US2538718A

US2538718A - Magnetic induction device for accelerating electrons

Info

Publication number: US2538718A
Application number: US720544A
Authority: US
Inventors: Wideroe Rolf
Original assignee: BBC Brown Boveri France SA
Current assignee: BBC Brown Boveri AG Germany; BBC Brown Boveri France SA
Priority date: 1946-08-06
Filing date: 1947-01-07
Publication date: 1951-01-16
Anticipated expiration: 1968-01-16
Also published as: GB652247A; BE475005A; FR950548A; CH251244A; DE851094C

Description

Jan. 16, 1951 R. WIDEROE 5 9 MAGNETIC INDUCTION DEVICE FOR ACCELERATING ELECTRONS Filed Jan. 7, 1947 2 Sheets-Sheet l J n- 16, 1951 R. WIDEROE 2538,71

MAGNETIC INDUCTION DEVICE FOR ACCELERATING ELECTRONS Filed Jan. 7, 1947 2 Sheets-Sheet 2 Patented Jan. 16 1951 PATENT oFsrciEi 2,538,718 MAGNETIC INDUCTION L'DEVICEEOR' AGOEILER'ATING ELECTRON S Rolf wideriieazurich, Switzerl-andl assignorto- AktiengOSGHSGhaftvBIOWD; .Boverifit .Cie, ,Baden,

Switzerland,,,atjoint-stock company Applicationdanuary '7, 1947; 'serial Noe 720544 m Switzerland Augu'st (19463 12 Claims. (cram-127.)

'I1his- .invention relates tm devices-for aocelerating; electrically; charged: particles such: as; electrons; 1 to; high velocity; and, hence. high: potential by; meansof: magnetic induction; effects: These devices: which areenow knowngenerally-as ray transformers; or betatronssaree comprised generally; 012 an. evacuated annnlarr' tube: into-. which elcctronnstreams- ElifisdiSChfiIQfidififiIIl an electron emissive cathode,,andxarlmagnetic system"; energized, by; alternating: current: which produces? a I m snetice field; Varying? ccliealhrwith: time: and having-= a; space; distribution such that the: in.- .iec edzelectmnsgareaaceelerated by thefield round and-wound; the tubesonanzorbital r-path-iknorwn as he; quilibrium circled? T1185, magnetic: field divides into two components one component will d;theaind einasfieldi p od'l qesz-thee electron accelerati n; h ther: omponent. called the control yfield! produces ,aacentripetal effect upon the electron 1 to; onset: the: centrifugal; forces; of

isea e.

Ops a etfiitr nuonr bZQthihZih/TGS' of the; wave i: he alte natmsz. current powerysnpply' usedifor and ype f: n ration-,-., an electron 3 7 132 11 itea fieie ted inzonedirectionearoundtthe ube durin apart-pfm ce-hair;ontne-cyclenrctne l erna ng power supply, and another nd; tl 1 e;t e=during a;--.part of.the V halt; of: the; alternati.I'Issj current: cycle. fiince h e woe ec rontreamer each: separated fronr the othenby substantially a. half cycle; of l'lre e c :eur Whfi zdiyfifl i l flmith fiquilibriunfr:circlectoime pinge upon the anode, the electrorrzstreams-are ih:: 1i y? d for herXeray reatm nt of The presentqknowni betatron usi-ngm pair: ofiielectron streams g e thniliboth;electronstreams 1:; ame ntensity:- and" vel ci y. When the betatron is usedifotzmeditai purposes, i rezlileiietionnnamely lite rim: .1 z leetrens aree aecens siernt t t-are usedltheetreatment of ;mis accelerated ln';theeopppsite v imiopmsite: directions In th 'nterestaof emciencyA-t is:-desiraldle=to sincennewill rarelyleverfind-two patients'eati-the same time :W'hO requireexactly theesarne intensity of radiation :or ray, hardness;

'Iihe object of this inventionis to'provi'de an improvedconstructioniona betatron using av-pa-ir of oppositely running electron streams 1 by which one may selectively control b'oththe intensity and 1 speed of each electron stream. independently of the other.

other" objects and; advantages to be derived from the-invention will become more apparent from :the following" detailed description and from the accompanying drawings which illustrate preferredzconstructionse.

In the drawings; Fig.- 1 isavertical central section of amagnetic induction accelerator embody-mg; one form ofthe-inventiong Fig-r2ti ea horizontal sectionttakenralongline 2-2-of Fig; 1 showing a:- fragmentary section ofthe annular tube and aicontrol circuit for one of the electron emittingcathodes; Figs-Brand 4 areviews similar to i Fig; 7 21 but illustrating modified forms of the invention by *which independent control :of the two electronastreamsis attained; Fig; 5. is-a,-cir:- cnit'v diagram; showing circuit by which i independent control over the respective: ejection velocities ofithetwo. electron .-streams is: brought about;- and :Fig:r6r -is.-.a;-'plot-.ofthe induction :flu-x curve showing. its-va riation withrtime. Y

Referring; now torthedrawings 1 and in particular to==Figs. 1; and 2;. the. magnetic induction accelerator which; is symmetrical 331301113 the axis aq-w is; comprised of a :magnetic fieldp structure l-U made up. from steel :laminations of apnro'oriate contour and includes-'a pair of cylindrical pole: pieces? I I-H separated by air gap =12":10- cated concentrically: along aXis a-ia', anda pair of annular i pole pieces I 3-! 35* facing :each other andsepara-tedbyair gap l4; Yokewmembersvlfi complete: the magnetic circuit for the cyclically varying fluxset up in'the annular=and-cy1indrical pole pieces-5 Poles l,-H' and l3-l3t arersu-rrounded- :by; arr annular winding pref erably-- split into two-coilsections: l6l5" which are connected: in seriesrfor energization'irom:aesource of alternatingecurrent of suitablelfrequency such aszforexamp-lee loo cycles/sece applied: to tert minals l'l:

An annular evacuated glass tube' l8 restsr in the ai-n" gap l 4- between: the pole pieces l3--l 3' andthereby surrounds apart of the? axial pole pieces H -H'. Fonproduoing the' 'two electron streams; a pair of? coiled:filamentarycathodes 295 2-1 eare used and? these extend? for: a substane tia'hdi staneex. in r a: directioniaparallele to:.. the'eaxis of symmetry of the tube 8. The cathodes are suitably supported within and near the outer wall of tube H3 and are partially enclosed within opposite sections of an H-shaped electrode 22 that is positively charged relative to the cathodes and 2| through ground and which serves to initially guide the electron streams alternately emitted from cathodes 2|), 2| in a direction generally tangential of the tube I8. As will be more fully explained in succeeding paragraphs, the two electron streams alternately emitted from cathodes 20, 2| for a brief instant at the start of each half cycle of the magnetic field produced by windings |6-|5' are then accelerated respectively under the influence of the changing field. When the electron streams reach their ultimate desired velocity which occurs not later than one-quarter of a cycle later, providing the magnetic control field is not premagnetized as described in my copending application Serial No. 708,552 filed November 8, 1946 they are each in turn pulled radially inward from the equilibrium circle is to impinge upon the anode 23. In the drawing, the electron stream emitted from cathode 2| is shown by arrow 24 striking the target anode 23 and producing X-rays indicated by arrow 25.

In accordance with the invention, independent control is exercised over the characteristics of the electron streams emitted from cathodes 2U and 2|. The circuit by which the electron stream emitted from cathode 2| is controlled includes a transformer 26 for heating the oathode, the secondary side 2612 of the transformer being connected in circuit with cathode 2| while 1 the primary side 26a is connected through a regulating resistance 21 to a source of alternating current applied to terminals 28.

The instant at which electron emission from cathode 2| occurs is controlled by a grid controlled valve 30. The plate 36a of valve 30 is connected to cathode 2| via the transformer secondary 26b, and the cathode 30b is connected to a condenser 32 that is charged from the secondary 33b of transformer 33 via rectifier 34. The primary winding 33a of transformer 33 is connected to terminals 35 supplied from an alternating current source. The grid 390 of valve 3B is connected through battery 36 to rotatable winding 31 of a phase shifting device as that is powered from B-phase mains 39 suitably related in phase to the phase of the alternating current supplied at terminals Thus, for example, terminals I! could be supplied by one phase of the B-phase mains 39.

The charge on condenser 32 is discharged at the proper instant in each cycle of the alternating current which supplies the electromagnetic field for accelerating the electrons by swinging the potential on the grid 300 of valve 39 with the aid of the phase shifter 38 to render valve 3|) conductive. As valve 30 becomes unblocked, the voltage on charged condenser 32 is applied to the cathode 2| and results in emission of a stream of electrons into the tube I8 which are then accelerated in a counter-clockwise direction along orbit Ic. By adjusting the position of the rotatable winding 31, the instant at which electron injection into tube 8 from cathode 2| takes place as related to the phase of the electromagnetic accelerating field may be varied as desired. Thus, and now referring to Fig. 6, the timing of the switching of the charge potential on condenser 32 to cathode 2| through the valve 30 may be such that the condenser potential is applied at the start T1 of a half cycle of the time varied magnetic field B, or if desired, electron injection may be delayed until time T2 by changing the position of the Winding 31 on phase shifter 38. A load resistor 4| for the condenser discharge is connected to the anode of tube 30.

not been shown. However, it is operated independently of the above-described circuit and identical with the latter in construction.

If desired, according to a modified form of construction, the current impulse reaching cathode 24 may be switched in by a relay instead of directly through the grid controlled valve 39, in which event the relay would be located in the anode circuit of a valve similar to valve 30.

A modified form of double and independently controlled cathode arrangement for a magnetic induction device is shown in'Fig. 3. Here the two cathodes 42, G3 are alike in construction and are controlled, in part, by

grids

24, 45 which are placed, respectively, in front of the cathodes. The electron stream injected into the tube i8 from cathode 42 can be adjusted as desired by placing a potential on grid 44 from battery 45 having suitable potential taps for this purpose. In a similar manner, the electron stream injected into the tube from cathode 43 may be adjusted by means of the battery that is connected in circuit with grid 45.

In the Fig. 3 arrangement, initial control'over the direction of the electron streams emitted from the cathodes 42 and 43 is provided by right angled plate electrodes 48, 49 which are placed back-to-back to partially enclose and shield the cathodes from each other and a flat plate electrode 55, which may be closest to the orbital path of the electrons, arranged parallel with one side of each of electrodes 48, 49. Electrode 50 is grounded and electrodes 48, 49 are charged negatively or eventually also positively with respect to plate 58 by means of a battery 5| which'is provided with a plurality of potential taps by which the potential of electrodes 48 and 49 with respect to electrode 56 may be adjusted independently of each other, the battery being earthed at a point intermediate its electrodes.

With like potentials on electrodes 48 and 5D, the direction of the electron stream emitted from cathode 42 is substantially tangent to the outer wall of the annular tube l8. However by adjusting'the taps shown at the left side of battery 5|, the potential on electrode 48 may be made negative with respect to electrode 50 and the resulting change in the electrostatic field between these electrodes will then cause the electron stream from cathode 42 to be deflected away from the tangential path, the magnitude of the deflection being dependent upon the extent of the difference in potential between electrodes 48 and 50.

The initial direction of the electron stream emitted from the other cathode 43 at substantially a half cycle later in the induction flux cycle may be changed in a similar manner by altering the position of the voltage tap at the right side of battery 5|.

The respective initial directions of the emitted electron treams as selected by the separate'adode "51! 'for Cathode 52 that controls acceleration of an ac-same "'justmentcr -the 'electrostatic'field's between the "two sets of electrodes are "deter-'rn'inativecfthe length of time that the electron streams remain in the tube 18, so that in this way th'eir final velocity can be adjusted separately'to' the desired extent.

Still another modification of the invention 'is shown in Fig. 4 in which the injection "of the two electron streams is controlled by application of a current impulse to two grids controlling "the emission of dual "electron streams from a "single cathode rather than by applicatio'noi the --control directly to the cathode itself. In this View, the electrontube is designated by it, "and "the-single cathode '52 is heated indirectly "by 'means of a filament 52a supplied by transformer "53. Juxtap'osed electrode plates "6! which may 'be charged to like "or different potential 'in'the "manner shown in Fig. niunction to control the initial path of the two electron streams emitted alternately and in opposite directions from cath- An initial potential on control grid electron stream emtted from cathode '52 in a counter-clockwise direction around the time 18" is obtained through an adjustable voltage bat- "tery-55.

The remainder of the circuit for the control of grid '54 is comprised of a relay "56 "through which the potential of a condenser is applied to the grid 55, a grid controlled valve "58 for controlling 'ener'gization of relay "56, a

phase shifter 59 powered from 3 phase mains til and having a rotatable winding 62 by which the potential on grid 58a of valve 58 is swung periodically to render valve fifi'conductive, an'da rectifier ESied from "transformer 66 for charging condenser 51. A load resistor 65 is provided in the c'onnectionsto grid 54 for the discharge from condenser 51.

The Fig. 4 arrangement operates much in the same manner as that shown in Pg 2. Briefly, each time that the voltage in windingtii of the phase shifter 59 reaches its maximum value, the

corresponding peak potential on 'grid'liea renders the valve 58 conductive and a pulse o'f'current flows through the energ zing winding of relay 58 which is connected in the cathode anode circuit of valve 58. The source of anode current for valve 5 3 is the battery so. As the relay contacts 5505 close, current "impulse from charged ccndenser't'i is switched into the grid .54 thus efiecting the discharge of an electron stream into tube 1-8 for acceleration in' a counodically injected into tube it" from cathode 52 for acceleration in a clockwise direction around the tube under the influence of the other half cycle of the magnetic induction field is identical with, independent of, the circuit assc'ciated with cathode grid 5 In the interest of simplifying the drawings, this other circuit has been shown only in part with corr sponding circuit components-indicated by like primed reference als.

As explained in an earlier part 'of do the electron 'scription; the -'electron streamiira niag-netic iii 'duction accelerator is divertedfromthe equilibrh um circle after it has reached the"dsird velocity maximum and caused to impinge upona target anode to produce'X ray radiations. Accordi-hgto the present invention, wherein the 'ele'ctronacceleratin'g device operates "onboth halves 'of the "and "uses alternately "discharged andc'ppositely rotating electro'nstreams;means are provided for independent 'ccntr'oiover the instants at which these twost'reamsare pulled away from the equi- -'librium "circleas related to the instant inagnitu'de or the induction flux. Referring now to Fig' 5 which =illnStratesa ereieriedarrangementrcrcontrolling the electron streams independently, the "circuit there shcwii iS "seen to be comprised a pair or phase shifters c1568 pcwderean cmtphase mains" c9, a an 'df' grid control v lves [0,

.H which may be thy'ratroris anda condenser '12 :able winding 186i phase 5s connected through ba'tte'ry maria resistors!) into "the c'a tl 'ioele grid circuit; of "valve 1 I. g

" is connected in the ."catho'de- 'grid"circuit'bf vaiye is "through battery lb and resistor Ti the "In the illustrated embodiments or the tion, as typified by the construction sh n in 'str'e'anis injected alternately fofi'i pulled radially inward frdin' thisiciicle.

magnetic induction ffluX.

"the alternating current applied to them 'du'ct'ion windings l fi-'i 5 direction, the electron strearn that ha bee 'Oii'e 26 at substantially the zero point on "the opposite direction, the conden er 12 is discharged through the time" Figs. 1 and 5 respectiv ly, the anode Z a-impinged upon from oppositefdirectio'ns by 'the electron I odes 2b, 2| is located radially ifiwaid flfim the dllll' iiiin circle is and hence theelectro n'strearn's fhust be I His bf course requires that the magnetic contro field acting through the control 'p'o 'efs JI E- B fbe strengthened atthe proper fiistaritto thereby increase the centripetal rcrce's acting uponthelectron stream 'so that the latter i'suriv'en radially inward. in the resent constructional examine,

strengthening of the control field as shown in ig. 5 is obtaine'd'by means "or-an 'aiiiiiliary wind ng :82 consisting of the two' haivescc anqTsIwhih isplabed ihthe magneticfstructure I'll so that when energized periodically by the dischafi ing 82 wi l increase "the total control magnetic field. If the target anode 23 were to relegated radially outward from the equilibrium circle 7c,

it would'oi course be necessary todrive the enc- 'tron streams radially outward'in which case the auxiliary magnetic field furnished by the additional winding in theima'gnetic' 'structure I0 would be arran ed so as to weaken the c'e'n tripetal effect of the control sen-component 'of'tfie The com onents in the Fig. "5 hired-tamarranged so that condenser l'2 is discharged altern'ativ'ely through the one of the halves oi the auxiliary winding 82 once each half cycle n Thus whentheindu tion flux anproaches its maximuinfvalue in tire troduce'd hem one of the cathodes such as- 1;-

er the induction fiuxcycle is driven'radi lyinwa'rdly rrom the eciiuibi ium circle k to 'u'pon th'e target anode '23. v the induction flux reverses and approaches its maximum value in Winding and wi t?! wh n rim. "that had becn'ir'itrbdllcfl by cat ode 2| driven radially inward from its accelerating orbit and impinge upon target anode 23 from the opposite direction.

The exact time in the induction flux cycle at which the two electron streams are diverted respectively from the equilibrium circle may be controlled independently of each other by means of the phase shifters B? and 68. Thus for example, the instant T3 (see Fig. 6) at which the grid 10a of control valve 19 renders the valve H5 conductive and which thereby permits the condenser 12 to discharge through the auxiliary winding 83 and drive the then accelerating electron stream injected for example at time T1 radially inward against the target anode 23 may be varied by adjusting the position of winding 15 on phase shifter 67. A change in the time of electron release to the target anode 23 thus changes their maximum speed as may be required to suit a particular condition. The time of release of the other electron stream which follows at substantially a half cycle later in the induction flux cycle may be similarly controlled by varying the position of the winding 78 on phase shifter 68. If desired, electron ejection from the equilibrium circle is may be delayed until time T4 which coincides with the maximum of the induction flux, in which case the electron streams would both be at maximum velocity.

I claim:

1. A magnetic induct on accelerator comprising, a chamber within which charged particles such as electrons may follow a closed orbital path, means adjacent said chamber for producing a cyclically varying magnetic field of alternating polarity, said field having such spacial distribution as to normaly confine the electrons to said orbital path while continuously accelerating them along said path, means including electron emission cathode means operated in timed relation w th the variation in said magnetic field for periodically injecting electron streams into said chamber for acceleration respectively in opposite directions along said path, the direction of the acceleration of a particu ar stream being dependent upon the polarity of said magnetic field, means operated in timed relation with the variation in said magnetic field for ejecting the accelerated electron stream of each direction, and independentlyoperated control means individual to the electron streams accelerated in opposite direct ons respectively for effecting independent changes in a characteristic of the electron streams of each direction.

2. A magnetic induction device as defined in claim 1 wherein the means for controlling electron streams of opposite direction includes means for independent adjustment of the intensity of each stream.

3. A magnetic induction device as defined in c aim 1 wherein the means controlling electron streams of opposite direction includes means for independent adjustment of the maximum velocity of each stream.

4. A magnetic induction device as defined in claim 1 wherein the means for controlling electron streams of opposite direction includes means for independent adjustment of the respective periods during which said streams are accelerated.

5. A magnetic induction devce as defined in claim 1 wherein the means for controlling electron streams of opposite direction includes means by which the entering angle of said streams may be independently adjusted.

6. A magnetic induction device as defined in claim 1 wherein consecutive electron streams are discharged into said chamber in response to consecutive current impulses, and the means for control'ing the electron streams includes means for adjusting the respective magnitudes of consecutive current impulses independently of one another.

'7. A magnetic induction accelerator comprising, a chamber Within which charged particles such as electrons may follow aclosed orbital path, means adjacent said chamber for producing a cyclically varying magnetic field of alternating polarity, said field having such spacial distribution as to normally confine the electrons to said orbital path while continuously accelerating them along said path, a pair of cathodes, means operated in alternation and in timed relation with the variation in said magnetic field for discharging streams of electrons from one cathode in alternat on with electron streams discharged from the other cathode for acceleration respectively in opposite directions along said path, the direction of acceleration of a particular stream being dependent upon the polarity of said magnetic field, means operated in alternation and in t med relation with the variation in said magnetic field for ejecting the accelerated electron streams of each direction, and independently operated control means individual to each said cathode for adjusting the electron emission from one cathode independently of the electron emission from the other cathode.

8. A magnetic induction device as defined in claim 7 wherein said cathodes are heated and said adjusting means includes means for independent adjustment of the heating of each cathode.

9. A magnetic induction device as defined in claim 7 where n a control potential is applied to each of said cathodes and said adjusting means includes means for adjusting the potential appied to one cathode independently of the potential applied to the other cathode.

10. A magnetic induction device as defined in claim '7 wherein sad adjusting means includes means for independent adjustment of the respective intensities of the two electron streams.

11. A magnetic induction accelerator comprising; a chamber within which charged particles such as electrons may follow a closed orbital path, a Wind ng adjacent said chamber and energized from a source of alternating current for producing a cyclically varying magnetic field of alternating poarity, said field having such spacial distribution as to normally confine the electrons to said orbital path while continuously accelerating them along said path, means operated periodically in timed relation with the variation in said magnetic field for periodically injecting electron streams into said chamber for acceleration respectively in opposite directions along said path, the direction of the acceleration of a particular stream beng dependent upon the polarity of said magnetic field, auxiliary winding means disposed adjacent said chamber and which when energized produces a magnetic field efiective to cause ejection of said electron streams from said path, and independently controlled circuit means for efiecting periodic energization of said auxiliary winding means in opposite directions, respectively, in tmed relation with the variation in said magnetic field, each said circuit means including a grid controlled va've, an adjustable phase shifter connected to said source of alternating current and connections between the valve grid and said phase shifter.

12. A magnetic induction accelerator comprising, a chamber Within which charged particles such as electrons may follow a closed orbital path, means including a magnetic structure and energizing winding therefor disposed adjacent said chamber for producing a cyclically varying magnetic field of alternating polarity, said field having such spacial distribution as to normally confine the electrons to said orbital path while continuously accelerating them along the path, means operated in alternation and in timed relation with the variation in said magnetic field for periodically injecting electron streams into said chamber for acceleration of successive injected streams respectively in opposite directions along said orbit, the direction of acceleration of a particular stream being dependent upon the polarity of said magnetic field, anode means, means operated in alternation and in timed relation with the variation in said magnetic field ejecting the accelerated electron streams of each direc- ,WMM 10 tion from said path and efiecting impingement of said streams against said anode means, and independently operated control means individual to the electron streams accelerated in opposite directions respectively for effecting independent changes in a characteristic of the electron streams of each direction.

ROLF WIDERGE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS