US2442848A

US2442848A - Electron control tube

Info

Publication number: US2442848A
Application number: US433899A
Authority: US
Inventors: Bernard C Gardner
Original assignee: Farnsworth Research Corp
Current assignee: Farnsworth Research Corp
Priority date: 1942-03-09
Filing date: 1942-03-09
Publication date: 1948-06-08
Anticipated expiration: 1965-06-08

Description

June 8, 1948. Q GARDNER 2,442,848

ELECTRON CONTROL TUBE Filed March 9, 19422.v

Ill;

GRID WVOLTAGE INVENTOR RDNER Patente June 8, i943 iD ST ATENT OFFICE ELECTRON CONTROL TUBE Application March 9, 1942, Serial No. 433,899

11 Claims.

This invention relates to an electron control system and more particularly to an electron control system in which the effect of random fluctuations of the velocity of a stream of electrons is minimized.

In conventional electron control systems, an electron stream is generated, in which the initial velocities of the various electrons in the stream show random fluctuations. As a result of this, there are limitations in the degree of control that can be exercised upon the electron stream. Applicants invention is directed to reduce these limitations.

In order more clearly to understand applicants invention, it will be described as adapted to a control system whose operating characteristics result in a high ratio of transconductance to the D. C. plate current. Such control systems are particularly important for use with electron multipliers in which the A. C. component and the D. C. component of the electron stream are equally multiplied. For voltage amplification, itis necessary to operate over a substantially linear portion of the grid voltage-plate current characteristic. If a conventional control device is operated over a linear portion of its grid voltageplate current characteristic, the ratio of the transconductance to D. C. plate current is relatively low. As a result, a large portion of the controlled electron stream consists of D. C. component. Since there is a certain maximum current density permissible in each stage of an electron multiplier, depending upon its physical size, the D. C. component of the current is a limiting factor on the use on electron multipliers in control systems, the function of which is to obtain voltage amplification of the A. C. component of an electron stream.

The object of the present invention, therefore, is to increase the control effects on a stream of electrons whose initial velocities show random fluctuations.

Another object of the present invention is to provide an electron control system having operating characteristics which result in a high ratio of transconductance to D. C. plate current.

Another object of the present invention is to provide an electron-control system which can be operated efficiently with an electron multiplier.

In accordance with the present invention, there is provided an electron control device comprising a source of electrons of varying velocities. Means are provided for controlling the flow of the electrons of varying velocities in such a manner that they are segregated in space in accordance with 2 their respective velocities. The segregated electrons are therafter controlled by means having control effects on the segregated elevtrons Varying in accordance with their respective velocities. Finally, means are provided for utilizing the controlled electrons.

For a better understanding of the invention, together with other and further objects thereof, reference is had to the following description, taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

In the accompanying drawings,

Fig. l is a diagrammatic sectional view of a control device in accordance with the invention;

Fig. 2 is a diagrammatic view of one embodiment of a control means adapted to be used in the control device shown in Fig. 1;

Fig. 3 is a, diagrammatic view of another embodiment of a control means adapted to be used in the control device shown in Fig. 1; and

Fig. 4 is a graph showing the grid voltageplate current characteristic curves for a conventional control device and for a control device built according to applicants invention.

Referring now more particularly to Fig. l of the drawings, there is shown an electron control device comprising an evacuated envelope l0 having a small neck portion II and a large neck portion I2. In the neck portion ll, there is provided a cathode 13, preferably of the type that produces a narrow emission spot. The cathode I3 is heated by a, battery M, as illustrated in Fig. 1. Adjacent the cathode l3, an electrode l6, preferably in the shape of a hollow cylinder, is provided for focusing the electrons emitted by the cathode. The focusing electrode it is energized by a battery H to a potential negative with respect to the operating potential of the cathode [3.

An electrode [8 in the form of a Faraday cage and having an opening 19 and a perforated portion 29 is provided in the main portion of the envelope It. The electrode I8 is energized by the battery 22 to accelerate the focused electrons through the opening [9.

In order to change the path of the electrons accelerated into the Faraday cage, there is provided, preferably, coil means 23, which is connected in series with a variable resistor 24 and a battery 25. However, this invention is not limited for use with an electromagnetic means, such as the coil means 23, for changing the paths of the electrons. Electrostatic means may be used for this purpose, or any other suitable means known in the art. The coil means 23 produces a magnetic field transverse to the longitudinal axis of the main portion of the envelope ID. This magnetic field causes the electrons in the Faraday cage to travel along paths indicated at 21, 28, 23 and 39, depending upon their initial velocities. Thus, it is seen that, when the electrons from the cathode l3 reach the perforated portion 29, they are segregated in space according to their respective velocities.

Adjacent the perforated portion 20 of the accelerating electrode l8 and parallel thereto, there is provided a control member 32 which has openings of gradually increasing size with the smallest openings of the member 32 nearest the electron path indicated at 30. The control member 32 is energized by means of a battery 33, as shown in Fig. 1. A terminal 34, to which a signal may be applied, is coupled to the control member 32 by means of a condenser 35 and a leak resistor 35 is included in the circuit in conventional manner. The member 32, in cooperation with adjacent electrode 38, serves to produce control effects on electrons which pass through the perforated portion 29 and which will be described hereafter.

The electrons controlled by the member 32 may be utilized directly or they may be multiplied before being utilized. According to the preferred embodiment of applicants control device shown in Fig. 1, there is provided an electron multiplier in the neck portion 12 of the envelope l which comprises a plurality of secondary electron emissive electrodes 38 and a collector 39. The electrodes 38 and the collector 39 are held at increasingly positive steady potentials, being connected by way of taps 40 arranged on a voltage divider 4!. As shown in Fig. 1, the collector 39 is energized through an output resistor 42. The voltage divider is energized, preferably by a battery 43. It is evident from the description and the drawings that the control member 32 operates at a potential negative with respect to the electrode 48; the plurality of secondary electron emissive electrodes 38 operate at successively increasing potentials with respect to the potential of the control member 32, and the collector 39 operates at a potential positive with respect to the highest potential applied to the electrodes 38. The output from the collector 39 is taken from any convenient output lead, such as lead 44.

While the preferred embodiment of applicants control device shown in Fig. 1 includes a plurality of electron multiplying stages, this control device may also be used without an electron multiplier.

Applicants control device illustrated in Fig. 1 may also be built with other embodiments of the control member 32. One such embodiment is shown in Fig. 2 where control member 32A is of high resistance material and disposed adjacent the perforated portion 20 of the electrode l8. A voltage drop is produced across the member 32A by a battery 45 and a resistor 46 which are connected across the member 32A, as shown in Fig. 2. The member 32A is energized and has a signal applied to it in the same manner as the member 32 of Fig. l, as is evident from Figs. 1 and 2.

The voltage drop across the member 32A created by the battery 45 is from left to right, viewing the member 32A in Fig. 2, and its effect on the electrons that pass through the perforated lggitiOli 23 is the same as the effect of the member Fig. 3 shows still another embodiment of apparatus for controlling the electrons that pass through the perforated portion 29. This apparatus is adapted to be placed in the neck portion l2 in such a manner that a perforated grid member 32B is disposed adjacent the perforated portion 23. The member 323 is energized and has a signal applied to it in the same manner as the member 32 of Fig. 1. This is clearly illustrated in Fig. 3. Adjacent the member 323, there is provided a collector 393 which is energized by a battery 4'! through an output resistor 48. The output from the collector 39B is taken from any convenient output lead, such as lead 49. The collector 33B is positioned relative to the control member 32B in such a manner that the distance between the members 323 and 39B gradually increases from left to right, as is shown in Fig. 3. The positioning of the member 39B relative to the member 323, in this manner, has the same efiect on the electrons which pass through the perforated portion 20 as does the varying of the size of openings in the member 32 (Fig. l) or in creating the voltage drop in the member 32A.

In Fig. 4, the curve 50 graphically illustrates the grid voltage-plate current characteristic of a conventional control device. The curve 5| graphically illustrates the grid voltage-plate current characteristic of applicants control device. The slopes of the curves 50 and BI represent, respectively, the transconductance of a conventional control device and the transconductance of applicants control device. Since the linear portion of the curve 5! extends closer to the abscissa than the linear portion of curve 50, it is evident that it is possible to operate applicants control device at a higher ratio of transconductance to D. C. plate current than a conventional control device and, at the same time, operate on a linear portion of the transconductance curve.

In describing the operation of applicants invention, reference will be made to the embodiment of the invention shown in Fig. 1. Electrons from the cathode I3 are accelerated by the electrode 18 and directed through the opening [9 by the focusing electrode [6. Under the influence of the magnetic field produced by the coil means 23, the electrons within the Faraday cage travel along paths indicated at 21, 28, 23, and 30, whereby the slowest electrons, that is, the electrons with the smallest emission velocity, follow path 27, and the fastest electrons follow path 30. The electrons which pass through the perforated portion 23 are decelerated by a field between the perforated portion 20 and the member 32 created by the bias potentials applied, respectively, to the perforated portion 20 and the member 32. The velocities of these electrons are controlled finally by an effective potential in such a manner that, when the electrons reach the plane of the member 32, all of them are at the same velocity. The effective potential is produced by the bias potentials applied, respectively, to the control mem ber 32 and the electrode 38 adjacent to the member 32 and by the variation in the size of the openings in the member 32, which has been explained hereinbefore. The segregated electrons from the perforated portion. 20' are decelerated to the same velocity when they reach the plane of the member 32 because the variation in the size of the openings in the member 32 causes the effective potential to radually decrease from left to right across the plane of the member 32. The variation in the effective potential is such that a relatively great amount of effective potential is provided in the path for the slowest segregated electrons, for example, the electrons following amaeas the path 21, and gradually smaller amounts of effective potential are provided in the paths of the electrons of correspondingly greater velocities. As a result of decelerating the electrons in the plane of the member 32 to the same Velocity, it is possible to operate applicants control device at an extremely sharp cut-off characteristic.

It is not possible to operate a conventional control device at an extremely sharp cut-off characteristic because the electrons that pass the plane of the control grid of a conventional control device have random velocities. In order to completely stop the flow of these electrons past the control grid, it is necessary to apply a potential to the control grid of a predetermined value. if this potential of predetermined value is decreased an incremental amount, the fastest electrons will pass through the control grid. If the potential of predetermined value is decreased a further incremental amount, the next fastest electrons, along with the fastest electrons, will pass through the control grid. If the potential of predetermined value is decreased further incremental amounts, eventually all of the electrons from the fastest to the slowest Will pass through the control grid. Thus, it is seen that in a conventional control device, a relatively large change in potential applied to the control grid is necessary in order to pass from a stage where no electrons are allowed to pass the control grid to a stage where all of the electrons are allowed to pass the control grid. And it necessarily follows that such devices do not have the sharp cut-ofi characteristics.

In applicants control device, as has been explained hereinbefore, all the electrons in the plane of the control member 32 have the same velocities. Therefore, only a relatively small change to the potential applied to the control member 32 is necessary to change from the stage where no electrons are allowed to pass the control member 32 to the stage where all the electrons are allowed to pass the control member 32. Since only a relatively small potential change to the member 32 will permit all the electrons from the cathode to flow through the openings of the member 32, applicants control device has an extremely sharp cut-off characteristic.

The controlled electrons which pass through the member 32 are multiplied by the plurality of electrodes 38 and are collected by the electrode 39, from which they are utilized for a useful purpose.

As has just been mentioned, where a plurality of electrons all have the same velocity when they 1 pass a control member, it is possible to control the flow of these electrons and obtain an extremely sharp cut-01f characteristic. This is illustrated by the curve 5| of Fig. 4 which, it is seen, has a linear characteristic extending far toward the abscissa. This results in a high ratio of transconductance to D. C. plate current component of the collected electron stream.

From the foregoing, it follows that an electron control device has been provided in which the effect of random fluctuations of the velocities of the stream of electrons is minimized. This is brought about by producing a stream of electrons of varying velocities in the control device, segregating in space the electrons in accordance with their respective velocities and controlling the segregated electrons with control effects varying in accordance with their respective velocities.

While there has been described what is at present considered the preferred embodiment 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. An electron control device comprising a source of electrons of differing velocities, means adjacent said source for controlling the flow of said electrons from said source to segregate said electrons to follow different paths according to their respective velocities thereby to produce a velocity spectral distribution in a plane in space and means adjacent said plane for controlling said segregated electrons, said control means comprising means for establishing an electron control field of comparatively higher intensity in the higher velocity electron paths than in the lower velocity electron paths.

2. An electron control device comprising a source of electrons of differing velocities, means adjacent said source for accelerating said electrons along a predetermined path in said device, means adjacent said path for establishing a magnetic field in a direction perpendicular thereto for changing the direction of flight of said electrons whereby they follow different paths according to their respective velocities for producing a velocity spectral electron distribution in a plane in space and a member positioned adjacent said plane to efiect a difierin degree of control on said electrons in accordance with said velocity spectral distribution, said control means comprising means for establishing an electron control field of comparatively higher intensity in the higher velocity electron paths than in the lower velocity electron paths.

3. An electron control device comprising a source of electrons of differing velocities, means adjacent said source for controlling the flow of said electrons from said source to segregate said electrons to follow different paths according to their respective velocities thereby to produce a source of electrons of differing velocities, means adjacent said source for controlling the flow of said electrons from said source to segregate said electrons'to follow different paths according to their respective velocities thereby to produce a velocity spectral distribution in a plane in space and a resistor member in a plane parallel and adjacent to said plane for controlling said segregated electrons, the resistance across said resistor member varying in accordance with the velocities of said segregated electrons passing therethrough for establishing an electron control field of comparatively higher intensity in the higher velocity electron paths than in the lower velocity electron paths.

5. An electron control device comprising a source of electrons of difiering velocities, means adjacent said source for controlling the flow of said electrons from said source to segregate said electrons in paths of flight in a predetermined pattern in accordance with their respective velocities and means including a control member and a collector spaced at an angle to said control member and adjacent thereta said. spacing being greater in the: path of higher. velocity electrons than in the path of lower velocity'electrons;

to effect a differing degree of control on. said:

segregated electrons in accordance with said; pattern.

6. An electron control device. comprising a cathode for emitting electrons of differing veIocities, an electrode adjacent said cathode for accelerating said electrons along a path having a predetermined direction, an electromagnetic means adjacent said path for establishing a magnetic field in a direction perpendicular to. said first-named direction to cause said electrons to follow differing paths according to their emission velocities thereby to produce a velocity spectral electron distribution in a plane in space, a control electrode positioned adjacent said plane for establishing an electron control field of comparatively higher intensity in. the higher velocity electron paths than in the lower velocity electron paths, and an electron collector adjacent tosaid control electrode.

7. An electron control device comprising. a source of electrons of differing velocities, means adjacent said source for determining the direction of flight of said electrons whereby they follow paths of flight distributed in a predetermined pattern according to velocity, and electron control means positioned. adjacent said paths of flight, said control means comprising means for establishing an electron control field of comparatively higher intensity in the higher velocity electron paths than in the lower velocity electron paths.

8. An electron control device comprising a source of electrons of diiiering' velocities, means in said device and accessible to said electrons. for accelerating said electrons along a path having a predetermined direction, means adjacent said path for changing: the direction of flight of said electrons whereby they follow paths of flight distributed. in a predetermined pattern according to velocity, and a control: means positioned adjacent said paths of flight, said control means comprising means for establishing an electron. control field of comparatively higher intensity inthe higher velocity electron paths than in. the lower velocity electron paths.

9-. An electron control device comprising a source of electrons of difiering. velocities, means adjacent said source and accessible to said electrons for accelerating said: electrons along a path having a predetermined direction, means adjacent said path for establishing a magnetic field in a direction perpendicular to said first-named direction for changing the direction of flight of said electrons whereby they follow paths of flight distributed ina predetermined pattern according to velocity; and a member positioned in a plane intersecting. said paths of flight comprising. a grid, the elements of. which are spaced in varying'd'egree inaccordance with said pattern for establishing an electron control field of comparatively higher intensity in the higher velocity electron: paths than: in" the lower velocity electron paths.

10;. An electron. control device comprising. an envelope, 2. source of electrons or differing velocities therein, means adjacent said source for controlling theflow of said electronsfrom said source to segregate said electrons in paths of flight distributed in a predetermined pattern inaccordance with their respective velocities and means disposed in said envelope adjacent said paths. for controlling said segregated electrons said control means-comprising means for establishing antelectron control field of comparatively higher intensity in the higher velocity electron paths than in the lower velocity electron. paths;

11. An electron control device comprising an envelope, 2. source of electrons of differing velocities therein, means adjacent said source for accelerating said electrons along a path having a first direction, means adjacent said path for changing the direction of flow of said electrons to segregate said electrons in paths of flight distributed in a predetermined pattern inaccordance with their respective velocities and means. disposed in said envelope adjacent said paths for controlling said. segregated electrons, saidcontrol means comprising means for establishing an electron control field of comparatively higher intensity in the higher velocity electron pathsthan in the lower velocity electron paths.

BERNARD C. GARDNER.

REFERENCES CITED The following references" are of record. in the file of this patent.

UNITED STATES PATENTS Number Name: Date 2,061,387 Prinz Nov.. 17, 1936" 2,092,893 Snow Sept. 14, 1937 2,115,093 Von Ardenne Apr. 26, 1938 2,138,928 Klemperer Dec.. 6, 1938 2,143,146 Farnsworth et a1. M- Jan; 10, 1939 2,157,585 Zworykin et al. May 9, 1939 2,163,787 Hennenberg et al. June 27, 1939' 2,175,697 Nelson Oct. 10, 1939 2,221,447 Flechsig Nov. 1-2, 1940 2,250,511 Varian et al. July 29, 194d 2,271,985 Morton Feb. 3, 1942 2,284,829 Ludi June 2, 1942.