US2822490A - Combination electron x-ray beam tube for a betatron - Google Patents

Description

D. T. SCAG Feb. 4, 1958 COMBINATION ELECTRON X-RAY BEAM TUBE FOR A BETATRON 4 Sheets-Sheet 1 Filed Jan. 14. 1955 Filed Jan. 14, 1955 Feb. 4, 1958 D, T S AG 2,822,490

COMBINATION ELECTRON X-RAY BEAM TUBE FOR A BETATRON 4 Sheets-Sheet 2 EM 5 '/cocg ZM/mw Feb. 4, 1958 D. T. SCAG 2,822,490

COMBINATION ELECTRON X-RAY BEAM TUBE FOR A BETATRON Filed Jan, 14, 1955 4 Sheets-Sheet 5 Feb. 4, 1958 COMBINATION ELECTR Filed Jan. 14, 1955 D. T. SCAG v 2,822,490

ON X-RAY BEAM TUBE FOR A BETATRQN 4 Sheets-Sheet 4 m2 r k m3 3 1 .40 (44 m2 V our United States atent fifice COMBINATION ELECTRON X-RAY BEAM TUBE FOR A BETATRON Dane T. Scag, Elm Grove, Wis., assignor to Allis-Chalmers Manufacturing Company, Milwaukee, Wis.

Application January 14, 1955, Serial No. 481,860 12 Claims. (Cl. 313-35 This invention relates in general to betatrons and in particular to an improved combination electron X-ray beam tube for betatrons.

The betatron is a type of charged particle accelerator which accelerates electrons in an orbital path enclosed in an evacuated annular envelope or tube. The tube is placed between a pair of pole faces which form a portion of a suitable magnetic structure, and winding means on the structure, when energized, causes a time varying magnetic flux to pass transverse to the tube.

Electrons are injected into the tube substantially tangent to the orbit. This injection takes place near the beginning of each half cycle of the alternating magnetic field and the electrons are thus accelerated during the quarter cycle of increasing flux. The electrons are guided into the orbital path by the fringing portion of the magnetic field which cuts through the orbital portion of the tube. Throughout the period of acceleration the strength of the field is at all times just right in proportion to the energy of the electrons to maintain a constant radious of curvature defining a stable orbit, referred to as the equilibrium or acceleration orbit. During the quarter cycle of increasing flux in which the electrons are accelerated, they make several hundred thousand revolutions and gain energy of something like 70 volts at each revolution.

Near the end of the quarter cycle a disturbance of the magnetic field is introduced to cause the acceleration orbit to be displaced causing the accelerated electrons to strike a suitable X-ray target disposed in the tube. Striking of the X-ray target by the electrons at a suitable frequency, for example, 180 times per second, produces an intense electromagnetic radiation commonly referred to as X-rays, having a highly penetrating characteristic.

The first practical application of the betatron was in industrial radiography because of the highly penetrating characteristics of the X-rays obtained. This characteristic also suggested the utilization of the X-rays obtained from the betatron for therapeutic purposes. The development of suitable techniques proceeded necessarily slowly, but carefully, until now the betatron is used in many hospitals for treating deep seated cancer. Due to the highly penerating characteristics of the X-ray beam obtained from the betatron, the intensity of the X-ray beam does not diminish rapidly with increasing depth as does other type of radiation. This characteristic enables a deep seated lesion to be treated with adequate dosage without seriously overtreating and destroying intervening tissue. However, X-ray beam treatment of cancer with the betatron is limited to the type of cancer which is relatively deep, and cannot be used in case of tumors in certain critical areas such as the eye, or the brain, because the underlying tissues would be seriously damaged.

It was found after careful study and experimentation that the electrons, which are accelerated to produce the X-rays, may by themselves be used to treat cancer in those certain critical locations. This is because, unlike X- rays, the electrons give up their energy within a definite path length and produce an ionizing effect in a rather narrow range of depth. -In the case of the electron beam the maximum dosage is delivered to a depth dependent on the energy of the electrons, with a relatively sharp falling off of the intensity of the beam to nearly zero. Thus the betatron, when the capability of the electron beam therapy is added thereto, becomes a doubly potent implement in the armamentarium against cancer.

The prior art has suggested tube arrangements in which either electrons or X-rays may be selectively obtained. In one of these arrangements the X-ray and electron beams emerge from the tube in a generally divergent relationship. The electron beam exit window of the tube is disposed closely adjacent to where the X-ray beam passes out of the tube and a shutter system is used to select the desired exit. This arrangement has been found impractical for therapeutic purposes for two reasons. First, the various therapeutic accessories which must be attached to the betatron in order to control or collimate the two different types of beams require more spacing than is alforded when the beams emerge from the same general area of the tube. As the beams emerge from the tube there is a natural tendency for them to spread or fan out. The field of the X-ray beam increases relatively fast as the distance from the target increases, but the field of the electron beam remains relatively small. The beams must therefore be collimated before they can be used. Collimation of the beam for therapeutic purposes reduces its cross section to any desired area, and is accomplished by special collimators which are attached to the betatron and accurately aligned with the beam. The material of the electron beam collimator is of low intensity material such as Lucite or Bakelite to absorb electrons without appreciable generation of X-rays. For collimation of the X-ray beam a very heavy material like lead or tungsten is used.

The characteristics of the electron beam being different than the X-ray beam in the apparatus described above, the therapeutic accessories have to be changed and an accurate alignment procedure followed each time a change in beams is desired. This is of course a serious disadvantage andis inherent in the arrangement where the two beams emerge from the same general area in the tube. The second reason why such an arrangement has been found impractical is that the betatron must be rotatable about an axis in order to readily direct the X-ray beam or the electron beam to the desired area. Since the beams are divergent with this type tube it is impossible to make both beams normal to the axis of rotation of the betatron and difliculty in aiming one of the beams is always encountered.

In order to overcome the disadvantages of the prior art, the present invention provides a combination electron X-ray beam tube for the betatron in which the respective beams emerge from the tube in parallel relationship to each other but spaced on opposite sides of a reference plane disposed parallel to the beam paths and containing the axis of the orbital path.

With this improved arrangement master jackets are permanently mounted to hold and precisely position vari-.

ous therapeutic accessories associated with the respective .beams. Various arrangements of the particular elements in the tube are possible to provide the necessary spacing for permanently mounting a pair of master jackets to position the accessories for the respective beams. For instance, the tube may be constructed so that when it is placed in the betatron the beams emerge normal to the axis of rotation of the betatron but in opposite directions with respect to that axis. This arrangement al- 3 lows mounting one master jacket on one side of the betatron and the other master jacket on the opposite side of the betatron. The betatron assembly may then be provided with means for rotating the betatron 360 degrees about the horizontal axis of rotation or 180 degrees about a vertical axis.

Preferably, however, the improved tube is constructed so that when it is placed in the betatron both beams are normal to an axis of rotation, usually a horizontal axis, and emerge from the tube in similar directions and on opposite sides of a reference plane disposed parallel to the beam paths and containing the axis of the tube. In other words, the paths of the beams when projected onto the reference plane are directed in the same direction.

In this preferred arrangement the improved tube is constructed so that in generating an X-ray beam the electrons are accelerated in one direction, for example clockwise, around the equilibrium orbit, and when it is desired to produce an electron beam the electrons are accelerated in the opposite direction, for example counterclockwise around the equilibrium orbit.

Since the electrons are accelerated in difierent directions around the equilibrium orbit for the different beams, means are provided in the tube for selectively injecting electrons in either of two directions into the equilibrium orbit. This injecting means is related in time to the alternating magnetic field which passes transverse to the tube so that depending on which type of beam is desired a difierent half of the cycle of the alternating magnetic field is used to accelerate the electrons in the appropriate direction.

The improved tube is also provided with an X-ray target so that electrons which are accelerated may be directed to the target and produce an X-ray beam.

The tube is further provided with means for extracting the electrons from the orbital path after acceleration to produce a well defined electron beam. This extracting means is disposed in the tube to cause the path of the electron beam to be parallel to the X-ray beam path. In other words the beams are directed in similar directions in parallel spaced relationship on opposite sides of a plane disposed parallel to the beams and containing the axis of the tube.

It is therefore an object of the present invention to provide a combination electron X-ray beam tube in which the respective beams emerge from the tube in parallel spaced relationship.'

Another object of the present invention is to provide a betatron from which both the electron beam and the X-ray beam emerge parallel to each other and normal to the axis of rotation of the betatron.

A still further object of the present invention is to provide in a betatron a combination electron X-ray beam tube which allows master jackets to be permanently installed on the betatron allowing devices for collimating the respective beams to be accurately installed and aligned with a minimum of time.

Objects and advantages other than those mentioned above will be apparent from the following description when read in connection with the drawing in which:

Fig. 1 illustrates a view in elevation of the betatron assembly provided with the improved tube;

Fig. 2 is an enlarged view of the assembly shown in Fig. 1 taken along the line 11-11;

Figs. 3 and 4 are enlarged views of the electron injector means shown in Fig. 2;

Fig. 5 is an enlarged view of the means for produc ing an X-ray beam shown in Fig. 2;

Figs. 6 and 7 are enlarged views of theelectron beam extractor shown in Fig. 2;

Fig. 8 is a modification of the X-ray target assembly shown in Fig. 5;

Figs. 9 and 10 are views of a modification of the electron beam extractor shown in Fig. 2;

Fig. 11 is a schematic view ofthe extractorwiring;

Figs. 12 and 13 illustrate a modification of the means shown in Figs. 6 and 7 for extracting the electron beam from the tube; and

Fig. 14 illustrates a modification of the arrangement of the elements in the tube shown in Fig. 2.

Inasmuch as the general principles of operation of magnetic induction accelerators are well known and fully described in prior art patents and publications, the description of the general construction and operation of the betatron assembly shown in Fig. 1 will be kept to a minimum and if necessary reference may be had to such other publications to supplement this general description.

Fig. 1 shows one embodiment of a betatron assembly in which the improved tube may be advantageously employed. The assembly of Fig. 1 comprises generally the betatron proper which is enclosed by a lead shielding assembly 11 provided with two suitable openings 1 13 on the front side of the betatron. The assembly also includes means for rotating the betatron about a horizontal axis and as shown this means may comprise a motor driven trunnion mounting 15 disposed in suitable overhead supports 16.

The betatron tube as usual is disposed between a pair of pole faces (not shown) with the axis of the tube substantially normal to these faces. The pole faces form a part of the magnetic structure which includes suitable energizing windings. These windings when en ergized cause a time varying magnetic field to pass transversely through the tube, the distribution of this field establishing an orbital path within the tube about which electrons are accelerated.

The improved electron X-ray beam tube and its position with respect to the axis of rotation of the betatron may be more readily seen by referring to Fig. 2 which is a view in section of the assembly shown in Fig. 1 taken along the line IlIl.

As shown in Fig. 2 the improved tube comprises an annular or doughnut shaped evacuated envelope 20 made of suitable material such as glass or porcelain. The tube is a sealed off type tube, which means the absence of any continuously pumping vacuum mechanism attached to the tube. The tube may however be a continuous pumped tube if desired.

The improved tube includes at one point means, referred to generally by reference character 21, for selectively injecting electrons in two directions into the orbital path created by the magnetic field of the betatron. The electron injecting means 21 shown in Fig. 2 isillustrated in more detail in Figs. 3 and 4 and comprises two similar electron guns 22 and 23 disposed back to back. Since both electron guns are similar in structure and operation, only one is described.

Electron gun 22 comprises a pair of connecting and supporting members 26 which carry at their outer ends a filament 27 which when heated provides a source of electrons. Surrounding the filament on three sides and connected to it is an electrode shielding member 28. The earth grounded anode electrode 31 is adapted to be rendered considerably positive with respect to the filament 27 by application of a negative voltage pulse to the filament to give electrons a desired initial direction and accelerat-ion. Electron gun 23 similarly comprises a filament 29, and shielding electrode 30. The anode 31 is provided with a pair of slots 32, 33 registering with the filaments 27, 29, providing an exit opening for the electrons.

As shown in Fig. 2 the electrons may be selectively injected into the tube 20 and accelerated in a clockwise direction or injected into the tube and accelerated around the orbit in a counterclockwise direction depending on which electron gun 22 or 23 is energized with the negative pulse and depending on when the pulse is applied to the electrode. When the injection operation is brought into action by suitable means associated with the betatron, one of the filaments, for example electrode 27 is pulsed highly negative with respect to the anode 31. This voltage pulse applied to the electrode 27 through the connecting members 26, 34 causes electrons to stream out of the slot 32 in the anode, with an initial velocity of the order of several thousand electron volts. These electrons are then acted upon by the magnetic field in such manner as not only to accelerate the electrons, but also to cause them to spiral inwardly toward the center of the toroidal tube to an equilibrium orbit.

The betatron is provided with means for displacing the orbit of the electrons after the electrons have obtained their desired energy, and the improved tube is provided with an X-ray target assembly disposed accordingly so that the accelerated electrons may be converted into X- rays when the orbit is displaced. The position of the X-ray target with respect to the acceleration orbit determines how the magnetic field is displaced to cause the electrons to strike the target. The target may be disposed either above or below the plane of the orbit and the field displaced to cause the orbit to move vertically up or down to strike the target, or the target may be disposed inside or outside of the orbit and the orbit accordingly contracted or expanded to cause the electrons to strike the target.

As shown, the X-ray target assembly, referred to generally by reference character 40, is disposed outside of the acceleration orbit and in the same plane as the orbit, and the betatron is provided with suitable means for causing the orbit to expand to cause the electrons to strike the target at the appropriate time.

The target assembly shown in detail in Fig. 5 comprises the target 41 proper and means for retracting the target. This retracting means 42 comprises an electric solenoid provided with a coil 43 and an armature 44. The target 41 is disposed on a supporting member 45 attached to the armature 44 so that it is moved when the coil 43 of the solenoid is energized. Biasing means 46 are provided to move the armature 44 to a retracted position when the coil 43 is deenergized. Energizing the coil 43 causes the X-ray target to move from a first position radially remote from the orbit to a second position radially inward of said electron injector means 21 and extractor means 51 to allow the accelerated electrons to strike the target 41 and produce X-rays as the orbit is gradually expanded.

In operating the betatron assembly shown in Figs. 1 and 2 to produce an X-ray beam, electron gun 22 of the injector structure 21 is energized with a negative pulse to cause electrons to stream out of the slot 32 in anode 31. The time that this pulse is applied to the filament 27 of the gun 22 is related to the time varying magnetic field produced by the betatron so as to cause the electrons after injection to be accelerated clockwise as shown in Fig. 2 around the equilibrium orbit. The electrons are caused to travel around the orbit for as many revolutions as may be desired, and for as long as the magnetic field of force is rising in strength, and are finally caused to follow an instantaneous orbit of slightly greater radius than the acceleration orbit and to impinge on the target 41, this impingement efiecting the desired generation of X-rays. t

The improved tube also includes means at another point in the tube for extracting an electron beam from the tube, parallel to the path of the X-ray beam but in spaced relationship thereto, or in other'words," so that the paths of the two beams lie on opposite sides of a plane disposed parallel to the path of the X-ray beam and containing the axis of the betatron tube.

The electron beam extracting means referred to generally in Fig. 2 by reference character '56 comprises a field diminishing element or member 51 disposed in the tube at a predetermined point to cause a relatively sudden change in direction of electron movement, enabling the electrons to be extracted from the tube in an electron beam. The field diminishing element 51, referredto as a magnetic peeler, is shown in detail in Figs. 5 and 7 together with its supporting and adjusting system 52. Referring specifically to Figs. 6 and 7 the magnetic peeler has a generally U-shaped cross section with inwardly extending arm portions 53, 54 providing a slot 55 therbetween in the plane of the equilibrium orbit. The purpose of this peeler is to convey, without exceeding saturation, and preferably at levels below saturation, all the magnetic lines of force which would normally exist in the entire area comprising a projection of the member 51 in the plane of the equilibrium orbit. That is, lines of magnetic force entering the top of the field diminishing member 51 should substantially entirely take a path through the back or solid portion 56 of this member rather than across the gap provided by the slot 55. The result is that the space in the 'slot 55 between the arm portions 53, 54 and even slightly outside the slot, comprises a space of very greatly reduced field strength at any time relative to the field strength existing in adjacent areas in the tube.

As will be readily apparent from a consideration of Fig. 2 the equilibrium orbit lies well to the inside (radially speaking) of the position of the magnetic peeler which is placed in the tube just ahead (speaking with respect to the counterclockwise direction of travel of the electrons) of an exit horn 59 provided with a window assembly 60 facilitating exit of the electrons from the tube. This Window assembly 60 may consist of a thin beryllium sheet mounted in a disk 61 with the disk positioned in an adapter 62 fitted to a Kovar mount 63 which is sealed directly to the exit born 59 of the tube.

In operation of the betatron assembly shown in Fig. 2 to produce an electron beam, electrons are injected into the orbit in a counterclockwise direction by means of gun 23 of the injector structure 21, at a suitable time with respect to the time varying magnetic field of the betatron. The electrons spiral inward to the equilibrium orbit and are accelerated in a large number of turns, as has been heretofore described. They are then caused to spiral away from the equilibrium orbit by any suitable arrangement for changing the field strength relationship. The outward path of the electrons is in a spiral with continually diverging turns. During one of these spiralling turns around the orbit the electrons suddenly find themselves in an area of What is substantially zero field strength so that there is little or no inward radial force to counteract centrifugal force and the electrons straighten out their path and move toward and through the window assembly 60 to provide a well collected beam of electrons. Since the magnetic peeler is disposed on the outside of the equilibrium orbit and the orbit is expanded to place the accelerated electrons into the field of free space, the X-ray target 41 which is used to produce an X-ray beam when the electrons are accelerated in the opposite direction around the orbit, must be retracted to a'position relatively remote from the expanding electron orbit.

However, when the betatron assembly is used to produce an X-ray beam, the X-ray target 41 is positioned so that the expanding orbit causes the electrons to strike the target 41 before they enter the field of free space caused by the magnetic peeler 51. Thus by using a retractable target assembly 40 the betatron need only be provided with an expanding circuit which functions both to produce an X-ray beam and an electron beam.

It should also be recognized that the improved tube may be provided with a stationary target disposed radially inward of the equilibrium orbit and the betatron provided with means, such as a contracting circuit, to cause the electrons to spiral inwardly to strike the target. In such arrangement the position of theelec'tron beam extractor 50 may remain as previously described.

Referring again to :Fig. 2, the electron X-ra-y beam tube 20 is disposed in the betatron so that the parallel paths of the respective beams are normal to the horizontal axis of rotation of the betatron.

The shield assembly 11 surrounding the betatron proper is provided with two suitable openings 12, 13 aligned with the respective beams. Each opening is adapted to receive a master jacket assembly.

The opening in the shield through which the X-ray beam passes, receives a master jacket assembly 70 comprising a cylindrical jacket 71, an X-ray beam monitor 72 and an X-ray beam compensator 73. The compensator 73 is cone shaped and is fixed to the jacket 71 with its axis coincident with the axis of the jacket, and the jacket 71 is disposed in the opening 12 and adjusted by suitable means so that its axis is coincident with the axis of the X-ray beam. The compensator 73 serves to produce a uniform field of X-rays, while the monitor 72 serves to measure the intensity of this field.

The jacket 71 is adapted to receive an X-ray beam collimator 75 which is a lead alloy insert having an accurately machined outside surface complementary to the inside receiving surface of the jacket.

Once the master jacket assembly 70 is disposed in the shield and aligned with the X-ray beam, different X-ray beam collimators may be readily inserted into the jacket 71 in position to collimate the beam to the desired shape.

The master jacket assembly also includes means for attaching a placement cone 76 to the betatron to aid in positioning the X-ray beam and to visually indicate at what point the X-ray beam enters the patient.

Since with the improved tube the electron beam emerges from the betatron in spaced relationship with respect to the X-ray beam, a master jacket assembly 80 for removably mounting the various therapeutic accessories associated with the electron beam may be permanently disposed in the shield assembly 11 of the betatron.

The master jacket assembly 30 for the electron beam includes a cylindrically shaped jacket 31 disposed in the opening 13 in the shield assembly 11 so that its axis is coincident with the axis of the electron beam. Au electron beam compensator 82 and a monitor 83, similar in function to those previously described, are fixed to the end of the jacket 81 nearest the tube. Means are also provided on the master jacket 81 for attaching an extension tube 86 to collimate the beam at increased focal skin distances. The electron beam collimator 87 may be attached to the master jacket 81 or to the extension tube 86.

Fig. 8 shows a modification of the X-ray target assem bly 40 shown in Fig. 5. The target assembly 90 is similar to that shown in Fig. except the means for moving the target is changed. As shown in Fig. 8 the means for moving the target 41 comprises a pair of telescoping members 91 and 92 and a bimetallic expansion coil 93. One of the telescoping members 91 is fixedly mounted in space while the other member 92 telescopes with the stationary member 91 and is moved by means of the bimetal coil 93. The target 41 is positioned at the outer end of the movable member 92. Heating the bimetal coil 93 by a flow of current, operates to position the target 41 similar to when the solenoid coil 43 of Fig. 5 is energized.

Figs. 9 and show a modification of the means for extracting the electron beam from the tube. This modification is referred to as an electromagnetic electron beam extractor and operates to create a field free region within the tube by a current flowing through a wire network, this magnetic field being equal and opposite to the magnetic field created by the betatron. The electromagnetic extractor 100 comprises an array of parallel spaced wires 101 disposed in a form 102 of suitable dielectric material. These wires 101 are normal to the tube radius at the extractor entrance 103 and in planes parallel to the acceleration orbit. The wires may be square or trapezoidal in cross section to obtain a greater conducting volume for wire sepaartion- The wires are connected into the array for the top half and for the bottom half, and the two halves placed in parallel. Fig. 11 shows in detail one arrangement of the wires 101 and the path of the current in these wires.

When the current pulse is applied to the array by any suitable known means, the flow of current through the parallel wires 101 creates over a localized region in the tube a field free space. The electromagnetic electron beam extractor is disposed in the tube so as to cause electrons extracted thereby to emerge from the tube parallel to the path of the X-ray beam.

Figs. 12 and 13 show another modification of the electron beam extracting means shown in Figs. 6 and 7. This modification is referred to as an electrostatic beam deflector and comprises a circumferentially elongated U-shaped support 105, a high voltage deflector 106, and a grounded foil member 107 spaced radially inward of deflector 106 and attached between the extended arms of the U. The U-shaped support is held in the tube by suitable positioning rods 108.

In operation deflector .106 of the electrostatic electron beam extractor is pulsed negatively, which deflects the spiralling electrons by means of electrostatic attractions to cause them to emerge through the exit window parallel to the path of the X-ray beam.

Fig. 14 is similar to Fig. 2 and shows schematically another arrangement of the elements within the tube. The embodiment of the invention shown in Fig. 14 comprises a tube 110, an electron injection means 111, a stationary X-ray target 112, and electron beam extracting means 113. With the arrangement shown in Fig. 14, electrons are injected into the tube so that they are accelerated counterclockwise around the acceleration orbit. An X-ray beam is produced by causing the accelerated electrons to spiral inward to the X-ray target 112. An electron beam is produced by causing the accelerated electrons to spiral outward into the electron beam extractor 113. The target 112 and the extractor 113 are arranged in the tube to cause the beams to emerge from the tube parallel to each other, the paths of the beams lying on opposite sides of a reference plane disposed parallel to the beam paths and containing the axis of the tube 110. The paths of the respective beams when projected onto the reference plane are directed in opposite directions. The betatron shield assembly must then be provided with openings on two opposite sides.

If desired, the circuits which operate in the betatron to produce the X-ray beam, may be modified by the addition of polarized reversing relays and these same circuits used to produce the electron beam. In practice this allows the operator of the betatron to switch from an X-ray beam to an electron beam by merely operating the reversing relays.

While only a few embodiments of the present invention have been illustrated and described it will be apparent to those skilled in the art that modifications other than those mentioned above may be made without departing from the spirit of the invention or from the scope of the appended claims.

It is claimed and desired to secure by Letters Patent: 7, l. A combination electron X-ray beam tube for a charged particle accelerator in which electrons are accelerated along an orbital path, said tube'comprising an evacuated envelope surrounding said orbital path, means for injecting electrons into said orbital path, means including an X-ray target to cause an X-ray beam to be radiated from said tube along a first path substantially tangent to said orbital path, and means to cause an electron beam to be extracted from said tube along a second path parallel to said first path, said first and second paths of said beams being on opposite sides of a reference plane disposed parallel to said beams and containing the axis of said orbital path.

2. A combination electron X-ray beam tube for a charged particle accelerator in which electrons are accelerated along an orbital path, said tube comprising an evacuated envelope surrounding said orbital path, means for selectively injecting electrons into said orbital path, means including an X-ray target to cause an X-ray beam to be radiated from said tube along a first path substantially tangent to said orbital path, and means to cause an electron beam to be extracted from said tube along a second path parallel to said first path, said first and second paths of said beams being on opposite sides of a reference plane disposed parallel to said beams and containing the axis of said orbital path, said first and second paths of said beams when projected onto said reference plane being parallel but directed in opposite directions.

'3. A combination electron X-ray beam tube for a charged particle accelerator in which electrons are accelerated along an orbital path, said tube comprising an evacuated envelope surrounding said orbital path, means for selectively injecting electrons in opposite directions into said orbital path, means including an X-ray target to cause an X-ray beam to be radiated from said tube along a first line substantially tangent to said orbital path, and means to cause an electron beam to be extracted from said tube along a second line parallel to said first line, said lines being on opposite sides of a reference plane containing the axis of said orbital path, said lines when projected onto said reference plane being parallel and directed in the same direction.

4. A combination electron X-ray beam tube for a charged particle accelerator which accelerates electrons around an orbital path, said tube comprising an annular evacuated envelope having disposed therein electron injector means operable to selectively eject a first stream of electrons into said orbital path in a direction to allow said electrons of said first stream to be accelerated around said orbital path in one direction and inject a second stream of electrons into said orbit in a direction to allow said electrons of said second stream to be accelerated around said orbital path in a direction opposite to said one direction, means including an X-ray target assembly to cause said electrons accelerated around said orbit in said one direction to produce an X-ray beam having a path substantially tangent to said orbital path, means including an electron beam extractor to cause said electrons accelerated around said orbit in said opposite direction to produce an electron beam having a path parallel to said X-ray beam path, and an electron permeable window disposed in said envelope in alignment with said electron beam path to facilitate exit of said electron beam, said paths of said beams being on opposite sides of a reference plane disposed parallel to said beam paths and containing the axis of said annular tube.

5. A combination electron X-ray beam tube for a charged particle accelerator which accelerates electrons around an orbital path, said tube comprising an annular evacuated envelope having disposed therein electron in jector means operable to selectively eject a first stream of electrons into said orbital path in a direction to allow said electrons of said first stream to be accelerated around said orbital path in one direction and inject a second stream of electrons into said orbit in a direction to allow said electrons of said second stream to be accelerated around said orbital path in a direction opposite to said one direction, means including an X-ray target assembly to cause said electrons accelerated around said orbit in said one direction to produce an X-ray beam having a path substantially tangent to said orbital path, means including a magnetic electron beam extractor to cause said electrons accelerated around said orbit in said opposite direction to produce an electron beam having a path parallel to said X-ray beam path, and an electron permeable window disposed in said envelope in alignment with said electron beam path to facilitate exit of said electron beam, said paths of said beams being on opposite sides of a reference plane disposed parallel to said beam paths and containing the axis of said annular tube.

6. A combination electron X-ray beam tube for a charged particle accelerator which accelerates electrons around an orbital path, said tube comprising an annular evacuated envelope having disposed therein electron injector means operable to selectively eject a first stream of electrons into said orbital path in a direction to allow said electrons of said first stream to be accelerated around said orbital path in one direction and inject a second stream of electrons into said orbit in a direction to allow said electrons of said second stream to be accelerated around said orbital path in a direction opposite to said one direction, means including an X-ray target assembly to cause said electrons accelerated around said orbit in said one direction to produce an X-ray beam having a path substantially tangent to said orbital path, means including an electromagnetic electron beam extractor to cause said electrons accelerated around said orbit in said opposite direction to produce an electron beam having a path parallel to said X-ray beam path, and an electron permeable window disposed in said envelope in alignment with said electron beam path to facilitate exit of said electron beam, said paths of said beams being on opposite sides of a reference planedisposed parallel to said beam paths and containing the axis of said annular tube.

7. A combination electron X-ray beam tube for a charged particle accelerator which accelerates electrons around an orbital path, said tube comprising an annular evacuated envelope having disposed therein electron injector means operable to selectively eject a first stream of electrons into said orbital path in a direction to allow said electrons of said first stream to be accelerated around said orbital path in one direction and inject a second stream of electrons into said orbit in a direction to allow said electrons of said second stream to be accelerated around said orbital path in a direction opposite to said one direction, means including an X-ray target assembly to cause said electrons accelerated around said orbit in said one direction to produce an X-ray beam having a path substantially tangent to said orbital path, means including an electrostatic electron beam extractor to cause said electrons accelerated around said orbit in said opposite direction to produce an electron beam having a path parallel to said X-ray beam path, and an electron permeable window disposed in said envelope in alignment with said electron beam path to facilitate exit of said electron beam, said paths of said beams being on opposite sides of a reference plane disposed parallel to said beam paths and containing the axis of said annular tube.

8. A combination electron X-ray beam tube for a charged particle accelerator which accelerates electrons around an orbital path, said tube comprising an annular evacuated envelope having disposed therein at circumferentially spaced points electron ejector means operable to selectively inject a first stream of electrons into said orbital path in a direction to allow said electrons of said first stream to be accelerated around said orbital path in one direction and inject a second stream of electrons into said orbital path in a direction to allow said electrons of said second stream to be accelerated around said orbital path in a direction opposite to said one direction, an X-ray target assembly including an X-ray target and means for moving said target from a first position radially outward of said electron injecting means to a second position radially inward of said electron injecting means to cause said electrons accelerated around said orbit in said one direction to strike said target in said second position and produce an X-ray beam having a path substantially tangent to said orbital path, an electron beam extractor disposed radially inward with respect to said injector means and radially outward with respect to said second position of said X-ray target to cause said electrons accelerated around said orbit in said opposite direction to produce an electron beam having a path parallel to said X-ray beam path and spaced laterally therefrom, said paths of said beams being on opposite sides of a reference plane disposed parallel to said beam paths and containing the axis of said annular tube.

9. In apparatus for accelerating charged particles in an orbital path which is enclosed by an annular tube of dielectric material and traversed by a time varying magnetic field, moans-disposed in said tube-operable to selectively produce an electron beam along a first line and an X-ray beam along a second line disposed parallel to said first line but on the opposite side of a reference plane parallel to said lines and containing the axis of said annular tube, said means including injector means for selectively injecting electrons into said orbital path in timed relation with said time varying magnetic field to cause said electrons to be accelerated around said orbit by said magnetic field, an X-ray target disposed to cause said accelerated electrons to strike said target and produce an X-ray beam having a path along said first line, an electrcn beam extractor to cause said accelerated electrons to emerge from said tube along said second line substantially parallel to said first line and an electron permeable window assembly disposed in a wall portion of said tube in alignment with said second line.

10. A magnetic induction accelerator comprising a laminated magneticxstructure includinga pair of opposing pole faces, an annular evacuated tube disposed between said pole faces with the axis of said tube normal to said faces, winding means disposed on said magnetic structure for providing a time varying magnetic field transverse to said tube having inductive and control components of such spatial distribution relative to said tube as to normally confine electrons within the tube to a substantially circular orbital path around the tube while accelerating them along said orbital path, said tube comprising an annular evacuated envelope, means for selectively injecting electrons in opposite directions into said orbital path, means including an X-ray target to cause an X-ray beam to be radiated from said tube substantially tangent to said orbital path, and means to cause an electron beam to be extracted from said tube parallel to the path of said X-ray beam, the paths of said beams being on opposite sides of a reference plane disposed parallel to said beam paths and containing the axis of said annular tube.

ll. A magnetic induction accelerator comprising a. laminated magnetic structure including a pair of opposing poie faces, an annular evacuated tube disposed between 7 said pole faces with the axis of said tube normal to said faces, winding means disposed on said structure for providing a time varying magnetic field transverse to said including an orbit displacing circuit and an X-ray target-" to cause an X-ray beam tobe radiated from saicbtubesubstantially tangent to said orbital path, meansinelud'- ing said orbit displacing circuit and an electron beam extractor to cause an electron beam to be extracted from said tube parallel tothe path of said X-ray beam,=-the,,

paths of said beams being on opposite sides ofi areference plane disposed parallel to'said beam paths and eonraining the axis of said annular tube. Q 12. A magnetic induction accelerator comprising a= laminated magnetic structure including 'alpair' of opposing pole faces, an annular evacuated tube disposed between said pole faces with theaxis-of said tube normal-to said: faces, winding means disposed on said structure for-pro v-iding a time varying magnetic field transverse -to., said tube having inductive and control components'of such: spatial distribution relative to said tube as to n'ormally confine electrons within the tube to a substantially circular: orbital path around the tube while accelerating them along said orbital path, Said tube comprising an annular'evacu ated envelope, means for selectively injecting electrons-in, opposite directions into said orbital path means including an orbit displacing circuitand an X-ray tar-gettocause an X-ray beam to be radiated from said tube substantia'lly tangent to said orbital path, means including said orbit displacing circuit and an electron beam extractor to cause an electron beamtobe extracted from said tube parallel to the pathof said X-raybeam, the paths of said beams being on opposite sides of a ref-'- erence plane disposed parallel to said beam paths andcontaining the axis of said annular tube, and first and second master jacket assemblies fixedly mounted-on said accelerator assembly'coaxially with said-beam pathsgeach of said jacket assemblies being adapted toremovabl-y position beam collimatingdevices in accurate axialalignment with the respective beams.

Wideroe. em 1951 Livingston. V. June- 3-,, 1952

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