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Publication numberUS3237059 A
Publication typeGrant
Publication dateFeb 22, 1966
Filing dateSep 23, 1963
Priority dateOct 4, 1962
Also published asDE1298646B
Publication numberUS 3237059 A, US 3237059A, US-A-3237059, US3237059 A, US3237059A
InventorsPaul Meyerer
Original AssigneeSiemens Ag
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Permanent magnet system for producing a magnetic field for the focused passage of a beam of electrons
US 3237059 A
Abstract  available in
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Claims  available in
Description  (OCR text may contain errors)

Feb. 22, 1966 P. MEYERER 3,237,059

PERMANENT MAGNET SYSTEM FOR PRODUCING A MAGNETIC FIELD FOR THE FOCUSED PASSAGE OF A BEAM OF ELECTRONS Filed Sept. 23, 1963 3 Sheets-Sheet l Feb. 22, 1966 MEYERER 3,237,059

PERMANENT MAGNET SYSTEM FOR PRODUCING A MAGNETIC FIELD FOR THE FOCUSED PASSAGE OF A BEAM OF ELECTRONS Filed Sept. 25, 1965 3 Sheets-Sheet 2 Fig.3

Feb. 22, 1966 MEYERER 3,237,059

PERMANENT MAGNET SYSTEM FOR PRODUCING A MAGNETIC FIELD FOR THE FOCUSED PASSAGE OF A BEAM 0F ELECTRONS Filed Sept. 23, 1963 3 Sheets-Sheet 5 United States Patent 3 237,059 PERMANENT MAGNE T SYSTEM FOR PRODUCHNG A MAGNETIC FIELD FOR THE FOCUSED PAS- SAGE OF A BEAM OF ELECTRONS Paul Meyerer, Ottobrunn, near Munich, Germany, assignor to Siemens & Halske Aktiengescllschaft, Berlin and Munich, a corporation of Germany Filed Sept. 23, 1963, Ser. No. 310,802 Claims priority, application Germany, Oct. 4, 1962,

9 Claims. (Cl. s17 20e The present invention relates vto a system of permanent magnets for producing a substantially homogeneous magnetic field for the focused passage of a beam of electrons over an extended path, especially for high power travelingwave tubes, comprising permanent magnets which are arranged with axial symmetry about the axis of the system, and are magnetized radially to the axis of the system, and the outwardly disposed poles of which are magnetically short-circuited in the longitudinal direction of the system, there being provided between the magnet poles of opposite polarity arranged at the two ends of the system in the longitudinal direction thereof, further magnet poles which are respectively of the same polarity up to the center of the system, which magnet poles efiect a homogenizing of the course of the magnetic field, at least in the region of said magnet poles.

In electronic tubes for very high frequencies, and particularly in traveling Wave tubes, it is, as is known, fre quently necessary to conduct a beam of electrons over an extended path and focused in such a manner that the diameter of the beam of electrons remains as constant as possible. it is known to use magnetic coils for this purpose. The field strength on the axis of a coil magnet is not homogeneous, but greater in its center that at its ends. One known method of homogenizing the coil field consists in arranging the winding of the magnet coil on a supporting body of step-shaped profile, the number of ampere conductors per inch increasing away from the center of the coil.

' Magnetic coils have the disadvantage that they consume electric power. The tendency therefore has been increasingly toward using permanent magnet systems for the focused guiding of the beam of electrons of a velocitymodulated tube. Tubular and barrel-magnets are known for use as permanent magnets for the production of a substantially homogeneous magnetic field for the focused guiding of a beam of electrons. In order, in the case of a system of permanent magnets having a tubular, cylindrical permanent magnet, to homogenize the magnetic field on the axis of the system, it is known to provide within the magnet a hollow cylinder of ferromagnetic material, the cross-section of which tapers from the center at least toward one end. It is likewise known, in connection with a system of tubular permanent magnets, in order to obtain a homogeneous distribution of the magnetic field, to compose the tubular magnet of two oppositely, radially magnetized tube parts which in part demagnetize each other, thus bringing about the desired magnetic potential distribution along the axis of the magnetic system.

In all of these known systems employing a tubular or barrel magnets, there is a considerable magnetic scattering flux or leakage in the outer space of the magnet so that very heavy magnets of high energy content are necessary, the magnetic induction of which contributes only to a slight extent to the useful magnetic flux.

In order to suppress the scattering flux in the outer space of a permanent-magnet focusing system, it is known to develop the focusing system of radially magnetized permanent magnets which are respectively grouped at the beginning and end of the system in star shape around the 3,237,059 Patented Feb. 22, 1966 axis of the system and rest with their outer ends against pieces of soft iron which extend in axial direction and magnetically connect together the outer poles of the permanent magnets. In order to obtain thereby sufiicient homogeneity of the magnetic field on the axis of the sys tem, the inner ends of .the permanent magnets are connected by a tubular shell of soft iron. As a result of the presence of the tubular shell of soft iron, a considerable part of the magnetic induction again does not contribute toward the focusing of the beam of electrons.

In order to avoid the tubular shell of soft iron, it is finally known, in one such system of permanent magnets, to provide, at a slight distance from the permanent magnets which are arranged at the two ends of the system, and parallel with them, another set of magnet bars arranged in star-shape with respect to the axis of the system, and which are magnetized in the same direction as the permanent magnets arranged at the ends of the system. These additional magnet bars should be so dimensioned that the focusing magnetic field is homogenized in their vicinity. A particularly good homogenization of the course of the magnetic field over the entire length of the magnet system, such as is obtainable by means of a soft-magnetic guide tube, is, however, not obtained hereby. The course of the magnetic field, rather, still shows noticeable undulations so that the system of permanent magnets is not suitable for the focused guiding of a beam of electrons over an extended path (for instance more than 20 cm). Furthermore, the corresponding construction has a considerable internal scatting fiux which necessarily draws energy from the two sets of permanent magnets arranged at the ends of the system. For thesepermanent magnets, there are therefore again required magnet materials which have a considerable magnetic energy content.

The object of the present invention is to create a system of permanent magnets for obtaining a substantially homogeneous magnetic field for the focused passage of a-beam of electrons over an extended path, and particularly for highpower traveling wave tubes, in which the Weight of the magnet, for a given useful flux, can be substantially reduced as compared with the known permanent magnets. To achieve this purpose, there is proposed a permanent-magnet system of the initially mentioned kind in which, in accordance with the invention, the permanent magnets form on their side facing the system axis, a plurality of magnetic poles following closely upon each other, the magnetic potential of which decreases in such a manner from the ends toward the center of the system that all lines of force extending from the individual magnetic poles extend inside the system substantially parallel to the system axis.

The invention makes it possible to use for the permanent magnets a material which has a low energy content and a very high coercive force (I-I 2000 oersteds). The reason for this is that in the case of a permanent-magnet system in accordance with the invention, the ratio of the magnetic useful flux to the magnetic scattering flux is very high and therefore essentially only the energy requirement of the magnetic useful flux need be covered. By material of high coercive force and low energy content, there is to be understood a magnet material in which the quotient of the magnetic induction at the operating point B A divided by the magnetic field strength at the operating point H is of the order of magnitude of a one place number. As magnet materials of this type, hardmagnetic ferrites or alloys having a platinum-cobalt base are, for instance, known. In accordance with the known laws of the dimensioning of permanent magnets of a material of high coercive force and low energy content, it follows that such permanent magnets are compact, thus resulting in a low magnet volume. Moreover, when using hard-magnetic ferrites instead of the Alnico alloys heretofore customary for permanent-magnetic focusing systems, the weight of a permanent magnet in accordance with the invention becomes even less since ferrites have a low specific weight.

A permanent magnet system in accordance with the invention advantageously consists of permanent magnets which are arranged in close succession, one behind the other, and the lengths of which continuously decrease from the two outer ends toward the center of the system. The individual permanent magnets are, in this connection, as close as possible to each other. In the border case, there is obtained a unitary permanent magnet which tapers from the end of the system to the outside of the system in a step-wise, or wedge-shape manner; The permanent magnets which are magnetized radially to the axis of the system may be annular or grouped as magnet bars in star-shape around the axis of the system.

Further details of the invention will now be explained with reference to the accompanying drawings showing embodiments thereof.

FIG. 1 shows a longitudinal section through a permanent magnet system according to the invention;

FIG. 2 indicates the course of the field of a permanent magnet system according to FIG. 1;

FIG. 3 represents an end view of a permanent magnet system according to the invention;

FIG. 4 is a longitudinal section through the system represented in FIG. 3; and

FIG. 5 shows a permanent magnet system comprising reinforcing end magnets for supplying the energy requirements caused by unavoidable scattering flux.

Referring now to FIG. 1, in a cylindrical soft-iron tube 1, there are arranged radially magnetized rings 2 which consist for instance of hard-magnetic ferrite of high coercive force. The inner diameter of the rings 2, the magnetic poles of which, facing the axis of the system, are in each case of the same polarity as each other from the end of the system to the center, increases progressively from the two ends of the system toward the center thereof. The height of the individual rings 2 is so dimensioned that their magnetic poles, facing the axis of the system, have a magnetic voltage of such a value that the magnetic lines of potential in the entire inner space of the system of permanent magnets are substantially perpendicular to the axis of the system and have practically the same spacing from each other. This potential pattern is indicated by the lines 3, the numerals which are provided in each case with a positive or negative sign in the magnet poles of the rings 2 facing the magnet axis, representing normalized values of the magnetic voltage. The result is then that all lines of force extending from the individual magnetic poles extend within the system substantially parallel to the axis of the system since, as is known, magnetic lines of force always are at right angles to the lines of potential. The lines 4 indicate how the magnetic lines of flux extend between the two magnetic poles arranged at the ends of the magnet system. The field distribution is in this connection more uniform, the finer the grading of the permanent magnets is effected. In the outer space of the system of magnets, there is no scattering flux at all, along the magnet system (in contradistinction to a known tubular or barrel magnet), due to the magnetic short-circuit represented by the soft-iron cylinder 1. Only at the two ends of the system is there a slight scattering flux which is indicated by the field lines 5. The result thus is that for a given required induction along the axis of the system of magnets (for instance an induction of 500 G), the energy content of the permanent magnets can be substantially less even over an extended path (or instance greater than 20 cm.) than in the case of the known initially described permanent magnet systems.

Below FIG. 1, there is shown in FIG. 2 the course of the field of a system of permanent magnets in accordance with FIG. 1, the x-axis of the rectangular coordinate system indicating the path 2 in axial direction of the system and the y-axis indicating the magnetic induction B The full line curve 6 then represents the value of the magnetic field 13 along the axis of the focusing system of FIG. 1. The dashed curve 7 indicates that in the case of a permanent-magnet system in accordance with FIG. 1, the field can be increased by a corresponding increase in the magnetic voltage on the output side of the magnet system, as required at times for traveling-wave tubes of high power.

In the permanent magnet system shown in FIGS. 3 and 4, there are used, instead of the annular permanent magnets 2 of FIG. 1, magnet bars 8 which are arranged in star-shape around the axis of the system and have their outer poles resting against soft iron bridges 9. In a manner similar to FIG. 1, the length of the individual magnet bars which are arranged in a row in close succession in the longitudinal direction of the system, decreases from the two ends toward the center of the system. With suitable dimensioning of the length of the magnet bars 8, there is again obtained a potential distribution such as that shown in FIG. 1. The individual soft iron rails 9 are connected with one another by a soft iron sheet 10 to form a screening housing which surrounds the system of magnets. The occurrence of scat tering flux in the outer space of the system, aside from the scattering flux at the ends, is in this way prevented. Numerals 11 indicate pole shoes around which are arranged the magnet bars on the two ends of the system and into which a traveling wave tube can be inserted. It may be pointed out that such pole shoes can also be used in permanent magnet systems, such as shown in FIG. 1.

It is in connection with a permanent magnet system according to the present invention, particularly advantageous to cover the energy requirement of the fundamentally unavoidable small scattering flux at two ends of the permanent magnet system, by reinforcing the two permanent magnets, arranged at the ends of the system by means of additional magnets which are also radially magnetized. FIG. 5 shows an embodiment utilizing this feature.

The permanent magnet system of FIG. 5 is substantally similar to the system shown in FIGS. 3 and 4. The two magnetic bars 12 disposed at the ends are merely reinforced by further magnetic bars 13. FIG. 5 shows both, the case in which the magnetic bars 13 have the same as well as the case in which they have a smaller magnetic voltage than the adjacent magnetic bars 12, depending on how high the energy requirement to cover the outer scattering flux is.

The invention is not inherently limited to the illustrated embodiments. In particular, it is not necessary for the permanent magnets to be stepped-down on the inside, as it is possible that they also be stepped down on the outside of the system. In such a case, the soft-magentic screening covering must have a shape corresponding to the mode of stepping. Furthermore, more than four magnet bars can be grouped in a plane at right angles to the axis of the system in star-shape about such axis. It is likewise possible to use instead of hard-magnetic ferrites, any other suitable and known material of high coercive force and low energy content.

Changes may be made within the scope and spirit of the appended claims which define what is believed to be new and desired to have protected by Letters Patent.

I claim:

1. A permanent-magnet system for producing substantially homogeneous magnetic field for the focused passage of a beam of electrons over an extended path, particularly for high power traveling-wave tubes, comprising permanent mangents disposed along and arranged with axial symmetry about the axis of the system, said magnets being magnetized radially to the system axis, means at the outer poles of said permanent magnets for magnetically short circuiting such poles in the longitudinal direction of the system, said permanent magnets being so disposed that the poles disposed at one end of the system have a polarity which is opposite to that of the corresponding poles at the other end of the system, said permanent magnets forming further magnetic poles arranged in the longitudinal direction of the systern, between said magnetic poles of opposite polarity arranged at the two ends of the system, the respective further magnetic poles being of the same polarity up to the center of the system and effecting a homogenizing of the course of the magnetic field, at least in the vicinity of said magnet poles, said permanent magnets forming on the side thereof which faces the axis of the system, a plurality of magnetic poles closely following one another, the magnetic potential of which decreases from the ends toward the center of the system so that all lines of flux extending from individual magnetic poles pass within the system substantially parallel to the system axis.

2. A permanent magnet system according to claim 1, wherein the permanent magnets are made of hard-magnetic ferrite material.

3. A permanent magnet system according to claim 2, wherein the permanent magnets have, as seen from the two ends toward the center of the system, a progressively decreasing height.

4. A permanent magnet system according to claim 3, wherein the permanent magnets are stepped down stepwise, the outer ends of the permanent magnet lying in a common plane.

5. A permanent magnet system according to claim 4, wherein the individual steps are respectively formed by annular radially magnetized permanent magnets which are arranged in a row in the longitudinal direction of the system.

6. A permanent magnet system according to claim 4, wherein the individual steps are respectively formed by magnet bars arranged in star-shape about the axis of the system, said bars being located one behind the other in the longitudinal direction of the system.

7. A permanent magnet system according to claim 5, wherein the permanent magnets, which are arranged at the two ends of the system, are reinforced by additional magnets which are likewise radially magnetized and which supply the energy for the external scattering flux.

8. A permanent magnet system according to :claim 7, wherein the additional magnets have magnetic potentials which are not greater than those of the adjacent permanent magnets.

9. A permanent magnet system according to claim 1, wherein the magnetic short-circuiting of the outer poles of the permanent magnets is effected via elongated softiron rails which are connected together to form a housing surrounding the system.

References Cited by the Examiner UNITED STATES PATENTS 2,876,373 3/1959 Vieth et al. 313-84 FOREIGN PATENTS 770,133 3/1957 Great Britain.

OTHER REFERENCES Parker et al.: Permanent Magnets and Their Application, New York, John Wiley and Son, Inc., 1962, QC. 757 F 37, pp. 271-274.

ROBERT K. SCHAEFER, Acting Primary Examiner.

JOHN F. BURNS, Examiner.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US2876373 *Dec 27, 1956Mar 3, 1959Siemens AgMagnet system for the focusing of electron beams
GB770133A * Title not available
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3436587 *Jan 21, 1966Apr 1, 1969Siemens AgPermanent magnet system for the generation of a substantially homogeneous magnetic field for the bundled guidance of an electron beam over a relatively long path,especially for traveling wave tubes
US3686527 *Dec 12, 1969Aug 22, 1972Sanders Associates IncHigh-speed synthesized field focus coil
US4433270 *Jan 28, 1980Feb 21, 1984Drozdov Sergei SReversible periodic magnetic focusing system
US4614930 *Mar 25, 1985Sep 30, 1986General Electric CompanyRadially magnetized cylindrical magnet
US4647887 *Dec 24, 1984Mar 3, 1987The United States Of America As Represented By The Secretary Of The ArmyLightweight cladding for magnetic circuits
US4654618 *May 1, 1986Mar 31, 1987The United States Of America As Represented By The Secretary Of The ArmyConfinement of kOe magnetic fields to very small areas in miniature devices
US4658228 *May 1, 1986Apr 14, 1987The United States Of America As Represented By The Secreatry Of The ArmyConfinement of longitudinal, axially symmetric, magnetic fields to annular regions with permanent magnets
US4701737 *May 30, 1986Oct 20, 1987The United States Of America As Represented By The Secretary Of The ArmyLeakage-free, linearly varying axial permanent magnet field source
US4720692 *Aug 11, 1986Jan 19, 1988The United States Of America As Represented By The Secretary Of The Air ForceLong, narrow, uniform magnetic field apparatus and method
US4953555 *Oct 12, 1989Sep 4, 1990The United States Of Americas As Represented By The Secretary Of The ArmyPermanent magnet structure for a nuclear magnetic resonance imager for medical diagnostics
US4999600 *Oct 13, 1987Mar 12, 1991Centre National De La Recherche ScientifiqueCylindrical permanent magnet to produce a transversal and uniform induction field
US5014032 *Oct 13, 1987May 7, 1991Centre National De La Recherche ScientifiqueCylindrical permanent magnet with longitudinal induced field
US5028903 *Oct 13, 1987Jul 2, 1991Centre National De La Recherche ScientifiqueSpherical permanent magnet with equatorial access
US5319339 *Mar 8, 1993Jun 7, 1994The United States Of America As Represented By The Secretary Of The ArmyTubular structure having transverse magnetic field with gradient
US5347254 *Jan 5, 1994Sep 13, 1994The United States Of America As Represented By The Secretary Of The ArmyTubular structure having transverse magnetic field with gradient
US5576679 *Oct 24, 1995Nov 19, 1996Shin-Etsu Chemical Co., Ltd.Cylindrical permanent magnet unit suitable for gyrotron
US5786741 *Dec 21, 1995Jul 28, 1998Aura Systems, Inc.Polygon magnet structure for voice coil actuator
US5828173 *Dec 4, 1996Oct 27, 1998Forschungszentrum Karlsruhe GmbhMagnetic system for gyrotrons forming a wavy magnetic field
US5929732 *Apr 17, 1997Jul 27, 1999Lockheed Martin CorporationApparatus and method for amplifying a magnetic beam
US7405502 *Sep 13, 2006Jul 29, 2008Lg Electronics Inc.Motor and washing machine including the same
US8179220 *May 28, 2008May 15, 2012Otto VoegeliConfined field magnet system and method
US8294543Oct 23, 2012Otto VoegeliConfined field magnet system and method
US20070182264 *Sep 13, 2006Aug 9, 2007Lg Electronics Inc.Motor and washing machine including the same
US20090295378 *May 28, 2008Dec 3, 2009Otto VoegeliConfined field magnet system and method
EP0476609A2 *Sep 18, 1991Mar 25, 1992TDK CorporationPermanent magnet magnetic circuit
Classifications
U.S. Classification335/210, 315/5.35, 335/306
International ClassificationH01J23/00, H01J23/02, H01J23/087, H01F7/02
Cooperative ClassificationH01F7/0278, H01J23/087, H01J23/00
European ClassificationH01F7/02C1, H01J23/087, H01J23/00