Microwave beam tube having an improved fluid cooled main body

[57] ABSTRACT

The relatively soft metal main body portion of an X band linear beam tube, such as a traveling wave tube, is rigidly supported in axial alignment with the linear electron beam by means of a relatively rigid tubular support structure, as of stainless steel, disposed coaxially surrounding the main body portion of the tube. The main body portion of the tube, which contains the microwave interaction circuit, is formed of an out-ofround transverse section such that out-of-round surface portions of the main body are radially spaced from the inner tubular wall of the support structure to define fluid coolant passageways therebetween for cooling the main body and microwave circuit in use. The main body coolant passageways are connected in series with the flow of coolant between the electron gun, at one end, and the beam collector, at the other end, whereby cooling of the tube is facilitated.

Claims, 4 Drawing Figures

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PATENTED APR 8 i975

3,876,901

SHEET 1 OF 3

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FIG.2

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PATENTED APR 81975

3.876,901

SHEET 3 OF 3

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3,876,901

MICROWAVE BEAM TUBE HAVING AN IMPROVED FLUID COOLED MAIN BODY

GOVERNMENT CONTRACT

The invention herein described was made in the course of or under a contract or subcontract thereunder, (or grant) with the U.S. Department of the Navy.

RELATED CASES

The magnetic pole piece structure disposed at the beam collector end of the tube and containing the input and output waveguides forms the subject matter of and is claimed in my copending U.S. application Ser. No. 421,196 filed Dec. 3, 1973, entitled “Collector Pole Piece for Microwave Linear Beam Tube,” and assigned to the same assignee as the present invention.

BACKGROUND OF THE INVENTION

The invention relates in general to linear beam microwave tubes and more specifically to such tubes having an improved fluid cooled main body and improved strengthening support structure for the main body.

DESCRIPTION OF THE PRIOR ART

Heretofore, linear beam microwave tubes have been constructed with a block-type main body containing the microwave interaction circuit which is disposed along a beam path intermediate the electron gun and the beam collector structure. In such block-type main body portions, the microwave circuit is formed, as by milling, boring, or the like, into a solid block of copper. Since the copper block is relatively soft, strengthening means have been provided for preventing deformation of the block which could cause misalignment between the beam holes through the circuit and the beam path, thereby resulting in unwanted beam interception and destruction of the circuit.

In one prior art block body strengthening arrangement, stainless steel rods, running lengthwise of the block body, were brazed into the four corners of a body of square or rectangular transverse cross section. The block body was cooled by means of a plurality of fluid coolant passageways or channels milled into the side of the block body and connected to a source of fluid coolant for directing a flow of coolant through the block body for cooling thereof. Such prior art tubes are disclosed and claimed in U.S. Pat. Nos. 3,281,616, and 3,327,159 issued Oct. 25, 1966 and June 20, 1967, and assigned to the same assignee as the present invention.

While the aforecited prior art tube was adequately strengthened and cooled by the aforedescribed strengthening and cooling means, it is desired to provide an improved strengthening and cooling means which is less costly to manufacture.

SUMMARY OF THE PRESENT INVENTION

The principal object of the present invention is the provision of an improved microwave linear beam tube.

In one feature of the present invention, an out-ofround relatively soft metallic block body portion of the tube is supported from and within a tubular strengthening and support structure.

In another feature of the present invention, an out-ofround block body portion of the tube is supported within a tubular strengthening and support structure by the use of an interference fit therebetween. The region of space between the out-of-round body and the inside wall of the tubular strengthening and support structure serves to provide coolant passageways extending along the length of the block body for cooling the tube in use.

In another feature of the present invention, the coolant passageways for cooling the main body portion of the tube are connected in series with coolant passageways for cooling the electron gun at one end of the tube and the beam collector structure at the other end of the tube, whereby fabrication of the cooling structure is facilitated.

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

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view, longitudinally foreshortened and partly in block diagram form, of a microwave linear beam tube incorporating features of the present invention,

FIG. 2 is an enlarged view of a portion of the structure of FIG. 1 delineated by line 2—2,

FIG. 3 is an enlarged sectional view of a portion of the structure of FIG. 1 taken along line 3—3 in the direction of the arrows, and

FIG. 4 is a sectional view of the structure of FIG. 1 taken along line 4—4 in the direction of the arrows.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1, there is shown an X-band linear beam microwave amplifier tube 11 incorporating features of the present invention. More specifically, the tube 11 includes an electron gun assembly 12 disposed at one end for forming and projecting a beam of electrons over an elongated beam path 13 to a beam collector structure 14 disposed at the terminal end of the beam path for collecting and dissipating the energy of the beam. A main body portion 15 (FIG. 2) of the tube is disposed intermediate the electron gun 12 and the beam collector 14.

The main body portion 15 includes a microwave circuit 10 disposed along the beam path 13 in electromagnetic wave energy exchanging relation with the beam to produce output microwave energy which is coupled from the tube 11 via an output waveguide 16 for propagation to a suitable utilization device or load, not shown. In the instant case, the microwave tube 11 is an amplifier tube and amplifies input microwave energy in the X-band frequency range coupled to the input end of the microwave circuit 10 via input waveguide 17. The input waveguide 17 passes axially the tube 11 to the input or gun end thereof for coupling microwave energy onto the microwave circuit 10.

An electrically energized solenoid 18 (FIG. 2) is disposed coaxially surrounding the main body portion 15 for generating an axial magnetic field within the beam path 13 for focusing the electron beam 13 through the microwave interaction circuit.

A fluid coolant chamber or reservoir 19 is disposed surrounding the electron gun 12. The coolant is electrically insulative and heat absorptive. A suitable coolant is a liquid fluorocarbon such as Coolanol No. 25 commercially available from Monsanto Chemical Company. Such liquid fluorocarbons are conventionally used as hydraulic oil in hydraulic systems. Coolant from the reservoir 19 passes through an inner and an

3,876,901 outer circular array of apertures 20 and 21, respectively, in the cathode pole piece 54 into the interior of the solenoid 18 wherein the flow of fluid coolant is divided into two streams one of which passes into the main body portion 15 of the tube via a circular array of circumferentially spaced apertures 22 in the main body 15 and thence along the length of the main body 15 via a plurality of passageways 23 (FIG. 2) to a collector pole piece structure 24, as of cold rolled steel.

The collector pole piece structure 24 contains a hollow chamber and the hollow chamber is placed in fluid communication with the longitudinal fluid coolant passageways 23 in the main body portion 15. A circular array of apertures 25 in the collector pole piece 24 provide fluid communication between the collector pole piece chamber and an annular fluid chamber 26 surrounding the beam collector electrode or bucket 27. The fluid coolant is directed through a multitude of perforated cooling fins coupled to the exterior of the beam collector electrode 27 for cooling same. The fluid coolant is collected in a manifold structure 28 connected via tubulation to the input of a heat exchanger and pump 29 for removing the heat picked up by the coolant. The cooled coolant is then returned to the cathode reservoir 19 for recirculation through the tube.

In addition to the longitudinal fluid passageways 23 through the main body portion 15, the solenoid 18 includes a plurality of coils 31 which are axially spaced apart and varied in inside and outside diameters such as to define an annular serpentine shaped fluid coolant passageway 32 in between and around the electrical coils 31 for cooling the solenoid in use. In a typical example, the fluid coolant flow rate through the entire tube is 3.3 gallons per minute, whereas the fluid coolant flow rate through the main body portion 15 is 1 gallon per minute, leaving 2.3 gallons per minute flow through the solenoid 18.

Referring now to FIGS. 2 and 3, there is shown the main body portion 15 of the tube in greater detail. More particularly, the electron gun 12 (FIG. 1) includes an anode portion 33 which is sealed in a gas tight manner to the exterior envelope of the electron gun assembly 12. Similarly, the main body portion 15 of the tube 11 is sealed in a gas tight manner to, and forms a part of, the anode 33.

The main body portion 15 of the tube includes a cylindrical tubular strengthening member 34 (FIG. 3), as of 0.020 inch wall thickness non-magnetic stainless steel, sealed, as by brazing, to the anode 33 and extending longitudinally of the tube 11 to the collector pole piece structure 24 to which it sealed in a gas tight manner as by brazing. The main body 15 includes a block body portion 35, as of copper, in which the microwave interaction circuit 10 is formed. More particularly, the block body portion 35 includes a series of rectangular cavity resonators 36 formed therein preferably in the manner as disclosed and claimed in U.S. Pat. No. 3,711,943 issued Jan. 23, 1973 and assigned to the same assignee as the present invention. The common walls 37 between adjacent resonators 36 are each centrally apertured to define a beam passageway through successive resonators 36. Adjacent resonators are coupled together via inductive coupling holes 38 (FIG. 3) in the common wall 37 therebetween. The inductive coupling holes 38 alternate from one side of the beam path to the opposite side of the beam path to provide a serpentine shaped path of wave propagation for wave energy traveling on the interaction circuit 10. This type of microwave interaction circuit has a backward wave fundamental space harmonic mode of operation and is operated on the first space harmonic having between π and 2π radians of phase shift per cavity of the circuit 10.

The interaction circuit 10 is divided into a plurality of severed microwave circuit portions. More particularly, there is an input circuit portion 39, an output circuit portion 41, and an intermediate circuit portion 42. The input circuit portion has wave energy to be amplified applied to the upstream cavity 36 thereof via the input waveguide 17 communicating with the upstream cavity resonator 36 via an input coupling iris 43. The input waveguide 17 extends longitudinally of the block body portion 35, is recessed therein and brazed thereto. The downstream end of the input circuit portion 39 is terminated in a lossy circuit sever 44 forming the subject matter of and being claimed in my copending U.S. Patent application Ser. No. 438,495, filed Jan. 31, 1974, entitled “High Power Solid Microwave Load,” and assigned to the same assignee as the present invention.

Briefly the circuit sever 44 includes a section of rectangular waveguide 45 recessed into a milled out portion of the block body portion 35 and brazed thereto. The circuit sever waveguide 45 is coupled to the last resonator 36” via a 90° E-plane bend section 46 and coupling iris 47. An E-plane tapered wave energy absorptive member 40 is disposed within the terminal end of the circuit sever 44 in heat exchanging relation with the walls of the circuit sever waveguide 45 and the fluid coolant within fluid coolant passageway 23.

The input and output ends of the intermediate circuit portion 42 include circuit severs 44 of the type described with regard to the input section 39 of the microwave circuit. These severs 44 are located in recessed portions of the block body 35 on opposite sides from each other and on the sides of the rectangular cross section block portion 35 displaced 90° circumferentially from the input waveguide 17, as shown in FIG. 3.

Likewise, the output section 41 of the microwave circuit 10 includes a circuit sever 44 coupled to the upstream end thereof and the output waveguide 16 is coupled to the downstream resonator 36”' via output iris 51.

The block body portion 35 of the tube is supported from and strengthened by means of an interference fit between the four corners 52 (FIG. 3) of the block body. 35 and the interior bore of the stainless steel strengthening tube 34. As previously described, the block body 35 is of generally rectangular cross section to provide a substantially out-of-round surface spaced from the interior bore of the strengthening tube 34 for defining the four longitudinally directed coolant passageways 23 in the region between the out-of-round block body portion 35 and the inside wall of the strengthening tube 34.

The collector end of the block body portion 35 is brazed to the inner end of an inwardly directed reentrant portion of the collector pole piece 24.

The collector pole piece structure 24 is hollow and is joined in a fluid tight manner as by brazing to the collector end of the tubular strengthening member 34. Rectangular apertures in the pole piece 24 are provided on opposite sides of the beam path 13 to permit the input and output waveguides 17 and 16, respec3,876,901 tively, to pass from the main body portion 15 into the hollow pole piece structure 24. The apertures which permit the input and output waveguides 17 and 16 to pass into the hollow pole piece 24 are slightly larger than the outside dimensions of the waveguides 16 and 17 to provide a fluid communication passageway interconnecting the longitudinal body fluid coolant passageways 23 with the hollow chamber of the collector pole piece 24. In addition, at the output end of the block body portion 35, the corners are removed to permit fluid communication between the side passageways 23, 90° rotationally displaced from the input waveguide 17, and the input'and output waveguide passageways 23.

The solenoid 18 includes an annular plate 54, as of cold rolled steel, forming the electron gun pole piece of the solenoid 18, and a similar annular plate 55, as of Cold rolled steel, forms the collector pole piece of the solenoid 18. The two pole pieces are joined together by means of an inside tubular jacket 56, as of nonmagnetic stainless steel and an outside tubular magnetic yoke 50, as of cold rolled steel. The jacket and yoke are sealed at their ends in a fluid tight manner as by brazing to each of the annular pole pieces 54 and 55, respectively. The inside ring of perforations 20 in the cathode pole piece 54 provide fluid communication between the cathode reservoir 19 and the body coolant passageways 23 via the ring of apertures 22 in the strengthening cylinder 34 and a similar matching ring of apertures 57 in the inside jacket 56. An annular septum 58 is provided in the solenoid between the inner ring of apertures 20 and the outer ring of apertures 21 in the cathode pole piece 54 for separating the flow of coolant to the solenoid 18 from that flow of coolant to the body 35 of the tube 11. At the collector end of the solenoid a ring of apertures 59 is provided in the collector pole piece 55 of the solenoid 18 and in the collector pole piece 24 of the tube 11 to allow the coolant to flow from the solenoid 18 into the hollow collector pole piece 24 of the tube 11.

The solenoid 18 is sealed in a fluid tight manner to the reservoir 19 by an annular mounting flange 61 (FIG. 1) and bellows 62. The bellows 62 is sealed between a cover 63 of the reservoir l9 and the mounting flange 61. The mounting flange 61 is secured to the cathode end of the solenoid 18 via a plurality of cap screws 64. An O-ring 65 is provided between the mounting flange 61 and the cathode pole piece 55 for providing a fluid tight seal therebetween.

Similarly, at the collector end of the solenoid 18, the collector pole piece structure 24 of the tube 11 is joined in a fluid tight manner to the collector pole piece 55 of the solenoid 18 via a plurality of cap screws 66. An O-ring 67 is provided between the mating pole pieces 24 and 55 to provide a fluid tight seal therebetween. The cap screws 66 also serve to secure a cylindrical collector housing 68, as of aluminum, to the tube pole piece 24. An O-ring 69 provides a fluid tight seal between the tube collector pole piece 24 and the housing 68.

The beam collector electrode 27 is secured to the collector pole piece structure 24 by an annular electrical insulator assembly 71 to permit the collector electrode 27 (beam collector bucket) to be operated at a depressed collector potential relative to the potential applied to the block body portion;35 of the tube 11. An O-ring electrical insulator and seal 72 is disposed encircling the collector fin assembly 80 in between the fins and thd inside wall of the collector housing 68. The Oring 72 serves to support the.collector bucket 27via the fins and to seal the annular space between the outside of the fins, which are. closed off by a cylindrical baffle 70, and the housing 68 such that the fluid coolant is forced to percolate through the perforated fins to the collector manifold 28 at the end of the tube 11.

Electrical potential is applied to the collector bucket 27 via an electrical feedthrough assembly 73 interconnecting the collector bucket 27 and the: center pair of the feedthrough via a flexible wire 74. The end of the collector bucket 27 is insulatively supported from an end wall 76 of the housing 68 via a cylindrical insulator 75 made of a high temperature resistant plastic, such as polyamide having a circular array; of· radially directed perforations therein permitting the coolant to flow radially into the center of the cylindrical insulator 75 and thence into the manifold 28.

The tube 11 is readily removed and: replaced within the solenoid 18 by loosening the collector cap screws 66 such that the tube is disconnected from the solenoid. The tube is then pulled out of the solenoid from the collector end. Since the cathode 12 and the main body portion 15 of the tube have generally the same outside transverse dimensions, the tube 11 is readily removed from the solenoid. The coolant tank 19 and solenoid are carried from a support structure via a mounting bracket assembly.

In a typical example, the tube 11 is utilized as an Xband (8-12.5 gHz) power amplifier providing 10 KW of power output at X-band, with 50 db gain and 8 percent instantaneous electronic bandwidth (between 1 db points). The solenoid 18 provides an axial magnetic field within the beam of 2,500 gauss for focussing the beam 13. The beam has a current of 2.5 amps and a beam voltage of 19 KV at a micropereance of 1.0. The tube, together with its mounting bracket, waveguides, coolant, connectors, solenoid, and hoses weighs approximately 55 pounds, and is approximately 18 inches long.

While there have been described and illustrated several specific embodiments of the invention, it will be clear that variations in the details of the embodiments specifically illustrated and described may be made without departing from the true spirit and scope of the invention as defined in the appended claims and their legal equivalents.