SPOT OPTIMIZATION IN A COLOR DISPLAY TUBE SYSTEM

摘要

A beam-index type color display tube uses index elements to control the position of an electron beam relative to a phosphor track on the display screen. In order to ensure color purity, the spot size of the electron beam in the direction perpendicular to the phosphor screen needs to be so small, that an adjacent phosphor track is not hit by any part of the beam. The color display tube comprises a first and a second magnetic quadrupole lens for varying the opening angle of the beam close to the screen. The first quadrupole is positioned between the second quadrupole and the main lens of the electron gun, in order to ensure good color purity. A particularly good spot uniformity over the entire display screen is obtained when the two quadrupoles are dynamically driven.