GB1318933A - Charged-particle-beam focussing and deflecting system - Google Patents

Abstract

1318933 Cathode-ray tubes RIKAGAKU KENKYUSHO 12 June 1970 [12 June 1969] 28693/70 Heading H1D A system for focusing and deflecting charged particles in which the beam, e.g. as emitted by an electron gun EG, is deflected towards a target screen SC by a deflecting system DPA, comprises a plurality of electrostatic or electromagnet lenses LMP adjacent the screen, each of which focuses the electron beam on to the screen when it is incident upon that lens. In one embodiment (Fig. 10) in which LB, LCL and LMP represent lenses of electrostatic or electromagnet origin, the beam is deflected by a directional deflection system LPA, focused by a focusing electrode LB and is then deflected by a positional deflecting system DPM through a collimator LCL on to one of the lenses LMP of short focal length. The angle of incidence on the lenses LMP is determined by the deflection by the directional UPA system while the position of incidence on LMPo or LMP as shown is determined by the positional - P - deflection. The deflection accuracy of the positioning DPM system need not be critical as the beam has only to impinge on a desired lens LMP. Additionally a positioning error of the beam on the screen due to an angular error in the directional LPA system is small since the error is proportional to the focal length f n of the LMP lens which is short. In the cathode-ray tube shown in Fig. 14 the directional and positional deflections are obtained respectively by LPA and LPMB coils and the focusing (cf. LB in Fig. 10) is obtained by the field of these coils. In front of the fluorescent screen SC are fine mesh electrodes FNS and BMS (e.g. 0À1 mm. pitch), the latter being connected to a cylindrical electrode RF the length of which is preferably 0À5 to 1À0 times its radius and which in combination with the coated anode AQ forms the collimator LCL. The short focusing lenses LMP may be produced by a 32 x 32 matrix of 1À5 mm. holes at 2 mm. intervals in a metallic plate at a voltage of about 0À4 to 0À5 times the voltage on the mesh electrodes FMS and BMS. The beam focusing arrangement as stated may be used in T.V. cathode-ray tubes, T.V. image pick-up tubes, electron beam memories, electron beam working apparatus, electron beam scanning microscopes and in positive ion focusing.