US2535886A - Electronic switch - Google Patents

Description

Dec. 26, 1950 w. R.'BAKER ETAL `?,535,886

ELECTRONIC SWITCH Filed July 26, 1949 TR/GGER INPUT INVENTORS. W/LL/AM BAKER e2 QUENTIN A. KER/vs A Tra/:wen

Patented Dec. 26, 1950 UNITED STATES PATENT OFFICE ELECTRONIC SWITCH William R.. Baker, Berkeley, and Quentin A. Kerns, Oakland, Calif., assignors to the United States of America as represented by the United States Atomic Energy Commission Application July 26, 1949, Serial No. 106,914

(Cl. Z50-27.5)

15 Claims.

and of these, certain types, namely spark gaps,

mercury vapor discharge devices, and hydrogen discharge devices have proven the most satisfactory for the switching of large amounts of power. Of these three, research has advanced hydrogen thyratrons as the most feasible in View of the multitudinous and exacting requirements which must be satised in addition to the requirement of large power rating. As a result of this research hydrogen discharge devices capable of passing a maximum pulsed anode current of approximately 350 amperes at 16 kilovolts are now known in the art. It appears that improvements in the techniques of tube construction and assembly may even double the power rating of these tubes and may also lengthen the life of these tubes. However, beyond this it appears that fundamental limiting factors preclude further improvements of hydrogen discharge devices of the type now known in so far as power ratings are concerned. For example, the destructive effects of inverse anode voltage limits not only the repetition rate of pulsed operation but also in part limits the maximum allowable forward anode voltage. Also the maximum current is in part limited by the amount of cathode emitting surface which may be made available, which in turn is limited by the practical limitations on size of the tube. Further undesirable limitations arise from the extensive control and baflling structure that has been found necessary to properly control discharge with a high potential impressed on the anode.

Thus in order to satisfy the ever increasing demands of industry for electric switches having larger and larger power ratings, it is necessary that some new and dilerent apparatus be advanced which circumvents these present limitations.

It is therefore an object of the present invention to provide an improved method and apparatus for the switching of thousands of amperes of current.

It is another object of the present invention to provide an electric switch capable of operating at a high repetition rate without damage from high inverse plate voltage.

It is still another object of the present invention to provide an improved electronic switch capable of passing hundreds of megawatts of pulsed power.

A further object of the present invention is to provide an electronic switch of large power rating having a precisely controllable time of tiring.

A still further object of the present invention is to provide an electronic switch wherein the current is substantially independent of emitting surface limitations.

Yet another object of the present invention is to provide an electronic switch of the gaseous discharge type having only two main elements to support and control the` discharge thereof.

Many other objects and advantages oi the invention will become apparent from the following description taken in connection with the included drawing wherein Figure 1 is a sectional elevation of the switch taken on a median plane, Fig. 2 is a sectional plan view of the switch taken as indicated by the line 2 2 of Fig. 1, and Fig. 3 is a diagram of electrical connections adaptable for use with the illustrated embodiment of the invention. With reference to Figs. 1 and 2, it may be noted that the envelope of the present invention preferably consists of a base unit l and a plate 2 separated by an insulating cylinder 3. The base unit l is in the form of a cup or a cylinder with one end closed, and has a rim or flange il projecting outwardly therefrom about the circumference thereof a short distance from the open end. Upon this flange i rests the insulating cylinder 3 whose inner diameter is substantially equal to the outside diameter of the base unit whereby lateral motion of the insulating cylinder with respect to the base unit is prevented when the insulating cylinder is resting upon the ange of the base unit. The plate 2 is also formed with a flange B about its periphery and the under surface of this flange rests upon the insulating cylinder 3 when the switch is assembled. Also, the outer diameter of the plate is substantially equal to the inner diameter of the insulating cylinder thereby preventing lateral motion therebetween when assembled. The insulating cylinder 3 is separated from the flange 6 of the plate 2 by a gasket 5 and from the flange 4 of the base unit l by a similar gasket ID thereby sealing oli the interior of the envelope and making these connections gas tight and vacuum tight. The plate 2 may be provided with a circumferential slot in the iiange thereof for the insertion of a small pipe l2 having inlet and outlet connections as shown in Fig. 1 and secured therein by any suitable means such as soldering. A similar ypipe Il also having inlet and outlet connections may also be secured to the under surface of the flange i on the base unit i. These pipes may be utilized to carry cooling water for the purpose of aiding in the dissipation or" heat generated in the device.

Interior to the envelope described above is a disc l mounted upon the base unit l and separating the interior of the base unit from the plate 2. The disc shown in the embodiment depicted in the drawing comprises a circular lid or cap engaging the open end of the base unit I and secured thereto by means of mutually cooperating threads on the periphery of the disc and the inner surface of the base unit wall; however, it will of course be appreciated that this disc may have a variety of coniigurations and may be secured in a variety of ways, all within the spirit and scope of the invention.

Further consideration of the illustrated embodiment of the disc reveals that it is circular with a substantially square transverse opening formed in the approximate center thereof. VEquispaced transverse keyways are formed along two sides of the square opening and a number oi straight bars 8 are mated therein whereby the bars are firmly secured. These bars 8 define a number of identical parallel transverse slots 9 through the disc. It will of course be appreciated that various other modes `of construction may be utilized, such as milling the slots directly in the disc l or inserting a slotted member in the disc.

The disc 'l is oi particular importance to the present invention and care should be exercised not to confuse its function to that of a conventional grid electrode. The disc has two primary functions and acts in entirely different capacities when performing these functions as is set iorth in detail hereinafter. In order to emphasize this point and also to refrain from referring to the disc as such, which is misleading inasmuch as the coniiguration is not limited to a disclike shape, the disc has been given a particular name. The name chosen is biacting electrode or in short, biactor, to indicate that it acts in two separate capacities. It is to be understood that this name has been coined to stand for the element 'i in this invention, and as used in the remainder of the specication and in the claims is intended to embrace all configurations and embodiments of the member l which falls within the scope of the present invention.

interior to the base unit i is situated a trigger plate 2i which is mounted on a trigger support rod 22, which is in turn joined to a trigger supply lead 23. The base unit l is provided with an opening 2li through which the trigger supply lead projects. This opening 2li is threaded'and has a shoulder thereabout against which rests a lead washer 26. A brass tting 2li threadably engages the base unit l at the opening 24 and when totally engaged crushes the lead washer 2t between the shoulder on the base unit opening 2d and the fitting 2l, thereby providing a gas tight sea at the opening 2e. The trigger support rod 22 is attached to a trigger support nut 25 which is in turn threaded onto a metal bolt 29 and heid in place by a lock nut 3i. The bolt 29 has a circular portion removed from the head thereof to receive the end of a metal-glass seal 32, the other end of which is secured to the f1tting 2i. Metal shims 33 are inserted between the head of the bolt 29 and the trigger support nut in order to properly center the trigger plate with respect to the walls of the base unit ionizab'le atmosphere.

l. The ion supply lead 23 thus supports the trigger plate 2i in position and insulates it from the base unit by the glass in the metal-glass seal. The trigger plate may be energized by a coaxial cable 35 which is inserted in the ion supply lead 23 and which is attached to a conical depression formed in the head of the bolt 29 as shown in Fig. 1. It will of course beappreciated that the details of the trigger supply lead are not vital to the invention and that any suitable element` lor combination of elements may be substi-tutedtherefor as long as the functions attributed thereto in the following disclosure are capable of being performed thereby.

In order for the present device to have a Very rapid current rise at the point of iiring it is necessary for the dischargeto take place in an This atmosphere may constitute any one of a number of commercially available gases or vapors; however, it has been found particularly advantageous to utilizelow pressure hydrogen in this connection as deionization time is minimized thereby. The particularembodiment o1" the invention depicted in the drawing employs circulating hydrogen which is preferably circulated through the device,` as by the pipes 3d shown in Figsl and 2, at a pressure of the order of a few hundred micronsi and continually iiltered exterior to the device by any suitablekmeans (not shown). It will oi course be appreciated vthat other gases or vapors such as helium maybe utilized for this purpose; however, rin general it is advantageous toemploy an atmosphere in which the electron mean-free path is-a maximum and the deionization time is a minimum.

The surfaces of tne plate 2 andthe biactor 'I are parallel and the spacing therebetween lis quite small as explained below. About this space between the plateand disc is situated a guard ring il which may be maintained in position by any suitable means such as spring elements 652 attached thereto and bearing against the insulating cylinder 3 as shown in Fig. 2. The base unit i has a stepped outer periphery about the top of' its wall and the plate 2 hasan Vinverted step periphery about its lower circumference .as shown in Fig. 1, thereby providing a space for the placement of the guard ring 4|.

The plate 2, base unit Land biactor l are preferably all formed of a metal having a high coeicient of heat conductivity, and furthermore are advantageously formed oi a metal having a small amount of'occluded gases. The property-of good heat conductivity coupled with the cooling means described above prevents damage tothe elements of the Vdevice under high power operation, `and the absence of occluded gases is important'in the revention of contamination oi the atmosphere within the device. Numerous metals satisfy the above prerequisites with oxygensfree copper being one of the most available and least'expensive. .Also oxygen-free copper is not subject to the disintegration which results from the use or" ordinary copper Ain a hydrogen atmosphere.

It may be further noted that the structure il'- lustrated minimizes the lead inductance of the device which is particularly advantageous in certain applications employing pulsed operation.

It is to be noted that conventional elements are utilized to supply the operating potentials oi the present invention, and thusno description thereof is included; however, the following is presented in combination withFig. 3 as a-brief description-of the connections `and potentials asso- 5. ciated with the device. The base unit I, and consequently the biactor I` to which it is electrically joined, is grounded. The positive operating potential of the invention is applied to the plate 2, and the trigger 2i is energized through the coaXial cable 35. The load is connected between the plate 2 and ground and for pulsed operation may constitute a pulse condenser 5! in series with the plate 2, and the primary of a pulse transformer E2 in series therewith to ground.

Considering now the operation of the invention, it is to be noted that the trigger electrode 2l is energized in order to produce a glow discharge in the space between the trigger electrode 2|` and the biactor l. The glow discharge may be produced by an alternating current voltage applied to the trigger electrode, or a direct current voltage may be utilized ii adequate precautions are taken to conne the resulting glow discharge to the space provided therefor. The present embodiment utilizes a radio-frequency voltage as a lesser amount of voltage is required and also the rapid reversal of voltage polarity reduces the distance traveled by the electrons comprising the glow discharge and thus they are more easily contained in the space provided therefor. The glow discharge provides a large supply of electrons which are available to ionize the gas in the region between the anode and biactor; however, these electrons are prevented from ionizing the gas and constrained to remain in the space between the biactor 'i and the trigger electrode 2i by the action of the biactor. This member is at ground potential and by virtue of the ratio of the slot width to slot depth masks he trigger electrode from the plate 2, or in other words, the field from the positively charged plate 2 is prevented from extending down past the biactor by virtue of the constriction of the slots in the biactor, and thus not enough electrons pass through the biactor to cause critical ionization, that is, sumcient ionization to discharge the device. Therefore, prior to discharge, the device has a large supply of free electrons hovering over the trigger electrode and a highly positive potential upon the anode which is prevented from attracting these electrons by the action of the grounded biactor.

Discharge of the device is initiated by the application to the trigger electrode 2l of a negative voltage pulse having a fast rise time. The negative voltage pulse repells the free electrons forming the glow discharge and drives them toward the biactor "i, Thus, initially after application of the negative voltage pulse to the trigger electrode the biactor is likened to an anode with the iree electrons moving toward it. However, a quantity of `these electrons pass through the slots 9 in the biactor and into the region inuenced by the positive field about the plate 2 whereby they are forceably attracted to the plate. The movement of a large number of free electrons from the vicinity of the trigger electrode 2| to the plate 2 ionizes the gas in the device. It is to be particularly noted at this point that the trigger electrode serves only to provide the initial supply of electrons in the glow discharge and to trigger the main discharge by repelling these electrons when energized by a negative voltage pulse. Following the initial ionization and breakdown the trigger electrode serves no further purpose. The trigger electrode is not a cathode within the generally accepted meaning of the term as it does not supply electrons during the course of discharge or operation of the device, but to the con'- trary serves only to initiate the discharge.

The discharge of the device is in the nature`of a glow discharge and the electrons forming the output current are produced by a number of interrelated actions. First, the ionization of the gas in the device frees a large number of electrons which are attractedto the plate 2 to form a part of the current. Second, the positive ions formed by the ionization of the gas in thev space between `the plate 2 and biactor l are attracted to the biactor 'l and owing to the action of the electric iield between the plate and biactor impinge upon the biactor with su'icient velocity to produce secondary emission of electrons from the biactor which `are also attracted to the plate to form a portion of the current. Third, the presence of a dense plasma between the plate 2 and biactor 1 results in eld emission from the biactor which also produces a portion of the output current. It may be further noted that following initiation of discharge the presence of plasma allows the electric field from the plate to extend down into the slots in the biactor and even slightly into the space below1 the biactor. This results in an increase in the effective length of the field with the resultant production of more ion pairs than would ordiarily result in the limited space between the biactor and the plate. Thus the circuit of the device when conducting is from the biactor 'l to the plate 2., through the load and ground return to the biactor.

Particular requirements should be kept in mind with regard to the construction of the pres.

ent invention. For example, the spacing between the biactor and the plate 2 must be maintained less than the mean-free path of electrons in the atmosphere within the device in order that the atmosphere in this region will not be ionized by spurious free electrons. The biactor-plate spacing must also be maintained greater than a critical minimum at which an excess of eld emission occurs from the biactor to the plate prior to triggering of the device. Thus the biactor-plate spacing may be easily,1 computed for any particular device with a knowledge of the type of atmosphere, atmospheric conditions, and desired anode voltage. With regard to the biactor structure, it is also advantageous to limit the slot width to the same dimens sion as the biactor-plate separation in order to prevent premature discharge of the device as a result of ionization of the internal atmosphere. As an example of an electronic switch embodying the principles of the present invention the following data is presented: biactorplate separation, 0.09, inch, biactor slot depth, inch; biactor slot width, le inch; atmosphere, hydrogen at a pressure of 20G-1000 microns of mercury; and plate voltage approximately 20 kilovolts.

It is to be noted that a number of factors tend to improve the ring characteristics of the device. With regard to the jitter time, or variations in the time after application of the trigger pulse that ring occurs, it is to be noted that it may be expressed as a function of the probability of free electrons causing ionization. This probability is dependent in part upon the energy imparted to the free electrons and in part on the number of free electrons provided. The present invention provides a tremendous reservoir of free electrons in the glow discharge above the trigger electrode and also insures that these electrons will cause ionization by the fact that the energy imparted thereto by the iield of the plate into which `they. are'projected isfar in excess of'that necessaryto produce ionization. Thus the probability of ionization ,is materially increased in the present device, and the jitter timeis consequently reduced; it being vof the orderof a few muli-microseconds.

A uniforindischarge from the disc .to the plate is insured by a combination ci the following effects. `In the vfirst piace theelectron cloud forced up through the biactor by the trigger electrode penetrates all of the openings therein. and thus initiates an even Land uniform discharge from the disc. Also, `if during discharge an arc should occur from one ofthe bars B of the biactor l tothe plate 2, the voltage between the plate and this bar .would immediately be reduced. Thus the higher voltage existing between the plate and the adjacent bars would immediately expand the discharge and extinguish .the arc.

It is also to be noted that all spacing between metaland insulator cylinder is less than the mean-free path of electrons in the atmosphere internal to the device at the pressure maintained therein, thereby precluding the possibility of untimely ionization from stray Vfree electrons. Furthermore,r the possibility of breakdown across the insulator Ais minimized by placing the insulator metal contacts in relative held-free regions.

Thus a brief` resume of the operation reveals that when the device is nonconducting a glow discharge is maintained above the trigger electrode 2i by the application of a small radio-frequency voltage thereto. The base unit i and attached biacting electrode l are maintained at ground potential and a highly positive potential is applied to the plate 2. The biactor 'i electrically rmasks the electrons forming the glow discharge from the strong electric field about Vthe plate 2 and thus prevents critical ionization of the atmospherewithin the device and thereby prevents discharge of the device. The device is rendered conducting by the energization of the trigger electrode with a pulse of negative voltage'which drives the electrons coinprising the `giov/discharge up through the slots in the biactorl and ionizes Vthe atmosphere in the device. This overcomes the restraining action of the biactor and the biactor then assumes the opposite function of sustaining the discharge which continues until the polarity of the `plate 2 is reversed.

From the yforegoing disclosure of the invention it will beapparent-to `those skilled in the art that thepresentinvention fulfills the objects specilically recited. An almost unlimited supp-ly of electrons is produced within the device, both prior Yto and following the actual discharge. Thus 'jitter time is minimized and output current is maximized. Also as a result of the simple rugged construction of elements possible with the present invention the usual difficulties at.- tending-highcurrent operation are eliminated. Furthermore, large inverse voltages do notinaterially affect the tube operation'or life as the cornplicated, structurally weak elements of prior dischargedevices have Ybeen eliminated and their successors are so constructed as to ce relatively undamaged even by reverse discharge. Also the novel construction employed, the biactor structure in'particular, enables the device to operate withra potential of the order of twenty kilovolts on .theplate Thus with a pulsed current capacity of the order of tens of thousands of amperes thedevice-is quite capable ofhandling hundreds of megawatts of .pulsed power.

It willof course beappreciated that the potentical purposes issubstantially.indestructible as times .by` the vincorporation of minor structural variations .within the scope .of the invention. Any vnumber of separated discs .may be employed and under experiment the present device. so modied has operatedsatisfactorily with 200,900 kilovolts applied. V,to the plate. In this respect. it may be noted that-additional means such as. suitable electrodes may be advantageously employed to-reduce the electron velocity when operating with such high potentials.

The trigger plate 2| serves the `purpose of sup-` plying electrons to initiate the discharge ofthe device and it willbe appreciated that numerous types of electrodes could be employed `in this respect. An oxide-coated electrode could. beV employed; however, certain-disadvantages aredattendant uipon this type of electron source. Also a loop of wire -or a needle could .be employed in place of the trigger plate; however, a plate 2 i, as shown, formed of a suitable material such `as tungsten has an extremely long life and for practical purposes is substantially indestructible as an electron source. Also the absence of sharp corners on the trigger electrode shown `precludes a tendency or these corners to cause initial spot-` ting of the .discharge4 in the device and .is .thus advantageous although not compulsory. It is also possible to eliminate the use of filament powerv by utilizing field emission from needle points by providing a large. .voltage .pulse tothe y points; however, although this may be advantages-us in certain-applications .there are certain attendant disadvantages sucnas increased jitter time and the requirementof high trggeryoltages.

Although the illustrated embodiment of ,the invention utilizes `a circula-ting gasY systemritV isof course possible for a closedsystemto beused. With a closed systemdiiferent insulating kand clamping Vmeans maybe advantageously employed and it may valsobe desirableto utilizea gas. reservoir in such .a system. However, only he application of basic. electronic, knowledge would be necessary in order to construct an electronic switch having a vvsealed system inaccordance withthe principles of the .present invention and thus no further description of such an embodiment is included herewith.

Whilethe foregoing descriptionhas ,setforth the vpreferred embodiment of the yinvention it will, of course, be apparent to those `skilled in the art that many modifications are possiblewithin the spirit and ,scope of the invention and it is not intended to limit the invention to the details disclosed except asmay be defined in the following claims.

What is claimed is:

, i. An electronic switch comprising an envelope containing an ionizalcle atmosphere, an anode, a trigger electrode, and a biacting electrode therebetween, said biacting electrode having apertures tlieretl'irough for thc passage of ionizing discharge from said trigger electrode and. being electron emissive only following ionization of said atmosphere thereby to support electrical discharge to said anode.

2. An electronic switch including an envelope comprising a metal cup, a metallic plate, and an insulating cylinder separating said cup and plate, an ionizable atmosphere vwithin ,said envelope, a trigger electrode within said cup, and a biacting `electrode withinsaid envelope separating said plate and said trigger electrode, said biacting electrode having transverse slots therethrough and being separated from said plate by a distance less than the mean-free path of electrons in the atmosphere of said envelope at the pressure therein.

3. An electronic switch comprising a gas-tight envelope containing a low pressure atmosphere of ionizable gas, a trigger electrode controllably providing high Velocity electrons to initiate ionization of said atmosphere, a biacting electrode preventing ionization of said atmosphere in the absence of said high velocity electrons and sus-- taining an electric discharge following the provision of said high velocity electrons, and a plate for the receival of said discharge.

4. The combination comprising an envelope containing an ionizable atmosphere, an anode having a highly positive potential impressed thereon, an electron source in close proximity with said anode, a biacting electrode separating said anode from said ion source, said biacting electrode being maintained at substantially the same potential as said electron source and having slots of a large depth to width ratio therein for the passage of electrons whereby said electrons are restrained from reaching said anode, and means impressing a negative potential upon said electron source, thereby imparting a high velocity to said electrons for overcoming the restraining action of said biacting electrode.

5. An electronic switch comprising an envelope containing an ionizable atmosphere, an anode, a trigger electrode acting to ionize said atmosphere, and a biactor restraining ionization of said atmosphere prior to the action of said trigger electrode and sustaining electric discharge between said biactor and said anode following the ionizing action of said trigger electrode.

6. An electronic switch comprising an envelope containing an ionizable atmosphere, an anode maintained at a highly positive potential, an electron source maintained at substantially ground potential and having a further controlled negative potential instantaneously impressed thereon whereby said atmosphere is ionized, and a biacting electrode between said anode and electron source, having openings therethrough of a large depth-to-width ratio whereby said electron source is electrically masked from said anode prior to ionization of said atmosphere, said biacting electrode being maintained at a substantially ground potential thereby supporting electric discharge to said anode following ionization of said atmosphere.

7. An electronic switch comprising an envelope containing an ionizable atmosphere and three electrodes, the first of said electrodes being maintained at a positive potential, the second of said electrodes comprising a source of electrons and having a controlled negative potential instantaneously impressed thereon, and said third electrode being interposed between said rst and second electrodes and having openings therethrough for the passage of said electrons, said openings being constricted to control said electron passage and thereby control ionization of said atmosphere and said third electrode being grounded whereby electric discharge is maintained between said rst and third electrodes following ionization of said atmosphere.

8. An electronic switch comprising an envelope containing an ionizable atmosphere, an anode, a trigger electrode operating solely to initiate ionization of said atmosphere, and a perforated `biacting electrode disposed between said anode and said trigger electrode, said perforations being constricted to prevent ionization of said atmosphere prior to the operation of said trigger electrode, and said biacting electrode being maintained at a negative potential with respect to said anode whereby electric discharge is maintained therebetween following ionization of said atmosphere.

9. A method of` switchingelectrical energy comprising the steps of establishing a potential difference region in an ionizable atmosphere, producing an electron glow discharge, preventing electrical energy transfer by establishing a t held-free region and separating said glow disload, an electron source at a negative potential with respect to said anode, a grounded biacting electrode separating -said anode and said electron source and electrically masking said electron source from the positive potential of said anode, said biacting electrode having constricted transverse openings therethrough for the passage of an ionizing discharge, and trigger means controllably accelerating electrons from said electron source toward said biacting electrode whereby an ionizing discharge is produced through said biacting electrode and electrical discharge is maintained between said anode and said biacting electrode.

ll. An electronic switch comprising an envelope containing an ionizable atmosphere, a planar anode within said envelope and having a large heat capacity, a planar perforated biacting electrode disposed adjacent and parallel to Said anode, said biacting electrode having a large heat capacity and being of rugged construction, and a trigger electrode separated from said anode by said biacting electrode and thereby electrically masked from said anode, said trigger electrode producing electrons for ionization of said atmosphere between said anode and biacting electrode upon the impression of a trigger voltage thereto, and said biacting `electrode and anode being adapted to sustain electric discharge therebetween over the entire mutually presented faces thereof upon ionization of said atmosphere.

12. An electronic switch as claimed in claim 1l further characterized by said anode and biacting electrode being formed of copper.

13. An electronic switch comprising an envelope containing an ionizable atmosphere, an anode having a large planar surface, and a biacting electrode having a large planar surface in close proximity with an parallel to the planar `surface of said anode, said biacting electrode having apertures therethrough for controlling the passage of an ionizing electron discharge and said anode and biacting electrode being adapted to have a large potential diierence impressed therebetween whereby electric discharge is maintained between the adiacent planar surfaces thereof following ionization of said atmosphere. `14. An electronic switch comprising an envelope containing an ionizable atmosphere, a trigger electrode emitting electrons, an anode at a high positive potential relative to said trigger electrode, and a perfcrated biacting electrode disposed intermediate said anode and trigger electrode and electrically masking said trigger electrode. from. said anode for a maximum potential difference therebetween and supporting electrical discharge ta said anode for, some greater potential difference causing' arlzatien of said atmosphere.

15. A method of electronic switching in an 10 ionizable atmosphere comprising establishing Va rst region having ,a high potential gradient therethrough and having a dimension in the direction of said gradient of less than the mean tree path of. electrons in said atmosphere,y establishing a4 second region adjacent said first region; and having a substantially zero potential gradient therethrough,l oontiollably introducing copious quantities of high velocity electrons into said second region and directed toward said rst m 12 region whereby ionization of, said atmosphere' is accomplished, and subsequently maintaining electric discharge. across saidiirstv region.

WILLIAM Rn BAKER. QUENTIN A.- KERNS.y

REFERENCES CITED The following referencesxarezo. record in the le, of: this patent z- UNITEDV STATES PATENTS Number Name Date 2,038,341 Bruche Apr; 2-1, 1936 2,067,529y Helsing Jan. 12, 1337 2,329,137 Richards Sept. 7, 1.943 2,462,885 lVIeOreY -n-Q- Mar.- l,A 17949 FOREIGN PATENTS Number Country Date 3451402 Germany May 17,` 1918 Certificate o1' Correction Patent No. 2,535,886 December 26, 1950 WILLIAM R.. BAKER ET AL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 5, line 35, for he read the; column 8, line 4, for tical purposes is substantially indestructible es read tial rating of the device ma/ z/ be plied many;

and that the said Lettere Patent should be read as corrected above, so that the same may conform to the record of the case in the Patent OIice.

Signed and sealed this 24th day of April, A. D. 1951.

THOMAS F. MURPHY,

Assistant Oommz'ssz'oner of Patents.

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