GB668168A - Improvements in or relating to electron discharge apparatus - Google Patents

Abstract

668,168. Travelling-wave tubes. STANDARD TELEPHONES & CABLES, Ltd. June 4, 1948 [June 7, 1947], No. 15151/48. Class 39 (i). In a travelling-wave amplifier a buncher is formed by a pair of coaxial metal ribbon helices 13, 14, Fig. 1, of different diameters but the same pitch, means are provided for projecting an annular beam of electrons through the space between the two helices, and the input wave is applied by lead 15 to one end of the two helices in parallel while the other end of the helices are connected to a single lead 16 terminated by a matchng impedance. The catcher 13A, 14A is similarly constructed and an annular drift tube 8 is arranged between the buncher and catcher. The width of the ribbons is parallel to the axis of the helices. Annular indirectly heated cathode 2 is surrounded by conical concentrating electrodes 3, 4. Decelerating electrodes 5, 7, 9 and retarding electrode 11 are provided between the gun and low potential collector 12. The drift tube 8 has a lower potential than either of electrodes 7, 9 to improve the bunching. The surfaces of electrodes 5, 7, 9, 11 facing the helices are formed to give a constant spacing between the surfaces and the end turn of each helix equal to half the pitch of the helices. The mean circumferential length of a complete turn of the helix structures is one or any odd number of half wavelengths at the mean frequency of operation, and the ribbons 13, 14; 13A, 14A are connected by low impedance conductors at quarter wavelength intervals to improve the electrical symmetry. When a complete turn is one half-wavelength, the low impedance conductors occur in diametrically opposite pairs and to prevent electrons from impinging thereon the annular cathode may be non-emissive at these points. Specification 7555/48 (as open to inspection under Sect. 91) and 668,827 are referred to. The Specification as open to inspection under Sect. 91 refers in addition to inductances as an alternative to low impedance connections between the two helices 13, 14; 13A, 14A. To compensate for the decrease in velocity of the electrons in the catcher the pitch of the catcher is progressively decreased towards its output end, or it is divided into a number of sections at increasing D.C. potentials. The device may be operated as an oscillator by coupling the buncher and catcher together. This subject-matter does not appear in the Specification as accepted.