US3043981A - Discharge device - Google Patents

Description

y 1962 G. w. HARVEY ET AL 3,

DISCHARGE DEVICE Filed March 23, 1959 Sates The present invention relates to a vapor-arc discharge device which employs a pool-type cathode, and more particularly such a discharge device which includes a novel electrode for initiating the formation of an are.

In previously available vapor-arc discharge devices of the type which employ mercury pool-type cathodes, commonly known as Ignitrons, the ignitor electrode, which is utilized to initiate the arc in the ignitron, has generally been disposed directly between the anode and the pooltype cathode. Ordinarily, the ignitor electrode, which is composed of suitable material, has been supported by a bridge-type structure so that its tip dips below the surface of the mercury pool. Because of the presence of the ignitor structure in the path of the are, there is rapid deterioration of the ignitor structure during high current operation. Moreover, it has been found that when the ignitor structure is located between the mercury pool cathode and the anode, high potential gradients are formed which adversely afiect the forward breakdown voltage.

An object of the present invention is the provision of a vapor-arc discharge device having improved life and electrical characteristics. Another object of the invention is the provision of a vapor-arc discharge device which is adapted to be utilized in extremely high current and high voltage pulse applications. Still another object i the provision of a vapor-arc discharge device which is provided with an ignitor which is generally electrostatically shielded from the anode, and which is displaced from the arc path between the anode and cathode.

Further objects and advantages of the P esent invention will become apparent by reference to the following description and accompanying drawings.

In the drawings:

FIGURE 1 is a longitudinal sectional view of a vaporarc discharge device embodying various features of the present invention; and

FIGURE 2 is a transverse sectional view taken along line 2--2 of FIGURE 1.

Generally, the vapor-arc discharge device shown in the drawings comprises an elongated evacuated envelope having a mercury pool-type cathode 12 disposed in one end thereof and an anode 14 extending from the opposite end into the interior of the envelope, the anode 14 being spaced above the cathode 12. The discharge device is also provided with an ignitor electrode 16 which is disposed laterally of the anode 14 with its tip dipping into the surf-ace of the mercury pool 12 at a point spaced laterally of the anode 14. In this way the ignitor electrode 16 is completely displaced from the arc path between the anode 14- and the cathode 12. More specifically, applicants have now discovered that are damage to the ignitor electrode of a mercury pool-type arc discharge device is eliminated by displacing the ignitor electrode 16 from the arc path between the anode 14 and cathode 12. Moreover, applicants have found that the forward break down voltage in such a discharge device is improved by electrostatically shielding the ignitor electrode 16 from the anode 14.

More specifically, the anode 14, pooltype cathode 12 and ignitor electrode 16 of the discharge device are all disposed in a conventional manner within an evacuated envelope 10 which may be of any suitable shape and construction. In the illustrated embodiment, the envelope 10 includes a tubular outer casing 22 which is preferably made of metal such as stainless or cold-rolled steel. The lower end of the outer casing 22 is closed by a plate 24, also of metal, having a downwardly turned peripheral flange 26, the rim of which is sealed as by welding to the outer casing 22. The mercury pool-type cathode 12 of the discharge device is situated in the lower portion of the envelope 10, and since the metallic outer casing 22 makes contact with the mercury pool, electrical connection thereto may be obtained by contacting the metallic casing 22 with a metal strap (not shown) or the like.

Extending downwardly into the upper end of the outer casing is the anode 14, which in the illustrated embodiment includes a lower arcuate portion 28 composed of graphite or the like, attached to a vertically extending rod-like stud 30 of conductive material. The anode 14 is supported within and insulated from the outer casing 22 by an upper closure wall 32, the upper closure wall including a cup-shaped metallic cap 34 having an outwardly and downwardly extending rim, and having an aperture 38 disposed in the center thereof. A reduced diameter upper portion 36 of the stud 30 extends through the aperture 38 and the shoulder 39 formed on the stud 30 is suitably sealed to the cap 34. A sleeve 40' is disposed over the reduced portion, the upper end of the sleeve 40 being threaded so that electrical connection may be made to the anode 14.

The edge of the rim of the cap 34 is sealed to the top rim of an insulating sleeve 42 of a material such as glass, Mycalex, etc., and, in turn, the lower rim of the insulating sleeve is sealed to an inner upturned flange 44 of a ring 46. The ring 46 also is provided withan outer upturned flange 48 which is sealed to the upper end of the outer casing 22.

To prevent deterioration of the ignitor 16 due to arcing, the ignitor 16 is positioned within the envelope 10 so that it is displaced from the arc path between the cathode 12 and the anode 14. In the illustrated embodiment, the tip of ignitor electrode 16 dips into the surface of the pool-type cathode 12 laterally of the anode 14 and extends upwardly and outwardly at an angle from its tip, The ignitor 16, which is partially made of a high resistance material such as silicon carbide, boron carbide, etc., includes an elongated body 52 which is reduced in diameter intermediate its ends for passage through the wall of the envelope 10. Electrical connection to the ignitor 16 may be made at its upper end.

In order to prevent the ignitor 16 from adversely affecting the electrostatic field existing between the anode 14 and the cathode 12 when a voltage is applied therebetween, the ignitor 16 is substantially electrostatically shielded from the anode 14. However, so that the are initiated by the ignitor 16 is transferred to the anode without delay, the tip of the ignitor electrode 16 is not electrostatically shielded. In the illustrated embodiment, the ignitor 16 is insulatingly supported within a metallic tubular member 58 which extends upwardlyv in coaxial relationship with the ignitor from an aperture 60 in the side of the casing 22, the aperture 60 being disposed partially above the surface of the cathode 12. The tip of the ignitor 16 is immersed in the cathode 12 at a position approximately even with the aperture 60. As illustrated, the end of the tubular member 58 is closed by a closure Wall 62 which includes an upwardly extending tubular portion 64. The reduced diameter intermediate portion of the ignitor 16 is sealed to the tubular portion 64 by a glass body 66, By the above described construction the metal tubular member 58 and the metal outer casing 22 act as an electrostatic shield between the ignitor 16 and the anode 14, thereby preventing the ignitor 16 from affecting the electrostatic field between the anode 14 and the cathode 12.

After the envelope is assembled, sulficient mercury is added to immerse the tip of the ignitor 16, and then the envelope is evacuated through a tubular member 68 which extends through the lower plate 24. The lower end of the tubular member 68 is sealed, as shown in FIG- URE 1, after the envelope 10 is evacuated. When it is desired to set the discharge device in operation, va high voltage source (not shown) i connected between the anode 14 and the cathode 12, and a second source of voltage (not shown) is connected between the ignitor 16 and the cathode 12. When a suitable positive voltage is applied to the ignitor 16, a cathode spot is generally formed in the mercury pool adjacent the location of the tip of the ignitor 16, and if a suitable positive voltage is applied to the anode 14, the discharge device will conduct a current.

a From the above it can be seen that a mercury pool vapor-arc discharge device is provided in which an electrostatically shielded ignitor is located so that it is displaced from the arc path between the anode and the cathode. Such a vapor-arc discharge device has an extended life since arcing between the anode and ignitor is eliminated. Moreover, the forward breakdown voltage in such a device is increased and tends to remain constant from discharge to discharge.

Various changes and modifications may be made in the above described discharge device without departing from the spirit and scope of the present invention, Various of the features of the invention are set forth in the following claims.

We claim:

. 1. A vapor-arc-discharge device comprising an elongated vertically disposed tubular casing, said casing having closure walls at both ends, a mercury pool-type cathode disposed in the lower portion of said casing, an anode extending through the upper closure wall and spaced above said cathode, said casing having an aperture disposed partially above the surface of the mercury pool, a tubular member extending upwardly and outwardly at ,4 an angle from the aperture and having a closure cap at its upper end, an electrode extending through said cap and having its inner end dipped into the surface of the mercury pool at said aperture, said casing and saidtubular members being composed of metal intermediate the upper portion of the electrode and the anode and being at the same potential as said cathode, the aperture extending a distance above the cathode surface such that the upper portion of the electrode is electrostatically shielded from the anode and an electrostatic field extends between the anode and said electrode at said inner end when voltage is applied to said anode.

2. A vapor-arc discharge device which comprises an evacuated envelope, a mercury pool type cathode disposed in the lower end portion of said envelope, an anode disposed in said envelope and spaced above said cathode, an ignitor electrode mounted laterally of said anode so that the tip thereof is below the surface of said mercury pool type cathode at a point spaced laterally from the normal arc path between said anode and said cathode, and an electrostatic shield disposed between said ignitor electrode and said anode to minimize distortion of the electrostatic field that exists between said anode and said cathode during operation of the discharge device, said electrostatic shield being spaced from the surface of said pool type cathode at a distance such that an electrostatic field is established directly between said anode and the tip of said ignitor electrode, whereby an arc initiatedby said ignitor electrode during operation of the discharge device is transferred directly to said anode without delay.

References Cited in the file of this patent UNITED STATES PATENTS 1,901,612 Schenkel Mar. 14, 1933 2,254,722 Aoki Sept. 2, 1941 2,595,716 Smith May 6, 1952 2,673,308 Herring Mar. 23, 1954

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