| 摘要 |
PURPOSE:To reduce the occurrence of the brooming by arranging a deceleration grid electrode at the main lens side of a prestage triode section while temporarily lowering the potential in the axis then performing the cross-over of the outside electron beam section of an electron beam directing toward the main less. CONSTITUTION:A deceleration grid electrode 6 is provided at the main lens side ML of a prestage triode section comprised of a cathode 2, first grid electrode 3 and a second grid electrode 5. For example, the applying voltages are 130V for the cathod, 600V for the second grid electrode and 150V for the deceleration grid electrode. Here only the outside electron beam section (B') of an electron beam emitted from the cathode 2 and crossed over near a prefocus lens (PL) will cross over again, and the virtual emitting point (P3) of the ouside electron beam section is shifted more than the virtual emitting point (P1) of the central electron beam section to the main lens (ML) side. Consequently the electron beam section passing through the circumferential section of the main lens is considerably reduced thus to reduce the occurrence of the brooming considerably. |
