US2212849A - High voltage gaseous rectifier - Google Patents

Description

Aug. 27, 1940.

c. M. sLAK ET AL HIGH VOLTAGE GASOUS RECTIFIER Filed Nov. 25, 1938 2 Sheets-Sheet l ifwf ` INVENTOR CZ/V. ZHC/Z L. 7/ BY /(E nimma ATTORNEY C. M. SLACK El' AL HIGH VOLTAGE GAsEoUs RECTIFIER Aug. 27, 1940.

Filed NOV. 25, 1938 2 Sheets-Sheetl 2 /lV/VER C' YIM/DER IDD n mae N WE T 0A.

Patented Aug. 27, 1940 UNITED STATES PATENT OFFICE HIGH VOLTAGE GASEOUS RECTIFIEB Application November 25, 1938, Serial No. 242,210

l tial. equally applicable to high vacuum devices as to Gaseous discharge devices are now employed gaseous discharge devices. extensively in the art as rectiers, inverters and Actual tests made on high potential gaseous control devices; but although capable of passing discharge devices wherein the eiect of autoelecrelatively large currents, they have been restricttronic emission is reduced to a minimum in the ed to voltages within the range oi a few thousand manner above noted are definitely limited in l0 volts. Eiorts have also been made to construct maximum voltage which can be impressed upon high potential gaseous discharge devices employthe electrodes without erratic performance, parlng mercury vapor as the discharge supporting ticularly when operating as a rectifier, which medium and in some instances such mercury vamaximum voltages have actually been found to il por devices when used as rectifiers are operable be materially less than 100,000 volts. Heretofore l5 at voltages as high as 20,000 volts. autoelectronic emission, as before noted, has been One type of high potential gaseous discharge attributed solely to eld emission at the anode; device'at present known to the art is what may but in addition to' the eld al? the anode con.- be termed a. multi-section tube which employs tributinglargelv to autoelectronic emission, there $0 mercury asthe discharge supporting medium, but are other phenomena which contribute to such the disadvantage of such a device resides in its emission. For example, autoelectronic emission size, which makes it cumbersome and -expenmay result from the impinging `0f gamma rays sive to construct inasmuch as the voltage has to or cosmic rays upon the anode of the tube. These be distributed between the various parts. being S0 feW in number may be ignored in Vac- It has also been suggested to construct a uom devices. In gas filled high Volta-gc de- 25 single section high potential gaseous discharge vices, denite structure must be provided. as here device wherein the peak voltage applied between disclosed, to prevent these few autoelectrons from the electrodes is alleged to be of the order of building up llnll ionization l5o o destructive diS- 100,000 volts and in which mercury vapor is charge commonly called flash back in the art.

utilized as the discharge supporting medium. The same conditions hold true for positive ion 80 The recognized dioulty with devices of this bombardment of the anode with subsequent emischaracter has been the inherent phenomenon of sion of electrons whether the positive ions have autoelectronic emission. This phenomenon has their origin at the Cathode 01 Within the gas. heretofore been attributed so1e1y tolthe heating In so far as We are aware. no high potential of the anode by bombardment, during the half gaseous discharge device has been constructed 85 wave of the alternating current oyo1e when the wherein the inherent phenomena of autoelecanode is positive, and the potential gradient at tronic emission is substantially eliminated and the anode.4 During the reverse half wave when wherein consideration has been given to the fact the anode is impressed with a high negative that such occurs by all of the phenomena above polarity, electrons are emitted due to the intennoted. 0n the Contrary, in the Construction n sive iieid at the anode, which must be prevented of prior art, high potential gaseous discharge defrom impinging on the glass envelope, cathode, vices, consideration has been given only to the inor other insulated parts of the device. Otherherent autoelectronic emission due to the ield wise, deleterious results ensue such as disruption effect and, in lieu of eliminating such emission,

of the cathode, liberation of the occluded gases, the effect thereof has Ibeen compensated for in 45 or puncture of the envelope. To prevent the efsome mannen We have found that by Substaniect of autoelectronic emission in which the tially eliminating autoelectronic emission when electrons are emitted normal to the surface, it caused by all of the above noted phenomena we has heretofore been the practice to so position can construct and operate a gaseous discharge an electrode of the device that the autoelectronic device at voltages far in excess of 100,000 volts. 50 electrons are intercepted before impinging upon using either a metallic vaporv or an inert gas as the glass envelope or other insulated parts of the the discharge supporting medium. device. A further suggestion has been that of For example, by employing an anode of high giving the anode surface such a contour or con- Work function having a smooth surface and free 56 ilguration that the electrostatic eld at certain of all edges and points having small radii of cur- 8 Claims.

The present invention relates to discharge devices and more particularly to a gaseous discharge device capable of transmitting relatively large currents and withstanding a high inverse poten- (Cl. 25o-27.5)

points is altered, thereby precluding autoelectronic emission at these points. This eld intensity is, however, independent of the nature of the gaseous medium and its pressure and is vature, concentration of an electrostatic field at the anode is prevented which thus contributes to the elimination of autoelectronic emission. In addition, the pressure of the gaseous medium within the envelope is maintained within a delinlte range so that the mean free path of electrons in the gas is not too small.

To still further minimize autoelectronic emission, the electrodes are formed as concentric cylinders to maintain minimum potential gradients at their respective surfaces. Coupled with the above, the spacing of the electrodes is made relatively small so that even in the event inappreciable autoelectronic emission occurs, the actual path of electron travel between the electrodes is always below or of the same magnitude as the mean free path of the electrons in the gas, thus minimizing collision with gas molecules and preventing positive ion bombardment from reaching a value where flash back occurs when the anode is subjected to a high negative potential.

It is accordingly an object of the present invention to provide a high potential gaseous discharge device capable of passing or blocking voltages in excess of 100,000 volts and wherein either a metallic vapor or an inert gas may be utilized with equal facility as the discharge supporting medium.

Another object of the present invention is the provision of a high potential gaseous discharge device wherein autoelectronic emission at the anode is substantially eliminated.

Another object of the present invention is the provision of a high potential gaseous rectifier device capable of withstanding a high potential in excess of 100,000 volts in the inverse or no-load portion of the alternating current cycle which passes relatively high current with a low voltage drop across the device in the useful or loaded portion of the cycle.

Another object of the present invention is the provision of a high potential gaseous inverter or interrupter tube capable of preventing the flow of current at relatively high voltage and wherein either mercury vapor or an inert gas is utilized as the discharge supporting medium.

A further object of the present invention is the provision of a high potential gaseous dis-charge device wherein the electrodes are so constructed and spaced within critical limits that autoelectronic emission is substantially eliminated, thus enabling operation of the device for long periods of time at voltages in excess of 100,000 volts,

Still further objects of the present invention will become obvious to those skilled in the art by reference to the accompanying drawings wherein:

Fig. 1 is a cross-sectional view of one form of high potential gaseous discharge device which the present invention may take for rectifying alternating current and wherein a iilamentary cathode is utilized;

Fig. 2 is a cross-sectional view taken on the line II-II of Fig. 1;

Fig. 3 is a cross-sectional view of another modification of a high potential gaseous rectifier which the present invention may take and wherein a. cathode in the form of a corrugated edgewisewound helical ribbon is utilized;

Fig. 4 is a cross-sectional view taken on the line IV-IV of Fig. 3;

Fig. 5 is a cross-sectional view of a high potential gaseous inverter or interrupter tube constructed in accordance with the present invention;

Fig. 6 is a cross-sectional view taken on the line VI-VI of Fig. 5, and

Fig. 7 is a graphic illustration showing the relationship of potential gradient on outer cylindrical electrode and inner cylindrical electrode for a given voltage and radius of outer electrode.

Referring now to the drawings in detail, we have shown in Fig. 1 a high potential gaseous rectifier comprising a vitreous envelope 5 having a reentrant stem 6. Sealed to the envelope 5 is a metal cup 'I which constitutes the anode electrode of the device and forms a closure member for the envelope. In the employment of a device as shown in Fig. 1 as a rectifier tube it is essential that it be capable of withstanding a high potential in the inverse or no-load portion of the alternating current cycle and passing current ywith a relatively low voltage drop across the tube in the useful or loaded portion of the cycle.

As previously noted, one of the inherent disadvantages of high potential gaseous rectiers has heretofore been that of autoelectronic emission, which phenomenon results from too intense fields at the anode or the combination of an intense eld and a low work function anode material enabling the passage of inverse current. In order to substantially eliminate autoelectronic emission, according to the present invention the anode 1 is made of a high work function material. One such material we have found to be admirably suited for this purpose is an iron-base alloy containing cobalt and nickel, as shown and described in the patentsto Howard Scott, #1,942,260, issued January 2, 1934, and #2,062,335, issued December 1, 1936, and known under the trade name of Kovar, which alloy can be readily sealed to the vitreous envelope 5.

As shown in the several figures, the anode is of cylindrical form and sealed to the envelope 5, thus forming an integral part of the tube wall. The edge of the anode is 'protected by the glass seal for a distance of approximately 1/8 of an inch so that autoelectronic emission due to intense field concentration at this point is eliminated.

To accomplish this it is essential that the glass seal completely covers the edge of the anode and at the same time does not extend too far inside the anode, otherwise internal puncture through the glass occurs. In addition, the inner surface of the anode is smooth and free of all edges and points having small radii of curvature, which prevents the formation of eld concentration otherwise occurring at such points, and since the edge which has a sharp curvature is insulated by the vitreous envelope, autoelectronic emission is eliminated thereat even under high electrical stress.

The reentrant stem 6 has sealed into the press portion 8 thereof a pair of leading-in and supporting rods 9 and I0 which are connected to the extremities of a filamentary cathode I2 of tungsten or other refractory metal. As will be seen from Fig. 2, this latter electrode is of a substantially N-shape configuration and at its intermediate points is supported by a further pair of supporting rods I3 and I4 sealed into the press 8.

The lamentary cathode I2 is disposed within a metallic cup I5 of suitable refractory metal, such as molybdenum, nickel, Kovarf or the like, which is supported by a further supporting rod IB sealed into the press 8 and connected to the cathode by a bushing I1. The periphery of this cup I5 is rolled to form a flanged recess I8. To protect the leading-in and supporting rods as well as to assist in supporting the cup I E, a metallic shield I9, which may be of the same material .as the cup I5, is supported by a band surrounding the reentrant stem with its upper extremity seating in the flange recess I8.

This shield I9 is thus coaxially located with respect to the anode and so proportioned relative to the latter which, as shown, constitutes an outer concentric cylinder, as to assist in keeping low the electrostatic field or potential gradient at the anode. inasmuch as the shield I9 surrounds the reentrant stem 6 and is connected thereto, a discharge from any of the leading-in and supporting rods 9, I0, I3, I4, and I6 is prevented and the reentrant stem is protected from any bombardment as well as from excessive heat of the filament, which prevents or minimizes sputtering of the filament. Moreover, this complete shielding thus equallzes the spacing between parts of opposite instantaneous polarity so that the electrons in general follow the shortest path between such parts, which we have found is one of the salient features that contributes to the high operating voltages possible with our device.

It is also essential that the spacing between the cathode I2 (and the shield I9 which is connected thereto and may accordingly be considered as an integral part of the cathode) and the surrounding concentric anode 'I be such that the paths of electron travel between the anode 'I and cathode I2 are less than, or of the same order of magnitude as, the mean free path of electrons in the gas. The effect of this is that the distance from any point on the anode I to the nearest point on the cathode I2 (and shield I9) is relatively small. This results in a lowering of the potential gradient at the anode to a value at which autoelectronic emission is inappreciable. Should some autoelectronic emission occur despite the low potential gradient at the anode, the electrons may not follow the absolute shortest path between the anode and cathode. Nevertheless, the electrons are conned to substantially the shortest path with their actual path of travel being below or of the same magnitude as the mean free path of the electrons in the gas. This means that due to the eld eiect the electrons may describe an arcuate path rather than traverse the shortest straight line distance between the electrodes. In so doing such path, being maintained below the mean free path of the electrons in the gas, will minimize collision with atoms of gas. Since collision is thus minimized, no appreciable ionization takes place, which would otherwise cause a deleterious discharge during that portion of the alternating current cycle when a high inverse potential is impressed between the electrodes.

The envelope 5 is exhausted and filled with a dis-charge supporting medium, such asmercury, or an inert gas, such as argon, neon, krypton, etc., after which it may be sealed off at the point 22. The gas pressure within the envelope is kept within a denite range so that with predetermined spacings between the anode and cathode, the mean free path of electrons in the gas will not be too small. We have found that in the case of mercury vapor where an excess is used, the ambient temperature must be maintained between 15 C. and 40 C. Also, when an inert gas is utilized in lieu of mercury vapor, it is preferable to keep the pressure such that all electron paths between anode 'I and cathode I2 are below the mean free path of the electrons in the gas, as before mentioned.

The range of pressure naturally depends on the voltage and currrent requirements and ranges from one to forty microns, depending also on the nature of the gas. For example, at one micron pressure the mean free path of an electron in Vargon is 38.0 centimeters; that of neon, 72.0 centimeters; and in the case of krypton, 40.0 centimeters. If ten microns of argon be consid- -ered a typical pressure, the mean free path is 3.8

centimeters and the preferable maximum spacing for voltages above 50 kilovolts is 3.0 centimeters.

Thus, depending upon the particular inert gas utilized, the mean free path of which is known at one micron pressure, the spacing of the electrodes is made such that, at any given pressure ranging from-one micron to forty microns, the pressure of the inert gas is maintained below that of the mean free path of the `electrons in that particular gas and for a given spacing between the electrodes.

Ingeneral, we have .found that for carrying current, the lower the ionizing potential and the heavier the gas, the better; but for standing high voltage, vjust the reverse of this condition holds true, so that a compromise must be arrived at to satisfy the characteristics demanded in any given tube. Accordingly, by keeping the presa sure of the gas within the range above noted and the spacing of electrodes such that the actual electron-paths are below the mean free path of the electrons in the particular gas utilized, together with maintaining a low potential gradient at the anode, cleanup of the inert gas during operation is prevented and in the case where il mercury vapor is utilized as the discharge supporting medium in lieu of the inert gas, too radical a change in the mercury vapor pressure is' prevented by maintaining the ambient temperature of the device during operation within a definite temperature range.

Also, by proper positioning of the cathode I2 in the cup I5 and properly spacing it from the anode, the voltage drop across the tube during the useful or full-load portion of the alternating current cycle is maintained under volts and preferably below 20 volts. Because of this low voltage drop, high energy positive ion bombardment of the cathode is precluded which, together with the fact that the discharge cannot strike the glass envelope, contributes to the absence of appreciable clean-up of the gas.

VIn Fig. '7 a typical example of the potential gradient at the surface of the concentric electrodes is shown for a given size outer cylinder of 5 centimetersy radius of curvature and for a desired voltage of 100 k. v. The abscissa indicates radius in centimeters required for the inner cylindrical cathode, and the ordinate, kilovolts per centimeter. Curve A shows the potential gradient at the surface of the outer cylinder or anode 'I which increases as the radius of the inner cylinder or cathode I2-I9 is increased.

On the other hand, it will be noted from curve B that the potential gradient at the surface of the inner cylinder or cathode decreases with an increase in radius up to a maximum of approximately 2 centimeters, after which, it again increases with an increase in radius.

It will thus be seen that for a device operable at 100 k. v. and with an outer cylindrical anode of 5 centimeters, the preferable radius of curvature for the innerv cylindrical cathode is 2 centimeters. This gives a potential gradient at the cathode of approximately kilovolts per centimeter and a gradient of approximately 23 kilovolts per centimeter at the anode. Furthermore, the spacing between the adjacent surfaces of the anode and cathode is but 3 centimeters, which is thus below the mean free path of the electrons in the space. In the case of a rectifier, the diameter of the inner cylinder may vary somewhat since the potential gradient at the cathode is not as important as at the anode but when the device is used to block current flow as in an interrupter tube, the diameter of the inner cylinder is very important and consequently must be more precise.

Referring now more specifically to Fig. 3, the structure therein shown is very similar to that above descri-bed with respect to Figs. l and 2, but differs therefrom in the construction of the cathode. In this particular modification, the filamentary cathode has been eliminated and a corrugated helica-lly wound ribbon 23 is employed. As shown, the helix is coaxial with the longitudinal axis of the device with the extremities thereo'f connected to the leading-in and supporting wires 9 and I0 in the same manner as that previously described with respect to the filamentary cathode I2 of Fig. 1.

The cathode 23, which is recessed within the metallic shield I9, is coated with an electron emitting material, such as the oxides of barium, strontium, etc., which gives off a copious flow of electrons when heated. The metallic disc 24, having a slightly smaller diameter than that of the shield I9, is supported immediately above the open end of the shield I9 by a supporting rod or the like 25 welded to the interior walls of the cylinder I9 and to the disc 24 and also electrically and mechanically connected to the leading-in and supporting rod 9 so that the shield I9 and disc 24 have the same potential as that of the cathode 23 during operation of the device.

Since the cathode 23 in the modification shown in Fig. 3 is coated with an electron emitting material, itis preferable to recess the same within the shield I9 so as to prevent undue deterioration .of the cathode by positive ion bombardment which problem is not present with pure refractory metal emitters such as'shown in Fig. 1. The shield I9, as well as the metallic disc 24, serves to almost entirely intercept positive ion bombardment originating outside the shield, and those ions originating in the field-free spa-ce Within the shield do not have sufiicient velocity to cause any damage when they strike the cathode, thus serving to prevent sputtering of the cathode electrode. In all other respects, particularly with regard to spacing of the electrodes, gas pressure, or temperature of operation when a metallic vapor is utilized, this modification is identical to that previously described.

By the construction of a rectifier tube inthe manner above described with reference to Figs. 1 to 4, inclusive, we have found that the voltage drop across the tube is exceedingly low, being of the order of 20 to 30 volts or less, while passing currents of as high as ten amperes, and blocking during inverse half waves at a voltage of 100 kilovolts and utilizing either mercury vapor or an inert gas as the discharge supporting medium. During actual tests of such devices, they have withstood an inverse potential of as high as 250 kilovolts.

Moreover, the discharge between the electrodes is effectively confined within the metal portions of the tube since the electrodes are concentric cylinders, with the anode forming a closure member for the tube. This contributes to the effective passage of' comparatively large currents and the withstanding of high inverse voltages without impairment of tube life.

In addition, due to the low potential gradient a-t the electrodes and the spacing thereof at the gas pressure employed, autoelectronlc emission which would otherwise be caused by the electrostatic field, gamma or cosmic rays, and positive ion bombardment, is substantially eliminated with any such emission being inappreciable and confined to the metal parts of the device.

In Figs. 5 and 6 we have shown a converter or interrupter tube which is substantially similar to the rectifier tube previously described. In this particular type of device the anode 1 forms a closure member for the tube in the manner previously described and the corrugated spiral ribbon cathode 23 is again concentrically disposed in the same manner as in Fig. 3. The envelope, however, is provided with a-n additional extension 26 on the reentrant portion thereof to the upper extremity of which is sealed a metallic grid structure 21.

As noted in Fig. 5, this grid is in the form of a closed cylinder electrically connected to a, leading-in conductor 28 sealed through the press portion 8 of the envelope, in the same manner as the leading-in and supporting conductors. 9 and IIl for the cathode, which is offset and may frictionally contact the inner Wall of the grid 21. The grid is formed of any suitable metal, such as molybdenum, "Kovar, or the like having a high work function and which readily seals to glass, and is provided with a plurality of' perforations 29. In this case the grid 21 is completely insulated from the cathode and must accordingly stand high voltage.

Inasmuch as the grid is the inner of two cylinders, the gradients will necessarily be higher than in the case of the anode of the rectifier tube, with the result that for a given size tube it is not possible to control as high a voltage as that which can be rectified with the construction of the preceding figures. Again, however, there is a certain optimum diameter for the grid with respect to the diameter of the outer cylindrical anode which must follow the gradients as shown, for example, in Fig. '7, even more closely for blocking than when operating as a rectifier. Also, as to the relative spacing between the grid and the anode, it is necessary to keep the shortest distance from any point on the grid to the nearest point on the anode small.

Again, as in the case of the rectifier tube, the surface of the grid structure must be kept relatively smooth and sharp corners, points and edges must be avoided, which it will be noted is again accomplished by the edge of the grid being surrounded bythe glass of the reentrant stein in the same manner as previously described with respect to the seal of the anode to the envelope.

By the application of suitable voltages between the grid and cathode, the flow of current between the cathode and anode is prevented until the desired potential has been built up across the tube and at the desired or preselected moment the potential of the grid can be altered to cause a discharge, after which the tube functions as a rectifier until the potential of the grid is again altered to prevent further discharge.

In utilizing an inert gas as the discharge supporting means in the application oi the tube as an inverter or interrupter tube, the gas is more readily subject to clean-up because the current passes at considerably higher voltages than in the case of pure rectification. However, in varvious applications ofthe tube the actual passage of current at this high voltage occupies such a short period of time. even though it be assumed that a discharge occurs onalternate half waves of the alternating current cycle, the tube is able er, mercury is subject to ambient temperature limitations. Also, for use as an inverter as distinguished from an interrupter tube, mercury vapor appears preferable due to the propensity toward clean-up of the inert gas, particularly under invertertube operating conditions.

It thus becomes obvious to those skilled in the art that we have provided a high potential gaseous discharge device capable of passing relatively large currents and of withstanding high inverse potentials. Moreover, by the proper selection of an anode material having a high work function and the spacing ofthe electrodes, which are in the form of concentric cylinders, so that the spacing is preferably less than the mean free path of the electrons in the gas, and

by the maintaining of minimum potential grad- A lents at the surface of the electrodes, we have substantially eliminated autoelectronic emission even though due to field emission, positive ion bombardment and the eiect of gamma and cosmic rays, is coniined to a minimum.

'I'he elimination of such emission enables operation of the device utilizing either a metallic vapor or an inert gas as the discharge supporting medium without clean-up of the inert gas or appreciable variation in the temperature of operation of the device. Furthermore, the surfaces of the electrodes being smooth and free of all points and edges, due to insulation thereof by the vitreous envelope itself, prevents the iornation of electrostatic field concentration which would otherwise cause puncture and contributes to the passage of large currents at high potential without destruction of the tube or shortening its useful life.

Although we have shown and described several embodiments of our present invention, we do not desire to be limited thereto as various other modifications o f the same may be made without departing from the spirit and scope of the appended claims.

We claim:

l. A high potential gaseous discharge devicecomprising a vitreous envelope having an ionizable medium therein and provided with electrodes energizable from ai high potential source of electrical energy, said electrodes including an anode and a thermionic cathode disposed substantially concentric to said anode to produce a low electrostatic eld at the anode and having a spacing therebetween such that at the pressure of the ionizable medium the distance between parts of opposite instantaneous polarity through which any electrons originating at the anode travel under the influence of the electrostatic ileld is below the mean free path of electrons in the ionizable medium, and said electrodes having such a radius of curvature at any point that autoelectronic emission from the electrode subjected to high negative potential is inappreciable.

2. A high potential gaseous discharge device comprising a vitreous envelope having an ionizable medium therein and provided with a.

thermionic cathode and a substantially concentrically disposed cylindrical anode of high work function forming a portion of said envelope and energizable from a high potential source of electrical energy, said anode and cathode having a spacing therebetween such that at the pressure oi the ionizable medium the distance between parts of opposite instantaneous polarity through which any electrons originating at the anode travel under the iniuence of the electrostatic ileld is below the mean free path of electrons inthe ionizable medium, and said electrodes 'having such a radius of curvature at any point that the potential gradient at the anode is maintained below a value at which appreciable autoelectronic emission occurs when the anode is subjected to a high negative potential.

3. A high potential gaseous discharge device comprising a vitreous envelope having an ionizable medium therein and provided with electrodes including an anode and a thermionic cathode energizable from `a. high potential source ,of electrical energy, said electrodes being in the form of concentric cylinders to produce a low electrostatic field at the anode and having a spacing therebetween such that at the pressure of the ionizable medium the distance between parts of opposite instantaneous polarity through which any electrons originating at the anode travel under the influence of theelectrostatic held is below the mean free path of electrons in the ionizable medium and the discharge is restricted entirely between metal parts oi the device, and said electrodes .being void of all sharp ypoints and edges having small radii of curvature to maintain the potential gradient at the electrode subjected to a high negative potential below a value at which appreciable autoelectronic emission occurs.

4. A high potential gaseous discharge device comprising a vitreous envelope having an ionizable medium therein and provided with a. cylindrical anode of high work function and-forming an integral part of the wall of said envelope, a cathode for supplying a copious ow of electrons when heated, and a cylindrical shield concentrically disposed relative to said anode surrounding said cathode and connected thereto to produce a low electrostatic eld at said anode for restricting the direction of electron ow substantially to the shortest straight line path between said cathode and anode, said anode and cathode having a spacing therebetween such that at the pressure of the ionizable medium the distance between parts of opposite instantaneous polarity through which any electrons originating at the anode travel under the influence of the electrostatic iield is below the meanY free path of electrons in the ionizable medium, to prevent the origination of detrimental positive ion borbardment at the cathode or within the ionizable medium suflicient to cause ash back during operation of the device, and said anode and shield having such a radius of curvature at any point that the potential gradient at the anode is maintained below a value at which appreciable autoelectronic emission occurs when the anode is subjected to a high negative potential.

5.'A high potential gaseous discharge device comprising a vitreous envelope having an ionizable medium therein and provided with a cylindrical anode of high work function and forming an integral part of the wall ot said envelope, a cathode for supplying a copious ow of electrons when heated, leading-in and supporting wires extending through a press in said envelope, and a cylindrical shield concentrically disposed relative to said anode and surrounding said cathode and leading-in conductors. and said shield being connected to said cathode and said press to produce a low electrostatic field at said anode for restricting the direction of travel of any electrons originating at the anode substantially to the shortest path between said cathode and anode, said anode and cathode having a spacing therebetween such that at the pressure of the ionizable medium the distance between parts of opposite instantaneous polarity through which any electrons originating at the anode travel under the iniiuence of the electrostatic field is below .the mean free path of electrons in the ionizable medium to prevent the origination of detrimental positive ion bombardment at the cathode or within the ionizable medium to cause flash back during operation of the device, and said anode and shield having such a radius with respect to each other that the potential gradient at the anode is maintained below a value at which appreciable autoelectronic emission occurs when the anode is subjected to a high negative potential.

6. A high potential gaseous discharge device comprising a vitreous envelope having an ionizable medium therein and provided with an anode, a cathode and a control electrode energizable from a high potential source of electrical energy for generating an electrostatic eld at said anode, said anode and control electrode having a spacing therebetween such that at the pressure of the ionizable medium the distance between said anode and control electrode through which any electrons originating at the anode travel under the inuence of the electrostatic eld is below the mean free path of electrons in the ionizable medium, and said electrodes having such a radius of curvature at any point that electronic emission from the electrode subjected to high negative potential is inappreciable and the potential applied to the control electrode is normally of such value as to prevent the ow of electrons from the cathode to the anode, and said control electrode being operable upon a reversal of the polarity of the potential applied thereto to cause the ow of electrons from the cathode to the anode to be restricted to substantially the shortest path therebetween.

'7. A high potential gaseous discharge device comprising a vitreous envelope having an ionizable medium therein and provided with a cathode, a cylindrical anode of high work function forming a portion of said envelope energizable from a high potential source of electrical energy for generating an electrostatic iield at said anode, a grid electrode interposed between said anode and cathode and completely surrounding said cathode,v and said grid having a spacing relative to the anode such that at the pressure of the ionizable medium, the distance therebetween through which any electrons originating at the anode travel under the influence of the electrostatic fleld is below the mean free path of electrons in the ionizable medium, and said anode and grid having such a radius of curvature at any point that the potential gradient at the anode is maintained below a value at which appreciable autoelectronic emission occurs when the anode is subjected to a high negative potential, and said grid being operable when impressed with a high negative potential to prevent the ow of electrons between the cathode and anode and thereafter causing the ilow of electrons to be restricted substantially to the shortest path therebetween upon the reversal of the potential applied to said grid.

8. A high potential discharge device comprising a vitreous envelopehaving an ionizable medium therein and provided with an anode, cathode and grid energizable from a high potential source of electrical energy for creating an electrostatic eld at said anode, said anode and grid being in the form of concentric cylinders having a spacing therebetween such that at the pressure of the ionizable medium, the distance therebetween through which any electrons originating at the anode travel under the inuence of the electrostatic field is below the mean free path of electrons in the ionizable medium, said anode and grid being of a metal having a high work function, said anode being sealed to said envelope and forming a part thereof, and said grid forming a closure member for the thermionic cathode and being sealed to a reentrant portion of said envelope and provided with a plurality of openings through which the electrons flow from the cathode to the surrounding anode, and said grid being operable when impressed with a high negative potential to prevent the flow of electrons from the cathode to the anode and operable upon a reversal of the polarity to cause the flow of electrons from the cathode to the anode and to confine the same substantially to the shortest path therebetween.

CHARLES MORSE SLACK. LOUIS FREDERICK EHRKE.

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