US2766398A

US2766398A - Electron discharge device

Info

Publication number: US2766398A
Application number: US346711A
Authority: US
Inventors: Richard K Orthuber
Original assignee: Deutsche ITT Industries GmbH
Current assignee: TDK Micronas GmbH; International Telephone and Telegraph Corp
Priority date: 1953-04-03
Filing date: 1953-04-03
Publication date: 1956-10-09
Anticipated expiration: 1973-10-09

Description

1956 R. K. ORTHUBER ELECTRON DISCHARGE DEVICE Filed April 3, 1953 Fig. 3

Fig. 5

INVENTOR. RICHARD K. ORTHUBER 50940074 2/,J1 (JM A TTORNEYS United States Patent v ELECTRON DISCHARGE DEVICE Application April 3, 1958, Serial No. 346,711 8 Claims. (Cl. 315 -3) The present invention relates to an electron discharge device and more particularly to an electrode construction for forming a beam of charged particles into a predetermined cross-sectional shape.

In electron discharge devices of the type which utilize an electron stream or beam of high density which extends along a relatively long path, certain difficulties have been encountered both in initiating the stream and in avoiding excessive dispersion of the electrons. It is well known that the electrons comprising the beam repel each other thereby tending to throw the peripheral electrons radially outwardly with consequent increase in beam cross-sectional dimensions. Certain principles and devices have been proposed for focusing-and collimating beams to prevent the aforementioned dispersion and to provide cross-sectional beam dimensions of sharply defined predetermined configuration. One method of collimatirn an electron beam resides in the use of beamforming electrodes which are so shaped as to produce at the beam-boundary an electrostatic potential distribution which simulates the potential distribution of the beam free of lateral boundaries. Beam-forming electrodes of this type have a predetermined shape and are usually considerably larger in radial dimension than the formed electron beam. Such a construction therefore ccnduces to a relatively largeelectron gun assembly whichnecessarily requires a correspondingly large envelope or housing.

It is therefore a principal object of this invention to provide for electron discharge devices a beam-forming electrode which controls the cross-sectional shape of an electron beam and which requires a minimum of space.

It is another object to provide for electron discharge devices a beam-forming electrode which prevents dispersion of electrons along a portion of the path of an electron stream by means of a controlling electric field. It is still another object of this invention to provide a beam-forming electrode which encompasses the path of the beam and which produces an internal electric field which varies progressively along the electrode length to provide varying acceleration of the beam electrons by an amount just adequate to maintain the individual electron paths collimated or uniformly convergent or divergent.

in accordance with the present invention, it is proposed to provide a space-discharge assembly having an accelerating electrode which surrounds an axial portion of the beam path. This electrode comprises a potential distribution element extending axially of the path, which produces an electric field having radially inwardly directed components progressively varying in intensity along the length of the element thereby accelerating the'charged particles of the beam by an amount just suflicient to maintain the beam cross-sectional dimensions uniform or varying them in a desired manner.

For a better understanding of, the invention, together with other and further objects thereof, reference is made to the following description taken in connection with the l 'atented Oct. 9, 1956 2 accompanying drawing with the scope being pointed out in the appended claims.

In the accompanying drawing:

Fig. 1 is a perspective illustration of one beam-forming embodiment of this invention;

Fig. 2 is an end view thereof showing the cathode;

Fig. 3 is a longitudinal section of Fig, 1;

Fig. 4 is a circuit diagram of the electrical components thereof;

Fig. 5 is a longitudinal section of another embodiment and Fig. 6 is a diagrammatic illustration of a vacuum tube incorporating either of the foregoing illustrated embodiments.

For certain types of electron tubes, it is desirable and often times necessary that the electron beam emitted by the cathode and collected by an anode or the like have a predetermined density and cross-sectional shape. For example, in some tubes, a beam of circular cross-section is used, while in others, a beam of sharply defined rectangular cross-section is needed; With reference to the rectangular beam, various means have been proposed and used, for obtaining such a shape, however, the means heretofore used has achieved the desired beam control only in one dimension.

With reference to Fig. 1, a single beam-forming electrode constituting one embodiment of this invention serves, by itself,- the purpose of forming a relatively sharply defined beam of rectangular cross section.

This electrode comprises a hollow support 1 of rectangular cross-section, whichis made of some insulating material such as ceramic. This support is open at both

ends

2 and 3, respectively, and has secured in registry with the opening at end 3 a cathode electrode 4 provided with a plane emitting surface and suitably centrally supthe position of ported by a carrier plate 5. The carrier plate 5 is suit- I ably aflixed to the end 3 of the support 1 by cementing ing 7 per unit length should be cons'ta nt. This winding may be produced by any means well known to the art such as by the evaporation of a suitable metal through a suitable mask onto the internal surface of the support 2 or by irridizing through a similar mask. By applying a source of D. C. potential, such as the battery 8, to the ends of this winding, the potential drop will increase linearly along the turns of the winding from left to right, the battery 8 being connected with its positive terminal to the right end of the winding and its negative terminal t0 the cathode end of the winding. By making the pitch of the winding constant through the axial length of the support, the potential change axially of the support will vary linearly. However, close examination of Figs. 1 and 3 of the drawings will reveal that the pitch of the winding progressively varies from one end to the other.

The spacing between turns is exaggerated for clarity. With the battery 8 in a circuit, diagrammatically shown in Fig. 4, which includes the resistor (winding) 7, cathode 4, and a collector or anode 911, connected as shown, electrons emitted by the'cathode 4 will flow unidi' rectionally toward the open end 2 for utilization, if desired, by a collector 9 spaced a suitable distance from end 2. Since the battery 8 is applied to the opposite ends of the resistor 7, an electric field from cathode to the open end will be produced. The intensity of this electric field will obviously vary progressively from the cathode to the open end 2, and will therefore exert a progressively varying influence on the flow of electrons. As was explained previously, the electrons comprising the beam tend to disperse; however, this tendency can be accurately counteracted by means of the electric field produced by the winding 7.

It is known that the dispersal force tending to throw the electron radially outwardly varies as the distance from the cathode increases; therefore, it logically follows, that if the inward component of the electric field produced by the winding 7 can be made to vary correspondingly as the distance from the cathode increases, the various electrons comprising the beam will be effectively collimatcd depending upon the field configuration.

The proper design of the winding 7 may be further elaborated by considering the following mathematical explanation. Langmuir-Childs law states that the potential produced by the charges along the length of the electron beam varies with the distance X from the cathode according to:

V=5680 f X where:

i=current density of the electron beam in amperes per square centimeter (ELDJPJCHLZ);

X =distance in centimeters from the cathode; and

V=potential in volts.

This condition of potential distribution as produced by the beam must now be equalized along the beam boundary.

By letting the factor 5680 1 equal the constant K, the formula may be expressed as indicating the relationship of the beam-boundary potential in terms of distance X from the cathode. The variable spacing a between turns determines the potential gradient at the beam boundary.

According to Langmuir-Childs law, this gradient must be dV 113 dX 4/3KX Making V increase in equal steps D for each turn, this gradient becomes and both gradients are equal for where a=pitch of the winding for any given distance X from the cathode.

The general observation to be derived from the foregoing is the fact that in order to produce a containing beam-boundary, the pitch of the coil is made variable so that the distance between the turns of the coil decreases with increasing distance X from the cathode.

Referring now to Fig. 5, another arrangement for producing the beam-boundary potential is illustrated, the principal difference between the arrangement of this embodiment and that of Fig. 1 being in the negligible amount of power needed to form the beam boundary. In this embodiment of Fig. 5, the insulating support 1 of rectangular cross section is provided on its internal surface with a system of interleaved axially extending wedges, these wedges being produced by metal evaporation or irridizing as explained in the description of the embodiment of Fig. 1. Essentially, there are two series of interleaved, axially extending areas of conducting wedges and 11, the areas comprising the conducting members 10 and 11 being mutually insulated from each other. These areas are tapered or wedge-shaped and extend substantially from one end of the support 1 to the other. The bases of the respective wedges are conductively connected together. The wedge system 11 is connected to the cathode 4, as diagrammatically illustrated, and the wedge system 10 is connected to an accelerating potential such as the positive terminal of the battery 8. The cathode 4 is conductively coupled to the negative terminal of this same battery.

Now with this system of wedges 10 and 11 completely surrounding the path of the electron beam emitted by the cathode 4, an electric field will be produced inside the support 1 which at any axial point has an intensity dependent upon the resultant effect of the adjacent portions of the two systems 10 and 11 which are at different potentials. The potential of the field developed by these two wedge systems will be a maximum at end 2 and zero at end 3 with intermediate potential values occurring along the length of the support 1. Thus, by reason of the peculiar shape of the two systems 10 and 11, it will be seen that the fields inside the support 1 will vary in intensity along the axis thereof in accordance with the relative effective wedge width. With these parts 10 and 11 thus arranged about the path of the beam, planes intersecting the beam at right angles will be approximately equipotential surfaces at all respective points along the length of the electrode, except in close proximity to the electrodes.

Thus at any point along the electrode, the gradient of the potential is given by the particular shape of the respective wedges 10, 11. In order to fulfill the beamboundary condition for maintaining the beam in truly collimatcd form, it is therefore only necessary to increase the width of the wedges 10 in accordance with the 4/ 35 power of the cathode distance X.

Since the wedge systems 10 and 11 are mutually insu" lated from each other, no current is needed for producing the boundary defining field, and consequently no power is consumed in the process of forming the beam.

From the foregoing it will be apparent that the space required by the electrode of this invention need only be slightly larger than that of the cross-section of the beam thereby conserving space in electron gun assemblies. In prior art devices, such as the Pierce gun, considerable skill is required in properly aligning the gun parts so that the proper field for guiding the beam is developed. The ad ustment of the Pierce gun parts is quite critical and requires a considerable amount of time and skill to achieve. Since in the present invention the beam-forming field 1s directly dependent upon the physical arrangement of the electrode members, and since this physical arrange ment may be achieved by the use of metal evaporation through masks, it is seen that mass production techniques may be utilized for producing such electrodes within tolerance dimensions, in considerable quantities.

The beam-forming electrodes described in the foregoing contain areas of insulator exposed to the path of the electron beam. In some instances, it is possible that these exposed areas will acquire an undesired charge due to the interception of electrons from the beam, but this is successfully overcome by superposing a continuous, very slightly conducting layer on the electrode internal surface which has a conductivity high as compared to the insulator but low as compared to the winding or wedges. By the use of this conducting layer, disturbance of the potential-distribution pattern developed by the winding or wedges is avoided.

While the invention has been disclosed in connection with the formation of collimatcd beams of rectangular cross-section, it will, of course, occur to any person skilled in the art that the principles of this invention may be utilized in the formation of other shaped beams composed of electrons which individually travel along straight rectilinear paths. Thus, it is possible to produce divergent or convergent beams. In the production of divergent electron beams, a cathode having a part-cylindrical or spherical, convex emitting surface is used, in contrast with a part-cylindrical or spherical, concave emitting surface for convergent beams. In all cases, the electrons emitted in a direction normal to the cathode surface will continue in the same straightline direction by reason of the beam-forming field produced by the electrode.

In such cases the pitch of the gradient-defining Winding or the shape of the interlaced wedges on the beamenclosing electrode must be derived in an anaiagous manner, as mentioned hereinbefore for a collimated beam, by substituting for the space charge equation the well known relationships between potential and radius for spherical or cylindrical space charge flow as derived by I. L. Langmiur and K. Blodgett. (Phys. Rev. J. 24, July 1924, p. 53, and Phys. Rev. 22, October 1923, pp. 347-357).

While there has been described what is at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. In an electron discharge device, an accelerating electrode surrounding an axial portion of the space charge path and comprising a potential distribution element extending axially of the path, said element producing an electric potential distribution which progressively varies from one end of the element to the other according to the four thirds power of the axial distance from the point of entrance of the path into the electrode to the point of egress therefrom.

2. In an electron discharge device, an accelerating electrode surrounding an axial portion of the space charge path and comprising a potential distribution element extending axially of the path, said element producing an electric potential distribution which progressively varies from one end of the element to the other to accelerate the components of the space charge just sufficient to maintain certain cross-sectional dimensions of said path along the length of said electrode, said element comprising a resistor which provides said potential distribution along its extent.

3. In an electron discharge device, an accelerating electrode surrounding an axial portion of the space charge path and comprising a hollow support open at opposite ends and made of insulating material, a resistive element mounted on the inner surface of said support in helixlike form which varies in pitch from one end to the other of said support in such a manner as to provide a potential distribution along the axial length of the support which progressively increases in amounts sufficient to maintain the cross-sectional dimensions of said paths uniform throughout the axial length of said resistive element.

4. In an electron discharge device, an accelerating electrode surrounding an axial portion of the space charge path and comprising a hollow support open at opposite ends and made of insulating material, a resistive element mounted on the inner surface of said support in helix-like form which varies in pitch from one end to the other of said support in such a manner as to provide a potential distribution along the axial length of the support which progressively increases in amounts sufficient 6 to maintain predetermined cross-sectional dimensions of said path throughout the axial length of said resistive element, and a space charge source mounted adjacent the open end of said support which is adjacent the minimum potential plane of said resistive element.

5. In an electron discharge device, an accelerating electrode surrounding an axial portion of the space charge path and comprising a hollow insulating support having a uniform cross-section along its axial extent, a series of turns of a resistive element mounted on the internal surface of said support and extending axially of the latter, said resistive element having a uniform resistance per unit length, the pitch of said turns varying from one end of the support to the other according to the reciprocal of the one thirds power of the distance from one end of the electrode to the other.

6. In an electron discharge device, an accelerating electrode surrounding an axial portion of the space charge path and comprising a hollow insulating support having a uniform cross-section along its axial extent, at least two series of interleaved axially extending areas of conducting members provided on the internal surface of said support, said members being insulated from each other and extending axially inwardly from opposite ends of said support respectively, the width of one series progressively increasing of the support according to the four thirds power of the axial distance from a point adjacent the smallest width dimension of said one series.

7. In an electron discharge device, an accelerating electrode surrounding an axial portion of the space charge path and comprising a hollow insulating support having a uniform cross section along its axial extent, two series of the interleaved areas of conducting members provided on the internal surface of said support, each series comprising a plurality of axially extending strips which vary in width progressively from one end to the other, the widest portions of each series being disposed adjacent opposite respective ends of said support, the width dimensions of said areas further varying progressively from one end to the other to produce an electric field internally of the support which varies progressively axially of the support in a manner to maintain the cross sectional dimensions of said path uniform for the length of said conducting members, the areas of said two series being insulated from each other, and means for applying different potentials to said two series respectively for producing the aforementioned electric field.

8. In an electron discharge device, an accelerating electrode surrounding an axial portion of the space charge path and comprising a resistive element in helix-like form which varies in pitch from one end to the other in such a manner as to provide a potential distribution along the axial length thereof which progressively increases in amounts sufiicient to maintain the cross-sectional dimensions of said path uniform throughout the axial length of said resistive element.

References Cited in the file of this patent UNITED STATES PATENTS 2,143,580 Ruska Jan. 10, 1939 2,179,097 Law NOV. 7, 1939 2,185,239 Von Ardenne Jan. 2, 1940 2,264,624 Dillenburger Dec. 2, 1941 2,266,411 Clavier et a1. Dec. 16, 1941 2,291,462 Gardner July 28, 1942 2,409,222 Morton Oct. 15, 1946 2,617,076 Schlesinger Nov. 4, 1952 2,617,077 Schlesinger Nov. 4, 1952 2,630,544 Tiley Mar. 3, 1953