Patent GB-733063-A (GB)
Title: Improvements in or relating to travelling wave apparatus
Inventor: KOMPFNER RUDOLF
IPC: H01J23/30
Filed: 1951-09-08
Abstract: 733,063. Travelling wave tubes; space charge wave tubes. NATIONAL RESEARCH DEVELOPMENT CORPORATION. Oct. 30, 1952 [Sept. 8, 1951; Nov. 3, 1951], Nos. 21229/51 and 25764/51. Class 39 (1). [Also in Group XL (b)] In travelling wave discharge devices, space charge wave devices, or plasma frequency variation devices (such as " velocity jump " tubes) having a wave propagating helix inside the envelope, a further helix is arranged external to the envelope, is wound in opposite sense to the inner helix, and provides microwave coupling therewith. The coupling is between the transverse fields of the helices. It is shown that by winding the helices in opposite senses the insertion loss is reduced even though the helices overlap to a very small extent compared with a system in which they are wound in the same sense. The broadband; coupling device preferably comprises a coaxial line 80, Fig. 8, the outer conductor 81 terminating in a #/2 diameter flange 82 and the prolongation of the inner conductor 83 forming the external helix 84. Inaccuracies in the construction of the inner helix may be corrected or the phase velocity altered by suitable selection of the length, pitch or diameter of the outer helix. The phase velocity of the system is different from that of either helix, and interaction may be obtained for an electron velocity equal to this phase velocity to provide input power to or output power from the beam-or equal to the phase velocity of the inner helix to give progressive amplification. Alteration of the parameters of the outer helix may give propagation of power in either direction or a controlled degree of reflection (including total reflection). As shown, 44, 45, Fig. 4, are input and output helices and 41 is the inner helix. Oscillation may be prevented by lumped attenuation, or alternatively by an outer helix 46 embedded in loss material 47. The loss material has tapered ends 48, 49 to avoid reflections. In another form, Fig. 5 (not shown), the outer output helix is of varying pitch so that the wave and progressively slower beam are kept in synchronism; such a helix may be in a 'number of sections, Fig. 6 (not shown). The inner helix is preferably also of varying pitch. In another form, Fig. 7, the inner helix is surrounded by a prehelix 71 to effect noise cancellation as described in Specification 696,058, input helix 72, "modifying"  helix 73 to give the .beam and wave the same velocity so that amplification occurs, and output helix 75. It is stated that when the helices are designed to have equal individual phase velocities and when their mutual capacity and inductance are equal and of the same sign, then their combined impedance lies between their individual impedances so that wave reflections are reduced at the point of overlap of the helices; this result is a maximum if the overlap is an odd number of quarter wavelengths long. The first and second Provisional Specifications refer to the flange 82, Fig. 8, as being optional. The coupling arrangement of Fig. 8 is especially suited for Brillounin type focused tubes where the magnetic field configuration is unsuited to wave-guide coupling. The first Provisional Specification states that the lossy material in which an outer helix is embedded may be of graphite mixed with ceramic. It is suggested that noise reducing arrangements may be provided at the output end of the tube. The second Provisional Specification refers to the use of the devices as generators, amplifiers, attenuators and modulators.