Plasma compression system utilizing poloidal field coils.

Abstract

An example plasma compression system is disclosed. The system includes a metal vessel configured to receive and contain a plasma. The system further includes a metal liquid liner within the vessel at least partially defining a plasma compression region having a longitudinal axis, and a means for moving the liquid liner inwardly toward the longitudinal axis to compress the plasma in the plasma compression region. The system further includes a plurality of conductive coils external to the plasma compression region configured to generate a poloidal magnetic field in the liquid liner and the plasma compression region. At least a portion of the poloidal magnetic field in the plasma compression region extends along the longitudinal axis, and at least a portion of the poloidal magnetic field in the liquid liner moves inwardly with the liquid liner toward the longitudinal axis as the liquid liner moves toward the longitudinal axis.

Description

[Technical field]

[0001] The present disclosure relates generally to plasma compression systems utilizing poloidal field coils and methods for operating the plasma compression systems. [Background technology]

[0002] Unless otherwise indicated herein, the material described in this section is not prior art to the claims in this application and is not admitted to be prior art by inclusion in this section.

[0003] General Fusion's Magnetized Target Fusion (MTF) technology uses liquid metal to compress a magnetized hydrogen isotope plasma, which is then heated until the hydrogen isotopes fuse initially into helium or tritium, respectively, releasing energy in energetic neutrons or protons. The energetic particles are absorbed into the resulting heated blanket of liquid metal. Heat can be extracted, providing an energy source.

[0004] Nuclear fusion is the process of combining two atomic nuclei, which causes the reaction to release energy. The release of energy is due to the small difference in mass between the reactants and the products of the fusion reaction, dE=dmc 2 The nuclear fusion of the reactants is defined by the formula: ##EQU1## The common reactants are deuterium (a hydrogen nucleus with one proton and one neutron) and tritium (a hydrogen nucleus with one proton and two neutrons). Nuclear fusion of these two reactants produces a helium-4 nucleus, neutrons, and energy that is captured as heat. Achieving nuclear fusion of the reactants requires high temperature and high pressure (density) of the reactants. For example, fusion conditions for a magnetized target fusion commercial power plant may be on the order of 150 million degrees Celsius and 800 megapascals of pressure. In the MTF approach to nuclear fusion, a plasma is generated and compressed to achieve these conditions.

[0005] A plasma is a gas-like state of matter, consisting of ionized gas atoms and free electrons. The presence of charged particles (e.g., positive ions and negative electrons) makes the plasma conductive, which allows it to respond to magnetic fields. Plasmas may be shaped and positioned using magnetic fields, and a particularly stable configuration for a plasma is the torus shape. A plasma torus is a free-standing magnetized plasma shaped into a toroidal configuration, with coupled poloidal and (in some cases) toroidal enclosed magnetic fluxes. The degree of coupling of the poloidal and toroidal magnetic fluxes defines the helicity of the plasma torus. A plasma torus confined to a simply connected volume is called a compact toroid (CT). Exemplary CT configurations include (i) a spherical tokamak (e.g., "spheromak") configuration that exists near stable magnetohydrodynamic equilibrium with an internal magnetic field that has both toroidal and poloidal components, and (ii) a field-reversed configuration (FRC), which also has a toroidal magnetic topology, but is more elongated in the axial direction and may resemble a prolate ellipsoid on the outer surface, with a predominantly poloidal magnetic field but no toroidal field component. CT plasmas can form in a range of magnetic configurations, including those that exist in states between the spheromak and FRC states. Other plasma configurations are possible, for example, if a conducting central axis is used in the tokamak. It is also possible for an initial plasma torus to develop and change its magnetic configuration over time.

[0006] Another approach to achieving fusion conditions is to mechanically compress the hydrogen plasma using means such as a mechanical piston compressing a liquid metal liner in an MTF reactor. These mechanical plasma compression systems compress a generally spheroidal Tokamak-type plasma in a fusion containment vessel by forming a substantially cylindrical vortex cavity in which the plasma is positioned. The cylindrical vortex cavity can be formed by spinning the liquid metal using a rotating cylinder in the containment vessel, whereby centrifugal forces move the liquid metal against the walls of the rotating cylinder, forming a liquid metal liner surrounding the vortex cavity. The liquid metal liner is collapsed by moving a piston, which implodes the vortex cavity radially and axially, forming a spheroidal, collapsing cavity. The plasma confined therein is compressed as the liquid metal liner collapses. When the liquid metal liner is forced inward around the enclosed spherical tokamak plasma, the spherical tokamak magnetic field that contains the plasma is incompletely excluded from penetrating the conductive liquid metal liner by a process of induction, whereby the spherical tokamak plasma induces currents that repel the magnetic field in the conductive liquid metal liner. Because the liquid metal liner has finite conductivity, these induced currents and associated magnetic fields do not completely repel the spherical tokamak magnetic field, and over time, some of the spherical tokamak magnetic field penetrates the liquid metal liner.

[0007] A particular challenge for plasma compression systems is the tendency of the plasma to transfer heat from its core to the exterior and vessel walls. This loss of heat to the vessel walls reduces the temperature of the plasma, thereby reducing the plasma's lifetime and therefore the likelihood of a fusion reaction occurring. This is particularly a challenge in MTF systems that use a liquid metal liner, where as the spherical tokamak magnetic field enters the liquid liner, the plasma comes into contact with the liquid liner and transfers heat to the vessel walls. It would therefore be advantageous to devise systems and methods to confine the plasma and limit or prevent it from interacting with the reactor vessel walls. This goal is relevant for reactors with static walls (e.g., tokamaks) or dynamic walls (magnetized target fusion). Summary of the Invention [Means for solving the problem]

[0008] According to one aspect of the invention, there is provided a plasma compression system comprising: a vessel configured to receive and confine the plasma and a metallic liquid medium circulating about a longitudinal axis of rotation to at least partially define a plasma compression region configured to receive and confine the plasma, means for controllably reducing a volume of the plasma compression region by moving the liquid medium inwardly toward the longitudinal axis of rotation, the liquid medium compressing the plasma, and a plurality of conductive coils outside the plasma compression region configured to generate a poloidal magnetic field in the vessel, the liquid medium, and the plasma compression region, wherein at least a portion of the poloidal magnetic field in the plasma compression region extends along the longitudinal axis of rotation, and at least a portion of the poloidal magnetic field in the liquid medium moves inwardly toward the longitudinal axis of rotation with the liquid medium as the liquid medium moves toward the longitudinal axis of rotation.

[0009] In some embodiments, the vessel may include a ferromagnetic or ferrimagnetic material. The plurality of conductive coils may include at least two substantially annular coils positioned substantially symmetrically around and substantially perpendicular to the longitudinal axis of rotation, the at least two substantially annular coils being at different corresponding positions along the longitudinal axis of rotation. The plurality of conductive coils may also include at least a first coil and a second coil spaced from and substantially parallel to the first coil, the plasma compression region being between the first and second coils. The conductive coils may be positioned relative to the vessel wall such that the vessel wall concentrates the poloidal magnetic field in the plasma compression region.

[0010] The vessel may include a wall portion having an inside radius along a direction substantially perpendicular to the wall portion in a range of 3.5 m to 5.5 m. Additionally, the plasma compression system may include a metal rotatable core within the vessel. The rotatable core is configured to rotate about a longitudinal axis of rotation, at least a portion of the rotatable core having an inside radius along a direction substantially perpendicular to the wall portion in a range of 1.5 m to 3 m.

[0011] The first power supply can be configured to apply a substantially constant current to the plurality of conductive coils while the liquid medium compresses the plasma. More specifically, the first power supply can be configured to apply a current having an AC component and a DC component, the AC component having a frequency less than 10 Hz and a magnitude less than 10% of the magnitude of the DC component. The first power supply can also be configured to apply a substantially constant current over the lifetime of the plasma in the plasma compression region.

[0012] The second power supply can be configured to generate a shaping magnetic field at the centerline (equatorial plane) of the vessel cavity in the plasma compression region in the range of 100 mWb to 700 mWb.

[0013] According to another aspect of the invention, there is provided a plasma compression system comprising: a metal vessel configured to receive and confine a plasma, a metal liquid liner in the vessel at least partially defining a plasma compression region having a longitudinal axis, means for moving the liquid liner inwardly toward the longitudinal axis to compress the plasma in the plasma compression region, and a plurality of conductive coils outside the plasma compression region configured to generate a poloidal magnetic field in the liquid liner and the plasma compression region, wherein at least a portion of the poloidal magnetic field in the plasma compression region extends along the longitudinal axis, and at least a portion of the poloidal magnetic field in the liquid liner moves inwardly with the liquid liner toward the longitudinal axis as the liquid liner moves toward the longitudinal axis.

[0014] The vessel is ferromagnetic or ferrimagnetic. The plurality of conductive coils can be positioned relative to a wall of the vessel such that the vessel wall at least partially concentrates a poloidal magnetic field in the plasma compression region. The plasma can be substantially toroidal and substantially symmetric about the longitudinal axis, and at least a portion of the poloidal magnetic field in the plasma compression region extends along a poloidal direction for the substantially toroidal plasma. A first power source can be coupled to the conductive coils and can be configured to generate a poloidal magnetic field in the plasma compression region with sufficient strength to prevent the plasma from acting on the liquid liner.

[0015] The plurality of conductive coils can include at least two substantially annular coils positioned substantially symmetrically around and substantially perpendicular to the longitudinal axis, the at least two substantially annular coils being at different corresponding positions along the longitudinal axis.

[0016] The system may further include a rotating core and a liquid medium in the vessel. The rotating core may be configured to rotate and circulate the liquid medium to form the liquid liner and the plasma compression region. The rotating core may have an outer surface spaced from an inner surface of the vessel by a gap. The means for moving the liquid liner may include a plurality of implosion drivers extending through the rotating core from the gap to the plasma compression region and confining at least a portion of the liquid medium.

[0017] In some aspects, the plasma compression system can further include a pressurized fluid source in fluid communication with the plurality of implosion drivers, the pressurized fluid source configured to controllably apply pressurized gas to the plurality of implosion drivers, whereby the implosion drivers apply a pressure pulse to the liquid medium, forcing the liquid liner inward, shrinking the plasma compression region, and compressing the plasma in the plasma compression region. In some other aspects, the means for moving the liquid liner can further include a plurality of compression drivers fixedly attached to the exterior surface of the vessel and in fluid communication with the plurality of implosion drivers. The compressed fluid in the gap is in fluid communication with the compression drivers and the implosion drivers. The pressurized fluid source is in fluid communication with the plurality of compression drivers and configured to controllably apply pressurized gas to the plurality of compression drivers, whereby the compression drivers apply a first pressure pulse to the plurality of implosion drivers via the compressed fluid, whereby the implosion drivers apply a second pressure pulse to the liquid medium, forcing the liquid liner inward, shrinking the plasma compression region, and compressing the plasma in the second region.

[0018] The plasma compression system may further include a plasma injector in fluid communication with the vessel and configured to inject the plasma into the plasma compression region.

[0019] According to another aspect of the invention, a method is provided that includes injecting a magnetized toroidal plasma into a plasma compression region, the plasma compression region being at least partially defined by a metallic liquid liner having a longitudinal axis, generating a poloidal magnetic field in the liquid liner and the plasma compression region, at least a portion of the poloidal magnetic field in the plasma compression region extending along the longitudinal axis, and compressing the liquid liner toward the longitudinal axis, thereby reducing the volume of the plasma compression region containing the plasma and compressing the plasma. The liquid medium can be rotated to form a metallic liquid liner, the liquid liner rotating about a longitudinal axis of rotation symmetrical to the axis of the plasma.

[0020] Generating the poloidal magnetic field can include passing a current through a plurality of coils external to the plasma compression region, the current can be substantially constant during said compression, and compressing the liquid liner can include adjusting a trajectory of the liquid liner to dynamically adjust the poloidal magnetic field within the plasma compression region.

[0021] Throughout the drawings, reference numbers may be reused to indicate correspondence between mentioned elements. The drawings are provided to illustrate exemplary embodiments described herein and are not intended to limit the scope of the disclosure. The sizes and relative positions of elements in the drawings are not necessarily drawn to scale. For example, the shapes and angles of various elements are not drawn to scale, and some of these elements have been arbitrarily enlarged and positioned to improve the legibility of the drawings. [Brief description of the drawings]

[0022] [Figure 1] FIG. 1 is a vertical cross-sectional view of a plasma compression system including a plasma injector, a liquid metal containment vessel with poloidal field coils, and a compression driver. [Figure 2A]1 is a vertical cross-sectional view of a different embodiment of a compression driver, the compression driver according to a first embodiment including a driver piston and a driver bore and multiple implosion drivers, each implosion driver including a pusher piston and a pusher bore. [Figure 2B] A compression driver according to a second embodiment includes an accumulator in fluid communication with the drive valve and a relief tank in fluid communication with the rebound valve. [Diagram 3] 13 is a photograph of some of the easily installed compression drivers according to the prototype embodiment. [Figure 4] FIG. 2 is a partial cross-sectional plan view of a plasma compression system having a compression driver according to a first embodiment, showing the orientation of the compression driver in the vessel and the orientation of the implosion driver in the rotating core. [Figure 5A] 1A-1C are vertical cross-sectional views of one compression driver and multiple implosion drivers in operation over time according to a first embodiment, showing the compression driver with the driver piston in a starting position before being triggered by a prime mover. [Figure 5B] Shows the driver piston at approximately one-third of its total travel limit within the driver bore. [Figure 5C] 1 shows the driver piston as it approaches the pusher piston, just before the pusher piston is accelerated. [Figure 5D] 1 shows a driver piston at a distal end of a driver bore as the pusher piston is accelerated in the pusher bore. [Figure 5E] The pusher piston is shown at the limit of its travel within the pusher bore. [Figure 6A] FIG. 13 is a vertical cross-sectional view of a portion of one compression driver according to the second embodiment throughout a compression shot, showing the valve state of the compression driver in the pre-shot phase. [Figure 6B] 1 shows the valve state during the compression phase. [Figure 6C] 1 shows the valve state during the rebound recovery phase. [Figure 6D]1 shows the valve state during the energy dissipation phase. [Figure 7A] FIG. 2 is a partial cross-sectional perspective view of a driver piston of a first embodiment of a compression driver and multiple pusher pistons adjacent a container wall; [Figure 7B] FIG. 13 is a partial cross-sectional perspective view of multiple accumulators and actuated valves of a second embodiment of a compression driver and multiple push pistons adjacent a vessel wall; [Figure 8] FIG. 2 is a cross-sectional perspective partial view of a pusher piston according to one embodiment. [Figure 9A] 1 is a graphical representation of the position trajectories over time of the driver piston, pusher piston and liner interface during a compression operation. [Figure 9B] 1 is a graphical representation of pressure pulses over time in the driver bore and in the pusher bore behind the liquid liner during a compression operation. [Figure 10A] 1A-1C are partial cross-sectional views of different embodiments of a plasma compression system showing a plasma confinement vessel having multiple ports formed in an outer wall of the vessel, a compression driver coupled to the ports of the vessel, and a rotating core, showing a first embodiment of the compression driver. [Figure 10B] 2 illustrates a second embodiment of a compression driver. [Figure 11A] Vertical cross-section of the experimental plasma injector and flux conserver system, including the vessel, solid conducting center shaft, and poloidal field coils. [Figure 11B] A vertical cross-section of the experimental plasma injector and flux conserver system, including the vessel, conductive liquid metal center conductor, and poloidal field coils. [Figure 12A] FIG. 11 is a horizontal cross-sectional half-side view of the flux conserver vessel showing the position and orientation of the plasma relative to the flux conserver walls and center shaft prior to compression. [Figure 12B]FIG. 11 is a horizontal cross-sectional half-side view of the flux conserver vessel showing the position and orientation of the plasma relative to the flux conserver walls and center shaft prior to compression. [Figure 12C] FIG. 11 is a horizontal cross-sectional half-side view of the flux conserver vessel showing the position and orientation of the plasma relative to the flux conserver walls and center shaft prior to compression. [Figure 13A] FIG. 11 is a horizontal cross-sectional half-side view of the plasma injector and flux conserver showing the magnetic flux configuration map when the poloidal field coils are not energized and no external poloidal magnetic field is present. [Figure 13B] FIG. 11 is a horizontal cross-sectional half-side view of the plasma injector and flux conserver, showing the magnetic flux configuration map when the external poloidal field coils are energized and the external poloidal field is present. [Figure 14] 1 is a graph showing one experimental result from an experimental system of plasma lifetime versus plasma current in the presence and absence of a poloidal magnetic field. [Figure 15] 1 is a graph showing a series of experimental results from an experimental system of plasma lifetime versus plasma current in the presence and absence of a poloidal magnetic field. [Figure 16] 1 is a graph of modeled data based on an experimental system showing that the improvement in plasma temperature tracks poloidal magnetic field fraction up to a 30% flux fraction. [Figure 17A] 11A-11C are graphs showing simulated results of plasma temperature gain versus percent of poloidal magnetic flux applied to the plasma from an experimental system, respectively. [Figure 17B] 11 is a table showing simulated results from an experimental system of plasma temperature gain versus percent of poloidal magnetic flux applied to the plasma; [Figure 18A]13 is a simulated mapping of magnetic flux lines over time within a liquid metal liner during compression of the plasma based on an experimental system in which the liquid metal liner is uniformly imploded in a cylindrical shape. [Figure 18B] 13 is a simulated mapping of magnetic flux lines over time within a liquid metal liner during compression of the plasma based on an experimental system in which the liquid metal liner is spherically imploded. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] The embodiments described herein relate to a plasma compression system 1 coupled to a plasma injector 2 and a method for compressing a plasma injected by the plasma injector 2 into a plasma compression region of the plasma compression system 1. The plasma compression system 1 can be used in an MTF reactor to generate nuclear fusion from the compressed plasma. The plasma compression system 1 generally includes a liquid metal containment vessel 3, a number of mechanical drivers 5a, 5b, a number of electrically conductive poloidal field coils 6, and an electrically conductive central conductor 7. The vessel 3 confines a liquid medium, such as a liquid metal, which can be circulated about a longitudinal axis of rotation to form a central cavity in the vessel 3 and define a plasma compression region. The plasma injector 2 is operable to inject a plasma into the central cavity in the vessel 3 for compression in the plasma compression region. The mechanical drivers 5a, 5b are operable to move the liquid medium toward the longitudinal axis of rotation and compress the plasma. An electrically conductive center conductor 7 extends coaxially from the plasma injector through the vessel 3 along the longitudinal axis of rotation to a lower end plate 29 of the vessel 3. The center conductor 7 is operable with the outer wall of the vessel 3 to act as a flux conserver to limit plasma interaction with the vessel wall 3.

[0024] In some embodiments, as shown in Figures 1-10, the vessel 3 further includes a rotating core 4 rotatable within the vessel 3. The rotating core 4 has a bore with a longitudinal axis coaxial with the longitudinal axis of rotation. In these embodiments, the mechanical drivers include a compression driver 5a fixedly mounted to the exterior of the vessel 3 and an implosion driver 5b extending through the rotating core 4 from the exterior surface to the interior (bore) surface. The rotating core 4 is rotatable about the longitudinal axis of rotation to circulate the liquid medium and form a liquid liner defining a central cavity within the bore, and the implosion driver 5b is operable to contract the liquid liner and compress a plasma compression region relative to the plasma in the cavity.

[0025] It will be appreciated by those skilled in the art that instead of multiple mechanical drivers 5a, 5b as shown in Figures 1-10, there are alternative means to controllably reduce the volume of the plasma compression region to move and contract the liquid medium inwardly, thereby compressing the plasma. For example, sound waves impinging on the liquid medium (not shown) can be used to impart a force to the liquid medium that causes the medium to move. In another embodiment (not shown), an explosive or compressed gas can be used to apply a force to move the liquid medium. When these forces are applied in a controlled manner, these means can be used to contract a hollow liquid liner into the cavity to compress the plasma disposed with that cavity.

[0026] It will be appreciated by those skilled in the art that instead of circulating the liquid medium to form a central cavity, such as by a rotating core as shown in Figures 1-10, a central cavity may be formed in the liquid medium by various means that do not require rotation of the liquid medium. For example, a central cavity in the liquid medium may be formed by the "hollow cylinder waterfall method" (not shown), where gravity moves the walls of a hollow cylinder of liquid medium from a liquid medium reservoir located at the top of the container to the bottom of the container, and a drain and pump are provided at the bottom of the container to capture and recirculate the liquid medium back to the top in a continuous manner. Other means of forming a cavity in a collapsible liquid medium are known in the art.

[0027] A first power source ("poloidal magnetic field generator" (not shown)) is electrically coupled to and supplies current to the poloidal magnetic field coils 6 to generate an external poloidal magnetic field in the vessel wall 3, the liquid medium, and the plasma compression region. The externally generated poloidal magnetic field prevents or impedes the plasma from contacting the liquid liner wall and undesirably cooling the plasma. At least a portion of the externally generated poloidal magnetic field in the plasma compression region extends along the longitudinal rotation axis, and at least a portion of the externally generated poloidal magnetic field is immersed in the liquid medium and tends to remain pinned within the liquid medium. As a result, the external poloidal magnetic field moves with the liquid medium as it moves inward toward the longitudinal rotation axis during plasma compression operation.

[0028] To act as a flux conserver, the vessel wall 3 is constructed of a conductive material such that when current is conducted along the central conductor 7, along the end plates 29, and then along the vessel wall 3 to the liquid medium, a magnetic force is generated, creating a magnetic repulsion between the liquid medium and the magnetized plasma. As a result, magnetic flux between the plasma and the liquid medium is conserved. In this configuration, the liquid liner acts as a flux confinement vessel or "flux conserver" to increase the duration of magnetic confinement of the plasma. As described in more detail below, the central conductor 7 can be a conductive solid metal shaft as shown in FIG. 11A, or a liquid metal that flows continuously from the plasma injector to the bottom of the vessel as shown in FIG. 11B. Although the flux conserver contributes to the confinement of the magnetized plasma, it may not be sufficient by itself to prevent the plasma from interacting with the liquid liner wall during plasma compression. Thus, current is conducted through the poloidal field coils 6 to generate a poloidal magnetic field that is applied to the plasma, effectively lifting the generated plasma away from the liquid liner wall. By reducing or eliminating the plasma-liquid liner wall interaction and the gradual diffusion of the plasma magnetic field to the liquid liner wall, it is expected that plasma confinement will be significantly improved.

[0029] Flux conservers also play a role in stabilizing magnetically confined plasmas. Rapid local changes to the plasma magnetic field configuration, such as those resulting from inherent magnetized plasma instabilities, react inductively to the liquid metal liner. These reactions provide a restoring force and local magnetic field perturbations in the plasma. This stabilizing effect is reduced when the plasma is kept away from the liquid metal liner by an external poloidal magnetic field. Without being bound by theory, it is theorized that there is an optimal practical amount of external poloidal magnetic field that is high enough to keep the plasma away from the liquid metal liner walls and reduce heat losses, but not so high that it moves the plasma so far away from the liquid metal liner walls that it does not benefit from the stabilizing effect of the proximal liquid metal liner walls.

[0030] According to one embodiment, and referring to Figures 1-10, a plasma injector 2 is coupled to the plasma compression system 1 and includes an outer electrode 23 that is coaxial with and surrounds an upper portion of the central conductor 7, thereby defining an annular plasma propagation channel 25 between the outer electrode 23 and the upper portion of the central conductor 7. A fuel injector (not shown) having one or more valves injects plasma fuel into the upstream end of the plasma propagation channel 25. One or more gas valves may be in fluid communication with a plasma fuel source (not shown) and may be arranged as a ring around the plasma injector 2 to symmetrically inject precise amounts of plasma fuel into the channel 25. The liquid metal containment vessel 3 has an upper end with an inlet opening aligned with and in fluid communication with the plasma propagation channel 25, an outer sidewall with a number of ports, and a lower end closed by a lower end plate 29. The central conductor 7 is connected to the plasma injector 2 and to the lower end plate 29 and extends into the vessel through the upper opening. The rotating core 4 is rotatable within the vessel 3 and has an outer surface spaced from the inner surface of the vessel outer sidewall 3 to define an annular gap 10 (see Figs. 2A, 4) and an inner surface defining an interior volume. The vessel 3 and the rotating core 4 in the illustrated embodiment are cylindrical, but the vessel 3 and the rotating core 4 can have different shapes according to alternative embodiments. For example, the vessel 3 can be spherical or ovoid (not shown) and the rotating core 4 can have an outer surface that is straight (cylindrical) or curved with a curvature that matches the curvature of the inner wall of the vessel 3, and an inner surface that can be straight (cylindrical) or curved (not shown). In another example, the inner wall of the vessel 3 may have a circular step of varying radial diameter (not shown) and the rotating core 4 may have a stepped outer surface with a radial diameter that follows the step in the inner wall of the vessel. The rotating core 4 may consist of a single cylindrical unit or, in an alternative embodiment, may consist of multiple molded sections (not shown) that are joined to form the rotating core 4.The construction of the rotating core 4 or sections thereof may use conventional metal forming and mill-wright techniques, or may use metal printing techniques to create an internal web-like structure that optimizes the topology and stress loading within the rotating core 4.

[0031] The structure of the vessel 3 may be a cylinder, or in an alternative embodiment, the vessel 3 may be assembled from a series of stacked rings (not shown) having an outer surface that is straight (cylindrical) or curved with a curvature that follows the curvature of the inner wall of the vessel 3, and an inner surface that may be straight (cylindrical) or curved (not shown). The assembled rings may be joined by means known in the art, for example, by welding the stacked ring interfaces or by the use of other means for applying axial tension to the stacked ring assembly, such as bolts. The outer wall of the vessel 3 may be made of a ferromagnetic or ferrimagnetic material.

[0032] The rotating core 4 contains a liquid medium that can be circulated by the rotating core 4 to form a liquid liner surrounding a cavity (not shown). A liquid circulation system (not shown) can be provided to direct the flow of the liquid medium in the vessel 3. The circulation system can include a number of valves, nozzles, a pipe network, and one or more pumps to obtain a desired flow of the liquid medium in the vessel 3. In this embodiment, the circulation system is configured to flow the liquid medium into the vessel 3 to form a liquid liner having a substantially cylindrical inner cavity, but in other embodiments, the circulation system can be configured to circulate the liquid medium in the vessel 3 to form a liquid liner having an inner cavity having other shapes, such as a sphere, a cone, or other desired shapes.

[0033] A plasma may be injected into the central cavity by the plasma injector 2, and the compression driver 5a is operable to compress a compressed fluid and transmit a pressure pulse across the annular gap 10 which causes the implosion driver 5b to force the liquid medium inwardly, contracting the liquid liner 27 and compressing the plasma. The liquid medium may be a liquid metal such as lithium and the compressed fluid may be a light gas such as helium.

[0034] In one embodiment, the central conductor 7 is a solid metal shaft as used in the experimental prototype shown in FIG. 11A. Referring to FIGS. 1 and 11A, the solid metal central conductor 7 includes an upper portion positioned within the plasma injector 2 and a lower portion positioned within the vessel 3. The distal end of the central conductor 7 is connected to an end plate 29 of the vessel 3. The upper central conductor portion can have a cylindrical, conical, or similar shape, while the lower central conductor portion can be an elongated shaft that extends centrally through the length of the vessel 3. The central conductor 7 is formed from an electrically conductive and vacuum compatible material. A second power source ("current pulse generator" (not shown)) is electrically coupled to the central conductor 7 and the forming field coil 31 and is operable to deliver forming current pulses and toroidal field maintaining current pulses to the upper portion of the current conductor 7, which travels along the lower portion, across the end plate 29, and again along the outer wall of the vessel 3. When the current pulse is delivered, a high voltage is created across the annular plasma propagation channel in the plasma injector 2, causing the plasma fuel there to break down and form a magnetized plasma in the plasma injector 2. A magnetic force is generated, creating a magnetic repulsion between the vessel wall 3 and the magnetized plasma. The current pulse generator can be configured to deliver the forming current pulse and the toroidal field maintaining current pulse to create a magnetic flux at the vessel cavity centerline (equatorial plane) in the range of 100 mWb to 700 mWb within the plasma compression region.

[0035] In another embodiment shown in FIG. 11B, the central conductor 7 contains a flowing liquid metal 7a that flows from the plasma injector 2 to the bottom of the vessel 3. A liquid metal reservoir 7b in the plasma injector 2 contains the liquid metal 7a, which flows out through an outlet formed in the liquid metal reservoir 7b. The liquid metal 7a flows through the vessel 3 and is collected in a catcher 7c, which may be positioned in the end plate 29. The liquid metal 7a from the catcher 7c may be recirculated back into the liquid metal reservoir 7b using one or more pumps (not shown). The flowing liquid metal conductor may flow continuously or the flow may be regulated using a valve in communication with the outlet of the reservoir. The liquid metal 7a may flow from the liquid metal reservoir 7b under gravity and / or may be drained under pressure.

[0036] With particular reference to Figures 2A, 4, 5A-5E, 7A and 10A, each of the compression drivers 5a includes a driver bore 13 and a driver piston 15 slidable within the driver bore 13 to compress a compressed fluid. The driver bore 13 has a driver bore wall 14 fixedly attached to the outer surface of the vessel wall 3 and has a distal end in fluid communication with a corresponding port 12 in the vessel wall 3. Each of the implosion drivers 5b includes a pusher bore 9 within which a pusher piston 8 is slidable. The pusher bore 9 extends through the rotating core 4 and has a proximal end in fluid communication with the annular gap 10 and a distal end in fluid communication with the liquid medium. A compressed fluid fills the annular gap 10 and is in fluid communication with the driver and pusher pistons 15, 6.

[0037] As the rotating core 4 rotates, for example by an electric drive motor, steam turbine, or other type of rotational drive, centripetal force causes the liquid medium to fill the pusher bore 9, forming a liquid liner 27 that defines a cavity 28. The plasma injector 2 injects plasma into this cavity. Because the liquid medium is completely confined within the rotating core 4 (i.e., does not contact the vessel wall 3), it is in a solid rotating state with minimal turbulence or cavity surface perturbation. In a compression action, a prime mover is actuated, forcing the driver piston 15 towards the port 12 in the vessel wall 3, thereby compressing the compressed fluid in the annular gap 10 and generating a pressure pulse. This exerts pressure on the pusher piston 6, which in turn forces the liquid medium inward, contracting the liquid liner 27 and compressing the plasma. A shear layer of compressed fluid is formed in the annular gap 10. Because the shear layer is a light gas, the power required to drive the rotating core 4 is significantly lower compared to designs that use a rotor immersed in a liquid medium and create a liquid medium shear layer.

[0038] Each implosion driver 5b has a pusher piston 8 with a mass less than the mass of the driver piston 15 and a pusher bore 9 with a length less than the length of the driver bore 13. As a result, the compression drivers 5a convert a longer, lower powered mechanical input in the stationary structure to a shorter, higher powered mechanical output in the implosion drivers 5b in the rotating core 4. This is useful in applications requiring short pulses of high pressure, such as the plasma compression systems developed by General Fusion Inc.

[0039] With particular reference to FIGS. 1 and 2A, the plasma compression system 1 includes multiple compression drivers 5a and implosion drivers 5b that together can implode a liquid liner 27 with the ability to adjust the implosion trajectory. The motive force in this example includes an accumulator 17 coupled to the proximal end of the driver bore 13 by a valve 16 that can be opened, thereby releasing a high pressure gas ("driver fluid"), moving the driver piston 15 and compressing the compressed fluid in the driver bore 13 in front of the driver piston 15. For purposes of this application, compressed fluid can mean any fluid that can be compressed, and in one embodiment can be a gas. In another embodiment, the compressed fluid can be a mixture of gas and liquid medium, so long as the compressed fluid in the driver bore 13 between the pistons 15 and 6 is compressible. In the illustrated example, each compression driver 5a includes its own accumulator 17. However, in alternative embodiments, multiple compression drivers 5a may share one accumulator, for example one accumulator may be provided for each layer of compression drivers 5 (not shown), or one accumulator may be provided for all compression drivers 5a (not shown).

[0040] In alternative embodiments, the motive force may include an electromagnetic source or the motive force may include a mechanical spring. An electromagnetic coil (not shown) may be wrapped around the driver bore 13 and controlled to drive the driver piston 15 along the driver bore 13.

[0041] Prior to the compression operation, the driver and pusher pistons 15, 8 are in an initial position (see FIG. 5A). In the initial position, compressed fluid fills the driver bore 13 and annular gap 10 in front of the driver piston 15 and is in fluid communication with the pusher piston 6. The pressure of the compressed fluid between the pistons 15 and 8 in the initial position is significantly lower than the driver fluid pressure in the accumulator 17. For example, in one embodiment, the pressure of the compressed fluid can be about 0.5 MPa, but can be lower or higher than 0.5 MPa, so long as it is significantly lower than the driver fluid pressure in the accumulator 17.

[0042] As the rotating core 4 rotates, the pusher bore 9 fills with liquid medium, which is forced against the inner surface of the pusher piston 8 by the centripetal force caused by the rotation of the rotating core 4. In another embodiment, a gas, mechanical means, or magnetic field can apply pressure to the pusher piston 8 to prevent it from being inadvertently accelerated in the pusher bore 9 (up to a predetermined / desired time). A retaining means, such as, for example, a ledge (not shown), can be provided at / near the open end of the pusher bore 9 to prevent the pusher piston 8 from being dislodged from the pusher bore 9. In addition, an additional retaining means can be provided at the proximal end (not shown) to prevent the pusher piston 8 from being pushed into the annular gap 10 by the pressure exerted by the liquid medium in the pusher bore 9.

[0043] The driver and pusher pistons 15, 8 may be formed from any suitable material, such as, for example, stainless steel, titanium alloy, or any other suitable material that does not react with the liquid medium and / or the driver fluid and / or the compressed fluid. In this embodiment, the diameter of each driver bore 13 and driver piston 15 is greater than the diameter of each pusher bore 9 and pusher piston 8. However, in alternative embodiments, the diameter of each pusher bore 9 (pusher piston 8) may be the same as or greater than the diameter of each driver bore 13 (driver piston 15).

[0044] Valve 16 can be any type of controllable fast valve. For example, valve 16 can be a gas-operated valve, a solenoid valve, or any other suitable fast acting valve. The valve size and driver fluid pressure can be selected to allow sufficient flow to accelerate driver piston 15 in driver bore 13 within a target period of time.

[0045] In operation, the acceleration profile of the driver piston 15 can be controlled by controlling the pressure of the driver fluid in the driver bore 13 behind the driver piston 15. The acceleration profile of the driver piston 15 can be adjusted by adjusting the pressure behind the driver piston 15 (the pressure of the accumulator 17). For example, the driver fluid pressure at the driver piston 15 can be adjusted by adjusting the opening size or duration of the valve 16 to control the flow of driver fluid from the accumulator 17 and / or by releasing the driver fluid from the driver bore 13 through ports 18 in the driver bore 13 behind the driver piston 15. These ports 18 have controllable valves (not shown) similar to the driver fluid valve 16. The means for adjusting the opening size or duration of the valve 16 to control the flow of driver fluid from the accumulator 17 can be accomplished by pneumatic valve control means or electromagnetic valve control means. The acceleration profile of the driver piston 15 can also be controlled by controlling the pressure of the compressed fluid ahead (downstream) of the driver piston 15. A port 18 (see FIG. 2A) in the wall of the compression driver 5a between the driver piston 15 and the vessel wall 3 can be controlled to inject or release compressed fluid. In addition, additional compressed fluid can be injected near the proximal end of the driver bore 13 to slow down the driver piston 15 and prevent collision with the vessel 3. The length of the driver bore 13 can be designed to be sufficiently long so that the trajectory of the driver piston 15 can be adjusted by varying the driver fluid pressure and / or the compressed fluid pressure. A number of sensors (not shown) can be provided to measure the position of the driver piston 15 or the open duration of the driver fluid valve 16 and provide measurement signals to a controller (not shown). In another embodiment, arc heating of compressed fluid by an electric arc generated across two electrodes 19 positioned at the distal end of the driver bore 13 between the compression driver piston 15 and the rotating core 4 can be used to adjust the trajectory of the compression driver piston 15 and the pusher piston 8.

[0046] In an alternative embodiment, an electromagnetic coil can control the open duration of the driver fluid valve 16, which in turn controls how much high pressure fluid enters the driver bore 13, and can be actuated to control the acceleration of the driver piston 15. Alternatively, the acceleration profile of the driver piston can be directly controlled electromagnetically. In an embodiment in which the motive force includes an electromagnetic coil wrapped around the driver bore wall 14, an electromagnet conductive element in the driver piston and an electromagnetic source coupled to the electromagnetic coil can be actuated to control the acceleration of the driver piston.

[0047] 4, compression driver 5a is positioned radially at the exterior surface of vessel wall 3, and implosion driver 5b, comprised of pusher piston 8 in pusher bore 9, extends radially within rotating core 4. Compression driver piston 15 is shown partway along its inward travel within driver bore 13 towards rotating core 4. In alternative embodiments, compression driver 5a and implosion driver 5b can be positioned non-radially relative to vessel 3 and rotating core 4, so long as compression driver 5a is positioned perpendicular (i.e., perpendicular) to the axis of rotation of rotating core 4 and implosion driver 5b is positioned perpendicular to the axis of rotation of rotating core 4.

[0048] With particular reference to Figures 5A, 5B, 5C, 5D, and 5E, the compression operation involves rapidly moving each driver piston 15 towards the vessel wall port 12, thereby compressing the compressed fluid in the annular gap 10 and generating a pressure pulse against the pusher piston 8, which then moves inwardly within the pusher bore 9, forcing the liquid medium inwardly through the rotating core 4 and into the vessel 3. Four basic stages of the compression operation are shown. Stage 1 is the initial (start) stage before the compression driver is triggered. At this stage, the accumulator 17 is fully charged, the valve 16 is closed, and the pistons 15, 6 are in their initial positions (Figure 5A).

[0049] In phase 2 (FIGS. 5B and 5C), the driver valve 16 is opened and the driver fluid in the accumulator 17 passes through the driver valve 16 and enters the driver bore 13 behind the driver piston 15, accelerating the driver piston 15 along the driver bore 13 towards the rotating core 4. During phase 2, the potential energy stored as high pressure of the fluid in the accumulator 17 is converted into kinetic energy in the movement of the driver piston 15, and the pressure of the compressed fluid contained in the driver bore 13 increases. In phase 3 (FIG. 5D, 15 ms), the driver piston 15 approaches the rotating core 4 and the compressed fluid pressure in the annular gap 10 rises sharply absorbing the kinetic energy of the driver piston 15, so that the compressed fluid pressure exceeds the pressure of the liquid medium in the pusher bore 9 and holds the pusher piston 6 in place. In phase 4 (FIG. 5E, 19 ms), the pusher piston 6 accelerates rapidly, forcing the liquid medium out of the pusher bore 9 and out of the rotating core 4.

[0050] Referring to FIG. 7A, an annular surface 11 is provided at the distal end of the driver bore 13 and the vessel wall port 12. During the compression operation, the compressed fluid exerts an inward force on the annular surface 11. In other words, the annular surface 11 exerts an inward force on the vessel 3 and acts as a pressure balancing lip, whereby the pressure pulses generated by the driver piston 15 offset or reduce the pressure pulses generated by the pusher piston pushing against the liquid medium in the pusher bore 16, thus reducing (minimizing) the stresses applied to the vessel 3 by the compression driver 4. In addition, the driver piston 15 has a distal end 20 designed to cooperate with the annular surface 11 to define an annular channel when the driver piston 15 reaches the vessel wall 3, and the compressed fluid is sufficiently compressed. The high pressure of the compressed fluid in the annular channel serves to decelerate the driver piston 15 and prevent it from colliding with the annular surface 41 and the vessel wall 3.

[0051] More specifically, the driver piston 15 includes a cylindrical first section with a distal end 20 and a diameter corresponding to the diameter of the vessel wall port 12, and a cylindrical second section with a proximal end 21 and a diameter corresponding to the diameter of the driver bore 13. The two sections are connected by an annular ledge. The annular rim of the first section and the annular ledge, together with the annular surface 11, form the aforementioned annular channel. Those skilled in the art will appreciate that the driver piston 15 can have other shapes in alternative embodiments. To further reduce weight while maintaining strength and rigidity, a number of gussets 22 are formed within the outer periphery of the driver piston 15.

[0052] 8, the pusher piston 8 in this embodiment has a flat or curved outer (proximal) wall 23, an inner (distal) wall 25, and a sidewall 24. The inner wall 25 faces the liquid liner 27, and the sidewall 24 connects with the pusher bore 9. The outer wall 23 faces the annular gap 10. The pusher piston 8 can further include a number of gussets 26 formed in the sidewall 24. The gussets 26 are configured to increase the stiffness of the pusher piston 8. In one embodiment, the sidewall 24 can be a solid plate that surrounds the gussets 26 such that the gussets 26 do not come into contact with the fluid contained in the pusher bore 9. One skilled in the art will appreciate that the gussets 26 can be omitted in alternative embodiments that may use a material that can provide the desired stiffness (and lightness) instead, or by adding different reinforcement features. The pusher piston 8 may further include a number of sealing seats (not shown) positioned around the side wall 24 or on the outer wall portion 23 .

[0053] FIG. 9A graphically illustrates the position trajectories over time of the driver piston (curve 801), pusher piston (curve 802) and liner inner interface (curve 803) during an exemplary compression operation. FIG. 8B illustrates pressure pulses in the accumulator (curve 804), driver bore (curve 805), pusher bore (curve 806) and the rear (outer) surface of the liquid liner (curve 807) during this compression operation. The compression driver 5a is used to implode the liquid liner to reduce a cavity formed in the liquid liner with a radius of about 1.5 m. As can be seen in the graph, the pusher piston and liquid liner (see curves 802 and 803, respectively) accelerate only when the driver piston (curve 801) is in close proximity to the pusher piston. The peak pressure at the end of the driver bore and the beginning of the pusher bore (curve 805) and the peak pressure at the wall of the container (curve 806) occur simultaneously as the pusher piston is accelerated.

[0054] 10A is a cutaway view of a portion of the plasma compression system 1, showing the nine layers of compression drivers 5a, the vessel 3, and the rotating core 4. The vessel 3 includes a number of ports 12 within which the compression drivers 5a are mounted.

[0055] 2B, 6A-6D, 7B and 10B, according to an alternative embodiment, the plasma compression system 1 includes a compression driver 40 that uses pressurized gas instead of a driver piston to deliver pressure pulses into the annular gap 10. The compression driver 40 shown in these figures has a generally cylindrical valve housing 42 fixedly attached at one end to the exterior surface of the vessel wall 3 and includes an actuated valve 44 in fluid communication with the vessel wall opening 3 and an accumulator 46. The accumulator 46 is a pressure vessel containing a sufficiently pressurized compressed fluid. The initial and intermediate pressures of the compressible fluid in the accumulator 46 and the timing of the release of the compressible fluid through the actuated valve 44 contribute to achieving a synchronized, shaped contraction of the liquid liner. In one embodiment, the pressure of the compressed fluid can be fine-tuned prior to the compression shot by using a heating element 53 disposed within the accumulator 46 to heat the compressed fluid. In another embodiment, the pressure of the compressed fluid can be fine-tuned during the compression shot by heating the compressed fluid with an electric arc generated across two electrodes 19 positioned in the accumulator 46. The compressed fluid can be any fluid that can be compressed, and in one embodiment, can be a gas such as helium. In another embodiment, the compressed fluid can be a mixture of gas and saturated steam (dry steam).

[0056] The actuated valve 44 may be a conical seat shut-off valve similar to the type disclosed in U.S. Patent No. 8,336,849. However, one skilled in the art will recognize that other suitable valve designs may be used. The actuated valve 44 is in communication with a controller having a processor and a computer readable memory encoded therein with instructions executable by the processor to open the actuated valve 44 to release accumulator gas into the annular gap during compression operations.

[0057] A pressure relief tank 48 is provided for receiving compressed fluid from the annular gap 10 after a pressure pulse activates the implosion driver 5a. The pressure relief tank 48 is fluidly coupled to the vessel wall opening 3 by a pressure fluid return conduit 50 which includes an annular passage extending longitudinally between the vessel wall opening 3 and the accumulator pressure vessel 46 and multiple manifolds extending longitudinally along the exterior of the accumulator pressure vessel 46 to an opening at the distal end of the pressure relief tank 48. A bounce valve 52 is located at the distal end of the compressed fluid return conduit 50 near the vessel wall opening 3 and in communication with a controller programmed to cause the relief tank 48 to open the bounce valve 52 to receive compressed fluid at the end of the compression operation.

[0058] 6A-6D, the controller controls the opening and closing of the actuated valve 44 and the rebound valve 52 during the four phases of the compression shot. As shown in FIG. 6A, during the pre-shot phase, both the actuated valve 44 and the rebound valve 52 are closed and the accumulator pressure vessel 46 is filled with compressed fluid at high pressure. As shown in FIG. 6B, during the compression phase, the controller opens the actuated valve 44 and the accumulator gas is released directly into the annular gap 10 as shown by the arrows. This creates a rapid pulse of pressure in the annular gap 10 and provides the motive force to accelerate the pusher piston 8, which in turn contracts the liquid liner and compresses the plasma target. As shown in FIG. 6C, during the rebound recovery phase, the controller opens the actuated valve 44 and keeps the rebound valve 52 closed, causing the liquid liner to rebound and allowing some of the compressed fluid to flow back into the accumulator pressure vessel 46 as shown by the arrows. As shown in FIG. 6D, during the energy dissipation phase, the controller closes the drive valve 44 and opens the bounce valve 52, and the remaining compressed fluid flows from the annular gap 10, through the bounce valve 52, through the compressed fluid return conduit 50, and into the removal tank 48. This process again reduces the pressure in the annular gap 10 to a level that resets the rest of the plasma compression system for the next compression shot, and serves to recapture some of the energy returned by the liquid line bounce to the rotating core and pusher bore. Once the pressures are balanced, the controller closes the bounce valve 52 to maintain the reset status of the system and begins preparation for the next compression shot.

[0059] Alternatively (not shown), the opening and closing of the valves during the four phases of the compression shot can be provided by a mechanical system instead of a controller, including mechanical timing devices known in the art, such as spring-activated poppets.

[0060] In the illustrated embodiment, each compression driver 40 includes its own accumulator 46. However, in alternative embodiments, multiple compression drivers 50 may share a single accumulator, for example, one accumulator may be provided for each tier of compression drivers 40 (not shown), or one accumulator may be provided for all compression drivers 40 (not shown).

[0061] 1, external poloidal field coils 6 are disposed around the containment vessel 3. In the illustrated embodiment, two substantially annular coils 6 are positioned above and below the rotating core 4, respectively, substantially symmetrically about the longitudinal axis of rotation and substantially perpendicular to the longitudinal axis of rotation, i.e., the first coil and the second coil are spaced apart from and substantially parallel to the first coil, with a plasma compression region being provided between the first and second coils.

[0062] The poloidal magnetic field generator is electrically coupled to the poloidal magnetic field coil 6 and provides a current to the poloidal magnetic field coil 6 for externally generating a poloidal magnetic field. In some embodiments, the poloidal magnetic field generator can be configured to provide a substantially constant current to the poloidal magnetic field coil 6 while the liquid medium compresses the plasma. More specifically, the poloidal magnetic field generator can be configured to provide a substantially constant current over the lifetime of the plasma in the plasma compression region. In some embodiments, the poloidal magnetic field generator can be configured to provide a current having an alternating current (AC) component and a direct current component (DC), the AC component having a frequency less than 10 Hz and a magnitude less than 10% of the magnitude of the DC component of the current.

[0063] In some embodiments, the vessel wall 3 has an inner radius along a direction substantially perpendicular to the wall in the range of 3.5 m to 5.5 m. In some embodiments, the rotating core 4 has an inner radius along a direction substantially perpendicular to the vessel wall 3 in the range of 1.5 m to 3 m.

[0064] In operation, the plasma injector 2 injects a magnetized toroidal plasma into a plasma compression region for compression by the plasma compression system 1. The plasma compression region is defined at least in part by a metallic liquid liner that rotates about the plasma's axis of symmetry. A poloidal magnetic field generator energizes a plurality of poloidal magnetic field coils 6 to externally generate a poloidal magnetic field by generating a magnetic flux within the liquid liner and the plasma compression region, such that at least a portion of the magnetic flux in the plasma compression region extends along the axis of symmetry. As described above, the current from the poloidal magnetic field generator can be substantially constant, and as the liquid liner is compressed, at least a portion of the magnetic flux moves within the liquid liner toward the longitudinal axis of rotation.

[0065] The drivers 5a, 5b compress the liquid liner toward the longitudinal axis of rotation, thereby reducing the volume of the plasma compression region that confines the plasma and compressing the plasma. Compressing the liquid liner includes adjusting the trajectory of the liquid liner to dynamically adjust the magnetic flux within the plasma compression region.

[0066] To utilize a flux conserver containing a thick flowing liquid metal cavity, an encircling mechanical compression driver 5a is used to generate a pressure pulse that rapidly contracts the cavity and compresses the plasma target. Generating and applying an externally generated poloidal magnetic field to help sustain the plasma in this configuration can be difficult for at least three reasons. First, the ideal location for the external poloidal field coils 6 that generate the external poloidal field is near the equator of the reactor vessel 3, which would interfere with the compression driver 5a used to drive the liquid liner compression to contraction. Second, even if the poloidal field coils 6 could be designed to be mounted in the available space near the equator outside the reactor vessel 3, the resulting externally generated poloidal magnetic field must penetrate the vessel walls 3 and the thick liquid metal vortex to affect plasma confinement. Third, the strength of the reactor vessel 3 is achieved by ferromagnetic steel walls, and the magnetic properties of steel tend to prevent the magnetic field from penetrating the vessel walls 3. Certain embodiments described herein advantageously avoid the interference that the equatorial coils have with the compression driver 5a. In addition, instead of shielding the plasma from the externally generated magnetic field, certain embodiments advantageously utilize a ferromagnetic vessel wall 3 to help direct the externally generated magnetic flux to the plasma. Certain embodiments also advantageously utilize a contracting liquid liner to "drag" the poloidal magnetic field along with the liquid liner during compression. Certain embodiments described herein achieve plasma confinement for a period long enough to allow mechanical compression of the plasma by achieving the benefits of an externally generated poloidal magnetic field while retaining the thick flowing liquid metal and compression capabilities for the plasma compression system 1.

[0067] In one embodiment, interference with the compression driver 5a is eliminated by positioning the external poloidal field coils 6 at the top and bottom of the reaction vessel 3 rather than at the equator. Rather than eliminating the poloidal field generated by the external poloidal field coils 6, with appropriate design considerations given to the magnetohydrodynamic configuration, when a ferromagnetic vessel 3 is used, the vessel 3 itself acts as a "magnetic yoke" to distribute the magnetic field within the vessel 3 in a near-optimal configuration. The ferromagnetic steel of the vessel 3 acts as a magnetic yoke, which has the desirable property of guiding the poloidal field to spread more evenly along the liquid metal than the external poloidal field coils themselves would allow. The poloidal coil design, placement, and control not only direct the externally generated poloidal magnetic field through the ferromagnetic vessel wall 3 into the liquid metal flux conserver, but certain benefits arise from control of the poloidal magnetic field prior to the rapid movement of the liquid metal flux conserver during compression, such as the benefit of preforming a distributed uniform magnetic flux within the liquid liner that is then retained during compression, thereby reducing heat flux and magnetic flux diffusion into the metal liner as the implosion progresses.

[0068] Experimental Examples Figure 11 shows an experimental plasma system 100 that was tested to model the behavior of a magnetized plasma in a liquid metal flux conserver in an MTF reactor. The experimental system 100 included a plasma injector 2 and a flux conserver that included a poloidal field coil 6, a solid metal central conductor 7, and a plasma confinement vessel 3. The elements of the experimental system 100 were configured to model the confinement of a magnetized plasma by a plasma compression system 1 with a liquid metal liner.

[0069] For the experiments, the system 100 was connected to a current pulse power supply (not shown) to provide a forming current pulse and a toroidal magnetic field sustaining current pulse to the central conductor 7 to form a magnetized plasma in the plasma injector 2. The vessel 3 received the magnetized plasma from the plasma injector 2. The curvature of the vessel wall simulated a curved implosion liquid liner during the plasma compression operation.

[0070] In the first experiment shown in FIG. 13A, the magnetized plasma was injected into the flux conserver with a magnetic flux configuration generated only by the forming current pulses from the forming field coil 31 and the toroidal magnetic field sustaining current pulses, i.e., without energizing the poloidal field coil 6. FIGS. 12A and 12B show the expected position of the plasma 9 under these conditions (the outer surface of the plasma shown in red), where the plasma 9 is in contact with the vessel wall 3 (FIG. 12A) or the central conductor 7 (FIG. 12B). In the second experiment shown in FIG. 13B, the magnetized plasma was injected into the flux conserver with a magnetic flux configuration generated by the forming current pulses from the forming field coil 31 and the toroidal magnetic field sustaining current pulses, and modified by the externally generated poloidal magnetic field from the energized poloidal field coil 6. FIG. 12C shows the expected position of the plasma 9 under these conditions, where the plasma 9 is ideally positioned away from the vessel wall 3 and the central conductor 7. Figure 14 shows the plasma lifetime of the plasma in the flux conserver when the poloidal field coil 6 is energized (second experiment, plot line 10) and when it is not energized (first experiment, plot line 11). It can be seen that the plasma lifetime is improved by the use of the external poloidal field coil 6.

[0071] The first and second experiments were repeated multiple times, as shown in Figure 15. With the collection of data from multiple tests of the experimental system 100, it is expected that the behavior of the magnetized plasma 9 under the influence of a poloidal magnetic field can be accurately modeled for plasma compression systems with liquid metal liners, including but not limited to the rotating core plasma compression system 1.

[0072] Experiments have confirmed that, prior to compression, an externally generated poloidal magnetic field can be generated by poloidal field coils 6 positioned above and below the reactor vessel 3 through manipulation of the operation of the poloidal field coils 6, and that the externally generated poloidal magnetic field can be introduced into both the vacuum region in which the plasma is positioned and into the rotating liquid metal liner flux conserver. The external poloidal magnetic field is said to be "immersed" in the liquid metal liner in that it is present in the liquid metal and tends to remain pinned to or in the liquid metal. Pre-compression control measures can include factors such as poloidal coil current, immersion duration before initial plasma formation, and relative current and immersion duration between two or more poloidal coils. Before and during plasma compression, the plasma introduced into the cavity is buffered (held away) from the liquid metal walls by the externally generated poloidal magnetic field. This buffer prevents the magnetic field of the plasma from dipping into the liquid metal wall, which can undesirably cool the plasma and make fusion conditions more difficult to achieve.

[0073] During compression, the externally generated poloidal magnetic field is shaped by the liquid metal wall, which is forced radially inward and contracts inward, such that deliberate and dynamic shaping of the liquid metal wall allows deliberate and dynamic shaping of the externally generated poloidal magnetic field. One embodiment for achieving this shaping is described above with respect to the embodiment shown in Figures 1-10, and other embodiments are disclosed in International Application Nos. PCT / CA2021 / 051824 and PCT / CA2021 / 051825, which are incorporated herein by reference in their entirety. The buffer region formed by the externally generated poloidal magnetic field is shaped by a mechanically driven liquid metal liner to maximize plasma compression and to prevent diffusion of the plasma's magnetic field into the liquid metal liner. Reducing diffusion has the advantage of longer lifetime of the magnetized plasma, improving the conditions under which fusion reactions can occur, and reducing mechanical design stress constraints.

[0074] In some circumstances, the liquid metal compression will result in several meters of liquid metal being interposed between the plasma and the vessel wall 3. Under these circumstances, the poloidal field coils 6 were not expected to add any significant effect to the poloidal field to isolate the plasma from the vessel wall 3. Only the flux conservers were expected to achieve a barrier between the plasma and the vessel wall 3. Surprisingly, the experiments revealed that during the pre-compression stage, the externally generated poloidal field is formed and diffused into the liquid metal liner in a nearly DC state, and that this external poloidal field remains "frozen into" the liquid metal, following the liquid metal deep into the compression and adding a significant beneficial buffering effect between the plasma and the contracting liquid metal liner wall.

[0075] The "dragging" of the embedded poloidal magnetic flux by the liquid metal during compression is a consequence of magnetohydrodynamic (MHD) design and control, and occurs in situations where the compression time scale is short compared to the time required to resistively decay the non-equilibrium currents. The primary control parameter is the magnetic Reynolds number, which is typically large in machines designed to compress the plasma using liquid metal. As a result, the embedded poloidal magnetic flux is carried along with the liquid metal, preserving a buffer layer between the metal and the plasma during compression.

[0076] Experiments have also revealed that there is an optimal amount of externally generated poloidal magnetic field above which there is a diminished benefit to plasma heating and lifetime. Conductive metal flux conservers serve to stabilize the magnetically confined plasma. Rapid local changes to the plasma magnetic field configuration, similar to those resulting from the inherent magnetized plasma instability, react inductively with the liquid metal liner. These reactions provide a restoring force and local magnetic field perturbations in the plasma. This stabilizing effect is diminished because the plasma is held away from the liquid metal liner by the externally generated poloidal magnetic field. This implies that there is an optimal practical amount of externally generated poloidal magnetic field that is enough to hold the plasma away from the liquid metal liner walls and diminish heat losses, but not so much that it moves the plasma so far from the liquid metal liner walls that the plasma does not benefit from the stabilizing effect of the proximal liquid metal solid metal walls.

[0077] Experiments have revealed that the confinement of a magnetized plasma by a liquid flux conserver can be less than optimal because A) the repulsive mechanisms do not hold the plasma far enough apart to prevent excited particles from contacting the walls, so the plasma interacts significantly with the walls, and B) the magnetic field from the plasma resistively diffuses into the walls, causing the plasma to gradually "fall" into the walls over time. These problems can be pronounced even in the "static" incompressible regime, where the flux conserver walls are fixed, and can be even more pronounced under dynamic liquid liner compression, where the flux conserver itself moves inward toward the plasma.

[0078] Optimal poloidal field coil (PFC) control parameters were determined using a validated simulation model to predict plasma heating and lifetime during compression in the plasma compression system 1. Figure 16 shows that the use of poloidal field coils 6 resulted in a linear improvement in the final plasma temperature during compression up to the studied limit of 30% flux fraction. However, further findings demonstrate that above 40% flux fraction, the final plasma temperature decreases. Thus, in experiments using the validated modeling with the plasma injector 2, an optimal poloidal field fraction was found that produced the highest plasma temperature. Figure 17A shows that simply increasing the poloidal field fraction does not produce optimal plasma temperature gains above about 40% flux fraction, and careful control over the ratio of PFC flux to plasma flux produces optimal plasma temperature gains during plasma compression at 30%-40% PFC flux fractions. Control over the PFC flux fraction is achieved by control over the PFC coil current, voltage, soak duration, and relative flux strength among the two or more external poloidal field coils 6. Another control parameter is the relative strength of the PFC flux rate, defined as (PFC flux) / (plasma flux). Figure 17B is a table of modeled results showing the effect on plasma temperature gain achieved during compression where the PFC flux rate is controlled at 30%-40% PFC flux rate.

[0079] Finally, use of the demonstrated magnetic flux modeling for the plasma compression system 1 shows that the poloidal magnetic flux remains embedded in the liquid metal liner as it moves inward toward the plasma and central conductor 7. An important aspect of using the poloidal field coils 6 in the presence of a mechanically compressed liquid liner is that the externally generated poloidal magnetic field, generated by the poloidal field coils 6 in the vacuum (not the liner), is compressed by the liquid liner during liner implosion. This is important because the increasing poloidal magnetic flux density, originally from the poloidal field coils 6, in turn tracks the compressing poloidal magnetic flux density from the target plasma. The resulting magnetic field balance is necessary to prevent the increasing target plasma magnetic flux density from diffusing into the liquid liner. Figure 18A shows the time sequence of the liner implosion and magnetic flux lines modeled for a cylindrical implosion. Note that the magnetic field lines in the vacuum cavity and liquid liner remain organized throughout the compression. The immersed flux density (in the liner) also tends to decrease during compression as the walls thicken during implosion. However, this shaped contraction profile is not valid for effective MTF plasma compression, which requires a spherical compression geometry, as known in the art. FIG. 18B shows a time series of shaped liner implosion and magnetic flux lines modeled for a spherically shaped implosion. Note that the magnetic field lines remain embedded throughout compression, and the immersed flux density also tends to decrease during compression as the walls thicken through implosion. However, in the case of spherically shaped liner compression, the magnetic field lines follow the nonlinear (e.g., spherical) liner shape throughout their inward trajectories. It is therefore expected that the poloidal magnetic field when pre-immersed into the vacuum cavity can be controlled in shape and compression by dynamically controlling the shape that occurs in the liquid liner during MTF mechanical compression.

[0080] Although specific elements, embodiments, and applications of the present disclosure have been shown and described, it should be understood that the scope of the disclosure is not limited thereto, since modifications can be made without departing from the scope of the present disclosure, particularly in light of the teachings set forth above. Thus, for example, in any method or process disclosed herein, the acts or operations making up the method / process 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 subcombinations are intended to be within the scope of the present disclosure. References throughout this disclosure to "some embodiments," "embodiments," and the like mean that a particular feature, structure, step, process, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, appearances of phrases such as "in some embodiments," "in embodiments," and the like throughout this disclosure are not necessarily all referring to the same embodiment, but 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, various omissions, additions, substitutions, equivalents, rearrangements, and changes in the form of the embodiments described herein may be made without departing from the spirit of the invention as described herein.

[0081] Various aspects and advantages of the embodiments have been described where necessary. 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 should 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.

[0082] In particular, conditional language used herein, such as "can," "could," "might," "may," "eg," and the like, is generally intended to convey that certain features, elements, and / or steps are included in one embodiment and not in another embodiment, unless specifically indicated otherwise or understood otherwise within the context as used. Thus, such conditional language is generally not intended to imply that features, elements, and / or steps are necessarily required for one or more embodiments, or that one or more embodiments necessarily include logic for determining, with or without operator input or prompting, whether those features, elements, and / or steps are included in or performed in any particular embodiment. A feature or group of features is not required or essential for any particular embodiment. Terms such as "comprising," "including," "having," and the like, are synonymous and used inclusively and in an open-ended manner and do not exclude additional elements, features, acts, operations, etc. Also, the term "or" is used in an inclusive sense (and not an exclusive sense), e.g., when used to connect a list of elements, the term "or" means one, some, or all of the elements in that list.

[0083] Conjunctive language such as "at least one of X, Y, and Z," unless specifically indicated otherwise, is understood in its context as it is generally used to convey that an item, term, etc. can be either X, Y, or Z. Thus, such conjunctive language is not generally intended to imply that an embodiment requires that at least one of X, at least one of Y, and at least one of Z, respectively, be present.

[0084] The exemplary calculations, simulations, results, graphs, values, and parameters of the embodiments described herein are intended to be illustrative and are not intended to limit the disclosed embodiments. Other embodiments may be configured and / or operated differently than the exemplary 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 invention disclosed herein.

Claims

1. 1. A plasma compression system comprising: a vessel configured to receive and confine the plasma and a metal liquid medium circulating about a longitudinal axis of rotation to at least partially define a plasma compression region configured to receive and confine the plasma; means for controllably reducing a volume of the plasma compression region by moving the liquid medium inwardly toward the longitudinal axis of rotation, the liquid medium compressing the plasma; and a plurality of conductive coils outside the plasma compression region configured to generate a poloidal magnetic field in the vessel, the liquid medium, and the plasma compression region, wherein at least a portion of the poloidal magnetic field in the plasma compression region extends along the longitudinal axis of rotation, and at least a portion of the poloidal magnetic field in the liquid medium moves inwardly with the liquid medium toward the longitudinal axis of rotation as the liquid medium moves toward the longitudinal axis of rotation; A plasma compression system comprising:

2. The plasma compression system of claim 1 , wherein the vessel comprises a ferromagnetic or ferrimagnetic material.

3. 3. The plasma compression system of claim 2, wherein the plurality of conductive coils are positioned relative to a vessel wall such that the vessel wall concentrates the poloidal magnetic field in the plasma compression region.

4. 4. The plasma compression system of claim 1, wherein the plurality of conductive coils includes at least two substantially annular coils positioned substantially symmetrically around and substantially perpendicular to the longitudinal axis of rotation, the at least two substantially annular coils being at different corresponding positions along the longitudinal axis of rotation.

5. 5. The plasma compression system of claim 1, wherein the plurality of conductive coils includes at least a first coil and a second coil spaced from and substantially parallel to the first coil, and the plasma compression region is between the first and second coils.

6. The plasma compression system of any one of claims 1 to 5, wherein the vessel includes a wall portion having an inner radius in the range of 3.5m to 5.5m along a direction substantially perpendicular to the wall portion.

7. 7. The plasma compression system of claim 6, further comprising a metallic rotatable core within the vessel, the rotatable core configured to rotate about the longitudinal axis of rotation, at least a portion of the rotatable core having an inner radius in the range of 1.5 m to 3 m along a direction substantially perpendicular to the wall portion.

8. 8. The plasma compression system of claim 1, further comprising a first power supply configured to apply a substantially constant current to the plurality of conductive coils while the liquid medium compresses the plasma.

9. 9. The plasma compression system of claim 8, wherein the first power supply is configured to pass a current having an AC component and a DC component, the AC component having a frequency less than 10 Hz and a magnitude less than 10% of the magnitude of the DC component.

10. 10. The plasma compression system of claim 8, wherein the power supply is configured to provide a substantially constant current over the lifetime of the plasma in the plasma compression region.

11. 11. The plasma compression system of claim 1, wherein the second power source is coupled to a plurality of forming field coils and configured to generate a forming magnetic field at a centerline (equatorial plane) of a vessel cavity in the plasma compression region in a range of 100 mWb to 700 mWb.

12. 1. A plasma compression system comprising: a metal vessel configured to receive and contain the plasma; a metal liquid liner in the vessel at least partially defining a plasma compression region having a longitudinal axis; means for moving the liquid liner inwardly toward the longitudinal axis to compress the plasma in the plasma compression region; a plurality of conductive coils outside the plasma compression region configured to generate a poloidal magnetic field in the liquid liner and the plasma compression region, wherein at least a portion of the poloidal magnetic field in the plasma compression region extends along the longitudinal axis and at least a portion of the poloidal magnetic field in the liquid liner moves inwardly with the liquid liner toward the longitudinal axis as the liquid liner moves toward the longitudinal axis; A plasma compression system comprising:

13. The plasma compression system of claim 12 , wherein the vessel is ferromagnetic or ferrimagnetic.

14. 14. The plasma compression system of claim 12 or 13, wherein the plurality of conductive coils are positioned relative to a vessel wall such that the vessel wall at least partially concentrates the poloidal magnetic field in the plasma compression region.

15. 15. The plasma compression system of claim 12, wherein the plasma is substantially toroidal and substantially symmetric about the longitudinal axis, and at least a portion of the poloidal magnetic field in the plasma compression region extends along a poloidal direction relative to the substantially toroidal plasma.

16. 16. The plasma compression system of claim 12, further comprising a first power supply coupled to the conductive coil and configured to generate the poloidal magnetic field in the plasma compression region with sufficient strength to prevent the plasma from acting on the liquid liner.

17. 17. The plasma compression system of claim 12, wherein the plurality of conductive coils includes at least two substantially annular coils positioned substantially symmetrically around and substantially perpendicular to the longitudinal axis, the at least two substantially annular coils being at different corresponding positions along the longitudinal axis.

18. 18. The plasma condensation system of claim 12, further comprising a rotating core and a liquid medium in the vessel, the rotating core configured to rotate and circulate the liquid medium to form the liquid liner and the plasma condensation region.

19. 20. The plasma compression system of claim 18, wherein the rotatable core has an outer surface spaced from an inner surface of the vessel by a gap, and the means for moving the liquid liner includes a plurality of implosion drivers extending through the rotatable core from the gap to the plasma compression region and confining at least a portion of the liquid medium.

20. 20. The plasma compression system of claim 19, further comprising a pressurized fluid source in fluid communication with the plurality of implosion drivers, the pressurized fluid source configured to controllably apply pressurized gas to the plurality of implosion drivers such that the implosion drivers apply a pressure pulse to the liquid medium causing the liquid liner to force inwardly, shrinking the plasma compression region and compressing the plasma in the plasma compression region.

21. The means for moving the liquid liner includes: a plurality of compression drivers fixedly attached to an exterior surface of the vessel and in fluid communication with the plurality of implosion drivers; a compressed fluid in the gap in fluid communication with the compression driver and the implosion driver; a pressurized fluid source in fluid communication with the plurality of compression drivers, the pressurized fluid source configured to controllably apply pressurized gas to the plurality of compression drivers such that the compression drivers apply a first pressure pulse to the plurality of implosion drivers via the compressed fluid, whereby the implosion drivers apply a second pressure pulse to the liquid medium, causing the liquid liner to be forced inwardly, shrinking the plasma compression region and compressing the plasma within the plasma compression region; The plasma compression system of claim 1 further comprising:

22. 22. The plasma compression system of claim 12, further comprising a plasma injector in fluid communication with the vessel and configured to inject the plasma into the plasma compression region.

23. injecting a magnetized toroidal plasma into a plasma compression region, the plasma compression region being defined at least in part by a metallic liquid liner having a longitudinal axis; generating a poloidal magnetic field within the liquid liner and the plasma compression region, at least a portion of the poloidal magnetic field in the plasma compression region extending along the longitudinal axis; moving the liquid liner toward the longitudinal axis, thereby reducing a volume of the plasma compression region containing the plasma and compressing the plasma, and at least a portion of the poloidal magnetic field in the liquid liner moving inwardly toward the longitudinal axis with the liquid liner as the liquid liner moves toward the longitudinal axis; A method comprising:

24. 24. The method of claim 23, wherein generating the poloidal magnetic field comprises passing current through a plurality of coils external to the plasma compression region.

25. 25. The method of claim 24, wherein the current is substantially constant during the compression.

26. 26. The method of any one of claims 23 to 25, wherein compressing the liquid liner comprises adjusting an orbit of the liquid liner to dynamically adjust the poloidal magnetic field in the plasma compression region.

27. 27. The method of any one of claims 23 to 26, further comprising rotating a metal liquid medium to form the metal liquid liner, the liquid liner rotating about an axis of rotation symmetrical to the longitudinal axis.

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