| 摘要 |
<p>PURPOSE:To limit the emitting area of an electron and improve the controllability of brightness or emittance, by arranging a mask member made of carbon on the tip end of the cathode portion of an electron gun. CONSTITUTION:The cathode portion 21 of an electron gun is made of lanthnaum hexaboride, an opening 22 is drilled in its tip end, and a mask member 23 made of inert carbon is arranged on the tip end. Then, a thermion is controlled by impressing a negative high voltage on the cathode 21, while impressing on grids 3, a little higher negative high voltage than that applied on the cathode 21, and earthing an anode 4. Accordingly, the increase of an emission current generated at the time of shallowing the grid bias can be prevented and the controllability of brightness or emittance can be improved, by limiting the emitting area of an electron by means of the opening 22.</p> |
