US1928202A - Gas filled discharge device - Google Patents

Description

Sept. 26, 1933. F. MEYER Er AL GAS FILLED DISCHARGE DEVICE Filed March 28, 1929 2 Sheets-Shget l Wl'fNESS H/i/VS J SPAN/YER QLM/MM Sept. 26, 1933. ER r AL 1,928,202

GAS FILLED DISCHARGE DEVICE Filed March 28, 1929 2 Sheets-Sheet 2 J4 7* 70 J w J 4 4 7 /d Patented Sept. 26, 1933 i GAS mum DISCHARGE DEVICE Friedrich Meyer and Hans Joachim Spanner, 1 Berlin Halensee, Germany, asslgnora to Eleotrons, Inc., a corporation of Delaware Application March 2s, 1929,- Serlal No. 350,778, and in Germany January 27, 1927 25 Claims- (Cl. 250-275) This application is a continuation in part of our bulb is awkward and expensive in construction. application Serial Number 214,192 filed 19 August From an operating point of view it is ineflicient 1927, and relates to gas-filled discharge devices, because of the'long discharge paths physically and particularly to rectifiers operating with a constricted in cross-sectional area, and further space current discharge in a gas-filled container electrically so constricted because of the collecwith the aid of an incandescent or heated electron tion of electrical charges on the side walls of these emitting cathode. paths, both of which effects make the overall A particular object of the invention is to direct drop of potential between cathode and anodes and control the discharges necessary to current high, inconstant and uncontrollable. rectifying actions to prevent improperly timed These Germershausen tubes have in them the discharges and discharges between the wrong advantage pointed out by him of substantially electrodes. eliminating the so-called cathode drop or dif- Another object is to conserve in the matter of ference of potential in the cathode dark space, space needed by the device, and at the same time and thus eliminate this drop from the over-all to provide for eflicient operation. potential. For example, in an argon atmosphere A further object is to provide an arrangement of about one millimeter of mercury pressure a permitting of rectifying high potential alternat potent a Component of 8b0uii'130 Volts is elimiing currents without resorting to widely spaced nated, which voltage b d the Cathode dark electrodes and awkward constructions of the conspace is necessary to impart suflicient velocity to 20 tainer or tube. 1 ions to create suflicient electron emission by A feature of the invention is the use of screens bombardment from a cold electrode when such is between and around electrodes and the use of used for starting the general ionization of the auxiliary electrodes for directing, confining and discharge path. The set of conditions above cited controlling the rectifying discharges to arrive at for argon are probably the most favorable for the results desired. Another feature is the use easy starting with cold electrodes, so that with 80 of the relative effects of an eliminated cathode other conditions, such as other gases and less drop" at an effective electron emitting cathode favorable cathode materials, the cathode drop is and the mean free path of electrons in a gaseven higher, and under these less favorable confilling. Simple and inexpensive construction is ditions the beneficial effect of the heated electron v an additional feature. emitting cathode is greater. 85

The general operating advantages of gas-filled As pointed out by Germershausen, the other rectifier tubes operating with the aid of heated drop of potential components of the discharge effective electron emittingcathodes, such as for path are small compared to the cathode drop. example the well-known oxide coated cathodes of These other components are two. in number and 5 Wehnelt, the German scientist, are ably pointed comp se t e d p in the luminous Portion of the 90 out by Germershausen in an article in the June path and the so-called anode drop, which is and July 1920 issues of Helios, an electrotechnirepresentative of the potential needed to create cal publication of Leipzig, Germany. However, ionization of the particular gas used, which in the Germershausen and others prior to us, have failed case of argon is about 12 volts. The drop in the to arrive at satisfactory simple and inexpensive luminous portion depends upon the length of the 5 constructions for such rectifying and like disdischarge path, its cross-sectional area, the incharge tubes with provisions for desirable eftensity of the discharge, the nature of the gas ficiency of operation, a fact readily appreciated and the pressure of the gas. In our practice by examining the tubes of Germershausen illusthis luminous drop is of the order of a few percent trated in. Fig. 14 of page 258 of the June 1920 isof the cathode drop; that is, a few volts. In the 10 sues of Helios. The tubes shown in this figure eased the Germershausen tubes, Fig. 14 for exare so-called full wave rectifiers. There is ample, the long, constricted and electrically a heated electron emitting cathode in the central charged paths keep this luminous drop high and portion of the bulb co-operating with two anodes inconstant because of the inconstancy of the in the ends of the two arms or extensions from charges on the walls with intensity of discharge 1 the main portion of the bulb, this to get wide sepacurrent. ration between the anodes to confine the dis- The manner in which our present invention imcharges alternately between the cathode and the proves over the prior art will be best understood respective anodes, and to avoid breakdown dis-- by reference to the several figures of the draw- (5 charges between the anodes. Obviously, such a ings in which like reference characters represent like parts so far as possible throughout the several figures, andin which Figure 1 is a diagrammatic view of the arrangement of electrodes and shields with a gas-filled tube. a

Figure 2 shows in perspective a full-wave alternating current rectifier of the gas-filled heated electron emitting cathode type in which provision is made for preventing undesired discharges between the anodes by using fiat anodes shielded from each other by a heated electron emitting cathode.

Figure 3 is a modification of the arrangement of elements as shown in Figure 2.

Figure 4 illustrates in perspective a full-wave rectifier in which a shield is interposed between the anodes so as to separate the tube into a plurality of electrically independent discharge spaces with a single emitting cathode so located as to function with both anodes, and includes auxiliary shielding and discharge control means.

Figure 4a is an elevation in part of the tube shown in Figure 4;

Figure 4b is a sectional plan view on the line 4b-4b of Figure 4a;

Figures 5 and 6 are modifications of the number arrangement and spacing of shields and electrodes of the type of tube shown in Figure 4;

Figure 'l is a fragmentary showing of a full wave rectifier tube in which provision is made for shielding the electrodes when such a tube is to be operated at high voltages;

Figure 8 illustrates a multi-phase alternating current rectifier in which provision is made by screening for an electrically separate space for each phase, and including multiple cathode elements connected in parallel in which there is one principal element for each space.

Figure 9 is a modification of a tube similar to that of Figure 8 wherein two anodes are utilized and a sectional cathode, each section of which cooperates with its corresponding anode and shielding devices for the space current paths within said tube, and

Figure 10 shows a tube having a sectional cathode, a plurality of anodes cooperating therewith, shields for the space-current paths within the tube and a shield surrounding the group of electrodes but independent of the coating-within the tube performing the functions thereof as.

hereinafter described with reference to Figure .4. Referring to the diagram of Figure 1, it is the substance of our invention to divide the space ,within a gas-filled envelope 1 containing a cathode 3 and a plurality of anodes 4', 4" into separate space current paths between each anode 4, 4" and the cathode 3 by means of shields 5, 5', 5" so that in the operation of a. tube of this character the space current will pass along the desired path within the tube and so that there will be substantially no leakage between the various electrodes whereby losses within the tube might occur.

In Fig. 2, there is shown a rectifier tube having the usual glass or like container 1 provided with the usual stem 2 through which the lead-in electrode wires pass as indicated in accordance with common practice. The tube is arranged for fullwave rectification by having a heated electron emitting cathode 3 and two co-operating anodes 4 and 4", the heating current for the cathode being supplied by way of the two conductors 9 and 10. There is a gas-filling in the tube of low pressure; for instance argon gas at about one millimeter of mercury pressure. The anodes 4' and 4" are flat and protected relatively to one another and the cathode by the interposed cathode 3 as shown. The protection is due to the fact that the interposed cathode and its emitted cloud of electrons act as screening or shielding efiects against break-down discharges between the anodes. A break-down discharge between the two anodes would require a condition of suflicient positive ionization in the gas path between them to generally ionize the discharge path. For example, considering that phase of the alternating current cycle when anode 4 is at a maximum positive potential and anode 4" is at a maximum negative potential, and the potential between the anodes is double that between either anode and the cathode, there is a discharge by general ionization between the cathode and anode 4'. At this time the strong negative potential of anode 4" is tending to draw to its neighborhood the positive ions from the field between the cathode and anode 4, and if it is successful in drawing suflicient positive ions to its neighborhood to energize this part of the space then a general break-down discharge will occur. However, for the positive ions between the cathode and anode 4' to reach the neighborhood of anode 4" it is necessary that they pass through the cloud of electrons continuously emitted by the cathode and the cathodes field action, and are thus subject to neutralization. Therefore, if the tendency for transferring positive ions is not too strong for the electron emission of the particular cathode suflicient neutralization takes place to prevent a break-down discharge. Thus in such an arrangement as that of Fig. 2 there is a limit to the amount of discharge current or rectifying action that can be had with a given emitting cathode.

There also has to be considered the possibility of a reverse action or discharge between the cathode and the anode that is negative. In the case of Fig. 2 the cathode is the screen or shield, and the flat anodes are located suificiently close to the cathode that each of the spacings between the cathode and the two anodes is comparable to the mean free path of the electrons in the particular gas and pressure of it used, an effect fully explained by W. Crookes as early as about 1905 as pointed out in German Patent 209,969 of November 10, 1908. By reason of employing a separation having this mean free path relation the electron flow from the negative anode to the cathode does not create positive ionization, so that there is no general ionization or break-down discharge at this part of the system.

Fig. 3 modifies the arrangement of Fig. 2 by locating the emitting cathode 3 above the anodes 4 and 4". Since in this arrangement the cathode is removed from its interposed position the anodes are moved closer together to arrive at the separation distance comparable to the mean free path relation to prevent a discharge therebetween. The same relation pointed out in connection with Fig. 2 as between the cathode and the two anodes is maintained. With this arrangement it is possible with not too high currents and potentials to prevent break-down discharges between the anodes and between the cathode and non-active anode for the reasons given in connection with Fig. 2. Obviously this second arrangement produces a better exposure of the anode surfaces to the cathode for better formation of discharge paths between the cathode by way of the electron field and the alternately operating or active anodes.

Figs. 4. 4a and 4b are different views of the same full-wave rectifier having two anodes 4' and 4" shielded from each other by a screen 5, the emitting cathode comprising the two spiral elements 3' and 3" connected in series relation and supplied with heating current by way of leads 9 and 10, this cathode arrangement being located at the top of the screen. This arrangement thus divides the tube 1 into two general discharge sections or spaces. The screen may be either of conducting material or insulating material superficially rendered conductive, a simple process for the latter being the'deposit thereon of the usual mirror ei'lect resulting from getter vapor condensation accompanying the usual clean-up process in making such tubes.

The walls of the tube also have a coating of the condensed getter material which may be used as screens to aid in directing and controlling the discharge by reason of the field action of electrical charges collected thereon, and for this reason it is not necessary to extend the space dividing screens to the walls of the tube to completely divide off the discharge spaces. The charges on the dividing screens and walls tend to prevent undesired discharges taking place by way of the spaces between internal screens and walls.

There is also shown an auxiliary screen 6 in the space above the cathode, which may or may not be necessary depending upon the size of the space, operating voltages and currents and resulting field actions. Its purpose is to prevent positive ions on the active side of the system from escaping in undesired number through this space to the inactive side. It acts as an auxiliary in this respect to the cloud of electrons above the oathode. As before stated, it need not span the space entirely if used, as the charges that collect on it will cooperate with the charges that collect on the getter surface of the walls of the tube to prevent discharges by way of passages between screen and walls. 7

The screens 5 and 6 are shown connected to the cathode by way of connections 8 and 7 re spectively and the getter conducting surface on the tube walls also so connected by way of crossconnecting element 17 between the walls and the screen 5. These connections permit of controlling the degree of electrical charges collecting on these elements, and therefore the resulting field actions of these charges on the operating discharges of the tube. Under some operating conditions of potential and current it is not necessary to connect the screens to the cathode or any other point of controlled potential, this because there is an inherent tendency for the positive ions in the operating discharge paths to neutralize the rapidly collecting negative charges on the screens originating with the operating electrodes, so that there is a natural tendency for the screens to automatically maintain an average potential the same as the potential of the cathode without a conductive connection thereto.

The anodes 4' and 4 Fig. 2, located so as to have a gap separation from the screen 5 which is comparable to the mean free path of electrons for the used gas and pressure of it, this to prevent break-down discharge between the anode of negative phase in the operating cycle as explained in connection with Fig. 2.

The operation of the device of Figs. 4, 4a, and 4b is readily appreciated from the inherent features of it. Considering the two discharge paths from are, as in the case of the electron emitting cathode to the anodes 4' and 4" of the alternating current cycle when anode 4' is positive and anode 4" is negative, the potential of the cathode being midway between the anode potentials, it is apparent that the cathode drop (at least 130 volts in argon gas of about 1 millimeter mercury pressure) is eliminated from the dis charge path between the cathode and positive anode 4' by reason of the electron emitting cathode, or in other words, the resistance in this path is decidedly lowered, the remaining resistance of the luminous portion and the anode drop being but small compared to the eliminated cathode drop. At the same time the cathode drop between the non-emitting shield 5 and anode 4' is maintained and since the anode drop is the same in both cases, there will be no discharge between anode 4 and screen 5 so long as the drop oi potential in the luminous section of the discharge path between cathode and anode does not exceed the sum of the particular cathode drop of screen 5 and the drop of the luminous section between screen 5 and anode 4'; that is, so long as the overall operating potential of the discharge path does not exceed that potential necessary to give the required velocity to ions to effectively free electrons from screen 5 upon bombardment in such Way that it can act in effect as a cathode.

Considering the discharge path between the cathode and anode 4", temporarily required to be inactive, the screen 5, charged walls of the tube, the cathode and its electron cloud, and screen 6 if used, serve to eifectively prevent positive ions in disturbing quantity from passing from the active section to the inactive section of the tube, so that there is no break-down ionization in this inactive portion from this source. Furthermore, anode 4" is spaced. from screen 5 a distance. comparable to the mean free path oi the electrons, and since this is also a point of strongest field action between screen 5 and anode 4", the electrons from anode 4" concentratedly escape to the screen without any effective positive ionization, but merely as a pure electron current of very small intensity. Thus, when anode 4 is so polarized in the operation as to be a cathode with respect to cathode 3' 3", the electrons are drawn off over a short mean free path of electrons and do not move in the main path over a long distance under high potential to start a reverse discharge to the emitting cathode. It is thus possible to operate with unusually high voltages without producing break down discharges.

It is further apparent that the main discharge paths are easily constructed to be short and of extensive cross-section with controlled directing fields which do not have excessive electrical destructive effects, thereby keeping the drop of potential in the luminous way small, which means low losses or high efiiciency.

The controlling of the charges on the screens and walls has the further benefit of suppressing tendency to produce auxiliary oscillations, a heretofore difiicult feature to handle in gas-filled tubes.

Fig. 5 illustrates a modification of the tube of Fig. 4, 4a and 4b in that two screens 5a and 5b are interposed between the anodes 4 and 4", the cathode 3 being placed between the screens. The discharge paths are bowed by the electrons having to pass over the tops of these arrangement often desirable for high potential operation.

It is sometimes desirable to apply auxiliary respectively, and assuming. that phase I screens, an

binediy cooperate in the open spaces above the screens.

' stantially as in Fig. '7. In

supply transformer of a rectifier system, series resistance 15 and 16 being usual in connections of this kind to prevent excessive current fiows in such an auxiliary part of the system. Secondary winding 14 of the supply transformer is shown connected to the filament or cathode 3 supply wires in a manner well-known to the art.

With the screens a and 5b so energized by the auxiliary potentialsthe ions in the discharge paths can be controlledly deviated to increase the length of the discharge paths and to prevent their entrance into the non-active sections, where even a small amount of ions not sumcient to start general ionization would, by reason of the high negative potential of the inactive anode imparting highvelocity to such ions, cause considerable disintegration of the anodes.

Fig. 8 is a modification of the arrangement of Fig. 5 in that the cathode 3 is removed from a position between the screens 5a and 5b to a position above them, which can be done for lower voltage operation. The screens-5a and 5b may or may not have auxiliary potentials as illustrated in Fig. 5 as the particular use and operation of the tube dictates.

Fig. '1 shows an arrangement diiferent from that of Figs. 4, 4a and 4b in that additional screens 5 and 5" are interposed in the paths between cathode 3 and anodes 4 and 4" respectively, this in order to bend out or lengthen the discharge paths for higher potential operation, and in this respect does not diiler materially from the result ob-. tained in Figs. 5 and 6. That is, the screens are arranged in such fashion that a straight line drawn from each of the anodes to the cathode cuts a screen, this as compared to the arrangement in Figs. 4, 4a and 4b in which such straight lines do not cut screens.

Fig. 8 shows a tube in which screens 5a, 5b and 5c divide the tube into three discharge sections for 3-phase current rectification, it being intended that an anode 4 be located in each one of the sections. In this case the cathodes 3a, 3b and 3c are shown so located that there is one cathode section preferably operating with each of the three discharge sections, the cathodes being shown connected in star for heating from the 3- phase supply source. Naturally the electron field effects of all three cathode sections comshielding effect in the Fig. 9 shows an arrangement in which a two section cathode is connected in series for heating, there being one cathode section superimposed over each discharge section.

Fig. 10 shows a tube particularly adapted for high voltage operation by having an auxiliary conducting screen 11 surrounding the electrodes and interposed screens which are arranged subthis construction the charges are prevented from collecting on the walls of the tube. This prevents interference with operation of the tube by the approach of the hand or conducting objects, and protects operatingv personnel from unpleasant electrical shocks.

To distinguish our invention from prior practice with respect to gaseous discharge tubes it is particularly pointed out that our screening effects are possible only in connection with an effective electron emitting cathode such as present heated potentials to the screens, which is provided for in types of cathodes wherein the cathode drop is substantially eliminated. For example a gaseous discharge tube operating with a cold cathode is described in British Patent 237,236 of June 26, 1925, and Fig. 1 of this patent shows the two anodes screened from each other by a cold cathode. As brought out by the patent the rectifying action is obtained by reason of an extremely large ratio of surface area of cathode to anode, such as 300 to l. The rectifying effect is therefore dependent upon the abnormal cathode drop when the small anode during its negative phase of the cycle acts as a cathode with regard to the more positive main cathode, which abnormal drop limits the amount of reverse positive ionization current. In other words, the amount of reverse positive ionization current is limited by the ratio of the surface areas. The cathode does not act as a shield to prevent positive ionization in the nonactive section of the tube. The cathode does serve as a screen to prevent excessive cross-currents between the two anodes in case the potential difference between them is high enough to overcome the abnormal cathode drop if the oathode were not placed between them. Obviously the anodes could not be located at distances from the cold cathode comparable to the mean free path of electrons of the used gas and pressure of it, as such location would prevent any efficient order of discharge at any time, thus rendering the device practically inoperative for the purpose intended.

In the case of our arrangement the elimination of the cathode drop and the presence of the electronic cloud about the heated emitting cathode-permits undisturbed operation between the cathode and the positively charged anode even when the screen connected with the cathode is located at a distance from the anodes within the mean free path of the electrons. At the same 115 time positive ionization in the negative section is suppressed effectively. Thus the cold screen between the anodes does not act as a cathode at all, but serves only to control the electrical conduct of the ionization effects by field actions. 1 0 Should the screen have any cathode action as in the case of the British patent the efficiency of the arrangement would be eliminated. Generally speaking, our screening effects are obtained by field actions and electronic clouds. Because our 125 rectification action does not depend upon proportioning the areas of cathode to anode we can use anodes of large surface, thereby facilitating cooling and reducing disintegration. which latter feature is further bettered by having lower voltage losses and. thus less destruction by ion acceleration. In fact, our cathodes can be even of lesser surface area than the anodes.

We have pointed out that our anodes are separatedfrom the screens by a distance comparable 135 to the mean free path of the electrons. Obviously a practical construction requires for mechanical reasons a separation that will not involve short circuits from vibration and expansion with heating contacts, and an actual separation 140 of one millimeter at least must be provided for such conditions. This separation translated into terms of mean free paths of the electrons of the rare gases usually employed in discharge tubes limits the gas pressures in the tubes to not exceed- 1 'ing 2 to 3 millimeters of mercury. Heretofore,

ions due to the high cathode drop in such low pressures would too rapidly disintegrate the small anodes. For example British Patent 237,236 referred to prescribes a pressure 01' not less than 19 millimeters of mercury. With such a pressure in our tube we would require a mean free path of the order of one-twentieth of a millimeter, which separation would obviously not permit '01 a practical construction.

As an example of a practical application of some of the features of our invention we have constructed among others a full-wave rectifier tube in general similar to the arrangements shown in Figs. 4, 4a and 4b which has been successfully used commercially to rectify alternating current of 350 volts between cathode and anode, or 700 volts between the anodes, with a rectified current output of 500 milliamperes. This tube has under such operating conditions an internal loss of potential of but about 30 volts, thus giving an unusually high efllciency for such a small device. The tube has a height of but 3 inches and a mean diameter of 2 inches. The cathode is a spiral winding about inches long and 1 inch in diameter. The anodes may be flat as shown in Figs. 4 and 4a or cylindrical in form as shown in Figs. 7 and 10, about inches in height and 3 inches in diameter. The screen between the anodes has an effective width of about 1 inches and a height of about 1 inch. The screen is fitted at the top with auxiliary screens as shown in Fig. 4 extending 1; of an inch on each side. The cathode spiral is of an inch above the screen. The top of the anode is about of an inch below the top of the screen. The anodes are spaced from the screen about I; of an inch. The walls of the tube have a coating of condensed magnesium getter connected to the screen by a metallic spring device. The gas pressure is about one millimeter of mercury of argon gas.

The operation of this practical tube as outlined completely proves the effectiveness of the screening features of our invention, as the 350 volts between the negative anode and the cathode exceeds by almost double the necessary ionization potential between cold electrodes in argon of the said gas pressure when not spaced within the mean free path of electrons.

Having fully described our invention, we claim:

1. A gas-filled discharge device having an electron emitting cathode, a plurality of co-operating anodes, a conductive screen separating said anodes from each other and intersecting all straight lines which may be drawn from one to another of said anodes, said cathode being disposed in discharge relation to all of said anodes, and a discharge deflecting screen in each of the discharge paths between said cathode and the several anodes.

2. A gas-filled full-wave alternating current rectifier tube including an electron emitting cathode, a pair of co-operating anodes, a conductive screen interposed between said anodes, said cathode being located at one edge of said screen, and an additional screen partially obstructing the direct paths between saidcathode and each of said anodes,'said anodes being spaced from said first screen a distance comparable to the mean free path of electrons in said gas-filling.

3. A gas-filled discharge tube comprising a cathode having a plurality of sections, a plurality of anodes corresponding in number to said cathode sections, means shielding each anode from another, a plurality of shields connected within said tube to said shielding means, and extending between said cathode sections and said anodes whereby straight line discharge between said anodes and their respective cathode sections is prevented, a shield within said tube surrounding said electrodes and the aforementioned shields'and shielding said tube conductively connecting all of said shields.

4. A gas filled discharge device having an electron-emitting. cathode, a plurality of cooperating anodes, a screen intersecting the direct paths between said cathode and each of said anodes for directing the operating discharges between said cathode and said anodes, and a shield within said tube and surrounding said cathode and anodes.

' 5. A gas-filled rectifier tube for alternating current including an electron-emitting cathode, a cooperating anode spaced from said cathode to provide a positive ionizing gas path therebetween, a conductive element spaced from said anode a distance comparable to the mean free path of the electrons in said gas-filling and connected to said cathode, said element being positioned in substantially non-interfering relation with the positive ionization of the discharge path in the direction of cathode and anode, and a shield within said tube and surrounding said cathode and anode.

6. An electric discharge tube containing a gas, a plurality of anodes, a barrier interposed between said anodes, said barrier being spaced a distance from said anodes comparable to the mean free path distance 01 said gas, an emissive cathode interposed between said anodes, and shielding means within and spaced from the walls of said tube and partially enclosing said cathode and anodes.

7. An electric discharge tube containing a gas,

a plurality of anodes, a barrier interposed between said anodes, said barrier being spaced a distance from said anodes comparable to the mean free path distance of said gas, a thermionic cathode interposed between said anodes, shielding means within and spaced from the walls of said tube and partially enclosing all of said electrodes, and means within said tube electrically connecting said shield and barrier. 8. An electric discharge tube containing a gas, a plurality of anodes mounted on lead wires, a barrier extending between said anodes and between said lead-in wires, the surface of said barrier extending beyond all edges of said anodes for substantially completely electrically isolating said anodes from each other, a thermionic cathode between said anodes, and a shield within and spaced from the walls of said tube and surrounding said cathode and anodes.

9. A gaseous discharge tube containing a plurality of anodes, a barrier extending between said anodes, the surface of said barrier extending beyond all edges of said anodes for substantially completely electrically isolating said anodes from each other, an incandescible cathode between said anodes, extensions on said barrier forming obstructions to straight line electron paths between said cathode and anodes, and a shield within and spaced from the walls of said tube and partially enclosing said cathode.

10. A space discharge device comprising the combination of an envelope, a gas-filling within said envelope, an electron-emitting cathode, a cooperating anode, a conductive element spaced from said anode a distance comparable to the mean free path of the gas, a conductor connecting said element to the cathode, and a barrier extending between said cathode and anode means, and means within" whereby the normal discharge path between the said cathode and anode is lengthened.

11. A rectifier comprising an envelope containing a cathode and a pair of anodes, said ,anodes being mounted on opposite sides of the cathode, an ionizable medium in the envelope at a pressure sufiiciently high to support a gaseous discharge, and shielding means mounted about the cathode and adapted to be maintained at a fixed potential with respect thereto, a part of said shielding means being closed at one end and providing a plurality of discharge openings for permitting the discharge between said cathode and said anodes.

12. A rectifier comprising an envelope containing an ionizable medium at a pressure sufilciently high to support a gaseous discharge, a plurality of anodes and a thermionic cathode, said cathode being subject to contamination by material sputtered from the anode, and means for shielding the cathode from negatively charged anode material and the anode from dislodged disintegration by bombardment, said means comprising a hollow metallic member shielding each anode from the discharge path to the other anode and adapted to be electrically charged and enclosing the cathode except for a plurality of oppositely disposed relatively small discharge openings for permitting a discharge between said cathode and anodes.

13. A rectifier comprising an envelope containing an ionizable medium at a pressure sufiiciently high to support a gaseous discharge, a plurality of anodes and a thermionic cathode, said cathode being subject to contamination by material sputtered from the anode and means for shielding the cathode from disintegrated anode material and the anode from destructive bombardment, said means comprising a hollow metallic member connected to the cathode and enclosing the latter except for a plurality of small discharge openings, each opening facing its respective anode.

14. A space discharge device comprising the combination of an envelope, 8. gas filling within said envelope, an electron emissive cathode, a pair of anodes and means adapted to be electrically charged placed between and shielding said anodes from each other and partially enclosing said cathode, said means having openings through which the main discharge current from said cathode is confined respectively to said anodes over paths deflected from the straight lines between said cathode and anodes, said means providing surfaces exposed to the discharge paths and adapted to reduce contamination of one electrode by another.

15. A gas filled discharge tube including an electron emissive cathode, a plurality of cooperating anodes, and conductive shielding means adapted to be electrically charged and disposed about the cathode, and means forming an opening toward each of the anodes through which the discharge from said cathode is restricted and whereby the discharge path from the cathode to each anode is greater than the mean free path of electrons in the gas filling, a portion of the shielding means being spaced from said anodes a distance comparable to the mean free path distance, said means providing surfaces exposed to the discharge paths and adapted to reduce contamination of one electrode by another.

16. A space discharge device comprising the combination of an envelope, a gas filling liberal a conductive member dividing said envelope-into a plurality of discharge compartments, an anode within each of said compartments, an electron emissive cathode within said gas filling in discharge relation to each of said anodes, and a conductive screen surrounding said cathode and said discharge compartments, the distance of the conductive member from said anodes being comparable to the mean free path of said gas filling.

17. A gas filled discharge tube comprising a thermionic cathode, a plurality of anodes, and means shielding each anode from another and forming a plurality of separate discharge sections between said cathode and the respective anodes,

said means comprising a conductive shield surrounding the cathode and connected thereto.

18. A gas filled discharge tube comprising a thermionic cathode, a plurality of anodes, and means for shielding each anode from another and from destructive bombardment by positive ions created in the discharge path between the cathode and another of said anodes, said means including the emissive cathode and shielding means connected to and partially enclosing said cathode, thereby providing openings which permit the development of a low voltage discharge between said cathode and each of said anodes.

19. A discharge device comprising an envelope containing gas at a pressure sufiicient to support a low voltage discharge, a thermionic cathode adapted to eliminate cathode drop, a cooperating anode, and electrostatic control means extending between said cathode and anode and substantially enclosing the discharge path, the said means being conductive and located to bend the gaseous discharge from a straight line path be tween said cathode and anode.

20. Electrical apparatus comprising the combination of an evacuated envelope containing an anode, a thermionic cathode and electrostatic control means adjacent thereto, a charge of inert gas in said envelope at a pressure sufiicient to sustain a gaseous discharge, said control means being open to the tube atmosphere and comprising metallic surfaces remote from the concentrated discharge path and substantially surrounding the entire length of the discharge path, a portion thereof being spaced from said anode a distance comparable to the mean free path of v the gas, and means connecting said control means.

to said cathode for maintaining it at a potential lower than that of the anode.

21. Electrical apparatus comprising the combination of an evacuated envelope containing an anode, a thermionic cathode and electrostatic control means adapted to cooperate therewith, a charge of inert gas in said envelope at a pressure sufiicient to sustain a gaseous discharge, said control means being open to the tube atmosphere and comprising a metallic surface positioned remote from the concentrated discharge path and substantially surrounding the cathode and anode, said means also having a portion spaced from the anode a distance comparable to the mean free path of said gas.

22. Electrical apparatus comprising the combination of an evacuated envelope containing an anode, a thermionic cathode and an electrostatic control element adjacent thereto, and a charge of inert gas in said envelope'at a pressure suflicient to sustain a low voltage discharge, said control element substantially surrounding the anode and cathode and having a portion also substantially surrounding the entire length of the discharge pat the said element being open to the tube atmosphere and being positioned in substantially non-interfering relation to the low voltage gas discharge but adapted to prevent discharge in the reverse direction.

23. Electrical apparatus comprising the combination of an evacuated envelope containing an anode, a thermionic cathode and electrostatic control means adjacent thereto, and a charge of inert gas in said envelope at a pressure sufiicient to sustain a gaseous discharge, said control means being conductive and disposed about the anode and cathode and having a portion also substantially surrounding the entire length of the discharge path, the said means being open to the atmosphere of said envelope and adapted to reduce the effects of wall charges on the starting of the gaseous discharge, said control means being positioned in substantially non-interfering relation to the gaseous discharge between the cathode and anode.

24. A gas filled discharge tube containing an electron emissive cathode, a plurality of cooperating anodes, and shielding means between said anodes and substantially enclosing said cathode, said means adapted to be electrically charged and providing a discharge opening between the cathode and each of said anodes, said anodes being spaced from the cathode a distance greater than the mean free path of electrons in the gas filling and a portion of said shielding. means being spaced from said anodes a distance comparable to said means free path.

25. A gas-filled discharge tube comprising a thermionic cathode, a plurality of cooperating anodes, and means for deflecting from a straight line path the operating discharge between said cathode and each of said anodes, and shielding each anode from the discharge path to the other anode, said means being adapted to be maintained at controlled potentials and forming a shield within said tube partially enclosing said cathode.

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