A focus mask for color picture tubes using dipolar and quadrupolar lensing

Post-deflection focus masks can increase the electron-beam transmission in a color picture tube over that achievable by conventional shadow masks. Various focus mask structures are considered here and most attention is given to one in which the electrostatic fields in each mask aperture consist of a dipole and a quadrupole component. A theory of the combination of dipolar deflection and quadrupolar focusing is given. Experiments on small masks are described and their quantitative behavior is evaluated. A demountable focus-mask color tube is described which has a 10-in diagonal flat mask. This has been used to display video and the 50-percent transmission of the focus mask has allowed high brightness operation with screen voltage of only 10 kV.