SPIRAL & COAXIAL GENERATORMOHD JAMIL ABDULLAH2011132445

INTRODUCTION

• Flux Compression Generators (FCGs) are defined to be devices that convert the chemical energy of high explosives into electromagnetic energy by using the explosive to mechanically compress a magnetic field complety enclosed within a metallic boundary.

• They utilise a tree-step energy conversion process. chemical ,kinetic and electrical.

• Two main application for FCGs 1)field generator-as as source of intense magnetic field

sometimes referred to as Type 1,Mark 1,MC-1,or MK-1 generators.

2)current generator-as a source electrical power sometimes referred to as Type 11,Mark 11,MC -11 or MK-11 generators.

INTRODUCTION

• FCG can be used only once as a pulsed power supply because the device is physically destroyed during operation. FCG package that could be easily carried by a person can produce pulses in the millions of amperes and tens of tera watts.They require a starting current pulse to operate, usually supplied by capacitors.

• Flux compression generators are popular as power sources for electronic warfare devices known as transient electromagnetic devices that generate an electromagnetic pulse without the costs and side effects of a nuclear weapon.

• They also can be used to accelerate objects to extreme velocities and compress objects to very high pressures and densities; this gives them a role as a physics research tool.

• The first work on these generators was conducted by the VNIIEF center for nuclear research in Sarov in the U.S.S.R. at the beginning of the 1950s followed by Los Alamos National Laboratory in the United States.

HISTORY

• At the start of the 1950s, the need for very short and powerful electrical pulses became evident to Soviet scientists conducting nuclear fusion research.

• The Marx generator, 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, were designed to fill this role.

C. M. (Max) Fowler

Andrei Sakharov,

HISTORY

Table 1 Magnetic field (flux density) energy and current which have been reported as acheved by the different countries

CONTRUCTION

CONTRUCTION

TYPE OF FC GENERATORS

• The shape of these conductors can take on different forms including planar,cylindrical,toroidal and spherical.The shape of their conductors and include.

plate generators strip generators bellows generators coaxial (cylindrical) generators spiral (helical) generators disk generartors loop generators spherical generators

TYPE OF GENERATOR

Basic flux compression generator schemes. (a) Diskgenerator (before detonation). (b) Coaxial generator. (c) Parallelplate generator. (d) Spiral generator all during operation. Arrowsindicate current flow in conductors

PRINCIPLES OF FUNCTION

• Magneto-explosive generators use a technique called "magnetic flux compression".

• 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 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.

PRINCIPLES OF FUNCTION

• 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.

• The compression process allows the chemical energy of the explosives to be (partially) transformed into the energy of an intense magnetic field surrounded by a correspondingly large electric current.

PRINCIPLES OF FUNCTION

• For a constant intensity magnetic field of magnitude B traversing a surface S, the flux Φ is equal to B × S.

Elementary description of flux compression

• An external magnetic field (blue lines) threads a closed ring made of a perfect conductor (with zero resistance).

• The nine field lines represent the magnetic flux threading the ring.

Fig. 1: Original magnetic field lines.

Elementary description of flux compression

• 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).

Fig. 2: Configuration after the ring's diameter has been reduced.

Elementary description of flux compression

• By adding together the external magnetic field and the induced field.

• The final configuration after compression can be obtained.

• The total magnetic flux through the ring has been conserved (even though the distribution of the magnetic flux has been modified), and a current has been created in the conductive ring

Fig. 3: Magnetic field lines after compression.

THE FUNDAMENTAL CONCEPTS

• Flux compression in the ideal case relies on Faraday’s law of flux conservation.

• This is best demonstrated by the diagram shown in figure 1: if the area changes the flux density BF must increase.

• This can be rewritten in terms of the current and inductance of the generator shown in equation 3 .

• In order to obtain a high magnetic field the moving liner should have as high a velocity as possible to prevent the dissipation of the flux through the liner therefore causing losses in the system.

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THE FUNDAMENTAL CONCEPTS

• For a high current output there should be a large initial inductance of the system and the final inductance should be as low as possible.

• The final inductance includes the load which in some cases requires the generator to be coupled to the load via a transformer.

• A lot of work performed with FCGs requires the calculation of the mutual inductances of the generator.

THE FUNDAMENTAL CONCEPTS

• The most common method used for these calculations is by using standard elliptic integrals K(k) and E(k).

• The energy component of the system comes from two main sources, these are defined in equation 4 & 5.

• The energy equations are written for a cylindrical system. The first is the initial energy in the magnetic field produced either by permanent magnets or by a capacitor bank and coil.

• Spiral 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.

• A spiral generator has a long metal armature that is packed with high explosive and placed within a solenoid.

SPIRAL GENERATORS

• As the capacitor bank discharges, the current generates a magnetic field in the space between the solenoid and the armature.

• The load switch is initially in the closed position, preventing the current from flowing through the load.

SPIRAL GENERATORS

SPIRAL GENERATORS

• The explosive is detonated at one end, and the armature expands like inflating a long balloon.

• The volume between the solenoid and the armature decreases in both the radial and longitudinal directions.

• This causes the magnetic flux to be compressed. • Flux conservation results in an enhanced magnetic field, which

induces a large current in the remaining loops of the solenoid.

• At peak flux compression, the load switch is opened, and a greatly enhanced current is delivered to the load.

SPIRAL GENERATORS

• The generator is particularly interesting for the production of intense currents, up to 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 × 106 gauss (200 T).

• The generators work because high explosives are detonated, and therefore, the entire experiment must be completed in substantially less than a millisecond, after which time the generator and most of the experimental apparatus is completely destroyed.

SPIRAL GENERATORS

COAXIAL GENERATOR

• Generator of this type are,also called cylindrical Flux Compression Generator or,more simply coaxial generator.

• The basic generator components include the stator ,the outer cyclinder and the armature,the explosive loaded inner cyclinder.

• The load coil pictured is annular or doughnut-shape.

• Initial current is supplied by a capacitor bank ,or commonly,by another FCG,through the annular input slot at the left.

COAXIAL GENERATOR

• Arrows show that the current flows along the outside cyclinder,through the load coil and back through the armature.

• Magnetic field lines B,indicated by circles and crosses,are circular tangential.

• They encircle the armature and are restricted essentially to the annular space between the stator and the armature and to the coil.

COAXIAL GENERATOR

• Detonation of the armature explosive is again timed to close the input current slot at such time that maximum current or flux is in the system.As the detonation proceeds.

• The armature expands into a conical front which moves at the detonation velocity.

COAXIAL GENERATOR

• The top sketch shows a variant of this class of generator.Here,the central cyclinder plays te role of stator of such while the outer cyclinder becomes the armature.

• These generators have low impedance ,but are extremely rugged,can carry very large current and are quite efficient in conversing flux.

• They are frenquenly built as an extension of spiral generator ,whose armature has been extended in lenght to power the coaxial section.

• It common to find that this stage of such a multi stage generator accounts for much of their overall again.

• In some cases,the stators have been especially contoured to approximately match the armature expansion angle so that closure in this last section is almost simultaneous near burnout to increase its effective impedance

COAXIAL GENERATOR

• The below photograph shows a series of increasingly large helical or spiral generators boosting a final output coaxial generator.

• The lower photgraph shows a coaxial generator with a spiral booster generator

Summary of generator Classes

• The various classes of FCG all operate on the same principle,yet each has its own unique set of capabilities.

• Coaxial Generator• Have low gain• Can generate very large currents and energies in low inductance load.

• Spiral Generator• Have high current and energy gains• often require power conditioning.• Are widely used as a booster for other generator.

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TYPICAL AREA OF USE

• The following lists are past and current areas that flux compression generators are used for.

• Historical uses: • Charged particle beam diodes • Imploding plasmas • Large collection of defence .• Modern day uses: • Biological samples • Environmental • Biomedical • Hydrodynamics programs and high magnetic field

research • Exploration for oil and minerals • Landmine detection

• Q & A Session

QUESTION

1.What is Flux Compression Generators?

2.Name the Basic component of generators?

3.Explain Faraday’s law of flux conservation ?

4.Why the generator and most of the experimental apparatus is completely destroyed after experiment done?

1. Flux Compression Generators (FCGs) are defined to be devices that convert the chemical energy of high explosives into electromagnetic energy by using the explosive to mechanically compress a magnetic field complety enclosed within a metallic boundary.

2. stator winding,armature,explosive charge and intiation point. 3. ifthe area changes the flux density BF must increase.4. because used high explosive elements like TNT.