US2452062A - Electrical discharge tube - Google Patents

Description

Ocl:...26 1948. J. D. LE VAN ELECTRICAL DISCHARGE TUBE 3 Sheets-Sheet. l

i aa' Filed July 29, 1943 Oct. 26, 1948. J. D. LE VAN 2,452,062

ELECTRICAL DISCHARGE TUBE Filed July 29, 1943 3 Sheets-Sheet 2 Q w T INVENTOR. JAMES 0. LEW/v,

Patented Oct. 26, 1948 UNITED STATES TENT QFFIC'E 2,452,052

ELECTRICAL DISCHARGE TUBE James-D. Le Van, Belmont, Mass, assignor to Raytheon Manufacturing Company, Newton, Mass,

a corporation of Delaware Application July 29, 1943', Serial No. 496,563

'7- Claims.

This invention relates to ultrahigh frequency velocity-modulated tubes, and more particularly to such tubes in which a stream of electrons is subjected to bunching and debunching efiects by passing successively through a pair of control electrodes.

In devices of the foregoing nature, the spacing: between the control electrodes must be accurately related to the frequency for which the device is intended and to the voltages impressed on the device which affect the speed of the electrons passing through the control electrodes, so that the. transit time of the electrons passing from one control electrode to the other bearsa definite relation with respect tothe period ofthe os-cillations'produced by the device. Unless-this spacing is. maintained constanathe frequency at which the device. operates tends to shift or the device drops out of adjustment and fails to operate properly. In many devices of this kind. it has been found that during operation changes occurred which requireda continuous external control of the voltages and the external circuit constants supplied to the tube in orderto keep it operating at the proper frequency and at the proper level of intensity. I have foundtthat such changes. have been due in considerable measure to temperature changes within.- the tube itself: which introduced variations in the: spacing ice-- tween the pair of control electrodes.

An object of this invention is substantially to eliminate the effiect of temperature on the frequency and intensity of response of an ultra high frequency velocity-modulated tube of the foregoing type.

Another object is to produce a spacing between a pair of electron bunching or debunching electrodes in such a tube which is substantially independent of temperature.

The foregoing and other objects of this invention will be best understood from the following description of. exemplifications thereof, reference being had to the accompanying drawing, wherein:

Fig. 1' is a longitudinal cross-section through an ultra high frequency velocity-modulated tube embodying my invention;

Figs. 2aand 3 are: diagrams illustrating certain geometrical principles involved in two forms of my invention; and

Fig.4 is. a. set of curves. illustrating the degree of temperature compensation which may be,ob-- tained in certain embodiments of my invention.

The tube'illustrated in the drawing consists. of an evacuated envelope I of some suitable material, such as glass, containing'the cathodev structure 2,. a reflecting electrode 3;an accelerating grid t adjacent the cathode, and'a pair of control electrode elements 5 and '6 interposedr'between the accelerating grid and the reflecting elec trode 3.

The cathode is of the hollow'indireotly heated type having a flat upper active surface, preferably coated with an electron-emissive material 1- which may consist of the usual mixture of barium and strontium oxides. Surrounding the hollow cathode is a focusing shield or ring 9 which tends to focuswthe electrons coming from the coating 1 into compact beam. Surrounding the focusing ring 9'- is an accelerating grid-supporting cylinder HI: having an opening, at the upper end thereof across which is supported a perforated grid member l I consisting of fine conducting wires so asto' interpose a minimum of grid surface for interoepting the electrons contained in the electron beam. A- cathode lead-in wirei2 is sealedthrough a, press l3 formed on the upper end of a reentrant stem lt'contained with-in the envelope I. The lead-in I2 is electrically connected to the":

tween a pair of insulating washers H, thus spam ing the members in proper relationship with respect to each other and: maintaining these members firmly in position with respect to. the reentrant stem M. Ihe focusing; ring Qmay. be welded to: the lower: end: of. the: cathoderfZ, and thus be electrically connected to and supported by the cathode: One of the standardsv I'G- may:

continue throughthe press: l3 so as to' provide an external electrical connection: to' theacceler-- ating grid 4.

The structure described above produces a com- 'pact beam of electrons which emerges through the perforated member I I with the requisite velocity. This electron beam is subjected to the action of the pair of control grids 5 and 6. The structure of the control grid 5 is formed by a lead-in ring I8 which is sealed through the side walls of the envelope I, the portions of envelope l above and below ring I8 providing separate rigid supporting elements for said ring. The internal edges of the ring I8 are turned upwardly and form a relatively elongated cylindrical member I9 which has an opening at its upper end across which a perforated conducting member is supported. Here likewise the perforated member 20 is made of fine conducting wires for the same reasons as specified in connection with member I I. The second control grid structure 8 is formed of a conducting ring 2! sealed through the side wallsof the envelope l, the portions of envelope I above and below ring 2| providing separate rigid supporting elements for said ring. The inner ends of the ring 2i are turned downwardly so as to form a relatively short cylindrical member 22 having an opening at the lower end thereof across which is supported a perforated member 23 likewise formed of fine conducting wires.

-The reflecting electrode 3 is supportedby an anode lead-in conductor 24 sealed through a reentrant stem 25formed in the upper end of the 1:

envelope I. A getter assembly 26 may be conveniently supported on the lead 24. Of course it is to be understood that the construction as described above is assembled and evacuated in accordance with standard vacuum tube practice, so as to produce a high vacuum within the envelope I, and to activate the coating 1, so as to provide for copious thermionic emission therefrom.

The outer edgesof the rings !8 and 2| form eX- ternal connections to the grids 5 and 6. In order for the tube, as described above, to generate ultra high frequency oscillations, a hollow resonant chamber 21, which may be conveniently in the form of a toroid open along its inner edge, is fastened with its upper and lower edges respectively to the rings 2I and I8. The resonant chamber member 21 is preferably formed of a highly conductive material, such as copper. The oscillations which are produced by the device may be picked up by a coupling loop 28 placed within the chamber 21 and led off by a conductor 29 which conveniently may be surrounded by apipe 30 fastened into the chamber 2! so as to form with the conductor 29 a concentric line. l

When the tube is energized with the proper potentials, a beam of electrons coming from the cathode I is accelerated by the grid I I, and passes through the grid structures 5 and 6. As the beam emerges from the grid structure 6, it is reflected by the reflecting electrode 3 back through the pair of control grids. As the reflected beam emerges from the grid 5, it is reflected by the structure below it so that it again passes through the grid members 5 and 6 to finally fall upon the outer surface of the ring 2| or upon the reflecting electrode 3 with relatively low velocities. As is well known, theinitial passage of the beam through the grids 5 and 6 produces a bunching action, and upon reflection and repassage of the beam through these control electrodes, a debunching action is produced which feeds ultra high frequency energy to the resonant circuit formed by the hollow resonant chamber 21, thus setting up ultra high frequency oscillations which may be led off from the concentric line 29, 3B.

In prior tubes of this kind it was recognized that it was desirable for various members of the tube, particularly the grid structures 5 and 6 which carry substantial amounts of ultra high frequency energy, to be made of hi h y 0 tive material, such as copper, in order to make for highly efficient devices. As already stated, such prior devices during operation underwent various changes which necessitated changes in the voltages and circuit constants applied to the tube in order to keep it operating properly. I have found that these changes were due to variations in temperature within the tube. These variations in temperature, particularly at the cylinder I9 and its associated supporting structure produced small variations in the dimensions of these elements which resulted in a reatly amplified movement of the upper end of the cylinder I9 with respect to the member 6. I have found that it was the resultant change in the spacing between the perforated members 20 and 23 which produced the difiiculties encountered in the prior art.

I have discovered that if the portion 3i of the ring I8 between the cylinder I9 and the inner walls of the envelope l is bent so as to form an angle between the side walls of the cylinder I9 and the portion 3| and said angle differs substantially from the difiiculties heretofore en-' countered are substantially eliminated. The manner in which this is accomplished will be made clearer by referring to Fig. 2, which is a geometrical representation of one-half of the grid structure 5 within the walls of the envelope I. In Fig. 2, R represents the radius of the cylinder I9; L represents the length of said cylinder; A is the distance between the side wall of the cylinder I9 and the inner side walls of the envelope I; B is the length of the ring I8 between the side walls of the cylinder I9 and the inner walls of the l envelope I; and Y is the vertical distance between the outer end of B and the lower end of the cylinder I9. The upper end of the cylinder I9 is represented by P and the lower end by Q. The angle between B and the side wall of the cylinder I9 is designated as 0. The arrangement, as shown in Fig. 2, may represent the conditions which exist in the tube at the cold or room temperature.

As the tube is put in operation, the energy liberated by such operation heats up the grid structure, diagrammatically shown in Fig. 2, and all parts thereof are subjected to a certain degree of expansion dependent upon its coefficient of expansion and the temperature rise. For any given structure we can calculate the extent of movement which results from such expansion. For purposes of analysis We will assume that all parts of the grid structure are of the same material and are subjected to the same temperature rise.

It will be seen that Y=A cot 0- (Equation 1) As the temperature of the structure increases by a temperature t, Y increases to Y1.

(Equation 3) We see also that B=A cosec 6 (Equation 4) From Equation '5 =we can calculate A Y, which thus represents-the" distance "by which the point Q moves-upon" an increase in temperature; With c an acute angle, this motion will be downward.

We-al'so' see that the amount of thlsmotionis calculations to a particular embodiment of y novel'tube in which Aiis .l"", R; is .22"".,.L is .27, a; is 1'I.8' 1 and t=300' C. In Fig. 4' the solid linecurve represents the values of AY plotted against" variations in the angle 0, derived from such calculations. AL is constant andi's also represented inFig. 4. From Fig. 4 we see that if'we make o equalto' 90, as was previously done, the lower end 'Qof the grid structure will move about thirteen times as much as the expansion in L. We see also that L being the longest linear dimension has a greater linear expansion than either R or B. As 0- decreases, the value "of AY fallseff veryrapidly, reaches a minimum value at about 30; and then rises rapidly. The curve of AY asymptotically approaches the 0 line. With the particular values selected for Fig. 4, exact compensation for temperature expansion cannotbeseoured. However, substantial compensation-is secured for all values at whic'h c becomes appreciably acute. For example, the compensationattaineol at values-of 0 between about-70 and 7 is sufficient to produce satisfactory operation formanypurposes.

- Th'evalue of'aatwhich the maximum compensation issecuredx will. vary withv difierent relative values of A,. R, L,. t and. a. the foregoin quantities, AY exactly equals AL. and thus exact compensation for temperature variations canzbe secured. In each instance however, thevalue-of 0 must be a' substantially acute angle to-obtain thebenefits of temperature expansion compensation.

In some applications of my inventionthe angle which. the portion 3| of ring I8 makes with. the side walls "of the cylinder t9 may be an. obtuse angle. Such an arrangement is illustrated diagrammatically in Fig. 3 in which the same reference letters-are applied as in Fig. 2. In Fig. 3 it will-be seen thatv the element B makes an obtuse angle x with the side wall PQ of thegr-idcylindeli. In Fig, 3' the angle 0 is represented between the line B and an extension of the line P-Q. The value of- 0 is, of course, .180- Exactly the same analysis as was applied above in connection with Fig. '2- can be applied to Fig. 3 in so far as derivingvalues of AY are concerned. The only 'difierenceis that in Fig. 3 .AP equals the sum of AY and AL instead. of thedi'fierenoe of these quantitles 'asin Fig. 2. However, from Fig. 4 we see that in the particular example thereinillustrated, thesum o'f'A'L and AYin the vicinity of the minimum value of AY is much less than the difference between AY and AI at 9'0". "Thus even with the useiof the obtuse angle arrangement of Fig. 3

At some values for the net motion of. the point P c'an be made-subastantially less than with the-.priori :arrange ment. However, in Fig. 3 the net motion of the point P is upward, whereas inFig. 2cthe netmotion of the. point. P is downward. with.the:-values as given in connection with Fig. 4. Inssome in stancesra :motion of the point P downwardly .introduces 'less disturbances. inv the system than an upward motion. i I

The analyses as. given above assume an ideal condition in which all. Of the parts are subjected to: a uniform temperature increase. Inactual practice the conditions may be substantiallydififerentin that the temperature of the cylinder I19. may be substantially higher than the temperature of the portion 3 of the ring I8. Ifwe assume that. portion 3| remains at a constant tempera:-. ture while the cylinder l9 increases in temperas ture,..we can again apply Equation. 5 to determine-the changes which. occur. In this case-the factor A cosec :Ooct in Equation 5 is alwaysnzero. The results of such. an analysis are .plottecllby the dotted curve inFig. 4. In a practicalrca'sethe larger values of .0 are used since such a. structure is easier to manufacturaand also at 'verysmall values. ofe; B becomes impractically large. ..At.th1e larger values of 0 it will be seen-that the predomia hating factor in producing the motionof point P isthe expansion of the radius R of the cylinder 5:9. From the. dotted curve of Fig. 4 -it-=wi 1l be seen that with the conditions. assumedin connection therewith, exact compensation is obtained at an angle of. about. 50; at whichp'ointA'P is zero. The actual operation of the tube probably lies somewhere between thesolid and -'dotted curves of Fig, 4 Erorn this we see -that for all acute angle values-forthe angle'between -th'e por tion 3 Landthe side walls of the cylinder l9, which are substantially different from 90*, excellent temperature compensationis secured. As 'al'ready pointed out, even with obtuse values bf this angle, the temperature compensation may-"be: suincientfor'many-purposes.

. Of course it .is'to be understood that this in vention is not limited tothe"particular'details"as described above as many equivalents will'suggest themselves to those skilled in the art: For examplepthertypes of ultra high frequency velocity modulated tubes may have my invention utilized therein, such as a tube-which contains a separate bunching and a separate debunc'hing pair of'grid electrodes; My invention may also beapplied to electrodesupports in other types of tubes." Varia ous other-modifications and adaptations of myin vention will readily suggest themselves tdthos skilled inthe. art. It is accordingly desired that the appended claims-be given a broad interpretation commensurate with the scope of'theinven tion within theart.

Whatis claimedis: 1. An electrical space discharge tube compris- 'ing a plurality of electrodes, a first of said "elec trodes being supported with respect to an'ad'ja cent electrode to provide-a linear electronpath betweensaid electrodes, said first'el'ectrode' being supported between rigid supporting elements by supporting means of substantial length; saidfirst electrode having a portion extending from-said supporting means along the direction 'or'said elec tron path, the length of r saidiportionv being: substantially greater than the shortest distance between said portion and said supporting elements; said. portion having a substantial thermal coeflicientof expansion.whereby'variations. in the tern!- perature ofsaid electrode wil1-tendwtorprodu'ce 7, substantial variations in the length of said electron'path, said supporting means likewise having a substantial thermal coemcient of expansion and forming an angle with the direction of said electron path, said angle being of a substantial value substantially diflerent fromninety degrees.

- .2.'An electrical space discharge tube comprising a plurality of electrodes, a first of said electrodes being supported with respect to an adjacent. electrode to provide .a linear electron path between said electrodes, said first electrode being supported between rigid supporting elements by supporting means of substantial length, said first electrode having a portion extending from said supporting means along the direction of said electron path, the length of said portion being substantially greater than the shortest distance between said portion and said, supportin elements, said portion having a substantial thermal coeificient of expansion whereby variations in the temperature of said electrode will tend to produce substantial variations in the length of said electron path, said supporting means likewise having a substantial thermal coemcient of expansion and forming an angle with the direction of said electron path, said angle being of a substantial acute value substantially different from ninety degrees.

3. An electrical space discharge tube comprising a plurality of electrodes, a first of said electrodes being supported with respect to an adjacent electrode to provide a linear electron path between said electrodes, said first electrode being supported between rigid supporting elements by supporting means of substantial length, said first electrode having a portion extending from said supporting means along the direction of said electron path, the length of said portion being substantially greater than the shortest distance between said portion and said supporting elements, said portion having a substantial thermal coefiicient of expansion whereby variations in the temperature of said electrode will tend to produce substantial variations in the length of said electron path, said supporting means likewise havin a substantial thermal coeflicient of expansion and forming an angle with the direction of said electron path, said anglebeing of a substantial obtuse value substantially difierent from ninety degrees.

i 4. An electrical space discharge tube comprising a plurality of electrodes, a first of said electrodes being supported with respect to an adjacent electrode to provide a linear electron path between said electrodes, one of said electrodes being a grid member extending substantially transverse to said electron path supported by a substantial length of a metallic supporting member substantially at right angles to said grid memher and substantially in line with said electron path, said supporting member being in turn supported between rigid supporting elements by supporting means of substantial length extending transversely of said electron path, the length of said supporting member being substantially greater than the shortest distance between said supporting member and said supporting elements, said supporting means and supporting member having substantial temperature coemcients of expansion, said supporting means forming a substantial angle substantially diiierent from ninety degrees with said supporting member.

. 5. A high frequency tube comprising an envelope containing an electron-emissive cathode, means in said envelope for accelerating a beam of electrons fromsaid cathode, a pair of control grids mounted in the path of} said beam, and an additional electrode, said pair of control gridsbeing adapted to be connected to a resonant circuit to impart velocity modulation to the electrons in said beam, one of said grids being spaced from the other of said grids and being supported by a substantial length of supporting member extending in the direction of said beam, said supporting member being in turn supported between rigid supporting elements by supporting means of substantial length extending transversely of said beam, the length of said supporting member being substantially greater than the shortest distance between said supporting member and said supporting elements, said supporting means having a substantial temperature coefiicient of expansion, said supporting means forming a substantial angle substantially different from ninety degrees with said supporting member whereby variations in the length of said supporting means produce variations in the angular relation between said supporting means and said electron path which produce a change in the position of said one grid along the direction of said beam which is substantially smaller than the change which would be produced if said angle were substantially ninety degrees.

6. A high frequency tube comprising an enve-' lope containing an electron-emissive cathode, means in said envelope for accelerating a beam of electrons from said cathode, a pair of control grids mounted in the path of said beam, and an additional electrode, said pair of control grids being adapted to be connected to a resonant circuit to impart velocity modulation to the electrons in said beam, one of said grids being mounted at one end of a tubular supporting member, said tubular member having its axis extending in the direction of said beam, said last-named grid and its supporting member being supp rted within a tu-- bular portion of said envelope by an annular member of a substantial length interconnecting the other endrof said tubular member and the inner wall of said tubular portion and extending substantially transverse to the direction of said beam, the length of said tubular member being substantially greater than the shortestdistance between said tubular member and said tubular portion, said annular member having a substantial temperature coeificient of expansion, said annular member forming a substantial angle substantially different from ninety degrees with the side walls of said tubular member whereby variations in the length of said annular member produce variations in the angular relation between said annular member and said electron path which produce a change in the position of said one grid along the direction of said beam which is substantially smaller than the change which would be produced it said angle were substantially ninety degrees. a

7. An electrical short wave generator tube comprising an hermetically sealed glass envelope, a pair of electrodes in said envelope for supporting an electron flow therebetween, a pair of annular metal plates between said electrodes, spaced therefrom and extending through the wall of said envelope and having spaced, aligned, lipped openi s through which said electron fiow may pass within said envelope, at-least one of said plates having a concentric annular depression therein within the envelope and between said envelope and the inner edge of said annular plate to counteract themovement of'its lipped opening under heatvariation, a grid in each of said openings,

and. an electrical connection between said plates Number Name Date and outside said envelope. 2,238,596 Mouromtsefi et a1. Apr. 15, 1941 JAMES D. LE VAN. 2,263,194 Glass Dec, 30, 1941 2,288,380 Wing, Jr June 30, 1942 REFERENCES CITED 5 2,301,490 Winans Nov. 10, 1942 2,303,166 Laico Nov. 24, 1942 fighgf fiol llligwgralfeggzferences are of lecord 1n the 2,413,364 McCarthy Dec 1946 2,418,844 Le Van Apr. 15, 1947 UNITED STATES PATE NTS FOREIGN PATENTS Number Name Date 10 Number coumy D t 2,146,365 Batchelo Feb. 7, 1939 1 a e Great Jan. 21,

2,228,939 Zottu et a1 Jan. 14, 1941 Certificate of Correction Patent No. 2,452,062. October 26, 1948.

JAMES D. LE VAN It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 5, line 2, Equation 5, for

AY= (A cosec 0+A cosec 0at) (A-RatY-A cot 0 read AY 4 (A cosec 0+A cosec 0at) (A-RaW-A cot 0 and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 15th day of February, A. D. 1949.

THOMAS F. MURPHY,

Assistant Oommz'ssioner of Patents.

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