US2749438A - Resonator structure - Google Patents

Description

June 5, 1956 u wrrsc EI'AL 2,749,438

RESONATOR STRUCTURE Filed Aug. 21, 1952 3 Sheets-Sheet l Inventors:

Anatole M.Gur-ewitsch,

Philip C. Noble,

27 by )Q/d W Th eir- Attorney.

June 5. 1956 A. M. GUREWITSCH ETAL 2,749,438

RESONATOR STRUCTURE Filed Aug. 21, 1952 3 Sheets-Sheet 2 Fig.5.

Inventors: Anatole M. Gurewitsch, i Philip C. Noble,

by 7 4. Their- Attorney.

United States Patent RESGNATQR STRUGTURE Anatole M. ,Gurewitsch andPhilip :C. Noble, Schenectady,

N. Y., assignors to GeneralElectr-ic Company, a corporation ,of New York The present invention relates to; high frequency resonators and, more particularly, to resonatorsfindin'g useful application in apparatus for-imparting hig'h energy tocharged particles. i

The invention is applicable in connection with appae ratus of the type disclosed in United States Patent No. 2,485,409, patented October 18, 1949 by Herbert C. Pollock and Willem F. Westendorp, and assigned to the assignee of the present invention. Such apparatus comprises means for initially accelerating charged particleswithin an evacuated annular envelope by the action of a field, produced by a time-varying magnetic flux, and for thereafter imparting additional energy to the particles by a' localized electric field'of cyclically-vary ing character.

In one-form of this charged particle acceleratingap paratus, the means employed for producing the localized.

electric fields comprises a space resonant structureor resonator suitably located along the path of the charged particles within the region of the time-varying magnetic flux. To facilitate the assembly of a vacuum-tight en velope enclosing the particle path and the desired close coupling-of the electric fields'with the path of the charged particles, the space resonant structure or resonator is formed'as a sector of the annular envelope which itself is divided into sectors of equal length. Sincethe physical-length of theresonator is thus determined, it'very often occurs that the resonant frequency of theresonator does not correspond to that required for the successful acceleration'of charged particles withinthe apparatus.

Accordingly, it is a principal object of the present-invention'to provide a novel space resonant structure-or resonatorin which the resonant frequencymay be'varied without. altering the physical. length thereof.

It is another object of the invention to provideanovel space resonant structure or resonator which is adapted for employment with charged particle accelerator apparatus and which may be tuned without any alteration inits physical length.

It is still another object of the invention to provide novel means for tuning a resonator without altering its physical length and without disturbing theelectrical symmetry of the structure.

It is-yet another object of the invention to provide novel means for tuning a resonator without deleteriously affecting the shielding of the electromagnetic oscillations produced therewithin.

Inaccordance with one aspect of the invention more fully-described hereinafter, there is provided a resonator formed of a tubular section of dielectric material .upon the outer and inner surfaces of which are supported layers of conductive material. 'These layers respectively constitute the inner and outer conductors of the resonaton; By-the provision of ca noneconductive gap around the inner periphery of the tubular section, high-frequency lectric-fields are caused to appear withinthe inner @011: ductorpf the resonator when it is, excited "with-high free que sy ene g In o 0 enable un of ilk- 9 9 2,749,438 Eatented June 5, 1956 tor,- .the outer conductor is made discontinuous along. at least a portion of the periphery of the tubular section, andx'aninductive member including a layer of conductive material is connected across the discontinuous portion. The inductive member is arranged to. have a desired length longer than the discontinuous portion of the outer conductor whereby the resonant frequency of the resona, tor may be varied Without changing its physical length;

Thefeatures of the invention desired to be protected herein are pointed out with particularity in the appended claims; The invention itself, together with further ob.- jectsand advantages thereof, may best be understood by reference to lheifOllOW'lrlg description, taken in con! nection .withthe accompanying drawings, in which Fig. l isapartially' sectionalized elevation .ofan accelerator suitablyembodying the invention; Fig. 2 is'a'plan' view' of the annular envelope or discharge vessel shown in Fig; 1; Fig. 3 isasectionview taken along lines -33 ofFig. 2; Fig. 4 isan enlarged perspective view of the resonator structure :ofiFig: 2; Fig. 5 is a partially sectionalized view of: apreferred arrangement for exciting. the resonator structure of the invention; Fig. 6 is a fragmentary sectionalized view of alternative resonator structure according to the invention; Fig. 7 is a fragmentary sectionalized view. of another alternative embodiment of resonator structure according to the invention; and Fig. 8 is a schematic representation of excitation apparatus -employed in connection. with the device of Fig- 1.

Referring particularly to Fig- 1, there is shownin section. a closed rotationally symmetrical envelope ll) which. defines withinits interior an annular chamber. Theenvelope. 10, which is preferably constructed. of glass. or ceramic material, provides a circular orbit-in which charged particles, e. g., electrons derived from a suitablyenergized source 11 supported from a side arm 12, .may be'acceleratcd to a high energy level. The envelope 10 is preferably highly evacuated and 'isprovided on itsinterior surface with a high resistivity, conductivecoating (not shown), .forexample, a layer of a metallic salt, in order to reduce the effect of wall charging, Forming a sector of envelope 10 is a resonator structure which does not appearin Fig. .1, but which will be shown. and described-at a later point.

Theenvelope or vessel ,1!) lies symmetrically around the axis of a laminated magnetic structure having acen! tral flux, path provided by an annular iron core 13. This .core is supported at its. extremities by attachment to the central portions of opposed pole pieces 14 and 15 which. have planar circular areas 16 and 17 and tapered annular areas 18 and 19. The pole pieces 14 and .15. are, in turn,. supported by a rectangular-frame 20:.oflaminated iron which surrounds-and extends transversely to the envelope 10.

Ihe ,endsfof the core 13 are separated from thepole pieces 14 and 15 .by narrow gaps 21 and 22 which are so proportioned .as to cause the core to saturate at a predetermined level of the magnetic flux passing through it. Preferably gaps 21 and 22 are filled by washers of nonmagnetic material (not shown) for the purpose of assistnelfin the proper support of core 11. Theiannular faces 18 and 19 of the two pole pieces each have a double taper aswshown, the purpose of this configuration beingexplained ata later point. An opening 23, which extends icontinuouslyihrough the frame 20,. pole pieces 14 and 15, andcore .13, permits .cooling air to be circulated through theseparts.

The'magnetic structure is excited by means of a pair gfseries connected coils 25 and 26 which. surround the polepieces and. which may be energized'in .such .a manner jas tof provide a time or .cyclically-varying-flux in the magnetic.circuit. Electrons produced within the envelope 10 .are affected in two ways by the variations in magnetic flux thus obtained. In the first place, since the magnetic flux traversing core 13 links the circular path provided by envelope 10, any variation of such flux necessarily produces an electric field tending to accelerate electrons projected along such paths. In this latter respect, the apparatus is comparable to a transformer with a secondary comprising a circular path along which the various electrons are accelerated.

In general, although the voltage per turn in such a transformer may be low, within a practically attainable range of flux variation, the electrons can be made to achieve very high energies, e. g., several million electron volts, because of the tremendous number of turns which they may execute during a single cycle of the magnetic flux variation. In addition to the acceleration produced by the time-varying magnetic flux linking the electron path, the flux produced by the annular pole pieces 18 and 19 in the region of the electron orbit tends to cause the electrons to follow an inwardly spiraling path. It has been shown that with a proper design of the magnetic structure, the centripetal force produced by the magnetic field existing at the electron orbit may be caused to'balance the centrifugal tendencies of the accelerated electrons. In general, this result requires that the following relationship be satisfied:

where 6 is the flux included in the electron orbit, r is the radius of the orbit, and Br is the field strength at the orbit. This equation indicates that the flux incuded in or linking the orbit must be twice as strong as that which would be produced by a homogeneous field equal to the field Br extending over the entire area enclosed by the orbital electron path. This conditon may be realized by making the reluctance per unit of cross-sectional area of the magnetic path at the electron orbit greater by an appropriate amount than its average reluctance Within the orbit. In order to maintain the desired proportionality between the enclosed fiux and the guide field, i. e., the field Br at all times during an accelerating period, one may adjust the air gap existing between pole pieces 18 and 19 to the appropriate value. It is readily practicable to control the dimensions of the gap from point to point over the pole piece in such a fashion as to effect the balanced relation of guide field and enclosed flux which is desired for the purpose specified above and which is further necessary for radial and axial stability of the electron orbit. This may be done, for example, by a construction such as that shown in Fig. l in which the pole pieces are doubly tapered. The principles governing the proper space distribution of the guide field are more fully set forth in United States Patent 2,394,070, granted February 5, 1946, to D. W. Kerst.

When all the conditions specified in the foregoing are fulfilled, electrons introduced into envelope in a period when the magnetic field is increasing may be expected to be drawn into the particular orbit in which a balance of centripetal and centrifugal forces exists and to be continuously accelerated along such orbit as long as the magnetic field increases in value. Assuming that the peak value of the magnetic field is sufficiently high, a total energy on the order of several million electron volts may be acquired by the accelerated electrons in a small fraction of a second.

It may be noted, however, that when an electron has obtained a velocity corresponding to an energy level of about three million electron volts, it is already within about 1 percent of the velocity of light. Accordingly, further gains in energy result primarily in an increase in the mass of the affected electrons and only insignificantly in further gain in electron velocity, this result being consistent with the Einstein mass-energy equivalence formula. Therefore, electrons which have attained a velocity within a few percent of the velocity of light will gyrate with a relatively constant periodicity, or at a relatively fixed where c is the velocity of light, r is the radius of the frequency, provided they can be confined to an orbit of relatively fixed radius. As is pointed out in the aforementioned United States Patent No. 2,485,409 of Pollock and Westendorp, this consideration makes it possible to impart further energy to the electrons by means of a localized electric field of fixed frequency acting repetitively on the electrons as they continue their gyrations within the envelope 10. By this means, extremely high energy levels can be reached through a mechanism which avoids difficulties associated with any attempt to achieve corresponding energy levels by a magnetic acceleration alone. With this in mind, the apparatus of Fig. l is so constructed that saturation of core 13 occurs after a sufficient acceleration of the electrons has been obtained by magnetic means, and an electric field accelerating device to be hereinafter described is brought into play. In order that the accelerated electrons may still be confined to the desired orbit, however, the guide field produced between pole pieces 18 and 19 continues to increase as a result of continued energization of coils 25 and 26.

As is illustrated in Fig. 2, envelope 10 is formed of a plurality of sectors 27 of dielectric material which may be joined together in vacuum-tight relation by means of suitable rubber gaskets (not shown) in a manner well known to those skilled in the art. T o assure the maintenance of an evacuable space within envelope 10, the surfaces of juncture of the rubber gasket and the envelope may be coated with a desired adhesive material, for example, an alkyd resin prepared by reacting a polybasic acid and a polyhydric alcohol, such as a resin being prepared from glycerol and phthalic anhydride. Alternatively, the rubber gaskets may be omitted and the abutting surfaces of sectors 27 coated with the adhesive material. The ease with which envelope 10 may be constructed is assisted by making each of the glass or ceramic sectors 27 of equal lengths, inasmuch as this permits the manufacture of the sectors such that closely matched end surfaces are obtained without an excessive expenditure of effort. Formed as a sector of envelope 10 is a space resonant structure or resonator 28 which will be more fully described later.

In connection with the description of the apparatus of Fig. 1, it has been stated that the electrons introduced into envelope 10 are first accelerated to within about 1 percent of the velocity of light by a time-varying magnetic flux, and then are further raised in energy level by means of a localized electric field of fixed frequency acting repetitively on the electrons as they continue their gyration within the envelope 10. In order to obtain repetitive acceleration of the electrons, the frequency of the localized electric field must satisfy the following relation:

orbit, and f is the frequency. It is apparent from Equation 2 that, once a desired orbital radius is selected, the frequency of the localized electric field is immediately determined. It will be observed, however, that resonator 28, which supplies the localized electric field according to the invention and which comprises inner and outer conductors supported upon a tubular section of dielectric material, has a resonant frequency which is a function of. the length of the resonator and the dielectric constant e of the material employed. Its resonant frequency is given by where h is the resonant frequency and L is the central arcuate length of the structure. Therefore, as may be seen from Equation 3, for a given dielectric material, the resonant frequency f1 of resonator 28 is determined by its length L which, in turn, is fixed by the above= 3 mentioned ..construction of envelope zfrom,,sec t ors,of equal: length. Accordingly, if the resonant, frequency, ft of resonator .28 does not correspond to thefrequency f required.:by.Equation 2, further energy cannot .besuccessfully imparted to the electrons by the localizedelectric field. within resonator 28.

The present. invention supplies anadvantageous and efiicient solution to this problem bytheprovision, of the novel resonator 28, the frequency of which may be varied without altering its physical length. As is more clearly shown in Figs. 3 and 4, space resonant structure or resonator 28 forms a sector of envelope 10 and comprises agtubular section 29 ofdielectric. material-having an approximately elliptical cross section whichconfo'rms, to the cross ,sectionof envelope 10. Since it is preferable to; utilize a dielectric material having a small highfrequency loss coefficient, tubular section 29 may be formedof a material such as .fused quartz or ceramic and shaped similarly tothe sectors 27 of. envelope .10. In order to provide means for conducting high frequency currents, tubular section 29is coated upon all its exposed surfaces with a layer 30 of conductive'material, such as silver. Portions 31 ofcoating 30 are removed. from the exterior surface ofsection 29 toforma plurality .of approximately evenly spaced conductive strips 32 extending longitudinally along both sides thereof- Portions 31 are discontinuous adjacent one end of section 29 in order to provide aperipheral conductiverstrip33. In alike manner, portions 34 are removed from coating30 on the inner. surface of section ,29to form a plurality of conductive strips 35; extending longitudinally. therealong. Portions 34 are discontinuous to provide peripheral conductivestrips 36 and 37. A peripheral gap 38 is provided byremovinga portion-between strips 36:and 37. Portions 39aareremovedfrom the end surfacestone of which is not shown) .of section 29 to produce a plurality of conducti-ve. strips 40; Portions 31, 39 and 34, removed respectively from the coating upon the exterior surface, end faces, and innersurfaceof section 29, are spatially interrelated sothat .each, strip 32' is conductively-connected to the oppositely disposed stripy35ruponthe adjacent inner surface of section29.

One convenient way of formingconductive layer 30 is as follows. A layer of silver paint. is placed upon the inner surface,..outer surface and endfaces ofrse ction 29 and subsequently baked to secure adherence thereto. The thickness of this layer may beincreascd by means of electroplating,.,or by repeated painting and baking, for the purpose of obtaining a layer havinga thickness greater than the depth of penetration of the high frequency current which flows therein when resonator 28 is excited. As an order of magnitude, the layer may have a final thickness of about 1 to 1 /2 mils when the resonator is to be excited at 160 me. The various portions removedifrom the conductive layer as above describedmay be made by masking'during th'e painting operation-, or-by burning-in grooves, after the painting and electroplating, with a tungsten disc which is rolled along the conductive-surface carrying a heavy current through the contact area;

As is disclosed in United States Patent-No. 2,579,315, patented December 18,:1951, and assigned to the assignee ofthe present invention, the subdividing -of coating 30 into longitudinal strips provides a convenientand direct means. of reducing eddy currents induced: in resonator 28rbyithe time-varying magnetic flux which traverses the stmcturetwhen.theaccelerator apparatus'of the invention isrin operation. With, the particular interconnection .of the. longitudinal; strips by peripheral conductive strips .33, 3.6-;and :37 in :the.manner illustrated, nearly complete compensation ofinducededdy currents may be; obtained whereby undesirable heating of the stripszis avoided; Moreover, this interconnection of the strips increases the coupling therebetween and. prevents the oscillationv of resonator 28 ,in undesirable ,modes. It, will, ,be observed that .theJQngitudinal subdivision 20f coating-.30: need .not

becontinned adjacent. the innerand outer circumference of, resonator -23 =inasmuch as. .-such.,.por.tions are nearly parallel to the :direction of the time-.varying-fiux andtherefore ,will not have appreciable'eddy currents induced therein.

With the :longitudinal dimensions determined in the above-described manner by the construction of the, envelope 10 from sectors of equal length, resonator-28 operates as aquarter-wave, closed concentric line resonator at a particular excitation frequency. The space between the conductive coating on the exterior surface of section 29 and the coating .on the interior surface ,con: stitutes in effect a space resonant system comprisinga quarter-wave transmission line section. Accordingly, if resonator. 28 is excited at its resonantfrequency, a cyclically reversible electric field of. high intensityappears across gap 38. If the resonant frequency of resonator v28 as expressedby Equation 3 corresponds "to the frequency of rotation of electrons moving within envelope 10 and section 29-as expressed by Equation 2,. an in crease in the energy level of such electrons may beeffected in accordance withthe principles previously outlined.v

Since the physical length of resonator 28 as determined by the constructional requirements of envelope 10 very seldom provides a resonant frequency which corresponds to the frequency-of rotation of electrons within envelope 10,- the present invention contemplates means for tuning or varying the resonant frequency of resona? tor ,28 without altering its physical length. In general, itisfeasible to increase the resonantfrequency of resona tor 28 by moving gap 38 along section 29 away from the end which it is adjacent. However, when it is :necessary to lower the resonant frequency of resonator 28, severe difficulties arise because-gap 38 obviously cannot be moved beyond the end of sectionv29 whichit is adjacent. According to the present invention, therefore, there ;is provided an inductive member 41 which'is PQSi? tioned adjacent the end of section 29 remote from gap 38; Inductivemember 41 comprises an-annular band 42 of dielectric material supported upon section 29 about theexterior surfaces of strips=32.- Extending along vthe exposed sufaces of band 42 is a layer ofconductive mate, rial. 43 which is ubdivided into strips 44 corresponding in peripheral position to conductive strips 32. Ifconductive coating 43-and strips44 are formed upon band 42 separate from the formation of conductive coating lid-and strips32 upon section 29, conductive connection therebetween may be assured by soldering the adjoining surfaces. Conductive coating 30 and strips 32 are made discontinuous to forma peripheral gap 45 wherebyconductive coating 43 and strips 44 constitute in effect ;a longitudinal extension of conductive coating 30 andstrips 32. Thus, conductive layer 43 and strips 44, which are connected across gap 45, add inductance togresonator 2S and lower its resonant frequency without requiring any alteration in the physical length of resonator;28.-.

it will be observed that inductivemember 41 is-posi'- tioned adjacent the end of resonator 2-3 where the high frequencycurrents are large and the electricfields Within the dielectric are small. Therefore, the choice of dielectric material required for band 42 isnot critical. Conveniently, it may consist of an organic material such aspolystyrene. Alternatively, band 42 may be constructed by impregnating strips of glass cloth With.a solventless varnish such as a resinsynthesized fromtiiethylene glycol 'maleate and diallyl phthalate, distributing the impregnated glass cloth within a suitable -rnold, and curing in accordance with principles Well known-to those skilled. in the art. If the dielectric material selected .for band-42 is not capable of withstanding the :heat: necessary for the application of a conductive coatingof silver in the manner heretoforedescribed, conductive..coating .43 and strips 44 may be formed of thin, conductive materialsuch as copper secured to the surface -0fjb3l'3d 42.by means otasuitable adhesive, e. g., the aboveamena tioned alkyd resin. If desired, conductive layer and strips 32 may likewise be formed of thin conductive material secured to the surfaces of section 29.

In Fig. 5, wherein like reference characters are employed to designate elements hereinbefore presented, there is illustrated a suitable means for exciting resonator 28 with high frequency energy. A portion 46 is removed adjacent the outer circumference of section 29 to provide a longitudinally extending conductive strip 47. Although strip 47 is shown as being joined at its lefthand extremity to the remainder of layer 30, it may in some cases be made entirely separate therefrom by extending portion 46. Energy may be supplied to resonator 28 by the combination of a conductor 48 which connects with the conductive strip 46 and a tubular element 49 surrounding the conductor to form with it a concentric transmission line. At the point where conductor 49 approaches resonator 28, it merges into a channel-shaped enlargement 50 which is of sufiicient longitudinal and lateral extent entirely to cover removed portion 41 and thus to afford high frequency shielding. While conductor 48 and the enlarged member 49 are shown as being of metallic cross section, it will ordinarily be preferable to form them of a non-conducting dielectric internally coated with a thin metal layer in order to minimize currents induced by the time-varying magnetic field. By choosing the correct dimensions and an appropriate point of connection to strip 47, it is possible to accomplish an excellent match of power from concentric line 48, 49 into the resonator. The length of strip 47 may be varied as desired to produce optimum tuning and matching of the system.

In some installations of the apparatus of Fig. 1, it may be inconvenient because of spatial requirements to extend inductive member 41 along the exterior surface of resonator 28 toward the gap 38. In the embodiment of Fig. 6, wherein like numerals are employed to designate similar elements described hereinbefore, inductive member 41 is shown as extending away from gap 38 over the juncture of the end of resonator 28 and the adjoining sector 27. Layer 43 and strips 44 extend along a substantial portion of the inner and outer surfaces of a flanged annular band 51 of dielectric material. The flange 52 of annular band 51 may be attached to section 29 by means of a suitable adhesive, thereby assuring adequate support of the inductive member. As will be seen, the construction of the inductive member illustrated in Fig. 6 provides a larger added inductance to resonator 28 for a given circumferential or longitudinal extension of band 51.

In Fig. 7, where like numerals are also utilized to additional support by the adjacent sector 27.

The operational correlation of the resonator structure and the other various elements of the accelerator heretofore considered may best be understood by reference to Fig 8 which shows diagrammatically the accelerating structure as a whole in combination with schematically illustrated excitation equipment. In this figure, parts which have been described bear numbers corresponding to those by which they have already been identified.

Referring particularly now to Fig. 8, there is shown a power source 55 adapted to supply excitation voltage of the desired frequency, for example, cycles, to wind ings 2S and 26 by which the magnetic system of the accelerator is energized. A second power source 56 which is assumed to be appropriately connected to source 11 of Fig. 1, and which may be an intermittently energized circuit of the type described in the aforementioned Pollock and Westendorp patent serves to inject electrons into the envelope 10 at appropriate intervals correlated with the cyclical reversals of the magnetic field. Finally, a high frequency power source 57 which may consist, for example, of an electronic oscillator, supplies when energized, high frequency potential through transmission line conductors 48 and 49, to the inner and outer conductors of a resonator 58 which is identical with one of the resonator structures shown in the preceding figures. Properly correlated energization of the magnetic field, the electron injecting means and the high frequency power supply for the resonator is accomplished by means of a timing circuit illustrated schematically by the block 59, it being indicated that the timing circuit is connected with the various power supplies by conductors 60, 61 and 62 respectively. Through the action of the timing circuit, the system as a whole is controlled in such fashion that initial acceleration of the injected electrons is accomplished by a variation of the magnetic field up to the point where the electrons have attained an energy level of several million electron volts. Thereafter by saturation of core 13, the accelerating effect of the magnetic field i substantially eliminated and subsequent acceleration of the electrons to high energy levels is accomplished by bringing into operation the resonator 58.

In each of the embodiments, inductive element 41 has been illustrated as extending completely around the periphery of section 29. This construction is preferred because the electrical symmetry of resonator 28 is thereby essentially unaffected. However, in some instances it may be desirable to extend inductive element 41 around only a portion or portions of section 29 and such is within contemplation of the present invention.

While the invention has been described by reference to particular embodiments thereof, it will be understood that numerous changes may be made by those skilled in the art without actually departing from the invention. We therefore aim in the appended claims to cover all such equivalent variations as come within the true spirit and scope of the foregoing disclosure.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. In apparatus for the acceleration of charged particles along a path which is enclosed by an envelope of dielectric material; a resonator forming a section of the envelope comprising an inner conductor which includes a conductive layer supported upon the inner surface of said section, and an outer conductor which includes a conductive layer supported upon the outer surface of said section and being discontinuous around at least a portion of the periphery of said section which discontinuous portion extends in spaced relation around a portion of the inner conductor; and an inductive member for tuning said resonator including a conductive layer connected across the discontinuous portion of said outer conductor, said last-mentioned conductive layer having a length greater than the length of the discontinuous portion of said outer conductor.

2. In apparatus for the acceleration of charged particles along a path which is enclosed by an envelope of dielectric material; a resonator forming a section of the envelope comprising an inner conductor which includes a conductive layer supported upon the inner surface of said section and being discontinuous to provide a non-conductive gap extending around the periphery of said section adjacent one end thereof, and an outer conductor which includes a conductive layer supported upon the outer surface of said section and being discontinuous around at least a portion of the periphery of said section which discontinuous portion extends in spaced relation around a portion of the inner conductor adjacent the end remote from said gap; and an inductive member for tuning said resonator including a conductive layer connected across the discontinuous portion of said outer conductor, said last-mentioned conductive layer having a length greater than the length of the discontinuous portion of said outer conductor.

3. In apparatus for the acceleration of charged particles along an orbital path which is enclosed by an annular envelope of dielectric material and traversed by a timevarying magnetic field; a resonator forming a sector of said annular envelope and comprising an inner conductor including a conductive layer supported upon the inner surface of said sector of said envelope and having portions thereof removed to form a plurality of spaced apart conductive strips extending longitudinally along said sector, and an outer conductor including a conductive layer supported upon the outer surface of said sector of said envelope and having portions thereof removed to form a plurality of spaced apart conductive strips extending longitudinally along said sector, said outer conductor being discontinuous around at least a portion of its periphery which discontinuous portion extends in closely spaced relation around a portion of said inner conductor; and an inductive member for tuning said resonator comprising a conductive layer connected across the discontinuous portion of said outer conductor, said last-mentioned conductive layer having a length greater than the length of the discontinuous portion of said outer conductor.

4. In apparatus as in claim 3 in which said last-mentioned conductive layer is supported upon a band of dielectric material extending around at least part of the periphery of said sector, said last-mentioned layer having portions thereof removed to form a plurality of conductive strips extending along said band.

5. In apparatus for the acceleration of charged particles along an orbital path which is enclosed by an annular envelope of dielectric material and traversed by-a timevarying magnetic field; a resonator forming a sector of said annular envelope and comprising an inner conductor including a conductive layer supported upon the inner surface of said sector of said envelope and having portions thereof removed to form a plurality of spaced apart conductive strips extending longitudinally along said sector, said conductive layer having adjacent one end a gap extending around the periphery theerof, and an outer conductor including a conductive layer supported upon the outer surface of said sector of said envelope and having portions thereof removed to form a plurality of spaced apart conductive strips extending longitudinally along said sector, said outer conductor being discontinuous adjacent the end of said sector remote from said gap in said inner conductive layer to form a gap extending around at least a portion of the periphery of said outer conductor which gap is spaced by said envelope from a portion of said inner conductive layer; and an inductive member for tuning said resonator comprising a conductive layer connected across the gap in said outer conductor, said lastmentioned conductive layer having a length greater than the length of the discontinuous portion.

6. In apparatus as in claim 5 in which said last-mentioned conductive layer is supported upon a band of dielectric material extending around at least part of the periphery of said sector, said last-mentioned layer having portions thereof removed to form a plurality of conductive strips extending along said band.

7. A resonator comprising an inner conductor which includes a conductive layer supported upon the inner surface of a tubular section of dielectric material, an outer conductor which includes a conductive layer supported upon the outer surface of said section and being discontinuous around at least a portion of the periphery of said section which discontinuous portion is spaced by said envelope from said inner conductive layer and an inductive member for tuning said resonator including a conductive layer connected across the discontinuous portion of said outer conductor, said last-mentioned conductive layer having a length greater than the length of the discontinuous portion of said outer conductor.

8. A resonator as in claim 7 in which said last-mentioned conductive layer is supported upon a band of dielectric material extending around at least part of the periphery of said section, and all of said conductive layers are longitudinally subdivided to form a plurality of conductive strips extending along said section.

9. A resonator as in claim 8 in which the discontinuous portion of said outer conductor is adjacent one end of said section and said inner conductor has a peripheral gap adjacent the end of said section remote from the discontinuous portion.

10. A resonator as in claim 9 in which said band of dielectric material and said last-mentioned conductive layer extend beyond said one end of said section.

References Cited in the file of this patent UNITED STATES PATENTS 2,304,540 Cassen Dec. 8, 1942 2,434,508 Okress Jan. 13, 1948 2,514,428 Varian July 11, 1950 2,553,312 Gurewitsch May 15, 1951 2,579,315 Gurewitsch Dec. 18, 1951 2,600,225 Ehrenfried June 10, 1952 FOREIGN PATENTS 976,767 France Nov. 1, 1950 OTHER REFERENCES Meagher and Markley: Practical Analysis of U. H. F., RCA Service Inc., August 1943, page 7.

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