US3374356A

US3374356A - Magnetic induction accelerator with means to deflect accelerated electrons to an x-ray target

Info

Publication number: US3374356A
Application number: US651280A
Authority: US
Inventors: Donald W Kerst
Original assignee: Atomic Energy Commission Usa
Current assignee: US Atomic Energy Commission (AEC)
Priority date: 1946-03-01
Filing date: 1946-03-01
Publication date: 1968-03-19
Anticipated expiration: 1985-03-19

Description

March 1968 D. w. KERST 3,374,356 MAGNETIC INDUCTION ACCELERATOR WITH MEANS TO DEFLECT ACCELERATED ELECTRONS TO AN X-RAY TARGET Filed March 1, 1946 2 Sheets-Sheet 1 140 2 Confrol F *o '1 Ni a \N \J if Q! N RE :9

WI TNESSES. IN V EN TOR.

/ BYDona/d' W.- Kersi A Wm M March 19, 1968 D. w. KERST 3,374,356

MAGNETIC INDUCTION ACCELERATOR WITH MEANS TO DEFLECT ACCELERATED ELECTRONS TO AN X-RAY TARGET Filed March 1, 1946 2 Sheets-Sheet 2 n v E a w h A N R I N (\1 n L -25 w N 1" .Eu v Q J E w -f WITNESSES. INVENTOR.

. 2 Dqnald W Kersi Wdm United States Patent 3,374,356 MAGNETIC INDUCTION ACCELERATOR WITH MEANS TO DEFLECT ACCELERATED ELEC- TRONS TO AN X-RAY TARGET Donaid W. Kerst, Urbana, Ill., assignor to the United States of America as represented by the United States Atomic Energy Commission Filed Mar. 1, 1946, Ser. No. 651,280 8 Claims. (Ci. 250-99) This invention relates generally to improvements in magnetic induction accelerators.

More particularly the invention relates to methods and apparatus for obtaining essentially a single pulse output from a magnetic induction accelerator of the type disclosed by the present applicant in US. Patent No. 2,297,- 305 issued Nov. 13, 1940.

One particular application of the invention resides in the provision of methods and apparatus for operation of a magnetic induction accelerator to obtain one or more bursts of X-rays of short time duration and great penetrating power.

In ballistic development it is often desired to study objects undergoing rapid physical change as a result of the explosive or implosive forces to which they are subjected. Since apparatus for carrying out such studies must ordinarily be protected from the effects of the abovementioned forces one of the most useful techniques employed is that of obtaining a shadowgraph of the object to be studied by causing a burst of X-rays at the proper time to pass through a suitable protecting barrier, luminous explosive gases if present, the object being studied, and through a second suitable barrier to the detecting apparatus.

Difficulties are experienced in obtaining X-rays of suflicient penetrating power to give a useful indication in the short time interval allowable, in timing the burst of X-rays with respect to the progress of the phenomenon to be observed, in confining the burst to a time interval sufliciently short to effectively stop the motion, and in obtaining successive X-ray pulses having consistant intensity and wavelength. Additional difficulties are encountered when it is desired to obtain a plurality of radiographs corresponding to a plurality of stages of a phenomenon separated in time by an interval which may be of the order of one microsecond.

While ballistic studies of the above-mentioned type have been carried out successfully with a modified X-ray tube of the type disclosed by Charles M. Slack in US. Patent No. 2,311,705, issued May 25, 1940, this apparatus has been found to have limitations under conditions which require reliability of output of a high degree, accurate timing, and high penetrating power as is the case when substantial distances must be provided between the X-ray source, the object to be studied, and the detecting apparatus.

The above-mentioned magnetic induction accelerator may be used to produce high-energy X-rays, but its use has heretofore been limited to applications employing X-rays which are etfectively generated continuously although these X-rays are actually produced in short bursts recurring at a definite rate, as for example, at the rate of five hundred per second.

A primary object of this invention is, therefore, to provide a method and apparatus for obtaining a single pulse output from a magnetic induction accelerator.

Another object of the invention is the provision of a method and apparatus for obtaining a single pulse output from a magnetic induction accelerator having a known and adjustable timed relationship in respect to a phenomenon to be studied, the relationship being determinable in the order of one ten-millionth of a second.

ice

Still another object is to provide a burst of X-rays having a time duration of substantially less than one millionth of a second.

A further object of the invention is to provide a burst of X-rays of penetrating power corresponding to energies in the order of 20 mev., of time duration substantially less than a microsecond, and with a timed relationship variable with respect to a known time and determinable to within a time in the order of one-tenth of one microsecond.

A still further object of the invention is to provide a plurality of X-ray bursts each of the above described character, separated in time by an interval which may be of the order of one microsecond.

Other objects and advantages of the present invention will become apparent to persons skilled in the art upon examination of the following description and the drawings forming a part of this specification, the inventive aspects of which are defined in the appended claims.

in the drawings:

FIGURE 1 is a schematic circuit diagram illustrating an embodiment of the invention; and

FIGURES 2, 3 and 4 represent various waveforms to be explained later in connection with the operation of the circuit of FIGURE 1.

The theory of a magnetic induction accelerator is given in detail by the applicant in Physical Review, vol. 60, No. 1, July 1, 1941, detailed description being omitted in this specification.

Briefly one preferred method of accomplishing the objects of the invention is as follows. The field producing structure of a magnetic induction accelerator is excited continuously to provide a sinusoidally varying magnetic field. Control means are associated with the magnetic structure and with a conventional electron injector to provide repetitive pulsing of the injector once in each cycle of the magnetic field. To prevent electrons injected in response to each pulse from being accelerated to high energies, the control means ordinarily causes electron injection to occur at a time in the cycle unfavorable for retention of electrons so injected by the magnetic field.

At the appropriate time the control means allows one electron injection to occur at a time in the magnetic cycle favorable for retention of the electrons in the magnetic field, the electrons so injected being then accelerated to high energies along a generally circular orbit. When the phenomenon to be studied has progressed to the desired stage the electron orbit is expanded in response to a voltage pulse which acts through an orbit expanding circuit to cause the electrons to leave their equilibrium orbit and spiral out to impinge on a suitable target. A single pulse of high energy X-rays is thus produced by the introduction of a single burst of electrons, acceleration of these electrons in an equilibrium orbit by the increasing magnetic field, and the impinging of these accelerated electrons on a suitable target in response to pulsing of the orbit expansion circuit.

One circuit adapted to carry out the above methods of producing a single burst of high energy X-rays is shown in schematic diagram in FIGURE 1 of the drawings. There is provided a peaking transformer 12 having a primary winding 13, a core 14, a secondary winding 15 and a tertiary winding 16. Core 14 is of a magnetic material which saturates at a low value of applied magnetomotive force; the inductance of the transformer windings therefore being small except at low values of magnetizing current. The primary winding 13 of transformer 12 is connected to a generator, not shown, which supplies energizing voltage to the energizing coil 142 of the magnetic structure of the accelerator.

The output voltage of the transformer 12, derived from the secondary winding 15, comprises a series of positive and negative pulses illustrated at 20, 21 and 22 in FIGURE 2 of the drawings. FIGURE 2 is to be compared with FIGURE 3, which shows the time variation of the magnetic field causing electron acceleration in the magnetic induction accelerator.

As shown in FIGURES 2 and 3, a positive voltage pulse of large magnitude and short time duration appears at the output of transformer 12 on each cycle of the accelerating fiux, at the time this flux changes from a negative to a positive value. Returning to FIGURE 1, the tertiary winding 16 of the transformer 12 is provided to permit precise control of the timing of pulses of the type illustrated at 20, 21 and 22, FIGURE 2. The tertiary winding 16 is connected to the same generator as is the primary winding 13, a capacitor 17, a choke 18 and a variable resistor 19 being provided in series with the winding 16. The variable resistor 19 operates to control the flux variation in the core 14 in a manner to permit precise timing of the output pulses from the secondary winding of the transformer 12.

The secondary winding 15 of transformer 12 is connected between a ground conductor and the control electrode of a gaseous discharge tube 30. A resistor 32 and a blocking capacitor 33 are interposed in series between the high side of winding 15 and the grid of the tube 30. Negative bias for the control grid of tube is furnished by a potential source 35, connected between the grid and ground conductor 25. A choke 37 and a capacitor 38 are provided in series between source and the grid of tube 30, a resistor 39 being connected in parallel with the capacitor 38 to provide a direct current path between the terminals thereof.

Tube 30 is preferably of the gaseous discharge type, the cathode being connected, as shown, to ground and the anode to a source of high positive potential connected between terminal 41 and ground. A current limiting resistor 45 is provided between terminal 41 and the anode of tube 30, to prevent excessive current flow through tube 30 when conducting.

Injection of electrons into the chamber of a magnetic induction accelerator is accomplished in the following manner. A capacitor 48 is connected between the anode of tube 30 and ground, a resistor 49 being connected in series between the anode of tube 30 and the capacitor 48, and a primary Winding 50 of an air core transformer 51 being connected in series between the capacitor 48 and ground. While tube 30 is nonconducting the capacitor 48 charges to approximately the potential available at the terminal 41 through the series resistors 45 and 49. Conduction in tube 30 is then suddenly initiated in response to a positive voltage pulse of the type shown at 20 and 22, FIGURE 2, which is applied to the control grid of tube 30. Initiation of conduction in tube 39 results in the rapid discharging of capacitor 48 therethrough since the internal resistance of tube 30 is relatively low when that tube is conducting. Since the primary winding 50 of transformer 51 is included in the path of discharge current from capacitor 48 a short high current pulse flows in the said winding as a result of initiation of conduction in tube 30, causing a negative voltage pulse of large amplitude and short duration to appear on an injector structure generally designated 55 connected to one side of a secondary winding 56 of the transformer 51. The other side of the secondary winding 56 is connected, as shown, to ground conductor 25. The tube 30 is extinguished or rendered nonconducting in response to the complete discharge of capacitor 48, since the resistor 45 prevents fiow of suflicient current from terminal 41 to maintain the discharge initiated in tube 30.

The injector structure 55 operates in a known manner to provide a copious supply of thermionic electrons within the evacuated chamber of a magnetic induction accelerator. Under the manner of operation preferred for the present purposes structure 55 includes a heated filament as a source of thermionic electrons and a partial electrostatic shield which also assists in supporting the filament. Structure 55 is normally at ground potential as is also a conducting coating on the interior surface of the evacuated chamber. Accordingly, when injector structure 55 is suddenly lowered in potential due to the negative voltage pulse appearing on secondary winding 56 of transformer 51 the electronic field is such as to cause electrons emitted from the heated filament of structure 55 to be injected into the evacuated chamber from structure 55.

To effect a suitable disturbance in the electron-accelerating magnetic field a pair of orbit expansion coils 60 and 61 are provided. Coils 60 and 61 are preferably situated in concentric relationship with the equilibrium orbit of the electrons being accelerated, one coil being positioned just above the evacuated chamber and the other below, and both coils having approximately the same radius as that of the electron equilibrium orbit.

The control circuit for establishing current in coils 60 and 61 at the appropriate time includes a phase shifting circuit 65. The circuit 65 includes an auto-transformer 67 which is connected to the generator providing energizing voltage to the energizing coil 142 of the magnetic structure of the accelerator. A capacitor 68 and a variable resistor 69 are connected in series across the terminals of the auto-transformer 67, a primary winding 71 of a transformer 72 being connected between a tap on the auto-transformer 67 and a point between the capacitor 68 and the variable resistor 69. The transformer 72 is provided with a core 74 of readily saturable material, the output voltage of the transformer, derived from a secondary winding 75, comprising a series of positive and negative voltage pulses as shown at 77, 78, and 79 in FIGURE 4 of the drawings. FIGURE 4 is to be compared with FIGURE 3 in which is shown the time variation of the magnetic field causing electron acceleration. The positive voltage pulses from transformer 72 are Seen to come at approximately the peak of the magnetic field corresponding to the time at which electrons have been accelerated to the highest energies.

Returning to FIGURE 1, the pulse output of transformer 72 is applied to the control grid of a gaseous discharge tube 88 through series resistors 81 and 82. A DPDT switch 83 is interposed between resistor 81 and 82 for a purpose which will be described later, for the present discussion it is assumed to make connection from resistor 81 to resistor 82. Negative bias for the control grid of tube is furnished by a voltage source 84 connected as shown between ground and a resistor 86 which is connected in turn to the resistor 82. Anode potential for tube 80 is provided from a terminal 88 which is connected to the positive side of a voltage supply source, not shown, in a manner to maintain terminal 88 at a suitable positive potential with respect to ground. An impedance 90 and a capacitor 91 are connected in series between the anode of tube 80 and ground, and a resistor 92, an inductance 93 and the impedance 90 are connected in series between terminal 88 and the anode of tube 80. The cathode of tube 80 is returned to ground through a resistor 95.

Conduction in tube 80 is normally prevented by the negative bias applied to the control grid thereof from source 84, the positive pulses illustrated at 77 and 79 of FIGURE 4 causing conduction to be initiated in tube '80 to permit discharge of the capacitor 91 therethrough. Discharging of the capacitor 91 through the tube 80 operates in conventional manner to produce a large positive voltage pulse of short duration across the resistor 95 which forms a cathode load for the tube 80, the tube 80 extinguishing when the capacitor 91 is nearly completely discharged. The impedance 90 included in the anode circuit of the tube 80 aids in extinguishing that tube.

The positive voltage pulse appearing across the resistor 95 is introduced on the igniter electrode of a gaseous discharge tube 97, which is preferably of the ignitron type. The orbit expansion coils 60 and 61 are connected in series in the anode circuit of the tube 97, an inductance 100' and a resistor 101 being connected in series with the coils 60 and 61 and with terminal 88. A capacitor 103 is connected between the point of connection of inductance 100 and coil 60 and ground to provide energy storage means. Current conduction in the tube 97 is initiated in response to the positive pulse appearing on the igniter electrode thereof; the capacitor 103, previously charged to the potential appearing at terminal 08, then discharges through the coils 60 and 61 and the tube 97 in series. The pulse of capacitor discharge current in coils '60 and 61 operates in conventional manner to set up a suitable momentary magnetic field which disturbs the equilibrium magnetic field causing electron acceleration. In response to this disturbance of the equilibrium magnetic field the accelerated electrons are caused to spiral out of the stable orbit and impinge upon a suitable target disposed in spaced relation thereto.

The tubes 80 and 97 may be replaced by a single tube,

it being evident that the function of the tube 80 is to amplify the pulse fed to the control electrode thereof to the degree that it will provide reliable triggering of the tube 97. It is desirable to substitute a single tube for the tubes 80 and 97 to avoid the slight delays which may be introduced in the triggering of these tubes. The single tube should have a large power-handling capacity and be triggered by a lower-power pulse and may be a hydrogen thyratron. Operation of the circuit as described to this point comprises injection of electrons from structure '55 as the acceler-ating magnetic field passes through the zero value, and ejection of these electrons from the equilibrium orbit at approximately the peak of the magnetic field, due to the pulse of current in coils 60 and 61. This manner of operation is indicated by the pulses 20 and 22, FIGURE 2.; and the pulses 77 and 79, FIGURE 4; taken with reference to FIGURE 3 which represents the time variation of the magnetic field causing electron acceleration.

To effect circuit control in a manner to produce a single burst of X-rays, a pair of gaseous discharge tubes 105 and .106, FIGURE 1, are provided, the tube 105 being associated with the transformer 12 and the tube 106 being associated with the transformer 72. As shown, the output voltage of the secondary winding 15 of transformer 12 is applied to the anode of the tube 105 through the resistor 32, a resistor 107 and a capacitor 108 in series. The output voltage of the secondary winding 7'5 of the transformer 72 is applied to the anode of the tube 106 through the resistor 81 and a capacitor 110 in series.

Tubes 105 and 106 are held in a nonconducting condition by the application of a suitable negative bias voltage, from a source 112, to the control electrodes of both tubes 105 and 106. The source 1.12 has its positive terminal connected to the ground conduct-or 25, and its negative terminal to the control electrode of tube 105 through a resistor 114, a resistor 115 and a resistor 116 connected in series. The negative terminal of source 112 is also connected to the control electrode of the tube 106 through a resistor 118, a resistor 119, and a resistor 120 in series.

To remove negative bias from the control electrode of tube 105, a switch 122 is provided, connected between ground and the point of connection of

resistors

114 and 115. A switch 124 performs a similar function in the circuit of tube 106, the switch 124 being connected between ground and the point of connection of resistors 118 and 119. The cathode of the tube 105 is connected directly to ground conductor 25; the anode of tube 105 is connected to the positive voltage terminal 88 through a resistor 126. The anode of the tube 106 is connected to terminal 88 through a resistor 128; the cathode of tube 106 is connected to the ground conductor 25 through a resistor 130. The cathode of tube 106 is further connected to the control electrode of the tube 105 through a capacitor 132 the magnetic induction accelerator to obtain maximum output therefrom, the accelerator is first operated in conventional manner with repetitive pulse output. This may be achieved by throwing switches 122 and 124 to the open position, thereby applying bias from source 112 to both the tubes 105 and 106 and preventing conduction in these tubes. In this mode of operation the electron injector circuit including the tube 30, and the orbit expansion circuit including the tubes 30 and '97 operate in conventional manner to produce electron injection and orbit expansion at the appropriate times in the accelerating magnetic field cycle.

After the accelerator generally has been adjusted for the desired output, switches 122 and 124 are closed, removing the bias provided by source 112 from the control electrodes of the tubes 105 and 106. The potential applied to the anode of the tube 105 from the secondary winding 15 of the transformer 12 through the resistors 32 and 107 and the capacitor 108 is then such as to cause conduction to be initiated in that tube approximately 60 electrical degrees before the positive voltage pulse of the type illustrated at 22, FIGURE 2, would normally arise.

Initiation of conduction in the tube 105 causes discharge of capacitor 108 therethrough, the discharge path for capacitor 108 including the secondary winding 15 of the transformer 12. This capacitor discharge current in the winding 15 gives rise to a magnetic flux in the core 12 such that the said core remains saturated until current of the opposite sign in the primary winding 13 provides sufficient flux in the opposite direction to substantially cancel that due to the current in the secondary winding 15. The net effect is to delay the positive pulse output of the secondary winding 15 is indicated at 1 34, FIGURE 2. The electron injector circuit including the tube 30 is operated in response to the pulse 134, but it can be seen from a comparison of FIGURES 2 and 3 that injection will occur at a time at which the accelerating magnetic field has attained an appreciable value. Therefore electrons injected due to the pulse 134 will not be captured by the magnetic field.

To prevent orbit expansion at peak magnetic field the tube 106 is operable upon closing of the switch 124 to conduct during substantially the complete cycle, being extinguished only by negative voltage peaks from the secondary winding of the transformer 72, of the type illustrated at 78, FIGURE 4. The tube 106 has a comparatively low resistance when conducting and hence operates to short circuit to ground the positive voltage pulses of the type shown at 77 and 79, FIGURE 4. This operation is illustrated at 136 and 137, FIGURE 4. Pulses of the type shown at 136 and 137, FIGURE 4, are of insuflicient magnitude to initiate conduction :in the tube FIGURE 1, hence orbit expansion does not occur so long as switch 124 remains closed.

Synchronization of the pulse output of the accelerator and the phenomenon being investigated, e.g., a device undergoing implosion, is provided through the switch 83. The switch 83 is operable to disconnect the transformer secondary winding 75 from the control electrode of the tube 80 and to apply the output voltage of winding 75 to an external control circuit 140 while connecting the circuit 140 to the control electrode of the tube 80 through the resistor 82. After adjustment of the accelerator has been effected under repetitive pulsing conditions, and the switches 12-2 and 124 have been closed, the switch 83 is thrown to connect in the control circuit 140.

Detonation of the implosive device is then effected in response to the opening of switch 124 in the following manner. Opening of the switch 124 applies the negative bias voltage from the source 112 to the control electrode of the tube 106. However the tube 106 continues conducting until the next negative voltage pulse from the transformer 72, e.g., the pulse illustrated at 142, FIGURE 4, lowers the anode potential of the tube 106 sufficiently to extinguish that tube. Cessation of conduction in the tube 106 removes the positive voltage appearing at the cathode thereof due to current in the resistor 130. This decrease in the potential at the cathode of tube 106 is transmitted as a negative voltage to the conrol electrode of the tube 105 through the capacitor 132 and the resistor 116, temporarily biasing the tube 105 so as to prevent initiation of conduction therein. Accordingly the next positive voltage pulse from the transformer 12 is not delayed since the tube 105 is held out off, and hence this pulse, i.e., that designated 144, FIGURE 2, causes electron injection to occur at the appropriate time for capture of the electrons so injected by the accelerating magnetic field.

The next positive output voltage pulse from the transformer 72, i.e., that designated 146, FIGURE 4, is not short-circuited to ground since the tube 106 is held nonconducting by the negative bias applied to the control electrode thereof. The positive voltage pulse illustrated at 146 is therefore transmitted to the control circuit 140 to ettect detonation of the implosive device under study. When the implosion has progressed to the desired stage with an elapsed time neglible compared to the period of the accelerator cycle, it operates in a known manner to transmit a positive voltage pulse through the circuit 140 to the control electrode of the tube 80, initiating conduction therein and effecting orbit expansion due to current in the coils 60 and 61 as described above. The pulse of X-rays is thus produced at the desired stage in the progress of the phenomenon being studied.

Before the occurrence of the next positive output voltage pulse from transformer 12, the negative voltage applied to the control electrode of the tube 105 due to the cessation of current in the tube 106 decays due to the discharging of the capacitor 132 so that the tube 105 resumes normal operation. In other words, the bias on the tube 105 decays in time to allow that tube to operate in the manner described earlier to delay the following positive voltage pulses fed to the electron injector circuit. This condition is illustrated in FIGURE 2, the pulse designated 148 being shown delayed in the same fashion as are the

pulses

134 and 135. Thus a second electron injection has been prevented and only the desired pulse of X-rays has been produced.

An important feature of this mode of operation is seen to reside in the avoidance of switching transients when it is desired to produce the X-ray pulse. As described above the entire sequence is initiated in response to the negative pulse shown at 142, FIGURE 4, which pulse extinguishes the tube 106 and permits normal operation of all circuits for the following cycle. The switch 124, FIGURE 1, may thus be closed at any time in the cycle, the only possible contusion arising if the switch 124 is closed simultaneously with the pulse 142. In this event, either the tube 106 extinguishes immediately and the operation is completed on that cycle, or the whole circuit simply waits one cycle for the next negative voltage pulse from the transformer 74 and the desired operation is then completed on the following cycle.

To provide variation in the timing of the burst of Xrays with respect to the progress of the phenomenon being studied, the pulse fed to the circuit 140 to cause orbit expansion may originate at a preselected time in the progress of the phenomenon being studied. It may then be delayed a known and variable amount of time in the control circuit 140 before being fed to the control grid of the tube 80; the actual circuit for effecting this type of control may be any of a variety of circuits well known to persons skilled in the art.

In accordance with the mode of operation of a magnetic induction accelerator as described in the present application, whereby a single, short, high-energy burst of X-rays may be obtained therefrom, various modifications may be employed to effect the production of a plurality of X-ray bursts separated by a short, controllable time interval. In this connection a plurality of magnetic induction accelerators may be provided operated in controlled phase relation to one another. For example, two acceleriii ators having similar characteristics may be operated in a known manner whereby the magnetic flux variation in each has the same cyclic frequency but the variations in one lag the other by a small fraction of the period of flux variation. In conventional operation this manner of ope"- ation of the two accelerators results in a series of pairs of X-ray bursts occurring at the frequency of flux variations, the two bursts of a pair being separated in time by an interval determined by the amount of phase lag of one accelerator with respect to the other. When both accelerators are operated in accordance with the teachings of the present application so as to produce a single burst of X-rays from each on essentially the same cycle, a pair of X-ray bursts is produced separated by any desired small time interval. Such a pair of X-ray bursts may be employed to examine two stages of a phenomenon undergoing rapid change.

White a presently preferred embodiment of the invention has been described in detail above, various modifications thereof are as follows:

For example, single pulse operation of a magnetic induction accelerator may be obtained by permitting the accelerating flux generator to run continuously while providing electron injection on each cycle in conventional manner. Electrons so injected will be accelerated to high energies, but if orbit expansion is withheld except on one cycle, then the electrons will be directed against the target on only one cycle and therefore only one burst of highenergy X-rays will result.

Again, a single pulse of X-rays may be produced by providing energy storage means such as a bank of capacitors charged to a predetermined potential, and permitting the capacitors to discharge through the field coils of a magnetic induction accelerator at the desired time. A control circuit embodying suitable modifications of the circuit described in the present application may be associated with the energy storage means and with the accelerator field coils to permit electron injection at the initiation of capacitor discharge and orbit expansion in response to the building up of the magnetic field to its maximum value. To provide a double pulse of X-rayS, the pulse causing orbit expansion may be so shaped as initially to cause the electrons to spiral out of their equilibrium orbit and subsequently to cause such electrons as have not struck to target to return to the equilibrium orbit for a second orbit expansion whereby the remaining electrons may be made to impinge on the target. Alternatively, a target made in two sections may be so disposed as to present to the electrons, as they spiral outwardly, essentially two targets which are struck in quick succession by different portions of the electron beam.

It is to be understood that the magnetic induction accelerator may be employed to accelerate particles other than electrons, producing other effects than the X-ray bursts described in the present applications. Also although orbit expansion has been used exclusively in the foregoing, for the purpose of illustrating one mode of operation, orbit contraction may be employed instead, or the beam of particles may be given a component of velocity along the axis of rotation of the System as well as perpendicular thereto, depending upon the location of the target with respect to the equilibrium orbit.

These and other modifications apparent to persons skilled in the art are intended to fall Within the spirit and scope of the present invention, the inventive aspects of which are defined with particularity in the appended claims.

I claim:

1. The combination with a magnetic induction accelerator having an alternating current source providing cyclic accelerating magnetic field energy and means for periodically injecting electrons at a time appropriate for acceleration through an orbit defined by said accelerating field energy, means coupled to said current source for controlling the timing of one of said injections to permit electron capture and acceleration through said orbit by said accelerating energy, and means for introducing phase shift to effect all subsequent injections at times inappropriate for electron capture and orbit acceleration thereof, whereby to produce a single effective injection.

'2. The combination with a magnetic induction accelerator of the type including cyclic energizing field for the establishment of a charged particle orbit, means associated with said field for the injection of electrons within said orbit and operative in response to an introduced pulse, and means for deflecting the injected electrons from said orbit after acceleration therein for the bombardment of a target and the production of an X-ray burst; of an electronic circuit associated therewith including electron dischargemeans responsive to one of a sequence of pulse signals introduced to said electron injection means for the initiation of said injection in proper phase with the cyclic energizing field to effect capture and acceleration within said orbit, said circuit being responsive to all other pulses of said sequence to effect phase shift between the resulting injections, energizing field, and the orbit expanding means, whereby one pulse of said sequence results in an X-ray burst and all other pulses of said sequence are ineffective to cause X-ray bursts.

3. A magnetic induction accelerator having in combination, means operative in response to a cyclic accelerating field to maintain a charge particle orbit, means for the periodic injection of electrons in said orbit, mean for the periodic disturbance of said orbit in a manner to direct said electrons injected therein, after acceleration, toward a suitable target for the production of X-rays, said magnetic field energy, injection means, and orbit disturbing means being operable by a common alternating energizing source, phase shifting means interposed between said orbit disturbing means and said energizing source, electron discharge means interposed between said injection means and said orbit expansion means and operative in response to signals introduced through said phase shifting means for the control of injections in a manner whereby an initial injection is introduced in proper phaserelation with said energizing source to permit acceleration within said orbit and deflection therefrom to produce an X-ray burst all subsequent injection-s being controlled by said phase shifting means for introduction within said orbit in proper phase relation to said energizing current to prevent resulting X-ray bursts.

4. In a magnetic induction accelerator of the type including a cyclic energizing field for the establishment of a charged particle orbit, means for the injection of electrons therein, Said injection means being responsive to an introduced pulse, and means electrically coupled to said injection meansfor the introduction of repetitive pulses thereto; means for causing one of said repetitive pulses to effect electron injection at a time appropriate for acceleration Within said orbit and electronic means responsive to an initial injection producing pulse for shifting the phase of all subsequent pulses to effect electron injection at times inappropriate for electron capture and orbit acceleration by said cyclic field.

5. In a magnetic induction accelerator of the type including a cyclic energizing field for the establishment of a charged particle orbit, means for the injection of electrons into said orbit, said injection means being responsive to an introduced pulse, and means coupled to said injection means for the introduction of repetitive pulses thereto; means for causing one of said repetitive pulses to effect electron injection at a time appropriate for acceleration within said orbit electronic means responsive to an initial injection producing pulse for shifting the phase of all subsequent pulses to effect electron injection at times inappropriate for electron capture and orbit acceleration by Said cyclic field and manually operable switch means for the control of said phase shifting means between inoperative and operative condition.

6. In a magnetic induction accelerator, a generator providing cyclic accelerating magnetic field energy, a first and second peaking transformer driven therefrom and having respective outputs comprising a sinusoidal voltage having superimposed thereon a sequence of positive and negative triggering pulses separated by one-half of said generator cycle, means for causing the output of said second transformer to lag that of said first transformer by approximately ninety electrical degrees, means coupled to said first transformer output and operable in response to positive triggering pulses to inject electrons into said magnetic induction accelerator at approximately the time of zero magnetic flux, orbit disturbance means coupled to said second transformer output and operable in response to positive triggering pulses to effect disturbance of the equilibrium orbit of said magnetic induction accelerator at approximately the time of maximum magnetic flux, a gaseous discharge tube connected in shunt with said first transformer output to be driven to conductance thereby prior to each of said positive triggering pulses therefrom to cause said pulses to be delayed and said injection means to effect electron injection at a time inappropriate for electrons so injected to be captured by themagnetic field, a second gaseous discharge tube associated in shunt with said second transformer output and driven to conductance thereby except during said negative triggering pulses in the output thereof, said second tube constituting an effective short-circuit to said second transformer output positive triggering pulses to prevent actuation of said orbit disturbance means there-by, switch means associated with said second tube and operable upon opening to apply cutoff bias thereto to prevent reestablishment of conduction therein subsequent to the cessation of conduction in that tube in response to the first negative triggering pulse following opening of said switch, and circuit means responsive to the cessation of conduction in said second tube for momentarily applying negative bias to said first tube to prevent said first tube being driven to conductance prior to the positive triggering pulse in said first transformer output next following the last-mentioned negative triggering pulse; whereby said last-mentioned positive triggering pulse actuates said injection means at a time favorable for the capture of electrons so injected by the magnetic field, the positive triggering pulse for actuation of said orbit disturbance means being non-short-circuited by said second tube.

7. Means for controlling the operation of a magnetic induction accelerator of the type having a generator providing cyclic accelerating magnetic field energy to maintain a normally undisturbed equilibrium orbit, comprising in combination, first and second means for the initation of sinusoidal voltage outputs having superimposed thereon a sequence of positive and negative triggering pulses at a phase differential of one-half of said generator cycle, a third means for effecting lag of the output of said second means in respect to the output of said first means, a fourth means connected to the output of said first means for the injection of electrons into said accelerator, said fourth means being responsive to said positive triggering pulses at approximately the time of zero accelerating flux, a fifth means coupled to the output of said first means and operable in response to maximum accelerator flux to effect unbalance of the equilibrium orbit, a sixth and seventh means coupled respectively in shunt with the outputs of said first and second means, said sixth means being rendered conducting by its corresponding output prior to each of said positive triggering pulses therefrom to effect pulse delay and electron injection at a time inappropriate for electron capture by said magnetic field energy, said seventh means being maintained conducting by the corresponding output except during said negative triggering pulses thereby preventing actuation of said fifth means, an eighth means electrically coupled with said seventh means for preventing re- 11 establishment of conduction therein subsequent to cessation of conduction therein in response to the negative triggering pulse first following actuation of said eighth means, and a ninth means responsive of the cessation of conduction by said seventh means for momentarily preventing conduction by said sixth means prior to the positive triggering pulse next following the last mentioned negative triggering pulse, whereby said last mentioned positive triggering pulse actuates said injection means at a time favorable for the capture of electrons so injected by the magnetic field, the positive triggering pulse for actuation of said orbit disturbing means being non-shortcircuited by said second tube.

8. The combination with a magnetic induction accelerator including means for the generation of a cyclic accelerating magnetic field energy, of a first and second voltage peaking means driven therefrom and having respective outputs comprising a sinusoidal voltage having superimposed thereon a sequence of positive and negative triggering pulses separated by one-half the cyclic magnetic field energy, means for causing the output of said second peaking means to lag the output of said first peaking means in the order of 90 electrical degrees, means associated with the output of said first peaking means and operable in response to said positive triggering pulse to inject electrons into said magnetic induction accelerator at the time .of zero magnetic flux therein, means electrically coupled to the output of said second peaking means and operable in response to said positive triggering pulses to eifect equilibrium orbit unbalance within said magnetic induction accelerator at approximately the instant of maximum magnetic flux therein, electron discharge means coupled in shunt with the output of said first peaking means to be rendered conducting thereby prior to each of said positive triggering pulses to simultaneously cause said pulses to be delayed, and to effect electron injection at a time inappropriate for the injected electrons to be captured by the magnetic field, a second electron discharge device coupled in shunt with the output of said second peaking means in a manner to be driven conducting thereby and to be driven nonconducting by said negative triggering pulses, said second electron discharge means effecting short-circuiting of said positive triggering pulses to prevent actuation of said orbit disturbing means thereby, manually operable switch means associated with said second discharge means for application of cutoff bias thereto to prevent reestablishment of conduction therein subsequent to the cessation of conduction therein in response to a negative triggering pulse first following actuation of said switch means, and circuit means responsive to the cessation of conduction of said second discharge means for momentarily rendering said first discharge means non-conductive thereby preventing said first discharge means from being driven conducting prior to the positive triggering pulse next following the last mentioned negative triggering pulse, whereby said last mentioned positive triggering pulse actuates said injection means at a time favorable for the capture of electrons so injected by the magnetic field, said positive triggering pulses causing actuation of said orbit disturbance means being non-short-circuited by said second electron discharge means.

References Cited UNITED STATES PATENTS WILLIAM F. LINDQUIST, Primary Examiner.

' L. MILLER ANDRUS, OTTO STRACHAN, Examiners.

Claims

2. THE COMBINATION WITH A MAGNETIC INDUCTION ACCELERATOR OF THE TYPE INCLUDING CYCLIC ENERGIZING FIELD FOR THE ESTABLISHMENT OF A CHARGED PARTICLE ORBIT, MEANS ASSOCIATED WITH SAID FIELD FOR THE INJECTION OF ELECTRONS WITHIN SAID ORBIT AND OPERATIVE IN RESPONSE TO AN INTRODUCED PULSE, AND MEANS FOR DEFLECTING THE INJECTED ELECTRONS FROM SAID ORBIT AFTER ACCELERATION THEREIN FOR THE BOMBARDMENT OF A TARGET AND THE PRODUCTION OF AN X-RAY BURST; OF AN ELECTRONIC CIRCUIT ASSOCIATED THEREWITH INCLUDING ELECTRON DISCHARGE MEANS RESPONSIVE TO ONE OF A SEQUENCE OF PULSE SIGNALS INTRODUCED TO SAID ELECTRON INJECTION MEANS FOR THE INITIATION OF SAID INJECTION IN PROPER PHASE WITH THE CYCLIC ENERGIZING FIELD TO EFFECT CAPTURE AND ACCELERATION WITHIN SAID ORBIT, SAID CIRCUIT BEING RESPONSIVE TO ALL OTHER PULSES OF SAID SEQUENCE TO EFFECT PHASE SHIFT BETWEEN THE RESULTING INJECTIONS, ENERGIZING FIELD, AND THE ORBIT EXPANDING MEANS, WHEREBY ONE PULSE OF SAID SEQUENCE RESULTS IN AN X-RAY BURST AND ALL OTHER PULSES OF SAID SEQUENCE ARE INEFFECTIVE TO CAUSE X-RAY BURSTS.