US3582707A

US3582707A - Air cooled coaxial magnetron having an improved arrangement of cooling fins

Info

Publication number: US3582707A
Application number: US5026A
Authority: US
Inventors: Richard M Hynes
Original assignee: Varian Associates Inc
Current assignee: Varian Medical Systems Inc
Priority date: 1970-01-22
Filing date: 1970-01-22
Publication date: 1971-06-01
Anticipated expiration: 1988-06-01
Also published as: GB1341101A; JPS5512697B1

Abstract

An air cooled coaxial magnetron is disclosed. The magnetron includes a coaxial arrangement of anode and cathode electrodes to define a magnetron interaction region in the space therebetween. The anode electrode includes an anode wave circuit and a coaxial circular cavity resonator with a cylindrical common wall disposed therebetween, such wall having an array of axially directed coupling slots communicating between the circular cavity and the wave circuit for controlling the frequency of the tube. An inner heat shunt is affixed to one end of the cylindrical anode wall and extends axially of the tube for connection to a radially directed heat shunt and to an array of radially directed cooling fins. An outer axially directed heat shunt interconnects the outer ends of the cooling fins to the radially directed heat shunt to enhance thermal conduction of heat from the anode wall to the cooling fins for improved cooling efficiency of the tube.

Description

United States Patent [72] Inventor Richard M. Ilynes Westfield, NJ. 211 Appl. No. 5,026 [22] Filed Jan. 22, 1970 [45] Patented June I, 1971 [73] Assignee Varian Associates Palo Alto, Calif.

[54] AIR COOLED COAXIAL MAGNE'IRON HAVING AN IMPROVED ARRANGEMENT OF COOLING FINS 7 Claims, 3 Drawing Figs.

[52] U.S. Cl 315/39.77, SIS/39.75, 313/40, 313/46, 313/36 [51] Int. Cl H01j 25/50 [50] Field ofSearch 315/3977, 39.75, 39.51; 313/40, 45, 46

[56] References Cited UNITED STATES PATENTS 3,169,2ll 2/1965 Drexler et al 315/3977 3,383,551 5/1968 Gerard ABSTRACT: An air cooled coaxial magnetron is disclosed. The magnetron includes a coaxial arrangement of anode and cathode electrodes to define a magnetron interaction region in the space therebetween. The anode electrode includes an anode wave circuit and a coaxial circular cavity resonator with a cylindrical common wall disposed therebetween, such wall having an array of axially directed coupling slots communicating between the circular cavity and the wave circuit for controlling the frequency of the tube. An inner heat shunt is affixed to one end of the cylindrical anode wall and extends axially of the tube for connection to a radially directed heat shunt and to an array of radially directed cooling fins. An outer axially directed heat shunt interconnects the outer ends of the cooling fins to the radially directed heat shunt to enhance thermal conduction of heat from the anode wall to the cooling fins for improved cooling efficiency of the tube.

PATENT El] JUN H911 SHEET 1 [1F 2 AIR S M R m WM WD IR A H m R BY W ATTORNEY PATENIEDJUH H371 3582707 SHEET 2 0F -2 INVENTOR.

RICHARD M. HYNES BY gwdbk :1 m

ATTORNEY AIR COOLEI) COAXIAL MAGNETRON HAVING AN IMPROVED ARRANGEMENT OF COOLING FINS DESCRIPTION OF THE PRIOR ART Heretofore, coaxial magnetron tubes having a cathode coaxially surrounded by an anode wave circuit which in turn communicates with an outer surrounding cavity via the inter mediary of an array of coupling slots through the anode wall have included an arrangement of cooling fins carried on the outside wall of the cavity resonator for cooling of the tube. Heat generated in the magnetron interaction region and picked up on the cylindrical anode wall was conducted axially of the tube to the end walls of the cavity and thence via the end wall of the cavity to the outer wall and thence to the inner ends of the colling fins. In such an arrangement the thermal path from the anode wall to the cooling fins was relatively long and resulted in relatively poor and inefficient cooling of the anode wall, thereby severely restricting the operating power level of the tube. Moreover, by placing the cooling fins on the outside wall of the cavity the diameter of the tube was thereby substantially increased tending to increase the size of the tube.

SUMMARY OF THE PRESENT INVENTION The principal object of the present invention is the provision of an improved air cooled coaxial magnetron.

One feature of the present invention is the provision, in an air cooled coaxial magnetron, of an axially directed inner heat shunt having an array of cooling fins affixed thereto and extending transversely of the tube together with a transverse heat shunt and an outer axial heat shunt interconnecting the outer ends of the cooling fins to the outer extremity of the transverse heat shunt for improving the conduction of thermal energy from the anode wall to the cooling fins and, thus, improving the cooling efficiency of the tube.

Another feature of the present invention is the same as the preceding feature wherein the cavity resonator is circular and coaxially surrounds the cylindrical anode wall and wherein the cooling fins are disposed adjacent one end of the cavity in a region nonaxially coextensive with the cavity, whereby the provision of the cooling fins does not appreciably increase the size of the tube.

Another feature of the present invention is the same as the first feature wherein the cylindrical anode wall coaxially surrounds the circular cavity resonator and the cathode surrounds the anode wall.

Another feature of the present invention is the same as the second feature wherein a pair of C-shaped permanent magnets are affixed to the tube and straddle axially the circular cavity resonator and array of cooling fins for providing an axially directed magnetic field in the interaction region.

Other features and advantages of the present invention will become apparent upon perusal of the following specification taken in connection with the accompanying drawing wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is an end view of a coaxial magnetron incorporating features of the present invention,

FIG. 2 is a sectional view, partly in section and partly in elevation, taken along line 2-2 of FIG. I in the direction of the arrows, and

FIG. 3 is a longitudinal view, partly in section, of an alterna tive coaxial magnetron incorporating features of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIGS. I and 2, there is shown a coaxial magnetron tube I incorporating features of the present invention. More specifically, the tube 1 includes'a circular central body portion 2 having a cathode insulator and stem assembly 3 depending axially from one end thereof and having a tuner assembly 4 inwardly extending from the other end thereof. The cathode stem assembly 3 supports a thermionic cathode emitter 5 centrally of the tube on the axis thereof. The other end of the cathode emitter 5 is supported via an insulator 6 from the body ofthe tube 2.

The main exchanging portion 2 includes a hollow cylindrical anode wall 7, as of copper, coaxially surrounding the cathode emitter 5 and having an array of vane resonators 8 radially inwardly projecting from the wall 7 to establish a wave circuit for supporting microwave energy in energy exchanging relation with an electron stream circulating in an annular interaction region 9 between the inner ends of the vane resonators 8 and the cathode emitter 5.

A toroid-shaped circular electric mode resonator II is contained within the central body portion 2 and surrounds the anode wall 7. The anode wall 7 includes an array of elongated wave energy coupling slots 12 providing wave energy communicating passageways between the circular electric mode resonator II and alternate vane resonators formed by the region between adjacent vanes 8. An annular electrically conductive tuning plunger 13 is disposed at one end of the circular resonator II and is axially translatable via tuner actuating rods I4 affixed to diametrically opposed portions of the annular tuning plunger l3 and extending axially of the tube.

A rectangular output waveguide 15 communicates through the outer wall 16 of the circular resonator llll via a coupling aperture 17 for coupling wave energy from the tube 1 to a load, not shown, via the intermediary of an output microwave window 18 sealed across the waveguide 15. The window structure 18 includes an output waveguide flange 19 for coupling the tube to a similar flange on a waveguide, not shown, incorporated in the load.

A pair of hollow cylindrical axially directed magnetic pole members 21 and 22 are axially spaced apart on opposite sides of the vane resonators 8 to define a magnetic gap in the interaction region 9. A pair of C-shaped

permanent magnets

23 and 24 have their ends connected to pole members 2k and 22 for providing the magnetomotive force to energize the magnetic gap with a strong axially directed DC magnetic field. The C-shaped magnets are diametrically opposed on the body 2 of the tube and extend outwardly from the tube in spaced quadrature from the position of the tuning plungers 14.

A lossy mode absorber ring 25, as of carbon impregnated alumina ceramic, is disposed on the inside of the anode wall 7 adjacent the upper end of the coupling slots 12 for absorbing undesired wave energy associated with a mode of oscillation in the coupled array of slots 12. The absorber ring is brazed to an annular thermally conductive channel-shaped frame member 26, as of copper, which in turn is brazed to a cylindrical absorber retaining ring 27, as of copper, which is affixed to the anode wall 7 via screws 28. The absorber frame 26 and retaining ring 27 serve to facilitate conduction of thermal energy generated in the absorber 25 from the region of the absorber to the anode wall 7 and thence in the axial direction of the tube. In addition, the absorber retaining ring 27 abuts the outside of the upper pole piece 2I such that thermal energy generated in the absorber is also conducted via a path including the retaining ring 27 and pole piece 22 in a direction axially of the tube.

An inner thermal shunt 29 is formed by a hollow cylindrical section of the tube body which is affixed, as by brazing, to the upper end of the anode wall 7 and which abuts the absorber retaining ring 27 and the pole piece 211. Two arrays of

cooling fins

31 and 32, respectively, are affixed as by brazing along their curved inner edges to the outer surface of the inner heat shunt 29. The cooling fins 3i and 32 have a typical thickness of 0.040 inches and are axially spaced by a distance, as of 0.047 inches. The

cooling fins

31 and 32 project radially outwardly from the inner thermal shunt 29 on diametrically opposite sides of the tube. Each cooling fin is a curved sector of a flat ring subtending approximately 130 of arc. At one end the

cooling fins

31 and 32 are spaced by approximately 25 of arc to accommodate one of the tuning plungers 14. At the other ends of the cooling fins the ends of the fins are spaced apart by approximately of arc and are terminated along a chord crossing the inner open end of a rectangular air duct 33 through which air is directed into the fins from an air blower, not shown.

The outer side edges of the fins are affixed to outer axially directed

heat shunts

34 and 35, as of one-eighth inch thick curved copperplate. The inner and outer heat shunts 29, 34 and 35, respectively, are interconnected at one end via a radially directed heat shunt 36 formed by an annular plate, as of seven-sixteenths inch thick copperplate. The heat shunts 29, 36 and 34, 35 are brazed together at their joining edges to provide thermally conductive joints therebetween to facilitate the conduction of thermal energy therethrough.

In operation, heat generated by interception of the electrons on the vanes 8, by transfer of thermal radiation and conduction from the cathode 5, and by absorption of microwave energy in the mode absorber 25 is conducted axially of the tube to the axial heat shunt 29 via anode wall 7, retaining ring 27 and via the pole piece 21. Heat is then conducted from the inner thermal shunt 29 to the

fins

31 and 32 and thence to the air stream flowing through the arrays of

cooling fins

31 and 32 from the duct 33. In addition, some of the thermal energy is conducted radially from the inner heat shunt 29 via the radial heat shunt 36 to the

outer heat shunts

34 and 35 and thence to the cooling fins for dissipation of thermal energy in the air stream.

In the absence of the outer

thermal shunts

34 and 35, the temperature of the

fins

31 and 32 would decrease in the radial direction as depicted by dotted line 37 in the plot of temperature versus distance depicted in FIG. 2 above the fin array 31. This reduction in temperature in the radial direction along the fin decreases the efficiency of the fins for cooling of the tube. The provision of the radial shunt 36 and

outer shunts

34 and 35 provides a second heat path to the outer ends of the fins such that the temperature of the inner and outer ends is approximately the same to maintain a more uniform temperature over the fins in the radial direction shown by curve 38.

Provision of the

cooling fins

31 and 32 in the position indicated in FIG. 2, namely, in axial alignment with and at one end of the cavity 11, substantially improves the cooling efficiency of the tube as contrasted with a prior art design wherein the fins were placed at the outer periphery of the cavity 11. More particularly, in the prior art design, 100 cubic feet per minute of air flow at a back pressure of 3.5 inches of water with a temperature rise in the air of 35 C. was required in order to dissipate approximately 1,100 watts in the tube. In the tube of the present invention, 65 cubic feet per minute of air with the same temperature drop and with a back pressure of only 2.0 inches allowed 1,200 watts dissipation in the tube. Moreover, the arrangement of cooling fins of the present invention substantially reduces the transverse dimensions of the tube as compared with the prior design.

The air duct 33 includes an arcuate cutout section at 41 to accommodate one of the tuning plungers 14. The tuning plungers 14 are sealed via bellows 42 to the upper end wall of the cavity 11 formed by the radial heat shunt 36. The tuning plungers are moved in the axial direction via a yoke member 43 connected to the ends of the tuning plungers 14 via screws 44. The yoke is connected centrally to a screw, not shown, which is translated in the axial direction by means of a captured nut which, in turn, is turned via a worm screw 45 mating with teeth at the outer periphery of the nut. An inner bore of the upper magnetic pole piece 21 is sealed off by a cylindrical plug 46 which also serves as a bearing member at its outer surface for the axially translatable tuner screw.

Referring now to F IG. 3, there is shown an alternative tube embodiment utilizing the cooling fin arrangement of the present invention. More particularly, the tube 48 is a reverse coaxial magnetron of the type generally described in US. Pat. No. 3,4l4,76l, issued Dec. 3, 1968 and having an inner circular cavity resonator 49 surrounded by an array of outwardly directed vane resonators 51 which, in turn, are surrounded by an annular cathode emitting ring 52. An array of axially, directed coupling slots 53 communicate through the outer well of the cylindrical resonator 49 with alternate vane resonators for locking the circular electric mode of the resonator 49 to the 1r mode of the vane resonator array. A mode absorber ring 54 surrounds the upper end of the anode wall adjacent the upper end of the slots 53 for absorbing wave energy from the slot mode to prevent slot mode oscillations.

A pair of hollow cylindrical

magnetic pole members

55 and 56 project toward each other along the axis of the tube 48 and are spaced apart at their inner ends to define an annular magnetic gap through the interaction region between the vane resonators 51 and the inner surface of the cathode emitter 52. The

pole pieces

55 and 56, as of iron, are sealed in a vacuum tight manner, as by brazing, to a pair of

transverse end walls

57 and 58, respectively, ofa hollow cylindrical main body portion 59 of the tube 48.

A high voltage cathode stern assembly 61 projects radially outwardly of the tube body 59 and includes a central lead for connection to the annular cathode emitter assembly 52 which is supported from and within the main body 59 via a plurality of axially directed standoff insulator assemblies 62 disposed at a plurality of points located about the periphery of the cathode emitter 52.

A pair of C-shaped

permanent magnets

63 and 64 are fixed at their ends to the

pole members

55 and 56 to provide the magnetomotive force for the magnetic gap. Output wave energy is extracted from the resonator 49 via a circular electric mode waveguide 65 axially aligned with the cavity 49. A microwave window 66, as of alumina ceramic, is sealed across the waveguide for maintaining the vacuum integrity of the tube.

The lower end of the cavity 49 is defined by an annular tuning disc 67, as of copper, which is carried upon an axially directed tuning rod 68 for producing axial translation of the tuning disc 67. The upper extremity of the rod 68 is coupled to a transverse crankshaft 69 in a tuning structure 71 disposed at the upper end of the tube 48.

The upper end of the circular electric mode cavity 49 is closed off by a hollow cylindrical axially directed inner heat shunt 72, as of copper. An array of radially directed annular cooling fins 73, as of copper, are brazed at their inner periphery to the outer periphery of the inner heat shunt 72. An annular radial heat shunt 74, as of copper, is brazed to the outer periphery of the inner heat shunt 72 and extends outwardly parallel to the fins 73. An outer axial directed curved heat shunt 75, as of copper, is brazed across the outer ends of the fins 73 and to the radial heat shunt 74 to provide a highly thermally conductive path from the inner heat shunt 72 via the radial and

outer shunts

74 and 75, respectively, to the outer ends of the fins 73 to maintain a relatively uniform temperature across the radial extent of the fins. The outer heat shunt 75 includes diametrically opposed apertures for mating with a cooling air duct, not shown, and an exhaust port for exhausting the cooling air. Thermal energy generated in the anode wall of the circular electric mode cavity 49 and in the mode absorbing ring 54 is conducted via the axial inner heat shunt 72 to the fin array 73 and thence to the cooling air to be carried away from the tube 48. A certain fraction of the thermal energy will be conducted by the radial shunt 74 to the outer heat shunt 75 and thence to the cooling fins 73 to be dissipated in the cooling air. The mode of operation and the advantages of the inner, radial, and outer heat shunts connected to the cooling fins 73 in the tube of FIG. 3 is substantially the same as the mode of operation and advantage obtained from the similar arrangement of parts in the tube of FIGS. 1 and 2.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention can be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What I claim is:

1. in an air cooled magnetron tube, means forming an anode electrode having a wave circuit portion for supporting wave energy thereon, means forming a cathode electrode substantially concentrically disposed of said anode in spaced relation from said anode wave circuit portion thereof to define an annular cross field interaction region in the space between said anode and said cathode electrodes, said anode electrode including a circular cavity resonator dimensioned to support a circular electric mode of resonance at substantially the operating frequency of the tube, said anode also including a generally cylindrical wall portion having an array of axially directed coupling slots therethrough providing wave energy communication between said anode wave circuit portion and said cavity resonator for locking the operating frequency of the wave energy on the anode wave circuit to the operating frequency of said cavity resonator, The Improvement Comprising, means forming an inner thermally conductive heat shunt structure connected in thermal conductive relation to one end of said cylindrical anode wall and extending axially of the tube for conducting thermal energy from said anode wall axially of the tube, means forming an array of relatively thin closely spaced thermally conductive cooling fins affixed at one edge to said inner heat shunt and extending radially outwardly therefrom, said fins being disposed with the plane of said fins generally transverse to the longitudinal axis of the tube, means forming a thermally conductive radially directed heat shunt connected to said inner heat shunt and extending radially outwardly therefrom, and means forming a thermally conductive outer axially directed heat shunt interconnecting the outer ends of said cooling fins and said radial heat shunt for enhancing thermal conduction from said anode wall to said cooling fins for improved cooling efficiency of the tube.

2. The apparatus of claim 1 wherein said inner heat shunt means comprises a generally tubular metallic structure coaxially disposed of said cylindrical anode wall and affixed at one end to one end of said cylindrical anode wall.

3. The apparatus of claim 1 including tuning means disposed at one end of said circular cavity resonator for axial translation within said cavity for tuning thereof, and a pair of tuner actuating rods affixed to said tuner means at opposed positions and extending axially of the tube in a region axially coextensive with both said inner thermal shunt and said fin means.

4. The apparatus of claim 3 including a pair of C-shaped permanent magnet members each affixed at both ends to the tube apparatus and disposed straddling said cavity and said cooling fins for providing an axially directed DC magnetic field in said crossed field interaction region.

5. The apparatus of claim 1 wherein said inner, outer, and radial heat shunts are made of copper, and said cooling fins are made of copper.

6. The apparatus of claim 1 wherein said cavity resonator coaxially surrounds said cylindrical anode wall, and said array of cooling fins and said radial heat shunt are disposed adjacent one end of said cavity in a region nonaxially coextensive with said cavity.

7. The apparatus of claim 1 wherein said cylindrical anode wall coaxially surrounds said circular cavity resonator.