US3334262A

US3334262A - High frequency velocity modulation electron discharge devices having replaceable beam forming and projecting assemblies

Info

Publication number: US3334262A
Application number: US332548A
Authority: US
Inventors: Richard B Nelson
Original assignee: Varian Associates Inc
Current assignee: Varian Medical Systems Inc
Priority date: 1963-12-23
Filing date: 1963-12-23
Publication date: 1967-08-01
Anticipated expiration: 1984-08-01
Also published as: GB1057009A

Description

Aug. 1, 1967 R. B. NELSON 3,334,262

HIGH FREQUENCY VELOCITY MODULATION ELECTRON DISCHARGE DEVICES HAVING REPLACEABLE BEAM FORMING AND PROJECTING ASSEMBLIES Filed Dec. 23, 1963 (ON Q lo FEGB I NVENTOR. RICHARD B. NELSON ATTORNEY United States Patent 3,334,262 HIGH FREQUENCY VELOCITY MODULATION ELECTRON DISCHARGE DEVICES HAVING REPLACEABLE BEAM FORMING AND PRO- JECTING ASSEMBLIES Richard B. Nelson, Los Altos, Calif., assignor to Varian Associates, Palo Alto, Calif., a corporation of California Filed Dec. 23, 1963, Ser. No. 332,548 14 Claims. (Cl. 315-539) This invention relates in general to high frequency velocity modulation electron discharge devices capable of operation in the microwave spectrum and more particularly to such devices wherein replaceable beam forming and projecting assemblies are provided therein.

High frequency velocity modulation electron discharge devices such as klystrons and traveling wave tubes capable of operating in the microwave spectrum having conventional electron guns are normally constructed such that the accelerating anode portion of the electron gun which is subject to high voltage fields is integral with the main tu'be body of the device. Such a construction does not lend itself readily to easy replacement and cleaning of the accelerating anode portion of the device upon failure of certain parts of the electron gun portion thereof. For example, assuming a cathode failure using conventional construction techniques, the tube can be reconstituted only by replacing the entire cathode assembly and cleaning the anode portion of the electron discharge device which is subjected to high voltage focusing and accelerating fields while in situ with the main body of the tube. When the aforementioned anode portion is cleaned while it is connected integrally with the main tube body there is danger of contamination of the internal cavities and drift tubes in the case of a klystron and of the slow wave structure in the case of a traveling wave tube. This danger results from the use of solvents and other cleansing agents for removing dirt on the anode surface which is subjected to high voltage focusing and accelerating fields. Removal of this dirt and other foreign deposits on the anode surface portion which is subjected to high voltage focusing and accelerating fields in a conventional type gun is necessitated in order to prevent high voltage arcing and positive ion bombardment and consequent poisoning and destruction of the cathode surf-ace with a resultant loss of emission.

The present invention resolves such difficulties through the utilization of a novel integral replaceable beam forming and projecting assembly. This assembly comprises conventional electron gun assemblies such as, for example, a Pierce type gun wherein the anode is integrally formed as part of the gun assembly. In the case of a klystron tube the anode is separated from the first drift tube and tube main body by means of a reworkable joint. In the case of a traveling wave tube the anode is separated from the circuit portion and main body of the tube through the utilization of reworkable joints. Through the utilization of an integral replaceable beam forming and projecting assembly upon cathode or other failures occurring in the electron gun port-ion of the tube the entire replaceable beam forming and projecting assembly would be removed from the tube main body and a new assembly inserted with a minimum of effort through the utilization of the techniques taught by the present invention. This concept has particular usefulness for high power velocity modulation devices capable of operation in the microwave spectrum where the cost of the gun assembly is substantially less than the cost of the remainder of the tube. The reworkable vacuum joint utilized between the anode portion which is subjected to high voltage focusing and accelerating fields and the main body of the elec- 'ice tron mscharge device may take any of several forms as taught by the present invention. For example, a low melting point brazed joint may be employed between the juncture of the anode and the tube main body surface. In other preferred embodiments, a welded joint flange may be employed or a mechanical seal such as, e.g., the Conflat high vacuum seal.

It is therefore an object of the present invention to provide a velocity modulation electron discharge device capable of operation in the 'crowave spectrum such as aahigh frequency klystron or traveling wave tube with an integral replaceable beam forming and projecting assembly.

A feature of the present invention is the provision of a klystron tube with an integral replaceable beam forming and projecting assembly.

Another feature of the present invention is the provision of a high frequency traveling wave tube with an integral replaceable beam forming and projecting assembly.

Another feature of the present invention is the provision of a high frequency electron discharge device having an integral replaceable beam forming and projecting assembly wherein the vacuum joint between the main body of the high frequency electron discharge device and the integral replaceable beam forming and projecting assembly comprises a reworkable brazed joint.

Another feature of the present invention is the provision of a high frequency electron discharge device having an integral replaceable beam forming and projecting assembly wherein the vacuum joint between the high frequency discharge device main body and the integral replaceable beam forming and projecting assembly is formed from a high vacuum mechanical seal.

Another feature of the present invention is the utilization in the preceding feature of a Conflat high vacuum mechanical seal.

Another feature of the present invention is the provision of a high frequency electron discharge device having an integral replaceable beam forming and projecting assembly wherein the juncture between the integral replaceable beam forming and projecting assembly and the main tube body of the high frequency electron discharge device is formed by a welded vacuum joint between opposing flanges of said main body and said assembly.

Another feature of the present invention is the provision of a high frequency electron discharge device capable of operation in the microwave spectrum having an integral replaceable beam forming and projecting assembly, said integral replaceable beam forming and projecting assembly having a main accelerating anode portion spaced from a cathode and integrated therewith, said main anode portion having a central beam entrance aperture of a given diameter and said main anode portion having an axial extent as measured downstream from the transverse plane of the central entrance aperture which is equal to or less than the diameter of the central entrance aperture.

Another feature of the present invention is the provision of a high frequency electron discharge device capable of operation in the microwave spectrum having an integral replaceable beam forming and projecting assembly, said integral replaceable beam forming and projecting assembly having a main accelerating anode portion spaced from a cathode and integrated therewith, said main anode portion having a central beam entrance aperture of a given diameter, said aperture serving to define a bore which extends through the main accelerating anode portion, said bore being partially defined by the main accelerating anode portion and the extent of said bore partially defined by the main accelerating anode portion, as measured downstream from said central beam entrance aperture having a physical length along the beam include all portions of the bore which are subjected to is hereinafter defined as an essentially field free region in the presence of beam accelerating potentials between cathode and the main ac: celerating anode portion.

Another feature of the present invention is the provision of a high frequency electron discharge device having an integral replaceable beam forming and projecting assembly wherein the juncture between the integral replaceable beam forming and projecting assembly and the tube main body is formed from a brazing composition having a liquidus temperature which is lower than the solidus temperature of any other brazed joint in the vicinity of said juncture.

These and other features and advantages of the present invention will become more apparent upon a perusal of the following specification taken in conjunction with the accompanying drawings wherein:

FIG. -1 is a cross-sectional view of a linear beam klystron tube partly in elevation, utilizing the novel replaceable beam focusing and projecting assembly taught by the present invention;

FIG. 2 is a cross-sectional view, partly in elevation of a traveling wave tube incorporating the novel replaceable beam forming and projecting assembly as taught by the present invention;

FIG. 3 is a fragmentary cross-sectional view of a replaceable beam forming and projecting assembly wherein a Conflat high vacuum seal is utilized;

FIG. 4 is an enlarged cross-sectional view taken along the lines 44 of FIG. 1 depicting the novel brazed joint between the replaceable beam forming and projecting assembly and the tube body;

FIG. 5 is an enlarged cross-sectional fragmentary view of the flanged welded joint utilized in the embodiment of FIG. 2 taken along the lines 5-5 of FIG. 2;

FIG. 6 is a fragmentary cross-sectional view, partly in elevation, depicting another embodiment of the novel replaceable beam forming and projecting assembly of the present invention;

FIG. 7 is an enlarged view of the sealing flange ridge portion shown in the embodiment of FIG. 3 taken along the lines 77 of FIG. 3; and

FIG. 8 is a fragmentary cross-sectional view partly in elevation depicting an integral replaceable beam forming and projecting assembly incorporating a modulating anode.

there is shown a high frequency electron discharge device 1 of the klystron type incorporating on the one end thereof a novel integral replaceable beam forming and projecting assembly 2, and on the other end thereof an electron beam collector 3 between which the tube main body 4 is located and attached thereto. The klystron depicted in FIG. 1 is afour cavity type wherein each of the individual cavities has tuning provisions therefor. The details of the tuners 5, cavities and collector sections of the klystron of FIG. 1 will not be discussed herein since they do not form part of the present invention. For the purposes of setting forth concise terminology in defining the present invention the following definitions are in order. Tube main body is defined as all'portions of the tube downstream from the replaceable beam forming and projecting assembly and includes all cavities in the case of a klystron and the entire interaction slow wave circuit in the case of a traveling wave tube. Directing our attention now to the novel replaceable beam forming and projecting assembly 2 incorporated in the klystron of FIG. 1, there is shown a conventional cathode 6 having a preferably concave emission surface, not shown, surrounded by a typical focusing eleczrode 7. The cathode and focusing electrode are disposed vithin an annular metallic tubing 8 which is integral with he accelerating anode portion thereof 9. A conventional axis which is limited to alumina or the like insulator 10 is disposed between the accelerating anode section 9 and the cathode and focusing anode structure 6 and 7, respectively. A suitable potted end cap or the like 11 completes the replaceable beam forming and projecting assembly. The tube main body 4 supports a drift tube 8' which is integral therewith. Suitable gun alignment means such as mating flange 15' disposed in annular offset 16 are provided as best seen in FIG. 4. The particular operating characteristics of klystrons are well known and reference can be made to any conventional text for further information on this point and a detailed explanation functioning thereof will not be given herein.

. The portion of accelerating anode 9 delineated by as best seen in FIG. 3 is representative of that portion of the anode which is highly critical with regard to the maintenance of clean surface conditions. Due to its close proximity to the cathode, it is subject to high electric fields and to evaporation of contaminants from the cathode and is therefore most subject to high voltage arcing. Therefore, this surface portion must be cleaned when a new cathode is inserted and as mentioned previously this presents a difficult problem with regard to maintaining the remainder of the tube isolated from possible contamination during the cleaning operation. The remainden of the tube main body 4 including cavities 4' and drift tubes 8' is also at anode potential but is not subjected to high voltage arcing problems such as are encountered between the cathode surface and that portion of the anode delineated by 99 since the remaining surface portions of the anode are relatively far removed from the cathode and the field strength falls off rapidly with axial penetratration inside the hollow drift tube. Therefore, the present invention teaches the concept of incorporating as part of the integral replaceable beam forming and projecting assembly all surface portions of the accelerating anode which are subjected to high voltage arcing problems between surfaces at anode potential and surfaces at or near cathode potential. It has been determined that the surface portions surrounding the electron beam of the main accelerating anode which are most subject to arcing can be limited in axial extent, as measured from a transverse plane T through the central beam entrance aperture of the main accelerating anode downstream along the tube or elongated beam axis to a distance which is at least equal to the diameter D of the central beam entrance aperture of the main accelerating anode.

An alternative method of defining just what anode surface portions of Pierce type guns are subjected to high voltage arcing problems is as follows. Since Pierce type guns can probably accommodate accelerating voltage field strengths of perhaps 200,000 volts/ cm. under pulsed con ditions and 100,000 volts/cm. under D.C. conditions and since the precise breakdown voltage for any given gun configuration is extremely complex and dependent on many variables an attempt to define just what accelerating anode surface portions are subject to high voltage arcing and therefore should be removed and/or cleaned, as mentioned previously, is not readily accomplished. The preceding definition is one approach and is probably equivalent to stating that all projecting assembly. Essentially field free regions can be defined as regions where approximately 10% of its value between the entrance aperture and the cathode during the presence of beam accelerating and'focusing voltages.

These surface portions would normally be cleaned and there is danger of tube contamination if cleaned while integrated with the main body of the tube.

FIG. '4 depicts an enlarged view of the brazed joint comprising braze material 12 located between the one surface 13 of the replaceable beam forming and projectof the operation and' ing assembly and the opposing surface 14 of the tube main body. A conventional pole piece 15 made of magnetic material such as iron is advantageously incorporated in the klystron tube of FIG. 1. The brazed joint between the end wall 13 of the main anode and the opposing wall 14 of the tube main body is formed with a brazing alloy 12 wherein the composition of the alloy is characterized by having a liquidus temperature which is lower than the solidus temperature of any other brazing alloy utilized in the vicinity of said brazed joint. Preferably, the materials utilized for the tube main body 4 and the main anode 9 of a conventional klystron such as depicted in FIG. 1 are of copper. There are many brazing alloys readily available on the commercial market which can be utilized to form reworkable vacuum tight joints in high frequency electron discharge devices. However, it is necessary in the present invention to utilize a brazing alloy which can be changed from the solid to the liquid state at a temperature which is lower than the solidus temperature of any other brazed joints located in the vicinity of the reworkable joints downstream from said reworkable joint in order that induction heating or other local heating techniques may be utilized to facilitate removal and replacement of the beam forming and projecting assembly without destruction of other joints. Preferably, a silver-copper eutectic, such as, for example, 72% silver and 28% copper is utilized in making vacuum tight brazed joints between copper members. Such a eutectic has a liquidus and solidus temperature of approximately 780 centigrade. Reference to any standard teXt listing the properties of brazing compositions (alloys) suitable for vacuum joints in electron discharge devices will provide a comprehensive list of suitable brazing alloys having higher liquidus and solidus temperatures than that utilized for the reworkable joint. To mention a few, there are the platinum-gold and nickel-copper and gold-copper alloys.

In order to more fully understand the importance of the characteristics of the brazing materials utilized for forming reworkable joints between the main anode and the remainder of the electron discharge device the following pertinent definitions are in order. Brazing alloys are conventionally defined temperature-wise in terms of their'transition states between solid and liquid phases. For any given brazing alloy composition the temperature above which any composition of the brazing alloy is liquid is known as the liquidus temperature. For any given brazing alloy composition the temperature below which all compositions of the brazing alloy are entirely solid is known as the solidus temperature. The eutetic of any given brazing alloy is a composition wherein the total transition between the liquid and solid states occurs at'a given temperature.

Conventional outgassing and exhausting techniques employed for processing electron discharge device as klystrons and traveling wave tubes utilize bakeout temperatures in the vicinity of 500 or 600 centigrade. Therefore, it is necessary that the brazing alloy utilized for the reworkable joint as taught by the present invention has a solidus temperature which is substantially higher than the bakeout temperature employed in processing the tube.

Directing our attention to FIG. 2, there is depicted therein a high frequency electron discharge device of the traveling wave tube type. The traveling wave tube 16 of FIG. 2 includes integral replaceable beam forming and projecting assembly 17 coupled by reworkable joint 18 to the tube main body 19 which houses a conventional slow wave circuit such as a helix 20 and terminates in a conventional collector assembly 21. A simple R.F. coupler of the coaxial type 22 is utilized at the input portion and a similar coaxial output coupler 23 is employed at the output for forward wave amplifier operation. The tube main body 19 may be of copper as well as the collector portion of the tube. The integral replaceable beam forming and projecting assembly 17 is similar to that utilized in the klystron device of FIG. 1. The replaceable beam forming and projecting assembly includes a tubular body portion 17 integral with the accelerating anode 24 and brazed to an annular ceramic insulator 25. A conventional cathode and focusing electrode 26 are employed therein, and a suitable end cap 27 such as of silicone rubber encloses the conductors to the electron gun assembly. Referring now in detail to the reworkable joint employed in FIG. 2, there is shown an enlarged view in FIG. 5 depicting same. In this particular embodiment a pair of

opposed flange members

28 and 29 are integrated with the

main anode portion

17, 24 and main body portions 19 of the traveling wave tube, respectively. The particular reworkable joint employed in this case is exemplified by the weld 30 which extends around the outer periphery of the opposing flanges 28-29 as best shown in FIG. 5. This exterior weld is suitable for ease of replacement by simply machining it oif and separating the parts. The flanges can-easily be rewelded or the replaceable beam forming and projecting assembly flange 28 can be replaced by another flange on a new assembly and the process repeated. Of course, suitable brazing materials as mentioned previously are utilized to form a vacuum seal between flange portions of the device of FIG. 2 as taught by the techniques of FIG. 1. The essence of the invention once again is employment of an integral replaceable beam forming and projecting assembly wherein the entire electron gun including the main accelerating anode is easily removed from the tube main body and a new integral replaceable beam forming and projecting assembly including an accelerating anode replaced therein. That portion of the anode of FIG. 2 which corresponds to the equivalent of FIG. 3 delineated by lines 9'9' is most susceptible to high voltage arcing and as previously discussed in connection with FIG. 1 is included .as part of the integral beam forming and projecting replaceable assembly.

Turning our attention now to FIG. 3 there is shown a fragmentary view of the replaceable beam forming and projecting assembly such as shown in FIGS. 1 and 2. The accelerating anode 33 is integral once again with the surrounding tubular portion 34 which encompasses the cathode and focusing electrode 35. The main tube body is represented by 36 and once again copper is advantageously employed for the accelerating anode and tube body. The reworkable joint in the body depicted in FIG. 3 includes a Conflat high vacuum mechanical seal. This Conflat seal is described in detail in US. patent application Ser. No. 144,458, by Maurice A. Carlson and William R. Wheeler, filed Oct. 11, 1961, now US Patent No. 3,208,758 issued Sept. 28, 1965 and assigned to the same assignee as the present invention. The Conflat seal depicted in FIG. 3 is characterized by a pair of annular main flange members 37, 38, of for example, stainless steel, straddling annular sealing gasket 41 made of, for example, copper having a rectangular or annular crosssection. The flange members 37, 38 are provided with a plurality of circumferentially arranged apertures which accommodate a plurality of bolts 39 made of, for example, stainless steel. Each of the bolts 39 has a nut 40 for providing a force to cause relative movement between the flange members 37, 38 and sealing gasket 41. The annular flange members 37, 38 have a generally rectangular cross-section, smooth inner 44 and outer 45 edges and one flat side 46. The second side 47 of the flange members 37, 38 is a fiat inner base portion 48 which is interrupted by circular ridge portion 49. See the enlarged view depicted in FIG. 7. The ridge portion 49 has a triangular cross-section, a vertical inner side 50' perpendicular to the flat faced portion 48 and a slanted outer side 50 which forms an acute angle 0. The slanted outer side 50 terminates at the inner side wall 51 of a shoulder 52 which forms the outer portion of the second side 47 of the flange members 37, 38. The inner side wall 51 of the shoulder 52 is perpendicular to the fiat base 48 and the top surface 53 of the shoulder 52 is parallel to the flat base somewhat further above it than the apex 54 of the ridge 459.

In the operation of the replaceable beam forming and projecting assembly depicted in FIG. 3, inner edges 44 of the flange members 37, 38 are secured by, for example, brazing to the exterior peripheries of the tube main body 36 and the replaceable anode portion 34. The brazing material employed may be of any suitable brazing alloy having solidus temperature above the bakeout temperature employed during exhaust procedures. The soft metal gasket 41 is positioned between the aligned opposing ridge portions 49 of the adjacent flanges 37, 38. The gasket 41 is of such size that its outer edge 55 lies closely adjacent the inner side walls 51 .of the shoulders 52 and its flat top and bottom surfaces 56, 57 engage the ridge portions 49. The nuts 40 are then tightened on bolts 39 which results in a relative movement between the flange members 37, 38 and the gasket member 41 in a direction perpendicular to the flat base surfaces 47.

The relative movement between the flange members 37, 38 and gasket 41 causes a penetration of the gasket by the ridge portions 49. A normal force proportional to the total force applied by the bolts 39 then exists between the gasket 41 and the slanted outer side 50 of the ridge portions 49. The normal force has a component A which is parallel to the direction of relative movement between the flanges 37, 38 and gasket 41 and a component B which is perpendicular to this direction of relative movement. However, the soft metal gasket material is prevented from moving in the direction of component A by the slanted side 50 of the opposing ridge portion 49 and in the direction of component B by the inner side wall 51 of the shoulder 52.

Thus, the inner side wall 51 of the shoulder 52 and the slanted side 50 of the ridge portion 43 form a compartment which traps the soft gasket material. The trapping of the gasket material results in the maintenance of extremely high pressure in the area of contact between the gasket 41 and the slanted sides 50 even after the repeated bakeout.

The preferable size of the angle has been found to be in the range between and 45. For a complete analysis of the Conflat type seal depicted in FIG. 3 see the aforementioned U.S. Patent No. 3,208,758. The mechanical sealing arrangement depicted in FIG. 3 which utilizes the Conflat seal shown therein, again results in an easily replaceable beam forming and projecting assembly for electron discharge devices. Replacement is simplified and results in ease of maintenance problems. The tube technician simply removes bolts 39 together with nuts 40 and separates the flanges 37, 38 and after the replaceable beam forming and projecting assembly which includes integral anode portion 33, 34 is removed it is a simple matter to substitute another replaceable beam forming and projecting assembly for the burned out assembly. In the alternative, flanges 37, 38 may advantageously be made integral with the main tube body 36 and the integral anode portion 33, 34 respectively.

FIG. 6 depicts another embodiment of the present invention wherein a replaceable beam forming and projecting assembly is utilized in an electron discharge device. Focusing electrode 60 within which a conventional cathode is disposed is mounted within and forms a replaceable beam forming and projecting assembly 61 in the same manner as depicted in FIGS. 1 and 2. A conventional pole piece 62 is brazed or the like, to a tubular casing 63 which surrounds the focusing electrode and cathode and is insulated therefrom by a suitable insulator such as element 10 of FIG. 1. Tubular casing 63 has a transverse header portion 64 which supports accelerating anode portion 65, which is brazed thereto. The tube main body 66 is brazed along the surface 67 to the adjacent adjoining surface of the replaceable beam forming and projecting assembly by a brazing composition which is characterized by having a liquidus temperature which is lower than the solidus temperature of any other brazed joint located in the vicinity of said brazed surfaces. Accelerating anode portion 65 is brazed to surface 68 of the transverse header portion 64 'by use of a brazing composition which has a solidus temperature which is higher than the liquidus temperature of the brazing composition used along surface 67. Thus, in effect, even though the accelerating anode 65 is a distinct element with respect to the transverse header portion 64 an inte gral replaceable beam forming and projecting assembly with reference to the main body portion of the tube is still taught by the embodiment depicted in FIG. 6. First drift tube 69 is integral with the tube main body 66 and of necessity if comprising a separate machined part must be brazed to the tube main body by a brazing alloy having a solidus temperature which is higher than the liquidus temperature of the reworkable joint brazing material. Obviously, the particular location of the joints and relative size of the accelerating anode portion with respect to the transverse header portion can be varied as desired. Alternatively, tubular casing 63 and transverse header portion 64 may be made of a high permeability material such as soft iron and thus function as pole pieces in conjunction with pole piece 62. A conventional flux return shield and focusing solenoid or permanent magnets may be utilized in any of the embodiments to provide the main focusing field.

FIG. 8 depicts an integral replaceable beam forming and projecting assembly 70 incorporating a modulating anode 71 such as, for example, as taught in U.S. Patent No. 2,842,742 by D. H. Preist. An alumina or the like ceramic insulator 72 and potted end cap 73 are coupled to accelerating anode portion 74 through the intermediate modulating anode 71 and annular insulator 75. A conventional cathode is disposed Within focusing electrode 76 as taught in FIG. 1. Since both modulating anode 71 and accelerating anode 74 are operated at DC. voltages which can be extremely high with respect to the cathode and focusing electrode these elements are included as part of the integral replaceable beam forming and projecting assembly. Again, as in FIG. 1, the tube main body 81 of FIG. 8 is fixedly attached to the integral replaceable beam forming and projecting assembly by a reworkable brazed joint wherein the liquidus temperature of the brazing alloy between the opposing surfaces 77, 78 is lower than the solidus temperature of any other brazed joint in the vicinity, such as, for example, brazed joint 79 between the first drift tube portion 80 and the tube main body 81. Suitable alignment means 82, such as shown in the embodiment of FIG. 1 are incorporated in the embodiment of FIG. 8. It is, of course, understood that any other reworkable vacuum joint capable of maintaining less than 10* mm. of Hg pressures, such as, for example, the peripheral weld or Conflat mechanical vacuum joints depicted in FIGS. 3 and 5, respectively, may be utilized in the embodiment of FIG. 8. Again, all anode surfaces which are subject to high voltage focusing and accelerating fields between cathode and anode potentials and which are susceptible to arcing are included as part of the integral replaceable beam forming and projecting assembly.

Obviously, the types of reworkable joints taught by the present invention are illustrative and not to be taken as all encompassing. Many other conventional metal joining techniques which are capable of forming vacuum tightreworkable joints are capable of maintaining vacuums on the order of IX 10* millimeters (mm.) of Hg, and less than 1X10 mm. of Hg can be utilized to form a reworkable joint between the tube main body and the accelerating anode and are contemplated and included herein. Regardless of what type of a reworkable vacuum joint is utilized between the replaceable beam forming and projecting assembly and the tube main body, the present invention teaches that said joint must be characterized incorporated in with suitable modifications are described in the following patents. US. Patent 2,915,670'by L. T.

Zitelli; US. Patent 2,939,036 by R. B. Nelson; U.S..

Patent 2,944,187 by R. L. Walter et al.; US. Patent 2,994,009 by R. C. Schmidt et al.; U.S. Patent 3,028,519 by R. L. Jepsen et al. Representative high frequency electron discharge devices capable of operation in the microwave spectrum in which the integral replaceable beam forming and projecting means taught by the present invention may be advantageously incorporated in with suitable modifications are also described in the following US. patent applications, each of which is assigned to the assignee of the present invention: Ser. No. 253,178 by Stanley E. Allen, Jr., filed Ian. 22, 1963; Ser. No. 148,520 by L. T. Zitelli et al., filed Oct. 30, 1961; Ser. No. 56,415 by John A. Ruetz et al., filed Sept. l6, 1960.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could 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 is claimed is:

1. A high frequency electron discharge device capable of operation in the microwave spectrum including means for forming and projecting an electron beam over an elongated beam path, means for collecting the beam at the terminal or downstream end of said beam path, means disposed intermediate said beam forming means and said beam collecting means for velocity modulating said beam by electromagnetic interaction with said beam at microwave frequencies, means disposed along said beam path for extracting microwave output energy from said beam for transmission to a suitable utilization device, means forming an elongated vacuum envelope enclosing said beam forming, modulating and collecting means, said beam forming and projecting means defining an integral replaceable beam forming and projecting diode assembly having a main accelerating anode with a central beam entrance aperture spaced from and integrated with a cathode structure, said modulating means defining a tube main body portion, said integral replaceable beam forming and projecting diode assembly being fixedly attached and vacuum sealed to said tube main body portion by means of a single reworkable high vacuum joint, said reworkable vacuum joint being characterized by case of disassembly and ease of reassembly without adversely affecting the remaining joints in the vicinity of said reworkable joint downstream from said joint, said integral replaceable diode assembly including only the main accelerating anode surface portions in the vicinity of the electron beam which are subjected to arcing due to the presence of high voltage focusing and accelerating fields.

2. The device defined in claim 1 wherein said reworkable high vacuum joint is a brazed joint.

3. The device defined in claim 1 wherein said reworkable high vacuum joint is a welded joint.

4. The device defined in claim 1 wherein said reworkable high vacuum joint is a mechanical joint.

5. The device defined in claim 2 wherein said brazed vacuum joint is formed from a brazing composition having a liquidus temperature which is lower than the solidus temperature of any other brazed joint in the vicinity of said reworkable joint downstream from said reworkable joint.

6. The device defined in claim 3 wherein said replaceable beam forming and projecting assembly and said tube main body each have outwardly extending opposed transverse flanges disposed on the ends thereof, said flanges being affixed together to form a vacuum seal by a peripheral reworkable welded joint on the outer edges of said flanges.

7. The device as defined in claim 4 wherein said reworkable mechanical vacuum joint includes a pair of annular main flange members adapted for movement relative to each other, one of said flange members being affixed to said replaceable beam forming and projecting assembly the other of said flange members being affixed to said tube main body, a soft metal gasket positioned between said flange members, a circular ridge portion projecting out of each of said flange members in a direction toward said soft metal gasket, each of said ridge portions being substantially triangular in cross-section with one side substantially parallel to the direction of relative movement and a slanted side at an acute angle to the direction of the relative movement, said ridge portions on said main flange members being directly opposite each other and separated by said soft metal gasket, each of said main flange members having a circular shoulder portion with an inner wall opposite said slanted side of said ridge portion forming a compartment therewith, said soft metal gasket having one edge closely adjacent to said inner walls of said shoulder portions, and said compartment formed by said inner wall and said slanted wall adapted to trap the soft metal material of said gasket upon penetration of said gasket by said ridge portions upon relative movement of said flange members.

8. The device defined in claim 1 wherein said reworkable vacuum joint is capable of maintaining pressures of less than 1 10 mm. of Hg.

9. The device defined in claim 1 wherein said replaceable beam forming and projecting assembly includes an annular pole piece, said annular pole piece having an aperture therein, said aperture having an accelerating anode mounted therein and wherein said pole piece and said accelerating anode are bonded to said tube main body by said reworkable vacuum joint.

10. The device as defined in claim 1 wherein said main accelerating anode surface portions in the vicinity of the electron beam are limited in axial extent as measured from a transverse plane through the central entrance aperture of the main accelerating anode downstream along the beam axis, to a distance which is at least equal to or less than the diameter of the central beam entrance aperture of the main accelerating anode.

11. The device as defined in claim 1 wherein said replaceable beam forming and projecting means includes a modulating anode integral therewith and disposed intermediate said cathode and main accelerating anode.

12. The device as defined in claim 1 wherein said main accelerating anode surface portions in the vicinity of the electron beam are limited in axial extent as measured from a transverse plane through the central entrance aperture of the main accelerating anode downstream along the beam axis, to a distance which includes all anode surface portions which are not essentially field free in the presence of high voltage focusing and accelerating potentials between the cathode structure and the main accelerating anode.

13. A high frequency electron discharge device capable of operation in the microwave spectrum including means for forming and projecting an electron beam over an elongated beam path, means for collecting the beam at the terminal or downstream end of said beam path, means disposed intermediate said beam forming means and said beam collecting means for velocity modulating said beam by electromagnetic interaction with said beam at microwave frequencies, means disposed along said beam path for extracting microwave output energy from said beam for transmission to a suitable utilization device, means forming an elongated vacuum envelope enclosing a tube main body forming and projecting diode assembly being fixedly attached and vacuum sealed to said tube main body portion by means of a single high voltage focusing and accelerating fields, said reworkable high vacuum joint being a mechanical joint.

14. The device as defined in claim said flange members being aflixed to said tube main body, a soft metal gasket positioned between said flange members, a circular ridge portion projecting out of each of said flange members in a direc- References Cited UNITED STATES PATENTS JAMES W. LAWRENCE, Primary Examiner. V. LAFRANCHI, Assistant Examiner.

Claims

1. A HIGH FREQUENCY ELECTRON DISCHARGE DEVICE CAPABLE OF OPERATION IN THE MICROWAVE SPECTRUM INCLUDING MEANS FOR FORMING AND PROJECTING AN ELECTRON BEAM OVER AN ELONGATED BEAM PATH, MEANS FOR COLLECTING THE BEAM AT THE TERMINAL OR DOWNSTREAM END OF SAID BEAM PATH, MEANS DISPOSED INTERMEDIATE SAID BEAM FORMING MEANS AND SAID BEAM COLLECTING MEANS FOR VELOCITY MODULATING SAID BEAM BY ELECTROMAGNETIC INTERACTION WITH SAID BEAM AT MICROWAVE FREQUENCIES, MEANS DISPOSED ALONG SAID BEAM PATH FOR EXTRACTING MICROWAVE OUTPUT ENERGY FROM SAID BEAM FOR TRANSMISSION TO A SUITABLE UTILIZATION DEVICE, MEANS FORMING AN ELONGATED VACUUM ENVELOPE ENCLOSING SAID BEAM FORMING, MODULATING AND COLLECTING MEANS, SAID BEAM FORMING AND PROJECTING MEANS DEFINING AN INTEGRAL REPLACEABLE BEAM FORMING AND PROJECTING DIODE ASSEMBLY HAVING A MAIN ACCELERATING ANODE WITH A CENTRAL BEAM ENTRANCE APERTURE SPACED FROM AND INTEGRATED WITH A CATHODE STRUCTURE, SAID MODULATING MEANS DEFINING A TUBE MAIN BODY PORTION, SAID INTEGRAL REPLACEABLE BEAM FORMING AND PROJECTING DIODE ASSEMBLY BEING FIXEDLY ATTACHED AND VACUUM SEALED TO SAID TUBE MAIN BODY PORTION BY MEANS OF A SINGLE REWORKABLE HIGH VACUUM JOINT, SAID REWORKABLE VACUUM JOINT BEING CHARACTERIZED BY EASE OF DISASSEMBLY AND EASE OF REASSEMBLY WITHOUT ADVERSELY AFFECTING THE REMAINING JOINTS IN THE VICINITY OF SAID REWORKABLE JOINT DOWNSTREAM FROM SAID JOINT, SAID INTEGRAL REPLACEABLE DIODE ASSEMBLY INCLUDING ONLY THE MAIN ACCELERATING ANODE SURFACE PORTIONS IN THE VICINITY OF THE ELECTRON BEAM WHICH ARE SUBJECTED TO ARCING DUE TO THE PRESENCE OF HIGH VOLTAGE FOCUSING AND ACCELERATING FIELDS.