Improvements in or relating to electron discharge devices incorporating electron lenses

摘要

821,295. Cathode-ray tubes. WESTERN ELECTRIC CO. Inc. Aug. 16, 1957 [Sept. 7, 1956], No. 25972/57. Class 39(1). To eliminate deflection defocusing, two or more electrons 26, 27, Fig. 2, having elongated apertures with mutually perpendicular axes are interposed between two or more further electrodes 25, 28 having circular apertures. Electrodes 26, 27 are each supplied with a variable potential from their respective coordinate voltage sources 32, 34, for example by non-linear circuits 31, 33. Thus the correct amount of astigmatism is introduced to compensate the deflection defocusing produced by electrodes 16, 17. Electrodes 25, 28 are maintained at a high potential, e.g. 1000 volts above the cathode, and electrodes 26, 27 at lower positive potentials so that the arrangement acts as a unipotential lens. Dimensions and electrode spacings for one particular embodiment are given. The apertures of electrodes 26, 27 are preferably elliptical, having a major to minor axis diameter ratio of about 1À3, and the four electrodes being equally spaced at a distance of the order of the minor axis diameter of the elliptical apertures. The lens arrangement 15, Fig. 1 is used in a barrier grid storage tube in which 16, 17 are deflection electrodes and the beam scans a target assembly 20, comprising back plate 22, dielectric sheet 23, and a barrier grid 24. Information is stored in the form of a charge pattern by modulating plate 22 while the target is being scanned, and may be retrieved by again scanning the target and collecting the modified secondary emission from the target by means of electrode 18.