An explosively pumped flux compression generator (EPFCG) is a device used to generate a high-power
electromagnetic pulse
An electromagnetic pulse (EMP), also a transient electromagnetic disturbance (TED), is a brief burst of electromagnetic energy. Depending upon the source, the origin of an EMP can be natural or artificial, and can occur as an electromagnetic fie ...
by compressing
magnetic flux
In physics, specifically electromagnetism, the magnetic flux through a surface is the surface integral of the normal component of the magnetic field B over that surface. It is usually denoted or . The SI unit of magnetic flux is the weber ( ...
using
high explosive
An explosive (or explosive material) is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure. An exp ...
.
An EPFCG only ever generates a single pulse as the device is physically destroyed during operation. An EPFCG package that could be easily carried by a person can produce pulses in the millions of
ampere
The ampere (, ; symbol: A), often shortened to amp,SI supports only the use of symbols and deprecates the use of abbreviations for units. is the unit of electric current in the International System of Units (SI). One ampere is equal to elect ...
s and tens of
terawatt
The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named after James Wat ...
s. They require a starting
current
Currents, Current or The Current may refer to:
Science and technology
* Current (fluid), the flow of a liquid or a gas
** Air current, a flow of air
** Ocean current, a current in the ocean
*** Rip current, a kind of water current
** Current (stre ...
pulse to operate, usually supplied by
capacitor
A capacitor is a device that stores electrical energy in an electric field by virtue of accumulating electric charges on two close surfaces insulated from each other. It is a passive electronic component with two terminals.
The effect of ...
s.
Explosively pumped flux compression generators are used to create ultrahigh
magnetic field
A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...
s in physics and materials science research and extremely intense pulses of
electric current
An electric current is a stream of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is measured as the net rate of flow of electric charge through a surface or into a control volume. The moving pa ...
for
pulsed power Pulsed power is the science and technology of accumulating energy over a relatively long period of time and releasing it instantly, thus increasing the instantaneous power. They can be used in some applications such as food processing, water treatme ...
applications. They are being investigated as power sources for
electronic warfare
Electronic warfare (EW) is any action involving the use of the electromagnetic spectrum (EM spectrum) or directed energy to control the spectrum, attack an enemy, or impede enemy assaults. The purpose of electronic warfare is to deny the opponen ...
devices known as transient electromagnetic devices that generate an
electromagnetic pulse
An electromagnetic pulse (EMP), also a transient electromagnetic disturbance (TED), is a brief burst of electromagnetic energy. Depending upon the source, the origin of an EMP can be natural or artificial, and can occur as an electromagnetic fie ...
without the costs, side effects, or enormous range of a
nuclear electromagnetic pulse
A nuclear electromagnetic pulse (nuclear EMP or NEMP) is a burst of electromagnetic radiation created by a nuclear explosion. The resulting rapidly varying electric and magnetic fields may couple with electrical and electronic systems to produce ...
device.
The first work on these generators was conducted by the
VNIIEF
The All-Russian Scientific Research Institute of Experimental Physics (VNIIEF) (russian: Всероссийский научно-исследовательский институт экспериментальной физики) is a research inst ...
center for nuclear research in
Sarov
Sarov (russian: Саро́в) is a closed town in Nizhny Novgorod Oblast, Russia. It was known as Gorkiy-130 (Горький-130) and Arzamas-16 (), after a (somewhat) nearby town of Arzamas,SarovLabsCreation of Nuclear Center Arzamas-16/ref ...
in the
Soviet Union
The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, it was nominally a federal union of fifteen national ...
at the beginning of the 1950s followed by
Los Alamos National Laboratory
Los Alamos National Laboratory (often shortened as Los Alamos and LANL) is one of the sixteen research and development laboratories of the United States Department of Energy (DOE), located a short distance northwest of Santa Fe, New Mexico, ...
in the
United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...
.
History
At the start of the 1950s, the need for very short and powerful electrical pulses became evident to Soviet scientists conducting
nuclear fusion
Nuclear fusion is a reaction in which two or more atomic nuclei are combined to form one or more different atomic nuclei and subatomic particles ( neutrons or protons). The difference in mass between the reactants and products is manifest ...
research. The
Marx generator
A Marx generator is an electrical circuit first described by Erwin Otto Marx in 1924. Its purpose is to generate a high-voltage pulse from a low-voltage DC supply. Marx generators are used in high-energy physics experiments, as well as to simulate ...
, which stores energy in capacitors, was the only device capable at the time 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
Andrei Sakharov
Andrei Dmitrievich Sakharov ( rus, Андрей Дмитриевич Сахаров, p=ɐnˈdrʲej ˈdmʲitrʲɪjevʲɪtɕ ˈsaxərəf; 21 May 192114 December 1989) was a Soviet nuclear physicist, dissident, nobel laureate and activist for nu ...
, were designed to fill this role.
Mechanics
Magneto-explosive generators use a technique called "magnetic flux compression", described in detail below. The technique is made possible when the time scales over which the device operates are sufficiently brief that resistive current loss is negligible, and the
magnetic flux
In physics, specifically electromagnetism, the magnetic flux through a surface is the surface integral of the normal component of the magnetic field B over that surface. It is usually denoted or . The SI unit of magnetic flux is the weber ( ...
through 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
Maxwell's equations, or Maxwell–Heaviside equations, are a set of coupled partial differential equations that, together with the Lorentz force law, form the foundation of classical electromagnetism, classical optics, and electric circuits.
...
. The most intuitive explanation of this conservation of enclosed flux follows from
Lenz's law
Lenz's law states that the direction of the electric current induced in a conductor by a changing magnetic field is such that the magnetic field created by the induced current opposes changes in the initial magnetic field. It is named after p ...
, which says that any change in the flux through an electric circuit will cause a current in the circuit which will oppose the change. For this reason, reducing the area of the surface enclosed by a closed loop conductor with a magnetic field passing through it, which would reduce the magnetic flux, results in the induction of current in the electrical conductor, which tends to keep the enclosed flux at its original value. In magneto-explosive generators, the reduction in area is accomplished by detonating explosives packed around a conductive tube or disk, so the resulting
implosion compresses the tube or disk. Since flux is equal to the magnitude of the
magnetic field
A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...
multiplied by the area of the surface, as the surface area shrinks the magnetic field strength inside the conductor increases. The compression process partially transforms the chemical energy of the explosives into the energy of an intense magnetic field surrounded by a correspondingly large electric current.
The purpose of the flux generator can be either the generation of an extremely strong magnetic field pulse, or an extremely strong electric current pulse; in the latter case the closed conductor is attached to an external
electric circuit
An electrical network is an interconnection of electrical components (e.g., batteries, resistors, inductors, capacitors, switches, transistors) or a model of such an interconnection, consisting of electrical elements (e.g., voltage sources, c ...
. This technique has been used to create the most intense manmade magnetic fields on Earth; fields up to about 1000
teslas (about 1000 times the strength of a typical neodymium permanent magnet) can be created for a few microseconds.
Elementary description of flux compression
An external magnetic field (blue lines) threads a closed ring made of a perfect conductor (with zero
resistance
Resistance may refer to:
Arts, entertainment, and media Comics
* Either of two similarly named but otherwise unrelated comic book series, both published by Wildstorm:
** ''Resistance'' (comics), based on the video game of the same title
** ''T ...
). The total magnetic flux
through the ring is equal to the magnetic field
multiplied by the area
of the surface spanning the ring. The nine field lines represent the magnetic flux threading the ring.
Suppose the ring is deformed, reducing its cross-sectional area. 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 ''(red arrows)'' in the ring by
Faraday's law of induction
Faraday's law of induction (briefly, Faraday's law) is a basic law of electromagnetism predicting how a magnetic field will interact with an electric circuit to produce an electromotive force (emf)—a phenomenon known as electromagnetic inducti ...
, which in turn creates a new magnetic field circling the wire ''(green arrows)'' by
Ampere's circuital law. The new magnetic field opposes the field outside the ring but adds to the field inside, 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, it can be shown that the net result is that the magnetic field lines originally threading the hole stay inside the hole, thus flux is conserved, and a current has been created in the conductive ring. The magnetic field lines are "pinched" closer together, so the (average) magnetic field intensity inside the ring increases by the ratio of the original area to the final area.
The various types of generators
The simple basic principle of flux compression can be applied in a variety of different ways. Soviet scientists at the VNIIEF in
Sarov
Sarov (russian: Саро́в) is a closed town in Nizhny Novgorod Oblast, Russia. It was known as Gorkiy-130 (Горький-130) and Arzamas-16 (), after a (somewhat) nearby town of Arzamas,SarovLabsCreation of Nuclear Center Arzamas-16/ref ...
, pioneers in this domain, conceived of three different types of generators:
[
]
* In the first type of generator (MK-1, 1951) developed by Robert Lyudaev, the magnetic flux produced by a wound conductor is confined to the interior of a hollow metallic tube surrounded by explosives, and submitted to a violent compression when the explosives are fired; a device of the same type was developed in the
United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...
a dozen years later by
C. M. (Max) Fowler's team at
Los Alamos.
* In the second type of generator (MK-2, 1952), the magnetic flux, confined between the windings of the external conductor and a central conductive tube filled with explosive, is compressed by the conical 'piston' created by the deformation of the central tube as the detonation wave travels across the device.
* A third type of generator (DEMG), developed by Vladimir Chernyshev, is cylindrical, and contains a stack of concave metallic disks, facing each other in pairs, to create hollow modules (with the number varying according to the desired power), and separated by explosives; each module functions as an independent generator.
Such generators can, if necessary, be utilised independently, or even assembled in a chain of successive stages: the energy produced by each generator is transferred to the next, which amplifies the pulse, and so on. For example, it is foreseen that the DEMG generator will be supplied by a MK-2 type generator.
Hollow tube generators
In the spring of 1952, R. Z. Lyudaev,
E. A. Feoktistova, G. A. Tsyrkov, and A. A. Chvileva undertook the first experiment with this type of generator, with the goal of obtaining a very high magnetic field.
The MK-1 generator functions as follows:
* A longitudinal magnetic field is produced inside a hollow metallic conductor, by discharging a bank of capacitors into the solenoid that surrounds the cylinder. To ensure a rapid penetration of the field in the cylinder, there is a slit in the cylinder, which closes rapidly as the cylinder deforms;
* The explosive charge placed around the tube is detonated in a manner that ensures that the compression of the cylinder commences when the current through the solenoid is at its maximum;
* The convergent cylindrical shock wave unleashed by the explosion produces a rapid contraction (greater than 1 km/s) of the central cylinder, compressing the magnetic field, and creating an inductive current, as per the explanation above (the speed of contraction permits, to first approximation, the neglect of Joule losses and the consideration of the cylinder as a perfect conductor).
The first experiments were able to attain magnetic fields of millions of
gauss
Johann Carl Friedrich Gauss (; german: Gauß ; la, Carolus Fridericus Gauss; 30 April 177723 February 1855) was a German mathematician and physicist who made significant contributions to many fields in mathematics and science. Sometimes refer ...
(hundreds of
teslas), given an initial field of 30 kG (3 T) which is in the free space "air" the same as H = B/μ
0 = (3 V
s/m
2) / (4π × 10
−7 V
s/Am) = (approximately 2.4 MA/m).
Helical generators
Helical generators were principally conceived to deliver an intense current to a load situated at a safe distance. They are frequently used as the first stage of a multi-stage generator, with the exit current used to generate a very intense magnetic field in a second generator.
The MK-2 generators function as follows:
* A longitudinal magnetic field is produced in between a metallic conductor and a surrounding solenoid, by discharging a battery of capacitors into the solenoid;
* After the charge is ignited, a detonation wave propagates in the explosive charge placed in the interior of the central metallic tube (from left to right on the figure);
* Under the effect of the pressure of the detonation wave, the tube deforms and becomes a cone which contacts the helically wrapped coil, diminishing the number of turns not short-circuited, compressing the magnetic field and creating an inductive current;
* At the point of maximal flux compression, the load switch is opened, which then delivers the maximal current to the load.
The MK-2 generator is particularly interesting for the production of intense currents, up to 10
8 A (100 MA), as well as a very high energy magnetic field, as up to 20% of the explosive energy can be converted to magnetic energy, and the field strength can attain 2 × 10
6 gauss (200 T).
The practical realization of high performance MK-2 systems required the pursuit of fundamental studies by a large team of researchers; this was effectively achieved by 1956, following the production of the first MK-2 generator in 1952, and the achievement of currents over 100 megaamperes from 1953.
Disc generators
A DEMG generator functions as follows:
* Conductive metallic discs, assembled in facing pairs to create hollow modules having the form of a lined
torus
In geometry, a torus (plural tori, colloquially donut or doughnut) is a surface of revolution generated by revolving a circle in three-dimensional space about an axis that is coplanar with the circle.
If the axis of revolution does not tou ...
, with explosive packed between pairs of modules, are stacked inside a cylinder;
[In practice, each prefabricated element, destined to be assembled into a cylinder, corresponds to an explosive device surrounded by two discs, which explains why the line of disks is terminated at each end by a hollow half module.] the number of modules can vary according to the desired power (the figure shows a device of 15 modules), as well as the radius of the discs (of the order of 20 to 40 cm).
* Current runs through the device, supplied by a MK-2 generator, and an intense magnetic field is created inside each module.
* When initiated, the explosion begins on the axis and propagates radially outwards, deforming the disc shaped protuberances with triangular section and pushing them away from the axis. The outward movement of this section of conductor plays the role of a piston.
* As the explosion proceeds, the magnetic field is compressed in the inside of each module by the conductive piston and the simultaneous drawing together of the inner faces, also creating an inductive current.
* As the induced current attains its maximum, the fuse opening switch fuses and the load switch simultaneously closes, allowing the current to be delivered to the load (the mechanism for the operation of the load switch is not explained in available documentation).
Systems using up to 25 modules have been developed at VNIIEF. Output of 100
MJ at 256 MA have been produced by a generator a metre in diameter composed of three modules.
See also
*
Pinch (plasma physics)
A pinch (or: Bennett pinch (after Willard Harrison Bennett), electromagnetic pinch, magnetic pinch, pinch effect, or plasma pinch.) is the compression of an electrically conducting filament by magnetic forces, or a device that does such. The con ...
*
Explosive-driven ferroelectric generator An explosive-driven ferroelectric generator (EDFEG, explosively pumped ferroelectric generator, EPFEG, or FEG) is a compact pulsed power generator, a device used for generation of short high-voltage high-current pulse. The energies available are fai ...
*
Explosive-driven ferromagnetic generator An explosive-driven ferromagnetic generator (EDFMG, explosively pumped ferromagnetic generator, EPFMG, or FMG) is a compact pulsed power generator, a device used for generation of short high-voltage high-current pulse by releasing energy stored in a ...
*
Explosively pumped gas dynamic laser
References
External links
Scientific Collaborations Between Los Alamos and Arzamas-16 Using Explosive-Driven Flux Compression GeneratorsAn Introduction to Explosive Magnetic Flux Compression GeneratorsGeneration of Ultra-High Magnetic Fields for AGEX (LANL)Superpower explosive magnetic energy sources (V.K. Chernyshev, VNIIEF)High-Strain-Rate Experiments to Determine the Dynamic Yield Strength of CopperMagnetized target fusion – an ultra high energy approach in an unexplored parameter space
{{Authority control
Energy weapons
Microwave technology
Pulsed power
Soviet inventions
Russian inventions