US3128408A

US3128408A - Electron multiplier

Info

Publication number: US3128408A
Application number: US23574A
Authority: US
Inventors: George W Goodrich; William C Wiley
Original assignee: Bendix Corp
Current assignee: Bendix Corp
Priority date: 1958-09-02
Filing date: 1960-04-20
Publication date: 1964-04-07
Anticipated expiration: 1981-04-07

Description

April 7, 1964 G. w. GOODRICH ETAL 3,128,408

ELECTRON MULTIPLIER Filed April 20, 1960 3 Sheets-Sheet 1 POWER SUPPLY 26 CATHODE 22 .jli III...

ANODE I ANooE CATHODE FIG- 2' ANODE/ exrnoos FIG- 3 INVENTOR.

GEORGE W. GOODRICH WILLIAM C. WILEY ATT NEY April 7, 1964 G. w. GOODRICH ETAL 3,128,408

ELECTRON MULTIPLIER Filed April 20, 1960 3 Sheets-Sheet 2 POWER PHOTOCATHODE POWER SUPPLY WAFER OF SECONDARY INVENI'OIZS. GEORGE W. GOODRKH WILLIAM C. WILEY Ap 1964 G. w. GOODRICH ETAL 3,128,408

ELECTRON MULTIPLIER Filed April 20, 1960 5 Sheets-Sheec- 5 POWER SUPPLY FIG. 7

POWER SUPPLY PHOTQCATHODE 8 INVENTOR. GEORGE w. GOODRICH y WILLIAM G. WiLEY Mia/9 ATTORNEY United States Patent 3,128,408 ELEQTRON MULTIPLIER George W. Goodrich, Oak Park, and William C. Wiley,

Northviile, Mich, assignors to The Bendix Corporation, a corporation of Delaware Filed Apr. 20, 1960, Ser. No. 23,574 21 Claims. (Cl. 313-103) This invention relates to a new type multiplier or light intensifier. This is a continuation in part of our copending application filed September 2, 1958, Serial Number 758, 425, entitled Electron Multiplier, now abandoned. In accordance with the invention, a region defined by a secondary emissive surface is provided with an electric field in a direction to accelerate electrons or other charged particles or photons through the region and to permit the release of secondary electrons when electrons strike any part of the emission surface. The multiplier is very simple and inexpensive to construct.

An object of this invention is to provide a new type electron multiplier or light intensifier.

Other objects and advantages will become apparent from the following detailed description and from the appended drawings and claims.

In the drawings:

FIGURE 1 is a perspective view, partly in block form, schematically illustrating an electron multiplier constituting one embodiment of this invention.

FIGURE 2 is an enlarged sectional view, illustrating the electric field produced in the multiplier shown in FIGURE 1.

FIGURE 3 is an enlarged sectional view illustrating the operation of the multiplier in FIGURE 1.

FIGURE 4 shows how a plurality of multipliers of the type shown in FIGURE 1 may be arranged to intensity a light image.

FIGURES 5 and 6 show another type light intensifier incorporating applicants invention.

FIGURES 7 and 8 illustrate different embodiments of applicants multiplier.

In FIGURE 1, an electron multiplier generally indicated at 16 is suitably supported in an air evacuated envelope 12. The multiplier 10 consists of a straight tube 14 of insulating material, such as glass, coated on its entire inside surface with a conductive coating 16. The conductive coating 16 is of uniform thickness throughout and is made of a secondary electron emissive material having a relatively high resistance, such as a tin oxide or carbon compound. The diameter of the tube 14 is relatively small compared to its length.

A source for emitting an incoming signal of electrons, such as a cathode 13 is positioned at one end of the multipler 10 to introduce electrons into the region 20 defined by the coating 16. An anode plate 22 is positioned at the other end of the multiplier 10 to receive any electrons emerging from the region 20. The anode 22 is connected through a resistance 24 to a power supply 26 which applies a constant voltage such as +1700 volts to the anode. A constant voltage, such as -1700 volts, is applied to the cathode 18 from the power supply 26, so that the anode to cathode voltage is 3400 volts.

A constant voltage, such as 1500 volts, is applied to one end of the coatig 16 adjacent to the cathode 18 and a constant voltage, such as +1500 volts, is applied to the other end of the coating from the power supply 26 to provide 3000 volts across the multiplier tube 10 and produce a current flow through the coating. The amount of current flow is relatively small because of the high resistance of the coating 16. This current flow results in a uniform voltage drop per unit distance across the surface of the coating 16 and also results in an electric field 21, substantially parallel to the surface of the coating 16, extending through the region 20 as illustrated in FIGURE 2. As will be appreciated by those skilled in the art, a uniform electric field accompanies a uniform voltage drop. A uniform electric field is a field that has field vectors of the same direction and magnitude throughout the field and in the embodiments shown, the field vectors are of the same magnitude and are all parallel to the surface of emission.

Electrons emitted by the cathode 18, will on the average have an initial velocity component normal to the axis of the tube 14. Because of this initial normal velocity, the electrons entering the region 20 will move towards the surface of the coating 16 and at the same time the electrons will be accelerated in the direction of the anode 2.2 by the electric field in the region. After traveling a certain distance in the region 20, the electrons will strike the surface of the coating 16. For example, some electrons may follow path 28 and other electrons may follow path 30 to strike the coating 16 as illustrated in FIGURE 3.

Because of their initial energy and the energy they acquire from the accelerating electric field, the electrons will strike the coating 16 with sufficient energy to produce secondary emission of electrons at a ratio greater than 1:1. The secondary electrons thus produced will also have a velocity component normal to the surface of the coating 16 and will, therefore, strike the coating 16 (FIGURE 3) after being accelerated a particular distance towards the anode 22, to produce a proportionately increased number of secondary electrons. These electrons will then pass out of the region 20 and impinge upon the anode 22 for detection of the amplified signal.

Although the electrons have been shown striking the coating 16 only twice, it will be understood by persons skilled in the art that the number of times that the electrons strike the coating 16 will depend on several factors. For example, if the tube 14 were made much longer, the electrons would strike the coating an increased number of times and, therefore, provide increased multiplication. Reducing the diameter of the tube 14 or reducing the electric field to slow up the travel of the electrons through the region would also increase the number of collisions.

As previously mentioned, the electric field produced in the region it) is substantially parallel to the coating 16. The provision of a substantially parallel field is important in that the field includes a substantially zero normal component directed into the coating 16 at all points so as not to prevent secondary emission from its surface. 7

In addition to having an extremely simple configuration, the multiplier disclosed above is advantageous in that no critical focusing adjustments are required since the lateral spread of the electron beam is limited to the region 20 defined by the walls of the multiplier, that is the coating 16. Because the lateral spread of the beam is limited, a plurality of independent multipliers may be arranged in parallel relationship, as generally indicated at '70 in FIGURE 4, for use as a light intensifier tube. A light image 72 focused on a photo cathode 74 would cause the cathode to release electrons which would enter the different tubes in the parallel array 70 and produce secondary emission to amplify various portions of the image and to produce an intensified image 76 on a fluorescent screen '78. In FIGURE 4, connections from the power supply are made to the opposite ends of only two tubes. Connections to the opposite ends of the other tubes have not been shown to avoid confusion in the drawing. The intensifier in FIGURE 4 could also be operated without a photo cathode by focusing a light image directly at the openings of the tubes. Photons from the light image would enter the tubes and anasaoa produce secondary emission of electrons to intensify the image. However, the use of a photo cathode is preferred.

A light intensifier tube may also take the form shown in FIGURES 5 and 6. A wafer 100 of secondary emissive material, such as glass having .012 inch thickness and having ohm-cm. resistivity, is provided with a plurality of perforations or holes 102 of relatively small size, such as .001 inch in diameter. The holes 102, in substantially parallel relationship to one another, could be etched through the wafer 100 by a photo-etching process. A coating 104 of conductive material such as silver is provided on both side surfaces of the wafer 100 leaving the holes uncovered. A photo cathode 106 is positioned adjacent to one side of the wafer 100 and fluorescent screen 108 is positioned adjacent to the opposite side of the wafer. A power supply 110 applies constant voltages to the photo cathode 106, to the conductive coatings on both sides of the wafer 100 and to the screen 108. For example, constant voltages such as 4000 volts, -3500 volts, -500 volts and 0 volt may be applied to the cathode, the conductive coating near the cathode, the opposite conductive coating and to the screen, respectively.

The voltage difference between the conductive coatings on opposite sides of the wafer 110 will produce a current flow through the wafer and an electric field through the holes 102 in a direction substantially parallel to the axes of the holes. When a light image is focused upon the cathode, the electrons released by the cathode are introduced into the holes 102 where they are multiplied in the manner previously disclosed to produce an intensified image on the screen 108.

Although the multiplier described above takes the form of the straight tube 10, other configurations can also be used. For example, the embodiment in FIGURE 7 includes a pair of

parallel plates

50 and 52 disposed close to each other to provide a narrow region between them. The

plates

50 and 52 are relatively wide to prevent the loss of electrons through the sides of the region. A conductive coating is provided on the inside surface of each plate and voltages are applied between the ends of the coatings to produce voltage drops across the surface of the coatings and to produce a substantially parallel electric field in the region between the

plates

50 and 52.

In FIGURE 8 is shown the further embodiment having an outer cylinder 60 with open ends and an inner cylinder 62 with closed ends, which are concentric and have conductive metallic coatings 64 along the periphery of each cylinder at one end and a similar coating 65 at the other end. Cylinder 60 has a secondary emissive resistive coating 66 on its inner surface which is in contact with

coatings

64, 65; cylinder 62 has a secondary emissive resistive coating 68 on its outer surface which is in contact with

coatings

64, 65. Adjacent one open end of the concentric cylinders is a photo cathode 70, or other assembly for providing electrons, ions, photons, or other units which are to be multiplied, and adjacent the other open end of the cylinders is an anode 72. Cathode 70 may be annular or of some other configuration as described. A potential source 74 supplies a negative potential to cathode 70, such as 1700 volts, a slightly more positive potential such as 1500 volts to metallic rings 64 at one end of the cylinders and a much more positive voltage such as +1500 volts applied to conductive rings 65 at the other end of the cylinder and a slightly more positive potential such as +1700 volts to the anode or collector 72. In the operation of this embodiment cathode 70 supplies electrons to the electron path which is between the inner cylinder 62 and the outer cylinder 60. Preferably, the end of cylinder 62 is blocked to prevent electrons from passing through the center. The total field at any point is an electric field parallel to the electron path in this as in the other embodiments. The electrons are accelerated along this path striking the secondary emissive walls due to the transverse components in the initial random velocity. In these embodiments, reproducible multiplication is obtained with the use of a very small and simplified multiplier.

Of course, in order to obtain specific results, certain portions of the wall area which defines the electron path may be open or not coated with the secondary emissive material. Also, for specific purposes, the cathode assemblies shown schematically herein may include an input connected grid or other member for controlling emission therefrom.

Although this invention has been disclosed and illustratcd with reference to particular applications, the principles involved are susceptible of numerous other applications which will be apparent to persons skilled in the art. The invention is, therefore, to be limited only as indicated by the scope of the appended claims.

Having thus described our invention, we claim:

1. A multiplier comprising wall means of secondary electron emissive material defining a multiplying path having its longitudinal dimension substantially larger than its lateral dimension,

entrance means into the multiplying path defined by said wall means,

exit means from the multiplying path defined by said wall means spaced from said entrance means by said longitudinal dimension,

said multiplying path being totally clear of a field producing wire on the longitudinal axis of the multiplying path,

said multiplying path being free of any superimposed oscillating electric field in a direction transverse to the longitudinal axis,

and means for producing a longitudinal electrical current flow in said wall means to establish in the multiplying path a total field which is an electric field having a component parallel to the wall means in its longitudinal direction and having a substantially zero component in a transverse direction to move electrons away from the region of secondary emission on said wall means so that the primary means for moving electrons away from the region of secondary emission on said wall means is the energy of secondary emission.

2. A multiplier as recited in claim 1 wherein said Wall means is a tube defining the multiplying path.

3. A multiplier as recited in claim 1 wherein said wall means is a pair of parallel plates in closely spaced relation.

4. A multiplier as recited in claim 1 wherein said wall means is a pair of concentric tubes and the multiplying path is defined between the outer surface of the inner tube and the inner surface of the outer tube.

5. A multiplier comprising wall means defining a multiplying path having its longitudinal dimension substantially larger than its lateral dimension,

said wall means having a secondary electron emissive surface on at least a portion thereof,

said surface being contiguous with the multiplying path,

entrance means into said multiplying path defined by said wall means at one end of said longitudinal dimension,

exit means from said multiplying path defined by said wall means at the other end of said longitudinal dimension,

said multiplying path being totally clear of a field producing wire on the longitudinal axis of the multiplying p said multiplying path being free of any superimposed oscillating electric field in a direction transverse to the longitudinal axis,

and means for producing a longitudinal electrical current flow in said secondary emissive surface to produce a uniform voltage drop across the secondary emissive surface in the longitudinal direction and a total field in the mulitplying path which is an electric field disposed in a direction such that the primary means for moving electrons away from the secondary emissive surface is the energy of secondary emission.

6. A multiplier as recited in claim 5 wherein said wall means is a tube defining the multiplying path.

7. A multiplier comprising wall means defining a multiplying path having its longitudinal dimension substantially larger than its lateral dimension,

said wall means having a secondary electron emissive surface contiguous with the multiplying path,

entrance means into the multiplying path defined by said wall means,

and means for establishing in the multiplying path a total field which for a major portion of said path is an electric field substantially parallel to the secondary emissive surface in the longitudinal direction.

8. A multiplier as recited in claim 7 wherein said means for establishing the field comprising means for producing a longitudinal electrical current flow in said secondary emissive surface.

9. A multiplier as recited in claim 7 Wherein said wall means is a tube defining the multiplying path.

10. A multiplier comprising a Wafer of secondary electron emissive material having a relatively high resistance,

a plurality of holes extending through the wafer in substantially parallel relationship,

the openings of said holes on one side of the wafer being disposed to receive an incoming signal for multiplication,

the multiplied signal emerging from the holes on the opposite side of the wafer,

each of said holes being totally clear of a field producing wire on the longitudinal axis thereof,

and means for producing an electrical current flow between the opposite sides of the wafer to produce an electric field in each hole in a longitudinal direction substantially parallel to the longitudinal axis of each hole,

said electric field in each hole being the total electric 11. A multiplier as recited in claim 10 wherein a conductive coating is provided on each of said opposite sides of the wafer in communication with the periphery of said holes,

said means for producing an electrical current flow between the opposite sides of said wafer being connected to said conductive coatings.

12. A multiplier comprising a plurality of straight tubes stacked in parallel relationship,

.:, One end of the stack of tubes being disposed to receive an incoming signal for multiplication and the multiplied signal emerging from the other end of the stack of tubes,

each of said tubes having an inner surface of secondary electron emissive material,

each of said tubes being totally clear of a field producing wire on the longitudinal axis thereof,

and means for producing an electrical current flow between the ends of each tube to produce throughout substantially all of the region defined by each tube an electric field which is substantially parallel to the inner surface of the tube in the longitudinal direction so that the only means for moving electrons away from the secondary emissive surface is the energy of secondary emission,

said electric field in each region being the total electric field.

13. A multiplier comprising wall means of secondary electron emissive material defining a multiplying path having its longitudinal dimension substantially larger than its lateral dimen- SlOIl,

entrance means into the multiplying path defined by said wall means,

means for establishing in the multiplying path a total electric field which is substantially parallel, in the longitudinal direction, to said wall means for a major portion of said wall means.

14. A multiplier comprising a straight tube of insulating material,

said tube having its longitudinal dimension substantially greater than its diameter,

a secondary electron emissive coating of non-insulating material provided on the inner surface of the tube of insulating material,

said secondary electron emissive coating of noninsulating material having a relatively high predetermined resistance to provide a path for an electrical current flow,

said tube being totally clear of a field producing Wire on the longitudinal axis of the region defined by the coating,

and means for producing an electrical current flow in the secondary electron emissive coating between the ends of the tube thereby establishing a total electric field in the region defined by the coating which is substantially parallel to the coating in the longitudinal direction.

15. A multiplier comprising a tube having its longitudinal dimension substantially greater than its diameter,

said tube having a secondary electron emissive inner surface,

said tube being totally clear of a field producing wire on the longitudinal axis of the region defined by the tube,

and means for producing a uniform voltage drop across the secondary emissive inner surface of the tube in the longitudinal direction to produce in the region defined by the tube a total electric field which is disposed in a direction such that the primary means for moving electrons away from the secondary emissive surface is the energy of secondary emission.

16. A multiplier as recited in claim 15 wherein the electric field is substantially parallel to the inner surface of the tube in the longitudinal direction.

17. A multiplier comprising wall means defining a multiplying path having its longitudinal dimension substantially larger than its lateral dimension,

means for introducing a signal to be multiplied into the multiplying path,

means for receiving the multiplied signal emerging from the multiplying path,

an air evacu ed envelope enclosing said wall means, said lyfiiicing means and said receiving means,

and me for producing a longitudinal electrical current flow in said secondary emissive surface to produce a uniform voltage drop across the secondary emissive surface in the longitudinal direction and a total field in the multiplying path which is an electric field disposed in a direction such that the primary means for moving electrons away from the secondary emissive surface is the energy of secondary emission.

18. A multiplier comprising a plurality of tubes stacked in parallel relationship,

means for introducing into one end of the stack of tubes a signal to be multiplied,

the multiplied signal emerging from the other end of the stack of tubes,

each of said tubes having an inner surface of secondary electron emissive material and defining a region totally clear of a field producing wire on the longitudinal axis of the region,

and means for producing an electrical current flow between the ends of each tube to produce throughout substantially all of the region defined by each tube an electric field which is substantially parallel in the longitudinal direction to the inner surface of the tube,

said electric field in each region being the total electric field.

19. A multiplier comprising a plurality of tubes stacked in parallel relationship,

the multiplied signal emerging from the other end of the stack of tubes,

means for receiving the multiplied signal emerging from the stack of tubes,

an air evacuated envelope enclosing said stack of tubes, said introducing means and said receiving means,

and means for producing an electrical current flow between the ends of each tube to produce a uniform voltage drop across the inner surface of the tube in the longitudinal direction and an electric field in the region defined by the tube,

the electric field in each region being the total field.

20. A multiplier comprising,

a tube of insulating material,

a secondary electron emissive coating of noninsulating material provided on the inner surface of the tube,

said coating being contiguous with the multiplying path having a relatively high resistance,

one end of the tube being disposed to receive an incoming signal for multiplication and the multiplied signal emerging from the other end of the tube,

means for receiving the multiplied signal emerging from the tube,

and means for producing an electrical current flow in the coating between the ends of the tube to produce a uniform voltage drop across the coating in the longitudinal direction and to establish an electric field in the region defined by the tube,

said electric field being the total field in said region.

21. A multiplier comprising wall means of secondary electron emissive material defining a multiplying path having its longitudinal dimension substantially larger than its lateral dimen- SlOIl,

entrance means into the multiplying path defined by said wall means,

means for producing a longitudinal current fiow in said wall means to produce along said wall means an electric potential which provides the entire field in said multiplying path.

References (Jilted in the file of this patent UNITED STATES PATENTS 2,203,048 Farnsworth June 4, 1940 2,210,034 Keyston Aug. 6, 1940 3,062,962 McGee Nov. 6, 1962 FOREIGN PATENTS 884,059 Germany July 23, 1953 916,257 France Aug. 12, 1946 OTHER REFERENCES Terman: Radio Engineers Handbook, published by McGraw-Hill (New York), 1943.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,128,408 April 7, 1964 George W. Goodrich et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected belo' Column 1, line l8, for "emission" read emissive line 63, for "coatig" read coating column 3, line 7, for "10 ohm-cm." read l0 1 ohm-cm.

Signed and sealed this 13th day of October 1964.

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents

Claims

1. A MULTIPLIER COMPRISING WALL MEANS OF SECONDARY ELECTRON EMISSIVE MATERIAL DEFINING A MULTIPLYING PATH HAVING ITS LONGITUDINAL DIMENSION SUBSTANTIALLY LARGER THAN ITS LATERAL DIMENSION, ENTRANCE MEANS INTO THE MULTIPLYING PATH DEFINED BY SAID WALL MEANS, EXIT MEANS FROM THE MULTIPLYING PATH DEFINED BY SAID WALL MEANS SPACED FROM SAID ENTRANCE MEANS BY SAID LONGITUDINAL DIMENSION, SAID MULTIPLYING PATH BEING TOTALLY CLEAR OF A FIELD PRODUCING WIRE ON THE LONGITUDINAL AXIS OF THE MULTIPLYING PATH, SAID MULTIPLYING PATH BEING FREE OF ANY SUPERIMPOSED OSCILLATING ELECTRIC FIELD IN A DIRECTION TRANSVERSE TO THE LONGITUDINAL AXIS,