US3461350A - Devices for producing a high intensity magnetic field - Google Patents

Description

Aug. 12, 1969 c. RIOUX 3,461,350

DEVICES FOR PRODUCING A HIGH INTENSITY MAGNETIC FIELD Filed April 20. 1967 United States Patent 3,461,350 DEVICES FOR PRODUCING A HIGH INTENSITY MAGNETIC FIELD Christian Rioux, Antony, France, assignor to Centre National de la Recherche Scientifique, Paris, France, a

French government administration Filed Apr. 20, 1967, Ser. No. 632,278 Claims priority, application France, Apr. 26, 1966,

Int. Cl. noni 47/22 US. Cl. 317-123 6 Claims ABSTRACT OF THE DISCLOSURE The device comprises two juxtaposed cylindrical elements divided into laminated portions by cylindrical slots of spiral-shaped cross section. The feed of current is effected at the periphery of said cylindrical elements which are insulated from each other by means of a transverse screen and electrically connected together along their inner walls by means of a coaxial sleeve.

The present invention relates to devices capable of producing high intensity magnetic fields in relatively large spaces and it is more especially concerned, among these devices, with those wherein the magnetic field that is produced is of the pulsing type.

The chief object of this invention is to provide a device of this kind which is better adapted than those existing at the present time to meet the requirements of practice, particularly concerning the improvement of their mechanical resistance, the reduction of their internal electric resistance and the nearly complete elimination of some noxious effects such as the skin effect.

The invention consists chiefly in making a device of this kind which comprises: two tubular elements of an electricity conducting material divided into laminated portions by at least one electrically insulating cylindrical layer having in cross section the shape of a spiral segment, said masses being disposed axially one at the end of the other with the interposition of an electrically insulating screen between them, the directions of their respective laminated portions being crossed, means for electrically connecting together in series the inner (or outer) annular edges of said two elements; and means for electrically connecting to a high intensity current source the outer (or inner) annular edges of said elements.

It is known that some single pole machines without iron elements in pulsing operation can deliver very intensive electric current pulses, which may reach or even exceed one million amperes, during a time period of about of a second and for an electromotive force of about 50 volts for instance.

The use of sources of this type in combination with conventional devices, of the kind of coils, for the production of high intensity magnetic fields presents a number of difiiculties.

In particular such devices have a bad mechanical resistance under the effect of the high intensity current that flows therethrough.

Furthermore, considerations relative to impedance adaptation require the use of systems of low impedance, for instance of the order of magnitude of some microhms, for the resistance and of one microhenry for the selfind-uction coil. Now the coils used up to this time do not have a sufiiciently low impedance, and furthermore, they are the seat of an important skin effect, account being taken of the very short duration of the pulses, which skin effect increases, as it is known, the impedance of the coil.

The present invention permits of obviating these defects.

Preferred embodiments of the present invention will be hereinafter described with reference to the appended drawings, given merely by way of example, and in which:

FIG. 1 is an axial section on the line II of FIG. 2 of a device for creating a high intensity magnetic field according to the present invention;

FIG. 2 is an end view corresponding to FIG. 1;

FIG. 3 is an axial sectional view of this device provided with a shielding cylinder;

FIG. 4 is a diagrammatical view explaining the reduction of the skin effect in the device according to this invention; and

FIG. 5 is an axial sectional view of still another embodiment of the device according to this invention.

The device of FIGS. 1 and 2 essentially comprises two masses 1 and 2 identical to each other (or at least symmetrical of each other with respect to a point) made of an electricity conductive material such as copper. Each of said masses is made of a cylinder of revolution in which has been provided a plurality of cylindrical slots 3, 4, 5, 6. In cross section, these slots substantially have the shape of spiral segments, as shown by FIG. 2. They have between them a plurality of laminated portions, such as 7 and 8, electrically insulated from one another by means of a solid insulating substance 9 provided in the slots.

Masses 1 and 2 are mounted on a conductive cylinder 10 provided with longitudinal slots 10a in order to avoid screen effects.

The whole is arranged in such manner that two faces of the same nature are disposed opposite one another. In these conditions, the spiral slots of the two masses and also the laminated portions between these slots are crossed, respectively.

FIG. 2 shows, in dotted lines, slots 11, 12, 13, 14, provided in mass 2 to limit between them laminated portions such as 15 and 16.

The edges of masses 1 and 2 that are adjacent to each other are separated by a screen 17 made of a molded electric insulating substance which may be either identical or not to that disposed in the slots. Around masses 1 and 2 are disposed two rings 18 and 19 provided with respective annular flanges 20 and 21.

In order to avoid screen effects, these rings 18 and 19 are preferably provided with slots as shown at 18w in FIG. 2 and, in this case, every laminated portion (such as 15) extends over one half revolution, or possibly an integral number of half revolutions.

If the two flanges 20' and 21 are connected to the respective terminals of a current source 34, an electric current flows in the laminated portions of masses 1 and 2 connected in series by cylindrical sleeve 10.

FIG. 1 shows, at 22 and 23, the direction of current in two laminated portions 8 and 15, account being taken of the polarity indicated in this figure.

FIG. 2 similarly shows by means of arrows the path of the current for instance in laminated portion 7 then in cylinder 10 and finally (in dotted lines) in the corresponding laminated portion 24 belonging to mass 2. This current, same as those passing through the other laminated portions, follows substantially the middle line of these laminated portions.

Concerning the magnetic eifects of these currents, it may be considered that in every laminated portion they may be decomposed into a series of radial and azimuthal components.

The radial components of said currents create in the zone comprised between masses 1 and 2 an azimuthal magnetic field, but the self-inductance of this field is negligible if said laminated portions extend over a sufficiently great portion of a circumference, for instance over at least one third or one half of a circumference.

The azimuthal components of the above mentioned currents create the main axial magnetic field represented by the lines of force 35 in FIG. 1.

This field may be of very high intensity and reach several hundred kilogauss during time periods of the order of from 100 microseconds to one second for current pulses of the order from 1 to ma, the total resistance of the coil that is formed being easily of the order of only some microhms and its self-inductance of the order of 1 microhenry.

Such a field may be applied to spaces or structures of relatively great volume disposed in the central portion 36 of the coil (the diameter of which is for instance of the order from 10 to cm.) in order to study the effects produced in these spaces or structures or to accelerate particles or to create high temperatures, or plasmas, in said zone, which may constitute only one portion of a closed tubular space.

As source 34 of current pulses of very high intensity, it is advantageous to make use of a machine of the type described in the United States Patent No. 3,270,228 filed on Mar. 15, 1963, and issued on Aug. 30, 1966, in my name for improvements in machines and methods for producing very high intensity electric currents.

Such a structure has a very high mechanical resistance but it may still be reinforced.

For instance, FIG. 3 shows a device such as above described but to which has been added an external shielding made of two cylinders 25 and 26. These cylinders may be made for instance of steel having a high mechanical resistance. FIG. 3 does not show the details of the inner arrangement as above described with reference to FIGS. 1 and 2. It should be noted that, with such a construction, the inner arrangement including the copper and insulating substance parts, works under compression stresses and in uniform conditions, which is favorable to a good behaviour of the materials. Only the terminals, consisting of flange portions and 21, are submitted to extrusion stresses. Another advantage of a structure according to the present invention is the possibility of obtaining a device of very low impedance. When the laminated portions extend over less than one half circumference, the system is equivalent to a coil having a number of revolutions lower than one. Therefore the length of the laminated portions will be chosen on account of the maximum impedance not to be exceeded.

FIG. 4 illustrates still another advantage of the invention, relative to the reduction of the skin effect.

It will first be reminded that inner cylinder 10 is provided with longitudinal slots 10a to avoid screen effects.

If the magnetic field produces parasitic current between the laminated portions, which might produce skin eifects, this current can flow only over the 8-shaped path such as shown at A, B, C, D, E, F in FIG. 4, which corresponds to two groups of laminated portions 27, 28 and 29, 30, respectively, in masses 1 and 2 (these laminated portions may be considered as forming a circuit closed through their current feed outer terminals).

For the sake of clarity, each laminated portion and the current that flows therethrough have been represented by two parallel lines close to each other and the structure of FIG. 2 has been reduced to two concentric circles.

The axial magnetic field inside the laminated portions of the device decreases slowly from the axis toward the periphery and the distribution of this field has a symmetry of revolution.

It follows that the total flux cut by the 8-shaped spire A, B, C, D, E, F is zero and that the electromotive force produced by this spire A, B, C, D, E, F is also zero whatever be the field instantaneous variations.

Therefore there is no flow of current between the laminated portions and the skin effect is limited to that which may exist within the thickness of every laminated portion considered separately.

The latter can be made negligible by choosing a. sulficiently great number of laminated portions (in practice at least equal to four and preferably of the order of six, eight or more, a construction including one hundred laminated portions and even more being possible).

It should be noted that the skin effect due to the radial component of the magnetic field is not eliminated. But this effect is negligible in relative value if the axial length of every cylindrical mass is sufficient and for instance at least of the order of magnitude of its mean diameter. Eventually, the coil might be divided into several coils juxtaposed axially end to end.

It should further be noted that the currents flowing along line A, B, C, D, E, F produce an azimuthal magnetic field which may be submitted to screen effects from the laminated conductors and modify the distribution of the magnetic field in the conductors. In order to make this effect negligible, it suffices, as above stated, to have the laminated portions extending over a sufficiently great portion of a circumference, for instance over at least one third or one half of a circumference.

Therefore all the parasitic current produced by the variations of the magnetic field may easily be made negligible as compared with the main currents which create this field.

FIG. 5 shows a modification of the structure of FIG. 3.

This modification may be used in the case of high intensity fields requiring very high currents.

It will be seen that the inner ring 10 of FIG. 1 which forms a junction between masses 1 and 2 has been replaced in this case by a sleeve 31 disposed on the outside of the laminated cylinders. The inflow of current is effected on the contrary on the inside by means of two cylindrical sleeves 32 and 33. The whole is shielded by means of a cylinder 37 provided with an axial recess for the passage of terminals 32 and 33. Of course, this cylinder 37 is made of two portions to permit the mounting of the inner structure.

With such a construction, the two terminals are subjected only to negligible stresses and there is no tendency to extrusion. A line provided with arrows indicates the general path of travel of the current through masses 1 and 2.

Of course for lower magnetic fields it will be preferable to choose the structure illustrated by the first figure wherein the disposition of current inlets is simpler.

The present invention has over the conventional systems many advantages, in particular concerning the good mechanical behaviour of the device under the effect of the high current that flows therethrough, the possibility of adjustment of its impedance to a very low value and a practically negligible skin effect.

In a general manner, while the above description discloses what are deemed to be practical and efiicient embodiments of the present invention, said invention is not limited thereto as there might be changes made in the arrangement, disposition and form of the parts without departing from the principle of the invention as comprehended within the scope of the appended claims.

What I claim is:

1. A device for producing a high intensity magnetic field which comprises, in combination,

two tubular elements having a common axis and disposed end to end so that the longitudinal walls of one form extensions of the longitudinal walls of the other, respectively, each of said elements comprising laminated portions of an electricity conducting material separated by slots in the form of surfaces of revolution about said axis having their generatrices extending in the general direction of said common axis, the cross sections of said cylindrical surfaces consisting of spiral segments, curved in opposed direction for said two elements respectively, said slots being filled with an insulating material, a screen of an insulating material transverse to said tubular elements forming a partition between them,

electricity conducting means for connecting together two corresponding respective longitudinal walls of said elements, and

a high intensity electric current source having its terminals connected to the other two corresponding longitudinal walls of said elements respectively.

2. A device according to claim 1 wherein the longitudinal Walls of said elements that are connected together are the inner walls and the longitudinal walls of said elements that are connected with the terminals of said current source are the outer walls.

3. A device according to claim 1 wherein the longitudinal walls of said elements that are connected together are the outer walls and the longitudinal walls of said elements that are connected with the terminals of said current source are the inner walls.

4. A device according to claim 1 wherein the means for electrically connecting together the two elements consist of a cylindrical sleeve of an electricity conducting material provided with a longitudinal slot and extending axially over the whole length of these two elements and of the inter-mediate insulating screen.

5. A device according to claim 1 wherein the electric connection between the current source and each of said elements is ensured through a ring of an electricity conducting material provided with a longitudinal slot, every laminated portion extending over an integral number of half circumferences.

6. A device according to at least claim 1 further characterized in that the two tubular elements are surrounded on the outside thereof by a high resistance shielding JOHN F. COUCH, Primary Examiner DENNIS JAY HARNISH, Assistant Examiner US. Cl. X.R.

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