US3305742A

US3305742A - High frequency electron discharge device and cooling means therefor

Info

Publication number: US3305742A
Application number: US307989A
Authority: US
Inventors: Earl W Mccune
Original assignee: Varian Associates Inc
Current assignee: Varian Medical Systems Inc
Priority date: 1963-09-10
Filing date: 1963-09-10
Publication date: 1967-02-21
Anticipated expiration: 1984-02-21

Description

Feb. 21, 1967 E. w. McCUNE 3,305,742

HIGH FREQUENCY ELECTRON DISCHARGE DEVICE AND COOLING MEANS THEREFOR Filed Sept. 10, 1963 INVENTORS EARL W. MC CUNE ATTORNEY United States Patent 3,305,742 HIGH FREQUENCY ELECTRGN DISCHARGE DE- VICE AND COOLING MEANS THEREFOR Earl W. McCune, Santa Clara, Calif., assignor to Varian Associates, Palo Alto, Calif, a corporation of California Filed Sept. 10, 1963, Ser. No. 307,989 2 Claims. (Cl. 313--21) The present invention relates generally to high frequency tubes and more particularly to improvements in klystrons, traveling wave tubes and other similar tube structures operable at relatively high frequencies for the generation or amplification of radio frequency energy via the mechanism of electromagnetic interaction between an electron beam and appropriately established radio frequency fields.

Extremely serious problems are encountered when attempts are made to design high frequency tubes of the designated type for operation at high power levels. As the output radio frequency power level increases, a corresponding increase in the beam power of the tube is requisite. In turn, the high powered electron beam is intercepted 'by various structural components of the tube wherefore substantial amounts of heat are generated, particularly under conditions of CW. operation as opposed to intermittent or pulsed operation. By way of example, a multi-cavity klystron amplifier arranged for C.W. operation with a radio frequency power output of 100 kw. will require an electron beam power in the neighborhood of 300 kw. Such beam, after traversing the klystron cavities, is conventionally collected bya bucket-like collector structure in which a considerable amount of heat will be generated. One problem then is to provide adequate and eificient cooling of the collector.

In addition, heat will be similarly generated in the cavity-forming structures themselves to an extent determined by the amount of beam interception with such cavity structures. Normally, a magnetic solenoid or the like can be utilized to focus the beam to a pencil-like shape which traverses most of the cavities Without appreciable interception. However, since the radio frequency power in the final or output cavity of the klystron is normally delivered therefrom through a laterally projecting output Waveguide, constituting the preferable structure for handling radio frequency power at high levels, a physical requirement for termination of the solenoid at the waveguide exists and the beam, in turn, will spread not only as a result of existent space charge forces in the beam itself but also as a result of certain transverse forces exerted on the electrons of the beam by the existent radio frequency fields in the final or output klystron cavity. As a result, substantial heat is commonly generated in the output cavity of high power klystrons, the amount being sufiicient to change the dimensions of the metallic structure forming the cavity to an extent such that detuning of the cavity and reduction in overall efficiency of the amplifier results.

Accordingly, it is a general object of the present invention to provide a high frequency tube which incorporates means arranged to control the generation of heat by a high power electron beam so that the tube is capable of operation at very high power levels.

A feature of the invention is the provision of a collector assembly for the electron beam including an extremely efficient coolant arrangement so that both the size of the collector and the amount of coolant requisite for tube operation are minimized.

More specifically, it is a feature of the invention to provide a collector assembly that incorporates a coolant arrangement maximizing the heat transfer between the collector walls and the coolant medium.

Additionally, it is a feature of the invention to provide a high frequency tube which incorporates a novel arrangement for connecting the supply of fluid coolant to the tube collector in a manner enabling maximum velocity and volume of coolant flow.

A related feature is the provision of such coolantconnecting means for a high frequency tube arranged to facilitate making or breaking of such connection and positional adjustment thereof.

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

FIG. 1 is a longitudinal view showing a multi-cavity klystron amplifier embodying the present invention,

FIG. 2 is an enlarged, longitudinal, fragmentary sectional view taken along line 2-2 of FIG. 1, illustrating details of interior construction,

FIG. 3 is a transverse section view taken along line 33 of FIG. 2 and FIG. 4 is an enlarged fragmentary transverse, sectional view taken along line 4-4 of FIG. 2.

With initial reference to FIG. 1, the klystron amplifier generally includes an elongated tubular metallic envelope arranged to maintain vacuum conditions therewithin. At one end, an electron gun assembly 12 is mounted and arranged to generate and direct a beam of electrons lengthwise through the entire tubular structure to a collector assembly 14 at its remote extremity. In its transit, the beam traverses sequentially four tunable cavity resonators,

two of which are indicated at 16, 22, each arranged with re-entrant drift tube portions defining cavity gaps 16a, 22a, which support standing-wave radio frequency fields in interacting relationship with the beam. 7

The radio frequency energy to be amplified is delivered to the'first cavity resonator 16 through a coaxial line 24 and an input coupling loop 26, and after amplification, the output radio frequency energy is transmitted from the final output cavity 22 through a conventional waveguide 28 which is connected to the final cavity resonator through a suitable coupling iris 30 and projects laterally therefrom. Briefly, the well known amplification mechanism includes an initial velocity modulation of the electron beam by the input radio frequency energy by way of coupling at the first cavity gap 16a. As the beam travels, a bunching or current density modulation results, the effect being further enhanced as the electrons traverse the second and third cavity gaps. The tightly bunched beam of electrons subsequently excites radio frequency fields in the final or output cavity resonator 22 which energy is then delivered through the output waveguide 28 to a suitable load (not shown). Further details of the described structure and its operation are not presented since they are not germane to the present invention and alternate known electron gun and/ or interaction structures can be substituted therefor.

The electron beam during its transit has a tendency to spread both as a result of space charge forces existent within the beam itself and also as a result of force components established within the resonator cavities, such forces attaining considerable magnitude in the final or output cavity resonator 22 where a high radio frequency power level has been developed through the described amplification mechanism. 'In order to maintain the beam in a confined pencil-like trajectory during its transit of the cavity resonators, a beam focusing solenoid 32 of generally tubular configuration surrounds the interaction region of the tube, terminating at one end adjacent the electron gun assembly 12 and at the other end adjacent the laterally projecting output waveguide 28. If the focusing effect of such single solenoid is considered by itself, substantially a constant magnetic focusing field can be established through the first three cavity resonators of the klystron amplifier but since the solenoid 32 terminates adjacent the output waveguide 28, fringing fields would exist in the final or fourth cavity resonator 22 and the focusing effect will thus diminish considerably and allow substantial interception of the electrons with the cavity forming structure.

An auxiliary coil 34, as most clearly illustrated in FIG. 2 encompasses the entrance end of the aforementioned collector assembly 14 so as to be positioned on the longitudinally opposite side of the output waveguide 28 from the described solenoid 32. More particularly, this auxiliary coil 34 surrounds a pole piece 340 integrated with the magnetic circuit of the main solenoid 32 and functions conjointly therewith so that ultimately a constant magnetic field exists across the entire magnetic gap, which with the addition of the auxiliary coil 34, encompasses all of the cavity resonators. Thus, defocusing of the electron beam in the fourth cavity resonator 22 is avoided.

Both the solenoid 28 and the auxiliary coil 34 are designed and constructed in accordance with known techniques wherefore details of such construction need not be spelled out. However, in such design and construction, it is preferred that the auxiliary coil 34 be designed with a number of turns such that the requisite magnetic field is obtained with a current flow identical to that in the main solenoid 32 wherefore a single magnet power supply (not shown) can be used and the electrical circuit can constitute a series connection. Additionally, both the main solenoid 32 and the auxiliary coil 34 can be supplied with coolant from an identical source (not shown). Thus, the necessity for additional complexity in both the coolant supply and the power supply for the magnetic focusing structures is obviated.

The described beam focusing arrangement provides for a high percentage of beam trans-mission to the collector assembly 14 which is arranged to provide for highly efficient dissipation of the heat generated during beam collection. The aforementioned beam focusing arrangement is claimed in copending US. patent application, Serial No. 308,880 entitled High Frequency Electron Discharge Device and Focusing Means Therefor by Earl W. McCune and Louis T. Zitelli, filed Sept. 13, 1963, since abandoned in favor of continuation-in-part application U.S. Serial No. 327,369 filed Dec. 2, 1963, and assigned to the same assignee as the present invention. As best shown in FIGS. 2 and 3, the collector assembly 14 is mounted in axial alignment with the remainder of the klystron amplifier and includes a collector bucket 40 composed of a hollow cylindrical tube 42 closed at its remote base end by an internally tapered cup 44, both elements being formed from a good thermal conducting material, such as copper. bucket 40 preferably includes, adjacent its open entrance end, an inwardly directed annular flange 46 which serves to minimize re-entry of secondary emission electrons from the collector bucket back into the interaction region of the tube.

The exterior surface of the hollow cylindrical collector tube 42 is milled to form a plurality of longitudinally extending, circumferentially spaced slots which are covered by a cylindrical copper partition 48 which is mounted in tightly pressed engagement over the slotted collector tube to thus form coolant channels 50. At its one end, the cylindrical partition 48 is secured to the perimetral edge of an annular flange 52 spaced from the base of the collector bucket 40 as formed by the described cup 44, the inner edge of the flange 52, in turn, being secured to the extremity of a smaller cylindrical tube 54 that is axially aligned with the collector bucket 40 and is arranged to deliver coolant to the channels 50, as will be explained in detail hereinafter.

At its other extremity, the cylindrical copper partition Additionally, the collector 48 terminates a short distance from an outwardly projecting portion 46a of the previously described annular flange 46 at the entrance end of the collector bucket 40. In a manner somewhat similar to that of the cylindrical collector tube 42 itself, the cylindrical partition 48 is milled on its exterior surface to provide a plurality of longitudinally extending and circumferentially spaced slots and is tightly encompassed by a copper sleeve 55 which is secured at its opposite extremities respectively to the exterior edge of the annular flange 46a at the entrance end of the collector bucket 40 and to another annular flange 56 that is slightly spaced from the partition supporting flange 52, thus forming return coolant channels 58. The inner edge of this sleeve supporting flange 56 is internally secured to a tube 60 concentrically mounted about the described inlet tube 54 for coolant so as to provide an annular outlet passage for the coolant received from the return channels 58. As illustrated by the arrows in FIG. 2, coolant, preferably in the form of distilled water supplied from the inner tube 54, first moves radially outward adjacent the base of the collector bucket 40, thence longitudinally through the channels 50 exterior to the collector tube 42 and thereafter through the return channels 58 and into the annular outlet passage in tube 60.

It is to he expressly observed that the coolant flowing through the

channels

50, 58 in both directions is encompassed by copper elements all of which are in direct metallic contact with the collector tube 42 itself, as best shown in FIG. 4. Since it is well established that the greatest impediment to efficient heat transfer exists at an interface between liquid and solid surfaces, the described arrangement wherein only one such interface exists between all coolant channels and the meal (i.e. the collector tube 42) from which heat is to be extracted, the efficiency of heat transfer is optimized.

At its entrance end, the collector assembly 14 is held in spaced, thermally and electrically isolated relation from the remainder of the tube by a ceramic ring 62 positioned between the collector flange 46 and a collector mounting flange 64 disposed adjacent the final cavity resonator 22. At its remote end, the described collector bucket 40 and coolant structure is provided with an axially flexible connection, generally indicated at 66, and which incorporates another ceramic ring 68, for mounting to an encompassing cylindrical shield which surrounds the entire collector structure and is brazed or otherwise secured to the exterior of the mounting flange 64 at the terminal end of the interaction region of the tube.

The flexible connection 66 allows axial motion which results because of the difference in thermal expansion between the copper collector and the steel shell 70. The flexible connection does not allow radial motion and therefore, keeps the collector located concentrically within the steel shell 70. The shell 70 is made of steel to provide a strong vacuum envelope and also to shield the collector region from undesirable magnetic fields. X-ray radiation is effectively stopped by the copper collector. Any small amount of radiation emanating from the copper collector would be further attenuated by the steel shell.

To facilitate ingress and egress of coolant to and from the collector assembly 14, the mentioned inlet tube 54 projects beyond the encompassing outlet tube 60 and both tubes are provided with circular openings 54a, 60a in their side walls adjacent their extremities which are closed respectively by a circular cap 72 and an annular cap 74. The stepped projecting tubular structure defined by the

tubes

54, 60 constitutes the male member arranged for pressed connection into the female stepped receptacle formed in a dual coolant manifold 76. Such manifold 76 constitutes a generally cylindrical structure having a smaller bore 78 extending substantially half-way therethrough and arranged to encompass the projecting smaller inlet tube 54 and a larger bore 80 extending through the other half thereof and appropriately dimensioned to encompass the terminal portion of the larger foreshortened outlet tube 60. Each of the

bores

78, 80 are centrally enlarged at a position such that the respective openings 54a, 60a in the wall of the inlet and outlet tubes are encompassed to establish liquid communication through inlet and

outlet stubs

82, 84 which are arranged for appropriate connection to the coolant supply lines (not shown). To avoid leakage, circular O-rings 79, 81 are supported in sealing relationship between the

bores

78, 80 and the encompassed

tubes

54, 60 on opposite sides of both the inlet and outlet openings 54a, 60a.

As can be readily visualized, the dual manifold 76 as illustrated, can be simply pressed over the projecting

tubes

54, 60 to establish connection to the coolant supply. Furthermore, the entire manifold 76 can be rotated about the axis defined by the

tubes

54, 60 to facilitate positional arrangement of the coolant connections. Once assembled, the manifold 76 can be held in position on the tubes by a washer 86 that is held in engagement with the manifold by a thumb bolt 88 arranged for threaded connection into the end cap 72 on the central tube 54. In view of the fact that all coolant pressures existent within the manifold 76 and the associated inlet and

outlet tubes

54, 60 for the coolant are exerted radially, substantially no pressure tending to unseat the manifold 76 from its support on the tubes will exist.

By the way of example, a klystron amplifier substantially as illustrated and having an overall length of substantially three feet has been successfully operated at a frequency of approximately two gigacycles with a C.W. radio frequency output power of 100 kw. and a beam power of 300 kw. The described collector assembly 14 has effectively handled the heat generated under such continuous wave operation with a coolant flow of approximately 40 gal./min. The described focusing arrangement, supplying a magnetic field of approximately 2000 gauss, has substantially eliminated beam interception Within the cavities, such result being clearly demonstrated by the fact that no observable differences in cavity dimensions between operation at 80 kw. and 100 kw. were found.

While the focusing and beam collection arrangement have been specifically described relative to a klystron amplifier wherein standing waves exist within resonant cavities, it will be apparent that the same heating problems would be encountered in traveling wave structures, such as for example, a disc loaded waveguide involving traveling wave interaction at high power levels.

Since many changes can be made in the above construction and many apparently widely different embodimentsof 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 tube which comprises an elongated, evacuated tubular envelope, means at one end of said envelope for producing and directing a beam of charged particles longitudinally through said envelope, means for establishing high frequency fields in interacting relation with said particle beam, a beam collecting bucket at the remote end of said envelope arranged to receive and collect the charged particles, means forming coolant channels for conducting fluid coolant in heat transferring relation with the exterior surface of said beam collecting bucket, a first coolant tube arranged to establish fluid communication with the ends of said channels at one end and having a lateral opening adjacent its remote end, a second foreshortened coolant tube surrounding the closed portion of said first coolant tube to form an annular passageway in communication with the remote ends of said channels and having a lateral opening therein, and means including a coolant manifold arranged to sealingly encompass both of said tubes for establishing flow of coolant through said tubes and said channels, said manifold being axially and circumferentially movable on said coolant tubes by being sealingly engaged to said cooling tubes via a plurality of axially spaced O-rings, said channel forming means including an exteriorly slotted partition closely encompassing said beam collecting bucket, said bucket being exteriorly slotted whereby reception of said partition thereover forms first coolant channels, a sleeve closely encompassing said slotted partition to form second coolant channels, said channels being in communication adjacent one end of said beam collecting bucket.

2. A high frequency electron discharge device including beam forming and projecting means disposed at the upstream end portion of said device and beam collector means disposed at the downstream end portion of said device, said beam collector means including a generally tubular collector bucket for receiving the electron beam, said collector bucket having a pair of coaxially disposed metal sleeves disposed thereabout and conductively interconnected to said collector bucket along the mutual axially coextensive portions thereof, said pair of sleeves forming bidirectional fluid flow passageways about the axial extent of said collector bucket, a pair of axially spaced ring members disposed at the downstream end portion of said collector bucket, said ring members being physically coupled at their exterior peripheral surfaces to the said coaxially disposed pair of sleeves at their respective downstream end portions to thereby form bidirectional fluid flow passageways having lateral flow directions with respect to the central axis of said collector bucket, a pair of radially spaced coaxial coolant tubes coupled to the respective internal diameters of said ring members to thereby form a pair of axially bidirectional fluid flow passageways coupled to said lateral bidirectional fluid flow passageways, each of said coolant tubes being provided with a plurality of circumferentially spaced apertures at axially offset regions with respect to each other, coolant manifold means disposed about said pair of coaxially disposed coolant tubes and forming a fluid tight seal thereabout, said manifold being fluid coupled to said respective coolant tubes via said plurality of circumferentially spaced apertures such that radial bidirectional fluid flow occurs therebetween.

References Cited by the Examiner UNITED STATES PATENTS 1,640,735 8/1927 SOderber-g 313-36 1,714,689 5/1929 Miller 31336 2,440,245 4/1948 Cherigny 31322 2,991,979 6/1961 Lincoln -90 2,994,009 7/ 1961 Schmidt 313-24 3,104,338 9/1963 Symens 3l324 DAVID J. GALVIN, Primary Examiner.

Claims

2. A HIGH FREQUENCY ELECTRON DISCHARGE DEVICE INCLUDING BEAM FORMING AND PROJECTING MEANS DISPOSED AT THE UPSTREAM END PORTION OF SAID DEVICE AND BEAM COLLECTOR MEANS DISPOSED AT THE DOWNSTREAM END PORTION OF SAID DEVICE, SAID BEAM COLLECTOR MEANS INCLUDING A GENERALLY TUBULAR COLLECTOR BUCKET FOR RECEIVING THE ELECTRON BEAM, SAID COLLECTOR BUCKET HAVING A PAIR OF COAXIALLY DISPOSED METAL SLEEVES DISPOSED THEREABOUT AND CONDUCTIVELY INTERCONNECTED TO SAID COLLECTOR BUCKET ALONG THE MUTUAL AXIALLY COEXTENSIVE PORTIONS THEREOF, SAID PAIR OF SLEEVES FORMING BIDIRECTIONAL FLUID FLOW PASSAGEWAYS ABOUT THE AXIAL EXTENT OF SAID COLLECTOR BUCKET, A PAIR OF AXIALLY SPACED RING MEMBERS DISPOSED AT THE DOWNSTREAM END PORTION OF SAID COLLECTOR, SAID RING MEMBERS BEING PHYSICALLY COUPLED AT THEIR EXTERIOR PERIPHERAL SURFACES TO THE SAID COAXIALLY DISPOSED PAIR OF SLEEVES AT THEIR RESPECTIVE DOWNSTREAM END PORTIONS TO THEREBY FORM BIDIRECTIONAL FLUID FLOW PASSAGEWAYS HAVING LATERAL FLOW DIRECTIONS WITH RESPECT TO THE CENTRAL AXIS OF SAID COLLECTOR BUCKET, A PAIR OF RADIALLY SPACED COAXIAL COOLANT TUBES COUPLED TO THE RESPECTIVE INTERNAL DIAMETERS OF SAID RING MEMBERS TO THEREBY FORM A PAIR OF AXIALLY BIDIRECTIONAL FLUID FLOW PASSAGEWAYS COUPLED TO SAID LATERAL BIDIRECTIONAL FLUID FLOW PASSAGEWAYS, EACH OF SAID COOLANT TUBES BEING PROVIDED WITH A PLURALITY OF CIRCUMFERENTIALLY SPACED APERTURES AT AXIALLY OFFSET REGIONS WITH RESPECT TO EACH OTHER, COOLANT MANIFOLD MEANS DISPOSED ABOUT SAID PAIR OF COAXIALLY DISPOSED COOLANT TUBES AND FORMING A FLUID TIGHT SEAL THEREABOUT, SAID MANIFOLD BEING FLUID COUPLED TO SAID RESPECTIVE COOLANT TUBES VIA SAID PLURALITY OF CIRCUMFERENTIALLY SPACED APERTURES SUCH THAT RADIAL BIDIRECTIONAL FLUID FLOW OCCURS THEREBETWEEN.