US3395306A - Dynode structure for an electron multiplier device - Google Patents

Description

July 30, 968 D. COLES 3,395,306

DYNODE STRUCTURE FOR AN ELECTRON MULTIPLIER DEVICE Filed Jan. 17. 193-5 3 Sheets-Sheet 1 llllllll H u INVENTOR. DONALD K.COI'.ES BY Haw M ATTORNEYS July 30, 1 D. K. COLES 3,395,306

DYNODE STRUCTURE FOR AN ELECTRON MULTIPLIER DEVICE Filed Jan. 1'7. 1966 5 sheets-sheet INVENTOR. DONALD K .OOLES BYA MM/M A TTORNEYS y 30, 8 D. K. COLES 3,395,306

DYNODE STRUCTURE FOR AN ELECTRON MULTIPLIER DEVICE Filed Jan. 17. 1966 5 Sheets-Sheet 3 INVENTOR. DONALD K. coLes ar/M/M/M ATTORNEYS United States Patent DYNODE STRUCTURE FOR AN ELECTRON MULTIPLIER DEVICE Donald K. Coles, Fort Wayne, Ind., assignor to International Telephone and Telegraph Corporation, a corporation of Delaware Filed Jan. 17, 1966, Ser. No. 521,108 Claims. (Cl. 313-95) ABSTRACT OF THE DISCLOSURE An extended area dynode for an electron multiplier has a multiplicity of apertures formed of slatted elements separated by ribs to provide a self-supporting planar structure having a maximum electron emissive surface with a high degree of transmission through the apertures.

The present invention relates to electron multipliers and more particularly to improved extended area dynodes for both single-stage and multi-stage tubes.

A single-stage electron multiplier tube basically consists of a source of electrons, such as an electron gun or photocathode, a secondary emissive electrode, or dynode, and a collector electrode, or anode. These electrodes have potentials applied thereto which establish an electric field operative to cause impingement of primary electrons on the dynode and secondary electrons therefrom to be collected by the anode. A multi-st-age electron multiplier provides a cascade of dynodes with successively higher potentials such that secondary electrons born in one dynode impinge on and are multiplied by the succeeding dynode.

Among the several desiderata of an electron multiplier are the reduction of cost, reduction of electron transit time, and compactness of structure. The ability of a multistage tube to carry greater currents may be enhanced by closer spacing between dynodes, this permitting the use of higher values of axial field strength for a given potential difference between dynodes. The multiplier should be capable of high-speed operation; the time of response to an input signal is limited by the trajectory between the electron source and the anode, and in multistage tubes by the dynode spacing. Time-resolution capability and time-distortion of input pulses are of importance in some applications, such as when the multiplier is used in conjunction with a wide bandwidth optical communication system. One method by which time-resolution may be improved is the use of a fine structure of apertures in the dynodes, so that consecutive dynodes may be placed close together.

Enhancement of the operation of a multiplier tube with respect to the above-mentioned considerations may be obtained merely by taking a given tube and making it proportionately physically smaller. The venetian blind type of dynode has many advantages over other structures and will be more fully described below, but in the known designs a small slat size leads to mechanical weakness and lack of rigidity. For tubes of fairly large diameter, slats of the desired small size cannot be constructed without an unacceptable loss of dimensional stability. The Weiss form of dynode is so designed in an attempt to overcome this limitation by utilizing a fine-mesh screen of round wires woven together. Disadvantages of this structure are that, first, if the apertures of the dynode screen are large compared to the wire size, few electrons will strike it, and amplification is degraded; secondly, if the apertures are made small in relation to wire size, secondary electrons generated in the dynode may pass through the dynode to the next dynode only with difliculty, again degrading amplification.

3,395,306 Patented July 30, 1968 Furthermore, secondary electrons are emitted'from the dynode surface with a component of velocity perpendicular to the plane of the dynode in a direction opposite to that desired, and with a more or less random component of velocity parallel to the dynode surface, which operates to decrease resolution.

A primary object of the present invention, then, is to provide a dynode structure for an electron multiplier tube which is of fine mesh size, mechanically strong in relation to its size, and requires no mechanical support except at its edges.

Another object of the invention is to provide a dynode structure having a slat configuration which presents maximum dynode area for electron impingement yet permits a maximum degree of transmission of secondary electrons to the succeeding electrode.

The invention in its broader aspects provides an extended area dynode structure of planar, sheet-like shape. The dynode is provided with a multiplicity of apertures separated by reinforcing band or rib portions, the apertures being defined by a plurality of spaced slat elements, these elements having secondary emissive surfaces which extend transversely to the plane generally defined by the dynode. The slat elements are elongated and are arranged in end-to-end relation, the rib portions being interposed between the ends of adjacent slat elements and, further, the rib portions having dimensions extending parallel to the plane of the dynode. The slat elements are of a size which renders them relatively stiff and self-supporting, the sizes and number of the rib portions being adequate to hold the slat elements in fixed position relative to each other whereby the dynode element is rendered self-supporting while presenting forwardly a maximum degree of electron-emitting surface for a given total degree of openness.

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a front-end view of a single-stage electron multiplier tube embodying one form of a dynode according to the present invention;

FIG. 2 is a sectional view taken substantially along section line 22 of FIG. 1;

FIG. 3 is an enlarged, fragmentary front view of a portion of the dynode of FIGS. 1 and 3;

FIG. 4a is a section taken substantially along section line 44 of FIG. 3;

FIG. 4b is a section like FIG. 4a but showing a slightly different embodiment of this invention;

FIG. 5 is a fragmentary front view, like FIG. 3, of another embodiment of this invention;

FIG. 6 is a sectional view taken substantially along section line 6--6 of FIG. 5;

FIG. 7 is a sectional view taken substantially along section line 7-7 of FIG. 5;

FIG. 8 is a fragmentary front view, like FIG. 3, of still another embodiment of this invention;

FIG. 9 is a cross-section taken substantially along section line 99 of FIG. 8; and

FIG. 10 is a section taken along line 10-10 of FIG. 8.

Referring more particularly to FIGS. 1 and 2 of the drawings, an evacuated glass envelope 1 has a fiat window 2 provided on its inner surface with an extended area, substantially transparent photocathode 3. A ring terminal 4 mounts the window 2 in the end of the tube and serves as an electrode for applying a potential to the photocathode 3. An extended area, disc-like dynode, indicated generally by the numeral 5, is fixedly positioned in parallel spaced relation with respect to the window 2 and is secured around its circumference to a ring electrode 6, which extends through the envelope 1. A fine wire mesh 7 of high electron-transmissivity and disc-like in shape is positioned a small distance in front of the dynode 5 and is clamped between, at the edges thereof, two conductive mounting rings 8 and 9. The ring 8 conductively fixedly secures the dynode 5 to the electrode 6 and maintains the mesh 7 in parallel spaced relation with and at the same electrical potential as the dynode 5. The advantages of using this mesh 7 are more fully described in US. Patent No. 2,871,368. The electrons secondarily emitted by the dynode 5 are collected by a planar anode 10. A conductive post 11 in the end of the envelope 1 serves both as mechanical support and electrical contact for the anode 10.

Referring to FIGS. 2, 3 and 4, the preferred, dynode embodiment of this invention is easily and inexpensively manufactured from a thin sheet of beryllium-copper or silver-magnesium by stamping and forming. The dynode configuration resembles a venetian blind in that it is provided with a multiplicity of elongated slats 12 arranged in parallel, spaced relation and also in columns, as indicated in FIG. 1 by the numerals 13, 14 and 15, respectively. Separating the columns are flat bands or rib portions 16 which are straight and parallel to each other. The slats 12, as shown more clearly in FIG. 3, in the various rows are arranged in end-to-end relation and are fiat, as shown more clearly in FIG. 4a. Additionally, the slats are turned at an angle of from 35 to 60 with respect to the plane of the dynode as defined by the bands 16, this plane being positioned midway between the front and rear edges of the slats 12 as shown more clearly in FIG. 4a. The spaces 17 between the individual slats 12 constitute the dynode apertures which admit primary electrons for impingement against the forwardly or cathode-facing surfaces of the slats 12 and permit the escape of the secondaries therefrom to the anode 10. As shown in FIG. 1, there are a multiplicity of the bands 16 spaced across the diameter of the tube 1 with the slats 12 being of minimum size consistent with the necessary strength and rigidity in the finished dynode. Preferably, and in order to obtain the maximum advantages inherent in this invention, the slats 12 should be of minimum width so as to provide as large a number as possible of the individual slats 12 and elongated apertures 17 therebetween. The bands 16 provide reinforcement for the dynode, and the slats 12 are of such size as to maintain the shape thereof when mounted in the tube 1 as previously described. A better understanding of the purpose of the bands 16 may be realized by assuming that the slats 12 extend for the entire diameter across the dynode without any reinforcement therebetween, these slats being so narrow and thin that they would sag under the weight thereof. By using slats of the same size and providing the bands or ribs 16 spaced at frequent intervals across the dynode diameter, it is seen that the dynode will present a sufiiciently strong and rigid structure so as to withstand the forces of the electric fields within the tube as well as ordinary shock and vibration.

Referring again to FIG. 4a, the numeral 18 indicates the cathode side or front of the dynode. When the dynode is viewed from this side, it will be noted that the structure is somewhat transparent. In order to present a solid projected area forwardly, reference may be had to FIG. 417, wherein it is shown that the bands 16 are provided with V-shaped crimps 19 which move the adjacent slats 12 (of FIG. 4a) closer together. Moved sutficiently close together, the dynode will be opaque as viewed from about the position of the numeral 18a.

Typical, although not minimum, dimensions of such a dynode having a diameter of about two inches may be a sheet thickness of .002 inch, :1 slat spacing of .020 inch, a spacing between bands 16 of about .200 inch, a slat width of about .020 inch, and a slat angle of about 45 with respect to the plane of the bands 16. Although the bands 16 may be reinforced (for instance, by welding a wire along the lengths thereof or by crimping them into a V-shape in cross-section), it has been found that the bands 16 alone provide more than adequate strength to prevent the slats 12 from bending. Both of the slat configurations of FIGS. 4a and 4b, respectively, present to the cathode 3 a relatively large dynode area available for secondary emission, the design of FIG. 4b presenting the most. It will be noted that while this design provides a relatively opaque dynode facing the cathode, still relatively large apertures 17 for electrons to pass through the dynode are present. Both of the conditions of the large percentage of dynode area and the relatively large apertures lead to the achievement of a multiplier tube having a relatively high gain. Considering the operation of the dynode thus far described in connection with the tube of FIGS. 1 and 2, potentials are applied to the cathode, dynode and anode which render the dynode sufficiently positive to cause electrons emitted by the cathode to impact the dynode with sufficient velocity to dislodge secondaries. Considering that the cathode 3 is positioned at the location identified by the numeral 18 in FIG. 4a, electrons emitted along the lines of the arrows 20 will impact the upper surfaces of the slates 12 and will dislodge secondaries which are drawn through the apertures 17 and collected by the anode 10.

Other dynodes structures may also give the advantages of small aperture size and a self-supporting configuration. Some possible variations are shown in FIGS. 5 through 10 and will now be described. In FIGS. 5, 6 and 7 is illustrated a second embodiment of this invention which may be fabricated from flat sheet stock the same as the dynode 5 of FIGS. 1 and 2. The sheet stock is lanced along straight, interrupted lines identified by the numeral 21 which are spaced apart and parallel. Also, these cuts are staggered as shown to provide ribs or hands 16a correspondingly stepped. This provides individual slats 22 in end-to-end relation spaced apart by the bands the individual slats being bent along parallel fold lines 23 and 24 as shown more clearly in FIGS. 5 and 6. Thus, laterally adjacent slats 22, as indicated by the two numerals 22a and 22b, are deliberately separated in parallelism to provide the elongated apertures 25 therebetween. As shown in FIG. 6, these apertures have approximately the shape of parallelograms.

The metal is displaced to a sufiicient extent that when the dynode is mounted in the tube of FIG. 2, the individual slats 22 will be set at an angle of approximately 45 with respect to a plane parallel to the cathode 3.

FIG. 7 indicates this angular relationship, the primary electrons travelling along the path 20a impacting the surface of one of the slats 22 and ejecting secondaries along the path of the arrow 26 toward the anode.

A still further embodiment of this invention is illustrated in FIGS. 8, 9 and 10 which, in configuration corresponds substantially identically to so-called expanded metal. A sheet 27 of metal is lanced along the lines 28 at spaced intervals and then expanded to provide the bent slats 29 which project both forwardly and rearwardly, as shown more clearly in FIGS. 9 and 10, from the intervening rib portions 30. The rib portions 30 separate the spaces between the cuts 28 in the sheet metal. As shown in FIG. 10, the slats 29 are separated to provide apertures 31, of substantially diamond shape. As is true of the preceding embodiments, the dynode defines a general plane and the slats 29 are set at an angle of something in the order of 45 with respect to this plane.

As previously explained, consistent with necessary strength and rigidity, all of the slats, rib portions and apertures are made as small as possible. Sizes in the orders explained hereinbefore, which are exceedingly small as compared to similar, prior art dynodes, while presenting a maximum surface area for primary electron impact and maximum openness for the escape of secondaries are all made possible by the basic concept of this invention involving the use of slat elements separated by reinforcing rib portions. It will be apparent to persons skilled in the are that the slat shapes may be varied from those disclosed in order to obtain different electric field configurations, secondary emission gains and other performance characteristics.

Dynodes made according to this invention are of exceedingly fine mesh and thin dimension. By reason of the thinness, several dynodes may be stacked in an array in accordance with conventional practice and positioned quite closely together. By reason of this closer spacing, space charge limitations and electron transit times may be materially reduced, thereby permitting the development of output currents of appreciable proportions and rapid rise times. Also by reason of the closeness of spacing, a multiplier tube may be made smaller and more compact.

While there have been described above the principles of this invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of the invention.

What is claimed is:

1. For use in an electron discharge device, an extended area dynode comprising a planar sheet-like element having a multiplicity of apertures separated by reinforcing rib portions, said apertures being defined by a plurality of adjacent spaced slat elements having secondary emitting surfaces which face a common forward direction and extend transversely to the plane generally defined by said sheet-like element, said slat elements being elongated and arranged in end-to-end relation, said rib portions being interposed between the ends of adjacent slat elements and extending along the plane of said sheet-like element, said slat elements being of a size which renders them relatively stiff and self-supporting, the sizes and number of said rib portions being adequate to hold said slat elements in fixed position relative to each other, whereby said sheet-like element is rendered self-supporting while presenting forwardly a maximum area of secondary-emitting surface for a given total degree of transmission of secondary electrons through the apertures.

-2. The dynode of claim 1 wherein said sheet-like ele ment is of secondary emissive material, said slat surfaces having portions which lie in substantially parallel spaced apart planes, said slat surfaces further being arranged in a configuration which presents a substantially non-perforate surface on said sheet-like element when viewed along a straight path normal to the parallel portions of said slat surfaces and a perforate surface when viewed along a path normal to the general plane of said sheet-like element.

3. The dynode of claim 2 wherein said rib portions and said slat elements are integrally joined and have thicknesses which are equal.

4. The dynode of claim 3 wherein said slat elements are fiat and parallel to each other, said rib portions being elongated, spaced apart and parallel and extending at right angles to the length dimensions of said slat elements, said sheet-like element having a perimetrical edge, said rib portions extending substantially from edge-to-edge of said sheet-like element.

5. The dynode of claim 4 wherein said slat elements are at an angle of about forty-five degrees (45) to the general plane of said sheet-like element.

6. The dynode of claim 3 wherein elongated portions of said slat elements are fiat and lie in parallel planes, said slat elements being arranged in a plurality of columns which are parallel to each other, said rib portions being elongated, spaced apart and parallel and extending at an acute angle with respect to the length dimensions of said slat elements, said rib portions defining planes which are parallel to each other and transverse to the planes of the elongated portions of said slat elements, the planes of both said rib portions and said elongated slat portions being transverse to the general plane of said sheet-like element.

7. The dynode of claim 6 wherein said rib portions have a stepped configuration and perimeters of said apertures define planes which are parallel to each other and normal to the planes of the elongated portions of said slat elements, said aperture-perimeters further having the shape of a parallelogram.

8. The dynode of claim 3 wherein the sheet-like element has diamond shaped apertures.

9. The dynode of claim 1 in combination with a cathode and an anode, said cathode and anode being planar and in parallel spaced relation with respect to said sheetlike element, and said sheet-like element being disposed between said cathode and anode.

10. The dynode of claim 3 wherein said slat elements are close enough together to present a substantially closed projected area when viewed along a path normal to the general plane of said sheet-like element.

References Cited UNITED STATES PATENTS 3,039,016 6/1962 Thomson et al. 313- 3,253,182 5/1966 Marchet 313- X JAMES W. LAWRENCE, Primary Examiner. P. C. DEMEO, Assistant Examiner.

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