In an exemplary embodiment, a transmitting tube has a coaxial design of the electrodes and their lead-ins and includes a cathode formed of a hollow cylinder which is secured at one end to an annular cathode lead, and at the other end is secured to a cathode cap which is supported at a power supply lead extending coaxially within the hollow cylinder. In this cathode, the carrier is not to consist of wire, so that inhomogeneities on the cathode surface are avoided. To this end, the disclosure provides that the hollow cylinder consist of pyrolytic graphite and be coated with a thin metal layer, preferably consisting of tungsten carbide and thorium, or a thorium oxide.
An ion thruster comprises a chamber in which propellant is ionized and an accelerator grid, whereby a flow of ions out of the chamber provides reactive thrust. Charge exchange between neutral atoms of propellant and fast moving ions produces slow ions which impact on the accelerator grid and erode it by sputtering, thus limiting the lifetime of the thruster. The invention includes an accelerator grid comprising a layer which includes graphite providing resistance to erosion and a support layer which overcomes the restrictions on engineering and strength of graphite. The accelerator grid can be constructed by machining a block of graphite 12 to produce an upper surface 13, to which the molybdenum grid 14 can be fixed. The block 12 can then be cut away to permit the graphite to be machined to the same contour as the surface 13. Apertures are drilled through the graphite using the existing apertures of the grid 14 as guides.
Flat and slightly convex pyrolytic graphite grid electrodes are very suitable for use in electric discharge tubes, are example in ion sources, cathode-ray tubes, travelling waveguides and transmitter tubes. It has proved possible to manufacture such electrodes by manufacturing the grid and the grid holder of the pyrolytic graphite electrode from one piece of pyrolytic graphite. Such integral grid electrodes have very good mechanical and thermal properties.
In an electron tube having coaxial cylindrical electrodes and at least one cylindrical grid of pyrolytic graphite, the grid is joined to the upper portion of a central conducting mast by means of a bell which is also of pyrolytic graphite and fixed on the mast. Slits are cut at uniform intervals around the periphery of the bell in order to form resilient strips which serve to establish an electrical contact between the grid and the conducting mast.
In a controllable high-power electron tube in the form of a tetrode, the anode direct voltage is reduced to less than 10 kV with an anode efficiency of greater than 80%. The tube includes coaxially arranged electrodes including a cylindrical indirectly heated full walled matrix cathode containing BaO, a cylindrical control grid, a cylindrical screen grid and an anode, where the spacing between the control grid and the cathode and the spacing between the control grid and the screen grid is less than 1 mm. Such a tube can be used for achieving AM broadcast transmitters which are distinguished by a compact construction, the overall efficiency remaining largely unchanged.
A cooling system for a screen grid electron tube such as a high power, high frequency transmitter tetrode which has coaxial formed electrodes and bushings and has an air cool screen grid terminal formed of two angular screen grid terminal elements 1 and 2 spaced from each other in the axial direction together with their bushings 3 and 4 so as to form a cooling air coaxial passage 7 so as to cool the screen grid terminal elements 1 and 2.
