US3493810A

US3493810A - Magnetron construction

Info

Publication number: US3493810A
Application number: US706119A
Authority: US
Inventors: Benjamin V Valles
Original assignee: Litton Precision Products Inc
Current assignee: Northrop Grumman Guidance and Electronics Co Inc
Priority date: 1968-02-16
Filing date: 1968-02-16
Publication date: 1970-02-03
Anticipated expiration: 1987-02-03
Also published as: GB1212948A; FR1596293A; DE6807594U; SE340132B; JPS4938067B1; DE1809691B2; NL6818179A; DE1809691A1

Description

Feb. 3, 1970 B. v. VALLES 3,493,810

MAGNETRON CONSTRUCTION Filed Feb. 16, 1968 2 Sheets-Sheet 1 Feb. 3,1970 l B. v, v'ALLEs MAGNETRoNcoNsTRUcTIN 2 Sheets-Sheet 2 Filed Feb. 16, 1968 United States Patent O MAGNETRON CONSTRUCTION Benjamin V. Valles, San Jose, Calif., assignor to Litton Precision Products, Inc., San Carlos, Calif., a corporation of Delaware Filed Feb. 16, 1968, Ser. No. 706,119

Int. Cl. H01j 25/50 U.S. Cl. S-39.51 13 Claims ABSTRACT 0F THE DISCLOSURE An improved magnetron construction is provided which includes an elongated evacuated container housing in a vacuum, both the conventional emissive cathode and the resonant cavity containing anode surrounding the cathode and separated by an annular space; a top end portion of the elongated container includes a microwave window through which the microwave energy is therefrom extracted; and means are provided for conventionally establishing a crossed electric and magnetic field within the annular space between the anode and cathode within the container. The means for establishing the magnetic field within the annular space includes, external of the container, a pair of spaced parallel substantially flat rectangular ferromagnetic pole pieces of approximately equal dimensions with each having a central passage. The t-op end portion of the elongated container protrudes through the central passage in one of these pole pieces, a bottom end portion of the elongated container protrudes through the central opening in the other pole piece, and the central portion of the container is accordingly located between the two pole pieces. Cylindrical permanent magnets extend -between the confronting ends of the spaced pole pieces to the iight and the left of the central passages to provide sources of magnetic flux. The improved construction encompasses a spaced plurality of horizontal cooling fins located Ibetween and aligned substantially parallel with the at surfaces of the pole pieces. A central passage and two spaced passages separated by the central passage are located in the substantially at major surface area of each cooling fin. In each cooling 1in the central passage is located so that it surrounds and is directly or indirectly in thermally conductive contact with the outer periphery of a portion of the elongated evacuated container, while each of the other passages is aligned with and surrounds a respective one of the two cylindrical magnets. Thus, a portion of each of the cooling fins extends outwardly from the magnets to form a grill or fence-like barrier in front of each magnet, and, accordingly, this prevents direct contact between the permanent magnets and any relatively large ferromagnetic object. Notably, each -cooling fin has a bent over lip portion along each of two opposed edges. Each lip portion extends from the cooling n from which it is formed, preferably to the next adjacent cooling fin to at least partially form an air duct or channel. The lip portions of each cooling lin are preferably aligned in the same direction. However, the bottom cooling fin has the lip portions extending in the opposite direction. The central passage of each cooling n preferably includes a slightly flared rim or lip portion surrounding the passage, which extends from the fin surface in the same direction as the lip portions. Moreover, a sleeve-like conductive body of the same material as the cooling iin advantageously surrounds the outer periphery of a portion of the elongated evacuated container and is thus interposed between the fins and the container to enhance heat conduction between the container and the cooling fins.

This invention relates to a magnetron, and more parlCC ticularly, to a novel construction of a magnetron in which the cooling fins protect the permanent magnets from undesired physical contact with large objects.

The magnetron is a well known device useful for the generation of high frequency electromagnetic energy and is in the group of electromagnetic devices which rely for operation upon the eifects of crossed electric and magnetic elds. In the magnetron, electrons are emitted from an electron emissive cathode into an annular space between the cathode and a circumferentially surrounding anode in a high vacuum environment of an evacuated container. The anode contains thereabout a plurality of resonant cavities commonly formed by vanes which protrude from a cylindrical portion of the anode into the annular region; and, the means are provided for establishing a crossed electric and magnetic eld in this annular region; the electric field being conventionally established radially between the cathode and the anode by the geometry and location of the elements and the application of suitable electric potentials, and the magnetic field being established perpendicular to such electric field suitably by arrangement of elements and the use of externally connected magnets and magnetic circuits.

Acting under the influence of the electric and magnetic field, electronic interaction and oscillation occurs within the annular space between the electrons emitted from the cathode and the electric fields established within the resonant cavities to generate electrical oscillations of a very high frequency. The particular details and theory of operation of such devices can be had by reference to available literature. The high frequency or microwave, as variously termed, energy generated within the container is conducted from one or more of the anode cavities to an exit or microwave window which maintains the evacuated cavity sealed, Ibut which permits the passage of the microwave energy. f

At this point it is best to clarify the nomenclature used to describe the magnetron. Some persons denote the component consisting of the anode and cathode in the evacuated container, while they describe the external magnets, pole pieces, cooling fins, and other ancillary elements that are used either as a necessary element or a proper element to support the generation of electromagnetic energy within the container as the fittings Others, however, denote the entire assembly of sealed evacuated container, pole pieces, magnets, cooling fins, and other necessary or proper elements as the magnetron, and denote rather ambiguously the sealed evacuated container portion thereof also as the magnetron.

Accordingly, to avoid this apparent difficulty of nomenclature and to avoid confusion for purposes of this patent application, it is believed best to refer to the entire assembly of elements as a magnetron or magnetron device and to denote the evacuated container portion which contains the anode and cathode in a vacuum environment only in broad geometrical terms. Suitable terminology as is available for the other external necessary or proper ancillary elements thereof is adopted herein or is otherwise clearly defined.

As is conventional with other energy conversion devices, the generation of heat occurs as an undesirable side effect which may render the magnetron less efficient or inoperative. Hence, the heat generated during operation is normally removed from the container. Typically, the heat is generated in the anode and is conducted away by passing through the walls of the evacuated container to the outside thereof for exposure to a cooling medium. Conventionally, cooling fins are attached to the container to receive and dissipate the heat. The cooling tins are thin metal sheets of a large area and expose the heat to a large area of cooling medium. The cooling tin with the cooling medium merely acts as a heat sink and by conduction and convection transfers heat to a cooling medium such as oil or ambient air. More typically, with a blower air is forced against the cooling fins to more rapidly dissipate such heat.

Conventionally, cooling fins may be placed in contact with the walls of the evacuated container and arranged geometrically either vertically or horizontally relative to the axis of the evacuated container. The size of the cooling fins is dictated and limited to an extent either by the available space within which it must fit, taking into account the size and shape of the other elements of the magnetron, such as the magnets and the pole pieces, the size of the air blower, and the amount of heat to be dissipated.

In one highly successful and efficient magnetron manufactured by Litton Industries, Electron Tube Division of San Carlos, California, under the designation I4-5001, a particularly eilicient construction for a magnetron is used. Basically, in that construction two rectangular shaped pole pieces substantially of the same dimensions are spaced apart parallel, and each contains a central passage or opening. An elongated evacuated container which encloses the cathode and anode exists between and through the central passages and substantially at right angles to the pole pieces. The front end portion of the evacuated container with the microwave window extends through the central passage of one pole piece, and a bottom end portion of the container extends through the central passage in the second pole piece. Surrounding the evacuated container and in physical Contact therewith is an apparently wide cylindrical body. Close examination shows that this body consists of a plurality of thin individual vertically arranged cooling fins strapped together to hold them in place. Each cooling fin includes two lip portions on opposed edges and extends radially outwardly from the periphery of the elongated container portion of the magnetron. The inner lip portion of each fin abuts the outer wall of and is parallel with the axis of the elongated evacuated container. A cylindrical shaped permanent magnet is located between each of the two confronting faces at the ends of the pole pieces and extends between those faces. In one model of this magnetron each of these cylindrical magnets is surrounded by a cardboard cylinder of appropriate thickness. In another, an aluminum shield is spaced from and partially encloses each magnet. The magnets and container are clamped into place between the pole pieces by bolts which extend between the pole pieces. A pictorial representation of such magnetron is found in U.S. Patent D. 208,861.

The cardboard cylinder or aluminum shield referred to prevents any foreign object of ferromagnetic material from being placed into direct contact with the magnetron. As is known, when large ferromagnetic (iron) objects are placed into contact with permanent magnets, they shunt some of the magnetic ux from the magnet and, when removed, the magnetic flux emanating from the magnet is altered, the magnet s partially demagnetized and the intensity of the flux available from the magnet is reduced. With magnetrons or other crossed field devices, it is absolutely necessary that such foreign objects be maintained away from the permanent magnets. Inasmuch as the operation of a magnetron device depends upon the maintenance of the critical design values of the electric and magnetic fields within the annular space between the cathode and anode, any departure of the magnetic fields from such critical levels renders the magnetron wholly or partially inoperative. Accordingly, great care is taken to prevent the demagnetization of the magnets when the magnetron is handled or is otherwise in use, which heretofore included the alternatives of an aluminum surround or cardboard wrapping. However, it is apparent that such preventatives require additional and different types of manufacturing processes and procedures than is used for the assembly of the other elements of the magnetron, which necessarily add to its cost.

Therefore, it is an Object of the invention t9 provide a magnetron in which the likelihood of accidental demagnetization of the permanent magnets is reduced;

It is a further object of the invention to prevent direct contact between the permanent magnets of a magnetron and a foreign ferromagnetic object; and

It is a still further object of the invention to provide a magnetron in which the permanent magnets cannot contact any large foreign ferromagnetic objects or be partially demagnetized thereby, even though special cardboard sleeves are not used; and

It is an additional object of this invention to provide a magnetron which requires no separate elements or assembly operations for providing elements which prevent contact between the magnets and large foreign magnetic objects.

The foregoing and other objects and advantages of the invention are better understood by considering the following detailed description together with the accompanying figures of the drawings, in which:

FIGURE l illustrates a partially exploded and cutaway perspective view of a novel magnetron Construction embodying the invention;

FIGURE 2 illustrates the construction of a cooling fin used in the embodiment of the invention shown in FIG- URE l and in FIGURE 3;

FIGURE 3 illustrates in perspective a novel magnetron embodying the invention; and,

FIGURE 4 is a side view of the embodiment of FIG- URE 3.

Briefly stated7 the invention is characterized by a construction of a magnetron in which a plurality of horizontally arranged parallel cooling fins in addition to being in thermally conductive contact with the elongated evacuated container surround two spaced permanent magnets, and thus present a grill or fence-like barrier to foreign ferromagnetic objects.

In order to permit a less obstructed examination of the detail in this embodiment of the invention, portions of elements in FIGURE 1 are cutaway and others are exploded. The magnetron includes `a sealed evacuated container portion indicated generally as one which includes internally (not illustrated) the conventional cathode anode, and the concentrically spaced annular anode to form therebetween an annular space, Such anode conventionally contains a plurality of spaced vanes which project from the anode walls to within a predetermined distance of the cylindrical cathode to form an annular space. This space may be termed the interaction region. Between each of the respective vanes a radio frequency cavity resonant at the particular design frequency which the magnetron generates is formed. Also included therein is a filament or heater, which extend externally of the container at terminal leads 3 and 5, provide electrical connections which extend into container 1 to the heater winding for connection to a suitable source of voltage and current.

The internal constuction of the magnetron elements looated within container 1 and container 1 itself may assume any conventional construction and, as presented here, is substantially the same as that heretofor designed, manufactured, and sold by Litton Industries, Electron Tube Division, San Carlos, California, under the designation L-500l.

A top end portion of container 1 contains a glass bulb or microwave window 7 which forms the exit for microwave energy generated in the annular region between the anode and cathode within container 1. As is conventional, such microwave energy is coupled from one of the resonant anode cavities to the microwave window 7 by means of a conductor 9 extending therebetween. The bottom portion of container 1 includes two protruding electrical terminals or leads, 3 and 5, which are insulated from each other and which are connected internally of Container 1 to a filament or heater winding.

A circular collar 11, constructed of ferromagnetic man terial is illustrated with a portion cutaway. This collar fits the outer periphery of the container and a passage in the pole pieces, hereafter described. Collar 11 forms part of the magnetic circuit and contacts a portion of container 1 that is constructed of ferromagnetic material. Elements internal of container 1 complete the magnetic circuit to the top of the interaction region. Another circular collar of ferromagnetic material is illustrated cutaway and exploded. Collar 13 also forms part of the magnetic circuit.

A cylindrical aluminum sleeve 15, illustrated with a portion cutaway, is mounted to container 1 by any conventional process, such as pressing on or shrink fitting. This ensures a strong mechanical connection between the cylindrical copper walls of container 1 and the inner walls of sleeve 15. A pair of fiat

rectangular pole pieces

17 and 19 are provided. Pole piece 17 is illustrated with a portion cutaway to permit a view of other elements hereinafter described. Upper pole piece 17 is constructed of ferromagnetic material and contains a circular opening or passage 21 therethrough. As is apparent, the upper portion of container 1, and, in particular, the microwave window 7 protrudes through this opening with the pole piece 17 abutting collar 11. A sutiable wire mesh seal 12, illustrated with a portion cutaway, fills the annular groove between window 7 and the edge of passage 21.

Likewise, the bottom pole piece 19 includes a central opening or passage 23 through which the bottom portion of container 1, including leads 3 and 5, upon assembly, protrudes. The bottom collar 13, upon assembly, tightly abuts both pole piece 19 and a wall of container 1 that is of ferromagnetic material. A first cylindrical magnet 25, suitably of Alnico V, is located between the confronting ends of

pole pieces

17 and 19 on one side of

central passages

21 and 23. Likewise, another cylindrical shaped permanent magnet 27 is located between the remaining two confronting ends of

pole pieces

17 and 19 on the opposite sides of the

central passages

21 and 23. The permanent magnets are polarized in the same direction. As assembled, finally pole piece 17 abuts the bottom of both

magnets

25 and 27 and a shoulder portion of collar 13. Collar 13 abuts a ferromagnetic wall portion of container 1. Thus, the external magnetic path is completed from one end of magnet 25 through pole piece 21, the top collar 11 and a ferromagnetic wall portion of container 1, through the magnetic path internal of container 1, a bottom ferromagnetic wall portion, collar 13 and pole piece 19, back to the other side of the magnet. A similar magnetic flux path extends from the top side of permanent magnet 27 through shoulder 11, the container 1 wall, intemal elements, bottom wall of the container, bottom collar 13, pole piece 19, returning to the 'bottom of the magnet 27.

As is conventional, elements internal of container 1 complete the path for magnetic flux from the container Walls to positions above and below the aforecited interaction region. A plurality of cooling fins 29, illustrated with a large portion -cut away, are provided. Each has a major substantially lfiat surface area 31 which is preferably arranged substantially parallel to the flat surface of the pole pieces and substantially perpendicular to the axis of the cylindrical

permanent magnets

25 and 27 and the axis of elongated container 1.

Reference is briey made to FIGURE 2 which shows in greater detail the construction of a cooling n 29 used in the embodiment of the invention disclosed in FIG- URES 1 and 3. In order to properly show the lip portion, hereinafter described, cooling iin 29 is inverted from the position in which it appears in both FIGURES l and 3.

Each of the cooling fins contains a central passage 35 which is substantially the same inner diameter as the outer diameter of sleeve 15. A second passage 37 and a third passage 39 are located on opposite sides of the central passage 35. The diameter of the latter passages is slightly larger than the diameter of the respective

permanent magnets

25 and 27. Geometrically the locations of the three openings in the cooling n are aligned with and correspond to the 4spacing and relative position of the sleeve surrounded elongated evacuated container 1 and

permanent magnets

25 and 27, illustrated in FIGURE l.

As is apparent, since

passages

37 and 39 are formed in the major surface area 31 of the cooling fin and surround the respective magnets, a portion of the cooling iin is situated between the edges of each of those passages and the edge of the cooling fin. Surrounding central opening 35 is a rim or lip portion 41 which is formed from and extends from the major surface area of the cooling fin. The depth of lip 41 may be substantially equal to the desired distance or spacing desired in the final assembly,

between adjacent cooling fins or less as desired. With the former depth the lip will function additionally to space adjacent cooling fins.

The inner diameter of lip portion 41 is substantially the same as the outer diameter of sleeve 15. Preferably, the diameter of the lip portion is slightly smaller than the diameter of central passage 35 at the surface 31 of the cooling fin in order to provide a slight inward are. The lip portion 41 compressively surrounds and engages sleeve 15 to form a tight fit, as assembled. Moreover, because the depth of lip 41 is greater than the thickness of the cooling fin, a substantially better thermal contact is effected between sleeve 15 and the major surface area 31 of the cooling fin than would be available if only the contacting portion was of the same thickness as cooling fin 29.

In addition, as shown in FIGURE 2, each cooling n includes two

edge lip portions

43 and 45 on opposed edges of the cooling fin. The lip portion is formed by bending over a portion of the cooling n substantially at right angles to major surface 31, and is preferably of a depth substantially the same as the distance desired for the adjacent cooling ns in the assembled magnetron.

Referring again to FIGURE 1, it is apparent that each cooling fin is forced onto sleeve 15 and slid along the sleeve until the surface of that cooling iin preferably abuts the end of a lip portion of a previously mounted cooling fin. Ideally in this final position,

lip portions

43 and 45 of a preceding cooling fin contact the edges of the cooling fin being mounted. This forms an air duct or channel 47. The bottommost cooling fin 29 is preferably inverted.

Accordingly, cooling fins 29 are assembled onto sleeve 15 and bottom pole piece is mounted into place. A plurality of rivets or bolts 49 extend between

pole pieces

17 and 19 passing through opposite poles therein to clamp the

permanent magnets

25 and 27 and the evacuated container 1 therebetween.

Reference is now made to FIGURE 3 which shows the preferred embodiment of the invention in assembled form to avoid confusion and simplify this explanation like elements of like figures identically labeled. In this View, a portion of sealed evacuated container 1 is visible, the microwave window 7 is shown, wire mesh seal 12,

pole pieces

17 and 19, and cooling fins 29 are clearly presented.

It is apparent that between the last and first cooling fins a plurality of substantially identical air ducts such as 47 are formed. Moreover, it is clearly seen that passage 39 surrounds a portion of permanent magnet 25 leaving a portion of the cooling fin surface protruding in front of the magnet. Not visible however, the other passage surrounds magnet 27.

As is further apparent, the protruding edges of the cooling fins 29 together form a grill or fence-like barrier to objects having a larger dimension than the distance between any two adjacent cooling fins. Since the larger ferromagnetic objects which cause the greater demagnetization of the permanent magnets, it is apparent that by a suitable choice of spacing between adjacent cooling fins, contact l"between the permanent magnets and such foreign objects is prevented.

lt is noted that the bottommost cooling lin 29 is preferably inverted; that is, it has its

lip portions

43 and 45 and lip portion 41 extending in a direction opposite to that on the other cooling ns vwhich forms an air duct or channel of a double thickness, and avoids the location of a sharp edge at the bottom.

FIGURE 4 illustrates a side view of the embodiment of the invention described in FIGURE 3. Again to avoid confusion and simplify this explanation, like elements of like figures are identically labeled. In this view it is clear that lip portion 41 is in physical contact with sleeve. Thus, since metal sleeve l5 is in tight physical contact with the walls of the elongated container, a good thermally conductive contact is provided between the walls of the elongated container and cooling fins 29. While a sleeve 15 is physically interposed between the fins and the container walls, it may with suitable changes in dimension of the elements be omitted, and the ns made to directly contact the container. However, the disclosed arrangements are clearly preferred. In addition, air ducts, such as duct 47, formed by fins 29 are clearly illustrated in this figure. In use, the embodiment of the improved magnetron, as is conventional with all other magnetrons, is connected to a conventional and suitable high voltage power supply and filament current supply. The filament supply is connected between terminals 3 and 5, and the high voltage supply is connected (negative polarity) to one of filament terminals and ground. ln the magnetron of the invention, the electron emitting cathode is internally within container i connected with the heater winding and the anode is connected to the metallic portion of container 1 which is in turn grounded. This is entirely conventional. Likewise, the electromagnetic energy generated within container 1 is extracted therefrom via the microwave window 7 and by means of waveguide or other conventional transmission line is transmitted to other conventional components of a system which uses the electromagnetic energy. Suitably such a system may be a conventional one in which the microwave energy is used to heat dielectric materials. Heat generated within container 1 is transmitted to the surfaces of cooling fins 29 where the heat is more rapidly dissipated, inasmuch as the heat is exposed to a cooling ambient, such as air, over a large number of large surfaces. Conventionally, to speed up the rate of heat dissipation, air is circulated through the formed air ducts between the cooling fins with a blower. The conventional function and use of magnetron elements is thus combined with the function of protecting the permanent magnets by encasement in the cooling fins to provide an improved magnetron.

It is understood that the embodiment and description presented are intended to clearly illustrate the invention and are not intended in any way to limit the invention, since numerous other equivalents suggest themselves to those skilled in the art and which do not depart from the spirit and scope of the disclosed invention.

For example, one or more of the collars 13 and 11 may be made integral with either the adjoining pole piece or with the adjoining magnetic wall portions of elongated container 1 by simply redesigning the geometry of the illustrated container or pole piece and machining the parts so that they properly match Moreover, while the illustrated embodiment shows a plurality of rivets 49 extending between

pole pieces

17 and 19 to permanently clamp the assembled elements together, such means may be deleted entirely. As an alternative, it is found that the magnetic strength of

permanent magnets

25 and 27 alone are sufficient to retain the ferromagnetic pole pieces and hence the other elements in position, although some slight amount of twisting movement is possible. However, to eliminate even this, small amounts of contact cement can be added to more firmly join the magnets and pole pieces. A further departure from the illustrated details which is within the spirit and scope of the invention is evident.

By suitable redesign of the elongated container 1, the aluminum sleeve 15 may be deleted and the cooling fins may be fitted directly onto the outer cylindrical walls of container 1. In such instance the outer walls of container portion 1 may have an annular portion extending from the bottom which surrounds portions of the length of the heater leads 3 and S to permit the use of the illustrated number of cooling fins.

Accordingly, it is to be expressly understood that the invention is to be broadly construed within the spirit and scope of the appended claims.

What is claimed is:

l. A magnetron of the type which includes: an elongated evacuated container having a microwave window at a top end portion thereof, electrical terminals at a bottom end portion thereof, and, including internally thereof, an electron emissive cathode and a resonant cavity containing anode surrounding and spaced from said cathode; and magnetic field means for establishing a magnetic field within the space between said anode and cathode within said elongated container; said magnetic field means further comprising, externally of said elo-ngated container: a pair of spaced pole pieces of ferromagnetic material, each having a central passage therethrough; a first permanent magnet means yextending between two confronting ends of said two spaced pole pieces to one side of said central passages; a second permanent magnet means extending between the remaining two confronting ends of said two spaced pole pieces; and wherein said microwave window protrudes through a central passage of one of said pole pieces and said electrical terminals protrude through the central passage in the other one of said pole pieces, the improvement comprising in combination: a plurality of metallic cooling fins located between said pole pieces and aligned substantially parallel thereto; and, wherein each of said cooling fins comprises: a major surface area; a central passage in said central Surface area surrounding and being in thermally conductive contact with the outer periphery of a portion o-f said elongated container; second and third passages in said surface area spaced from the edges of said major surface and spaced from each other on opposite sides of said central passage; said second passage being aligned with and surrounding said first permanent magnet means; and, said third passage being aligned with and surrounding said second permanent magnet means, whereby said cooling fins form a grill-like barrier in front of each permanent magnet means to prevent physical contact between the magnet and most geometries of foreign ferromagnetic objects.

2. The invention as defined in claim 1 wherein said thermally conductive contact between `said fins and said container comprises: a metallic sleeve on its inner periphery surrounding and tightly fitting the outer periphery of a portion of said elongated container and 0n its outer periphery tightly engaging each of said cooling fins.

3. The invention as defined in claim 2 in which said metallic sleeve and said cooling fin comprise the same ma` terial.

4. The invention as defined in claim 2 wherein each of said cooling fins includes bent over lip portions formed along each of two opposed edges, each of said lip portions being aligned at substantially a right angle to and extending in the same direction from said major surface of said cooling fin.

5. The invention as defined in claim 4 wherein each said lip portion extends between the cooling fin from which it is formed to an adjacent cooling fin to form an air duct therebetween.

6. The invention as defined in claim 5 further comprising: a rim lip portion surrounding said central opening in each of said cooling fins to enhance thermal conduction between each said cooling fin and said elongated container.

7. The invention as defined in claim 6 wherein each of said pole pieces comprises a fiat rectangular shape geometry of substantially similar dimensions, and wherein each of said permanent magnet means comprises a cylindrical shape geometry, and each of said passages in said cooling fins and pole pieces comprises a circular geometry.

8. The invention as defined in claim 6 wherein said rim lip portion extends substantially between the surface of the cooling fin from which it is formed to the next adjacent cooling fin.

9. A magnetron device for the generation of high frequency electromagnetic energy of the type which includes: an elongated evacuated container; an electron emissive cathode and a resonant cavity containing anode surrounding and spaced from said cathode enclosed within said container; a microwave Window for the extraction of microwave energy located at a top end of said container; electrical terminals at a bottom end of said container; and, wherein a crossed electric and magnetic field is to be established within the annular space in said container between said anode and cathode; and, wherein means for establishing a magnetic field within said annular space includes externally of said container: a pair of spaced substantially at pole pieces of ferromagnetic material of approximately equal length; each of said pole pieces having a central passage therethrough; a first cylindrical permanent magnet means which extends between two confronting ends of said two spaced pole pieces at substantially right angles thereto, a second cylindrical permanent magnet means which extends between the remaining two confronting ends of said two spaced pole pieces at substantially right angles thereto; and, wherein said microwave window protrudes through a central opening in one of said pole pieces, and said electrical terminals protrude through a central opening in the other one of said pole pieces; the improvement comprising in combination: a plurality of cooling ns located between said pole pieces and aligned substantially parallel with the flat surfaces of said pole pieces, each of said cooling fins having a substantially flat major surface area, a central passage in said surface area surrounding and being in thermally conductive contact with the outer periphery of a portion of said evacuated container, and having second and third passages in said surface area spaced from the edges of said major surface and spaced from each other on opposite sides of said central passage; said second passage being aligned with and surrounding said first permanent magnet means, and said third passage being aligned with and surrounding said second permanent magnet means, whereby said cooling fins forms a grill-like barrier in front of each permanent magnet means and prevent physical contact of the magnet with most geometries of ferromagnetic objects.

10. The inventionas defined in claim 9 wherein each of said cooling fins includes a bent over lip portion along each of two opposed edges, and wherein said lip portion is aligned at substantially a right angle to the major surface of said cooling fin and substantially extends between the major surface area thereof and an adjacent cooling fin to form an air duct therebetween.

11. The invention as defined in claim 10 wherein substantially all lip portions of all cooling fins face the same direction, and the lip portions of a bottom cooling fin faces an opposed direction.

12. The invention as defined in claim 11 wherein said central passage of each of said cooling fins includes a rim lip portion surrounding the -passage opening.

13. The invention as definedin claim 12 including a cylindrical metal sleeve of the same metal as said cooling fins which surrounds lthe body of said elongated evacuated container and which engages the rim lip portions of said central passage in each of said cooling fins to form a thermally conductive contact between said evacuated container and each of said cooling fins.

References Cited UNITED STATES PATENTS 671947 Martin 315-3951 21/1967 staats 315 39.71X

t `Us. C1. xn.

313-46, 15s; sis-39.53, 39.71