Oct. 22, .1946'.v I ` _ ` . c.-M. sLAcK ETAL y 2,409,717 FIELD EMISSION ARC DISCHARGE TUBE ‘ Filed sept. 2s, 194;'v \\\\ INVENTORS C2 M «S2/76K A?. PFE/F'FEÑ B c'. E; t‘wwf/L EY ' ATTORNEY Patented Oct. 22, 1946 2,409,717 NUNITED STATES PATENT OFFICE 2,409,717 FIELD EMISSION ARC DISCHARGE TUBE Charles M. Slack, Glen Ridge, and Andrew Pfeiifer and Clarence E. Dawley, Bloomfield, N. J., assignors to Westinghouse Electric Cor poration, East Pittsburgh, Pa., a corporation of Pennsylvania Application September 26, 1942, Serial No. 459,774 7 Claims. (o1. 25o-27.5) l 2 The `present invention relates to discharge de the electrostatic pull of the voltage from varying the electrode spacing and causing erratic per vices and more particularly to such devices wherein operation is initiated by a “field emis sion arc” as an electron source, and constitutes formance. Still iur-ther objects of the present invention an improvement over the structure such as 5 will become obvious to those skilled in the art shown in copending application, Serial No. 412,566, ñled Sept. 27, 1941, in the name of -Charles M_ Slack, 4Louis F. Ehrke and Clarence E. Daw le , and assigned to the same assignee as the present invention. by reference to the accompanying drawing wherein: Fig. l is a perspective View partly in section and with parts thereof broken away to better 10 illustrate the device, and schematically shown in In discharge devices of this type and as pointed out in the above-identiiied copending applica an `operating circuit; Fig. 2 is a sectional view taken on the line II-II of Fig. 1; the high potential gradient at the cathode. The Fig. 3 is a sectional View similar to Fig. 2 and resulting electrostatic field in turn causes a mi 15 showing a slight modification which the elec nute arc to forni between the starting electrode trode structure may take; and the cathode, apparently due to evolved me Fig. 4 is a sectiona1 View similar to Fig. 2 and showing another modification which the elect tallic particles and the positive ion bombardment, resulting from ionization of the evolved metal . trode structure may take; tion, held emission of electrons occurs due to vapor caused by the arc, forming a cathode spot 20 and a reduction in the space charge. This causes Fig. 5 is a sectional View similar to Fig. 2 and showing a still further modification which the the impedance oi the device to be so reduced electrode structure may take, and that an electron discharge is almost instantane ously initiated between the cathode and the an ode of the device. Fig. 6 is a side fragmentary view showing some of the electrodes after a period of operation oi 25 the device. Referring now to the drawing in detail, the discharge device 4 of the present invention as shown in Fig. 1 comprises a vitreous envelope -5 provided with a pair of electrodes 6 and 'l shown paramount importance. For example, it is de sirable that loss of the‘evolved metallic particles 30 as of rectangular pieces of metal of substantially from one of the electrodes in no way adects the uniform cross-section, such as copper, gold, silver, We have found that for extended useful life and reliability of operation of discharge devices of this type certain considerations become of characteristics of the device‘and that a uniform uranium, or the like, and riveted or otherwise añixe'd to very rigid leading-in conductors 8 and electrode spacing be maintained throughout life. 9 so that the free ends of the rectangular elec It is accordingly an object of the present in vention to provide a discharge device operating v35 trodes 6 and 'i are disposed in a veritcal plane parallel to each other with a small spacing of by iield emission of electrons and wherein the the order of a .0l in. therebetween depending same has a` relatively long commercially useful `upon the voltage to be applied. liie in comparison with such devices previously y" The leading-in conductors 8 and I9 are each in known to the art. Another object of the present invention is the 40 turn welded, soldered, or otherwise secured to metallic terminals l0 and Il. These terminals provision of a discharge device operating by ñeld may be of tantalum, molybdenum, or the like, emission of electrons and wherein the operating but preferably are of copper and as shown, these characteristics of the device remain substantially terminals l0 and li are provided with an en constant during` a relatively long commercially 45 larged ñanged portion, the periphery of which useful life. _ is feather-edged and forms an hermetical seal Another object of the present invention is the with an annular projection l2 provided at the provision of a discharge device operating by iield bottom of the envelope. emission of electrons and wherein the electrode spacing is maintained substantially uniform An anode electrode I3 of a refractory metal throughout a relatively long commercially use 50 having a higher melting point than that of the electrodes t and l, such as tungsten, molybdenum ful life of the device. or the like, is also provided interiorly of the en A still further object of the present invention is the provision of a discharge device operating velope 5. As shown in Fig. 1, this anode is of by" field emission of electronsl and wherein the ` substantially _U-shaped configuration and sup electrodes arè'ri'gi‘dly supported~ so" asmto-- prevent 55 portedin an inverted posîtiori'bya rigid leading 2,409,717 3 in conductor I4 so that the sides of the anode I3 are equi-distant on both sides of the elec trodes 6 and 'I and overlap the gap between the latter, as shown in Fig. 2, which allows an in crease in the thickness of the electrodes 6 and 'I without reducing the accessiblity of the cur rent ñow tothe anode. The ano-de leading-in conductor I4 is secured to the top of the envelope 5 by a terminal I5 hermetically sealed to a pro jection I6 in the same manner as the leading in conductors 8 and 9. After assembly of the device, it is exhausted to loss of evolved material does not always occur from the cathode 'I but, as we have found, from the starting electrode 6 and, in fact, the cathode 'I may accumulate material so that after consid erable operation the appearance of the electrodes 6 and ‘l may be somewhat as shown in Fig. 6 with the starting electrode 6 eaten away and a deposit built up on the cathode l. For this rea son it is desirable to reverse the connections to 10 the electrodes 6 and 'I so that the transfer of ma terial will be in the opposite direction, Thus since the electrodes 6 and 'I are of uniform cross a high degree of evacuation through an exhaust section and of similar material, it is a simple matter to operate ñrst one and then the other oughly degasified as is customary in the art so of the electrodes 6 and 'I as cathode, by changing that satisfactory operation is entirely independ the reversing switch 2| from its full line position ent of vapor or gas present in the device. If de to that shown in dotted lines in Fig. 1, and so ex sired, however, a metal vapor such as mercury tend the useful life of the device. may be introduced into the envelope 5 prior to It is also to be noted that while most of the “tipping-off” at Il which also results in satisfac 20 electrode material is transferred from one of the tory operation so long as its pressure is such that electrodes 6 and l to the other, there is some of the spacing between the electrodes is less (and this material vaporized away. This accumulates preferably many times less) than the mean free on the anode I3 and in the absence of provisions path of electrons in the vapor so that ignition to the contrary, since in most instances it is de and operation of the device is entirely independ 25 sirable to have the anode fairly closely spaced, a ent of the mercury vapor present. further reduction in the spacing would result As illustrated in Fig. l, the electrode 6 consti from the accumulated material on the anode, tutes the starting electrode while the electrode l thus changing the operating characteristics of is the cathode. In order to initiate a discharge the tube. For this reason it is preferable to em between the Starting electrode 6 and the cath 30 ploy a refractory material which operates con ode 1, a high tension transformer I8 is shown, tinuously or intermittently at a temperature the primary winding I9 of which may be oon above the melting point of the material of which nected to the customary commercial source of the electrodes 6 and 'I -are composed. Moreover, supply of 115-230 volts. The secondary wind by the anode I3 overlapping the gap between the ing 20 has one end grounded at 22 while the op 35 electrodes 6 and 'í allowance is thereby made for posite end is connected to the terminal Iil an increase in thickness of the electrodes 6 and through one blade of a reversing switch 2I and ’l without reducing the accessibility of the cur hence to the starting electrode 6. Inasmuch as rent flow to the anode. the device of the present invention is particular It will thus be seen that although the spacing ly operable as a control tube, a source of supply 40 between the electrodes is rather minute, their tip I‘I with the various metallic parts being thor such as a transformer 23 is shown which may likewise have its primary winding 24 connected to the customary commercial source of 115-220 volts. The secondary winding 25 of this transformer 23 has one end thereof connected to ground at 25 and to the terminal Il through the remain ing blade of the reversing switch 2|, thus con necting to the cathode l, while the remaining end of the secondary winding and a connection from the anode terminal I5 extends to the “load,” thus positioning the discharge device be tween the source and the load in order that en ergization of the latter may be controlled by the device 4. When it is desired to operate the discharge device 4, a high voltage impulse is applied be tween the starting electrode 6 and the cathode i mounting is not as critical as might be supposed since any irregularity in the spacing will be elim inated after operation of the tube. Also through out tube life a uniform spacing is maintained be ¿ tween the electrodes at all points. This follows because any point that tends to become nearer than another will cause the discharge to transfei to such point with resultant vaporization of ma terial and the discharge thus moves around con stantly maintaining an equalized spacing. For exceptionally long tube life electrodes in parallel may be employed such as shown in Figs. 4 and 5. In these ñgures the starting electrode 6 and cathode 'I may be formed of a plurality of - parallel metallic plates and the anode I3 formed in the same manner as shown in Fig. l except that tarily energizing the primary winding I9. This it is provided with a plurality of tines disposed between the parallel plates of the starting elec trode 6 and cathode 'I and also overlapping the 'i from the transformer i8, such as by momen causes ñeld emission of electrons from the cath space therebetween. ode 'I due to the high potential gradient atthe cathode with the resulting electrostatic field A still further requirement for stable operation is rigidity of the electrode structure for if the causing a minute arc to form between the start electrode supports, and particularly the supports ing electrode 6 and cathode 1 because of evolved metal vapor. The positive ion bombardment re sulting from ionization of the evolved metal par ticles caused by the arc forms a cathode spot on the electrode 1, and the impedance of the device is so reduced that an electron discharge is almost instantaneously initiated or transferred between the closely spaced cathode -I and anode I3, re sulting in the “load” being energized from the for the starting electrode 6 and cathode 1, are not sufficiently rigid, the electrostatic pull of the volt age tends to affect the electrode spacing and produce erratic performance. Although it is not possible to state the exact amount of rigidity re quired for all applications, it is believed preferable to have rigidity greater than that obtainable with 100 mil diameter molybdenum three inches long. Also to increase rigidity the leading-in and sup porting conductors 8, 9, and I4 may be formed high tension transformer 23~ Contrary to what might be expected, the net 75 as channels such as shown in Fig. 3 with the 2,409,717 5 electrodes 'ô and 1 welded or riveted thereto in 6 between with attendant evolution of metallic par the same manner as when rods are employed. ticles from one of said electrodes which build up It thus becomes obvious to those skilled in the on the adjacent surface of the other of said elec art that a discharge device operable by field trodes, a refractory metal anode positioned on emission of electrons is herein provided in which each side of said oppositely disposed electrodes a substantially uniform electrode spacing and and overlapping the space therebetween for sup hence constant operating characteristics are porting an electron discharge with one of the maintained throughout a relatively long commer electrodes of said pair immediately following the cially useful life. Moreover, the device is of ex ñeld emission arc discharge between said pair ceptionally rigid construction so that electro l0 of electrodes and said anode being operable at static pull of the voltage has no material affect a temperature above the melting point of the on the device, which still further contributes to metal of said pair of electrodes to prevent ac the elimination of erratic perfomance during cumulation of evolved metallic particles from the operation. latter on said anode, and means for reversing Although several embodiments of the present current flow between said pair of electrodes to cause the evolved metallic particles accumulated invention have been shown and described, it is to be understood that still further modifications of on one of the electrodes of said pair to be re the’ same may be made without departing from turned to the other of said electrodes from which the spirit and scope of the appended claims. such particles originated. 5. A discharge device wherein operation is ini We claim: . l. A discharge device wherein operation is ini tiated by ñeld emission of electrons comprising a pair of oppositely disposed spaced metallic elec tiated by field emission of electrons comprising a pair of oppositely disposed spaced electrodes trodes each consisting of a plurality of parallel between which a. field emission arc discharge oc plates and between which electrodes a i'leld emis sion arc discharge occurs upon the application curs upon the application of a potential thereto, and an anode positioned on each side of said op of a potential thereto, and an anode provided positely disposed electrodes and overlapping the with a plurality of portions and positioned to dis space therebetween for supporting an electron pose a portion thereof on each side of the paral discharge with one of the electrodes of said pair immediately following initiation of the ñeld emis sion arc discharge between said pair of electrodes. 2. A discharge device wherein operation is ini tiated by ñeld emission of electrons comprising a lel plates of said pair of electrodes and overlap ping the space therebetween for supporting an electron discharge with one of the electrodes of said pair immediately following initiation of the trodes between which a field emission arc dis ñeld emission arc discharge between said pair of electrodes. 6. A discharge device wherein operation is ini charge accompanied by evolved metallic particles tiated by ñeld emission of electrons comprising occurs upon the application of a potential thereto, and a refractory metal anode positioned on each a pair of electrodes including metallic plates dis posed in a common plane with their edges in pair of oppositely disposed spaced metallic elec spaced parallel relation to each other and between side of said oppositely disposed electrodes and overlapping the space therebetween for support 40 which a field emission arc discharge occurs upon ing an electron discharge with one of the elec the application of a potential thereto, and a sub trodes of said pair immediately following initia stantially U-shaped refractory metal anode po sitioned to dispose its parallel portions substan tion of the ñeld emission arc discharge between tially equi-distant on each side of said pair of said pair of electrodes and said anode being operable at a temperature above the melting point 45 metallic plate electrodes and being of a width greater than the spacing between said pair of of the metal of said pair of electrodes to prevent electrodes so as to overlap the latter and opera accumulation of evolved metallic particles from ble to support an electron discharge with one of » the electrodes of said pair immediately following 3. A discharge device wherein operation is ini tiated by field emission of electrons comprising a 50 initiation of the field emission arc discharge be tween said pair of electrodes. pair of oppositely disposed spaced> metallic elec 7. A discharge device operable by field emission trodes, means for applying a potential to said of electrons comprising a pair of oppositely dis electrodes of sufficient magnitude to cause the the latter on said anode. posed spaced metallic electrodes and between initiation of a ñeld emission arc discharge there between with attendant evolution of metallic par 55 which a field emission arc discharge occurs upon the application of a potentia1 thereto, leading ticles from one of said electrodes which build up in and supporting conductors for said electrodes on the adjacent surface of the other of said elec having a rigidity greater than that attainable trodes, an anode positioned on each side of said with molybdenum of 100 mil diameter to pre oppositely disposed electrodes and overlapping the space therebetween for supporting an electron 60 vent the electrostatic pull of the voltage from changing the electrode spacing and causing er discharge with one of the electrodes of said pair ratic performance of the device during operation, as cathode immediately following initiation of and a refractory metal anode supported by a the ñeld emission arc discharge between said pair leading-in conductor of equal rigidity as the lead of electrodes, and means for reversing current ing-in conductors for said pair of electrodes and flow between said pair of electrodes to cause the provided. with a portion thereof on each side of evolved metallic particles accumulated on one said pair of electrodes which portions overlap the spacing therebetween and said anode being operable to support an electron discharge with particles originated. 4. A discharge device wherein operation is ini 70 one of the electrodes of said pair immediately fol lowing the initiation of the field emission arc tiated by field emission of electrons comprising a pair of oppositely disposed spaced metallic elec discharge between said pair of electrodes. CHARLES M. SLACK. trodes, means for applying a potential to said of the electrodes of said pair to be re-transferred to the other of said electrodes from which such electrodes of sufficient magnitude to cause the initiation of a field emission arc discharge there 75 ANDREW PFEIF‘FER. CLARENCE E. DAWLEY.