US3445722A - Plasma manipulation method and apparatus - Google Patents

Description

May2o,19s9 ..-,R.SCOTT Em. 3,445,722 'I l PLASMA MANIPULATION METHOD AN) APPARATUS Filed Nov. 4. 1964 United States Patent 3,445,722 PLASMA MANIPULATION METHOD AND APPARATUS Franklin R. Scott, Hans H. P. Fleischmann, and Ralph G.

Tuckfield, Jr., San Diego, Calif., assignors, by mesne assignments, to Gulf General Atomic Incorporated, San

Diego, Calif., a corporation of Delaware Filed Nov. 4, 1964, Ser. No. 408,946 Int. Cl. H01j 7/24, 17/26; H05b 31/26 U.S. Cl. 315-111 16 Claims ABSTRACT F THE DISCLOSURE A method and apparatus for manipulating plasma is provided utilizing a direct current linear multipolar magnetic eld with stationary linear poles and an axis parallel to the poles on which the magnetic field strength is zero. Gas or plasma is injected along the axis. An electrostatic eld may be produced which is orthogonal with the magnetic field and has its maximum and minimum potentials at linear poles each associated with each of the magnetic field poles. Variation of the magnetic or electric field strength permits manipulation of the gas or plasma. The axis may be curved to permit plasma purification.

This invention relates generally to methods of and apparatus for producing and manipulating electrical plasma and, more specifically, to a device in which a plasma may be produced and manipulated by multipolar electric and magnetic fields and a method of producing and manipulating a plasma with such fields.

In recent years methods and apparatus have been developed for producing and manipulating electrical plasmas, which plasmas are ionized gases comprising approximately equal numbers of positively charged ions and free electrons at high temperatures. Such plasmas may be utilized as sources of electron beams which in turn may be used in processing, forming or joining materials as well as in a variety of other useful applications. Plasmas may also be utilized to produce positive or negative ion beams which may be used, for example, to clean or etch surfaces without destructive heating. In addition, if a plasma is formed from a suitable gas or mixture of gases such as deuterium or tritium, fusion reactions may occur within the plasma body. Such fusion reactions may produce highly energized protons or neutrons, thus providing a source of neutrons or protons. If the proper conditions are realized the energy obtained from the fusion reactions may exceed the input energy and provide useful power.

In all of these applications it is necessary to produce the plasma by ionizing a gas and heating the gas to temperatures at which ionization will be maintained. Various manipulations of the plasma may then be desired such as confiing it in a stable geometrical configuration, heating it to still higher temperatures, accelerating, guiding, focusing, bunching or phasing the plasma or performing two or more of these operations.

One of the major problems in manipulating a plasma in various ways arises from plasma impurities. For example, plasma manipulation may be hampered by the presence of neutral atoms or molecules which are not affected by the electric or magnetic fields ordinarily used to manipulate the plasma. Such impurities usually originate in the region of a plasma gun wherein the plasma is produced and have a velocity spectrum similar to the charged particles in the plasma, which makes their separation difficult. Accordingly, a need has arisen for an improved method and apparatus with which plasma may be purified. A plasma purification device which can also 3,445,722 Patented May 20, 1969 ice produce a plasma from an un-ionized gas will be still more useful because the initial impurities arising from the use of a plasma gun may thereby be eliminated. Furthermore, such a device which also may be utilized to confine, heat and otherwise manipulate a plasma in a variety of ways will be extremely useful in many of the applications of plasmas.

It is, therefore, an important object of this invention to provide an improved method of and apparatus for producing and purifying an electrical plasma and performing a variety of manipulations of the plasma and its component particles.

A further object of the invention is to provide an improved method and apparatus for ionizing a gas to form a plasma and for heating and storing the plasma in a stable configuration.

A still further object of the invention is to provide an improved method and apparatus for accelerating and guiding a plasma in a predetermied manner.

Yet another object of the invention is to provide a method and apparatus for focusing, bunching and phasing a moving electrical plasma.

Another object of the invention is to provide a device for producing and manipulating electrical plasma which is relatively simple in operation and construction.

Other objects and advantages of the invention will become apparent from the following description when considered in conjunction with the accompanying drawings in which:

FIGURE 1 is a partially broken away perspective view of a device showing various of the features of the invention;

FIGURE 2 is a sectional elevational view taken along line 2-2 of FIGURE l;

FIGURE 3 is an end elevational view taken along line 3 3 of FIGURE 2;

FIGURE 4 is an end elevational view taken along line 4-4 of FIGURE 2;

FIGURE 5 is a partially schematic and partially sectional view taken along line 5-5 of FIGURE 2; and

FIGURE 6 is a plan View of another embodiment of the present invention.

As shown in the accompanying drawings the present invention generally includes a vacuum sealed housing 10 which encloses means 12 for producing a multipolar magnetic field within the housing and means 16 for producing a multipolar electric field within the housing. The electric and magnetic fields produced by the means 12 and means 16 have configurations, as shown in FIGURE 5, such that the two fields are orthogonal at all points with the exception of a central axis 17 Where no fields exist. Plasma introduced into the housing may be purified, confined, heated, accelerated, guided, focused, bunched and phased by suitable manipulation of the two fields. In addition, by suitable manipulation of the electric field an un-ionized gas introduced into the housing 10 may be transformed into a plasma.

More specificaly, the housing 10 illustrated in FIG- URE 1 is in the form of an elongated parallelepiped having its longitudinal dimension horizontally disposed and having rectangular vertical faces 18 and 20 at its opposite ends. The housing 10 is connected through an opening 22 in one wall to a device for evacuating the housing (not shown) such as a diffusion pump. A circular port 24, through which un-ionized gas or plasma may lbe introduced into the housing 10, is provided at the center of the vertical face 18. As shown, a plasma gun 26 for producing and injecting plasma into the housing 10 is attached to the face 18 with its output end 28 being adjacent to the port 24 and the interface between the output end 23 of the plasma gun and the face 18 of the housing being vacuum sealed. A fast acting mechanical valve for introdcing un-ionized gas into the housing may, of course, be substituted for the plasma gun when it is desired to utilize the present invention to produce the plasm aas well as to manipulate it.

As best appears in FIGURE 2 the means 12 for producing the magnetic field in the housing 10 generally includes a plurality of straight conductors 32 arranged parallel to one another and extending horizontally through the housing 10 and the faces 18 and 20. The conductors 32 are spaced at equal intervals on the circumference of a circle which is concentric with the circular port 24 and is oriented in a vertical plane, thereby defining a generally cylindrical space 33 in which plasma may be confined and manipulated. The conductors 32 are electrically interconnected with each other and a source of electric current 34, as will be hereinafter described, so that the current through adjacent conductors fiows in opposite directions.

More specifically, in the embodiment illustrated in FIGURE 1 the conductors 32 are in the form of six 3t-inch diameter bare copper rods which are electrically insulated from the faces 18 and 20, although rods or wires of other conductive materials and other dimensions could, of course, be used. The rods are spaced on a circle having a radius of 7.5 centimeters in the illustrated embodiment. The ends of the rods 32 which extend through the face of the housing 10 are each attached to a fiat ring 38 fabricated of a conductive material which serves to interconnect the rods 32. The ring 38 comprises a circumferential portion 40 having a radius of l5 centimeters and six posts 42 extending radially inward to which the rods 32 are attached. Adjacent rods are thereby connected in series.

Similarly, the ends of the rods 32 which extend through the face 18 of the housing 10 are each attached to one of two fiat conductive rings 44 and 46 disposed parallel to and in spaced relation to one another. The rings 44 and 46 each comprise a circumferential portion 48 having a radius of 15 centimeters and posts 50 extending radially inward to which the ends of the rods 32 are attached. One half of the rods 32 are attached to each of the rings 44 and 46. The rings 44 and 46 interconnect the rods in series and to a source of electrical current 34, shown in the illustrated embodiment as a step down transformer 54 connected through a switch means 55 to a capacitor bank 56 which is charged by a suitable means (not shown).

The magnetic field created by currents in the rods 32 is a linear multipolar magnetic field having the cross sectional configuration shown in FIGURE 5. With this so-called multiple cusp configuration, in which the magnetic field is convex toward the central axis 17 of the space 33, the magnetic field increases with the radial distance from the axis 17. Consequently the equilibrium position of plasma is at the center of the cusped geometry. Perturbations of the plasma in this equilibrium position protrude into regions of stronger magnetic fields which force the perturbations back to the equilibrium position. Even individual particles escaping from the main body of plasma find themselves in a stronger magnetic field from which they are ejected back into the body of the plasma. The effect of the currents through the connecting rings 38, 44 and 46 on the magnetic field in the space 33 is minimized by the interconnection of the rods 32 on the circumferential portions of the rings which have a larger radial dimension than that of the space 33.

It will be apparent that plasma, injected by the plasma gun 26 parallel to the axis 17 will be generally confined in the central portion of the space 33 by the magnetic field. The field may thus guide the plasma in a straight line by generally preventing radial diffusion of the plasma. In addition if the conductors 32 are curved as shown in FIG- URE 6 axially injected plasma may be purified. In such an embodiment the charged particles in the plasma are guided around the curve by the magnetic field while the neutral particles follow straight paths uninfiuenced by the magnetic field.

Although a magnetic field having a cusped geometry is a generally stable confinement configuration for plasma, some particle loss at the points of the cusps is caused by particles attaching themselves to the lines of maximum magnetic force between conductors (separatrices). A particle passing through one of these points will momentarily travel in a straight line and its subsequent motion will bear little relationship to its motion prior to its passage through the center. Such particles may be carried out of the confinement space along these lines of maximum magnetic force leading out of the confinement space.

A means of minimizing such losses as well as of producing plasma and performing various manipulations of plasma is provided by the present invention through means 16 for producing an electric field having the configuration shown in FIGURE 5, in which the electric lines of force are at all points in the space 33 perpendicular to the magnetic lines of force.

The means 16 for producing such an electric field comprises a plurality of straight conductive tubes 58 equal in number to the number of rods 32, each tube being disposed coaxially about and insulated from one of the rods. In the illustrated embodiment, the tubes are formed of .015 inch thick stainless steel and have internal diameters of one inch. Alternate tubes are connected through a switch means 59 to opposite sides of a capacitor bank 60 which is charged by a suitable means (not shown) thus creating a mutlipole electric field Within the housing 10. Since the tube surfaces are also fiux surfaces of the magnetic field created by the current in the rods 32, the electric and magnetic fields are orthogonal at all points in the space 33, except the central axis 17 Where no fields exist.

The superimposition of this linear multipole electric field on the linear multipole magnetic field tends to minimize the loss of particles at the points of the cusps since the greatest electrical field strength is at the cusp points and is directed at right angles to the magnetic lines of force, thus tending to force particles at such points into the central region of the confinement space.

In addition, these superimposed fields impart to a plasma introduced into the space 33 a drift velocity parallel to the central axis 17 which is equal to 10m/B at all points in the space 33, where E is the electric field strength and B is the magnetic field strength. This is true because the E and B vectors are orthogonal at all points and lie in planes perpendicular to the axis 17. This drift velocity has the same direction for both positively and negatively charged particles. It will be apparent that a variety of manipulations of plasma may be performed by varying either the electric or magnetic field strengths or both, either axially or temporarily. Among such manipulations are acceleration of a plasma body, focusing a beam of particles on a point, bunching of particles and phasing of particles, i.e. segregating positive and negative particles.

Furthermore a plasma may be produced from an unionized gas introduced into the space 33 by pulsing the electric field. Thus the impurities usually introduced into a plasma by use of a conventional plasma gun are eliminated.

In one embodiment of the invention, as previously described in part, the conductors 32 are formed of 3% inch diameter bare copper rods approximately centimeters long and are mounted on a circle having a radius of 7.5 centimeters. The rings 38, 44 and 46 have a radial dimension of 15 centimeters. The tubes 58 are formed of .015 inch thick stainless steel and have internal diameters of one inch. The housing 10 is evacuated to a pressure of approximately 1 106 torr prior to injection of plasma or un-onized gas. In operation a fast valve permits approximately .05 cubic centimeter of helium gas at atmospheric pressure to enter the space 33 eighty microseconds before firing the capacitor bank '56 supplying current to the rods. Current is supplied to the rods by means of an 80:1 step down transformer 54, the primary of which is connected to a 12 kv., 120 uf. capacitor bank 56 which is charged to 6 klovolts. A current through the rods of 7000 amps produces a magnetic field strength of `800 gauss between the rods. The tubes S8 are connected to a gf. capacitor bank 60 which is charged to 1 kilovolt resulting in an electric field strength of 80 v./cm. The capacitor bank 60 is connected to the tubes 58 at the same time as the capacitor bank y56 is connected to the rods 32.

Various changes and modifications may be made in the above described device for producing and manipulating plasma without departing from the invention. For example the orthogonal electric and magnetic fields could be in the form of a toroid or curved in a great variety of ways which would fall within the spirit and scope of the present invention, various features of which are set forth in the accompanying claims.

What is claimed is:

1. Apparatus for manipulating plasma comprising means for producing a direct current linear multipolar magnetic field in a space with a plurality of stationary linear poles and a linear axis parallel to said poles on which the magnetic field strength is zero, and means for injecting gas into said space along said axis, said gas being ionized to produce a plasma.

2. Apparatus for manipulating and purifying plasma comprising means for producing a direct current curvilinear multipolar magnetic field in a space with a plurality of stationary linear poles and a linear axis parallel to said poles on which the magnetic field strength is zero, and means for injecting gas into said space along said axis, said gas being ionized to produce a plasma.

3. Apparatus for manipulating plasma comprising means for producing a direct current multipolar magnetic field in a space with a plurality of stationary linear poles and a linear axis parallel to said poles on which the magnetic field strength is zero, means for producing a multipolar electrostatic field in said space with a plurality of stationary parallel linear poles at which the electrostatic field has its maximum and minimum potentials, each pole being associated with a respective magnetic field pole, and a linear axis collinear with the magnetic field axis on which the electrostatic field strength is zero, said magnetic field and said electrostatic field being orthogonal at all points in said space, and means for injecting gas into said space along said axes, said gas being ionized to produce a plasma.

4. Apparatus for manipulating plasma comprising means for producing a direct current multipolar magnetic field in a space with a plurality of stationary linear poles and a linear axis parallel to said poles on which the magnetic field strength is zero, means for producing a multipolar electrostatic field in said space with a plurality of stationary parallel linear poles at which the electrostatic field has its maximum and minimum potentials, each pole being associated with a respective magnetic field pole, and a linear axis collinear with the magnetic field axis on which the electrostatic field strength is zero, said magnetic field and said electrostatic field being orthogonal at all points in said space, means for injecting gas into said space along said axes, said gas being ionized to produce a plasma, and means for varying the strength of said magnetic field.

5. Apparatus for producing and manipulating plasma comprising means for producing a direct current multipolar magnetic field in a space with a plurality of stationary linear poles and a linear axis parallel to said poles on which the magnetic field strength is zero, means for producing a multipolar electrostatic field in said space with a plurality of stationary parallel linear poles at which the electrostatic field has its maximum and minimum potentials, each pole being associated with a respective magnetic field pole, and a linear axis collinear with the 6 magnetic field axis on which the electrostatic field strength is zero, said magnetic field and said electric field being orthogonal at all points in said space, means for injecting gas into said space along said axes, said gas being ionized to produce a plasma, and means for varying the strength of said electrostatic field.

6. Apparatus for producing and manipulating plasma comprising means for producing a direct current multipolar magnetic field in a space with a plurality of stationary linear poles and a linear axis parallel to said poles on which the magnetic field strength is zero, means for producing a multipolar electrostatic field in said space with a plurality of stationary parallel linear poles at which the electrostatic field has its maximum and minimum potentials, each pole being associated with a respective magnetic field pole, and a linear axis collinear with the magnetic field axis on which the electrostatic field strength is zero, said magnetic field and said electrostatic field being orthogonal at all points in said space, means for injecting gas into said space along said axes, said gas Ibeing ionized to produce a plasma, means for varying the strength of said magnetic field, and means for varying the strength of said electrostatic field.

7. Apparatus for guiding plasma comprising a housing, means for evacuating said housing, an even number of stationary linear conductors within said housing, said conductors being disposed parallel to one another and spaced about the circumference of a circle in a plane perpendicular to said conductors, means for causing a direct electric current to flow in opposite directions in adjacent conductors so that a direct current linear multipolar magnetic field exists in the space adjacent to the conductors with a plurality of stationary linear poles and a linear axis parallel to said poles on which the magnetic field strength is zero, and means for injecting gas into said space along said axis, said gas being ionized to produce a plasma.

8. Apparatus for guiding and purifying plasma comprising a housing, means for evacuating said housing, an even number of stationary curvilinear conductors within said housing, said conductors being disposed parallel to one another and spaced about the circumference of a circle in a plane perpendicular to the conductors, and means for causing a direct electric current to flow in opposite directions in adjacent conductors so that a direct current curvilinear multipolar magnetic field exists in the space adjacent to the conductors with a plurality of stationary curvilinear poles and a curvilinear axis parallel to said poles on which the magnetic field strength is zero, and means for injecting gas into said space along said axis, said gas being ionized to produce a plasma.

9. Apparatus for producing and manipulating plasma comprising a housing, means for evacuating said housing, an even number of stationary linear conductors within said housing, said conductors being disposed parallel to one another and spaced about the circumference of a circle in a plane perpendicular to the conductors, means for causing a direct electric current to flow in opposite directions in adjacent conductors so that a direct current linear multipolar magnetia field exists in the space adjacent to the conductors, a conductive tube disposed about and insulated from each of said conductors, the surface of each of said tubes being a flux surface of the magnetic field, and means for placing equal and opposite charges on adjacent tubes, so that a stationary linear multipolar electrostatic field is created in the space which is orthogonal with the magnetic field at all points in the space with a plurality of stationary parallel linear poles at which the electrostatic field has its maximum and minimum potentials, each pole being associated with a respective magnetic field pole, and a linear axis collinear with the magnetic field axis on which the electrostatic field strength is zero, and means for injecting gas into said space along said axes, said gas being ionized to produce a plasma.

10. A method of manipulating plasma comprising creating in a space a direct current magnetic eld with a plurality of stationary parallel linear poles and a linear axis parallel to said poles on which the ,magnetic field strength is zero, and injecting a gas into said space along said axis, said gas being ionized to create a plasma.

11. A method in accordance with claim 10 wherein said magnetic eld poles and said magnetic field axis are curvilinear so that the plasma is puried.

12. A method in accordance with claim 10 comprising creating in said space a multipolar electrostatic eld having a plurality of stationary parallel linear poles at which the electrostatic field has its maximum and minimum potentials, each pole being associated with a respective magnetic field pole, and a linear axis collinear with said magnetic field axis on which the electrostaticl field strength is zero, said electrostatic field and said magnetic field being orthogonal at all points in Said space.

13. A method in accordance with claim 12 comprising selectively-varying the strength of said magnetic eld.

14. @method in accordance with claim 12 comprising selectively varying the strength of said electrostatic field.

15. A method in accordance with claim 14 comprising 8 injecting an un-ionized gas into said space and ionizing said un-ionized gas to produce said plasma.

16. A method in accordance with claim 10 wherein said gas is ionized before it is injected into said space.

References Cited UNITED STATES PATENTS 2,933,646 4/1960 Reder 313-231 X 3,002,912 10/1961 Spitzer 313-63 X 3,029,199 4/ 1962 Baker 176-6 3,113,427 12/1963 Meyer 313-231 X 3,156,621 11/1964 Josephson 313-161 X 3,283,205 11/1966 De Bolt 315-111 FOREIGN PATENTS 158,026 1/1964 U.S.S.R.

JAMES W. LAWRENCE, Primary Examiner.

R. F. HOSSFELD, Assistant Examiner.

U.S. Cl. X.R. 313-231

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