US2165806A - Electric discharge device - Google Patents

Electric discharge device Download PDF

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Publication number
US2165806A
US2165806A US8630A US863035A US2165806A US 2165806 A US2165806 A US 2165806A US 8630 A US8630 A US 8630A US 863035 A US863035 A US 863035A US 2165806 A US2165806 A US 2165806A
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United States
Prior art keywords
electrode
electrons
electron
multiplying
electrodes
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Expired - Lifetime
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US8630A
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English (en)
Inventor
George A Morton
Leslie E Flory
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RCA Corp
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RCA Corp
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Priority to NL47025D priority Critical patent/NL47025C/xx
Application filed by RCA Corp filed Critical RCA Corp
Priority to US8630A priority patent/US2165806A/en
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Publication of US2165806A publication Critical patent/US2165806A/en
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Expired - Lifetime legal-status Critical Current

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J43/00—Secondary-emission tubes; Electron-multiplier tubes
    • H01J43/04—Electron multipliers
    • H01J43/06—Electrode arrangements
    • H01J43/18—Electrode arrangements using essentially more than one dynode
    • H01J43/20—Dynodes consisting of sheet material, e.g. plane, bent

Definitions

  • Our invention relates to electric discharge devices and more particularly to devices of the type wherein amplification of a primary electron stream, such, for example, as is emitted from a thermionic cathode or from a photo-sensitive surface exposed to light, is accomplished through utilization of the phenomenon of secondary emission.
  • an electrode If an electrode is subjected to electron bombardment, it will emit secondary electrons.
  • the ratio of the number of secondary electrons to the number of primary electrons depends, in part, upon the character of the bombarded surface and upon the potential diiference between the surface and the source of the electrons. This ratio can be made considerably greater than unity.
  • a ratio of three or more secondary electrons to one impinging electron is readily obtainable with metallic surfaces treated in known ways and subjected to discharges at potentials. of 300 to 400 volts. Since the emitted electrons exceed the impinging electrons in number, the electrodes emitting them, hereinafter, will usually be referred to as "multiplying electrodes.
  • the ratio of secondary emission from the second multiplying electrode may also be greater than unity.
  • n multiplying electrodes in cascade for example, an amplification of the original or primary electron current equivalent to the amplification per electrode raised to the nth power. A million-fold amplification may be obtained in a single device.
  • an object of our invention to provide an electric discharge device, utilizing secondary electron emission, wherein maximum gain per stage is obtained and linearity may be obtained between input excitation and output current.
  • Another object of our invention is to provide an amplifier or electron multiplier of the secondary electron emission type in which the secondary electron stream from each emitter is con- 0 centrated and is directed accurately to the desired target, and interference between the various secondary electron streams is minimized.
  • Another object of our invention is to provide an amplifier or electron multiplier wherein there is practically no loss of secondary electrons and in which the best conditions for amplification, or other desired results, can easily be obtained by external potential adjustments.
  • Another object of our invention is to provide an amplifier or electron multiplier that is efiicient and reliable in operation and in which the amplification obtainable is very great as compared with the amplification obtainable with a thermionic amplifier of usual type.
  • Another object of our invention is to provide a device of the type described that may be used for substantially any purpose for which thermionic tubes of present types are used, such,
  • an amplifier for example, as an amplifier, a demodulator, an a oscillator, a combined oscillator and demodulator, etc.
  • Another object of our invention is to provide a combined phototube and amplifier that shall be responsive to the very highest frequencies encountered in television transmitting apparatus.
  • a still further and more specific object of our invention is to provide a device of the type described that lends itself readily to mass production methods.
  • electron lenses are made use of for the purpose of concentrating and directing the primary electrons toward the first secondary emitter, the secondary electrons from the first emitter toward the second emitter and so on. This process may be repeated a number of times within the same container and the final greatly amplified stream of secondary electrons is collected by an output electrode.
  • a preferred embodiment of our invention is constituted by an evacuated zig-zag-shape container wherein are supported a plurality of successively disposed electrodes and the inner walls of which, between the electrodes, are provided with conductive coatings which, when supplied with proper potentials, function as electron lenses.
  • the zig-zag shape of the container is not absolutely essential but it readily lends itself to manufacturing methods and it has been found most convenient for experimental purposes.
  • each of the successive electrodes and each of the coatings, going to make up the electron lenses is provided with a lead extending exteriorly of the container, by means of which proper potentials may be applied thereto in operation.
  • Figure l is a view in perspective of a preferred embodiment of our invention, portions of the wall being broken away to more clearly disclose the electrode structure and disposition,
  • Fig. 2 is a diagrammatic view of the device shown in Fig. l, exemplifying the manner in which the several electrodes are energized when the device is utilized for certain of the purposes to which it is adapted,
  • Fig. 3 is a diagrammatic view of an alternative embodiment of our invention.
  • Fig. 4 is a diagrammatic view exemplifying the utilization of our electric discharge device as a degenerative amplifier.
  • an electron discharge device constructed according to our invention, may be constituted by an N- shape evacuated container 5 in one end of which is disposed an electron source constituted by a photo-sensitive cathode 3 and in the other end of which is mounted an output electrode 5.
  • the cathode is shown mainly by Way of example, since the electrons can be introduced into the device from a source exterior thereof.
  • a multiplying electrode 1 having a surface capable of secondary emission is mounted within the container at the junction between the first leg 9 of the container and the connecting portion l 1 between it and the second leg i3, and a similar multiplying electrode i5 is mounted within the container at the junction between the connecting portion and the second leg.
  • Each multiplying electrode is so disposed that the axes of the leg and connecting portion adjacent thereto make substantially equal angles therewith.
  • This lens is constituted by a foraminous cylinder ll adjacent to the cathode and a conductive coating 59 upon the inner wall of the container leg adjacent to the first multiplying electrode, to each of which appropriate potentials may be applied.
  • primary electrons emitted from the cathode are focused and directed toward the first multiplying electrode '1 by means of the electron lens just mentioned and thereby cause the profuse emission of secondary electrons.
  • a second electron lens constituted by a plurality of spaced apart conductive wall coatings 23 and 25, between the first multiplying electrode and the second multiplying electrode. To these coatings the proper potentials may also be applied, as will later be shown.
  • the screen is not an absolutely essential of our improved device. If it is omitted, the first element of the electron lens adjacent to the multiplying electrode, if maintained at a higher potential, will serve to remove the secondary electrons and direct them toward the next multiplying electrode.
  • the second leg 83 of the container may be replaced by a second connecting tube provided with an additional accelerating screen, analogous to the screen element 2!, as well as suitable electron-lens-forming elements, and the secondary electrons from the second emitter may again be concentrated and directed toward a third multiplying electrode.
  • a second connecting tube provided with an additional accelerating screen, analogous to the screen element 2!, as well as suitable electron-lens-forming elements, and the secondary electrons from the second emitter may again be concentrated and directed toward a third multiplying electrode.
  • the output electrode 5 we wish it also to be clearly understood that the elements constituting the electron-lenses may be disposed exteriorly of the container without departing, in any way, from the spirit of our invention.
  • the photo-sensitive cathode is constituted by a disc of pure silver about three-quarters of an inch in diameter and ten-thousandths of an inch thick.
  • the foraminous cylinder is made of nickel 32 mesh screen, which material was also utilized for the accelerating screen electrode.
  • the multiplying electrodes or targets are also of pure silver, substantially one inch in diameter and tenthousandths of an inch thick.
  • the output electrode is preferably made of tantalum or an analogous metal three-quarters of an inch in diameter and five-thousandths of an inch thick.
  • the photo-sensitive electrode, the several multiplying electrodes, the accelerating screen and the electron-lens elements may be supplied with suitable potentials from any available source of direct current.
  • This source is exemplified in the drawings by a potential divider 26 to the negative terminal of which is connected the cathode 3 and to the positive terminal of which, through an output resistor 28, is connected the output electrode 5. From an inspection of Fig. 2, it will be noted that, starting with the cathode, each element is connected to a successively more positive point upon the potential divider.
  • the foraminous cylinder I! is an element of the first electron-lens adjacent to the oathode, it, of course, could be replaced by a conductive coating on the inner wall of the tube.
  • the form shown, however, is advantageous in that it permits the ingress of light from any suitable source.
  • This source might be modulated by a moving photographic sound record or it might be any other source of light corresponding to the fluctuations of which an amplified electric current is desired.
  • the glass envelope was first fabricated in the form shown, the ends of the legs and the junctions between the legs being left open in order to permit the sealing therein of the respective electrode-supporting presses.
  • the positions of the metallic coatings on the glass were marked off and, on the inside of the blank, Was deposited a commercially available platinizing solution following the marks previously made.
  • the whole blank was then heated to approximately 400 centigrade in order to reduce this platinizing solution to metallic platinum.
  • the electrodes, previously described, were mounted on the wires of the glass presses which. were then sealed in place.
  • the tube was sealed to a high vacuum system by means of a tubulation (not shown), through which the tube could be evacuated.
  • a caesium compound such as caesium chromate
  • a reducing agent such as aluminum powder or silicon powder
  • the tube was then baked at 450 centigrade, being evacuated at the same time. The bake continued for approximately thirty minutes after the oven reached the final temperature. After the baking, the tube was cooled and a small amount of pure oxygen was introduced into it at a pressure of approximately 1 mm. of mercury. The cathode and multiplying electrodes were next oxidized by passing an electrical discharge from these elements to some other element in the tube until the electrode surfaces acquired a bluish-green tinge. The oxygen was then pumped out and the pellets of caesium compound and reducer were heated sufficiently to start the reaction which yields metallic caesium. The metallic caesium was driven, by means of heating the appendage, into the main body of the tube. The tube was once more baked at 200 centigrade for approximately ten minutes and allowed to cool. The caesium appendage was then sealed off the tube and the tube sealed off the vacuum system.
  • the caesium would be deposited upon the lens-elements and the electrodes other than those which are intended for primary or secondary emission. Such is undoubtedly the case, but, by reason of the greater affinity of caesium for an oxide, particularly silver oxide, when the tube was heated in the final heating, most of the caesium was driven oii the other elements and was taken up by the oxidized silver electrodes.
  • the caesium forms a chemical compound with the silver oxide which is reasonably stable, although the actual chemical reaction that takes place is not definitely and accurately known.
  • our improved device in addition to its capability of providing a fluctuating current in response to a fluctuating light source, is also capable of giving non-linear amplification. That is to say, in either the photosensitive type or the thermionic type, output current may be obtained which is not directly proportional to input excitation but which follows some other curve.
  • Non-linearity may be, for example, obtained by interposing an impedance device 2'5 between the potential divider and the first multiplying electrode T.
  • This impedance device may be a resistor or an inductor having such electrical characteristics that when the current therethrough changes, the potential on the secondary emitting electrode also changes to alter the gain in proportion thereto.
  • An inductor of course, would be preferable if a characteristic non-linear with re spect to frequency is desired.
  • our improved device may be so operated a degenerative amplifier that a variation in the output current therefrom causes a corresponding variation in the primary electron stream in such direction as to oppose the original stream-variation which causes the said output variation.
  • a resistor 29 is interposed between the potential divider 26 and the second multiplying electrode.
  • a similar resistor 3i is interposed between the potential divider and the photosensitive cathode, the two resistors being coupled through a capacitor 33.
  • a signal to be amplified may be applied to the screen element 2lA interposed between the second multiplying electrode l5 and the output electrode 5 as, for example, by means of an input element, such as a resistor 35, included between the otential divider and the screen. Assuming that the light which energizes the cathode 3 suffers an undesired momentary increase in intensity, this gives rise to (a) increased. photo-emission from the cathode, (b)
  • additional multiplying stages may be interposed between the second multiplying electrode and the output electrode in the manner indicated by Fig. 3.
  • Our improved device either of the photosensitive cathode or the thermionic cathode type, is capable of generating sustained oscillations. This be accomplished through utilization of any of the conventional regeneration circuits which permit of feeding back a portion of the output potential to the input circuit in proper phase.
  • An electric discharge device comprising an evacuated envelope, an electron-source, a secondary emitter-electrode, an accelerating electrode and a target electrode mounted in the order named within said envelope, said emitter-electrode being accessible to electrons from said source and said accelerating and target electrodes being accessible to secondary electrons from said emitter-electrode, and a plurality of apertured electrodes serially disposed between said emitter and target electrodes for focusing said secondary electrons upon said target electrode, the apertures being substantially symmetrical with respect to a line drawn between said emitter, accelerating and target electrodes.
  • An electric discharge device comprising an evacuated envelope, an electron source, a secondary emitter electrode and a collector-electrode mounted in spaced relation in the order named within said envelope, said emitter-electrode being accessible to electrons from said source and said collector-electrode being accessible to secondary electrons from said emitter electrode, and means comprising an accelerating electrode and a plurality of electrically separate electron-lens elements mounted in the space between said emitter and collector-electrodes for directing the electrons in their passage therebetween.
  • An electric discharge device comprising an evacuated envelope, a plurality of electrodes capable of secondary emission mounted in spaced relation within the envelope and means comprising an accelerating electrode and a plurality of electron lens elements mounted in the space between two adjacent secondary emitter electrodes for guiding secondary electrons from one electrode to the other electrode of the pair.
  • An electric discharge device comprising an evacuated envelope, a plurality of electrodes capable of secondary emission and an output electrode mounted in spaced relation in said envelope, an accelerating electrode and a plurality of electron lens elements mounted in the space between two adjacent secondary emitter electrodes for directing electrons therebetween, and a second accelerating electrode mounted in the space adjacent said collector electrode for drawing the electrons from the preceding secondary emitter electrode thereto.

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  • Electron Sources, Ion Sources (AREA)
US8630A 1935-02-28 1935-02-28 Electric discharge device Expired - Lifetime US2165806A (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
NL47025D NL47025C (en:Method) 1935-02-28
US8630A US2165806A (en) 1935-02-28 1935-02-28 Electric discharge device

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Application Number Priority Date Filing Date Title
US8630A US2165806A (en) 1935-02-28 1935-02-28 Electric discharge device

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US2165806A true US2165806A (en) 1939-07-11

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