US2818523A - Storage tube - Google Patents

Description

DecgBl, 1957 STORAGE TUBE Filed Feb. s, 1954 f :fiel 44! M. c. JoHNsoN ETAL 2,818,523 Patented Dec. 31,l 1.957

STORAGE TUBE Miles C. `Johnson, Pennsauken, N. J., and Walter W.

Weinstock, Philadelphia, Pa., assignors to Radio Corporation of America, a corporation of Delaware Application February 3, 1954, Serial No. 407,864

3 Claims. .(Cl. 315-12) This invention relates to electron discharge devices, and particularly to collector electrode HERES Within an electron discharge device.

Although the invention is applicable to several known types of devices, or tubes, it will be described in connection with a storage tube having a dielectric target upon which a charge pattern may be established. One such type of storage tube is a storage tube of the type disclosed in U, S. Patent 2,548,405 to R. L. Snyder, Jr. Such a storage tube comprises an electron gun for producing an electron beam along a path. Mounted transversely to the beam path is a target electrode consisting of an insulating lm having a dielectricV surface facing the electron gun and a conductive coating, or signal plate, spanning the other surface of the insulating lm. Mounted closely adjacent to and overlying, the dielectric surface is a line mesh screen,

Such storage tubes, as described'above, have many applications. YIn some of these applications, such as a radio frequency signalV separation system employing phase detected output signals, the output current contains both amplitude and phase modulted types of information. In applications of this type utilizing the phase modulated information as the output signal has proved to be an excellent method of using the tube. However, one disadvantage to this method of .Utilizing the tube is that the output current varies with the position of the electron beam when the beam lands on an area where no signal is present, i. e., an equilibrium condition. This variation of output current with beam position results in curvature of the baseline associated with the output signal.

The phase modulated information associated with the output signal is due to the fact that the average normal velocity of the secondary electrons emitted from the target varies with the input drive signal. Because the secondary electron emission current is radio frequency modulated, the variation in average normal velocity thereof with varying drive signal, is translated into a Variation in phase of the radio frequencyvmodulated output current.

The reason for the curvature of the baselinev in the output signal is as follows: because of the variation in angle of incidence of the primary electron beam with respect to the point at which the beam strikes the target, a variation in the number of secondary emitted electrons leaving the target occurs, and therefore a variation in equilibrium potential occurs with beam position. Due to the fact that during equilibrium, i. e. a no signal condition, the secondary emission electron current from the target is equal to theprimary electron beamV current, and because the secondary electron emission ratio varies across the target, there must be a variation in average normal secondary electron emission velocity to correspend to the variation in secondary electron emission ratio. lf there were not a variation in the secondary electron emission velocity, then equilibrium could not be established across the entire target. This means that the average secondary electron velocity, and consequently the phase of the output equilibrium signal, varies with the position of the electron beam on the target. This results in baseline curvature in the output signal. In order to remedy this disadvantage means must be provided to make the average normal secondary electron ,emission velocity independent of beam position.

It is, therefore, an object of this invention to provide a new and improved storage tube.

It is a further object of this invention to provide an electron storage tube in which phase shift as a function of beam position is substantially eliminated.

It is another object of this invention to provide an electron discharge device that includes a new and irnproved electron collector means.

These and other objects are accomplished in accord ance with this invention by providing an electron discharge device having a pair of collector electrodes of particular size and spacings, arranged adjacent the target. By operating the two collector electrodes at independent potentials, an output signal that is uniform throughout the entire storage surface is achieved, i. e. the average secondary electron emission from the storage surface is constant during equilibrium. This means that the phase of a radio frequency output current is constant, so that the phase detected output -inherently has a at base line, resulting in a decrease inthe amount of circuitry required to process the output signals and an increase n the dynamic range of the system.

The novel features which are believed to be characteristic of this invention are set forth with particularity in the appended claims, The invention itself Awill best be understood by reference to the following description taken in connection with the .accompanying single sheet of drawings in which:

The single gure discloses a fragmentary sectional view of a storage tube in accordance with this-invention.

Referring now to the single ligure in detail,` the electron storage device, or tube 8 comprises an elongated tubular vitreous envelope l0 having a central axis and including an electron Agun 12 mounted within one `end of the envelope 10. The electron gun 12 is to provide an electron beam 14 along a path extending substantially coaxially with the tubular envelope 10. Mounted at the other end of the tubular envelope 10 is a target electrode 16 arranged transversely to the path of beam 14. The electron gun consists somewhat of conventional parts and includes a cathode electrode 18, whichv may be a short tubular member having a closed end facing the target electrode 16. Enclosing cathode electrode 18 is a tubular control grid electrode 20 coaxially mounted with respect to cathode 1S. Arranged along the tube axis, and spaced from each other, are successively a first accelerating electrode 22, a focussing electrode l24 and a second accelerating plate electrode 26. Each of the electrodes 20, 22, 24 and 26 have openings' therethrough on the tube axis to provide for passagetherethrough of electrons from cathode 18. These electrons are formed into a beam 14 by the several gun electrodes and directed and focussed by gun 12 to alfine point on the surface of target 16.

The electron beam 14 passes between a pair of horizontal deflecting plates 28 and a pair of vertical deflecting plates 30, to which appropriate potentials are applied to cause the electron beam to be scanned in a desiredmanner over the surface of target 16, The pairs of deflecting plates 28 and 30 are respectively connected to sources of varying voltages (not shown) of any desiredrtypefwhich provide any arbitrary scan such as line and framescansion ofthe electron beam over thev targetsurface. The. scanning of lthe beam 14 is well-known and is of a conventional type that is not further described.

Between the pairs of deflecting plates 28 and 3l) there is mounted a shield electrode 36. A conductive coating 38 is deposited on the inner surface of envelope 1) to form substantially a tubular electrode enclosing the second accelerating plate electrode 26 and the pairs of deflecting plates 2S and 30. The conductive coating 38 may be of any appropriate type such as a colloidal suspension of carbon in a binder, which may be painted on the glass wall surface; or a metallic coating such as silver or aluminum, which can be put down on the glass wall surface by metallic evaporation. Also, the coating 38 may constitute a metal tube mounted in the same relative position. Wall coating 38 is tied conductively to the second accelerating electrode 26 which is in turn electrically tied to the first accelerating electrode 22. The several gun electrodes shown are respectively connected to appropriate sources of potential which will be explained hereinafter.

The target assembly 16 comprises a tine mesh screen 46 which serves as a barrier grid and which is connected across an inwardly extending flange 48 `of a support ring 48. Within the support ring 48, and abutting the ange 48 is a thin sheet of dielectric material 44, which may be of a material such as mica or the equivalent. The dielectric material44 is supported by the pressure of a signal plate 42. abutting the opposite side of the dielectric material 44 to press the dielectric 44 against the flange 48. Abutting the back of signal plate 42 is an annular insulating disk 51 which is held in position by an annular backing plate 50. The backing plate 50 is in contact with the insulating disk 51 to sandwich the electrodes t0- gether and against flange 48. The backing plate 50 is held in position by a plurality of locking tabs 55 which are welded to the inside of support ring 43 and to the backing plate 50.

The target assembly is mounted and supported within envelope by means of the lead-ins and support rods 52 and 54 which are sealed through an insulating closure plate 45 of the envelope 10. The closure plate 45 is an insulating material such as glass and is sealed by any of the well-,known means of sealing glass-to-metal as represented by seal 43, to the inwardly extending ange 47 of an annular metallic member 47. The annular member 47 Includes an outwardly extending ange 47 and an inwardly extending ange 47' as shown. The flanged ring 47 is constructed of some type of metal, such as Kovar, which can be sealed to glass. Sealed to body portion of envelope 10 at seal 41 is also an annular metallic member 49. The metallic member 49 includes an outwardly extending flange 49. The seal 41 may also be any of the conventional glass-to-metal seals. When the ring 47 has been placed within ring 49 the two rings are sealed t0- gether on the periphery thereof by means of a welding operation such as an inert-gas arc-weld.

In accordance with this invention there is provided a pair of collector electrodes 39 and 40 within the device 8. The collector electrodes 39 and 4i? may be conductive coatings deposited on the inner surface of envelope 10 as shown. Each of the conductive coatings 39 and 40 may be of any of the appropriate type of coatings such as a colloidal suspension of carbon in a binder, which may 'be painted on the glass wall surfaces; or metallic coatings such as silver or aluminum, which can be put down on the glass wall surfaces by metallic evaporation. Also, the collector electrodes 39 and 40 may'constitute metal tubes mounted in the same relative positions.

As can be seen from the drawing, the hollow tubular collector electrode 39, which is the principal collector electrode for secondary electrons, is connected to the apertured shield 56 which is sealed through the envelope 10 and forms a lead-in for the collector electrode 39. The collector electrode 39 extends from shield 56 to well within the larger portion of envelope 10. Closely spaced adjacent the end of collector electrode 39 is the narrow collector or hollow ring electrode 40. The collector electrode 40 is spaced from target 16 by an amount such that when a predetermined potential, with respect to mesh 46, is applied to the hollow ring collector electrode 40 secondary electrons from all areas of target 44 arrive at the space between the hollow tubular collector electrode 39 and the hollow ring collector electrode 40 at a uniform velocity. It should be understood that the spacings and sizes of collector electrodes 39 and 40, and the spacings with respect to target 16, may vary with the potentials applied thereto to attain this result. The specic example of potentials disclosed in the single gure are for a tube having a diameter of 3 inches and a length of 11% inches, with collector electrode 40 spaced 1% inches from the end of the tube, a spacing of Ms inch between collector electrodes 39 and 40 and collector electrode 40 is 1/2 inch wide. It should be understood that these dimensions, and the potentials shown in the figure, are not given with the intent of limiting the invention but merely as a specific example of successful operation of the device.

A specific example of the potentials for operation of the `device 8 is shown in the single figure of the drawings. Generally the operation of device 8 is as follows: The tine mesh screen 46 and the signal plate 42 are maintained at a fixed potential (-69 volts) with respect to ground. The electron beam is modulated by a radio frequency sine wave applied to grid 20 and is scanned over the dielectric surface 44 of the target 16; simultaneously therewith, incoming signal pulses are applied between the signal plate 42 and the tine mesh screen 46 by means of lead-in 52 and resistor 58. Due to the close capacitive coupling between the various elements of target 16, and due to the resistor 58, for any given repetitive input signal, equilibrium is established on the target 16. The equilibrium potential, for any area of target 44, is xed when measured from the bombarded face of the dielectric surface 44 to the tine mesh screen 46. However, the voltage across an incremental area of dielectric material 44 is dependent upon the amplitude of the repetitive input signal. In other words, for any given repetitive input signal there will be as many primary electrons arriving, in beam 14, as secondary electrons being collected, by collector electrodes 39 and 40. This equilibrium condition is a condition of no signal output.

When the incoming signal is changed, the potential of elemental areas of target 44 is changed which, in turn, changes the equilibrium condition of elemental areas of the target 44. Due to this initial change in equilibrium condition, the number of secondary electrons collected by collectorV electrodes 39 and 40 will be more or less, depending upon the polarity of the deviation from equilibrium, than the number of primary electrons in beam 14. Due to the change in collected secondary electrons, a signal output is developed across an irnpedance (not shown) in the current return path from target 16 to cathode 18. An example of the impedance could be a tuned radio frequency circuit (not shown) connected to the lead-in 54 of barrier grid 46.

As is obvious, if the potential of equilibrium is not independent of the position of beam 14 relative to the surface of the target 44, then output signals will be developed when no signals are applied and furthermore, the phase of the output signals will be incorrect. Since the equilibrium potential of the target 44 near the edge thereof is a higher potential than the equilibrium potential near the center, a tube constructed in accordance with this invention includes the split collector, i. e., cellector electrodes 39 and 40, and collector electrode 40 is operated at a slightly positive potential with respect to mesh 46 to produce an additional voltage gradient which is more positive at the edge of the target 44 than at the center thereof. Due to this additional positive voltage gradient, the varying (with the position of beam 14) ycornponentof the negative gradient is cancelled out, re* sulting in a uniform voltage gradient between mesh 46 and target 42. The net eiect during equilibrium charging is to make the average secondary electron emission velocity constant. In other words, the phase of the radio frequency output current is constant so that the phase detected output inherently has a flat ba-se line,

What is claimed is:

1. An electron discharge device comprising, means for forming a beam of electrons along a path, a target electrode mounted in the path of said electron beam, said target electrode including a surface providing secondary electron emission when struck by said electron beam and a line mesh screen overlying said target surface, a pair of spaced apart hollow tubular collector electrodes intermediate said target and said beam forming means for collecting the secondary emission from said target electrode, one of said pair of collector electrodes being the sole electrode intermediate the other of said pair of collector electrodes and said target lead means respectively connected to each of said collector electrodes and to said ne mesh screen for connecting said screen to a given potential source and connecting each of said collector electrodes to sources of dilerent potential, yboth of said sources of diieren't potential being positive with respect to said target electrode, the potential of said other collector electrode most remote from said target being the most positive potential of said collector electrodes whereby secondary electrons from all points of said target pass the space between said collector electrodes at substantially the same velocity.

2. An electron discharge device comprising, means for forming a beam of electrons along a path, a target electrode mounted in the path of said beam, said target electrode including a surface providing secondary electron emission when struck by said electron beam and a mesh screen overlying said target surface, a hollow collector electrode for collecting said secondary electron emission closely spaced next to said target surface and intermediate said target and said beam forming means, a hollow tubular collector electrode for collecting said secondary electron emission closely spaced from said iirst collector electrode and intermediate said lirst collector electrode and said beam forming means, said hollow tubular collector electrode comprising a larger electron collector area than said hollow collector electrode, and means adapted to apply potentials to each of said collector electrodes whereby said secondary electron emission from all points of said target pass the space between said first and said second collector electrodes at substantially the same velocity.

3. An electron discharge device comprising, means for forming a beam of electrons along a path, a target electrode mounted in the path of said beam, said target electrode including a surface providing secondary electron emission `when struck by said beam, a hollow tubular collector electrode for collecting said secondary electron emission mounted intermediate said means and said target, a hollow ring electrode spaced closely adjacent to said target, said ring electrode being the sole electrode between said tubular electrode and said target, and means for applying potentials that are positive with respect t0 said target electrode to said tubular electrode and to said ring electrode whereby sa'id secondary electrons from al-l points of said target pass the space between said ring electrode and said tubular electrode at substantially the same velocity.

References Cited in the tile of this patent UNITED STATES PATENTS 2,503,949 Jensen et al. Apr. 11, 1950 2,549,072 Epstein Apr. 17, 1951 2,573,777 Sziklai Nov. 6, 1951 2,598,919 Jensen June 3, 1952

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