US2394070A

US2394070A - Magnetic induction accelerator

Info

Publication number: US2394070A
Application number: US445465A
Authority: US
Inventors: Donald W Kerst
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1942-06-02
Filing date: 1942-06-02
Publication date: 1946-02-05
Anticipated expiration: 1963-02-05
Also published as: GB585992A

Description

Feb. 5, 1946. D. w. KERST 2,394,070

MAGNETIC INDUCTION ACCELERATOR Filed June 2. 1942 4 Sheets-Sheet 1 Inventor Fig. l.

b y His Attorney.

. Donald W. KeTst,

D. w. KERST 2,394,070

MAGNETIC INDUCTION ACGELERAIOR Feb. 5, 1946.

Filed June 2, 1942 A Sheets-Sheet 2 Mfg Invelhcor Donald .W. KeTso His fitorn ey.

Feb. 5, 1946. w, KERST 2,394,070

' MAGNETIC INDUCTION ACCELERATOR I Filed June 2, 1942 4 Sheets-Sheet s Fig 3.

PHASE SHIFTER J2 Ihventor:

Donald W. Kerst,

H is Attorney.

Feb. 5, 1946.

D. w. KERST 2,394,070

MAGNETIC INDUCTION ACCELERATOR Filed June 2. 1942 Fig.6.

4 Sheets-Sheet 4 Inventor: Donald W. Kerst,

H is Attorney.

Patented Feb. 5, 1946 MAGNETIC INDUCTION ACCELERATOR Donald W. Kerst, Champaign, Ill., asslgnor to General Electric Company, 7 a corporation of New York Application June 2, 1942, Serial No. 445,465

10 Claims.

The present invention relates to apparatus for accelerating charged particles, such as electrons, by means of magnetic induction effects, and is especially applicable in connection with apparatus of the general character described in my prior U. S. Patent No. 2,297,305, patented September 29, 1942, said Patent being assigned to the General Electric Company, a corporation of New York.

Apparatus of the character referred to typically includes a closed vessel and a magnetic system for producing a time-varying magnetic field of such space distribution as to confine charged particles projected within the vessel to a circular orbit along which the particles are continuously accelerated by the electric field produced as the magnetic flux through the orbit increases in magnitude. When the particles have been accelerated to a high velocity, they may be diverted from the accelerating orbit and used for the generation of X-rays or for the production of other useful effects.

A major problem in the operation of magnetic induction apparatus oithe type specified consists in the provision of suitable means for diverting the orbitally moving particles after their acceleration has proceeded to the desired degree. In one instance, the effective utilization of the accelerated particles involves deflecting them sufficiently so that they may be intercepted by an X-ray producin target positioned in proximity to the accelerating path, and it is one object of the present invention to provide improved means by which this type of diversion may be accomplished. A further object consists in the provision of an arrangement by which the acceler-- ated particles may be collected into a more or less collimated beam for utilization outside the accelerating vessel.

In general, the first of the above mentioned objects is accomplished in accordance with the invention by the use of auxiliary field-producing means operative near the end of the accelerating period for producing a symmetrical disturbance of the magnetic field of such character as to permit expansion or contraction of the path of gyration of the accelerated particles. The second object is accomplished by combining with an orbit-disturbing arrangement of the type just specified means for producing a highly localized deflecting force which is operative after the accelerated particles have experienced a predetermined critical deviation from their normal orbital path abruptly to remove the affected particles from the influence of the accelerating field, i. e. by causing the particles to be projected bodying certain important aspects of the inven-' tion; Fig. 2 is a'section taken on line 2-2 of Fig. 1; Fig. 2a represents on an enlarged scale certain electrode structures shown in Fig. 2; Fig. 2b is a still further enlarged view of part of the structure of Fig. 2a, as seen in a different plane. Fig. 3 is a schematic representation illustrating diagrammatically the coil system employed in producing the normal accelerating field of the device of Fig. 1; Fig. 4 is a further schematic view showing a coil system usable to produce a diversion of accelerated particles from their normal orbit; Fig. 5 is a circuit diagram illustrating one mode of energization of the coil systems of Figs. 3 and 4; Figs. 6 and 7 are related sectional views illustrating a further important aspect of the invention; and Fig. 8 is an enlargement of a portion of the structure of Fig. 6.

Referring particularly to Fig. 1, there is shown in section a closed glass vessel l0 providing within it an annular chamber l I. As will be explained in greater detail at a later point, the vessel in encloses a circular orbit in which electrons may b accelerated to a high voltage, say on the order of several million volts. The vessel is preferably highly evacuated, e. g. by connection to a vacuum pump (not shown) and a high resistance coating, such as an extremely thin layer of silver, is applied to the interior surface of the vessel to prevent wall charging and the like.

The accelerating mechanism comprises a magnetic structur having rotationally symmetrical (i. e. circular) pole pieces l4, [5 which are coaxial with the annular vessel Ill. These pole pieces are constituted of laminated iron held in assembly by insulating rings l6 and have central portions ll and I8 which are of essentially planar character. Near their outer edges, the poles are of tapered configuration, as indicated at 20 and 2B. A. second or reverse taper is provided adjacent the periphery of each pole piece (i. e. at 22 and 23) for the purpose of providing a desired shaping of the marginal field. For decreasing the reluctance of the path between the opposed pole faces ll and I8, there is provided an insert in the form of two laminated iron cylinders 25, the component elements of the cylinders being held in assembly by means of an. insulating casing 26 which surrounds them and being spaced from one another and from the other elements of the magnetic structure by spacers 28. A bolt 28' holds these parts in clamped relation. An externally closed magnetic circuit between the base portions of the pole pieces is provided by U-shaped

iron cores

29 and 30 joined in end-toend relation to form a unitary structure. The upper pole piece It is supported from this structure by a bolting connection secured to an insulating plug 3! keyed into the interior of the pole piece.

The magnetic structure is excited by means of a pair of series connected coils 32 and 33 which surround the pole pieces 14 and I5 and which are energized in such manner as to produce a time-varying flux in the magnetic circuit. The energizingmeans may appropriately be of the character shown in Fig. 3 which illustrates diagrammatically a portion of the structure of Fig. 1.

The coils 32 and 33 are shown connected in series with one another and with a condenser 35 which is assumed to be of such capacity as to resonate with the inductance of the coils at a frequency corresponding to the desired frequency of operation of the apparatus. (This may be, for

example, on the order of six hundred cycles per second although frequencies differing widely from this value are also usable.) To supply the losses of the resonant circuit thus formed the coils 32 and 33 may be coupled to primary coils 31 and 38 which are directly energized from an A.-C. power source 39. A relatively small amount of power supplied by the source 39 will serve to maintain the resonant system in excited condition.

Within the closed vessel I0 (Fig. 1) and also within the region of influence of the magnetic field produced by the pole pieces I4 and 85 there is provided a thermionic cathode 40 which, in connection with associated electrodes 4! and 42 (Figs. 2a and 2b) serves to generate an intermittent stream of electrons. The electrodes ll) to 62 are supported by a stem 43 and are supplied with potential and with heating current (i. e. in the case of the cathode 40) by lead-in wires 64 sealed into the stem.

These electrons are afiected by the magnetic field in two ways. In the first place, since the field is in a direction transverse to the plane of the electron motion, it tends to capture the electrons and to cause them to follow a generally circular orbit. (This orbit should'be inwardly displaced from the region occupied by the injecting electrodes 40 to 42 so that electrons drawn into the orbit are free to gyrate without interception by the electrode structure.) Secondly, the time-varying flux enclosed by the orbit of any particular electron necessarily produces an electric field tending to accelerate the electron. In this latter respect, the apparatus as a whole consists essentially of a transformer with a secondary comprising a circular path along which the various electrons are accelerated. Although, in general, the voltage per turn in such a transformer is low, the electrons can achieve very high velocities (e. g. several million volts) because of the tremendous number of turns which they execute during a single cycle of the magnetic flux variation.

It has been shown that by a proper design of the magnetic structure the field existing at the electron orbit may be caused to produce a centripetal force in balance with the centrifugal tendencies of the accelerated electrons. In general, this result requires that the following relationship be satisfied:

where is the flux included within the electron orbit, r is the radius of the electron orbit, and Hr is the field strength at the orbit. This equation obviously means that the flux must be twice as strong as that which would be produced by a homogeneous field equal to the field Hr extending over the entire area enclosed by the orbital electron path.

The condition just specified may be realized by making the reluctance of the magnetic path greater by an appropriate amount at the electron orbit than its average reluctance within the orbit. In order to maintain fixed 'proportinality between the enclosed fiux and the guide field (i. e. the field Hr) at all times during the accelerating pe riod, one may include in the magnetic path an air gap or its equivalent. It is readily practicable to control the dimensions of such a gap from point to point over the pole area 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 faces are outwardly tapered. (The reverse taper indicated at 22 and 23 is for the purpose of controlling the edge fiux and does not produce any actual increase in flux near the outer edge of the pole faces.)

As has been previously stated, the functioning of the electrodes 40, 4! and 42 is such as to inject electrons into the accelerating chamber at interv mittent intervals, injection being preferably accomplished at times when the magnetic field between the pole pieces l4 and i5 is near its zero value. The electron bursts thus provided within the chamber are accelerated by the electric field produced by the increasing magnetic flux in accordance with the principles previously described. Assuming the magnetic field to be of appropriate intensity, 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. calculated that each orbital gyration of a given electron produces an increase in its energy of 70 electron volts, and that as many as 400,000 gyrations may be completed within the period of a single accelerating cycle.)

It is, of course, desirable to provide some practical way in which the energy of the fully accelerated electrons may be effectively utilized. In the arrangement of Fig. 1 this is accomplished by so arranging matters that while the normal accelerating orbit of the electrons is inside the space occupied by the injecting electrode assembly, the electron orbit may be expanded to cause the electrons to impinge on the exposed parts of the assembly as the end of the accelerating cycle is approached." The resultant impact of the accelerated electrons (e. g. on the exposed surface of the electrode 4|) which thus functions as a target will produce X-rays of an intensity corresponding to the velocity of the electrons involved. These X-rays may, of course, be utilized outside the apparatus in any appropriate way, as for the (In a particular construction. it has been examination of thick metallic objects or other bodies.

In accordance with the present invention, expansion of the electron orbit is produced in a very eifective fashion by the use of auxiliary field-pro ducing means operable to cause a symmetrical disturbance of the field between the pole pieces it and i5. In the first instance, this means comprises a pair of similar coils i and 52 (Figs. 1 and 2) which are respectively supported above and below the plane of the accelerating orbit (i. e. by attachment to the tapered pole faces and 2!). These coils are preferably connected in series and are arranged inside the circumference of the normal electron orbit. (This last condition is to some degree afiected by the shaping of the pole faces, and in certain instances the coils may be of approximately the ame diameter as the accelerating orbit.) With this arrangement the field of the coils which is effective in the air gap between the pole pieces of the magnetic structure is such as to destroy the balance between the accelerating and guide fields. In particular, the flux within the electron orbit and the radial gradient of the magnetic field (i. e. the change in held with radial position) are both altered, the direction of change depending upon the direction of the current in the coils 5i and 52. This occurrence serves to make the electron orbit unstable radially so that electrons are permitted to escape from it eithe in an inward or an outward direction according to the sense in which the field of the auxiliary coil disturbs the balanced condition of the magnetic system. For the purpose of permitting orbit expansion, the direc- 3 tion of energization of the coils 5i and 52 should be such as to cause the magnetic field produced by these coils at and outside the normal orbit to oppose that produced by the coils 32 and 33. And to cause the magnetic flux enclosed by the orbit to be increased. This is brought about by causing the currents in coils 5i and 52 to flow in the same rotational direction as in coils 32 and 33.

On the other hand, in a case in which orbit contraction rather than orbit expansion is desired (i. e. in a construction in which the intercepting target is inside the normal orbit) the magnetic field produced at the normal orbit by the auxiliary coils should have the same direction as that produced by the main coils, which can be brought about by currents of opposite rotation to those in the main coils. Moreover, in this case, the auxiliary coils should be inside the circumference of the smallest orbit the electrons are desired to attain upon energization of the coils.

By appropriate arrangement of the coils 5| and 52, i. e. inside or near the orbital path of the accelerated particles, it is possible to cause the neutral point of the two coils, that is, the point of zero field attributable to the coils, to coincide with the orbital path. T is is advantageous in that the radial gradient of the coil field is maximum at and near the aforesaid neutral point, this being the condition most favorable to disturbance of the stability of the electron orbit.

Inasmuch as the coils 5i and 52 are linked by a large proportion of the flux passing between the poles M and i5 and produced by the coils 32 and 33, there is a voltage generated in the coils by this flux which may have an unfavorable reaction on the agency by which the coils 5i and 52 are supplied with current. Moreover, the selfinductance of these coils tends to be quite high Fi l as a result of the fact that the flux produced by them has a substantially closed iron path through the

magnetic cores

29 and 80. Both the feedback effect above referred to and the self-inductance of the coils may be reduced by the use of additional compensating coil 54 and 55 connected in series with the coils 5| and 52 and differentially wound with respect to the latter coils as indicated diagrammatically in Fig. 4. Obviously with this arrangement any voltage induced in the coils 5i and 52 by the variations of the magnetic flux is substantially offset by an opposing voltage generated in coils 54 and 55. Furthermore, assuming that the coils 5d and 55 have the same number of turns as the coils 5| and 52, it is apparent that the former coil pair completely neutralizes the magnetizing effect of the latter pair insofar as the magnetic flux through coils 5| and 52 is concerned. That is to say, in view of the mutually bucking efiect of the coils 5|, 52 and 5B, 55, no flux attributable to these coils can exist inside the coils 5i and 52. Since there is no other low reluctance path for flux linking the coils in question, the overall self-inductance of the circuit in which the coils are included will be very much reduced and the voltage required to energize the circuit will be lowered to a readily attainabl value.

A still further advantageous result gained by the use of

coils

55 and 55 arises from the fact that the presence of these coils tends to increase the magnitude of the orbit-disturbing field within the space occupied by the vessel I0.

In order to make the best use of the orbitexpanding coils, it is desirable that their energization be appropriately correlated to the action of the magnetic flux produced by the coils 32 and 33. This may be done in one way by interconnecting the two field-producing systems by an arrangement such as that illustrated in Fig. 5. In this figure, represents the alternating current supply source by which the main magnetic flux is supplied. The coils 32 and 33, the coils 31 and 38 and the coils 5!, 52, 54 and 55 correspond to the similarly numbered elements described in connection with Figs. 3 and 4.

The energizing system for the coils 5!, 52, etc. is coupled to the main magnetic flux by means of a coil which is disposed within the influence of the said flux. This coil is in series through a phase shifting device 65' with the primary winding of a peaking transformer 55 which connects with the grid 61 of a discontinuously conductive discharge device 58 (e. g. a thyratron). The plate 69 of the device 68 is connected to one terminal of a condenser 10 and is also connected to the positive terminal ll of a unidirectional current supply source (not shown) by which the condenser i0 is charged during periods when the device is non-conductive. A resistor 72 and a reactor 12', located as shown, serve respectively as a current limiting means and as a commutating agency for the tube 58. The phase shifter 65' may be so adjusted that when the main magnetic flux approaches its peak value, the tube 68 is triggered by the action of the peaking transformer 66 and the potential of the condenser 1c is impressed across a resistor 73 which .is in circuit with the cathode id of the device. Since this resistor is in its turn connected across the coils 5!, 52, etc., these coils are abruptly energized and cause an immediate change in the distribution of the field between the pole pieces it and i5 (Fig. 1). Assuming that the coils 5| and 52 are excited in the proper direction, this will lead at once to expansion of the orbit of gyration of the accelerated electrons and will permit them to impinge upon the exposed surface of the electrode 4| as previously explained.

In order to assure the return of the device 08 (Fig. 5) to non-conductive condition after a brief period of current flow, an inductance I may be connected in the discharge circuit of the device to produce an instantaneous reversal of potential after the condenser I0 is discharged.

The orbit-shifting system described in the foregoing has the primary advantage that it is highly positive and reliable in its action. In addition, it is characterized by the further advantage that it is readily controllable both as to time of operation (e. g. by adjustment of the elements of the circuit of Fi and as to the direction and force of the electron diverting effects which it produces.

For some uses of the induction accelerator it is desirable that the accelerated electrons be projected from the accelerating chamber in such a way as to permit their effective utilization outside the chamber. From a practical standpoint this means that the electrons must be projected through a wall of the chamber in a reasonably well-defined beam. This obviously is a result which cannot be obtained merely by expanding the orbit of the electrons in the manner described in the foregoing for the reason that even if the expanded orbit is made to reach the wall of the containing vessel, any electrons which escape by penetration through the wall will be released in random directions.

A further important aspect of my invention consists in the provision of means by which, after initial expansion of the electron orbit to a critical point, the electrons retained in the orbit may suddenly be wholly released from the influence of the guide field and allowed to escape in a preselected direction. The structural aspects of an arrangement which serves this end are shown in Figs. 6, 7 and 8 of the drawings.

As in the construction previously described, electron acceleration is accomplished within an annular glass vessel 80 by means of a time-varying field produced by coils 8| and 82 between appropriately tapered

pole pieces

83 and 84. .A low reluctance flux path is provided at the center of the pole system by a pair of laminated iron cylinders 85 separated by insulating disks 85'. However, in this case the electrode system by which the electrons to be accelerated are initially introduced into the accelerating vessel is positioned near the inner periphery of the vessel as indicated at 86. The energizing connections for the injecting electrodes are brought across the bottom of the vessel 80 from a stem press 88 by means of a cable 89 which is preferably externally coated with a conductive substance to prevent disturbance of the accelerating field by ac-- cumulation of electrostatic charges on the cable. Once released into the accelerating chamber by the electrode structure 86, the electrons are drawn into the accelerating orbit in substantially the same manner as in the construction of Fig. 1.

In order to expand the orbit of the electrons after they have been fully accelerated, an auxiliary coil system comprising

inner coils

92 and 93 and outer coils 94 and 95 is provided. The respective coil pairs are diflerentially connected and are preferably in series for reasons previously given herein.

In addition to the orbit-expanding means Just described, there is further provided a magnetic structure -I00 which is 01 small dimensions and which is enclosed within the accelerating vessel 00 mini; relatively near its outer periphery. fins magnetic structure is or curved elongated configuration (see Fig. 7) and includes a pair of opposed poles I02 and, I08 (Figs. 6 and 8). It is energized by means of an exciting winding I04 having terminal connections I 05 which are brought through the wall of the enclosing vessel by means of a stem press I08.

' The disposition of the magnetic structure I00 is such that its field does not affect the gyrating electrons as long as they are confined to the normal accelerating orbit, i. e. the circular orbit indicated by the dash line A in Fig. 'I. The structure is, in fact, sufiiclently displaced from this 1' it se that the electrons can be brought between its poles only after a relatively great expansion of the orbit has been produced. By this arrangement, it is possible to produce a result such as that which is indicated diagrammatically in Fig. *7. In this figure the dash lines B, C and D respectively indicate the successive turns of the stream of accelerated electrons as the orbit of the stream is progressively increased by the expanding effect of the

coils

92, 93, etc. (Fig. 6). It will be noted that the displacement between. turns B and C is relatively slight, but that this displacement increases as the orbit expansion continues to the point where the electrons are forced into the fringing field of the main magnetic system (i. e. where the constraining effect of the field is considerably less). Accordingly, by appropriate disposition of the magnetic structure I00, that is, by disposing it at a location where the distance between successive turns of the expanding electron orbit is relatively great, it is possible to assure the result 40 that the outwardly spiralling electrons shall be brought more or less suddenly into the region of influence of the magnetic structure I00. The field of this structure is of such strength direction as materially to augment the centrifugal tendency of the affected electrons, thus permitting them to escape abruptly from the outer fringes of the main guide field.

The released electrons are free to follow a substantially straight line course and therefore impinge on the wallof the confining vessel after leaving the magnetic structure I 00. In order to facilitate the use of the directed electron beam thus realized, it is expedient to provide in the expected path of the beam a readily pervious window such as a specially thinned portion in the container wall, such a window being indicated at I08 in Fig. '2.

In order to obtain the results specified in the foregoing, it is desirable that the energization of the magnetic structure I :18 be correlated to the energization of the expanding coils 92, 98, etc., and in this connection it is appropriate that these elements be excited from a common source. This may be done, for example, by the use of a circuit arrangement such as that shown in Fig. 5 by placing the energizing coil I04 of the magnetic structure I00 in parallel with the coils of the orbit-expanding system.

Due to the fact that the magnetic structure I I00 is necessarily placed in relatively close proxfimity to the main accelerating orbit, there is some tendency for its field prematurely to disturb the symmetry of the main accelerating field prcduced between the poles 33 and Ii. In order to minimize this effect, it is advantageous to provide in connection with the magnetic structure I shielding means which in a particular case may comprise a sheet of conducting metal (e. g.

copper) bridging the gap between the poles of case with the field of the magnetic structure Hi0 when excited from an intermittently operated source of the character illustrated in Fig. 5.

The action of the magnetic structure I00 may well be described by comparing it to a knife held at the outer edge of a spirally expanding beam. If the beam is not spiralling outwardly rapidly but is moving outwardly in very small steps, then the thickness of the knife edge will intercept a great deal of the beam. It is only when the distance between successive spirals is equal to or large compared with the width of the knife that a great deal of the beam can be efiectively shaved ofi. In the present connection, the width of the knife corresponds to the width of the fringing fiux of the local magnetic field produced by the structure Hill, and it is, therefore, desirable that the displacement between the successive electron gyrations C and D be at least as great as this width.

While the invention has been described by reference to particular embodiments, it will be understood that numerous modifications may be made by those skilled in the art Without actually departing from the invention. I 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 I claim as new and desire to secure by Letters Patent of the United States is:

1. A magnetic induction accelerator including an enclosure within which charged particles may execute orbital movements along a, generally circular path, means in proximity to the said enclosure for producing a time-varying magnetic field linking the said path and producing an accelerating electric force on charged particles within the enclosure, said means including juxtaposed pole pieces which are rotationally symmetrical about an axis coincident with the axis of the said circular path and which are shaped to produce a field distribution of such form as normally to confine particles within the enclosure to the said circular path while they are being accelerated, and means symmetrically disposed with respect to the axis of said pole pieces for producing a radially symmetrical disturbance of the magnetic field between the pole pieces of such magnitude as to permit deviation of the accelerated particles from the said orbital path.

2. A magnetic induction accelerator including an enclosure within which charged particles may execute orbital movements along a generally circular path, means in proximity to the said enclosure for producing a time-varying magnetic field linking the said path and producing an accelerating electric force on charged particles within the enclosure, said means including juxtaposed pole pieces which are rotationally symmetrical about an axis coincident with the axis of the said circular path and which are shaped to produce a field distribution of such form as normally to confine particles within the enclosure to the said circular path while they are being accelerated, and means operable to permit accelerated particles to deviate from said path, said last named means comprising a pair of similar coils which are respectively disposed symmetrically with respect to the axis of said pole pieces on opposite sides of the plane of the said orbital path, being of smaller diameter than the path, and which are effective when energized to modify the distribution of the magnetic field normally existing between the said pole pieces.

3. A magnetic induction accelerator including an enclosure within which charged particles may execute orbital movements along a generally circular path, means in proximity to the said enclosure for producing a time-varying magnetic field linking the said path and producing an accelerating electric force on charged particles within the enclosure, said means including juxtaposed pole pieces which are rotationally symmetrical about an axis coincident with the axis of the said circular path and which are shaped to produce a field distribution of such form as normally to confine particles within the enclosure to the said circular path while they are being accelerated, a first pair of similar coils respectively positioned on opposite sides of the plane of the said orbital path and coaxial with it, said coils being of smaller diameter than the said orbital path, and a second pair of coils differentially energized withrespect to the first pair and of larger diameter than the said orbital path, the individual coils of said second pair being also disposed on opposite sides of the plane of the orbital path whereby conjoint energization of both pairs of coils produces sufficient modification of the magnetic field between the said pole pieces to permit deviation of the accelerated particles from the said orbital path.

4. A magnetic induction accelerator including a chamber within which orbital gyrations of charged particles may occur, means in proximity to the chamber for producing a time-varying magnetic field of such space distribution as normally to confine charged particles within the chamber to a restricted orbital path while continuously accelerating them by means of the associated induced electric field along such path, means which is symmetrically arranged with respect to said path and is operable to modify the distribution of the said magnetic field to permit accelerated particles to deviate from said orbital path while still remaining within the infiuence of said acceleratingelectric field, and further means operative upon the accelerated particles only after they have experienced a predetermiend critical deviation from said orbital path for abruptly removing the affected particles from the influence of the accelerating field.

5. A magnetic induction accelerator including a, chamber within which orbital gyrations of charged particles may occur, means in proximity to the chamber for producing a time-varying magnetic field of such space distribution as normally to confine charged particles within the chamber to a restricted orbital path while continuously accelerating them by means of the associated electric field along such path, means which is symmetrically arranged with respect to said path and is operable to modify the distribution of the said magnetic field to permit accelerated particles to deviate from said orbital path while still remaining within the influence of said accelerating electric field, and further means for producing a localized magnetic field which is operative upon the accelerated particles only after they have experienced a predetermined critical deviation from said orbital path, said last named means being effective abruptly to remove particles afiectecl by it from the influence of the accelerating field so as to facilitate their utilization outside the accelerating chamber.

6. A magnetic induction accelerator including a chamber within which orbital gyrations of charged particles may occur, means in proximity to the chamber for producing a time-varying magnetic field of such space distribution as normally to confine charged particles within the chamber to a restricted orbital path while continuously accelerating them by means of the associated electric field along such path, means dis= posed coaxially with respect to said orbital path and being operable to modify the distribution of the said magnetic field to displace the orbital path of said particles while still remaining within the influence of said accelerating electric field, a magnetic structure 'within the accelerating chamber and energizing means for said structure correlated with said field-distribution modifying means for producing a localized magnetic field which is traversed by the accelerated particles only after they have experienced a predetermined critical deviation from said orbital path. said magnetic structure being efiective to assure at least the partial collimation of particles influenced by it.

7. A magnetic induction accelerator including a chamber within which orbital gyrations of charged particles may occur, means in proximity to the chamber for producing a time-varying magnetic field of such space distribution as normally to confine charged particles within the chamber to a restricted orbital path while continuously accelerating them by means of the associated electric field along such path, mean operablcto modify the distribution of the said magnetic field to permit accelerated particles to deviate from said orbital path while still remaining within the influence of said accelerating electric field, a magnetic structure for producing a localized magnetic field which is traversed by the accelerated particles only after they have experienced a predetermined critical deviation from said orbital path, said magnetic structure being efiective to remove particles afiected by it from the influence of the accelerating electric field, and shielding means for preventing the field of the magnetic structure from extending into the said orbital path.

8. A magnetic induction accelerator including a chamber within which orbital charged particles may occur, means in proximity to the chamber for producing a time=varying magnetic field of such space distribution as normally to coufine charged particles within the chamber to a restricted orbital path while continuously accelerating them by means of the as sociated electric field along such path, means op-= yrations of era'ole to modify the distribution of the said magnetic field to permit accelerated particles to deviate from said orbital path while still remaining within the influence of Said accelerating electric field, a magnetic structure for producing a localized magnetic field which is traversed by the accelerated particles only after they have experienced a predetermined critical deviation from said orbital path, said magnetic structure being effective to remove particles aifected by it from the influence of the accelerating field, and a conductive metal shield associated with said magnetic structure for preventing the field of the structure from extending into the said orbital path.

9. A magnetic induction accelerator including the combination of an annular evacuated enclosure, means for injecting electrons into said enclosure, means in proximity to said enclosure for producing a time-varying magnetic field whereby an electric force is exerted causing electrons to execute accelerated orbital movements in the circular path provided by said enclosure, said means including juxtaposed pole piece which are rotationally symmetrical about an axis coincident with the axis of the said circular path and which are shaped to producea field distribution of such form as normally to confine electrons within the enclosure to said circular path while they are being accelerated, and auxiliary fieldproducing windings arranged above and below said circular path and being symmetrically disposed with respect to the axis of said pole pieces for modifying the magnetic field between the pole pieces thereby causing predetermined deviation to occur of the accelerated electrons and target means upon which said electrons may be caused to impinge.

10. A magnetic induction accelerator including the combination of an annular evacuated enclosure, means for injecting electrons into said enclosure, means in proximity to said enclosure for producing, a time-varying magnetic field whereby an electric force is exerted causing electrons to execute accelerated orbital movements in an annular path provided by said enclosure, said means including juxtaposed pole pieces which are rotationally symmetrical about an axis coincident with the axis of the said annular path and which are shaped to produce a field distribution of such form as normally to guide electrons within the enclosure to an annular path while they are being accelerated, and auxiliary fieldproducing means which is rotationally symmetrical with respect to said path and is operabie to modifythe distribution of said magnetic field to cause controlled deviations to occur of the accelerated electrons from their original annular path.

mrmm 'v'v'. WEST.