US2078123A

US2078123A - Electric discharge device

Info

Publication number: US2078123A
Application number: US34919A
Authority: US
Inventors: John M Cage
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1935-08-06
Filing date: 1935-08-06
Publication date: 1937-04-20
Anticipated expiration: 1954-04-20
Also published as: DE716403C

Description

nventor John VI. Ceze, l)

His

45 with particularity in the appended claims.

Patented Apr. `20, 193'? UNITED sr TES PATENT CFFICE ELECTRIC DISCHARGE DEVICE New York Application August e, 1935, sei-iai No. 34,919

3 Claims.

My invention relates to arc discharge tubes of the type having one electrode thereof in the form of a pool of readily vaporizable material. More particularly, my invention relates to an improved lead-in connection for such a tube and to means for protecting the same from the destructive effects of the arc discharge.

rIn tubes of the type to which my invention especially pertains, the enclosing envelope typi- 10 cally comprises a relatively large glass cylinder closed at its ends by conducting metal plates fused directly thereto. While the technique of making glass to metal seals by the use of properly matched materials is now Well understood, it is l5 Still considered desirable for mechanical reasons to avoid passing metallic conductors through glass wall areas. For this reason, where it is necessary to use auxiliary electrode connections in tubes 0f the nature under consideration, it is generally preferable to introduce them into the interior of the envelope by passing them through the metallic end caps, suitable insulating provisions being made.

In adapting such an envelope assembly to the requirements of pool type tubes, I have found it expedient to make the auxiliary electrode lead-in connections at the cathode end of the tube rather than through the anode cap. With this arrangement, however, it is necessary for the connecting 50 structure to pass through the body of the pool,

projecting above its surface and consequently subject to the deteriorating effects of the arcspot.

It is an object of my present invention to provide shielding means associated with that portion of the auxiliary electrode lead-in connection which extends above the pool for protecting the same from the destructive effects of the arc discharge. For the attainment of this purpose, I

40 provide an enclosing sleeve, of a nature described more fully hereinafter, for shielding the vulnerable portion from the moving cathode spot.

The novel features which I consider to be characteristic of my invention will be pointed out My invention itself, however, may best be understood by reference to the following specification taken in connection with the accompanying drawing, in which Fig. 1 represents a side elevation partly 50 in section of a discharge tube embodying my invention, While Fig. 2 is a sectional view taken on line 2-2 of Fig. 1.

Referring more particularly to the structure illustrated in Fig. 1, I have shown an enclosing envelope comprising a cylinder I of glass, or

other suitable insulating material. The cylinder is closed at the top and bottom by metallic caps or headers and 3, which take the form of disklike members having r-eentrant portions extending toward the interior of the envelope. The material of which the headers are made is of such nature as to be capable of being fused directly to the glass Wall. Such a material is described, for example, in an article by Dr. A. W. Hull and Mr. E. E. Burger appearing in Physics, Vol. 5, No. l2, pages 38e-Lili, inclusive. As there explained, an alloy suitable for fusion with standard hard glass (Corning CTI/l) may be formed by the combination of 5e per cent Fe, 28 per cent Ni and 18 percent Co.

rEhe header E in the embodiment which I have illustrated is adapted to serve as the positive electrode or anode of the discharge device. A current connection may be made thereto by a heavy copper lug 5 which is welded or otherwise secured to the upper header surface, and is slotted to engage with a supporting terminal (not shown). A similar element, designated by the numeral 5', is associated With the header 3.

The cathode comprises a pool of mercury i collected in the base of the cylinder i and of such quantity as to immerse completely the inner surface of the header 3. It will further be noted that the tube illustrated is of the controlled discharge type in which the initiation of an arc is governed by an auxiliary electrode t of semiconducting material having its tip projecting loelow the surface of the mercury. When a potential is applied between starting electrode G and the mercury pool, an ionizing action will take place at their surface of contact of such nature as to tend to produce a main discharge to the anode header i2, assuming that electrode to be at the time positively charged with respect to the cathode ifi. The nature and operation of such a controlling electrode is described in an article by J. Slepian appearing in the Transactions of the A. I. E. E. for 1933, Vol. 52, page 693. Since its exact character is not essential to an understanding of my invention, further explanation at this point will not be attempted.

For supporting the immersion electrode, I may employ a mounting tube "l, swaged or otherwise conductively secured to the electrode body and suspended by a rigid lead-in conductor 9. manufacture of tubes such as that illustrated I have found it most practical to conduct the leadin connection for the auxiliary electrode i5 upwardly through the surface of the metal header 3 in the manner shown. This construction ob- In the viates the necessity of having sharply projecting metal elements in the vicinity of the anode structure where they might occasion back-fire occurrences and requires no additional seal to be made to the large glass area comprising the cylinder I. Furthermore, with an assembly of the type illustrated, great mechanical rigidity and convenience of assembly can be realized.

In the construction of the seal, the flanged thimble 8 is welded in gas-tight relation with the inner surface of the metal header 3, the two parts being made of similar material. A vacuum-tight conductor seal is then produced by passing the conductor 9 through the thimble 8 and fusing the same in place with an appropriately formed glass closure I I capable f wetting both the metal parts when subjected to heat.

In spite of mechanical advantages inherent in the lead-in construction just described, it is subject to the diiculty that the thimble 8 tends to become eroded and to deteriorate rapidly in the presence of an arc discharge, The cathode spot, which moves swiftly over the surface of the mercury pool, may from time to time become anchored on the projecting metal with destructive effects. In order to overcome this difficulty, my invention provides an enclosing sleeve l2 which surrounds the lead-in connection at the mercury surface and shields it from the cathode spot. As

` Will appear more clearly in Fig. 2, this sleeve laterally encloses the exposed portion of the thimble 8 and tends to prevent the cathode spot from moving into contact with it.

While my invention contemplates that the shielding member l2 may be of any material highly resistant to the destructive eifects of a mercury arc discharge, I prefer to form it of a conducting arc-resisting metal such as molybdenum or tungsten. These metals, which are of the class capable of being wet by mercury, may in the application described serve the additionally useful ypurpose of anchoring the cathode spot. This is of considerable advantage in the rectification of alternating currents Where it is desired to have f the tube conductive for as great a proportion of the voltage cycle as possible. It is known, for example, that in mercury vapor devices in which the cathode spot is fixed to some stationary anchor, the minimum current required to maintain an arc is reduced substantially below that required when the spot is moving rapidly about the mercury surface. Consequently, the arc tenacity is increased and the arc itself made to endure almost to the zero point of the voltage Wave,

It has been found that tubes constructed in accordance with the principles of my invention are capable of being used for very long periods of time with no appreciable deterioration of the leadin connections. In the use of the structure disclosed, it is unnecessary to take precautions to exclude all mercury from the interior of the sleeve i2. Even after a substantial quantity of mercury has been admitted, the cathode spot is still found to be confined to the outlying mercury surface by the action of the shielding means.

While I have shown a particular embodiment of my invention, it will of course be understood that I do not wish to be limited thereto, since many modications in the structure may be made, and I contemplate by the appended claims to cover all such modifications as fall within the true spirit and scope of my invention.

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

l. In an electric discharge device, an evacuated envelope enclosing an anode, an apertured metal header forming a portion of the wall of said envelope, a pool-type cathode comprising a quantity of mercury covering at least a portion of the surface of said header, a thimble of a metal suitabie for sealing to glass surrounding an aperture in said header and comprising a portion extending upwardly through the surface of the mercury, said metal being subject to deterioration when exposed to an arc discharge, an electrode lead-in conductor suported axially of said thimble and insulated therefrom by a sealing body having the characteristics cf glass, and a sleeve surrounding said thimble, said sleeve being of metal of the group consisting of tungsten and molybdenum.

2. In an electric discharge device, an elongated envelope, an anode mounted in said envelope, an apertured metal header closing one end of said envelope, a cathode comprising a quantity of mercury covering at least a portion of the surface of said header, a starting electrode in contact with said mercury, a mounting structure for said starting electrode having a metal portion thereof projecting through the surface of said mercury adjacent the center thereof and a shield surrounding said mounting structure, said shield comprising an arc-resisting material capable of being wet by mercury thereby to cause anchoring of the cathode spot thereon during operation of said discharge device.

3. In an electric discharge device, an elongated envelope, an anode mounted in the envelope, a metal header closing one end of the envelope, a cathode comprising a quantity of mercury covering at least a portion of the surface of said header, a starting electrode arranged above the cathode and having a depending portion in contact with the mercury, means for mounting said electrode on said header, said means comprising a supporting member projecting through the surface of the mercury, and a shield surrounding said member at the mercury surface, said shield being constituted of a metal of the group consisting of tungsten and molybdenum.

JOHN M. CAGE.