US2745018A - Beam current regulator - Google Patents

Description

May 8, 1956 w. R. BAKER ET AL 2,745,018

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BEAM CURRENT REGULATOR Filed Sept. 26, 1947 4 Sheets-Sheet 5 i l 3 POWER g. SUPPLY AA0/0- a RADIO- FREQUENCY o-GC-o FREQUENCY REcE/VEP TRANSM/ITEP APc SUPPLY F/LAME/VT SUPPLY HEATER SUPPLY REGULATOR \.-.2 O VOLTAGE 7 o Real/mm o 26 7 POWER /NvEN7'0Ps MLL/AM A? BAKER Supp 1: 5 hosL-Pr DE L/BA/V A rToPA/Ev May 8, 1956 w. R. BAKER ET AL 2,745,018

BEAM CURRENT REGULATOR Filed Sept. 26, 1947 4 Sheets-Sheet 4 //\/l EN7'0R$ MAL/AM A. BAKER Poss/P7- DE L/BAN A TTORNE Y United States Patent BEAM CURRENT REGULATOR William R. Baker and Robert De Liban, Berkeley, Calif., assignors to the United States of America as represented by the United States Atomic Energy Commission Application September 26, 1947, Serial No. 776,222 7 Claims. Cl. 250-419 The following invention relates to calutrons and more particularly to an apparatus for automatically regulating the ion beam in a calutron.

Calutrons are described in general in Atomic Energy for Military Purposes by H. D. Smyth, and in great detail in the copending application of Ernest 0. Lawrence, Serial No. 557,784, filed October 9, 1944, now Patent No. 2,709,222, issued May 24, 1955. Y

Calutrons have been principally employed, though not exclusively, in separating the isotopes of uranium for militaryatomic energy purposes. sideration of the principles .of operation of the device that the calutron as herein set forth, is readily adapted to the separation of isotopes of most of the elements.

In general, .an ion source projects the ions of a polyiso-- topic source material into a transverse magnetic field, the

- ions of greater mass describing curved paths with greater radii of curvature than the ions of lighter mass.

Ion collecting electrodes or pockets are disposed at suitable points along each. path, preferably at the 180 point in the arcuate travel, to collect and discharge the ions. In this manner the atoms of different masses that were originally in a polyisotopic mixture are distributed in diiferent regions and are substantially separated from each other.

Since both the accelerating potentialand the magnetic field are factors in determining the path of the beam, it is possible to regulate one of these factors to compensate for variation in the other. i

In practice it has been found thatcomplete resolution of the beam paths becomes increasingly diflicult as ions of heavier mass numbers are separated. As these heavier substances are treated the ions in the beam are not. entirely separated into distinct'paths but are directed toward the collector pocket so as to achieve, on the average,

a maximum separation or a minimum degree of con- Consider, for example, the separation of the isotopes of uranium having mass numbers'238 and 235 of which the isotope of mass number 238 is in greater abundance by a factor of approximately 140 to 1. In this separation, which is typical, the peak of the distribution of the U is obscured by the distribution of the more abundant. U so that no discrete peak in the beam is present. at

the collector pocket for U In operating a calutron it is necessary for optimum performance, to maintain the collecting electrodes at an unchanging low potential. It is also important in the successful-operation of a calutron that the accelerating voltage applied between the arc block and the accelerating electrodes be maintained constant for proper focus of the calutron beam in the collector pockets, since any change in this accelerating voltage will be effective in moving It is obvious from a conof the col' 2,745,018 Patented May 8', 1956 the beam across the collector pocket, resulting in con tamination of the concentrates of the isotopes. However, maintaining the accelerating voltage constant is not sufficient in itself since variation in the intensity of the magnetic field will result in changes in the beam position.

Regulating the accelerating potential by conventional electronic means proves to be relatively simple, but it is a more complicated problem to maintain an absolutely constant magnetic field, particularly over a period of several hours. Thus it will be seen that in order to provide thoroughly satisfactory calutron operation it is necessary to overcome any wandering or shifting of the beam position with respect to the collector elements whether from changes in the ion accelerating potential-or from alterations in magnetic field. Further, it is necessary to maintain the beam constant at a position so oriented with respect to the collector elements that a lesser: isotope which produces no discrete peak in beam density is nevertheless directed toward the appropriate collector element.

It is'therefore an object of this invention to stabiliz the beam in a calutron.

- It is a further object of this invention to provide an apparatus for reguating the ion beam in a calutron.

. Another object of this invention is to provide an apparatus for automatically adjusting the accelerating volt- It is another object of this invention to provide a beam regulator for a calutron which does not materially affect the potential of the ion collecting electrodes.

Other objects and advantages of the invention will be apparent to those skilled in the art to which it pertains by reference to the following specification and drawings which illustrate the invention and certain preferred embodiments thereof and wherein Figure l is a block diagram of a calutron system in combination with the preferred embodiment of the invention;

"Fig. 2 is a schematic diagram of the basic circuit in cornbination'with a typical amplifier;

Fig. '3 is a block diagram of a further embodiment of the basic circuit for coupling by a radio frequency link to the high potential end of the accelerating potential;

Fig. 4 is a schematic diagram of a suitable radio frequency link. I

Turningnow to Fig. l, a calutron is shown in part, the basic elementsof which will be seen to consist of a tank 10 comprising upstanding wall members disposed between the pole faces '11 of the magnet and effecting a closed chamber in which a vacuum is maintained.

The ion source 12 is a conventional filament arc type comprising a charge reservoir-13 and an ionization chamber .14. Within the charge reservoir is a heater 16 while "within the ionization chamber are located the arc block 1'] and afilament 18.

The accelerating potential is supplied by a conventional power supply .26 and series regulator circuit 27, which develops a voltage across a bleeder resistor 28 having two intermediate tap positions 29 and 31. Any variation the bleeder to counteract the change. The total voltage is thus regulated to a constant value aside from changes 3 introduced between the tap 31 and the negative end of the bleeder.

Accelerating electrodes 19 are shown adjacent the ion exit slit 21 formed in the wall of the ionization chamber. The ion accelerating potential is applied between the accelerating electrodes 19 which are negative and the arc block 1 7 which is positive. The ions in the beam follow the paths defined by the position of the dashed lines 22. Collector electrodes 23 and 24 are suitably oriented as shown in this illustrationto collect and discharge the ions of two of the constituent isotopes.

In. the preferred embodiment of the invention the total voltage is in fact altered by the insertion of a voltage, from an external source, comprising a beam regulator' 32 and amplifier 33, said device introducing a voltage into theportion of the bleeder resistor mentioned above.

The input of the beam regulator 32 is connected between one of the collector pockets 24 which receives one of the less abundant isotopes of the treated substance and. the negative or grounded end of the bleeder resistor. The output therefrom is increased by the amplifier 33 which. delivers its output voltage across the bleeder between tap 31 and the negative or grounded end. The voltage produced across this portion of the bleeder is a function of the current due to the ion beam striking the collector 24.

Should the total accelerating voltage increase, the beam describes a path of lesser curvature, and the current to the collector decreases. Similarly, if the magnetic field intensity diminishes the same. change of the ion beam curvature results. In either case the beam regulator responds with an insertion voltage which decreases the total applied accelerating potential which stabilizes the beam at, or very near, its original position. In short, the regulator maintains a particular and predetermined current flow at the monitored collector pocket, i. e., pocket 24.

The circuit attaining these results and certain other of theobjects of the invention is shown in schematic form in Fig. 2.

The voltages needed for bias, plate and screen grid potentials are developed by a conventional full wave rectifier which includes transformer 34, rectifier tube 36, filter condensers 37, 39 and 42, choke 38 and resistor 41. A voltage dividing network is provided which includes resistors 43, 44, 46, 47 and 48 and. gaseous voltage regulator tubes 49, 51 and 52.

The beam collector pocket 24 is connected to the control grid of the first amplifying stage comprising pentode 53, by means of a resistor 54 which together with condenser 56 forms an integrating network. It should be noted that the grid bias resistor 55 of this stage is also the cathode bias resistor of a second stage comprising pentode 57. The plate of pentode 53 is direct coupled to the control grid of pentode 57 through resistor 58, while plate voltage is supplied through resistor 59 and bias voltage for pentode 57 is supplied from the power supply via resistor 61. Screen grid potential is obtained from the junction of resistors 43 and 44 connected across the power supply.

The output of the second pentode 57 is obtained at the junction of resistors 62 and 63. Screen grid potential is supplied directly from the power supply while plate potential is supplied through load resistor 64. Resistor 63 provides coupling to the succeeding circuits While resistor 62 determines the bias potential of a succeeding stage.

Output terminal 67 of the beam regulator is shown in 2 connected to input terminal 68 and through a limiting resistor 66 to a conventional two stage direct coupled amplifier having a pentode 69 as the first stage'driving a triode power amplifier 71. The coupling and biasing network comprises resistors 72, 73 and 74.

In operation a predetermined current flows to the collector pocket 24 resulting in a particular grid potential at pentode 53. Any variation in the beam position re- 4 sults in a change in this current which causes a change in the potential applied to the gridof pentode 53. Minor transient variations are eliminated by the integrating circuit but all enduring variations produce their effect.

For purposes of illustration the separation of U ions from U ions will be considered. If, for example, the beam is curved more sharply, the current increases as the portion of the beam consisting predominantly of U ions falls upon the U pocket causing an increased voltage drop across resistor which is communicated to the control grid of pentode 53 via the integrating circuit. Pentode 53 is thus biased more positively causing an increased plate current to flow. The fall in potential at the plate due to this increased current is communicated to the control grid of the second pentode 57 wherein the plate current is reduced accordingly. Since the plate current of this second pentode passes through the resistor 55, the change being in opposition to the original change in current, tends to' maintain the potential of the input at a constant potential which is desirable for successful calutron operation.

The plate of the output triode amplifier 71 is connected to the aforementioned tap 31 on the bleeder resistor 28 as shown in Fig. 1. Positive plate potential is thus applied to triode 71 and the output voltage changes are injected into the portion of the bleeder between tap 31 and the negative end.

In the example of beam deflection cited, the grid of pentode 53 was driven more positive, resulting in an increased plate current. This caused a reduction in the voltage applied to the grid of pentode 57 and a consequent decrease in plate current therein. Thus the grid of the driver amplifier 69 was made more positive and in turn the grid of the output stage becomes more negative so that a decreased plate current flowed in the output stage.

It will be recalled that the original beam variation was brought about by a more sharply curved beam which is caused by a lowered accelerating potential or a strengthened magnetic field. In either case the reduced plate current in the output triode 71 results in a correction of this beam variation since the accelerating potential is increased.

Following a similar line of reasoning it can be shown that in this example for the separation of isotopes of uranium, a deflection of the beam toward a less curved path will cause a decreased collector current and an increased plate current in the final triode amplifier stage. Here again the change in accelerating potential will be such as to restore the beam to its normal position.

It should be further noted that in either case the potential of the collector pocket is virtually unchanged because of the compensating change in current from pentode 57 passing through the grid resistor 55.

In a further application of this regulating principle the conventional amplifier is discarded in favor of a radio frequency transmission link'as shown in Fig. 3.

Here the output of the beam regulator of Fig. 2 is connected to an oscillator circuit so that a radio frequency signal is modulated in amplitude by changes in output voltage.

Coupled loosely to the oscillating circuit, but well insulated therefrom is a rectifying or demodulating circuitthe output of which is connected to a portion of the bleeder resistor 28 between a tap 72 and the positive end.

It is to be noted that this portion of the bleeder resistor is a part of the bleeder from which the voltage regulator is operated. Because of this fact, voltages introduced by the beam regulator into this portion of the circuit cause'a much greater changein the total accelerating voltage because of the amplifyin'gaction of the regulator.

Aradiofrequency link isemployed to inject the output fromthe beam'regulator into the bleeder resistor circuit because of the very high D. '0 potential difference between the two points. The voltage regulator 27 is noroperated at the potential of the positive end of the in Fig. 4. The oscillator circuit employs a multielement vacuum tube 73 in a modified Colpitts circuit comprising a tuning capacity 74, inductances 75 and 76, and coupling link 77. Additional elements consist of a blocking condenser 78, by-pass condenser 79, grid bias resistor 81, screen grid dropping resistor 82, and by-pass condenser 83.

The output from the beam regulator is connected to the second control grid which serves as a modulating element for altering the amplitude of the oscillations produced by the circuit.

The demodulating network consists essentially of a tuned circuit and a full wave rectifier. The tuned circuit comprises inductances 84 and 86, link 85 and condenser 87. The rectifier, a double diode is shown at 88 having connections to a filament supply transformer 89. The rectified output of the signal is developed between the cathode of rectifier 88 and the juncture of inductance 84 and link 85, and depends for its magnitude upon the amplitude of the radio frequency signal transmitted. An adjustable resistance 91 is provided across the output to alter the sensitivity of response.

As in the preferred embodiment a deflection in the position of the beam which results in an increased flow of current causes a more positive voltage to be developed at the plate of pentode 57 of Fig. 2. In this particular embodiment of the invention the positive potential communicated to the second and modulating grid of the oscillator 73 of Fig. 4 whereby the amplitude of oscillation is increased.

Since the radio frequency energy is transmitted to the demodulator by means of the links 77 and 35, a larger voltage is produced across resistor 91. As shown in Fig. 3 this voltage is injected into the total accelerating potential between the positive end and tap 29, which is the regulating portion of the bleeder, in opposition to the supply voltage. That is, the negative terminal of the rectifier R. F. signal is connected to the positive end of the bleeder while the positive end of the rectified signal is connected to the tap 72. Thus the voltage regulator 27 responds to a reduced input voltage by decreasing its series resistance which results in an increased total accelerating potential. The beam is accordingly directed to an arc of greater radius of curvature which restores it to the original position wih respect to the collector.

While it is generally considered that this particular embodiment is less desirable in that additional elements of complex character are involved, in specific cases this objection may well be overcome by the added sensitivity of response which is obtained. In either of the embodiments the principles of operations have been described with respect to the separation of the isotopes of uranium in which the less abundant isotope is also the lighter in mass.

It is obvious that in many separation applications this situation may well be reversed. Consider, for example, the separation of ions of Ca from the ions of Ca in which the ions of Ca are more abundant, in natural samples, by a factor of approximately 150 to l and are also the lighter ions.

In this case and in similar appliactions, it will be necessary to alter the response produced by either em bodiment of the invention in order to provide a regulating etfect. This is required since the collecting element for C21 ions will of necessity be disposed in the more remote position with respect to the ion source, and hence any change in the accelerating field or the magnetic field which tends to increase the curvature of the beam will, in this case, decrease the current flowing to the pocket for Ca ions. It will be recalled that this change in 6 curvature causes an increase in current for the previous example cited No difliculty is incurred in altering the apparatus to overcome this problem as it is simply a matter of proper phasing of the potential injected into the total accelerating voltage. In the first or preferred embodiment a conventional phase inverting circuit involving either a triode or pentode may be employed; In the second embodiment it is only necessary to reverse the connections from the detector circuit connected to the positive end of the bleeder resistor 28 and the tap 72 of Fig. 3.

To summarize in brief, the invention consists of a beam regulator whichoperates in response to changes in the current flowing to a collector element provided for one of the less abundment isotopes in such a manner as to alter the ion accelerating voltage applied to the accelerating electrodes of the ion source so as to produce a constant and predetermined current at said collector element. For this purpose an amplifier is employed having an input which is connected to the aforementioned collector so that the current flowing to the collector to discharge the ions received therein, passes through an input resistor provided for that purpose;

A voltage drop is thus produced which varies with the aforementioned current and is amplified by suitable direct coupled amplifying circuits and injected into the supply voltage for the ion'accelerating electrodes. In order that the potential of the collector element be maintained low and of constant value, a feedback path is' provided so that the plate current of the second stage of amplification passes through the input resistor in opposition to the beam current therein. This has the result of reducing the apparent or effective impedance of the input to a very low value since a given incremental change in beam current causes very small change in voltage drop across the input terminals.

Unavoidable changes in the operating conditions of the calutron which cause the beam to be displaced from that the invention shall be limited to these embodiments and it will be further understood that various modificatrons may be made therein which fall within ,the spirit and scope of the invention as set forth in the appended claims.

What is claimed is:

. l. A beam regulator for a calutron comprising in combination a calutron having an ion generator, accelerating electrodes disposed adjacent said ion generator, a source of potential connected between said ion generator and said accelerating electrodes for producing a beam of ions, means establishing a magnetic field transverse to the direction of travel of said ion beam, current collecting elements disposed in the normal path of said beam, means responsive to the current flowing to one of said collector elements for providing a voltage proportional thereto, and means for impressing said voltage upon said accelerating electrodes for regulating the position of said beam of ions with respect to said collecting elements.

2. A beam regulator for an electromagnetic isotope separator comprising in combination, an ion generator, accelerating electrodes disposed adjacent said ion generator, a source of potential connected between said ion generator and said accelerating electrode for forming a beam of ions, a resistor connected across said power supply, a transverse magnetic field for curving said beam of ions in an arcuate path, current collecting elements disposed in the normal path of said curved beam and, means responsive to the current flowing to one of saidtcollector elements providing a potential in proportion thereto and connected across said resistor, thereby altering said accelerating potentialwhereby the path of said arcuate beam of ions is regulated with respect to said collecting elements.

3. In an apparatus for the electromagnetic separation of isotopes, the combination comprising an ion generator, accelerating electrodes disposed adjacent said ion generator, a source of potential connected between said ion generator and said accelerating electrode for forming a beam of ions, a resistor connected across said power supply, a transverse magnetic field for curving said beam of ions in an arcuate path, current collecting elements disposed in the normal path of said curved beam for separately collecting the ions of said isotopes, an impedance connected to one of said collector elements, current respon sive means connected across said impedance providing a voltage proportional to the current therethrough, and electrical connections impressing said potential upon said resistor for adjusting said accelerating potential whereby the position of said beam of ions is regulated with respect to said collector pocket.

4. In a calutron having an ion source, ion accelerating electrodes, means establishing a magnetic field in the vicinity of said ion source, means to supply a potential to said accelerating electrodes whereby ions from said source are accelerated into said magnetic field transversely thereto and an arcuate beam of ions is formed, and collecting elements disposed in said beam to collect and discharge the ions; the combination comprising an impedance connected to one of said collector elements whereby the beam current flowing to said element passes therethrough, amplifying means connected to said impedance for producing a voltage responsive to said beam cur-rent, feedback means connected between said impedance and said amplifying means for producing an opposing current in said impedance whereby an essentially constant potential is maintained at said collector element, and voltage regulating means responsive to the voltage produced by said amplifying means for adjusting the potentialupon said accelerating electrodes whereby the position of said beam of ions is maintained constant with respect to said collector elements.

5. In a calutron including a source of polyisotopic ions, means establishing a magnetic field, accelerating electrodes disposed adjacent said ion source having a potential asso ciated therewith for forming and directing in conjunction with the magnetic field an arcuate beam of ions, and collecting elements disposed in said beam to collect and discharge the ions of different isotopes contained therein; the combination comprising an impedance connected to the collecting element provided to collect the ions of a less abundant isotope, whereby the discharge current for the ions collected therein passes through said impedance, amplifying means connected to said impedance for providing a voltage responsive in magnitude to said current, feedback means connected between said impedance and. said amplifying means for providing an opposing current in said impedance whereby the potential of said collecting element is maintained essentially constant, and voltage regulating means for altering said potential associatedwith said ion accelerating electrodes in accordance with the voltage produced by said amplifying means whereby the position of the beam of ions is regulated with respect to said collecting element.

6. A beam regulator for a calutron comprising means establishing a magnetic field, means including accelerating electrodes having a potential for directing ions into said magnetic field to form an arcuate beam of ions, current collecting elements disposed in the normal path of said beam of ions, an impedance connected in series with one of said collecting elements, amplifying means connected to said impedance for producing a voltage in accordance with the flow of beam current therein, feedback means connected between said impedance and said amplifying means for providing an opposing current in said impedance whereby a constant potential is maintained thereacross, and means to alter the potential upon said accelerating electrodes in accordance with the voltage produced by said amplifying means whereby the position of said beam of ions is regulated with respect to said current collecting elements.

7. In :a calutron having an ion source, ion accelerating electrodes disposed adjacent said ion source, a supply of potential connected between said ion source and said accelerating electrodes for forming a beam of ions, a transverse magnetic field for bending said beam in an arcuate path, and beam collecting elements disposed in the normal path of the ion beam for separately collecting the ions of different masses; a beam regulator operating in combination with said calutron and comprising van impedance connected in series with one of said beam collecting elements, amplifying means associated with said impedance for pro ducing a voltage in accordance with a predetermined beam current through said impedance, means responsive to said voltage for effecting the supply of potential connected between said ion source and said accelerating electrodes whereby said arcuate beam of ions is regulated with respect to said collector pockets, and means to provide an opposing current in said impedance for maintaining a constant potential thereacross, whereby the potential of said beam current collecting element is unchanged with changes in beam current.

Smythe et al,: Physical Review, vol. 51, February 1, 1937, pages 178-182.

Claims (1)

1. A BEAM REGULATOR FOR A CALUTRON COMPRISING IN COMBINATION A CALUTRON HAVING AN ION GENERATOR, ACCELERATING ELECTRODES DISPOSED ADJACENT SAID ION GENERATOR, A SOURCE OF POTENTIAL CONNECTED BETWEEN SAID ION GENERATOR AND SAID ACCELERATING ELECTRODES FOR PRODUCING A BEAM OF IONS, MEANS ESTABLISHING A MAGNETIC FIELD TRANSVERSE TO THE DIRECTION OF TRAVEL OF SAID ION BEAM, CURRENT COLLECTING ELEMENTS DISPOSED IN THE NORMAL PATH OF SAID BEAM, MEANS RESPONSIVE TO THE CURRENT FLOWING TO ONE OF SAID COLLECTOR ELEMENTS FOR PROVIDING A VOLTAGE PROPORTIONAL THERETO, AND MEANS FOR IMPRESSING SAID VOLTAGE UPON SAID ACCELERATING ELECTRODES FOR REGULATING THE POSITION OF SAID BEAM OF IONS WITH RESPECT TO SAID COLLECTING ELEMENTS.

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