US2754419A - Magnetic induction accelerator - Google Patents

Magnetic induction accelerator Download PDF

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Publication number
US2754419A
US2754419A US295852A US29585252A US2754419A US 2754419 A US2754419 A US 2754419A US 295852 A US295852 A US 295852A US 29585252 A US29585252 A US 29585252A US 2754419 A US2754419 A US 2754419A
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voltage
capacitor
curve
electron
tube
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US295852A
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English (en)
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Wideroe Rolf
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BBC Brown Boveri AG Germany
BBC Brown Boveri France SA
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BBC Brown Boveri France SA
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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H11/00—Magnetic induction accelerators, e.g. betatrons

Definitions

  • the present invention relates to apparatus for imparting high energy to charged particles such as electrons by repeated acceleration to such particles.
  • the particular apparatus referred to is known as a ray transformer or magnetic induction accelerator.
  • a magnetic induction accelerator or so-called ray transformator that is, a device in which the electrons are accelerated in the eddy current field of a magnetic flux up to a velocity or ultimate electron voltage of millions of electron volts
  • so-called expansion or contraction coils are used for deflecting the electron stream out of the equilibrium orbit. These coils are subjected to the main accelerating fiux of the magnetic induction accelerator.
  • one stream of electrons is shot into an annular tube for acceleration in one direction around the tube at the beginning of the first halfcycle of the main accelerating flux which varies in a generally sinusoidal manner, and a second stream of electrons is shot into the tube for acceleration in the opposite direction around the tube when the main accelerating flux reaches its maximum amplitude in the next half-cycle.
  • the first stream of electrons is ejected from its orbit after a predetermined acceleration and so also is the second stream.
  • the present invention relates to an improved arrangement for ejecting the two electron streams, there being a single capacitor used for the control of the ejection instants of the two streams connected in series with an auxiliary winding surrounding only the induction pole portion of the magnetic circuit and inductively coupled to the main accelerating flux producing Winding so as to periodically recharge the capacitor, and the charge on the capacitor being discharged periodically in opposite directions through the auxiliary Winding by means of a pair of grid-controlled gas discharge tubes connected in back-to-front relation in circuit between the capacitor and the auxiliary winding.
  • means are so provided for the control grids of the gas discharge tubes that each tube can be fired, i. e. made conductive at a selected instant, independent of the other, to the end that each electron stream can be ejected at a selected instant of time during its acceleration phase.
  • Fig. 1 is a view in central vertical section of a magnetic induction accelerator having an auxiliary winding for effecting an ejection of the electron streams from their orbit after acceleration, there being a capacitor in series with the auxiliary winding and a pair of grid-controlled gas discharge tubes connected in back-to-front relation in circuit between the capacitor and auxiliary winding;
  • Fig. 2 is a graph illustrating the course of the voltage induced in the auxiliary winding by the flux produced from the main winding of the accelerator, the course of the current flow through the auxiliary winding and the 2,754,419 Patented July 10, 1956 course of the voltage on the capacitor, in accordance with a known arrangement for operating the gas discharge tubes;
  • Fig. 3 is a graph similar to that of Fig. 2 illustrating the courses of the voltages, currents and fluxes in accordance with the present invention
  • Fig. 4 is a schematic electrical diagram showing the control circuit for the gas discharge tubes in accordance with the present invention.
  • Figs. 5, 6 and 7 are graphs correlated to Fig. 3 showing the courses of the various components of the grid voltages produced in accordance with the invention to control the firing instants of the gas discharge tubes;
  • Fig. 8 is a graph showing the course of the voltage induced in the auxiliary winding when the central core portion of the accelerator is magnetized to saturation, the departures from the generally sinusoidal form of curve being much exaggerated;
  • Figs. 9 and 10 are graphs showing different magnitudes of impulse currents from the capacitor required in the auxiliary winding for ejecting the electron streams in dependence upon diiferent desired ampltiudes of accelera tion of the streams;
  • Fig. 11 is a graphical presentation of two conditions for expansion of the orbit of the electron streams, one when the central core is saturated and another when the central core is unsaturated.
  • Fig. 1 shows schematically a magnetic induction accelerator with a magnetic field structure 10, two coils 11 and 12 which supply the main flux and at the same time also the socalled control or guiding flux, as well as an annular tube 13 which like the field structure and coils is also shown in section and inside of which the electrons are accelerated.
  • the pole shoes 14 and 15 for the accelerating flux are provided with two expansion or contraction coils 16, 17 which are connected in series.
  • these coils are supplied with a short current impulse, so that the magnetic flux corresponding to this impulse when there is an expansion of the electron orbit acts through the pole shoes 14, 15 in the same sense as the accelerating flux but through the guiding field space of the magnetic inductor in the opposite sense to the guiding flux (or in case a contraction of the electron orbit is desired the effect is reversed and the magnetic flux acts through the pole shoes 14, 15 in the opposite sense to the accelerating flux and through the guiding field space in the same sense as the guiding flux), so that the electrons which during the acceleration travel around the equilbiirum orbit deviate from this latter, either in the inward or outward direction, and strike the anti-cathode.
  • Coils 16, 17 are thus called either expansion or contraction coils depending upon whether the anti-cathode is located on a radius which is greater or smaller than that of the equilibrium orbit.
  • expansion coil is used throughout the following description.
  • the expansion coils are connected in series with a capacitor 18 and two tubes 19, 20, the latter being arranged in parallel but with opposed current passing directions i. e. in back-to-front relation.
  • curve A in Fig. 2 represents the voltage produced in the expansion coils by the accelerating flux and if it is desired to accelerate the electrons during each accelerating period up to the maximum ultimate electron voltage, there must be a voltage on capacitor 13 corresponding to the rectangular curve B of Fig. 2.
  • the phase position of the ultimate electron voltage is indicated in Fig. 2 by the dotted curve C.
  • the polarity-reversing current in the form of a current impulse J1 flows through the expansion coils and thus causes the desired expansion of the orbital path.
  • tube 20 which up to then has remained non-conductive is fired and the capacitor by means of a fresh current impulse J2 over the expansion coils has its polarity changed back again to that which it possessed shortly before the instant t1. If the induction accelerator has a second stream, this is also deflected from the equilibrium orbit to its anti-cathode.
  • the current impulse J1 (and also the current impulse J2 when there are two electron beams travelling in opposite directions) must already occur at some instant depending on the desired ultimate electron voltage and falling within the interval T1 or T2 respectively, that is to say before the end of the interval in question. It is obvious that for this purpose the voltage on capacitor 18 will have to diifer from the rectangular curve B not only as regards the position in time of the vertical flanks but primarily as regards its amplitude.
  • the first discharge gap is ignited at an instant which is variable and depends on the desired ultimate voltage, whilst the second discharge gap is ignited as much after the ignition point required for the maximum ultimate voltage of the second stream as the ignition point of the first discharge gap is in advance of the ignition point required for maximum ultimate voltage of the first stream.
  • FIG. 3 A practical example of this method is now explained by means of the curves in Fig. 3.
  • reference letter A again indicates the voltage produced in the expansion coils by the accelerating flux.
  • the acceleration interval for the first electron stream is again T1.
  • the ultimate voltage which can be attained during this interval is given bythe ordinates of the sine wave C which coincides with curve C of Fig. 2 and has been drawn with the same amplitude as the curve A.
  • Capacitor 18 discharges at the instant t4 through the tube 19 and begins at point 1 on curve D, Fig. 3.
  • the voltage at the capacitor decreases very rapidly according to a steep cosine curve (in Fig. 3 vertical line 21), intersects curve A and ends (undamped discharge assumed) at point 2 which lies as far below curve A as the point 1 lies above this curve.
  • the charge on capacitor 18 has now the opposite polarity to that which it previously had, that is the charge has the plus and minus signs shown below the capacitor leads.
  • the grid voltage consists of two voltages in series which are taken from two separate windings of a phase transformer 23.
  • the first part of the voltage is tapped off from the first secondary winding 24 to which a double-wave rectifier system comprising tubes 25, 26 and load resistor 27 is connected.
  • the second part of the voltage is obtained from a second secondary winding 28 which is connected ri idly with the first secondary winding 24, as indicated by th dashed line extending between the two windings, and together with the latter can be rotated relatively to the primary winding 29.
  • the second secondary winding has a circuit consisting of resistor 30 and a capacitor 31 connected to it for shifting the phase of this secondary voltage by 45.
  • the voltage on capacitor 31 is in series with the voltage on load resistor 27.
  • Primary winding 29 is in parallel with the energizing winding 32 of the induction accelerator, the winding 32 corresponding in function to coils 11, 12 in Fig. 1. From Fig. 5 it is clear that with this grid circuit the position of firing point t4 can be selected anywhere within the interval T1.
  • a pulsating direct voltage now occurs at load resistor 27 corresponding to the dotted curve 33, whilst at capacitor 31 there is a sinusoidal voltage corresponding to the dotted curve 34 and the sum of both these voltages thus appears at grid 19, that is a voltage according to curve 35.
  • the peaks of curve 35 serve for firing tube 19 and the phase position of these peaks can be varied within the interval T1 by means of the phase transformer.
  • the second discharge gap 20 is now ignited during the time interval T2 in Fig. 3, this being achieved by means of the total bias voltage consisting of three voltages in series obtained with the circuit shown in Fig. 4.
  • the first part of this grid voltage is the voltage at capacitor 18, because the path between the cathode of tube 2% and its control grid first of all contains capacitor 18.
  • the grid circuit furthermore contains the secondary winding 36 of transformer 37 whose primary winding 38 is connected to a capacitor 39 which is in series with a resistor 40 and is connected to the energizing winding 32 or" the induction accelerator.
  • the resistor-capacitor organization 39, 46 causes the phase of the voltage at the energizing winding 32 to be shifted so that a voltage occurs at the secondary winding 36 which as regards magnitude and phase corresponds to the curve D in Fig. 3.
  • Curve D in Fig. 3 is also designated by G2 to indicate that it forms the second part of the grid voltage for tube 20.
  • the third part of the grid voltage is shown in Fig. 6 as a function of the time. It consists of a sine wave the upper parts of which corresponding to the interval T2 and of a quarter cycle duration being cutoff. The cut-off part of the sine wave is shown dotted in Fig. 6; the third part of the grid voltage is thus always negative except during the interval T when it is zero.
  • the third part of the grid voltage is thus shown in Fig. 6 by the full-line curve.
  • This bias voltage is produced by means of transformer 41 the primary winding 42 of which is connected over a phase-shifting series connected resistor-capacitor organization 43, 44 in parallel with the energizing winding 32, a rectifier 47 with a bias voltage 46 being arranged in parallel with the secondary Winding.
  • the grid circuit of tube 20 thus contains in series arrangement: (a) the voltage at capacitor 18, (b) the voltage G2 which is supplied from winding 36, and (c) the third part of the grid voltage, namely the voltage according to Fig. 6 which only allows tube 20 to be fired during the interval T2 and otherwise causes the control grid of this tube to have a blocking elfect.
  • the capacitor voltage and the voltage at 36 is reduced by the voltage divider 48 to the magnitude required for the control range of the grid of tube 20.
  • that part of the capacitor voltage which due to voltage divider 48 lies in the grid circuit of tube 20 has a magnitude and polarity corresponding to the horizontal line 22 in Fig. 3.
  • Curve G2 that is a fraction of the voltage from winding 36 has at the beginning of the interval T2 a negative value which is considerably greater than the ordinate of line 22.
  • the third part of the grid voltage, that is the curve in Fig. 6 assumes zero value at the beginning of interval T2; the blocking effect on tube 20 ceases.
  • curve G2 intersects the line 22, that is at the instant t5
  • the grid bias voltage of tube 2% becomes positive because the positive capacitive voltage exceeds the negative secondary voltage of winding 36, so that tube 20 is fired.
  • Capacitor 18 now reverses its charge through expansion coils 16, 17 and tube 29, whereby an expansion impulse again occurs in the expansion coil of the same magnitude but in the opposite direction as at 24.
  • the corresponding voltage jump at capacitor 18 which in Fig.
  • capacitor 18 will have a voltage which corresponds to the ordinate of curve D at this instant and the capacitor commences to discharge at point 5.
  • This discharge after the capacitor voltage has dropped to a value corresponding to the opposing voltage of coil 16, 17, continues down to avoltage value 6 which lies as much below curve A aspoint 5 lies above this curve, when an undamped discharge is assumed.
  • the change in voltage at the capacitor is indicated in Fig. 3 by the dotted vertical line 51.
  • the first electron stream is accelerated during the interval T1 less the interval T1, that is during a time which is less than a quarter of a cycle of the energizing voltage by the amount T1, whilst the second stream already commences to be accelerated at the instant ts, thus first of all up to the maximum ultimate electron voltage which is reached at t9, whereupon a retardation occurs which only ends at the instant r10.
  • the ultimate electron voltage of the second stream is just as high as that of the first stream at the instant t4.
  • circuit according to the invention possesses the great advantage that without making any alterations to that part of it which serves to produce the expansion impulses, it is possible to have a second electron stream in the induction accelerator if desired so that the output of X-ray energy is double that of a single stream induction accelerator.
  • the initial voltage at capacitor 18 automatically adjusts itself to the correct value for any optional position of the firing point within the interval T1; for this purpose it is not necessary to understand the operating process which has been explained in detail by means of Fig. 3. It is only necessary that in the circuit shown in Fig. 4 the control voltage for the discharge gap 19 should be arranged according to Fig. 5, that is the firing point should be fixed once and for all at some instant during T1 to correspond with the desired ultimate electron voltage. The correct control for the second discharge gap 20 then adjusts itself quite automatically when the circuit in Fig. 4 is used, no adjustment depending on the selected ultimate electron voltage being necessary.
  • Fig. 11 gives a graphical representation of conditions for expansion, the same designations being used for the curves as in Figs. 2 and 3.
  • The. reference letters with a prime refer to the case of a saturated central core whilst the reference letters without a prime indicate the curves when there is no saturation, that is the curves already shown in Fig. 3 and described in detail.
  • Fig. 11 also shows that the voltage D required for igniting the second discharge gap can for instance be obtained by shifting the phase of the voltage D required for the unsaturated core, because actually only that part of the curve D is of interest where it is about to pass through zero in the rising direction.
  • the method according to the invention thus deals with producing expansion or contraction impulses for an induction accelerator with variable ultimate electron voltage and with one electron stream or two electron streams gyrating in opposite directions and employing an expansion or contraction coil which is energized by the accelerating flux of the accelerator as well as a capacitor in series with said coil and two grid-controlled discharge gaps in inverse parallel connection, and for the general case this method consists of igniting the first discharge gap periodically at an optionally adjustable instant depending on the desired ultimate voltage, whilst the second discharge gap is ignited at an instant which is about as much after the ignition point which has to be adhered to for the maximum ultimate voltage of the second electron stream as the ignition point of the first discharge gap lies in advance of the ignition point for the maximum ultimate voltage of the first electron stream.
  • an electron accelerator of the type comprising an annular tube into which streams of electrons are injected in succession for acceleration respectively in opposite directions on an orbit established within said tube, a magnetic structure including a central core portion extending through the central opening within said tube and annular control pole portions confronting one another at said tube, a main winding on said magnetic structure surrounding said control poles, and a source of alternating voltage connected cross said main winding to establish an alternating current therein producing a time varied cycle of magnetic fiux of alternating polarity, said fiux comprising a first component through said central core portion effecting acceleration of said electrons and a second component through said control poles confining the electron stream during the accelerating period to a path of travel along an orbit of substantially fixed radius; of means for effecting a change in the radius of said electron orbit to discharge each electron stream from the accelerator, said means comprising, an auxiliary winding surrounding only said central core portion and which is inductively coupled with said main coil so as to cause an alternating voltage to be induced therein, a condens
  • Apparatus for effecting a change in radius of the electron orbit as defined in claim 1 wherein the means for deriving the control voltage for the grid of said first tube is comprised of an adjustable phase transformer having its primary connected to said source of alternating voltage and said control voltage is constituted by the sum of two voltage components connected in series with the grid of said first tube and which components are derived from the secondary of said transformer, one of said components being constituted by the output of a double-wave rectifier connected to the secondary and the other of said components being constituted by a sinusoidal voltage taken from another secondary and having a phase displacement of 45 relative to said magnetic flux.
  • Apparatus for effecting a change in radius of the electron orbit as defined in claim 1 wherein the means for deriving the control voltage for the grid of said second tube is constituted by the sum of three voltage components connected in series with the grid of said second tube, one of said components being the voltage of said condenser, a second component being a sinusoidal voltage derived from the source of said alternating voltage and having a phase displacement of 45 relative to said magnetic fiux, and a third component of the same frequency as said second component also derived from said source of alternating voltage, said third component being negative between O and 270 of the cycle of the magnetic flux and cut oii during the positive portion thereof between 270 and 0.
  • Apparatus for effecting a change in radius of the electron orbit as defined in claim 5 wherein said second component of said control voltage for the grid of said second tube is produced in the secondary of a transformer whose primary winding is connected to said source of alternating voltage through phase displacement means, and wherein said third component of said control voltage for the grid of said second tube is constituted by the out- 1 1 putof'a second transformer secondary having a series arranged half wave rectifier and a source of unidirectional voltage connected across said second secondary, said second secondary being energized from a primary winding connected to said source of alternating voltage through 5 phase displacement means.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Particle Accelerators (AREA)
US295852A 1951-06-29 1952-06-27 Magnetic induction accelerator Expired - Lifetime US2754419A (en)

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CH709390X 1951-06-29

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CH (1) CH293279A (xx)
FR (1) FR1063237A (xx)
GB (1) GB709390A (xx)
NL (1) NL87569C (xx)

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2797322A (en) * 1952-08-19 1957-06-25 Bbc Brown Boveri & Cie Magnetic induction electron accelerator
US2819393A (en) * 1952-04-03 1958-01-07 Bbc Brown Boveri & Cie Magnetic induction type electron accelerator
US3090921A (en) * 1958-11-10 1963-05-21 Gen Precision Inc Microwave pulsing circuit
EP0481865A1 (en) * 1990-10-16 1992-04-22 Schlumberger Limited Circular induction accelerator for borehole logging
US20070182498A1 (en) * 2006-02-06 2007-08-09 Mitsubishi Electric Corporation Electromagnetic wave generating device
CN101530003B (zh) * 2006-10-28 2011-08-03 史密斯海曼有限公司 具有可变的轨道半径的电子回旋加速器
CN101530002B (zh) * 2006-10-28 2011-08-03 史密斯海曼有限公司 具有可取出的加速器模块的电子感应加速器

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102006050953A1 (de) * 2006-10-28 2008-04-30 Smiths Heimann Gmbh Betatron mit Contraction- und Expansion-Spule

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2394072A (en) * 1943-09-10 1946-02-05 Gen Electric Electron accelerator control system
US2480169A (en) * 1946-10-26 1949-08-30 Gen Electric Apparatus for imparting high energy to charged particles
US2535710A (en) * 1942-06-17 1950-12-26 Gen Electric Controller for magnetic induction accelerators
US2538718A (en) * 1946-08-06 1951-01-16 Bbc Brown Boveri & Cie Magnetic induction device for accelerating electrons
US2654838A (en) * 1947-09-06 1953-10-06 Bbc Brown Boveri & Cie Impulse circuit

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2535710A (en) * 1942-06-17 1950-12-26 Gen Electric Controller for magnetic induction accelerators
US2394072A (en) * 1943-09-10 1946-02-05 Gen Electric Electron accelerator control system
US2538718A (en) * 1946-08-06 1951-01-16 Bbc Brown Boveri & Cie Magnetic induction device for accelerating electrons
US2480169A (en) * 1946-10-26 1949-08-30 Gen Electric Apparatus for imparting high energy to charged particles
US2654838A (en) * 1947-09-06 1953-10-06 Bbc Brown Boveri & Cie Impulse circuit

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2819393A (en) * 1952-04-03 1958-01-07 Bbc Brown Boveri & Cie Magnetic induction type electron accelerator
US2797322A (en) * 1952-08-19 1957-06-25 Bbc Brown Boveri & Cie Magnetic induction electron accelerator
US3090921A (en) * 1958-11-10 1963-05-21 Gen Precision Inc Microwave pulsing circuit
EP0481865A1 (en) * 1990-10-16 1992-04-22 Schlumberger Limited Circular induction accelerator for borehole logging
US20070182498A1 (en) * 2006-02-06 2007-08-09 Mitsubishi Electric Corporation Electromagnetic wave generating device
US7619375B2 (en) * 2006-02-06 2009-11-17 Mitsubishi Electric Corporation Electromagnetic wave generating device
CN101530003B (zh) * 2006-10-28 2011-08-03 史密斯海曼有限公司 具有可变的轨道半径的电子回旋加速器
CN101530002B (zh) * 2006-10-28 2011-08-03 史密斯海曼有限公司 具有可取出的加速器模块的电子感应加速器

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FR1063237A (fr) 1954-04-30
NL87569C (xx)
GB709390A (en) 1954-05-19
CH293279A (de) 1953-09-15

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