GB726894A - Improvements relating to cathode ray tubes employing ion traps - Google Patents

Abstract

726,894. Ion-trapping in cathode ray tubes. ELECTRIC & MUSICAL INDUSTRIES, Ltd. Nov. 12, 1951 [Nov. 17, 1950], No. 28110/50. Class 39 (1) The second anode 8, Fig. 1, is tilted as a whole relatively to the common axis of the cathode 2, modulator 3 and first anode 5, so that the electrostatic field between 5 and 8 has a transverse component acting on electrons and ions, a magnetic deflecting field opposing the electrostatic field being provided for separating the electrons and ions and trapping the ions. The magnetic field is produced by pole pieces 11 secured to flange 7 on opposite sides of the axis, and co-operating with an external permanent magnet (not shown). A further final anode (not shown) may be provided as a wall coating, and may be connected to second anode 8. The electric and magnetic deflecting fields are such that the electrons are undeviated and pass through aperture 10, also on the common axis, to the fluorescent screen, while the ions are collected by anode 8. An ion stop in the form of an apertured disc may be positioned inside and supported from anode 8. Aperture 10 may be centrally disposed in end wall 9 provided that it remains on axis x-x. The common axis of electrodes 2, 3, 5 can be tilted with respect to the tube axis x-x so that the beam is finally on the tube axis if the electric and magnetic deflecting fields are slightly out of balance. In another embodiment, Fig. 2, the first and second anodes 14, 15 are discs and second anode 15 is tilted. Disc 15 may have a tubular member similar to 8, Fig. 1, attached thereto, and disc 14 may have a flange as in Fig. 1. In all forms the gun electrodes are bonded together by ceramic rods to form a unitary structure. The Provisional Specification describes other ion trap arrangements in which the first and second anodes are relatively tilted and/or offset.