US2807741A - Electron multiplier - Google Patents

Description

Sept. 24, 1957 N. c. FULMER ELECTRON MULTIPLIER Filed April 17?', 1954 1JNVENTOR. NORMAN c. F-ULMER v ATTORNEYS aperture 14 therein.

United States Patent ELECTRON MULTIPLIER Norman C. Fulmer, Pearl River, N. Y., assignor to Allen B. Du Mont Laboratories, Inc., Clifton, N. J., a corporation of Delaware v Application April 13, 1954, Serial No. 422,900

Claims. (Cl. 313-105) This inventionrelates to electron multipliers of the type in which dynodes are employed between a cathode and an anode for the purpose of multiplying or increasing electrons.

It is an object of the invention to provide an electron multiplier capable of functioning in a magnetic field. Another object is to provide an electron multiplier so constructed that a plurality of electron multipliers may be arranged in a camera pick-up tube for color television, so as to function as electron-multiplying targets for color signals. Other objects will be apparent.

In the drawing:

Fig. 1 is a cross-sectional view of the side of the electron multiplier;

Fig. 2 is a cross-sectional view of the device taken on the line 2-2 of Fig. l; and

Fig. 3 is a schematic diagram of preferred electrical connections to the electron multiplier elements.

The invention is particularly applicable for use in the color pick-up tube shown and described in the Neal Diepeveen patent application, Serial Number 369,888, in which there is shown a means for deriving electrons from a photocathode in a color television camera tube, means for scanning the electrons across an apertured plate, and magnetic field means for separating the electrons which pass through the aperture into respective color-representative signals.

In the drawing, vsuch a tube as described above is shown, having an electric coil or magnetic means 11 for producing a magnetic field therein. The tube 10 also comprises the photocathode 12 and a plate 13 with an Representative electrons 15 pass through the aperture 14 and enter into the magnetic field 16. The magnetic field 16 causes the electron beam 15 to curve downwardly and to separate into. a plurality of electron beams 17, 18 and 19, these different beams being representative, respectively, of differing colors of light which produced the electrons on the photocathode 12 in the camera tube. For example, the electrons 15 which have been omitted from the photocathode due to excitation by red light, will have a relatively low velocity and will be curved, by the magnetic eld 16, on a relatively short radius, as indicated at 17. The electrons which are emitted from the photocathodedue to excitation by green light, will have an intermediate velocity and will be curved on an intermediate radius in the magnetic iield 16, as indicated at 18. Electrons 15,

which are emitted from the photocathode due to excitation by blue light, Will have a relatively high velocity and thus will be curved on a relatively large radius in the magnetic field 16, as indicated at 19.

In accordance with the present invention, the redrepresentative electrons 17 are collected by an electron multiplier target 21; the green-representative electrons 18 are collected by an electron multiplier target 22; and the blue-representative electrons 19 are collected by an electron multiplier target 23. These targets are somewhat circular, as shown in Fig. 2, and each comprises a g 2,807,741 Patented. Sept. 24, .1957

circular shield housing 26 having an opening 27 near the center thereof through which the electrons 15 may pass to strike a cathode or first dynode 28, which is of a material which will produce secondary electrons when struck or excited by primary electrons. The opening 27 in the center of each electron multiplier housing 26 permits electrons to pass through the other electron multipliers 21 or 22, in order to strike the following electron multipliers 22 or 23.

Fig. 2 is a sectional view of one representative electron target unit 23, such as blue; only the blue-representative electrons 19 are shown as they enter the opening 27. The cathode 28 is positioned so as to be struck by such blue-representative electrons 19.

A plurality of secondary- emissive dynodes 29, 30 and 31, and an output anode 32, are arranged circularly in order within the field housing 26 and about the axis of the electron beam .15.

As shown in Fig. 3, a source 36 of voltage is connected to the cathode 28, dynodes 29, 30, 31 and anode 32 through series-connected voltage-dropping resistors 41-45. The resistor 41, between the high voltage and the anode 32, functions as an output load impedance. Output terminals 46, 47 are connected respectively to the' anode 32 and to the cathode 28.v

As illustrated in Fig. 2, the electrons 19 strike the cathode 28, causing secondary electrons 51 to be emitted therefrom. l The higher-positive polarity voltage on the first dynode 29 causes the secondary electrons 51 to strike the first dynode 29, resulting in a'larger number of secondary electrons 52 to be emitted therefrom. Similarly, still greater numbers of secondary electrons 53 'and 54 are emitted from the second and third dynodes 30, 31. The greatly multiplied number of electrons 54 strike the anode 32, and cause an amplified output signal to be developed across the load impedance 41 and at the terminal 46.

The electron- multiplier targets 21 and 22 are each constructed similarly to the structure of the target 23, which has been described.

The targets 21, 22 and 23 are tilted as shown, so that the cooperative effects of the electrostatic fields produced by the voltages on the dynodes and anodes, and the magnetic field 16 produced by the magnets 11, will be such as to cause the secondary groups of electrons 51, 52, 53, 54, to strike the proper dynodes and anode. When electrons move through a magnetic field perpendicular to the ux lines, the motion of the electrons will become curved at right angles to the flux lines. Accordingly, the magentic field flux 16 will cause the secondary groups of electrons 51, 52, these groups of electrons moving in an upward direction, to deflect towards the front end 56 of the tube 10. However, with the top ends of the targets 21, 22 and 23 tilted towards the front end 56 of the tube in accordance with this invention, the dynodes 29 and 30 are properly positioned so that the magentically-dellected electron groups 51, 52 will properly strike the dynodes 29, 30.

The dynodes 30 and 31 are positioned symmetrically, i. e., without relative longitudinal displacement. vNo compensation is necessary here, because the group 53 of secondary electrons moves substantially parallel to the magnetic uX lines 16 and, hence, there will be no magnetic deflection ofthe electrons 53. The downwardly moving secondary electrons 54 will be caused, by the magnetic flux 16, to be deflected toward the rear end 57 of the tube 10. However, it will be noted that the tilt of the targets 21, 22, 23, is such that the anode 32 is olset rearwardly of the position of the dynode 31, so that the electrons 54 which are deflected rearwardly by the magnetic field 16 will properly strike the anode 32. As shown in Fig. 1, the mutually adjacent edges 6162, 63-64 etc. of the cathode 28, dynodes 29-31 and anode 32, are dispersed substantially parallel with the axis 66 of the electron beam 15. This arrangement of the edges of the cathode, dynodes, and anode, tends to cause theelectrostatic elds between these elements tobe in a more nearly vertical alignment than would be the case if the adjoining edges of these elements were perpendicular to the tilted planes of the targets 21, 22 and 23. The effect of the aforementioned more nearly vertical electrostatic fields tends to counteract partly the horizontal deflection of the secondary electrons 51, 52 and 54, caused by the magnetic field 16.

It will be appreciatedthat the invention provides a compact arrangement of electron-multiplying elements, the arrangement permitting a beam of primary electrons Vto pass through some of the electron multiplier units so as to activate the cathodes of other electron multiplying units. The invention also achieves electron-multiplication in a magnetic eld, by virtue of utilizing the effect of the magnetic eld to help guide, in cooperation with electrostatic lields, secondary electrons to the proper dynodes or anode.

While a preferred embodiment of the inventionhas been shown and described, various modifications thereof will be apparent to those skilled in the art. The scope of the invention is dened in the following claims.

What is claimed is:

1. An electron multiplier tube comprising a source of electrons, means to accelerate said electrons to form an electron beam, an electron multiplier structure having elements comprising a cathode, a plurality of dynodes and an anode circularly arranged around the axis of said electron beam and lying in a plane tilted with respect to said axis, and means producing a magnetic field per pendicularly through said tube to cause said electron beam to deect and strike said cathode.

2. The structure in accordance with claim l, the mutually adjoining edges of said elements being sub stantially parallel to said axis.

3. An electron multiplier system comprising means for producing a beam of electrons, and an electron multiplier structure having elements comprising a cathode,` a plurality of dynodes and an anode arranged substantially circularly around said axis and means producing a magnetic field perpendicular to the axis of said electron beam to deflect said electrons to strike said cathode, the plane of said electron multiplier structure being tilted with respect to said axis.

4. The device in accordance with claim 3, in which each of said elements extends substantially parallel to said axis, the mutually adjoining edges of said elements being substantially parallel to said axis.

5. An electron multiplier tube comprising means `for producing an electron beam, a plurality of multiplier targets, each of said targets having an anode, a cathode, and a plurality of dynodes encircling the axis of said beam, said plurality of targets disposed along the axis of said beam.

References Cited in the le of this patent UNITED STATES PATENTS 2,225,786 Langenwalter et al. Dec. 24, 1940 2,231,676 Muller Feb. 11, 1941 2,238,607 Schnitger Apr. 15, 1941

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