US2617959A - Electron discharge device - Google Patents

Description

Nov. 11, 1952 c. EQFAY ELECTRON DISCHARGE DEVICE 2 SX'IEETS-SHEET 1 Filed Sept. 30, 1950 llllll II II INVENTOR C. EFA Y ATTORNEY Nov. 11, 1952 c. E. FAY 2,617,959

I ELECTRON oxscmmcs DEVICE Filed Sept. so, 1950 I 2 Smms-sx-mm 2 uwzlvrok C. E. FAY

ATTORNE V Patented Nov. 11, 1952 annc'raon DISCHARGE DEVICE Clifford E. Fay, Gliatham, N. J assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application September 30, 1950, Serial No. 187,813

is claims. (Cl. 313-293) This invention relates to electron discharge devices and more particularlyto such devices especially suitable for use as high-power generators or amplifiers at ultra-high frequencies.

In such devices, of which that disclosed in the application of D. A. S. Hale and R. J. Kircher, Serial No. 54.92%, filed October 16, 1948' now Patent 2,531,623 is exemplary, the cathode, gridand anode are planar electrodes closely spaced adjacent each other. As the function of the grid or control electrode is to control the potential of a section of the stream-of electrons between the cathode and the anode in-a plane per-, pendicular to the electron stream, the ideal'control electrode would consist of a very large number of small points arranged in that plane'. As this is physically impossible, a control electrode having a finite mass and pervious to electrons must be employed as an approximation to the ideal. A plurality of very fine wires uniformly spaced or extending out from a central hub as radial spokes and slotted plates are types of control electrodes that have priorly been employed.

A control electrode of whatever type in effect shields the anode from the cathode. In this ideal case mentioned above, of a very large number of points this shielding would'be uniform over the cathode surface. By a uniform shielding effect a uniform electron emission over the entire-face of the cathode is obtained. However, when the control electrode comprises a plurality of wires which vary "in position relative to each other shielding of the cathode consequently is not constant over the cathode surface.

A.v uniform shielding is attainable by several means, but difiiculty has priorly been encountered in attaining it without sacrificing other design considerations; such as maintaining the mass of the control electrode at a minimum. Thus in certain types of operation of such devices," for example in grounded-grid operation, the con- 'trol electrode is common to both the input and output circuits,- and charging current flows in the control electrode as current of the input circuit and other chargin'gcurrent flows as current in the output circuit. If the control electrode has appreciable impedanceto these currents, 9. "voltage is developed across'portions of the'control electrode which is common to both circuits and results in feedback between the two circuits. Such feedback is generally undesirable in the operation of these devices. As the impedance of the control electrode is determined by] the paths which the current must followinflowinginto the electrode and'the number of such paths available,

2 p it is advantageous tomake these paths as short and direct as possible and to provide aimaximum number thereof.

However there are also numerous other desiderata to be met by the control electrode. In electron discharge devices designed for ultrahigh frequencies, the electrodes are closely spaced to minimize electron transit-time efiects. With close electrode spacings the inter-electrode capacitances per unit area become high :and in operation high charging currents flow in the electrodes. Thesehigh charging currents result in heating of the electrodes, which may also be heatedby radiation from other. electrodes and by bombardment by electrons. In order to prevent uneven heating of the control electrode and also to prevent an uneven distribution of impedance between parts of the control electrode it is desirable to have a uniform current flowing at all points equidistant from the center of the control electrode and feeding the inter-electrode capacitances.

Cathodes employable in such ultra-high frequency electron discharge devices are advantageously made in the form of a disc as an equipotential cathode by applying active coating material to one side or the face of .thedisc and providing means for heating the disc from the opposite side. In operation at ultra-high frequencies, charging current to the cathode-control electrode capacitance must flow over the surface of the cathode in addition to the convection current whichleaves the cathode via the emitted electrons. These currents, being of ultra-high frequency, are constrained to the surface of the cathode. The coating materialon the cathode disc is of the nature of a semiconductor and has appreciable resistance, so that the powerloss' resulting from the ultra-high frequency current 'flowing. through the resistance of the cathode as wires. These and the other heating'efi'ects mentioned above may cause thecontrol electrode to operate at such an excessive temperature that it emits electrons by thermionic emission, which is undesirable as it results in a decreased efficiency of operation and may in turn result in the over heating of other electrodes. It is therefore desirable to both prevent electrons impinging on the control electrode and also to allow a rapid and even cooling from all parts of the control electrode.

Further because of the close spacings between the electrodes it is desirable that any expansion of an electrode be confined to its plane so that the expansion will not affect the inter-electrode spacings.

It is one object of this invention to'improve the efiiciency and stability of operation of electron discharge devices and particularly of such devices operable at high power output and ultrahigh frequencies.

It is a further object of this invention to provide agrid' structure which achieves each of the desired control electrode characteristics. Thus objects of this invention are to attain in a control electrode, both severally and togethenan even shielding effect onthe emitting cathode surface, a small control electrode impedance and. particularly a small control electrode inductance, a uniform current flow in all-parts of the control electrode, even heat. distribution and an even and rapid cooling of the control electrode, and expansion of the control electrode only in the plane'of the electrode. Further, it is an object of this invention to attain each of these advantages in a'simple structure without the sacrifice of others.

.A still further object of this invention is to reduce'the power loss and resultant heating along the emitting surfaces of the cathode.

These and other objects of this invention are obtained in accordance with features of this invention in one specific illustrative embodiment by a control electrodeposi-tioned between closely spaced planar cathode and anode electrodes. The control .electrode comprises a support, for example a disc, havinga central aperture, a hub member centrallypositioned in the aperture, and a plurality'of fine wires extending from the hub to the disc, the distance between neighboring wires beingat all times constant and equal for'all wires. A plurality ofxsupport rods'or straps-also extend between the central hub and the disc support and conform to the same geometric configuration.

Further, in another specific embodiment of this invention the control electrode is positioned adjacentacathode whose surface has radial grooves -therein,ex=tending from a central hub portion to the edge, each ofthe grooves conforming t the same geometric configuration as the elements of the control electrode. These grooves are filled withan electron emissive material and the cath- "odef is so aligned that the emissive material is opposite the spaces between the wires of the control electrode, while the ridges between the grooves are opposite the wires themselves.

' 'It is one feature of this invention that'an electrode for an electron discharge device have active portions extending out from a central'hub portion and be of such. a geometrical configuration that each of the active portions isat all points equidistant from the neighboring active portions and that the distance is the same for each pair of neighboring active portions; This feature is accomplishedin one's'pecific way by havingeach active portion extending from the central hub portion in the form of a curve any point r,

above coordinates.

along which is given by the equation in polar coordinates 0 T constant where T1 is the radius of the circle whose radii at the point 11.

It is a feature of this invention that the control electrode wires extending to an outer disc support each follow the curve defined by the It is also a feature of this invention that all the grid wires intersect the circle defined by the outer disc support at the same angle.

It is a further feature of this invention that a cathode have grooves or depressions in its surface emanating from a central hub portion, each of the grooves being curved to follow the above coordinates and each of the grooves being filled with an electron emissive material.

It is a further feature of this invention that such a cathode and control electrode be cooperatively related in an electron discharge device, the cathode being positioned adjacent the control electrode and oriented so that the emitting or active portions of the cathode are spaced between the wires or activeportions of the control electrodeand the rid es between the grooves in the cathodesurface are positioned opposite the wires of the control electrode.

A complete-understanding of this invention and of the various features thereof may be gained from consideration of the following detailed description and th accompanying drawings, in which:

Fig. l is-anelevational view of an electron discharge device incorporating the'various features of this invention, a portion of the device being shown in section to show the close spatial relationship of the electrodes;

Fig. 2 is-a plan view of a control electrode illustrative of one specific embodiment of this invention and employable in the device of Fig. 1;

Fig. 3 isan exploded perspective view of the coplanar electrodes of the device of Fig. 1;

Fig. 4 is a sketch of two of the wires of the control electrode of Fig. 2 illustrating the derivation-of theequation of the curve of the wires;

Fig. 5 is a plan View of a cathode illustrative of one, embodiment of this invention; and

Fig. 6 is a sectional view-along the line -B6 of Fig. 5.

Referring nowto the drawings, Fig, 1 shows a grounded-.grid'type ultra-high frequency electron. discharge "device; operable at high power output in which the various features of: this invention may advantageously be incorporated. The device illustrated inFig. 1 is of the type described inthe application of D. A. S. Hale and R. J .Kircher, Serial; No. 54,924, filed October 16, 1948, now Patent 2,531,623, As more fully described in that; application, the-device comprises similarly shaped anode section, 10 and cathode section II; joined to a; medial copper ring l3 to formthe enclosing vesselfor thecooperating cathode M, control electrode l5,and anode it within the device. The glass bell portions 11 and 18 of the anode and cathode sections I 0 and H are joined to the copper ring l3 by-eopper ring members I9 and 20, respectively.

The anode l6 advantageously comprises a'hollow cylindrical housingn ha'ving' athick copper 'disc 24 secured to the lower end of the housing 23. "The'disc 24 has a central groove 25 and radial grooves 26, as best seen in Fig. 3, in its surface adjacent the other electrodes, as explained more fully below. A protective shield 28 "through the end of the anode section !8 allow "a cooling fluid to be circulated and projected against the anode disc 24 in a thin film to carry away the heat absorbed by the anode disc during operation of the device, as more fully disclosed in the above-mentioned copending application.

The cathode assembly !4 comprises a sleeve 36, which-may be ,of copper-plated Kovar alloy, a slotted ring member 31,as of nickel, secured to the end of the sleeve 36, and a castellated ring -member 38, which may also be of nickel, which is secured to the ring member 31. The .ring member is provided with a number of vertical slots 39.. to form a plurality of resilient fingers -48 whichare spot-welded to a heavy nickel disc 4!.- The surface of the disc is coated with an active electron emissive material, such as barium .and' strontium oxides, the coating 42 being applied to only certain areas of the disc 4|, as best seen in Fig. 3 and discussed more fully below. The fingers 48 form yielding supports fOI'.'th8 disc, being forced outwardly by expansion of the disc during heating so that the planar position of the disc is practically unchanged in the axial direction regardless of expansion and contraction of the disc. x

, Referring now to Fig. 2, the grid or control electrode in accordance with this invention comprises a copper ring frame or disc !3 which has a central aperture 45 therein, a hub member .46- located axially within that aperture and con- ;centric with the ring frame !3, heavy support rods or straps 4'! and grid wires 48, the support ,rods or straps 4'! and the grid wires extending out from the hub member 46 and connecting it to ring frame I 3. g

The ring frame !3 and the hub 46 advantageously both have grooves adjacent the aperture 45 in which grooves the support rods or straps 4! are positioned so that they do not risesub- ;.stantially above the surface of the ring frame !3. The rods or straps are advantageously secured in the grooves by stakes 49. The grid wires 48 may belsecured to the hub 46 and ring frame 3 as by being spot welded to ledges 5! .ancl 52- onthe hub and ring frame members 46 and !3, respectively. L In accordance with this invention, each grid wire 48 is secured to the hub 46and in extend- ,ing across the aperture 45 to the ring frame 3 iremains at all points equidistant from each of the neighboring wires. Thus it is a characteristic 8 of the grid wires 48 that they are so curved that each wiremakes the same acute angle with the outer of the circles bounding the aperture 45,-

desired conditions. Two of'the grid wires 48! and 482 are shown in Fig. 4 and are illustrated as being tangent to-the radii 55! and 552 of a circle 468, which circle determines the origin of each of the curves ofthe electrode and has a radius of a specific value 11. As more fully discussed below after the derivation of the general equation of the curve, the circle 468 may or may not be in actuality the hub circle, that is; the physical hub 46 of the electrode shownin Fig. 2. In this derivation it shall-be so referred to, as it is thus shown in the electrode of Fig. 2 and discussed above. However whether the circle 468 is the hub circle or not, the radius 11 in the following derivation is known constant whose value is given by the theoretical circle defined by having its radii tangent to the curves of'theelectrodefi In the electrode shown in Fig.

2, as noted above, this theoretical circle is the hub 46.

The angle between the two radii 55! and 552 and therefore between the grid wires 48! and 482 at the point of intersection with the hub circle is 01. The pitch distance or the distance between the two wires 48! and 482 on the circle 468 is Distance between wires=r10i (1) where 01 is given in radians. :AS One desired ,the two grid wires 48! and 482 will intersect any circle 56 between the hub and rimcircles=468 and I38 at points A and B which are separated by the angle 01 or by the distance 101 where r is the radius of the circle 56. The line 5! is tangent to the curve of the wire 48! at the point A and makes an angle o with the radius 58 of the concentric circles. Line 59 is drawn through point A normal to the curve of the wire 48! and thus to the line 5'! and intersects wire 482 at point C. The wire. 482 intersects the circle 56 at point B and line 6! is theradius of the concentric circles through that-point. If the angle 01 is considered to be small the curves AB and BC may be assumed to be straight lines, which assumption becomes correct as these .distances approach the limiting conditions. Then ABC is a right triangle with an angle BAC' equal to the angle g2, that is, the angle between the normal line 59 and the are of the P- us -As the initial condition is that be always constant and thus is equal to 1101 from Equation 1 theremay besubstituted AC=r101 3) in Equation 2. Thus,

1- 0 =r6,' cos a (4) which gives the requirement of the curve of the wires for the grid desired, namely that each wire acre-tee iof-z'thegri'd' be of. such shape that. at. any point along: the wireithe ratio between. an initial radius and the radius at thatpoint be equalto the. cosine of the angle between the tangent tothe curveand the. radius at that point.

Todetermine the. equation of the. curve of any wire in the grid we may consider the incremental 'drjof the radius GI and the triangle formedby the incremental dr and the. incremental do. In the limittherelationship between these. increments may be written'as -tan (90- p.) cot. c (6) which gives the rate of change. of the; curve in terms. of. r andv a. However Substituting-Equation 5 in Equation 8 wev have Tan p Equation 9 may be substituted in Equation '7 to obtain the equation which'may'betintegrated to obtain the equation of the curve Theconstant is'the value of for the initial condition ofr=rr and may be defined as l so that the general equation'of'the curve is If m; isassumedtobeequal to unity-then the equation simplifies down to 8: r lcos (13) or, where, \pthe initial angle is zero,

wherer isthe-radius in units of n, the radius of thehub I30 and the angles are expressed in radians. V

In the above development the hub was assumed to beatradiusrr wherethe wires became tangent to radii. This of course is the minimum-radius hub for which thedesired conditions are obtained. It. is. quite possible to make the hub of radius larger than T1. in which case the angle q: is not zero at the hub. It is usually desirableto make wires curvedin accordance withthe generalequation12 providean even; shielding effect. over the face. of the cathode becauseof the equal. and even spacing. of. the active portions of the electrodes relative to each other. Further as allof thewires of-the electrode are directly connected to the disc or frame 13 the charging currents are carried substantially uniformly by all the wires, thereby providing a minimum inductance of. the electrode. Further all the wires conduct heat to thedisc or frame l3, .thusaiding in enabling the wires. to operate at reasonable temperatures such that thermionic electron emission from them is. minimized.

As all of the electrode wires 48 are of thesame length,- they present substantially equal impedances. to the charging currents thereby permitting even distribution of current flowinto the electrode from frame I3. Further since all of the wires 48 and the support rods or straps 41 have a curvature in the plane of the control electrode. any expansion of. these members. is. biased in this plane, there being no constraints to cause buckling normal to the. plane.

Referring again to Fig. 3 it is seen that the cathode, control electrode, and anode are so oriented that the support. rods 4! are positioned opposite. the non-coatedportions of the cathode disc 4| and in turn alsofi't into the groove 26 in the anode disc 24, each of these also following the contour of the curve of the control electrode wires 48. Similarly'the-hubmember ifi, uncoated hub portion of the cathode disc 42 and central groove 25 in the anode disc are positioned in alignment. Thus collection of electrons. by the control electrode support rods 4! is avoided and closer inter-electrode spacing with a concomitant reduction in electron transit time and increase in transconductance is-obtained.

Referring now to Fig. 5, there is shown a cathode embodying further the principlesof this invention. The cathode comprises a disc 6'! of similar over-all configuration to disc and similarly adapted to be held in the cathode assembly M by the resilient fingers 49, as discussed above. The surface of the disc 61 adjacent the other electrodes of the device has a central or hub portion 62 from which emanate a plurality of grooves 63. Each of the grooves 63 is filled with an electron emissive material 64 and comprises the active portion of the cathode. The grooves 63 are closely spaced together being separated by the ridges E5 integral with the cathode disc 6t. *Portions -66 are left withoutgrooves 63 therein.

Thegrooves 63, ridges 65, and portions 66 each advantageously are curved to follow thee quation /r r cos -.so that the active portions of the electrode are everywhere equidistant from the neighboring portions and that distance is constant over the whole electrode. I

The cathode is advantageously employed in an electron discharge device together with a control. electrode in accordance with this invention by being aligned so that the emissive material '64 in the, grooves 63 isoppositethe spaces between the wires 48; the ridges 65 between the grooves 63 are opposite thewires 48 themselves, and the portions 65' are opposite the support rods or straps 41. Electrons emitted from the electron emissive material-BA.wil1:then:tend to be formedinto beams which. will. substantially avoid the-grid wires as well I asthesupportrodsand thus thenumber of; electrons impinging on the control electrode and collected thereby will be greatly. reduced.

considerably reduced allowing a higher efiiciency of operation.

It is to be understood that the above-described arrangements are illustrative of the application of the principles of the invention. Numerous other' arrangements may be devised by'thos'e skilled. in the art without departing from the spirit and scope of the invention. 1

" 'What is claimed is:

1. An electrode for an electron discharge device having a central hub portion and curved active portions attached to and emanating out from said hub portion and coplanar therewith, said active portions being curved so that the distance between adjacent active portions is substantially constant at any point along said active portions.

2. An electrode for an electron discharge device having a central hub portion and curved active portions emanating from said hub portion, each of said curved active portions following the equation dr m-cos? where n is the radius of the circle whose radii are tangent to said curved active portions, 1// is the angular coordinate of the point of tangency, and r, is a point further along the curve.

3. An electrode for an electron discharge device comprising a, plurality of wires each of which is a curve following the equation where n is the radius of the circle whoseradii are tangent to the curves, 1/1 is the angular coordinate of the point of tangency, and r, 0 is a sec end point further along the curve. 1.

4. An electrode for an electron discharge de-' vice comprising a conducting member. having an aperture therein, a plurality of curved wires attached to said member and extending inwardly across said aperture, each of said wires having a curvature such that the distance from one of said. wires to an adjacent wire in a, direction normal to said first wire is substantially constant at any position along the length of said wires in said aperture.

5. An electrode for an electron discharge device comprising an outer member having a circular aperture therein, a central hub member: substantially concentrically positioned in said aperture, and a plurality of wires extending across said aperture between said outer and said hub members, each of said wires being curved such that the distance from any wire to an adjacent wire in a direction normal to said first, wire is substantially the same at any point along any 10 wire between saidouter and said hub members.

6. An electrode for-an electrondischargedevice comprising an' outer support member having a circular aperture therein, an inner" support member positioned in said aperture, anda 'plurality of curved wires connected to each of said support members, the curve of each of said wires being of the same equation and each wire intersecting the circular inner boundary of the'outera support member at the same acute-angle. Y 7. A planar electrode foran electron dischargedevice comprising a conducting 'disc havingacentral circular aperture therein, 'a' circular hub? member located substantially concentrically '"ins said aperture, a plurality ofv wires extending across, said aperture and securedto said discand said hub member, said wires-"each conformingis'ub stantially to a'curve of the equation f f l 'r -m-cbsi 0- where 0 is the angular coordinate, .r is the radial coordinate, 1'1 the radius of said circular hub, member, 4/ the angle of intersection of the wires with the periphery of each circular hub member, and the origin of the polar coordinates is at the center of said aperture and said hub member.

8. An electrode for an electron discharge device in accordance with claim 7 wherein certain of said wires are of greater thickness than the remainder of said wires, said thicker wires serving to support said hub member in said aperture.

9. A planar cathode for an electron discharge device comprising a metallic disc member having a plurality of grooves therein, said grooves being closely spaced and defining metallic ridges therebetween, said grooves and ridges extending from the periphery toward the center of said disc member, and an electron emissive material positioned in said grooves only whereby high frequency charging currents for the cathode control electrode capacitance ar constrained to the surface of the cathode and flow substantially entirely in the low resistance metallic ridges.

10. A planar cathode for an electron discharge device comprising a metallic disc member having a central surface hub portion and a plurality of closely spaced grooves therein emanating from said central surface portion, said grooves defining a plurality of ridges therebetween and an electron emissive material positioned in said grooves only, whereby high frequency charging currents for the cathode control electrode capacitance traverse the surface of said cathode between the periphery thereof and said hub portion by flowing substantially entirely in the low resistance metallic ridges.

11. A planar cathode for an electron discharge device comprising a metallic disc member having a central surface hub portion and a plurality of closely spaced curved grooves therein emanating from said central hub portion, said grooves defining a plurality of curved ridges therebetween, and an electron emissive material positioned in said grooves only, the curve of each of said grooves and said ridges following the equation where n is the radius of the circle whose radii are tangent to said grooves, 1/1 is the angular coordinate of the point of tangency, and r, 0 is a point further along the curve.

12. A high frequency high power electron disch t-g nericscomprisinaa kfi na-v s han 'aj cl gsely esp/Med planar cathode, control, and a odea lectrodes in said 'yessel, said control electrode comprising a metallic discmemberextendof QlQsely spaced curved grooves-therein. emanatingifrom sa-id :hub portion, said grooves defining lurality of curved ridges therebetween, :and

an. electron .emissive material positioned 'insaid grooves solely, said cathodeland-control electrode being oriented sothatthegroovesare opposite the space between said wires .and said ridges are opposite said wires, the curve of each of said grooves, ridges, and wires conforming substantially to the equation v '12 W r ."?:1;l 1.mQIIQdiQ EO fLmGI circle-whose: radii .dvgroovea. msitheaanaularzsoordinate1-,of; t1 1 e: point of,- --tangency,-and r :issa point: :ip he al nswthercurte- 13. An el ctr discharge. device accordnc w th; claim wherein ach o th urve i ibia y aicontinuationzatth peripheryzof said huhmember tor saidrc ntralzsurtacel hubmort Of :a radiusof said :hl b memberor". said :central surface; ahub :tno t nwrespectively- .REE KE GES GIT- The 'f ollowing references are of record: in the file-of this patent:

V UNITED STATES{BATENTS Numher 'iliam Date 12315331428 .lsloluthw rtnnamnnnprun,,1939 ';3;3 As2 lTllQlll Qn. fir ,4 2 0 dl y...= -.w-. .Januzfi, .1949 2,538,054 Smith Jan. 1 1 1,951

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