US 3527977 A
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Sept. 8, 1970 F11ed June 3, 1968 POWER SUPPLY A. E. RUARK NS IN 2 Sheets-Sheet 1 14 NV '25 MOLECULAR 15 -26 ION SOURCE POWER SUPPLY INVENTOR.
Arfhur E. Ruark ATTORNEY Sept. 8,1970 A. E. RUARK 2 77 MOVING ELECTRONS AS AN AID T0 INITIATING REACTIONS IN THERMONUCLEAR DEVICES Flled June 3. 1968 2 Sheets-Sheet 3 r\ 57 POWER 64- SUPPLY MOLECULAR "M/WFWWT ION SOURCE Fig; 48\ MOLECULAR ION SOURCE MOLECULAR -52 ION SOURCE INVENTOR. Arfhur E. Ruark 48* MOLECULAR ATTORNEY United States Patent US. Cl. 315111 7 Claims ABSTRACT OF THE DISCLOSURE Molecular ions of a high energy are injected into an evacuated container within a magnetic field into the path of an energetic oscillating electron stream and the plasma it creates which dissociates and/or ionizes the molecular ions into atomic ions. The resulting atomic ions are trapped by the magnetic field to form a circulating beam of atomic ions within the container. One or more pairs of opposing molecular ion beams may be utilized to strike each other in the electron stream for dissociation or ionization thereof, and, if desired, an energetic arc discharge may also be utilized in conjunction with the energetic oscillating electron stream as an aid in the process of forming the atomic ions.
BACKGROUND OF THE INVENTION The invention described herein was made in the course of, or under, a contract with the United States Atomic Energy Commission.
It is known that the sun produces energy by thermonuclear reactions which proceed at exceedingly high temperatures. These reactions and all controlled thermonuclear reactions depend upon collisions between nucle to liberate energy. It can be shown that extremely high temperatures must be reached to attain useful thermonuclear power, but at those temperatures the energy loss due to radiation is also great. Deuterium and tritium release energy at relatively low temperatures and emit relatively little radiation, so they are suitable thermonuclear fuels. Confinement of the fuel at such temperatures with present materials is not feasible, so that it is necessary to confine the fuel in a leak-proof magnetic bottle-a strong magnetic field.
One method of trapping ions in a magnetic field utilizing dissociation and/ or ionization of molecular ions and trapping the ions as a result of a change of charge-to-mass ratio is set forth in the patent of John S. Luce, No. 3,080,543, issued Apr. 17, 1962. In the device described in that patent, high-energy molecular ions such as D are injected into a confining magnetic field, perpendicular to the lines of magnetic force. At some point in the orbit of these ions in the magnetic field, a portion of them are caused to be dissociated and/or ionized by an energetic arc discharge to form atomic ions. These resultant atomic ions have one-half the momentum of the original molecular ions, when said molecular ions are diatomic, and hence have one-half the radius of curvature in the field. If the center of the orbits of these atomic ions coincides with the axis of the magnetic field, the ions will circulate in a ring. If the center of the orbits of these atomic ions and the axis of the machine do not coincide, the atomic ion orbit center will precess about the magnetic field. The ions will circulate until a charge exchange occurs with one of the neutral gas atoms in the system or until some other process causes the ions to be lost. The mecha nism of charge exchange between. atomic ions and neutrals causes large energy losses which prevent attainment of thermonuclear temperatures, so that some means for removing the neutrals from the heating region is required and this can be accomplished by providing an input current of the molecular ions large enough to burnout the residual neutral particles and other neutral particles as fast as they are flooding into the system in the manner as described in US. Pat. No. 3,032,490 to Albert Simon, issued May 1, 1962.
Any mechanism that will be effective in destroying neutral particles is highly desirable in any thermonuclear machine. The method of injecting a high-intensity molecular ion beam, of sufiicient current to produce a trapped beam of circulating atomic ions of sufficient current to etfect burnout of neutral particles in a thermonuclear device, as set forth in the above-mentioned Simon patent, is one way to establish a hot ionized plasma. The establishment of a hot plasma is a necessary step in any controlled thermonuclear reactor. The invention set forth herein is another way of forming such a plasma.
' SUMMARY OF THE INVENTION It is a primary object of this invention to provide a method and apparatus for trapping atomic ions within a strong magnetic field by using an energetic oscillating stream of electrons as a dissociating and/ or ionizing mechanism for an injected beam or beams of energetic oscillating molecular ions.
It is another object of this invention to effect trapping of atomic ions within a strong magnetic field by utilizing both an energetic oscillating arc discharge and an energetic oscillating stream of electrons for dissociating and/ or ionizing an injected beam of energetic molecular ions.
It is another object of this invention to provide apparatus in which opposing ion beams strike each other in such manner as to effect trapping of atomic ions within a strong magnetic field.
The above objects have been accomplished in the pressent invention by providing an energetic oscillating stream of electrons in a confining magnetic field within an evacuated enclosure, and injecting one or more beams of energetic molecular ions into the interior of the enclosure and into the path of the stream of electrons where a portion of the molecular beam is dissociated and/or ionized by the stream of energetic electrons, to thereby form a hot plasma of ionized particles. When particles are injected with sufficient energy into a region containing relatively stationary electrons, it is possible for the electrons to excite or ionize the particles. In the case of molecular particles, excitation to a repulsive state leads directly to dissociation. Excitation to an attractive state, on the other hand, leads to easy ionization in a subsequent collision. This is possible because molecules or atoms, in the excited state, have lower ionization energies, and the cross section for ionization is, in general, several times larger for the excited state than for the equivalent entity in the stable state. The metastable two-quantum state of the hydrogen atom is of particular interest since these metastable atoms have a life long enough to permit further excitation and eventual ionization.
The following table shows the energies required for various effects occurring using fast ions, atoms, or molecules when electrons are at rest; column 4 shows the electron energy required when the ions, atoms, or molecules are at rest.
Voltages required for deuterium ions, atoms, or molecules will be twice the above values.
It can be seen from the above table that, with electrons at rest, H or H must have an energy of about 40 kev. for eflicient dissociation and about 230 kev. for efficient ionization. The relative velocity between the ions and electrons for eflicient breakup, however, can be supplied at much lower voltage and much smaller power consumption by raising the energy of the electrons. As shown in the above table, about 11 volts is sufficient for eifective dissociation of H by electrons and about 60 volts for maximum ionization of H fi' or H by electrons. Some assistance, of course, can be had from electrons having lower energies closer to the threshold values.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic showing of one embodiment of a mirror-type thermonuclear device for establishing a hot plasma of ionized particles.
.FIG. 2 is a schematic showing of another embodiment of a mirror-type thermonuclear device for establishing a hot plasma of ionized particles.
FIG. 3 is a cross-sectional view on the line 3-3 of the device of FIG. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENTS Refer now to FIG. 1, which illustrates one embodiment in which the principles of this invention may be carried out. Negatively charged rings 1 and 2 are insulatingly supported by insulators 7 and 8, respectively, on the enclosing chamber wall 11. Rings 1 and 2 are each placed just outside the mirror windings 3 and 4, and positioned perpendicularly with respect to the magnetic field. Positively charged rings 5, 6 are positioned adjacent and parallel to the negative rings 1, 2, but further removed from the mirror coils 3, 4, so as to retain slow ions within the plasma volume. Rings 5 and 6 are insulatingly supported on the chamber wall 11 by insulators 9 and 10, respectively.
A positively charged cylindrical member 13 encloses the mirror coils 3, 4, as shown. A plurality of annular magnetic coils 12 are disposed around the member 13 and between the mirror coils 3 and 4. Coils 12, together with mirror coils 3 and 4, provide the containing magnetic field for the ionized particles which are formed in the area formed by these members.
Power supply 28 is provided to supply the operating potentials to the rings 1, 2, 5, and 6, and member 13. A positive line 29 from supply 28 is connected by line 30 to positive ring 5, and by line 31 to positive ring 6. Member 13 is connected by positive line 32 to supply 28. A negative line 33 from supply 28 is connected by line 34 to ring 1, and by line 35 to ring 2. An oscillating energetic stream 23 of electrons is maintained between rings 1 and 2 by the potentiail gradient maintained between rings 1, 2 and member 13. This operation is based upon the well known PIG principle. In other words, the electrons forming the energetic stream 23 of electrons oscillate between the rings 1 and 2 and follow the magnetic field lines provided by the coils 3, 4, and 12 such that the electron stream 23 is essentially hollow and substantially cylindrical. It should be understood that where reference is made to the energetic 4 oscillating stream of electrons hereinafter in connection with FIG. 1, such a stream of electrons will have the above-mentioned configuration.
It may be desired to employ an energetic arc discharge in conjunction with the energetic oscillating stream of electrons. When use of such a discharge is desired, it may be provided between suitable electrodes in a manner as set forth in the patent of John S. Luce, No. 2,920,- 234, issued Jan. 5, 1960; the patent of John S. Luce, No. 2,927,232, issued Mar. 1, 1960; or the patent of Persa R. Bell et al., No. 2,920,235, issued Ian. 5, 1960. The first patent relates to an energetic carbon arc discharge and the latter two patents relate to energetic deuterium arc discharges. For the purposes of this application, an energetic arc discharge is defined as one in which an arc current in excess of amperes can be maintained. As set forth in these above-mentioned patents, an energetic arc discharge is an effective and eificient dissociating mechanism for molecular ion beams. An energetic arc discharge 24 may be initiated and sustained between a cathode 21 and an anode 22 in the manner set forth in the aforementioned patents. Cathode 21 is mounted in a base 19 which is in turn supported on the chamber wall 11 by an insulator 36. Anode 22 is mounted on a base 20, which in turn is supported on wall 11 by an insulator 37. A source of power 27 is connected to base 19 by a lead 25, and is connected to base 20 by a lead 26,
A beam of molecular ions 17 is injected from a source 15 and through accelerator tube 16 into the path of the energetic oscillating electron stream 23 and, when desired, in the path of arc discharge 24, where a portion of the molecular ions are dissociated and/or ionized by the electron stream, and by the are discharge when used, into a trapped circulating beam 18 of atomic ions.
The interior of the chamber 11 is evacuated by connecting a vacuum pump, not shown, to the chamber through a tubular member 14 in the chamber wall. The pressure in the chamber is maintained at a value of about 10* mm. Hg or less, for example.
The accelerator tube 16, referred to above, may be energized by a conventional high-voltage generator. A suitable high-current source of molecular ions from source 15 may be provided by apparatus such as set forth on page 18 of Nucleonics, vol. (3), 1951; or on page 394 of Rev. Scientific Instruments, vol. 24, 1953; or by the duo-plasmatron described by Von Ardenne, Tabellen der Elektronenphysik, Ionenphysik und Ubermikroskopie, VEB Deutscher Verlag der Wissenschaften, Berlin, 1956.
The mirror coils 3 and 4 have an inside diameter of 17 inches and a spacing between the inner faces of the coils of 18 /2 inches, for example. The plasma which is formed by dissociation of the high-current molecular ions as they pass through the energetic oscillating stream of electrons is coinfined and trapped within the volume inscribed by the mirror coils by the magnetic field H. The gas used for the ion source input is deuterium and/or tritium, for example, and the injection voltage is about 600 kev.
The strength of the mirror fields of coils 3 and 4 is about 21 kilogauss at points near the center of a mirror throat, for example, and the midplane field of the inscribed volume is about 6 kilogauss, for example. These field strengths are considered adequate to confine the hot plasma which is trapped within the inscribed volume, but the fields may be increased in proportionate amounts to higher strengths, if desired.
An energetic oscillating electron stream is an effective dissociating and/or ionizing mechanism for an injected beam of molecular ions. The energetic oscillating electron stream has the additional advantage of ionizing neutrals, thus reducing the flow of neutrals caused by the charge ex change process. The use of an energetic arc discharge in conjunction with the stream of oscillating electrons may be used as discussed above for assisting in the dissociation and/or ionization of the injected molecular beam. Use of such a discharge would supplement the oscillating electron stream as a dissociating mechanism and decrease the time required to form a plasma of ionized particles Within the confined magnetic field.
The stream of electrons does not necessarily need to be oscillated. For example, one of the negative rings 1 and 2 may be connected to a positive power source and the positive potential removed from the cylinder 13. However, the use of oscillating electrons is preferred.
Referring now to FIG. 2, which illustrates another embodiment in which the principles of this invention may be carired out, it can be seen that the oscillating stream of energetic electrons may be sustained between a pair of negatively charged plates rather than a pair of rings as set forth in the device of FIG. 1. In FIG. 2, the oscillating electron stream is not hollow as it is in the embodiment of FIG. 1.
In FIG. 2, the enclosing chamber wall is not shown, but it should be understood that such as chamber wall is provided in this embodiment in a manner similar to that for FIG. 1.
In FIG. 2, a pair of spaced, negatively charged plates 40 and 41 are insulatingly mounted in any desired manner and in such a position that their faces are perpendicular to the direction of the magnetic field H and just outside the magnetic mirror windings 44, 45. Positively charged rings 42 and 43 are positioned adjacent and parallel to the negative plates 40 and 41, respectively, but further removed from the mirror windings 44, 45, so as to retrain slow ions within the plasma volume.
A positively charged cylindrical members 46 encloses the mirror windings 44, 45, as shown. A plurality of annular magnetic colis 47 are disposed around the member 46 and between the mirror windings 44, 45. Coils 47 and mirror windings 44, 45, provide the containing magnetic field for the ionized particles which are formed in the area formed by these members.
Power supply 57 is provided to supply the operating potentials to the plates 40, 41, rings 42, 43, and member 46. A positive line 58 from supply 57 is connected by line 59 to positive ring 42, and by line 60 to positive ring 43. Member 46 is connected by positive line 61 to supply 57. A negative line 62 from supply 57 is connected by line 63 to plate 40, and by line 64 to plate 41. An oscillating energetic stream 56 of electrons is maintained between plates 40, 41 by the potential gradient maintained between plates 40, 41 and member 46. This operation is based upon the well known PIG principle. It should be understood that a potential gradient may be maintained between plates 40, 41 if such is desired, and this can be accomplished by connecting plate 41 to a positive source of power and removing the positive connection to member 46.
A beam 50 of molecular ions is injected from ion source 48, and through accelerator tube 49 into the path of the energetic oscillating electron stream 56 where a portion of the molecular ions in beam 50 are caused to be dissociated and/ or ionized by electron stream 56 to form a circulating beam 51 of atomic ions. Another beam 54 of molecular ions is injected from ion source 52, and through accelerator tube 53 into the path of oscillating electron stream 56 and in opposing relation to beam 50, as is more clearly shown in the cross-sectional view in FIG. 3, taken on the line 3-3 of FIG. 2. A portion of the molecular ions in beam 54 are caused to be dissociated and/or ionized by the electron stream 56 to form a circulating beam 55 of atomic ions. The accelerator tubes 49 and 53 are not shown in their complete length in FIG. 2 for the sake of clarity in showing the ion paths in the center of the device.
FIG. 2 shows the use of two opposing molecular beams which has the advantage of reducing the injection voltage that is required for the molecular beams to promote efiective formation of a hot plasma within the confining magnetic field. It should be understood that the device of FIG. 2 is not limited to the use of two opposing molecular beams. Only one molecular beam may be employed, or a plurality of pairs of opposing molecular beams may be employed if so desired, only two having been shown for the sake of clarity.
The device of FIG. 2 may also employ the use of an energetic gas are discharge in conjunction with the energetic oscillating stream of electrons, in a manner similar to that of FIG. 1, for effecting dissociation and/ or ionization of one or more molecular ion beams. The device of FIG. 1 may also employ one or more pairs of opposing molecular ion beams in a manner similar to that shown in FIG. 2.
The operating parameters for the device of FIG. 2 are the same as those for FIG. 1, set forth above, when only one molecular ion beam is employed, and the parameters are the same when two opposing beams are used, with the exception that the injection voltage for the molecular beams may be, for example, about onehalf the injection voltage for the molecular beam of FIG. 1. This injection voltage would correspondingly be decreased further as additional pairs of opposing molecular beams are added to the system.
In both FIG. 1 and FIG. 2, the trapped beam or beams of atomic ions may be injected either at a steady rate or at a variable rate. In either case, there will be a plasma of cooler ions and electrons below the beam energy which immediately begins to degrade the beam energy by the usual energy loss processes. The beam or beams tend to retain their original uniformity in direction and slowly spiral down in Larrnor radius as the energy decreases. However, as the energy of the degraded particles approaches that of the plasma particles, the beam is randomized in direction and goes in to the plasma.
The principles of this invention may be employed in a thermonuclear reactor such as disclosed in the patent of Persa R. Bell et al., No. 2,969,308 issued Jan. 24, 1961. The energetic oscillating stream of electrons of the instant invention could be used to supplement the energetic arc discharge in the Bell et al. patent in the formation of a hot plasma in the initial stage of operation of the reactor.
This invention has been described by way of illustration rather than limitation and it should be apparent that the invention is equally applicable in fields other than those described.
What is claimed is:
1. A device for trapping and building an ionized plasma of particles comprising a chamber; means for evacuating said chamber; a pair of spaced, negatively charged electrodes and a positively charged cylinder all mounted within said chamber; means establishing a containing magnetic field within said chamber and oriented along the axis of said chamber and cylinder, said last named means including a pair of magnetic mirror colis mounted on said charged cylinder, one each of said coils being disposed adjacent to each of said pair of charged electrodes, and a plurality of additional magnetic coils being disposed between said mirror coils and mounted on said charged cylinder, said mirror coils having a greater field strength than said additional coils; a second pair of spaced, positively charged electrodes, one each of said second pair of electrodes being positioned adjacent and parallel to one each of said first pair of electrodes, but further removed from said respective mirror coils; electrical power means connected between said first pair of electrodes and said cylinder to establish and maintain an oscillating stream of electrons of selected energy between said first pair of electrodes, said electron stream oriented through said charged cylinder and in alignment with the axis of said chamber; a source of molecular ions; means injecting and accelerating ions from said source into said chamber and said field in a direction normal to said field and into the path of said oscillating electron stream, said stream exciting, dissociating, and ionizing said molecular ions into atomic ions and atomic neutrals, said magnetic fields being of such strength that said atomic ions move into the central portion of said cylinder and are trapped by said field.
2. The device set forth in claim 1, wherein said second pair of positively charged electrodes are in the shape of rlngs.
3. The device set forth in claim 2, wherein said first pair of negatively charged electrodes are in the shape of rings such that said oscillating stream of electrons therebetween is in the form of a substantially hollow 7 cylinder.
" 4. The device set forth'in claim 3, in which there is further provided an anode and a cathode, means initiating and sustaining an energetic arc discharge between said anode and cathode, said discharge having a direction parallel to said magnetic field and oriented in such a position that said molecular ions pass therethrough to thereby supplement said stream of electrons in exciting, dissociating, and ionizing said molecular ions.
5. The device set forth in claim 3, in which there is provided a second source of molecular ions, means injecting and accelerating ions from said second source into said chamber and said field in a direction normal thereto and into the path of said oscillating stream of electrons in opposing relation to the molecular ions injected from said first source.
6. The device set forth in claim 2, wherein said first pair of negatively charged electrodes are in the shape of plates oriented along said chamber axis.
7. The device set forth in claim 6, in which there is provided a second source of molecular ions, means ininjecting and accelerating ions from said second source into said chamber and said field in a direction normal thereto and into the path of said oscillating stream of electrons in opposing relation to the molecular ions injected from said first source.
References Cited UNITED STATES PATENTS 2,927,232 3/1960 Luce 3l363 3,030,543 4/1962 Luce 313-161 3,258,633 6/1966 Swartz 313230 RAYMOND F. HOSSFELD, Primary Examiner U.S. Cl. X.R.