US2115147A - Electrical discharge device - Google Patents

Description

April 26, 1938. 1.. K. MARSHALL ELECTRICAL DISCHARGE DEVICE Original Filed April 14, 1932 2 Sheets-Sheet l April 1938- 1 K. MARSHALL ELECTRICAL DISCHARGE DEVICE Original Filed April 14, 1932 2 Sheets-Sheet 2 Patented Apr. 26, 1938 UNITED STATES PATENT OFFICE or. by mesnc assignments, to Raytheon Manufacturing Company, Newton, Mass, at corporation of Deiaware Application April 14,

1932, Serial No. 605,249

Renewed July 13, 1937 36 Claims.

This invention relates to electrical discharge devices, and more particularly to full-wave rectifiers of the gaseous discharge type.

One of the objects of my invention is to produce such a device which is capable of handling large values of current, power and voltage in a glass container.

Another object of my invention is to provide two anodes cooperating with a single cathode in a device of this kind, and to avoid the difficulties which the use of such two anodes involves in a simple and efficient manner.

Another object of my invention is to produce all of the above results with very low losses, low voltage drop, and high efliciency.

A still further object of my invention is to design a structure for such a device'which is particularly simple and rugged.

The foregoing and other objects of my invention will be best understood from the following description of an exemplification thereof, reference being had to the accompanying drawings, wherein:

Fig. 1 is a vertical cross-sectional view of a full-wave rectifier, illustrating one embodiment of my invention;

Fig. 2 is a cross-sectional view taken along line 22 of Fig. 1;

Fig. 3 is a cross-sectional view of one of the anodes taken along line 3-3 of Fig. 1;

Fig. 4 is a bottom view of the cathode taken along line 44 of Fig. 1; and

Fig. 5 is a diagrammatic view of a circuit which may be used with the rectifier shown in Fig. 1.

The production of a gaseous discharge device of high power rating and efficiency involves various difficulties which must be met before such a device can be considered suitable for modern commercial purposes.

First of all, in such a device, a cathode must be provided which, for long periods and at low voltage drop, furnishes such a copious supply of electrons that currents of arc intensities may readily be drawn therefrom.

Secondly, the drop from the tube in the conducting direction must be as low as can possibly be produced in order not only that the efficiency shall be high but also so that the heat losses in the device shall not rise above a value which can satisfactorily be dissipated without elaborate cooling means.

Thirdly, when such devices are to be used as rectifiers, they must be able to withstand comparatively high reverse voltages impressedbetween the anode and the cathode.

High power discharge devices have heretofore been constructed in metal containers. This is the fourth difficulty which I have eliminated in my device. It is desirable to use glass as the envelope to contain such devices.

Fifth, it is desirable to devise means for keeping the vapor pressure within the device from rising to an excessive value.

The sixth problem is that of a sufficiently rugged construction so that excessive mechanical strains shall not appear in the device, either during use or transportation. By utilizing devices constructed in accordance with my invention, each of the above problems are solved.

The above features will be more readily understood by referring to the drawings wherein an envelope I of refractory insulating material, such as glass, encloses the cathode structure 2 and two anodes 3 and 4. The envelope l is approximately circular in cross-section, as shown in Fig. 2, and is considerably longer than it is wide, as shown in Fig. 1. The upper end of the container I is provided with a tubular neck 5 having a reentrant stem 6. This reentrant stem has a lower wall 1. A heavy conducting rod 8, preferably of tungsten, serves as the main cathode lead and is sealed through the wall I by a seal 9, preferably of the type as described in the patent of James D. LeVan, No. 2,057,661. The upper end of the rod 8 is provided with a stranded copper conductor l0 through which connections to an external circuit may be made. The rod 8 extends from the upper end of the glass container l to a point adjacent the bottom thereof, and at its lower end serves as the main support for the cathode structure 2. This cathode structure consists primarily of a hollow tubular member ll provided with a series of external radial fins l2. The lower end of member II is closed by a cap I3. To the upper end of member II is welded a tubular extension M. The walls of this tubular extension may be considerably thinner than the walls of the member II. This tubular member II is formed by a strip of metal, which is folded back on itself to form the tubular member II at the central portion thereof, as shown most clearly in Fig. 4. At one side of the tubular member, the two sides of this strip are riveted together to provide a radial supporting arm l5. At the outer end of this supporting arm, the two sides of the strip are formed to provide a tubular clamping section 16. The outer ends I! and I8 of the strip are flattened and disposed parallel to each other, and are also provided with a series of holes through which clamping bolts l9 pass. The lower end of the rod 8 is inserted in the clamping section II, and the cathode structure is securely clamped thereto by means of the clamping bolts I. A tubular shield 28 surrounds the member II and the radiating fins l2, and is formed of a thin strip of metal riveted at its outer edges to the radial supporting arm IS. The space between the upper end of the shield 20 and the tubular member II is closed by an annular cap 2|. A heating filament 22, preferably of tungsten, is supported within the hollow member II by an insulating plug 23 closing the upper end of the tubular extension l4. This heating filament 22 consists of a double helix, the two ends 24 and 25 of which project through the insulating plug 23. Two lead-in conductors 2i and 21, which are preferably of tungsten, are also sealed through the wall I of the reentrant stem 8. Two intermediate conductors 28 and 29, which are preferably of molybdenum or nickel, are provided to connect the lead-in wires 26 and 21 to the ends 24 and 25 of the heating filament 22. The outer ends of each of the lead-in wires 28 and 21 are also provided with stranded copper conductors 38 and 3| in order that electrical connection may be made with the external circuit. The entire cathode structure below the insulating plug 23 is constructed preferably of tantalum. The external surface of the tubular member H and the radiating temperature. The coating which I prefer to use consists of a mixture of the oxides-of barium,

calcium, potassium, sodium and thorium. This coating may be formed by applying a coating of the nitrates of the above materials, and then heating the surfaces in the presence of air to a temperature sufficient to oxidize the nitrates. I have found that such a cathode surface is capable of withstanding discharges of arc intensities for very long periods without any substantial impairment of such surface. At the end of the tubular member near the cap i3 is pro,- vided a series of apertures 32 which enable electrons emitted from the filament to pass out into, the external discharge space for the purpose of aiding in the starting of the discharge. The shield 20, together with the annular cap 2 I, forms a hollow cathode chamber within which the vapor pressure is to be maintained at a higher value than the pressure outside of said cathode, in accordance with the invention set forth in the patent of Charles G. Smith, No. 1,929,122.

It will be noted that the active portion of the cathode is located as remotely as possible from the seals through which the cathode lead 8 and heater leads 26 and 21 pass. Also the opening in the cathode from which the discharge 'is initiated is directed away from the stem 8 in which said lead-in conductors are sealed. The bombardment of lead-in seals by ions generated in a gaseous discharge has been a serious problem even in devices of moderate power. Such continued bombardment has often resulted in the destruction of the seal. In devices of high power and voltage, the problem becomes even more acute. It will be seen, however, that the location and spacing of the cathode with respect to its lead-in seals are such as to effectively eliminate all such bombardment of these seals. This spacing also eliminates the problem of excessive heating of the seals. Practically the only way in which heat can reach these seals is along the conductors 8, 28 and 29. Since 28 and 23 are comparatively small, they will not conduct a sufficient amount of heat to injure the seals. Conductor 8 being much larger will conduct a larger amount of heat. Also, substantially the entire load current is carried by conductor 8. This current is so large that a substantial amount of heat is generated thereby in said conductor. In order to get rid of this heat before it reaches the seal 9, conductor 8 is provided with an external sleeve of a material which is a good heat radiator, such as, for example, carbon. This sleeve also increases the total heat radiating surface of the conductor 8, and thus most of the heat carried by and generated in said conductor is radiated out into the gaseous filling of the tube and through to the walls of the tube before it reaches the seal 8. In previous devices of this type under very heavy loads, failure has occured due to the discharge localizing on a portion of the cathode lead-in structure, and causing it to burn out. It will be noted that all of the metal parts connected to the cathode and exposed to the gaseous discharge space are made of refractory metals which can withstand high temperatures without burning out. Thus if such a discharge takes place on said metal parts, they will not burn out. The provision of the sleeve 8a also tends to prevent such a localization of the discharge on the cathode lead 8. This sleeve is made of a material which not only possesses the properties of good heat radiation but also has a high work function. Thus the sleeve 8a not only tends to keep the temperature of the lead 8 below its electron emission temperature but also covers said conductor with a material which will not emit electrons even if the temperature of the lead-in structure does rise, due to excessive loads, to comparatively high values.

Since it is the emission of electrons from the' lead-in conductors which causes the discharge to localize on them, the sleeve 8a by eliminating such emission eflectively eliminates such localization of the discharge.

In order to provide a supply of vapor to said hollow cathode, I provide the spout arrangement immediately below the cathode 2, as shown in Figs. 1 and 2. This spout arrangement is supported from a tubular extension 33 formed integrally with the bottom wall of the envelope I. Within this tubular extension is provided an insulating plug 34, preferably of lava, held within the tubular extension by the side walls of said tubular extension being pressed into indentations in the sides of the insulating plug 34 at points 35 and 36. The upper end of the insulating plug 34 is provided with a circular recess in which is seated the combined spout and shield 31. The bottom of the insulating block 34 is provided with a concave recess 38 in the outer end of which is received a cup 39. This cup is retained in place by wires 54 projecting into holes in the block 34 provided for that purpose. A longitudinal passage 40 extends through the insulating plug 34 from the upper to the lower recess. The combined spout and shield 31 consists of an inner tubular member 4| having a partition 42 extending across said tubular member at a slight distance above its lower end. This partition 42 is provided with an opening 43 on one side of the center thereof. The tubular member 4| is approximately cf the same size and diameter as the shield 28, and is positioned concentric therewith in such a manner that the outer ends of said shield 28 and tubular member 4| are at a short distance from each other. The tubular member M is concentrically surrounded by a heat shielding member 44 having a lower wall 45 joined to the lower end of tubular member 4|. The wall 45 has a central opening 46 registering with the upper end of the passage 40. The heat Shield 44 is contained within the circular recess in the upper end of the insulating block 34, and may be maintained in place thereon by some such means as a wire 41 fixed to the bottom wall 45, extending through the insulating block 34 and bent over onto the lower face of said block within the recess 38. The upper end of the heat shielding member 44 carries an enlarged shielding member 48 which extends above the lower end of the shield 20 and completely surrounds the cathode. This shield 48 may be provided with an offset portion 49 at one side thereof in order to accommodate the ends l1 and I8 and the clamping bolts IS. The shield 48 is provided with a lower wall 49 which is joined to the upper end of the shield 44. A fiat heat-shielding member 50 is connected to the outer wall of the shield 44 and interposed between the wall 49 of the shield 48 and the adjacent wall of envelope I. It will be noted that although the discharge opening of the cathode is quite near the lower wall of the envelope I, yet between the cathode discharge opening and all portions of the wall of the envelope nearest said cathode opening there are interposed two spaced heat shields, while between the cathode discharge opening and those portions of the wall which are farther away from said opening there is interposed the single heat shield 48. Those portions of the wall of envelope I which are in line with the cathode discharge opening and have no interposed shield are so far away from said cathode that they are not unduly affected by the heat radiations emitted at said discharge opening. The heat shields not only protect the walls of the envelope I, but also keep the heat liberated at the cathode within the cathode chamber, am. by the resultant increased thermal agitation of the vapor therein assist in the ionizing of the vapor, thus aiding in reducing the cathode drop.

The tubular extension 33 is adapted to be filled with a vaporizable material, such as, for example, mercury 380., which furnishes the discharge supporting vapor and which normally fills the spout arrangement to a level above the partition 42. The insulating block 34 is provided with grooves which enable the condensed vapor to run back into the lower end of the tubular extension 33.

Each of the anodes 3 and 4 is disposed transversely of the envelope l at right angles to the line of the cathode structure. Each anode consists of a hollow elongated tubular member 55 composed of a conducting refractory material having a very high work function, or at least a work function which is sufficiently high so that electrons are not readily liberated even under conditions of fairly high temperature and bombardment by excited atoms. This material is preferably carbon. The opposite ends of this tubular member 55 are supported by two reentrant stems 56 and 51, provided in tubular extensions 58 and 59 formed integrally with the walls of the envelope l. The tubular member 55 is supported on these reentrant stems by means of plugs 60 and GI which are threaded into the opposite ends of said tubular member 55. These plugs consist preferably of insulating refractory material, such as lava, while if not of insulating material they also are formed of a material having the requisite high work function. In the inner wall at the outer enlarged end of each of said plugs is provided an annular recess 62 in which is contained a coiled annular spring 63. The inner diameter of each of the plugs GI! and 6| is made so as to fit snugly around the outer diameter of the reentrant stems 56 and 51. The springs 63 take up any clearance which may exist between the plugs and the walls of the reentrant stems, and thus the anode structure is resiliently supported at both ends thereof. Through the inner wall of one of the reentrant stems is sealed an anode lead 64, consisting of a heavy tungsten rod. This lead 64 is sealed through the wall of the reentrant stem by means of a seal 65 similar to seal 9 referred to above. The outer end of the rod 64 is also provided with a stranded copper conductor 66, whereby connections may be made to the external circuit. Around the inner end of the conductor 64 is clamped a laminated spring connecting member 61. This connecting member is clamped to the rod 64 by some suitable clamping arrangement, such as 68, consisting of clamping plates and bolts. The tubular member 55 is interiorly thickened to provide an annular ledge 69, and at diametrically opposite points on this ledge the two outer ends of the connecting member 61 are clamped to the tubular member 55. This clamping arrangement is provided by bolts extending through the walls of the tubular member 55 and the outer ends of the connecting member 61, and being screw-threaded into clamping plates 1| mounted on the outer ends of said connecting member. Upon operation of the device, the temperature of the anode structure and of the walls of envelope i will increase. Since the coefficient of expansion of each of these members is different, motion must be permitted to occur between these members if strains are to be avoided. It will be seen that the anode is free to move longitudinally with respect to the reentrant stems 56 and 51, and also any resultant variation in the clearance between the plugs 60 and Bi and the stems 56 and 51 will be taken up by the springs 63. The resilient connection between the anode and its lead-in conductor afiorded by the connecting member 61 permits relative motion between the anode and its lead-in conductor 64, and thus prevents any excessive strain from occurring at the seal 65. It should also be noted that substantially none of the weight of the anode is supported by the lead 64 or seal 65, and thus this source of strain on the seal is also eliminated. This structure functions so that no strains are developed even during large variations in temperature, and the anode is always firmly but resiliently supported on the stems 56 and 51.

The outer Walls of the tubular member 55 are countersunk to receive the heads of the clamping bolts 10. These counter-sinks are sufficiently deep so that plugs 12 may be inserted therein to cover the heads of the clamping bolts. These plugs are also of the requisite high work function material, and are also preferably constructed of carbon. Upon inspection of the anode structure, it will be seen that the portions of the anode and of the members which are connected to the anode and which are exposed to the discharge vapor within the envelope I are composed solely of a refractory material of a work function high enough to prevent the emission of electrons from said material, due either to high temperatures or to collision therewith of excited gas atoms. When these materials are of carbon and of insulating material, such as lava, as suggested above, it will be seen that no metal parts whatsoever, whether of the anode itself or of members connected to the anode, are exposed to the discharge vapor within the envelope I.

As will be pointed out below, an activating agent, such as an alkaline earth or alkali metal is placed within container I. In the specification and claims I use alkaline metal as a generic term to cover both alkali and alkaline earth metals. The vapor of such metals has a strong tendency to settle on metal surfaces, making them good electron emitters at comparatively low temperatures. These activating materials have very little tendency to settle upon the materials of the anode structure which I have specified as being exposed to said vapors. While in known structures the introduction ofsuch activating materials would increase the tendency for reverse currents to be drawn from the anode leadins and similar parts, yet due to the peculiar arrangement of my device, the introduction of these materials does not materially diminish the property of my device to withstand high reverse voltages without appreciable reverse currents passing. The anodes 3 and l are located on opposite sides of the cathode, and since the cathode is placed adjacent the lower wall of the envelope, the anodes can be placed at such a level above the discharge opening of the cathode that the line which connects the cathode discharge opening and each anode when projected intersects the wall of envelope I at the greatest possible distance from the cathode discharge opening. The arrangement affords an additional measure of protection for the walls of envelope I. In discharge devices of very high power'and voltage rating, the bombardment of the walls of the device by high speed electrons and ions, may become so severe as to injure the wall, particularly if it is made of glass. The shielding structure around and below the cathode effectively prevents such bombardment of the wall of the envelope adjacent the cathode. Moreover the form of my device enables the maximum distance between the walls in line with the discharge, and the active portion of the cathode as described above, to be suflicently long so 'that the rest of the envelope wall is likewise protected against bombardment;

In order to maintain the pressure within the envelope I at its proper value, I provide condensing chambers 13 and H. A large part of the energy which is liberated in the device manifests itself as heat liberated adjacent the cathode. This heat, if allowed to be transmitted to the condensing chambers, would raise the temperature thereof. Also there is a considerable amount of other radiations liberated from excited atoms within the vapor. These radiations, if absorbed by the walls of the condensing chambers would also raise the temperature thereof. Thus it is necessary to remove these condensing chambers to a point remote from the cathode itself so as to decrease the amount of heat which is transmitted directly to these condensing chambers and also to provide means for shielding the walls of these chambers against the radiations referred to. The particular form of container which I use enables me to obtain sufliciently remote spac ing of these chambers from the cathode and the shielding of their walls from the radiations with no increase in complexity of the device. This is accomplished by providing on the envelope I on its outer extremities of its longitudinal dimension, tubular extensions I5 and I6. In the upper walls of these tubular extensions and 16 are formed the condensing chambers II and I4. It will be seen that each of these condensing chambers is removed as far as possible from the cathode itself, and their locations are sufllciently remote from the cathode so that the heat liberated there does not raise the temperature of these condensing chambers to any considerable extent. It will be noted that the position of these condensing chambers also is such that the walls of the envelope I absorb all radiations generated in the vapor within said envelope before they can reach the condensing chambers. Thus these chambers are effectively shielded against these radiations and their temperatures are therefore not ail'ected by said radiations. Thus the temperature of the condensing chambers will at all times be very slightly higher than that of the surrounding space which under ordinary circumstances will be at the usual room temperatures. Since there is very little resistance to the flow of vapor from the interior of envelope I to the condensing chamber 13, the vapor pressure in envelope I is substantially dependent upon the temperature of its coolest portion. This pressure will be determined by the temperature of the condensing chambers. By maintaining these chambers at the temperatures indicated, the vapor pressure is kept within the desired limits. If it is desired, the chambers I3 and H can be provided with additional cooling means, such as cooling coils and the like.

The voltage drop through a vaporous atmosphere, such as, for example, mercury vapor, can be greatly decreased by providing a clean-up agent which cleans up or combines with the impurities which may be present. Some materials not only possess this property, but also increase the electron-emitting properties of the cathode, or help to maintain the electron-emitting properties thereof unimpaired throughout the life of the tube when deposited upon said cathode. I prefer to introduce a material which possesses all of the above properties, and have designed my device particularly with a view to utilizing each of the above effects. As my clean-up and activating agent I prefer to use an alkali or alkaline earth metal, and in the particular tube which I have illustrated I utilize barium as said agent. The usual method of introducing a clean-up agent into a discharge tube is merely to vaporize the clean-up material within the tube, and deposit it indiscriminately upon the walls of the container. If such a procedure is adopted in a vapor discharge device, such as I have described, some clean-up will be eifected. However, it is desirable that this clean-up agent be active throughout the life of the tube, and therefore It should be intimately mixed or amalgamated with the vaporizable material in order that this material shall constantly be kept clean by the cleanup agent. The indiscriminate depositing of the clean-up agent on the walls of the tube, however, makes the mixing of the vaporizable material in the clean-up agent a very uncertain one, inasmuch as but a small amount of the vaporizable material ever comes into actual contact with the clean-up agent. In accordance with my invention, however, I provide a liberal supply of the clean-up agent in direct contact with the body of vaporizable material. I place a mixture which upon heating liberates the clean-up and activating material within the cup 39 before said cup is inserted in place within the tube. This mixture is preferably one which liberates an alkali or alkaline earth metal, such as, for example, barium.

The entire structure is then assembled, as shown in the drawings, except that exhaust tubes are connected to the outer ends of each ofthe condensing chambers I3 and 14. The envelope is then thoroughly evacuated, and all of the electrodes and other elements within the envelope I are thoroughly freed of occluded gases in the usual manner, by heating and the like. However, during this process, the mixture within the cup 39 is not flashed. After the envelope is thoroughlyevacuated, the cup 39 is heated, as, for example, by inducing high frequency currents therein, and is raised to a sufficiently high temperature to flash the mixture contained therein. Upon flashing, the clean-up and activating material which is liberated will deposit upon the walls of the recess 38, the interior walls of the passage 40, and probably also on the inside walls of the combined spout and shield member received in the upper recess of the insulating block 34. A quantity of vaporizable material, such as mercury, is then introduced into the envelope suflicient to fill the structure within the tubular extension 33 to a level above the partition 42. It will be noted that the walls upon which the clean-up and activating material has been deposited are those walls upon which the mercury comes into direct and constant contact. Thus the mercury is brought intimately into contact with the clean-up agent. This intimate contact continues throughout the life of the tube so that there is always a supply of clean-up agent directly available to absorb any impurities which enter the mercury. The intimate contact between the mercury and barium produces an amalgam or mixture of these two materials. I wish it to be understood that the term mixture as used in the claims is to be construed in its broad sense of meaning the result of the admixture of two materials even if such a mixture might also be termed an amalgam, alloy, solution, or the like. When such a mixture has vaporized and vapors. of both materials are given off, it is also proper to call such resultant vapors a mixture of the two materials.

Although materials, such as alkali and alkaline earth metals, when deposited upon the cathode will improve its electron-emitting properties, as indicated, yet when these materials are simply mixed with the principal vaporizable material, it is diflicult to cause the activating material to be deposited upon the cathode surface. This is probably due to the fact that the vaporizing temperatures of the activating agent and of the principal vaporizable material are different. Although the vapor of the activating material may be detected within the container along with the principal vapor, yet this amount is ordinarily insufiicient to utilize to its fullest extent the activating properties of said agent. My arrangement, however, enables me to secure the direct deposition of particles of the activating agent upon the cathode surface. This is accomplished by disposing the active cathode surface fairly close to the upper surface of the body of vaporizable material within the tubular member 4|. During the operation of the tube, the heat generated by the heating filament 22 and by the discharge passing from the active cathode surfaces is substantially confined within the shield 20 and the tubular member 4| by the surrounding heat shielding structure. The surface of the vaporizable material within the tubular member 4| is exposed directly to the heat so generated. As a result, this vaporizable material is raised to a temperature at which it begins to vaporize violently. The upper surface of the vaporizable material is consequently in a constant state of vigorous agitation, whereby small particles 11 are thrown off said surface. Since these particles are liberated by the mechanical motion of the surface, they contain not only the vaporizable material but also a considerable amount of the activating agent. The degree of agitation of the surface of the vaporizable material is sufficient to cause a large number of the particles so thrown off to come in contact with the cathode electronemitting surfaces. These surfaces appear to have a very strong ailinity for the activating agent, and therefore the material comprising this agent is readily deposited upon the cathode surface. In this manner throughout the operation of the device, the cathode surface is being constantly renewed by a continuous deposition of the activating agent thereupon,

The spout arrangement below the cathode, in addition to the other functions, operates to prevent the pressure within the cathode chamber from rising to too high a value. Since the pressure outside of the cathode is fairly constant as determined by the temperature of the condensing chambers 13 and 14, upon an increase in pressure in the cathode chamber the surface of the vaporizable material in the tubular member 4| will be depressed by said pressure. This depression has no appreciable effect until the pressure in the cathode chamber rises to such a value that the surface of the vaporizable material is depressed below the partition 42. When this occurs, the partition 42 acts as a heat shield between the heat generated ln the cathode chamber and the vaporizable material below said partition. Since the vaporizable material is evaporated solely by the heat furnished from the cathode chamber, no additional material is vaporized as long as the surface of the vaporizable material is below the partition 42. Since there is a constant flow of vapor out through the oathode discharge opening into the lower pressure region, upon the vaporization of the vaporizable material ceasing, the pressure within the oathode will drop until the surface of the vaporizable material again rises above the partition 42. Thus the maximum pressure which can be reached within the cathode chamber can be controlled by properly designing the spout arrangement, particularly with respect to the location of the partition 42. The higher this partition is placed, the lower will be the maximum pressure within the cathode chamber, while the lower the partition is located, the higher will be the maximum pressure developed within said cathode chamber. Such an arrangement is a particularly simple and effective pressure control.

It will be seen that the cathode is supported very close to the bottom wall of the envelope for various reasons as set forth above, such as, for example, to obtain a distant location of the envelope wall in the direction of the discharge and to obtain close spacing between the cathode and the body of vaporizable material. Since the cathode should also be supported from. the opposite wall to protect the seals and the like, the length of the supporting stem lead-in and supporting wires might be excessively long with some shapes of envelopes. By making my envelope longer in one direction than in another and disposing my cathode support across the shorter dimension, my cathode supporting structure can be kept as short as possible. This shortening of the cathode supportingstructure can be obtained without decreasing the advantages which follow as a result of the relative spacing of the various parts as set forth above.

The device described above may be connected in some suitable utilization circuit which may be, for example, such as that shown in Fig. 5. A transformer 18 is provided with a primary 18 connected to a suitable source of alternating current. This transformer carries a secondary 88 to the opposite terminals of which are connected two anodes 3 and 4. A conductor 8i is connected from the midpoint of the secondary 88 to one end of an inductive choke 82, the other end of said choke being connected by means of a conductor 88 to one side of some suitable load 84. The other side of said load 84 is connected by means of a conductor 85 to the cathode 2. The heating filament 22 is energized by an auxiliary secondary 88 of the transformer 18. This secondary 88 furnishes heating current to the filament 22 through conductors 81 and 88. An additional secondary 89 is provided on the transformer I8. A conductor 90 connects one end of this secondary to the conductor 85, the other end of said secondary 89 being connected through a resistance 8| and a conductor 92 to the conductor 81 of the heating filament 22. Upon energizing the primary I8, the filament heating winding 86 heats the filament 22 to incandescence, whereupon said filament not only starts heating the cathode electron-emitting surfaces, but also itself begins to emit electrons. A potential difference is established between the heating filament 22 and the surrounding cathode structure by means of the winding 88. A discharge is therefore initiated between said filament 22 and said surrounding cathode structure, which discharge is limited by the resistance 8|. This discharge not only increases the heating effect on the surrounding cathode structure, but also causes some of the electrons generated by said discharge to pass out through the openings 82 provided in said surrounding cathode structure. Thus, very early in the operation of the device, a large number of electrons appears at these openings 82. The presence of these electrons assists in the immediate starting of the discharge between the anodes and the cathode. Also the fact that the number of electrons adjacent these openings is in excess of the number of electrons adjacent any other portion of the cathode surface tends to cause the discharge to concentrate at these points rather than on some external surface of the cathode where such a concentration would be objectionable. Upon the starting of the discharge between the anodes and the cathode, a direct current will flow through the load device 84. Although the amount of current which ordinarily passes between the anodes and the cathode is so large that it might injure such a filament as 22, yet since this filament is entirely enclosed within the hollow member II, it is not placed in the path of this main discharge and is consequently not affected by it. However, said filament continues to emit electrons and is therefore always ready to aid in initiating the main discharge if for any reason this discharge should be cut off at any time.

By constructing a device in accordance with the invention described above, I have been able to construct such a rectifier as shown which has been able to rectify 300 amperes at volts with a drop of about 4 volts. However, it should be borne in mind that this is merely one embodiment of my invention, and that even better results can be obtained by constructing devices in accordance with the invention herein described.

This invention is not limited to the particular details of construction, materials and processes described above. For example, certain features of my invention may be utilized with the anodes constructed of some suitable refractory metal, such as, for example, iron, molybdenum, or the like. Also instead of using mercury vapor as the gaseous atmosphere within the tube, other vapors or gases, such as the vapors of alkali metals or rare, monatomic gases, could be utilized. Various other equivalents of these and other features of my .invention will suggest themselves to those skilled in the art. It is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of the invention within the art.

What is claimed is:

1. A gaseous discharge device comprising a hermetically sealed envelope containing a cathode, two anodes, and an atmosphere of an ionizable vapor, said envelope being considerably longer in one dimension than in another, the active portion of said cathode being supported adjacent one wall of said envelope at substantially the central portion thereof, said wall having as one of its dimensions said longer envelope dimension, said anodes being supported on opposite sides of said cathode, the length of the line extending from the active portion of said cathode to each of said anodes and extended to the wall of the envelope being a maximum for said envelope, and condensing chambers located at the opposite extremities of the longer dimension of said envelope.

2. A gaseous discharge device including a hermetically sealed envelope containing an anode, a cathode including a hollow chamber, means for supplying an ionizable vapor to the interior of said hollow chamber, the pressure within said hollow chamber to be maintained higher than the pressure outside of said hollow chamber and within said envelope during operation of said device, and means responsive to the difference in pressure between the interior and exterior of said chamber to prevent said difference from rising above a predetermined value.

3. A gaseous discharge device including a hermetically sealed envelope containing an anode, a cathode including a hollow chamber, means for supplying an ionizable vapor to the interior of said hollow chamber, said means comprising a hollow member, a body of vaporizable material within said hollow member and serving as the source of said vapor, means for supplying heat to the surface of said vaporizable material to vaporize said vaporizable material, the pressure within said hollow chamber to be maintained higher than the pressure outside of said hollow chamber and within said envelope during operation of said device, means for rendering the levelof the surface of said vaporizable material inversely responsive to the difference in pressure between the interior and exterior of said hollow chamber, and a heat shield at a predetermined level in said hollow member and interposed between said heat supplying means and the surface of said vaporizable material when the level of said surface drops below said predetermined level, whereby the said pressure difference is maintained below a predetermined maximum.

4. A gaseous discharge device comprising a hermetically sealed envelope containing an anode, an ionizable atmosphere, said anode being in the form of a hollow cylinder, said envelope having a reentrant stem projecting into and substantially closing one end of said hollow cylinder, means for 7' ode outside of said hollow anode, said anode com-.

pletely shielding said anode lead-in wire from exposure to the atmosphere within the discharge space in said envelope.

5. A gaseous discharge device comprising 'a hermetically sealed envelope containing an anode, said anode being in the form of a hollow cylinder, said envelope having two reentrant stems in line with one another in opposite walls of said envelope, said reentrant stems projecting into opposite ends of said anode and supporting said anode, and a cathode outside of said hollow anode.

6. A gaseous discharge device comprising a hermetically sealed envelope containing a cathode, an anode, said anode being in the form of a hollow cylinder, said envelope having two reentrant stems in line with one another in opposite walls of said envelope, said reentrant stems projecting into opposite ends of said anode and supporting said anode, a lead-in wire for said anode, said lead-in wire being sealed through one of said stems within said hollow cylinder, said lead-in being connected to said anode by a resilient conductive connector.

'7. The method of introducing vaporizable material and a vaporizable clean-up agent into a gaseous discharge tube comprising, first evacuating the tube, then vaporizing said clean-up agent and depositing it from vapor phase upon selected surfaces within said tube and covering said surfaces with said vaporizable material as it is introduced into said tube.

8. The method of introducing vaporizable material and an alkaline metal into a gaseous discharge tube comprising first evacuating the tube, then vaporizing said alkaline metal and deposit-- ing it from vapor phase upon selected surfaces within said tube and covering said surfaces with said vaporizable material as it is introduced into said tube.

9. The method of introducing mercury and barium into a gaseous discharge tube comprising first evacuating the tube, then vaporizing said barium and depositing it from vapor phase upon selected surfaces within said tube and covering said surfaces with said mercury as it is introduced into said tube.

10. The method of introducing vaporizable material and an alkaline metal into a' gaseous discharge tube comprising placing said alkaline metal at a selected place within said tube, evacuating the tube, and covering said place with said vaporizable material as it is introduced into said tube.

11. The method of introducing mercury and barium into a gaseous discharge tube comprising placing said barium at a selected place within said tube, evacuating the tube, and covering said place with said mercury as it is introduced into said tube.

12. A gaseous discharge device comprising a hermetically-sealed envelope containing a hollow cathode, an anode, an atmosphere of an ionizable vapor, a body of vaporizable material for supplying said vapor, means to conduct the vapor from said material to said hollow cathode, comprising a hollow conduit extending from said body to said hollow cathode, and a heat shield around said conduit comprising a metal member surrounding and spaceda small distance from the outer walls of said conduit.

13. A gaseous discharge device comprising a hermetically-sealed envelope containing a hollow cathode, an anode, an atmosphere of an ionizable vapor, a body of vaporizable material for supplying said vapor, means to conduct the vapor from said material to said hollow cathode, comprising a hollow conduit extending from said body to said hollow cathode, and a heat shield around said conduit comprising a wall member surrounding and spaced a small distance from the outer walls of said conduit.

14. A gaseous conduction device comprising a gas-tight vessel containing an anode, a cathode having a solid, substantially non-vaporizable discharge surface, a'body comprising a mixture of a vaporizable material for furnishing an ionizable vapor for supporting a discharge between said discharge surface and said anode, and an activating material which maintains the electron-emitting qualities of said surface when conveyed thereto, said'body positioned in said vessel to prevent thedischarge from emanating from said body during normal operation, and means for separating from said body some of said vaporizable material and said activating material and conveying the materials so separated to said surface during operation.

15. A gaseous conduction device comprising a gas-tight vessel containing an anode, a cathode having a solid, substantially non-vaporizable discharge surface, a body comprising a mixture of a. vaporizable material for furnishing an ionizable 'vapor for supporting a discharge between said discharge surface and said anode, and an alkaline metal, said body positioned in said vessel to prevent the discharge from emanating from said body during normal operation, and means for separating from said body some of said vaporizable material and said alkaline metal and conveying the materials so separated to said surface during operation.

16. A gaseous conduction device comprising a gas-tight vessel containing an anode, a cathode having a solid, substantially non-vaporizable discharge surface, a body comprising a mixture of mercury for furnishing mercury vapor for supporting a discharge between said discharge surface and said anode, and barium, said body positioned in said vessel to prevent the discharge from emanating from said body during normal operation, and means for separating from said body some of said mercury and said barium and conveying the materials so separated to said surface during operation.

17. A gaseous conduction device comprising a gas-tight vessel containing an anode, a thermionic cathode having a solid, substantially nonvaporizable discharge surface, a body comprising a mixture of. a vaporizable material for furnishing an ionizable vapor for supporting a discharge between said discharge surface and said anode, and an activating material which maintains the electron-emitting qualities of said surface when conveyed thereto, said body positioned in said vessel to prevent the discharge from emanating from said body during normal operation, and means for separating from said body some of said vaporizable material and said activating material and conveying the materials so separated to said surface during operation.

18. A gaseous conduction device comprising a gas-tight vessel containing an anode, a cathode having a discharge surface, separate heating means for heating said discharge surface to temperature of thermionic emission during operation, a body comprising a mixture of a vaporizable material for furnishing an ionizable vap'or for supporting a discharge between said discharge surface and said anode, and an activating material which maintains the electron-emitting qualities of said surface when conveyed thereto, and means for separating from said body some of said vaporizable material and said activating material and conveying the materials so separated to said surface during operation.

19. A gaseous conduction device comprising a gas-tight vessel containing an anode, a cathode having a solid, substantially non-vaporizable discharge surface, a body comprising a mixture of a vaporizable'material for furnishing an ionizable vapor for supporting a discharge between said discharge surface and said anode, and an activating material which maintains the electron-emitting qualities of said surface when conveyed thereto, said body positioned in said vessel to prevent the discharge from emanating from said body during normal operation, and means for vaporizing material from saidbody and conveying the material thus separated from said body to said surface during operation.

20. A gaseous conduction device comprising-a gas-tight vessel containing an anode, a cathode having a solid, substantially non-vaporizable discharge surface, a body comprising a mixture of a vaporizable material for furnishing an ionizable vapor for supporting a discharge between said discharge surface and said anode, and an activating material which maintains the electronemitting qualities of said surface when conveyed thereto, said body positioned in said .vessel to prevent the discharge from emanating from said body during normal operation, means for vaporizing material from said body and conveying the material thus separated from said body to said surface during operation, and means for condensing the vapor in said vessel and returning said condensed vapor to said body.

' 21. A gaseous conduction device comprising a gas-tight vessel containing an anode, a cathode having a discharge surface, said surface .being provided with a coating of electron-emissive oxide, a body comprising an activating material which maintains the electron-emitting qualities of said surface when conveyed thereto, and means for separating from said body some of said activating material andconveying the material so separated to said surface during operation.

22. A gaseous conduction device comprising a gas-tight vessel containing an anode, a cathode having a discharge surface, said, surface being provided with a coating of electron-emissive oxide, a body comprising an alkaline metal, and means for separating from said body some of said alkaline metal and conveying the materials so,

separated to said surface during operation.

23. A gaseous conduction device comprising a gas-tight vessel/containing an anode, a cathode having a disc arge surface, said surface being provided with a coating of oxide, a body comprising an alkaline metal, and means for separating from said body some of said alkaline metal and conveying the materials so separated to said surface during operation.

24. A gaseous conduction device comprising a gas-tight vessel containing an anode, a cathode having a discharge surface, said surface being provided with a coating having a high aiiinity for alkaline metal, a body comprising a. mixture of a vaporizable material for furnishing an ionizable vapor for supporting a discharge between said discharge surface and said anode, and an alkaline metal, and means for separating from said body some of said alkaline metal and conveying the materials so separated to said surface during operation.

25. A gaseous conduction device comprising a gas-tight vessel containingan anode, a hollow cathode having an interior solid, substantially non-vaporlzable discharge surface and a discharge opening, a body comprising a mixture of a vaporizable material for furnishing an ionizable vapor for supporting a discharge between said discharge surface and said anode, and an activating material which maintains the electron-emitting qualities of said surface when conveyed thereto, said body positioned in said vessel to prevent the discharge from emanating from said body during normal operation, means for separating from said body some of said vaporizable material and said activating material during operation, and a conduit extending from said body to the interior of said hollow cathode for conveying the material so separated to said surface.

26. A' gaseous conduction device comprising a gas-tight vessel containing an anode, a hollow cathode having an interior solid, substantially non-vaporizable discharge surface and a restricted discharge opening maintaining a higher pressure inside said hollow cathode than outside said cathode, a body comprising a mixture of a vaporizable material for furnishing an ionizable vapor for supporting a discharge between said discharge surface and said anode, and an activating material which maintains the electron-emitting qualities of saidsurface when conveyed thereto, said body positioned in said ,vessel to prevent the discharge from emanating from said body during normal operation, means for vaporizing material from said body and conveying the material thus separated from said body to said surface during operation comprising a conduit extending from said body to the interior of said hollow cathode, and means for condensing the vapor in said vessel and returning said condensed vapor to said body.

27. The method of preserving the electronemitting properties of a cathode having a solid, substantially non-vaporizable electron-emissive surface which comprises conveying to the electron-emissive surface of the cathode during operation a mixture of an easily vaporizable material and a material which maintains the electronemitting-properties of said surface.

28. The method of preserving the electronemitting properties of a cathode having a solid, substantially non-vaporizable electron-emissive surface which comprises conveying to the electron-emissive surface of the cathode during operation a mixture of an easily vaporizablematerial and an alkaline metal.

29. The method of preserving the electronemitting properties of a cathode having a solid, substantially non-vaporizable electron-emissive surface which comprises conveying to the electron-emissive surface of the cathode during optron-emissive oxide which comprises'conveying to the electron-emissive surface of the cathode during operation a material which maintains the electron-emitting properties of said surface.

31. The method of preserving the electronemitting properties of a cathode coated with electron-emissive oxide which comprises conveying to the electron-emissive surface of the cathode during operation a mixture of an easily vaporizable material and an alkaline metal.

32. The method of preserving the electronemitting properties of a cathode having a solid, substantially non-vaporizable electron-emissive surface in a gas-tight vessel which comprises separating material from a body of a mixture of an easily vaporizable material and a material which maintains the electron-emitting properties of said surface, and conveying the materials so separated from said body to said surface during operation.

33. The method of preserving the electronemitting properties of a cathode having a solid, substantially non-vaporizable electron-emissive surface in a gas-tight vessel which comprises separating material from a body of a mixture of an easily vaporizable material and an alkaline metal, and conveying the materials so separated from said body to said surface during operation.

34. The method of preserving the electronemitting properties of a cathode having a solid, substantially non-vaporizable electron-emissive surface in a gas-tight vessel which comprises vaporizing material from a body of a mixture of an easily vaporizable material and a material which maintains the electron-emitting properties of said surface, and conveying the materials so separated from said body to said surface during operation.

35. The method of preserving the electronemitting properties of a cathode having a solid, substantially non-vaporizable electron-emissive surface in a gas-tight vessel which comprises vaporizing material from a body of a mixture of an easily vaporizable material and a material which maintains the electron-emitting properties of said surface, conveying the materials so separated from said body to said surface during operation, condensing the vapor in said vessel, and returning the condensed vapor to said body.

36. The method of preserving the electronemitting properties of a cathode having a solid, substantially non-vaporizable electron-emissive surface in a gas-tight vessel which comprises vaporizing material from a body of a mixture of an easily vaporizable material and an alkaline metal, conveying the materials so separated from said body to said surface during operation, condensing the vapor in said vessel, and returning the condensed vapor to said body.

LAURENCE K. MARSHALL.

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