US3073991A

US3073991A - Electron sorting devices

Info

Publication number: US3073991A
Application number: US763856A
Authority: US
Inventors: John M Osepchuk
Original assignee: Raytheon Co
Current assignee: Raytheon Co
Priority date: 1958-09-29
Filing date: 1958-09-29
Publication date: 1963-01-15
Anticipated expiration: 1980-01-15

Description

Jan. 15, 1963 I J. M. OSEPCHUK 3,073,991

ELECTRON SORTING DEVICES Filed Sept 29, 1958 5 Sheets-Sheet 1 INVENTOR l JOHN M. OSEPCHUK ATTORNEY Jan. 15, 1963 J. M. OSEPCHUK ELECTRON SORTING DEVICES 5Sheecs-Sheet 2 Filed Sept. 29, 1958 lEna FIG. 3

' lEnc. b

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llvvnvroR' JOHN M. OSEPCHUK Jan. 15, 1963 J. M. OSEPCHUK 3,073,991

ELECTRON SORTING DEVICES Filed Sept. 29, 1958 5 Sheets-Sheet 3 SORT/N6 PEG/0N PERTURBAT/ON REG/0N IN TERACT/O/V PEG/0N INVENTOR v JOHN M. OSE'PCHUK v MM ATTORNE) Jan. 15, 1963 J. M. OSEPCHUK 3,073,991

ELECTRON SORTING DEVICES Filed Sept. 29, 1958 5 Sheets-Sheet 4 SORT/N6" REG/01V INTERACTION REG/ON l f I su/v PER TURBA TION PEG/0N REG/0N l/V Vf/V TOP JOHN M. OSEPCHUK FIG. 8 /WM M A T TOR/YE Y Jan. 15, 1963 J. M. OSEPCHUK 3,073,991

ELECTRON SORTING DEVICES Filed Sept. 29, 1958 5 Sheets-Sheet 5 FIG 90 l0,

c1 :1 I: :1 1:1 63 1:1 1:1 97 E GB 981, .96 93 INVENTOP JOHN M. OSEPCHUK ATTORNEY 3,073,991 ELECTRON SORTENG DEVICES John M. Osepchuk, Waltham, Mass, assignor to Raytheon Company, Lexington, Mass, a corporation of Delaware Filed Sept. 29, 1958, Ser. No. 763,856 14 Claims. (Cl. 315-393) This invention relates in general to an electron sorting device for producing a density modulated electron beam and is particularly concerned with a device utilizing the interaction between a traveling electromagnetic wave and an electron beam moving in synchronism with a component of the wave and in which the interaction occurs in an 'unvarying electric field having its lines of force at right angles to an unvarying magnetic field. The invention has general utility in electronic apparatus utilizing a density modulated electron beam.

The invention contemplates utilizing a phenomenon denoted electron sorting to initiate modulation of an electron beam. In an electron sorting device, electrons having an orbital component of motion are injected into a high frequency field in such a manner that the electrons follow a generally arcuate trajectory while moving in synchronism with the phase velocity of the electromagnetic wave associated with the high frequency field. The influence of the high frequency field causes some electrons to move upwardly with respect to the field and other electrons to move downwardly. Those electrons which move downwardly are absorbed by a negatively polarized electrode and thus are removed from the stream of electrons injected into the field. The result of this electron sorting mechanism is a density modulation of the electron stream since some segments of the stream have a deficiency of electrons. The electrons remaining in the stream are caused to further interact with the high frequency field and progressively deliver energy to that field whereby the electron sorting mechanism, once initiated, is self-sustaining.

The invention finds immediate employment in high frequency oscillatory and amplifying devices which utilize the prolonged inter-action between a stream of .charged particles and a guided electromagnetic wave traveling along a wave retardation circuit. Devices of this type are customarily designated traveling wave tubes. Traveling wave tubes employing crossed electric and magnetic fields are commonly termed M-type tubes. M-type tubes may be operated as amplifiers or oscillators and may be further classified as either forward wave tubes or backward wave tubes. In a backward wave tube, the electron beam travels at a velocity which is synchronous with the phase velocity of a traveling wave space component moving in a direction opposite to that of the energy flow along the wave circuit. That is, a backward wave tube is characterized by an electron beam traveling in one direction and the energy of the induced wave traveling in the opposite direction. In a forward wave tube, the electron beam and the energy of the induced wave characteristically travel in the same direction.

A baclmard wave tube is customarily provided with a wave retardation line, more usually termed a delay line, constructed so that the phase velocity of the fundamental wave travels in a direction inverse to the direction of the group velocity. A forward wave tube, in contradistinction, is provided with a delay line constructed so that the phase velocity of the fundamental wave is in the same direction as the group velocity. The fundamental wave is defined as that component of a wave having the largest phase velocity.

The usual crossed field type of traveling wave tube utilizes an elongated delay line spaced from a coextensive electrode, known as the sole and a DC. field is impressed between the delay line and the sole in such a manner that the delay line constitutes the positive elec- 3,073,991 Patented Jan. 15, 1963 ice trode and the sole constitutes the negative electrode. The space between the delay line and the sole is denoted as the interaction region. In order to achieve maximum efiiciency in M-.type tubes, an electron beam, emanating from an electron gun, is projected into the interaction space in a manner intended to cause the beam to follow a linear path through the interaction region. Bunching of electrons in the beam (beam modulation) is caused by a phenomenon known as phase focusing which has been analyzed and is documented in the technical literature e.g. the article entitled, Fundamental Phenomena in Traveling Wave Tubes appearing in LOnde Elec trique No. 325, April 1954. In the conventional M- type tube the electron beam enters the interaction region initially unmodulated and modulation of the beam by phase focusing occurs progressively in the interaction region together with the induction of H.'F. (high frequency) currents in the delay line. Because phase focusing has heretofore been utilized exclusively as the initial mechanism for modulating the electron beam it has not been feasible to build a traveling wave tube having a negatively polarized delay line because negative polarination of the line causes unfavorable phase focusing of the beam. That is, with a negative delay line the phenomenon ofphase focusing opposes favorable bunching of electrons in the beam.

This invention includes utilizing the phenomenon denoted electron sorting to commence modulation of the electron beam in M-type tubes. By employing electron sorting rather than phase focusing, it has been found to be feasible to construct an M-type traveling wave tube employing a negatively polarized delay line. In positive line tubes the mechanism of electron sorting is employed to aid the normal phase focusing modulation of the beam. By means of electron sorting there is introduced .a controlled initial modulation of the beam at the appropriate high frequency. A successful realization of a negative line tube is particularly advantageous, since efficient operation of such a tube causes much of the beam current to flow to the positive electrode and to the collector electrode and the beam current which does flow to the :delay line arrives with low kinetic energy. For this reason, a negative line tube avoids the problems and power limits concerned with the heat dissipation capabilities of positive delay lines in which an appreciable portion of .the beam current normally flows in the delay line. A negative line traveling wave tube employing beam sorting now makes possible the realization of a high powered device for amplifying and generating wave energy in the millimeter and centimeter wave length regions.

The nature of the present invention, together with its various features and advantages, can be more readily understood by perusal of the following detailed description when considered in conjunction with the illustrative embodiments shown by the accompanying drawings in which:

FIG. 1 diagrammatically illustrates the phase focusing action which occurs with relation to a positively polarized delay line;

FIG. 2 diagramatically illustrates the electron sorting mechanism with relation to a positively polarized delay line;

FIG. 3 diagrammatically illustrates the phase focusing action occurring in relation to .a negatively polarized delay line;

FIG. 4 diagrammatically illustrates the electron sorting mechanism with relation to a negatively polarized delay line;

FIG. 5 represents electron sorting in a high frequency field supported .by a modulated electron beam;

FIG. 6 represents an elemental form of traveling wave tube employing electron sorting;

FIG. 7 is a schematic representation of a traveling wave tube having a positively polarized delay line and in which the mechanism of electron sorting is employed;

FIG. 3 is a schematic representation of a traveling wave tube having a negatively polarized delay line and in which the mechanism of electron sorting is employed to provide initial modulation of the electron beam;

FIG. 9 illustrates a modification of the tube shown in FIG. 8;

FIG. 10 schematically depicts a traveling wave tube having two oppositely polarized delay lines and in which the mechanism of electron sorting is employed;

FIG. 1 -l shows, in schematic form, an improvement upon the tube shown in FIG. 10; and

FIG. 12 depicts another type of traveling wave tube employing electron sorting.

Referring now to FIG. 1, which diagrammatically illustrates the force lines of the high frequency field of a travelling electromagnetic wave as they would appear to an electron moving with a translational velocity V which is equal to-the velocity of a space harmonic of the wave, there is shown a delay line 1 of the interdigital type along which the wave propagates, and a sole electrode 2 spaced from the relayline. An unvarying electric field E is established between the delay line and the sole by impressing a positive potential on the delay line. 7 An unvarying magnetic field B is established at right angles to the D.C. electric field to cause electrons subject to the action of the crossed fields to move in a desired direction, from left to right for example, at an average velocity t The dashed line 3 represents an equipoten-tial surface along which electrons are introduced at the average velocity V Assuming that a component of a high frequency wave is propagating along the delay line, the lines of force of its field are displaced in space at the phase speed of the wave component. That is, the HF. field moves along the delay line, from'left to right for example, at a speed which is equal to the phase velocity of the wave component. To an electron moving with the same velocity as the phase velocity of the traveling wave component, however, the field appears to be stationary. It will be seen from FIG. 1 that the transverse component E of the HF. field in the regions a and c is in the same direction as the electric field E and the transverse component E in the region b ,is opposed to the electric field E so that the resultant field becomes alternately weaker at b and stronger at a and c than the D.C. field.

' ,Two components of the high frequency field come into play in the interaction mechanism between electrons and the traveling wave. The transverse component E of the HF. field accelerates or decelerates, according to its direction, the electrons velocity parallel to the delay line and bring electrons in the field into a position such that they are bunched in the favorable phase and are subjected to a force which pushes them towards the anode without changing their longitudinal speed, thereby causing the electrons to 'give up part of their potential energy to the HF. field. It is seen thus, that the normal phase focusing action which is present in'a traveling wave tube having a positive delay line isaccomplished by redistributing the electrons in the HF. field so that those electrons which initially were in an unfavorable phase are moved into a favorable phase. This can be more fully appreciated by considering an electron, having an initial rectilinear trajectory, that is, an electron having no orbital motion, which is injected at point 4 in FIG. 1 into the interaction space between delay line 1 and sole 2. Since the'transverse H.F. field component E at point 4 reinforces the field E the electron is accelerated'vand, as electrons in an electric field tend to responds to a favorably phased electron.

move perpendicularly to lines of force of the field, the electron moves along the curve 5 toward the delay line delivering its potential energy to the HF. field. An electron at point 6 is subjected to a decelerating force because the transverse HF. field component E now opposes the constant field E therefore the electron at point 6 is slowed down and moves along the curve 7 toward the delay line. A similar analysis shows that an electron at point 8 will move along the curve 9 toward the delay line. Thus, phase focusing causes a bunching of electrons in the beam in the favorable phase.

An electron at point 10 in FIG. 1 is in the more unfavorable phase since the action of .the RF. field causes that electron to move downwardly toward the sole 2. The sole, however, in a conventional traveling wave M-type tube, is usually maintained sufliciently negative so that none or only a small fraction of electrons strike the sole and are absorbed.

The mechanism of electron sorting is distinct from phase focusing in that Where electron sorting is employed 'most of the unfavorably phased electrons are removed stood by considering that an electron following a cycloidal trajectory is, in its own frame of reference, traveling in a circular orbit. That is, if an orbital electron is moving, from left to right for example, synchronously with the high frequencyfield in FIG. 2, then to the electron it will 'appear to be moving in a circle with respect to that field,

although to a stationary observer the electrons track will describe a cycloid. When the cusp of the cycloidal trajectory just grazes the surface of the sole 2 in FIG. '2, to the electron it will appear that its circular orbit is tangent to the surface of the negative electrode. Thus, if an electron 11, traveling along a circular orbit is introduced into the HF. field of FIG. 2 so that the orbit of the electron is represented by the circle 12 tangent to the negative electrode 2, an analysisof the effect of the HF. field on the electron shows that the circular orbit 12 is lifted upwardly toward the positive electrode and that the electron 11 does not strike the sole. The electron 11 cor- The orbit of an unfavorable phased electron 13, for comparison, is

represented by the circle 14 in FIG. 2. An analysis of the effect of the HF. field on the electron 13 shows that its circular orbit is pushed downwardly so that the electron strikes the negative electrode 2 and is absorbed. In tubes employing electron sorting, the negative electrode must not be biased so heavily negative that approaching electrons are repelled. In tubes employing phase focusing,

kinetic energy in approaching that electrode and therefore strike the negative electrode with reduced velocity at which time their remaining kinetic energy is transformed into heat energy. For this reason the negative electrode does not have stringent heat dissipation requirements. If electrons absorbed by the negative electrode 2 strike that electrode with sufiicient energy, secondary electrons will be emitted and may interfere with efiective electron sorting. To inhibit secondary emission, the negative electrode may be coated with a material having low secondary emission characteristics, such as carbon, or the negative electrode may be fabricated of a material selected for its low secondary emission properties. The removal of unfavorable phased electrons in an electron stream by the electron sorting mechanism produces a density modulation of the'stream and the density modulated stream may then be used in a multitude of applications in the electronics art.

The discussion of phase focusing and electron sorting, in connection with FIGS. 1 and 2, has been limited to the interaction occurring between electrons and a traveling wave propagating along a delay line 1 polarized positive with respect to the sole 2. There will now be considered, with reference to FIG. 3, the phase focusing action occurring between electrons and a traveling wave propagating along a delay line 15 polarized negative with respect to a sole electrode 16 and it will become apparent, as the explanation proceeds, that with this arrangement, the effect of phase focusing is adverse to propitious modulation of an electron beam. FIG. 3 illustrates the force lines of the high frequency field of a traveling electromagnetic wave propagating along the delay line 15, the latter member being negatively polarized with respect to the sole. Since a potential difference exists between delay line and sole, an electric field E is established which extends between the two members. A constant magnetic field B, at right angles to the DC. electric field, is established by any suitable means, such as a permanent magnet. As with FIGS. 1 and 2, it is to be understood that to an electron traveling with the same velocity as the phase velocity of the traveling wave, the high frequency field appears to be stationary. It will be observed in FIG. 3 that the transverse component E of the HF. field in the regions a and c is in the same direction as the electric field E and the transverse component E in the region b is oppositely directed to the field E so that the resultant field E is stronger at a and c and weaker at 11 than the electric field E Consider an electron having a rectilinear trajectory, viz, no orbital component of motion, injected at point 17 in FIG. 3 with a velocity equal to the phase velocity of the traveling wave. Since the transverse HF. field component E at point 17 reinforces the field E and the electron is accelerated and moves along the curve 18, perpendicularly to the lines of force, until the electron meets and is absorbed by the delay line. An electron at point 19 is subject to a decelerating force as the trans verse field component E now opposes the field E therefore, the electron at point 19 is slowed down and moves along the curve 2% until it is absorbed by the delay line. Similar analysis shows that an electron at point 21 will move along the curve 22 until it is absorbed by the delay line. In order for electrons to deliver their potential energy to the HF. field they must move closer to the positive line. In FIG. 3, it is seen, however, that the effect of phase focusing is to cause electrons to be bunched in the unfavorable phase where they are pushed toward the negative electrode. Hence, Where the delay line is polarized negative, the effect of phase focusing is adverse to the transfer of energy from an electron beam to the high frequency field. More than this, the effect of phase focusing tends to cause absorption of the electron beam by the negatively polarized delay line.

The electron sorting action which occurs with a negatively polarized delay line is diagrammatically shown in FIG. 4 which depicts the same delay line, sole, electric, magnetic, and high frequency fields illustrated in FIG. 3. Consider first an electron, having an orbital motion, situated in the favorable phase of the HF. field. Such an electron is the electron 23 moving in the circular orbit 24. The effect of the favorable phase of the HR field is to push the electron 24- upward toward the positive polarized sole 16 so that the electron at its nadir does not strike the delay line and as time progresses the average position of electron 24 gradually approaches closer to the sole whereby energy is delivered by the electron to the HF. field. Since the H.F. field is strongest adjacent the negatively polarized delay line and weakest adjacent the sole and because the average position of electrons injected into the field is close to the delay line, a strong initial interaction is achieved between electrons and the HP. field. Of course, the interaction grows weaker as the favorably phased electrons move closer to the positive electrode 15. An electron 26, situated in the unfavorable phase of the HF. field, is shown in FIG. 4 traveling in the circular orbit 27. The efiect of the unfavorable phase of the field is to pull the electron 26 downwardly toward the delay line 15 so that at some point in its orbit the electron strikes the delay line and is absorbed. The electron sorting mechanism removes from an electron beam electrons in the unfavorable phase by causing their absorp- .tion in the negative electrode, and the remaining electrons are predominantly in the favorable phase so that the electron beam is, in effect, density modulated. It is seen, therefore, that with a negatively polarized delay line, the effect of phase focusing adversely affects the desired bunching of electrons in the beam, whereas electron sorting produces electron bunches which are in the desired phase of the high frequency field. By injecting electrons which have an orbital component of motion into the H.F. field, the mechanism of electron sorting is made to predominate over the adverse phase focusing effect and the desired density modulation of the electron beam is attained. It is noteworthy that space charge effects tend to aid the electron sorting action because electron bunches, by virtue of space charge effects, tend to congregate into spherical charges and thus electron bunches, once formed, tend to form coherent electron aggregates which resist the disintegrative phase focusing force.

The mechanism of electron sorting has thus far been described with reference to an electromagnetic wave propagating along a delay line. The delay line may be replaced by a density modulated electron beam as a wave circuit element since it is known that a density modulated electron beam does support a high frequency field. Thus, in FIG. 5 an electric field E is established between two parallel plates, the upper plate 28 being polarized positive with respect to the lower plate 29 by impressing a potential between the two plates. A magnetic field B is established transversely to the DC. electric field. In lieu of a delay line, a modulated electron beam 30 is caused to flow between the two plates, the electron beam being positioned adjacent the positively polarized plate 28. A stream of electrons, in which the electrons have an orbital component of motion, is introduced into the crossed fields so that in the absence of a high frequency field the electrons follow the arcuate trajectory 31 which lies adjacent to the negative plate 29. Since the electron beam 34) is density modulated, it sustains a high frequency field which influences the orbital electrons to cause those electrons in the unfavorable phase to be pushed downwardly onto the negative electrode and those electrons in the favorable phase to be pulled upwardly and follow the arcuate path 32. Now, it is known that an energy transfer between two beams of charged particles may be made to occur if at least one of the beams carries a density or velocity modulation. This energy transfer between the beam following the path 32 and the density modulated beam 30 causes an amplification of the space charge variation in beam 30 and hence an intensification of the high frequency field which in turn enhances the effectiveness of the electron sorting action. Thus, once an effective transfer of energy from the beam 32 to the beam 30 occurs the interaction tends to become self-perpetuating, inasmuch as better electron sorting permits more energy to be transferred to the HF. field. While the beam 30 was described as being initially density modulated, it should be understood that an unmodulated electron beam contains sufficient density variations so that a weak high frequency field accompanies the unmodulated beam. For this reason, electron sorting will occur in the apparatus of FIG. 5 even though the beam 30 is initially unmodulated. Once electron sorting commences, the m teraction between the two beams will rapidly build up to permit a considerable amount of energy to be transferred to beam 30. By this means two density modulated beams are produced. The ultimate utilization of one or the other or both of the modulated beams will, of course, depend upon whatever apparatus employs the beam sorting device.

An elemental form of the invention is schematically illustrated in FIG. 6 which depicts the internal elements of a traveling wave tube of the M-type and the potentials which are applied to such elements. An electron gun, here indicated by a cathode 41 and an accelerating electrode 42, is positioned at one end of the tube and a collector electrode 43 is disposed at the opposite end. A delay line 44 is spaced from a sole electrode 45 and a DC. source of electric potential, represented by the battery 46, is connected to cause the delay line to be polarized negatively with respect to the sole, thereby establishing an electric field E between those two members. A constant magnetic field B is established transversely to the electric field E so that the combined effect of the crossed fields causes electrons subject to the crossed fields to travel from the gun toward the collector. The electron gun is constructed to cause electrons ejected from the gun to have an orbital component of motion and the electrons, therefore, follow an arcuate trajectory, since the electrons are moving in an orbit while simultaneously being translated under the action of the crossed fields. In the absence of any other fields, an electron, once ejected from the gun along an arcuate path, continues to maintain an arcuate path, as indicated by the broken line 47. However, a wave propagating along delay line 44 has associated with it a H.F. field which tends to move electrons away from or toward the delay line, depending on the phase of the electrons with respect to the HF. field. Thus, if wave energy is present on the delay line, some of the electrons traveling along the arcuate path 47 are driven into the negatively polarized delay line 47 and are absorbed upon contact with that member whereas other electrons are raised toward the posi tively polarized sole 42 and continue to interact with HF. field of the traveling wave. Electrons which completely traverse the interaction space between delay line and sole are absorbed by collector electrode 43 which is maintained at a potential below the potential impressed on the sole 45. If desired, the collector electrode need not be an independent element but may be an extension of the sole 45. However, by employing an independent collector electrode the beam can be collected at a lower voltage thereby decreasing the heat which must be dissipated by the tube. Assuming that the tube of FIG. 6 is utilized as an oscillation generator, and that delay line 44 is constructed to have a backward wave fundamental, an output signal is derived from an output coupling 48 located at the end of the delay line adjacent the electron gun. Moreover, as the H.F. field associated with a backward wave delay line is most intense adjacent the electron gun end and least intense adjacent the collector end, the intense H.F. field at the gun end of the delay line causes immediate and potent electron sorting of the beam emanating from the electron gun. It is to be understood that when an electron beam is initially injected into the interaction space, noise components in the beam induce waves on the delay line so that a HP. field is always present whenever a beam is present to cause beam sorting to be initiated in an oscillator tube. An osc1l lator tube having a negatively polarized delay line is ad vantageous inasmuch as the electron beam is injected along an arcuate path lying adjacent to the delay l ne, thereby permitting the electrons to interact with the untially weak field which exists close to the delay line at the outset before oscillations have built up to appreciable strength.

Where the tube shown in FIG. 6 includes a delay line having a backward wave fundamental and is to be employed as an amplifier, an input signal is impressed on the delay line 44 through the input coupling 49 so that a high frequency field of appreciable strength is present in the interaction space. In this circumstance the arcuate path of the electron beam may be spaced somewhat farther from the delay line than is the case in an oscillator tube since the high frequency field of the wave present on the delay line in an amplifier can influence electrons at appreciable distances from the delay line and effectuate electron sorting.

Referring now to FIG. 7 of the drawings, which represents in diagrammatic form a crossed field traveling wave tube employing electron sorting, there is shown a delay line 50, constructed to have either a backward wave or forward wave fundamental, spaced from an elongated electrode 51, known as the sole, and a sorting electrode 52 which is preferably coplanar with the sole, although this disposition is not essential. An electron gun, here indicated by a cathode 53A, a grid structure 533 and an accelerating electrode 53C, acts as an electron source and a collector electrode 54 is positioned at one end of the tube to absorb those electrons which completely traverse the interaction region. It is to be understood that the aforementioned structure'is contained within an evacuated envelope, not illustrated, provided with the necessary leads for establishing electrical connections with the internal elements. An unvarying magnetic field B is established throughout the tube by any suitable means, such as a permanent magnet or an electromagnet. The symbol signifies that the magnetic field is directed into the plane by the drawing. A DC. electric field is established between the delay line 50 and the sole 51 by the voltage source 55 so that the polarity of the delay line is positive with respect to the sole. By means of a variable voltage source 56 the sorting electrode 52 may be made more positive or more negative with respect to the cathode 53A. The delay line is provided with couplings 57 and 58 at either end by means of which input signals may be impressed and H.F. energy extracted. If the tube is employed as an auto oscillator, only an output coupling need be provided and the frequency of oscillation may be changed by varying the voltage between the delay line and the sole. In a backward wave oscillator the output coupling would be located adjacent the gun end of the tube, whereas in a forward wave oscillator the output coupling may be located at either end. Where the tube is employed as a backward wave amplifier, input signals are coupled into the tube at 58 and the output taken from coupling 57. If the tube is a forward wave amplifier the output is taken at 58 and the input signal inserted at 57. The optics of the electron gun causes electrons emitted from the cathode 53A to have an orbital component of motion, and the electrons therefore follow a generally cycloidal path 69A which path may be adjusted by the variable voltage source 56 to cause the electrons to graze the negatively polarized sorting electrode 52 at the collection point 59. .Assuming that H.F. wave energy is traveling along the delay line 50, the associated H.F. field can be resolved into a longitudinal component B and a transverse component E as previously de scribed in connection with FIG. 2. Electrons entering the sorting region which encounter a positive longitudinal component E of the H.F. field are caused to be defiected upwardly toward the delay line and do not strike the negative electrode; those electrons which encounter a negative longitudinal component E are deflected downwardly and are absorbed by the sorting electrode 52. Thus, there takes place in the sorting region an absorption of electrons which are in an unfavorable phase with respect to the HP. field so that most of the electrons which leave the sorting region enter the interaction region in the favorable phase of the HP. field. Since the unfavorable phase of the HF. field has associated with it less electrons than the favorable phase, the beam can be considered as consisting of bunches of electrons. In

its simplest aspect, this sorting process is the result of the movement of individual electrons perpendicular to the HF. field of the delay line and the magnetic field B. It should be understood that the initial trajectory of the electrons need not be cycloidal but may follow any arcuate path which will just graze or closely approach the sorting electrode 52. When the bunched electron beam enters the interaction space, it will continue to follow a generally cycloidal path unless a perturbation is introduced to change the beams trajectory. For the most efiicient operation, it is necessary that the electron beam follow a rectilinear path in the interaction region. The traveling wave tube is, therefore, provided with means to perturb the beam to cause the beam to follow a rectilinear path. The perturbation is caused, as here illustrated, by an electrode 62, termed a phasing electrode, which is situated between, and insulated from, the sole 51 and sorting electrode 52. By establishing an electric field between the phasing electrode and the delay line, a perturbation is introduced which, if properly adjusted, will cause the trajectory of the electron beam to be changed from a cycloidal to a more rectilinear path. To

those familiar with electron optics, it is manifest that the desired perturbation may optionally be achieved by locally distorting the magnetic field in the tube at appropriate locations. In FIG. 7 the electrons spend approximately one half of the period of a cycloid in the sorting region so that there is only one electron collection point, indicated at 59. The sorting region can be extended, if desired, to permit the electrons to remain in that region for a longer period of time for more effective initial modulation of the beam. Thus, the region may be extended to provide two or more collection points so that the favorably phased electrons describe three halves or more of a cycloid in traversing the sorting region. As the beam enters the interaction region, the trajectory of the electrons is changed from a cycloidal to a rectilinear path, by the phasing electrode 62. By means of the phasing electrode, a phase shift may be introduced between the electron bunches in the beam and the RF. field. The phasing electrode is convenient, since, if the sorting action does not bunch the electrons at exactly the favorable phase of the HF. field, the phase of the electron bunches can be corrected. The required location of the phasing electrode varies according to the intended application of such a system. The phasing electrode is maintained, by the variable voltage source 61, at a DC. voltage which alters the relative phase between the electrons in the beam and the interacting space component of the Wave traveling along the delay line, the sense depending on whether there exists in the phasing region the first or second half of the cycloid period of the electron trajectory. The electron beam formed in the sorting region proceeds through the perturbation region and thence into the interaction region where the modulated beam transfers energy to the wave traveling along the delay line. The electrons in the interaction region deliver their po' tential energy to the high frequency field and, in doing so, move closer to the positively polarized electrode 50. The predominant number of electrons in the interaction region follow a path exemplified by the trajectory 60B and are absorbed by the collector electrode 54 An appreciable number of electrons in the interaction region, however, deliver all of their potential energy and strike the delay line 56, whereupon the kinetic energy of the impinging electrons is transformed into heat energy. The heat energy which is required to be dissipated by the delay line is related to the output power delivered by the tube, and, because a delay line cannot easily be cooled, the heat dissipating capabilities of the delay line impose a limitation upon the maximum power obtained from such a tube.

The construction of the traveling wave tube depicted in FIG. 7 permits the tube to be pulsed merely by varying the potential of the voltage source 56. It can be appreciated that if the sorting electrode, 52 is'made sufficiently positive with respect to the cathode 53A of the electron gun, all the electrons emanating from the gun will be attracted toward the sole and the entire electron beam will be absorbed in the sorting electrode. Hence, by varying the voltage of source 56, the tube can be pulsed on and off. If the tube is employed as an oscillator, its frequency of oscillation may be changed by adjusting the voltage impressed by battery 55 between delay line 56 and sole 51. The amplitude of the oscillations may be modulated by adjusting the voltage impressed by battery 56 between sort ing electrode 52 and the cathode of the electron gun, since the potential of the sorting electrode with respect to the cathode 53A determines the proportion of the beam which is absorbed. Thus, frequency modulation and amplitude modulation are effected in the tube by simply varying the voltages supplied by sources 55 and 56. As is well known, the frequency of a backward wave oscillator may be continuously varied over an extremely wide frequency range and, of course, the delay line 50 shown in FIG. 7 may be of the backward wave type. v

FIG. 8 illustrates an embodiment of the invention employing electron sorting in a traveling wave tube having a delay line 63 negatively polarized with respect to the sole 64 by means of a battery 65. It is to be understood that delay line 63 may be constructed to have either a forward or backward fundamental wave component. By suitable .means, such as an electromagnet or a permanent magnet,

an unvarying magnetic field B is established in the tube transversely to the electric field existing between the delay line 63 and sole 64. An electron gun, represented by a cathode 66, a grid '77, and an accelerating electron 67, is designed to cause electrons having an orbital component of motion to follow an arcuate path 68 into the sorting region. If the tube is to be employed as an oscillator the cusp of the arcuate path preferably grazes the surface of the delay line at the collection point 69. The sorting region, in this illustration, is extended so that the electrons in the unfavorable phase may also be collected at a second point 70 which is spaced from the first collection point by one cycloidal period. The HP. field in the sorting region causes electrons in the favorable phase to be deflected upwardly and electrons in the unfavorable phase to be deflected downwardly, as previously explained in connection with FIG. 4. Electrons which are deflected downwardly in the sorting region are removed from the electron beam upon striking the delay line 63 and being absorbed by that member. In order to inhibit secondary emission, the delay line in the sorting region is coated with carbon or some other suitable material which has low secondary emissivity. After transit of the sorting region, the electrons remaining in the beam enter a perturbation region where the beam is acted on by a perturbation field established by the phasing electrode 71, whereby the beam is thenceforth caused to follow a rectilinear path to the collector electrode 72. The phasing electrode 71 is situated in, but insulated from the positive sole electrode 64. In establishing an electric field between the phasing electrode and the sole 64 by means of a variable voltage source 73, a perturbation is introduced which causes the trajectory of the electron beam to be changed from an arcuate to a more rectilinear path. The electron beam passes through the perturbation region into the interaction region where the density modulated electron beam trans fers energy to the wave traveling along the delay line. As the electrons in the beam deliver energy to the traveling wave, the electrons move closer to the positive electrode 64 since it is the potential energy of the electrons which is transferred to the wave. The majority of electrons in the interaction region, therefore, follow a path exemplified by the trajectory 74 and are absorbed by the collector electrode 72 which is maintained at a potential less positive than the potential on the sole to reduce the heat generated by the impinging beam. Notall the electrons in the interaction region are absorbed by the collector elec- 1 I trade since an appreciable number of electrons in the interaction region deliver all their potential energy and strike the positive electrode 64. The kinetic energy of electrons striking sole 64 is turned into heat energy which must be dissipated by the positive electrode if the tube is not to be damaged. Since the sole essentially is a flat plate, it is readily cooled by circulating a coolant fluid through channels in the plate. A delay line, on the other hand, is a more complex structure and cannot be so readily cooled. As a matter of interest, the power developed by a traveling wave tube of the type shown in FIG. 7 is largely limited by the heat which must be dissipated by the delay line 50. It has been experimentally found that the power required to be dissipated in heat by a positively polarized delay line (FIG. 7) is in the order of one to three times as great as the output power derived from the tube, whereas the power required to be dissipated as heat by a negatively polarized delay line (FIG. 8) is in the order of one tenth to three tenths of the output power of the tube. Therefore, for tubes having comparable power output, the heat dissipated by a delay line in a tube of the type shown in FIG. 8 is in the order of ten times less than the heat dissipated by a delay line in a tube of the type shown in FIG. 7. Because of this gmcumstance, traveling wave tubes having a negatively polarized delay line of the type portrayed in FIGS. 6 and 8 can be constructed to deliver amounts of output power which are quite beyond the ability of comparable traveling waveemployed, depending upon the construction of the delay line 63, as a forward Wave amplifier, forward Wave oscillator, backward wave amplifier, or backward wave oscillator. Where the tube is used as a forward wave amplifier or oscillator, the delay line is constructed to have a fundamental wave component which travels in the same direction as the electron beam. The output from a forward wave tube is extracted through the coupling 75 extending from the delay line adjacent the collector end of the tube and signal energy is introduced into the tube through the coupling 76 secured to the delay line adjacent the gun end of the tube. Where the tube is used as a backward-wave amplifier or oscillator the delay line 63 is constructed so that the fundamental component of a wave propagates along the delay line in a direction opposite to the direction of the electron beam. The output of a backward wave tube is derived through the coupling 76 and input signals are coupled into the tube at 75'.

While the embodiments of the invention shown in FIGS. 6, 7 and 8 are illustrated in the form of linear tubes, it is entirely feasible to embody. the invention in tubes of circular form. A circular tube, in essence, is simply a linear tube, such as is shown in FIGS. 6, 7 and 8, which has been bent into a circle. For example, FIG. 9 depicts a circular tube which is essentially the same as the tube con-.

taining a negatively polarized delay line. It will be observed that within the envelope 80 of the circular tube there is contained a delay line 81, preferably of the interdigital type and constructed to have a backward fundamental Wave component, a sole electrode 82. concentric with the delay line, a phasing electrode 83 situated in and insulated from the sole electrode, a collector electrode 86, and an electron gun represented by a cathode 84, a grid 88 and an accelerating electrode 85. It is to be understood that the potentials applied to these internal elements are similar to the potentials applied to the tube elemens of FIG. 8. It will be observed that the delay line 81 of the circular tube is concentric with the sole 82 and that the sole is internally situated with regard to the delay line. The delay line 81 is mechanically attached to the metallic tube envelope 8% and, therefore, for reasons of safety, it is desired that the delay line and tube envelope be maintained at ground potential. Since the delay line 81 is polarized negatively with respect to the sole, a high positive voltage is required to be impressed on the sole. By locating the positively polarized electrode 82 in the interior of the circular tube, an advantage is derived in that a somewhat weaker magnetic field B is required than is the case where the negative and positive electrodes in the circular tube are reversed in position. The reason for this is that the average speed of electrons in the beam is equal to the ratio where E is the intensity of the DC. electric field and B represents the intensity of the magnetic field. The elec tric force acting on the electrons is balanced by the Lorentz force due to the speed of electrons and to the magnetic field. The centrifugal force exerted on an electron moving along the circular path 87 tends to aid the Lorentz force exerted on the electron by the magnetic field B so that the magnetic field intensity B can be reduced in intensity by an amount which offsets the centrifugal force. The significance of this is that a smaller magnet may be used to supply the required magnetic field intensity.

FIG. 10 schematically depicts a species of traveling wave tube employing electron sorting in which two oppositely polarized delay lines are utilized. An electric field is established between the positively polarized delay line 99 and the negatively polarized delay line 91 by suitable connections to a voltage source, here represented by the battery 92. A magnetic field B is established transversely to the electric field by any suitable means, such as an electromagnet. An electron gun comprising a cathode 93, grid 94, and accelerating electrode 95 is designed to inject electrons having an orbital component of motion into the crossed field region whereby the electrons follow an arcu ate path, such as the path 96. At the end of the tube opposite the electron gun end, there is disposed a collector electrode 97 which absorbs the electron beam after it traverses the interaction region between the two delay lines. The two delay lines may be constructed to have either a forward or a backward fundamental wave component. Now a wave traveling along one of the

delay lines

99 or 91 will induce a wave on the other delay line. By appropriate design of the delay lines, the HF. fields of the two waves may be phased so as to enhance the interchange of energy between the electron beam and V the traveling Waves. Since two complementary H.F. fields are present in the interaction region, one high frequency field being associated with the traveling wave on delay line and the other HF. field being associated with the traveling wave on delay line 91, effective electron sorting of electrons emanating from the electron gun is achieved. Electrons which are favorably phased will form a density modulated beam and the beam will gradually approach closer to the positive delay line 90 along the path 98, for example, while delivering its energy to the traveling waves. High frequency energy may be extracted from the tube by coupling to either or both of the delay lines. For example, if the tube is utilized as a backward wave oscillator, energy may be extracted from the tube through the coupling 99 associated with the delay line 90, through the coupling 100 associated with the delay line 91, or through both couplings. As a corollary, if the tube is utilized as a backward wave amplifier, input signals may be impressed on either of the couplings 101 and 102 or on both couplings. Where the tube is utilized as a forward wave oscillator, energy may be extracted from the tube at any of the

couplings

99, 100, 101 and 1M. Where the tube is utilized as a forward wave amplifier the input and output terminals are they reverse of those in a backward wave amplifier.

FIG. 11 schematically illustrates an improvement upon the tube shown in FIG. 10. As shown in FIG. 11, an

electric field is established between the positively polarized delay line 165 and the negatively polarized delay line 106 by connecting those members to a source of electric potential, such as the battery 1W. Transversely to the electric field there is established a magnetic field by any suitable means, such as a permanent magnet. A sorting electrode 1&8 and a phasing electrode lit-9 are preferably coplanar with the negative delay 1%. An electron gun, represented by a cathode 116, a grid 11:1, and an accelerating electrode 112, is arranged to cause electrons emitted from the cathode to have an orbital component or" motion and to inject such electrons along an arcuate path into the sorting region where the electrons are subjected to the high frequency field of a wave propagating along delay line 105. As explained in connection with PEG. 2, electron sorting occurs so that the unfavorably phased electrons are absorbed by the nega tive electrode, which in the case of the tube shown in FIG. 11, is the sorting electrode 108. By means of the adjustable voltage source 113, the potential of the sorting electrode with respect to the potential of the cathode 116 may be changed to obtain the optimum condition for electron sorting. The sorting electrode may also be employed for any of the purposes set forth in discussing the sorting electrode in the embodiment of FIG. 7, that is, for pulsing or amplitude modulating the output of the tube. After electron sorting of the beam has occurred, the beam in FIG. 11 enters a perturbation region where the beam is caused to change its trajectory to a more linear path, exemplified by the path 114. The beam then enters the interaction region Where electrons deliver up their potential energy and are absorbed by the collector electrode 115. As previously explained in connection with FIG. 10, a wave traveling along one of the delay lines induces a wave on the other delay line. Thus a wave traveling along delay line N in FIG. 11 induces a wave which propagates along delay line 1%. It will be noted that energy is extracted from the tube by means of a coupling 116 or 117 situated at the ends of the positively polarized delay line 105. If delay line 105 is of the forward wave type, energy may be extracted from either coupling, whereas if the delay line is of the backward wave type, energy is extracted from coupling 116. The ends of delay line 106 are appropriately terminated to obtain maximum power output from the tube which is consistent with the desired frequency range.

FIG. 12 illustrates electron sorting as it applies to a type of traveling wave tube known as a linear torotron and shows a vertical section through the tube. The delay line 11% of such a tube may, by way of example, be comprised by a metallic cylinder 12!} having annular discs 121 extending inwardly to form a disc loaded waveguide. Disposed along the longitudinal axis of the cylindrical delay line is a sole electrode 122 which may be simply a metallic rod capable of accommodating the flow of a very high current furnished from the secondary of the transformer 123, for example. An electron gun 124, represented by an annular cathode 125 and an annular accelerating electrode 126, is disposed at one end of the delay line and a collector electrode 127 is arranged at the opposite end. A radial electric field is established between delay line 119 and sole 122 by suitable connections to the voltage source 128 such that the delay line is positively polarized and the sole is negatively polarized. In order to establish a magnetic field transversely to the radial electric field, a high current is caused to fiow in the sole by the transformer 123. When the current flow is in the appropriate direction, the crossed electric and magnetic fields cause electrons to be propelled from the electron gun end of the delay line toward the collector electrode 427. Electron gun 124 is constructed to form a hollow cylindrical beam of electrons in which the electrons have an orbital component of motion. The hollow cylindrical bearn,'therefore, in effect, constricts and enlarges its diameter as the electrons flow through the region between the sole 122 and delay line 119. Due to the effect of the HF. field associated with an electromagnetic wave propagating along delay line 119, electron sorting occurs which causes a density modulation of the hollow cylindrical beam. Electrons which are in the unfavorable phase are drawn radially inward toward the negatively polarized sole 122 and are absorbed, whereas electrons in the favorable phase are pushed radially outward toward the delay line 119 and continue to travel toward collector electrode 127 in synchronism with a component of the electromagnetic wave propagating along the delay line. It should be noted that tubes of this type are usually operated by pulsing as very high currents are required to be driven through the sole 122 in order to establish the necessary magnetic field in the interaction space. High currents cause rapid heating of the sole so that continuous operation of such a tube is not feasible unless the sole can dissipate the generated heat. This implies some means of cooling the sole, such as by circulating a coolant through the center of that electrode. In its simplest aspect, the toroidal tube of FIG. 12 is analogous to a tube of the type shown in FIG. 6 which has been rotated about a longitudinal axis.

Electron sorting devices have been illustrated herein as incorporated in various types of crossed field tubes, but it should be understood that these illustrations are exemplars only, and that electron sorting devices may be employed in other types of tubes such as injection magnetrons, for example.

This completes the description of the embodiment of the invention illustrated herein. However, modifications and advantages thereof will be apparent to persons skilled in the art without departing from the spirit and scope of this invention. Accordingly, it is desired that this invention not be limited to the particular details of the embodiment disclosed herein except as defined by the appended claims.

What is claimed is:

1. An electronic device comprising a source of electrons, delay means for guiding an electromagnetic wave whereby a high frequency field is established in a region of said device bounded by said delay means, means for injecting electrons from said source into said region, means producing steady transverse magnetic and electric fields in said region imparting an orbital component of motion to said electrons and causing said injected electrons to travel in synchronism with the phase velocity of a component of said wave, and means for causing a substantial portion of said injected electrons which are in unfavorable phase with respect to said high frequency fields to be removed from said region during movement of said injected electrons within said region.

2. An electron sorting device comprising a source of electrons, means for establishing an electric field in a region of said device, means for establishing a magnetic field in said region transverse to said electric field, means in said region for guiding and retarding the propagation of a wave along said region, means for injecting electrons from said source into said region whereby said transverse fields impart an orbital component of motion to said electrons and cause said electrons to travel at a velocity equal to the velocity of a component of said wave, said means for establishing an electric field including an electrically polarized element situated adjacent the initial path of said injected electrons, and means including said polarized element for causing a substantial portion of the injected electrons which are in unfavorable phase with respect to said high frequency fields to be absorbed by said element.

3. An electron sorting device comprising a source of electrons having an orbital component of motion, a pair of spaced electrodes, at least one electrode of said pair comprising a wave retardation line, means for establishing an electric field between said electrodes, means for establishing a magnetic field transverse to said electric field, means for injecting electrons from said source into the crossed electric and magnetic fields whereby said electrons are caused to have an orbital component of motion and travel synchronously with a component of a wave propagating along said retardation line, and one of said electrodes being situated adjacent the path of injected electrons and maintained at a potential suitable for allowing absorption of a substantial portion of said injected electrons which are in unfavorable phase with respect to said high frequency fields, said electron phase being determined by said orbital component of motion.

4. An electron sorting device comprising a source of electrons, means including a delay line for establishing an electric field in a region of said device, means for establishing a magnetic field in said region transverse to said electric field, means for injecting electrons from said source into said region whereby said transverse fields impart an orbital component of motion to saidinjected electrons and cause said electrons to travel synchronously with a component of an electromagnetic wave propagating along said delay line, and said means for establishing an electric field including an element situated adjacent the initial path of said injected electrons, said element being maintained at a potential suitable for absorption of a considerable portion of said injected electrons which are in unfavorable phase with respect to said high frequency fields.

5. An electron sorting device comprising a source of electrons having an orbital component of motion, a pair of spaced delay lines, means for electrically polarizing one of said delay lines negative with respect to the other delay line of said pair to establish an electric field, means for establishing a magnetic field transverse to said electric field, means for injecting electrons at least some of which have an orbital component into the crossed electric and magnetic fields whereby said electrons are caused to have an orbital component of motion and travel synchronously 'with a component of a wave propagating along said delay line, and said one delay line being receptive of a substantial portion of said injected electrons which are in unfavorable phase with respect to said high frequency fields, said electron phase being determined by said orbital component of motion.

6. A traveling wave interaction device comprising a delay line, an elongate member spaced from said delay line, said delay line and member comprising a pair of electrodes defining a single continuous interaction space, means for electrically polarizing said delay line negative with respect to said elongate member to establish an electric field therebetween, means for establishing a magnetic field transverse to said electric field, means forinjecting electrons into the crossed electric and magnetic fields to have an orbital component of motion and cause said electrons to travel synchronously with a component of a wave propagating along said delay line, the negatively polarized one of said electrodes extending adjacent the initial path of injected electrons and maintained at a potential permitting absorption of'asubstantial portion of said orbital electrons which are in'unfavorable phase with respect to said high frequency fields, said electron phase being determined by said orbital component of motion whereby a density modulated beam of electrons is produced, and a collector electrode positioned to intercept said modulated beam.

7. A traveling wave interaction device comprising a single continuous delay line for guiding an electromagnetic wave whereby a high frequency field is established in a region bounded by said delay line, an elongate sole electrode spaced from said relay line and bounding therewith an interaction region, a sorting electrode spaced from said delay line and bounding therewith a sorting region, means for establishing an electric field in each of said regions, means for establishing a magnetic field transverse to the electric field in each of said regions, and means for injecting electrons into said sorting region 16 whereby said transverse fields impart an orbital component of motion to said electrons and compel said electrons to move in energy-imparting relation with said high frequency field throughout said interaction and sorting regions.

8. A traveling wave interaction device comprising a first delay line, a second delay line spaced from said first delay line and bounding therewith an interaction region, said delay lines guiding an electromagnetic wave whereby a high frequency field is established in a region bounded by said delay line, a sorting electrode spaced from said said first delay line and bounding therewith a sorting region, means for establishing an electric field in each of said regions, means for establishing a magnetic field transverse to the electric field in each region, and means for injecting electrons into said sorting region whereby said transverse fields impart an orbital component of motion to said electrons and compel said electrons to move along a path approaching said sorting electrode and in energy-imparting relation with said high frequency field throughout said interaction and sorting regions.

9. A traveling wave interaction device comprising a delay line, an elongate member spaced from said delay line and bounding therewith an interaction region, a perturbation means spaced from said delay line and disposed adjacent a portion of said elongate member, means for establishing an electric field in each of said regions, means for establishing a magnetic field transverse to said electric field in each of said regions, means for injecting electrons into said sorting region whereby said transverse fields impart an orbital component of motion to said electrons and compel said electrons to move through said interaction region along an arcuate path approaching said elongate member, a substantial portion of said electrons approaching said elongate member being absorbed by said member, said perturbation means causing electrons traversing said interaction region to alter their arcuate trajectories to a more linear path, and a collector electrode positioned to intercept electrons which completely traverse said interaction region.

10. A traveling wave tube comprising a delay line, an elongated sole electrode spaced from said delay line and including therebetween an electron sorting region and an interaction region, means for establishing an electric field between said delay line and said sole, means for establishing a magnetic field transverse to said electric field, an electron gun positioned adjacent said sorting region, the optics of said electron gun causing electrons emitted fromsaid gun to have an orbital component of motion whereby said electrons follow an arcuate trajectory into said sorting region, perturbation means for establishing a perturbation region between said sorting region and said interaction region, said perturbation means causing electrons traversing said sorting region to alter their arcuate trajectories to a more linear path, and a collector electrode situated adjacent the end of said interaction region for intercepting electrons which completely traverse said interaction region.

11. A traveling wave tube comprising a delay line, an elongated sole electrode spaced from said delay line and including therebetween a sorting region separated from an interaction region by a perturbation region, means applying an electric potential between said delay line and said sole for establishing an electric field and causing said delay line to be polarized negative relative 'to said sole, an electron gun positioned adjacent said sorting region, said electron gun having optics causing electrons emitted therefrom to follow an arcuate path into said sorting region which path intercepts said delay line in the absence of radio-frequency energy on said delay line, perturbation means, said perturbation means causing the electrons traversing said sorting region to alter their arcaute trajectories to a susbtantially rectilinear path, a collector electrode situated at the end of said interaction space for absorbing electrons which com- 17 pletely traverse said interaction region, and means for establishing a magnetic fieldin said tube normal to said electric field whereby electrons are urged from said gun toward said collector electrode.

12. A traveling wave tube comprising a delay line constructed to cause the phase velocity of the fundamental wave to be directed inversely to the direction of group velocity, an elongated sole electrode spaced from said delay line and including therebetween a sorting region separated from an interaction region by a perturbation region, means applying an electric potential between said delay line and said sole for establishing an electric field and causing said delay line to be polarized negative relative to said sole, an electron gun positioned adjacent said sorting region, said electron gun having optics causing electrons emitted therefrom to follow an arcuate path into said sorting region which path closely approaches the surface of said delay line in the absence of radiofrequency energy thereon, a phasing electrode located in said perturbation region adjacent said sole, means for applying an electric potential to said phasing electrode, a collector electrode situated at the end of said interaction spac for absorbing electrons which completely traverse said interaction region, and means for establishing a mag netic field in said tube normal to said electric field whereby electrons are urged from said gun toward said collector electrode.

13. A traveling wave interaction device comprising a source for providing electrons having an orbital component of motion, an arcuate delay line, an arcuate sole electrode spaced from and concentrically disposed within the arc formed by said delay line, means for electrically polarizing said delay line negative with respect to said sole to establish an electric field therebetween, means for establishing a magnetic field transverse to said electric field, means for injecting orbital electrons into the crossed electric and magnetic fields to cause said electrons to travel in the region between said delay line and said sole, said delay line extending adjacent the initial path of injected electrons, said delay line polarization permitting absorption of a substantial portion of the orbital electrons whereby a density modulated beam of electrons is produced, and a collector electrode positioned to intercept said modulated beam.

14. A traveling wave interaction device comprising a delay line, an elongate electrode spaced from and surrounded by said delay line, means for establishing an electric field between said delay line and said electrode whereby said electrode is negatively polarized with respect to said delay line, means for establishing a magnetic field transverse to said electric field, and means for injecting electrons having an orbital component of motion into the crossed electric and magnetic fields whereby some of said electrons follow a path approaching said negatively polarized electrode, said polarization permitting absorption of a substantial portion of those electrons approaching said negatively polarized electrodes by said electrode.

References Cited in the file of this patent UNITED STATES PATENTS 2,295,315' Wolfii Sept. 8, 1942 2,687,777 Warnecke et a1. Aug. 31, 1954 2,702,370 Lerbs Feb. 15, 1955 2,861,212 Lerbs Nov. 18, 1958 2,880,353 Warnecke et al Mar. 31, 1959 2,976,455 Birdsall et a1. Mar. 21, 196-1 2,992,360 Reviden July 11, 1961 FOREIGN PATENTS 209,957 Australia Aug. 8, 1957 1,141,687 France Mar. 18, 1957 712,565 Great Britain July 28, 1954 733,349 Great Britain July 13, 1955