US2407297A - Electron discharge apparatus - Google Patents

Description

Sept. l0, v1946. A, M, sKELLET-r- 2,407,297

ELECTRON DISCHARGE APPARATUS Filed Oct. 11, 1941 3 Sheets-Sheet 2 F/G- 4 F155 TTORNEIQ Patented Sept. 10, 1946 UNE S'TES PATENT GFFICE Bell Telephone Laboratories, Incorporated,

New York, N. Y., a corporation of New York -application Gotober 1l, 1941, Serial No. 414,630

(c1. escaso) 1s clanes. l

This-invention relates to electron discharge apparatus and more particularly to oscillation generators including electron discharge devices of the beam type.

One general object of this invention is to enable the generation, electronically, of high frequency oscillations. More specifically, objects or this invention are to: n

Attain a high operating efiiciency for electronicJ oscillation generators;

Enable the generation of oscillations over a Wide band of frequencies including frequencies corresponding to wave-lengths in the centimeter range;

Simplify the construction of electronic oscillation generators; and

Enable the generation of high power oscillam tions.

In accordance with one feature of this invention, an electron stream is controlled to produce a periodic bunching or grouping of the constituent electrons thereof, the electron bunches or groups are accelerated and are then projected at constant average velocity through a time gradient of alternating potential and along a path adjacent which one or more oscillating electrodes are mounted, in such manner that the direct current potential energy of the electrons is converted into high frequency energy.

In one specific embodiment ol this invention, the accelerated electron stream is projected to- Ward a positive target electrode through a pair of coaxial cylindrical electrodes mounted in endto-end relation and between which the oscillatory circuit is connected, the coaxial and target electrodes being maintained at successively higher positive potentials with respect to the source of the stream, and the cylindrical electrodes are made of such length relative to the operating frequency and the accelerating potential eiective upon the electrons that the electrons deliver energy to the coaxial electrodes alternately and that at the time the electrons cross the gap between the coaxial electrodes these electrodes are at substantially the same instantaneous potential.

The invention and the above-noted and other features thereof will be understood more clearly and fully from the following detailed description with reference to the accompanying drawings in which:

Fig. l is a view, partly schematic, of an electronic oscillation generator illustrative of one embodiment of this invention;

Fig. 2 is a diagram showing the time-potential relation for the cylindrical oscillating electrodes in the electron discharge device illustrated in Fig. 1;

Figs. 3, 4 and 5 are circuit diagrams illustrating several modifications of the oscillation generator shown in Fig. 1;

Figs. 6 and '7 show electronic oscillation generators illustrative of another embodiment of this invention and wherein the discharge device comprises a singleoscillating cylindrical electrode;

Fig. 8 illustrates another embodiment of this invention wherein the first cylindrical electrode is effective to produce a bunching of the electrons in the stream passing therethrough;

Fig. 9 is a .diagram showing the time-potential relation for the cylindrical electrodes in the oscillation generator Ishown in Fig. 8;

Fig. 10 is a detail view in section illustrating a form of oscillatory circuit particularly suitable for use in oscillation generators constructed in accordance with this invention and operable at extremely high frequencies, for example frequencies corresponding to wave-lengths in the centimeter range; and

Figs. 11, 12 land 13 illustrate other embodiments of this invention wherein velocity variation is utilized to effect the bunching of the electrons in the stream.

Referring now to the drawings, the oscillation generator illustrated in Fig. 1 comprises an electron discharge device including an evacuated enclosing vessel l5 housing a cathode lt, which may be of the equipotential indirectly heated type and circular as shown, a control electrode or grid Il and an accelerating electrode or grid I8 parallel to and coaxial with the cathode I6, a cup-shaped collector or target electrode I9, and a pair of cylindrical electrodes 20 and 2| mounted in end-to-end relation and coaxial with the cathode I6.

The accelerating electrode I8 is maintained at radio frequency ground potential and at a posttive direct current potential with respect to the cathode I6 -by a suitable source, such as a battery 22. The control grid l1 is connected to the cathode i6 through the grid leak resistor 24, shunted by the condenser 25, and the input resistor 23; the control grid is thus biased by the grid leak-condenser method. The cylindrical electrodes 20 and 2| and the collector or target electrode I9 are maintained at successively higher direct current potentials with respect to the accelerating grid I8 by a suitable source, Isuch as a battery 21, connected across the resistors 28, 29 and 3S. In a particular embodiment, the resistances 28 and Si! may be equal and half as large as the resistance 29. i

Connected between the cylindrical electrodes and 2| is an oscillatory circuit comprising a condenser 3|, which may be variable as shown, and a pair of equal inductances 32 connected to opposite plates of a blocking condenser 33 which is of large capacity relative to the c-ondenser 3i to allow maintenance of the cylindrical electrodes 2Q and 2| at different direct current potentials. The cylindrical electrode 2l is connected to the control grid Il by way of a condenser 34 so that the alternating current potentials of the two are in phase, the connection by way of the condenser 34 providing feedback vof some of the oscillating energy from the oscillatory circuit to the control grid. i y

For reasons which wil1 appear hereinafter, the cylindrical electrodes 2|) and 2| are made of the same length, given by the relation 7 :2.99310 w/v f (l) where f is the oscillating frequency desired in cycles per second, o is the potential of the accelerating grid I8 relative to the cathode I 5 in volts, and L is the length of eachV of the cylindrical electrodes in centimeters.

The device will be set into oscillation upon application of the direct `current potentials to the electrodes thereof. The mode of operation will be understood from the following considerations with particular reference to the time-potential relation illustrated in Fig. 2. VWhen the device is oscillating, because of the connectionrbyl way of the condenser 34, the alternating potential of the control grid I'I varies in phase with that of the cylindrical electrode 2|. The alternating potential of the cylindrical electrode 2 2 is 180 degrees out of phase with that of the control grid I'I' and the electrode 2I. The accelerating grid I8, as noted heretofore, is at alternating current ground potential.

Because of the positive potentials upon the electrodes I9, 2U and 2|, the electrons owing by the accelerating grid I8 will have potential energy equal to Ve, Where V is the potential of the battery 21 and e is the electron charge. ,Inasmuch as, as noted heretofore, the control grid vI 'I modulates the electron stream, the electrons emanating from the cathode I6 will ow by the accelerating grid I8 more or less in bunches or groups and the maximum electro-n current will flow when the control grid I1 is at its highest potential. At this time, indicated at T1 in Fig. 2, the cylindrical electrode 2!) is at its lowest potential and at the same potential as the accelerating grid IB. I-Iencethe electrons enter the cylindrical electrode 20 with no appreciable change in their velocity.- i

The electrons projected into the electrode 20 traverse this electrode while its potential, and theirs, is increasing gradually, .as indicated in Fig. 2, and at the time T2 reach the gap between the electrodes 20 and 2|. In thus traversing the electrode 2o, the electrons, because of their in..

of the cylindrical electrodes.

equal. Consequently, the electrons in crossing the gap between the electrodes 2E! and 2| suffer no appreciable change in velocity. The electro-ns then traverse the electrode 2| while its potential is increasing and deliver some of their energy to the electrode 2| and thus to the oscillating circuit. In traversing the electrode 2|, the electrons have their potential increased to a value, at time T3, equal to that of the target or collector electrode IS and, hence, subsequently :dow to the target or collector electrode with no appreciable change in Velocity. This action is repeated by each group of electrons so that energy is delivered alternately to the two electrodes 20 and 2| whereby oscillations are generated in the circuit 3|, 32.

It will be noted that the electrons in the device move through a time gradient of potential soy that they do not experience any acceleration nor any change in their kinetic energy. Hence, in the production of oscillations, the direct current potential energy of the electrons is converted or transformed into oscillating energy at the electrodes 2E! and 2|. It will be noted also that because of the phase relationships noted above, when the potential of the electrode 2| is increasing thatl of the electrode 2D is decreasing and when the potential of the former electrode reaches its maximum value, at time T3, the potential of the latter electrode is at its lowest value at a time one cycle later than the time T1, and at which, due to the irl-phase variation in potentials of the electrode 2| and grid I`I, the next group of electrons enters the cylindrical electrode 28. It will' be noted further from Fig. 2 that the direct current potentials on the electrodes Zil and 2| are of such magnitude that the direct current potential diierence between them is substantially equal to twice the maximum value of the alternating potential appearing on the electrodes 20 and 2|. The direct current potential difference between the accelerating grid I8 and the electrode 2E) and between the electrodes 2| and I3 is substantially equal t0 the maximum amplitude of the alternating potential appearing on the electrodes 20 and 2 I.

The generation of oscillations by conversion of the direct current potential energy into high frequency has been found to be highly efficient. It will be apparent, furthermore, from Equation 1 that the invention enables generation of oscillations throughout a wide range of frequencies and at exceedingly high frequencies, by correlation of the accelerating potential 'U and the length L Also, it will be appreciated that this invention enables the efficient generation of oscillations with an electron discharge device of simple construction and enables the production of oscillations of high power.

In some cases a magnetic field along and parallel to the axis of the enclosing vessel I5 may be utilized to concentrate the electron stream. Alternatively, an electron gun designed to prolduce and project a highly concentrated electron stream may be employed in place of the cathode, control grid and accelerating grid construction illustrated in Fig. 1.

In the modification, illustrated in Fig. 3, of the embodiment of this invention shown in Fig. 1 and described hereinabove, the several resistances 28, 29 and 3|! for producing the requisite potential diierences between the positive electrodes are connected directly between these electrodes and blocking condensers 35 are connected between the oscillatory circuit and the electrodes 2U and 2 l, which circuit is grounded at the mid-point of the inductance 32. Hence, the blocking condenser, such as the condenser 33 in Fig. 1, is eliminated from the oscillatory circuit.

In another modification, illustrated in Fig. 4, of the embodiment of this invention shown in Fig. 1, the condenser 34 is omitted and energy is fed back inductively from the oscillatory circuit Iii, 32 by way of a coil 35 inductively coupled to this circuit.

In a further modiiication illustrated in Fig. 5, a tunable circuit 31, 38, inductively related to the oscillatory circuit 3|, 32 is connected to the control grid l1 and the requisite negative bias for this grid is provided by a battery 39. It will be understood, of course, that such a battery may be utilized also in place of the grid leaks shown in Figs. 1,. 3 and 4.

Although in the oscillation generators illustrated in Figs. 1, 3, 4 and 5 a pair of oscillating electrodes 'Eo and 2i has been shown, a number of pairs of such electrodes may be employed, one group of alternate electrodes being connected to one side of the oscillato-ry circuit and the remainder to the other side, the various electrodes being biased at successively higher positive potentials toward the collector electrode i9 and of such relative magnitudes that when the electrons cross the gap between adjacent electrodes such adjacent electrodes are at substantially the same instantaneous potential.

In the oscillation generators illustrated in Figs. 6 and 7, a single cylindrical electrode is employed and the oscillatory circuit is coupled to the control grid i l either inductively, as shown in Fig. 6, or directly, as shown in Fig. '7. As in the generators described hereinabove, the control grid l1 is biased negative and the accelerating grid i8 is maintained at radio frequency ground potential and at a positive direct current potential relative to the cathode. The electron groups emanating from the cathode are accelerated by the positive grid i3 and projected into the cylindrical electrode iii at a time When the instantaneous potential of the electrode 2i is at its minimum value, equal to that of the accelerating grid, and rising, so that the electrons suffer no substantial change in their velocity or kinetic energy. In traversing the cylindrical electrode 2i, the electrons deliver energy thereto by Virtue of the inductive action of the stream upon the electrode 2 i whereby the direct current potential energy of the electrons is converted into high frequency energy. After leaving the electrode 2l, the electrons flow to the target or collector electrode i9 with no appreciable change in velocity.

In the oscillators described thus far the bunching or grouping of the electrons is obtained by the use of the negatively biased control grid l?. This may be eiTected also in other ways, one of which is illustrated in Fig. 8. As illustrated in the latter figure, the control grid is omitted and the cylindrical electrode 23a is twice as long as the cylinder 2l, for reasons which will be apparent from the description hereinafter, the cylindrical electrode 2l being of the length given by Equation 1. The oscillating circuit 3i, 32 is connected between the cylindrical electrodes Zila and 2l through the blocking condensers 35 and the electrodes 2l and i9 are maintained at successively higher positive potentials by the battery 27a. The accelerating electrode I8 is at radio frequency ground potential and is maintained at a positive direct current potential with respect to the cathode I6 by the battery 22. The cylindrical electrode 2ilais biased negatively with respect to the accelerating grid i8 by the battery di) and at such a value that the maximum instantaneous potential of the cylindrical electrode 29a during oscillation of the device is substantially equal .to the potential of the accelerating grid, as indicated in Fig. 9. The direct .current potential of the cylindrical electrode 2| is such that, as indicated in Fig. 9, the minimum instantaneous potential of the electrode is substantially equal to the maximum instantaneous potential of the electrode 2M so that electrons crossing the gap between the electrodes 29a and 2l suier no incre-ase in velocity.

When the device is oscillating, electrons enter the cylindrical electrode 20a when the potential of the latter is at its maximum value at a time, indicated at T1 in Fig. 9, and traverse this electrode in one cycle during which the potential of the electrode 20a rst decreases to its minimum value and then increases to its maximum value, so that no conversion of the potential energy of the electrons occurs. The electrons are projected into the electrode 2| at the time T4 and then traverse this electrode until time T5, While its potential is rising whereby the electrons deliver energy to the electrode 2|. It will be noted that because of the magnitude of the direct current potential upon the electrode Zta and the length of this electrode, electrons will be projected through the electrode in groups or bunches so that groups or bunches of electrons are projected periodically and in the proper phase relation into the electrode 2|. When the instantaneous potential of the electrode 2Go is appreciably negative with respect to the accelerating grid I8, projection of electrons into the electrode Za is prevented. As in the other embodiments of this invention described hereinabove, in the oscillator shown in Fig. 8 the electrons traverse the cylindrical electrodes with substantially no change in velocity or kinetic energy and oscillations are produced by conversion of the direct current potential energy of the electrons into high frequency energy.

In oscillation generators operable at extremely high frequencies, the oscillating circuit preferably is in the form of a cavity resonator. A suitable construction for such a resonator is illustrateol in Fig. 10 and comprises a pair of complementary semitoroidal halves 4i having annular peripheral anges 42 between which a dielectric ymember 43 is disposed, the twohalves being joined at their inner edges to the electrodes 2li and 2l. In order to maintain the alternating current potentials at the opposite ends of each of the electrodes 20 and 2| substantially equal, the halves of the cavity resonator may be provided with apertures 44 to allow some leakage of the alternating current field from within the resonator. This is particularly desirable in cases 7 where the electrodes 2U and 2l are of fairly large length relative to their diameter in which, because of the wave guide character of these electrodes, the alternating current potential between the juxtaposed ends of the two electrodes may be considerably higher than that between the outer ends of these electrodes.

The bunching or grouping of the electrons projected into the cylindrical electrode 20 may be effected also by velocity variation of the electrons emanating from the cathode I6, in conjunction with a drift space between the gap at which the velocity variation'is produced and the inlet end of the electrode 20. Two illustrative constructions are shown in Figs. 11 and 12. In Fig. 11, a toroidal cavity resonator`45 is provided with juxtaposed central reticulated portions deiining a velocity variation gap 46 across which the electrons emanating from the cathode i6 are projected. Connected to the resonator 45 are the accelerating grid I8 and a cylindrical electrode 4'! which is coaxial with the electrodes 20 and 2| and denes a drift space through which the electrons are projected. The drift space electrode 41 is made half as long as the electrodes 20 and 2i so that the electrons are bunched or grouped at the gap between the electrodes il and 20 and the bunches are substantially one cycle apart in time relation. The oscillating circuit, which is ofthe construction shown in Fig. 10, is connected between the electrodes 20 and 2| and energy is fed back from the circuit to the resonator 4'5 by way of coaxial lines 48 and 49.

In the construction illustrated in Fig. 12, an additional cylindrical electrode 50, coaxial with the electrodes 41, 20 and 2i, and an additional grid 5l connected directly to the electrode 4'! are provided. During operation of the device, the electrode il is operated at a high direct current potential and the electrode 56 is operated at a low direct current potential as by a battery 55.

For example, the electrode 41 may be operated at of the order of 1000 volts positive and the electrode 50 at of the order of 50 volts positive. The electrons emanating from the cathode i6 are velocity varied at the gap d6, projected at high potential through the electrode 4?, slowed down, from 1000 volts to 50 volts in the specific example given, and then speeded up, from 50 to 1000 volts in the specic example given, and projected into the electrode 20. This action upon the electrons produces a very highly concentrated launching thereof, which ,bunching is maintained during the flow of the electrons through the electrodes Z0 and 2i and to the target or collector electrode IS. The potential energy of the electrons is converted at the electrodes 20 and 2l in the manner described hereinabove whereby oscillations are generated.

In the oscillation generator shown in Fig. 13, which is generally similar to that shown in Fig. 1 except that the control grid il is omitted, vthe electron stream is velocity varied at the gap between the accelerating grid I8 and the cylindrical electrode 20 in such manner that most of the electrons pass through the electrode 2| during the half cycle in which the potential of the electrode 2| is increasing so that the electrons give up energy to this electrode. The electrons are, in eiiect, segregated in time so that most of them are phased correctly to deliver energy to the electrode 2|. 1

Although several specific embodiments of this invention have been shown and described, it will be understood that they are but illustrative and that various modifications may be made therein without departing from the scope and spirit of this invention as dened in the appended claims.

What is claimed is:

1. An electronic oscillation generator comprising a target electrode, means including a source and control means in cooperative relation therewith for projecting periodically groups of electrons toward said target electrode, means maintaining said target electrode at a positive potential relative to said source, and means for converting the direct current potential energy of said electrons into high frequency energy, said last means including an output electrode intermediate said source and said target electrode and adjacent the electron path to said target electrode, means biasing said output electrode at a Ypositive potential lower than the potential of said target electrode relative to said source, an oscillatory circuit coupled to said output electrode, and feedback means coupling said circuit and said control means.

2. An electronic oscillation generator comprising a target electrode, means including a source for projecting an electron stream toward said target electrode, means maintaining said target electrode at a positivepotential relativeto said source, and means for producing a grouping of the electrons in said stream and increasing the potential of said electrons at a region intermediate said source and said target electrode, Without substantially altering the velocity of said electrons in said region, said last means including an output electrode at said region in inductive relation to said electron stream, means biasing said output electrode at a positive potential lower than the potential of said target electrode relative to said source, a control means adjacent said source, and an oscillatory circuit connected to said output electrode and coupled in feedback relation to said control means.

3. The method of generating electrical oscillations which comprises producing a stream of electrons, accelerating the electron stream, successively increasing the potential of the electrons in said stream in a pair of regions traversed thereby while maintaining the velocity of said electrons substantially constant, extracting energy from said stream alternately at said regions, and feeding back a portion of the energy thus extracted to said stream adjacent the region of acceleration thereof.

4. An electronic oscillation generator comprising a target electrode, means including a source for projecting a stream of electrons toward said target electrode, means for producing along the path traversed by said stream a direct current electric field increasing positively with distance away from said source and for producing also along said path a time gradient of electric potential, said last means comprising an output electrode adjacent said path, means biasing said output electrode and said target electrode at positive potentials with respect to said source and an oscillatory circuit connected to said output electrode, and means coupled to said oscillatory circuit for cyclically varying said stream adjacent said source.

5. An electronic oscillation generator comprising a cylindrical electrode, an oscillatory circuit connected to said cylindrical electrode, a target electrode opposite one end of said cylindrical electrode, means opposite the other end of said cylindrical electrode for projecting periodically groups of electrons into said cylindrical electrode and toward said target electrode, said means including a cathode, means for controlling the electrons emanating from said cathode and an accelerating grid, means maintaining said accelerating grid, cylindrical electrode and target electrode at successively higher positive potentials with respect to said cathode, and alternating current coupling means between said oscillatory circuit and said controlling means.

6. An electronic oscillation generator comprising a target electrode, means for projecting a stream of electrons toward said target electrode,

means for successively increasing the potential of the electrons in said stream at a pair of spaced regions along the path traversed by said stream, said means including a pair of electrodes at said regions and direct current potential means biasing said electrodes at different potentials positive with respect to said rst means, the biasing potential of the one of said electrodes furthest along said path being greater than the biasing potential of the other of said electrodes, an oscillatory circuit connected between said electrodes, and control means for said stream coupled to said oscillatory circuit.

'7. An electronic oscillation generator comprising a target electrode, means for projecting an electron stream toward said target electrode, and means for producing along the path traversed by said stream a direct current potential increasing with distance toward said target electrode and for producing along said path a time gradient o-f electric potential, said last means including a pair of coaxial hollow electrodes mounted in end-toend relation along said path, direct current biasing means for said hollow and target electrodes and an oscillatory circuit connected between said hollow electrodes.

8. An electronic oscillation generator comprising means for producing an electronv stream, means for cyclically varying the intensity of said stream, means for accelerating the varied stream, means for producing a direct current electric eld along which the accelerated stream is projected and increasing positively in the direction of projection of said stream, said last means including a pair of cylindrical electrodes mounted in end-to-end relation and traversed by said stream, a target electrode for receiving said stream and means for impressing direct current potentials upon said cylindrical and target electrodes, an oscillatory circuit connected between said cylindrical electrodes, and means coupling said circuit to said stream varying means.

9. An electronic oscillation generator comprising a target electrode, means including an electron source for projecting an electron stream toward said target electrode, a rst electrode between said source and said target electrode and adjacent the electron path between said source and said target electrode, a second electrode between said first electrode and said target electrode and adjacent said path, means maintaining said first, second and target electrodes at successively higher positive potentials with respect to said source, an oscillatory circuit connected between said n'rst and second electrodes, and means for controlling said electron stream coupled Vto said oscillatory circuit.

10. An electronic oscillation generator comprising a cathode, a control electrode and an accelerating electrode in cooperative relation with said cathode, a target electrode, a pair` of coaxial cylindrical electrodes mounted in end-to-end relation between said cathode and said target electrode, means biasing said control electrode negatively, means capacitively connecting said control electrode to the cylindrical electrode furthest removed from said cathode, means biasing said accelerating electrode, said cylindrical electrodes, and said target electrode at positive potentials with respect to said cathode successively higher in accordance with their positive relation to said cathode, and an oscillatory circuit connected between said cylindrical electrodes.

11. An electronic oscillation generator comprising a cylindrical electrode, a target electrode opq 10 posite one end of saidcylindrical electrode, means opposite the other end of said cylindrical electrode for projecting an electron stream therethrough and comprising a cathode, a control means and an accelerating electrode, an oscillatory circuit connected to said cylindrical electrode, a feedback coupling between said circuit and said control means, means maintaining said accelerating and target electrodes at positive direct current potentials with respect to said cathode, said cylindrical electrode being of the length given by the relation where L is said length, v is the direct current potential of said accelerating electrode and ,f iS the operating frequency, and means biasing said cylindrical electrode at a potential such that the minimum instantaneous potential thereof is substantially equal to the direct current potential of said accelerating electrode.

12. An electronic oscillation generator comprising a pair of coaxial cylindrical electrodes mounted in end-to-end relation, a target electrode opposite one end of one of said cylindrical electrodes, means opposite the other end of the other of said cylindrical electrodes for projecting an electron stream thereinto, said means including a cathode and an accelerating electrode, an oscillatory circuit connected between said cylindrical electrodes, and means applying positive direct current potentials to said accelerating, cylindrical and target electrodes such that the minimum instantaneous potential of said one cylindrical electrode is substantially equal to the maximum instantaneous potential of said other cylindrical electrode and the minimum instantaneous potential of said other cylindrical electrode is substantially equal to the direct current potential of said accelerating electrode.

13. An electronic oscillation generator in accordance with claim 12 wherein said cylindrical electrodes are each of the length given by the relation where L is the length, o is the direct current potential of said accelerating electrode and f is the operating frequency.

14. An electronic oscillation generator in accordance with claim 12A wherein said other cylindrical electrode is of twice the length of said one cylindrical electrode and said one cylindrical electrode is of the length given by the relation.

where L is the length, o is the direct current potential of said accelerating electrode and J is the operating frequency.

15. An electronic oscillation generator comprising a cylindrical electrode, a target electrode opposite one end of said cylindrical electrode, means opposite the other end of said cylindrical electrode for projecting periodically groups of electrons thereinto, said means comprising a cathode and means for velocity varying the electrons emanating therefrom, an oscillatory circuit connected to said cylindrical electrode, means coupling said oscillatory circuit to said velocity varying means, and means biasing said cylindrical electrode at a positive potential with respect to said cathode and applying a higher positive direct current potential to said target electrode,

16. An electronic oscillation generator compris-V ing a Apair of coaxial cylindrical electrodes mounted in end-to-end relation, a target electrode opposite one end of one of said cylindrical electrodes, means opposite the other end of the other of said cylindrical electrodes for projecting periodically groups of electrons thereinto, said means comprising a cathode, means in cooperative relation therewith for velocity Varying the electrons emanating therefrom and means dening a drift space into which the velocity varied electrons are projected, an oscillatory circuit connected between said cylindrical electrodes, means coupling said oscillatory circuit to said velocity Varying means,- and means applying positive potentials, successively higher, to said other cylindrical electrode, said one cylindrical electrode and said target electrode.

17. Electron discharge apparatus comprising a pair of coaxial cylindrical electrodes mounted in end-to-end relation, a target electrode opposite one end of one of said cylindrical electrodes, means opposite the other end of the other of said cylindrical electrodes for periodically projecting groups of electrons thereinto, said means comprising a cathode, a control means and an accelerating anode, a resonant circuit connected between said cylindrical electrodes, and means applying successively higher positive potentials relative to said accelerating electrode to said other cylindrical electrode, said one cylindrical electrode and said target electrode, such that the minimum instantaneous potential of VSaid one cylindrical electrode is substantially equal to the maximum instantaneous potential of said other cylindrical electrode and the minimum instantaneous potential of said other cylindrical electrode is substantially equal to the direct current potential of said accelerating electrode, each 0f said cylindrical electrodes being of a length such that the electron transit time therethrough is substantially equal to one-half the periodicity of projection of said electron groups.

18. The method of generating electrical 0scil` lations which comprises producing a stream o1 electrons, accelerating the electrons constituting said stream, projecting said electrons through an electric field, maintaining a substantially fieldfree space adjacent the path traversed by said electrons in flowing through said electric field, and extracting energy from said electrons at a region in said path without substantially altering the kinetic energy of said electrons.

. ALBERT M. SKELLETT.

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