Selective Erasure and Nonstorage Writing in Direct-View Halftone Storage Tubes

A new type of direct-view halftone storage tube that can selectively erase as well as simultaneously display stored and nonstored information has been developed. Heretofore, incorporation of these features into direct-view halftone storage tubes has proved impractical because of the nature of the secondary-emission effect on which the writing and erasing of stored information depend. In this new tube, this limitation is overcome by the use of a dual-effects target. One effect, secondary emission, charges the storage surface positively, while the other, bombardment-induced conductivity, charges it toward the backing-electrode potential, wihch in this case is negative. Selection of the effect and, consequently, the charging direction, is determined by the incident beam energy. At low energies secondary emission predominates and the target is written on, i.e., charged positively. At high energies, the bombardment-induced conductivity prevails and the target is erased, i.e., the positively charged areas are discharged. The two effects cancel at an appropriate intermediate beam energy, thus permitting presentation of nonstored information without otherwise disturbing the display, by means of that portion of the beam current which passes through the backing electrode and strikes the viewing screen. A 5-inch, direct-view halftone storage tube that utilizes such a dual-effects target is described. At writing speeds between 10,000 and 15,000 inches per second, the stored resolution is 40 to 50 lines per inch. At erase speeds between 30,000 and 40,000 inches per second, the stored resolution is 100 to 120 lines per inch.