Patent GB-762137-A (GB)
Title: Electronic storage tube
Inventor: HAEFF ANDREW V
IPC: H01J31/18
Filed: 1954-04-28
Abstract: 762,137. Charge storage tubes. HUGHES AIRCRAFT CO. April 28, 1954, No. 12376/54. Class 39(1). The charge laid down on the storage target of a memory tube is converted by flood electrons to one of two critical potentials which influence the writing beam in producing a visual presentation or signals representative of the charge laid down. The storage tube comprises two scanning guns 12, 14 for writing and reading respectively and a flooding or holding gun 16. The scanning guns each comprise modulating, accelerating and deflecting electrodes 41-44 and 22, 24 and the holding gun has a beam forming electrode 76 and an accelerating electrode 78 biased to give a diverging beam. The deflecting plates 22, 24 are connected across isolating resistors 62-65 and capacitors 66-69 giving saw tooth wave-carrying voltage, but they may be replaced by magnetic deflection coils. Wall electrodes 11, 13 accelerate the beams on to the screen assembly which comprises three meshed screens or grids 26, 28, 30 and a collector electrode 32. The storage screen 26 consists of a flattened fine mesh screen 84 of stainless steel, nickel or alloy 250 wires per inch and having good secondary emission, but it may be coated with silver, magnesium or aluminium to give it this property. The side of the mesh away from the guns is coated with a dielectric, e.g. a Zn S : Ag or Zn2 Si O4: Mn phosphor sprayed on in a binder whilst a high velocity air stream is simultaneously directed at the mesh to prevent clogging of the holes. The mesh is sprayed at an angle to secure penetration by the dielectric and render a considerable portion visible from the gun side of the mesh. The mesh is cleared by brushing. The mesh screen 28 is for viewing in any colour and the phosphor is sprayed on in an air stream using slitted masks for the colour stripes. Contrast control grid 30 is of a fine metallic mesh, e.g. of nickel or a glass mesh coated with a transparent conducting material e.g. Nesa. Its primary function is to repel the secondary electrons generated on mesh 26 back to the viewing screen 28. The transparent conductive coating 36 of collector 32 is at a potential and spacing such as to attract the primary electrons produced by the guns. The writing gun 12 lays down a positive charge on the dielectric surfaces of screen 26 which is proportional to the signal and to the capacitance of the elemental area relative to the metal mesh 84, the dielectric thickness being variable, and the holding gun converts this charge to a maximum or a minimum value according to whether its value when laid down is above or below a critical potential. Predominantly positive and negative areas are obtained the relative values of which determine whether secondary electrons can penetrate the mesh, appropriate voltages being put on the tube electrodes. The operation is explained in the specification. The reading beam generates secondary electrons at the metal surface of the electrode which can escape if the charge on the neighbouring dielectric surface is predominantly positive, the contrast control grid repelling the electron stream to cause it to impinge on the viewing screen 28. Electrons from the reading or writing guns not impacting the screens pass direct to collector electrode 36. Resistors 87-89 across the grids enable signals representative of the stored information to be derived from any of three terminals 90, 91, 92. The storage time of the tube can be controlled by means of the potentials of the holding gun the cathode 74 and the metal mesh 84. In Fig. 5A (not shown) the dielectric material 550 is deposited on the gun side of the storage mesh in the form of random sized particles whereby the capacitance of each elemental area varies across the surface of the mesh. The phosphor is applied in narrow stripes of different colour, and automatic pattern correction is obtained by positioning electrodes and auxiliary vertical deflection plates. Wires 514, 516, Fig. 5C, mounted separately on conductors 504, 506 are aligned with the colour strips, the upper edge of one wire and the lower edge of the other coinciding with the centre of the fluorescent strip so that any departure from correct scan produces unbalance in conductors 504, 506 which are connected to vertical deflecting plates and correct the scanning position. Plates behind and in front of the wire 514, 516 are at potentials which prevent secondary emission from these correction electrodes. Similar scan positioning electrodes are described for radial and sector scans, Figs. 5D and 5E (not shown). In Fig. 6 (not shown) the target is a metal plate 608 with fine grooves which are triangular, crescent or semi-elliptical in shape and containing dielectric material such as silicon dioxide, the holding gun converting the charge laid down to one of two potentials as before. The charge storage is erased by reducing the potential on the collector grid by an appropriate amount. The target may also be a metal plate on which are disposed random sized dielectric particles.