A microspot tube with very high resolution

A 5-inch microspot tube with a spot size of 8 to 9 microns and a beam current of 1.5 µa is described. The neck of this tube uses an accelerating spiral anode, in combination with a decelerating prefocus lens. This combination stretches the 6-inch neck structure to an effective length of 13 to 16 inches. The resulting demagnification of 0.6 permits realizing the above spot size as an electron image of a 1/2 mil object-aperture. The latter is illuminated with a current density of 20a/cm²by a microgun, which uses an impregnated cathode at 2a/cm². The microgun operates by the FRM principle ("Focus Reflex Modulation"). An improved vapor-reacted screen is employed, whose light output is more than tripled from previous types of transparent phosphors.