GB792002A - Improvements in centralising means for electronic devices making use of a focussed electron beam - Google Patents

Abstract

792,002. Magnets. MARRISON & CATHERALL, Ltd. April 10, 1956 [April 12, 1955], No. 10388/55. Class 35. [Also in Group XL (a)] A periodic magnetic focusing arrangement for a travelling wave tube comprises a series of permanent magnets magnetized radially with respect to central ring poles and a soft magnetic surround made up of a plurality of members in contact with one another. The magnetic field distribution is substantially sinusoidal in space. In one form, Fig. 1, the magnet assembly comprises radially magnetized discs 12, 21, 28 enclosed in and abutting against shoulders of housings 13, 19, 24 of soft magnetic material such as mild steel and having brass tubes 4, 9, 10 passing through apertures therein, the end brass tubes 9, 10 being of larger diameter than the central tube 4 which has a long central section and short end sections to accommodate the enlarged gun and collector ends of the travelling wave tube, and the brass tubes being connected with waveguide feeders 5. A shunt plate 30 of soft magnetic material is rotatably mounted (with an axial component of motion) by threaded stud 31 passing through an inclined slot in the housing, a lock-nut 33 locking the device in any adjusted position. The sections of surround 13 are secured together by spigot and socket connections. The travelling wave tube is located by a socketed brass spacer 34. The magnetic discs must be accurately machined as to inner and outer diameter and may be press fits with the inner and outer sleeves or may preferably be fixed by thermosetting or hard setting cement; similar cement may be used to lock the spigot-and-socket connections and between the magnet units and waveguide housings 2. The mild steel end plates 18, 26 eliminate any external field and increase the field strength between the members of the end pairs of magnets and this is corrected by the larger bore of the magnets at each end. The magnet discs taper radially so as to give equal cross-sectional areas at all radii. There may be 16 magnets in a length of 12 in. In a modification, Fig. 5, each magnetic unit comprises five bar magnets abutting the flat faces of a central approximately annular pole piece and are held by locating shoulders 39 of a multisection surround 35, while brass lengths 37 are inserted in central apertures therein. The magnets of the assemblies preferably register in radial position with one another. The magnets are of alnico or for high-duty operation of Fe-Ni-Al-Co-Cu alloy which preferably containing Cb also, as in Specifications 634,686 and 634,700, [both in Group II]. In another form, Fig. 6 (not shown), the bar magnets are wider than in Fig. 5 and have tapered inner ends so that they can all abut the central pole. The radial magnetization and heat treatment for amsotropy need not be effected simultaneously. Specification 757,369 also is referred to.