Patent GB-704323-A (GB)
Title: Improvements in electron beam tubes
IPC: H01J3/02
Filed: 1950-03-24
Abstract: 704,323. Electron beam apparatus. COMMISSARIAT A L'ENERGIE ATOMIQUE. March 24, 1950 [March 29, 1949], No. 7501/50. Class 39(1) An electron gun comprises two circular end plates 1, 2, Fig. 1, with annular grooves 6, to receive glass sleeve 3, plate 1 having a central opening carrying guide 10 through which passes cathode supporting rod 12 carrying cathode 13, and plate 2 having an opening 5 for the beam accurately centred on the cathode and carrying a screen 15 defining with plate 2 a cathode chamber, and a focusing electrode 11 surrounding the cathode. Plates 1, 2 are preferably metallic and plate 2 serves as an accelerating electrode. In the form shown the two metal plates 1, 2, are turned on a lathe to ensure a precise centering of the central openings 4, 5, and plate 2 has a further groove 8 for the reception of shield 15. Members 3, 15 originally have diameters slightly larger than the walls of the grooves and are then turned or ground until they may engage the grooves with a tight fit. The shield 15 protects sleeve 3 from metallization from the cathode. A tube 9 is soldered or welded into aperture 4 to support the cathode 13 and Wehnelt electrode 11. In assembly, the cathode support rod 12 carrying cathode 13 and Wehnelt electrode 11 is fitted in guide 10, and the guide is then inserted in tube 9 so that its shoulder 14 butts thereagainst. The parts 9, 10, 11, 12, 13 are also turned on a lathe to ensure precision fits. The adjacent surfaces of 11, 13 are threaded so that they may be made relatively movable by a micrometer adjustment. The assembly is completed by fitting glass sleeve 3 into the grooves 6, 7. The cathode 13 comprises the plane or hollowed out end face of the rod 12, or alternatively may comprise a member separate from support 12. The plate 2 may be surrounded by a cooling fluid jacket, or may be provided with channels or cavities when moulded or cast to allow for circulation of a cooling fluid. The gun may be used in television transmitters, oscillographs, electron microscopes, or in X-ray tubes. The devices may be gasfilled and have thermionic or cold cathodes or may be evacuated and have thermionic cathodes. The' envelope may be gas-tight or may be connected to a pump to adjust the composition and/or pressure of the gas filling. Alternatively, in the case of an X-ray tube, a capillary tube may be inserted between the tube and an adjustable pressure container ' and the pressure in the container varied to adjust the pressure in the tube. In Fig. 2, the plate 2 is provided with a neck 16 having an internal flange for supporting the anticathode 17, parts 16. 17 being turned on a lathe to give a precise fit, and also having one or more windows 20 for the X-rays. Alternatively the neck 16 may be short and a sleeve also turned on a lathe is interposed between it and the anticathode; the windows are formed in the sleeve, Fig. 3 (not shown). The anticathode 17 may be cooled by fluid circulated in cavity 19 which may also be in the cooling circuit of plate 2. The neck 16, and intermediate sleeve if provided, may also be fluid cooled. The beam may be slightly deflected near the impact point by a transverse magnetic field. The opening 5 in plate 2 may be used as a diaphragm or a separate diaphragm may be inserted therein. The screen 15 may be screwed into groove 8 instead of being a tight fit therein.