Patent GB-863672-A (GB)
Title: Improvements in or relating to travelling wave tubes
IPC: H01J25/38
Filed: 1959-12-14
Abstract: 863,672. Travelling wave tubes. WESTERN ELECTRIC CO. Inc. Dec. 14, 1959 [Dec. 31, 1958], No. 42416/59. Class 39(1). In a travelling wave tube the helix is supported by an insulating rod divided into sections along its length and glazed to the helix and a conductive block (part of the tube envelope) having a groove to align and mount the rod sections. There may be only one helix but preferably there are two helices 13, 14, Fig. 1 and separate aligning rods 24, 25 of which on or more such as 27 are conductive to form D.C. leads to the helices and are brazed to the helices and envelope groove. The support rods 24, 25 are glazed to the envelope groove in which they are mounted. Transverse grooves crossing the first groove accommodate excess glaze. The helices or support rods may be coated with "Aquadag" (Registered Trade Mark) as loss and tapered ceramic lossy incomplete cylinders surround the helix sections. The lossy cylinders arenear or touching the end turns of the helices and are glazed to further grooves in the envelope. The envelope parts surrounding the helix sections are each in two portions and are of Cu or Mo and the rods 24, 25 are of sapphire and act also to inhibit backward wave oscillations. In manufacture the Mo helix sections are wound on a Cu or Mo mandrel, glaze is put in the envelope groove and 24, 25 are mounted in this groove, glaze is sprayed on the rods 24, 25 in the area to contact the helices, and conductive rod sections 27 are brazed to the envelope groove and helices. The two regions of glaze :i.e. helix-support rods and support rods-envelope may be melted in one step or in two discrete steps. Next the mandrel is chemically dissolved out and the "Aquadag" (Registered Trade Mark) coating applied to the helices. Now the left hand helix and rod and envelope and input window 36 are placed a jig, ceramic lossy cylinder 47 is inserted, the polepiece 15 is also inserted, followed by the right hand helix and rod and envelope and output window 38 and envelope parts 34, 98, 96 and the envelope parts are brazed together. Pt washers are interposed between the ceramic windows 36, 38 and other envelope parts. The envelope of small diameter so assembled is pushed through end plate 43 until the collar on 33 abuts 43. The gun alignment, platform 74 is screwed to platform 43, the gun envelope parts are sealed together and the collector cooling circuit which is adjustable by lock-nut 95 to vary gap 93 is attached to the collector end. The end turns of the helices are tightly wound and brazed together as described in U.S.A. Specification 2,716,202. The input and output couplers 32, 34 are threaded to the envelope so can be adjusted during manufacture 'to optimise the impedance match. The magnetic -circuit comprises a plurality of permanent bar magnets 45, 46 or two annular permanent magnets or solenoids bridging polepieces 40, 41, 42 and gives periodic focusing as described in Specification 757,369. The polepiece 40, 15 is tapered to avoid distortion of the longitudinal magnetic field lines at the point of magnetic field reversal. The conductive envelope parts are of Cu or Mo. The tube has a glass or ceramic base 62 through which passes exhaust tube 65. A Ba or Mg getter 69 is mounted on ceramic shield 66. The gun has support rods 71, 72 held by platform 74 and wire supports 73, the rods 71 being carried at the left hand ends by tube 63. The cathode 79 is spaced from cylinder 78 by wires 77. The beam may be cylindrical or may be accompanied by an annular beam outside the helix. An envelope part 98 of ceramic insulates the collector from the helix. Prior art constructions in which a helix is bonded to a cylinder or a member with a polygonal aperture or to support rods of sapphire which is bonded to a Mo envelope (all bonds by glazing) are referred to.