| 摘要 |
PURPOSE:To give a sufficient passing area to a beam and to prevent the scattering of a getter to an electrode by providing a cylindrical shielded electrode at the large end of the second electrode's diameter. CONSTITUTION:A cylindrical shielded electrode 19 having a hole of an inner diameter (b) at an end side of a chinny-shaped cylinder of an inner diameter (a) is provided at a pointed end part of the second anode 11 so that the pointed end diameter can be shielded. As for the cylindrical shielded electrode 19, its structuring condition is phia>=phib. For example, when an inner diameter BD of a bulb neck is predetermined as 31mm., an inner diameter P2D of the second anode 11, an inner diameter P1D at a large pointed end part 17 of the first anode 10, an inner diameter P1D' of a neck part 16, an inner diameter (a) of the cylindrical part of the cylindrical shielded electrode 19, and a diameter of a hole (b) at a pointed end part can be set 26mm., 20mm., 12.4mm., 11mm. and 9mm., respectively. A length P2L of a cylinder part at a large diameter of the second anode 11, a length P1L of a pointed end part at a large diameter of the first anode, and a height C of the cylindrical shielded can be set at 40mm., 16mm., and 16mm., respectively. |
