GB777979A - Improvements in or relating to travelling wave tubes - Google Patents

Abstract

777,979. Travelling-wave tubes. TELEFUNKEN GES. Nov. 19, 1954 [May 22, 1954], No. 33533/54. Class 39(1). Power loss at the collector electrode of a travelling-wave tube is reduced by providing in the space between the delay electrode of the tube and the collector electrode a screen electrode which is connected to the delay electrode and prevents substantial penetration of electronic field lines from the collector electrode back into the interaction space of the delay electrode, thus enabling the collector electrode to be maintained at a considerably lower positive potential than that present on the delay electrode. The tube shown comprises an electron gun 5 for projecting an electron beam through a helix 3 to a collector electrode 6, the beam being concentrated by the magnetic field of a coil 7. High-frequency waves to be amplified are fed to an input electrode 1 by a waveguide 4 having an extension tuned by a plunger 8, and the amplified waves are fed from an output electrode 1<1> to a waveguide 41 having an extension tuned by a plunger 81. Alternatively the input and output waveguides may be replaced by hollow tubular line sections terminated by short-circuited quarter-wave line sections. The helix 3 is supported by three ceramic rods 2 provided with strips 10 of lossy material such as carbon which are shaped at their ends for matching purposes. The rods 2 extend between the coupling electrodes 1 and 1<1> which, together with the electron gun 5 are held in position by a support system including three ceramic rods 9. The end of the helix 3 is connected to a tubular extension 15 of a screen electrode 11 in the form of a metal disc which is fused to the envelope 12 and lies between the end of the helix 3 and the collecting electrode 6. The aperture in the tubular extension 15 is slightly larger than the electron beam crosssection, and the diameter of the bore in the collector electrode 6 is larger than or equal to the diameter of the said aperture. The main body of the screen electrode 11 may be made of ferromagnetic material and the tubular extension 15 of non-ferromagnetic material. The arrangement enables the potential of the collector electrode 6 to be as low as 200 volts, with the helix 3 at a potential of 1200 volts positive relative to the cathode. The power loss is sufficiently low to enable power tubes to be operated without compressed air blast or other forced cooling, the cooling fins shown on the collector electrode structure being sufficient. In the case of low power tubes even these cooling fins can be omitted.