US2663813A

US2663813A - Magnetic induction accelerator

Info

Publication number: US2663813A
Application number: US198325A
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: 1949-12-02
Filing date: 1950-11-30
Publication date: 1953-12-22
Anticipated expiration: 1970-12-22
Also published as: FR1028434A; DE908394C; GB693307A; CH277136A; NL72582C

Description

Dec. 22, 1953 R. WIDERE 2,663,813

MAGNETIC INDUCTION ACCELERATOR Filed Nov. 30, 1950 3 Sheets-Sheet l INVENTOR 20?. MIM

BY m, QSDLWNIPMJQW ATTORNEYS Dec. 22, 1953 Filed Nov. 30, 1950 R. WIDERE MAGNETIC INDUCTION ACCELERATOR 3 Sheets-Sheet 2 INVENTOR ATTOR NEY-S Dec. 22, 1953 Filed NOV. 30, 1950 R. WIDERE MAGNETIC INDUCTION ACCELERATOR 5 Sheets-Sheet I5 Huss INVENTL )h ATTORNEYS Patented Dec. 22, 1953 UNITED STATES PATENT OFFICE MAGNETIC INDUCTION ACCELERATOR Application November 30, 1950, Serial N o. 198,325

Claims priority, application Switzerland December 2, 1949 8 Claims.

This invention relates in general to devices for accelerating charged particles such as a stream of electrons to high velocity and hence high potential on an orbital path by the principle of magnetic induction.

Electron accelerators of the magnetic induction type now generally known as a betatron or ray transformer are comprised of an evacuated toroidal tube into which electrons are introduced from an electron emissive cathode or electron gun, and a magnetic system which produces a magnetic field varying with time having a space distribution such that the injected elecn trons are accelerated by the iield along a circular orbit. The magnetic iield divides into components, one component being known as the induction field which produces the electron acceleration and the other as the control or guiding iield which produces a centripetal effect upon the electrons to offset the centrifugal forces resulting from the circular motion. The electrons reach an enormously high energy level at which time they can then be diverted from the orbit for producing desired results such as for example to bombard a target and produce Xrays.

In the control eld space or" the betatron, the radial eld components above and below the plane in which it is calculated the orbital path will lie should be of like magnitude and exactly opposite one another. However this ideal relationship is not always possible. For example, if it should happen that a removable part of the magnetic structure above the tube is not aligned exactly with the corresponding structural part below the tube when initially installed or when replaced after lhaving been removed to replace the tube, the mis-alignment between the two parts may cause the orbit to become established in a plane other than the one calculated for it with a possible attendant loss of those electrons in the stream which should happen to impinge against the wall of the tube in the course of their range of normal oscillatory displacement from the orbital path during their acceleration along the path. Other factors may also result in impingement of some electrons in the stream upon the tube wall thus reducing the potential yield of the electron stream.

The general objective of the present invention is to prevent any reduction in yield of the electron stream, and is attained through the use of like circularly curved conductors disposed respectively above and below the equatorial plane of the tube and which are counter-connected, i. e. short-circuited with each other.

Various diiierent arrangements for the conductors are possible within the scope of this invention and a few typical embodiments are shown in the accompanying drawings.

Fig. 1 is a view in vertical diametral section on line l-I or Fig. 2 through a magnetic induction accelerator in which the short circuited, arcuate conductors, located respectively above and below the equatorial plane of the annular tube are comprised of a plurality of interconnected sets of substantially single turn coils stepped in diameter and arranged in planes parallel with the equatorial plane.

Fig. 2 is a horizontal sectional View on line 2-2 of Fig. 1;

Fig. 3 is a View in top plan of a tube showing a modified arrangement for the leads interconnecting the corresponding conductor coils above and below the equatorial plane in opposition;

Fig. 4 is a view in top plan of a tube illustrating a somewhat diierent construction for the arcuate conductors in which the latter extend for only a portion of a complete circle;

Fig. 5 is a view in transverse section on line 5 5 of Fig. 4;

Fig. 6 is a view in vertical section of a further modification of the invention wherein the upper and lower short-circuited arcuate conductor sets are comprised of bands having a curvature cor-y responding to that of the lines of flux of the magnetic control field; and

Fig. 7 is a diagrammatic view showing the arrangement for one set of the arcuate conductors.

With reference now to the drawings, and Figs. 1, 2 in particular, the magnetic induction accelerator is seen to be comprised of a magnetic structure I0 made up from steel laminations of appropriate contour stacked radially on edge to provide a pair of confronting cylindrical induction poles Il ll' separated by air gap l2 and located concentrically along the central Vertical axis rit-a, and a pair of confronting annular control poles I3-l3 also concentric with axis a-a with an air gap i4 therebetween. Yoke members I5 complete the magnetic circuit for a cyclic, time varied magnetic flux set up in the annular and cylindrical poles. The magnetic flux in the control poles constitutes the guiding or control field previously mentioned, and the iiux in the induction poles constitutes the induction field.

The magnetic flux is produced by a winding split into two coil sections 16-16 connected in series for energization from a source, indicated by terminals l1, of alternating current of suitable frequency as for example 100 cycles/sec.

An annular evacuated glass tube le rests in the air gap I4 between control poles i3-I3. Tube I8 is also concentric with axis a-a and the particular one illustrated has a substantially trapezoidal cross-section. By means of an electron emissive .cathode not shown and which may be located within the tube I8 or in an arm portion arranged tangentially thereto, streams of electrons are injected in timed relation to the time-varied magnetic field produced .in -the structure l by the time-Varied current in the energizing coils Iii-I5 and are continuously accelerated along an orb-ital path indicated by .the circle lc. Upon completion of the acceleration phase, the electron stream is thencausedtoleave the orbit and iinpinge upon an .anode also not shown to yield X-rays, or the stream may ,be removed `from the tube for other purposes as for use in an ionization chamber.

None of the interrelated controls for injectingftheelectron streams into the tube and removing the streams from the orbit have 4been illustrated .Since many different systems of .control are well known and moreover are not essential .to .an understanding of Athe present invention.

All the structure so far described is conventional. Coming now' .to the present invention, it will be seen that on the exterior `wall surface of the .tube it VIl Vhave located a plurality `of circularly curved, .electrical-ly conductive wires stepped in diameter and arranged in spaced, parallel yrelation in planes parallel with the Yhorizontal equatorial piane'bb through the tube, and in which plane the orbit 1c will also lie under perfect design conditions. All of the .conductors are Vconcentric with the r vertical axis c-Tc, i. e. the axis vof tu-be .118. The .three conductors i9, 20 and '2| located above the equatorial plane -b-.b are paired with twin counterparts I6', 2e and 2l located at like spatial positions below plane b b, .and each .pair Iii'fi, 28--20 and lfi--i' are interconnected by conductor portions ica- '.la and ESB-2lb, respectively.

The conductor portions 2da, 21a and 2%-, Zib interconnecting arcuate conductorV seits Z-Q-Q' and 2|.-2I pass through the central opening Within tube t8 while the conductor portions 19a, i912 interconnecting arcuate conductor set Iii-i9" pass over the outer side of the tube. However all the interconnecting conductors could pass through the tube center, orv all could be passed over the outer side of the tube as shown in Fig. 3 wherein the various arcuate conductors havebeen given the saine reference numerals for purpose of comparison.

Each of the arcuate conductors IQ-Zi and {Bf-2 I extends for substantially 360i and hence the interconnecting conductors l-Qaf--'Ia and 49h- 2 I-b would actually be much closer together than appears in the drawing where a rather wide spacing has been maintained for purposes of clarity. Assuming equal radial iiux components above and below the equatoriall plane b---bY of tube I8, the nux c traversing the conductor turns |9-l9' will produce in each identical voltages e, e', respectively, as indicated in Fig. 'L and these voltages nullify one another since the two turns lB-IQV are connected in opposition. The same will be true for conductor turns 2li-26! and 21h-2li. If however', the radial ux' components at corresponding spatial positions at opposite sides of the equatorialV plane are not alike in all respects, the, voltages e-ef will .diner thus Setting up a compensating shcrecircuit current in the interconnected turns I3-4 9?.

4 The same result will obtain for the other conductor pairs 20--20 and 2I--2I which likewise function as short-circuit windings.

Experience has shown that with the aid of short-circuit windings of the `type illustrated in Figs. 1 and 2, the electron yield .of thebetatron and .hence also the intensity of X-rays produced vby impingment of the accelerated electron stream against an anode, or the ionization effected in .an ionization chamber by the accelerated electron stream will be increased substantially.

A vsomewhat diiferent arrangement for the compensating short-circuited conductors is illustrated Vin Figs. 4 and 5 wherein each of the arcuate conductors concentric with the vertical axis c c, extends over only a portion of the complete circumference. Each of the six sets I-VI of paired conductors extends over 60 of arc. In set I, conductors 22--26 disposed at the upper side of tube I8 are paired with and counterconnected to conductors l222' disposed .at the under side of tube i6 and located at .correspending vradial distances from axis ,ca -a. The connections between the conductor .pairs aredesignated 22a-26a and 22h-26h, and it will be observed that all of these connections pass over the outer side of tube i8. The paired conductors the other five sets II-VI are arranged in identically the same manner as those of sety I, and lie at corresponding radial distances from -axis .a.-.a. That is, the conductors 22.-22 of .each set lie on the same radius, and the conductors 23.-23 of each set lie on the same but shorter radius, etc.

Another embodiment of the invention -is illustrated in Fig. 6 wherein the .paired conductors are constituted by bands of electrically conductive, metallic strip material, preferably copper having a thickness of the order of l mm. or less and a width of the order of 5 mm. -or more. The si-X radially spaced bands disposed along the upper surface of tube ,I8 concentric with axis a--a are numbered 2,8-33, and those disposed at the lower surface of the tube are numbered 28-33'. As in the Fig. 1 construction, the paired' conductive bands extend over an arc of substantially 360 and are interconnected by conductors 28a- 33a and 28h-33h. Each band is curved in the direction of its width to lconform to the curvature of the path taken by the control field ce shown in broken lines ,between the confronting faces of the control poles Iii-i3', Basically these counter-connected bands function in the same manner as the conductor wires of the other previously described embodiments. However, in the case of the band which also prevents, through the short-circuit eifect, the occurrence of magnetic fluxes extending perpendicularly to it, the-niagnetic control lines of force between the vbands are brought exactly Vinto the desired direction and will therefore take the desired course within the tube i3 with better approximation than can be obtainedwhen band-shaped conductors are not used.

The construction shown in Eig, 6 also. includes two more bands Sli, 35 disposed respectively at the inner and outer sides of tube i3 andfsymmetrically with respect to the equatorial plane. b b. The strip material forming these latter bands is 'heu/isc given a curvature conforming to the path of the control flux c@ and the bandsextend inthe directicnof. thisrpath from the upper edges of the upper set of bands 21H-fst to the lower edges. ofthe lower set of bands 28h-331. Because of the relatively greater widths the two bands .3.4; 351111.-

fiuence the control field cc especially effectively through the short circuited currents produced in them. The bands 34, are broken at one point in their circumference such as by narrow slots 34a and 35a, respectively.

In all of the embodiments of the invention which have been illustrated, the compensating conductors preferably are disposed on the exterior surface of the wall of tube i8 and may be attached to the same by any suitable adhesive such as glue or cement.

It is to be understood that the various embodiments of this invention which have been described and illustrated are but typical of the many practical structural arrangements possible within the scope of the basic inventive concept disclosed and as hereinafter defined in the appended claims.

I claim:

1. A magnetic induction accelerator for charged particles comprising a toroidal evacuated tube, means including a magnetic structure adjacent said tube and winding means thereon for producing a time-varying magnetic field having induction and control components of such spatial distribution relative to said tube as to normally conne electrons within the tube to a substantially circular orbit around the tube while accelerating them along said orbit, a pair of curved conductors having a like radius of curvature mounted concentric with the axis of said tube and disposed at corresponding positions above and below the equatorial plane of said tube in planes parallel with said equatorial plane, and means interconnecting said conductors in shortcircuit relation with each other whereby the voltages induced respectively therein by said magnetic iield are opposing.

2. A magnetic induction accelerator as dened in claim 1 wherein said conductors are secured directly upon the exterior surface of said tube.

3. A magnetic induction accelerator as defined in claim 1 and which further includes a curved band of electrically conductive metallic strip material mounted concentric with the axis of said tube and disposed symmetrically with respect to the equatorial plane of said tube, said band being also curved in the direction of its width to coincide with the curvature of the path taken by the control component of said magnetic eld.

4. A magnetic induction accelerator as defined in claim 3 wherein said band is located within the central opening of the said toroidal tube.

5. A magnetic induction accelerator as dened in claim 3 wherein said band surrounds the said toroidal tube.

6. A magnetic induction accelerator for charged particles comprising a toroidal evacuated tube, means including a magnetic structure adjacent said tube and winding means thereon for producing a time-varying magnetic i'ield having induction and control components of such spatial distribution relative to said tube as to normally confine electrons within the tube to a substantially circular orbit around the tube while accelerating them along said orbit, a plurality of pairs of curved conductors mounted concentric with the axis of said tube, each pair of conductors having a different radius of curvature and the conductors of each pair being disposed at corresponding positions above and below the equatorial plane of said tube in planes parallel with said equatorial plane, and means interconnecting the conductors of each pair in shortcircuit relation with each other whereby the voltages induced respectively therein by said magnetic field are opposing.

7. A magnetic induction accelerator for charged particles comprising a toroidal evacuated tube, means including a magnetic structure adjacent said tube and winding means thereon for producing a time-varying magnetic iield having induction and control components or" such spatial distribution relative to said tube as to normally conne electrons within the tube to a substantially circular orbit around the tube while accelerating them along said orbit, a pair of curved bands of electrically conductive metallic strip material having a like radius of curvature mounted ccncentric with the axis of said tube and disposed at corresponding positions above and below the equatorial plane of said tube parallel with said equatorial plane, said bands being also curved in the direction of their width to coincide with the curvature of the path taken by the control component of said magnetic iield; and means interconnecting said bands in short-circuit relation with each other whereby the voltages induced respectively therein by said magnetic neld are opposing.

8. A magnetic induction accelerator for charged particles comprising a toroidal evacuated tube, means including a magnetic structure adjacent said tube and winding means thereon for producing a time-varying magnetic field having induction and control components oi such spatial distribution relative to said tube as to normally confine electrons Within the tube to a substantia-lly circular orbit around the tube while accelerating them along said orbit, a plurality of pairs of curved bands of electrically conductive metallic strip material mounted concentric with the axis of said tube, each pair of bands having a diierent radius of curvature and the conductors of each pair being disposed at corresponding positions above and below the equatorial plane of said tube parallel with said equatorial plane, said bands being also curved in the direction of their width to coincide with the curvature of the path taken by the control component or said magnetic field, and means interconnecting the bands of each pair in short-circuit relation with each other whereby the voltages induced respectively therein by said magnetic field are opposing.

ROLF WnDERE.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,394,070 Kerst Feb. 5, 1946 2,447,255 Kerst et al. Aug. 7, 1948 2,558,597 Westendorp June 26, 1951 2,622,194 Lawson et al Dec. 16, 1952