GB615257A - Improvements in or relating to electron microscopes and other electronic apparatus employing electron lenses - Google Patents

Abstract

615,257. Electron lenses. LIEBMANN, G., and CATHODEON Ltd. May 13, 1946, No. 14465. [Class 39 (i)] An electron microscope, diffraction camera, cathode-ray tube, or X-ray tube comprises a vacuumtight envelope 1, Fig. 1, of non-magnetic material such as brass or nickel-copper alloy, one or more solenoids 4, 13 shrouded in magnetic material 5, 14, such as iron, forming a sliding fit on the external surface of the envelope 1, and each solenoid is provided with iron polepieces 7, 8; 16, 17 registering with air-gaps 6, 15 in the iron shroud or shrouds and spaced apart by non-magnetic spacers 11, 20, preferably of brass and the pairs of polepieces (if more than one pair) are spaced apart by non- magnetic spacers 22 also of brass; the polepieces and spacers form a sliding fit within the envelope 1. The envelope 1 may be a single tube or (as shown) made up of two tubes 1a, 1b, the polepieces and spacers being assembled in the tube 1b and the resulting assembly being inserted as a unit within the tube 1a. Additional spacers 23, 24 are provided, and beam stops may be included in the assembly of polepieces and spacers, which is located as a whole by stops 25, 2G and the tube 1b is supported on a flange 27. Magnetic shielding means (not shown) may be provided to exclude extraneous fields. The joints between the tube 1 and other parts of the apparatus each comprise a socket 28, a rubber gasket 29, a metal washer 31, and a gland ring 30 which screws into the socket 28. A weak transverse magnetic field may be applied to the beam for centring purposes, and is produced by a permanent magnet, a coil or coils mounted on the envelope or an electromagnet, Fig. 2 (not shown), mounted within a housing 32 and having soft iron polepieces 38. Soft iron inserts within the envelope 1 may concentrate and " parallelize " the field. A number of such centring devices may be provided, one between each successive pairs of lenses as well as one before the point of entry of the beam into the first electron lens. The beam finally falls on a fluorescent screen or photographic plate. A prior art arrangement in which the inner walls of iron-shrouded solenoids form part of the vacuum-tight envelope, being joined to the other envelope parts by flexible metal bellows, polepieces being provided inside the envelope to register with annular gaps in the inner walls of the shrouds, and the gaps being closed by brass inserts to complete the vacuum-tight enclosure, is referred to.