US2245614A - Electron discharge device - Google Patents

Description

Patented June 17, 1941 ELECTRON DISCHARGE DEVICE William Shockley, New York, N. Y., assigner to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application November 26, 1937, Serial No. 176,565

1S Claims. Y (Cl. Z50-175) 'Ihis invention relates -to electron discharge devices and more particularly to such devices generally known as electron multipliers.

In multistage electron multipliershaving aseries of auxiliaryfor secondary cathodes successively arranged between a primary cathode and an anode or collector electrode, a stream of secondary electrons emanates from each of the auxiliary cathodes and som'e of these electrons flow to and impinge upon the next succeedingelectrode. Because of a number of factors, among which are the difference in the velocities of the secondary electrons emanating from. the auxiliary cathodes and characteristics inherent in known structures, a divergence of these secondary electron streams occurs. As a result, some ofthe electrons impinge upon other than desi-red portions of the next succeeding electrode and other of these electrons may traverse such paths that they do not flow to or impinge upon the desired electrode. Consequently, a relatively low operating eiliciencyA and variable characteristics obtain. Y

One general object of this invention is to improve the operating efficiency and characteristics of multistage electron multipliers.

More specifically, an object of this invention is to obtain substantial convergence of the secondary electron streams emanating from the secondary or auxiliary cathodes in electron multipliers.

Another object of this invention is to obviate the use of magnetic focussing or concentrating fields in electron vmultipliers A further object of this invention is to segregate effectively each of the secondary or auxiliary cathodes in a multistage electron multiplier from the field of the preceding electrode so that the field at the emitting surface of each of the auxiliary cathodes does not include a component toward this surface.

In accordance with one feature of this invention, the electrodes, particularly the auxiliary electrodes or cathodes, in a multistage electron multiplier are so constructed and arranged that the various velectron streams emanating from the cathodes are confined to restricted paths and are substantially converged upon desired portions of the next succeeding electrode.

In accordance with another feature of this invention, reticulated members or rscreens are provided in cooperative relation with thev secondary or auxiliary cathodes, the reticulated members or screens serving to prevent the field of each cathode from producing a component toward the secondary electron emitting surface of a succeeding auxiliaryor secondary cathode. The invention. and the foregoing and other features thereof will be understood more clearly and fully from the following detailed description with reference to the accompanying drawing, in

which: l y

Fig. 1 is an elevational View in perspective of an electron multiplier illustrative of one embodiment of this invention, a portion of the enclosing. vessel and of the electrode assembly being brokenv away to show'elements of the multiplier more clearly;

Fig. 2 Vis a side View, partly in section, of the electron multiplier shown in Fig. 1;

Fig, Bis an enlarged view in perspective illus-v trating the construction of the auxiliary or secondary cathodes embodied in the electron multiplier shown in Figs. 1 and 2;

Fig. l is av circuit diagram illustrating the utilization of .an electron multiplier constructed in accordance with thisinvention in an amplifying system; and

Fig. 5 is a ,diagrammatic view illustrating the form and arrangement of kthe electrodes in an electron multiplier illustrative of another embodiment 4of this invention. v

Referring now to the drawing, the electron multiplier illustrated in Figs. 1 and 2 comprises an enclosing Vessel I0 having a reducedf domey portion II at one end and an inwardly extending stem at the other end, the stem terminating in a press I2 from which ,a unitary electrode assembly is supported. Theelectrode assembly includes a U-shaped insulating frame having a pairof parallel arms or uprights I3, which may be, for example, mica strips, joined and spaced at one endfby an insulating disc I4, which also may .be of mica. The disc I4 is provided with parallel slots into which integral tongues I5 of the arms or uprights extend and are frictionally fitted.

lMounted upon the insulating frame I3, I 4 are a I primary cathode I6, a'collector electrode or anode I1, and a plurality of auxiliary or secondary cathodes |81 to I86 inclusive.' As shown clearly in Fig.A 2, the various electrodes are arranged in staggered relation and in #two rows,vone row including the primary cathode I6 and the secondary or auxiliary cathodes I82, I84 and |86, and the other row including the secondary or aux iliary cathodes |81, |83 and I85 and the anode or collector electrode l1.

The primary cathode I6 is in theform of la metallic frame fabricated, for example, of a strip or strips of nickel or silver, and is supported at an angle, for example, 45 degrees to the longitudinal axis of the vessel I by a pair of rigid wires I9 secured thereto and extending between and through the arms or uprights I3. Electrical connection to the cathode I6 may be established through a rigid metallic rod or support 2D embedded in the press I2, connected to one of the wires I9 and afxed to the disc I 4 as by an eyelet 2|. The inner surfaces, and preferably only the inner surface of the wall 22 of the cathode I B may be coated with a photoelectric material. For example, if the cathode is of nickel, the inner surfaces thereof for only the inner surface of the wall 22 may be coated with beryllium. Alternatively, if the cathode or the wall 22 thereof is of silver, the inner surfaces, or only the inner surface of the wall 22, may be treated to form a photoelectrically active coating or matrix including silver, cacsium oxide and somev free caesium.

As shown clearly in Fig. 3, each of the auxiliary or secondary cathodes I8 is in the form of a rectangular box, which may be fabricated of metal sheets, for example, nickel or silver, having a solid -base 23, a solid wall 24 at substantially right anglesto the base 23, end Walls or field plates 40, an open side 25 and an open top. Secured to each of the secondary or auxiliary cathodes I8 are a pair of rigid metallic supports or Wires 26 which extend between, and are fitted in apertures in the insulating uprights or arms I3. The supports or wires 26 mount the cathodes I8, with the base 23y of each at equal angles, for example, degrees, to the longitudinal axis of the Venclosing vessel I0. Electrical connection to the secondary cathodes I8 may be establishedthrough metallic rods or uprights 21 extending through the disc I4 and connected at one end to the Wires 26 and at the other end to leading conductors 28 embedded in the press I2. 'Ihe inner surfaces of the base and walls of each :of the cathodes I8, preferably only the inner surface of the base 23, are treated so that they are rendered capable of emitting relatively large secondary electron currents. For example, these surfaces may be treated to form a coating or matrix Vthereon of silver, c'aesium oxide and free caesium. Alternatively, these surfaces m-ay be sensitized with beryllium.

As shown clearly in Fig. 4, the auxiliary or secondary cathodes |8are mounted so that the open side 25 of each of these cathodes is opposite the base 23 of the nextsucceeding secondary or auxiliary cathode and the base 23 lof each of the secondary cathodes *|82 to I8 is lat substantially right angles to the base of the next preceding secondary cathode. The ybase`23 of the auxiliary or secondary cathode I81 is at substantially right anglesto the wall 22 ofthe primary cathode I6.

The top of each ofthe secondary or auxiliary cathodes I8 has extending thereacross a metallic gridor screen which may be composed oi a plurality of thin parallel wires 29 secured at their ends to the su-pportsor rods 26, as lby welding.

The anode or collector electrode I'I may be a metallic box, for example, of sheet nickel, having an `open top opposite the grid or screen 29 of the secondary orA auxiliary cathode |86 and having its base at an angle, for example, substantially 90 degrees, to the base 23 of the cathode |86. Rigid metallic wires or rods 30 secured to the sides of the anode and having their ends tted in apertures in the arms or uprights I3 mount the anode upon the insulating frame I3, I4. Electrical connection to the anode or collector electrode may be established through a leadingin conductor 3| connected to one of the wires or rods 38, embedded in the press I2, and aflixed to the disc I4 as by an eyelet 32. The top of the anode or collector electrode I'I may be provided with 'a grid or screen 33, which may be composed of thin parallel wires afixed at their ends to the Wires or -rods 30.

During operation of the electron multiplier each of the secondary or auxiliary cathodes I8 is maintained at a positive potential with respect to the next preceding cathode. For example, the secondary cathode I81 may Abe maintained at a potential of the order of volts :positive with respect to the primary cathode I6 and each of the other secondary or auxiliary cathodes I8 may be maintained at a potential of the order of 100 volts positive with respect to the next preceding one. As shown in Fig. 4, the various potentials for the cathodes Vmay be obtained from -a ypotentiometer or voltage divider including a resistance 34 having a source, such as a rectifier 35, connected to the ends thereof, the cathodes being connected to equally spaced taps on the resistance 34. The anode may be operated at a potential of the order of 100 volts positive with respect to the secondary cathode |86, the potential being obtained from a source, such as battery 36. Y

The primary cathode I6 may be activated or energized by focussing a light beam, indicated by the line L in Fig. 4,' emanating from a suitable source 31 of light of variable intensity, upon the inner surface of the wall 22. When the primary cathode I6 is thus energizedor activated, `photoelectrons are emitted from the inner surface of the wall 22 and are attracted toward the grid or screen 29 of the secondary or auxiliary cathode I81 because :of .the potential upon this secondary cathode. Most of these electrons pass through the grid or screen and impinge uponthe base 23 of theA secondary cathode |81, the trajectory thereof being -rep-resented by the arrow in Fig. 4. inasmuch as the inner surface ofthe base 23 of the cathode I81 is sensitized as described heretofore, the impinging photoele'ctrons will cause the emission of secondary electrons from this base 23, the secondary electron current being several times as great as the photoelectric current. Consequently', in effect, an electron multiplication and hence an ampliiication of the primary or initial current is obtained.

- The secondary electrons emanating from the auxiliary or secondary cathode |81, under the influence of the potential upon the auxiliary or secondary cathode |82, pass through'the grid or screen 29 of the latter cathode, as indicated by the arrow in Fig. 4, and impinge upon the base 23 of this cathode to cause the emission of other secondary electrons therefrom. The secondary electron current thus produced is several times as great a-s the current composed of the impinging electrons so that -a further amplification of the initial electron current is obtained.

This phenomenon is repeated at each of the succeeding secondary or auxiliary cathodes at each of which "a further electron multiplication and hence effective amplification of the initial current, occurs. The secondary electrons emanating `from the secondary or auxiliary cathode Ifi flow to the anode or collector electrode I'I and constitute the output current ofthe electron multiplier.

y istics are obtained. v f

trons is substantially prevented. The end"walls 40 of the severalvcathod'es' 's'erve asrfleldlplates and conne thefelectronlstreams laterally,'.and

the solid sides 2li-'of the auxiliary orvse'condary cathodesl i8 constitute ybaille members. Which Aassist in converging 'the I' electron streams so that they 'are confined-v and'are directed 'to only the next succeeding electrode. Henceja relatively high efficiency and" stable operating character- Each' `of' the grids or 'screens 129,1 being at? the same potential `as 'the corresponding cathode, screens the corresponding base 23 from the 'adjacent cathodes and vtherebyfprevents the field Of vvthe adjacent cathodes,"particularly the adj-ar cent cathode in thesamerow,"fromproducing a component 'towardthe'baseywhich Would materially hinder or prevent the emission-of 'seccndary electrons therefrom.

It will' be noted vthat in electron multipliers constructed 'in' accordancewith' this -invention the electrons may `be acted-upon only by electrostatic elds and vhighlydesirablt-i convergence of the electron streams isr effected without'the use of magnetic fields. v Hence, suchznultipliers may be utilized satisfactorily in instances Where magnetic fields are objectionable For example,de vices constructedV in accordance Withthis invention may utilize a thermionic cathode, the electron lcurrent ,from which, 'not being Vdistorted by'a magnetic field, maybe controlled readily in accordance With a signal, by -a control grid mounted adjacent the ,primary cathodel Furthermore, uctuations in over-all voltages applied to the electrodesdo not affect the focussing properties of the electrodes.

In the embodiment of this invention illustrated in Fig. 5, the various electrodes, which may be of the same form and construction as the electrodes in the embodiment shown in Figs. 1 and 2, are arranged in somewhat honeycomb fashion so that the dimensions of the multiplier are relatively small and a compact structure is obtained. The multiplier may be connected in circuit and operated in the same manner as that shown in Figs. 1 and 2.

Although specific embodiments of this invention have been shown and described, it will be understood, of course, that various modifications may be made therein Without departing from the scope and spirit of this invention as defined in the appended claims. l

What is claimed is: y

1. An elec-tron multiplier comprising a primary cathode, an auxiliary cathode in cooperative relation with said primary cathode and having an emissive portion facing toward said primary cathode, a second auxiliary cathode in cooperative relation with said rst auxiliary cathode and having an emissive portion at substantially right angles to said rst emissive'portion, and a collector electrode -in cooperative relation with said second auxiliary cathode, said emissive portions being substantially plane and said second auxiliary cathode being offset diagonally with respect to said first auxiliary electrode.

2. An electron multiplier in accordance with claim 1 comprising means integral with said primary cathode and means integral With each of said auxiliary cathodes for confining the electrons emitted from each of said cathodes to restricted paths toward-the electrode in cooperativev relation therewith. r Y

3. Ani electron multiplier lin accordance with claim 1 comprising field platesat opposite sides of saidemissive portions of said auxiliary cathodes, and 'a plurality of baiilemembers, one for each of lsaidv portions, each extending fromthe corresponding one of said portions toWard'the preceding cathode. f

4; An electron multiplier comprising a pri- ;marycathode having a substantially plane electron-emitting portion, 'an auxiliary electrode having-"a substantially' plane 'secondary electron emitting surface facing toward, diagonally offset-'With respect to, and at-right angles to said portion, aV secon-d auxiliary electrode having a substantially VVplane secondary electron emitting surface"facing" toward, diagonally offset with respect to', andffat substantially right angles to saidfr'st surface',and a collector electrode in cooperative relatio'nfwith said-second surface.

v5. An Aelectron multiplier in accordance with claim 4 comprising kmeans electrically integral with saidlauxiliary electrodes and at opposite ends-ofsaid rsurfaces for confining the' electron streams emanating from said-surfaces'. v

' 6.'An` electrn multiplier 'in' accordance with claim 4 comprising a baille member extending from the emitting surface of each of said-fauxiliary cathodes, at an, angle thereto and toward the preceding cathode.' 7i electron'multiplier in accordance With claim 4 comprising field plates at 'opposite ends' of said surfacesfand a baffle member electrically integral with eachv of said 'auxiliary cathodes extending from` the emitting surface thereof and to'vvardl the preceding cathode.v

8.3Anv electron multiplier comprising a pri-l m-ary cathode, a collector electrode, a plurality of superposed, electrically separate substantially parallel plate members having corresponding surfaces thereof coated with a secondary electron emissive material, and a plurality of other superposed substantially parallel plate members in staggered relation with said rst plate members and at substantially right angles thereto, each of said other plate members having the surface thereof toward said first plate members coated with a secondary electron emissive material.

9.' An electron multiplier in accordance With claim 8 comprising bailie members electrically integral with said first plate members and substantially parallel to said other plate members.

10. An electron multiplier in accordance with claim 8 comprising a plurality of baie members each electrically integral with a corresponding one of said first and said other plate members, the bailie members integral with said first plate members being substantially parallel to said other plate members, and the baffle members integral with said other plate members being substantially parallel to said first plate members.

11. An electron multiplierv comprising a primary cathode, a collector electrode, a plurality of electrically separate auxiliary electrodes each having a substantially plane secondary electron emissive portion, and an equal number of other auxiliary electrodes in staggered relation With said first auxiliary electrodes and each having a substantially plane secondary electron emissive portion in cooperative relation with and at substantially right angles to the emissive portion of a corresponding one of said iirst auxiliary electrodes.

1.2. An electron multiplier comprising a primary cathode, a collector electrode, and a pair of rows of successively mounted auxiliary electrodes between said primary cathode and said collector elect-rode, the electrodes in each of said rows being in staggered relation with the electrodes in the other of said rows, and each of said auxiliary electrodes including a secondary electron emissive portion and a substantially plane baffle portion extending from one edge of the electron emissive portion and toward the opposite row, both said portions of said auxiliary electrodes being oblique with respect to the corresponding portion of the next preceding electrodc.

13. An electron multiplier comprising a primary cathode, a collector electrode, a plurality of successively disposed auxiliary electrodes between said primary cathode and said collector electrode, each having a secondary electron emissive surface, the secondary electron emissive surface of each of said auxiliary electrodes except the auxiliary electrode nearest said primary cathode being oblique to the emissive surface of the next preceding auxiliary electrode, and ret-iculated screen members between the emissive surfaces of successive auxiliary electrodes and each overlying one of said surfaces, each screen member being electrically integral with a corresponding one of said auxiliary electrodes.

14. An electron multiplier comprising a primary cathode, a collector electrode, and a plurality of auxiliary electrodes mounted succesively in staggered relation between said primary cathode and said collector electrode, each of said auxiliary electrodes having a secondary electron emissive portion, a baille member extending toward the preceding electrode and a grid portion opposite said first portion, the electron emissive portions of successive auxiliary electrodes being oblique to one another.

l5. An electron multiplier comprising a primary cathode, a collector electrode, and a plurality of auxiliary electrodes mounted successively in staggered relation between said cathode and said collector electrode, each of said auxiliary electrodes including a portion adapted to emit secondary electrons, eld members at opposite ends of said portion, a baiile member extending from said portion and at an. angle thereto toward the preceding electrode, and av grid extending from said baffle member and opposite said portion.

16. An electron multiplier in accordance with claim 15 wherein the emissive portions of alternate auxiliary electrodes are substantially parallel and the emissive portions of successive electrodes are at substantially right angles to one another.

17. An electron multiplier comprising a unitary cathode structure including a secondary electron emissive member and a reticulated member spaced from, overlying and substantially parallel to the emissive surface of said secondary electron emissive member and electrically integral therewith.

Y 18. An electron multiplier comprising a unitary cathode structure including a plate member having a secondary electron emissive surface, electron coniining iield plates extending from two opposite edges of said emissive surface, a. baille extending from another edge of said surface land at an angle thereto, and a screen overlying said emissive surface.

WILLIAM SHOCKLEY.

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