US2185283A - Cathode ray discharge device - Google Patents

Description

I jam v 194@- H. w. WEINHART CATHODE RAY DISCHARGE DEVICE Filed Aug. 20, 1936 INVENTOR H. W WEINl-[ART Patented Jan. 2, 194% ,rss

CATHQDE RAY DISCHARGE DEVICE Application August 20, 1936, Serial No. 96,925

18 Claims.

This invention relates to cathode ray discharge devices and more particularly to means for controlling the production of an electron beam within such devices.

An object of the invention is to provide an improved arrangement for electrostatically controlling the production of the electron beam.

Another object is to provide an electrode assembly which includes means for preventing the production of field effects that tend to distort the beam.

Still another object is to provide means for monitoring the operation of the electrode assembly.

A feature of the invention relates to the provision of an electrode assembly, including a toroidal accelerating electrode or its equivalent for controlling the production of the electron beam.

A construction illustrative of the invention comprises an evacuated vessel consisting of a cylindrical portion and an enlarged spherical portion sealed to one end of the cylindrical portion, and a reentrant stem sealed into the other end of the cylindrical portion and adapted to support therein an electrode assembly for producing and controlling an electron beam. The electrode assembly comprising a thermionic electron-emitting cathode, a control cylinder surrounding the cathode and closed at its outer end by a disc having a small aperture, an accelerating electrode or anode, comprising a tubular element having a torus of semi-circular cross section mounted Within its end which is adjacent the apertured disc of the cylinder and a disc-shaped flange secured externally of its other end, and the usual beam deflecting plates. The opening in the toroidal member converges from a relatively large size adjacent the apertured disc to a small size intermediate the length of the member, to provide an aperture which defines the electron beam. The spherical portion of the vessel is provided with an inwardly directed stem adapted to sup-' port a light sensitive electric surface, constituting an image target, in the path of the beam and at an angle of approximately 15 degrees to the axis of the undeflected beam, so that an image of a picture or field of view may be projected thereon along an axis substantially at right angles to this surface. A fluorescent screen is also mounted within the spherical portion in such manner that it can be rotated from a position close to the light sensitive electric surface in the path of the oathode beam to a position outside of this path, and vice versa. The outer diameter of the flange applied to the tubular anode element is somewhat less than that of the cylindrical portion of the vessel, the difference in these dimensions being such as to provide a space between the disc and a conductive coating applied to the inner Wall of the vessel, including the cylindrical portion. By supplying suitable potentials to the cathode, control cylinder, the anode and the conductive coating, the electrons emitted from the cathode may be formed into a beam of small cross-section and high intensity, for scanning the light sensitive surface of the image target. With the fluorescent screen moved into position in front of the target and the beam directed thereon, the characteristics of the latter are visibly indicated and, if desired, may be modified by varying the operating potentials applied to the electrodes and the coating.

Since the electrode assembly, to be hereinafter described in detail, operates to produce a sharp- 1y defined electron beam of high intensity which may be deflected by fields produced by the application of suitable control potentials to the defleeting plates, the discharge device may be used to scan a fluorescent screen for the purpose of controlling the production of a pattern indicative of the characteristics of the deflecting potentials, or the beam may be varied by incoming image currents and deflected by suitable potentials to control the production of an image of a field of view scanned at the cooperating transmitting station of a television system.

A detailed description of the invention follows and is illustrated in the attached drawing in which:

Fig. 1 illustrates a television scanning device including the invention;

Fig. 2 is a section through the electrode assembly included in the device of Fig. 1.

Fig. 3 is a section of part of an electrode assembly which may replace that shown at the left of section line 3-3 in Fig. 2.

Referring now to Fig. 1 there is shown an enclosing vessel comprising a spherical section I a cylindrical portion 2 having one end thereof sealed to the spherical section at 3, and its opposite end provided with a reentrant stem l adapted to support an electrode assembly to be hereinafter described.

The spherical portion of the vessel has a radially directed stem 5 for supporting a target 8 which is provided with a light sensitive electric surface l, and a support 8 carrying a rotor 9 of magnetic material, which is freely rotatable on the support 3 and is connected by a small glass rod H] to a mica plate I l, coated with fiuorescent material.

The target 6 is supported at an angle of substantially 45 degrees with the axial line passing through the cylindrical portion 2 of the vessel, and an optical system, indicated by a lens l2, may be used to project an image of an object 13 upon the light sensitive electric surface I.

A magnet may be associated with the rotor 9, for the purpose of rotating it on the support 8 and thereby cause the fluorescent screen, carried by the mica plate I I, to be moved into a position in front of the target, or away from this position to a point within the sphere such that it does not intervene between the target and the electrode assembly.

As shown in Fig. 2, the electrode assembly comprises a cathode 14 adapted to be heated to electron emitting temperature by current supplied from a source l5, a control cylinder l6 spaced apart from the cathode and closed at its outer end by a disc I! provided with a central aperture l8, a tubular element IQ of conductive material having a toroidal member 20, also of conductive material, mounted within its end adjacent the disc ll, so as to form a good electrical contact with the tube, and an outwardly directed discshaped flange 2! secured to and in good electrical contact with the outer end of this tube. The toroidal member, tube and disc constitute a single electrode. The inner wall of the vessel, including the cylindrical portion, has a carbonaceous coating 22 applied to it and constitutes another electrode. The external diameter of the flange 2! is less than that of the coating applied to the wall of the cylindrical portion for the purpose of providing an intervening space, which serves to insulate the electrode, comprising the toroidal member, tube and disc, from the coating and hence to permit diiferent operating potentials to be applied to this electrode and the coating.

The single electrode A comprising elements l9-20-2|, and the coating 22, when supplied with positive potentials, serve to accelerate the electrons emitted from the cathode l4 and thereby to control the production of a beam of electrons, the shape and size of which is defined by the aperture 23 in the element 20.

While the member 20 is herein shown as semicircular in, cross-section, other forms may be used. Essentially this element should be of such shape as to provide an opening which is relatively large adjacent the control disc but which tapers rapidly to the point where it merges into the beam defining aperture 23. The opening may be conical, pyramidal or of similar shape in which the intersection of the walls with planes in which the axis lies are straight lines. However, it is preferable to employ an opening such that the said intersecting lines are curved sufiiciently to give a better distribution of the field in the gen eral region of the edge of the aperture at the apex of the opening. By varying this curvature different field distributions are obtainable, thus enabling the paths of the electrons as they approach the aperture to be controlled by the design of this opening.

Sources 24 and 25, respectively apply positive potentials to the electrodes l6 and the anode A and source 26 applies to the lining 22 a much higher positive potential than that supplied to the electrodes by sources 24 and 25.

Because of the small diameter of the aperture 23 which defines the beam and the shape and depth of the opening through which the electrons travel just prior to reaching this aperture, no field, effective on the electron beam, exists at or in the aperture and hence the electrons pass through it in a small beam. The field-free space 23 is important, in that no focussing occurs in the aperture which determines the size of the beam, consequently it cannot be distorted by the field effects of any minute burrs in the aperture or by any irregularity in its roundness, such as would occur if a thin fiat apertured disc was used and where the focussing field is effective at the edge of, and in the aperture.

One advantage of the structure according to this invention is that it operates to substantially eliminate the discharge of secondary electrons, which result from the bombardment of the member 20 by the electron beam at and near the aperture, into the space beyond this member and thereby substantially prevents either the production of extraneous fields in that space which fields tend to distort the beam, or the projection of secondary electrons over a large area of the fluorescent screen thereby causing the production of a halo of light surrounding the spot excited by the beam. In general, secondary electrons, emitted from any portion of the wall of the opening in the toroidal member subjected to bombardment by the electrons supplied by the emitter, will be directed to and absorbed by a nearby adjacent portion of this wall, since the wall recedes from the center of the small aperture in both directions.

Since the toroidal element operates to substantially eliminate effects which tend to interfere with efficient operation of the device, it is an important factor in the production of a sharply defined electron beam.

The control cylinder l6 may have applied thereto a potential of definite value positive with respect to the cathode while a positive potential of higher value is applied to the anode A, and a positive potential of still higher value to the coating 22.

It has been found that the above described structure gives satisfactory results even when a positive potential of the same value is applied to the control cylinder l6 and the anode A, and a higher positive potential is applied to the coating 22.

As shown in Fig. 1, the electrode assembly comprises, in addition to the cathode control cylinder and anode A, two pairs of deflecting plates 2'! and 28. This assembly is supported on leads extending from the stem 4. The cathode is carried by the leads 3! the control cylinder by lead 3|, the anode A by the lead 32, the pairs of defleeting plates by leads 33 and 34, respectively, which are enclosed in glass tubes to insulate them from the other electrodes and thereby prevent electrical discharges to these electrodes. The carbon coating 22 is connected by means of a contact 35, consisting of one or more turns of conductive wire, to a lead 36. The leads which extend externally of the device are connected through terminal contacts (not shown) to the respective sources. The cathode leads are conne'cted to the source [5, the control cylinder and anode leads respectively to the sources 2 1 and 25, the lead 36 to source 26, and the deflecting plates are connected through the pairs of leads 33 and 34, respectively, which are insulated from the disc 2|, to separate sources (not shown) adapted to produce the desired deflecting fields, and lead 31 provides means for applying a biasing potential to the cathode. Any suitable sources may be used for eifecting deflection. For example, these sources may be of the type disclosed. in Knoop Patent No. 1,613,954, issued January 11, 1927. The waves supplied by the respective sources should be of such frequencies and character that the beam is caused to scan successive lines of the target so that each complete scanning is effected within the period of persistence of vision.

In case the electron beam is to be used to scan an image illuminated target, comprising a light sensitive surface as shown in. Fig. 1, or one up of a series of individual light sensitive electric cells. for the purpose of controlling the production of an image current, it is essential that the area of the beam should not be greater than the area of an elemental area of the surface or of. that of the individual cells. In order to monitor the operation of the beam producing means, movable fluorescent screen ll pro vided. With the fluorescent screen in the posithe monitoring operation has been completed, a

magnet may be associated with the rotor 9 and operated to rotate the support it carrying the screen, whereby the latter may be moved from a position in front of the target to one where it does not interfere with the scanning operation.

As the electron beam is swept across the image illuminated surface '5, an image current varying as the tone values of successive elemental areas of the field will be supplied to an external circuit, whence it may be transmitted to a receiving device adapted to control the production of image of the object being scanned. For example, an apparatus of the type disclosed in Fig. l of Patent 2,159,160, issued March 4, 1939, to F. Gray, may be used to control the production of image current in the resistance R, connected between the target and the coating 22.

Fig. 3 illustrates a section of an electrode assembly which. may be used in place of that shown between the section lines (Fig. 2). The sub stitute assembly difiers from. that of Fig. 2 in that it includes an additional accelerating element ll in the form of a short cylinder having the some internal diameter as the tubular element 2 and extending very close to the defiecting plates. Element M is spaced. 9. small distance from the outer end of the tube Ell, is supplied with the same onerating potential as that tube, and its purpose i to prevent the deflecting fields, even if of high intensity, from aifecting the size or shape of the beam.

If the apparatus is to be used to control the production of a television image, the control cylinder and anode are preferably maintained the same positive potential, incoming image current is applied to the control cylinder to cause the electron beam to be modulated accordance with variations in this current, and the deflecting plates are supplied with suitable deflecting potentials, for example, with saw-toothed waves of the type produced by the device disclosed in the abovennentioned Knoop patent, to cause the beam. to completely traverse the fluorescent screen within the period of persistence of vision and in synchronisn'l and phase with the scanning of the field of View at the transmitter. Any well known means, such as that disclosed in Fig. 4 of application Serial No. 67,057 of F. Gray filed March 4, 1936, may be used for synchronizing purposes.

In the case of image production, the fluorescent screen carried by the end wall of the discharge device may be used to monitor the operation of the means for producing the beam, and, as disclosed in connection with Fig. l, the beam may be controlled by adjusting the operating potentials applied to the electrodes and the coating 22. For oscillograph work, the signal to be investigated is applied 'to the deflecting plates.

Although cathode ray discharge devices of the type herein disclosed have been successfully perated with a potential as low as 300 volts applied to the conductive coating on the wall of vessel and voltages which correspond thereto applied to the respective electrodes of the assembly, the apparatus is not essentially a low voltage device, since it can be operated to produce equally satisfactory results with a potential which ranges from this value to several thousands of volts applied to the coating .andwith potentials of related values applied, in each case,

to the respective electrodes of the assembly. Again, it has been found that these devices may be operated with either the same or diiferent potentials applied to the control cylinder and the accelerating electrode, and that the ratio of the potentials respectively applied to the coating and to the electrodes of the assembly, namely, the control cylinder and accelerating electrode, are not critical. However, the potential applied to the coating being variable over a wide range of values, the potential or potentials applied to the control cylinder and accelerating electrode should be varied over a somewhat similar range, in order to control the production of a sharply defined beam,

As illustrative of the operation of the cathode ray discharge device described above, a cathode ray oscillograph tube of the type disclosed in United States Patent 1,632,080 to J. B. Johnson, issued June 14, 1927, which depends upon gas ionization for focussing the beam, was modified by substituting an electrode assembly of the type herein disclosed, after which the device was degassed and the vessel pumped to a high vacuum.

The assembly used in this case embodied an inend coated with electron emitting material, a

control cylinder approximately n of an inch in diameter having its outer end closed by a disc provided with an aperture about of an inch in diameter, a toroidal element having a maximum opening of about of an inch, with one of its boundaries removed approximately of an inchfrom the apertured disc of the cylinder, the minimum diameter of the opening in this element being approximately of an inch, and the center of this aperture being removed about of an inch from the above-mentioned boundary. This device was operated with the cathode and cylinder at zero potential, a positive potential of 150 volts applied to the anode A and a positive voltage of 1090 volts applied to the coating 22. Under these conditions, the modified.

discharge device operated to produce a beam of electrons having a cross-sectional area at the screen which was substantially the same as that of the aperture in the toroidal element, and the fluorescent screen was thereby excited to produce a highly intense spot of light with sharply defined edges.

. With the potential applied to the cylinder changed to plus 30 volts, the potential applied to the anode raised to plus 160 volts, and the potential applied to the coating reduced to plus 500 volts, the spot of light produced by the fiuorescent screen did not vary in size from that previously produced, it had sharply defined edges and the intensity of the light was greater than that supplied by the tube when it was operated as originally designed, i. e., as a gas operated device including the original electrode assembly.

While one embodiment utilizing the invention has been described in detail and certain specific details have been set forth for the purpose of disclosing its principles, it will be apparent from the above description that various modifications may be made without departing from the spirit of the invention.

The present invention provides high vacuum cathode ray discharge devices in which an elec trostatically focussed electron beam is produced, which can be operated at voltages and to effect results that are comparable with previously known low potential devices in which a gas is used to efiect focussing of the beam, and also at voltages of the order heretofore generally employed in high vacuum cathode ray discharge devices.

Throughout the specification and claims the word toroidal is used to define a ring-shaped member having an opening the walls of which taper axially of the member and the term is not to be construed to be limited to an element having a semi-circular cross-section except where so stated.

What is claimed is:

1. A cathode ray discharge device comprising a container enclosing an electrode assembly including an electron emitter, and an accelerating electrode provided with a converging opening which merges into a field-free aperture for defining the cross-sectional area of an electron beam, the depth of said opening being at least many times the distance across said aperture.

2. A cathode ray discharge device comprising an evacuated container enclosing an electrode assembly including a free field electron emitter, and an accelerating electrode having an opening which in general is cone-shaped and merges into an aperture for defining the cross-sectional area of an electron beam, the depth of said opening being at least many times the distance across said aperture.

3. A cathode ray discharge device comprising a container enclosing an electrode assembly including an electron emitter, and an accelerating electrode the cross-section of which is semi-circular in longitudinal plane passing through the axis of the device to provide an aperture for defining the cross-sectional area of an electron beam.

4. A cathode ray discharge device comprising a container enclosing an electrode assembly comprising an electron emitter and an anode having an opening terminating in an aperture for defining the limits of an electron beam, said opening being circular and of a diameter very small compared to the depth of said opening as a whole, said aperture being generally conical and said aperture being substantially fieldfree.

5. A cathode ray discharge device comprising a container enclosing an electron emitter and an electrode which serves as an anode, said electrode being provided with an opening which in general is cone-shaped having its base directed toward the emitter and terminating in an aperture which defines the limits of said beam and is substantially field-free, the diameter of said base being at least several times the diameter of said aperture.

6. In a cathode ray discharge device, an electron emitter, an accelerating electrode including an element which is substantially semi-circular in cross-section in a longitudinal plane passing through the axis of the device to provide an opening having a minimum diameter of the order of a few hundredths of an inch and a maximum diameter at least several times as great '7. In a cathode ray discharge device, an electron emitter, and an accelerating electrode provided with an aperture defining an electron beam and an opening converging in the direction from said emitter to said aperture in a longitudinal plane passing through the axis of the device, the maximum cross-sectional area of said opening being at least hundreds of times that of said aperture.

8. In a cathode ray device, the combination with means for generating a cathode beam of an element having an elongated aperture therein for defining the cross-sectional area of said beam, the cross-sectional area of said aperture gradually increasing in both directions with distance along the axis from a plane normal to the axis:- through a point at or near the center of the aperture, the length of said aperture being greater than any transverse dimension thereof.

9. A cathode ray device comprising an electron emitter, an electrode for accelerating the emitted electrons and having an elongated aperture for defining the cross-sectional area of the cathode beam, the cross-sectional area of said aperture gradually increasing in size at an increasing rate outward in both directions from a plane normal to the axis of said aperture at a point at or near the center of said aperture, the length of said aperture being greater than any transverse dimension thereof.

10. A television scanner comprising a cathode. ray discharge device including means adapted to be excited by an electron beam, and means for producing an electron beam comprising an electron emitter, an accelerating electrode including a member which is semi-circular in cross-section in a longitudinal plane passing through the axis of the device to provide an opening which terminates in a beam defining aperture, said opening serving to direct the electrons to said aperture and being of such axial depth as to prevent the production therein of a field of force which may affect the focus of the beam, and means for deflecting the beam to cause it to change its position of impact on said first-mentioned means.

11. In a cathode ray discharge device, means for concentrating emitted electrons into a beam comprising an electrode providing an extended plane surface, and an electrode having an opening diverging toward said surface and terminating in an elongated aperture the longitudinal axis of which is at right angles to said surface for accelerating the emitted electrons, the maximum cross-sectional area of said opening being at least hundreds of times that of said aperture.

12. In an electron gun for a cathode ray tube, a plate-like conductive element lying in a plane perpendicular to the axis of the tube and having a small aperture centered on said axis, means for generating free electrons at said opening, a second conductive element at a higher electric potential than said first element, and an aperture in said second element centered on said axis, said second element having a surface diverging from its said aperture toward a face of said first element for a distance at least many times greater than that across said aperture.

13. In an electron gun for a cathode ray tube, a plate-like conductive element lying in a plane perpendicular to the axis of the tube and having a small aperture centered in said axis, means for generating free electrons at said opening, a second conductive element at a higher potential than said first element, and an aperture in said second element centered in said axis, said second element having a surface diverging symmetrically from its aperture toward a face of said first element, the rate of divergence taken along the intersection of said surface with any plane including said axis decreasing with the distance from the aperture.

14. In a cathode ray device, an electron emitter and means for accelerating the emitted electrons and forming them into a cathode beam comprising a conductive ring-shaped element defining an opening extending toward said emitter and terminating in an aperture for defining the crosssectional area of the beam, said opening having its walls, which are defined by one side of said ring-shaped element, converging symmetrically toward and to a plane normal to the axis of said element, the rate of said convergence taken along the intersection of said walls with any plane including said axis decreasing in the direction away from said emitter and the length of any of said intersections being at least many times greater than the distance across said aperture.

15. A cathode ray discharge device comprising a container enclosing a light sensitive surface, an electron emitting cathode, means cooperating with said cathode for producing a beam of electrons directed toward said surface, and a screen, adapted to become luminous when bombarded by electrons, movable into and out of position in front of and adjacent to said light sensitive electric surface.

16. A cathode ray discharge device comprising an electron emitter and means for accelerating electrons emitted thereby, said means including a tubular anode provided with a toroidal element, the opening in said element being concentric with said tubular anode and serving to define the crosssectional area of the beam.

17. A cathode ray discharge device comprising an electron emitter and means for accelerating electrons emitted therefrom, said means including a tubular anode provided with a toroidal element, the opening in said element serving to define the cross-sectional area of the beam, means for producing a field for deflecting said beam, and means, between said anode and said deflecting means, for shielding said beam from the defocussing effect of said deflecting field.

18. A cathode ray discharge device comprising a container enclosing a target, an electron emitting cathode, means cooperating with said cathode for producing a beam of electrons directed toward said target, means for deflecting said beam to cause it to scan said target along parallel elemental paths, means for adjusting the cross-sectional area of said beam in the vicinity of said target, and a test-target comprising a luminescent screen, adapted to become luminous when bombarded by electrons, movable into and out of position in front of and adjacent to said target to give a visual indication of said crosssectional area when moved into a position in front of said target.

HOWARD W. WEINHART.

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