JPS56128550A - Electron gun - Google Patents

Abstract

PURPOSE:To obtain a focusing action only in one direction with a control electrode, by dividing the control electrode provided between a cathode and anode into a plurality of elements and applying two different potentials to the plurality of electrode elements. CONSTITUTION:A control electrode is constituted by electrode elements 4, 5, 6, 7. The divided electrode elements 4-7, if all operated at the same potential, can obtain an equal lens action to the conventional one. In case that potential of the electrode element is near the cut-off potential, an electron emitted from a cathode is generated almost in a round shape in the center portion despite shape of a center hole in the electrode element. To sets of the electrode elements 4 and 6 and 5 and 7 at a face-to-face position, if respectively different potentials are applied from electrodes 8, 9 to apply the cut-off potential to one set while change the other set in a positive direction from the cut-off potential, the equipotential surface immediately before a cathode is displaced from a shape almost near roundness to that axially unsymmetrical, thus the focusing action of a lens can be obtained only in one direction.