Patent GB-692705-A (GB)
Title: Improvements in and relating to ultra-high frequency amplifying tubes
IPC: H01J25/44
Filed: 1950-02-14
Abstract: 692,705. High frequency discharge apparatus. COMPAGNIE GENERALE DE TELEGRAPHIE SANS FIL. Feb. 14, 1950 [Feb. 23, 1949], No. 3792/50. Class 39(i) [Also in Group XL(b)] In a high frequency amplifying electron discharge device one or more electron beams at least one of which is initially density modulated are subjected to crossed static electric and magnetic fields in a space which does not contain a retardation line, i.e. one free of high frequency fields, the arrangement being such that the ratio between the electric and magnetic fields varies transversely across the space so as to give the electrons different average forward velocities which accentuates the initial density modulation, and the electron groups finally give up amplified energy to an output circuit. The desired field variation is obtained by designing the electric and/or magnetic means to produce non-uniform fields or by the use of auxiliary cathodes to produce a controllable space charge, or the space charge of the beam may be relied on if the current density is sufficiently great. In one form, Fig. 4, a single beam is produced by indirectly heated cathode 10, is focused and accelerated by electrodes 11, 12, and is velocity modulated by the input wave travelling along helix 13. When the velocity modulation has become density modulation density modulated beam is subjected to the crossed electric and magnetic fields, the electric field between cylindrical electrodes 7, 8 varying inversely with the radius while the magnetic field is uniform. The beam now with accentuated density modulation generates a wave on output helix 16 and is finally collected by target 6 which may be cooled by compressed air or water. The input and output are coupled into and taken off from the tube via coaxial lines 14, 15; 17, 18. The electrode 7 is earthed, and electrode 8 biased negatively by lead 9; the electrode 8 is supported from the walls of the device by means of quartz or ceramic insulators, Fig. 4a (not shown). The helices 13, 16 may be of circular or rectangular cross-section. The free ends of the helices 13, 16 are connected to the tube wall 7. In a modification, Fig. 5 (not shown), the output helix 16 is replaced by a cavity resonator which has a deformable wall for tuning. The resonator grids are formed by fins. In another modification, Fig. 6 (not shown), the input helix 13 is replaced by a modulating grid made up of fins. In another form, Fig. 7, the modulating and energy extracting circuits are cylindrical waveguides loaded with apertured plates 26, and are coupled to input and output coaxial lines 27, 28; 30, 30a the inner conductor 27 containing the cathode 10 and the inner conductor 30a forming the collector. The disc openings are graduated where the guides are coupled to the coaxial lines so as to provide an impedance match. The discs may be replaced by fins. As the distance between deflecting electrodes 7, 8 is small the electric field between them is almost uniform so that it is necessary to produce a non-uniform magnetic field; this is done by tapering the air gap between the pole pieces, Fig. 7a (not shown). Auxiliary coils 31, 32 focus the beam in the input and output waveguides. The tube may be linear instead of curved. Two or more cathodes may be used in any of the forms of Figs. 4-7. In another form, Fig. 8, the tube is linear and the modulation and energy extraction circuits are helices 13, 16. The device may have only one cathode but preferably has two cathodes 10a, 10b at different negative potentials. The transverse electric field is applied between flat electrode 8 and metal tube wall 7 and is therefore uniform; the transverse magnetic field is therefore made non-uniform, Fig. 8a (not shown). The output section of the tube is slightly inclined as shown so as to take into account the shape of the electron paths. In a modification of this arrangement, Fig. 9 (not shown), the transverse magnetic field is uniform; to vary the transverse electric field, a plurality of hot cathodes are inserted in the interaction space and the heating current and therefore the emission can be varied to give optimum results. The auxiliary cathodes may be dispensed with if the current density of the beams is sufficiently high, the variation in the shape of the electric field being obtained due to the space charge of the beams. Specifications 663,728 and 681,425 are referred to.