GB1101748A - Thermionic generator - Google Patents

Abstract

1,101,748. Thermionic generators. NATIONAL RESEARCH DEVELOPMENT CORPORATION. 12 May, 1965 [12 May, 1964], No. 19806/64. Heading HID. A controllable thermionic generator includes a plurality of auxiliary anodes located within, or at the boundary of, the emitter-collector discharge space, the total area of the auxiliary anodes being less than one-thousandth of the area of the emitter. The anodes are preferably energized with positive pulses, e.g. of 1-5 microsecond duration at a 5 to 10 Kc./s. repetition rate, such that they operate under transient rather than steady state conditions, whereby an improved ratio of collector to auxiliary current may be obtained. The anodes number 1 to 4 per cm.<SP>2</SP> of emitter surface, and preferably have resistors in series to ensure a distribution of the auxiliary discharge over the whole plurality. To prepare an anode assembly a right-angle section metal strip is coated first with insulant-alumina or enamelexcept in regions 8, Fig. 5c, and then over the interior of the angle, with a resistive layer of nickel/chromium alloy 9. Tungsten, molybdenum, or tantalum wires 3, welded to a metal tape 10, are then introduced into the angle, which is closed to clamp them, Fig. 5g, whereafter the tape is cut off and the wires cut to length, and the assembly, except for the wires, resprayed with insulant. The wires 3 are located mid-way between successive conductive portions 8, whereby the lead to each wire is constituted by the angled strip, and two sections of the resistive layer 9 in parallel. If resistors in series with the anodes are not required, tape 10 itself may be clamped within the angled strip, to form the lead for the wires which project outwardly therefrom. A plurality of such linear assemblies may be seated in parallel grooves formed in the collector surface (Fig. 7, not shown), to form an array of wires both projecting and insulated from the collector surface, the assemblies being connected to a common tantalum lead which is insulated with a ceramic cement, or by anodizing. Alternatively, the resistive layer may be applied to only one of the inner faces of the insulantcovered metal strip, the anodes being constituted by patches of refractory metal or by metal plates 13, Fig. 6, exposed beneath perforations 12 formed in the other face of the strip; the completed assembly can be held flat on the collector surface by metal strips welded across it, and may be wound as a helix (Fig. 8, not shown) on the outer surface of a tubular, coolant-carrying collector. In a further arrangement (Figs. 1 and 2, not shown); the wires constituting the anodes pass through enamel beads in the envelope, which forms the collector electrode and is immersed in coolant; the wires may be either ground flush with the collector surface, or project therefrom, and have their ends sharpened by electrolytic etching. The tube contains argon, krypton, or xenon, and possibly a metal vapour, at a pressure of 0À1 to 5 torr, and the emittercollector spacing is about 2 mm.