US2919367A

US2919367A - Arc discharge device

Info

Publication number: US2919367A
Application number: US616865A
Authority: US
Inventors: Karl G Hernqvist
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1956-10-18
Filing date: 1956-10-18
Publication date: 1959-12-29
Anticipated expiration: 1976-12-29

Description

Dec. 29, 1959 K. G. HERNQVIST ARC DISCHARGE DEVICE 2 SheetsSheet 1 Filed Oct. 18. 1956 ARC DISCHARGE DEVICE Karl G. Hernqvist, Princeton, N.J., assignor to Radio Corporation of America, a corporation of Delaware Application October 18, 1956, Serial No. 616,865

14 Claims. (Cl. 313-171) This invention relates to are discharge devices of the type utilizing starter electrodes.

It is known that an arc discharge, once it is established, will conduct very high currents at comparatively low voltages. For example, an arc discharge between two electrodes. in an ionizable gas will have a conductivity approaching that of a copper conductor. For this reason, are discharge devices have been used as switches in high power circuits where their ability to control high currents is a prerequisite.

The problem of establishing an arc discharge in such a device is not a simple one since a very high electric field between two electrodes is required. However, this problem has been overcome by the use of three electrodes, two of which act as main electrodes between which the primary discharge occurs and the third which serves as a starter electrode and which co-operates with one of the main electrodes to establish the arc discharge. In operation a comparatively low operating voltage is applied between the main electrodes while a relatively high voltage pulse is applied to the starting electrode to initiate the arc discharge. The initialed discharge is then taken up between the main electrodes.

Starter electrodes may be divided into two general categories, namely the spark gap category and the contact category. The simplest form of spark gap starter comprises a conductor close spaced from the cathode to which a high voltage is applied to produce a spark similar to that of a spark plug. This type of starter has the inherent disadvantages of having a short life due to deformation or destruction by repeated use, of having erratic starting characteristics due to such deformation, and a dependence on the surface condition of the cathode with respect to time of occurrence of the arc. The simplest form of contact starter comprises a conductor in contact with the cathode. This type of starter has the inherent disadvantages of requiring large amounts of power and of having a short life due to the repeated heating and cooling thereof during operation.

Complex combinations of the two above types of starters are known and include, e.g., the dip starter and the resistive or semi-conductive starter. However, these too, according to prior art design have not provided a satisfactory answer to the basic attendant problems discussed above.

It is therefore an object of this invention to provide a novel and improved starting electrode for an are discharge device.

It is another object of this invention to provide a starter electrode for an arc discharge adapted for long life.

It is a further object of this invention to provide an arc discharge device having a starting arrangement characterized by low power consumption.

It is a still further object of this invention to provide an arc discharge device having a starting arrangement characterized by the regular and highly predictable formation of an arc discharge.

Sttes Patent O It is yet another object of this invention to provide an improved arc discharge device.

Briefly, an arc discharge device according to this invention comprises a gas tight envelope containing an ionizable medium, an anode, a pool type cathode and a starting electrode, such starting electrode comprising a reservoir having an aperture adapted to hold a quantity of liquid metal in accurate close spaced relation to the cathode.

This invention will be better understood when the following detailed description is read in conjunction with the appended two sheets of drawings, wherein:

Figure 1 is a cross-sectional view of an arc discharge device according to one embodiment of this invention;

Figure 2 is an enlarged fragmentary view in crosssection of the starting arrangement shown in Figure 1;

Figure 3 is a cross-sectional view of a starting electrode according to another embodiment of this invention;

Figure 4 is a cross-sectional view taken along lines 4-4 of Figure 5; I

Figure 5 is a cross-sectional view of an arc discharge device according to another embodiment of this invention and;

Figure 6 is a view partially in cross section of the starting arrangement shown in Figure 5.

Referring to Figure 1 of the drawing, an arc discharge device 10 may comprise an evacuated glass envelope 12 containing an anode 14 and cathode 16. The anode 14 may comprise a carbon cylinder, for example, and may be mounted on the end of a heavy lead-in conductor 1d sealed through the envelope 12. The cathode 16 may comprise a pool of mercury which is located in the opposite end of the envelope 12 from the anode 14 when the device it} is in operating position. A heavy cathode lead-in conductor 21) is sealed through the envelope 1 2 and extends into the mercury pool cathode 16 to provide electrical connection thereto. 1

According to the embodiment of the invention shown in Figure 1, a starting or igniting arrangement is provided which includes a starting electrode or starter 22 comprising a member having a funnel-like cavity 24 therein, the restricted aperture 26 of which is in close spaced relation (e.g. 8 mils) to the cathode pool 16, and a spot anchoring electrode 28 electrically mounted on the cathode lead-in 2t) and comprising a sharp pointed portion 30 projecting slightly above the surface of the cathode pool 16 in alignment with the restricted aperture 25 of the cavity 24 in the starter 22.

The starter is made of glass and the funnel-like cavity 24 of the starter is filled with mercury 32. The restricted aperture 26 of the cavity is dimensioned such that a given head of mercury will be supported in the starter 22 without flow of mercury through the aperture. A lead-in 34 is sealed through the envelope 12 adjacent the starter 22 and the end of the lead-in 34 projects into the mercury 32 contained in the starter 22 to provide an electrical connection thereto.

In operation, a high voltage pulse (e.g. 10 to 20 kv. for an 8 mil gap) from a source 36 is applied between the cathode pool16 and the mercury 32 in the cavity 24 of the starter 22 through lead-

ins

20 and 34. The high voltage pulse will produce a very strong electric field between the starter 22 and the cathode pool'16 which will be highly concentrated between the sharp pointed portion30 of the spot anchoring electrode 28 and the mercury in the restricted aperture 26 of the funnel-like cavity 24. The concentrated electric field will produce a spark discharge between the starter 22 and the cathode pool 16. Assuming that an operating voltage from asource 38 has been applied between the anode 14 and the cathode pool I 16 through

leaddns

18 and 20 such that the .anode 14,.is

positive with respect to the cathode 16,. the spark between the starter 22 and the cathode 16 will expand into an arc discharge between the anode 14 and the cathode 16. The are or main discharge between the cathode 16 and anode 14 will continue until the operating voltage is removed from between the cathode and anode.

During operation, a quantity of mercury will be vaporized from the pool cathode 16 and the starter 22 due to the heating thereof by ion and electron bombardment, respectively. The mercury vapor rises upwardly in the device coming into contact with the upper portion of the envelope wall where it is cooled and condenses on the envelope wall. The condensed mercury flows downwardly due to the force of gravity.

In order to replace the mercury evaporated from the starter 22 during operating a glass channel or upwardly concave ledge 40 is provided about the inner periphery of the envelope wall extending spirally and terminating in the cavity 24 of the starter 22. Thus, mercury vaporized from either the starter 22 or the cathode pool 16, and which condenses on the upper portions of the envelope wall, will flow downwardly into such channel or ledge 40 where it will be collected and caused to flow into the funnel-like cavity 24 of the starter 22.

Asstated above, the restricted aperture 26 of the cavity 24 is dimensioned such that a given head of mercury will be supported therein due to the surface tension of the mercury, such that flow of mercury through the aperture does not occur. As the term flow is herein used, the passage of replacement mercury through the starter aperture which occurs due to the vaporization hereinbefore described is not considered a flow, since in the absence of vaporization no passage of mercury would exist. The relationship between the height of the head of mercury which may be so supported and the radius of a circular aperture 26 is expressed by the following equation:

2X gR Y- where:

h=head of mercury in centimeters R=radius of the aperture 26 in centimeters X=surface tension of mercury in dynes per centimeter g=gravitational constant in centimeters per second squared (981), and

Y=specific weight of mercury in grams per cubic centimeter (13.596).

A similar equation for determining the height of head which will be supported by any given aperture which is not circular can be established but it would be considerably more involved and will not be attempted here. However, it is pointed out that this invention contemplates the use of any shape aperture which will support a usable head of mercury. In order for the above relationship to hold true it is necessary that at least the outer surfaces of the starter 22 adjacent the aperture 26 be made of a material which is not wet by mercury since if such outer surface is wet by mercury the effect will be that of en larging the aperture and mercury will drip from such effectively enlarged aperture at a very low head. Thus, in the embodiment of this invention shown in Figure 1, the starter 22 is fabricated of glass which is not wet by mercury.

It will be seen from the above equation and discussion that the height of head of the mercury 32 in a starter according to this embodiment of the invention must approach the ultimate head that a given size aperture 26 will support since as the head decreases the mercury will tend to recede upwardly in the divergent cavity 24 from the aperture 26, seeking an etfective aperture corresponding to such decreasing head. However, the height of the head of mercury 32 in the starter 22 also must not exceed the ultimate head that a "given aperture 26 i will support. For this ill) reason, an outlet 42 is provided near the top of the starter 22 at a height, above the aperture 26, equal to that of the head corresponding to the size of the aperture 26. The outlet 42 communicates with the cavity 24 and drains off any excess mercury which may be collected by the channel 40 during heavy operation of the device. The outlet 42 prevents the excess mercury from filling the cavity 24 and causing the discharge of mercury from the aperture 26 in the form of large drops when the head corresponding to the aperture size is exceeded. Such large drops might short the starter to the cathode 16 during a starting pulse, and would at least change the gap space between the starter 22 and the cathode 16. The opening of the outlet 42 should be made small enough so that the excess mercury will be discharged therefrom in the form of large drops since if a steady stream of mercury were discharged from such outlet 42 the starter 22 would be shorted to the cathode 16.

As is best shown in Figure 2, the aperture 26 of the starter 22 is accurately aligned and spaced from the sharp pointed portion 30 of the spot anchoring electrode. The sharp pointed portion 30 of the spot anchoring electrode 28 projects slightly above the surface of the mercury pool cathode and is made of a material which is readily wet by mercury. For example, the sharp pointed portion 30 may be made of nickel treated to remove oxides and may project a tenth of an inch above the surface of the cathode 16. Due to the wetting action, a thin film 44 of mercury will extend over the entire projecting surface of the portion 30 including its ultimate point.

The operation of the starting arrangement according to this invention is believed to be as follows:

(1) The application of the starting pulse between the starter 22 and the cathode 16 produces an electric field which is highly concentrated at the point of the pointed portion 30 of the spot anchoring electrode 28;

(2) The concentrated field causes the emission of electrons from the mercury at the point of the pointed portion 30;

(3) The electrons are drawn to the starter 22 where they bombard and heat the mercury in the aperture 26;

(4) The heating of the mercury in the aperture 26 causes vaporization which increases the mercury vapor pressure between the aperture 26 and pointed portion 30;

(5) Subsequent electrons from the pointed portion 30 tend to ionize the vapor as they proceed to the starter 22;

(6) The ions produced are drawn to the pointed portion 30 where they increase the cfiective field, and thus the electron'emission, due to their positive charge;

(7) The increased electron emission further increases the vapor pressure and ionization which, again, increases the electron emission, establishing an avalanche effect.

Thus, it is seen that the starting arrangement according to this invention provides an efficient and rapid start ing action. Furthermore, the spacing between the starter 22 and the cathode 16 will remain constant, since the mercury in the aperture 26- and on the pointed portion 30 is constantly replaced and since the wetted, pointed portion 30 of the spot anchoring electrode 28 projects far enough above the surface of the cathode 16 to reduce the possibility of a change in spacing between the starter 22 and such portion 30 due to ripples or waves in such surface.

A starting arrangement according to this invention enables very accurate and reliable control of an are dis charge device with very low starting power consumption. In applications such as in high power radar systems where it is desired to pulse large amounts of current at high repetition rates the accuracy and reliability of starting is essential. With the improvements hereinafter described, repetition rates as high as 4,000 pulses per second have been obtained with accuracy and-stability. This upper limit has been imposed by the starting circuit and not by the arc discharge device. It is believed that, by redesigning the starting circuit, repetition rates as high as 30,000 pulses per second can be optained with the accuracy and stability necessary for radar applications, for example.

Referring to Figure 3, another embodiment of a starter according to this invention is shown. According to this embodiment the starter 46 is made of a metallic material that is readily wet by mercury (e.g. nickel, treated to remove oxides). Since the starter 46 is made of metal, it may be supported on the end of a lead-in conductor 48 as by means of a metallic band 50. Thus, both electrical connection to and support for the starter 46 are provided by the lead-in conductor 48. According to this embodiment of the invention, the channel or ledge terminates in a lip 52 which projects over the cavity 54 of the starter 46 rather than forming a part of the support for the starter.

The cavity 54 in the starter 46 according to this embodiment of the invention comprises three major portions, namely, the reservior 56, the damping passageway 58 and the aperture 60. Since the starter 46 is made of a material that is readily wet by mercury, a coating 62 of glass frit or some other material that is not wet by mercury is provided over the outer surface of the starter 46 adjacent the aperture 60. The coating 62 is necessary, as pointed out hereinabove, to prevent mercury from leaking or flowing through the aperture due to the Wetting of such outer surface.

A starter according to this embodiment of the invention has the advantage of being relatively insensitive to changes in the head of the mercury 64 contained in the cavity 54 of the starter 46. This is due to the fact that since the starter 46 is made of a material that is wet by mercury, the mercury 64 in the starter will always flow down the damping passageway 58 to the aperture 60 regardless of the height of such head. The mercury will flow down such passageway 58 even if the size of the passageway is the same as, or smaller than that of the aperture 60. The function of the damping passageway 58 is to provide a fixed head which is an appreciable portion of the total head of mercury in the starter 46 thus making certain that the mercury present at the aperture 60 will protrude slightly therefrom even when the reservoir is almost empty. Thus, it is seen that the spacing between the mercury in the aperture 60 and the point of the spot anchoring electrode will remain substantially constant regardless of the height of head of the mercury in the reservoir.

Referring to Figures 46, yet another embodiment of this invention is shown. According to this embodiment of the invention the starting arrangement is mounted as a unit to enable better control of the spacing between the aperture of the starter and the spot anchoring electrode. As is best shown in Figure 6, the starter 66 and the spot anchoring electrode 68 are mounted on opposite ends of an insulating cylinder 70. The spot anchoring electrode 68 comprises a screw like member having a sharp pointed head 72 and a threaded shaft 74 and is made of a material which is readily wet by mercury. The threaded shaft 74 is screwed into a tapped hole in a mounting plate or strip 76 which extends at a right angle to the axis of the insulating cylinder 70 and which is fixed to one end of the insulating cylinder 70 by means of a screw 78.

The starter 66 is mounted on an electrically conductive plate or strip 80 having a double bend therein to provide

end portions

82 and 83 which extend at right angles to the axis of the insulating cylinder 70 and a middle portion 84 which extends along the side of the cylinder 70. One end portion 82 of the strip 80 is fixed to the other end of the cylinder 70 from the spot anchoring electrode 68 by means of a screw 86. The opposite end portion 83 of the strip 80 is provided with a hole 88 through which a portion of the starter 66 projects, a surface of the starter 66 being electrically and mechani- 6 cally connected to the upper surface of such end portion 83 of the strip 80. Thus, the gap or spacing between the statrer 66 and the spot anchoring electrode 68 will be determined by the length of the middle portion 84 of the strip 80.

It will be seen from the above, that the starting arrangement may be assembled prior to the assembly of the device and that the starter 66 and spot anchoring electrode 68 may be accurately aligned with and spaced from each other independently of the other parts of the device. The starting arrangement is mounted on the end of a heavy lead-in 90 (in Figures 4 and 5) which is inserted into a transverse hole or passageway 92 through the insulating cylinder 70 adjacent the upper end thereof and secured in such hole 92 by the screw 86. As shown in Figures 4 and 5 the lead-in 90 is sealed through the envelope 94 (Figures 4 and 5) of the device and supports the starting arrangement within such envelope 94. Electrical connection to the starter 66 is made through the lead-in 90, the screw 86, and the supporting strip 80. Electrical connection to the spot anchoring electrode 68 is made by immersing it in the cathode pool thus causing it to assume the cathode potential.

According to the embodiment of the invention shown in Figures 4-6, the starter 66 comprises a cylindrical member made of a metallic material which is not necessarily wet by mercury (e.g. molybdenum). The starter 66 is hollow to provide a cup-shape reservoir cavity 96 therein which contains a quantity of mercury 98. The major portion of the bottom surface of the starter is fiat to enable stable contact between the supporting strip 80 and the starter 66 but a thickened portion or embossment 100 is provided at the center of such bottom surface. A hole or passageway 102 communicating with the cavity 96 extends through the embossment 100 axially of the starter 66. A tubular insert 104 made of a material that is readily wet by mercury (e.g. specially treated nickel) and having an outer diameter and length substantially equal to the inner diameter and length of the passageway 102 is placed in the passageway to provide a damping passageway as described hereinabove. The inner diameter of the tubular insert is dimensioned so that the lower aperture 106 thereof will support a selected head of mercury within the reservoir cavity 96. A coating 108 of a material which is not wet by mercury (e.g. glass) is applied to the outer surface of the embossment 100 adjacent the edges of the aperture 106 to prevent mercury from' wetting such outer surface and escaping from the starter 66 as described hereinabove.

Referring now to Figures 4 and 5, an arc discharge device 110 according to this embodiment of the invention comprises a glass envelope 94, a main anode 112 supported on a lead-in 114 sealed through one end of the envelope 94, a mercury pool cathode 116 located in the opposite end of the envelope 94 fromthe main anode 112 when the device is in operating'position, a cathode lead-in 118 sealed through such opposite end of the envelope 94 and projecting into the pool cathode 116, and an auxiliary anode 120 supported on a lead-in 122 sealed through the side wall of the envelope 94 in closer spaced relation to the cathode 116 than is the main anode 114. The lead-in 90 for the starter 66 is sealed through the side wall of the envelope 94 and supports the starting assembly, as described hereinabove, with the spot anchoring electrode 68 partly immersed in the pool cathode 116 but with the point thereof projecting slightly above the surface of the cathode 116 and being wetted with mercury.

According to this embodiment of the invention a mercury pump is provided to replenish the change of mercury 98 in the starter 66 in place of the inclined channel described hereinabove. The pump is used since it may be desirable to operate the device 110 in such a way that the main discharge will be of too short duration to evaporate sufficient mercury from the cathode to maintain the charge. of mercury 98 in the starter 66 by the method heretofore described. The mercury pump comprises a first glass'tube 124 extending at a right angle to the axis of the envelope 94 (i.e. horizontally when the device 110 is in operating position) and communicating with the interior of the envelope 94 well below the surface of the mercury pool cathode 116. The free end 126 of the first tube is enlarged and is closed by a lead-in 128 sealed therein and projecting into the tube 124. An enlarged, glass reservoir tube 130' is sealed to one side of the first tube 124 in communication with the interior thereof. The reservoir tube 139 extends at right angles to both the first tube 124 and the axis of the device 1161 and the free end thereof is sealed. A glass delivery tube 132 is sealed to the opposite side of the first tube 124 in communication with the interior thereof and comprises a first portion 134 extending in the opposite direction from the reservoir tube 131 at right angles to the axis of the first tube 124 and the axis of the device 110, a middle portion 136 extending upwardly parallel to the axis of the device 110 and along side the device 110, and an end portion 138 extending at a right angle to the axis of the device 110 and through the envelope 94 into the interior of the device. The end portion 138 of the delivery tube 132 terminates in a downwardly extending spout 146 which projects into the cavity 96 of the starter 66. A magnetic field is established transversely of the first tube 124 of the pump as by means of pole pieces 142 at the junction of the reservoir tube 130 and delivery tube 132 withthe first tube 124.

It will be seen from Figure that the first tube 124, the reservoir tube 130 and the lower part of the delivery tube will be filled with mercury due to the force of gravity. To operate the pump, a voltage is applied between the cathode lead-in 118 and the lead-in 12$ sealed in the free end 126 of the first tube 124. Such applied voltage will cause current flow between the cathode lead-in 118 and the lead-in 128 through the mercury in the first tube 124. The current flow will interact with the magnetic field and impel the mercury in the

tubes

124, 130, 132 up the delivery tube 132 and out the spout 14-1 into the cavity 96 of the starter 66. The enlarged end portion 126 of the first tube 124- and the enlarged reservoir tube 130 assure a sufiicient supply of mercury to enable a given pulse length of a given current flow through the mercury in the tube 124 to fill the starter to a desired head. The pulse length may then be shortened to supply whatever lesser amount of mercury may be needed to maintain the desired head.

The are discharge device 110 according to this invention is operated by applying a starting voltage between the cathode 116 and starter 66. The starting action is substantially the same or has been heretofore described. Substantially simultaneously a voltage pulse is applied between the auxiliary anode 124) and the cathode 116. The starting spark is thus taken up immediately by the auxiliary anode 12% which is adjacent the starter 66 and in line of sight orientation to the starting spark. Operating voltage is then applied between the main anode 112 and the cathode 116 and the arc is taken up therebetween from the auxiliary anode 12th. The purpose of the auxiliary anode 12d) is to assure immediate response when theoperating voltage is applied to the main anode 112 by expanding the starting spark into an arc which is in line of sight of the main anode 112 and not shielded from the main anode 112, as the starting spark is, by the starting assembly.

Arc discharge devices according to this invention have the advantage of requiring comparatively low starting power, of exhibiting stable and highly predictable starting characteristics, and of being inherently adapted for long life. It is believed that those skilled in the art will find many new and useful applications for are discharge devices constructed in accordance with this invention.

What is claimed is:

1. A vapor electric discharge device comprising a gas tight envelope enclosing an anode, a pool type cathode, and a starting electrode, said starting electrode comprising a reservoir containing liquid metal and having a restricted aperture through the bottom thereof in closespaced relation to said cathode, said aperture being dimensioned to prevent the flow of said liquid metal therethrough and adapted to maintain a quantity of said liquid metal in close-spaced but non-contacting relation to said cathode.

2. A vapor electric discharge device comprising a gas tight envelope enclosing an anode, a pool type cathode and a starting electrode, said starting electrode comprising a reservoir having an aperture through the bottom thereof in close spaced relation to said cathode, said aperture being dimensioned to support by virtue of surface tension a given head of liquid metal in said reservoir and to prevent the flow of said liquid metal through said aperture and being defined by a material Which is not wet by said liquid metal.

3. An electric discharge device comprising an anode, a pool type cathode of vaporizable liquid metal, and a starting electrode, said starting electrode comprising a reservoir, having an opening through the bottom thereof in close-spaced relation to said pool cathode, said opening being of dimensions capable of preventing by surface tension the flow of said liquid metal therethrough, at least theoutermost portion of said opening being defined by a material which is not wet by said vaporizable metal.

4. A mercury vapor electric discharge device comprising an envelope enclosing an anode, a mercury pool cathode, and a starting electrode, said starting electrode cornprising a reservoir containing mercury and having a restricted, aperture through the bottom thereof in closespaced. relation to said cathode and adapted to prevent by surfacetension the flow of mercury therethrough and thus maintain a quantity of said mercury in close-spaced relation to said cathode. 1

5. A vapor electric discharge device comprising an envelope enclosing an anode, a cathode of liquid metal and a starting electrode, said starting electrode comprising a reservoir member made of a material which is not wet by said liquid metal and having an aperture through the bottom thereof in close-spaced relation to said cathode and. dimensioned to prevent by surface tension the flow of said liquid metal therethrough.

6. A vapor electric discharge device comprising an envelope enclosing an anode, a cathode of liquid metal, and a starting electrode, said starting electrode comprising a reservoir member made of a material which is wet by said liquid metal and having a restricted aperture through the bottom thereof in close-spaced relation to said cathode, and a coating of material which is not wet by said liquid metal on the outside of said reservoir member about the edge of said aperture, said aperture being dimensioned to prevent by surface tension the flow of said liquid metal therethrough.

7. A vapor electric discharge device comprising an envelope enclosing an anode, a cathode of liquid metal, and a starting-electrode, said starting electrode comprising a reservoir member having a passageway in the bottom thereof, said passageway being dimensioned to prevent by surface tension the fiow of said liquid metal therethrough and terminating in an aperture close-spaced from said cathode, the inner surface of said passageway being of a material which is wet by said liquid metal, and a coating of material which is not wet by said liquid metal on the outer surface of said reservoir at least about the edge of said aperture.

8. A vapor electric discharge device comprising an envelope enclosing an anode, a pool type cathode and a starting electrode, said starting electrode comprising a reservoir member containing a quantity of liquid metal and having van aperture close-spaced from said cathode and a passageway extending to said aperture and a coating of material which is not wet by said liquid metal on the outside of said reservoir and at least about the edge of said aperture, said passageway being dimensioned to prevent by surface tension the flow of said liquid metal therethrough and at least the inner surface thereof being of a material that is wet by said liquid metal, said aperture being dimensioned to support a given head of mercury within said reservoir.

9. A vapor electric discharge device comprising an envelope enclosing an anode, a pool cathode of liquid metal, and a starting electrode, said starting electrode comprising a reservoir containing a quantity of said liquid metal and having an elongated passageway at the bottom thereof terminating in an aperture in close-spaced relationship to said cathode, a tubular insert member in said passageway, said insert member being of a material which is wet by said liquid metal, and a coating on the outside of said reservoir of a material which is not wet by said liquid metal at least at the edges of said aperture, said aperture being dimensioned to support without flow therethrough a head of said liquid metal within said reservoir.

10. A vapor electric discharge device comprising an envelope enclosing an anode, a pool type cathode of liquid metal, and a starting arrangement comprising a reservoir and a spot anchoring electrode close-spaced from each other, said spot anchoring electrode comprising a sharp pointed member of a material which is wet by said liquid metal immersed in said pool cathode and projecting above the plane of the surface of said cathode, said reservoir having a restricted aperture through the bottom thereof aligned with said spot anchoring electrode, said aperture being dimensioned and adapted to prevent the flow of said liquid metal therethrough to maintain a head of said liquid metal in said reservoir and to provide therefrom a depending quantity of said liquid metal.

11. A vapor discharge rectifier device comprising a sealed enclosure, an anode in one end of said enclosure, a liquid type cathode in the other end of said enclosure, said liquid type cathode being of a vaporizable material, a spot anchoring electrode extending through said liquid cathode to extend slightly above the level of said cathode, said spot anchoring electrode being of a material that is wet by said liquid cathode whereby the level of said liquid cathode is raised at said spot anchoring electrode, a starting electrode closely spaced from said spot anchoring electrode, said starting electrode comprising a funnel shaped member having an aperture in the bottom thereof dimensioned to prevent by surface tension the flow of said liquid cathode therethrough, said starting electrode being at least partly made of an insulating material which forms a meniscus with said liquid cathode whereby a portion of said liquid cathode is maintained closely adjacent to said spot anchoring electrode, a drain type baffle member in said device between said liquid cathode and anode and emptying into said funnel shaped member wherebyv portions of said liquid cathode condensing on the walls of said device return to said funnel shaped member, and said funnel shaped member including an overflow device for emptying some of said condensed portions into said cathode.

12. A vapor discharge rectifier device comprising an elongated sealed enclosure having a main anode in one end of said device, a liquid cathode in the other end of said device, a starting anode supported adjacent to said cathode and to one side of the axis of said device, a starting cathode arranged closely adjacent to said liquid cathode and on the other side of said axis, said starting cathode including a pointed anchoring electrode immersed in said liquid cathode and supported to extend slightly above the level of said liquid cathode, said pointed anchoring electrode being of a material that is wet by said cathode whereby the level of said liquid cathode is raised slightly at said anchoring electrode, said starting cathode further including a reservoir for supporting a portion of said liquid cathode, said reservoir including an aperature in the bottom thereof when said device is in an upright portion, and said reservoir including a portion made of a material that forms a meniscus with said liquid cathode whereby a portion of said cathode extends through said aperture toward said raised level when said device is in an upright portion and means for filling said reservoir when said device is in an upright position including a magnetic type pump one end of which is connected to said other end of said enclosure and the other I end of which empties into said reservoir, and magnetic means for pumping said liquid from said main cathode to the reservoir in said starting cathode.

13. Starting means for a vapor type discharge device comprising a container for holding a quantity of vapor izable liquid, said container having an aperture in the bottom thereof, means for supporting said liquid by virtue of surface tension and preventing the flow thereof through said aperture whereby a meniscus of said liquid depends from said aperture.

14. A starting means for a vapor type discharge device comprising an elongated insulating member, a starting electrode mounted on one end of said insulating member, and a spot anchoring electrode mounted on the other end of said insulating member, said starting electrode comprising a reservoir containing a quantity of liquid metal and having a restricted aperture through the bottom thereof adapted to prevent by surface tension the flow of said liquid metal therethrough, said spot anchoring device comprising a pointed member of a material which is Wet by said liquid metal, said electrodes being supported on said insulating member with the point of said spot anchoring electrode in close spaced relation to said aperture of said starting electrode.

References Cited in the file of this patent UNITED STATES PATENTS 1,110,553 Hewitt Sept. 15, 1914 1,533,900 Reynolds Apr. 14, 1925 1,696,023 Zworykin Dec. 18, 1928 2,016,885 Braband Oct. 8, 1935 2,205,231 Steenbeck June 18, 1940 2,225,757 Ramsay Dec. 24, 1940 2,465,421 Bertele Mar. 29, 1949 2,728,015 Vang Dec. 20, 1955 FOREIGN PATENTS 154,084 Germany Aug. 25, 1938 905,287 Germany Mar. 1, 1954 55,643 Holland Dec. 15, 1943