Patent GB-727759-A (GB)
Title: Direct-viewing electronic storage tubes
IPC: H01J31/18
Filed: 1953-01-08
Abstract: 727,759. Cathode-ray tubes. HUGHES AIRCRAFT CO. Jan. 8, 1953 [Jan. 12, 1952], No. 662/53. Class 39 (1). A direct viewing electronic storage tube for converting a continuously applied electrical signal into a continuously visible visual presentation comprises a foraminous storage screen including a plurality of secondary electron emissive storage elements, means responsive to the applied signal for charging the storage elements either positively or negatively as is temporarily required to produce a charge replica of the signal on the storage screen, a viewing screen disposed closely adjacent the storage screen, and means for directing a continuous flood of electrons uniformly over the surface of the storage screen simultaneously with the continuous application of the signal, the storage screen and viewing screen being held at potentials such that by electrostatic action alone the flood electrons are caused to pass through the foramina included in each of the storage elements in proportion to the charge on the storage elements and are directed in a collimated beam to the viewing screen to produce the continuously visible presentation of the charge replica. In one embodiment, Fig. 1, the tube comprises a writing gun 12, a flooding gun 14, a storage electrode in the form of a conducting grid 78 coated on one side with dielectric material such as a phosphor, and a luminescent screen 88 which may be a. three-colour screen. The potential between the cathode, 22 and grid 24 of the writing gun may be varied by means of a variable potential source 28 to control the intensity of the beam, and input signals are applied through condenser 19 to both cathode and grid to vary the velocity of the beam. The beam is accelerated to a velocity near that of the second cross-over of the secondary emission curve of the material of the dielectric 80, corresponding to a potential of about 3000 volts, and the dielectric elements 80 are thereby brought to the potential corresponding to this cross-over. As the potential of the cathode is varied by the input signals, corresponding variations in the potentials of the elements 80 are produced by the beam to form a charge image on the storage screen; if the writing beam current is low a single impingement of the beam will not suffice to change the potential of an element 80 by the full amount corresponding to the input signal and several scans may be necessary to lay down the charge image, thus producing a signal integration effect which may be desirable in some cases. The flooding gun comprises a cathode 70 and control grid 72 surrounded by an accelerating electrode 74 which may be connected to accelerating electrodes of the writing gun and serves also to shield the flooding gun. The potential of the cathode and grid may be varied over a range of about 2 volts at high frequency by a high frequency source 73 to increase the velocity spread of the beam. The wall coating electrodes 56, 60, 62 direct the beam orthogonally towards the storage screen. The cathode 70 is at a more positive potential than the maximum potential on the storage surface 80, and the grid 76 is at a potential above that of cathode 70; thus when elements 80 are sufficiently positive electrons from the flooding beam can pass through and on to the luminescent screen, but the beam can never reach the elements 80 and discharge them. In a modification of this arrangement, Fig. 14, the writing gun has two cathodes 124, 126 between which is maintained a potential of about 200 volts, which is twice the potential corresponding to the first cross-over point of the secondary emission curve. Regarding the two beams as a single beam, the curve for the current against the potential of the storage screen has the form shown in Fig. 16, and the elements 80 assume potentials corresponding to point 156; the input is applied to both cathodes and the method of operation is the same as for the tube shown in Fig. 1. In a further modification, Fig. 18 (not shown), the tube is as in Fig. 1 except that grids are provided near the storage target on the side facing the guns. The grid nearest the guns is maintained at a positive potential, the grid nearest the target is modulated with respect to earth by the input signals to cause corresponding variations in the potential of the elements 80. In the tube shown in Fig. 7 the dielectric elements are on the opposite side of the target 76 from the guns, and a grid 102 is provided between the target and the luminescent screen. Input signals are applied to the grid 102 and the storage target is charged by secondary emission from grid 102. In a modification of this arrangement, Fig. 13 (not shown), an additional grid is arranged between grid 102 and the luminescent screen and maintained about 200 volts negative with respect to grid 102 to assist the process of charging the storage target.