GB669473A - Travelling wave amplifier discharge device - Google Patents

Abstract

669,473. Travelling-wave tubes. WESTERN ELECTRIC CO., Inc. Oct. 22, 1947 [Oct. 22, 1946], No. 28258/47. Class 39 (i). In a travelling-wave tube the highfrequency wave travels along a helix 2, Fig. 2, and the helix 2 is supported and spaced from the tube wall by insulating-rods 15. Magnetic coils 23, 24 focus the beam, coil 24 being enclosed in a magnetic shield 25. The wire of the helix may be of steel or molybdenum. Alternatively it may be of high-loss material such as iron or an alloy which may be plated at both ends only or along its whole length with low-loss material such as copper or silver or may be unplated, in order to provide a desired uniform or non- uniform attenuation along the length of the helix and so to prevent any tendency to selfoscillation. Another way of introducing attenuation is to surround the central portion of the helix with a cylinder 36, Fig. 4, of loss material such as a mixture of ceramic and metallic materials. The input and output are injected and removed by wave-guides 3, 4, Fig. 2, coupled to the helix by strips 7, 9 designed to give a good impedance match and integral with short cylinders 6, 8. Cylinders 6, 8 may be a quarter-wavelength long and together with shields 10, 11 form open-ended low-impedance lines. A shield 12 extends between the waveguides 3, 4. Cylinders 6, 8 are positioned by ceramic spacers 13, 14 and have circumferential notches to receive the rods 15 which may be of a ceramic material containing zirconium oxide. The indirectly-heated cathode 16 is positioned in the aperture of focusing electrode 17. Accelerating electrode 18 and collector 19 are also provided. The cavity resonator 26 is resonant at the mid-frequency of the band and serves as a choke to prevent leakage of highfrequency energy along the lead to the helix from D.C. source 22. It is stated that the wave velocity is slightly less than the beam velocity. In Fig. 4 the rods 15 are in two parts on either side of the cylinder 36, the latter having circumferential notches to receive the ends of the rods remote from cylinders 6, 8. In another embodiment, Figs. 8, 9 (not shown), further magnetic focusing coils are provided, one of the coils surrounding the electron gun which is made of non-magnetic material. The coils are arranged to produce a uniform field over the whole length of the discharge device. In the form of Fig. 9 (not shown), the envelope is uniformly slender throughout its length and has no enlarged portion. Specifications 669,474 and 652,155 are referred to.