Patent GB-810832-A (GB)
Title: Tungsten concentrated arc lamp
IPC: H01J61/82
Filed: 1955-09-02
Abstract: 810,832. Discharge lamps. CREED & CO. Ltd. Sept. 2, 1955 [Sept. 8, 1954], No. 25283 /55. Class 39(1). A tungsten arc discharge lamp, which can be used as a flash lamp, comprises a metallic plate anode 22 having a light aperture 23 and a cathode comprising a tungsten wire 26 having a tungsten ball 28 formed on the end thereof and positioned immediately behind the aperture 23, the diameter of the ball 28 being greater than that of the wire 26 to prevent light from the wire passing through the aperture 23. The diameter of the ball 28 can be at least twice that of the wire 26. To facilitate starting a small amount of radioactive cobalt or radium bromide is applied to the press 15. The anode 22 can be of zirconium, tungsten, tantalum or molybdenum and is supported by two nickel lead-in wires 20 having Dumet metal sections where they pass through the press. The lead-in wires 20 may be surrounded by pieces of uranium glass tubing. A nickel-Dumet metal lead-in wire 24 is connected to the wire 26 and is surrounded by an insulating sleeve 30 which may be of uranium glass to facilitate starting. A small closed loop of wire 32 including a getter pill 33 is supported by one of the lead-in wires 20. The nickel lead-in wires in the completed stem are cleaned by dipping in hot concentrated nitric acid, washing in tap water, and drying in an air blast. The plate anode 22 is degreased in trichlorethylene, rinsed in alcohol and fired in a dry hydrogen furnace for about half an hour at 1000‹C. The tungsten wire 26 is cleaned by firing in a dry hydrogen furnace for 2 to 3 hours at 1000‹C. The envelope 10 is evacuated at a temperature of approximately 750‹F. for half an hour at a pressure of about 1 micron and the plate 22 is bombarded by a H.F. bombarder to a cherry red for a few seconds. The envelope is then filled with an inert gas, preferably 99À8 per cent. pure argon, to just below atmospheric pressure. The tungsten ball 28 is formed by connecting a D.C. pulse forming circuit across the plate 22 and wire 26, maintaining predetermined values of voltage and current in the circuit such that when current pulses are applied to the electrodes an arc will flow between the plate 22, and wire 26 to form, by melting a ball on the end of the wire, timing the length of each pulse so that the ball will reach a predetermined diameter and no greater, and applying such pulses until a ball of such diameter is produced. The end of the tungsten wire can extend downwardly while the ball is being formed. After formation of the ball 28 the envelope is evacuated to about 1 micron, the getter pill 33 is flashed by H.F. bombardment and the envelope refilled with argon which can be from 100 mns. to above 1 atmosphere. The arrangement of the electrodes and lead-in wires can be such that light is emitted through the side of the envelope 10 as shown or upwardly or in other directions. The ball 28 can be reformed after prolonged use. The lamp can be used with a facsimile scanning system as described in Specification 778,985 [Group XL(b)] or for target practice when mounted on, or within the bore of a rifle, &c., the lamp being flashed in response to an electrical discharge controlled by the trigger.