US2658999A - Bevatron acceleration regulation - Google Patents

Description

NOV. 10, 1953 FARLY 2,658,999

BEVATRON ACCELERATION REGULATION Filed Jan. 5, 1951 2 Sheets-Sheet 1 CYGLOTRON ACCELERATING VOLTAGE SOURCE AND REGULATOR CURRENT SOURCE MAGNET CURRENT SOURCE INVENTOR. GEORGE M. FARLY Law/4M ATTOR/VE).

Nov. 10, 1953 Filed Jan. 5, 1951 MAGNET CURRENT CURRENT SOURCE G. M. FARLY 2,658,999

.BEVATRON ACCELERATION REGULATION 2 Sheets-Sheet 2 MULTI- VIBRATOR I m I DISCRIMINATOR 27 CURRENT REGULATOR AMPLIFIER AND MIXER i H l l I INVENTOR. T T T3 T4 GEORGE M. FAELY TIME BY ATTOR/VE).

Patented Nov. 10, 1953 UNITEB STATES PATENT QFHQE BEVATRON ACCELERATION REGULATION Application January 5, 1951, Serial No. 204,616

8 Claims. 1

The present invention relates generally to an electronic frequency control system and in more particular to the control of the accelerating vol"- age in a particle accelerator.

Modern emphasis upon nuclear research has directed a large amount of effort to the development and improvement of particle accelerators. The need is for higher energy particles with which to carry out bombardment experiments and conventional limitations upon maximum energies'that may be imparted to free subatomic particles has constituted an obstacle of no mean proportions. While numerous highly successful particle accelerators have been developed, as for example cyclotronsand synchrotrons, theneed still remains for apparatus capable ofimparting even greater energiesfto particles.- One recent development'in'this' field is an apparatuscalled a bevatron and disclosed in the copending applicationof W. M; Brobeck 'et al., 'Serial No. 196,048, filed November 16; 1950 an .abstra'ctof which was publishedv January 30,1951, in the Ofiicial Gazette of the United States Patent Office, I

6420. G. 1480. As will be' appreciated from a reference to this 'application,l the mode of "ac celeration requires a precise control of the acceleratin'gvoltage which is even more exact than in conventional,accelerators.. The present vention is adapted'to provide the requisite ac curacyjjof controlpf theac'celerating voltage of a particle accelerator of the bevatron type'and does 'so by "the "accomplishment of the following objects.

It is an object of the present invention to pro-1 vide an improved method and means for co 3 trolling the accelerating voltage of a particle accelerator.

lItf is' anther object of thefpresent invention" to provide. an improved method and means of frequency 'inodulating the accelerating. voltage of a particle acceleratorpf It is anotherobject or the resent invention to provide an" improved method and means for initiating and terminating the application of an accelerating potential in a particle accelerator.

Many. other objects and'advantages of .the

present inventionwill become apparent to those skilledin the art from the following descri'ption taken together ,with the attached drawings,

wherein Figure l with associated equipment including the present invention;

.Fig. Zshows present invention in block form; and

shows a bevatron particle accelerator one preferred embodiment of the;

Fig. 3 shows a typical magnet field pulse as employed in a bevatron and having indicia thereon referenced to periods during one cycle of bevatron operation.

Considering first a particle accelerator with which the present invention may be advantageously associated, reference is made to Fig. 1 wherein there is shown a bevatron as an example of such an accelerator. As shown in Fig. l the bevatron includes four arc uate electromagnet sections H, which are hollow and encompass arcuate tubular elements I2. 'Magnet sections H are arranged in a roughly circular fashion with straight-tubular sections [3, l4, l5, and I6 interposed one between each magnet section and connected to the tubuIarelements IZ at each end thereofto forma continuous chamber ll. Electromagnet sections II are wound in such a manner that upon. energization they produce magnetic flux in a direction normal to the plane of Fig. 1 and consideration of bevatron theory shows that the electrical "geometry of thebevatron is notaffected by straight sections l3-l6. These sections are inserted in order to provide access to. theinterior of chamber ll without interference withthe magnetv structure and vacuum pumpsv l8 are connected to sections ill-l6 forthe purpose of establishing and maintaining a 'highivacuum in chamber l1. Also connected to chamber IT is an injector mechanismflQ which may'consi's't of asmall cyclotron 2| having deflecting means 22 leading therefrom into straight section l3; anoutlet port 23 which may be, insertedvin section !4; and as shown in Fig.2 acceleratingmeans' 2a which may be mounted within'section [6. f

I Alsoincludedin the composition of a complete bevatroni's' a. magnet current source 2E5 which may "be connected through electrical leads and 2 8 to they windings of electromagnet sections H. Current source 26 must provide'a very large amount -of pulsed current, in order to produce befreceived ,as well as, transmitted, all of which is explained in more detail below. An accelerating voltage source and regulator 29 is also provided for the energization'of accelerating means i 3 andin connection therewith there is included a current source 3|. Voltage source 29 is inter-.

connected with the windings of electromagnet sections H, bymeans of a low resistance shunt 32 inserted in series in one of the electromagnet connected externally to shunt 32, lead to an amplifier it! which amplifies the voltage signal produced across shunt 32. In addition, amplifier Hll contains a mixer circuit noted more" detail below. The amplified signal from shunt 32 is fed into a current regulator :02 which may in part comprise a losser tube connected in series between external current source 3| and control windings it's of a saturable reactor HM.- Of course the mode of current regulation is not critical and numerous arrangements may be employed to regulate the magnitude of the direct current voltage a-pplied to windings Hi3. Saturable reactor tilt is employed as a variable inductance controlled by the magnitude of the direct current voltage applied to the control windings I03 thereof. In composition, saturable reactor EM may consist of conventional apparatus or may include a core 86 of ferromagnetic non-metal having control windings I03 and impedance windings I07 which may be separate as shown or may alternatively be combined into a single winding in the manner disclosed in the copending application of Robert L. Anderson, Jr., Serial No. 191,304, filed October 1950. It is desirable to prevent feedback of high frequency signals into the direct current control equipment and this may be accomplished by employing two balanced control windings connected to cancel out voltages induced therein or, inthe case of single winding saturable reactors may be accomplished by employing two reactors, with the direct current connections being reversed so that cancellation of induced voltages therein is effected. Impedance windings [ill of reactor H3 5 have a capacitance 1'08 connected in shunt therewith to form the tank circuit of an oscillator tube Hi9; which has its anode connected through a capacitance- I H to one side of the tank circuit and its cathode to the other; Oscillator tube I09 is controlled by a multivibrator H2 whose output is impressed upon the control grid of; tube HIS and which in turn obtains control signals from above noted peaking'strip's 3S and 31 through terminals 38 and 39', respectivelyv Grid excitation for oscillator tube I09 is obtained from a feedback coil H3 con nected to one end of saturabl'e reactor winding i0! and through a capacitance to a grid of tube 109; Plate supply for tube I09 may be provided either, by an internal or external power supply, the details of which are of no importance and which is consequently indicated only as a on Fig, 2'. The output of theoscillatoriSapplied via a feed throughinsulator to the accelerating electrode 2c in bevatron section [6". There is further provided a discriminator circuit H4 which has an input lead connected to a' tap on the im-- pedance winding fill of saturable'reactor' Hi l and which applies a signal'to'the mixer circuit of amplifier H! l Rather than further described thecompo'nents of the accelerating voltage regulator'by recitation as above, consideration will now be given to the operation of the invention; together with general bevatron operation as pertinent, and therein further defining the composition and function oi the composite elements. In conjunction with the description of operation, reference is made to Fig. 3 showing a typical bevatron magnet current pulse and including time indicia corresponding to changes between individual phases of operation within one cycle of operation of a bevatron.

In operation of a bevatron the chamber l1 thereof is evacuated by means of vacuum: pumps l 8 and all included power supplies are energized. Energization of the electromagnet sections II is then initiated by switchgear integral with magnet current source 26. At this time (T1) no parti'cle injection is taking place and no accelerating voltage is applied. After a short interval, during which the magnet field increases from zero to some small desired: intensity, particle injection is commenced from cyclotron 2| through deflector 22 or by other suitable means. At the same time (T2) accelerating voltage is applied to accelerating means 24 as described in more detail below. Particle injection continues for only a relatively short period from T2 to'Ta; however, acceleration of the injected particles continues for the reater part of the periodduring which the magnetic field is increasing, Ta-T4 on Fig. 3. This accelerating voltage is regulated in relation to the mag.- netic field strength by accelerating voltage source and regulator 29 to maintain the mean particle orbit within chamber i1 and upon termination of acceleration (T4) a further increase in magnetic field reduces the radius of the particle orbit so that the particles bombard a target, not shown, which may be mounted upon the inner wall of one of the tubular members 12" in line outlet port 23 whereby high energy neutrons passthere through. The magnet current thereupon is decreased and the energy stored within the magnet windings may be advantageously returned to the magnet current source and stored. therein by means such as a flywheel; the magnet current and magnet field reducing thereby to zero and completing. one cycle of bevatron operation. It will be appreciated that variations in the operating cycles may be employed, as for example retarding the application of accelerating" voltage until the cessation of particle injection; how'- ever, the choice of same is" dependent upon design considerations unrelated to the present invention and are therefore only noted herein.

The present invention accomplishes control of" the initiation and cessation of the application of acceleratingvoltage by means of signals obtained from the magnet field current rather than by" direct time control. The more obvious method wherein phases of operation are referenced to a time base is limited by the difiiculty in precisely regulating the magnet field pulses because of their extreme magnitude, and the present system' is advantageous in controlling accelerating voltage in accordance with the actual disposition of the particles as determined by the magnetic field rather than by the calculated disposition of the particles based upon a time-field relationship which is in fact variable: The control signals in the present embodiment are obtained from magnetic peaking strips 36 and 31', one of which, for example strip 35", is designed to saturate at a magnet field strength corresponding to the magnet field current at T2 on Fig. 3 and to thereby provide a voltage pulse across terminals 38, and the other strip 3'! is designed to saturate at a much higher magnet field strength corresponding to the magnet field current at T4 on Fig. 3, thereby providing a second voltage pulse which appears across terminals 39-. As

shown in Fig. 2, terminals 38 and 39 are both connected to multivibrator H2 which may constitute a conventional one shot multivibrator operating upon a single pulse to initiate operation and a single pulse to cease operation. Oscillator tube I09 is biased to cutoff by appropriate potentials applied thereto and thus the oscillator has no output until the signal from peaking strip 35 causes multivibrator H2 to operate and thereby apply a signal to the gridof oscillator tube I9!) which initiates operation of the oscillator (T2 on Fig. 3). Oscillator operation continues until the magnet field current reaches some predetermined value (T4 on Fig. 3), at which time peaking strip 3'! applies a second signal to multivibrator H2 which turns it oh, thereby returning oscillator tube I09 to a non-conducting state and ceasing the operation of the oscillator. During this period, T2 to T4, accelerating electrode 25 is energized by the oscillator output.

In addition to the above-noted control of the portion of the magnet field cycle during which particles are accelerated it is further necessary to regulate the application of the accelerating voltage in such a manner that the particles are in fact accelerated rather than decelerated as would result from an improper phasing of the accelerating voltage. As the particles travel about their orbit with increasing velocity theyiapproach any particular-point, such as the point ofaccel eration, at increasingly shorter-intervals oftim'c and the accelerating voltage .must be pulsed at thev proper time to attract theparticles so. approaching Proper timing of. the accelerating voltage pulses is accomplished :by frequency modulation of the accelerating .voltageandthis, too,

is based upon the instantaneousmagnet field current rather than upon. a time relationshipxwhich is susceptible to variations as :noted above. I The low resistance shunt 32 providesavoltage signal. proportional to the magnet current and this sig=.

nal is impressed across terminals 33 of amplifier Hit, The strength of. this-signal is increased-by amplifier it! which applies theamplifiedsignal to the control circuit of .current'regulator 102, whiehin turn regulates, the" output of :current supply 3! in accordance with the applied signal; This regulated current. from power supply 3| is applied to thedirect current windings 1030f sat urable reactor 104 and by'varying' the saturationof the'core Hi6 thereof consequently controls the. impedance of the alternatingcurrent windings H31. As windings lfl'l of saturable reactor! 94 are. connected together with, capacitor. J08 to form thetankcircuit of oscillator tube we there. is

formed in efiect an oscillator having a variableinductance and whose frequency of oscillation is controlled by the current-applied to the direct current windings Hi3 of saturable. reactor Hi4.-

As the inductance in the tank circuit of. the oscillator is controlledby the magnetv field current,

the frequency of the accelerating voltage output of the oscillator is thereby modulated in accordance with the magnet field current.

The above frequency modulation system relates the accelerating voltage to the magnet field strength by way of the magnet field current; however, it will be appreciatedthat the relation-' ship obtained by directcontrolof. 'the frequency with the magnet current may not be-the one desired for the particular bevatron operation can: templated.- For example, a'linear relationship.- between the magnet current and the frequency, of the acceleration voltage may beads-sired, while the saturation characteristics of reactor 16 may well produce some other relationship. Thus modification of the frequency control as described above is ordinarily necessary, and this may be accomplished either by utilizing a specially designed saturable reactor having the requisite saturation characteristics or by introducing a correction signal into the system to compensate for the deviation from the desired relationship. The illustrated embodiment of the invention employs the latter of the two above suggested alternatives in preference to the complexities of reactor design necessitated by the first, and further in view of the flexibility afforded by systems competent to introduce corrective signals. As shown in Fig. 2, a discriminator H4 is employed for the purpose of supplying a corrective feedback signal. The discriminator input signal is obtained from the tank circuit of oscillator tube I09 by means of connection to a low voltage tap on the impedance winding l 0'! of reactor I04 and the discriminator output signal is-applied to a mixer circuit in amplifier It! wherein it is algebraically added to the original control signal from shunt 32 in magnet winding lead 21. The amplified control signal applied to current regulator m2 is thus compensated so that the saturating current of reactor !94 produces the requisite inductance varia tion in the tank circuit of the oscillator and the frequency'of the accelerating voltage therefrom has the desired relation to the magnet'field. The discriminator circuit may be designed ma conventional manner well known to those skilled in" the art although it, like the other'conv'e'ntional circuits shown in block form, may alternatively be particularly designed for specific results required in an individual'a'pplication.

From the foregoing it isbelieved evident that the present invention is capable of providing ra cise accelerating voltage controlfor a device such as a bevatron, and that the system employed for accomplishing this result is freefrom the diflicul v ties and errors either inherent to or introduced into conventional regulating means employedin'. such as capacity as the present invention. While the invention has been disclosedwith 'resp e'ct to but a'single preferred embodiment; it will be ap parent to those skilled in the art that numerous variations and modifications may be made with-;.

in thespirit andscope of the invention amine; it is not intended to limit the inventiomexcept defined in the following claims.

, What is claimed is:

variable inductance in the tank circuitthereof; means connectedinto said electrical conductors for developing a voltage proportional to current.

flow therethrougn and control means connected between said last-named means and said variab1e-- inductance whereby; the frequencyv :of said.oscil-.

-la-tor is varied in accordance with the value-of the magnet current. c

2. In. combination witha bevatron having mag-z net windingsenergized through electrical conductors and electrostatic particle accelerating means, a an improved control system including an oscillator having a tank :circuit .with 'a variable inductance therein and. impressing the output-v voltage thereof upon said accelerating mean's'i'in ductance control means associated with-said variable inductance and controlling the fre aecegeec quency :of said oscillator by controlling the inductance of the tank circuit -thereof, aresistance shunt'c'onnected in series with one of said ma net winding conductors, and electrical connections impressing the voltage signal across said shunt upon said inductance control means whereby the frequency of the voltage impressed upon said accelerating means is controlled by the-current through the-conductors to said ma net windings.

3. In combination with a bevatron having a magnetic field established by electromagnet windings energized through electrical conductors from a current source and electrostatic particle accelerating means, the improvement comprising an accelerating voltage frequency control system including an oscillator circuit electrically connected to said accelerating means for impressing an accelerating voltage thereon, said oscillator circuit including an oscillator tube having a control electrode and an associated tank circuit having a variable inductance therein for varying the frequency of the oscillations, inductance control means having an input circuit including a resistance shunt connected in series with one of said electromagnet conductors and controlling said variable inductance in said oscillator tank. circuit to control the frequency of the voltage impressed upon said particle accelerating means in accordance with the current flow to said electromagnet, and a pair of current responsive means associated with said electromagnet conductors and connected to said oscillator tube control electrode to initiate and cease operation of said oscillator in accordance with the magnitude of current flow to said electromagnet.

, 4. In combination with a bevatron having an evacuated chamber within the poles of an electrom'agnet having windings energized from a current source and particle injection and accelertion means, the improvement comprising an accelerating voltage frequency control system connected to said particle accelerating means and including an oscillator circuit having an oscillator tube with a control electrode "and a tank circuit comprising a capacitor and inductor, said inductor having inductance windings and control windings wound about a magnetic core, current supply means connected to and energizing the control windings *of said inductor, a resistance shunt connected in series with said electromagnet windings, and electronic control means connected across said shunt and to said current supply means to vary the current to'said inductor control windings as a function of the current to said :electromagnet windings whereby the in-' controlwinding and an effective inductance pro- 7 portional to the current through said control winding, and current supply means producing a current proportional to the current through said electromagnet and connected to said inductor 8 control winding whereby the effective inductance thereof and consequently the frequency of said oscillator voltage is varied in proportion to said electromagnet current.

6. An accelerating voltage :control system for a bevatron having an accelerating electrode and magnet windings energized from a current source through conductors and comprising an oscillator vacuum tube having an anode, cathode, and controi' electrode with the anode thereof connected to the accelerating electroderof said bevatron, a saturable reactor having control and induction windings, a capacitor connected across said induction windings and between the anode and cathode of said vacuum tube to define a tank circuit "therefor, a current source, a current regulator connected between said current source and the control windings of said saturable reactor, a resistance shunt connected in series with a magnet winding "conductor and to said current regulator to impress thereon a voltage proportional to the mag-net winding current, whereby the current to said saturabl'e reactor control windings and thus the inductance of said inductance windings is varied in "accordance with the magnet winding current to control the oscillator tube frequency, a multivibrator connected to the control electrode of said oscillator vacuum tube, and a pair of peaking strips disposed adjacent the magnet winding conductor and connected to said multivibrator to initiate and cease operation of said multivibrator and attached oscillator vacuum tube at predetermined values of magnet winding current.

7. An accelerating voltage control system for a b'evatr'on having magnet windings energized through conductors to establish a magnetic field and an accelerating electrode for imparting en'- ergy to particles traveling in said magnetic field, said accelerating voltage control system comprising an ocsillator circuit including an oscillator vacuumtube having a control electrode and a tank circuit including a saturable reactor having control and inductance windings, means connecting said oscillator circuit to said bevatron accelerating electrode to energize same, a current source, a current regulator connecting said current source to the control windings of said saturable reactor, an amplifier and mixer circuit connected to said current regulator and impressing a control signal thereon, a resistance connected .in a magnet winding conductor and being connected to said amplifier and mixer circuit to impress thereon a voltage proportional to, the magnet winding current, a discriminator circuit connected between said amplifier and mixer circuit and a point on the inductance winding of said saturable reactor whereby the current to said s'aturable reactor control windings and thus the frequency of said oscillator circuit is controlled in accordance with the magnet winding current as modified by said discriminator circuit signal.

8. An accelerating voltage control system as claimed in claim 10 further defined by a first magnetic peaking strip which is satura ble at a predetermined low magnet field strength, a sec-- ond magnetic peaking strip which is saturable at a predetermined high magnetic field strength, said first and second peaking strips being disposed adjacent the magnet Winding conductor having said resistance shunt connected therein, a multivibrator circuit having an output circuit connected to the control electrode of said oscillator tube to energize :same and an input cir- 9 10 cuit connected across said peaxmg strips where- Number Name Date by initiation and cessation of operation of said 2,407,270 Harrison Sept. 10 1946 oscillator circuit is controlled in accordance with 2,489,082 De Forest Nov. 22, 1949 the magnitude of magnet winding current. 2,495,634 Hepp Jan. 24, 1950 GEORGE FARLY' 5 OTHER REFERENCES References Cited in the file of this patent Brubeck et 21., abstract of application Serial Number Name Date 10 I 2,291,715 Hepp Aug. 4, 1942

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