GB480779A - Electron-optical arrangement - Google Patents

Abstract

480,779. Cathode-ray tubes. RADIOA,KT.-GES. D. S. LOEWE. June 26, 1936, No. 17804. Convention date, June 27, 1935. [Class 39 (i)] A cathode-ray tube preferably of the high vacuum type is provided with a diaphragm 1, an aperture in which is to be electronoptically reproduced on the fluorescent screen of the tube, the diaphragm having a potential which is near cathode potential (e.g. 100 volts positive relatively to the cathode when the anode potential is 2000 volts), and means are provided for producing between the diaphragm and electron optical system an accelerating field which is homogeneous and exempt from transverse components in those parts of the tube traversed by the beam. The homogeneous field may be produced by a tubular member 2, the diameter of which is large compared with the diameter of the beam and which is separated from the diaphragm 1 by a distance 18 of the same order of magnitude as the diameter of the member 2, thus providing a substantially field-free space between the members 1, 2, through which the electrons travel with the speed they possess on passing through the diaphragm. This is made as low as possible by providing a low potential on the diaphragm, the beam being maintained sufficiently intense by means of a screening grid 21 at higher potential and concentrated by a cylinder 22. Suitablepotentials, examples of which are given in the Specification, are obtained from tappings on a potentiometer 17. The homogeneous field may also be obtained by replacing the member 2 by a high resistance layer, one end of which may be connected to the potential of the diaphragm 1 and the other to that of the anode 3, while in a further form a helicallywound resistance layer may be used, one end being connected to the diaphragm and the other to the anode 3, a magnetic focusing coil being provided in the plane of the anode. Specification 442,511 is referred to.