US2648794A - Electron discharge device such as television transmission tube - Google Patents

Description

4 m 9 .m nl 8 nm m nw* ,m n r 2 Tm -m V .A n C/ e u., l S A HE mw T N8 Nmmm OV Smm?, NEW.. EGANA. HRRb .MTN Fwwd All-Ie DSH.. WWF RE TL CE ET L E 3 5 9 1 L, 1 uw u A Patented ug. 11, 1953 ELECTRON DISCHARGE DEVICE SUCH AS TELEVISION TRANSMISSION TUBE Alec Frank Henson, Whitton, England, assignor to Electric & Musical Industries Limited, Middlesex, England, a company of Great Britain Application February 17, 1948, Serial No.v 8,875 In Great Britain February 18, 1947 8 Claims.

This invention relates to electron discharge devices such as television transmission tubes of the kind comprising a target electrode elemental areas of which are capable of acquiring varying potentials, an electron gun for producing a beam of electrons which can be caused to scan said target electrode and an electron multiplier to which electrons returning from said target electrode can be directed. Devices of this kind are referred to hereinafter as devices of the kind described.

In one form of device of the kind described the beam of electrons, in operation of the device, is caused to approach the target electrode at such a low velocity that the elemental areas thereof are restored to an equilibrium potential corresponding substantially to that of the cathode of the electron gun, the electrons of said beam which are not utilised in restoring equilibrium being reflected at said target electrode and returned along substantially the same path as the scanning beam and are directed into said multiplier, .from which a signal output can be obtained. In this form of device the anode of the electron gun is commonly utilised as the rst multiplying electrode of the multiplier, and the other multiplying electrodes are of the grid type and surround the electron gun being spaced from each other along the axis thereof, the returning electrons impinging on said anode and the secondary electrons released therefrom being deflected to the next multiplyingr electrode, and so on. With this arrangement, however, the aperture in said anode, through which the scanning beam emerges, is liable to give rise to spurious signals and it is difcult to treat the anode to give satisfactory secondary electron emission without damaging the aperture or contaminating the cathode. There have also been proposals to displace the electron multiplier so that it is no longer coaxial with the elect-ron gun but these proposals have also given rise to diiiiculties.

The object of the present invention is to provide an improved electron discharge device of the kind described with a view to reducing the difculties associated with the employment of an electron multiplier.

According to the present invention there is provided an electron discharge device adapted to generate electrical signals corresponding to an optical image, comprising-a target, elemental areas of which are capable of being charged to different potentials, an electron gun comprising at least a cathode and an anode for producing a beam of electrons which can be 1.1566, t Scan said target, an electron multiplier comprising a plurality of electrodes separate from said anode and angularly spaced about the axis of said gun, and means for directing electrons from said tar- -get to the rst of said multiplier electrodes without causing said latter electrons to impinge on said anode.

Preferably the multiplier comprises means for producing mutually perpendicula-r electrostatic and magnetic iields whereby electrons released from oneof said multiplier electrodes can be deiiected to another of said multiplier electrodes.

In order that the said invention may be clearly understood and readily carried into eiiect, the same Will now be more fully described with reference to the accompanying drawings, in which:

Figure l illustrates diagrammatically in longitudinal section a television transmitting tube according to one example of the invention,

Figure 2 is a vtransverse sectional view on the line II-II of Figure l,

Figure 3 is a transverse' sectional view similar to Figure 2 of a modication of the television transmission tube illustrated in Figures 1 and 2, and l Figure 4 is a fragmentary View of a further modification.

In the television transmitting tube illustrated, the target comprises a mosaic screen 2 provided near the end wall of the tube l and comprising a multiplicity of discrete photo-sensitive conducting elenients which in known manner acquire varying positive potentials' when an optical image is projected on to the mosaic screen. Of course, instead of being photo-sensitive the target electrode 2 may be of the kind arranged to acquire varying potentials when an electron image from a separate photo-cathode is projectedon to it. The tube is enclosed Within a solenoid 3 which produces an axial focussing magnetic iield, the solenoid 3 as shown extending to the full length ci the tube, and at the end of the tube l opposite the screen 2 an electron gun il, comprising a thermionic cathode, screen electrode and anode a, is provided for producing a beam of electrons 5 for scanning the screen 2 when potentials of about 2 Volts negative and 360 volts positive with respect to the cathode are applied-respectively to the screen electrode and anode of the gun as shown; VThe gun i is oir-set with reference to the axis of the tube i and the beam on emerging from the gun passes y between a pair of llift plates t to which suitable potentials are appliedso that the beam is deiiected in known manner and leaves the plates 6 cio-incident with the tube axis. The beam then passes through an aperture in a shield 1 into a Iregion enclosed by a wall anode 8, which as shown is maintained at a potential of 250 volts positive with respect to the gun cathode, and horizontal and vertical scanning deflections are imparted to the beam by means of magnetic deecting coils, one pair 9 of which is indicated. rThe shield 'i is maintained at the same potential on the anode of the gun 4 and the mean of the potentials applied to the lift plates B is also arranged to be the same as the potential of the gun anode. The beam 5 on leaving the gun Li has a velocity of about 300 volts but as it approaches the target 2 it is decelerated by an annular decelerating electrode IU maintained as shown at approximately the same potential as the gun cathode so that the screen 2 is scanned by a low velocity beam which restores the conducting elements of the screen to an equilibrium potential corresponding substantially to that of the gun cathode. Electrons in the beam 5 which are not utilised in discharging the conducting elements of the screen 2 are reiiected at the screen and form a modulated return beam II which travels back approximately along the path of the beam 5 until it reaches the lift plates 6 where the return beam II is deflected in known manner in the opposite sense from the beam 5 so that it is separated therefrom and is led to the first multiplying electrode or dynode I2 of the electron multiplier of the tube, the said electrode I2 being separate from the anode da of the electron gun li.

The multiplier, as shown more especially in Figure 2, comprises multiplying electrodes I2, I3 and id and a collecting electrode I5 angularly spaced about the axis of the gun 4, which is 01T- set from but parallel to the axis of the tube I. The electrodes I2 to I5 face the axis of the gun 4 and are located at equal radial distances from a cylindrical accelerating electrode I6, and the multiplier as a whole is located behind the gun .1, that is at the end of the gun remote from the target electrode 2. The first electrode I2 is inclined as shown to the axis of the gun d while the electrodes I3, I 4 and I5 comprise segments of a cylindrical surface co-axial with the gun Il, as shown in Fig. 1. The electrodes I2, I3, I4 and i5 have applied to them respectively positive potentials of, for example, 300, 450, 600 and 750 volts While the accelerating electrode I5 has applied to it, for example a potential of 1,000 volts positive. The secondary electrons released by the return beam II when it strikes the electrode I2 are, due to the mutually perpendicular electrostatic and magnetic fields produced respectively by the electrode I6 and the solenoid 3, accelerated in a curved path indicated at Il to the second multiplying electrode I3. Similarly the secondary electrons emitted from the electrode i3 travel to the electrode I4 and those from electrode I4 to electrode I5, where they are collected, the signal output of the tube I being obtained vfrom a load impedance I3 connected to the electrode I5. Instead of collecting the electrons on the electrode I5, they may be collected on the electrode I6, and the number of multiplying electrodes may be carried, the number which can be used depending on the spread of the electrons proceeding through the multiplier.

in the modilication illustrated in Figure 3 the accelerating electrode I6 is replaced by separate segmental electrodes I9. -20 and ZI at suitable potentials for accelerating the secondary electrons released from the multiplying electro-des I 2, I3 and It, and said multiplying electrodes and also the collecting electrode i5 are arranged progressively nearer to the accelerating electrodes I9, 2li and 2I, so that the electrodes .I2 to I5 are arranged in a spiral as shown Whose origin is co-linear with the axis or" the gun 4.

The return beam of electrons II will not in general follow exactly the path oi the emergent beam 5 but will scan a small area and Where lift plates such as 6 are employed for separating the return beam II from the beam 5 it is desii-able that the area scanned by the return beam should be as small as possible. Uniform deceleration of the scanning beam of electrons approaching the target electrode 2 contributes to this result and in some cases it may be desirable to modify the arrangement of electrodes and potentials at the end of the tube I. For example, the decelerating electrode I0 may be dispensed with and the Wall anode t extended to the plane of the target electrode 2, or several axially spaced annular electrodes It may be employed, maintained at progressively decreasing potentials towards the target electrode 2. Alternatively as illustrated in Figure 4, the electrode Iii may be replaced by a mesh electrode 22 arranged parallei to and a short distance in front of the target electrode 2, and maintained for example at a positive potential of 250 volts with respect to the cathode. This positive potential however may vary in a wide range down to a few volts positive with respect to the cathode, dependent upon the design of the tube and the electrode spacing.

Since, in accordance with the invention the return beam I l is deflected from the path of the scanning beam 5 without impinging on the anode of the gun d, said anode d@ does not require to be treated so as to render it an emitter of secondary electrons. Moreover since the electron multiplier as a Whole is separate from the gun 4 and located at the end thereof remote from the target electrode 2, the electrodes l2, I3 and I4 can be treated to give a uniform high secondary-electron emission, for example by polishing their surfaces and evaporating suitable layers of secondary electron-emitting material on to them, Without damaging the aperture of the gun anode, or contaminating the gun cathode. ln addition said aperture Will not appear in the reconstituted picture, and since the electron gun i is off-set with reference to the axis of the tube I, and hence with reference to the aperture in the shield l, said shield intercepts light from the heated cathode on the gun and so prevents it illuminating the screen 2 and giving rise to spurious signals. It is also possible to provide long leakage paths and good insulation between the electrodes of the multiplier and the evaporation of secondary electron-emitting material on to the multiplying electrodes can be readily effected. The evaporated material may be antimony, which is subsequently activated to give a high secondary emission.

While the invention has been described as applied to an electron discharge device in which the target electrode is stabilized substantially at cathode potential, the invention may also be applied to devices stabilized at other than cathode potential, such for example as described in the specification of co-pending United States patent application Serial No. 792,576.

.I claim:

:1.An electron discharge device adapted to generate electrical signals corresponding to an optical image, comprising a target, elemental areas of whichcan be charged to different potentials, an electron gun disposed to one side of said target and comprising at least a cathode and an anode spaced along the axis of said gun for producing a beam of electrons directed along said axis for scanning said target, an electron multiplier disposed to the same side of said target as said gun and comprising a plurality of electrodes separate from said anode and angularly spaced about said axis of said gun, and means disposed between said target and said multiplier for directing electrons from said target to the first of said multiplier electrodes along a path avoiding said anode.

2. An electron discharge device adapted to generate electrical signals corresponding to an optical image, comprising a target, elemental areas of which can be charged to different potentials, an electron gun disposed to one side of said target and comprising at least a cathode and an anode spaced along the axis of said gun for producing a beam of electrons directed along said axis for scanning said target, an electron multiplier disposed to the same side of said target as said gun and comprising a plurality of electrodes separate from said anode which are angularly spaced about said axis of the gun and face said axis, and means -disposed between said target and said multiplier for directing electrons from said target to the first of said multiplier electrodes along a path avoiding said anode.

3. An electron discharge device adapted to generate electrical signals corresponding to an optical image, comprising a target, elemental areas of which can be charged to different po.- tentials, an electron gun disposed to one side of said target and comprising at least a cathode and an anode for producing a beam of electrons for scanning said target, an electron multiplier disposed to the same side of said target as said gun and comprising a plurality of electrodes separate from said anode, said multiplier electrodes facing the axis of said gun being angularly spaced about said axis and including electrodes conforming to segments of a cylindrical surface coaxial with said gun, and means for directing electrons from said target to the rst of said multiplier electrodes along a path avoiding said anode.

4. An electron discharge device adapted to generate electrical signals corresponding to an optical image, comprising a target, elemental areas of which can be charged to different potentials, an electron gun disposed to one side of said target and comprising at least a cathode and an anode for producing a beam of electrons for scanning said target, an electron multiplier disposed to the same side of said target as said gun and comprising a plurality of electrodes separate from said anode, said multiplier electrodes facing the axis of said gun being angularly spaced about said axis and including electrodes conforming to segments of a spiral surface whose origin is colinear with the axis of said gun, and means for directing electrons from said target to the first of said multiplier electrodes along a path avoiding said anode.

5. An electron discharge device adapted to generate electrical signals corresponding to an optical image, comprising a target, elemental areas of which can be charged to diiferent potentials, an electron gun disposed to one side of said target and comprising at least a cathode and an 6. anode producing a beam of electrons for scanning said target, a plurality of electron multiplying electrodes separate from said anode and angularly spaced about the axis of said gun and facing said axis, said multiplying electrodes being disposed to the same side of said target as said gun, means for directing electrons from said target to the rst of said electron multiplying electrodes along a path avoiding said anode, said last-mentioned means being disposed between said target on the one hand and said gun and said electron multiplying electrodes on the other hand, an electrode for collecting electrons released from the last of said electron multiplying electrodes, and means for producing mutually perpendicular electric and magnetic fields for defiecting electrons released from one of said electron multiplying electrodes to the next of said electron multiplying electrodes.

6. An electron discharge device adapted to generate electrical signals corresponding to an optical image, comprising a target, elemental areas of which can be charged to different potentials, an electron gun disposed to one side or" said target and comprising at least a cathode and an anode producing a beam of electrons for scanning said target, an electron multiplier comprising a plurality of electrodes separate from said anode and angularly spaced about the axis of said gun, said multiplier being disposed to the same side of said target as said gun and being located at the end of said gun remote from said target, and means disposed between said target and said gun for directing electrons returning from said target to the first of said multiplier electrodes along a path avoiding said anode.

7, An electron discharge device adapted to generate electrical signals corresponding to an optical image, comprising a target, elemental areas of which can be charged to different potentials, an electron gun disposed to one side of said target and comprising at least a cathode and an anode producing a beam of electrons for scanning said target, a plurality of electron multiplying electrodes separate from said anode, said electron multiplying electrodes being angularly spaced about the axis of said gun and facing said axis, said electron multiplying electrodes being disposed to the same side of said target as said gun and being located at the end of said gun remote from said target, means disposed between said target and said gun for directing electrons returning from said target to the first of said electron multiplying electrodes along a path avoiding said anode, an electrode for collecting electrons released from the last of said electron multiplying electrodes, means for producing an axial focussing magnetic field between said gun and said target and extending to said electron multiplying electrodes, and means for producing an electric field perpendicular to said magnetic field in the region of said electron multiplying electrodes to direct electrons released from one of said multiplying electrodes to the next of said multiplying electrodes.

8. An electron discharge device such as television transmission tube, comprising a target, elemental areas of which can be charged to different potentials, an electron gun disposed to one side of said target and comprising at least a cathode and an anode producing a beam of electrons for scanning said target, said electron gun being off-set with respect to the axis of the device, a shield between said electron gun and target for intercepting light passing from said electron gun toward said. target, an electron multiplier' on the same side of said shield as said electron g-u-n and comprising a plurality of electrodes separate from said anode and angularly spaced about the axis of said gun, means for producing an axial magnetic field and means at the same side of said shield for producing an electric field at right angles to said magnetic field te deflect electrons emanating from said electron guninone sense te pass said shield on 19 their path to said target and to deect electrons on their return path from said target and 8 having passed said shield i-n the opposite sense toward the first of said multiplier electrodes.

ALEC FRANK HENSON.

References Cited in the iile of this patent UNITED STATES PATENTS Number Name Date 2,213,177 Iams Aug. 27, 1940 2,288,402' Iams JuneA 30, 1942 2,365,006 Ricketts Dec. 12, 1944 2,492,976 Ferguson Jan'. 3, 1950

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