US2957106A - Plural beam gun - Google Patents

Description

H. c. MOODEY PLURAL BEAM GUN Oct. 18, 1960 2 Sheets-Sheet 1 Filed Aug. 12, 1954 IN VEN TOR.

I ae n Oct. 18, 1960 Filed Aug. 12, 1954 H. c. MOODEY 2,957,106

PLURAL szmcuu 2 Sheets-Sheet 2 INVENTOR.

WMMA C M0005 United States Patent PLURAL BEAM GUN Hannah C. Moodey, Lancaster, Pa., assignor to Radio Corporation of America, a corporation of Delaware Filed Aug. 12, 1954, Ser. No. 449,317

15 Claims. (Cl. 315-13) This invention is directed to a cathode ray tube and particularly to an electron gunstructure for providing a plurality of electron beams for use in a cathode ray tube such as one for color television.

A plurality of electron beams in a cathode ray tube has been used in color television picture tubes. Also, plural beams have been used in cathode ray tubes for oscilloscope work. In some of these applications, it is desirable that the plural beams be converged to substantially the same point on a target electrode within the tube envelope.

Many factors enter into the design and construction of plural beam electron gun structures. In some applications of plural electron beams, it is desirable to provide an electron gun structure of minimum dimensions for mounting within a small tubular neck portion of the tube envelope. This necessitates the close spacing of electron gun parts and permits the use of common focusing electrodes and deflecting fields. At the same time, however, it is also desirable to have control of each beam for beam modulation and beam focus.

Structurally, it is easier to utilize a minimum amount of space in the tube neck by using an electron gun structure forming closely spaced beams directed along substantially parallel paths. Parallel beams require an electron lens or field-forming structure, either electrostatic or magnetic, to converge the beams to a common area or point at the target electrode. Furthermore, it is an added advantage to provide converging means independent of the beam focusing means so that adjustment of convergence will not produce corresponding changes in beam focus at the target or changes in beam focus will not cause variations in beam convergence.

A type of cathode ray tube having electron gun means for forming a plurality of electron beams, utilizes beam converging means in the form of a common electrostatic lens near the end of the gun means and between beam focusing lenses and the target of the tube. When a varying or modulating dynamic voltage is applied to the convergence electrode of such a tube, this varying voltage must be superimposed on a rather high direct current potential with attendant insulation problems. On the other hand, if the convergence means is placed near the cathode end of the gun means and between the electron source and the beam focusing lenses, the modulating or dynamic voltage is applied to an electrode at a low direct current potential level. The peak-to-peak voltage requirement for the modulating or dynamic voltage may also be reduced.

It is, therefore, an object of this invention to provide a novel electron gun assembly for forming a plurality of electron beams which are focused and converged at a predetermined point.

It is another object of this invention to provide a cathode ray tube having a novel electron gun means for forming, converging and focusing a plurality of electron beams.

It is another object of the invention to provide a novel electron gun structure for a cathode ray tuberfor providing a plurality of electron beams which are converged independently of the focus of each beam.

It is a further object of this invention to provide a novel gun structure for converging a plurality of beams electrostatically.

Generally, the invention is an electron gun structure having a plurality of cathode electrodes associated with common beam forming, converging and focusing electrodes, in that order. The electron gun includes electrodes spaced from the cathode electrodes and designed to form a plurality of beams convergent toward each other and focused substantially independently of convergence on the target electrode. The specific structure is that in which an asymmetric or tilted electron lens is formed in the path of each beam between beam-forming electrodes and focusing electrodes, so that when the beams pass through respective focusing fields, they are already converging toward each other.

Figure 1 shows a sectional view of a cathode ray tube having a gun structure in accordance with my invention;

Figure 2 is an enlarged sectional view of the gun structure shown schematically in Figure 1;

Figures 3, 4 and 5 are enlarged sectional views of modifications of the invention of Figures 1 and 2.

Figure 1 shows a cathode ray tube having an evacuated envelope with a large bulb portion 10 and a neck portion 12 axially aligned with the bulb portion. Within the neck portion 12 is mounted an electron gun structure 14 for forming a plurality of electron beams directed substantially in the same direction along the axis of the tube neck into the bulb portion 10. The end of the bulb portion 10 is closed with a glass wall or face plate 16, which has on its inner surface a phosphor coating 18. The electron beams are directed toward the coating 18 and are caused to strike the coating with relatively high energies. The phosphor coating upon being struck with the electron beam, luminesces with a visible light. The electron beams are simultaneously scanned over the surface of the screen 18 by magnetic deflecting fields formed by a plurality of coils formed into a deflection yoke 20 mounted around the tube neck 12. The scansion of the beams can be of any desired configuration and is normally a rectangular shape, when tubes of the type described are used for viewing television pictures.

The plural beams of the tube Figure 1 may be focused on the phosphor screen 18 to strike the screen surface at different spots which are spaced, or the plural beams may be converged a sufiicient amount to strike a common point at the surface of the phosphor screen 16 or on the mask 22.

One utility for plural beam tubes is in color television where each beam is modulated with signals corresponding to one of the primary colors of the televised picture. One type of color television tube is similar to that shown in US. Patent 2,677,779 to H. C. Goodrich. Tubes of this type utilize an apertured mask electrode 22, which may consist of a thin metal sheet conforming with the curvature of face plate 16, as shown in Figure 1. The apertured mask has a multitude of apertures therethrough of elemental size and spacing as disclosed in the above cited patent to H. C. Goodrich. The mask 22 is used with a phosphor screen formed of groups of three phosphor dots, each phosphor dot of each group luminescing with a different primary color under electron bombardment. One group of phosphor dots is aligned with each aperture of the mask 22 of the tube. The operation is that in which the mask 22 shields each dot from all of the electron beams except one. Each electron beam passing through any one of the apertures of mask 22 will strike a single dot of the corresponding group of three dots.

Accordingly, then the phosphor dots struck by the electron from one gun are those which luminesce with a red light, while the phosphor dots struck by a second and third gun luminesce with a green and blue light, respectively.

An embodiment of the invention is shown in Figure 2 in greater detail and consists essentially of an electron gun structure for forming a plurality of electron beams together with means for converging the beams at the target or screen structure of the tube. The beam forming structure of the gun of Figure 2 consists of a plurality of cathode electrodes 24, which consist essentially of short tubular members mounted in a substantially parallel relationship through apertures in a ceramic support and insulating member 26. One end of each cathode cylinder 24 is closed by solid wall portion 28 which is coated with a well known electron emittiing material. During operation, the cathode electrodes 24 are heated by filaments 30 mounted within each cathode cylinder. Surrounding the cathodes 24 is a common tubular control electrode 32 closed by a wall portion 34 having an aperture shown overlying each coated cathode portion 23. Closely spaced from the control grid wall 34 is an apertured accelerating electrode plate 36 having an aperture aligned respectively with each aperture in control grid portion 34 and the corresponding cathode surface.

Spaced along the axis of the tubular envelope portion 12 from the accelerating electrode 36 are beams converging and focusing electrodes including two tubular accelerating electrode members 38 and 40. The opposite ends of electrodes 38 and 40 are closed with apertured Wall portions 42 and 44, respectively. Spaced toward :he screen 18 from accelerating electrode 40 is another accelerating and focussing apertured plate electrode 46 :onsisting essentially of a curved apertured plate having 1 very short tubular extension 48. The apertures of the : lectrodes 36, 38, 40 and 46 are each aligned with a :orresponding aperture of an adjacent electrode to prowide substantially a straight line path for the passage of :lectrons from cathodes 24 respectively toward the screen [8.

Appropriate voltages are applied to the several elecrodes of gun 14 and in the order of values indicated in =igure 2. The values are placed adjacent to arrows from :ach electrode, respectively to indicate the connection of :ach electrode of gun 14 to the appropriate source of Jotential. The potential values shown in Figure 2 are hose which can be used to operate the gun 14 in the manner to be described. However, these values are not imiting.

As shown in Figure 2, the several electrodes of gun 14 re fixed in operative alignment with each other by being mounted on insulating support rods 50 by short metallic tuds 51 welded to each electrode respectively. Electrode 6 is connected by spring fingers 52 to a conductive raphite wall coating 54 which is formed on the inner urface of the envelope portion 12. Wall coating 54 exends from electrode 4-6 into the envelope bulb portion and to a point adjacent the masking screen 22. The pring fingers 52 maintain wall coating 54 at the same otential as electrode 46. Also, the masking screen 22 nd the aluminizing phosphor screen 18 may be connected the same potential source as the coating 54 to form a lbstantially field free space between the gun 46 and 1e phosphor screen 18. This arrangement, however,

not limiting as the potential of either the masking elec- 'ode 22 or the phosphor screen 18 may be established 2 different values from that of the accelerating electrode and for such purposes as beam acceleration and beam eceleration or beam focusing, etc.

The cathode electrodes 24 together with the negative id electrode 32 and the accelerating electrode 36 conitute the beam forming means. During tube operation, )ltages are applied to these electrodes with values as dicated in Figure 2. Due to the positive potential on electrode 36, electrons from the coated surfaces 28 are urged through the apertures in grid plate 34 and are formed into a plurality of beams, accelerated along paths 55. The cathodes 24 are spaced equidistant from an axis of symmetry 57 which may be the common axis of gun 14. If two cathodes 24 are used, they may be disposed in a common plane on opposite sides of axis 57. Three cathodes 24 may be arranged in a deltagrouping about axis 57. Apertured wall portion 42 of electrode 33 is curved as indicated in Figure 2. If two cathode electrodes 24 are used, plate 42 may be formed with a'curved surface facing electrode 36 and normal to the common plane of cathodes 24. With a delta arrangement of three cathodes 24, plate 42 has a spherical surface facing plate 36 and normal to axis 57 at the center of plate 42.

With electrodes 38 and 36 operated at diiferent positive potentials, there is established an electrostatic field between these electrodes which is non-uniform with respect to each electron beam passing between electrodes 36 and 38. As shown in Figure 2, the apertures in the electrode plates 36 and 42 are spaced from the common axis of these two electrode plates, which is also the axis of gun 14. The electrostatic field between plates 36 and 42 is non-uniform or non-symmetrical in each beam path passing between the aligned apertures of plates 36 and 42. This is due to the fact that adjacent surfaces of plates 36 and 42 are non-parallel and form in the path of each beam an asymmetric lens which bends each electron beam toward the gun axis, as schematically shown in Figure 2. The potential diiference between electrodes 36 and 38 is adjusted to control the convergence of the electron beams for bringing the beams to closely spaced spots on the target or screen portions 18 and 22 of the tube. The convergence of the beams can also be controlled to bring the beams together at a common point either on the mask 22 or on the phosphor screen 16.

The apertures in electrode plates 44 and 46 are placed in the paths of the converging electron beams. These electrode plates 44 and 46 are also provided with appropriate curved surfaces normal to the beam paths so as to form a symmetrical lens field therebetween when different potentials are applied to the electrode plates. This lens field extends into the aligned apertures of plates 44 and 46 and forms a focusing action on each electron beam to focus it to a sharp point at the screen end of bulb portion 10. Because of the curvature of plates 44 and 46, the electron lens portions between the aligned apertures of these plates are each symmetrically disposed about their respective electron beam paths so that the eifect of each lens thus formed is to focus the electrons of each corresponding beam with no elfect on the convergence of the beam toward the gun axis.

Electrodes 38 and 40 are tied to substantially the same DC. potential so as not to provide any effective field therebetween. However, electrodes 38 and 40 are insulated one from the other so that the potential of electrode 38 can be varied independently of the potential of electrode 40 to control the convergence of the several beams in any desired manner without aifecting the focus ing fields between electrodes 44 and 46. For example, in the simultaneous scanning of the several beams over the surface of the target screen structure 18-22, variation in the convergence in the beams is necessary to maintain the convergence of the beams at the target. Accordingly, a varying potential or convergence modulation signal is applied to electrode 38 to vary the convergence of the several beams in accordance with the deflection of the beams over the target surface and in a manner to maintain convergence of the beams always at the target. Such convergence modulation is not a part of this invention. Such convergence modulation can be applied to electrode 38 by connecting the electrode electrically to a signal generator 56, which provides a voltage varying with the deflection of the several beams by the fields of yoke 20. The insulation of electrode 40 from electrode 38 also enables the individual focus of each beam to be varied substantially independently of the convergence of the beam.

Figure 3 shows an alternative structure for providing substantially the same results as the structure of Figure 2. Parts of the gun structure of Figure 3 which are identical to corresponding parts of the gun structure of Figure 2 have been given the same identifying numbers. However, the second accelerating electrode 38 of Figure 3 utilizes an aperture end wall 58 whose surfaces are substantially parallel to the first accelerating electrode plate 36. However, the apertures of plate 58 are offset toward the axis of the gun from the corresponding apertures of plate 36 with which they are aligned. This then provides a distorted, tilted or asymmetric electrostatic field in the path of each beam which deflects the beam from its path substantially parallel to the tube axis into a second beam path directed toward the tube axis. Again by varying the potential difference between electrodes 38 and 36, the bending or deflection of each beam toward the common gun axis can be controlled so that the beams can be converged to any desired degree and as described above relative to Figure 2.

The structures shown above in Figures 2 and 3 constitute a novel gun structure which provides a plurality of closely spaced electron beams along substantially parallel paths. By utilizing common electrode structures, it is possible to avoid the use of separate individual gun structures for each electron beam which results in an economy of space within the tube neck portion 12. This arrangement also enables the use of smaller diameter tube necks and smaller deflecting yokes. Furthermore, the novel gun structure provides relatively simple electrode structures which can be easily manufactured, assembled and aligned. Furthermore, the electrode means for converging the several beams are substantially independent of the beam focusing electrodes and the beam forming electrodes as pointed out above.

The design of the electrode structures shown in Figures 2 and 3 can be varied to change the covergence sensitivity of the electron gun. The convergence sensitivity is defined as the change in converged spot position on the target electrode per percent change in convergence electrode voltage. In Figure 2, for example, the curvature of the plate 42 will determine the strength of the bending field between the electrode portions 42 and 36 and then the convergent sensitivity would be dependent on the curvature of plate 42. Thus, if low convergence sensitivity is desired to minimize the effect of power supply instability, it may be produced with the structure of Figure 2 by decreasing the radius of curvature of plate 42. Likewise, to provide low convergence sensitivity, the apertures of plate 58 of the structure shown in Figure 3, may be offset to a less degree toward the axis of the tube relative to the apertures of plate 36.

Figures 4 and 5 disclose further alternative forms of the invention. The structure of Figure 4 provides a plurality of cathode electrodes 60 formed as short tubular electrodes of conventional design. These cathodes are mounted so that their axis meet at the point of convergence on the tube target at which it is desired that the electrons beams converge. Furthermore, the control grid plate 62, the first accelerating electrode plate 64, the second accelerating electrode plate 66, as well as plates 68 and 70 of subsequent accelerating electrodes, are all formed with surfaces which are concentric with the point of convergence of the beams on the target or any point near the target. The surfaces of these plates must be symmetrical about the axis 61 of symmetry of the plural cathode electrodes 60. This axis extends through the point of convergence of the plural undeflected beams at the tube target. The arrangement of cathodes 60 may be varied as desired to provide a delta arrangement or one with all cathodes in-line with a common plane, for example. Thus, the surfaces of electrode portions 62., 64,

66, 68 and 70 may be spherical, cylindrical or only normal to each beam at the region of each electrode through which the beam passes.

With the gun structure shown in Figure 4, convergence of the three beams on the target screen is provided by the mechanical arrangement of the cathodes and gun electrodes as described. If these electrodes are accurately mounted and aligned, the electron beams will converge in the manner desired as dictated by their mounting arrangement. of the electron beams, the curvature of electrode plate 64 or electrode plate 66 would have to deviate a small amount from the curvature described. Then a change in the potential difference between electrode plates 64 and 66 would change the direction of those electron beams which are not on the axis of the tube. However, instead of causing the curvature of either plate 64 or 66 to deviate from that described, it would also be within the scope of the invention to offset the apertures of plate 66 from the apertures of plate 64 to provide a bending field between the electrode plate, in which case, the beam bending could be varied by applying a dynamic voltage between plates 64 and 66.

- Figure 5 discloses a different structure for providing convergence of a plurality of electron beams. The cathode electrodes 72 are mounted parallel to each other and symmetrically spaced about the axis 73 of a common control grid cylinder 74. The first accelerating electrode 76 consists of an aperture plate, as shown, having a plurality of short tubular members 78 each of which is fixed concentrically about one aperture through plate 76. The tubular members 78 as well as the corresponding apertures in plates 76 and electrode 74 are all coaxially aligned with an electron emitting surface of the cathode electrodes 72. Spaced from the first accelerating electrode 76 is a second tubular accelerating electrode closed by end wall 82 adjacent electrode 76. The end of each tubular member 78 adjacent wall 82 is formed at an angle to the axis of symmetry 73, 'as shown. The wall portion 82 may be a conical or spheroidal configuration or may be formed as a pyramidal surface in which each face of the pyramidal surface overlies an adjacent end of one tubular electrode 78. Thus, a diflerence of potential between electrodes 76 and 80 will provide an asymmetric or tilted lens in the path of each electron beam and will bend the beams toward the axis of symmetry 73. The amount of bending is determined by the tilt of the lens which is adjusted in accordance with the degree of convergence desired.

The several plural beam gun structures shown in Figures 2, 3, 4, and 5 all utilize electrostatic lens fields to converge the electron beams to a point on the tube target electrode. These converging fields are established at the low voltage end of the gun and between the first accelerating fields of the gun and the high voltage focusing fields. Thus, when these tubes are used in circuits providing a modulating or dynamic voltage source to vary the convergence relative to the scanning of the beams over the target surface, two results ensue, which may be advantageous from the point of view of circuit design: (1) these modulating voltages are applied to convergence electrodes having relatively low potentials during tube operation; and (2) the peak-to-peak voltage requirements for the dynamic voltages used are relatively small compared to the voltages which would be required if the converging lenses were formed in the high voltage end of the electron guns.

Since the novel structures disclosed above in accordance with the invention utilize convergence electrodes in the low voltage end of the electron gun, there is an additional advantage in that these novel gun structures are less sensitive to changes in the power supply needed to maintain beam convergence. An important factor in tubes of this type is the convergence sensitivity of the tube which is a measure of the stability of the power supply needed to maintain beam convergence. Since the con However, to provide dynamic convergence lergence electrodes of the structures described have low iensitivity as well as low DC. voltage requirements, there s far less severe voltage regulation requirement of the )OWel supply to the convergence electrodes. The gun :tructures set forth above are advantageous from this oint of view.

What is claimed is:

1. An electron discharge device comprising, a first elecrode means for producing a plurality of electron beams tlong spaced paths having a common general direction, a arget electrode mounted transversely to said beam paths, t second electrode mean spaced along said beam paths )etween said first electrode means and said target for orming a separate focusing lens field in the path of each ieam, and a third electrode means between said first and econd electrode means for forming an asymmetric lens ield in the path of each beam for converging said beams.

2. An electron discharge device comprising, a first elecrode means for producing a plurality of electron beams [long spaced paths having a common general direction, a arget electrode mounted transversely to said beam paths, second electrode means spaced along said beam paths :etween said first electrode means and said target for orming a focusing lens field in the path of each beam, and third electrode means between said first and second elecrode means for forming an asymmetric lens field in the ath of each beam for converging said beams, said third lectrode means including an electrode plate structure havng a plurality of apertures therethrough with one aperure thereof in each beam path, said plate structure being ton-planar.

3. An electron discharge device comprising, a first lectrode means for producing a plurality of electron eams along spaced paths having a common general diection, a target electrode mounted transversely to said eam paths, a second electrode means spaced along said earn paths between said first electrode means and said arget for forming a focusing lens field in the path of each eam, and a third electrode means between said first and econd electrode means for forming an asymmetric lens eld in the path of each beam for converging said beams, aid third electrode means including a pair of nonparallel late structures, each of said pair of plate structures hav- 1g a plurality of apertures therethrough, one aperture 15 each of said plate structures being aligned on each beam ath.

4. An electron discharge device comprising, a first elecode means for producing a plurality of electron beams long spaced paths having a common general direction, a lrget electrode mounted transversely to said beam paths,

second electrode means spaced along said beam paths etween said first electrode means and said target for formig a focusing lens field in the path of each beam, and a rird electrode means between said first and second elec- 'ode means for forming an asymmetric lens field in the ath of each beam for converging said beams, said third lectrode means including a pair of electrode plate struclres each having a plurality of apertures therethrough, ne aperture of each of said plate structures being aligned n each beam path, the surface of one of said pair of late structures facing the other of said pair of plate strucires being non-planar.

5. An electron discharge device comprising, a first lectrode means for producing a plurality of electron earns along spaced paths having a common general dizction, a target electrode mounted transversely to said eam paths, a second electrode means spaced along said earn paths between said first electrode means and said trget for forming a focusing lens field in the path of each earn, and a third electrode means between said first and :cond electrode means for forming an asymmetric lens eld in the path of each beam for converging said beams, lid third electrode means including a pair of electrode late structures each having a plurality of apertures therelrough, one aperture of each of said plate structures being'aligned on each beam path, the surface of one of said pair of plate structures facing the other of said pair of plate structures being curved.

6. An electron discharge device comprising, a first electrode means for producing a plurality of electron beams along spaced paths having a common general direction, a targetelectrode mounted transversely to said beam paths, a second electrode means spaced along said beam paths between said first electrode means and said target for forming a separate focusing lens field in the path of each beam, and a third electrode means between said first and second electrode means for forming an asymmetric lens field in the path of each beam for converging said beams, said third electrode means including a pair of electrode plate structures, each having a plurality of apertures therethrough, one aperture of each of said plate structures being aligned on each beam path, said aligned apertures being oifset one from the other relative to said beam path.

7. An electron discharge device comprising, a first electrode means for producing a plurality of electron beams along spaced paths having a common general direction, a target electrode mounted transversely to said beam paths, a second electrode means spaced along said beam paths between said first electrode means and said target for forming a focusing lens field in the path of each beam, and a third electrode means between said first and second electrode means for forming an asymmetric lens field in the path of each beam for converging said beams, said third electrode means including a pair of electrode plate structures each having a plurality of apertures therethrough, one aperture of each of said plate structures being aligned on each beam path, one of said plate structures being substantially normal to said common general direction, the adjacent surface of the other of said plate structures to said one plate structure being unequally spaced from said one plate structure.

8. An electron discharge device comprising, a first electrode means for producing a plurality of electron beams along spaced paths having a common general direction, a target electrode mounted transversely to said beam paths, a second electrode means spaced along said beam paths between said first electrode means and said target for forming a focusing lens field in the path of each beam, and a third electrode means between said first and second electrode means for forming an asymmetric lens field in the path of each beam for converging said beams, said third electrode means including a pair of electrode plate structures each having a plurality of apertures therethrough, one aperture of each of said plate structures being aligned on each beam path, said first electrode means including a plurality of tubular cathode electrodes mounted with their longitudinal axes converging to a point adjacent to said target, said pair of electrode plate structures being curved, one of said pair of plate structures having the center of its curvatures substantially at said point of convergence, the other of said plate structures having a curvature differing from that of said first plate structure to provide an unequal spacing between said pair of electrode plate structures.

9. An electron discharge device comprising, a first electrode means for producing a plurality of electron beams along spaced paths having a common general direction, a target electrode mounted transversely to said beam paths, a second electrode means spaced along said beam paths between said first electrode means and said target for forming a focusing lens field in the path of each beam, and a third electrode means between said first and second electrode means for forming an asymmetric lens field in the path of each beam for converging said beams, said third electrode means including a pair of electrode plate structures each having a plurality of apertures therethrough, one aperture of each of said plate structures being'aligned on each beam path, a plurality of tubular members mounted on one of said pair of plate structures and extending between said pair of plate structures with one of said tubular members coaxially surrounding each of the apertures of said one plate structure, the ends of each of said tubular members adjacent to the other of said plate structures lying in surfaces at an angle other than normal to said common general direction.

10. An electron gun structure for a cathode ray tube, said gun structure comprising a plurality of electrodes for forming a plurality of electron beams along substantially parallel paths, electrode means spaced from said beam forming electrodes for forming a separate focusing field in the path of each of said electron beams, and electrode means positioned between said beam forming electrodes and said focusing electrode means for converging said electron beams toward each other.

11. An electron gun structure for forming a plurality of electron beams within a cathode ray tube, said gun structure comprising first electrode means for producing a plurality of electron beams along spaced paths having a common general direction, a second electrode means spaced along said beam paths between said first electrode means and said target for forming a focusing lens field in the path of each beam, and a third electrode means between said first and second electrode means for forming an asymmetric lens field in the path of each beam for converging said beams, said third electrode means including an electrode plate structure having a plurality of apertures therethrough with one aperture thereof in each beam path, said plate structure being non-planar.

12. An electron gun structure for producing a plurality of electron beams within a cathode ray tube, said gun structure comprising a first electrode means for producing a plurality of electron beams along spaced paths having a common general direction, a second electrode means spaced along said beam paths between said first electrode means and said target for forming a separate focusing lens field in the path of each beam, and a third electrode means between said first and second electrode means for forming an asymmetric lens field in the path of each beam for converging said beams, said third electrode means in cluding a pair of electrode plate structures, each having a plurality of apertures therethrough, one aperture of each of said plate structures being aligned on each beam path, said aligned apertures being ofiset one from the other relative to said beam path.

13. In a cathode ray tube the combination comprising electron beam control means having a longitudinal axis, a target electrode mounted in spaced relationship with said beam control means and disposed transverse to said longitudinalv axis, said beam control means comprising first electrode means for producing and directing a plurality of spaced electron beams toward said target electrode, and second electrode means interposed between said first electrode means and said target electrode, said second electrode means being formed to provide an electrostatic field having rotational asymmetry about an axis lying substantially coincident with said longitudinal axis for converging said beams at said target electrode.

14. An electron discharge device having: means for producing and directing a plurality of electron beams in the same direction; bipotential lens means having a first electrode and a second electrode for causing said beams to converge upon one another; said first electrode having means for reducing the potential gradient of said lens in the regions of entry of said electron beams.

15. An electron discharge device having: means for producing and directing a plurality of electron beams in the same direction; bipotential lens means having a convergence electrode for causing said beams to converge upon one another; said convergence electrode having means for reducing the potential gradient of said lens in the regions of entry of said electron beams relative to adjacent regions, said last named means including a wall member disposed transversely of the path of said beams and having apertures to admit electron beams into said lens means.

References Cited in the file of this patent UNITED STATES PATENTS 2,289,319 Strobel July 7, 1942 12,301,743 Nagy et a1 Nov. 10, 1942 2,348,133 Iams May 2, 1944 2,457,175 Parker Dec. 28, 1948 2,496,127 Kelar Jan. 31, 1950 2,660,612 Wood Nov. 24, 1953 2,677,779 Goodrich May 4, 1954 2,690,517 Nicoll Sept. 28, 1954 2,714,688 Reed Aug. 2, 1955 2,721,287 Van Ormer Oct. 18, 1955 2,726,347 Benway Dec. 6, 1955 2,726,348 Benway Dec. 6, 1955 2,729,759 Kratz Jan. 3, 1956 2,735,031 Woodbridge Feb. 14, 1956 2,761,990 Amdursky Sept. 4, 1956 OTHER REFERENCES Proceedings of the I.R.E., October, 1951; pages 1236 to 1240.

Disclaimer 2,957,106.Han'nah U. Moodey, Lancaster, Pa. PLURAL BEAM GUN. Patent dated Oct. 18, 1960. Disclaimer filed J an. 14:, 1972, by the assignee, ROA Uorpomtion. Hereby enters this disclaimer to claims 6 and 12 of said patent.

[Ofiicz'al Gazette J2me 2'7, 1.972.]

Disclaimer 2,957,106.-Ha4mah 0. Moodey, Lancaster, Pa. PLURAL BEAM GUN. Patent dated Oct. 18, 1960. Disclaimer filed J an. 14:, 1972, by the assignee, ROA Corporation. Hereby enters this disclaimer to claims 6 and 12 of said patent.

[Ofiioial Gazette June 27, 1.972.]

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