US3142776A - Unitized gun mount and envelope - Google Patents

Description

y 1964 .F. c. WELLS ETAL 3,142,775

UNITIZED GUN MOUNT AND ENVELOPE Filed May 1, 1961 4 Sheets-Sheet l g iil 7 1 5 II HI I ?g -fip m I I a 2 i I '0 -8 I i [0 Z 4 4. I 22 s an :mtlll INVENTORS STANLEY E SWIADEK FRANK C. WELLS ATTORNEY July 28, 1964 F. c. WELLS ETAL UNITIZED GUN MOUNT AND ENVELOPE 4 Sheets-Sheet 2 Filed May 1, 1961 INVENTORS STANLEY E SWIADE'K FRANK C. WELLS gym/M A T TORNE Y July 28, 1964 F, c. WELLS ETAL 3,142,776

UNITIZED GUN MOUNT AND ENVELOPE Filed May 1, 1961 4 Sheets-Sheet 3 INVENTORS STANLEY F SWIADEK FRANK C. WELLS m Y Z AT TO RNE Y July 28, 1964 F. c. WELLS ETAL UNITIZED GUN MOUNT AND ENVELOPE 4 Sheets-Sheet 4 Filed May 1, 1961 p x d mm Hg-cm ALTITUDE ABOVE SEA LEVEL IN FEET (X I000) INVENTORS STANLEY E SWIADEK BY FRANK C. WELLS l; T0 RNE Y United States Patent 3,142,776 UNITIZED GUN MOUNT AND ENVELOPE Frank C. Wells, Los Altos Hills, and Stanley F. Swradek,

Sunnyvale, Calif, assignors to Sylvania Electric Products Inc., a corporation of Delaware Filed May 1, 1961, Ser. No. 106,807 8 Claims. (Cl. 313-489) This invention relates to traveling wave tubes having ceramic envelopes and particularly to an improved mount for the component parts of the gun structure of such tubes.

The method of manufacturing traveling wave tubes has progressed to the point that automatic machinery may be used in the assembly of the component parts of the tubes. To facilitate such manufacture, tubes have been designed to allow annular gun electrodes and cylindrical support sleeves, within which a cathode is mounted, to be stacked and separated by electrically insulating spacers.

These spacers have heretofore been made of a ceramic material which has good electrical insulating properties but which introduces a problem of effecting a bond between the surfaces of the spacers and the gun elements or, alternatively, between the spacers and the cathode support sleeves. If the usual means of attachment are used, i.e., brazing the previously metallized surfaces of the ceramic spacers to respective surfaces of the members, the sealing joint may develop minute openings or a series of openings which can not be immediately detected. During subsequent high temperature processing of mounts incorporating such joints, impurities within the gun elements are liberated as gases at the mating surfaces of the members and metallized spacers. These gases migrate through the minute openings in the joint to the exterior surface of the envelope, or in the other direction, into its bore portion, thereby enlarging the openings and effectively destroying the seal. This necessitates the time consuming and costly operation of rescaling.

Another disadvantage of prior ceramic gun construction is the tendency of electrical breakdown between adjacent closely spaced metallized spacer joints, especially in a low pressure environment. Such breakdown frequently occurs in tubes in high altitude aircraft wherein arcing across the exterior of the gun can result in total destruction of the tubes.

In accordance with our invention, the advantages of a ceramic construction are realized while avoiding the disadvantages mentioned above by forming the cylindrical gun envelope with a plurality of straight ceramic rods having axes parallel to the longitudinal axis of the tube. The various gun elements are axially spaced apart within the rod envelope by stacked ceramic spacers which fit snugly against the rods inside the envelope. Electrical contact with the gun elements is made by metallized joints or bands which extend between the rods at circumferentially spaced points on the envelope. The spacing between contact bands on the exterior surface of the envelope is thus measured by the circumferential as well as axial displacement.

The ceramic glaze which bonds the rods together 'into an envelope preferably is on the outside of the envelope so that the longitudinal grooves between rods on the inside of the envelope form convenient open passageways to carry gaseous impurities away from the gun elements during the high temperature outgassing phase of tube processing.

Av primary object of this invention, then, is to provide a traveling wave tube gun structure and envelope which avoids the above described disadvantages of conventional ceramic stacked guns.

A more specific object is the provision of a vacuumtight envelope having means for readily expelling gaseous 3,142,776 Patented July 28, 1964 impurities of gun structures after assembly in the envelope.

Another object is the provision of an envelope having means providing external high voltage connections to gun electrodes while minimizing the danger of arcover between adjacent electrodes.

These and other objects will become apparent from the following description of a preferred embodiment of the invention, reference being made to the accompanying drawings in which:

FIGURE 1 is a schematic view, partially broken away, of a traveling wave tube embodying the invention;

FIGURE 2 is a transverse section of the gun structure taken on line 2-2 of FIGURE 1;

FIGURE 3 is a longitudinal section of the gun structure taken along line 33 of FIGURE 2;

FIGURE 4 is an enlarged view of a portion of FIGURE 2 showing details of the construction of the envelope wall;

FIGURE 5 is a greatly enlarged view of a portion of FIGURE 3 showing details of the support structure of the gun structure;

FIGURE 6 is a plot of breakdown voltagev versus the product of pressure and electrode spacing; and

FIGURE 7 shows a set of voltage breakdown curves which compare the result of voltage breakdown on operating capabilities of traveling wave tubes. 1

In a preferred embodiment in FIGURE 1 a traveling wave tube is disclosed comprising an elongated envelope 1 having enlarged end portion enclosing a gun assembly 3. The cathode 4 (see FIGURE 3) of the gun assembly produces a beam of electrons which is focused and accelerated by focus electrode 5 and first and second anode electrodes 10 and 11, respectively, along axis A through helix 6 to collector 7. As the electrons pass the helix, interaction between the electrons and a signal applied to. input 8 occurs such that the signal is amplified when extracted at output 9.

The efliciency of the tube depends upon the axial travel of the electrons through the helix 6, and a contributing factor in achieving this type of flow is a precisely formed gun structure. This invention concerns such gun structures and particularly those gun structures'having integral enclosures adapted to and compatible with mechanized manufacturing techniques.

In accordance with the invention, the gun assembly '3 shown in FIGURES 2 and 3 comprises a'cathode subassembly 12 mounted within an electrode-spacer subassembly 13 about which is formed gun housing 14 of tube envelope 1.

For convenience in describing this invention, the term cathode subassembly 12 is used in this specification to describe the cathode body 28, its cylindrical support, heater, and focus electrode 5 located adjacent thereto. Also, the term electrode-spacer subassembly 13 refers to anode electrodes 10 and 11 (hereinafter described as rearward and forward electrodes, respectively), outer cathode support sleeve 16, and ceramic spacers 17, 18, and 19 located between these members. The term forward describes the end of the assembly from which electrons are accelerated after emission and refers to the right end of the gun structure 3 in FIGURE 3. Similarly, rearward" designates the left end of the gun structure, as viewed.

Accordingly, the electrode-spacer subassembly 13 comprising electrodes 10 and 11 and rearward cylindrical cathode support sleeve 16, spaced between annular ceramic spacers 17, 18, and 19, is mounted within aceramic gun housing 14 such that the outer peripheral surface edges of the parts are in tangential contact with inner surface 42 of wall 40. A shown in FIGURES 2 and 3, wall 40 extends axially of the parts along the entire length of the assembly and comprises a plurality of elongated, tangentially joined rods 15 having axes which are parallel to each other and to axis A of the tube. These rods preferably have the same diameter and each makes longitudinal line contact with two adjacent rods so that their peripheries merge at a junction to form a cusp. These cusps are indicated at 39 in FIGURE 4 and facilitate the cleaning of the tube parts as explained hereinafter.

The rods 15 are secured and sealed together at their junction into a vacuum tight enclosure by ceramic fillets 41 made of a material described in patent application Serial No. 9,701, filed February 19, 1960, and assigned to the assignee of this application. The enclosure thus formed radially confines the parts of the assembly throughout their respective tangential contacts with the wall 40.

The ends of rods 15 are permanently secured to the end walls 31 and 35 of housing 14 to prevent axial movement of the confined parts and provide a complete gun enclosure. As viewed in FIGURE 1, forward ends 52 of these rods are mounted in contact with the rearward surface of end wall 35 in the annular space defined between the exterior radial surface 53 of forward ceramic spacer 17 and interior surface 54 of annular lip 55, while the peripheral surfaces of rearward ends 5-6 (see FIG- URE 3) are permanently secured in the annular space between side wall 37 of cathode support sleeve 16 and inner surface 58 of annular lip 59 on rearward end wall 31.

Axial confinement, as well as electrical isolation of the assembly, is provided by locating ceramic spacers 17, 18, and 19 between electrodes and 11 and cathode support sleeve 16 such that respective end surfaces of this assembly are in contact with walls 31 and 35 of gun housing 14. The assembly thus formed facilitates fabrication of gun structures by remotely operated machinery by the inherent virtue of the stacked gun arrangement, and provides a mechanically rugged support, the parts being wedged between the end wall of the gun enclosure to prevent their axial movement.

In detail, forward acelerating electrode 11 comprising forward cylinder 20, radially extending annulus 21, and central aperture 23, is axially constrained by forward spacer 17 and central spacer 18 having surfaces 26 and 27, respectively, in contact with the forward and rearward annulus surfaces 25 of annulus 21. The forward and rearward surfaces of the spacers in turn contact the forward end wall 35 of gun housing 14 and surface 36 of annular body 29 of rearward electrode 1%, respectively.

Adjacent electrode 10, between rearward spacer 19 and rearward end wall 31, is cylindrical cathode support sleeve 16 having a side wall 37 and forward wall 32 whose forward surface 33 is in contact with surface 36 of rearward spacer 19. It should be noted that the term contact as used in this specification is a relative term, depending upon many factors one of which is the surface conditions of the parts. In maintaining close tolerances necessary for traveling wave tube guns, it is usually necessary that the surfaces of the parts in contact must be ground to obtain a surface finish compatible with alignment requirements, say 32 microinches. In FIGURE 5, in a greatly enlarged scale, the mating surfaces 33 and 36 of support sleeve forward wall 32 and of ceramic spacer 19, respectively, typical of this assembly and illustrative of this type of joint, comprise a series of peaks 57 and valleys 61 contacting one another at referenced points 64. Although these undulated surfaces prevent a vacuum-tight seal between the parts, the gaseous impurities-driven from the metal electrode during the high temperature process cycle are easily expelled from the tube because of the interconnected passageways between surfaces 24 and 24a of ceramic spacer 18 (see FIGURE 3).

Possible directions of the gaseous migration, in this instance, are indicated in FIGURE 5 by upwardly projecting arrow 68 and downwardly projecting arrow 7t If the direction is upwards, the gases eventually enter the longitudinally extending passageways or cusps 39 formed by the junctions of rods forming wall 40 of the gun housing 14 and then migrate from right to left as viewed in FIGURE 3 to be expelled from the tube through open fitting 63, which snugly contacts opening 62 in end wall 31.

Sources of gas contamination are not, however, limited to the parts comprising electrode-spacer subassembly 13. but may include those of cathode subassembly 12, mounted coaxially within subassembly 13. In this arrangement (see FIGURE 3), support of subassembly 12 relative to subassembly 13 is provided by locating the outer surface 67 of focus electrode 5 of subassembly 12 in contact with the inner surface 76 of side wall 37 of subassembly 13. Movement in the rearward direction is prevented by locating the surface 69 of end wall 31 adjacent to the end edge of the focus electrode 5 while forward movement is constrained by placing rearward surface of forward wall 32.0f cathode support sleeve 16 in contact with the forward portion of electrode 5.

Cathode 4, located so that upper cathode body 28 is axially adjacent to central aperture 71 of the focus electrode 5, is mounted to the forward edge of inner cylindrical support member 72, which is enlarged in its forward and rearward portions to form outwardly extending lips 72a which are atached to the inner surface of a second support member 73. Electrical connection to heater 22 is provided by leads 66 which pass through fitting 65 in end wall 31 to external energizing sources (not shown).

On the exterior surface of second support member 73, three circumferentially spaced radial isolation posts, one of which is shown at 74, are provided. Each post comprises an annular ceramic member 75 interconnecting two metal legs 77, and attached to the inner surface of focus electrode 5 to allow a bias voltage to be applied independent of the focus electrode to gate the electron beam. In steady state operation, however, both cathode 4 and focus electrode 5 are operated at the same potential as illustrated hereinafter.

As shown in detail in FIGURES l3, electrical contact is made with electrode 11 as well as with acceleration electrode 10 and focus electrode 5 by metal bands 44, 45, and 46, preferably made by plating copper on a thin, molybdenum-manganese film attached to and coaxia-lly disposed about rod members 15 forming wall 40 of housing 14. Leads, referenced L L and L are in turn attached at contact points 49, 56, and 51 to the respective bands 44, 45, and 46 to facilitate energizing the electrodes of the tube by external energizing sources 91, 92, and 93.

Referring specifically to FIGURES 1 and 2, electrode 11 is located such that its peripheral edge 78 is in contact with band 44- at contact point 48, located degrees from point 49, the contact point of the band 44 and lead L Electrode 10 is energized at point 79 by band 45 which is connected in turn at point 50 to lead L The minimum exterior distance between point 49 and point 50 is the circumferential spacing indicated as S in FIG- URE 1. This spacing S illustrates that the contact bands of axially adjacent electrodes are separated not only by axial dimension B but also by a geometric arc of 180 degrees, see FIGURE 2.

As a result of the increased spacing between adjacent contacts, the probability ofionization of the air separating bands 44 and 45 so as to support an arc discharge during operation of the tube is greatly reduced since the value of voltage diiference at which arcing takes place is directly related to the distance (d) between the electrodes as well as the pressure (p) of the surrounding air. This relationship is shown graphically in FIGURE 6 wherein curve 81 is a plot of breakdown voltage versus the product of pressure (p) and distance (d) in air. This curve shows that breakdown voltage falls to a minimum at a value of the parameter (p d) down of about 0.5 mm. Hg-cm., and rises rapidly for increasing values of (PXd). Thus the curve 81 has a saddle 82 between its positive and negative slopes. The significance of saddle 82 to the tube designer is the fact that tubes having stacked ceramic gun constructions and operating over a wide range of air pressures must have sufiicient distance (d) between exposed electrodes to avoid low values of Vs. Thus distance between electrodes in certain low pressure environments is a critical design factor directly related to the ability of such tubes to operate at all.

By way of example, for the tube shown in FIGURES 1, 2, and 3, operating in X-band frequencies (8.0 to 12.5 kilomegacycles), the breakdown voltage-pressure characteristic is illustrated and compared by curves shown in FIGURE 8. In this plot, the abscissa is in terms of altitude which is essentially inversely proportional to pressure. Curve 83 represents the breakdown voltage characteristic between forward electrode and rearward electrode 11 of tube 1 (the most critical case) operated at 0 to 80,000 feet above sea level. Curve 84 represents a similar voltage characteristic for a tube using a conventional ceramic stack gun having comparable electrode spacings and which depends solely upon the axial spacing for separating the external contact points. The horizontal line 87 represents the voltage at which breakdown (arc-over) occurs, for the particular gun at certain operating voltages.

The electrode spacing, dimensions and operating voltages of the gun for which the curves of FIGURE 7 were plotted were as follows:

It will be noted that curve 84 for the conventional construction crosses the breakdown voltage line 87 at an altitude of approximately 17,000 feet whereas curve 83 crosses line 87 at approximately 63,000 feet.

It should be understood that this invention in its broadest aspects is not limited to the specific example herein illustrated. The appended claims are intended to include all changes and modifications within the true spirit and scope of the invention.

We claim:

1. In an electron discharge device, a plurality of electrodes spaced apart along an axis, insulating spacer means separating axially adjacent electrodes, an annular vacuumtight envelope circumscribing said electrodes and spacer means, said annular envelope comprising a plurality of parallel axially extending insulated rods sealed together in a circumferential series arrangement, and means for energizing said electrodes comprising an electrical conductor for each electrode and extending through said envelope, said conductors being connected to axially adjacent electrodes and penetrating said envelope at circumferentially spaced locations.

2. The device according to claim 1 in which said spacer means comprise annular spacers of insulating material having peripheral surfaces, each of said electrodes extending between and being supported on adjacent surfaces of adjacent spacers, said envelope engaging the peripheral surface of each spacer.

3. The device according to claim 2 in which said envelope engages each spacer at circumferentially spaced locations and defining therewith a plurality of circumferentially spaced longitudinal passages.

4. In an electron gun, a plurality of annular insulating spacers, a plurality of annular electrodes stacked axially between and engaged with said spacers, an envelope formed about and in contact with said spacers, and means for energizing said electrodes comprising contact bands disposed in and integral with said envelope in tangential contact with a like number of said electrodes, with adjacent bands circumferentially spaced degrees, said envelope comprising a plurality of insulating rods coupled together in permanent tangential engagement having tangential line contact with peripheral edges of each of said spacers and electrodes.

5. In a traveling wave tube adapted to operate in an environment having substantial changes in atmospheric pressure, an electron gun and an envelope containing said gun, said gun having an axis, a cathode for producing a beam of electrons along said axis, a cylindrical sleeve supporting said cathode, a plurality of annular electrodes for focusing and accelerating said beam, and a plurality of insulating spacers stacked in engagement with and separating said sleeve and electrodes; said envelope comprising a plurality of insulating rods having a generally circular cross section and coupled together in permanent, tangential engagement and with axes parallel with said axis and being in tangential contact with said sleeve and with said electrodes, and means to facilitate energizing said electrodes comprising contact bands coaxially disposed about said rods in tangential contact with said electrodes, with adjacent bands circumferentially spaced apart by 180 degrees.

6. In a traveling wave tube adapted to operate in an environment having substantial changes in atmospheric pressure, an electron gun and an envelope containing said gun, said gun having an axis, a cathode for producing a beam of electrons along said axis, a cylindrical sleeve supporting said cathode, a plurality of annular electrodes, means for energizing said electrodes to focus and accelerate said beam, and a plurality of insulating spacers stacked in engagement with and separating said sleeve and said electrodes; said envelope comprising a plurality of insulating rods coupled together in permanent, tangential engagement and with axes parallel with said axis and being in tangential Contact with said sleeve and said electrodes, said means for energizing said electrodes comprising con tact bands coaxially disposed about said rods in tangential contact with said electrodes, adjacent bands being circumferentially spaced apart by 180 degrees.

7. In an electron discharge device adapted to operate in an environment having substantial changes in pressure, an electron gun and an envelope containing said gun, said gun having an axis, a cathode for producing a beam of electrons, a plurality of electrodes for focusing and accelerating said beam along said axis, and a plurality of insulating spacers stacked in engagement with and separating said electrodes; said envelope comprising a plurality of insulating rods having a generally rounded cross section and coupled together in permanent, tangential engagement with said spacers and said electrodes; and means to facilitate energizing said electrons comprising contact bands coaxially disposed about said rods contacting a like number of electrodes, adjacent bands circumferentially spaced on said envelope.

8. In an electron discharge device, an electron gun and an envelope containing said gun, said gun having a means for producing electrons, a plurality of electrodes for focusing and accelerating said beam, and a plurality of insulating spacers stacked in engagement with said electrodes; said envelope comprising a plurality of insulating members coupled together about said spacers and said electrodes, and contact means integral with said envelope comprising a plurality of circumferentially spaced metal bands, each of said bands being electrically connected to one of said electrodes.

References Cited in the file of this patent UNITED STATES PATENTS 1,955,899 Zworykin Apr. 24, 1934 2,808,528 Martin Oct. 1, 1957 2,859,372 Stangl Nov. 4, 1958 2,938,133 Hueter May 24, 1960

Claims (1)

1. 8. IN AN ELECTRON DISCHARGE DEVICE, AN ELECTRON GUN AND AN ENVELOPE CONTAINING SAID GUN, SAID GUN HAVING A MEANS FOR PRODUCING ELECTRONS, A PLURALITY OF ELECTRODES FOR FOCUSING AND ACCELERATING SAID BEAM, AND A PLURALITY OF INSULATING SPACERS STACKED IN ENGAGEMENT WITH SAID ELECTRODES; SAID ENVELOPE COMPRISING A PLURALITY OF INSULATING MEMBERS COUPLED TOGETHER ABOUT SAID SPACERS AND SAID ELECTRODES, AND CONTACT MEANS INTEGRAL WITH SAID ENVELOPE COMPRISING A PLURALITY OF CIRCUMFERENTIALLY SPACED METAL BANDS, EACH OF SAID BANDS BEING ELECTRICALLY CONNECTED TO ONE OF SAID ELECTRODES.

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