US2941107A - Flashtube - Google Patents

Description

June 14, 1960 Fig}.

E. NoLLE FLASHTUBE Filed Dec. 28, 1956 lnven tov: firns t NciLLe His A t tow-neg.

United States Patent FLASHTUBE Ernst Niille, Berlin-Charlottenburg, Germany, assignor to Patent-Treuhand-Gesellschaft fiir Elektrische Gliihlampen m.b.H. (Patent Fiduciary Company for Electric Incandescent Lamps Ltd.), a German company Filed Dec. 28, 1956, Ser. No. 631,179

Claims priority, application Germany Jan. 27, 1956 2 Claims. (Cl. 313-185) This invention relates to an electric discharge lamp of the flashtube type for pulse or stroboscopic applications, the cathode of which consists of or contains a sintered porous body for the purpose of obtain ng a rapid discharge and assuring long life.

For the operation of flashtubes at higher flashing frequencies or repetition rates, rapid development of the arc discharge is required as well as quick extinction and tie-ionization. It has already been proposed to use as a cathode for a flashtube a non-homogeneous and porous body of sintered metallic powder whereby the transition from the first starting glow discharge into the are discharge is facilitated and a decrease of the extinguishing voltage is obtained.

The object of the invention is to provide a flashtube having an improved cathode construction which achieves more rapid development and subsequent extinction of the arc discharge.

According to the invention, a flash tube or electric discharge lamp for pulse operation is provided with a cathode body consisting of sintered nickel powder provided with cavities such as borings, recesses or grooves. These cavities act as hollow cathodes and assure that an arc discharge takes place shortly after the glow discharge has started; in other words, they assure rapid build-up of the discharge. The cavities also augment the cathode surface available and thereby increase the life of the cathode and consequently of the lamp. It has proved advantageous to make the grooves about 0.5 mm. deep and to choose a diameter of about 0.5 mm. for the borings. Suitably the cathode is activated with caesium chloride which is highly advantageous in a lamp intended for stroboscopic applications because of the self-extinguishing efiect obtained thereby. Flashtubes With such cathodes are suitably provided with a neon filling at a pressure in the range of 10 to 40 millimeters of mercury.

The accompanying drawing shows an example of a cathode for a flashtube according to the present invention wherein:

Fig. 1 is a side view of the cathode end of a flashtube shown partly in section.

Fig. 2 is a plan view of same, that is a view looking along the axis of the tube.

Referring to the drawing, a metal cup 1 contains a cathode body 2 consisting of sintered nickel powder; a current inlead 3 is attached as by welding to the cup and serves also as a support. The cathode body 2 is provided with axial borings 4, the diameter of which is about 0.5 millimeter. The borings open into the front face oi the body on which the discharge terminates, and, as illustrated in Fig. 2, they may be five in number. The cathode body is also provided on its circumference with numerous axial grooves 5 which are about 0.5 millimeter deep in a transverse or radial direction. The active surface of the cathode is increased by the cavities consisting of the borings and grooves, whereby a rapid ice change from glow to are discharge is achieved and a long length of life is realized for the flash tube.

The sintered cathode body is activated with caesium chloride, for instance by immersion in a saturated solution thereof in distilled water followed by drying. It has been found that activation with caesium chloride reduces the time required for extinction and de-ionization in the flashtube after a discharge or flash; thus a higher repetition rate of flashing may be achieved.

The instant cathode is mounted in a slender elongated vitreous tube 6 of which one end is illustrated in the drawing, the current inlead 3 being sealed or pressed into the flattened or pressed tube end 7. The tube may be of straight linear form or curved into a U-shape or helix in known manner. In the preferred embodiment of a flashtube illustrated in the drawing, the metal cup 1 is large relative to the internal diameter of the vitreous tube 6 and has a diameter not less than approximately half the internal diameter of the tube. The other end of the tube may be provided with an anode which may, if desired, be merely the end of an inlead. The tube is filled with an ionizable medium such as an inert gas at a low pressure. A suitable filling consists of neon at a pressure of in the range of 10 to 40 millimeters of mercury, preferably at about 15 millimeters of mercury.

While a certain specific embodiment of the invention has been illustrated and described in detail, the same is intended as an illustrative example only, and the scope of the invention is to be determined by the appended claims.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. An electric flashtube comprising a slender elongated vitreous envelope having sealed into opposite ends thereof a cathode and an anode, said cathode comprising an open-ended metal cup having a diameter not less than approximately half the internal diameter of said envelope and containing a porous body of sintered nickel powder provided with cavities achieving a hollow cathode effect for rapid build-up of a flash discharge and activated with caesium chloride to assure rapid extinguishment and de-ionization subsequent to said discharge, said cavities having a transverse dimension of approximately 0.5 millimeter and a filling within said envelope of an inert gas at a pressure in the range of 10 to 40 millimeters of mercury.

2. An electric flashtube comprising a slender elongated vitreous envelope having sealed into opposite ends thereof a cathode and an anode, said cathode comprising an open-ended metal cup having a diameter not less than approximately half the internal diameter of said envelope and containing a porous body of sintered nickel powder provided with cavities achieving a hollow cathode effect for rapid build-up of a flash discharge and activated with caesium chloride to assure rapid extinguishment and deionization subsequent to said discharge, said cavities having a transverse dimension of approximately 0.5 millimeter and a filling within said envelope of neon at a pressure of approximately 15 millimeters of mercury.

References Cited in the file of this patent UNITED STATES PATENTS 1,552,310 Kayko Sept. 1, 1925 1,716,545 Mackay June 11, 1929 2,107,945 Hull Feb. 8, 1938 2,147,447 Kolligs Feb. 14, 1939 2,159,747 Mendenhall May 23, 1939 2,180,988 Lemmers Nov. 21, 1939

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