WO1990013136A1

WO1990013136A1 - Magnetic fusion reactor and ignition method

Info

Publication number: WO1990013136A1
Application number: PCT/US1990/002056
Authority: WO
Inventors: Richard C. Auchterlonie
Original assignee: Auchterlonie Richard C
Priority date: 1989-04-17
Filing date: 1990-04-17
Publication date: 1990-11-01
Also published as: AU6068190A

Abstract

To eliminate the need for high-speed capacitor bank, a plasma focus device stores energy in a magnetohydrodynamic vortex ring (10). To suddenly release the stored energy, the magnetic field vector (Be) on the outer surface of the ring (10) is rotated, and the external magnetic field (Be) is increased to compress the ring until it becomes unstable and collapses due to magnetic field-line reconnection (Fig. 5). Therefore most of the energy in the internal magnetic field (Bo) of the vortex ring (10) is converted to kinetic energy or heat on an Alfven time scale. The result is a smaller high-density, high-temperature force-free vortex ring (10).

Description

MAGNETIC FUSION REACTOR AND IGNITION METHOD Technical Field

This invention relates to magnetic fusion nuclear reactors, and in particular to plasma focus devices in which plasma is concentrated, heated, and confined by magnetic fields arising from electrical current conducted in the plasma itself. Background Art

In a dense plasma focus reactor, an electrical discharge heats, compresses, and concentrates a plasma of thermonuclear fuel at a focus point within a reaction chamber. Typically the power for the electrical discharge is provided a capacitor bank. For "break-even" size reactors the capacitor voltage should be on the order of megavolts, and the capacitor bank should be designed to have a low-inductance discharge circuit. Such a capacitor bank is described in U.S. Patent 4,446,096. Development along these lines has been conducted by the Department of Defense in its "Advanced Power Project." Aside from the fact that the Department of Defense has not released its neutron yield data, the commercial development of the dense plasma focus has been hampered by the lack of public or private funds for the construction of a sufficiently large high-voltage, high-speed capacitor bank. Interest has therefore been directed to using the plasma itself for energy storage to reduce the required energy storage capacity of the capacitor bank. It was reported that Nikola Tesla could do this with his tesla coil to simulate natural "ball lightning." Although Tesla's claim has been met with skepticism, the formation of "ball lightning" apparently was observed in a minuteman missile silo, provoking the U.S. Army missile command to conduct a "Survey on Ball Lightning" under contract No. DAAK40-79-C-0231. It has been reported that "ball lightning" plasmoids have been generated in a high-speed plasma focus device owned by CONVECTRON Ltd. and located in Rotterdam, Holland. The work has been attributed to Dr. Duijhuis.. The CONVECTRON device has been said to include a spherical 4 megavolt air dielectric capacitor housed in a five story building. An electrical current is fed to the capacitor to provide repetitive 5 to 50 kiloampere discharges, and a "ball lightning" plasmoid has been said to have been formed as a result of cumulative discharges.

According to Zucker & Bostic, "Theoretical and Practical Aspects of Energy Storage and Compression," Lawrence Liver ore Laboratory Report UCRL-76091 (April 17, 1975) , the prerequisites for longitudinal energy compression are said to be energy storage, nonlinearity, and coherence. As energy is compressed in space and time, eventually the scene of action is transformed into a plasma. The compression process is continued providing the prerequisites in the plasma as is done in some fusion devices such as the plasma focus, laser fusion and electron beam fusion. For a wave traveling along a string where the wave velocity is progressively reduced, the ultimate in energy compression is for the string to form a loop (analogous to a vortex) . A large-amplitude nonlinear Alfven wave executes energy compression by becoming a traveling force-free vortex filament. In the [dense] plasma focus, the energy is stored in complementary modes in the form of helical mass flow in the filaments and as local magnetic fields due to the parametric behavior of the plasma in the filaments. The stronger vortex filaments absorb the^J*w.taker ones, leading to concentration of the energy in a smaller number of filaments. Approaching the pinch stage, some of the pairs of vortex filaments annihilate each other, releasing energy to the plasma with the emission of soft X-rays and some neutrons (in a deuterium plasma) . Other vortex filaments appear to form toroidal solenoids.

A process of plasma contraction said to be occurring on an inter-stellar scale is described in Wells, "How the Solar System Was Formed," 21st Century Science and

Technology,, July-August 1988 pp. 18-28. According to the "White Owl Effect," a plasma vortex ring will, with the right initial and boundary- conditions, contract azimuthally (along the circumference of the ring) to a blob at some point on the circumference. The minimum-energy structure is force-free and collinear. The model is not self- consistent unless there is at least a small magnetic field present in the original gas nebula. The magnetic field gets compressed and intensified, and is said to provide a vital role in the structure.

In Ugai & Tsuda, "Magnetic Field-Line Reconnection By Localized Enhancement of Resistivity," Journal of Plasma Physics. Vol. 17, part 3, (1977) pp. 337-356, it is said that field-line reconnection is essential in a variety of solar and astrophysical phenomena. It is said that because of localized enhancement of resistivity, the reconnection takes place in an initially antiparallel magnetic field and that an X-type configuration develops, occupying an extended region. There is a remarkable release of magnetic energy into kinetic and thermal energies. The global flow pattern can spontaneously set up through the field-line reconnection under no specially imposed boundary conditions. Dense plasma focus devices have been powered directly by homopolar generators for repetitive pulsed operation. Unfortunately in this case the voltage from the homopolar generator is too low for high-speed operation. But a homopolar generator is a relatively inexpensive energy storage device. As described in Walls and Manifold,

"Application of Lightweight Composite Materials in Pulsed Rotating Electrical Generators," 6th IEEE Pulsed Power Conference, Arlington, VA (July 1987) , an air-core homopolar generator 1.5 m long and 1.2 in diameter stores 250 megajoules and is capable of generating 3 megaamperes peak output current at 500 volts. Disclosure of Invention

The primary object of the invention is to provide a plasma focus device that can be scaled to commercial size without the need for a high-voltage, high-speed capacitor bank.

Another object of the invention is to provide a plasma focus device in which the plasma focus can ignite substantially continuous fusion reactions in which the plasma is magnetically confined in the conventional toroidal cofiguration.

Yet another object of the invention is to provide a fusion reactor configuration that uses air core inductive 5 components for energy storage, and confining and heating the plasma so that the device may be economically scaled to any desired size.

In accordance with a basic aspect of the invention, energy is stored by forming a magnetohyrodynamic vortex

10 having an internal magnetic field aligned with the axis of the vortex, and applying an external magnetic field having a substantial component aligned antiparallel with the internal magnetic field. Therefore the vortex is unstable and collapses due to magnetic field-line reconnection,

15 which causes the palsma to be concentrated and heated. In accordance with a preferred method, an external magnetic field of continuoulsy increasing intensity is _§ f. applied to the plasma vortex so that the vortex undergoes compression throughout the process. To suddenly release

20 the stored energy, the magnetic field vector on the outer surface of the ring is rotated, and the external magnetic field compress the ring until it becomes unstable and collapses due to magnetic field-line reconnection. Therefore most of the energy in the internal magnetic field

25 of the vortex ring is converted to kinetic energy or heat on an Alfven time scale. The result is a smaller high- density, high-temperature force-free vortex ring. Brief Description of Drawings

Other objects and advantages of the invention will

30 become apparent upon reading the following detailed description and upon reference to the drawings in which:

FIGURE 1 is a schematic diagram of a magnetohydrodynamic vortex of the kind used in practicing the method of the present invention;

35 FIG. 2 is a schematic diagram of the magnetohydrodynamic vortex of FIG. 1 undergoing longitudinal compression under the effect of an applied external magnetic field having a direction antiparallel to the direction of the magnetic field along the axis of the vortex ;

FIG. 3 is a schematic diagram of the vortex of FIG. 2 at the end of longitudinal compression;

FIG. 4 is a schematic diagram showing a pinch coil pinching a vortex to overcome the stabilizing effect of the mass flow and thereby initiate magnetic field-line reconnection;

FIG. 5 shows the vortex of FIG. 4 after magnetic field- line reconnection and at the beginning of longitudinal compression;

FIG. 6 is a schematic diagram of an apparatus according to the present invention which uses an iron core for inducing a current in a toroidal vortex ring aligned with the axis of the vortex; FIG. 7 is a schematic diagram showing the cusps or minima in the alternating magnetic field which induces mass flow in the vortex ring of FIG. 6;

FIG. 8 is a timing diagram showing the various currents which are applied to external conductors in the apparatus of FIG. 6; and

FIG. 8 is a schematic diagram of an alternative apparatus for practicing the present invention without the use of an iron core.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof has been shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that it is not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the invention as defined by the appended claims. Modes for Carrying Out the Invention

Turning now to the drawings, there is shown in FIG. 1 a magnetohydrodynamic vortex 10 in plasma about at axis 11, and having an internal magnetic field Bo aligned with the axis. Readers unfamiliar with the properties and characteristics of a magnetohydrodynamic vortex should refer to Wells cited above. For the present invention, it should be understood that such a vortex is a quasi force- free plasma structure in which the magnetic field B is aligned substantially parallel or antiparallel to the mass flow ¥. The mass flow has the effect of stabilizing the structure so that it is effective for storing magnetic energy and quickly releasing the stored energy in a coherent fashion. The stored magnetic energy includes a _*substantial portion of the energy of the magnetic field component in the vortex that is aligned with the axis 11. To release the stored energy, the vortex 10, shown in FIG. 2 as a filament, is longitudinally compressed by the tension of the internal magnetic field (Bo) which is connected to an antiparallel external magnetic field component (Be) . Due to the circumferential mass flow of the vcttex filament, the entire structure undergoes longitudinal compression in a coherent fashion on an Alfven time scale, resulting in the force-free vortex ring 12 shown in FIG. 3. The difference in magnetic field energy between FIG. 2 and FIG. 3 is converted to kinetic energy and heat in the vortex ring 12.

Turning now to FIG. 4, there is shown the vortex filament 10 being pinched by a magnetic field from a pinch coil 14 to induce magnetic field-line reconnection between the internal magnetic field Bo and the applied external magnetic field Be. The filament 10 at this time is, for example, closed to form a vortex ring so that the longitudinal compression of FIG. 2 cannot occur prior to magnetic field-line reconnection. The circumferential component Vp of the mass flow in the vortex filament normally stabilizes the filament against the m=0 or pinch instability mode, because conservation of angular momentum about the ^xis of the filament ensures that the circumferential component of tiie mass flow will increase in magnitude in the pinch region 15 and provide an opposing force, but this_*; is at the expense of the axial component of the mass flow. With a sufficiently strong pinch field, the axial component of the mass flow is reduced to zero and the plasma is reflected, so that the filament is severed and magentic field-line reconnection occurs as shown in FIG. 5. It should be noted that it is not necessary to use a pinch coil for the present invention, since a reverse pinch of the entire filament will increase the circumferential component of the mass flow without substantially increasing the axial component, leading eventually to an unstable condition at which magnetic field-line reconnection will occur and sever the filament. Also, a non-uniformity in the external coils (shown in FIG. 6 or 9 and described below) leading to a localized increase in the applied external magnetic field will have the same effect as a separate pinch coil in localizing the region of magnetic field-line reconnection.

Turning now to FIG. 6, there is shown a schematic diagram of an apparatus for performing the method of the present invention. The magentohydrodynamic vortex is formed as a toroidal ring 10 inside a vacuum chamber 15 (such as a tube of fused quartz) containing plasma such as ionized deuterium or borane. For forming the vortex about the toroidal axis of the vacuum chamber, a plurality of electrical conductors 16 are helically wound about the vacuum chamber in a quasi force-free configuration and are excited with respective phases of plural-phase alternating current so that the plasma in effect forms the rotor of an induction motor. In FIG. 6, three phases are supplied to the conductors 16 from sources II, 12 and 13. In addition to causing the plasma to rotate, the plasma is also caused to circulate axially to establish the boundary condition for the mass flow V as shown in FIG. 1. The mass flow vector at the outer surface of the vortex ring 10 is generally perpendicular to the direction of alternating current flow in the conductors 16.

To establish the desired magnetic field B in the vortex ring, the conductors 16 are pulsed with a component of current at a lower frequency than the frequency of the plural-phase alternating current. The current pulse is supplied by a source Ip, such as a homopolar generator, compensated alternator, battery bank, or bank of electrolytic capacitors. The same conductors 16 could be used for conducting the current pulse as well as the plural-phase alternating current. In this case the source Ip is isolated from the sources II, 12, 13 by inductances 17, 18, and 19, and the alternating currents are fed through capacitors 20, 21 and 22. The inductances 17, 18 and 19, for example, form parts of the series field coil for the homopolar generator or compensated alternator (see Walls & Manifold cited above) providing the pulsed current source Ip, and the capacitors 20, 21, 22 serve to resonate the conductors 16 at the frequency of the plural-phase alternating current. Alternatively, separate conductors 16 could be used for conducting the current pulse independent of the plural-phase alternating currents.

After the vortex ring 10 is formed, the current pulse from the generator Ip is reversed to reverse-pinch the vortex ring, as was shown in FIG. 4. To prevent the vortex ring from expanding during this current reversal due to magnetic pressure from the internal field Bo, a current is induced in the vortex ring along the direction of the axis of the vortex. For this purpose the vortex ring 10 is coupled through an iron transformer core 23 to a current source Io. The current source Io provides a current pulse when the magnitude of the pulse from the source Ip is zero. This has the effect of rotating the magnetic field vector at the outer surface of the vortex ring. Turning now to FIG. 7, there is shown a cross section of the vacuum chamber 15 showing the magnetic field configuration established by the plural-phase alternating currents. The field has a cusp or minimum at the axis of the vortex ring, so that the field has a tendency to locate or center the vortex ring 10 in the vacuum chamber 15 due to the repulsion effect of AC magnetic induction.

Turning now to FIG. 8, there is shown a timing diagram for the various current sources in the schematic of FIG. 6. At time to, the alternating current sources II, 12 and 13 are turned on, causing the deuterium or borane in the vacuum chamber (15 in FIG. 6) to ionize and causing a cavitated vortex to form in the chamber at or very close to the inner chamber wall. At time tl- the current source Ip is turned on, causing the initial vortex to become compressed and establishing the magnetic fields in the vortex as shown in FIG. 1. At about time t2 formation of the vortex ring is about finished. The source Io is turned on, the source Ip stops increasing, and the alternating current sources II, 12, 13 are turned off. At time t3 the external applied magnetic field component aligned with the axis of the vortex has been reversed, so the pinch coil source Ic is energized to initiate magnetic field line reconnection, which occurs at time t4. Turning now to FIG. 9, there is shown an alternative to the apparatus of FIG. 6. In this case iron core transformer 23 has been eliminated by the use of conductors 16' helically wound about the vacuum chamber 15, but having a helicity opposite from the helicity of the conductors 16. Another feature of this alternative is that the conductors 16' can be excited with alternating current sources II¹, 12• , 13' when the magnetic field vector is rotated at the outer surface of the vortex. This applies a force by induction to the outer surface of the vortex at that time so that the flow of plasma is redirected by the force to flow along the direction of the magentic field. This would reduce shedding of plasma from the vortex as the vortex would otherwise establish alignment of the mass flow V and the magnetic field B at the outer surface of the vortex. This would also permit more precise control of all of the parameters that would affect the final plasma vortex ring (12 in FIG. 3) in order to select the optimum values for achieving ignition.

Claims

Claims ;

1. A method for compressing and heating a plasma comprising:

1) forming a magnetohydrodynamic vortex in said plasma about an axis, said vortex having associated with it an internal magnetic field aligned with said axis; and

2) applying an external magnetic field to said vortex, said external magnetic field having a substantial component aligned antiparallel to said internal magnetic field aligned with said axis, whereby magnetic field-line reconnection occurs between said internal magnetic field and said external magnetic field to compress and heat said plasma. 2. The method as claimed in claim 1, wherein said magnetohydrodynamic vortex is established by plural-phase magnetic, induction between the plasma and a set of external conductors carrying respective phases of plural-phase alternating current, whereby the plasma vortex is the rotor of an induction motor.

3. The method as claimed in claim 2, wherein the external conductors also carry a lower frequency component of current flowing first in a first direction establishing said internal magnetic field aligned with said axis, and later flowing in a second direction opposite from said first direction to establish said external magnetic field having a substantial component antiparallel to said internal magnetic field aligned with said axis.

4. The method as claimed in claim 2, wherein said external conductors are arranged and excited with said plural-phase alternating current so that the magnetic field from said plural-phase alternating current has a minimum intensity near said axis tending to locate and confine said vortex.

5. The method as claimed in claim 1, wherein the plasma vortex is confined by an external magnetic field which increases in intensity continuously during the formation of the plasma, vortex and up until magnetic field- line reconnection occurs.

6. The method as claimed in claim 5, wherein the direction of the magnetic field applied to the outer surface of the vortex is rotated between the time of forming the vortex and the applying of the external magnetic field having a substantial component antiparallel to said internal magnetic field aligned with said axis.

7. The method as claimed in claim 1, wherein an external magnetic field having a substantial component aligned parallel to said axis is applied to said plasma during said forming of the vortex.

8. The method as claimed in claim 1, further comprising inducing a current in said vortex aligned with said axis between the time of said forming of the vortex and said applying of the external magnetic field having the substantial component aligned antiparallel to said internal magnetic field.

9. The method as claimed in claim 1, wherein said plasma vortex is formed as a toroidal vortex ring.

10. The method as claimed in claim 1, further comprising initiating said magnetic field-line reconnection at a predetermined axial location on said vortex by exciting a pinch coil to constrict the vortex at that location.

11. A method for compressing and heating a plasma comprising:

1) forming a magnetohydrodynamic vortex in said plasma about an axis by magnetic induction from currents conducted in a set of external coils, said currents establishing a magnetic field within said vortex and aligned with said axis;

2) reversing the currents which establish said magnetic field within said vortex, and while reversing these currents, inducing in said vortex a current aligned with said axis so as to provide a magnetic field encircling said vortex to prevent expansion of said vortex due to magnetic pressure from the magnetic field within the vortex; and

3) compressing said vortex by applying an external magnetic field aligned antiparallel to said internal magnetic field aligned with said axis, whereby magnetic field-line reconnection occurs between said internal magnetic field and said external magnetic field to heat said plasma.

12. The method as claimed in claim 11, wherein the vorticity of the vortex is established by induction with plural-phase alternating currents so that the vortex is a rotor of a plural-phase induction motor.

13. The method as claimed in claim 12, wherein said reversing said current and inducing of a current in said vortex causes the direction of the magnetic field at an outer surface of the vortex to rotate, and said method further comprises applying a force by induction with plural-phase alternating currents to the outer surface of the vortex during the rotation of the magnetic field at the outer surface so that the flow of plasma is redirected by said force to flow along the direction of the magnetic field.

14. The method as claimed in claim 11, wherein said compressing said vortex is concentrated at a predetermined axial location of said vortex so that magnetic field-line reconnection is initiated at that location.

15. An apparatus for confining and heating a plasma comprising? l) means for forming a magnetohydrodynamic vortex in said plasma about an axis, said vortex having associated with it an internal magnetic field aligned with said axis; and

2) means for applying an external magnetic field to said vortex, said external magnetic field having a substantial component aligned antiparallel to said internal magnetic field aligned with said axis, to cause magnetic field-line reconnection to occur between said internal magnetic field and said external magnetic field to heat said plasma.

16. The apparatus as claimed in claim 15, wherein said means for forming the vortex includes a first set of external conductors disposed helically about said axis, and means for exciting the external conductors with respective phases of plural-phase alternating current.

17. The apparatus as claimed in claim 16, wherein the means for forming the vortex further comprises means for exciting said external conductors with a lower frequency component of current flowing in a first direction to establish said internal magnetic field aligned with said axis, and wherein said means for applying said external magnetic field comprises means for exciting said external conductors with a lower frequency component of current flowing in a second direction opposite from said first direction to establish said external magnetic field having a substantial component antiparallel to said internal magnetic field aligned with said axis.

18. The apparatus as claimed in claim 16, further including a second set of external conductors disposed helical about said axis for inducing in said vortex a current aligned with said axis, said second set of external conductors having a helicity opposite from the helicity of said first set of external conductors.

19. The apparatus as claimed in claim 15, further comprising means for inducing in said vortex a current aligned with said axis.

20. The apparatus as claimed in claim 15, wherein said means for forming the vortex includes means for forming the vortex in the form of a toroidal vortex ring, and wherein said apparatus further comprises means for initiating said magnetic field-line reconnection at a predetermined axial location on said vortex.

21. A method of forming a magnetohydrodynamic vortex about an axis in a plasma, said magnetohydrodynamic vortex having associated with it an internal magnetic field aligned parallel to said axis, said method comprising the steps of: a) creating a plasma of ionized material within a set of external conductors extending helically about said axis; and b) exciting said external conductors with electrical currents to establish said magnetohydrodynamic vortex, said electrical currents including respective phases of plural- phase alternating current which establish by electromagnetic induction helical mass flow in said plasma about said axis, whereby the vortex is a rotor of a plural- phase induction motor.

22. The method as claimed in claim 21, wherein at least one of the external conductors is excited with a lower frequency component of current to establish said internal magnetic field aligned parallel to said axis.

23. The method as claimed in claim 22, wherein the direction of said lower frequency component of current is reversed to establish about said plasma vortex an external magnetic field having a substantial component antiparallel to said internal magnetic field aligned parallel to said axis.

24. The method as claimed in claim 23, wherein said external conductors are arranged and excited with said plural-phase alternating current so that the magnetic field from said plural-phase alternating current has a minimum intensity near said axis tending to locate and confine said vortex.

25. The method as claimed in claim 21, wherein the plasma vortex is confined by an external magnetic field - which increases in intensity continuously during the formation of the plasma vortex.

26. The method as claimed in claim 25, wherein the direction of the magnetic field applied to the outer surface of the vortex is rotated.

27. The method as claimed in claim 21, wherein an external magnetic field having a substantial component aligned parallel to said axis is applied to said plasma during said forming of the vortex.

28. The method as claimed in claim 21, further comprising inducing in said vortex an electrical current aligned with said axis.

29. The method as claimed in claim 21, wherein said plasma vortex is formed as a toroidal vortex ring.

30. The method as claimed in claim 21, further comprising initiating magnetic field-line reconnection at a predetermined axial location on said vortex by applying to said vortex an external magnetic field aligned anti¬ parallel to said axis, and exciting a pinch coil to constrict the vortex at said predetermined axial location.