Патент USA US2412842код для вставки
Dec“ KY, 1946.. P_ L, SPENCER 2,412,842 ELECTRON I C DI S CHARGE CATHODE Original Fil‘ed Sept. 30, 1941 2 Sheets-Sheet 1 ~65 + (I, E624.- ‘ w 34%”2“ Dec. 17, 1946. 2,412,842 P. L. SPENCER ' ELECTRONIC DISCHARGE I GATHODE Original Filed Sept; 30, 1941 2 Sheets~Sheet 2 F7615 /6. f7” hllllillllll — Patented Dec. '17, 1946 2,412,842 UNITED srA'r as PATENT omcai ' 2,412,842~ * ELECTRONIC DISCHARGE carnonn Percy L. Spencer, West Newton, Mara, assignor to Raytheon Manufacturing Company, Newton, Mass., a corporation of Delaware Original application September 30, 1941, Serial No. 412,993. Divided and this application May " 23, 1944, Serial No. 538,998 1 2 Claims. (Cl. 250-275) This is a division of my copending application, Serial No. 412,993, ?led September 30, 1941, for an improvement in electronic discharge devices. 2 being had to the accompanying drawings, ‘where in: Figs. 1 and 2 are diagrammatic representations This invention relates to an electronic dis of a magnetron illustrating certain principles of charge device, particularly of the magnetron type. operation of my invention; and to a cathode for such a device capable of sup Fig. 3 is a cross-sectional view of one embodi plying large peak values of current. ment of my novel cathode; In electronic discharge devices, particularly of Fig. 4 is a fragmentary view. partly in section the magnetron type which are called upon to sup of another embodiment of my nove1 cathode; ply relatively large peak values of current, various 10 Fig. 5 is an illustration of one type of mag difiiculties have heretofore existed. The cathodes netron incorporating my invention, the view in of such devices have been heated to relatively Fig. 5 being taken along line 5-5 in Fig. 6; and high temperatures in an attempt to supply suin Fig. 6 is a cross-section of the magnetron in cient thermionic emission to carry such peak Fig. 5 taken along line 6-6 of Fig. 5, together values of current. Such cathodes have had an 15 with a. diagrammatic representation of ,a circuit unusually short life due to the fact that the emis with which said magnetron may be used. sive coating with which the cathodes are normal In Fig. 1 A1 and A: represent two anodes of a ly coated was rapidly driven oil! from the cathode. split anode magnetron. C is the centrally lo This effect was increased by the fact that the load cated cathode thereof. As is usual in this type current through the tube tended to overheat and 20 of device, a longitudinal magnetic field is im burn out the cathode. The arthas resorted to pressed thereon in a direction at right angles the use of complicated regulating and protective to the plane of illustration in Fig. 1. The cath devices in order to protect the cathodesor such ode C is connected to a negative potential while magnetrons from being burned out. However, the anodes A1 and A: are connected together to such protective and regulating devices did‘ not 25 a positive potential. Devices of this kind are substantially affect the loss of coating due to evacuated to high vacuum conditions in which high operating temperatures of the cathode which the gaseous atmosphere plays substantially no resulted in short life for such cathodes. part in the discharge. This type of magnetron An object of this invention is to produce an when energized sets up high frequency oscilla electron discharge device of the type which sup 30 tions, creating an oscillating electrostatic ?eld be plies high peak values of current with its cathode tween the anode A1 and A2. At one instant of normally operating at a temperature substantial time the anode A1 may be more positive than the ly below that necessary to cause such peak values anode A2. Under these conditions an electron of current to be emitted thermionically. e emitted from the cathode C is accelerated to Another object is to accomplish the above in 35 ward the anode A1 by the potential thereof. How a magnetron type ofgcharge device. ever,‘ the magnetic ?eld causes the electron e to Another object is to cause such peak values of travel in a curved path which de?ects the elec— current to be supplied largely by secondary emis tron to such an extent that it misses the anode sion. A1 and falls upon the anode A2. This imparts A further object is to devise a cathode in such 40 a negative characteristic to the device, and causes it to operate as an oscillator. I . a device which will emit large numbers of sec~Under the conditions of operation which I con ondary electrons without substantial time delay, template in my invention, in addition to the ac and which will have a long life. tion described in connection with Fig. 1, another A further object is to devise a magnetron which does not need special regulating and protecting 45 action, as exempli?ed byFig. 2, also takes place. The electron emission from C causes a swarm S devices'to prevent the cathode from being burned of electrons in the space surrounding C. An elec out. tron e'. which otherwise might follow the path A still further object is to devise such a mag described in Fig. 1, however, encounters inter netron which is capable of supplying much larger 50 as ference from the other electrons in the swarm S. amounts of power than have heretofore been pos and thus never reaches the anodes A1 or A2, but sible. The foregoing and other objects of this inven tion will be best understood from the following falls back onto the cathode. The interaction be tween the electrons in the swarm S may impart considerable energy to the electron e’ by collision description oiexempli?cations thereof, reference}555 or otherwise by the time it reaches the cathode 8,419,842 4 C. Assuming the tube to be oscillating, the elec . a temperature or thermionic emission. The ends of the sleeve I are closed by insulating plugs trons s’ also may receive a considerable amount of energy directly from the oscillating field be tween the two’anodes Ar and A2. The magnetic 'I-'|, preferably of alumina. The ends of the heater coil 8 extend through said plugs so that heating current may bev supplied thereto. An ?eld tends to give to the electron e' a de?nite . orbital period in its travel around C, which pe ' electrical connecter tab 8 has one end thereof riod is substantially equal to the period of oscil welded to the sleeve I and the other end welded lation of the voltage appearing between the anodes to one of the heater ends 8, so that electrical A1 and A2. This condition permits said oscil connection may be established to the emitting lating ?eld to arert its accelerating force upon 10 surface of the cathode. ‘ the electron e’ in the proper phase and at the Instead of making the cathode as illustrated in proper time to successively impart energy to said Fig. 3, it can take a variety of other forms‘, one of which is illustrated in Fig. 4. In this ?gure, Due to the above e?ects, electrons of the a’ instead of using round wire, the sleeve I is wound . electron. - type can be'made to fail upon the cathode C with 15 with a ?at ribbon 3’, also preferably of tantalum. considerable speed and energy, which may be This ribbon, for example, may be .0005 inch thick substantially above 100 volts. If the cathode C and .050 to .100 inch wide. Such a ribbon may be is made so as to be a good secondary electron initially coated with emitting materials, as de emitter, then such impinging electron may give scribed above, and wound upon the sleeve I with rise to the emission of several additional electrons. 20 about half of each turn of the ribbon overlapping The current due to secondary emission may be the preceding turn. Here again the coating may .made several times the current due to simple be baked in air as described above, and the coat thermionic emission at the operating temperature ing scraped from the outside of the cathode struc of the cathode. In addition, when the tube is ture, leaving the top surfaces 4’ of the ribbon called upon to supply greatly increased peaks of 25 current, then the secondary electron emission material 3' bare. ' The cathode structures as described above pos can be made to increase enormously to carry such peak currents without substantial time delay. In other words, such a device can be made to oper sess the property of being excellent secondary electron emitters, particularly from the scraped tantalum surfaces, as well as good thermionic ate as an electron multiplying arrangement in 30 emitters from the exposed oxide surfaces. The which the normal thermionically-emitted elec tantalum has a tendency to reduce the barium trons are multiplied to give an increased supply oxide, liberating small amounts of barium on the of electrons which in turn are again multiplied by a similar-process. ' surface of the coating which tends to give excel lent electron emission. Also the barium so lib ‘ In accordancewith my invention I utilize such 35 erated tends to coat the bare surfaces of the tan secondary emission to supply a- large part of the talum, making it an excellent secondary electron peak currents which such a device may be called emitter. Even without any barium coating, tan upon to supply. For this purpose I prefer to talum in itself is a good secondary emitter. construct the cathode of the discharge device in Cathodes of'the type as illustrated in Figs. 3 a special form, as shown for example in Fig. 3. 40 and 4 may be incorporated, for example, in a The cathode illustrated consists of a sleeve I magnetron of the type as illustrated in Figs. 5 and 6. The magnetron therein illustrated com made of some suitable material, such as tantalum or nickel. In one example of this cathode the prises an envelope I I which is preferably made of cylinder was about six millimeters in diameter, a block of conducting material, such as copper. and about fifteen millimeters long. Thesleeve 45 This block forms the anode structure of the mag is coated, except for the end portions thereof, netron. Said block has hollow end sections with a layer 2 of a mixture of barium and stron which are covered by end caps I2 and I3, likewise tium carbonates in a nitrocellulose-amylacetate of conducting material, such as copper; Between binder. ‘In some instances I prefer to add from the hollow end sections of the block I I is a central one to one and one-half per cent. of borax in‘ 50 bridging portion I4. The portion I4 is provided with a central bore I5 within which is supported order to decrease the'evaporation rate of the substantially at the center thereof a cathode I0 coating material during operation. The sleeve so which, as pointed out above, is preferably of the coated is baked in air at a temperature of about type as illustrated in Figs. 3 and 4. The cathode 400° F. Thereupon a winding 3, preferably of tantalum wire, is wound over said coating. In 55 I0 is supported by a pair of lead-in conductors I6 and ‘I1 fastened respectively to the ends 0 of the embodiment mentioned above, this wire has th cathode structure, and sealed through glass consisted of tantalum .004 inch in diameter, seals I8 and I9 mounted at the outer ends of pipes spaced .003 inch between adjacent turns. In 20 and 2| hermetically fastened within the walls orderto retain the winding upon the cathode and of the block I I adjacent the upper and lower hol to insure good electrical contact with the under 60 low end sections. lying sleeve, the ends 5 of the wire 3 may be welded directly to the sleeve I. After the wire 3 has been wound upon the cathode, the cathode is again coated with the coating material de scribed above and again baked in air at a tem perature of about 400° F. Thereupon the coat ing is scraped off the outside of the cathode structure. leaving the top surfaces 4 of the wire . 3 bare. The baking of the carbonate coatings in air not only drives 01! the binder material, but 70 also- largely converts the carbonates into the A plurality of slots 22 extend radially from the central bore I5 to within a short distance of the outer wall of the block I I. when such a magnetron is placed between suit able magnetic poles 23 and 24 to create a longi tudinal magnetic?eld and the device is energized, oscillations are set up whose frequency and conse quently whose wave length are determined pri marily by the dimensions of each of the slots 22. It is also desirable that the value of the magnetic ?eld is such as to impartto the electrons travel ling around the cathode an orbital frequency sub stantially equal to the frequency of said oscilla the turns of which are coated with insulating tions. Moreover the voltage applied to the anode material, is inserted within the sleeve I for the purpose of enabling the cathode to be raised to 75 structure should be of the proper- value to cause oxides. ‘A heater coil 6, preferably of tungsten, 2,412,842 5 such oscillations to occur and for the desired peak value of current to ?ow between the cathode and anode structure. The oscillations produced in cathode to a temperature at which some therm ionic emission occurs. This thermionic emission may emanate largely from the oxide coating which is exposed to the discharge area, through the spaces between the coiled winding on the out side of the cathode. Some of this‘ thermionic ‘emission may occur from the surface of the coiled the'slots 22 reinforce each other and may be led out from the tube by means of a coupling con ductor 25 fastened to the cen ral bridge portion I4 in the central bore 15 betwe 11 two of the slots 22. The coupling conductor 25 leads out from winding itself, particularly if the metal thereof the magnetron through a glass seal 21 at the has a thin film of barium coated upon it. How outer end of a pipe 25 likewise hermetically fas 10 ever, during operation the electrons which fall tened through the wall of the envelope II adja upon the cathode largely impinge upon the bare cent the' upper hollow portion thereof. metal surface of the coiled external winding, and The magnetron may be connected in any suit liberate the secondary electrons therefrom. The able circuit, one of which is shown diagrammati oxide coating between the turns of this winding cally in Fig. 6. In this circuit the cathode is sup 15 is largely shielded from such electron bombard plied with heating current from the secondary winding 28 of a heating transformer 29 whose pri mary winding 30 is adapted to be connected to a ment, and thus forms very little, if any, tendency for such bombardment to drive any of the oxide coating from the cathode. However, such coat ing is always available to supply barium for the suitable source of alternating current. Inter posed in the circuit of a. secondary winding 28 is 20 initial electron emission as well as barium which a switch 3| and a current-regulating resistance tends to increase the secondary electron-emitting 32. A source of potential 33, which in a, practical qualities of the metal surface of the external embodiment may be of the order of 12,500 volts, winding. An additional advantage of the con is connected between the envelope ll, constitut struction which I have illustrated is that the sur ing the anode, and the lead-in wire I 6 for the 25 faces from which the secondary electrons are cathode l0. Interposed in the circuit for the emitted are directly electrically connected to the source 33 is an interrupter or “chopper” 34 which sleeve I by having the ends 5 welded thereto. In interrupts the circuit so that the magnetron gen this way the current can flow through a direct erates short pulses of high intensity high fre low resistance metallic path to the very surface quency oscillations. The frequency of interrup 30 at which the electrons are being liberated. This tion may be of the order of two thousand times is in contrast to the usual oxide-coated cathode a second. The duration of each energization of in which the current must ?ow through the rela the tube may be of the order of a half a micro tively high resistance oxide coating before it second. reaches the emitting surface. In this way the I have constructed a. considerable number of 35 present cathode structure is much more effective devices substantially as shown in Figs. 5 and 6 and e?icient. and embodying a cathode as illustrated in Fig. 3, By my present invention I have been enabled to as well as the various parameters recited herein. construct practical magnetron devices which have Tubes of this kind were designed to produce oscil generated enormous peak quantities of micro lations of a wave length of about three centi 40 wave length power entirely outside of the range meters. In such a tube I have found that during of anything which has heretofore been practicable each half micro-second during which the device with such devices. was energized, the anode current rose substan Of course it is to be understood that this in tially instantaneously to a value of about twelve vention is not limited to the particular details as amperes and continued throughout at this value 45 described above as many equivalents will sug for substantially each period of energization. gest themselves to those skilled in the art. For The average anode current throughout the entire example, it may be possible to incorporate oer time was of the order of about fourteen milliam tain fundamental features of this invention in‘ peres. _ other devices which are called upon to supply In starting the operation of such a device, the 50 high peak values of current, particularly in con cathode was raised to a temperature at which nection with micro-Wave generators, It is ac enough thermionic emission occurred to initiate cordingly desired that the appended claims be the operation of the device, such emission being given a broad interpretation commensurate with of the order of milliamperes and being much less the scope of the invention within the art. than that required to supply peak currents of the What is claimed is: order of amperes. However, as pointed out above, when operation started, peak currents of the order 1. An electric discharge device including spaced anode and cathode electrodes the surface of one of which electrodes is covered in part with loose of amperes were supplied. Furthermore, after the operation of the device had begun, it was and outwardly projecting particles of material possible to open the heating circuit by the switch 60 subject to being removed therefrom by the elec 3|, and the device continued in operation with no trostatic forces between the two said electrodes, discernible difference, the tube continuing to means to prevent the removal of said particles of generate oscillations in the same Way and to sub material, said means comprising an electrostatic stantially the same degree as before the opening shield comprised of a helically wound wire coil of said circuit. Also under these conditions, when having a coil-turn spacing and extending in con the pole pieces 23 and 24 were deenergized so as tact for its full length with said electrode having to remove the magnetic ?eld on the device, the the projecting particles, said‘ coil being of highly current to the anode structure fell to zero and refractory non-emissive metal and being electri the operation of the device ceased. This is in cally connectedto said electrode having the pro strong contrast to the usual magnetron device in 70 jecting particles, said coil having its convolu which if during operation the magnetic ?eld is deenergized, the current between the cathode and tions exposed in front of said electrode having the projecting particles and in front of said pro the ‘anode structure rises rapidly. jecting particles, said coil providing for the loca As pointed out above, the heater 6 is supplied tion thereon of the electrostatic lines of force in with heating energy so as to initially raise the 75 front of\said electrode surface having the pro 9,412,849 jecting particles and front or said particles in preference to the loca ion of said lines of force on the said electrode surface having the project ing particles, and said coil providing for the pas sage between the convolutions thereof of elec trons to and from said electrode surface having the projecting particles. 2. An electric discharge device comprising a her overlying and exposed in front of and c! , tending from end to end of the surface of said . , electron emissive surface and in contact there cathode electrode provided with an electron emis sive surface consisting of relatively loosely ad -10 herent material and an electrostatic shield mem with throughout the length 01' said shield mem ber and electrically connected to the electrode, said shield member consisting of high refractory non-emissive metal and having a plurality of openings therethrough for the free passage of electrons to and from the electrode surface. PERCY L. SPENCER.