GB536932A - Improvements in electric discharge devices of the type employing liquid cathodes - Google Patents

Abstract

536,932. Metal-vapour rectifiers. BRITISH THOMSON-HOUSTON CO., Ltd. March 28, 1940, No. 5612. Convention date, March 30, 1939. [Class 39 (i)] A mercury-vapour rectifier of the pool cathode type is provided with an anode for producing a holding arc enclosed in a casing of insulating material dipping into the cathode pole and provided with a narrow opening in the neighbourhood of which the material of the casing is so treated, as by sputtering with metal such as molybdenum, iron or tungsten, that it is wetted by the mercury giving a concave meniscus where the mercury touches the casing. The arrangement shown comprises a double-walled casing 11 containing a main anode 20 on a stem 26 attached to the casing by a glass seal 21, the joints being protected by screens 24, 25. The holding-on anode 30 is enclosed in a quartz casing 38 dipping into the mercury pool 27, and formed with a slit 40 through which the holding-on arc communicates with the discharge space. The surface of the quartz near the slot is sputtered with molybdenum from a wire 45 passing through an insulating sheath 47 to a resistance 52 connected to one phase 51 of a three-phase supply, another phase 50 of which yields the current to be rectified. The holding-on arc is anchored near the slot 40 by means of a molybdenum rod 42 projecting from the pool 27. A starting-anode 34 is also provided. Modifications are described in which the slot 40 is formed in a separate tube branching from the casing 38 and in which the holding-on arc is held at the required point of the cathode by a magnetic field. Specification 520,183 is referred to.