US2673928A - Apparatus for imparting high energy to charged particles - Google Patents

Description

4 Sheets-Sheet l Tl|...................h um H........H.M www. .I|.......H i I l G HIGH ENERGY lL. L.

A. M. GuREwlTscl-l APPARATUS FOR IMPARTIN TO CHARGED PARTICLES Figi.

March 30, 1954 Filed sept. 20.421950 Inventor: Ahatol M. Gurewbsch, byk )QJ d. 7M/4v `Hs Attorney.

March 30, 1954 M. GuREwn-scH 2,673,928

APPARATUSD FOR IMPARTING HIGH ENERGY TO CHARGED PARTICLES Filed Sept. [20V 1950 4 Sheets-Sheet 2 Inventor Anatole M. Gurewitsch,

by A7/221W@ His Attorney.

March 30, 1954 A. M. GuREwlTscH 2,673,928 APPARATUS FOR IMPARTING HIGH ENERGY TO CHARGED PARTICLES Filed Sept. 20, 1950 4 Sheets-Sheet 3 AwnzaxtoleA M. Gurewitsch,

March 30, 1954 V Filed sept; 20, 195o A.Y M. GUREWIC'VI'SCH APPARATUS FOR IMPARTIN HIGH ENERGY TO CHARGED PARTICLES 4 Sheets-Sheet 4 Inventor: Anatole M. Gurewltsch,

by )QJ .4. uw/O His Attorney Patented Mar. 30, 1954 APPARATUS FOR 'IMPAR TINGHIGH AENERGY T0 `CHARGED PARTICLES AnatoleM. Gurewitsch, Schenectady. N. Y., assignox-.to General `Electric Company, a corporation of.`New York Application September 20, 1950,:Serial No. 185,763

(Cl. vZ50-n.27.)

4 Claims. l

.The present invention relates kto apparatus for imparting high energy-to charged particles, ,-pa1.- ticularlyielectrons.

.In ran article .entitled wIhe Synchrotron-A Rroposed High AEnergy Particle Accelerator, Physical Review68, 143-4 (19.45),E. M.,McMil lanv has discussed in .generalterms :a device'which makes :use .of a fphase stability possessed by certain orbits in apparatus such as `that disclosed .in v4U. ,.S. .Patent No. 1,948,384-Lawrence commonly `.termed a cyclotron. As proposed, such .a device :involves the repeated application of A.an oscillating electric -.eld '-.to charged :particles as they :move within a magnetic .field essentially normal Vr to the electric ,eld @at the point of application. In `these circumstances charged particles :having .anenergy suchthat their angu.- lar velocity corresponds to the 'frequency of the electricneld l.will have an .equilibrium .energy and astationaryorbit.iftheynrriveat the point of application of the ,oscillating .electric eld eas the field .passes lthrough zero. yParticles which arrive'at .the point of application of vtheelectric eld either before or after the :electric `eld passesthrough .zero irwill Yfollow ldisplaced orbits oscillating about vrthe .stationary orbit with lboth phase and energy varying about -their .equilibrium ralues. Acceleration of etheiparticles may be p changing the V`value of the equilibrium .energy which, translated `into practical terms, means varying eitherthe'magneticfeldor .the frequency of'fthe electricziield.

yApparatus employing .the .abovesmentioned phase stability principle at least :in part has proved .to be exceptionally successful :in the 4`acceleration yof electrons to thigh v.energy levels. However, it has been .considered inadvisable to utilize .this vprinciple throughout v.the acceleration cycle inasmuch .as the electrons "would :follow a relatively greatly expanding vspiral .orbit zuntil their velocity approached `V.tl'iat .of light; vconsequently apparatus of this character :has `.usually embodied .other .means `ior .pre-accelerating electrons .to approximately y.the velocity iof light before :initiation .of vmeans embodying .the abovementioned principle. It .is a foremost robect of the present invention .to provide simple, .3compact and .eilicient .apparatus for .accelerating charged particles to .high yenergy levels by applying this ,fphase stability principle ,of opera-,- tion throughout the acceleration -cycle after electron injection.

According .to one :important aspect A:ci the apresent invention moreifu-lly explained-and described hereinafter, there .is iprovided .-a magnetic struc.-

ture .having a pairof opposed rotationally symmetrical polepieces defining a gap between the noie .faces thereof `and `means .associated .therewith for exciting itheimagneticstructure to ,produce a `cyclic timefvarying magnetic iield be,- tween the pole `faces. The pole faces are outwardly tapered to provide a .desired varying radial field strength and `an ,evacuated .envelope is disposed within the gap defined therebetween. High vfrequency Velectric field directing means is positioned tosenclose a Aportion of the evacuated envelQDe, and a ,source of `charged particles. such as electrons, 4is suitably positioned foi` Vinjection of ycharged particles into the evacuated envelope. When :the magnetic structurcfis excited, charged particles are injected at la .desired time in lthe cycle .of magnetic field .and thereafter are .accelerated in 4stable lexpanding spiral paths by the .high frequency .electric .field directing means which acts :repetitively to apply anaccelerating force to the particles as .they traverse the .electric eld generated thereby. When Vthe `charged particles have been accelerated .to ya desired energy level, they may be directed to .a suitable target for the useful production .ofX-rays.

The features -of the invention ,desired `fto be protected herein Yare pointed out in .the appended claims, .The invention itself, ytogether' Withiur ther .objects and advantages thereof, may best be understood by :reference to the .following description, taken in connection vwith the accom.- panying drawings in which Fig. l is Ia ,partially sectionalized viewof accelerator apparatus suitey ably embodying the invention; Fig. 2 is `a sectionalized view taken along ,line A2--2 of `l Withthe discharge vessel partly broken away; Fig. is YVa sectionalized 4view taken .along line Snail-of Fig. 2; Fig. 3a ,-is a Ifragmentary view .of the apparatus of -Fig. 1; Eig. A 3b is a diagram-.- matic Iview `-,useful .in explaining fthe invention.; Fig. 4 is :a simplined schematic representation of circuitry suitable for .energizing the accelerator .apparatus -of the invention; Rigs. Scand 5b are fragmentary eviews illustrating alternative mea-ns for exciting the resonant structure: Fig-:6 is a,partially.sectionalized -view of one alter-naa tive .form .for `:the :envelope and .resonant `,structurelofFig. A1; Fig. 7 is .a .partially seetionalized view :taken along .line 'f1-11 .of Fig. 6; B .is-.a

view showing :another alternative form of the' envelope tand resonant :structure `of Fig. 1 with the resonant .structure part-ly broken away; and Fig. A9 is a `:sectionalized view taken 'along line 9--e9 aOf Fig, r8.

.Beterrine particularly to Figs. .1, '2. and y3 windings 1 and 8 are disposed respectively about' pole pieces 4 and 5 and connected, as indicated, in circuit with power factor correcting capacitors 9 to a conventionally represented source of j,

cyclic time-varying voltage I0. In order that the time-varying magnetic field existing in gap 6 when magnetic structure I is energized by windings 1 and 8 may have a desired radial variation in accordance with principles to be ward extensions 33 of strips 3| are made in order that strips 3| may be short-circuited to strips 25 to provide in effect a short-circuited quarter wave resonator as will be more fully described hereinafter. Strips 3| are also short-circuited to each other by means of a transverse peripheral conductive strip 25 positioned opposite peripheral conductive strip 28.

Strips 25 and 3| may consist of a material such as copper and may be secured respectively to boxes 23 land 30 by means of a suitable ad- 1 jhesive material, i. e. an alkyd resin prepared by reacting a polybasic acid and polyhydric alcohol, such as a resin being prepared from glycerol and phthalic anhydride. To prevent excessive radiation losses when resonator 2| is excited by a source of high frequency, outer conductor 29, y including the sides of box 30 and conductive described hereinafter, pole pieces 4 and 5 are provided respectively with pole faces II and I2 having an inverse slope with radius as shown.

Positioned within the gap 6 between pole faces II and I2 is a closed generally cylindrical vessel I3 of dielectric material which defines within its interior a chamber I4. As will be explained in greater detail at a later point, vessel or envelope I3 provides a spiral orbital path along which charged particles (i. e. electrons) may be accelerated to high energy levels. Envelope I3 is preferably highly evacuated and is provided with an axial side arm I5 of dielectric material which extends into a central opening I6 in magnetic structure I and supports a charged particle source I1 within chamber I4. Charged particle `source I1 may comprise a shield member |8 and a filamentarycathode I9 supported and energized through conductors sealed into side arm I5. vA more detailed description of a charged particle source suitable for employment in this connection may be found in U. S. Patent 2,499,192, granted` February 28, 1950 to James M. Laiferty and assigned to the assignee of the present invention.

For the purpose of providing means for accelerating electrons within envelope 3 after they have been injected from charged particle source I1, there is shown high frequency field directing means 2| which encloses a portion of envelope I3 in gap 6 betweenpole faces II and I2. High frequency field directing means or resonator 2| comprises an inner conductorV 22- which includes a box of dielectric material 23i supported upon the exterior surface of envelope I3. Box 23 may be open-ended or may be closed as shown at the end 24 remote from envelope I3. Attached to the outersides oibox 23 is a plurality of longitudinally extending spaced apart conductive strips 25 which may project over the end 24 of box 23 as is indicated at 26.' Near end 21 opposite end 24 of box 23 conductive strips 25 may terminate adjacent the axis of envelope I3. To connect together or shortcircuit strips 25, transverse peripheral conduc tive strip 28 is positioned adjacent the termination of strips 25 near end 21 of box 23. The outer conductor 29 of resonator 2| includes a rectangular shaped box of dielectric material 30 upon the interior sides of which are positioned longitudinally extending spaced apart conductive strips 3| similar to those attached to inner box 23. Box 30 may also be open-ended, may have an inwardly projecting flange 32 to support the inward extensions 33 of strips 3|, or may be completely closed at the end remote from envelope I3-as is indicated at. 34. IThe instrips 3|, is extended beyond end 21 of inner conductor 22 as is shown at 35. Envelope I3 and-inner conductor 22 may be supported from outerv conductor 29 by means of an arcuate dielectric spacer 35, and outer conductor 29 may be supported by arcuate dielectric spacer 36'. Slots 31 and 31 are provided in the undersides of outer conductor 29 and inner conductor 22 respectively to facilitate the insertion ofenvelope I3 within resonator 2|. Means-for conducting energy to resonator 2| may comprise a section of concentric transmissionv line 39 extending downwardly through central opening I6 and being constructed of a cylinder 38 of dielectric material lined with a thin conductive strip 39serving as an outer conductor. Strip 39 extends around the lower end of dielectric cylinder 38 to make contact with a flanged sleeve 40, positioned within an aperture 4| inI box 30 and, in turn, making contact withvstrips 3|. Sleeve 40 may be attached to liner 39 'and strips 3| by any convenient means such as solder. The inner conductor 42 of concentric transmission line section 38 may consist of a metallic rod43 terminated with a disk 44 attached to.' peripheral conductive strip 28.

With the proper selection of longitudinal di, mensions, such dimensions being in the directionindicated by the line labeled I in^Fig. 2; resonator 2| operates as a short-circuited quar-y ter Wave concentric line resonator at a particue lar excitation frequency. l".lhespace between conductive strips 25 and 3| constitutesv in effect a space resonant system comprising a quarter wave transmission line section. Accordingly, if resonator 2| is excited at the proper frequency by a high frequency voltage source (not shown). connected to concentric line 38 in a manner well known to those skilled in the art, a cyclically reversible. electric eld of high ,intensity may be made to appear between inner conductor. 22 and outer. conductor 29 as is indicated byarrows `45 of Fig.' 3a. At the lend offinner conductor 22 adjacent the axis of envelope I3. however, the electric eld will extend inwardly and within envelope I3 as is indicated byl arrows 46. 'By choosing the frequency of reversal of this electric eld to correspond to the frequency of rotation' of charged particles moving within envelope |3,l i.' e. equal to or a multiple of the frequency of` rotation ofthe charged particles, an increasev in the energy level of vsuch charged particlesl may-be effected in accordance with the princi# ples which will be presently described. f f

Ashas been mentionedheretofore, the present invention contemplates'the initiation` of 'excita-'f tionof resonator.2| early in thecycle of mag-- atrasos `matic-field between lpole faces Stil and- I2, 1i. Yefat o1'.shor.tly after 'the .injection .of .electrons into envelope .|13 Efrom gunfll .After injection of :electrons -a-nd .fthe .excitation of resonator 2i the .electrons are .repetitively accelerated twice per .revolution as they pass `into andoutof resonator .12| As .is .apparent `from Fig. 3a, .the region 41 within inner .conductor 22 and envelope I3 is .electric eld-free; .hence no .acceleration occurs while .the electrons are within this region. Thus the electrons are .repetitively .accelerated :with a -constant angular velocity throughout a .number .of .revolutions .while they are retained within expanding spiral orbital paths by .the .magnetic eld. ingap 6 traversing .envelope lf3. ln Fig. 3b I.wherein `the fluxidensity B in .gap 6 is plotted vs. time for present purposes B may fbeconsidered .to `be sinusoidal as shown), .line a represents .the Atime at which electrons `are injected :from `gun 4ITI and .also the time at which resonator 2| vis i energized. The electrons are accelerated throughout the portion indicated by the shaped .area vunder the B curve until the time represented by line e is reached .at .or slightly after vthe peak magnetic flux density is reached.. At

this time resonator `2i may be .de-energized whereby the .electrons spiral outwardly to strike a target 48 (Figs. l and '2) of tungsten or other lsuitable material supported by a stud 419 `sealed into .the wall of envelope 13.

In the `construction .of the above mentioned .apparatus .the following relations may be con- .veniently employed:

11i where Rzthe radius of the particle orbit, v=the linear velocity ofthe particles, and

vw=the angular velocity of the particles.

Since in the above described apparatus w lis maintained constant (by virtue of a constant frequency of excitation of resonator 2l and the .above-described phase stability principle)k Vwhile o varies from the velocity of injection to, in some cases, nearly the Velocity of light, the radius R will increase during acceleration of the particles to a value approaching the maximum value oi 2) where c=the velocity of light.

The total energy possessed by the particles, including rest energy and kinetic energy evidenced by a relativistic increase in mass, may be eX- pressed as where B=the flux density of the magnetic eld traversing the particle orbit.

It may now be shown that z -z ifa 1- where mo-:the rest mass of the particles, and

ezthe charge upon the particles.

I-f now B is made to vary with time, i. e. sinuscidally as represented in Fig. 3b, vthen at the iii.)

6 time of injection tu, .B .will fbe determined :by alle `relation Bar-Bo Sill wmfa '65) where wm=21r fm, ythe frequency of the magnetic eld, and

.Bo=the peak value of magnetic flux density.

With .this value of B the totalenergyof the par- ,ticles at the timeof injectionmay be ascertained `from Equation 3; hence the. injection voltage may be determined. Furthermore, ,Equation i4 :may vbe employed `todetermine aradius at which iinjectionshould takeplace. The remaining nec- -zessary quantity which must be determined, viz. athenecessary gainoi energy of the .particles per turn, may be determined from the following equation:

j=the frequency of the `electric field produced by resonator 2i, and

ifm=the frequency -.of the magnetic iield (e. g.

.60 cycles).

.At higher energies where radiation loss .takes place, `an additional amount of energy per turn .must be supplied as is indicated by the following relation:

L 8.8 X' 75X '10-32 7:)

where L=the gain per turn in electron .volts necessary to compensate 'for radiation losses.

From the above stated relationships it may be ascertained that, for the acceleration of e1ec trons to a nal energy of million electron volts, a ux density of .8 weber/meter2 and a nal orbit radius of approximately 4:2 centimeters may be employed. The frequency of the electric eld produced by resonator .2i may be of the order` of megacycles.

In order to maintain stability of the charged particles undergoing .acceleration to produce a desired stable beam, the magnetic ux density B in the plane of the orbit in gap 6 must satisfy the following relation:

B= BG) (s) where r=the radius of the point under consideration. r0=the maximum radius of the orbit, and

n=an exponential having a value `lying between 0 and unity.

Otherwise expressed this relation is where H=the magnetic :field intensity.

To meet this requirement pole faces Il and vI2 are formed with an outward taper as shown and described heretofore.

Referring now .to the simplified schematic representation in Fig. 4, wherein reference characters employed hereinbefore serve to represent similar parts, there is shown in diagrammatic fashion circuitry which may be utilized to secure desired operational characteristics for the abovedescribed apparatus. A pulse generator 50 supplies intermittent Venergization through concluetors 20 to electron gun |1 (not shown) at a desired instant in the cycle of magnetic eld produced by energizing windings 1 and 8 as determined by a saturable strip around which is positioned a winding 52. It will be understood 'by those Well skilled in the art that saturable strip 5| may be arranged such that it will produce a triggering pulse in winding 52 at a desired time instant in the cycle of magnetic field and that this pulse may be directed through conductors 53 to pulse generator 50 for initiating the energization thereof. In a similar manner, high frequency voltage source 54 may be triggered by means of a saturable strip 55 coupled with a winding 56 which is connected through conductors 51 to high frequency voltage source 54. For a more complete description of circuitry which may be suitably adapted for these purposes, reference may be had to U. S. Patent 2,485,409, issued October 18, 1949 to Herbert C. Pollock and Willem F. Westendorp and assigned to the assignee of the present invention.

In the fragmentary elevation of Fig. 5a, Wherein similar numerals are used to designate like parts hereinbefore described, there is shown alternative means for exciting resonator 2|. In this embodiment resonator 2| is excited through a concentric transmission line 58 suitably introduced through the side of dielectric box 30 near the end remote from envelope I3. Proper magnetic coupling of a high frequency voltage source (not shown) is assured by making a right angle loop in the inner conductor 59 as is illustrated in the fragmentary view of Fig. 5b. Loop portion 60 of inner conductor 59 should be perpendicular to the plane of the paper in Fig. 5a and may be directed either into or out of the plane of the paper.

Referring now to Figs. 6 and 7 there is shown alternative resonator and envelope structure which may be employed in connection with the apparatus illustrated in Fig. l. In this embodiment a generally' cylindrical envelope ||3 is supported by means of an arcuate spacer member |35 within a resonator |2|. Resonator |2| comprises an inner conductor |22 which includes spaced apart radial conductive strips |25 attached to the outer surface of envelope ||3 and terminating at their innerqends in a semi-circular shortening strip |28. Outer conductor |29 comprises a generally cylindrical box portion |30 of dielectric material enclosing a portion of envelope ||3 and having attached to its inner surface a plurality of spaced apart radial conductive strips |3| which terminate at their inner ends on a conductive short-circuiting strip |35. To facilitate the insertion of envelope ||3 within outer conductor |39 the latter is provided with a transverse slot |31 as shown. High frequency energy may be introduced into the structure by means of a concentric transmission line portion |38 which is directly coupled into a concentric line section or stub |38' as illustrated. If more convenient, portion |38 may be coupled into the outer end of stub |38' as will be understood by those skilled in the art. Stub |38' comprises a cylindrical portion |39 of dielectric material which is lined with thin conductive material |39. At its lower end the liner |39 is connected to strips |3| as illustrated at |40, and at its upper end it is short-circuited to an inner conductor |42 which comprises a metallic rod |43 extending downwardly and terminating in a disk |44 which makes contact with strips |25. With the proper selection of dimensions this structure also operates as a quarter wave concentric line resonator at a particular excitation frequency. The space between conductive strips |25 on the exterior surface of envelope ||3 and conductive strips |3| on the interior surface of dielectric box |30 may be considered as forming a lumped capacitance across the inner end of concentric line stub or section |38. Accordingly, if the structure has the proper dimensions and is excited at the proper frequency, a cyclically reversible electric eld of high intensity may be made to appear across the inner and outer conductors in a manner similar to that described in connection with Fig. 3a.

In Figs. 8 and 9 there is shown another alternative form of resonator and envelope structure which may be advantageously employed in connection with the apparatus of Fig. l. In this embodiment charged particles may be accelerated within a closed annular envelope 200 of dielectric material within the wall of which there are sealed energizing conductors 20| supporting a charged particle source or electron gun 202. Enclosing a portion of annular envelope 200, there is shown resonator structure which comprises an inner conductor 203 including a plurality of spaced coaxial conductive strips or loops 204 suitably attached tothe outer surface of envelope 200. An outer conductor 205 comprises a plurality of spaced coaxial conductive strips or loops 205 suitably attached to the interior surface of an annular section 201 of dielectric material. Inner conductor 203 along with envelope 200 may be supported in spaced coaxial relationship with respect to outer conductor 205 by means of dielectric spacers 208. Inner and outer conductors 204' and 206 have discontinuous peripheries to form respectively aligned gaps 209 and 2|0. Positioned along the outer surface of annular section 201 are three arcuate spaced parallel plates 2| 2|2, and 2|3 forming extensions of inner conductor 203 and outer' conductor 205. The inner conductive plate projects through gap 2|0 and terminates at its inner end in gap 209 to make contact with loops 204 as shown. The two outer plates 2|| and 2|3 terminate in gap 2|0 to make contact with loops 206. At their outer or distal ends plates 2|I, 2|2, and 2|3 are short-circuited by an arcuate plate 2|4. High frequency energy may be conducted into the resonator structure by means of a concentric line 2|5 having an inner conductor 2|6 connected directly to plate 2|2 and an outer conductor 2|1 connected directly to plate 2|3. It will be now understood by those skilled in the art that this structure will operate in a similar fashion to that disclosed in Figs. 6 and 7 to accelerate charged particles twice per revolution as they pass into and out of the structure. The space between conductive loops 204 and 20S may be considered as forming a lumped capacitance across the inner end of parallel plates 2|l, 2|2, and 2|3 which act as a transmission line short-circuited at the opposite end.

From the foregoing description of the various embodiments of the invention it will be apparent that advantageous accelerator apparatus is provided. Since it is not necessary to produce a timevarying magnetic flux linking the charged partcle orbit to pre-accelerate the particles, opening |6 may be employed as a means of reducing the amount of iron in magnetic structure and also as a means of introducing various lead-in conductors. Furthermore, the strips from which the l generation of. eddy-currentsby thetime-varying magnetic eld.. Moreover, large radial spaces are available for initial oscillations of` the charged particles about the orbit and, therefore, the increase in/ output of the apparatus is facilitated.

WhatI claim as new and' desire to secure by Letters Patent of the UnitedA States is:

1. A chargedl particle accelerator which coniprises a; magnetic structure having a pair of opposed rotationallyfsymmetrical pole pieces delining a gap between thespole facesl thereof, energizing windings about said pole pieces,` a source of cyclic time-varyingy voltage connected to said energizing windings for exciting said magnetic structure, the pole faces of said pole pieces having an inverse slope with radius such that the magnetic neld" intensity` H in the gap between the pole faces will follov: the proportionality Haflwhereris the radius andn is an exponent having'a veluelying between zeroand unity, a closed envelope capable of being evacuated disposed in the gap between-the pole faces of said pole pieces, a source of charged particles within said envelope, means'for intermittently energizing said charged particle source at a desired time near zero` in the cycle ofi'magnetic field generated by said energizing windings to inject charged particles into said envelope; high frequency electric held directing means for. accelerating` said injected particles to high energy levels in an expanding orbit, the radius R of said orbit at any instant being determined by the relation R= w where w is a constant representing the angular velocity of the particles and o represents the linear velocity of the particles which varies from the velocity at injection to a desired nal velocity, said electric field directing means including e resonator coupled to the particle orbit and comprising subdivided inner and outer conductors, both said inner and outer conductors being hollow and enclosing a portion of said envelope between the pole faces of said pole pieces, and a source of high frequency voltage connected to said resonator, said resonator being short-cir cuited at one end and open-circuited at the other end to provide a high frequency electric field for accelerating particles within said envelope.

2. A charged particle accelerator which comprises a magnetic structure having a pair of opposed rotationally symmetrical pole pieces defining a gap between the pole faces thereof, energizing windings about said pole pieces, a source of cyclic time-varying voltage connected to said energizing windings for exciting said magnetic structure, the pole faces of said pole pieces having an inverse slope with radius such that the magnetic neld intensity H in the gap between the pole faces will follow the proportionality [fai T11 where r is the radius and n is an exponent having a value lying between zero and unity, a closed evacuable envelope disposed in the gap between the pole faces of said pole pieces, a source of charged particles within said envelope, means for intermittently energizing said charged particle source at a desired ltime near zero in the cycle of magnetic field generated by said energizing y10 windings to inject charged. particles into said envelope, high. frequency electr-ic eld directing means for accelerating said injected particles to high energy levels in an expanding orbit, the radius R of said orbit at any instant being determined by the relation where w is a constant representing the angular velocity of the particles and o represents the linear velocity of the particles which varies from the velocity at injection-toa desired final velocity, said electric eld directing means including a resonator coupled to the'particle orbit and formed of subdivided inner and outer conductors, both said inner and outerk conductors being hollow and positioned exteriorly ofV said envelopeaand a source of high frequency voltage connected to said resonator, said resonator being short-circuited at one end and open-circuited at the other end,l the open-circuited end' of said resonator traversing said envelope to provide a high frequency electric eld within said envelope for accelerating particles within said envelope.

3. A charged particle accelerator which comprises a magnetic structurev having a pair of opposed rotationally symmetrical pole pieces defining a gap between the pole faces thereof, energizing windings aboutsaid pole pieces, a source of cyclic time-varying voltage connected to said energizing windingsl for' exciting said` magnetic structure, the pole faces of said pole pieces having an inverse slope with radiusl such that the magnetic field intensity H inthe gap between the pole faces will follow the proportionality l Het where r is the radius and n is an exponent having a value lying between zero and unity, a generally circular closed envelope disposed in the gap between the pole faces of said pole pieces, a source of charged particles within said envelope, means for intermittently energizing said charged particle source at a desired time near zero in the cycle of magnetic field generated by said energizing windings to inject charged particles into said envelope, high frequency electric field directing means for accelerating said injected particles to high energy levels in an expanding orbit, the radius R of said orbit at any instant being determined by the relation where w is a constant representing the angular velocity of the particles and o represents the linear velocity of the particles which varies from the velocity at injection to a desired final velocity, said electric eld directing means including a resonator comprising subdivided hollow inner and outer conductors enclosing a portion of said generally circular envelope between the pole faces of said pole pieces, one end of said resonator being open-circuited and lying in a plane including the axis of said envelope, the other end of said resonator being short-circuited, and a source of voltage of constant high frequency connected to said resonator to produce a high frequency eld across said open-circuited end of said resonator whereby charged particles will be accelerated twice per revolution within said envelope.

4. A .charged particle accelerator which comprises a magnetic structure having a pair of rotationally s ymmetrical pole pieces dening a gap between the pole faces thereof, there being a central opening extending through said structure including said pole pieces along the axis of said pole pieces, energizing windings about said pole pieces, a source of cyclic time-varying voltage connected to said energizing windings for exciting said magnetic structure, the pole faces of said pole pieces having an inverse slope with radius such that the magnetic iield intensity H in the gap between the pole faces will follow the proportionality 1 Han Where r is the radius and n is an exponent having a value lying between zero and unity, a generally circular closed envelope disposed in the gap between the pole faces of said pole pieces, a source of charged particles Within said envelope, means for intermittently energizing said charged particle source at a desired time near zero in the cycle of magnetic eld generated by said energizing windings to inject charged particles into said envelope, high frequency electric field directing means for accelerating said injected particles to high energy levels in an expanding orbit, the radius R of said orbit at any instant being determined by the relation where w is a constant representing the angular` velocity of the particles and v represents the linear velocity of the particles which varies from the velocity at injection to a desired nal velocity, said electric field directing means including a rectangular resonator comprising subdivided hollow inner and outer conductors enclosing a. portion of said generally circular envelope between the pole faces of said pole pieces, one end of said resonator being open-circuited and adjacent the axis of said envelope, the other end of said resonator being short-circuited, a section of coaxial transmission line extending through said central opening in said magnetic structure and having its inner and outer conductors connected respectively to the inner and outer conductors of said resonator, and a source of voltage of constant high frequency connected to said transmission line section for exciting said rescnator.

ANATOLE M. GUREWITSCH.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,948,384 Lawrence Feb. 20, 1934 2,079,248 Fritz May 4, 1937 2,229,572 Jones Jan. 2l, 1941 2,531,384 Bailey Nov. 28, 1950 2,545,623 MacKenzie Mar. 20, 1951 2,553,312 Gurewitsch May 15, 1951 2,563,585 Dallenbach Aug. 7, 1951 OTHER REFERENCES Post, Proposed High Energy Particle Acceler ator, Physical Review. vol. 69, 2nd series No. 3 and 4, pp. 126, 127, Feb. 1. 1946

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