Patent GB-1078832-A (GB)
Title: Electrostatic electron optical system
IPC: H01J31/38
Filed: 1964-08-19
Abstract: 1,078,832. Cathode-ray tubes. GENERAL ELECTRIC CO. Aug. 19, 1964 [Sept. 16, 1963], No. 33805/64. Heading H1D. An all-electrostatic electronoptical system, e.g. for a television receiver or camera tube, includes, disposed in order along an axis, an electron beam source, an electrostatic focusing lens, electrostatic deflection means, and a collimating lens for bringing the deflected beam into parallelism with the axis, the collimating lens including a spiral electrode for producing equipotential surfaces which are coasymptotic coaxial hyperboloids concave away from the beam source. In a vidicon tube having a photo-conductive target 29, the focusing field between gun anode 43 and control electrode 44 produces a demagnified virtual cathode whereby a very high density beam passes through the aperture 45 of electrode 46 into the focusing section 4. The latter section is formed by two resistive spiral electrodes 52 and 53, mounted or painted on the inner surface of insulating cylinder 51, and joined by a conductive sleeve 54 which is held negative with respect to the outermost ends of each spiral, which are themselves held at anode potential. The electrostatic deflection section 6 is composed of sinusoidal electrodes 78, 79, 80 and 81. Collimating section 8 includes a conductive sleeve 91 connected to a helix 92 on the inner surface of insulating cylinder 93, the helix exhibiting either an abrupt or a progressive increase in turns density towards the target end, where it is terminated by a mesh electrode 96 held at the maximum accelerating potential of the system, a decelerating field being formed between electrode 96 and target 29. Helical electrode 92 is arranged to provide an axial potential which increases parabolically up to electrode 96, such that the equipotential surfaces within section 8 approximate to hyperboloids of revolution asymptotic to a conical surface having its apex, of 109 degrees, on the axis and near the target end of the deflection section 6. The sleeve 91 is either held at gun anode potential, via the conductive shielding member 94, or is separately connected to an independent and adjustable potential source (Fig. 3, not shown). In another embodiment (Fig. 6, not shown), the gun end of electrode 91 is replaced by another helical electrode, with a turn density increasing towards the gun end, where it is terminated by a mesh electrode, which, together with electrode 96, is held at gun anode potential, the central portion 91 being held at a lower potential, such that the collimating section provides no net acceleration. The collimating electrodes may be mounted directly on the inner surface of the envelope. In a further embodiment (Fig. 2, not shown), the focusing section 4 consists of two three-element decelerating-accelerating einzellens separated by a drift space. A circuit for providing adjustable potentials to the deflection electrodes, to permit adjustment of beam cross-section and centring, is described (Fig. 7, not shown). All the electrodes of the system may be coupled together through resistors mounted within the envelope.