US3090885A - Electronic high frequency dual electron beam return wave tube with cycloid beam - Google Patents

Description

May 21, 1963 R. MULLER 3,090,835

ELECTRONIC HIGH FREQUENCY DUAL ELECTRON BEAM RETURN WAVE TUBE WITH CYCLOID BEAM Original Filed Nov. 25 1957 3 Sheets-Sheet 1 Fig.1

(negative energy transport) slow space charge Wave (negative energy transport) C/pn c/ vom fast space charge wave (positive energy transpori) \(n egative energy transporl) (positive energy transport) fim /rgfor May 21, 1963 R. MULLER 3,090,885

ELECTRONIC HIGH FREQUENCY DUAL ELECTRON BEAM RETURN WAVE TUBE WITH CYCLOID BEAM Original Filed Nov. 25, 1957 3 SheetsSheet 2 Fig.2

(negative energy t ranspori) (positiveenergy transport) (positive energy transport) (negative energy transport) J;ZZ/6i@ 07 May 21, 1963 R MULLER 3,090,885

ELECTRONIC HIGH FREQUENCY DUAL ELECTRON BEAM RETURN WAVE; TUBE WITH CYCLOID BEAM Original Filed Nov. 25, 1957 3 Sheets-Sheet 5 3,99%,885 Patented May 21, 1963 ice ELECTRONIC HIGH FREQUENCY DUAL ELEC- TRQN BEAM RETURN WAVE TUBE WITH CY- CLGID BEAM Rudolf Miiller, Strasslach, Germany, assignor to Siemens & Halske Aktiengesellschaf Berlin and Munich, a corporation of Germany Griginal application Nov. 25, E57, Ser. No. 698,576. Di-

vided and this appiication Get. 5, 1959, Ser. No. 844,562 Claims priority, application Germany Dec. 7, H56

6 Claims. ((31. 315-3.6)

This invention is concerned with a twin electron beam return-wave tube comprising a decoupling system for the high frequency energy and a focusing system for bundled conduction of the electron beams. This application is a division of copending application Serial No. 698,576, filed November 25, 1957, now abandoned.

The theory of the coupled wave has been developed in order to comprehend in a common point of view the physical phenomena taking place in propagation field tubes referred to respectively as traveling field tubes and traveling wave tubes and return-wave tubes. For this purpose, the individual structural elements of the tubes, the line and the electron beam, are separately investigated, that is, the so called free waves are determined. The reciprocal action between the beam and the line is thereafter observed by the introduction of a coupling which is effective along the entire discharge path, thus obtaining as the resultant the coupled wave. The advantage of this approach is, that the structural elements are individually investigated, thus making it possible to determine their properties or characteristics in advance. The tube can then be constructed in accordance with the building block principle, by combining the properties of the individual structural elements. It is in this manner possible to provide for operating conditions as, for example, self-excitation or amplification, by the combination of the properties of the structural elements.

As is known from the theory of the delay line, the phase velocity of a (partialor sub-) wave may have a direction corresponding to that of the group velocity or a direction opposite thereto. Waves with identical direction of the phaseand group velocity are referred to as forward waves and waves with opposite phaseand group velocity are referred to as return waves.

if the delay line with periodic structure is substituted by an electron beam having properties corresponding to those of the delay line, the electron beam may be considered in the nature of a moving delay line.

The electron beam has in its unmodulated condition a kinetic energy which is determined by the velocity and the number of electrons passing through a cross-sectional area. If the electron beam is excited in a control path, there will be produced two space charge waves. The art distinguishes thereby between slow and fast space charge waves. The fast space charge wave effects accumulation of the fast electrons and consequently an increase of the energy passing the corresponding cross-section, this behavior being referred to as positive energy transport. The slow space charge wave effects accumulation of the slow electrons, therewith decrease of the energy passing the cross-section, the corresponding behavior being referred to as negative energy transport.

The above explained two possibilities concerning the energy transport, and the distinctions between forward and return waves, result in four groups of properties (waves) with respect to the individual structural elements of ultra high frequency tubes, namely, 1) forward waves with positive energy transport; (2) return Waves with positive energy transport; (3) forward waves with negative energy transport; and (4) return waves with negative energy transport.

Waves of the groups (1) and (2) are the known partial or subwaves along lines. The free space charges in a homogeneous electron beam are for the most part waves of the groups (1) and (3). (A wave of the group (1) becomes a wave of the group (2) only in the case of low frequencies.)

In case of a diffusing field, as is present with delay lines of periodic structures, there will be several partial waves which have a common group velocity. The energy transport is defined only for the entirety of all partial waves. The entirety or totality of all partial waves affects the electrons of the electron beam. The effect of the non-synchronous partial waves may be neglected only over lengths which are great as compared with the cycle of the line structure. The arrangements and modes of operations according to the invention apply, accordingly, only to lengths which are very much greater than a cycle of the periodic structure.

Several kinds of arrangements and modes of operation for the amplification and generation of ultra high frequencies are possible based upon combinations of the four previously mentioned groups.

The combination of the group (1) with group (3) will result in an amplifier operating according to the principle of the known traveling field tube. The wave of the group (l)-forward wave upon a delay line with periodic energy transport-is coupled with wave of group (3)--for- Ward wave in the electron beam, with negative energy transport. The combination of the group (2) with the group (3) results in the known return-wave tube which is likewise based upon the principle of propagating field tubes with delay lines. In such case, a forward wave with negative energy transport is coupled with a return wave with positive energy transport.

These known ultra high frequency tubes, which are used for amplification as well as for the generation of ultra high frequencies, comprise as a structural element a delay line which is operative to delay the electromagnetic wave with respect to its diffusion velocity, so as to match its velocity to that of the electron beam. Delay lines have the drawback that the electric field, required for the coupling of the electron beam, decreases exponentially with the distance from the delay line. The electron beam must for this reason he guided very close to the delay line. Heating of the delay line by electron bombardment is, accordingly, unavoidable and, in addition, cumbersome focusing devices are required for the bundling of the electron beam. 7

Electron beam tubes for the amplification of ultra high frequencies are also known, wherein two electron beams extend mutually parallel in identical direction, reciprocally affecting one another. The structure accordingly constitutes a type of traveling field tube operat ing according to a combination of groups (1) and (3). The drawback of such tube is, that its efiiciency is low zl s compared with traveling field tubes comprising delay mes.

The object of the invention is to eliminate the above described drawbacks by the provision of tubes for generating ultra high frequencies, operating without delay lines, and simplifying, if not entirely eliminating, the costly expenditures for extensive magnetic focusing devices for the bundling of the electron beam.

The essential feature of the return wave tube with two electron beams and an uncoupling system for ultra high frequency energy and focusing systems for bundling the electron beams resides therein, that the two electron beams are propagated in opposite directions, and that they are periodically in reciprocal interaction such, that a forward Wave with positive energy transport of one electron beam is coupled with a return wave with negative energy transport of the other electron beam (combination of groups (1) and (4)) or, that a return wave with positive energy transport of one electron beam is coupled with a forward wave with negative energy transport of the other electron beam (combination of the groups (2) and (3)).

If an electron beam exhibits along a given coordinate a periodic structure, for example, periodic acceleration and delay or periodic cross-sectional alterations, it will be impossible to explain the behavior of the beam merely by the two space charge waves; a multitude of partial waves of identical frequency and different phase velocity will be obtained for each of the two space charge waves. This phenomenon of splitting or subdividing into partial waves is similar as in the case of delay lines with periodic structure, with the difference, that, in the case of electron beams with periodic structure, the partial waves will be allotted to the space charge Waves. All partial waves associated with the slow space charge wave transport negative energy; all partial waves associated with the fast space charge wave, transport positive energy. Waves of all four groups are thus obtained, but of these waves, only that of the group (4) can be generated by a periodic electron beam. However, the periodic electron beam can also generate waves of the group (3).

As'has been said before, in the case of space charge waves in the electron beam, a distinction is made between a fast and a slow space charge wave. From this distinction flows the manner of recognizing the positive and negative energy transport. If one group of the previously noted combinations is allotted to one electron beam and another group to the other electron beam, care must be taken to achieve the reciprocal action between both electron beams by suitable coupling of the Waves that are present therewith. This coupling is only made possible (as will be apparent from the dispersion diagram to be presently discussed) by coupling one partial Wave of the electron beam which transports negative energ with the wave of the other electron beam. Accordingly, there must obtain a periodicity which generates the partial wave, to make this coupling possible.

i The foregoing considerations indicate that there are several ways to realize the invention. Some of the possible embodiments shall now be described with reference to the accompanying drawings, showing examples of embodiments in simplified partially schematic representation. All details not absolutely necessary for an understanding of the invention, for example, focusing systems, vacuum vessels, uncoupling devices, etc., have been omitted from the drawings.

7 FIG. 1 is a dispersion diagram showing the partial waves contained in the electron beam;

FIG. 2 repeats the dispersion diagram of FIG. 1, showing in addition the dispersion curves of waves of a second electron beam;

FIG. 3 indicates an example of an embodiment for efiecting the operations according to FIG. 2; and

FIG. 4 represents an embodiment wherein one electron beam is propagated as a cycloid while the other beam is propagated as a homogeneous beam.

Referring now to FIG. 1, a distinction is made between partial waves n +1; 1; +2; 2; etc.) belonging to the slow space charge wave (negative energy transport) and to the fast space charge wave (positive energy transport), respectively. The dispersion curve of the slow space charge wave is indicated by dot-dash lines, and the dispersion curve of the fast space charge wave is indicated in full lines. vacuum, and the ordinate plots the ratio (c/pn) of the speed of light to phase velocity. Reference c/vom represents the ratio of the speed of light to average electron velocity of the unmodulated electron beam. The ratio The abscissa plots the wave length 1 inv 4 of speed of light to phase velocity is determined by the equation:

L L A .h pn v0m R L wherein c speed of light;

pn=phase velocity of the nth partial wave; vom average electron velocity; k vacuum-wave length;

X =average plasma wave length; and L=length of the spatial cycle.

The plus or minus symbol preceding A /x will designate the presence of negative or positive en ergy transport, respectively. The factor n, preceding M/ L expresses the partial wave that is to be considered.

It will be seen from FIG. 1, that the waves n=0 have only slight dispersion. The partial waves for n= l have great dispersion and intersect the abscissa. These partial Waves above the abscissa are forward waves, and those below the abscissa are return waves. FIG. 1 shows merely the dispersion diagram for one electron beam with space charge waves, in a-case when partial waves are produced by a periodicity aifecting the corresponding electron beam or contained therein, respectively.

FIG. 2 again shows the dispersion diagram according to FIG. 1 and in addition thereto, underneath the abscissa, the waves of a second electron beam having a direction of propagation which is opposite to that of the first beam. The partial waves (n=l) of the electron beam are, underneath the abscissa-intersecting points a and b return waves which intersect the forward waves (21:0) of the electron beam at the points 1 and 2. (FIG. 2). At point 1, there will result the combination of groups (1) and (4), and at point 2, there will result the combination of the groups (2) and (3). The conditions for self-excitation are present in both combinations and there will, therefore, result a return wave generator.

The physical operation is essentially based upon the manner in which one electron beam affects .or influences the other electron beam. The coupling is effected over partial waves depending upon the electron velocities and the cycle length. Accordingly, when one electron beam is affected by electrons of the other electron beam, such influence is transported due to the electron velocity of the first beam, thus affecting again the other electron beam. It will, therefore, be apparent that one electron beam must have :a forward Wave with positive energy transport and that the other electron beam must have a return Wave with negative energy transport. It will likewise be apparent that, to obtain the same mutual influencing, one of the electron beams may have a return wave with positive energy transport and the other electron beam may have a forward wave with negative energy transport. The particular action of the arrangement according to the invention is primarily achieved by the propagation of two electron beams, which are carriers of space charge waves, in opposite directions.

FIG. 3 shows an embodiment for obtaining with simple means the mutual periodicity of two oppositely propagated electron beams 12 and 13 which are produced by respective electron guns 10 and 11. The direction of propagation of the electron beams 12 and 13 to respective collectors 29 and 21 is indicated by arrows 12 and 13. The electron beams are propagated in cycloid courses. The periodic approach of the electron beams is effected with the large arcs of the cycloids. The length L of a period or cycle extends from closest approach to closest approach. The cycloid courses of the electron beams 12 and 13 are produced jointly by static electric fields E2 and E1 in connection with a static magnetic field H extending perpendicular as indicated at '14. In order to produce the two electrostatic fields E1 and E2, thereare provided along the sides of the electron beams 12 and 13,

conductive layers in the form of plates 15 and 16, extending over the entire discharge length. Furthermore, there is provided a grid 17, between the electron beams, extending in parallel with and between the plates 15 and 16 and lying on a potential which exceeds the potential connected to the plates 15 and 16.

The periodic approach of the electron beams 12 and 13 may also be eflfected with respect to the cycloid loops by differently polarizing the magnetic field.

The arrangement shown in FIG 3 may be modified, for example, by forming the electron beam 13 as a homogeneous beam and the electron beam 12 as a periodic cycloid beam, or vice versa. A corresponding arrangement is shown in FIG. 4, wherein the electron beam .12 is propagated from the gun 10' in the direction 12' toward the collector 20, just as in FIG. 3, while the beam 18 is propagated from the gun 11' in the direction 18' to the collector 21' as a homogeneous beam. The deflection device for the cycloid course must thereby be omitted on the side of the homogeneous electron beam.

It will be apparent from the foregoing explanations that there occurs a mutual influencing of the electron beams at the points of approach, such influencing always continning in opposite direction with respect to the electron beams and causing renewed influencing at the next successive point of approach.

As will be seen from FIG. 2, the partial wave (21:0) is always coupled with a partial wave (11: This coupling is made possible by dimensioning the period or cycle length L and the electron beam velocity (vom) so, that one partial wave (n=1) of one electron beam is coupled with the partial wave (11 of the other electron beam. It is, however, also possible to dimension the period or cycle length L and the electron velocity (vom) so, that a partial wave (n=1, '2, 3 of one electron beam is coupled with a partial wave (n=l, 2, 3 of the other electron beam. Coupling of a partial wave (n=()) with another partial wave (11 :0) is unfavorable because, as is apparent from FIG. -2, the point of intersection or crossing occurs at great wave lengths and the structure would accordingly become too long.

The embodiment illustrated in FIG. 3 provides the great advantage of eliminating delay lines, especially those with finest periodic structures and, due to the oppo itely directed propagation directions of the electron beams, a period or cycle length for very short waves, particularly millimeter waves, which is, as compared with previously known ultra high frequency tubes with delay lines, about twice as great. Accordingly, structures for ultra short waves will not require elements demanding high mechanical precision. For the decoupling of the generated electromagnetic waves, there may be used devices such as they are employed primarily in klystrons, wherein an electrical double layer is permeated by a density-modulated electron beam and wherein the double layer is connected with cavity resonators. Other decoupling devices, such as they are employed in connection with traveling field tubes, may likewise be used when it is desired to obtain greater band width of the return wave tubes.

Changes may be made Within the scope and spirit of the appended claims which define what is belived to be new and desired to have protected by Letters Patent.

I claim:

1. A twin electron beam return wave tube, comprising means forming a decoupling system for the high frequency energy and a focusing system for the focused guidance of the electron beams in a single plane, said electron beams being propagated in opposite directions and periodically entering into mutually reciprocal action, said system comprising means for propagating said beams in mutually crossing static magnetic and electric fields which are directed transverse to the discharge direction, at least one of said electron beams being a cycloid beam.

2. A twin electron beam tube according to claim 1, wherein said system comprises means for propagating both of said beams as cycloids.

3. A twin electron beam tube according to claim 2, wherein said electron beams are periodically moved toward each other along portions of the large cycloid arcs.

4. A twin electron beam tube according to claim 3, wherein the cycloid paths of said electron beams are produced by means forming a static magnetic field directed perpendicularly to the beam plane thereof and by means forming at least one electrostatic field which is directed in the beam plane perpendicularly to the discharge direction.

5. A twin electron beam tube according to claim 3, including a device for producing oppositely directed electrostatic fields, said device comprising a metallic sheet positioned respectively alongside each electron beam and extending substantially for the length of the discharge path, said metallic sheets being respectively directed perpendicularly to the respective electron beam plane, and means forming a grid disposed between said electron beams and extending in parallel with said metallic sheets.

6. A twin electron beam return wave tube according to claim 1, wherein one of said electron beams is propagated as a homogeneous beam while the other beam is propagated as a cycloid beam.

References Cited in the file of this patent UNITED STATES PATENTS 2,684,453 Hansell July 20, 1954 2,794,146 Warnecke et a1 May 28, 1957 2,857,548 Kompfner et al Oct. 21, 1958 2,899,597 Kompfner Aug. 11, 1959 2,9 ,556 Charles et al Nov. 3, 1959 2,926,281 Ashkin Feb. 23, 1960 FOREIGN PATENTS 1,106,301 France July 20, 1955

Claims (1)

1. A TWIN ELECTRON BEAM RETURN WAVE TUBE, COMPRISING MEANS FORMING A DECOUPLING SYSTEM FOR THE HIGH FREQUENCY ENERGY AND A FOCUSING SYSTEM FOR THE FOCUSED GUIDANCE OF THE ELECTRON BEAMS IN A SINGLE PLANE, SAID ELECTRON BEAMS BEING PROPAGATED IN OPPOSITE DIRECTIONS AND PERIODICALLY ENTERING INTO MUTUALLY RECIPROCAL ACTION, SAID SYSTEM COMPRISING MEANS FOR PROPAGATING SAID BEAMS IN MUTUALLY CROSSING STATIC MAGNETIC AND ELECTRIC FIELDS WHICH ARE DIRECTED TRANSVERSE TO THE DISCHARGE DIRECTION, AT LEAST ONE OF SAID ELECTRON BEAMS BEING A CYCLOID BEAM.

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