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Publication numberUS3662205 A
Publication typeGrant
Publication dateMay 9, 1972
Filing dateJul 2, 1970
Priority dateJul 2, 1970
Publication numberUS 3662205 A, US 3662205A, US-A-3662205, US3662205 A, US3662205A
InventorsKenneth T Lian
Original AssigneeHughes Aircraft Co
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Electrical switch device having a fed liquid-metal cathode and partially intercepting anode
US 3662205 A
Abstract
The electrical switch device has an envelope in which is mounted a liquid-metal cathode, an anode, and a condenser. The cathode is capable of very high electron-to-atom emission ratio. A desirable value for the electron-to-atom emission ratio is on the order of 100 or more and is attainable by means of a cathode such as disclosed in U.S. Pat. No. 3,475,636. The condenser has a very much larger area than the exposed liquid metal area on the cathode, and it is kept at a low enough temperature to efficiently condense the liquid-metal vapor emitted by the cathode. With mercury used as the liquid metal, the condenser temperature is kept substantially below 0 DEG C., preferably at about -35 DEG C. which is just above the melting point of mercury. When arcing occurs from the liquid metal, a plasma jet of electrons, ions, and neutral particles is emitted from the arc spot. The anode is mounted between the cathode and the condenser, and it partially intercepts the plasma jet. The combination of the high electron-to-atom emission ratio of the cathode with the large, low-temperature condenser results in an equilibrium background pressure (i.e., pressure outside the plasma jet) of at least as low as 10<->3 Torr during arcing, and lower than 10<->4 Torr during non-arcing periods. These low pressures are obtained by maintaining the condenser in the range of low temperatures defined above. This low background pressure, in turn, permits the essentially unperturbed propagation of the plasma jet between the cathode and the surfaces upon which it impinges, i.e., condenser and anode. Such a discharge mode is commonly referred to as a "vacuum arc." The fact that the plasma jet is emitted only during arcing, and that the pressure within the space surrounding this jet is kept low, results in the ability to hold off electric fields up to 50 kV per centimeter between anode and cathode immediately after cessation of arcing.
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United States Patent Lian [ 1 May 9,1972

[54] ELECTRICAL SWITCH DEVICE HAVING A FED LIQUID-METAL CATHODE AND PARTIALLY INTERCEPTING ANODE [72] Inventor: Kenneth T. Lian, Thousand Oaks, Calif.

[73] Assignee: Hughes Aircraft Company, Culver City,

[63] Continuation-impart of Ser. No. 720,707, Apr. 11

1968, abandoned.

s21 U.S.Cl ..3l3/34,3l3/163,3l3/l73 s11 rm.c|. ..l-l0ljl/10 58 Field ofSearch ..313/29, 33, 34, 163, 167,170,

[56] References Cited UNITED STATES PATENTS Steenbeck ..3 13/34 Eckhardt ..3 13/163 X Primary Examiner-Roy Lake Assistan! Examiner-Palmer C. Demeo Attorney-James K. Haskell and Allen A. Dicke, .lr.

[ ABSTRACT The electrical switch device has an envelope in which is mounted a liquid-metal cathode, an anode, and a condenser. The cathode is capable of very high electron-to-atom emission ratio. A desirable value for the electron-to-atom emission ratio is on the order of 100 or more and is attainable by means of a cathode such as disclosed in U.S. Pat. No. 3,475,636. The condenser has a very much larger area than the exposed liquid metal area on the cathode, and it is kept at a low enough temperature to efficiently condense the liquid-metal vapor emitted by the cathode. With mercury used as the liquid metal, the condenser temperature is kept substantially below 0 C., preferably at about 35 C. which is just above the melting point of mercury. When arcing occurs from the liquid metal, a plasma jet of electrons, ions, and neutral particles is emitted from the are spot. The anode is mounted between the cathode and the condenser, and it partially intercepts the plasma jet. The combination of the high electron-to-atom emission ratio of the cathode with the large, low-temperature condenser results in an equilibrium background pressure (i.e., pressure outside the plasma jet) of at least as low as 10' Torr during arcing, and lower than 10" Torr during non-arcing periods. These low pressures are obtained by maintaining the condenser in the range of low temperatures defined above. This low background pressure, in turn, permits the essentially unperturbed propagation of the plasma jet between the cathode and the surfaces upon which it impinges, i.e., condenser and anode. Such a discharge mode is commonly referred to as a vacuum arc." The fact that the plasma jet is emitted only during arcing, and that the pressure within the space surrounding this jet is kept low, results in the ability to hold off electric fields up to 50 kV per centimeter between .anode and cathode immediately after cessation of arcing.

14 Claims, 4 Drawing Figures PATENTED MAY 9 I972 sum 2 OF 2 INVENTOR.

ALLEN A. DICKE Jr.,

AGENT.

ELECTRICAL SWITCH DEVICE HAVING A FED LIQUID- METAL CATIIODE AND PARTIALLY INTERCEPTING ANODE CROSS REFERENCE This application is a continuation-in-part of U.S. Pat. application Ser. No. 720,707, filed Apr. 1 l, 1968, now abandoned. This application is related to U.S. Pat. application Ser. No. l,868,filed July 2, 1970.

BACKGROUND OF THE INVENTION This invention is in the field of mercury arc electrical devices where an arc extends from a cathode to an anode, to pennit electron current flow therebetween.

Prior art devices which permit rectification and inversion by means of a mercury arc are well known. These prior devices employ a large mercury pool against which the arc strikes. However, the prior devices are very limited in the amount of forward and reverse voltage standoff between the anode and cathode because of the presence of the large mercury pool. The pressure within the tube is fairly high, because of the evaporation from the mercury pool, even though the mercury pool temperature is kept as low as is possible consistent with arcing. The relatively high mercury vapor pressure in such tubes, when non-conducting, limits the permissible peak forward and reverse voltage as well as the recovery and deionization rates. An example of such structures is shown in Steenbeck U.S. Pat. No. 2,205,231. To overcome this limitation, state of the art high voltage mercury tubes are provided with grading electrodes. These grading electrodes lead to another limitation: the current which can pass to one anode through such a set of grading electrodes is limited to such extent that for higher currents, a number of parallel anodes and sets of grading electrodes are required. These limitations thus lead to the need for complex multi-anode tubes, with current dividing transfonners to divide the current uniformly between parallel anodes, and grading electrodes with attendant voltage dividers.

The voltage holdofi' properties of the conventional mercury pool liquid cathode devices are determined by a tradeofl between the desired voltage holdofi, and the peak current, the voltage drop across the arc and voltage recovery rates. These conflicting requirements do not permit the device to be designed for high voltage holdoff and high current without the complex grading electrodes and the multiple anodes mentioned above.

SUMMARY In order to aid in the understanding of this invention, it can be stated in essentially summary form that it is directed to an electrical switch device having a fed liquid metal cathode and a partially intercepting anode. The anode, cathode and a condenser are positioned within a vessel. The cathode has a metal in other than the solid state fed thereto to maintain a small pool or film of liquid metal for electric arcing. The condenser maintains the background pressure in the vessel below Torr during arcing so that arcing occurs in the vacuum arc mode wherein neutral particles, electrons and ions are expelled in a farily well defined plasma cone from the arc spot at an electron-to-atom emission ratio of at least 100 to l. The condenser is arranged downstream along the cone to capture essentially the entire metal atom and ion efilux jetting from the cathode spot. The anode is positioned intermediate the cathode and condenser to partially intercept the plasma arc cone to provide maximum electron capture on the anode with minimized interference with the ions and neutrals in their flight to the condenser. In order to maintain these conditions, and in order to maintain high holdofi of electric fields during non-arcing, when mercury is used as a liquid metal, the condenser is maintained at least as low as 238 K to provide an envelope pressure of at least as low as about 5 X 10' Torr during non-arcing.

It is thus an object of this invention to provide an electrical high voltage, high current, single gap switch device which has a small liquid-metal cathode emitting a substantially conical plasma jet and an anode structure positioned with respect to the cathode so that the anode structure has direct electrical coupling but minimized interference with the conical plasma jet emitted from the cathode. It is a further object to provide an enclosed switch device with the background pressure maintained therein at a sufficiently low level, such as 10" Torr or less, that it does not interfere with the plasma jet cone so that the plasma jet cone is not distorted and an anode structure can be positioned partially within the plasma jet cone but is arranged for maximum electrical coupling and minimum interference with the atoms and ions in the cone. It is another object of this invention to provide an enclosed switch tube having an anode structure, a cathode, and a condenser, and arranged so that the condenser, optionally together with vacuum pumping devices, maintains the pressure within the tube at a sufiiciently low level that the pressure in the tube does not interfere with the flow of neutrals and ions from an are spot, so an anode structure can be positioned with respect to the plasma jet cone for maximum coupling with the plasma jet cone issuing from the arc spots. It is a further object of this invention to provide a liquid-metal cathode which is fed with non-solid metal so that a small area of liquid metal is provided for arcing activity, which area defines the position of arcing activity and thus defines the apex of the plasma cone issuing from the liquid-metal area to accurately define the plasma cone position and thus permit anode positioning with respect to the plasma cone. It is a further object of this invention to provide a liquid-metal cathode which is fed with non-solid metal so that a small area of liquid metal is provided for arcing activity. Said area of liquid metal is small enough and maintained at a low enough temperature so that the emission of neutral atoms is kept sufficiently small to maintain in conjunction with the condenser the low background pressure required for the essentially unperturbed propagation of the plasma jet between the cathode and the condenser and anode surfaces upon which it impinges, said unpertumed propagation of the plasma jet characterizing the mode of gas discharge commonly referred to as a vacuum arc." Said area of liquid metal is also small enough and maintained at low enough temperature so that the emission of neutral atoms is kept sufficiently small to maintain in conjunction with the condenser a background pressure low enough to prevent breakdown even in the absence of grading electrodes between the cathode and the anode. Other objects and advantages of this invention will become apparent from a study of the following portion of the specification, the claims and the attached drawings.

DESCRIPTION OF THE DRAWINGS FIG. 1 is an isometric view of an electrical switch device having a liquid-metal cathode and having a partially intercepting anode in accordance with this invention.

FIG. 2 is a vertical section therethrough.

FIG. 3 is an enlarged, partial vertical section showing a portion of the cathode and a portion of its associated anode.

FIG. 4 is a view taken generally on line 4 4, with parts broken away.

DESCRIPTION The electrical switch device of this invention is generally indicated at 10 in FIGS. 1 and 2. The electrical switch device has a cathode 12, an anode 14 and a condenser 16 positioned within vessel 18. The vessel is closed so that a low pressure can be maintained interiorly thereof. Vacuum pump connection 20 is optionally provided for the purpose of aiding to maintain the low pressure necessary for proper operation of the switch device.

It is essential that the cathode 12 be the type of cathode taught in Wilfried O. Eckhart U.S. Pat. No. 3,475,636. Any one of the cathode embodiments illustrated in that patent can be employed, or any other specific cathode configuration falling within the teachings of that patent is useful herein.

Cathode 12 is illustrated in more detail in FIG. 3 wherein cathode body 22 has liquid-metal passage 24 therein. Passage 24 terminates in flow restriction 26 which can either take the form of the porous plug shown, or of a narrow capillary flow control tube or any other flow impedance. Liquid metal is made to pass through passage 24 and through flow restriction 26. One method of accomplishing this is by use of liquid-metal pump 28 which delivers liquid metal through line 30. An example of such a pump is found in H. J. King, U.S. Pat. No. 3,444,816. If recirculation is required, the metal can be drawn from condenser 16. In such a case electrical isolator 32 is inserted in line 30. Said isolator 32 can be of the type taught in H. J. King, U.S. Pat. No. 3,444,570. An evaporative type transport system or a suitably arranged gravity feed system could optionally be used to transfer the liquid metal from the vessel 18 to the electrical isolator 32. In some cases, no heating is required to maintain the metal in its liquid state as it is delivered to passage 24, but in other cases, heating may be necessary to maintain the liquid state. The question of whether or not heating is employed is dependent upon the choice of the metal, and the ambient conditions.

In the case of mercury, the specified condenser temperature is kept substantially below C. In the case of mercury, a preferred condenser temperature is about 35 C., this being just above the melting point of mercury and permitting the maintenance of a background pressure no higher than about 10 and as low as 5 X Torr during non-arcing conditions. The cathode is cooled as taught in U.S. Pat. No. 3,475,636 so as to keep its evaporation from the liquid metal into the background atmosphere negligible during non-arcing conditions. Such evaporation is said to be negligible when the pressure of the background atmosphere is approximately equal to the vapor pressure of the liquid metal at the condenser temperature, this vapor pressure being approximately 5 X 10 Torr for mercury at a temperature of 35 C. Of course, during arcing the cathode heats up with the result that the pool of mercury is above that temperature. However, the pool size is sufficiently small in comparison to the size of the condenser that during arcing the background pressure is maintained at as low as 10 Torr. When heating is necessary for metals other than mercury to maintain the liquid state, such heating can be applied to the pump, the isolator and the connecting line 30. Additionally, heating or cooling of the cathode body 22 may be necessary to maintain the cathode at proper operating temperature, depending on the choice of liquid metal, the cathode current, heat losses to the atmosphere, and the like.

The front of cathode 12, in front of flow restriction 26, has pool-retaining walls 34. These pool-retaining walls are preferably conical, and are preferably formed with the total included angle of the apex of the cone of approximately 60 or more. The apex of the cone is positioned at the face of flow restriction 26. In the downward, direction in FIG. 3, below the conical area, the walls are curved outward to present a substantially planar front face 36. For further details of the construction and operation, attention is drawn to W. 0. Eckhardt U.S. Pat. No. 3,475,636, the entire disclosure of which is incorporated herein by this reference.

As is seen in FIG. 2, cathode 12 is insulated from the anode 14 by means of insulator 38. Insulator 38 is sealed to both the anode and cathode to provide closure of the interior of the device 10 from the external atmosphere. The front face 36 is formed on the front of a skirt 40 which extends outwardly and up into the interior of the space enclosed by insulator 38. This skirt helps to prevent deposition of liquid-metal particles on the insulator adjacent the cathode and protects the junction between insulator 38 and cathode 12 from high electric fields.

Anode structure 14 has an interior frusto-conical surface 42. The surface has the same projected apex and approximately the same total included cone angle as the plasma cone emitted from the cathode as described below. The plasma jet cone is emitted with its-outer surface substantially defined by a 60 to 70 solid cone angle. in order to provide optimum electrical coupling between the plasma cone and the anode, coaxial, hollow frusto cones 44 and 46 are coaxially positioned interiorly of the anode opening defined by interior surface 42. The hollow cones 44 and 46 have lesser cone angles, but have their apexes coincident with the apex of the cone of interior surface 42. Thus, they are edgewise arranged in the plasma jet for minimum flow interference with the plasma jet. However, being within that plasma jet, they are closely electrically coupled with this jet to provide a minimum voltage drop. Hollow cones 44 and 46 are supported interiorly of surface 42 by means of suitable webs 48, which are also thin and are edgewise arranged toward the conical apex. The hollow cones 44 and 46, together with their support webs 48, form electrical coupling panels which electrically couple the main body of the anode with the plasma jet. Any convenient number of hollow cones and webs can be used, consistent with proper support and minimized interference with plasma jet flow. Alternatively, a plurality of webs alone can be mounted on surface 42 and extend into the plasma jet. The skin 40, anode l4 and insulator 38 are maintained at a temperature such that metal vapor will not condense on these surfaces. Anode structure 14 can comprise one electrical structure, or can be sectioned in any convenient way to provide a plurality of electrically separate anode sections. In each case, however, the configuration remains substantially the same.

Anode 14 is mounted upon insulative support ring 50 which is secured to anode 14 on its upper side, and is secured to the body of vessel 18 on its lower side. Connector 52 extends outwardly from anode 14 to permit electrical connection thereto. Additionally, skirt 54 extends upward from anode 14 into the space of the interior of insulator 38, and substantially parallel to skirt 40, to protect the junction between insulator 38 and anode 14 from sputtered metal deposition and high electric fields. Heat exchanger 51 controls anode temperature.

Condenser 16 is built up of a plurality of thin truncated conical shells or fins 56 which are coaxially arranged with cathode 12. Condenser 16 can be mounted on legs in the bottom of vessel 18, or by any other conventional, convenient support structure. Alternatively, it can also consist of a single cup-shaped container or of a container in the form of a closed box with an appropriate opening to permit entrance and capture of the plasma jet past the anode. Again, the total included cone angle is approximately 60 to 70 so that the shells are arranged edgewise to material flow. The shells 56 are mounted on top of shells 58 which are cylindrical tubes. The shells 56 and 58 are cooled by appropriate cooling means such as circulating coolant which flows through jacket 60 through connections 62 and 64. The shells are maintained at a suitably low temperature to condense metal vapor into the liquid or optionally the solid state and permit it to gravitationally discharge out of the bottom of vessel 18. Drainage openings at the bottoms of shells 58 permit the condensed liquid metal to drain therebetween to line 66 so that it moves through line 66 to liquid-metal pump 28 or any other appropriate recirculating means or other appropriate means of disposition.

The term liquid metal is used to define those metals which are liquid at or somewhat above room temperature. While called liquid metal, it is not necessarily in the liquid state when fed to the pool-keeping surfaces. Mercury is a convenient liquid metal because it is normally liquid at room temperatures. Additionally, cesium, lithium, and gallium are also examples of suitable materials to act as the liquid metal, If necessary, the liquid-metal circulating system can be heated to maintain the liquidity of the liquid metal, as is discussed above.

Cathode 12 and anode 14 are preferably of refractory metal. When mercury is employed as the liquid metal, molybdenum serves as a suitable material for the anode and cathode. Liquid metal is pumped through inlet pipe 30 to cathode 12, to form a small pool 84 which is retained between walls 34. Alternatively, liquid-metal vapor is fed to the pool-keeping walls, whereon it transiently condenses.

US. Pat. No. 3,475,636 discloses the cathode in more detail. Any one of the cathodes disclosed in that patent is useful herein. The pool-keeping walls are indicated at 34, and the liquid metal is delivered thereto. When a liquid pool is employed, it rests in the cone between the pool-keeping walls and is as small a pool as possible, consistent with reliable arcing.

When liquid metal vapor is fed through passage 24, flow restriction 26 is normally not necessary, the passageway itself providing the flow control pressure drop. The passageway 24 can be quite small in diameter, and enter directly into the apex of the cone defined by pool-keeping walls 34. When liquid metal vapor is fed, the pool-keeping walls 34 are maintained at a temperature where transient condensation occurs. This is a temperature within a few degrees above equilibrium temperature so that vapor molecules can stick to the surface for a short time, but cannot build up into a layer which is multimolecule thick. In such a case there is no pool" which comprises a drop of liquid mercury, but instead, molecules of mercury upon the surface of walls 34 supply the liquid metal for arcing. Under the circumstances, the walls 34 can be larger in physical size, although the amount of mercury transiently condensed thereon is preferably far less than the surface coverage. This method of feeding liquid metal to a cathode is disclosed in more detail in U.S. Pat. No. 3,538,375, to Wilfried O. Eckhardt, the entire disclosure of which is incorporated herein by this reference.

The pressure within vessel 18 is maintained sufficiently low that when arcing occurs, it occurs in the vacuum arc mode. The vacuum arc mode is broadly defined as an are having electrons, positive ions and neutrals supplied in a plasma jet by are spots within a vessel having a background pressure sufficiently low that it does not substantially afiect the trajectories of the atoms and ions in this plasma jet. In the vacuum arc mode there must be negligible permanent gas (outside of the arcing material) present in the arc. Thus, when the arc becomes extinguished, the pressure in the arc space returns to a sufficiently low value to provide high electric field holdofi. To maintain a vacuum arc mode of operation, the vessel must not contain large areas of liquid metal or other material available for evaporation into the atmosphere of the vessel.

The background pressure in the vessel during non-arcing and during arcing is sufficiently low that the mean free path of the gas molecules or atoms of the background gas is large compared with the greatest dimension of the arc. The vacuum arc is therefore dependent for the atmosphere in which it burns on the emission of metal vapor and plasma from its cathode spots in the form of a plasma jet. This plasma jet being essentially electrically neutral because of the presence of a sufficient number of the positive ions to substantially neutralize the electronic space charge, the discharge runs at a low arc voltage.

Current between the plasma jet and the anode is carried by the plasma electrons reaching the anode. Current between cathode and plasma jet is believed to be carried both by electrons emitted from the cathode and by ions falling back from the cathodes spots to the cathode. Neutral metal vapor from the cathode condenses on the condenser, as well as ions reaching the condenser from the plasma jet.

Conditions in the vacuum arc plasma are characterized by the fact that the vacuum arc depends for its plasma on the metal vapor emitted from its own cathode spots, and that this plasma and metal vapor are emitted from the region of the cathode spots in the form of a jet, called here the plasma jet. It is by these characteristics that the vacuum arc differs most markedly from the more common low pressure are.

The pressure within vessel 18 is maintained sufficiently low that when arcing occurs, it occurs in the vacuum arc mode. As discussed above, the vacuum arc mode is broadly defined as having electrons, positive ions and neutrals supplied by the are spot, and the background pressure within the vessel is sufficiently low that it does not substantially afiect the trajectories of the atoms and ions emitted from the arc spots. More complete discussion of the vacuum arc and of the arcing voltage metals are found in the Proceedings of the Institute of Electrical Engineers, Volume 110, No. 4, April 1963, Pages 793802. in this specification, arc voltage and arcing voltage are interchangeably used. To provide the vacuum arc conditions described above, the pressure in the background volume outside of the plasma jet should not exceed about 10' Torr or less in the background volume outside of the plasma jet during arcing, a condenser temperature of about l0 C. or less is necessary when mercury is used as the liquid metal. A preferred condenser temperature for mercury is about 35 C., which corresponds to just-liquid mercury on the condenser surface, and permits to attain a pressure as low as 5 X10 Torr during non-arcing. The pool size and condenser temperature are such as to permit the arc to operate so that the ratio of electrons to atoms within the plasma cone is at least as high as about 50.

The are is initiated by any convenient means, including those well known in the art, such as auxiliary electrode igniters, semiconductor igniters, and the like. Alternatively, laser igniter directed onto the liquid-metal surface is suitable, but schematically illustrated is igniter 86 which emits a puff of plasma into the space between the anode and the cathode to initiate arcing. Plasma puffers are well known. One is described in detail in an article by Winston H. Bostick, entitled Plasma Motors, at pages 169 through 178 in the proceedings of the CONFERENCE ON EXTREMELY HIGH TEMPERATURES, edited by Fischer and Mansur and published by Wiley, 1958. Other suitable igniters are disclosed in GASEOUS CONDUCTORS" by James D. Cobine, Dover Publications, New York, 1941, particularly at pages 421-426. Once the arc is initiated, a plasma jet is emitted from the liquid metal cathode. This plasma jet contains electrons, ions and neutral particles. The jet issues forth from the are spot on the liquid metal and in a solid cone having a cone angle of about 60 to 70. The interior surface 42 of anode 14 is positioned in such relationship with the plasma cone that it does not substantially interfere with the progress of ions and neutral particles to the condenser. The condenser rapidly captures these particles, so that the background pressure inside of vessel 18 remains low. Furthermore, the small liquid metal area adjacent to wall 34 is sufficiently small and maintained at sufficiently low temperature that the evaporation therefrom does not adversely affect the pressure inside the vessel, this pressure being maintained sufficiently low that vacuum arc conditions are maintained, that there is no substantial interference with the high velocity of the plasma jet, and that low enough pressure can be maintained to prevent breakdown. Electrons are extracted from the plasma cone and captured on anode 42 to thus cause current conduction.

One advantage of vacuum arc operation as defined above, is that when arcing ceases, the high velocity jet of particles from the are spot is rapidly captured on the condenser so that the space between the anode and the cathode very quickly returns to vacuum conditions wherein the vacuum has high insulative value. This permits rapid application of reverse voltage without conduction, at a rate of voltage rise up to 10 kilovolts per microsecond or even more. This makes the electrical switch device 10 of great utility for high voltage rectification, controlled rectification, and inversion, particularly at high currents.

The cessation of arcing can occur in operation by the change in polarity applied to the terminals. Additionally, cessation of arcing can be made to occur by stopping the flow of liquid metal to the liquid-metal pool 84. Thus, the device is useful for do switching, for when it is desired that current be stopped, the liquid-metal flow is stopped to starve the pool and thus cause cessation of arcing. The material of the cathode around the pool is of such high arc voltage that the arc is extinguished rather than transferred to this material. To maintain stable current flow in the device under the desired condition of high electron-to-atom emission ratio at the cathode, it is desirable to operate at approximately constant electron-to-atom emission ratio. To this effect, the feeding of the liquid metal must be proportional to the arc current. When the average current is constant, the liquid metal can be fed at a constant rate. Additionally, the electrical switching device can act as an overcurent fault protector. When an adequate amount of liquid metal is fed in an amount proportional to normal current, up to a predetermined maximum feed rate of liquid metal is fed to the cathode to supply normal current needs, when a fault occurs which draws a larger amount of current, the liquidl-metal pool rapidly becomes exhausted because of its small volume. When the pool is exhausted, again arcing stops so that excessively high fault currents can be interrupted. Of course, modulated feeding of the liquid metal produces controlled forced current interruption when the current starves the pool.

This invention having been described in its preferred embodiment, it is clear that is is susceptible to numerous modifications and embodiments within the ability of those skilled in the art and without the exercise of the inventive faculty.

What is claimed is: 1. An electrical switch device, said electrical switch device comprising:

a vessel;

anode means within said vessel, cathode means within said vessel and condenser means having a condensation surface within said vessel;

said cathode means having a high are voltage material wall;

means for feeding a low arc voltage metal in other than the solid state to a position adjacent said cathode wall so that liquid metal is on said wall;

said condensation surface: (1) having a sufi'iciently large area with respect to the liquid metal area on said cathode means, and (2) being positioned with respect to said cathode means and anode means, and (3) said cathode means, said anode means and said condenser means being operated, for causing an electric discharge between said cathode means and said anode means wherein an are spot is formed on the liquid metal on said cathode wall from whence is ejected a plasma cone containing electrons, ions and neutral particles issuing directly toward said condensation surface, and said condensation surface is maintained at a sufficiently low temperature to capture substantially all of the neutral particles and ions emitted from the are spot to permit maintenance of the background pressure within said vessel during arcing sufiiciently low that the atmosphere in said vessel does not substantially interfere with the plasma cone so that discharge in a vacuum arc mode is maintained;

said anode means being positioned between said cathode means and said condensation surface in the path of said plasma cone and being formed of a plurality of panels edgewise directed toward said cathode means so as to minimally perturb the ions and neutral particles in the plasma cone and so as to electrically couple said anode means with the plasma cone.

2. An electrical switch device comprising:

a vessel;

condenser means having a condensation surface within said vessel for condensing ions and neutral particles in said vessel to maintain a sufficiently low background pressure within said vessel during arcing that the atmosphere in said vessel does not substantially interfere with arcing so that a plasma cone is formed, so that electric arc discharge in a vacuum arc mode can be maintained, said condensation surface being positioned in the path of the plasma cone;

cathode means within said vessel for carrying a low arc voltage metal in sufficiently small area to minimize evaporation of low arc voltage metal from said cathode means into the atmosphere within said vessel to permit said condensation means to maintain the background pressure within said vessel during arcing sufficiently low so that the plasma cone is an arc discharge in a vacuum arc mode;

anode means within said vessel for interacting with said cathode means so that an electric arc discharge in a vacuum arc mode is maintained from the low arc voltage metal on said cathode means to said anode means, said anode means being formed of a plurality of panels in the path of the plasma cone edgewise directed toward said cathode means so as to minimally perturb the ions and neutral particles in the plasma cone in their flow toward said condensation surface, and so as to electrically couple said anode means with the plasma cone to extract electrons therefrom.

3. The electrical switch device of claim 2 wherein said low arc voltage metal is mercury and said condenser means is maintained below 273 K to maintain a pressure within said vessel outside of the plasma cone at least as low as 10 Torr during arcing and lower than 10' Torr during non-arcing.

4. The electrical switch device of claim 3 wherein said cathode means has a high arc voltage material wall and said switch device further includes:

means for feeding the low arc voltage metal in other than the solid state to a position adjacent said wall of said cathode means so that liquid metal is on said wall.

5. The electrical switch device of claim 4 wherein at least one of said panels is in the form of a truncated hollow cone with its apex substantially on said high are voltage cathode material wall.

6. The electrical switch device of claim 5 wherein said anode means has an annular body having an interior frustoconical surface, said interior surface of said annular body having its apex substantially at said high are voltage cathode material wall.

7. The electrical switch device of claim 6 wherein said panels extend inwardly from said annular surface on said anode body.

8. The electrical switch device of claim 7 wherein said panels include a hollow frusto cone having its apex substantially on said high are voltage cathode material wall, said hollow cone being connected to said panels extending from said surface on said anode body so as to support said hollow cone interiorly of said surface on said anode body.

9. An electrical switch device, said electrical switch device comprising:

a vessel;

an anode within said vessel, a cathode within said vessel and a condenser having a condensing surface within said vessel; said cathode having a high are voltage material wall, means for feeding mercury in other than a solid state to a position on said wall so that an electric discharge in the vacuum arc mode can take place between said anode and an are spot on the mercury on said wall from whence is ejected directly toward said anode a plasma cone containing electrons, ions and neutral particles; said anode being positioned between said cathode and said condenser surface in the path of said plasma cone and being formed of a plurality of panels edgewise directed toward said cathode so as to minimally perturb the ions and neutral particles in the plasma cone and so as to electrically couple said anode with the plasma cone; and

cooling means connected to said condenser for maintaining said condensing surface between 273 K and 238 K;

said condensing surface having a sufliciently large area with respect to the mercury area on said cathode and being positioned with respect to said cathode and said anode structure and being maintained at a sufficiently low temperature to capture substantially all of the neutral particles and ions emitted from the are spot to permit maintenance of the background pressure within said vessel during arcing outside of the plasma jet, at least as low as 10 Torr so that the arc occurs in the vacuum arc mode and the atmosphere in said vessel does not substantially interfere with the plasma cone.

10. The switch device of claim 9 wherein said condenser has a sufficiently large condensing surface area with respect to the liquid metal area on said cathode and is maintained at least as low about about 273 K so that pressure within said vessel outside of said plasma jet is not higher than about Torr during arcing and not higher than about 10 Torr during nonarcing.

11. The electrical switch device of claim 10 wherein said cathode is operated so that the ratio of electrons to atoms within said plasma cone is at least as high as about fifty.

12. The switching device of claim 9 wherein said panels on said anode comprise at least one truncated hollow cone with its apex substantially on said higher are voltage cathode material wall and at least one width attached to and supporting said truncated hollow cone.

13. The process of switching an electric current comprising the steps of:

maintaining a vessel in which is positioned a condenser surface of sufficient size to dominate the vapor equilibrium in said vessel at a reduced pressure by maintaining the condenser surface at a reduced temperature;

feeding liquid metal to a cathode in the vessel for arcing;

cooling the condenser surface a sufficient degree so that arcing which occurs between the cathode and an anode in the vessel is in a vacuum arc mode; discharging an are between the anode and cathode which produces a plasma jet containing electrons, ions and atoms with the ratio of electrons to atoms being at least 30-1; and

directing the plasma jet through the anode toward the condenser so that the anode partially intercepts the plasma jet so that the anode is directly electrically coupled with the plasma jet for electron flow from the plasma jet to the anode and the condenser surface receives substantially all the ions and neutral particles.

14. An electrical switch device comprising:

a vessel;

anode means within said vessel, cathode means within said vessel, condenser means having a condensation surface within said vessel, feed means for feeding a low arc voltage metal in other than the solid state to an accessible position on said cathode means;

said anode means, said cathode means, and said condenser means being for causing an electric discharge between said cathode means and said anode means in a vacuum arc mode wherein an arc spot is formed on the low arc voltage metal on said cathode means from whence is ejected a conical plasma jet issuing directly toward said condensation surface, said plasma jet containing electrons, ions, and neutral particles, a plurality of panels on said anode means edgewise directed toward said cathode means and extending into the plasma jet to electrically couple said anode means with the electrons in the plasma jet, and said condensation surface is maintained by said condenser means at a sufficiently low temperature to capture substantially all of the neutral particles and ions emitted from the are spot and passing past said anode to permit maintenance of the background pressure within said vessel during arcing sufficiently low that the atmosphere in said vessel does not substantially interfere with the plasma jet so that discharge in a vacuum arc mode is maintained.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US2205231 *Aug 17, 1938Jun 18, 1940Hermes Patentverwertungs GmbhElectric discharge device for high operating voltages
US3475636 *Nov 14, 1967Oct 28, 1969Hughes Aircraft CoLiquid-metal arc cathode with maximized electron/atom emission ratio
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3777814 *May 19, 1972Dec 11, 1973Gulf Research Development CoClamped detector
US4060748 *Jul 23, 1976Nov 29, 1977Hughes Aircraft CompanySurface breakdown igniter for mercury arc devices
Classifications
U.S. Classification313/34, 313/173, 313/163
International ClassificationH01J13/04
Cooperative ClassificationH01J13/04, H01J2893/0089
European ClassificationH01J13/04