阅读说明：本技术 用于生成和加速磁化等离子体的系统和方法 (System and method for generating and accelerating magnetized plasma ) 是由 斯蒂芬·詹姆斯·霍华德 道格拉斯·哈维·理查森 米歇尔·乔治斯·拉伯格 梅瑞特·维恩·雷诺兹 于 2020-05-28 设计创作，主要内容包括：用于稳定生成和加速磁化等离子体的方法和系统包括使等离子体发生器中的注入气体电离并生成形成磁场以形成具有闭合极向场的磁化等离子体,在磁化等离子体后方产生反向极向场并且反向极向场具有与闭合极向场的后缘相同的场方向且具有与形成磁场相反的场方向,并且生成逆着闭合极向场推动反向极向场的推动环场,借此通过等离子体发生器下游的等离子体加速器使磁化等离子体加速。反向极向场用于防止在形成磁化等离子体后,形成磁场和闭合极向场的重联,这将使得推动环场与闭合极向场混合并引起不稳定性和降低的等离子体约束。(Methods and systems for stably generating and accelerating a magnetized plasma include ionizing an injected gas in a plasma generator and generating a forming magnetic field to form a magnetized plasma having a closed poloidal field, generating a reverse poloidal field behind the magnetized plasma and having a field direction the same as a trailing edge of the closed poloidal field and having a field direction opposite the forming magnetic field, and generating a push ring field that pushes the reverse poloidal field against the closed poloidal field, whereby the magnetized plasma is accelerated by a plasma accelerator downstream of the plasma generator. The reverse poloidal field serves to prevent the formation of a magnetic field and a closed poloidal field reconnection after the formation of a magnetised plasma, which would cause the push-ring field to mix with the closed poloidal field and cause instability and reduced plasma confinement.)

1. A system for generating and accelerating a magnetized plasma, the system comprising:

a plasma generator comprising an ionizing electrode operable to ionize a gas and a forming magnetic field generator;

a plasma accelerator fluidly coupled to the plasma generator and including an accelerator electrode operable to generate a thrust ring field, a downstream end of the plasma generator and an upstream end of the plasma accelerator collectively defining an acceleration gap and a relaxation region;

a reverse poloidal field generator operable to generate a reverse poloidal field across the acceleration gap; and

at least one power supply electrically coupled to the ionization electrode and the accelerator electrode and operable to: generating a magnetized plasma torus having a closed poloidal field moving from the plasma generator to the relaxation zone, wherein the opposite poloidal field is located behind the magnetized plasma torus and has the same field direction as the trailing edge of the closed poloidal field and has a field direction opposite the forming magnetic field; and generating the push ring field to push the reverse poloidal field against the closed poloidal field, thereby accelerating the magnetized plasma ring through the plasma accelerator.

2. The system of claim 1, wherein the forming magnetic field generator comprises at least one magnetic coil or at least one permanent magnet.

3. A system according to claim 1 or 2, wherein the opposite polar field generator comprises at least one magnetic coil or at least one permanent magnet.

4. The system of any one of claims 1 to 3, further comprising ferromagnetic material positioned on each side of the acceleration gap to increase a reverse poloidal field across the acceleration gap.

5. The system of claim 4, wherein the ferromagnetic material comprises at least one of a ring, an annular disk, and a series of spaced segments circumscribing one or both of an upstream end of an inner electrode of the accelerator electrode and a downstream end of an inner electrode of the ionizing electrode.

6. The system of any one of claims 1 to 5, wherein the number and location of the opposite poloidal magnetic generators are selected to generate 0.1-0.25 ψ_CTOf reverse polar flux of where_CTIs the total poloidal flux of the magnetized plasma torus.

7. A system according to claims 2 and 3, wherein the forming magnetic field generator comprises three forming magnetic coils and the opposite polar field generator comprises one opposite polar magnetic coil.

8. The system of any one of claims 1 to 7, wherein the ionizing electrode is annular and defines an annular plasma-forming channel.

9. The system of claim 1, wherein the plasma loop is a compact loop or a spherical tokamak.

10. The system of claim 1, wherein the relaxation region is configured for the plasma loop to expand and stabilize therein.

11. The system of any one of claims 1 to 10, wherein the accelerator electrode is annular and defines an annular transport channel that tapers inwardly from an inlet to an outlet.

12. The system of any of claims 1 to 11, wherein the at least one power supply comprises at least one capacitor bank and is operable to provide a first current pulse to the plasma generator and a second current pulse to the plasma accelerator.

13. A method for generating and accelerating a magnetized plasma, comprising:

ionizing a gas in a plasma generator and generating a forming magnetic field and generating a magnetized plasma torus with a closed poloidal field moving from the plasma generator to a relaxation zone;

generating a reverse poloidal field behind the magnetized plasma toroid, the reverse poloidal field having a same field direction as a trailing edge of the closed poloidal field and having a field direction opposite the forming magnetic field; and is

Generating a push ring field that pushes the reverse poloidal field against the closed poloidal field, thereby accelerating the magnetized plasma torus by a plasma accelerator downstream of the plasma generator.

14. The method of claim 13, wherein the plasma generator comprises an annular plasma forming channel, and wherein forming the magnetized plasma comprises injecting the gas into the annular plasma forming channel to form the magnetized plasma torus.

15. A method according to claim 13 wherein the magnetized plasma torus is a compact torus or a spherical tokamak.

16. The method of any one of claims 13 to 15, wherein the gas comprises any one of hydrogen, isotopes of hydrogen, neon, argon, krypton, xenon and helium, or mixtures thereof.

17. A method according to any one of claims 13 to 16, wherein the magnetised plasma torus expands and stabilizes in the relaxation region after being generated in the plasma generator and before being accelerated in the plasma accelerator.

18. The method of any of claims 13 to 17, further comprising sending a first current pulse to the plasma generator to ionize the gas and generate the closed poloidal field, and sending a second current pulse to the plasma accelerator to generate the push ring field.

19. The method of any one of claims 13 to 18, wherein the reverse poloidal field is generated across an acceleration gap between a downstream end of the plasma generator and an upstream end of the plasma accelerator.

20. The method of claim 18, wherein generating the reverse poloidal field comprises generating at 0.1-0.25 psi_CTIn the range of (1), wherein ψ_CTIs the total poloidal flux of the magnetized plasma torus.

21. The method of any one of claims 13 to 20, wherein the plasma accelerator comprises a tapered annular channel, and the method further comprises compressing and heating the plasma loop while accelerating through the tapered annular channel.

Technical Field

The present disclosure relates generally to systems and methods for generating magnetized plasma, and more particularly to systems and methods for generating magnetic field configurations in plasma devices to facilitate plasma confinement during plasma formation and plasma acceleration.

Background

Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.

A plasma is a gas-like state of matter in which at least a portion of the particles ionize. The presence of freely moving charged particles (e.g., positive ions and negative electrons) makes the plasma conductive. A plasma having a magnetic field strong enough to influence the motion of the charged particles is called a magnetized plasma. If the magnetic field lines are configured to loop back on themselves in a closed trajectory (which may be infinite in length), the magnetic field within the plasma may confine the plasma particles and prevent them from striking the vessel wall for an extended period of time. The volume occupied by the plasma may be shaped like a ring so that the closed magnetic field curve will circulate in a circular or spiral path on the surface of a particular ring layer within the volume of the plasma. The closed magnetic field acts as a very good insulator, maintaining a temperature gradient of millions of degrees kelvin per cm between the thermal plasma core and the vessel wall temperature. The magnetic field used to confine the plasma particles can be generated and maintained by some combination of external currents flowing in the coil and conductive walls, and currents flowing inside the plasma itself. The range of possible magnetic confinement devices is parameterized by obtaining a degree of trade-off between the use of external and internal currents of the magnetic field. A star simulator is a device that uses a completely external coil to generate a magnetic field with little plasma current. Tokamak has a major external-source field, but does rely on plasma current for plasma heating and rotation of the control helical field lines. The Reverse Field Pinch (RFP) device relies on significant internal plasma currents generated by the time-dependent flux-core transformer action through the central aperture of the ring vessel. In a Compact Toroid (CT) device, the closed magnetic field is generated entirely from the internal plasma current, and therefore the CT plasma is referred to as a self-contained plasma. The CT plasma can be further stabilized and prevented from expanding by being contained within a conductive housing or externally generated magnetic field, however, these external sources are not responsible for generating the closed portion of the magnetic field that directly confines the plasma. By being self-confining, the CT plasma can be formed at one location and then transferred to another location without destroying its confinement capability.

There are two different magnetic field directions on the surface of the plasma torus: a polar direction, which as it does, takes a proximal path around the ring through the central bore, and a ring direction, which takes a distal path rotated around the axis of rotational symmetry of the ring. Any axisymmetric vector field (e.g., a balanced magnetic field) present throughout the volume of the ring may have a vector at each location described as the sum of the ring component and the poloidal component.

For the magnetic field of the plasma torus, the polar component of the magnetic field is generated by the current passing through the toroidal core of the plasma in the torus direction. The magnetic field may also have a loop component at a given point in space if there is a current flowing in the polar direction on the loop surface that includes the problem in question. In this way, the poloidal current near the plasma edge generates a toroidal magnetic field inside the plasma core, and the toroidal current near the plasma core generates a poloidal magnetic field near the plasma edge. A given magnetic field line within axisymmetric equilibrium will wrap around a particular sub-ring surface and not move away from it, which means that the amount of poloidal flux surrounded by each ring circle on that surface will be a constant value; we therefore represent this as a flux surface (flux weber]Field strength tesla]Multiplied by the area [ meter ]²]). The degree of topological connection of the two components of the magnetic flux is called the degree of magnetic helicity and is proportional to the product of the total poloidal magnetic flux and the amount of the ring magnetic flux contained within it. Finally, when we denote a surface as ring-like, we mean that it may have a cross-section in the poloidal plane that is not necessarily completely circular. Any smooth closed curve (without self-intersection) can be used as a poloidal cross-section and rotated about the z-axis to create a ring-like surface or ring.

A hash ring (CT) can be divided into two main subclasses; spheromaks (sphenomaks) and Field Reversed Configurations (FRCs). The magnetic field of the spheromak plasma has both polar and ring magnetic fluxes, related to the generation of significant helicity. It is generally close to the relaxation lowest energy condition, where the current flows only mainly parallel to the magnetic field lines and can be Magnetohydrodynamically (MHD) stable with respect to destructive instabilities. The FRC field is almost completely poloidal and has almost zero helicity.

The thermal insulating ability of the magnetic field of an axisymmetric MHD equilibrium is theoretically high, but it can be significantly reduced if plasma fluctuations cause deviations from this equilibrium. Since the path of charged particles in the magnetic field is constrained to the helix aligned with the field linesThe rotational path, therefore, should be careful to ensure that the magnetic field lines move in the ring and poloidal directions, but not radially to avoid a direct path from the core to the plasma edge. The ratio of the loop to the poloidal field in the flux plane can be best described by tracking the field lines and counting the number of loop turns it completes before one poloidal turn is completed, and this value is referred to as the "safety factor" and is represented by the variable q. How this varies in the radial direction within the plasma is described by a function called the q-spectrum, and the exact shape of the q-spectrum is the main factor in determining the MHD stability of the plasma. For example, when the safety factor takes a completely reasonable valueWhere m and n are integers (typically worst for the smaller of m, n, which is less than or equal to 3), then each field line in the flux plane is fully closed on itself after a relatively short finite path length. Then, the displacement perturbations of adjacent field lines constructively increase in phase with each other, and if other conditions are met, this results in a gradual deviation from the axial symmetry (instability) localized to a reasonable q-surface vicinity. If some of these unstable regions overlap, the magnetic field line displacements away from the original flux surface mix themselves across all surfaces, and the single field lines can then move back and forth in a radial direction against the hot plasma core, eventually meandering all the way to the cold edge, and greatly reduces the thermal energy confinement of the plasma, acting as a direct path for heat to flow from the core to the plasma edge.

Disclosure of Invention

In one aspect, a system for generating and accelerating a magnetized plasma is provided. The system includes a plasma generator for generating a magnetized plasma torus and a plasma accelerator fluidly coupled to the plasma generator for accelerating the magnetized plasma torus by a distance. Positioning the accelerator downstream of the plasma generator such that a downstream end of the plasma generator and an upstream end of the accelerator collectively define an acceleration gap and a relaxation zone. A power supply is in electrical communication with the plasma generator and the plasma accelerator is configured to provide a power pulse therethrough. A magnetic field generator (format magnetic field generator), such as a set of coils or permanent magnets, is used to provide a forming magnetic field in the plasma generator. A reverse polar field generator, such as one or more other coils or permanent magnets, is positioned in proximity to the acceleration gap to provide a reverse polar magnetic field across the acceleration gap. The radial component of the reverse poloidal field is opposite to the direction in which the poloidal field is formed, so that when a current pulse is supplied by a power supply across the accelerator, the reverse poloidal magnetic field is pushed out into the relaxation zone behind the magnetized plasma, and then in the same radial direction, to the trailing edge of the closed poloidal field of the plasma, but opposite to the direction in which the poloidal field is formed in the plasma generator.

According to another aspect, there is provided a method for generating and accelerating a magnetized plasma, comprising: ionizing a gas in a plasma generator and generating a magnetic field; generating a magnetized plasma torus with a closed poloidal field moving from the plasma generator to a relaxation zone; generating a reverse poloidal field behind the magnetized plasma toroid, the reverse poloidal field having a same field direction as a trailing edge of the closed poloidal field and having a field direction opposite the forming magnetic field; and generating a push ring field that pushes the reverse poloidal field against the closed poloidal field, whereby the magnetized plasma ring is accelerated by a plasma accelerator downstream of the plasma generator.

More specifically, the method may include sending a first current pulse to the plasma generator to ionize a gas and generate a closed poloidal field, and sending a second current pulse to the plasma accelerator to generate a push ring field. The magnetized plasma torus can expand and stabilize in the relaxation region after being generated in the plasma generator and before being accelerated in the plasma accelerator.

May span the sum between the downstream end of the plasma generator and the upstream end of the plasma acceleratorThe fast gap generates the reverse poloidal field. Generating the reverse poloidal field may include generating 0.1-0.25 psi_CTIn the range of (1), wherein ψ_CTIs the total poloidal flux of the magnetized plasma torus.

The plasma generator may comprise a toroidal plasma formation channel, and the method may further comprise injecting the gas into the plasma formation channel and forming the magnetized plasma torus, such as a compact torus or a spherical tokamak. The gas may comprise any one or a mixture of hydrogen, isotopes of hydrogen, neon, argon, krypton, xenon and helium. The plasma accelerator may further comprise a tapered annular channel, and the method may further comprise compressing and heating the plasma loop while accelerating through the tapered annular channel.

According to another aspect, a system for generating and accelerating a magnetized plasma torus is provided that includes a plasma generator, a plasma accelerator, at least one oppositely poled magnetic field generator, and at least one power supply. The plasma generator includes an ionizing electrode operable to ionize a gas, and at least one forming magnetic field generator operable to generate a forming magnetic field. The plasma accelerator is fluidly coupled to the plasma generator and includes an accelerator electrode operable to generate a push ring field. The downstream end of the plasma generator and the upstream end of the plasma accelerator together define an acceleration gap and a relaxation region, and the opposite poloidal magnetic field generator is operable to generate an opposite poloidal field across the acceleration gap. The magnetized plasma torus may be configured with a relaxed region to expand and stabilize therein. At least one power supply is electrically coupled to the ionization electrode and the accelerator electrode. The at least one power source is operable to: generating a magnetized plasma torus having a closed poloidal field moving from the plasma generator to the relaxation zone, wherein the opposite poloidal field is located behind the magnetized plasma torus and has the same field direction as the trailing edge of the closed poloidal field and has a field direction opposite the forming magnetic field; and generating the push ring field to push the reverse poloidal field against the closed poloidal field, thereby accelerating the magnetized plasma ring through the plasma accelerator. The forming magnetic field generator and the opposite polar magnetic field generator may each comprise one or more magnetic coils or permanent magnets.

Ferromagnetic material may be positioned on each side of the acceleration gap to increase the reverse poloidal field across the acceleration gap. The ferromagnetic material may comprise at least one ring, annular disk or series of spaced segments circumscribing the inner electrode of the accelerator or ionization electrode. For example, there may be an annular disk positioned at the upstream end of the inner electrode of the accelerator electrode and an annular ring positioned at the downstream end of the inner electrode of the ionization electrode. The number and location of the at least one oppositely poled magnetic field may be selected to generate a magnetic field of 0.1-0.25 x ψ_CTOf reverse polar flux of where_CTIs the total poloidal flux of the magnetized plasma torus. For example, the forming magnetic field generator may include 3 forming magnetic coils and the opposite-polarity field generator may include one opposite-polarity magnetic coil.

The ionizing electrode may be annular and define an annular plasma-forming channel that produces a magnetized plasma annulus, such as a compact toroid or a spherical tokamak. The accelerator electrode may be annular and define an annular transport channel (propagation channel) tapering inwardly from the inlet to the outlet.

The at least one power supply may include at least one capacitor bank and may be operable to provide a first current pulse to the plasma generator and a second current pulse to the plasma accelerator.

Drawings

Throughout the drawings, reference numerals may be reused to indicate correspondence between reference elements. The accompanying drawings are provided to illustrate example embodiments described herein and are not intended to limit the scope of the present disclosure. The sizes and relative positions of elements in the drawings are not necessarily drawn to scale. For example, the shapes of various elements and angles are not drawn to scale, and some of these elements are arbitrarily enlarged and positioned to improve drawing legibility.

Fig. 1(a) - (c) are schematic cross-sectional side views of a portion of a system for generating and accelerating a magnetized plasma, and including a reverse polar field generator, the portion shown being annular about an axis a, according to an embodiment of the present invention.

Fig. 2(a) - (d) are schematic cross-sectional side views of a portion of a system for generating and accelerating a magnetized plasma without a reverse poloidal field generator, used in experimental tests.

Fig. 3(a) shows an example of a computer simulation of a polar magnetic field configuration using the system shown in fig. 2(a) - (d) without a reverse polar magnetic field.

Fig. 3(b) shows an example of a computer simulation of the formation of a poloidal magnetic field configuration and a reversed poloidal magnetic field configuration across the acceleration gap using the system shown in fig. 1(a) - (c).

Detailed Description

As mentioned earlier herein, the majority of the magnetic field in a magnetized plasma is generated by currents flowing in the plasma itself and/or in flux-conserving chamber walls. The closed magnetic field configuration confines the plasma thermal energy by inhibiting the transport of heat and particles from the plasma core to its edge. Some of the major factors that affect the lifetime and stability of the plasma are the plasma formation flux configuration, the timing of the gas valve, the timing of plasma destruction, the plasma temperature, the density and level of undesirable impurities, the current pulse profile, and the size and geometry of the plasma apparatus. One basic way to limit heat transfer is to control MHD stability through control of the q-spectrum. The q-spectrum is controlled indirectly by a combination of control of the internal plasma current, design of the plasma geometry and the current flowing in the vessel and electrode walls.

Embodiments described herein relate to systems and methods for stably generating and accelerating magnetized plasmas. Embodiments of the method include ionizing gas injected in a plasma generator and generating a forming magnetic field to form a magnetized plasma having a closed poloidal field, thereby generating a reverse poloidal field that is behind the magnetized plasma and has a same field direction as a trailing edge of the closed poloidal field and has a field direction that is opposite to the forming magnetic field, and generating a push ring field that pushes the reverse poloidal field against the closed poloidal field, thereby accelerating the magnetized plasma by a plasma accelerator downstream of the plasma generator. The reverse poloidal field serves to prevent the reconnection of the forming magnetic field and the closing poloidal field after the formation of the magnetized plasma, which would cause the push ring field to mix with the closing poloidal field and cause instability and reduced plasma confinement.

Embodiments of the system are shown in fig. 1(a) - (c) and 3 (b). More specifically, fig. 1(a) and (b) schematically illustrate a portion of a system 10 for generating and accelerating a magnetized plasma torus 11, such as a Compact Torus (CT) or a spherical tokamak or combination thereof, wherein the illustrated portion is annular about an axis a. The system 10 includes a toroidal plasma generator 12 and a toroidal accelerator 14 positioned downstream of the plasma generator 12 such that downstream of the plasma generator 12 and upstream of the accelerator 14 collectively define an acceleration gap 13 and a relaxation zone 22. For example, the system 10 may be based on a two-stage marshall gun to form a plasma loop 11 in a plasma generator 12 (first stage) and accelerate such a plasma loop 11 in an accelerator 14 (second stage). The plasma generator 12 includes an inner, generally tubular, forming electrode 15, and an outer, generally tubular electrode 16 (collectively "ionizing electrode") coaxial with the inner forming electrode 15 and surrounding the inner forming electrode 15. The ionizing electrodes 15, 16 define an annular plasma-forming channel 17 therebetween. A forming magnetic field generator comprising a series of forming magnetic coils 18 is disposed around the outer electrode 16 and/or within the forming electrode 15 and coupled to a power supply (not shown) (coils 18 are omitted from fig. 1(c) to improve clarity of presentation). Alternatively, the magnetic field generator may comprise one or more permanent magnets (not shown). A series of forming magnetic coils 18 are provided to generate an initial poloidal forming magnetic field 19 which radially intersects between the ionizing electrodes 15, 16. For example, the magnetic coil 18 may be a DC solenoid. The magnetic field lines forming the magnetic field 19 can be led out from the inner forming electrode 15 and into the outer electrode 16. In one implementation, the magnetic field 19 may be established such that the magnetic field lines are directed radially inward through the outer electrode 16, into the inner electrode 15, without departing from the scope of the present invention.

To form the plasma loop 11, a ring of equidistant fast acting gas valves (not shown) arranged around the outer electrode 16 is provided to inject a predetermined amount of gas symmetrically into the plasma formation channel 17. The valve may be a solenoid valve, a piezoelectric valve, or any other suitable valve or combination thereof. The amount of gas injected through the valve may be determined by the open time of the valve or by a known volume of gas filled gas with a known pressure. The gas may be hydrogen and/or its isotopes (deuterium, tritium), helium, neon, argon, krypton, xenon or any other suitable gas or mixture of any of these gases. For example, the gas may be a mixture of 50/50 deuterium-tritium gas.

The system 10 also includes a power supply that includes a first power supply 28a (shown only in fig. 1 (a)), which may, for example, include at least one capacitor bank and preferably two or more capacitor banks and which is operable to provide current pulses to the plasma generator 12. In addition, the system 10 includes a second power supply 28b (shown only in fig. 1 (a)) that includes at least one capacitor bank and preferably two or more capacitor banks to provide current pulses to the accelerating electrodes of the accelerator 14. For example, the first and second power supplies 28a, 28b in one configuration may be configured to provide 0.5-5MJ of energy in the plasma generator 12 and/or accelerator 14, respectively. Once the gas fills the formation channel 17, the first power supply 28a may be activated and a current may be discharged between the ionizing electrodes 15, 16. For example, in one configuration, the first power supply 28a may provide pulses of 10-40kV between the ionizing electrodes 15, 16. In another amplification configuration, the power supplies 28a, 28b may be configured to provide 0.5-50MJ of energy in the plasma generator 12 and/or accelerator 14, and the first power supply 28a may provide 10-100kV pulses between the ionizing electrodes 15, 16. The voltage applied between the ionisation electrodes 15, 16 acts to ionise the gas and form an initial plasma. The current flowing through the initial plasma in a substantially radial direction along the forming magnetic field lines 19 further increases the temperature and density of the plasma. This current generates a ring magnetic field in the plasma behind the current layer, and the magnetic field pressure gradient will exert a lorentz force J × B that urges the plasma in an axial direction towards the accelerator 14. As the plasma moves forward it interacts with the forming magnetic field 19, distorting and stretching the field lines until the advancing plasma is detached by the magnetic reconnection process, thereby forming a plasma torus 11 with a toroidal magnetic field obtained from the toroidal magnetic field by the current, and forming a closed poloidal field 25 due to the interaction of the plasma with the originally formed magnetic field 19 and possible poloidal flux expansion caused by the plasma dynamic effects.

Downstream of the plasma generator 12 is fluidly coupled to an accelerator 14. The accelerator 14 includes an inner accelerating electrode 20 (collectively, "accelerating electrode") coaxial with the outer electrode 16. The outer electrode 16 and the inner accelerating electrode 20 define an annular transfer channel 21. In this embodiment, downstream of the internal formation electrode 15 and upstream of the internal acceleration electrode 20 together define the acceleration gap 13. In other embodiments, the acceleration gap 13 may be formed in the outer electrode 16 without departing from the scope of the present invention. When the plasma loop 11 formed in the plasma generator 12 enters the relaxation region 22 (see fig. 1(b)), it slightly expands and the magnetic field lines recombine so that the plasma loop 11 can stabilize before it is accelerated along the accelerator 14 towards its exit. When the second power supply 28b discharges a second current pulse between the accelerating electrode 20 and the outer electrode 16, the plasma loop 11 is accelerated axially downstream of the accelerator 14 due to the loop field 24 generated by the current flowing between the accelerating electrode 20 and the outer electrode 16. The toroidal field 24 is referred to as a "push toroidal field" because it is located behind the plasma torus 11 and pushes the plasma torus 11 along the accelerator 14 towards its exit. The accelerator 14 may have a tapered configuration that narrows towards the outlet so that as the plasma loop 11 accelerates along the accelerator 14 it is both compressed and heated. For example, the second power supply 28(b) may provide 20-100kV across the accelerator 14 to accelerate along the accelerator 14 and, in some cases, compress the plasma loop 11.

A reverse poloidal field generator comprising one or more coils 32 is operable to generate a reverse poloidal field 30 across the acceleration gap 13 which acts to prevent a reconnection of the poloidal forming magnetic field 19 and the closed poloidal field 25. The direction of this reverse poloidal field 30 is established so as to be in the same direction as the trailing edge of the closed poloidal field 25 of the plasma loop 11, but opposite to the direction of the poloidal forming magnetic field 19 (the term "trailing edge" means upstream of the closed poloidal field, which is to the left of the closed poloidal field as shown in figure 1 (b)). The fact that the reverse poloidal field 30 across the acceleration gap 13 has a polarity opposite to that of the poloidal forming magnetic field 19 in the formation region (leading from the forming electrode 15, across the gap 13 and to the accelerating electrode 20) is why this magnetic field 30 is referred to as a "reverse" poloidal magnetic field. Any plasma that is pushed through the acceleration gap 13 and into the forming electrode 16 and due to the ring field 24 generated by the acceleration pulse gushes out into the relaxation zone 22 will have a reverse poloidal field 30a (see fig. 1(b)) in the same direction as the trailing edge of the closed poloidal field 25 of the plasma ring 11, but opposite to the direction in which the magnetic field 19 is formed. Thus, the plasma emerging from the accelerating gap 13 with the reverse poloidal field 30a will not be recoupled with the closed poloidal field 25 of the ring 11, thus preventing the push ring field 24 from diffusing into the plasma ring 11. The push ring field 24 will need to diffuse first through the reverse poloidal field 30a before reaching into the outer layer of the plasma loop 11, thus delaying the rise in q near the edge and keeping the plasma loop 11 stable for a longer time.

The magnetic coils 32 of the opposite poloidal field generator are coupled to a power source (not shown) and the parameters of the opposite poloidal field 30 can be adjusted by adjusting the current through the magnetic coils 32 so that the generated opposite poloidal field 30 is in the opposite direction to the forming magnetic field 19 generated by the forming magnetic coils 18. Alternatively, the oppositely poloidal field generators may comprise one or more permanent magnets (not shown) rather than electromagnetic coils.

In one implementation shown in FIG. 1(c), ferromagnetic material 34a, 34b, such as grade 430 stainless steel, may be placed in the acceleration gap13 to increase the amount of reverse poloidal field 30 bridging the gap 13. For example, the ferromagnetic material may be an annular disk 34b circumscribing the ring 34a upstream of the accelerating electrode 20 and/or circumscribing the inner (forming) electrode 15 downstream. Alternatively, the ferromagnetic material may comprise a series of spaced ferromagnetic segments (not shown) circumscribing one or both of the upstream of the accelerating electrode 20 and the downstream of the internally formed electrode 15. The amount of reverse poloidal field 30 depends on the total poloidal flux of the plasma and it may be in the range 0.1-0.25 psi_CTIn which ψ_CTIs the total poloidal flux of the plasma. For example, for ψ_CTFor a CT of 300mWb, the reverse polar flux may be about ψ_RP30-75 mWb. This is for illustrative purposes only and the reverse flux of the reverse poloidal field 30 across the acceleration gap 13 can therefore be established to a smaller or larger value for plasma loops having a poloidal flux of less than or greater than 300 mWb. The polar flux ψ of the CT can be controlled by forming the number and positions of the magnetic coils 18 and the magnetic coils 32 of opposite polarities and the current flowing through these coils 18, 32_CTParameter and reverse flux psi_RPAnd (4) parameters.

Experiments with plasma generation and acceleration systems with and without an inverse poloidal field generator conducted in General Fusion, Inc.

Referring to fig. 2(a) - (c), experiments were conducted using a plasma generation and acceleration system without a reverse poloidal field generator, and it was found that when the configuration forming the magnetic field 19 provides more open field lines in front of the plasma (across the acceleration gap 13, in the relaxation zone 22), the resulting plasma loop 11 has a more compact configuration and longer temperature lifetime in the plasma generator 12. However, this configuration of the forming field 19 prevents good acceleration of the plasma loop 11. The reason for the relatively poor acceleration performance may be that the push ring field 24 may escape along the open field lines in front of the plasma loop 11, between the plasma loop 11 and the open field lines (see figure 2(a)), so instead of pushing the plasma loop 11 downwards, it dissipates (blow out) these open field lines while most of the plasma loop 11 is in the relaxation region 22.

It is also noted that during the formation of the plasma loop 11, some of the plasma (ionized gas) escapes through the acceleration gap 13 into the inner (forming) electrode 15. Thus, when the second (accelerating) current pulse is released, the pushing torroidal flux of the torroidal field 24 pushes the plasma forward, causing the magnetic field lines poloidal to form the magnetic field 19a to distort in the accelerating gap 13 and pass through the gap 13, causing it to flood out into the relaxation region 22 behind the plasma torus 11 (see fig. 2 (c)). The magnetic field lines crossing the pole of the acceleration gap 13 toward the formation magnetic field l9a are guided from the acceleration electrode 20 to the formation electrode 15. Since the poloidal forming magnetic field 19a is in the opposite direction of the trailing edge of the closed poloidal field 25 of the plasma torus 11, the two poloidal fields 19a, 25 are coupled so as to open an unobstructed path 26 for the toroidal field 24 to enter the plasma edge or perhaps even reach the core of the plasma torus 11, thereby expanding it with additional toroidal flux, rather than pushing the plasma torus 11 along the accelerator 14 (see fig. 2 (d)). In this case, since the push ring field 24 flowing in the plasma loop 11 will push the poloidal field 25 of the plasma outward, the push ring field 24 mixes with the closed poloidal field 25 of the plasma and produces the plasma loop 11 having a hollow configuration. In the hollow configuration of the plasma loop 11, more plasma current flows near the plasma edge than in the core, thus creating instabilities within the plasma that may disrupt plasma confinement. The mixing of the push ring field 24 with the closed poloidal field 25 of the plasma loop 11 raises the q near the edge, altering the q spectrum of the plasma and creating plasma instabilities that can disrupt plasma confinement. The mixing of the push ring field 24 with the closed poloidal field 25 is measured by surface magnetic field sensors (not shown) located along the length of the plasma generator 12 and accelerator 14. The sensor indicates an increase in the ring field 24 and simultaneously an increase in the poloidal field 25, which indicates a mixture of the ring and poloidal fields 24, 25. Then, as the plasma loop 11 passes over these sensors, the poloidal field 25 is lowered and the toroidal field 24 is raised due to the pushing toroidal field 24 behind the plasma loop 11.

The following theory is established: trying to accelerate such a hollow plasma loop 11 (which contains too much loop flux) by, for example, increasing the power of the accelerator will increase the probability of a leakage effect. Leakage may occur when the magnetic field pressure of the push current lifts the plasma loop 11 from the accelerating electrode 20, expanding the loop push flux of the loop field 24 in front of the plasma loop 11. Thus, if the shape of the current pulse across the accelerator 14 is such that the generated toroidal field 24 rises too quickly, it can lift the plasma torus 11 "up" towards the outer electrode 16 and pass "under" the plasma against the accelerating electrode 20 surface.

Referring now to fig. 3(a) and (b), simulations of plasma generation and acceleration systems with and without an inverse poloidal field generator were conducted using the open source finite element analysis code FEMM (available from David Meeker, dmeeker @ _ ieee. Fig. 3(a) shows a magnetic field configuration in which only polar directions are provided to form a magnetic field 19 and no reverse polar direction field 30 is provided. Using 3 forming magnetic coils 18a, 18b, 18c generates a forming magnetic field 19. Less than or greater than 3 forming magnetic coils 18 may be used to provide polar forming magnetic field 19. The current flowing through each of the forming magnetic coils 18 is carefully adjusted and predetermined according to the parameters of the plasma. Fig. 3(b) shows magnetic field confirmation in which the forming magnetic field 19 is generated using 3 forming magnetic coils 18, and the opposite polar field 30 is generated using 1 opposite polar magnetic coil 32. A ferromagnetic plate 34a and an annular ring 34b are also provided to increase the amount of reverse poloidal field 30 that bridges the acceleration gap 13. The direction of the oppositely poled field 30 is opposite to the direction of the formed magnetic field 19, as indicated by the arrows. Those skilled in the art will appreciate that more than one antipodal magnetic coil 32 may be added to adjust the configuration and parameters of the antipodal field 30 across the acceleration gap 13. One or more oppositely poled magnetic coils 32 may be positioned immediately to the left of the acceleration gap 13 (as shown in fig. 3 (b)) and near the axis of symmetry so that they can change the magnetic field configuration so that the magnetic field lines move toward the left of the accelerator gap. The parameters of the current through the forming magnetic coil 18 and the opposite pole to magnetic coil 32 can be preset according to predetermined parameters of the plasma loop 11 and parameters of the power supplies 28a, 28 b.

Embodiments of the system for plasma generation and acceleration systems can be used to generate high energy density plasmas suitable for applications in neutron generators, nuclear fusion, nuclear waste remediation, medical nucleotide generation, for materials research, for remote sensing imaging of internal structures of objects by neutron radiography and tomography, x-ray generators, and the like.

While particular elements, embodiments and applications of the present disclosure have been shown and described, it will be understood that the scope of the present disclosure is not limited thereto, since modifications may be made without departing from the scope of the present disclosure, particularly in light of the foregoing teachings. Thus, for example, in any methods or processes disclosed herein, the acts or operations making up the methods/processes may be performed in any suitable order and are not necessarily limited to any particular disclosed order. Elements and components may be configured or arranged differently, combined and/or eliminated in various embodiments. The various features and processes described above may be used independently of one another or may be combined in various ways. All possible combinations and sub-combinations are intended to be within the scope of the present disclosure. Throughout this disclosure, references to "some embodiments," "an embodiment," etc., indicate that a particular feature, structure, step, process, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases "in some embodiments," "in an embodiment," and the like throughout this disclosure are not necessarily all referring to the same embodiment and may refer to one or more of the same or different embodiments. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, in the forms of embodiments described herein, various omissions, additions, substitutions, equivalents, rearrangements, and changes may be made without departing from the spirit of the invention described herein.

Aspects and advantages of embodiments have been described where appropriate. It is to be understood that not necessarily all such aspects or advantages may be achieved in accordance with any particular embodiment. Thus, for example, it will be recognized that various embodiments may be implemented in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other aspects or advantages as may be taught or suggested herein.

Unless specifically indicated otherwise or otherwise understood within the context as used herein, conditional language as used herein, such as where "may", "for example (e.g)", etc., are generally intended to convey that certain embodiments include, while other embodiments do not include, particular features, elements and/or steps. Thus, such conditional language is not generally intended to imply that features, elements and/or steps are in any way required for one or more embodiments or that one or more embodiments necessarily include decision logic, with or without operator input or prompting, whether such features, elements and/or steps are included or are to be implemented in any particular embodiment or not. No single feature or group of features is required or essential to any particular embodiment. The terms "comprising," "including," "having," and the like, are synonymous and are used in an open-ended fashion, and do not exclude other elements, features, acts, operations, and the like. In addition, the term "or" is used in its inclusive sense (and not in its exclusive sense) so that when used, for example, to connect a list of elements, the term "or" means one, some, or all of the elements in the list.

Unless specifically stated otherwise, a conjunctive phrase, such as the phrase "at least one of X, Y and Z," should be otherwise understood by the context as used to generally express that an item, term, etc., can be either X, Y or Z. Thus, such conjunctions are generally not intended to indicate that certain embodiments require the presence of at least one of X, at least one of Y, and at least one of Z, respectively.

Example calculations, simulations, results, graphs, values, and parameters of the embodiments described herein are intended to illustrate and not to limit the disclosed embodiments. Other embodiments may be configured to operate and/or different from the illustrative examples described herein. Indeed, the novel methods and apparatus described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions disclosed herein.