US2477122A

US2477122A - Electron discharge device

Info

Publication number: US2477122A
Application number: US445131A
Authority: US
Inventors: Lloyd P Garner
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1942-05-30
Filing date: 1942-05-30
Publication date: 1949-07-26
Anticipated expiration: 1966-07-26
Also published as: GB627287A

Description

July 26,1949. L. P. GARNER ELECTRON DISCHARGE DEVICEy 4 Sheets-Sheet l Filed May 30, 1942 1 VENToR. Lloyd Garner". BY

Wwf A-r--rnmNEY July 26, 1949. j P, GARNER 2,477,122

ELECTRON DI S CHARGE DEVICE Filed May 50, 1942 4 sheets-sheet 2 NVENToR. Lloyd Garner.

ATTORNEY July 26, 1949. P. GARNER ELECTRON DISCHARGE DEVICE Filed May 50. 1942 /MMMl/WWWW I INVENT0R- Garner.

July 26, 1949. .,P. GARNER Y 2,477,122

ELEGTRON DISCHARGE DEVICE Filed May 30, 1942 4 Sheets--Sheet 4;vv

l VENTOR. Lloyd Garner:

ffl, f,

-ATTRNEY Patented July 26, 1949 ELECTRON DISCHARGE DEVICE Lloyd P. Garner, Princeton, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application May 30, 1942, Serial No. 445,131

(Cl. Z50-27.5)

11 Claims. 1

My invention relates to electron discharge devices and more particularly to such devices adapted for the generation and amplication oi ultra high frequency electric waves.

One electron discharge device that is adapted to generate centimeter waves is the so-called magnetron which comprises a tubular anode with a coaxial cathode and a magnet for producing a magnetic eldvparallel to the cathode. The cathode of such a device is usually of the filamentary type stretched between supports at opposite ends of the anode, and the anode is usually of sheet metal with the necessary slits and connected resonant circuits to tune the slit anode. Such sheet metal anodes are diicult to manufacture and cannot be eliectively cooled. While the anode with simple cavity shapes may be fashioned from a solid block of metal, as suggested in the Samuel Patent 2,063,342 issued December 8, 1936, the material and labor costs are high, and desired electrical characteristics cannot be obtained. Experimentation indicates the desirability, for example, of spiraled, tapered and other irregular shaped cavities that cannot be made in the solid block by ordinary machining.

An object of my invention is an improved electron discharge device that is easy and inexpensive to manufacture, and that is capable oi generating considerable ultra high frequency power.

A more specific object of my invention is an electron discharge device in which anode cavities of any desired shape may be easily constructed.

A further object of my invention is an anode for an electron discharge device that can be easily cooled.

A still further object of my invention is an improved electron discharge device of the magnetron type.

The characteristic features of my invention are defined in the appended claims and preferred embodiments thereof are described in the following specification and shown in the accompanying drawing in which Figure l is a longitudinal sectional view of one magnetron embodying my invention,

Figures 2 and 3 are views, respectively, of opposite ends of the tube shown in Figure 1,

Figure 4 is a detailed sectional view taken along line 4 4 of Figure 3,

Figure 5 is an enlarged longitudinal section taken on line 5-5 of Figure 2,

Figure 6 is a sectional view of the cathode support taken on line 6-6 of Figure 2,

Figure 7 is a perspective View of my improved lanced or slotted cathode sleeve,

Figure 8 shows in plan view the anode laminations of my tube and is taken fon line 8-8 of Figure 1,

Figures 9, 10 and 11 are plan views of other anode discs embodying my invention,

Figures 12 and 13 show anode discs which when stacked with the discs of Figure 8 will form the cavities shown developed in Figure 14,

Figures 15, 16 and I7 are perspective views of other cavities of my invention, plane developed,

Figure 18 is a half sectional view of a laminated an'ode having discs with openings of varying size to produce a cone-shaped anode bore,

Figure 19 is a plan view of an anode embodying my invention with a, plurality of cathodegrid assemblies,

Figure 20 is a longitudinal sectional view of a conventional electron discharge device having an anode embodying my invention,

Figure 21 is a plan view taken along the line 2 I-ZI of Figure 20, and

Figures 22 and 23 are sectional views of modied anodes embodying my invention.

The anode of my invention is a tubular laminated cylinder and comprises a plurality of thin sheet metal plates, extending in planes perpendicular to the axis of the anode, each plate having central openings or holes corresponding in size and shape to the desired transverse crosssectional conguratlon of the finished anode. These plates are plated with a fusible or solderable metal, are stacked with their openings in registry, and are consolidated, by brazing, into a unitary gastight anode cylinder.

The electron discharge device shown by Way of example in Figures 1 to 8, and embodying the characteristic features of my invention, is of the magnetron type and. comprises a cathode I mounted centrally in the anode 2. The cathode illustrated is of the indirectly heated type, is exteriorly coated with an electron emitting oxide, and has an internal heating element 3. The anode is fabricated with a plurality of sheet metal discs having central openings corresponding in size and shape to the desired transverse cross sectional configuration of the anode. The particular magnetron anode of Figure 1 has a round hole or bore 5, Figure 8, and eight radially extending resonant cavities 6, separated by inwardly extending teeth 6a, the round holes and cavities being of the same size and shape in each disc in the particular magnetron of Figures 1 to 8. Each disc is preferably of a non-magnetic material such as copper and' is plated or tinned with a high melting solder, such as pure silver or silver alloy, which will hermetically join the discs when heated to brazing temperature. During brazing the stacked discs are conveniently held in registry with rivets or bolts extending through holes l punched along the peripheries of the discs. As will be more fully hereinafter pointed out, the inner peripheries of the holes and cavities in the discs may be varied in site and shape, from one disc to the next, to provide discharge spaces of desired longitudinal shapes, and the outer peripheries of some of the discs may extend beyond the stack to provide cooling iins. Further, the discs may be spaced apart longitudinally of the anode by washers, the washers being plated or tinned and brazed in place in the stack.

The ends of the anode are hermetically closed by drawn sheet metal cups or bulbs 8. The centers .of the bottoms of the cups are apertured and fitted against the ends of the anode where they may conveniently be sealed in place by a rolled over collar 9, the collar and cups being joined to the stack also by brazing. The ends of the cups are closed by anged sheet metal headers I B which when pressed into the bulbs may be hermetically closed by welding along the rim II of the cup and header as shown in Figure 1. By grinding away the welded rim, the header may be removed for tube repairs without damage to the parts.

To realize the benefits of the accurately formed cavities of the laminated anode of my invention, the cathode must be permanently and accurately mounted on the axis of the anode. The indirectly heated cathode sleeve oi the particular magnetron shown is supported at each end .on a bridge I2 extending across the end of the anode and mounted on brackets I3 within the end cups of the envelope. Each bridge comprises three flat end-to-end metal sections or strips I4, I5 and i6 joined by two loops I'I of commercial cane glass. The end pieces I 4 and I6 of each bridge are preferably attached to their bracket by a short thin ribbon I8 with an expansion fold across the ribbon to permit slight lengthwise movement of the cathode when heated. The end of the cathode sleeve clears an enlarged .opening in the center section I5 of the bridge and is arc or spot welded along its rim to the up-turned flange of a thin metal disc I9, which in turn is riveted to the bridge. The disc is thin and of low heat conducting metal, such as commercial Kovarf to reduce cathode end losses. A heat shield 29, comprising a copper plate with a central opening to clear the cathode sleeve, is mounted coaxial with the sleeve and suspended out of contact with the bridge and between the bridge and the anode-cathode space of the tube. The heat shield is preferably attached by rivets 2| placed on a diagonal at right angles to the rivets which hold the sleeve disc to the bridge. It is comparatively simple to align the ends .of the sleeve with dowel pins or screws at the ends of the bridge so that'when the parts are assembled the cathode sleeve is rmly and accurately held on the center line of the anode. While the cathode sleevecannot move laterally to change the anode-cathode spacing, it is free to expand lengthwise. The two heating circuit conductors 2a are sealed through the side of the envelope cup, and the cathode sleeve is conveniently connected to one side of the heating circuit by strap 3b. Exhaust tube 8er-may be sealed, or connected to a pump for continuous exhaust.

As shown in Figure '1, staggered slots 22 may be 4 cut in the ends of the sleeve'to further constrict the flow of heat from the sleeve to its end supports.

The length of the slots in the disc are measured by the length of the wave to be generated by the magnetron. The depth of the slots shown in Figure 8 is preferably equal to about a quarter wave length. T.o increase the electrical length of the slots, without increasing the diameter of the anode, the slots may be rounded at their outer ends as shown at 23 in Figure 9. To reduce the capacity between the teeth or inwardly projecting portions of the anode cavities, the slots may be tapered as shown in Figure 10. If desired, the straight sided slots may be disposed tangentially to a circle within the bore as shown in Figure 11 to reduce the overall anode diameter. Secondary emission from the anode may be effectively suppressed when the primary electrons enter the tangential slot from a space charge revolving in a counterclockwise direction, in Figure 7.

In operation the cathode is heated to electron emitting temperature and a high positive potential is applied to the anode with respect to the cathode, and a magnetic field is produced parallel to the cathode. Preferably an electromagnet is used so that the intensity of the magnetic field may be adjusted by varying the current in the magnet coil. The pole pieces of an iron core may be placed outside of the envelope and opposite the ends of the cathode, or a solenoid may be mounted around the anode and coaxial with the cathode. By proper adjustment of the electromagnetic and electrostatic iields, electrical oscillations of considerable power, of a few centimeter wave length may be produced. The operating characteristics of the device bears out the commonly accepted theory of one mode of operation in which it is assumed that electrons leave the cathode and spiral about the cathode in fairly well dened clouds or space charges. The space charges induce voltages in the ends of the teeth as the electrons pass across the gaps between the teeth, much in the manner the pole of a rotary generator induces alternating voltages in the windings of the generator. When the electron speed is properly related to the electrical length of the resonant cavity, oscillating currents and voltages build up on the walls of the cavities. The several resonant cavities around the periphery of the anode bore are in conductive series, and are inductively coupled in such a way that useful A.C. electrical power may be derived from the anode by inductively coupling a load circuit to the field produced by the currents in the cavities. Alternatively, power may be derived by conductively connecting the work circuit to any two points on the anode having voltages displaced in phase. degree voltage phase displacement may be found between the ends of two adjacent teeth of a resonant cavity. The work circuit may be connected between the tooth and the base of one of the cavif ties as shown in Figure 4, where the center conductor 24 of a concentric transmission line is connected to one end of one of the teeth and the outer tubular conductor 25 is connected to the base or frame of the anode. The bent metal detail 26 is tted to the end of the tubular conductor 25, and is brazed over one of the teeth. The conductor 25 is sealed in the side of the cap, and the inner conductor 24 is sealed with glass in the outer conductor.

It has :been found desirable to space the discs or laminae of the anodar--to break up metallic conduction along the anode axis and also aid secondary emission suppression. Spacings of any desi-red amount and at any desired region may-- be easily obtained by inserting thin washers 2T between the anode discs and brazing them in place with the discs. It appears that some of the electrons circling the cathode have a velocity` component lengthwise of the anode and hence are capable of inducing voltages between the ends of the anode. By spacing the teeth of the anode discs or groups of discs, resonant cir-- cuits extending` lengthwise of the anode may thus be effectively open circuit-ed-and spurious oscillations are minimized.

Alternate cavities can conveniently be conf nec-ted in thel magnetron of my invention, as shown in Figure 14, so` that the magnetic flux linkage paths maybe predetermined and the mode. of oscillation of the cavities interlocked. By stacking the discs of Figures 8, 12 and 13 as suggested in Figure 14, the teeth of one cavity may be conductively connected to the teeth of any other cavity. In the example shown alter nate vertical rows of teeth are connected by a wide tooth 23 as shown in Figure le. Teeth 28 are interleaved with the teeth '25m Figure 12, and the teeth 6a., Figure 8.

According to a further feature oi inyinvention, 'some of the discs or some of the teeth of the discs may be of magnetic material and be inserted in the stack to. distort or reshape the magnetic iieldY as desired.

@ne ot the advantages of an anode constructed according tc my invention is that the sizes and Shapes of the lanode bore and the resonant cavities, are not. limited by the capabilities of metal cuttingtools. Punch press dies are easily designed and made to stamp out discs for any desired cavityv coniiguration. Further, the teeth Of. till? discs of my anode may be aligned to produce straight parallel cavities as shown in Figure 15, or the discs may be rotationally displaced or skewed to produce curvedor spiraled cavities asshown in Figures 16 and 17.

Where the cloud or pencil of hunched electrons extending substantially parallel to the cathode rotates about the cathode, and where the load circuit is coupled to one end only of the anodey there arises the difficulty of delivering in phase powerfrein all sections of the anode to ther load circuit. Although the voltages at 0913651158, ends of the anode may be in phase, they cannot be coupled in phase to the output circuit because of the current propagation time along the anode. It becomes desirable, therefore, to phase displace the voltages induced in the two ends of a segment by an amount equal to the propagation time of current from one end of the anode to the other. The amount of spiralling of the cavities of Figure 16 is easily adjusted to obtain the necessary voltage phase displacement between the ends of the anode. Alternatively the laminae may be skewed or displaced as shown in Figure 17 when it is desired that the gaps of cavities define an elongated reverse curve opposite the cathode. A load circuit could be coupled to each end of the anode of Figure 17.

Still further, it may be desired to shape the anode bore into a right cone coaxial with the cathode. Such a cone is easily made by cutting the diameter of the hole of each lamina progressively larger than the next adjacent lamina. Such anode shapes could be machined from a solid block of metal only with the greatest difclllties. The anode of Figure 18 may be further modified, if desired, Iby closely spacing the ends of the anode to the ends of the cathode and expanding the anode bore to itsl maximum diameter intermediate the ends of the anode so that the cavity is somewhat egg-shaped.

`lili/There transit, time and other factors require close spacing :between the cathode and anode and yet where the required power output and heat dissipatins capacity is high, a plurality of cathode-.grid assemblies 23 3.3, may be installed in separate cavities 3l as shown in Figure 19. Here, the anode cavities may communicate at the center es shown or be unconnected and individual to each assembly. In such an arrangement the output circuits of each amplifier assembly is in electrical parallel. As in the other illustrated embcdlmcnt of my invention alternate discs may ce oversize in diameter and longitudinally spaced so as to f lmction as cooling :uns for the anode. An important advantage of my laminated anode lies in the fact that it can be easily cooled in operation. Some of the anode discs la are Oversized and extend beyond the body of the anode. Airfcooled anodes of the usual Constructien comprise a drawn thin-.Walled metal cylinder with cooling ins soldered to the outside surface of the cylinder. Such a construction is not only e. but is inelective in conducting away the. heat generated at the electron collecting surface of the anode because the soldered, ccneeeicns betwee the anode and the ns erreciively constriet the flow of heat outwardly through the amide to the fins Due in part to the inability cf; heat t@ flow transversely throne-l1 the interfaces of similar or dissimilar metals, the power dissipation in ccnventicnal tubes. is limited to. 20 to SQ Watts per square centimeter ci useful anode surface. In my improved anode the edges of the cooling discs extend through and into the envelope when the edges of the discs constitute the electron collecting Surface of the amide.. Because of the greater heat conductivity 0f the walls of; my anode= I have successfully.

increased the dissipation 0i an anode of given ,Size by more than 5i) percent. The desired spacing between the radiating surfaces of the ns or cooling discs 4a for best an circulation may be obtained by inserting the appropriate number of Smcllcl.' imode discs 4c between the oversized discs. Such a finned anode construction may be employed in the magnetren of Figure l es Well a5 the. ccnventional amplifier of Figure 20.

As. shown in Figures 2c and 23, a collar 32 may be conveniently brazed. to one end 0f my anode stack and the usual glass bulb 33 sealed to the collar. In the bulb is sealed the lead-in conductors for the grid 3A and cathode 35. The opposite end of the anode may be closed with a plate 36, as shown. In place of the spacer washers of Figure 20, the disc elements may, as shown in Figure 23, be centrally punched out and the inner rim 31 of the hole turned back against the side of the disc as shown. The radial extent of the area of contact between the spacer-discs and the n-discs may be large so that heat entering the edge of the spacer discs will easily escape to the fins. If desired, the spacers may be swaged, cast, or embossed as integral parts of the fins as shown at 38 in Figure 22.

Unusually high frequency power has been obtained from the nned magnetrons of the type shown in Figure l. Stable oscillations of the magnetron at a 3 centimeter wave length have been obtained with an estimated useful intermittent power output of 25 kilowatts where the anode is only 1.5 centimeters long and the anode bore is 8.5 millimeters in diameter, the cathode coated area being 1 centimeter long and 4 millimeters in diameter, and the radial depth of each of the twelve cavities being slightly over l millimeters.

My improved electron discharge device may be made with anodes having cavities of any desired size or shape. The anode is easily cooled and has high power rating, is capable of generating power at ultra high frequencies, and is easy and inexpensive to manufacture.

I claim:

l. An electron discharge device comprising a laminated tubular anode, the laminae of the anode comprising discs each with an opening eccentric to the center of the disc, the discs being stacked and hermetically joined with their openings in registry, each disc being rotationally displaced with respect to the next adjacent disc to provide spiral-shaped cavities about the center hole of the anode.

2. A tubular anode comprising a plurality of stacked metal discs, each disc having a central hole, the hole in each disc being of a diameter dierent from the hole in the next adjacent disc, and a cathode in and coaxial with the anode.

3. A laminated anode comprising a plurality of stacked and hermetically joined metal discs, each disc having a central opening, the rim of the opening in one disc extending inwardly beyond the rim oi the opening in the next adjacent disc, the discs being xed in the stack with the opening of each disc so placed with respect to the anode axis as to provide an anode cavity of irregular volumetric configuration.

4. An electron discharge device comprising a laminated tubular anode, the laminae of the anode .comprising discs with openings in the center thereof, the size of the opening in one disc being larger than the opening of the next adjacent disc so that the nrst mentioned disc overhangs the second mentioned disc within the anode cavity, and a cathode in and coaxial with the anode.

5. An electron discharge device comprising a tubular laminated anode, the laminae of the anc-de being interleaved with washers, the laminae and the washers being hermetically joined, and a cathode in and concentric with the anode.

G. A laminated tubular anode, the laminae of the anode comprising a plurality of thin sheet metal discs, the discs having registering central holes, the hole of each disc having a slot extending outwardly from the hole, the slots being tangential to a circle inside said hole.

7. An anode for an electron discharge device comprising a plurality of metal discs, each disc having a central hole, the inner rim of the disc being folded back upon the disc, the folded portion of one disc being laid in contact with the side of the next disc and the discs being brazed together.

8. An electron discharge device comprising a tubular anode, a tubular cathode, a bridge supporting said cathode concentric with and in said anode, said bridge comprising three end-to-end metal strips insulatingly joined with glass, the end strips of the bridge being attached to the end ci the tubular anode on opposite sides of the opening through the anode, the end of the cathode being attached to the center strip of the bridge.

9. The method of fabricating a tubular envelope wall for an electron discharge device comprising plating thin sheet metal with solderable material, cutting discs from said sheet metal, and cutting a hole in each disc, stacking the discs one on the other with the holes in the discs in communication, and heating the stack to soldering temperature to hermetically seal the discs together.

10. An indirectly heated cathode comprising a metal sleeve exteriorly electron emissive, a heating element in the sleeve, a metal support member attached to one end of said sleeve, said one end of the sleeve having a plurality of transverse cuts in the sleeve wall to constrict the flow of heat to said support member.

1l. An ultra high frequency electron discharge device including a resonator block comprising a plurality of stacked metal plates, each plate having an opening, the plates being xed in the stack with the rim of the opening in one plate extending inwardly beyond the rim of the opening in the next adjacent plate providing a cavity resonator of irregular volumetric conguration.

LLOYD P. GARNER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,684,947 Daumann Sept. 18, 1928 1,924,368 McCullough s Aug. 29, 1933 2,043,733 Brasch et a1. June 9, 1936 2,053,126 Bentley Sept. 1, 1936 2,063,342 Samuel Dec. 8, 1936 2,143,390 Schroter Jan. 10, 1939 2,267,128 Mouromtsei etal. Dec. 23, 1941