| 摘要 |
PURPOSE:To improve durability and reliability of cathode as well as resolution of a pickup tube by forming a crossover point in a position of high potential on an axis. CONSTITUTION:A plate electrode 31 making the first grid is thickened while the depth l1 of a recess to be formed in the center of said plate electrode 31 is made not less than d1/2 to the inside diameter d1 of said recess. The deepened recess produces and effect of shielding an electric field caused by the second grid 4, a divergent lens is formed near the first grid opening 13, an electron beam 12 passing through the opening 13 once diverges then forms a crossover point 15 at a point away from the first grid opening 13. The rising of the potential V(2) (full line) on the axis near the electrode is gentle and the peak value (crossover point) of the current intensity J(2) (dotted line) on the axis is formed in a position more distant from cathode, wherein the potential on the axis is high, causing stronger control of the expansion of width of speed distribution of an electron group. |
