| 摘要 |
PURPOSE:To achieve a high precision focus, by causing a cylindrical coil filament to project toward the anticathode, said filament being surrounded by a focusing wall relatively close thereto and rising from the bottom of a relatively wide focusing groove. CONSTITUTION:A cylindrical filament 1 is surrounded by a focusing wall 7 relatively close thereto. A recess 8 opened toward the anticathode is formed outside the periphery of the focusing wall 7. In this cathode structure, equipotential surfaces 5 have the form of concentric cylindrical surfaces with the center of the coil filament being the center of said surfaces, and further, a virtual electrode 4 of a relatively concentrated form is produced. |
