US2748313A - Electron beam tube - Google Patents

Description

y 29, 1956 I J. R. PERILHOU ETAL 2,748,313

ELECTRON BEAM TUBE Filed April 10, 1952 2 Sheets-Sheet l J13 10y b J6 INVENTORS Jeun Robert Perilhou Johan Lodewijk Hendrik Jonker AGE/VT y 29, 1956 J. R. PERILHOU ET AL 2,748,313

ELECTRON BEAM TUBE Filed April 10, 1952 2 Sheets-Sheet 2 INVENTORS Jeun Robert Perilhou Johan Lodewijk Hendrik Jonker BY %W@% AGENT 2,748,313 Patented May 29, 19.

ELECTRON BEAM TUBE Jean Robert Perilhou and Johan Lodewijk Hendrik Jonker, Eindhoven, Netherlands, assignors to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application April 10, 1952, Serial No. 281,612

Claims priority, application Netherlands May 2, 1951 6 Claims. (Cl. 315-25) This invention relates to devices comprising an electron beam tube having an electrode system comprising at least a cathode, an accelerating anode, a collecting electrode and a grid provided between the accelerating anode and the collecting electrode. It furthermore relates to electron beam tubes for use in such devices.

There are in principle two kinds of electron tubes, viz. firstly tubes in which the electrons after leaving the oathode are subject to electrostatic or electromagnetic forces such that the electrons are united to form a beam, and secondly tubes in which such a beam does not occur. The present invention relates to the first-mentioned kind of tubes and to devices comprising such tubes. They include inter alia cathode-ray tubes for oscillography or television purposes and also tubes by which electrical oscillations are produced, amplified, rectified or influenced in other manner. The invention is of general use in such kind of tubes and relates more particularly to the manner in which the electron beam is controlled. Two methods of control may be used in electron beamtubes. The first is similar to the control which may also be used in tubes in which the electron current is not formed into a beam; as a rule, it is referred to as intensity control. In the second method of control, socalled deflection control, the whole of the electron beam is deflected in some direction or other. The intensity control is, as a rule, brought about by an electrode in grid form which transmits a greater or smaller portion of the electron current. In many cases, for example in oscillography or television tubes, this grid has the shape of a plate having a small aperture.

In deflection control use is made of an electrostatic or electromagnetic transverse field.

Since the invention uses deflection control by means of a grid-like electrode, the explanation following hereinafter is necessary for correct understanding of the invention.

It is known that a grid provided between a cathode and an anode and to which a positive voltage with respect to the cathode is applied exerts a certain concentrating action upon an electron current. In passing such a grid, the electron current is divided into a plurality of narrow beams, the number of which corresponds to the number of meshes of the part of the grid covered by the electron current. Said narrow beams may be convergent or divergent, according to the charge on the grid. The charge on the grid is determined by the potential applied and by the position of the grid in the potential field between the cathode and the collecting electrode or anode. If the potential of the grid is lower than the potential which would prevail at the area of the grid in the absence thereof, the grid assumes a negative charge. In this case the beams after the grid are convergent. Consequently, as viewed from the cathode, there are beyond the grid a series of focal points which may be located before, on or after the anode.

The above-mentioned phenomenon naturally also occurs if the electron current passing to the grid is already united into a beam. This beaming need not necessarily be understood to mean that all of the electrons extend in parallel paths, but that there is a distinct main direction of the electron current. If the electron beam before the grid is wide with respect to the width of the meshes of the grid, a plurality of convergent beams occur after the grid, if this has a negative charge, which beams are each narrower than the initial beam. If the initial width of the beam is equal to or smaller than the width of the meshes, a concentrating action is exerted upon such a beam by the grid with negative charge, so that a focus may be produced which may be located before, on or after the collecting electrode.

The phenomenon underlying the invention is the following. When an electron beam after passing a grid having applied to it a positive voltage enters an electrostatic field between the grid and collecting electrode in which the direction of the lines of force intersects the direction of the incident beam, deflection of the electron beam takes place, which is dependent inter alia upon the difference in potential between the grid and the collecting electrode.

If the grid is negatively charged by the arrangement with respect to cathode and anode, then of course, the above-described concentration occurs in addition to the deflection.

A device according to the invention comprises an electron beam tube having an electrode system comprising at least a cathode, an accelerating anode, a collecting electrode and a grid provided between the accelerating anode and the collecting electrode and having applied to it apotential higher than that of the cathode and lower than that of the collecting electrode. The collecting electrode and the grid are so positioned that the direction of the electron beam just before the grid intersects the lines of force between the grid and the collecting electrode, whilst furthermore, an alternating control voltage, with respect to the collecting electrode is set up at the, grid which results in a varying deflection of the electron. beam between the grid and the collecting electrode being v obtained.

It is evident that, as a rule, an electron beam tube re-. quires the use of more electrodes for producing a beam than the above-mentioned electrodes. Since the inven-- tion is independent of the manner in which the beam is produced, the simplest system for producing a beam is given in the description following hereinafter and in the claims. However, any suitable means for producing a beam, either divergent or convergent, can be used in an electron beam tube and a device according to the invention.

In a device according to the invention, the beam in the discharge tube may furthermore be controlled by other means than by the grid provided between the collecting electrode and the accelerating anode. Thus, for example, the intensity of the beam may be varied by means of a diaphragm or a so-called Wehnelt cylinder. The beam may also be deflected in an electrostatic or electromagnetic manner before reaching the grid (hereinafter referred to as the deflection grid) provided between the collecting electrode and the accelerating anode.

The invention increases the number of possibilities for acting upon the beam, of which an advantageous use may' be made for many purposes, since apart from the re quirements for obtaining the above-mentioned deflection by the grid, there are no restrictions with regard to the structure of the electrode system. Consequently, use may' be made, for example, of grids comprising solely parallel' wires or grids comprising crossing wires. The simplest form of the grid is constituted by two parallel wires between which the electron beam passes. Furthermore, a

plurality of control methods may be used in combina tion.

The direction of the deflection brought about by the deflection grid in a tube in which deflection is also used before said grid may coincide with this direction or differ therefrom, for example it may be at right angles thereto. In the former case the deflection grid permits, for example, of providing a correction of the deflection already produced.

, In tubes in which the beam is deflected before the deflection grid, the angles of the beam in its various positions with respect to the grid are in most cases different. However, the deflection brought about by the grid is inter alia dependent upon the said angles. If it is desired, on account of a given variation in potential of the grid, to bring about on the collecting electrode a shift of the striking point of the beam on the collector which is independent of the angle made by the incident deflected beam with the grid, it .is necessary to take particular steps.

For this purpose, for example, the grid electrode and, if necessary, the collecting electrode may be given a predetermined curvature. For plane electrodes there is a different solution, since if the deflection grid and the collecting electrode are located in different planes, the envisaged object is attained if said planes are at an angle to one another such that the direction of each electron beam just before reaching the grid makes, with the grid surface at this area, an angle which is more acute than that made with the plane of the collecting electrode.

If in a tube in which deflection takes place before the deflection grid, this grid has an even width of meshes or pitch, it is unavoidable that the angle enclosed by two lines passing through the centre of rotation of the swinging beam and two adjacent grid wires is different for different positions of the grid. 'The beam, so to say, views the grid meshes from the centre of rotation at a different angle, resulting in a difference in intensity of the focal spot behind each mesh of the grid.

Said difference may be obviated if the spacing between every two adjacent grid wires is made smaller, according as the direction of the electron beam just before the grid encloses a larger angle with the plane of the grid at the area at which the beam passes through it.

It is evident that the above-mentioned steps may be used in combination.

As a rule, it suifices if the voltage supplied and the position of the deflection grid are such that the beam upon reaching the grid is concentrated by the grid so that the width of the beam, measured at right angles to the direction of the grid wires, at the area at which the beam strikes the collecting electrode, is at the most equal to half the width of the beam at the moment at which the beam reaches the grid.

It will have appeared from the aforegoing description that the spacing between the deflection grid and the collecting electrode acts upon both the concentrating action of the grid and its deflecting action. As a rule, the smallest spacing between the grid and the accelerating anode is larger than the smallest spacing between the grid and the collecting electrode.

As explained above, it is necessary that an electrostatic field may be built up between the deflection grid and the collecting electrode. If the collecting electrode consists of metal, difficulties are not to be feared, However, if the collecting electrode is a luminescent screen, steps must be taken to build up said field. For example, it is possible in known manner to mix the luminescent substance with conductive material, for example metal. As an alternative, that side of the luminescent screen which is adjacent the cathode may be covered with a metal layer permeable to electrons (so-called metal backing). Another solution consists in providing a grid before or after the luminescent screen, which grid fulfils the function of the collecting electrode, but which does not prevent the electrons from striking the luminescent screen. For carrying off the charge then acquired by the screen, one has to have recourse to means already known for avoiding said charge, consisting inter alia in a sufficient secondary emission of the screen. The secondary electrons may in this case be collected by the grid-like collecting electrode.

In order that the invention may readily be carried into effect, a number of examples will now be described in detail with reference to the accompanying drawings, of which:

Fig. 1 shows diagrammatically the manner in which the electron beam is deflected;

Figs. 2, 3 and 4 are other embodiments of the system shown in Fig. 1;

Figs. 5, 6 and 7 show diagrammatically an electron beam tube with the necessary connections for the electrodes, together with a source of supply.

In Fig. l, the reference numeral 1 indicates a cathode, emitting electrons which are united to form a beam by means which are not shown. 2 is the collecting electrode and 3 the deflection grid provided in front of it. The electrode 2 has applied to it a potential higher than that at the grid 3, which in turn has a potential higher than that of the cathode 1. The lines of force between the electrodes 2 and 3 extend in accordance with the lines designated 4. The beam indicated by 5 passes through the grid in a direction such that the direction of the lines of force 4 is intersected. Since the electrons after the grid have a tendency to follow the lines of force, a curved path ensues as indicated by 6. It is to be noted that naturally the beam has a particular cross-section, which is not shown for the sake of simplicity. If the grid 3 has a negative charge, the curved path 6 is convergent. This may be of importance if, for example, a sharp focus on the collecting electrode 2 is desired,

The operation of a device according to the invention is based on the fact that an alternating control-voltage is set up between the grid 3 and the electrode 2, so that the field gradient between the grid 3 and the collecting electrode 2 varies. This will also result in variation of the curvature of the path 6, so that the beam strikes the electrode 2 at another point.

Since the operation is based on the fact that the direction of the electron beam before the grid intersects the direction of the lines of force between the grid and the collecting electrode, it will be evident that there is one casein which deflection cannot occur at all, viz. if both grid and collecting electrode are at right angles to the direction of the beam. However, either of the electrodes 2 and 3 may be at right angles to the beam. An example in which the grid is at right angles to the beam is shown in Fig. 2, in which identical elements bear the same reference numerals as in Fig. 1. It is evident that in this case the lines of force extend according to curved paths.

In Figs. 1 and 2 there was no question of deflection of the beam 5 before the grid 3. As explained before, irregularities occur if the beam 5 is deflected over the grid 3. The irregularities are due to the fact that the beam which shifts to and fro over the grid, from the centre of rotation, views the apertures between the grid wires at different angles. Fig. 3 shows an arrangement of the electrodes in which grid 7 has a pitch which regularly decreases from one end to the other. The electron beam 9 is deflected by deflection-plates 10 and 11, shifting to and fro over the surface of the grid 7. If 12 indicates the centre of rotation of the electron beam, the spacing between the grid Wires is such that the angles a and b are equal. The collecting electrode in this figure is indicated by 13.

In Fig. 4, the grid and the collecting electrode are designated 14 and 15 respectively. In this construction it is assumed that the beam turns about a point 16. 1f the grid 14 were parallel to the collecting electrode 15, the deflection brought about by the grid would be greater at the upper end than at the lower end. Consequently, the shift of the striking point of the beam on the collecting electrode 15 for the same variation in potential of the grid 14 would be larger at the upper end of the collecting electrode 15 than at the lower end. The difference in deflection and hence in shift of the striking point is due to the more acute angle which the electron beam in this case would enclose with the grid at the upper end of the grid, since the more acute this angle, the greater is the deflection. If the grid is positioned at an angle to the collecting electrode, as shown in the figure, the length of the electron paths between the electrodes 14 and 15 is at the upper end of the grid smaller than at the lower end. Consequently, with a suitable arrangement it may be ensured that the shift of the striking point on the collecting electrode 15 for the same variation in potential between the electrodes 14 and 15 is the same throughout.

Fig. shows diagrammatically one form of construction of a device according to the invention with the associated connections and a source of supply. An electron beam tube 17 comprises a system (shown here in greatly simplified form) for producing, concentrating and deflecting the electron current emitted by a cathode 18. The cathode 18 is heated by a filament 19 to emit an electron current concentrated inter alia by an accelerating anode 20 to form a beam. The electron beam may be deflected by means of a set of deflection plates 21 and 22 and is deflected over a grid 23, which is equivalent to the grids 3, 7 and 14 from Figs. 1, 2, 3 and 4. Behind grid 23 is a collecting electrode 24, which may be coated with luminescent material. The various voltages for the electrodes are derived from a potentiometer 25, which is connected to a source of supply 26. The alternating voltages bringing about the deflection of the electron beam between the grid 23 and the collecting electrode 24 are supplied by way of a transformer 27.

Fig. 6 shows a particularly simple form of construction of a device according to the invention, suitable for push-pull amplification of electrical oscillations. The general structure of the discharge tube is quite similar to that of Fig. 5 except for the deflection electrodes, since in a tube as shown in Fig. 6 the beam is not deflected between the accelerating anode 28 and the grid 29. The latter comprises only two wires, the beam bedirected into the centre space between said wires. Behind the grid is the collecting electrode which is constituted by two parts, viz. 30 and 31. When alternating voltages are supplied to the grid 29 by way of a transformer 32, the beam may be directed alternately onto the electrode 30 and 31. Consequently, in this case also the operation is similar to that of the deflection plates as used in conventional cathode-ray tubes. The great difference is, however, that there is only one electrode with only one voltage which brings about the defiection.

Fig. 7 shows a device which is substantially identical with that shown in Fig. 6, except that here, so to say, a multiple collecting system is provided. The electrons in this case travel after an accelerating anode 33 in the form of a divergent beam, which is divided by a grid 34 into a plurality of narrower beams 35 which move according to curved paths towards a collecting electrode 36. The collecting electrode 36 is subdivided into a plurality of small electrodes which are alternately connected to another. In supplying an alternating voltage to the grid 34 it may be ensured that all of the beams 35 simultaneously strike one group of electrodes or the other group of the electrode 36. Consequently, there is push-pull action similarly as in Fig. 6. The great advantage is, however, that the beam is divergent and hence, capable of controlling a considerable amount of electricity. Consequently, the effect of this device is very great.

It will be clear that greatly difierent electrical phenomena may be produced or acted upon in numerous ways with a device according to the invention. Thus, for example, a device as shown in Figs. 6 and 7 permits of producing oscillations in a simple manner by providing a coupling between the output electrodes and the grid.

The invention is thus not limited to the embodiments shown.

What we claim is:

l. A circuit-arrangement comprising a cathode-ray tube including a cathode for producing electrons, means including an accelerating anode for forming said electrons into an electron beam, a planar collector electrode positioned in the path of said electron beam, a planar grid electrode positioned in the path of said electron beam between said collector electrode and said anode, the planes of said collector electrode and grid electrode being oblique to the path of said electron beam, means connected to apply to said collector electrode a positivepolarity potential with respect to said cathode whereby a voltage field is produced which has a finite value in the region of said grid electrode, means connected to apply to said grid electrode a potential intermediate the potentials of said cathode and collector electrode and having a value which is negative with respect to said finite value whereby said grid assumes a negative charge thereby to cause said electron beam to converge as it approaches said collector electrode, and a source of alternating voltage connected to said grid electrode to produce a varying deflection of said beam with respect to said collector electrode, said grid electrode being substantially completely transmissive for said electron beam so that substantially all of said electron beam passes through said grid electrode at all times and impinges upon said collector electrode.

2. A circuit-arrangement as claimed in claim 1, in which said collector electrode comprises a coating which luminesces in response to impingement by said electron beam, and including a beam deflecting means positioned to deflect said electron beam before it reaches said grid electrode.

3. A circuit-arrangement as claimed in claim 2, in which the planes of said collector electrode and said grid electrode are positioned at an angle with respect to each other, whereby the amount of deflection of said electron beam due to said alternating grid voltage is substantially uniform throughout the surface of said collector electrode.

4. A circuit-arrangement as claimed in claim 3 in which said grid electrode comprises a plurality of mutually parallel wires.

5. A circuit-arrangement as claimed in claim 4, in which the spacing between adjacent grid wires is successively larger toward the edge of the grid which is farthest from the source of said electron beam.

6. A circuit-arrangement as claimed in claim 5, in which the potential applied to said grid electrode is adjusted to a value to cause said electron beam to converge to a width at said collector electrode of substantially onehalf of the width of said electron beam at said grid electrode.

References Cited in the file of this patent UNITED STATES PATENTS 2,071,382 Balsley Feb. 23, 1937 2,136,105 Jobst Nov. 8, 1938 2,144,085 Rothe et a1 Jan. 17, 1939 2,201,587 Krawinkel May 21, 1940 2,212,645 Morton Aug. 27, 1940 2,401,740 Kilgore Jan. 11, 1946 2,463,535 Hecht May 8, 1949 2,529,408 Montani Nov. 7, 1950 2,570,790 Gray Oct. 9, 1951 2,577,038 Rose Dec. 4, 1951

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