Patent GB-710929-A (GB)
Title: Improvements in or relating to travelling wave tubes
IPC: H01J25/38
Filed: 1952-10-17
Abstract: 710,929. Travelling-wave tubes. WESTERN ELECTRIC CO., Inc. Oct. 17, 1952 [Nov. 1, 1951], No. 26081/52. Class 39(1) A travelling-wave tube comprises a gun and collector each surrounded by separate magnetic housings 11, 12, aligning sleeves 13, 40 supported by the housings and carrying hollow tubes 54, and a helix 52 carried by support rods 53 extending between hollow tubes 54. In the form shown, the envelope comprises ceramic tube 10, preferably of steatite, sealed to cups 11, 12 of magnetic material preferably that known under the R.T.M. " Kovar ", which house and shield the gun and collector assemblies, by the method described in Specification 702,437. A solenoid surrounds tube 10 and has pole pieces surrounding cups 11, 12; the solenoid may be replaced by permanent magnets. Gun anode 16 is held in aperture 14 in cup 11 by means of aligning sleeve 13 and cup-shaped member 17; members 16, 17 may be integral. Indirectly heated cathode 19 having a spherical or spheroidal surface carries beam forming electrode 21 by wires or struts 26. 23 is a heat shield, and electrode 21 has apertures 25 to facilitate evacuation. The gun electrodes are maintained in position coaxially and radially by spring 28 and insulating rings 30, 31, 32. The heater leads may be sealed through an insulating disc sealed in turn through a U-sectioned expansion joint to cup 11. The seals between the leads and disc and expansion member and disc are made by an intermediate glaze which completely covers the external surfaces of the disc. A getter is connected across the heater leads. Aligning sleeve 40 is supported and insulated from cup 12 by disc 41 coated with insulating glaze 43 so that the helix and collector can carry different D.C. potentials. Alternatively they may have the same D.C. potentials as one another and as gun anode 16 in which case sleeve 40 is mounted directly in cup 12. Disc 41 has apertures 42 to facilitate evacuation, and is held in position by insulating ring 44 held by spring fingers 46 of cylinder 45. Hollow cup-shaped collector 47 is carried directly from the envelope and has an aperture at its base carrying a sealed off exhaust tube, Fig. 1 (not shown). The helix 52 is carried by ceramic rods 53 sealed by a glaze to metal tubes 54 which are held at their free ends in aligning sleeves 13, 40. In one method of assembly, tungsten and molybdenum wires are wound side by side on a molybdenum mandrel and the ends of the wires are secured to tungsten tubes 54. The assembly is placed in an alumina jig and three rods 53 glazed to. the helix and to tubes 54, after which the molybdenum parts are removed by etching. Loss material is applied to rods 53. Since cups 11, 12 are of magnetic material the magnetic field does not extend to the gun, except to a small degree through the central aperture, thereby facilitating focusing, or to the collector structure so that the beam expands before striking the inner sides of the collector. The latter feature reduces the escape of secondaries from the collector structure. The input and output guides contact cups 11, 12, helix 53 being coupled directly at the input end (via 54, 13, 11) and capacitatively at the output end (via 40, 41, 43, 12).