US2785328A - Storage tube - Google Patents

Description

March l2, 1957 H. KIHN STORAGE TUBE Filed Feb. 21, 1952 Uhr STORAGE TUBE Harry Kinn, Lawrenceville, N. I., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Air Force Application February 21, 1952, Serial No. 272,778

4 Claims. (Cl. 313-68) This invention is directed to an electron discharge device and in particular to a storage tube wherein information may be stored for a period of time and reproduced as an output signal of the tube.

One type of storage tube is that in which in formation in the form of electrical signals are `used to modulate the electron beam of a gun within the tube. The modulated beam is caused to scan ,over the surface of a target electrode to establish on the target surface a distribution of charges corresponding to the modulations of the electron beam. A second electron beam is also scanned over the target surface to discharge the charge pattern to an equilibrium potential. As each charged portion of the target surface is discharged by the second beam, a succession of electrical signals are produced to form an output signal of the tube. Normally the target electrode is of a nature whereby the charge pattern established by the rst or modulatedbeam remains on the target for an indenite length of time.

A tube of this typemayf be used to convert signals coming into the tube with one type of scansion to output signals from the tube in another type of scansion. For example, the modulated electron beam can be scanned over the target electrode inaccordance with a radial or radar type of scansion which is synchronized withthe' radar antenna. The charge pattern then established on the target corresponds to a radar picture. However, to transmit this picture to various points for viewing, it is desirable to use signals in accordance with a television or rectangular scansion. Thus, the second electron beam is caused toscan the charge pattern in accordance withthe desired scansion, such as television, to produce` an output signal from the tube which is synchronized with the television scansion. This output signal then may be fed into a television receiver or an oscilloscope and the radar picture may` now be observed for some desired length of time.

A disadvantage of storage tubes of the type' described is that through interaction of parts, the modulated writing beam causes direct video signals to occur in the output of the storage tube. Since the time sequence of incoming and outgoing signals of the tube are completely unrelated and in no Way synchronized with each other, direct coupling of the input and output signals cause interference and spurious signals inthe tubeA output.

It is, therefore, an object of this invention to provide a storage discharge device `of `improved design.

It is a further object ofthe invention `to provide a storage tube `wherein `the input and output portions of the tube are separated in a manner to preventinteraction between the tube portions. i.

It is another object of the invention to provide a storage tube in which the inputand output signals are so arranged that there is no interaction between the two.

It is a further object of the inventionto provide a storage discharge tube in which the input signals'can be stored on the target electrode of the tube independently States Patent ice 2 and without electrical coupling to the output portion of the tube.

The Vinvention is specifically directed to a storage discharge tube having a target electrode which separates the input and output electrodes of the tube. The target electrode includes a thin film of metal which forms a shielding electrode to prevent coupling between the input and output tube structures. The metal iilm of the target is coupled directly to ground so that the input signal pulses will not cause direct video signals in the output portion of the tube.

Figure 1 is a sectional view of a storage discharge tube in accordance with the invention.

Figure Zis an enlarged view of a portion of the target electrode of the tube of Figure 1.

The tube, shown in Figure l, has an evacuated envelope 10 of substantially tubular coniguration. Mounted in the central portion of the tube is a target electrode 12 mounted transversely to the axis of the tube envelope. On one side of the target electrodeV 12, there is positioned an electron gun structure 16, which is used to establish a charge pattern on the target 12. Electron gun 16 is referred to as the writing gun. On the opposite side of target 12 and 'coaxially aligned with the writing gun 16:, there is a sound electron gun 18 or reading gun for providing a low velocity electron beam 29, which is scanned over the adjacent surface of target 12. The low velocity beam Ztl is modulated by the charge pattern established by the Writing gun on the -target surface to provide the output signal of the tube.

The writing gun 16 is of a conventional type and consists of a tubular cathode 22 having a closed end portion facing target 12, and which is coated by a mixture of strontium and barium oxides to provide a source of electrons. Enclosing cathode 22 is a tubular control gridl p is formed as a conductive wall coating on the inner surface of the tube envelope and is operated at a higher positive potential than the lirst accelerating electrode 28 to provide therebetween a focussing field for bringing the electrons of beam 27V to a small Well-defined spot onrthe surface of target 12. Electron beam 27 is scanned over the surface of target 12 in any well-known manner, such as by magnetic scanning elds provided by two pairs of coils mounted around the tubular envelope 1i) as a neck yoke 32.- If the writing gun 16 is used with radar signals, the deflection yoke 32 may be of the Y type to produce a radar P. P. I. scan pattern. Such a scansion is Well known and is also disclosed in U. S. Patent 2,412,670. Figure l indicates voltage values which may be applied to the several electrodes of the writing gun 16. These are by Way of example only and are not limiting.

The reading gun 18 is of the type used in the Image Orthicon pickup tube and is disclosed in greater detail in U. S. Patent 2,540,621 to Ralph E. Johnson. The gun consists of a cathode, a control grid (both not shown), a rst accelerating electrode 34,' and a second accelerating electrode consisting of a conductive wall coating 36. When appropriate voltages are applied to the several electrodes of the reading gun, the electron emission from the cathode is formed into an electron Patented Mar. 12, ias?.

apanage beam 20. A magnetic focussing ield is provided by a coil 38 between the accelerating electrode 34 and target 12 to focus the electrons of beam 20 to a well defined point on the surface of the target 12.

In accordance with the invention, there is provided a novel target electrode 'consisting of a thin ilm 40 of electron permeable metal, such as aluminum on the writing gun side of the target as shown in greater detail in Figure 2. On the surface of aluminum film 40 facing the reading gun 18 there is formed a thin film 42 of a dielectric material such as silica, magnesium fluoride, or a ceramic material such as a titanate or a borate mixture. The target films 40 and 42 usually are so thin Ithat they are extremely fragile and in some cases are not elf-supporting.

The target electrode may be formed by first providing a mounting ring 44 across the open center of which is fixed by welding, brazing, etc. a fine mesh screen 46. The screen 46 is one having large transmission or in which the solid areas are a small percentage of the open areas. Screen 46 may be made in any desired manner and specifically by the method disclosed in U. S. Patent 2,529,086 issued to Harold B. Law November 7, 1950. The aluminum film 40 is next laid down by evaporating a film of aluminum on one surface of meshr 46. To do this successfully, a iihn of lacquer is first floated on the surface of a pool of water and the mesh screen 46 is brought up underneath the iilm so that, as the screen 46 is brought out of the water, the lacquer film will lay down over the screen. This may be done in any manner such as that, for example, disclosed in the co-pending application of Meier Sadowsky, Serial No. 742,117, tiled April 17, 1947, now Patent No. 2,625,493. Upon drying, the lacquer film will produce ahard film firmly attached to the screen 46. The aluminum film 4t) can then be evaporated from heated tungsten filaments in the vacuum directly onto the lacquer film. Following this, the ceramic or insulating lilm 42 may be put down,V in any manner such as by the evaporation of silica or magnesium fluoride, for example. After target 12 has been mounted in the tube envelope `and the tube exhausted and degassed by baking at an elevated temperature, the lacquer film usedto support the aluminum vfilm 40 will be volatilized and the vapors pumped from the tube.

In accordance with the invention and asv shown in Figure l, aluminumY tilm 40 is connected by a lead 41 through a condenser 43 to ground as shown. The potential established on the aluminum film 40 maybe varied several volts on either side of ground by adjus-tably connecting lead 41 to a potential source 4S.

Adjacent to target 12 on the reading side ofthe target there is mounted a screen electrode 43,' which during tube operation is maintained slightly positive with respect to the accelerating electrode coating 36 to repel positive gas ions passing down the tube toward the target and which would discharge the negative charge pattern established in the target. As indicatedA in Figure l, Vscreen 48 may be mounted across a supporting ring'tl. which is sealed through the envelope wall 10 to provide an external terminal for screen 48. e

During tube operation, the electron beam 2t? is inagnetically scanned over the adjacent surface of target 12 by fieids provided by two pairs of scanning coils indicated in Fiure l by the deection yoke 52. The dciiection yoke is of a conventional design, and as is weilknown, each pair ol coils are connected respectively in series with each other to sources of sawtooth currents 54aiid 56 for respectively providing frame and line scansion of face negatively toward gun cathode potential.

so that it will strike the target electrode 12 with an energy of only a few volts. The energy of the beam electrons under these conditions is below that required for initiating secondary electron emission from the dielectric surface of film 42. With the writing gun 16 turned off, the electrons of beam Ztl approaching target 12 will land on the insulating surface of film 42 and will drive the sur- At this point the remaining electrons of the beam are reflected as n return beam 58 back toward the reading gun 1S.

The electrons of the return beam 58 pass down the tube 10 and strike a dynodc surface 69 with energies sufficiently great to initiate a secondary emission therefrom which is directed by a persuader electrode 62 into an electron multiplier section 64 of the type disclosed in U. S. Patent 2,433,941 to Paul K. Weimer. The electrons arc multiplied through several stages and finally collected by the multiplier anode electrode 66 to provide an output'signal in the circuit 68 of anode 66.

A charge pattern corresponding to signals to be stored, is established by the high velocity beam 27 on the surface of the dielectric sheet 42 facing the reading gun 13. The incoming signals may be from any source such as, for example, thoseV produced by the reception of reflected radar signals. These signals are applied between the control grid 24 and cathode 22 of the writing gun i6, which are connected in a circuit with a triode tube ti for driving the control grid 24. The signals applied to gun i6, modulate the high velocity electron beam 27, as it is scanned over the surface of target 12. As mentioned above, the scansion of' beam 27 may bc a radar P. P. l. pattern by coupling the deflection yoke 32 to the move ment of the radar antenna, as is well known.

-Electron beam 27 will `strike target 12 at energies sufficiently great that beam 27 will penetrate through both the aluminum film 40 and the dielectric lm 42. The voltage of aluminum film 40 is adjusted so that beam 27 just penetrates film 42 to the surface facing gun 18 and provides secondary electron emission from this surface. In this manner, those portions of the surface of dielectric film 42, which are bombarded by beam 27, will be driven positively due to loss of charge by secondary emission. The degree to which each surface element becomes positive is lin proportion to the beam current penetrating that elemental portion of dielectric sheet 42. Thus, as the modulated beam is scanned from point to point the target surface, apositive charge pattern will be formed on the exposed surface of lm 42 and corresponding along the scanning path to the modulationsl of beam 27.

vThe reading beam 20, on being scanned over the surface of target 12, will be retiected from those portions of the target surface which have not been charged positively by secondary emission resulting from the writing beam 27. However, where the writing beam has penetrated through target 12 and established a positive charge by secondary emission, the positively charged elemental area will cause low velocity electrons of beam 26 to land in an amount necessary to drive the surface of the charged element back to cathode potential, at which point the remaining part of beam 20 is reflected. The number of electrons landing on the target surface will be proper tional to the positive charge established at the point by the electronbearn 27. In this manner the return beam 58 becomes modulated in accordance with the number of electrons lost to the positive areas of the target surface as the beam is scanned over that surface. As described above, the modulated beam 58 is amplified by the multiplier section 54 and provides an output signal iii the circuit 68 of the collector electrode 66.

The time that the positive charge pattern is stored on the surface of lm 40 depends upon several factors. For example, the beamcurrent of the reading gun 18 may be of a low enough value that many scans of the charged pattern` can be undertaken before the positive chargesv are dissipated orV neutralized. For example, in a radar application, the beam 27 takes approximately 6 seconds to return to any single element a second time. The beam current of beam can be adjusted so that the positive pattern on target lm 42 may remain readable for this period of time and until beam 27 can write information the target element again. The storage time of the target also depends upon the current leakage through the insulating film 42 to the negative or grounded aluminum lm 40. However, due to the high insulating properties of such materials as silica and magnesium iluoride, for example, such current leakage can be for practical purposes eliminated.

The charge pattern estab-lished by the writing gun 27 may at any time be completely erased and the target restored to a new condition for storage by turning the writing beam 27 oi and scanning the surface of target film 42 with the reading beam 20 to drive all of the surface back to ground or gun cathode potential.

Thus, in accordance with the invention, the provision of the aluminum or metal iilm 40 in the target 12 provides an `electrostatic screen between the input portion and the output portion of the tube. Thus, incoming signals applied to control grid 24 of the Writing gun can not aifect the low velocity beam 20 in the reading section of the tube envelope 10. This, then prevents the occurrence of cross talk between the writing and reading sections of the tube or in other words, the formation of spurious signals in the output circuit of the tube due to the modulations applied to the control grid 24 by the input signals.

While certain specific embodiments have been illustrated and described, it will be understood that various changes and modications may be made therein without departing from the spirit and scope of the invention.

I claim: Y

1. An electron storage tube comprising, a target electrode including a supporting member, a first imperforate electron permeable conductive film on said supporting member and an imperforate electron permeable dielectric layer having one surface in contact with said conductive film and the other surface exposed, an electron gun means for providing modulated secondary emission from the exposed surface of said dielectric layer, and means for scanning said exposed dielectric surface with a low velocity beam.

2. An electron discharge device comprising, an imperforate target electrode including an electron permeable conductive lm and an electron permeable insulating lm having adjacent surfaces in contact with each other and opposite surface exposed, an electron gun means spaced from the side of the target of said exposed opposite surface of said conductive lm for providing modulated secondary emission from the exposed surface of said insulating film, and means spaced from the side of said target electrode of said exposed opposite surface of said insulating film for scanning said exposed insulating iilm surface with a low velocity beam.

3. An electron storage tube comprising, an imperforate target electrode including a supporting member, a conductive I'ilm on said supporting member and a dielectric layer having one surface in contact with said conductive tilm and the other surface exposed, a first electren gun spacedfrom the side of said target electrode away from the exposed surface of said dielectric layer for providing a modulated secondary emission from said exposed surface of said dielectric iilm, and a second electron gun means spaced from the side of said target electrode of said exposed surface of said dielectric layer for scanning said exposed surface of said dielectric layer with a low velocity beam.

4. An electron storage tube comprising, an imperforate target electrode including a supporting member, an electron permeable conductive lm on said supporting member and an electron permeable dielectric layer having one surface in contact with said conductive film and the other surface exposed, a first electron gun spaced from the side of said target electrode away from the exposed surface of said dielectric layer for scanning said conductive film with a high energy modulated electron beam, and a second electron gun means spaced from the opposite side of said target electrode for scanning said exposed surface of said dielectric layer with a low velocity beam, and lead means connected to said conductive ilm for grounding said lm.

References Cited inthe tile of this patent UNITED STATES PATENTS 2,464,420 Snyder Mar. 15, 1949 2,547,638 Gardner Apr. 3, 1951 2,549,072 Epstein Apr. 17, 1951 2,570,858 Rajchman Oct. 9, 1951 2,711,289 Zworykin .Tune 21, 1955 2,728,020 Pensak Dec. 20, 1955 2,734,145 Reed Feb. 7, 1956

Images