US2988671A - Particle accelerating system - Google Patents

Description

June 13, 1961 w. R. ARNOLD 2,988,671

PARTICLE ACCELERATING SYSTEM Filed June 30, 1958 a .../2 ,ff QP l| I "M E azi m/O l il 53 ,armure M (C) g I 6J' y/z/d E K d) IN V EN TOR. May/1e 10mn/a', deceaea,

Patented June 13, 1961.

2,988,671 PARTICLE ACCELERATIN G SYSTEM Wayne R. Arnold, deceased, late of Ridgefield, Conn., by

Marian H. Arnold, executrix, Falls Church, Va., as

signor to Schlumberger Well Surveying Corporation,

Houston, Tex., a corporation of Texas' Filed June 30, '1958, Ser. No. 745,439 12 Claims. (Cl. 315-111) This invention relates to particle accelerating systems and, more particularly, pertains to a new and improved particle accelerating system adapted to utilize an undulating potential.

'I'here are in present use various devices for deriving radioactive radiation which, in general, comprise a source of electrically-charged particles and a charged-particle accelerator for directing the particles at a high velocity against a reactive target. By properly selecting the type of particles, the target material and the particle velocity at the instant of bombardment, a particular type of nuclear reaction may be obtained at the target.

To energize the particle accelerator in apparatus of the foregoing type, ordinarily a unidirectional potential is employed. For example, a potential in a range from 50-100 kilovolts is needed where ions of deuterium areV accelerated toward a target containing tritium to produce nuclear reactions from which neutrons are emitted. Of course, there are many other reactions in which even higher voltages are required.

Various forms of generators and power supplies have been proposed to provide high voltages required for particle accelerators of the foreging type. For instance, van de Graaff machines have been employed in which an insulating conveyor carries charges deposited at a relatively low potential to a relatively high potential where they are removed. These generators, while satisfactory for laboratory use, are usually quite bulky and are not well suited to applications in which the source of radioactive radiation must be portable, such as in apparatus for use in a borehole drilled into the earth.

High voltages may also be obtained through the use of a step-up transformer, an associated voltage-multiplying rectifier and a smoothing filter. This type of power supply, however, may be relatively complex in design where a larger number of stages of multiplication is required. If fewer such stages are used, the design requirements on the step-up transformer become quite severe for a given high D.C. output voltage.

It is an object of the present invention, therefore, to provide a new and improved particle accelerating system operable on an alternating potential.

Another object of the present invention is to provide a new and improved particle accelerating system for use in a source of radiant energy providing a yield or radiant energy flux representative of a -D.C. voltage equal to the peak-to-peak voltage of an applied alternating potential.

Yet another object of the present invention is to provide the new and improved particle accelerating system and associated power source of relatively small size and thereby compatible with the space requirement of well logging service. i

A particle accelerating system in accordance with one aspect of the present invention comprises an envelope having one closed section enclosing a pair of electrodes which conjointly define an accelerating gap. Another closed section of the envelope encloses a cathode associated with one of the aforementioned electrodes to define therewith a diode rectifier. Another electrode is associated with the remaining of the pair of electrodes to define therewith a discharge gap. Capacitive means is provided for coupling a source of alternating potential to the diode erating system further comprises means for selectively causing a gaseous discharge to occur substantially only in the discharge gap.

According to another aspect of the present invention, a particle accelerating system is comprised of an evacuated envelope including ion source and ion accelerating sections. Means are provided for periodically introducing an ionizable gas to said ion source section and the system includes means associated with said ion source section for ionizing such gas. Means associated with said ion accelerating section provides an electric eld for accelerating some of the ions derived in the ion source section.

In accordance with still another aspect of the invention, a particle accelerating system is adapted to employ a source of alternating potential and includes an ion source and ion accelerating means. The source of alternating potential is capacitively coupled to the accelerating means, and the ion source is operatively conditioned in synchronism with the alternating potential of the source.

The novel features of the present invention are set forth with particularity in the appended claims. The present invention, both as to its organization and manner of operation, together with further objects and advantages thereof, may best be understood by references to the following description taken in connection with the accompanying drawing in which:

FIG. 1 is a view in longitudinal section of a radiant energy source embodying a particle accelerating system constructed in accordance with the present invention; and

FIG. 2 includes a series of curves representing various operating conditions in the apparatus illustrated in FIG. l plotted to a common time scale, and useful in explaining its operation.

As shown in FIG. l of the drawing, a particle accelerating system embodying the present invention comprises a cylindrical, elongated envelope 10. 'I'he envelope may be manufactured from out-gassed glass or other conventional electrical insulating material and is pressureresistant.

A pair of electrically conductive cylindrical tubes 11 and 12 are disposed within envelope 10 in end-to-end relation and in alignment with the longitudinal axis of the envelope. These tubes have a diameter almost equal to the inner diameter of the envelope for a purpose to be more apparent from discussion to follow. Each tube is supported by a respective one of integral extensions 13 and 14 which project inwardly from the inner wall of envelope 10. Thus, individual annular seats are provided to which opposite ends of the tubes 11 and 12 are connected, such as by means for conventional metal-to-glass junctions.

The tubes 11 and 12 are provided with respective end closures or discs 15 and 16 having particle-admitting apertures 17 and 18, respectively. These discs are `disposed adjacent to one another and conjointly define an accelerating gap. They are spaced apart at a distance arranged in a known manner in relation to the meanfree-path of ions` within the atmosphere of envelope to minimize the possibility of break down. Ordinarily, this-Y distance will be smaller than the mean-free-path.A

To minimize the possibility of electrical break down in' operation, envelope 10 is provided with a section 19 of'- reduced diameter extending between the discs IS-and 16.

This increases the effective length of the interveningV sec- 3 inner wall of tube 1'1 which, in turn, is sealed to projectlon 13 of the envelope. Thus, a first closed chamber section 21a is defined by envelope 10 above barrier 20.

A- second closed section 2lb is defined between barrierv 20 and an adjacent end 22 of the envelope which. may be evacuated through means of a suitable tubulation (not shown) in end 22 that is sealed so as to maintain a high Vacuum. Electrical connections 23 and 24 pass through the open end of tube 11,1 and extend through respective openings in wall 22, to which they are appropriately sealed. Their free ends are connected to a filamenttype cathode 25. The filament and a portion of its leads are enclosed by a shield cylinder 26 having an end closure 27 adjacent wall 20 provided with a central electron-emitting aperture 28. Supporting leads 29 and 30 are connected to the open end of the shield cylinder and extend through the wall 22 of envelope 10 via appropriately sealed openings. Filamentary cathode 25 and transverse wall portion 20 of tube 11 together define a diode rectifier the purpose of which will be more apparent from the discussion to follow.

A post or support 3-1 constructed of an electrically resistive material is connected to wall 20 and extends toward closure 15. Its free end is connected to a target plate '32 which is thus supported adjacent opening 17 of closure 15. The target is associated with accelerating gap 15, -16 and includes an isotope of hydrogen, such as tritium, for reacting with accelerated ions to produce neutrons as will be more apparent from a discussion to follow. The target may, for example, be constructed of zirconium, tantalum or other material which is adapted to absorb or be combined with the required reactive material. Of course, deuterium may be employed instead of tritium where neutrons at 3 million electron volts (m.e.v.) instead of 14 m.e.v. are desired.

Through a sealed opening in the upper end 34 of envelope extends a conductor 33 connected to and functioning as support for an electrode 35 in the form of a at plate. Electrode 35 is spaced from disc 16 a distance greater than the mean-free-path of ions within the atmosphere of the envelope 10. This is determined in a known manner in view of the voltage applied to the electrodes and the gas pressure within the envelope so as to provide a discharge gap. To ensure an appropriately long path for charged particles and thus facilitate the occurrence of an electrical discharge, an insulating tube 36 sealed to a further extension of annular wall portion 14 of the envelope 10` extends into tube 12. The open end of insulating tube 36 terminates just short of disc 16.

A pair of conductors 37 and 38 pass through sealed openings in end 34 of the envelope. 'They are connected to and support a filament 39 constructed so as to emit and absorb a selected ioni'zable gas as a function of the filament temperature. For example, the filament may be fabricated of zirconium appropriately loaded With the isotope of hydrogen, deuterium, so that depending upon the current supplied to the filament, deuterium gas may be selectively introduced to the envelope 10, exclusive of the diode section 2lb. Through an appropriate tubulation in end 34, the envelope `10 may be evacuated and a slight amount of deuterium gas introduced before it is sealed. For example, the gas pressure may be a micron of mercury or so.

The envelope 10 is received by a cylindrical, closely fitting, electrically conductive member 40 of a length substantially equal to the length of the envelope. Thus, the member 40 has tubular portions disposed outside of the envelope and coextensive respectively with tubes 11 and 12 to define capacitors conjointly therewith. These capacitors are employed to couple a source of alternating potential to the diode rectifier 20, 25 and to the discharge gap 16, G5.

To energize the device just described', a source 41 ofv alternating potential of moderate voltage, for example on the order of hundreds of volts, is coupled to primary winding 42 of a step-up transformer 43 having a high voltage secondary winding 44. One terminal 45 of the secondary winding 44, is connected to conductive mem- -ber 40 and the remaining terminal 46 is connected to one of conductors 29, 3@ and via a connection 47 to conductor 33 of electrode 35.

Secondary 44 is also provided with low voltage sections 48 and 49. Section 48 has a terminal 50 connected to filament lead 24 to provide a relatively low potential difference between the filament 25 and its shield 26. The remaining terminal 51 of low voltage section 49 is connected to filament lead 23 thereby providing a relatively low voltage for energizing the filament 25. Extending from terminals 50 and 5.1 are connections 52 and 53 to leads 37 and 38 of the deuterium-emitting filament 39. In series with one of these leads is a battery 5-4 providing a unidirectional current to establish a minimum current through the filament 39 bringing it to a deuteriumabsorbing temperature. In the event the current from battery S4 tends to saturate the core of transformer 45, an alternating current source of appropriate frequency and/or phase may be used in its stead.

-Filament 39 is fabricated of an appropriately thin material so that it may be heated and cooled in synchronism with the frequency of source 41. The size and capacity of filament 39 are arranged so that the pressure within the envelope 10 can vary in a range from l to l0 microns. The frequency of the alternating potential supplied is selected in view of the capacitances provided between tubes 11 and 12 and member 40 so that suitable electrical charges may develop in these capacitors during operation of the system as will be more readily apparent from the discussion to follow.

In describing the operation of the device illustrated in FIG. l, occasional reference will be made to FIG. 2 in which several curves representing various characteristics of the apparatus for a single cycle of operation are plotted as a function of time. Of these, curve 60 in FIG. 2a represents the alternating voltage at secondary `44 of the transformer 43 using terminal 45 as a reference. Initially, the voltage is negative (during the portion of a cycle designated to, t1) and cathode 25 is negative relative to anode electrode 20. Thus, current lwill ow through diode 20, 25 and since the condenser defined by elements 11 and 40 is in a series circuit with the diode, a charge collects on the condenser. In this way, electrode 11 attains negative potential relative to sleeve 40 represented by broken line 61 in FIG. 2a. By making the circuit leakage sufficiently small, this voltage is substantially equal to the peak value of the applied alternating voltage. An increase in the capacitance of the system can obviously be arranged by an external circuit to allow for greater current peaks than obtained by employing condenser 11, 40 alone.

During this portion of an operating cycle, the current supplied to filament 39 is at a minimum value, as may be seen from curve 62 in FIG. 2b, and the deuterium pressure Within the envelope 10 is correspondingly low. Thus, no discharge can occur between electrodes 16 and 35. It is therefore evident that during the portion of an operating cycle between t0 and t1, namely the negative half cycle of the applied alternating potential, a high negative potential is developed at element 11 relative to 40 and this potential is applied via resistive post 31 to target plate 32.

After the voltage passes through z-ero, and during `interval tl-tz, conduction in diode 20, 25 ceases, and as may be seen from curve 62 (FIG. 2b), the current through deuterium-emitting filament 39 increases to bring this filament to its deuterium-emitting temperature. Thus, the deuterium pressure within the envelope 10 increases, as represented by curve 63 in FIG. 2c. When the pressure becomes high enough, a glow discharge occurs between gassen electrodes 16 and 35. This discharge establishes a conductive path and current iiow between electrodes 16 and 35 to charge the condenser defined by elements 12 and 40. Element 12 thus is brought to a high positive potential relative to member 40, as represented by broken line curve 64 in FIG. 2a. Y

- The glow discharge between electrodes 16 and 35 produces positive ions of the deuterium within sleeve 36. Some of these ions are attracted toward electrode 16 and a portion continues through opening 18 of electrode 16. Since electrodes 16 and 15 are electrically connected to elements 12 and 11, respectively, ions that pass through opening 18 experience an acceleration of a voltage equal toga peak-to-peak voltage of the applied alternating potential. Accelerated deuterium ions impinge on target' 32 where they react with tritium to produce neutrons in a known manner. Thus as represented by curve 65 in FIG. 2d, a burst of neutrons is derived once during each complete cycle of the applied alternating potential.

Since target 32 is connected to electrode 11, 15 via resistor 31, its voltage is slightly more positive. Accordingly, secondary electrons produced in the target as a result of bombardment by deuterium ions are repelled and cannot be accelerated between the electrodes 15 and 16 in the direction opposite to ion acceleration.

.From the foregoing description it is evident that a particle accelerating system constructed in accordance with the present invention is adapted to operate with a source of alternating potential without requiring any external rectifier and smoothing filter. Accordingly, it may be relatively small in size and is easily adaptable to various portable applications. By virtue of the cylindrical configuration of the device illustrated in FIG. 1, it is ideally suited for use in well logging service, for example, as described in copending application Serial No. 275,932 of Clark Goodman filed March l1, 1952 or copending application Serial No. 414,761, tiled March 8, 1954 in the name of the present applicant, and which is now U.S. Patent No. 2,914,677 granted November 24, 1959, both of which are assigned to the present assignee.

Instead of energizing lament 39 by the use of an alternating potential, as provided by secondary winding 49 and a unidirectional potential supplied by battery 54, an appropriate pulser may be employed in a known manner. Secondary winding 49 may be used to synchronize the pulser and a conventional time delay device can be inserted in this circuit that ya pulse of current is supplied to filament 39 in appropriate timing relation to alternating voltage 60 (FIG. 2a) to provide a mode of operation similar to the described hereinbefore. i

' Although no reference point or ground terminal has been shown, one may be provided. For example, any one of the secondary terminals of transformer 43 may be grounded.

While a particular embodiment of the present invention has been shown anddescribed, it is apparent that changes and modifications may be made without departing from this invention in its broader aspects, and thereforethe aim in the appended claims is to cover `all such changes and modifications as fall within the true spirit and scope of-this invention. I

1. Apel-ticle accelerating system comprising: an evacuated envelope including first and second sections; a pair of electrodes supported within said first section of said envelope and conjointly defining an accelerating gap; a cathode supported within said second section of said envelope and associated with one of said electrodes to define therewith a diode rectifier; another electrode supported within said first section of said envelope and associated with the remaining of said pair of electrodes to define therewith a discharge gap; capacitive means for coupling a source of alternating potential to said diode rectifier and to said discharge gap; and means for selectively causing a gaseous discharge to occur in said discharge gap.

2. A particle accelerating system comprising: an evacuated envelope; first and second electrodes supported within said envelope and conjointly defining an accelerating gap; a cathode associated with said first electrode and defining therewith a diode rectifier; a third electrode associated with said second electrode and defining therewith a discharge gap; means associated with each of said first and said second electrodes providing respective capacitors for coupling a source of alternating potential to said diode rectifier Iand to said discharge gap; and means for selectively causing a gaseous discharge to occur in said discharge gap.

3. A particle accelerating system comprising: an evacuated envelope including first and second independent sections; a pair of electrodes supported within said first section of said envelope and conjointly defining an accelerating gap; a cathode supported Within said second section of said envelope and electrically associated with one of said electrodes to define therewith a diode rectifier; another electrode supported within said first section of said envelope and associated with the remaining of said pair of electrodes to define therewith a discharge gap; capacitive means for coupling a source of alternating potential to said diode rectifier and to said discharge gap; and means for selectively introducing an ionizable gas to said envelope to cause a gaseous discharge to occur in said discharge gap.

4. A particle accelerating system comprising: an elongated, evacuated envelope of an electrically insulating material; first and second electrically conductive members each including one of a pair of tubes supported within said envelope in end-to-end relation to one another and including individual end closures `disposed adjacent one another, each of said closures having a particle-admitting aperture, and said closures conjointly defining an accelerating gap; a cathode supported within one of said tubes and defining with a portion thereof a diode rectifier; a third electrically conductive-member supported within said envelope in operative relation with the other of said tubes and defining with a portion thereof a discharge gap; a fourth electrically conductive member comprised of tubular portions disposed outside of and receiving said envelope to define capacitors conjointly with said firstmentioned tubes for coupling Ia source of alternating potential to said ydiode rectifier and to said discharge gap; and means for selectively causing a gaseous discharge to occur in said discharge gap.

5. A particle accelerating system comprising: an elongated, evacuated envelope of an electrically insulating material; first'and second electrically conductive members each including one of a pair of tubes supported within said envelope in end-to-end relation to one another, said tubes having individual end closures adjacent one another, each of said closures having a particle-admitting aperture, said closures conjointly defining an accelerating gap, a first one of said tubes including a conductive, transverse wall spaced from said end closure of said first tube; a cathode supported within said first tube and defining with said transverse wall a diode rectifier; a third electrically conductive member supported within said envelope in operative relation with the other of said tubes and defining With'a portion thereof a discharge gap; a fourth electrically conductive member comprised of tubular portions disposed outside of and receiving said envelope to define capacitors conjointly with said first-mentioned tubes for coupling a source of alternating potential to said diode rectifier and to said `discharge gap; and means for selectively causing a gaseous discharge -to occur in said discharge gap.

6. A particle accelerating system comprising: an elongated, evacuated envelope of an electrically insulating material; electrically conductive members each including one of a pair of conductive tubes supported within said envelope in end-to-end relation to one another and including individual end closures adjacent one another, each 7 of said closures naving a particle-admitting aperture, and said closures conjointly defining an accelerating gap; a first one of said tubes including a conductive transverse Wall separate from the end closure of said first tube; a cathode supported within said first tube and defining with said transverse wall a diode rectifier; a sleeve of electrically insulating material connected to the inner wall of said envelope in the vicinity of the open end of the other of said conductive tubes and having a portion of a diameter smaller than said other tube extending therethrough to a location adjacent the end closure thereof; a third electrically conductive member supported within said envelope in the vicinity of the open end of said other tube and spaced from the end closure thereof to define therewith a discharge gap; a fourth electrically conductive member comprised of tubular portions disposed outside of and receiving said envelope to define capacitors conjointly with said first-mentioned tubes for coupling a source of alternating potential to said diode rectifier and to said discharge gap; and means for selectively causing a gaseous discharge to occur in said `discharge gap.

7. A particle accelerating system for use with a source of alternating potential comprising: an evacuated envelope; a pair of electrodes supported Within said envelope and conjointly defining an 'accelerating gap; a cathode associated with one of said electrodes and defining therewith a diode rectifier; another electrode associated with the remaining of said pair of electrodes and defining therewith a discharge gap; capacitive means for coupling one terminal of a source of alternating potential individually to each of said electrodes of said accelerating gap; means for connecting an oppositely poled terminal of the source of alternating potential to said cathode and to said another electrode; and means for selectively causing a gaseous discharge to occur in said discharge gap.

8. A particle accelerating system comprising: an evacuated envelope; a pair of electrodes supported within said envelope and conjointly defining an accelerating gap; a cathode associated with one of said electrodes and defining therewith a `diode rectifier; another electrode associated with the remaining of said pair of electrodes and defining therewith a discharge gap; capacitive means for coupling a source of alternating potential to said diode rectifier and to said discharge gap; a controllable source of ionizable gas associated with said `discharge gap; and means operative synchronously with the frequency of the source of alternating potentiall for causing said source to emit gas when said another electrode is positive relative to said remaining electrode `defining said discharge gap.

y9. A particle accelerating system comprising: an evacuated envelope; a pair of electrodes supported within said envelope and conjointly ldefining an accelerating gap; a cathode associated with one of said electrodes and defining therewith a ydiode rectifier; another electrode associated with the remaining of said pair of electrodes and defining therewith a discharge gap; capacitive means for coupling a source of alternating potential to said diode rectifier and to said discharge gap; a temperature-responsive source of ionizable gas associated with said discharge gas adapted to emit and to absorb said gas; and means operative synchronously with the frequency of the potential source of alternating potential to` heat said gas source to a gas-emitting temperature when said another electrode S is positive relative to said remaining electrode defining said discharge gap, and to permit said gas source to attain a gas-absorbing temperature when said another electrode is negative relative to said remaining electrode defining said discharge gap.

10. A particle accelerating system comprising: an evacuated envelope; rectifier means within said envelope including at least one electrode; discharge gap means within said envelope and including at least one other electrode defining with said one electrode a particle accelerating gap; capacitive means for coupling a source of alternating potential to said rectifier means and to Said discharge gap; means operative synchronously with the frequency of said alternating potential for causing an ion-producing Agaseous discharge to occur in said discharge gap whereby ions are supplied to said accelerating gap; and a target associated with said accelerating gap upon which accelerated ions may impinge.

11. A particle accelerating system comprising: an evacuated envelope; rectifier means within said envelope including at least one electrode; discharge gap means within said envelope and including at least one other electrode defining with said one electrode a particle accelerating gap; capacitive means for coupling a source of alternating. potential to said rectifier means and to said discharge gap; means operative synchronously with the frequency of the source of alternating potential for causing an ion-producing discharge of an isotope of hydrogen to occur in said discharge gap whereby ions are supplied to said accelerating gap; and a target associated with said accelerating gap and including an isotope of hydrogen for reacting with accelerated ions.

12. A particle accelerator system comprising: an cnvelope including a barrier sealed transversely within said envelope to define first and second isolated sections; a pair of electrodes supported within said first section of said envelope and oonjointly defining an accelerating gap; a cathode supported within said second section of said envelope and electrically separated from one of said electrodes by a high vacuum gap to` define therewith a diode rectifier; another electrode supported within said first section of said envelope and electrically separated from the remaining of said pair of electrodes by a gap containing an ionizable gas to define therewith a discharge gap; means vfor coupling an alternating potential `from a power source to said diode rectifier and to said discharge lgap to develop a negative potential charge on said one electrode and periodically to drive said another electrode positive with respect to said remaining electrode; and means for selectively causing a gaseous discharge to occur in said discharge gap when said another electrode is driven positively thereby to build up a positive charge on said remaining electrode.

References Cited in the le of this patent UNITED STATES PATENTS 2,211,668 Penning Aug. 13, 1940 2,489,436 Salisbury Nov. 29, 1949 2,591,825 Johnson et al Apr. 8, 1952 2,640,952 Swanson June 2, 1953 2,769,096 Frey Oct. 30, 1956

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