Cathode ray tube with an electron lens for deflection amplification

Claim 1

In apparatus including a cathode ray tube having a target, an electron gun for emitting an electron beam directed toward the target deflection means disposed along the path of the beam from the gun to the target for deflecting the beam in two orthogonal directions, a scan expansion lens system disposed between the deflection means and the target for amplifying the deflections of the beam, and a postdeflection electrode disposed adjacent the lens system so that an electric field due to the postdeflection electrode acts at least upon a target side end portion of the lens system, the improvement wherein: (a) the lens system comprises first and second tubular electrodes of substantially rectangular cross sectional shape disposed in axial alignment to allow the passage of the beam therethrough, each of the first and second electrodes having a beam entrance end directed toward the electron gun and a beam exit end directed toward the target, the second electrode enveloping at least a beam exit end portion of the first electrode with a gap sufficient to provide electrical insulation therebetween; (b) the first electrode having a first pair of opposite sides oriented in one of the two orthogonal directions of beam deflection and a second pair of opposite sides oriented in the other of the orthogonal directions, the beam exit ends of the first pair of opposite sides being each curved in an arc that is convex in a first direction, the beam exit ends of the second pair of opposite sides being each curved in an arc that is convex in a second direction opposite to the first direction; and (c) the apparatus further includes means for applying such electrical potentials to the first and second electrodes of the lens system and to the postdeflection electrode that there are created: (1) a first electron lens composed of the first and second electrodes for amplifying beam deflection in said one of the orthogonal directions by inverting within the second electrode the traveling direction of the beam that has been deflected in said one of the orthogonal directions by the deflection means, the first electron lens being further effective to amplify beam deflection in said other of the orthogonal directions by acting within the second electrode the beam that has been deflected in said other of the orthogonal directions by the deflection means; and (2) a second electron lens composed of the beam exit end portion of the second electrode and the postdeflection electrode, the second electron lens being located adjacent the beam exit end portion of the second electrode and acting to converge the beam in said one of the orthogonal directions.