US3412279A

US3412279A - Electromagnetic wave energy absorbing elements for use in high frequency electron discharge devices having traveling wave tube sections

Info

Publication number: US3412279A
Application number: US486924A
Authority: US
Inventors: Richard R Allen; Rodney R Rubert
Original assignee: Varian Associates Inc
Current assignee: Varian Medical Systems Inc
Priority date: 1965-09-13
Filing date: 1965-09-13
Publication date: 1968-11-19
Anticipated expiration: 1985-11-19
Also published as: GB1149591A; DE1541091B1

Description

NOV. 19, 1968 RALLEN ET AL R 3,412,279

ELECTROMAGNETIC WAVE ENERGY ABSGRBING ELEMENTS FOR USE IN HIGH FREQUENCY ELECTRON DISCHARGE DEVICES HAVING TRAVELING WAVE TUBE sEcTIoNs 2 Sheets-Sheet 1 Filed Sept. 13, 1965 INVENTO RS RICHARD R. ALLEN RODNEY R BUBERT BY Ail /TORNEY United States Patent 3,412,279 ELECTROMAGNETIC WAVE ENERGY ABSORBIN G ELEMENTS FOR USE IN HIGH FREQUENCY ELECTRON DISCHARGE DEVICES HAVING TRAVELING WAVE TUBE SECTIONS Richard R. Allen, Redwood City, and Rodney R. Rubert, Santa Clara, Calif., assignors to Varian Associates, Palo Alto, Calif., a corporation of California Filed Sept. 13, 1965, Ser. No. 486,924 9 Claims. (Cl. 315-35) ABSTRACT OF THE DISCLOSURE Electromagnetic wave energy absorbing elements (attenuators) for use in high frequency electron discharge devices, particularly traveling wave type devices, and a specific means for mounting and cooling such elements are disclosed. Various structural embodiments of such electromagnetic wave energy absorbing elements are described as incorporated into certain specific types of high frequency electron discharge devices.

This invention relates in general to improvements in high frequency electron discharge devices incorporating traveling wave interaction sections and more particularly to novel means for fluid cooling lossy electromagnetic wave energy absorbing elements utilized in high frequency electron discharge devices which fluid cooling means serves the additional function of providing suflicient fluid pressure on the defining walls for said lossy elements such as to obviate the necessity of utilizing conventional brazing techniques to retain said lossy elements in situ.

High frequency electron discharge devices incorporating traveling wave interaction sections conventionally employ circuit sever portions along the active circuit length thereof in order to prevent undesired oscillations in operation. These circuit severs can take many forms one of which is the utilization of lossy attenuator materials for absorbing electromagnetic Wave energy at the severed region. In Ia conventional forward wave amplifier traveling wave tube such circuit severs are utilized both for absorbing fonward wave traveling wave energy in the input or upstream portions of the traveling wave tube and for absorbing backward traveling wave energy in the down stream or output portions of the tube. In a hybrid type of electron discharge device wherein a klystron input section is utilized in conjunction with a traveling Wave output section the utilization of a circuit sever between the klystron and traveling wave sections is primarily for the absorption of backward wave energy in a forward wave amplifier. Further circuit severs in the traveling wave tube section may also be utilized in a conventional manner.

Common problems encountered with circuit severs of the prior art type utilizing lossy ceramic attenuator discs for absorbing electromagnetic wave energy at the severed regions are destruction of the lossy discs due to arcing problems encountered in use, fabrication difficulties encountered during the brazing operations to maintain a rigid positioning of the ceramic discs Within a particular portion of the traveling wave circuit sever portion and power handling limitations inherent with the utilization 3,412,279 Patented Nov. 19, 1968 of a ceramic lossy material. These and other problems of the prior art are obviated by the teachings of the present invention which provides utilization of fluid pressure to maintain a rigid mechanical joint between the lossy ceramic absorbing discs and their respective defining walls. The present invention furthermore eliminates the utilization of any metallurgical brazes and so forth which require extensive and time consuming brazing cycles in the fabrication of the slow wave circuit sever portions by the utilization of the aforementioned fluid pressure mlaintenance technique. The present invention furthermore provides great increases in power handling capabilities for the prior art types of lossy ceramic discs by the use of the aforementioned fluid cooling and pressure techniques.

It is therefore an object of the present invention to provide an improved high frequency electron discharge device incorporating novel fluid cooled electromagnetic wave energy absorption means.

A feature of the present invention is the provision of a high frequency electron discharge device including an electron beam-wave interaction section having incorporated therein a lossy electromagnetic wave energy absorption element provided with novel fluid cooling means therefor.

Another feature of the present invention is the provision of a high frequency electron discharge device incorporating an electromagnetic wave energy interaction section including lossy electromagnetic wave energy attenuating means having novel cooling provisions therefor, said cooling provisions serving to rigidly maintain said lossy means within said interaction circuit portion by means of fluid pressure.

Another feature of the present invention is the provision of a high frequency electron discharge device incorporating a traveling wave interaction section having a circuit sever portion which includes at least a plurality of lossy electromagnetic wave energy absorption elements, said lossy electromagnetic wave energy absorption elements being provided with fluid cooling channels along the major transverse dimensions thereof in a rnann er such that said fluid cooling channels serve to fixedly maintain said lossy attenuating elements in place by means of the effective hydrostatic pressure of collant fluid flowing within said coolant channels.

Another feature of the present invention is the provi sion of a high frequency electron discharge device incorporating Ia traveling wave interaction section having a lossy electromagnetic wave energy absorption element disposed therein, said lossy absorption element being provided with fluid coolant means along a major dimension thereof, said fluid coolant means comprising a fluid flow channel separated from said major dimension of said lossy wave energy absorbing element via the interrnediary of a deformable wall portion.

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

FIG. 1 is a fragmentary longitudinal view of a traveling wave tube partly in elevation, partly in cross-section which incorporates the novel fluid cooled lossy attenuator wave energy absorption means of the present invention,

FIG. 2 is a cross-sectional view partly in elevation 3 taken along the lines 22 of the traveling wave tube depicted in FIG. 1,

FIG. 3 is a cross-sectional view partly in elevation taken along the line 33 of the section depicted in FIG. 2,

FIG. 4 depicts a fragmentary cross-sectional view partly in elevation of an alternative fluid cooled circuit sever section incorporating the techniques of the present invention,

FIG. 5 is a fragmentary longitudinal elevational view of a hybrid microwave amplifier incorporating the teachings of the present invention,

FIG. 6 is a cross-sectional view partly in elevation taken along the line 66 of FIG. 5,

FIG. 7 is a cross'sectional view partly in elevation taken along the line 77 of the section of FIG. 6,

FIG. 8 is an alternative wave energy absorption portion utilized between the klystron and traveling wave tube sections in a hybrid amplifier incorporating the teachings of the present invention, and

FIG. 9 is a cross-sectional view taken along the line 99 of FIG. 8 in the direction of the arrows.

Referring now to FIG. 1 there is depicted a high frequency electron discharge device 11 of the traveling wave type incorporating a beam forming and projecting means 12 disposed at the upstream portion thereof and an electron beam collector 13 disposed at the downstream portion thereof. Intermediate the upstream and downstream portions of the traveling wave tube 11, slow wave circuit sections 14 and 15 of the clover-leaf type, more fully disclosed in an article by M. Chodorow et al. entitled, Some New Circuits for High Power Traveling Wave Tubes, Proc. I.R.E., August 1957, pps. 1106-1118, are located. One or more circuit sever sections such as 16, 17 may be incorporated between the upstream and downstream portions of the traveling wave tube of FIG. 1 for absorbing electromagnetic wave energy for purposes of stabilization in a manner well known in the art. The electron beam forming and projecting means 12 preferably is a conventional Pierce-type gun which includes a focusing anode 18, a main accelerating anode 19 and an electron emission surface or cathode, not shown. Since the details thereof are well known, no further discussion of the same will be made herein.

Turning now to the particular details of the

circuit sever portions

16 and 17, reference to FIGS. 2 and 3 will now be made for enumeration thereof. In a traveling wave tube of the type depicted in FIGS. 1-3, it is common practice to utilize a plurality of lossy attenuator elements such as 20, 21, 22, 23 in both the upstream sever section 16 and the downstream sever section 17. The specific purpose of the lossy attenuator elements in the upstream sever section 16 are to absorb all electromagnetic wave energy present in the input slow wave circuit portion 14 and to allow only the current density modulated electron beam to pass therethrough to the downstream portions of the tube for stabilization purposes in a manner well known in the art. The particular purposes of the lossy ceramic elements in the downstream circuit sever portion 17 in a forward wave amplifier tube such as depicted in FIG. 1 is to completely absorb any backward traveling wave energy produced in the downstream section 15 in order to stabilize the tube in a manner well known in the art. Many problems have heretofore been encountered with the utilization of lossy ceramic discs used for the attenuator means which heretofore have been conventionally made of ceramic loaded carbon with regard to the metallurgical techniques utilized to secure a rigid bond between the lossy elements and the transverse defining

walls

24, 25 of clover-leaf cavity 30. A typical brazing operation therebetween may take four to five hours and result in costs of perhaps $100 per tube per brazing cycle. Inherent in the utilization of metallurgical brazing between the transverse defining

walls

24, 25 and the major faces of each lossy ceramic element are the differential expansion problems occurring therebetween in use which very often result in cracking of the lossy ceramic element itself under high power operating conditions and/or during the brazing cycle itself. Furthermore, imperfections in the bond may occur which would result in separations occur ring between one or the other or both of the

defining walls

24, 25 and the respective major faces of the ceramic elements which renders the disc susceptible to breakdown due to high power arcing in use. Further problems encountered in the utilization of lossy ceramic elements such as 20, 22, etc., have been the power handling limitations inherent in such discs. Power handling capabilities are improved by better than a factor of two by the utilization of fluid coolant flow channels 28 separated from one or the other of the major faces of the lossy discs via the intermediary of a thermally conductive deformable wall portion 29.

In a traveling wave tube such as the type depicted in FIG. 1 which utilizes a clover-leaf slow wave circuit and includes a plurality of substantially circular periodic sections or cavities 30, of clover-leaf configurations, each cavity 30 is defined by a pair of spaced transverse end wall portions such as 24, 25, 26, etc. Each end wall has an annular beam passage aperture 32 axially disposed therein which also serves as a capacitive coupling between sections. Each clover-leaf section or cavity 30 includes a sinuous four element clover-leaf side wall, such as 33, which is generally brazed between the aforementioned transverse end walls of each clover-leaf section 30 and which includes four space rotated radially oriented and inwardly directed finger portions 33'. Each of the transverse end walls 24, 26, etc., with the exception of the one sever end wall 25, includes a plurality of coupling apertures such as 34 to provide a negative mutual inductive coupling between sections in order to provide a forward wave amplifier having high interaction impedance characteristics in a manner well known in the art. See for example, US. patent application Ser. No. 7,481 entitled, Conductive Coupling Means and Methods for High Frequency Apparatus, filed Feb. 8, 1960, by M. Chodorow, now US. Patent 3,233,139, assigned to the same assignee as the present invention.

The circuit sever section 16 is formed by loading the last clover-leaf section or cavity 30 with four 90 space rotated

lossy attenuator elements

20, 21, 22, 23 disposed in cut-out portions at the ends of each of fingers 33, and brazing said elements along their major face dimensions to the transverse defining

walls

24, 25 by means of any suitable brazing materials such as molybdenum-manganese. Such prior art lossy elements have been found to be capable of handling around 10 kilowatts average power before destruction thereof set in due to arcing if loosened or simple excessive heating due to inadequate prior art fluid cooling mechanisms connected therewith. By providing a fluid coolant channel such as 28, having a cross-sectional configuration conforming to the major dimension or major face, e.g., 22, of the lossy discs 20-23, excellent cooling thereof is achieved in use and CW powers up to 20 kilowatts and above are easily handled according to the teachings of the present invention. Furthermore, multimegawatt pulse powers are easily handled when fluid coolant flow channels are disposed adjacent the major face of the lossy elements in thermal conductive heat transfer relationship as shown in FIGS. 2 and 3.

A typical example of a suitable lossy attenuator material used for discs 20-23 is carbon loaded alumina ceramic. Other lossy materials which have better thermal conductivities than carbon loaded alumina ceramic are loaded porous beryllium oxide ceramics and loaded forsterite ceramics which, however, require in the case of the beryllium oxide ceramics, special enclosed furnaces to handle the toxic vapors generated in the brazing operation and which in the case of the forsterite ceramics present breakage and cracking problems at the brazed joint due to poor thermal shock resistance and poor impact strength, By utilizing the fluid coolant flow channels and eliminating the brazing operations many of the problems heretofore encountered are obviated and the tube designer is given greater design choices which are not burdened by metal-to-ceramic bonding considerations. Ordinary tap water emanating from a city water supply system will provide 80 p.s.i. pressure capabilities and thus the T-junction input coupling port 37 may be tied into any typical city water supply system preferably via a common manifold system which is generally utilized to couple all fluid cooled portions of the device together. Any suitable water pump capable of maintaining a 40 p.s.i. effective hydrostatic pressure on the deformable walls may obviously be used to supply the coolant fluid. The terminology effective hydrostatic pressure is utilized herein to define the fluid pressure in p.s.i. exerted on the deformable wall portion by the pressure of the coolant fluid flowing through the coolant flow channels. For example, if a standpipe were substituted for a deformable wall portion such as 29 and oriented vertically, a 40 p.s.i. fluid pressure caused by coolant fluid flowing through coolant flow channel 28 would produce a 90foot head in the standpipe. Hence the terminology effective hydrostatic pressure is appropriate to define the pressure exerted by flowing fluid. Obviously the example of 40 p.s.i. is not to be taken in a restrictive sense since innumerable variations in the paramters involved which will produce effective compressive forces on the captured lossy elements would be readily apparent to one skilled in the art. Therefore the following example is merely illustrative of a specific embodiment.

The breakage problems heretofore encountered and the problems due to cracking of the discs and separation thereof from the transverse defining walls 24, are still present if conventional brazing methods are utilized to maintain the lossy attenuator elements in place as stated above. Therefore, according to the teachings of the present invention the common defining wall of flow channel 28 separating the major faces of the lossy elements 20 from the channel, e.g., 28, is made to conform to the dimensions of the element 20 and to have a thickness which is sufliciently thin to permit the wall to be deformed by fluid pressure of the fluid coolant flowing through flow channels 28 to thereby obtain a very rigid sandwich construction through compression of said elements which will not loosen in use and which does not require any brazing operations. Effective hydrostatic pressures of approximately 40 p.s.i. (pounds per square inch) when utilizing copper for the deformable wall portion 29 of approximately .025 inch thick in conjunction with one-inch diameter discs have been found quite satisfactory to achieve the aforementioned rigid sandwiched construction.

The coolant flow channels 28 can be interconnected in various ways as shown more clearly hereinafter. For example, in FIG. 2 two copper or the like tubulations 36 are used to interconnect adjacent flow channels 28 to permit a unidirectional fluid flow therethrough. Coolant fluid such as tap water is coupled via a T-junction 37 along copper or the

like tubes

38, 39 into channels 28 via fluid coupling ducts 40 in the embodiments of FIGS. 2 and 3 which are located in the enlarged flanged extions 41 of the transverse defining wall 25. Coolant flow channels 28 are enlarged to conform to the major dimensions of each of the lossy elements as best seen in FIG. 2 and fluid coupling members such as

tubes

35, 36 of reduced dimensions are utilized to couple the fluid into the remaining two channels 28 whence a similar output coupling arrangement employing a T-junction 42 in conjunction with tubes 43, 44 is utilized to remove the coolant fluid from the sever section. In the embodiment of FIGS. 2 and 3 the downstream end wall of each of the channels 28 is formed by disc-shaped copper plates 45 having a handle portion 46 as shown which are brazed or the like in suitable off-set ridge portions 47 in transverse wall 25, as shown. Fabrication of the cooling chan- 6 nel 28 in the embodiment of FIG. 1 is thereby facilitated by simply machining out the area conforming to the particular physical configuration of the lossy elements 20-23. Circuit sever 17 can be made identical to section 16 and independent thereof as shown in FIGS. 1-3.

Alternatively, the circuit sever depicted in FIG. 4 may replace

sections

16 and 17 and has the advantage of utilizing a composite single flow channel arrangement rather than two separate ones such as shown in the embodiment of FIGS. 1-3. Briefly, the composite circuit sever depicted in FIG. 4 includes a plurality of lossy attenuating elements 50 disposed in space rotated relationship preferably with azimuthal periodicity with respect to the beam axis as shown in FIG. 2 in the aforementioned upstream and downstream clover-leaf end sections or cavities 51, 52, respectively, and retained therein between the transverse defining

walls

54, 55, 56, 57, respectively. A fluid coolant flow channel 60 is common to both portions of the composite circuit sever depicted in FIG. 4 and obviates the necessity for the dual feed arrangements of 16 and 17 in the embodiment of FIG. 1. The fluid coolant flow channels 60 are enlarged dimensionally relative to the fluid coupling channels denoted by 61, 62 in a manner similar to that depicted in FIG. 2 by machining out an area of the defining walls 55, 56 conforming to the lossy elements 30 to thereby provide deformable wall portions 56'. Suitable input and output coupling ports 63 and 64 provide ingress and egress of fluid from any conventional pumping system. Once again the copper defining walls or the like 55, 56 are dimensionally thin in the area conforming to the major transverse dimension of the lossy attenuator elements 50 as mentioned above in order to provide flexible or deformable wall portions 55', 56' such that the effective hydrostatic pressure within coolant flow channels will provide the required oppositely directed compressive forces on the lossy elements 50 in order to maintain a rigid sandwich construction between

elements

54, 50, 55 and 56, 50, 57.

The tube main body 6 and the transverse defining walls for the clover-leaf sections are advantageously made of copper or the like material and any suitable brazing material or other metal joining techniques may be employed to provide rigid vacuum tight bonds between the various elements. In the embodiments of FIGS. 2 and 3 and 4, the transverse defining walls which are subjected to a relatively high amount of pressure due to the pressure developed in the cooling channel portions 28 and 60, namely

transverse walls

24 and 54 and 57 are made of a higher strength material than copper, such as stainless steel, so as to provide a more rigid non-deformable wall portion in order to minimize any possible variation of cavity dimensions for the cloverleaf sections due to the effective hydrostatic compressive forces.

Turning now to FIG. 5 there is depicted therein a hybrid tube apparatus 70 comprising a stagger tuned klystron driver section 71 followed by a traveling wave tube section 72. Since the literature is replete with details of stagger tuned klystrons such as section 71 and slow wave circuits such as 72 the particular details thereof will not be specified further herein. Suffice it to say that the hybrid tube depicted in FIG. 5 includes an electron beam forming and projecting means 74 disposed at the upstream end portion thereof and a suitable electron beam collector 75 disposed at the downstream end portion thereof in a manner well known in the art. Once again, the electron beam forming and projecting means 74 may comprise any suitable Pierce-type gun arrangement which includes a focusing anode 76 and an accelerating anode 77 as *well as a cathode structure disposed within focusing anode 76 in a manner well known in the art.

Turning now to FIGS. 6 land 7 which represent sectional views of a suitable electromagnetic wave energy absorbing section disposed between the klystron section and the traveling Wave tube section of the hybrid tube in FIG. 6. In order to eliminate any possible instability problems arising in a hybrid amplifier such as depicted in FIG. 5, the traveling Wave tube section 72 is terminated at its upstream end portion by means of both a drift tube 79 coupling arrangement between the last cavity 80 of the klystron section and in the case of a clover-leaf type of slow wave structure the last clover-leaf section or cavity 81. A plurality of spatially displaced lossy attenuator elements such as carbon loaded alumina ceramic or silicon carbide, etc., are utilized to absorb all backward traveling wave energy along the traveling wave circuit section in a manner well known in the art. An axial feed arrangement is utilized in the embodiment of FIGS. 6 and 7 to inject suitable coolant fluids such as tap water, etc., into enlarged coolant flow channels 81, 82 which generally conform to the major face dimensions of the lossy elements. Once again a pair of spaced transverse end wall members 83, 84 are utilized to define the last clover-leaf section 81 and the lossy attenuator discs 85 are disposed therebetween as shown. Wall 84 is preferably made of stainless steel as mentioned previously to withstand deformation due to the effective hydrostatic pressures induced by coolant fluid flowing through channel 82 and transverse wall member 83 is preferably made out of copper and has a reduced thickness dimension in the areas conforming to the lossy element major dimensions as mentioned previously such that a deformable wall portion is formed in order to allow the compressive forces of the coolant fluid to apply fluid pressure to the wall member and thereby obtain a rigid sandwiched construction for the lossy elements.

An input axially directed fluid coupling port 86 is utilized to provide the coolant fluid to flow channels 82 and a plurality of reduced dimension fluid coupling channels 88, 89, 90, etc., are used to interconnect the various enlarged fluid channel portions 82. An output fluid cou pling port 87 is utilized in the embodiment of FIGS. 6 and 7 to extract the coolant fluid from the wave energy absorption section. As in the embodiments depicted in FIGS. 14, a effective hydrostatic pressure of approximately 40 pounds per square inch when utilized with a one-inch diameter lossy disc in conjunctionwith an approximately .025 inch thick deformable copper Wall portion which defines one transverse portion of each fluid flow channel 82 has been found adequate to provide an effective sandwich fit between the transverse end walls 83, 84 and the various lossy attenuator elements. The directive arrows depicted in FIGS. 6 and 7 are utilized to illustrate the fluid flow directions between input port 86 and output port 87. In lieu of the separate channel defining members 45 uitilized for each of the enlarged channel portions 28 of the embodiments of FIGS. 2 and 3, the embodiment of FIGS. 6 and 7 utilizes a transverse ring member 91 to define the upstream end wall portion of the flow channels 82 and coupling channels 88, 89, 90, etc.

In the embodiment of FIGS. 8 and 9 an alternative fluid cooling arrangement in a hybrid tube with regard to the fluid coupling arrangement is depicted. In the embodiment of FIGS. 6 and 7 a bidirectional split flow arrangement is utilized Whereas in the embodiment of FIGS. 8 and 9 a unidirectional fluid flow arrangement which may have advantages in certain system applications is employed. An arcuate shaped flow channel 94, best seen in FIG. 9 is utilized in the embodiment of FIGS. 8 and 9 to provide the necessary effective hydrostatic pressure and cooling for the lossy attenuator elements 95. Input channel 92 and output channel 93 serve as coupling ports for the coolant fluid and are connected to any suitable pumping system. Quite obviously, the various parameters of the fluid coupling arrangements depicted in the embodiments of FIGS. 1, 4, 6 may be interchangeably utilized to take advantage of the permutations and combinations thereof. Again, the lossy attenuator elements, discs 95,

are sandwiched between a pair of transverse defining end walls 97, 98 with wall 97 again having reduced thickness in the area 99 common to the major face dimensions of each of the discs. The flow channels 100 are then coupled in a series feed arrangement via coupling flow channel 94 which is segmented by radial wall portion 161 as seen in FIG. 9. This type of fluid feed arrangement permits the tube designer to have increased freedom of design such that electron discharge devices employing the teachings of the present invention are more easily incorporated int-o systems having diverse spatial and coolant flow parameter requirements.

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 drawing shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A high frequency electron discharge device including an electron beam forming and projecting means disposed at the upstream end portion thereof, electron beam collector means disposed at the downstream end portion thereof, slow wave circuit means disposed intermediate said electron beam forming and projecting means and said electron beam collector means, said slow wave circuit means being adapted and arranged to provide a cumulative energy exchange between an electron beam and electromagnetic wave energy propagating along said slow wave circuit within a predetermined frequency range, said slow wave circuit means including lossy attenuator means disposed therealong for absorbing electromagnetic wave energy traveling along said slow wave circuit, said lossy attenuator means being disposed between at least a pair of spaced transverse conductive wall members in a sandwiched arrangement, at least one of said transverse Wall means forming a confining surface for a fluid coolant flow channel, said transverse wall means forming said common boundary between said lossy attenuator means and said fluid coolant flow channel having a thickness dimension such as to be deformable in the presence of coolant fluid flowing through said coolant channel whereby said lossy attenuator means is compressed between said pair of transverse wall members by fluid pressure.

2. A high frequency electron discharge device having an electron beam forming and projecting means disposed at the upstream end portion of said device and an electron beam collector means disposed at the downstream end portion thereof, high frequency electromagnetic slow wave circuit interaction means disposed therebct ween, said interaction means including at least one lossy attenuator element for absorbing electromagnetic Wave energy and a rigid structural member in contact with one side of said lossy attenuator element, a fluid coolant flow channel in contact with the other side of said lossy attenuator element, said fluid coolant flow channel having a Wall thickness dimension such as to be deformable in the presence of coolant fluid flowing therethrough, whereby said lossy attenuator element is maintained under compression against said rigid structural member by means of fluid pressure in said fluid coolant flow channel.

3. A high frequency eltctron discharge device including an electron beam forming and projecting means disposed at the upstream end portion thereof and an electron collector means disposed at the downstream end portion thereof, a slow wave interaction circuit disposed between said electron beam forming and projecting means and said electron collector means along the electron beam axis of said device, said slow wave circuit means including a circuit sever portion for absorbing electromagnetic wave energy and permitting passage therethrough of an electron beam, said circuit sever means including a lossy attenuator element fixedly secured between a pair of spaced transverse wall members forming a portion of said slow wave interaction circuit, a fluid coolant flow channel disposed in heat transfer relationship with respect to said lossy attenuator element, at least a portion of one of said transverse wall members forming a common radial boundary with respect to the beam axis between said lossy attenuator element and said fluid coolant channel, said portion of said transverse wall member having a thickness such as to be deformable under fluid pressure.

4. A high frequency electron discharge device including an electron beam forming and projecting means disposed at the upstream end portion thereof and an electron beam collector means disposed at the downstream end portion thereof, an electromagnetic Wave-beam interaction means disposed between said beam forming and projecting means and said beam collector means, said interaction means including lossy attenuator means disposed therein for absorbing electromagnetic wave energy, said lossy attenuator means including at least a pair of axially displaced lossy elements, said axially displaced lossy elements having a fluid coolant channel disposed therebetween, the walls of said fluid coolant flow channel having a thickness dimension such as to be deformable in the presence of coolant fluid flow therethrough, said lossy elements being subjected in use to compressive forces within said interaction means by fluid pressure elfectuating deformation of said walls of said fluid coolant flow channel.

5. A high frequency electron discharge device including an electron beam forming and projecting means disposed at the upstream end portion thereof and an electron beam collector means disposed at the downstream end portion thereof, a slow wave interaction circuit disposed along said electron beam axis between said beam forming and projecting means and said beam collector means, said slow wave interaction circuit means being provided with lossy attenuator means for absorbing electromagnetic wave energy traveling on said slow wave interaction circuit means, said lossy attenuator means including a lossy element having a major face dimension radially disposed with respect to said beam axis, said lossy attenuator element being maintained in a fixed position within said slow wave interaction circuit by being nested between a pair of transversely disposed conductive wall members, at least one of said conductive wall members forming a common radial boundary between a fluid coolant flow channel and said lossy attenuator element, said common wall portion having a thickness such as to be deformable by fluid pressure introduced within said coolant channel in use whereby said lossy attenuator element is subjected to compressive forces due to said fluid pressure.

6. A high frequency electron discharge device having electron beam forming and projecting means disposed at the upstream end portion thereof, an electron beam collector means disposed at the downstream end portion thereof, slow wave circuit means disposed along and about said electron beam path for propagating electromagnetic wave energy within a predetermined frequency range in order to provide a cumulative energy exchange between the electron beam and electromagnetic wave energy propagating along said slow wave circuit means, said slow wave circuit means including a plurality of lossy attenuator elements disposed in at least one portion of said slow wave circuit means, said plurality of lossy attenuator means comprising a plurality of azimuthly displaced disc-shaped elements each of which is sandwiched between a pair of axially spaced conductive wall members forming a portion of said slow wave circuit means, said slow wave circuit being provided with fluid coolant flow channels, at least one of said wall members forming a common wall between a radial oriented major face of said disc-shaped elements and said fluid coolant flow channels, said common wall having a thickness such as to be deformable by fluid pressure introduced within said coolant channel in use whereby said disc shaped elements are compressed between said pair of axially spaced conductive wall members by fluid pressure, said fluid coolant flow channels being provided with fluid coupling channels interconnected between at least two of said fluid coolant flow channels for at least two of said lossy attenuator elements, means for introducing and extracting coolant fluid within said fluid coolant flow channels and said fluid coupling channels in a unidirectional manner such that coolant fluid flows therethrough in a unidirectional manner.

7. A high frequency electron discharge device including an electrom beam forming and projecting means disposed at the upstream end portion thereof and an electron beam collector means disposed at a downstream end portion thereof, slow wave interaction circuit means disposed intermediate said beam forming and projecting means and said beam collector means, said slow wave interaction circuit means including at least one cavity member formed by a pair of axially spaced transverse end walls, said cavity having side walls formed in a manner such as to provide a clover-leaf shaped side wall configuration, said clover-leaf shaped side wall configuration having at least four finger elements radialy directed therein such as to form said clover-leaf configuration, each of said finger elements having a lossy attenuator disc disposed at the end portions thereof and nested between said pair of transverse conducting wall members forming said cavity end walls, at least one of said transverse end walls forming a common boundary between a fluid coolant flow channel and said lossy attenuator discs, said fluid coolant flow channel having radial dimensions in the vicinity of each of said lossy attenuator discs which encompass at least a major portion of the transverse cross-sectional face dimension of each of said lossy attenuator dics and which have a wall thickness such as to be deformable in the presence of coolant fluid flowing therethrough, whereby said lossy attenuator discs are maintained in compression and improved fluid cooling of said lossy attenuator discs is achieved in use.

'8. A high frequency electron discharge device including an electron beam forming and projecting means disposed at the upstream end portion thereof and an electron beam collector means disposed at the downstream end portion thereof, slow wave interaction circuit means disposed along the electron beam axis intermediate said beam forming and projecting means and said beam collecti-ng means, said slow wave circuit including at least one clover-leaf shaped cavity, said clover-leaf shaped cavity having a pair of axially displaced transversely dis posed end wall members, the side walls of said cloverleaf cavity including a plurality offingers protruding radially therein, said fingers having lossy attenuator elements disposed at the end portions thereof, said lossy attenuator elements having fluid cooling means which include a fluid coolant flow channel having a thickness dimension such as to be deformable in the presence of coolant fluid flowing through said coolant channel whereby said lossy attenuator elements are compressed between said pair of end wall members.

9. A high frequency electron discharge device including an electron beam forming and projecting means disposed at the upstream end portion thereof for introducing an electron beam along a central beam axis of said device, an electron beam collector means disposed at the downstream end portion of said device, a slow wave interaction circuit means disposed along and about said electron beam axis between said downstream and upstream end portions thereof, said slow wave interaction circuit means including at least a pair of axially spaced cavities each of which includes lossy attenuator elements disposed therein, said lossy attenuator elements being disposed in nesting relationship between the respective transverse end walls of each of said cavities, a fluid coolant flow channel disposed intermediate said pair of axially 1 1 i 2 spaced cavity members and dimensioned such as to prospaced transverse wall members and said opposing major vide a fluid channel cross-sectional dimension which entransverse faces of each of said lossy attenuator elements.

compasses at least a major portion of the major end faces of said lossy attenuator elements, the common Walls References cued between said fluid coolant flow channel and said lossy 5 UNITED STATES PATENTS attenuator elements having thickness dimensions such 2,939,993 6/1960 Zublin et al. 31535 that said wall portions are deformable by fluid pressure 3,335,314 8/1967 Espinosa et al. 31536 in a manner such as to subject each of said lossy attenuator elements to oppositely directed compressive forces HERMAN KARL SAALBACH Primary Exammer' so as to provide a rigid joint between each pair of axially 10 S. CHATMON, JR., Assistant Examiner.