GB739394A - Improvements in or relating to travelling wave devices - Google Patents

Abstract

739,394. Travelling-wave tubes. WESTERN ELECTRIC CO., Inc. June 9, 1953 [June 12, 1952], No. 15841/53. Class 39 (1). A travelling-wave tube has means for forming electrons from the source into an initially divergent beam and means for collimating the divergent beam into a parallel-sided beam whose cross-sectional area is substantially greater than the emissive area of the source. The invention, which is applicable to cylindrical, rectangular or annular beams, is stated to reduce noise. The cathode 31, Fig. 2, may have a circular or annular emissive coating and is spaced by insulating ring 39 from beam forming electrode 35; 36, 37 are accelerating anodes. A. diverging lens field is set up between 35 36, and a collimating lens field between 36 and 37. The beam is maintained parallel-sided by the external solenoid 45 which may be of strength suitable to give Brillouin flow. The gun is shielded from the magnetic field by soft iron plate 46 and preferably endplate 37 is also of soft iron. The helix may bo conventional or of the form described in Speci. fication 730,773. The ends of the helix are of varying pitch for impedance matching, as described in Specification 669,475. In a, modification, Fig. 3 (not shown), the second accelerating electrode 37 is replaced by a short solenoid outside the tube wall, and in a further modi. fication, Fig. 4 (not shown), the whole tube is immersed in a longitudinal magnetic field. The helix may be replaced by other forms of delay line. The design is discussed mathematically for an initial beam emission diameter one-ninth of its final diameter, and having noise space charge waves due to thermal fluctuations in the neighbourhood of the cathode. The beam is space charge limited. Specification 545,835 also is referred to.