemical catalysts, which act mostly just to bring together the reactants in the correct configuration. A closer chemical analysis would be something like electron transport in photosynthesis, perhaps, but that really doesn't add anything useful to the discussion). 

 Elementary description of flux compression 

An external magnetic field (blue lines) thread a closed ring made of a perfect conductor (with zero resistivity). The nine field lines represent the magnetic flux threading the ring.

After the ring's diameter is reduced, the magnetic flux threading the ring, represented by five field lines, is reduced by the same ratio as the area of the ring. The variation of the magnetic flux induces a current in the ring (red arrows), which in turn creates a new magnetic field, so that the total flux in the interior of the ring is maintained (four green field lines added to the five blue lines give the original nine field lines). 

By adding together the external magnetic field and the induced field,