US2190069A - Space discharge device - Google Patents

Description

V Feb. 13, 1940. H. E. HOLLMANN SPACE DISGI IARGE DEVICE Filed April 14, 1957 ATTORNEY.

Patented Feb. 13, 1940 UNITE STATES PATENT orrlca SPACE DISCHARGE DEVICE Application April 14, 1937, Serial No. 136,748 In Germany June 23, 1938 10 Claims. (Cl. 250-27) The present invention relates to electric space discharge devices for use in the amplification, modulation and rectification of electric currents or potentials, more particularly to devices of the type wherein a concentrated electron discharge beam is impinged upon a target or output electrode and deflected in accordance with a controlling signal or magnitude so as to strike the target electrode with varying cross-sections to 10 cause a corresponding variation or modulation of the curent in an associate output circuit. De-

vices of this character are known as deflector or beam discharge tubes as distinct from the ordinary type of electron tube wherein the intensity 5 or density of an electron discharge current is controlled by varying the so-called "space charge" within the tube by means of a grid or equivalent control element.

In a known type of deflector discharge tube of :u the above character, two output or target anodes are arranged adjacent to each other and connected to a common output circuit in push-pull arrangement. In the normal position the electron beam strikes both targets equally resulting in the same current flow in the associate output circuits. If the beam is deflected in either direction in accordance with a controlling signal or magnitude. more current will be collected by one of the target anodes than by the other target anode in such a manner that the current diflerential in the associate output circuits may serve to operate a translating device or to produce a control potential for a subsequent amplifying stage.

A disadvantage of discharge devices of the aforementioned character is the fact that secondary electron emission may take place from the output or target anode when struck by the primary electrons of the impinging electron beam. Since the secondary electrons emitted 0 from a target anode cannot move against the field accelerating the electron beam, they will accumulate and form a space charge or electron cloud in front of the target anode. This disadvantage is of a specially serious nature it a high 5 potential difference exists between the target anodes as is the case in a push-pull arrangement of the type described. In the latter case, the secondary electrons will pass from the less negative target anode to the more positive target anode thereby forming an electronic resistive path therebetween which greatly impairs the sensitivity and effectiveness of the electron beam control.

In order to eliminate the above defect it has been suggested to provide a suppressor grid in front of the target anode in the path of the electron beam. This suppressor grid serves to collect the secondary electrons emitted from the target anode in a manner similar to the suppressor grids provided in the ordinary pentode amplifying tubes known in the art. While it is possible by this expedient to secure an almost complete elimination of the effect of secondary emission from the target anode, a new difficulty arises by reason of the fact that the primary electrons of the discharge beam become decelerated by the action of the opposing field between the suppressor grid and target anode, resulting in a substantial impairment of the concentration of the electron beam. As a result, the impinging crosssectional area of the electron beam upon the anode becomes more diifused causing a substantial decrease .of the sensitivity of control which latter as is understood depends directly on the size and sharpness of the impingingcross-sectional area 01' the beam.

An object of the present invention is to remove the above difliculty and to utilize the secondary electron emission for additional amplification oi the output current.

Another object of the invention is to increase the sensitivity and efllciency of a' discharge device of the above character using a concentrated electron beam deflected in accordance with a controlling signal or magnitude.

Another object is to provide a composite amplifier and electron beam discharge device char-' acterized both by increased efliciency and sensitivity as well as fldelityoi the deflection by a controlling signal or magnitude.

A further object 01' the invention is the provision of a composite direct coupled amplifier and cathode ray device adapted for recording or translating variable magnitudes and character-' lzed by increased fidelity of the record or output current obtained substantially without dependence on the frequency or rate of change of the signal or magnitude being recorded or translated.

The above and further objects and aspects oi the invention will become more apparent from the following detailed description taken with reference to the accompanying drawing forming a part of this specification and wherein Figure 1 illustrates diagrammatically one form of a discharge device constructed according to the invention,

Figure 2 shows a modification of a discharge device of the type according to Figure 1,

Figure 3 is a partial view of a discharge device according to the preceding figures illustrating a further modification oi the invention, and- Figureflsafurtherpartialviewmustratinga composite discharge amplifier and cathode ray device constructed in accordance with the invention..

Like reference numerals identify like parts in the diiferent views of the drawing.

According to the improvements of the present invention, the target or collecting electrodes in a deflector tube of the general type described above is of foraminous construction such as in the form of a flnely meshed wire net or grid referred to as a target grid for the purpose of this specification. The latter preferably consists of a material having high secondary electron emission by the use of a suitable metal or metal alloy having a high work flmction or conditioned by special treatment, such as by oxidation or the like, well known in the art. The secondary electrons released due to impact of the electron beam are removed or attracted in the direction of the beam by a further anode or positive electrode disposed behind the target grid and maintained at a positive potential relative to the latter. The electric field produced by this anode extends through the target grid in such a manner that not only secondary electrons released from within the meshes oi the grid. but also those released trom the front side of the grid are removed and attracted towards the anode. From this it is seen that a decelerating or braking field opposing the main electron beam is avoided wherebythe latter may reach the target grids without disturbance and impairment.

Referring more particularly to Figure l of the drawin the same represents a discharge tube il ustratin the basic principle oi the invention. There is shown at it a vessel or envelo e includin a cathode H which may be a thermionic cathode of either the direct or indirectly heated tyne maintained at a suitable tem erature for electron emission by means of a heating source to be connected to terminals ii. The electrons emitted bv the cathode are concentrated or focused into a sharp beam by the aid of a suitable focusing or electron lens system consisting in the example illustrated of a air of annular acceleration electrodes l2 and i3 maintained at positive potentials relative to the cathode. As is understood. the potential of the electrode I3 is hi her than that of the electrode l2. The design of the elements and operating characteristics are furthermore chosen in such a manner that a. sharp image of the cathode is formed in a lane containing a pair of grid sha ed tar et anodes IR and I1 maintained at a suitable positive accelerating potential. The electron beam is deflected in accordance with a controlling signal or magnitude by the aid of any of the well known deflecting means such as a pair of electrostatic deflecting plates ll and I! connected to the terminals of a control circuit supplying the current or potential variation to be translated.

As is understood, any other type of deflecting arrangement may be provided such as a pair of magnetic field coils well known in the art of cathode ray tubes. If the deflecting force, that is in the example shown, the controlling electric field, iszero, the axis of the cathode ray will be symmetrical to both the target grids l6 and ii. If the beam is deflected from its zero position towards either the left or the right, it will impinge upon one of the grids II or I! with a greater portion of its cross-sectional area than upon the other grid. In the extreme deflection the entire beam current will be impinged upon either of the target grids.

According to the present invention there are further provided a pair of solid collecting anodes or suppressor electrodes i8 and is disposed behind the target grids II and I'I, respectively, and serving to attract the secondary electrons emitted from the latter by impact of the electron beam. The suppressor anodes l8 and I9 are maintained at a higher positive potential relative to the target grids IO and II. to produce an accelerating field therebetween in such a manner that substantially all the secondary electrons and if desirable the primary electrons passing through the meshes of the target grids l6 and I! will be attracted towards the anodes without reacting upon or influencing the primary discharge beam prior to its reaching the target grids l6 and II.

In accordance with a further improvement of the invention, the collecting or suppressor anodes i8 and i8 serve not only for suppressing the effect of secondary electron emission, but are further utilized for amplifying or multiplying the primary electron current. For the latter purpose the anodes l8 and i9 serve as output electrodes and are connected to the high tension source indicated by the sign in series with load impedances 2t and 25 while the grids i 8 and H are constructed of a. suitable material or treated to produce high secondary electron emission and are biased by fixed potentials. An output or utilization circuit may be coupled with either or both of the load impedances 20 and 2t in a manner well understood. Since the number of secondary electrons substantially exceeds the number of primary electrons, provided the target grids consist of a suitable material or conditioned to have a high secondary emission .or work function, a considerable amplification or multiplication of the primary electron current is obtained substantially free from distortion due to the absence of coupling impedances depending on the frequency or rate of change of the deflecting potentials or currents. As is understood, the output circuit may be connected directly to the target grids i8 and H in case no further amplification by secondary emission is required in which case the load impedances 20 and 2| are connected to the grids l8 and I1 and the suppressor anodes i 8 and I9 are maintained at a fixed potential.

In order to prevent mutual reaction between the discharge paths enclosed by the target grids and the associate output or suppressor anodes due to stray electrons or other coupling eflects, there is provided a screen 22 which may be grounded or biased to a potential equal to that of the target grids l6 and 111. Since the latter are at equal positive potential and do not carry alternating currentsthe control effect by the target grids is due exclusively to the change in the distribution of the current-the two grids may be directly jointed or constructed in the form of a single electrode. In the latter case, as is understood the output anodes l8 and i9 may remain unchanged.

The electric isolation of the two discharge paths for the secondary electrons may be further improved by arranging the target grids l6 and I 'l at. an angle with the axis of the electron beam such as shown in Figure 2. If both grids are Joined as described above, an angular target electrode is obtained whose bisecting plane includes the aids of the electron beam when the latter is in its zero or resting position. There is further shown in Figure 2 an arrangement for further multiplication comprising a plurality of additional secondary emission grids 28, 26 and 26. 27 disposed intermediate the target electrodes 18 and I1 and the collecting or output anodes I8 and I9, respectively. For each of these grids the preceding grid acts as a secondary emission source whereby the number of impinging electrons is multipled by secondary emission. To obtain this eflect the potential of the grids should increase in succession such as by the connection of the grids to successive taps of a suitable biasing source such as a potentiometer or battery shown at 29. By a cascade multiplication of this type considerable final output currents and an extremely high amplification or gain is obtained from a comparatively weak initial electron emission which latter is desirable in the interest of the concentration or electron optical focusing of the electrons into a sharp beam. There is further shown in Figure 2 a resonant output circuit comprising an induction coil shunted by a condenser 81 connected to the output anodes l8 and 19. The coilSB has a center tap connected to the positive pole of the source 29 to provide the necessary high tension or anode potential. A tube of this type may be used for the amplification of high frequency currents in a variety of circuit connections known in circuits using the ordinary type of electron discharge tubes. Thus, there may be provided a feedback or regenerative circuit such as is shown in Figure 2 wherein portions of the potential drop developed across the inductance 30 are fed back to the input or deflecting plates 14 and i5 for either increasing (regeneration) or decreasing (degeneration) the amplification or for maintaining sustained oscillations to be utilized in an associate output circuit coupled with the inductance 30.

As is obvious, the new deflector discharge tube according to the invention has many uses, especially where distortionless amplification is required independent 01 the frequency or rate of change of an input signal or magnitude. In a tube constructed according to the invention, the frequency range practically extends from zero, that is pure direct current amplification up to the highest practical frequencies due to the fact that no coupling impedances dependent on frequency or causing electric inertia effect are required, with the exception of the inherent inertia eflect of the electron movement and the inertia of the secondary electron emission.

As is understood, the discharge tube as described may comprise a single target grid and anode only in place of the differential or pushpull construction described hereinabove. In the latter case, oneof the target grids and associated anode are omitted and replaced by a suitably shaped collecting electrode or screen. As is understood, however, the efficiency and effectiveness of such a tube is inferior to the push-pull construction described.

If the entire primary current is impinged upon the target grids IE or I'll considerable anode currents are set up due to the amplification by secondary emission. The sum of these currents should remain constant throughout the operation to insure optimum sensitivity and fidelity. The output currents produce voltage drops across the load impedances 20 and 2| dependent on the current distribution whereby the anode supply voltage is decreased by the amount of these voltage drops. Thus, in order to remain within the saturation region and to maintain optimum operating conditions for secondary emission, it is necessary to choose a sufliciently high anode potential or to limit the load impedances 20 and SI. In the latter case, the amplifying action of the tube may not be utilized to the fullest extent possible.

In order to overcome this disadvantage, there is provided according to Figure 3, an additional target electrode 32 interposed between the main target grids l6 and i! which serves to collect the central portion of the primary electron beam having a limited and well defined focusing area. The operating conditions are chosen in such a manner that the two target grids are struck only by the marginal cross-sectional zones of the electron beam. Thus, for instance, if the entire focusing area has a width of 3 mm. the auxiliary target 32 may have a width of 2 mm. leaving 1 mm. for both marginal zones; that is mm. for each side. From this it is seen that in a tube of this type, the full control or maximum sweep can be obtained by a deflection of mm. while in an ordinary construction without the auxiliary target 82, a 3 mm. deflection would be required for the same control swing.

In order to prevent the primary electrons impinged upon the auxiliary target 32 from producing a secondary space charge, the auxiliary target 82 is constructed in the form of a grid or wire net so that secondary electrons emitted from it may be attracted by a further anode or suppressor electrode 83 similar to the anodes l8 and i9. To prevent mutual reaction between the discharge paths by stray electrons or the like, a pair of screens 84 and 35 are provided which may be connected to ground or biased to a positive potential equal to the potential of the target grids I8, I I and 82.

The primary electrons attracted towards the anode 3S and the secondary electrons emitted by the auxiliary target 32 are normally lost for the amplification process. However, since the intensity of these electrons remains constant as long as the controlling current or potential of the tube does not become excessive, they may be utilized in accordance with a further improvement of the invention to serve as a source for an electron current in an associate amplifier or cathode ray section combined with the first amplifier section of the tube.

A composite tube construction of this type is illustrated in Figure 4. In the latter, the arrangement of the outer target grids l6 and I1 and the central discharge path between the auxiliary target and suppressor 33 is substantially similar as shown in Figure 3 with the exception that the target grids I6 and I1 and associated output anodes i8 and iii are arranged at an angle to the axis of the electron beam and that further multiplying secondary emission grids are provided in a. manner substantially similar as shown in Figure 2.

Figure 4 diilers from Figure 3 by the fact that the auxiliary or suppressor anode for the control portion of the electron beam is constructed in the form of a finely meshed wire net or grid capable of or conditioned to have high secondary emission similar as the remaining multiplying grids in the tube. This suction anode shown at 36 serves as a cathode for producing an electron beam in the adjacent section of the tube which in the example shown is a cathode ray oscillograph but which may be a similar deflector type amplifier as the first section as is understood. For this purpose, the electrons accumulating in the vicinity of the anode 36 are collected and concentrated by means of a focusing system comprising a pair of suitably biased annular electrodes is and ll in such a manner as to produce a sharply focused. reduced electron image upon a target or iluorescent screen 52 as shown in the example illustrated. The electrode 38 may serve as a large suri'ace cathode for the cathode ray in which case the size and shape of the luminous spot will depend on the electron optical focusing characteristics, or alternatively a small part of the electron bundle emitted by the anode 38 may be segregated by means of an apertured disc or screen 38 whereby a sharp image of the aperture is formed on the fluorescent screen. Electron optical systems for producing and focusing electron images are well known in the art and further details are not thought to be necessary as being outside the scope of the invention.

There is shown in Figure 4 a further improvement and modification of the invention in that the output potentials produced at the output anodes l8 and it serve for directly controlling the deflection of the beam of the cathode ray section. For this purpose the anodes l8 and it are directly connected to the deflecting plates 43 and Ed respectively as shown. However, it is understood that the electron beam produced by the electrodes 36, 39, 4B and 4| may cooperate with one or more target or output electrodes to obtain a further amplification of the input signals initially applied to the deflecting plates II and ii. In this manner, a very compact construction and arrangement is obtained with the shortest possible connections between the associate elements in such a manner that the amplification or recording is substantially independent or the frequency or rate of change or the recording impulses or signals and a sensitivity and amplifying gain is obtained which has heretoiore been impossible with arrangements known in the prior art.

As is understood, the invention has many uses in connection with the amplification, modulation or generation of electric as well as in recording of electric current or potential variations. One of 1 for illustration, but that the novel thought and underlying idea oi the invention is susceptible oi numerous variations and modiflcations'coming within the broader scope and spirit of the invention as defined in the appended claims. Accordingly, the drawing and specification should be regarded in an illustrative rather than a limited sense.

I claim:

1. In a discharge device, means for producing a concentrated electron beam, means for deflecting said beam, apair oi foraminous target anodes having high secondary electron emission characteristics and arranged at an angle whose bisecting plane coincides with the axis of said electron beam in its normal position, whereby said target anodes are impinged diflerentially by gradsally varying cross-sectional portions of said electron beam when the latter is deflected in oppomenace anodes opposite from said electron beam in weed relation to said target anodes, means for maintaining said further anodes at a positive potential relative to said target anodes, and a push-pull output circuit connected to said fur-- ther anodes.

2. In a discharge device, means for producing a concentrated electron beam, means for deflecting said beam, an angularly bent ioraminous target electrode having high secondary electron emission characteristics and arranged with its bisecting plane coinciding with the axis of said electron beam in its normal position, whereby the angular surfaces of said target electrode are impinged diflerentially by gradually varying cross-sectional portions or said electron beam when the latter is deflected in opposite directions from its normal position in accordance with variations of an applied input signal to be translated, and a pair or iurther anodes each disposed in spaced relation to one of the angular surfaces of said target anode and at the side of said target anode opposite from saidelectron beam, means for maintaining said further anodes at a posttive potential relative to said'target anode. and an output circuit connected to each of said further anodes. I

3. In a discharge device, means for producing a concentrated electron beam, means for deflecting said beam, a pair of i'oraminous target anodes having high secondary electron emission characteristics and arranged to be impinged difleren- "tially by gradually varying cross-sectional por tions of said electron beam when the latter is deflected between a central and opposite limit positions in accordance with variations of an applied input signal to be translated, a pair of further anodes each disposed in spaced relation to said target anodes at the side or said target anodes opposite from said electron beam, means for maintaining said further anodes at a positive potential relative to said target anodes, output impedance means connected to each of said further anodes, and at least one further ioraminous electrode arranged intermediate said target anodes and said further anodes, each of said intermediate electrodes being capable of high secondary electron emission and biased at a potential positive relative to the potential or the preceding electrode.

4. In a discharge device, means for producing a concentrated electron beam, means for deflecting said beam, 9. pair of ioraminous target anodes, a further foraminous target anode arranged intermediate said first target anodes, whereby said first target anodes are difl'erentially impinged by varying cross-sectional portions or said electron beam when the latter is deflected in accordance with variations of an applied input signal to be translated, said target anodes being conditioned to have high secondary electron emission, and output anodes disposed in spaced relation to each of said target anodes at the side of said target anodes opposite from said electron beam, means for maintaining said output anodes at a positive potential relative to the associated target anodes, and an output impedance connected to each of said outputanodes associated with said first mentioned target anodes. 7

5. In a discharge device, means for producing a concentrated electron beam, means for deflecting said beam, 9. pair 0! foraminous target anodes, a further foraminous target anode intermediate said flrst target anodes, whereby said first target anodes are diflerentially impinged by varying cross-sectional portions of said electron beam when the latter is deflected in accordance with variations of an applied input signal to be translated, said target anodes having high secondary electron emission characteristics, output anodes disposed in spaced relation to each of said target anodes, a source of potential for maintaining said output anodes at a positive potential relative to said target anodes, and output impedance means connected between said output anode associated with said first target anodes and said,

source of potential.

6. In a discharge device, means for producing a concentrated electron beam, means for deflecting said beam, a pair of foraminous target anodes, a further i'oraminous target anode disposed intermediate said first target anodes, whereby said first target anodes are diflerentially impinged by varying cross-sectional proportions of sadi electron beam when the latter is deflected in accordance with variations of an applied input signal to be translated, said target anodes being conditioned to have high secondary electron emission, output anodes disposed in spaced relation to each of said target anodes at the side of said target anodes opposite from said electron beam, output impedance means connected to said iurther anodes associated with said first mentioned target anodes, the output anode associated with said intermediate target anode being conditioned to have high secondary electron emission to serve as an electron source, and means for utilizing the electrons produced by said source in a separate discharge stream of said device.

"I. In a discharge device, means for producing a concentrated electron beam, means for deflecting said beam. 9. pair of ioraminous target anodes, a further toraminous target anode disposed inther anodes associated with said first mentionedtarget anodes, the anode associated-with'said intermediate target anode being of foraminous construction and conditioned to have high secondary electron emission, and means for concentrating and utilizing the electrons emitted by said last mentioned anode in a separate beam within said device.

8. In a device as claimed in claim 7 including means for deflecting said last mentioned electron beam.

9. In a device as claimed in claim '7 including means for deflecting said last mentioned electron beam, and means for directly controlling said last mentioned deflecting means by potential variations developed at said further anodes associated with the first mentioned target anodes.

HANS ERICK HOHMANN.

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