US2087748A - Electric gaseous discharge device - Google Patents

Description

July 20, 1937. c, BQL 2,087,748

ELECTRIC GASEOUS DISCHARGE DEVICE Filed May 51, 1935 ATTORNEY Patented July 20, 1937 UNITED STATES ELECTRIC GASEOUS DISCHARGE DEVICE Cornelis Bol, Eindhovcn, Netherlands, assignor to General Electric Company, a corporation of New York Application May 31, 1935, Serial No. 24,449 In Germany June 4, 1934 4 Claims.

The present invention relates to electric gaseous discharge devices and in particular to electrodes therefor.

A particular object of the invention is to provide a gaseous discharge device with an improved cathode. A further object of the invention is to provide an electrode assembly which can be readily degassed and activated. Another object of the invention is to provide a structure which will maintain an arc discharge at a central point on the cathode. Another object of the invention is to provide a structure which will facilitate the initiation of a discharge in a' gaseous discharge device. Still other objects and advantages of the invention will appear from the following detailed specification or from an inspection of the accompanying drawing.

The invention consists in the new and novel structure hereinafter set forth and claimed.

In the manufacture of electric gaseous discharge devices it is frequently desirable to utilize a single inlead for each electrode in order to simplify the seal structure. This structure introduces a complication in many cases, however, in that it makes it impossible during manufacture to pass a current through the electrodes by conduction to raise them to the high temperature necessary to degas them and to reduce and activate the thermionic material with which they are usually coated. The general practice has therefore been to heat these electrodes by the currents induced therein by a high frequency field. This method of heating the electrodes is attended with special difiiculties, however. utilize this method in an efficient and economical manner it is necessary that the electrode structure should provide a closed circuit in a plane which is substantially perpendicular to the axis of the tube forming the discharge device, so that it will be possible to obtain good fiux linkage with a high frequency coil which is placed around the tube. Furthermore, in order to induce currents of sufficient intensitythe electrode must be designed in such a way that this closed circuit encloses the maximum possible number of lines of force; in other words, it must be of virtually the same shape and dimensions as the cross section of the tube within which it is enclosed. This, however, results in the disadvantage that the electrode is extremely close to the wall of the tube,

with the danger that the discharge to said electrode will damage the wall of the tube. This hazard is especially marked in discharge devices, such as the high intensity mercury are, where the discharge is extremely constricted and has a high current density and temperature.

I have now discovered that this difiiculty is overcome by providing these devices with an electrode of novel configuration. According to my invention this electrode is made of wire, a

Thus in order to.

portion of which is bent into a loop which has a large diameter, while the remainder thereof projects considerably further into the discharge path, and consists of a loop or a series of smaller turns or the like, the ends of said wire being connected together to form a continuous closed electrical path through said electrode. The loop of large diameter provides an exceptionally effective linkage which is augmented, of course, by the linkage of the other coils of smaller diameter, so that the inductive heating of this novel electrode is extremely efilcient. This large loop does not offer any hazard to the envelope wall, however, due to the fact that the discharge always takes place to the portion of the electrode which projects further toward the other electrode. Since this portion is of smaller diameter the discharge is maintained substantially at the axis of the tubular envelope. This latter result is also enhanced by forming the projecting portion of the electrode more or less into a point, as by bending the wire back on itself and then passing it down through the coils to the point of beginning of the loop. In addition to thus centering the discharge this somewhat pointed structure has also been found to reduce the potential necessary to initiate a discharge in the device.

In order to enclose the largest possible number of lines of force with the smallest possible length of winding the loop portion of the electrode is ordinarily made circular, but under certain conditions this shape is modified. Thus it is well known that in metal vapor are devices of the high intensity type it is necessary to place the electrodes close to the ends of the tube to prevent the condensation of the vapor at these points. Hence where these electrodes are used in a device which is closed by a pinch seal, the loop on my novel electrode is preferably somewhat elongated so as to better conform with the shape of the tube adjacent to the seal, and thus permit the mounting thereof closer to the seal.

For the purpose of illustrating my invention I have shown a preferred embodiment thereof in the accompanying drawing, in which Fig. 1 is an elevational view of a high intensity mercury vapor arc lamp employing a pair of my novel cathodes, and

Fig. 2 is an elevational View of the same device taken at right angles to Fig. 1.

As shown in this drawing my novel lamp has a tubular envelope l of hard glass or other suitable material. Near the ends of said envelope a pair of electrodes 2 and 3 are arranged. Each of these electrodes consists of a helical coil with three turns 4 of small diameter and a fourth turn or loop 5 of much larger diameter, the turns of larger diameter being adjacent the respective ends of the envelope l. The axis of these coils approximately coincides with the .previously been given a helical shape is helically wound. These coils are preferably coated with a substance of high electron emissivity, such as an alkaline earth oxide. The turn 5 of these coils is but slightly smaller diameter than the tube I, so that the largest possible! numberof lines of force are enclosed by this turn when a high frequency coil is placed about the tube I during manufacture of the lamp. The discharge never centers upon this turn, however, due to the fact that it is more removed from the discharge path than the turns 4, the discharge always centering upon the latter and thus being maintained in an axial position within the tube I.

The tube i is provided with an external pinch seal 6 at one end thereof, with the result that the tube section adjacent to this 'end is somewhat elongated rather than circular. In order to arrange the electrode 2 close to this end of the tube the turn 5 of thiselectrode is made with a similar shape. Thus the width of this turn as shown in Fig. 2 is less than that shown in Fig. l.

The electrodes 2 and 3 are fastened to supporting wires 1 which are sealed in through the pinch 6. Within the envelope I these wires are each surrounded by insulating tubes 8 of glass or any other suitable material. In the vicinity of the electrode 2 there is an auxiliary electrode 9 consisting of a thin tungsten wire. This auxiliary electrode is adapted to be connected to the inlead to the electrode 3 through a high impedance in a well known manner.

The envelope i contains a suitable gaseous atmosphere. Thus in a high intensity mercury vapor arc lamp this envelope is filled with a rare gas, such as argon or neon, at a pressure of a few millimeters, plus enough mercury to develop the desired pressure of the order of an atmosphere or more. The amount of mercury is preferably so limited, however, that it is entirely evaporated before the lamp reaches thermal equilibrium when it is operated with normal rated wattage, so that the arc discharge occurs in unsaturated mercury vapor. When a discharge is formed in a device having these characteristics the arc is extremely constricted, due to the high pressure. In addition to being a highly eflicient source of light this are is also an exceptionally good source of ultra-violet radiation which can be utilized by making the envelope l of a material, such as quartz, which is transparent to these radiations.

When the tube is placed in] operation an auxiliary discharge is formed between the main electrode 2 and the auxiliary electrode 9, by means of which the electrode is heated, while at the same time ions and electrons are produced in the main discharge path, whereby the initiation of the main discharge between the electrodes 2 and 3 is greatly facilitated. The main electrodes are then heated by the discharge current to a thermionic emitting condition.

Although the electrodes of the lamp illustrated in the drawing have three turns ofsmall diameter, this is not essential, one or moresuch turns being employed, as desired. Likewise more than one loop or turn of larger diameter may also be used if desired. The smaller turns furthermore may also be given the shape of a conical coil instead 01' being helical. Various other changes, omissions and substitutions, within the scope of the appended claims, may likewise be made in the structure illustrated without departing from the spirit of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:-

1. An electric gaseous discharge device comprising a sealed envelope containing a gaseous atmosphere and having electrodes sealed therein, at least one of said electrodes having a single inlead and consisting of a plurality of turns forming a continuous closed circuit within said envelope, the turn more remote from the discharge path in said device being larger than the turn nearest to said path, the latter turn projecting a considerable distance beyond the nearest large turn in order to attract the discharge thereto.

2. An electric gaseous discharge'device comprising a sealed envelope containing a gaseous atmosphere and having electrodes sealed therein, at least one of said electrodes having a single inlead and consisting of a series of turns which are coaxial with said envelope with a connection between the ends of said turns which passes through said turns and completes an' electrical circuit therethrough within said envelope, said turns being of different diameters, the turn more remote from the discharge path being much larger than the one nearest to said path, the latter turn projecting a considerable distance beyond the nearest large turn in order to attract the discharge thereto.

3. An electric gaseous discharge device comprising a sealed envelope containing a gaseous atmosphere and having electrodes sealed therein through an external pinch seal, the electrode adjacent to said seal having a single inlead and consisting of a plurality of turns forming a continuous closed circuit within said envelope, said turns being of diflerent diameters, the turn more remote from the discharge path being much larger than the one nearest to said path and having a somewhat elongated shape to conform to the shape of said envelope at the pinch, whereby it may be mounted close to the end of said envelope, the turn nearest said discharge path projecting a considerable distance beyond the nearest large turn in order to attract the discharge thereto.

4. An electric gaseous discharge device comprising a sealed envelope containing a gaseous atmosphere and having electrodes sealed therein, at least one of said electrodes having a single inlead and consisting in part of a loop which is coaxial with said envelope, said loop being considerably larger in diameter than the remainder of said electrode which extends axially farther into the discharge space and presents a small pointed surface which attracts the discharge to the end thereof, said electrode having an activated surface supported by a continuous core which is short circuited on itseii'within said envelope.

.CORNELIS 30L.

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