US2412772A - Electron discharge device generator - Google Patents

Description

Dec. 17, 1946. c w HANSELL 2,412,772 7 ELECTRON DISCHARGE DEVICE GENERATOR Fild Feb. 6, 1945 1 2 heets-Sheet l FIELD COIL 90 205 I INVENTOP.

clarerwe lVfikuw eu ATTOQIVE) Dec. 17, 1946. c. w. HANSELL ELECTRON DISCHARGE DEVICE GENERATOR Filed Feb. 6, 1943 2 Sheets-Sheet 2 0.63 some:

F/EL D COIL JOUPOE OF a/vooE' a. o. POTE/Vjf/QL IN VE/v Top: 582 dlanelwe Wflansell/ Patented Dec. 17, 1946 ELECTRON DISCHARGE DEVICE GENERATOR Clarence W. Hansell, Port Jefferson, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application February 6, 1943, Serial No. 474,943

This invention relates to electron discharge device oscillators, and more particularly to such oscillators which require the use of a magnetic field. One such oscillator is known in the art as a magnetron.

An object of th present invention is to enable a high frequency oscillation generator to operate on the magnetic induction acceleration principle.

Another object of the present invention is to provide an electron discharge device oscillator employing a changing magnetic field to accelerate the electrons to a high velocity and to curve them to follow an orbital path.

A further object is to provide a magnetron oscillator employing an alternating magnetic field to produce high velocity electrons, which in turn produce current pulses of very high radio frequency energy.

A still further object is to provide an electron discharge device oscillator of the magnetron type which requires only moderate anode-to-cathode potentials, and employs a changing magnetic field to accelerate the electrons to velocities corresponding to much larger potentials.

The principles underlying the acceleration of electrons by means of magnetic induction for the purpose of obtaining X-rays and nuclear disintegration are known and have been described in such articles as The acceleration of electrons by magnetic induction by D. W. Kerst, published in Physical Review, July 1, 1941, pages 47-53; Electronic orbits in the induction accelerator, by D. W. Kerst and R. Serber, published in Physical Review, July 1, 1941, pages 5358; A twenty million electron volt betatron or induction accelerator, by D'. W. Kerst, published in The Review of Scientific Instruments, September, 1942, pages 387 to 394; and United States Patent No, 2,103,303, granted to M. Steenbeck, December 28, 1937, to which reference is made for an understanding of electron phenomena and theory forming the basis of the present invention.

Generally speaking, it is known that in an induction accelerator for producing X-rays and nuclear disintegration, an alternating magnetic field is made to traverse an evacuated chamber containing free electrons. As a consequence of the presence of the changing magnetic field, the electrons are givenan acceleration by a force proportional to the rate of change of magnetic field intensity. At the same time, the presence of the field causes the electrons to be bent into curved paths which, due to centrifugal force, tend to become spirals of increasing diameter 24 Claims. (Cl. 25036) as the electrons speed up. However, if the field is increasing, this tends to increase the cene tripetal force and decrease the diameter of the spirals. As an overall. result, during a considerable portion of each half cycle of the magnetic field variation, the increase in electron velocity and the increase in magnetic field strength may have a combined effect which causes the electrons to move around a circular path of nearly constant diameter while the electrons accelerate continuously and eventually reach very great velocities corresponding to very high poto a field intensity having an average magnitude twice as great as the guiding field.

In accordance with the preferred embodiment of the present invention, oscillations are produced in an electron discharge device of the multi-anode segment type, in which the electrons are accelerated to a high velocity by means of an alternating magnetic field whose frequency is very low compared to the frequency of the radio frequency oscillations. Preferably, the mean magnetic field intensity within the area bounded by approximately circular electron paths at some distance inside the anodes should be somewhat more than twice the magnetic field intensity along the electron path, so that electrons accelerated bythe field tend to be thrown out into the paths of increasing diameter, as the velocity increases, but for electron paths at and close to the anodes the field intensity inside the paths should be somewhat less than twice the magnetic field intensity along the paths so that electrons tend to be thrown inward toward paths somewhat less in diameter than the anode diameter. Thus, electrons tend to move toward a common orbit having a diameter somewhat less than the inside diameter of the anode, while they are be ing accelerated by th changing magnetic field.

rapidly inside the anode structure, and by negative resistance effect this accumulation produces, momentarily, extremely powerful oscillations at extremely high frequencies.

During oscillation,"

the energy which is extracted from the electrons by the high frequency oscillations tends to reduce the diameters of the electron paths. The frequency of the alternating magnetic field may, for example, be of the order of 500 cycles per second. The accelerated electrons then produce short duration pulses of radio frequency energy. Each pulse of radio frequency energy may have a duration of one microsecond more or less. The repetition rate of the pulses under an assumed condition of a 500 cycle alternating magnetic field will be 1000 per second. By superimposing a direct current magnetic field upon the alterhating magnetic field, the repetition rate of the pulses may be made to be 500 per second. The frequency of the oscillations produced by the oscillator of the invention may range anywhere from 100 megacycles to 10,000 magacycles and higher, depending upon the design of the oscillator and the values and adjustments of the associated circuit elements. The pulse rate can, if desired, be changed by changing the frequency of the alternating magnetic field, and the phase of the pulses can be changed (i. e., advanced or retarded) by changing the phase of the alternating magnetic field with respect to asource of reference current of the same frequency as the alternating field.

According to one embodiment of the invention,

' and in order to assist in forcing electrons out from the surface of the cathode, there is employed an induction accelerator magnetron device for producing pulses of ultra high frequency oscillations, wherein the pole faces are so constructed and arranged that the alternating magnetic field which drives the electrons decreases in strength, at first, with the distance from the axis of the device and then increases in strength. This is done by so shaping the magnetic pole faces that they are more closely spaced near the axis of the magnetron along which the cathode lies, and not soclosely spaced as the distance from the axis increases. Preferably, the distance between the pole faces again decreases in the vicinity of the anodes. Putting it in other words, the strength of the instantaneous magnetic field varies or tapers from a maximum in the vicinity of the cathode to a minimum at a certain distance from the cathode, and then increases again in thevicinity of the anodes.

Further, over most of the range in which the magnetic field intensity decreases with increasing distance from the axis, the rate of decrease is preferably such that the average intensity of the field inside any given radius is greater than twice the intensity at the radius. For radii approaching'the radius of the inner surfaces of the anode, the field then stops decreasing and preferably increases with increasing radius.

One feature of the invention relates to the means for making the electron current substantially independent of cathode temperature, so

long as the temperatur remains higher than the temperature which would cause saturation of electron current. Such means may comprise a grid or control electrode surrounding the oathode and positively charged relative thereto, and a resistance in the cathode electrode current connection.

.Other objects and features will appear from a reading of the following description, which is accompaniedby drawings wherein:

Figs. -1 and la show, in cross-section, the constructional details of one embodiment of the magnetic induction accelerator oscillation generator of the invention;

Fig. 2 shows, partly schematically and partly in cross-section, another embodiment of a magnetic induction accelerator of the invention to gether with the associated circuits for suitably energizing the elements of the'oscillator; and

Fig. 3 shows, in cross-section, the constructional details of another embodiment of the invention.

Referring to Figs. 1 and la, there are shown in these two figures the essential constructional details of a magnetron electron discharge device oscillator designed to function on the magnetic induction accelerator principle, in accordance with one embodiment of this invention. Fig. la is a cross-section of Fig. 1, along the lines Y-Y. The anode and cathode elements of the magnetron are mounted in an evacuated envelope located in a gap in the central leg of a three-legged magnetic core .353 made of laminated iron suitably machined, or of powdered iron moulded into shape with av suitable binder. The cathode is not shown in Fig. 1 but is identified by reference numeral 2% in Fig. la. The core 350 is excited with a relatively low frequency magnetizing current flowing through a pair of coils 35H, 35!. These coils are mounted on opposite sides of the anode and cathode structures and encircle the magnetic pole pieces am, In use, they are preferably tuned by means of a condenser so that only the power current must be supplied from an alternating current generator. The relatively low frequency source for magnetizing the coils and r' the condenser is not shown in Figs. 1 and 111 but is illustrated and described in more detail later.

in connection With Fig. 2. The magnetic field lines are illustrated in Fig. 1 by the dotted endless lines 220. The central leg of the magnetic core is so designed that the pole faces m, 3H] on opposite sides of the magnetron anode structure are shaped to provide a tapered magnetic field.

In Fig, 1 the curved lines 3! illustrate gen-- r desired even number (preferably six .or eight, al-

though a lesser or greater number may be employed) are shown in Fig. la insulated from one another by insulating spacers 205, to prevent short circuiting for the potentials induced by the changing magnetic field. The insulation spacers 205 are of high-resistance material to permit a small amount of direct current to flow over them for enabling positive polarizin potentials to be applied to the anode segments. Alternatively, they may be of good insulating material and may be shunted with resistances for passing the relatively smalldirect current anodecurrents.

The anode structure as a whole surrounds a cathode .290 which is a ring affair.

the interior thereof,- in the manner of an indirectly heated cylindrical cathode, or, if desired, may be of a type which can be heated by induction from the alternating current driving magnetic .field. By virtue of the shaping ofjthe pole The annular ring cathode 200 may be heated by a filament in Ia'ceszin the manner illustrated in Fig. 1 (and als'oinfFig. 2 to be described later), there are obtained variations in the magnetic field intensity with variation in distancefrom the axis of the tube. The magnetic field intensity is made to be highest near the cathode and the intensity first diminishes at a certain minimum rate of diminution until the distance approaches the anode radius, then increases again more or less abruptlynear the radius of the inner surface of the anodes.

The output coupling loop 352 serves to abstract the high frequency energy from the oscillation generator. l

It ispreferred that the anodes be given a moderate positive potential'relative to the cathode as an aid to drawing a larger number of electrons from the cathode than is possible without this positive potential on the anode. This potential will usually be far less than would be required to give electrons the final velocities required for oscillation at the desired frequencies.

The shaping of the magnetic pole faces as illustrated in Figs. 1A and 2 enables the alternating current magnetic driving field to be most intense at the cathode surface, and then to decrease in strength rather rapidly with distance from the axis and then increase again. The desired taper in magnetic field intensity toward lower values with increasing distance from the cathode is obtained in the arrangements illustrated, by shaping the pole pieces of the laminated electromagnet more or less as shown in cross-section, instead of using flat'pole pieces. This pole shape has the additional advantage of tending to concentrate the electrons leaving the cathode longitudinally of the axis toward a plane midway between the pole pieces and at right angles to the axis. Preferably, the mean magnetic field intensity within the area bounded by a circular electron path near the anodes should be somewhat more than twice the magnetic field intensity along the electron path, so that electrons accelerated by the field tend to be thrown out into paths of increasing diameter as the velocity increases, up to a diameter somewhat less than the anode diameter, after which, if they reach larger path diameters, they tend to be thrown inward toward the preferred path diameter. By this means, as the electrons are accelerated they may be made to accumulate in more or less cylindrical sheet rotating rapidly past the anode, and, by negative resistance effect, this accumulation can momentarily produce extremely powerful oscillations at extremely high frequencies.

With the arrangement of Figs. 1 and 1a, when the field eoils 35!, 35f are energized with an alternating current of, let us say, 500 cycles per second, then maximum electron velocities are reached in one direction or the other around the axis twice per cycle. If these maxim-um velocities are high enough, they will reach or pass through the velocities required to produce high frequency oscillations of the magnetron. It is possible to predict, in any particular case, whatthe approximate maximum attainable electron velocity potentials will be, up to a point where oscillations start, by knowing the maximum obtainable magnetic field intensity along a circular path taken by the electrons just inside the anodes. The electron potentials andvelocities for elec-' trons moving in an orbit of any given radius in any value of magnetic field, over a large range, are listed in tables which appear in certain physics .text books. See, for exampla'the tables in the book Electron and Nuclear Physics, by. J. BartonaHoag, published by D. Van Nostrand Company.

.The magnetic assembly, as described above, should be made of laminated or molded powdered iron and should be so shaped as to bring about an accumulation of electrons emitted for a relatively long period of time into a ring of space charge circulating inside the anode segments in a stabilized location, which, when the electrons reach sufficiently high densities and velocities, will cause oscillations to start. The starting of oscillation, by slowing the electrons, will: render the electron orbits unstable so that the diameter of the orbits will decrease and stop the oscillation again, after which the space charge will be dis sipated as the magnetic field decreases again and extracts the remaining energy from the elec trons; Theoretically, at least, it is possible to accumulate electrons bver a period which is, say, 1000 times longer than the duration of the pulse of high frequency oscillation. For example, we may be able to obtain pulses of high frequency l power which are less than one microsecond in length but which result from accumulation of electrons for, say, 1000 microseconds. Therefore, the instantaneous electron current taking part in producing the oscillations may corre-,

current. In practice, even if much lower ratios of peak circulating current to cathode electron emissioncurrent are obtained, still there will be great benefit derived from the electron current accumulation effect.

Although the induction accelerator magnetron pulser devices of Figs. 1 and la have been shown and described as having many anode segments, it

should be distinctly understood that for the lower radio frequencies of oscillation, and for lower power outputs, it maybe advisable to use only one pair of anode segments in the magnetron. For considerably higher frequencies, and for higher power outputs, a greater segments is preferable.

Fig. 2 illustrates one form of magnetron, together with associated circuit elements, which can be employed in producing a complete inducall tion accelerator magnetron pulser system. The constructional details of the magnetron per seare substantially like those shown in Figs. 1 and 1a.. However, in Fig. 2 an anode structure having only two segments has been illustrated. In Fig. 2, the magnetron is shown as having a coiled filament 360 in the center thereof along theaxis. The anode structure and the cathode are contained within an evacuated glass envelope 35L The output coupling loops 352 are also shown within the evacuated structure. The envelope 36I is shown mounted in the gap of the central leg of a three-legged magnetic core made of laminated or powdered iron molded into shape with a suitable binder. manner illustrated in Fig. l to accumulate and (55 concentrate electrons into a whirling'ring. The:

two driving coils 35l, 35! providing the alternating current magnetic field are shown on oppo site sides of the evacuated envelope in a manner similar to that illustrated in Fig. 1. A protective. metallic can 365 surrounds the foregoing assemj pracblage, though this is not essential in the tice of the invention.

The cathode is heated by means of any suitable, power source, illustrated by battery3 2ll,' Whose leads extend through suitable apertures spondingly be 1000 times the cathode emission.

number of anode The pole faces are'shaped in the 7 both sides of the central leg of the magnetic: core, as shown. The two anodes obtain. their. positive polarizing potentials from an anode biasing. powtune the. generator and the coils. It is preferred that the tuning condenser 315 be adjustable. It has a capacitance which is large compared. to the tuned circuit or folded radiators 310, .310.

In. order to have the electrons thrown. out from. the cathode, the rate of diminution of field intensity with distance from the axis along which the cathode lies mustv be such that the intensity along. any chosen circle concentric with the axis should: be somewhat less than one-half the mean field intensity in the area enclosed by the circle. In practice, this conditioncannot be fulfilled for small distances. from the-cathode but this is not important because the electric field due to direct current potential between.v the Y anode segments and. cathodeserves to pull electrons away rom the cathode sufliciently to get them into orbits which tend to expand out toward the limiting orbit diameter inside the anode. Likewise, to have electrons which. reach orbits too large in diameterv thrown. back toward a chosen diameter of orbit, the mean field intensity inside any great or diameter orbit than the preferred one must be somewhat lessv than twice the average intensity of magnetic field enclosed by the chosen orbit. When the taper or variation in relative magnetic field: intensity is. correctly proportioned, electrons accelerated inmost of the space inside the anodes are simultaneously thrown out toward the an- I odes, but at a chosen distance from the anodes this tendency for the electrons to be thrown out is reversed and in the space near the anodes the radial force is toward the. cathode. As av result, when the magnetic field is increasing, there is an accumulation ofelectrons effective for a relatively long time into a whirling space charge ring at a little distance inside the anodes. As the density of the electrons in the whirling ring increases,'while the magnetic field is increasing from zero to its maximum, the velocity of the electrons is also increasing rapidly. This velocity may reach extremely high values for practical values of magnetic field intensity, (a few thousand g-aussese or less). By means. of suitable adjustments of field and potential, the velocities maybe made to reach such a value as to cause negative resistance oscillations to start between the anode segments and the frequency of these oscillations may be extremely high. By so designing. and adjusting the device that the velocity of electrons reaches close to that for starting'oscillations, at the lowest frequency for which the anodes. tune, at just about the top of the cycle of magnetic: field intensity, the magnetron maybe caused to develop two pulses of very high radio,

frequency oscillation per cycle of low frequency drive current. The beginning of oscillation is accompanied by abstraction of energy from the whirling. electrons. in a manner to slow them down and decrease the diameter of their orbit. This tends to destroy the velocity and electron pathv diameter required for oscillation and, therefore automatically quenches the oscillations. The an rangement of Fig. 2 shows the anode segments tion, the whole' oscillator assemblage may. be mounted in a reflector for obtaining directive: transmission. Alternatively the conductors of the output circuit may be shielded, and oscillation energy conveyed to a radiator, or to radiators', by means of. a wave guide or a transmission line. This feature is shown in more detail in connection with Fig. 3.

The arrangement of Fig. 2 has one very great advantage in that there should be no spurious oscillation frequencies anywhere near thedesired output frequency, since all other resonances in the anode system are at frequencies too high-to make oscillation at these frequencies possible. This freedom from. spurious modes'of oscillation is madepossible by the very high electron velocities which permit extremely high frequency scillation with only two anodes. The-foregoing statement does not mean that magnetron-s with. more than two anode segments may not be used. when frequencies :higher than obtainable with only .two anode segments are desired. The statement merely means that the inductively driven magnetron with two anode segments can reach the same frequency band as that now obtained with conventional magnetrons having a. greater number of anode segments.

In the operation of .magnetic" induction eleccillation may take place while the magnetic field is increasing. This happens when the maximum value of the alternating current magnetic field, also taking into account the direct current an.- ode-to-cathode potential, is too'great for: single pulse operation of a particular magnetron oscillator assembly. For this condition of excess mag.- netic field, it appears that, before thefield has: come near to its maximum value, a sufiiciently rapid and intense electron space charge maybe accumulated to cause oscillations to start. There is then a momentary pulse of oscillations which dispels much of the space charge due to high frequency electric fields. Then, as the magnetic field continues to increase, another ring of circulating space charge accumulates with increasing density'and velocity which may reach the pointof oscillation before the magnetic field" has passed through its maximum and begun to decrease again. 7

Thus, it appears that if sufficiently intense magnetic fields are used, there may be a series of pulses produced whilethe magnetic field is increasing. For somepurposes this may not be objectionable but may even be desirable. For most signaling purposes, it is undesirable and may be a source of operating difficulty which requires tuned with conductors 3'50, 310, which simultaneously. form. folded radiators.v With this combinarather close design and adjustment- To overcome this diiiiculty, by making it possible to obtain only one pulse of oscillation-each time the magnetic field increases, I may make use of the arrangement of Fig. 3.

Fig. 3 shows in cross-section theconstructional details of amulti-anode segmentmagnetron having associated therewith several desirable features not shown or described in connection with: the other figures. In Fig. 3 the output energy derived from. loop 352 is passed. through. a glass seal. to. a coaxial transmission. line 38!] from which the energy is utilized by an antenna or radiator (not shown). In order to. improve: and control thequenching of the oscillations, and to prevent desired multiple pulses, a small partof the high frequency energy is taken by a capacity Coupling; probe 38! rectified by the diode: rectifier 3823. and:

applied: (amplified if necessary) as a cut-E biasing potential to a control electrode or grid 383 surrounding the cathode. This cut-off biasing potential is appliedtothe control electrode383 fora sufiicient time to prevent undesired multiple pulses. This is accomplished by charging a condenser withthe rectified current and by controlling the value of resistance through which the charge leaks off to control the time. Fig. 3 also shows an adjustable resistance 390 in the cathode electron current connection, as a result of which the electron current may be made to be substantially independent of filament temperature, so long as the temperature remains higher than the temperature which would cause saturation of electron current. It should be noted that the control electrode 383 may be at, either a negative or a positive potential relative to the cathode. The circuit arrangement illustrated provides an automatic bias for the grid 333 due to current flowing in the resistance 39!]. The current through the resistance 390 tends to hold more nearly constant charging current between pulses, and thus makes the system independent of Variations in cathode emission, provided the emission is suficiently high to supply the required current. If desired, the control of electron current through the grid electrode may, be utilized to cause only one pulse of oscillation for each period of increasing magnetic field by controlling the rate of accumulation of rotating electron space charge. By this means, rectifier 382 may be made unnecessary.

In certain embodiments successfully tried out in practice, the alternating current magnetic field was created by an audio frequency generator of 500 cycles. This audio frequency is merely mentioned by way of example, because where the system is utilized for airplanes, the audio frequency generator may be of a standard frequency of say 400 cycles, in view of the fact that 400 cycle generators have been standardized for use in some airplane installations. token, a generator of greater audio frequency currents may also be utilized, let us say of 800 cycles or more.

If desired, a steady magnetic field of suitable value may be superimposed on the alternating current magnetic field and this may be done by the same or another field winding with direct currentfiowing in it. This additional steady field can thus act as a biasing field, so that only the positive peaks of the alternating current magnetic fieldare capable of reaching values which will allow the tube to oscillate. This feature is shown in Fig. 2 wherein the D. C. source I00 serves to providethe steady magnet field superimposed on the alternating magneticfield. The condenser I (H is a bypass condenser for the alternating output from generator 315.

What is claimed is:

1; An ultra high frequency electron discharge deviceoscillator comprising amagnetic core made of iron material, said core having a leg made of two parts separated by a gap, an evacuated envelope in said gap, said envelope containing thereina cathode surrounded by a plurality of anodes, a circuit for. producing a changing magnetic field including a coil surrounding each part of said leg, and means for causing a whirling ring of electron space charge surrounding said cathode, said means including means for exciting said coils with audio frequency currents and over a range of values which results in the substantial transfer of energy from the resulting changing magnetic field tothe electron space charge circulating around By the same the cathode and in the production of pulses of radio frequency energy. i i i 2. An ultra high frequency electron discharge device oscillator comprising a multi-legged iron magnetic core having at least one leg divided into two parts by a gap, an evacuated envelope in said gap, said envelope containing therein a cathode surrounded by an anode structure, said cathode extending in a direction generally parallel to, the lines of flux across said gap, and means for ments, and means for producing a changing magnetic field varying at an audio frequency rate and having flux lines extending generally parallel to said cathode, whereby the electrons are accelerated to'high velocities by said changing magnetic field and caused tofollow substantially circular paths near said anodes, the mean magnetic field intensity within the area bounded by some of said circular electron paths within saidv anode structure and whichare smaller than the stable orbit necessary to produce oscillations being greater than twice the magnetic field intensity along the electron path of the stable orbit.

4. A magnetic induction accelerator oscillator comprising an electrondischarge ,devicehaving meansfor producing electrons, a resonant anode structure surrounding said means, and means for. producing an alternating magnetic field which varies at a rate considerably lower than the frequency of the generated oscillations, said alternating magnetic field serving to accelerate the electrons to high velocities and to cause very high frequency oscillations to take place while said field is changing and to cause them to follow substantially circular paths.

5. A magnetic induction accelerator oscillator of. ultra high frequency oscillations comprising a cathode, an anode structure surrounding said cathode and composed of an even number of anode segments located on a circle, means for causing a whirling ring of electron space charge surrounding said cathode, said means including means for producing an alternating magnetic field having flux lines extending generally parallel to said cathode and which varies at an audio. frequency rate, said alternating magnetic field serving to accelerate the electrons emitted by said cathode to high velocities and to cause very.

high frequency oscillations to take place while said field is changing and to cause them to follow substantially circular paths. i

6. A magnetic induction acceleratoroscillator of ultra high frequency oscillations comprising apair of poles of magnetic material, an electrode structure located between said poles and including a cathode surrounded by an anode, the flux lines between said poles being parallel to said cathode, means in circuit with said poles for producing an alternating magnetic field which varies at an audio frequencyrate, whereby the electrons emitted by said cathode are accelerated. to high velocities and caused; to follow substantially circular paths, the pole faces being shaped "7. A magnetron oscillator including a cathode and a surrounding anode, and means for producing a magnetic field which varies from a maximum near the cathode to a minimum in the space between said cathode and anode.

8. A magnetron oscillator including a cathode and a surrounding anode, and means for producing a magnetic field which varies from a maximum near the cathode to a minimum in the space between said cathode and anode, and then increases at the location of said anode.

.9. A magnetic induction accelerator oscillator comprising a cathode, an anode structure composed of an even number or anode segments surrounding said cathode, a control electrode surrounding" said cathode and located in the space between said cathode and anode structure, means for producing an alternating magnetic field which varies at an'audio frequency rate and which has flux lines extending parallel to said cathode, a circuit for maintaining said control electrode at a positive potential relative to said cathode, and'a connection between said cathode and said control electrode, a resistance in the cathode circuit, said resistance having such value that the electron current is substantially independent of cathode temperature, so long as the temperature remains higher than the temperature'which would cause saturation of electron current.

.10; An electron discharge device oscillator comprising a cathode, an anode structure composed of an even number of anode segments surrounding said cathode, means for causing a whirling ring of electron space charge surrounding said cathode, said means including an electromagnet for producing a magnetic field having flux. lines extending substantially parallel to said cathode, "asource of audio frequency current of constant amplitude continuously" exciting the coil of said. electromagnet for producing a changing magnetic field to thereby accelerate electrons, 'a' condenser in shunt to said source for tuning said source and said coil, and a source of unidirectional current for maintaining said anode structure at a positive potential relative to? said cathode, the values or said magnetic field and saidsour-ce of unidirectional current being such and so related that said oscillator produces radio frequency oscillations in pulses primarily as a result or the absorption of energy by .the accelerating electronsfrom the changing magneticfield.

11. A magnetic induction accelerator high frequency oscillator having a cathode, a plurality of. anodes, a magnetic field, and means for causing a whirling ring of electron space charge surrounding said cathode, said means including means to. cyclically and continuously vary the strength of the magnetic field at a frequency far less than the frequency of oscillation and over a. range of values which-causes the oscillator to produce pulses of radio frequency energy, said eIect-rons'ibeing periodically accelerated to a high velocity primarily as -a result of the rate of" change of; the magnetic field.

l 12. -A magnetic induction accelerator oscillator generating high frequencyenergyin pulses. I which are short in duration compared with the time space between them, comprising a cathode, and an anode surrounding said cathode, and means for causing a whirling ring of electron space charge surrounding said cathode, said means including means for producing a magnetic field of desired intensity, and means for chan ing the strength of said magnetic field at a ire-- quency which is half the frequency of repetition of the pulses, said electrons being periodically accelerated to a high velocity primarily as a result of the rate of change of the magnetic field.

13. A magnetic induction accelerator oscillator generating high frequency energy in pulses which are of short duration compared to the time space between them, comprising a cathode, an anode surrounding said cathode, means for causing a whirling ring of electron space charge surrounding said cathode, said means including means for producing a unidirectional magnetic field, and

means for modulating the unidirectional magnetic field strength at the frequency of repetition of the pulses, said electrons being periodically accelerated to a high velocity primarily a a result of the rate of change ofthe magnetic field.

14. In an electron discharge device oscillation generator for producing pulses of radio frequency oscillation, comprising a cathode, an anode,-

means to provide a unidirectional electric potential between anode and cathode, means for producing a rapidly rotating cylinder of' electron space charge surrounding said cathode, and

means comprising a cyclically changing magnetic field of such value as to accelerate the electrons to high velocities corresponding to those -obtain-' able by the application of considerably larger anode-to-cathode potentials, and as a result of this acceleration to produce pulses of radio frequency energy.

15. In a magnetron high frequency oscillator including a cathode, an anode, and means "for producing a magnetic field, means to accumulate. electrons into a whirling high velocity electron space charge ring surrounding said cathode for a relatively long period of time followed by utilization of the space charge to produce high frequency oscillations for a relatively short time,

said last means including source of unidirectional potential coupled between said anode and cathode for producing an electric field and a.

source of cyclically varying current for produc ing an increasing magnetic field, said last sources? being so related and having such values that said oscillator produces radio frequency oscillations. primarily as a result of the absorption of energy by the whirling electron, space charge from the increasing magnetic field.

16;, An electron discharge device oscillation. generation system comprisinga cathode, a. reso-l nant' anode structure surrounding, said cathode a magnetizable core structure formed, to provide; an aperture adapted to accommodate saidanode. structure and a pair of polar projection on 09-, posite sides of said aperture, said polar p'rojed-i tions defining a pair of pole faces, said pole faces. being non-planar and so shaped to. provide] clearly definedareas of maximumand minimum; magnetic field strength within the diameter of; said; aperture which graduallyfmerge into one another.

17. An oscillation generator system com pris-" ing a magnetizing winding, and a laminated core structure formed to provide an aperture for accommodating an evacuated envelope containing an electrode structure therein, and a pair of polar projections on opposite sides of said aperture, said electrode structure including a linear cathode and a resonant anode, said projections defining pole faces having curved surfaces to provide a magnetic field which changes from a maximum value to a minimum value in a direction perpendicular to said cathode and at points between said cathode and anode, said cathode being positioned at a point near where the maximum value occurs.

18. An electron discharge device oscillation generator for producing pulses of high frequency energy, comprising a cathode and a surrounding coaxial resonant anode structure, a source of unidirectional potential for maintainin said anode structure at a positive potential relative to said cathode, and means for accelerating the electrons emitted by said cathode to cause them to follow orbital paths of very high velocities corresponding to those obtainable by the application of appreciably larger anode-to-cathode potentials, said means including a coil and a source of alternating current of audio frequency coupled to said coil for producing a changing magnetic field which changes at an audio'frequency rate, the mean magnetic field intensity within the area bounded by approximately circular electron paths at some distance inside the anodes being somewhat greater than twice the average magnetic field intensity along the electron path, whereby electrons accelerated by the field tend to follow paths of increasing diameter as the velocity increases, the magneticfield intensity, however, inside the electron paths at or close to the anodes being somewhat less than twice the magnetic field intensity along said last paths, whereby electrons tend to follow paths of less diameter than the anode diameter.

19. A magnetron oscillator including a cathode and a surrounding resonant anode, and means for producing a magnetic field which varies in a radial direction from said cathode from a maximum value to a minimum value in the space between said cathode and anode.

20. A magnetic induction accelerator oscillation generator of high radio frequency Waves, including an electron emitting cathode and an anode, means for cyclically producing a timevarying magnetic field of non-uniform space distribution so proportioned as to tend to confine electrons from said cathode to a desired closed orbit which is inherently stable for said space distribution while continuously accelerating them along the orbit, and means for causing said generator to produce oscillations only after the electrons have been accelerated to a high velocity.

21. in an electron discharge device oscillation generator for producing pulses of radio frequency oscillation, comprising a cathode, an anode, means to provide a unidirectional electric potential between anode and cathode, means for producing a rapidly rotating cylinder of electron space charge surrounding said cathode, and means comprising a cyclically changing magnetic field of such value as to accelerate the electrons to high velocities corresponding to those obtainable by the application of considerably larger anode-to-cathode potentials, and to produce pulses of radio frequency energy, there being means in said generator which provide a distribution of magnetic field intensity which causes electrons accelerated to seek a common orbit.

22. An electron discharge device having a cathode, an anode structure surrounding said cathode and comprising a plurality of anode segments, and means for producing a changing magnetic field varying at a audio frequency rate and having flux lines extending generally parallel to said cathode, whereby the electrons are accelerated to high velocities by said changing magnetic field and caused to follow substantially circular paths near said anodes, the mean magnetic field intensity within the area bounded by some of said circular electron paths nearer to said anode than to said cathode being greater than twice the magnetic field intensity along the electron path of the stable orbit.

23. A magnetron oscillator including a cathode and a, surrounding anode, means for producing a magnetic field which varies from a maximum near the cathode to a minimum in the space between said cathode and anode, and means for superimposing a direct current magnetic field upon said varying magnetic field.

24. A magnetic induction accelerator oscillator of ultra high frequency oscillations comprising a cathode, an anode structure surrounding said cathode and composed of an even number of anode segments located on a circle, means for causing a whirling ring of electron space charge surrounding said cathode, said means including means for producing an alternating magnetic field having flux lines extending generally parallel to said cathode and which varies at an audio frequency rate, said alternating magnetic field serving to acceleratethe electrons emitted by said posing a direct current magnetic field upon said alternating magnetic field.

CLARENCE W. HANSELL.

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