US2212881A - Electric gaseous discharge device - Google Patents

Description

Aug. 27, 1940.

=ZEW/ J. LECORGUILLIER 2,212,881

ELECTRT C GASEOUS DISCHARGE DEVICE Filed Feb. 2, 1939 INVENTOR l Jean Lecorgullhery- 25. Ai mmiv Patented Aug. 27, 1940 UNITED STATES 2,212,881 PATENT OFFICE 2,212,881 Emc'rmo Gaseous mscnanon DEVICE Jean Lecorguillier, Suresnes, France, assignor to General Electric Company, a corporation of New York Application February 2, 1939, Serial No. 254,148 In Switzerland February 2, 1938.

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in straight or bent arms of a length depending on the voltage which must exist between the anodes in order to avoid short-circuits between 15 them. Such a construction is bulky and fragile especially when applied to tubes used for fighting and moreover, the initial cost is high, as the tube can hardly be produced except by hand.

The present invention has for its chief object the provision of an assembly of small bulk and great strength having excellent electrical stability and easily lending itself to mechanical production by reason of the fact that the anodes of the discharge tube are attached to one and the same 25 foot tube in the interior of the discharge tube.

However, this method of mounting the anodes, where, in the case of Cooper-Hewitt tubes, the working conditions justify the use of anode arms, is suitable only if in the tube under consideration 30 it does not cause a reverse current, which might result in a considerable volatilization of the anodes and a strong absorption of the gaseous filling, or in short-circuits between theanodes.

According to the invention this result is obtained by so arranging the anodes that the anode parts which extend along the wall of the tube are for at least a portion of their length, measured from their front ends facing the discharge, locatedat a distance from the said wall sufli- 40 ciently small to allow the anodes to be affected by. the discharge substantially only in the vicinity of their front ends and that the parts of the anodes which are adjacent one another are separated by a distance which is at least equal to 45 the minimum spacing which is, practically attainable without risk of contact between the anodes, but is less than the distance at which a harmful reverse current is produced, the current leads to the anodes being so arranged as to avoid 50 any discharge between the said leads.. The two distances in question depend upon the particular conditions under whichthe tube is to operate, viz. the nature and spacing of the electrodes, the nature and pressure of the gaseous filling and the .5 tude of the rectified current and o inter-anode voltage. The distance here considered between the anode parts and the wall is sufficiently small to prevent the ionization of the space situated at the rear of the front ends of the anodes; the distance between the" two anodes is of the order of magnitude of a few mean free paths of the electrons in the gaseous filling of the tube.

Thanks to this arrangement the desired effect is easily obtained by suitably selecting the work- 5 ing conditions of the tube, It sufiices, for example, when considering the minimum spacing between anodes, which is the optimum condition for the purpose desired, to take the inter-anode voltage as a variable and to determine by known means the other data, so that the reverse current is sufliciently small to prevent any appreciable absorption of thegaseous atmosphere and that its point along the curve which gives the efiective inter-anode voltage as a function of the reverse current is located on the straight portion of the said curve.

. The invention relates more especially to tubes having a positive luminous column and filled with rare gas or metallic vapor (with or without an auxiliary rare gas). It is however also capable of other applications, notably for the construction of tubes intended tor rectifying alternating current, particularly in the case of low output tubes.

The invention will be more clearly understood from the following description taken in conjunction with the accompanying drawing which shows a number of examples, In the drawing:

Fig. l is an elevational view of a self-rectifying single-phase lamp having anodes of the novel structure herein disclosed at one end thereof,

Fig. 2 is a sectional elevation of the anode end. of this lamp, I

Fig. 3 is a transverse section of the same lamp, taken on the line 3-3 of Fig. 2,

Fig. 4 is a sectional elevation of a modification of the lamp of Figs. 1-3, and

Fig. 5 is a graph showing the relation of the voltage impressed between the anodes to the current flow therebetween.

In this drawing, with particular reference to Figs. 1 to 3, the anodes 3, which are preferably of graphite, are of semi-cylindrical shape and are located at a distance a from the mass wall of the tube 1 which distance is sufflciently small to prevent the' ionization of the intermediate space. The distance 1) between the two half-cylinders is also very small, of the order of a few mean free Y paths of the electrons in the gaseous atmosphere.

of the tube. Further, in order'to prevent a discharge from occurring between the current leadas s which are the only ones which. are of substantial length, constitute no serious danger of faulty operation. The assembly is mounted on 0 the foot tube II. At the other end of the tube lthere is located a cathode I of any suitable construction, preferably of the activated thermionic type.

In the modification shown in Fig. 4 the two anodes l2 and i3 are concentrically arranged the one within the other, the radial distance d between them being of the order of a few mean free paths. The anode I 2 is provided :with a flange and it is the plane surface of this flange, facing the positive column of the discharge which, almost alone, is affected by the discharge. The radial space between the flange 'and'the wall of the tube being small, the existence of discharge paths such as t which pass around the anode I2 is avoided as is also the ionization of the space at the rear of the said flange.

The end of the anode l2 opposite the front end has an inwardly directed portion l6 which is screwed to a threaded piece I! electrically con-- nected to the current lead-in wire l9, while the anode I3 is screwed to a threaded part l4 which in turn is connected to the lead-in wire I5. A tube I8 made of. refractory material surmounts the cap 20 on the stem-press and extends slightly into a recess provided in the anode l3. The object of this tube is to fix the spacing between the upper plane surface of the portion it of the anode l2 and the adjacent extremity of the inner anode l3 so as to give it a value of the same order of magnitude as. d, and to prevent any discharge between the two lead-in wires. As a further precautionary measure this'refractory tube is preferably cemented to the cap 20 by means of a suitable cement. The assembly is mounted. on the foot tube 2|.

Figure shows the curve C giving the effective voltage '0 between the anodes as a function of the reverse current -i for a given tube. It will be-seen that the said curve comprises a straight portion along which must be taken the point P working conditions.

By wayof a practical example the following are the dimensions of a preferred embodiment of a mercury vapor tube having an auxiliary filling .of rare gases and constructed as shown in Fig. 4:

Internal diameter of tube ..mm 32 Length of tube L metre 1 Rectified current emitted by the cath0'de r amps 2.5 to 3 External diameter of flange of the external anode mm 30 Diameter of internal anode mm 1% Space between anodes mm 2.5

Using argon as auxiliary filling gas at a pressure of 0.4 mm. of mercury such a device can withstand an effective voltage of 400 between it is to be understood that the invention is not confined thereto, and that various changes, omis- 'at the other end thereof, said anod'es being mounted coaxially and one within the other, the smaller anode having an outer cylindrical surface and the larger anode having cylindrical inner and outer surfaces the outer cylindrical surface of the larger anode extending along the wall of the tube being for at least a portion of its length, measured from the front end of said anode facing the discharge} located at a distance from the said wall which is less than several times the mean free electron path in said at mosphere to allow the said larger anode to be affected by the discharge substantially only in the vicinity of its front extremity, and wherein the cylindrical surfaces of the anodes which are adjacent one another are separated by a distance which is at least equal to the minimum spacing which is practically attainable without risk of contact between anodes but is less than a distance of several mean free electron paths in said atmosphere at which a harmful reverse current is produced, the current lead-in wires to the anodes being shielded to avoid any discharge between the said wires.

2. An electric discharge tube containing a gaseous atmosphere and having a cathode at one end and atleast two anodes mounted adjacent each other in the interior of the discharge tube at the other end thereof, said anodes being mounted coaxially and one within the other, the smaller anode having an outer cylindrical surface and the larger anode having cylindrical inner and outer .surfaces, the outer cylindrical surface of the larger anode extending along the wall of the tube being for at least a portion of its length, measured from the front end of said anode facing the discharge, located at a. distance from the ,said wall which is less than several times the mean free electron path in said atmosphere to allow the said larger anode to be affected by the discharge substantially only in the vicinity of its front extremity, and wherein the cylindrical surfaces of the anodes which are adjacent one another are separated by a distance which is at least equal to the minimum spacing which is practically attainable without risk of contact between anodes but is less than a distance of several mean free electron paths in said atmosphere at which a. harmful reverse current is produced, said outer anode being provided with a flange at. its front 'end and a radially inwardly directed portion at its other end, the plane upper surface of the said inwardly directed portion being spaced from the adjacent end of the inner anode by dis- JEAN"

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