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K y s mi '*'*'. W * w.: - Dr. R. P. Stone, another of the development team, puts final touches on the new tube before testing. making them glow in a pattern that creates the picture. In the new storage tube, however, the writing beam does not produce the picture directly — it scans a special storage grid mounted about one-tenth of an inch behind the phosphor-coated screen. The grid is a fine-mesh screen (160,000 openings per square inch) supporting a thin insulating film. As the writing beam scans the insulating film, it builds up local electrical charges whose intensity varies with the pattern of the picture signal. As the picture is thus built up on the grid, the con- tinuous shower of electrons from the second gun passes through the charged openings of the grid, acquiring as it passes the pattern built up at these openings by the writing beam. The shower, or "flooding beam", then strikes the phosphor coating of the viewing screen, creating the picture for the observer. The Erasing Beam Because the flooding beam continues to pass through the charges built up on the grid, the picture remains for some time on the screen. The erasing beam, controlled either by the viewer or automatically by associated cir- cuits, may be brought into play at any time to clear the tube face for a new picture. It does this by altering the charges on the storage grid in such a way that the flood- ing beam is blocked at all points, preventing the shower of electrons from striking the phosphors of the tube face. A non-electronic analogy to the process can be found in coating a window screen with heavy paint and hold- ing it above a table in the sunlight. If a pattern is traced on the screen with turpentine, clearing paint from some of the holes, sunlight may pass through and create an image of the pattern on the table surface. Repainting the screen will cause the image to disappear. In this analogy, the table represents the phosphor-coated view- ing screen, the window screen represents the storage grid, the action of the turpentine compares to the action of the writing beam, the sunlight to the flooding beam, and the repainting to the erasing process. In its present form for radar application, the tube has a viewing screen 4 inches in diameter, capable of presenting an image of hundreds of foot lamberts of brightness in its high-lighted portions. To produce this brightness, the tube requires considerably less anode volt- age than does the standard television picture tube, largely because of the tube's ability to light every spot on the viewing screen continuously with the flooding beam rather than intermittently, as is the case in the TV kinescope. RAD/O AGE 77