GB722096A - Improvements in or relating to electron lens - Google Patents

Abstract

722,096. Cathode-ray tubes. SIEMENS & HALSKE AKT.-GES. May 31, 1951 [Oct. 1, 1948; Oct. 1, 1948]. No. 12955/51. Class 39 (1). The strength of the magnetic field for concentrating the electron beam in a cathode-ray tube, such as an electron microscope, is adjustable by a magnetic member, the position of which is regulable relative to a magnet. Magnets 9, Fig. 1, are arranged between poles 1 and the concentrating fields are formed between poles 1, 3, 3, 5 and 5, 6. Magnets 13 connect the magnets and the poles together and the rotatable magnetic members adjust the strength of the magnetic field in the pole gaps. The magnets can form part of the walls of a microscope which is connected to a vacuum pump through channels formed in the poles 1. A three stage lens, Fig. 2 consists of four poles each fitted to a limb 25, Fig. 2, of two U- shaped magnets between which is arranged a slidable magnetic shunt 34. In a modification, circular magnets are arranged in parallel planes and each magnet is connected, respectively at each end. to an axial pole and an outer disc-shaped pole. A soft iron armature parallel to the lens axis is slidable in a cylindrical track determined by the two magnets. A bar magnet may be extended by a soft-iron armature, which is slidable longitudinally in holes in the poles of the-lens. Iron cylinders 58, 60, Fig. 4, are rotatable on the poles 55, 56 to rotate bar magnets 59, 61, past magnet poles 54, 57 and a spiral-shaped iron member 62. A twostage lens for a microscope consists of cylindrical magnets 203, 204, Fig. 6, and the lenses are formed between poles 205, 209 and 208, 210. A jacket 211 screens the lens from external fields. Rotatable or slidable. armatures 212, 213, 222 adjust the magnetic strength of the lens. Further adjustment of the field for the projection lens is obtained by inter-changeable poles 215 which are carried by the rotatable holder 214. A similar arrangement for a four stage lens consists of cylindrical magnets 204, Fig. 6, between which are clamped four poles 210; the shunt 213 is slidable. The magnetic shunts are connected to a driving mechanism so that they slide in opposite directions to prevent rotation of the electron image. Bar magnets 231, 232, Fig. 7, are provided with poles 236, 237 and are arranged within a jacket 239 of which the end plates 235, 237 constitute the outer poles of the lens. The field strength is adjustable by the armatures 240 ... 243. A fourstage lens consists of two cylindrical magnets 261, 262, Fig. 8, poles 258, 259, 250, further poles formed by the end walls of the jacket.257, slidable armatures 263, 266, 267 and of toothed members 264, 265 one of which is rotatable to alter the magnetic reluctance. The operating mechanism for the armature may be calibrated.