US3441756A - Electrical devices - Google Patents

Description

c: .L u "1 1 5x nunlwu DUUIII 5 12 8502 ER 5 Q 412756 April 29, 1969 GSJANES ETAL 3,441,756

ELECTRICAL DEVICES Filed April 5, 1965 Sheet of 3 GEORGE S. JANES RICHARD H. LEVY F l l INVENTOR.

Maw B MW WM 5 W ATTORNEYS.

April 29, 1969 G, 5, JAMES ET AL 3,441,756

ELECTRI CAL DEVICES Filed April 5, l965 Sheet 2 of 5 TO CURRENT 8: HIGH VOLTAGE SOURCE FIG. 2

GEORGE S.JANES' RICHARD H. LEVY INVENTOR,

I I m 7, FIG. 3 ,ATTORNEYS.

April 29, 1969 G. s. JANES ET AL 3,441,756

ELECTRICAL DEVICES Filed April 1955 Sheet of 3 GEORGE S. JANES RICHARD H. LEVY INVENTOR.

MM w WJMZ? ATTORNEYS United States Patent 3,441,756 ELECTRICAL DEVICES George S. Janes, South Lincoln, and Richard H. Levy,

Boston, Mass., assignors to Avco Corporation, Cincinnati, Ohio, a corporation of Delaware Filed Apr. 5, 1965, Ser. No. 445,357 Int. Cl. H02k 45/00 US. Cl. 310-11 17 Claims ABSTRACT OF THE DISCLOSURE This invention relates to electrical devices and more particularly to an improved construction for and method of operating crossed field electronic devices having a geometry which permits the trajectories of electrons in the crossed electric and magnetic fields to close on themselves.

Apparatus in accordance with the present invention may comprise an evacuated chamber having a geometry which permits the trajectory of an electron in the chamber to close on itself in the presence of static crossed electric and magnetic fields, means for providing in the chamber a magnetic field having a strength sufiicient to provide an electron gyro radius in the chamber that is small compared to the size of the chamber, means for varying the magnetic flux within the chamber and means for injecting a suflicient quantity of electrons into the chamber to produce an electric field. This electrostatically induced electric field will generally be greater than the induced electric field produced by the time varying magnetic field.

The present invention resulted from our research on plasma accelerators operating under conditions such that the electron gyro radius is small compared to the apparatus size which is in turn small compared to the ion gyro radius, and on radiation shielding in space which uncovered a new single component domain of plasma physics containing a wide variety of applications. The term 0 single component is used herein to describe plasma con ditions wherein the number density of electrons exceeds the number density of ions and neutrals to such an extent that the plasma motion is controlled by magnetic and collective electrostatic forces rather than by magnetic and collective inertial (or pressure) forces, i.e. e E /2 nkT or v where s is the permittivity of free space, E is a characteristic electric field in volts per meter, n is a characteristic number density of electrons per cubic meter, k is Boltzmanns constant, T is a typical temperature in degrees Kelvin, p is a typical mass density in kilograms per cubic meter, and v is a typical streaming velocity in meters per second. The presence of a large excess of charged particles of one sign leads to strong electric fields. If the magnetic field B is strong enough to make E/B less than the speed of light and the electron gyro radius smaller than the minimum significant apparatus dimension, then the charged particles will drift with average speed E/B in the direction perpendicular to both E and B. In certain applications, however, e E 2 may be less than nkT or p1 In accordance with the present invention, the electrons 3,441,756 Patented Apr. 29, 1969 are provided by injecting them onto magnetic flux shells simultaneously with the creation or variation of the magnetic field. Thus, if it is assumed that the electron motions are adiabatic, i.e., E+(v B)=0, the electrons can be considered as being confined to flux shells. As used herein, the term flux shell has the following meaning: each magnetic field line can be considered an equipotential since the electrons can flow rapidly along the field lines to nullify any potential gradient that does develop. The equipotential surfaces will in this case contain a family of magnetic field lines; such a family of magnetic field lines comprising an equipotential surface is called a flux shell. If the external magnetic field is changed slowly, such surfaces retain their identity, even though the value of the potential may change. The flux shells serve as a vehicle for transporting electrons away from their point of origin, thus creating strong electric fields. Since the electrons on a particular flux shell also retain their identity as a group, we can also refer to electron shells. This concept, which is basic to the present invention and which we call Inductive Charging, while in a sense analogous to the betatron concept is distinguishable therefrom in that power input in the present invention is utilized to increase the potential energy of the individual charged particles in an electric field While the betatron merely increases the kinetic energy of individual charged particles.

It is an object of the present invention to provide by the use of magnetic fields electron shells which may serve as mobile and indestructible equipotential surfaces.

Another object of the present invention is to provide a high voltage generator.

Another object of the present invention is to permit the production of high electrostatic energy densities in predetermined geometric configurations which may produce high power, short duration oscillations in a manner analogous to pulsed lasers.

A still further object of the present invention is to provide apparatus having an electron shell which constitutes a highly conductive surface as well as an energy source.

A further object of the present invention is to provide apparatus wherein a movable electron shell may form part of a tunable cavity and/ or wave guide.

A still further object of the present invention is to permit the generation of ultra-high temperature electrostatically contained plasma which results in preferential ion heating and ion trapping. When an atom is ionized in crossed electric and magnetic fields, the electron acquires a perpendicular energy equal to the quantity where m is the mass of an electron, while the ion can acquire a perpendicular energy equal to the quantity (E/B) (m /2) where m is the mass of the ion. In the case of deuterium, the deuteron, for example, can acquire more than 3000 times more energy than the electron. Thus, if the electric field is created by a cloud of electrons which are magnetically trapped on the interior axis of a hollow torus or mirror geometry in accordance with a feature of the present invention, the ions will be automatically trapped by the electrostatic field.

According to an embodiment of the present invention for providing ultra-high temperature plasma, there is provided a high vacuum system of tubular geometry closed on itself and surrounded by a toroidal coil which can be energized in a short time, and electron gun means for injecting electrons into the vacuum at velocities in excess of E/B. Electrons which are injected into the high vacuum system, while the magnetic field is rising, are trapped and transported inward away from the outer walls of the high vacuum system on contracting magnetic flux shells. This results in the generation of a radial electric field which in turn produces a region near the axis in which the electrostatic potential is depressed. Thus, when a deuterium (or other gas) atom is ionized in the aforementioned electron shell, the electron thus produced is trapped in the magnetic field while the relatively heavy ion is trapped by the electric field. Because of its greater mass, the ion can acquire a larger kinetic energy in this configuration than can the electron. Thus, the device causes both the preferential heating of ions and the trapping of ions.

According to another embodiment of the present invention for generating a high DC electrostatic potential, there is provided a highly evacuated tubular region defined at its inner and outer periphery by cylindrically shaped electrically conductive walls, which serve as negative and positive electrodes insulated one from another by electrically nonconductive circular end plates which define the ends of the tubular region. Surrounding the tubular or annular region is a coil supplied from any suitable DC source for creating in the annular region an axial DC magnetic field. Provided at the tubular axis of the region is a ferrite core surrounded by a second coil coupled to a source of AC current for varrying the total magnetic flux enclosed within and/or by the tubular or annular region. Electron gun means carried by the inner electrically conductive wall is provided for injecting electrons into the annular region. The electrons which are injected from the electron gun means are carried to the outer wall on typical trajectories in accordance with the present invention. This transport of charge (electrons) is driven by the changing magnetic flux and results in the generation of a high voltage DC potential between the electrically conductive walls. The cyclic repetition of this transport of charge results in the production of high voltage DC power. This feature of the present invention incorporates into a single package both the secondary transformer windings and the high voltage rectifiers which are normally employed in high voltage DC generators.

The novel features that are considered characteristic of the invention are set forth in the appended claims; the invention itself, however, both as to its organization and method of operation, together with additional objects and advantages thereof, will best be understood from the following description of a specific embodiment when read in conjunction with the accompanying drawings, in which:

FIGURE 1 is a schematic top view of a'DC generator in accordance with the present invention;

FIGURE 2 shows details of the electron gun;

FIGURE 3 is a schematic of the electron gun circuit; and

FIGURE 4 is a schematic sectional view illustrating a modificatioin having a generally toroidal configuration for generating electrostatically contained 'high temperature plasma.

Referring now to FIGURE 1, there is shown, by way of example and not of limitation, apparatus in accordance with the present invention for generating a high DC electrostatic potential. As shown in this figure, there is provided a highly evacuated annular region defined by electrically nonconductive cylindrical side walls 11 and 12 and annular end walls 13 and 14, only end wall 13 being shown. The side walls and end walls may be comprised of any suitable electrically nonconductive material such as glass or a ceramic. Assuming that the axial dimension of walls 11 and 13 is greater than their radial spacing, the latter is deemed to be the minimum significant size of region 10.

The inner surface of the side walls 11 and '12 are coated with an electrically conductive material such as silver, which form respectively negative and positive electrodes 15 and 16. These conductive layers are sufficiently thick to carry away any electrostatic surface charges thereby maintaining the surface as a equipotential, but not so thick as to interfere with the passage of magnetic flux through the surface separating adjacent radial regions. Disposed within the cylindrical space defined by wall 12 is a ferrite core 17 surround by a coil 18 which is coupled to an AC source of current 19. Coil 18 may be coupled to a DC source of current and pulsed by means of a conventional thyratron circuit (not shown), if desired. In this case, the electron gun, designated generally by the number 20, should also be pulsed such that it is turned on just before or when coil 18 is pulsed.

Surrounding side wall 11 is a second coil 21 which is coupled to a DC source of current 22.

Disposed within the annular region 10 is conventional electron gun means for injecting electrons into the annular region v10. A suitable configuration for the electron gun is shown in FIGURE 2. As best shown in FIG- U-RE 2, the electron gun may comprise an emitter 30 of tantalum or tungsten supported on two relatively rigid standoff leads 31 and 32. The accelerator 33, which may also be supported on a standofi lead 34 grounded to electrode 16, may for example be comprised of a screen of nickel or stainless steel plate having a large number of small holes to permit the passage of electrons through the accelerator from the emitter 30. Directing attention now to FIGURE 3, there is shown a schematic diagram for providing pulsed operation of the electron gun. As shown in FIGURE 3, the accelerator 33 is grounded. Emitter 30 is coupled across a battery 35 and series connected resistors 36 and 37. The output of a conventional thyratron circuit, designated generally by the number 38, is connected between resistors 36 and 37. Thus, it will be apparent that when the thyratron fires, a negative 2000 volts will be applied intermediate resistors 36 and 37 to actuate the electron gun.

Returning now to FIGURE 1, electrons which are injected into region 10 from the electron gun 20 are carried to the outer electrode 15 on typical trajectories 40 similar to that illustrated in FIGURE 1 in accordance with the inductive charging concept of the present invention. This transport of charges or carrying of electrons to electrode 15 is driven by the changing magnetic flux in region 10 and results in the generation of high voltage DC power which may be utilized by connecting a load across electrodes 15 and 16.

It should be noted that the apparatus shown in FIG- URE l incorporates into a single device both the secondary transformer windings and the high voltage rectifiers which are normally employed in high voltage DC generators. It is to be understood that the present invention, as applied to apparatus for generating a high DC electrostatic potential, is not limited to that shown and described. Thus, for example, the disclosed apparatus will operate without the ferrite core although at the probable expense of a decrease in efficiency. Furthermore, the AC coil 18 may be incorporated into or combined with the outer DC coil 21. The use of the ferrite core merely represents one way in which the flux enclosed by the annular region can be varied thereby altering the equilibrium radius of the enclosing electron shells. Further, the role of the outer and inner electrodes 15 and 16 may be interchanged by mounting the electron gun on the outer wall. Still further, if desired, axial electric fields and radial magnetic fields may be used. In this case, the end walls 13 and 14 must be silvered and serve as the electrodes while the inner and outer cylindrical walls 11 and 12 serve as simple insulators. Also the wall carrying the electron gun may be made up of a single cylinder of highly conducting material which is split axially at one point, thereby allowing the magnetic flux to enter over a small portion of the total circumferential coordinates. In this embodiment, the electron gun is located in the split.

It will now be appreciated that the moving magnetic field provided in region 10 eliminates the necessity for example of the belt in a high voltage Van de Graalf generator. Further, those skilled in the art will now appreciate that the inductive charging concept of the present lnvention may be utilized in the field of microwave corn munications such as, for example, by generating movable electron shells for the provision of tunable cavities and/ or wave guides. Those skilled in the art will further appreciate that movable electron shells which function as grids may be provided in accordance with the present invention and that such grids are immune to the heating and erosion problems commonly associated with conventional metallic grids. Accordingly, a grid formed in accordance with the present invention may be used, for example, for the acceleration of ions in space propulsion applications.

Attention is now directed to FIGURE 4 which shows a modification of the present invention having an essentially toroidal geometry for generating an electrostatically contained high temperature plasma. The apparatus shown in FIGURE 4 comprises a toroidal region 45 defined by the inner surface of an electrically nonconductive tubular container 46 composed of an electrically nonconductive material such as glass or quartz. Surrounding the container is a multi-turn coil 47 coupled to a source of current 48 through a switch 49. Disposed within and carried by the container 46 is an electron gun 50 of the type previously described for injecting electrons into the toroidal region 45 at velocities in excess of E /B, where E,. is the radial electric field and B is the circumferential magnetic field.

Pipe 51 and means 52 are provided for injecting a gas or ions such as, for example, deuterium ions, into region 45.

The injection of electrons into region 45 while the magnetic field B produced by the coil 47 is rising in region 45 results in these eectrons being trapped by the rising magnetic field and transferred into or toward the center of region 45 on magnetic flux shells. The aforementioned trapping and movement of electrons results in the generation of a radial electric field which, in turn, depresses the electrostatic potential in the central portion of region 45. Neutral atoms (deuterium atoms) in or introduced into region 45 wi l be ionized by the trapped electrons therein. The electrons produced by this ionization will in turn be trapped by the magnetic field while the relatively heavy ions will be trapped by the electric field. The ions of course have a considerably greater mass than the eectrons and for this reason can acquire a larger kinetic energy than the electrons. Thus, in the apparatus of FIGURE 4, both the preferential heating of ions and the trapping of ions occur simultaneously. For the embodiment shown in FIGURE 4, the minimum significant size of region 45 is deemed to be the radius about its I tubular axis. Ions can be injected into or provided in region 45 in several Ways. For example, deuterium gas may be introduced through pipe 51 and means 52 and thereafter ionized in region 45. In this case, means 52 may be a control valve. On the other hand, if ions rather than atoms are to be injected into region 45, means 52 may comprise a conventional ion source wherein deuterium gas or the like is ionized exterior of region 45 and only the ions are injected into region 45. A suitable ion source for this purpose is disclosed in National Aeronautics and Space Administration Technical Note D-585, January 1961, entitled An Ion Rocket with an Electron- Bombardment Ion Source, by Harold R. Kaufman.

Attention is directed to a previously suggested similarity in configuration of the chambers shown in FIGURE 1 and FIGURE 4. Thus, whereas the region of FIGURE 1 has been referred to as annular and the region 45 of FIGURE 4 has been referred to as toroidal for clarity, it is to be noted that both of these regions may also be described as being tubular in shape, the ends of tubular region 10 merely being closed whereas tubular region 45 is endless in that it is closed on itself. Accordingly, tubular as used in the claims is generically descriptive of both regions. Since both regions may be defined as tubular, they of course each have a tubular axis which in the case of region 10 is straight and in the case of region 45 is ring-shaped.

The various features and advantages of the invention are thought to be clear from the foregoing description. Various other features and advantages not specifically enumerated will undoubtedly occur to those versed in the art, as likewise will many variations and modifications of the preferred embodiment illustrated, all of which may be achieved without departing from the spirit and scope of the invention as defined by the following claims.

What is claimed is:

1. In an electrical device, the combination comprising:

(a) an evacuated chamber having at least one substantially cylindrical side wall defining at least in part a region which permits the motion of an electron in said chamber to close on itself in the presence of crossed electric and magnetic fields;

(b) means for providing in said chamber a magnetic field substantially everywhere parallel to said side wall and having a strength sufiicient to provide an electron gyro radius in said chamber that is small compared to the minimum significant size of said chamber;

(0) means for rapidly increasing the magnetic flux within said region; and

(d) means for injecting electrons into said chamber during said increase of magnetic flux at a rate sufiicient that the induced electric field of said electrons is greater than the electric field produced by variation of said magnetic field.

2. In an electrical device, the combination comprising:

(a) an evacuated chamber having at least one side wall substantially cylindrical at substantially any given cross section defining at least in part a region which permits the motion of an electron in said region to close on itself in the presence of crossed electric and magnetic fields:

(b) means for providing in said chamber a magnetic field substantially everywhere parallel to said side wall and having a strength sufficient to provide an electron gyro radius in said chamber that is small compared to the minimum significant size of said chamber;

(c) means for rapidly increasing the magnetic flux within said region; and

(d) means for injecting electrons into said region during said increase of magnetic fiux at a rate sufficient that the induced electric field of said electrons is greater than the electric field produced by variation of said magnetic field, the mean direction of travel of said electrons being normal to both the induced electric field of said electrons and said magnetic field.

3. In an electrical device, the combination comprising:

,(a) an evacuated tubular chamber having a tubular axis wherein the motion of an electron in said chamber may close on itself about said axis in the presence of crossed electric and magnetic fields;

(b) means for providing in said chamber a magnetic field substantially everywhere parallel to said tubular axis and having a strength sufficient to provide an electron gyro radius in said chamber that is substantially less than the minimum significant size of said chamber;

(c) means for rapidly increasing the magnetic flux within said chamber from a first value as low as zero to a second higher value; and

((1) means for injecting electrons into said chamber during said increase of magnetic flux at a rate sufficient that the induced electric field of said electrons is greater than the electric field produced by variation of said magnetic field, the means direction of travel of said electrons being about said tubular axis and normal to both the induced electric field of said electrons and said magnetic field.

4. In a direct current potential generator, the combination comprising:

(a) an evacuated annular chamber defined by two concentric cylindrical side walls and two circular end walls;

(b) means for providing in said chamber a magnetic field substantially everywhere parallel to said side walls and having a strength sufficient to provide an electron gyro radius in said chamber that is small compared to the minimum significant size of said chamber;

(c) means for rapidly increasing the magnetic fiux within said chamber; and

(d) means for injecting electrons into said chamber during said increase of magnetic flux at a rate sulficient that the induced electric field of said electrons is greater than the electric field produced by variation of said magnetic field, the mean direction of travel of said electrons being normal to both the induced electric field of said electrons and magnetic field.

5. In a direct current potential generator, the combination comprising:

(a) an evacuated annular chamber defined by two concentric cylindrical side walls and two circular end walls;

(b) means for providing in said chamber a magnetic field substantially everywhere parallel to said side walls and having a strength sufficient to provide an electron gyro radius in said chamber that is small compared to the minimum significant size of said chamber;

(c) means for rapidly increasing the magnetic flux within said chamber;

((1) means for injecting electrons into said chamber during said increase of magnetic flux at a rate sulficient that the induced electric field of said electrons is greater than the electric field produced by variation of said magnetic field, the mean direction of travel of said electrons being normal to both the induced electric field of said electrons and magnetic field; and

(e) electrode means disposed on the surfaces of said side walls within said chamber.

6. The combination as defined in claim 5 wherein said means for injecting electrons into said chamber includes electron gun means.

7. The combination as defined in claim 5 wherein said means for providing said magnetic field includes an electrical coil surrounding the outermost side wall.

8. The combination as defined in claim 7 wherein said means for varying the magnetic flux within said chamber includes an electrical coil and a ferrite core surrounded by the innermost side wall.

9. In a direct current potential generator, the combination comprising:

(a) an evacuated tubular chamber having a tubular axis and closed on itself;

(b) means including a coil surrounding substantially all of said chamber for providing in said chamber a magnetic field substantially everywhere parallel to said tubular axis and having a strength sutficient to provide an electron gyro radius in said chamber that is small compared to the minimum significant size of said chamber;

(0) means for rapidly increasing the magnetic fiux within said chamber; and

(d) means for injecting electrons into said chamber during said increase of magnetic flux at a rate sufiicient that the induced electric field of said electrons is greater than the electric field produced by variation of said magnetic field, the mean direction of travel of said electrons being about said tubular axis and normal to both the induced electric field of said electrons and said magnetic field.

10. In a direct current potential generator, the combination comprising:

(a) an evacuated tubular chamber having a tubular axis and closed on itself;

(b) means for providing in said chamber a magnetic field substantially everywhere parallel to said tubular axis and having a strength suflicient to provide an electron gyro radius in said chamber that is small compared to the minimum significant size of said chamber;

(0) means for rapidly increasing the magnetic flux within said chamber;

(d) means for injecting electrons into said chamber during said increase of magnetic flux at a rate sufficient that the induced electric field of said electrons is greater than the electric field produced by variation of said magnetic field, the mean direction of travel of said electrons being about said tubular axis and normal to both the induced electric field of said electrons and said magnetic field; and

(e) means for injecting at least components of a gas into said evacuated chamber.

11. The combination as defined in claim 10 wherein said components are ions.

12. The combination as defined in claim 10 wherein said components are atoms.

13. In an electrical device, the combination comprising:

(a) an evacuated tubular chamber having a tubular axis and closed on itself;

(b) means comprising an electrical coil surrounding substantially all of said chamber for providing in said chamber a magnetic field parallel to said tubular axis and having a strength sufiicient to provide an electron gyro radius in said chamber that is small compared to the minimum significant size of said chamber;

(c) means for varying the magnetic flux within said chamber;

(d) means for injecting electrons into said chamber at a rate sufficient that the induced electric field of said electrons is greater than the electric field produced by variation of said magnetic field, the mean direction of travel of said electrons being about said tubular axis; and

(e) means for injecting a gas into said evacuated chamber.

14. The method of generating electric fields comprising the steps of:

(a) providing in an evacuated environment having a tubular axis a magnetic field comprising magnetic lines of flux substantially everywhere parallel to said tubular axis and having a strength suflicient to provide an electron gyro radius in said envoronment that is small compared to the diameter of said environment;

(b) rapidly increasing the lines of flux enclosed by said evacuated environment; and

(c) injecting electrons into said magnetic field during said increase of magnetic flux at a rate to generate an induced electric field due to said electrons that is greater than the electric field produced by said increasing magnetic field, the mean direction of travel of said electrons being about said tubular axis and normal to both the induced electric field of said electrons and said magnetic field.

15. The method of generating electric fields comprising the steps of:

(a) providing in an evacuated environment having a tubular axis a magnetic field comprising magnetic lines of flux substantially everywhere parallel to said tubular axis and having a strength sufiicient to provide an electron gyro radius in said environment that is small compared to the diameter of said environment;

3,441,756 9 10 (b) rapidly increasing the lines of flux enclosed by said 17. The method of generating electric fields comprising evacuated environment; the steps of: (c) injecting electrons into said magnetic field during (a) providing in an evacuated environment having a said increase of magnetic flux at a rate to generate an induced electric field due to said electrons that tubular axis a magnetic field comprising magnetic lines of flux substantially everywhere parallel to said is greater than the electric field produced by said tubular axis and having a strength sufficient to provarying magnetic field, the mean direction of travel vide an electron gyro radius in said environment that of said electrons being about said tubular axis and is small compared to the diameter of said environnormal to both the induced electric field of said elece trons nd aid magnetic fi 1d;and (b) rapidly increasing the lines of flux enclosed by said evacuated environment;

(d) providing ions in said magnetic field.

(c) injecting electrons into said magnetic field during 16. The method of generating electric fields comprising the steps of: said increase of magnetic flux at a rate to generate (a) providing in an evacuated environment having a, an induced electric field due to said electrons that is tubular axis a magnetic field comprising magnetic greater thaf} the electric field Produced by Said ylines of flux substantially everywhere parallel to said magnetlc l the mean direction of travel of tubular axis and having a strength sufficient to sa1d electrons being about said tubular axis and norvide an electron gyro radius in said environment that mal to bot}? the mdllced elecmc field of sa1d elecis small compared to the diameter of said environtrons arida1dmagnenc field; and menu (d) permlttmg electrons to flow through an electrical p y increasing the number of lines of flux em load coupled across sa1d induced electric field.

closed by said evacuated environment;

(c) injecting electrons into said magnetic field during said increase of magnetic flux at a rate to generate References Cited UNITED STATES PATENTS an induced electric field due to said electrons that g 7- is greater than the electric field produced by said {ex er e a varying magnetic field, the mean direction of travel 3304463 2/1967 Wllbur 3315-39 of said electrons being about said tubular axis and normal to both the induced electric field of said elec- DAVID Primary Examiner trons and said magnetic field; and US. Cl. X.R.

(d) injecting a gas into said magnetic field. 3 13 157

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