US2080449A - Cathode ray tube - Google Patents

Description

May 18, 1937. M. VON ARDENNE CATHODE RAY TUBE Filed May 24, 1934 INVENTOR NHNFRED VUN HRDENNE BY %w/% ATTORNEY 2 Pi .Ea E9: (9 Q m -1 Fl E1 1-: 53.;

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8 43 a BT50 Patented May 18, 1937 PATENT QFFICE 2,080,449 cA'rHooE any TUBE Manfred von Ardenne, Berlin, Germany, assignor, by mesne assignment-a to Radio Corporation of America, a corporation of Delaware Application May 24, 1934, Serial No. 727,206

In Germany June 12, 1933 12 Claims.

My invention relates to improvements in and methods of operation of cathode ray tubes, in particular for use as oscillographs and in cathode ray television systems. The general form of 5 cathode ray tubes heretoforeknown in the art used, for oscillographs or in cathode ray television comprises the three essential parts: a

thin beam or pencil of electrons, a fluorescent...

target or luminous screen for the electron 10 pencil to strike against to produce a recording high spot, and a mechanism for deflecting the electron beam and varying the intensity of the luminous spot on the screen for producing an image or pattern of desired configuration and l5 characteristics.

In the ordinary cathode ray tubesas known in the art used for oscillographic and television purposes, deflecting potentials of several hundred volts are necessary to move the electron beam 20 over the entire surface of the fluorescent screen. This low sensitivity of deflection necessitates the use of very high anode voltages and high amplification in the sweep or control circuits for produring the deflecting potentials.

25 It is a main object of my invention to provide a novel method of and means for deflecting the electron beam in a cathode ray tube which is characterized by considerably increased sensitivity of the deflection while enabling the use of 30 very high electron velocities required for insuring a brilliant luminous spot upon the fluorescent screen produced by the impact of the electron ray.

As is well known, the sensitivity of deflection 35 of an electron ray may be increased if the deflection takes place at a place where the electrons travel at low speed. In recognition of this fact it has already been attempted to construct tubes in which the electron beam is initially accelerated to a fraction only of the desired final speed and is then passed. through the deflecting system whereupon a final acceleration is applied to secure sufficient kinetic energy of the electron beam striking the fluorescent surface to produce a 45 bright luminous spot' thereon. By this scheme the further advantage is obtained especially in tubes containing a gaseous atmosphere that on account of the low velocity in the ray producing system, the destruction of the cathode by gaseous 50 ions is limited to a minimum. I

However, it has not been possible in practice to satisfactorily carry out the aforementioned scheme for the following reasons among others.

It was not possible to apply an additional or 55 final acceleration to an electron pencilsubjected to a large deflection in both coordinate directions, without'causing serious interference with the proper operation of the tube.

Accordingly it is a further object of my invention to provide a means in the path of a concentrated electron ray for additionally accelerating or decelerating the electrons substantially independent of the direction and/or degree of deflection of the electron pencil relative to a normal or zero position and without any additional impairment of the proper functioning of the tubes. 7

It was furthermore found especially in the case of gas filled cathode ray tubes, that the electron speed in the ray-producing and reflecting 5 space had to be of comparatively high value (several hundred volts) in order to secure a sufficient current intensity at the top of the ray or in turn a sufficiently brilliant luminous spot on thefiuorescent screen.

Accordingly, a further object of my invention consists in a novel method and means whereby an extremely low electron speed may be employed within the space of the deflecting system, resulting in aconsiderably increased sensitivity of reflection while maintaining simultaneously high velocity of the electron ray at the place where the ray strikes against the fluorescent screen.

Still a further object of my invention is the 30 provision of a novel electrode construction in a cathode ray tube for deflecting the beam at a place immediately near the cathode where the electrons move with the lowest velocity, resulting in greatly increased sensitivity of the deflection.

One of the difficulties experienced with cathode ray tubes as known heretofore in the art is the fact that a substantial reaction, especially capacitative reaction, may take place between the 40 deflecting systems used for deflecting the beam in both a vertical and horizontal direction, in particular if two pairs of capacitative deflecting plates are used. This deflection may result in substantial decrease of the sensitvity of deflection, in distortion, and otherwise greatly interfere with the proper operation of the tube.

Accordingly it is a further object of my invention to provide efficient screening means between the deflecting systems in a cathode ray tube for substantially eliminating interaction between deflecting systems.

These as well as further objects and aspects of my invention will be better understood by reference to the following detailed description taken together with the accompanying drawing wherein I have shown several cathode ray tube constructions embodying my invention. The embodiments shown are to be taken as being illustrative only of the underlying principle and novel features of the invention which, as will become obvious, is subject to various modifications and variations coming within the broadest scope thereof as expressed in the appended claims.

In the drawing; in which similar reference nu-' merals identify similar parts in the different views;

Figure 1 illustrates an electrode .construction for accelerating or decelerating an electron beam in accordance with my invention;

Figure 2 schematically illustrates a cathode ray tube having an electrode according to Figure 1 embodied therein;

Figure 3 illustrates another form of cathode ray tube embodying an electrode system enabling the deflection of the cathode ray immediately near the cathode, resulting in greatly increased sensitivity of the reflection;

Figure 4 illustrates a bottom view of the tube according to Figure 3 and the connections to the deflecting plates from a controlling source;

Figure 5 is a front view of the anode or shielding electrode provided in the tube shown by Figure 3; and

Figures 6, 6a and 7, 7a schematically illustrate electrode systems for cathode ray tubes employing the shielding element in accordance with my invention.

In accordance with my invention I provide a means in a cathode ray tube for accelerating an electron ray from either an initial very low velocity or a reduced velocity obtained by previous deceleration to a desired final acceleration without otherwise impairing the operating characteristics and sensitivity of deflection of the electron y.

In accordance with the preferred embodiment of my invention, I have devised an accelerating electrode insuring a gradual potential variation from the place of the initial or starting potential to the final potential to which the ray is to be accelerated. According to a preferred construction, I use a tubular shaped unit as an accelerating electrode comprising substantially two cylindrical elements provided with wedge-shaped teeth engaging each other whereby the accelerating potential is applied to one of said elements.

This construction is shown in more detail by Figure 1 of the drawing. This illustrates the cylindrical metallic unit, or unit provided with a metal coating, used as an accelerating means in which the cylinder is shown to be cut open lengthwise and spread out into a plane. I have shown the one element at I 4 provided with wedgeshaped teeth l4 and the second cylindrical element at l2 provided with similar wedge-shaped teeth l2 engaging the teeth of the first element as shown. The embodiment as shown by Figure l is. of a specific and preferred form to be used for both final acceleration and previous deceleration of the electron beam, and for this purpose I have shown further wedge-shaped teeth I 4' connected to the other side of the cylindrical element I 4 and a further cylindrical element I5 provided with teeth l5 engaging teeth Id of the element M. The arrangement and function of this con-' struction will be explained further in connection with Figure 2.

By providing a suflicient number of teeth in the cylindrical elements forming the acceleration or deceleration electrodes, the conditions obtained are such that a highly homogeneous electric field consists for both undeflected and largely deflected rays passing inside the cylindrical unit.

Generally, the electrode structure for accelerating or decelerating an electron beam in accordance with the invention is of such configuration and design as to produce an accelerating or decelerating electric field which exerts a substantially equal force upon the electrons independent of the direction of the beam through the field. In this manner both the deflected and undeflected beam is accelerated or decelerated in an equal manner without in any way effecting the characteristics of the beam, such as its initial velocity, degree of concentration, etc. liable to produce distortion of the pattern or image produced by the beam upon the luminescent screen.

I have furthermore discovered that obviously on account of conditions prevailing -in the ray generating a concentrating space in gas filled cathode ray tubes and furthermore due to the high stray losses of slow electron rays even within ranges of only 5 centimeters, it is impossible to maintain the electron velocity within the deflecting space at very low values in order to obtain a very high sensitivity of deflection.

I overcome this defect by using a higher initial acceleration voltage in the ray producing system equal to about one-half to one-eighth of the desired electron velocity at the luminous screen. I then provide means for decelerating the electrons within the deflecting space and in this manner I have found it possible to secure extremely high degrees of sensitivity of deflection especially in gas filled cathode ray tubes. The deceleration may be carried out to substantially lower electron volt velocities as would be possible in the above mentioned case where low initial velocity is employed in the space where the ray is produced and initially concentrated, such as by means of a negatively biased concentration cylinder.

When using an initial high electron velocity and subsequently decelerating the electrons to a lower velocity in the deflecting space, the deceleration may be carried out by means of ordinary electrodes, such as by the provision of a pair of circular plates with central openings for passing the electron ray whereby the braking or decelerating voltage is applied to the second electrode. However, I have found that in the case of very high decelerating voltages that the ray is deviated from its central position and deflected more or less in a lateral direction so that it is finally prevented from passing through the opening of the decelerating electrode.

In accordance with a further feature of the invention, I prevent the aforementioned deviation of the beam by the decelerating field by the provision of a similar shaped cylindrical electrode system with mutually engaging wedge-shaped teeth as hereinbefore described for efiecting a final or re-acceleration of the electron beam to the desired final velocity.

Referring to Figure 2 of the drawing, I have shown a cathode ray tube embodying an electrode system as described by Figure 1 used for both decelerating and subsequently accelerating an electron beam for the purpose as described. Referring to the drawing, I have illustrated a cathode ray tube comprising a glass bulb I having a neck shaped portion housing the electrode systems for producing and deflecting the electron ray and a spherical shaped end portion including an inclined luminous screen l6 as describedin in? cope'nding application entitled Improvements in and methods of operating cathode ray tubes of even date. Numeral 2 represents a cathode which may be a thermionic filamentary cathode as shown, but it is understood that any other type of cathode may be provided, such as an indirectly heated cathode of known design in the art. The cathode is shown to be heated by a battery I and is surrounded by a cylindrical or concentration electrode 3 negatively biased relative to the cathode by means of a biasing battery as shown at 8 for concentrating the electron stream into a sharply focused pencil. At 4 I have shown a positive or anode electrode for producing an initial acceleration of the electron beam emanating from the cathode and the concentration cylinder 3. The electrode 2 may be of ring-shape with a central opening and provided with a cylindrical unit having wedge-shaped teeth l5 similar to the unit l5 as described by Figure 1. The electrode 2 is connected to a high positive operating potential of about 1000 volts such as shown by the battery 9 to initially accelerate the electron beam. Numeral 10 represents a breaking or deceleration electrode having a lower positive potential applied to it than the electrode 2, such as by means of battery II as shown. The electrode l0 may also be of circular shape with a central opening for passing the electron ray and connected to the cylindrical unit M with teeth l4 engaging the teeth l5 of element 2 as shown in more detail in Figure 1. In this manner a decelerating electric field is produced within the space between the electrodes 2 and ID of favorable potential distribution to enable the electron ray previously accelerated by the electrode 2 to be decelerated to a very lowelectron velocity without deviating from the central position, In this manner high sensitivity of deflection is obtained, such as by means of the usual deflecting mechanism such as the two pairs of electrostatic deflecting plates 5, and 6, respectively, arranged at right angle to each other as shown in the drawing.

I 'The'thus deflected electron ray is subsequently reaccelerated to its final velocity by means of the tubular accelerating electrode f2 provided with wedge-shaped teeth l2 engaging the teeth I4 of the electrode Hi. In this manner as pointed out, a re-acceleration of the electron beameven when deflected to its fullest degree in both coordinates isinsured without any substantial impairment of its characteristics.

I have shown the accelerating potential which may be of the same value as the breaking potential (1000 volts in the above example) applied by a battery ISconnected to the element l2. It was furthermore found that the conditions and the operation can be improved by biasing the screen 16 to a potential equal to the accelerating potential such as shown by the connection of the screen to the plus pole of the battery [3. In the example as illustrated the potential of the battery ll may be within the order of 100 volts or less.

In an arrangement for gas filled cathode ray tubes as described, it is possible to decrease the velocity of the electrons down to almost the ionization potential of the gas, especially if the deflecting system is so constructed that the path over which the electrons travel at the lowest velocity through thegas does not exceed two to three centimeters. If still lower voltages are employed, this will result in an impairment of the definition or Sharpness of the luminescent spot on the screen. Thusflt is preferable to use gases 7 with very low ionization potential in order to secure very high degrees of sensitivity of deflection as is understood. It has furthermore; been found advantageous to use heavy gases with the added advantage of increased ray intensity or correspondingly decreased losses caused by stray electrons.

While I have described a specific arrangement comprising both deceleration and acceleration of the electron ray, it is obvious that I am not. limited to the specific combination as shown. Thus, it is possible to use the decelerating mechanism in connection with any other accelerating arrangement.

In accordance with a further feature of the invention, it is advisable to provide the electrode Ill with a very small aperture through which the low. speed electrons pass, especially in the case of very high deceleration to very low electron velocities. In some cases I found it advantageous to cover the opening of the electrode lll with a fine wire net or grid to secure as straight a course of the lines of field as possible.

Referring to Figure. 3 of the drawing, I have shown another cathode ray tube construction for deflecting the electron beam immediately at the source or'cathode where theelectron speed is a minimum, thus obtaining a maximum sensitivity of the deflection, as is obvious. This type of construction is especially suited for partly or highly evacuated tubes in which the electron velocity at the cathode may be of a very low value as compared with gas filled tubes hereinbefore mentioned.

I have shown a special electrode construction mounted at the cathode serving both for deflecting the electron beam preferably in one direction and at the same time acting as a means for con.- centrating and focusing the electron stream into a sharp beam together with a specially construct ed anode electrode, as will be described hereinafter.

Referring to the drawing Figure 3, Lhave again shown a cathode ray tube comprising a glass bulb I mounted upon a base ll andprovided with an inwardly projecting press it} for carrying the cathode, anode and the deflecting system. The cathode ray tube shown in this figure differs from Figure 2 by the arrangement of the luminous screen 19 directly applied to the inner end wall of the tube in accordance'with well known constructions in the art. Numeral 20 represents the cathode similar as described by Figure 2 connected to terminals 20' mounted at the sides of the base II. I have furthermore shown a box-like system comprising four plates 2|, 22, 23 and 24 arranged in square shape close to each other and surrounding the cathode. Each of the plates'is connected to a connectingterminal or prong 2|, 22', 23 and 24', respectively, mounted at the bottom of the base H, as shown by Figure 4. Figure 4 also shows a cross-section of the plate system and the connection to the prong terminals. By the use of an arrangement of this type the electron beam can be deflected in one direction by applying the controlling potential supplied from a transformer or other source [8 shown in Figure 4 to a pair of opposite plates, in the example illustrated plates 23 and 24. In order to obtain deflection in both directions from the central or zero position of v the electron beam, the remaining plates 2! and 22 should be connected to the mid-tap point, of the controlling source H3, in the example the secondary of the transformer winding as illustrated.

In order to increase the sharpness of the beam which has already been focused by the proper choice of the cathode and by the action of the electrode system II to 24 acting similar to a. concentration cylinder, I have found it advisable to provide an anode 25 surrounding the cathode structure at all sides, such as by means of a circular anode plate 25 covering the cylinder 2T surrounding the. entire cathode structure.

In order to insure large deflections of the cathode ray by the deflecting plate system as shown and preventing the ray from being obstructed by the anode plate. 2.5, I have shown the latter provided with a lengthwise slit 25" to allow the beam to sweep over the entire surface of the luminous screen in a horizontal direction according to the specific example as shown in more detail by Figure 5. If it is further desired to sweep the beam in a vertical direction, a pair ofordinary deflecting plates as shown at 26 may be arranged behind the anode 25.

In an arrangement as described, the anode 25 furthermore acts as a screen between the two deflecting systems for preventing decrease of sensitivity of the deflection and distortion caused by electrostatic interaction between the deflecting systems.

It is furthermore understood that a shielding electrode as shown at 25 in Figure 3 may be employed in connection with any other electrode system in cathode ray tubes and is not limited to the particular construction according to Figure 3- in which the shielding electrode simultaneously acts as an anode for the electron stream.

Thus, referring toFigures 6 and So I have indicated schematically an electrode system of usual construction in combination with a shielding electrode according to the invention. Numeral 28 indicates the cathode ray source such as the concentration cylinder surrounding a cathode. Numeral 29- represents the usual anode which may be in the form of" a disc with a central opening for passing the cathode ray. Numeral 30 shows a first pair of deflecting plates to sweep the beam in a vertical direction. Numeral 3t represents a shielding electrode in accordance with the invention comprising a disc provided with a vertical slit to allow the beam to sweep vertically between the upper and lower deflecting positions, and numeral 32 indicates a second pair of deflecting plates for sweeping the beam in a horizontal direction.

Figures 7 and 72 illustrate a similar system with the succession of the deflectionreversed, in which case the shielding electrode 3 is arranged with its slit in a horizontal position, as will be understood.

I claim:

1. The method' of operating cathode ray tubes consisting of producing a concentrated electron beam; initially accelerating said beam to a velocity being a fraction of the desired final velocity; subsequently non-uniformly decelerating said beam to a very low velocity; deflecting said beam and re-accelerating the deflected beam for securing a desired final electron velocity.

2. In combination, a cathode ray tube having an envelope; means for producing a concentrated electron beam therein; means for accelerating said beam to a low velocity; means for deflecting the accelerated beam; means for applying final acceleration tothe deflected beam, said lastv means aoson ra comprising a pair of tubular elements provided with wedge-shaped teeth engaging each other in comb fashion and means for applying electric potential to one of said elements to secure a gradually increasing accelerating potentialdistribution from the initial velocity of said beam to its desired final victory.

3. In combination with a cathode ray tube; means for producing a concentrated electron beam; means for varying the speed of said beam comprising a. tubular shaped electrode unit through which the beam is passed having substantially two elements provided with wedgeshaped metallic teeth engagingeach other, the open. ends of said units being covered with. disc shaped members provided with central openings for passing the electron beam; and means for applying an electric potential difference between said elements.

4.. A cathodev raytube comprising an envelope; means for producing a concentrated. electron beam therein; a luminous screen for said beamto strike against; a first substantially discshaped positive accelerating electrode to initially accelerate said beam to a predetermined velocity; a second substantially disc shaped decelerating electrode of lower positivepotential than said first electrode for decreasing the velocity of said beam to a predetermined value, said second electrode being also provided with a central opening for passing the electron beam, both of said electrodes having tubular extensions mounted thereon with wedge-shaped teeth engaging each other; means for deflecting the d'ecelerated electron beam; and. further means for subsequently re-accelerating the deflected beam, said last means consisting of a tubular electrode structure comprising substantially two tubular elements provided with wedge-shaped teeth engaging each other with a positive accelerating potential applied to the element closest to said luminous screen.

5. In a cathode ray tube as claimed in claim 4 in which a combined decelerating and accelerating electrode structure is provided comprising two outer and one intermediate tubular elements provided. with wedge-shaped teeth engaging each other; means for applying initial accelerating potential to one of the outer units; means for applying decelerating potential to the intermediate unit; and further means for applying reaccelerating potential to the other outer unit.

6. A cathode ray tube comprising an envelope; a cathode therein; an electrode structure comprising two pairs of opposite plates symmetrically surrounding said cathode and an anode closely surrounding said cathode and said electrode structure whereby the electron stream emitted by said cathode is concentrated into a narrow beam, said anode being provided with an opening for passing said electron beam; and means for applying deflecting potential to one pair of said plates.

'7. A cathode ray tube comprising an envelope; a cathode therein; an electrode structure comprised of twopairs of parallel plates symmetrically enclosing said cathode; a cylindrically shaped anode concentrically enclosing said cathode and said electrode structure whereby the electron stream emitted from said cathode is concentrated into a sharp beam, and a cover mem her for said. anode having a central opening for passing the said electron beam; and meansfor applying deflecting potential difference between one pair of said electrode structures and a luminescent screen for the electron beam to strike against.

8. In a cathode ray tube as claimed in claim '7 in which said cover member is provided with a lengthwise slit to allow sweeping of said beam over the surface of said luminescent screen.

9. A cathode ray tube comprising an envelope; a thermionic cathode therein; an electrode structure being comprised of two pairs of parallel metallic plates arranged at right angle and symmetrically enclosing said cathode; a substantially symmetrical anode enclosing said cathode and said electrode structure whereby the electron stream emitted by said cathode is concentrated into a beam; a cover member for said anode provided with an opening for passing said beam; a source of deflecting potential being con nected to a pair of said plates enclosing said cathode; a connection from the remaining pair of plates to the central point of said source; and a luminescent screen for said beam to strike against.

10. In a cathode ray tube as claimed in claim 9 in which said cover member is provided with a lengthwise slit for enabling said beam to sweep over the surface of said screen.

11. In combination, a cathode ray tube having an envelope; means for producing a concentrated electron beam therein; means for accelerating said beam to a low velocity; means for deflecting said beam; and means for applying final acceleration to said deflected beam, said last means comprising an electrode structure;

and means for applying an electric potential thereto to secure a gradually increasing accelerating potential distribution from the point of initial velocity to the point of final velocity of the electron beam.

12. The method of operating cathode ray tubes comprising producing a concentrated electron beam, initially accelerating said beam to a veloc ity being a fraction of the desired final velocity, subsequently non-uniformly decelerating said beam to a very low velocity, deflecting said beam and non-uniformly re-accelerating the deflected beam for securing a desired final electron velocity.

MANFRED VON ARDENNE.

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