US3278793A - Multiple-beam r.f. apparatus - Google Patents

Description

Oct. M, w65 R. A. DEHN 3,27'8,793

MULTIPLE-BEAM R F APPARATUS Filed Dec. 1,2. 1962 @ONPE/VSA 7'/ C 0/ L POWER S UPPLV P0 WER SUPPLY HEKJ TER SUPPLY /f MAX/MUM /f Ffesczufnfcy A/ 1 SEPA RA r/o/v masq UE/vcy fr? V@ rv''or-'r pudo/ph A.. De/m) United States Patent 3,278,793 MULTIPLE-BEAM RF. APPARATUS Rudolph A. Delm, Schenectady, N.Y., assigner to General Eiectric Company, a corporation of New York Fiied Dec. l2, 1962, Ser. No. 244,154 7 Claims. (Cl. S15-5.14)

This invention relates to multiple-beam R.F. apparatus capable of generating and handling high electromagnetic Wave power at relatively high frequencies and more particularly to new and improved means for focusing the multiple electron beams in such a device.

Magnetically-focused single R.F. beam devices such, for example, as klystron tubes, are usually operated with the axis of the device coincident with the axis of the magnetic field. This arrangement minimizes undesirable field aberrations in directions transverse to the direction of electron flow, which aberrations can cause adverse effects in the RF. performance of the device. When a plurality of electron beams are to be opera-ted in a single multiplebeam KF. apparatus, such for example, as that disclosed and claimed in copending U.S. application S.N. 173,724 of M.R. Boyd et al. filed February 16, 1962 and assigned to the same assignee as the present invention, it is not technically feasible to provide separate magnet coils around each beam to provide an individual collimating magnetic field therefor. In such devices it is preferable to utilize an arrangement which provides a single or common large uniform beam-collimating magnetic field in which the several individual beam paths of the device are disposed to meet the R.F. circuit requirements.

In accordance with accepted magnet practice, and as disclosed in the above-mentioned Boyd et al. application, an iron yoke of low reluctance is used and extends about the space in which the magnetic field exists. The individual electron beams are produced outside this field and enter it through apertures which are provided in the yoke and which generally are not coincidental with the symmetry axis of the magnetic eld. inasmuch as the yoke is carrying fiux and its reluctance is finite, a component of magnetic field transverse to the direction of electron motion ordinarily exists in each aperture in the yoke. This component tends to defiect the beams and thus prevents them from extending coaxially in the respective individual beam paths with undesirable R.F. effects.

The present invention contemplates the provision of multiple beam RF. apparatus including new and irnproved means whereby a single uniform magnetic field can be reliably employed in collimating the several electron beams of the apparatus and maintaining such beams parallel and coaxially disposed in their respective beam paths. More specifically, the present invention contemplates new and improved means for compensating for the effects of unwanted magnetic flux in those regions of a magnet yoke where such flux can defiect the beams from their desired coaxial positions and thus adversely affect the R.F. performance of the apparatus.

It is, accordingly, an object of this invention to provide new and improved multiple-beam RF. apparatus incorporating new and improved electron beam focusing means.

Another object of this invention is to provide new and improved means effective for use with a multiple-beam R.F. device and whereby a single uniform magnetic field can be effectively employed in collimating a plurality of individual electron beams.

Another object of this invention is to provide in a multiple beam R.F. apparatus wherein electron beams extend through an apertured magnet yoke, new and improved means for compensating for undesirable effects of unwanted magnet flux components in the yoke which can adversely affect the R.F. performance of the apparatus.

3,278,793 Patented Oct. 11, 1966 Further objects and advantages of this invention will become apparent as the following description proceeds and the features of novelty which characterize this invention will be pointed out with particularity in the claims annexed to and for-ming part of this specification.

In carrying out the objects of this invention, and according to one embodiment thereof, there is provided multiple-beam R.F. apparatus comprising input, output and preferably at least one intermediate, longitudinally-resonant tunable waveguides supported in spaced parallel relation. Extending perpendicular to and in operative association with the waveguides are a plurality of parallel klystron-like beam devices. Each of such devices includes a plurality of axially-spaced drift tubes defining input, output and one or more intermediate capacitive interaction gaps located in respective ones of the mentioned waveguides, an electron gun for projecting a beam of electrons along the beam paths defined by the drift tubes and past the interaction gaps and into a collector for collecting the electrons emerging from the last drift tube. In each waveguide the interaction gaps defined by the opposite ends of adjacent drift tubes comprise equally-spaced active capacitance elements. Also, in each waveguide and interposed midway between each pair of active elements there is provided a passive, or dummy, capacitance element having a capacitance value substantially equal to that of an active element. Further, the periodic electrical spacing between adjacent capacitance elements and between the outermost capacitive elements and adjacent end walls in each waveguide is made equal to 1A of the loaded guide wavelength at a predetermined operating frequency. Suitable means is provided for exicting the input waveguide to establish therein a standing electromagnetic wave of the afore-mentioned frequency which results in the occurrence of an electric field maximum at each active capacitive element in the input waveguide and a voltage node at each passive element. Thusly, and in accordance with the invention of the above-mentioned Boyd et al. application, the apparatus is adapted for cooperative maximum-efficiency energy exchange between the wave in the input section and all of the beams passing therethrough for effecting velocity modulation of the beams which results in the beams becoming density-modulated in the subsequent field-free drift regions. The density-modulated beams cooperatively excite similar standing waves in the intermediate resonators which results in further density modulation of the beams in subsequent drift regions and, finally, the density-modulated beams cooperatively, and with maximum-efficiency energy exchange, induce a corresponding amplified electromagnetic wave in the output waveguide resonator wherein the electric field maxima occur at the active gaps and voltage nodes at the passive elements. The electromagnetic wave energy is extracted from the output waveguide by any suitable means. The several beams are individually focused by a large common magnetic field provided by means of a suitable solenoid positioned about the apparatus. The field is made uniform to insure parallel collimation of the beams by iron yoke members extending transverse the apparatus just inwardly of both the electron guns and the collectors. The individual beams extend through apertures in the yoke member and unwanted flux components in the apertures in the yoke member adjacent the guns tends to deflect the beams and thereby subtract from R.F. performance. This deflection tendency is compensated by magnetic means located adjacent the guns and effective for predeterminedly defiecting the beams amounts and in directions which insure proper alignment of the beams when subsequently they are influenced by the fiux in the apertures in the yoke member. The compensating means can be adapted for compensating for undesirable magnetic field components extending in one or more directions.

Also, the compensating means located at different apertures can be adapted for compensating for different magnitudes and different magnetic component directions depending upon the magnetic fields encountered in the associated apertures.

For a better understanding of the invention reference may be had to the accompanying drawings in which:

FIGURE 1 is a fragmentary elevational view of a multiple-beam electric discharge device constructed according to an embodiment of the invention;

FIGURE 2 is a fragmentary sectional view taken along the lines 2-2 in FIGURE 1 and looking in the direction of the arrows;

FIGURE 3 is an wdiagram showing the graphical relation between the frequency of operation of a periodically loaded waveguide and the phase shift per section of such a waveguide; and

FIGURE 4 is a fragmentary view of a section of a solenoid yoke member illustrating the magnetic field con- ,dition in the yoke apertures, the effects of which are compensated by the present invention.

Referring no`w to FIGURE 1, there is shown multiplebeam R.F. apparatus constructed in accordance with the invention. More specically, the arrangement of FIG- .URE 1 is an electric discharge device in which D C.

energy from four electron beams is converted into electromagnetic wave energy having substantially four times the power generating and handling capacities of a single beam klystron of comparable beam dimensions and which is adapted for affording coaxial extension of properly collimated individual electron beams through respective sections, or along respective beam paths, of the apparatus, thereby -to insure against adverse effects on the mentioned power generating and handling capabilities thereof. However, fr-om the outset, it is to be understood that the present invention can be used with multiple-beam devices having more or less than four electron beams.

The device of FIGURE l is constructed as a unitary evacuated envelope comprising four longitudinally-resonant waveguides designated 1-4 arranged in spaced parallel relation and a plurality of transversely extending cooperating klystron-like beam devices designated 5 8. In this arrangement, and according to the invention of the above-referenced Boyd et al. application, each of the waveguides 1-4 is a short-circuited or longitudinally resonant section of a periodically-loaded waveguide. The waveguides are preferably rectangular in cross-section as shown; however, it is to be understood that the invention is not limited to use of waveguides of this particular crosssectional configuration. Additionally, the periodic loading, which will be described in detail hereinafter is provided by interaction gaps of the beam devices and passive capacity gaps which are predeterminedly and periodically arranged in the waveguide.

The lowermost waveguide 1 in FIGURE 1 constitutes an input resonator and is adapted to be excited for having a standing electromagnetic wave established therein. In a manner generally similar to that well known in the klystron art, the input resonator is effective when resonated for velocity modulating the beams of the devices 5-8. The uppermost waveguide 4 in FIGURE 1 constitutes an an output resonator and is adapted for having an amplified electromagnetic wave induced therein. Interposed between the input and output resonators 1 and 4 are intermediate resonators 2 and 3 which are shown as two in number but which can be employed in any desired number, which intermediate resonators serve to increase beam modulation and bunching efiiciency in generally the same well-known manner as intermediate resonators found in the klystron art. The frequency characteristics of each of the resonators 1-4 can be selectively variable by means of adjustable tuning members 10, which, as seen in FIG- URES 1 .and 2, can be provided at an end of each waveguide 1 4. Associated with the input and output waveguides 1 and 4 are input and output coupling loops generally designated 11 and 12, respectively.

The beam devices 5-8 each comprise an electron gun section 13 including a tubular section 14 sealed and extending reeritrantly in one side of the input resonator 1 and an emitter generally designated 15 adapted for directing a beam of electrons longitudinally through the section 14. The electron guns 13 can be supplied with operating potentials from any suitable sources indicated by the legends Anode Power Supply and Heater Supply and which are well known to those skilled in the art. Axially aligned with each section 14 are a plurality of drift tubes 15, and axially aligned therewith and extending from the output resonator 4 is a tubular section 17 connected to a collector 18. In the described arrangement the tubular lsections 14 and 17 and drift tubes 16 define parallel beam paths and, additionally, these elements extend reentrantly in the several resonators to define therein reentrant active capacitive gaps, or elements, designated 20 which have uniform capacitance values across each waveguide. As seen in FIGURE 1, the active gaps in each waveguide are coaxially aligned with the corresponding gaps in all of the other waveguides along the above-mentioned parallel beam paths. Also, there is provided midway between each pair of adjacent active gaps a dummy element 21. These dummy elements 21 constitute passive capacitive elements and each has a capacitance value substantially the same as the capacitance value of one of the active gaps; and the outermost gaps 20 are spaced from the end walls of the resonators an amount equal to the spacing between the active and passive impedance elements. Thiisly, and in accordance with the mentioned Boyd et al. invention, the input and output waveguides are periodically loaded with alternate active and passive capacitance-s of equal values. i

The described device is surrounded by a solenoid c oil 22 adapted for providing a single magnetic field extending generally parallel to the longitudinal axes of the beam devices for focusing the several electron beams originating in the gun sections 13.

Ideally, the mentioned magnetic field is uniform -throughout its cross-section for insuring parallel relation of the several beams and coaxial extension of each beam in its respective beam path and across its associated gaps. Where this is accomplished the above-described device operates such that a standing electromagnetic wave is eS- tablished in each waveguide resonator. Also, in each resonator and at a predetermined operating center frequency the electric field maxima occur at each of the active gaps 20 and electric field minima, or nodes, occur at the passive gaps and at the waveguide end walls. This, as seen in FIGURE 3, results in a maximum frequency separation between the desired 1r/2 mode and adjacent undesired modes.

The establishment of a common magnetic field which is generally uniform throughout its cross-section is accomplished through `the use of a casing 23 which encloses the assembly and includes upper and lower yoke members 24 and 25, respectively, formed of a low magnetic reluctance material such as :soft iron. As seen in FIGURE 1, the electron gun sections 13 in the beam devices 5-8 are all located outwardly of the casing 23 and beams from such gun sections extend in the tubular sections through suitable apertures 26 formed in the lower yoke member 25; and, as also :seen in FIGURE l, the axis of none of these apertures coincides with the longitudinal axis of the magnetic field. In this arrangement, and inasmuch as the yoke member is carrying magnetic flux and its reluctance is finite, a component of magnetic field which extends transverse the direction of electron motion exists in each aperture 26. More specifically, and as shown schematically in FIGURE 4, the magnetic fiux in the yoke member 25 indicated by lines 27, when reaching an aperture 26, does not fully divide and extend around the aperture. Instead, and because of the finite reluctance of the soft iron of which the yoke member is formed, the flux only partially divides and a finite portion of the magnetic field traverses, or is established in, the air gap defined by the aperture. Although the liux density in the apertures is small relative to that in the yoke member, it is sutiicient to cause undesirable deflection of the electron beams as they pass through the apertures. This deflection can result in 4the beams being unparallel and non-coaxial with respect to the predetermined beam paths or beam sections of the device and thus can cause partial interception of the beam current by the drift tubes 16, and thereby degrade the R.F. performance of the apparatus.

In accordance with the present invention and as seen in FIGURES 1 and 2, the undesirable deflection caused by magnetic fields in the yoke apertures is compensated by means providingT equal andV opposite deflections of the beams at a point between the electron gun sections and the yoke apertures 26, More specifically, I provide compensating magnetic means which can be in the form of magnet coils 30 positioned adjacent each aperture in the yoke member 25. When the magnetic compensating means constitute coils 30, the coils are each energized appropriately to provide a magnetic field which is of substantially the same magnitude as the undesired field in the corresponding aperture but is of opposite polarity in respect thereto.

As shown in FIGURE 1, each compensating coil 30 can comprise a first and second coil section 31 and 32, respectively, connected in series, and being similarly wound on a common axis. The common axis is normal to the axis of the associated electron beam section of the apparatus and intersects the beam perpendicularly between the two coil sections. The emitters are aimed for directing the electron beams precisely coaxially down the beam paths of the apparatus. However, the direction of the radial fiux in yoke at the point of the associated aperture determines the horizontal angular location of the common axis ywith the axis being aligned with the aperture flux and the coils being energized in such a direction as to establish an equal but opposite fiux. The magnitude Of the magnetic field in each of the apertures can be determined either by calculation or experimentation. Thus, when an electron beam enters the magnetic field established by the compensating coil 3i), it is deflected through a first angular displacement and when the electron beam enters the associated aperture 26 and is subjected to the magnetic field therein, it is redeflected through an equal angular displacement of an opposite sense to the first displacement so as to bring the electron beam back into proper aligned position in which it is coaxial with the tubular sections 14, 16 and 17 or, in other words, the beam paths defined by such sections.

Each of the compensating coils 30 is provided with respective energizing terminals 33 and 34 and the coils 30 can be energized with a suitable power :supply indicated by the legend Compensating Coil Power Supply. Inasmuch as the compensating coils 30 are positioned at different locations adjacent the yoke member 25 and the magnetic flux within the yoke member 25 is a function of the radial position of the aperture relative to the focusing field axis, with the magnetic fiux becoming denser as the apertures are positioned near the circumference of the yoke member, the coils require difierent degrees of energization to compensate 4properly for the magnetic field existing within the associated aperture. If it is desired to provide but a single set of energizing terminals for all the coils, it is necessary to provide coils with different positions and number of turns to provide varying -field strengths for the `different apertures. Alternatively, shunt resistances (not shown) can be included in the coil circuits to adjust predeterminedly the coil flux.

As seen in FIGURE 2, there can be provided at each gun location a pair of orthogonally arranged compensating coils including the above-discussed coil 30 and a perpendicularly extending cooperating coil 35. The coil 35 can also comprise a pair of first and second coil sections connected in series and being similarly wound on a common axis with the sections located on opposite sides of the beam. This double-coil, or orthogonal, structure enables greater controllability of the beams before they enter the yoke apertures and can be particularly desirable in arrangements wherein the configuration of the solenoid 23 results in the appearance of `more than one transversely extending magnetic field component in each aperture or, in other words, results in magnetic field components in both the X and Y directions in the aperture 26. Use of the second set of compensating coils 35 is particularly desirable when, as in the apparatus of FIGURES 1 and 2, a focusing field magnet which is non-symmetrical in the circumferential direction is employed inasmuch as such a magnet will usually establish magnetic components in both the X and Y directions in the yoke apertures. The second set of coils also can be individually adapted for fiux densities in accordance with the density of the magnetic field in the aperture with which they are associated.

While the present invention has been shown and described with respect to the mode of operation of a specific embodiment, the invention is not limited to use of the shown embodiment. Instead, many modifications will be suggested by the foregoing to those skilled in the art which will lie within the scope of the invention. For example, the invention is not limited to use of a device having fou-r electron beams in a linea-r array, but may be used in a device having any desired number of electron beams in any form of array in which the beams extend parallel to each other. Also, the invention is not limited to use in a device operating in a 1r/2 mode, but can be used in such a device operating in any `mode. And, in fact, the invention is applicable to any -form of beam device wherein objectionable deection results from flux in the aperture of a magnetic yoke member through which the beam must pass. Additionally, no compensating coils are provided adjacent the collectors 18 due to the fact that RF. performance of the tube is not adversely affected bv deflection of the beams as they enter the collectors. However, it is to be understood from the foregoing that the compensating coils could be effectively employed at the collectors wherever the exist aperture defiections may be found objectionable, such, for example, where elongated collectors might be employed and undesirable defiections of the beams may tend to cause collector damage.

Further, while the magnetic coils have been shown and described as the magnetic compensating means it is to be understood from the foregoing that permanent `magnet elements can be effectively employed in providing the desired compensation. Where permanent magnets are employed in place of the coils it will be necessary to employ elements of permanent magnet .strength predeterminedly selected in accordance with the magnitude of the specific opposite magnetic components to be compensated or counteracted. With the use of permanent magnet compensating elements orthogonal arrangements will not be required inasmuch as individual permanent magnets can be predeterminedly angularly located with respect to the apertures in the yoke members for the purpose of nullifying the beam defiections caused by magnetic fields in the apertures.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. RP. apparatus comprising means defining a plurality of electron beam paths having parallel axes. means providing a common beam-collimating magnetic field, said last-mentioned means comprising a solenoid coil surrounding all said paths and having its axis parallel to the axes of said paths, magnetic yoke members extending normal to said axes of said paths at opposite ends of said apparatus for rendering said common magnetic field more uni form in the region of said paths, a plurality of apertures in each said yoke members for extension of said beam paths therethrough, means for directing a plurality of electron beams coaxially along said paths from a point outside the space defined by said yoke members, means associated with at least kone of said yoke members for detiecting each said electron beams through a predetermined angle ybefore said beams pass through the apertures in said yoke member to compensate for undesirable deflection of said beams from said coaxial positions as caused by magnetic fields located in said apertures in said one yoke member.

2. R.F. apparatus according to claim 1, wherein said means for deflecting each said electron beams through a predetermined angle are each individually adaptable to compensate for different undesirable deflections of said beams as caused by Imagnetic elds of different magnitudes in said one yoke member.

3. R.F. apparatus according to claim 1, wherein said means for deflecting each said electron beams comprises a plurality of magnetic deflection coils, each of said deflection coils being associated with a respective beam and being positioned adjacent a respective one of said apertures in said one yoke member, and means to energize said deflection coils to establish respective magnetic eld components of predetermined magnitude and direction adjacent each said aperture in said one yoke member.

4. R.F. apparatus'according to claim 1, wherein said means for deccting each said electron beams comprises a plurality of magnetic deflection coils each of which comprises a pair of series connected, similarly wound coil sections having a common axis and straddling the axis of an associated electron beam, and means to energize said deection coils to establish a respective magnetic field of predetermined magnitude and direction adjacent each said aperture in said one yoke member.

5. R.F. apparatus according to claim 1, wherein said means for defiecting each said beams comprises a plurality of magnetic deflection coils having transversely extending axes and being positioned adjacent a respective one of said apertures in said one yoke member, and means to energize said deflection coils to establish respective magnetic field components of predetermined magnitude and directions adjacent each said aperture in said one yoke member.

6. R.F. apparatus according to claim 1, wherein said means for detiecting each said beams comprises a plurality of magnetic deflection coils having transversely extending axes and each being subdivided into a pair of series connected, similarly Wound coaxial coil sections straddling the axis of an associated electron beam adjacent a respective one of said apertures in said one yoke member, and means to energize said deflection coils to establish respective magnetic field components of predetermined magnitude and directions adjacent each said aperture in said one yoke member.

7. R.F. apparatus comprising a plurality of waveguide sections periodically loaded by impedance means including interaction gaps, means supporting said waveguide sections in spaced relation with lthe interaction gaps of said waveguide sections in axial alignment, means defining a plurality of axially extending electron beam paths each traversing aligned ones of said interaction gaps, means providing a common beam collimating magnetic field, said VYlast-mentioned means comprising a solenoid coil surrounding all said paths and having its axis parallel to the axes of said paths, magnetic yoke members extending normal to VVsaid paths at opposite ends of said apparatus for rendering said common magnetic field more uniform in the region of said paths, a plurality of apertures in each said yoke members for extension of said beam paths therethrough, a plurality of electron guns located outwardly of the space defined by said yoke members and adjacent one said yoke members for projecting a respective electron beam along the axis of each said paths, and magnetic means for deflecting each said electron beams through a predetermined angle before it passes through an aperture in said one yoke member to compensate for undesirable deflection of said beams from said axes of said paths as caused by magnetic fields located in said apertures in said one yoke member for thereby avoiding undesirable R.F. performance of said apparatus as may be caused by non-coaxial extension of said beams along said paths.

No references cited.

HERMAN KARL SAALBACH, Primary Examiner. S. CHATMON, IR., Assistant Examiner.

Claims (1)

1. R.F. APPARATUS COMPRISING MEANS DEFINING A PLURALITY OF ELECTRON BEAM PATHS HAVING PARALLEL AXES, MEANS PROVIDING A COMMON BEAM-COLLIMATING MAGNETIC FIELD, SAID LAST-MENTIONED MEANS COMPRISING A SOLENOID COIL SURROUNDING ALL SAID PATHS AND HAVING ITS AXIS PARALLEL TO THE AXES OF SAID PATHS, MAGNETIC YOKE MEMBERS EXTENDING NORMAL TO SAID AXES OF SAID PATHS AT OPPOSITE ENDS OF SAID APPARATUS FOR RENDERING SAID COMMON MAGNETIC FIELD MORE UNIFORM IN THE REGION OF SAID PATHS, A PLURALITY OF APERTURES IN EACH SAID YOKE MEMBERS FOR EXTENSION OF SAID BEAM PATHS THERETHROUGH, MEANS FOR DIRECTING A PLURALITY OF ELECTRON BEAMS COAXIALLY ALONG SAID PATHS FROM A POINT OUTSIDE THE SPACE DEFINED BY SAID YOKE MEMBERS, MEANS ASSOCIATED WITH AT LEAST ONE OF SAID YOKE MEMBES FOR DEFLECTING EACH SAID ELECTRON BEAMS THROUGH A PREDETERMINED ANGLE BEFORE SAID BEAMS PASS THROUGH THE APERTURES IN SAID YOKE MEMBER TO COMPENSATE FOR UNDESIRABLE DEFLECTION OF SAID BEAMS FROM SAID COAXIAL POSITIONS AS CAUSED BY MAGNETIC FIELDS LOCATED IN SAID APERTURES IN SAID ONE YOKE MEMBER.

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