US2674661A

US2674661A - Electron multiplier device

Info

Publication number: US2674661A
Application number: US43851A
Authority: US
Inventors: Russell R Law
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1948-08-12
Filing date: 1948-08-12
Publication date: 1954-04-06
Anticipated expiration: 1971-04-06

Description

April 6, 1954 R. R. LAW 2,674,661

ELECTRON MULTIPLIER DEVICE HfllHl/lllllliHlllllll j ag Z! @l Gttorneg April 6, 1954 R. R. I 'Aw ELECTRON MULTIPLIER DEVICE 7 Sheets-Sheet 2 Filed Aug. 12, 1948 :inventor RUSSELL 'R LAW 8g a Gttorneg April 6, 1954 R. R. I Aw 2,674,661

ELECTRON MULTIPLIER DEvCE:

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ELECTRON'MULTIPLIER DEVICE Filed Aug. l2. 1948 7 Sheets-Sheet 7 Zhwentor' l RUSSELLR LAW .aj/Magw.

' attorney Patented Apr. 6, 1954 UNITED STATES TENT OFFICE ELECTRON MULTIPLIER DEVICE Application August 12, 1948, Serial No. 43,851

24 Claims.

In this application, I disclose an improved electron multiplier device wherein a large amount of electron multiplication is produced as a result of secondary emission initiated by a relatively small number of electrons.

The electron discharge device of my system is of wide and general use in the electron art. My invention is especially useful for translating, amplifying, generating and/or controlling radio frequency power.

An object of my invention is to provide an improved electron discharge device of the beam type for generating considerable power of very high frequency.

A further object of my invention is to provide Improved means for increasing greatly the magnitude of high frequency currents or voltages.

An additional object of my invention is to provide an electron multiplier system of the secondary emission type which provides more electron multiplication than any electron multiplier system known in the art.

A further object of my invention is to provide in a beam tube an electron multiplier of the secondary emission type which is suitable for use where high power at high frequency is to be generated.

Another object of my invention is to provide an improved electron multiplier of the secondary emission type for generating and controlling or modulating the magnitude of large amounts of high frequency currents or voltages.

A specific object of my invention is to provide an improved dynode element which makes possible high frequency, high power electron multicurving sides to guide the electrons to the secondary electron emitting dynodes which are roughly rectangular with inwardly curving sides. Although the dynodes are small in cross section, the spacing is close and a large number of elements are-used to give large output currents. Other novel features are included, such as diierentially arranged collector electrodes and a novel electron beam blocking electrode which cooperates with the beam deflection or sweep to provide a dilerential output which may be modiiied as to magnitude and phase by shaping the beam blocking electrode edges to correct for non-linearity in the device or to provide a non-linearity.

In describing my invention in detail, reference will be made to attached drawings wherein Figure 1 illustrates diagrammatically and by symbols an electron multiplier system arranged in accordance with my invention and comprising parallel groups of multiplier elements. This gure also illustrates the collector electrode or electrodes and the manner in which corresponding dynodes or electron multiplier elements are strapped together to operate certain ones thereof at like potentials, and, groups thereof at unlike potentials.

Figure 2 illustrates schematically a beam source, beam deecting electrodes, an electron multiplier assembly arranged in accordance with my invention and a target or electron collector electrode structure in the beam path.

Figure 3 illustrates schematically a modication of the arrangement of Figure 2. In Figure 3 there is a nat beam source. Figures 2 and 3 illustrate also the manner in which operating potentials may be supplied to the electrodes of my novel electron discharge devices including the deecting elements. Figure 3 illustrates my novel knife-edge beam blocking electrode interposed betweenv the deflecting elements and my novel electron multiplier electrode assembly.

Figures 4, 5, 6, 7, 8 and 9 illustrate in detail the shape of the dynode electrodes, the manner in which they are supported and grouped and how they are positioned relative to the collector electrodes. In Figure 4, the dynodes and one collector electrode are shown in perspective with portions in cross section to better illustrate the structure thereof.

Figures 10 and 11 illustrate the manner of mounting the dynodes and collectors within a sealed envelope. Figure 10 is a plan view partly in cross section through an axis of the tube on which both collectors are seen. Figure 11 is a perspective partly in section through the axis of the electron discharge device at right angles to the section on which Figure 10 is taken.

Figures 12, 13, 14 and 15 illustrate details of the electron gun which emits the electrons in a wide concentrated sheet toward the dynode elements. These figures also illustrate the beam focussing and deiiecting electrodes and the manner of mounting the gun in the electron discharge tube. Figure 12 is a cross section on the line I2-l2 of Figure 14. Figure 14 is a cross section on the line I4-I4 of Figure 13, and Figure 15 illustrates the knife-edge beam blocking electrode as mounted in the electron gun structure. Figure 15 is a cross section view on the lines I5--l5 of Figure 12. Figure 16 shows the beam blocking electrode in perspective.

In Figure 1 it is assumed that an elongated beam of electrons is produced and fed in the direction indicated by thel arrows to the input of an electron multiplier system'arranged in` accordance with my invention. The elements marked a, c', etc. are focussing or steering electrodes and serve the purpose of guiding the electrons toward the multiplier electrodes or dynodes b, b', c, c', d, d', e, e', f, y, y', h, h. Of these elements, b, b', etc. are herein designated as` input electrodes,'since the` electrons from the source are guided tothe surface thereof to release secondary electrons which pass tothe next row of elements to repeat the electron multiplying process. Electron trajectories are shown. The elements b, b', etc. constitute the iirst electron multiplier stages and also serve the purpose of steering the electrons toward the next row of elements c, c', etc. In Figure 1 I have shown electron multiplier velements b to h inclusive. It will be obvious that the number of electron multipliers in each row may be increased to increase the multiplying eect. Moreover, a plurality of rows as shown,'or `more rows, or fewer rows, may be provided. By virtue of the amplication by secondary emission at each successive multiplier stage, only a relatively small number of electrons from the source need be controlled to correspondingly control a very large number of electrons reaching the electron collector electrodes. This reduction in necessary driving power makes it possible to use beam defiection control in amplification and modulation of high frequencyY currents. In contrast with grid control, class-C operation is possible at very high frequencies. The amount of driving power needed to control, by beam deection, the small number of electro-ns used in the input of my novel electron multiplier is reduced and it thereby becomes practical to control the power generation by,` for example, control potentials or modulation potentials of very highfrequency because uniform velocity electrons may be injected into the multiplier in very short pulses. `inasmuch as the total `transmit time through the multiplier is of no import, the only frequency limitationv arises from transit time dispersion which tends to smear the pulses. As will appear hereinafter, electron dispersion is reduced to a negligible amount in my improved dynode assembly. In Figure 1 it is assumed that the collector electrodes No. 1 and No; I2 are insulated each from the other and the output is taken from both electrodes as described hereinafter. It will be understood that my electron multiplier lsystem may be used with a single collector output.

Figure 1 also illustrates the manner of applying operating potentials tothe dynode electrodes. As shown hereinafter, the electronmultiplier groups are eiectively in parallel in the beam path between the electron' source and the collector .electrodes Moreover, the parallel groups of dynodes may feed afsingle collector electrode or a pair of separate collector electrodes. In

applying operating potentials, the electron multiplier elements may also be grouped in parallel in another manner. For example, steering electrodes a, c', etc. may be strapped together as shown diagrammatically at Sa to operate at like direct current potentials. These straps are shown in the group at the right of Figure 1 but the strap-s for applying direct current potentials have not been shown as being connected to the group of elements at the left of Figure 1, since this would interfere with the clearness with which other features are illustrated. Dynodes b, b', etc. are connected in parallel by a strap Sb, while dynodes c, c', etc., of each of the other rows are similarly grouped in parallel with respect to applied direct current potentials. The potentials appliedA to the s raps Sa to Sh may be increasingly positive relative to the direct current potential on the electron source electrode but these electrodes in practice are less positive than the collector electrodes. The electron input is from the top of the diaphragm and the electrons are to be visualized as being introduced thro-ugh the elements a, a', etc., oi the first row', which serve as the steering electrodes so that the electrons strike on dynode electrodes b, b', etc., which constitute the first electron multiplier stages. From the dynode electrodes b, b', etc., some of the primary electrons introduced from the` source and those electrons which are released from .the dynode surfaces are drawn to electrodes cyc', etc. Again the primary electrons and secondary electrons are drawn toward the following dynodes c, e', etc., that nnally a very large num-z ber of electrons reach the. collector `electrodes through each series of dynodes and the totall electron stream to the collector electrodesiNo. 1 and No. 2 is a. great many times Agreater than the original electron stream, in fact, mayl be -in amperes.

1Eteturning to the straps Sa, Sb, etc., Wemay assume that strap Sa is at potential I, strap Sb at potential 2, etc., so that Vin the embodiment described there are eight different direct current potentials applied to the groups of elements. If the number of dynodes grouped in this manner is increased, the magnitude of the final current is increased with a corresponding increase in the number of direct current potentials and strapping elements for the added groups yof dynodes.

The essential features to be kept in mind in connection with Figure 1 is the fact that Vmany elements are put in parallel. The figure `is not drawn to scale, but each dynode, c, d, e, etc. lhas a top dimension of the order of 75 thousandth of an inch and a height slightly more than they Width. With the spaces between dynodes of corresponding scale, ten stages of the electron multiplier of my invention then occupies a space less than one inch long. Ten stages in parallel-ten deepmight then occupy a one inch square area and have a length appropriate for the electron beam provided.

Since control of a very small number of electrons controls an exceedingly large number of output electrons, my invention has made possible the use of beam. deection controll of the'initia-ting electrons to thereby control the final output. Such deection control systems have been shown schematically in Figures 2 and 3 of the drawings. In Figure 2, the two collector electrodes No. l and No. 2 might each be fed by a multiplier section (shown in part only) which might be of the order of two inches high, two inches wide, and one inch deep. The sections may be treated as a single multiplier assembly and the dimensions thereof may vary through a wide range. A somewhat concentrated beam of electrons is supplied from cathode A and fed between the deflector elements or plates B and C. The beam when at rest is focussed to fall at a point on the multiplier assembly intermediate the four boundaries thereof, preferably aboutv half way between the upper and lower boundaries and half way between the extreme side boundaries thereof. When control potentials are applied to the delecting plates B-C, the beam is swept across the entrance to the multiplier in a horizontal direction so that first collector No. l and then collector No. 2, and vice versa, are predominantly supplied with output current. Deflection serves to spread the electrons of the beam across the multiplier structure in a horizontal direction. Space charge spreads the electrons in a vertical direction as they go through the multiplier. The deflecting plates B-C may be excited by a signal voltage of the desired frequency which may be very high. Any appropriate coupling means may be used. In an example given, a transformer coupling CT is used. The 1*--f output appears in a circuit OT coupled differentially to the collector electrodes.

In the embodiment of Figure 3, A represents an electron source which emits a wide iiat beam of electrons drawn by the collector electrode through the deflection plates B-C. This beam is focused by the deflecting electrode plates B-C to line L on the blocking electrode D-E. The letter L represents the position of rest of the beam. Portion D blocks emission toward collector No. 2 when the beam is swept up above L and portion portion E blocks emission toward collector No. 1 when the beam is swept down below L. Now assume an alternating current voltage AC is applied to the deection plates B-C to deflect the beam in a vertical arc iirst upward and then downward. Since the beam at rest is on the line L, electrons will not pass by the blocking electrode until the deflecting voltage has approximately reached its crest F as shown schematically by the curve in Figure 3 adjacent to electrode D-E. Similarly when the deiiecting voltage reverses and the beam is deflected in the opposite direction, the beam will not pass the electrode D--E until the voltage has reached the value F'. I-l'ad the deflection been relatively greater then the beam would have been passed the knife edge electrode sooner in the electrical cycle, for example, at the electrical positions G and G. If th edges O and P of the blocking electrode are other than a straight line and parallel, a desired modulation characteristic may be obtained. Such an electrode might be employed to correct for non-linearity in the device or to specifically provide a desired non-linearity. When electrodes as shown diagrammatically in Figure 3 are used-the collector electrodes may be as illustrated in Figure 1 and the output is in effect differential.

The `electron multiplier and collector electrode assembly is shown in perspective in Figure 4 with portions broken away to show the structure of the steering and dynode elements, and their relation to each other and to the collector electrodes. Roughly 1/4, of the assembly, in the third quadrant, and one collector electrode is shown.

The electrodes have been labelled as in Figure l and it will be noted that the depth of the assembly of Figure 4 is not as great as that of Fig ure l. More specifically, in Figure 1 layers a to h. inclusive are shown whereas in Figure '4 layers.

a to f are shown. The dynodes are all initially of like cross section area having the form of dynodes c to f or h, inclusive. Elements a and b are then formed by cutting away a portion of the metal as at X in Figure 4. Fragmentsv only of dynodes c, d, e and f are shown in order to show better the manner of assembling the dynode electrodes and mounting the same in front of the colletcor electrodes. The individual elements cut away as at X, Figure 4, or in their original form are formed at the ends as illustrated in Figures 6, 7, 8 and 9 with extensions I0 that are spot l welded to apertured metal discs I4. The elements are off-set or staggered on the various discs so that interleang of the elements take place as shown in Figures 1 and 4. For example, the metal disc nearest the cathode may carry elements a, "c," etc. and the next metal disc then would carry elements 1), b, etc. The elements a and "b are olf-set or staggered. The third and fourth discs then carry elements "c and d respectively and these dynode elements are staggered as fastened to the discs to facilitate compact assembly and proper reflection of the electrons. Disc I4 of Figures 'l and 8 is assumed to carry dynodes as at c, Figure 1. Since the groups a, b, c, etc. operate at different direct current potentials, the discs I4 are, with exceptions explained hereinafter, assembled as shown in Figures 4 and 5 between mica or the like insulating discs I. In order to get the proper spacing, apertured metal discs I8 as shown in Figures 8 and 9 are spot welded to each side of the disc I4. The elements I4 and I3 may be of one or two or three or more pieces as desired. The mica discs I6 are similar in shape to the discs Iii and cooperate with the larger aperture in the filler members or discs I8 to provide long leakage paths between the groups of dynodes on the discs I4. An enlarged cross section of the dynode assembly is shown in Figure 5.

Each collector or target electrode has a. bombarded block tu with slots or channels 2| therein spaced so that the edges of the dynode elements of alternate rows remote from the electron gun are within the slots thus assuring that nearly all of the electrons leaving the final dynode elements fall on the collector electrodes. The portions 2t of the collector electrodes are integral with or fastened to anode bases 22, 22 f The general character thereof is shown in Figures 10 and 11 which also show the manner of mounting the dynode and collector assembly of the prior figures. Figures 1G and 11 taken with the remaining figures also show the essential features of the electron gun, deflecting electrodes and their mounting in an electron discharge device arranged in accordance with my invention. In the sake of simplicity, like parts are designated by corresponding reference numerals, letters and symbols throughout the several figures insofar as possible.

Figure 10 is a cross section through the longitudinal axis of the tube while Figure 1l is a cross section through the longitudinal axis of the tube at right angles to the section in Figure 10. 40 is a main element support base which comprises a heavy copper ring member to which is fastened, by a vacuum tight joint, a lower base shell 42. The base shell 42 has soldered or otherwise fastened thereto `a kovar metal truncated cone-like member 44 to. which the lower glass cap -46 is fase tened by a vacuum tight seal. The glass cap member 46 supports the tubular kovar elements '48 and 48 which are sealed into glass base 46 and have several functions. These members support the base blocks 22 and 22' for the collector electrodes No. 1 and No. 2. They also serve as output connections for the collector electrodes and for the direct current paths to the collector electrodes and are tubular for circulating a cooling medium through the collector electrodes. The `cooling circuit, per se, is not being claimed herein and details of the fluid circuit have been omitted. The collector electrodes No. I and No. 2 are shaped in the embodiment being described substantially as disclosed here and in the prior figures.

`An upper main element support 50 takes the form of a heavy copper ring with counter sunk bolt holes therein. Bolts 52 are passed therethrough and threaded into registered openings inthe main support base 40. The dynode structur-e described in detail above and illustrated in Figure 5 is clamped tightly between the elements '40 and 50. The output dynode adjacent the collectors may run at ground potential and in the embodiment being described it is so assumed. Then the discs I4, |8 on which the final dynodes are mounted are clamped tightly in contact with the main base ring 40 as shown in Figure 5. This is also illustrated in Figures 2 and 3 as described hereinafter where the final dynode is grounded. Three discs I4 only are shown in Figure 5 but more may be added. The rst disc I4 is insulated from the tube base and other tube elements by an insulating disc I6.

An upper base shell 54 is fastened to the ring 40 and extends up over the outer periphery of the ring 50 and is anged inwardly to cover the lower outward extending flange of a cup-like closure member 55. These joints are vacuum tight and the cup-like member 56 is sealed to a smaller cup-like member 58 through which the various` electrode leads other than the anode leads extend. These leads 62 are sealed through a glass top member 50 which is sealed to the top end of cup-like member 58. Corresponding leads 62' are sealed in a second glass member 64 fastened to a flanged ring member BB which is slid into the member 53. Metallic connector members 68 slip over the ends of leads B2 and 62' to complete these circuits and make it easy to assemble the electron discharge device elements.

As shown in Figure 11, the flanged member 66 which slides into the end cap 58 is supported by two U-shaped channel stands 'I0 and 10 cut away at 1| for clearance. These stands are flanged at the lower ends and bolted to the top main element 50 by bolts 14 to hold the elements 62', 64, 56` rigidly in alignment with the tube structure.

The electron gun assembly including the cathode, the deflecting electrodes and knife-like blocking electrode are supported by a rectangular-like member |00, Figures 5, 10, 11, 12, 13, 14 and 15 with one dimension much greater than the other to accommodate the flat, wide electron beam and elongated cathode, knife-like electrode, etc. (Figure 3). The member |00 is flanged outwardly at its lower end ||l| and spot welded to the apertured metal disc I4 used to support the steering electrodes a, a and this disc I4 is clamped tightly between main support members 40 and 50. The steering electrodes, deflecting electrodes B-,-C and aperture electrode may -all 8 operate at the same potential which is different than the potential at which the output dynodes operates. To obtain this operation the end |0| and disc I4 to which it is fastened is insulated from base ring 50 by a mica disc IB.

The open ended box-like member |00 is cut away at the upper portion at each end as shown at |02, Figures 13, 14 and 15, to accommodate the electron gun structure. The upper end of the cut away box member is flanged outwardly at |03 along its longest dimension to provide a support for the cathode and deflecting electrodes and knife edge blocking electrode. Two double offset aperture electrode members |04 and |04', supporting electrode structure described in detail hereinafter, extend into the rectangular can |00 and are fastened to the flanges |03 by bolts or spot welding at the points |06. These electrode support members |04 and |04' are assembled and the electrodes fastened thereto before they are placed in the box |00. The electron beam, emitted byv cathode |08, Figure 14, passes down through ofi-set members |04, |04 and toward the dynode elements. The cathode |08 is heated by filament wires |09. The cathode |08 is of considerable axial length as shown in Figures 12, 13 and 14 and is supported on metal rods ||2, spot welded at points ||4 to a U-shaped metal rod IIB mounted in ceramic beads I8. Rotation of the U-shaped rod is prevented by its shape. The ceramic beads ||8 are held in place by metal straps |22, spot welded to the top of the double off-set members |04 and |04'. The leads to the heating elements |00 are omitted in the sake of simplicity but may extend from adjacent ends of filaments |00 toward the connectors 62'. Then the remaining adjacent ends of filaments |09 are connected together. The deflecting electrodes may comprise metal or a metallic deposit on insulating material such as mical with connections thereto. In the drawings they are represented at |24 and |24. The double off-set members |04V and |04 have cut away portions leaving legs |28 and |26' to which the members |24 and |24 are fastened at |28 (Figure 12). In the sake of mechanical strength, the edges of the cut away portions are turned outwardly at |21 and |21', Figures 12 and 14. The sides of leg members |26 and |26 are treated in like manner at |29 and |29 to stien the structure. To further strengthen the structure, strap-like braces |3| and |3|' are spot Welded or otherwise fastened to portions |21 and |21' of the two off-set members |04 and |04 to hold them rigidly in the desired spaced relation. Strap members |33 and |33 serve a similar purpose for the legs |26 and |26' and also serve as a support for the knife edge electrode described hereinafter.

The off-set members |04 and |04' are fastened or strapped together at points |3| and |3|' and |33 and |33' and the electrodes mountedtherein before the structure is4 assembled in the rectangular can |00. Then the entire apparatus is dropped into the can |06 and spot welded as described above at points |06.

The relation of the electron multiplier electrode of my invention to the beam forming electrodes will now be described. This multiplier electrode comprises a plurality of dynodes eectively in layers when considered as traversing the path of the beam and in parallel when considered with respect to the electrons passing through the electrode assembly from the cathode to the collector electrodes, The separate elements of each group, for example, elements a, a and/or elements b, b and/or elements c, c', etc. are mounted in metallic disc-like rings M having rectangular apertures therein and the ele ments are built up in layers and laid in positions transverse to the beam path. The dynode stacks are then positioned between the members 40 and 5I] to be clamped in place. The cathode beam focussing and knife edge electrodes are also mounted in a member Nit fastened to an apertured disc-like member Ed which is clamped between members @c and 5t. Relative adjustment of the dynode and electron gun assembly is easily made and the structure after alignment is clamped tightly in place by means of bolts M.

My electron discharge device may be put to various uses in the electronic art. No attempt will be made to list allof such uses here. It may be used as an R. F. amplifier and in Figures 2 and 3 I have shown circuit connections for putting my novel tube to such use. In these basic diagrams I have included only the essential features. Variations will be obvious to those skilled in the art. In these figures the tube electrodes are numbered as in the prior figures. The cathode IUS may be indirectly heated by an IL-C. source. R. F. is applied by coupling transformer CT to the deilecting plates 22e-i215', D. C. potentials are applied as shown. The values of D. C. potentials given are merely by way of example and may be changed as desired to meet different tube electrode spacing, different uses, etc. In Figure 2, deflection sweeps the beam in a direction to cause it to pass back and forth from No. 1 to No. 2 collector and vice versa. The output then appears in the differential A.C`. circuit OT. In other words in Figure 2 the beam sweep is in a direction at right angles to the sweep of the beam in the embodiment of the following gures. This involves merely an appropriate change of the deflection elements H2L-|24 to set up the deflection force as desired. In both embodiments amplified R. F. is taken from the output coupling transformer OT. As stated above, the dynode stages operate at diiferent potential and are insulated from each other. The nal stage may operate at ground potential as shown in Figures 2 and 3 and its disc I4 is in contact with ring iii also conductively connected to ring 50, etc. The initial dynode stage may operate at the potential at which the knife edge electrode D-E, Figure 3, and aperture electrodes IM, Figures 2 and 3, operate and to permit such operation closure memmer i!) and the disc i4 to which it is fastened are insulated from main base ring 5U by an insulating disc I6 as shown in Figure 5.

From the foregoing description'it is obvious that I have provided new and improved electron discharge device means for multiplying electrons to an extent greater than possible heretofore and various novel electron dischargev device features and circuits which. take part in'provding increased electron multiplication and means for controlling the character of the electrons as multiplied. It is also clear that variations may be made in the apparatus and means of the embodiment shown without departing from the spirit of my inventions or set forth in the claims which follow.

I claim:

l. An electron multiplier comprising at least three spaced dynode elements, each element having two concave secondary electron emitting surfaces on opposite sides thereof, the dynode elebeing staggered so that secondary electrons released from two dynode elements fall on the secondary electron emitting surfaces of an intermediate dynode element.

2. An electron multiplier assembly comprising at least three spaced dynode elements, each element having two concave secondary electron emitting surfaces on opposite sides thereof, the dynode elements being staggered so that secondary electrons released from one element fall on secondary electron emitting surfaces of the remaining two dynode elements.

3. An electron multiplier structure comprising at least three rows of dynode elements, they dynode elements of the middle row each having two concave secondary electron emitting surfaces and being displaced with respect to the elements of the remaining rows so that electron flow takes place from the elements of the middle row to the elements of the other two rows.

fi. An electron multiplier as in claim l, wherein said dynode elements are interposed between a primary electron source and a collector electrode.

5. An electron multiplier as in claim 4, further including an electron focussing electrode positioned between said source and said dynode elements to guide primary electrons toward the secondary electron emitting surfaces of said two dynode elements.

6. An electron multiplier structure comprising at least three rows of dynode elements, the dynode elements of the middle row having two concave secondary electron emitting surfaces and being displaced with respect to the elements of the remaining rows so that electron flow takes place from the elements of the middle row to the elements of the other rows, means for feeding electrons to the dynode elements at one of said rows and a collector electrode for receiving multiplied electrons from the dynode elements at the other ends of said rows.

7. An electron multiplier structure including a plurality of rows of dynode elements each having two concave active electron releasing surfaces, the dynode elements in adjacent rows being displaced in position so that flow of electrons may take place between the curved active surfaces in adjacent rows, and an electron focussing electrode having two concave surfaces at the input end of at least one of said rows.

8. An electron multiplier structure including at least three rows of dynode elements, the elements of end rows having at least one active concave electron releasing surface facing the inner rows, the elements of the inner rows having two active concave electron releasing surfaces facing in opposite directions, and means for feeding electrons to be multiplied to the dynodes at adjacent ends of said rows.

9. An electron multiplier device including a plurality of rows of dynode elements each having two concave electron releasing surfaces, the dynode elements in adjacent rows being displaced in position along the length of the rows so that flow of electrons between rows takes place, means for feeding electrons to be multiplied to dynode elements at one end of said rows, and an electron collector electrode for receiving multiplied electrons from the dynode elements of the other ends of said rows.

10. An electrode structure comprising an apertured substantially non-emissive metallic disc and a plurality of elongated dynode elements each mounted across said aperture and each having at least one active concave electron releasing surface.

'11. An electrode structure comprising an apertured metallic disc and a plurality of dynode elements mounted in spaced relation across said aperture, certain of said elements having two substantially opposed concave surfaces for receiving electrons passing through said aperture.

12. An electron beam tube, comprising an electron multiplier electrode assembly including at least three rows of dynode elements, each row having a plurality of dynode elements including initial and final elements, an electron collector electrode comprising an active surface wherein channels are formed and means for mounting said electron multiplier electrode and electron collector electrode in iixed relation with portions of the final dynode elements of alternate rows positioned in said channels.

13. An electron discharge device comprising, in combination, an electron source, two electron collector electrodes in the path of emission from said source, a knife edge blocking electrode in a plane transverse to the said electron path, said knife edge blocking electrode comprising apertures in opposed quadrants of a circle having its origin substantially in the axis of the path of the electron beam when at rest and deflecting electrodes adjacent the path of said beam between the electron source and said knife edge blocking electrode.

14. An electron discharge device, comprising a source of electrons, an electron target electrode comprising a channeled active surface, and at least three rows of electron multiplier electrodes interposed between said source and said target electrode.

15. An electron discharge device, comprising a source of electrons for producing an electron stream along a predetermined path, an electron target electrode toward which the electrons are directed, three or more rows of electron multiplier electrodes interposed between said source and said target and electron stream deflecting electrodes on opposite sides of said path and between said source and said electron multiplier electrodes.

16. A beam tube comprising in combination, an apertured main support member, a closure member at one side thereof fastened thereto and including an insulating member, a target electrode supported by the insulating member and extending into said aperture, an electron multiplier electrode clamped to the other side of said support member and comprising in series dynode elements with the nal elements facing said target electrode in said aperture, an electron beam source mounted on the other side of said support member to feed electrons to the initial dynode elements, and a closure member fastened to the said other side of said main support member and enclosing said beam source.

17. A beam tube comprising, a metallic support member having an aperture formed therein, a closure member on one side thereof fastened thereto, Va target electrode supported by said closure member and insulated therefrom and extending into said aperture, said target electrode comprising an active surface wherein channels are formed, an electron beam source mounted on the other side of said support member for producing an electron beam and directing it toward said target electrode, an electron multiplier electrode positioned between said electron beam source and said target electrode, said electron multiplier electrode comprising a plurality of parallel rows of dynode elements with the final dynode elements of alternate rows interposed in said channels, delecting electrodes positioned between said beam source and the initial dynode elements of said parallel rows, and a closure member fastened to the other side of said main support member for enclosing said beam source, deflecting electrodes and multiplier electrodes.

18. A beam tube comprising, a metallic support member having an aperture formed therein, a closure member on one side thereof fastened thereto, a target electrode supported by said closure member and insulated therefrom and extending into said aperture, said target electrode comprising two active surfaces in each of which channels are formed, an electron beam source mounted on the other side of said support member for producing an electron beam and directing it toward said target electrode, an electron multiplier electrode structure positioned between said electron beam source and said target electrode, said electron multiplier electrode structure comprising a plurality of parallel rows of dynode elements with the final dynode elements of alternate rows interposed in said channels, deflecting electrodes positioned between said beam source and the initial dynode elements of said parallel rows, a knife edge blocking electrode between said source and said multiplier electrode structure, and a closure member fastened to the other Side of said main support member for enclosing said beam source, deecting electrodes, knife edge electrode and multiplier electrodes.

19. A beam tube comprising in combination, a metallic support member having an aperture formed therein, a closure member on one side thereof fastened thereto, a target electrode supported by said closure member and insulated therefrom and extending into said aperture, said target electrode comprising two active surfaces insulated each from the other, an electron beam source mounted on the other side of said support for producing a fiat, wide electron beam and directing it toward the active areas of said target electrode, an electron multiplier electrode structure positioned between said electron beam source and said target electrode, deecting electrodes between said beam source and said electron multiplier structure to sweep said beam over said active surfaces simultaneously, a knife edge blocking electrode between said deiiecting electrodes and said electron multiplier structure, said knife edge blocking electrode comprising Va member positioned across the path of the beam and having apertures in opposite quadrants of a circle, the center of which is on the beam axis vwhen at rest,l and a closure member fastened to the other side of said main support for enclosing said beam source, deecting electrodes, knife edge electrode and electron multiplier electrode.

20. A beam tube comprising in combination, a support member having an aperture formed f i, I

therein, a closure member on one side thereof fastened thereto, an electron beam source mounted on the other side of said support member for producing an electron beam and directing it toward said aperture, a target electrode supported by said rst named closure member and insulated therefrom and extending into said aperture in the path of said beam, said target electrode comprising two active surfaces insulated from each other, an electron multiplier structure positioned between said electron beam source and said target electrode, said electron multiplier electrode structure comprising dynode elements with initial elements in the path of said beam and iinal elements adjacent said active surfaces, deecting electrodes positioned between said beam source and the initial dynode elements and arranged to deect said beam back and forth between paths directed toward the respective surfaces and a closure member fastened to the other side of said main support member for enclosing said beam source, deiiecting electrodes and multiplier electrodes.

21. An electron multiplier tube including a target electrode, an electron beam source for directing a beam of electrons toward said target electrode along a predetermined path, electron beam deflecting means on opposite sides of said path, an electron multiplier structure comprising three or more rows of dynodes elements in parallel between said source and said target electrode, an envelope for said electrodes and connections through the wall of said envelope for applying operating potentials to said elec- A circuit coupled to said deecting electrodes and connections to groups of said dynode electrodes for applying thereto potentials which increase progressively by steps as the dynode element distance from said means increases.

23. La combination, an electron discharge device including two target electrodes insulated from each other', a differential output circuit connected to said target electrodes, a beam source for directing an electron beam toward said target electrodes, at least three rows of electron multiplier electrodes in parallel between said beam source and each of said target electrodes, beam deflecting electrodes adjacent the path between the beam source and target electrodes and an input circuit coupled differentially to said beam deiiecting electrodes.

24. An electron multiplier assembly comprising a plurality of electrode structures as claimed in claim 11 stacked in spaced relation with apertured insulating members between said discs.

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