Direct energy converters for axisymmetric mirror fusion reactors.

Abstract

A direct converter for an axisymmetric mirror confinement system comprises a set of radially symmetric vanes that are charged to trap ions escaping along the axis of the confinement system and convert their energy into electrical power. An electron trap located in front of the charged vanes uses a magnetic field to guide and collect the electrons and separate them from the ions. The electron trap is capable of supporting a radial electric field that controls the plasma. The charged vanes may be made of or have a coating of a getter material that absorbs neutrals from the trapped ions.

Description

[Technical field]

[0001] STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT This invention was made with government support under DE-AR0001258 awarded by DOE / ARPA-E. The U.S. Government has certain rights in this invention. CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Non-provisional Patent Application No. 17 / 654,920, filed March 15, 2022, which is incorporated herein by reference.

[0003] The present invention relates to devices for generating high energy plasma capable of promoting nuclear fusion, and in particular to a direct energy converter for generating electrical energy from high energy ions produced in a mirror fusion reactor. [Background technology]

[0004] A magnetic mirror containment system can confine the hot plasma away from the physical vessel, thereby preventing vessel damage and possible plasma quenching. Such a containment system can provide an axial magnetic field extending between two ends where the magnetic flux lines converge. Plasma ions moving within this axial magnetic field spiral along the magnetic flux lines at the local cyclotron frequency and are "reflected" by the axial component of the magnetic force acting on the spiraling ions. This reflecting magnetic force is caused by the convergence of the magnetic flux lines and the associated increase in magnetic field strength, and is directed away from the convergence. Furthermore, the reflecting force is proportional to the component of particle kinetic energy perpendicular to the magnetic field. A similar reflecting force acts on the plasma electrons.

[0005] Nuclear fusion can be promoted by generating a plasma at sufficiently high energy and density in a magnetic mirror confinement system. One way to reach this high energy / density state is to inject electrically neutral particles (neutral beams) into the plasma through a magnetic confinement field. The neutral particles of the neutral beam are then ionized (i.e., split into plasma ions and electrons). Because the neutral beam has an initial energy higher than that required for nuclear fusion, the resulting plasma ions retain an energy suitable for nuclear fusion, even with the expected collisional loss of energy of the plasma ions after injection into the plasma. High energy ions are better confined than low energy ions because the density and energy of the plasma are determined by the loss rate of fast ions injected by the neutral beam, which decreases as the beam energy increases.

[0006] Providing a neutral beam that can generate a sufficient flux of energetic particles with sufficient energy to sustain high fusion power in a magnetic mirror confinement system is difficult and costly from an energy standpoint. One way to offset this energy usage is to directly convert the escaping ions into electricity, which can be used, for example, to accelerate the particles of the neutral beam or to power other energy needs of the system. Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made to solve the problems in the conventional techniques described above. [Means for solving the problem]

[0008] The present invention provides a direct energy conversion system suitable for axisymmetric mirror fusion systems that employs a radially symmetric structure that matches the expanding cone of escaping protons and their rebound trajectories. The radial structure also supports the generation of a radial electric bias for spin control of the plasma. The direct energy conversion system may also use novel magnetic electron separator and plate getter materials, which are also advantages over other types of fusion systems.

[0009] In one embodiment, the present invention provides an apparatus for generating a high energy plasma, comprising: a magnetic mirror confinement field extending axially and substantially radially symmetrical about the axis to provide magnetic flux lines converging at first and second opposing ends of a confinement volume for holding the plasma; a fuel beam delivery system for injecting fusion fuel into the confinement field; a direct energy converter disposed along the axis outside the magnetic mirror confinement field, comprising a plurality of arrays of radially spaced charged plates separated by gaps and substantially aligned with the trajectories of ions escaping the magnetic mirror confinement field, for generating electrical power from the ions.

[0010] Thus, a feature of at least one embodiment of the present invention is to achieve highly efficient direct energy conversion by aligning plates with diverging ion trajectories to reduce the impact characteristics of energetic ions that should not be intercepted by a given set of plates.

[0011] The charged plates may be frustums of nested cones centered on an axis, with the apex of the cone pointing towards the containment volume.

[0012] Thus, one feature of at least one embodiment of the present invention is the provision of a plate array that provides high capture efficiency for conical orbits in axisymmetric fusion systems.

[0013] The set of charged plates may have an outer surface of a getter material (such as tantalum) for absorbing neutrals derived from the trapped ions.

[0014] Thus, one feature of at least one embodiment of the present invention is to increase the efficiency of direct energy conversion by reducing exchange losses when ions strike neutrals as well as the possibility of arcing promoted by the presence of excess neutrals near the plates.

[0015] The plate may include cooling channels in thermal communication with the plate for cooling the plate.

[0016] Thus, a feature of at least one embodiment of the present invention is to support larger currents and, in some cases, provide a mechanism for plate temperature control (e.g., to expel trapped neutrals by allowing the plate to heat up).

[0017] In some embodiments, the direct energy converter may include an electron separator consisting of a set of radially spaced magnetic elements between the charged plate and the containment volume, the magnetic elements having a spacing and axial length adapted to magnetically deflect electrons into the magnetic elements.

[0018] It is therefore a feature of at least one embodiment of the present invention to provide an improved electron separator that takes advantage of the substantial mass difference between ions and electrons, and therefore their Larmor radii, to preferentially enable capture of electrons.

[0019] The spaced magnetic elements may be ferromagnetic and may be magnetized by the axially extending magnetic flux lines of the magnetic mirror confinement field.

[0020] Thus, one feature of at least one embodiment of the present invention is to provide a simple structure that may be made from common materials such as iron and may take advantage of existing magnetic environments.

[0021] The magnetic element may be electrically biased with respect to the charged plate to allow a current to flow between the charged plate and the magnetic element.

[0022] The magnetic elements may be electrically biased relative to one another by a controller, which varies the electrical bias to generate a radially oriented electric field adapted to control the plasma.

[0023] Accordingly, a feature of at least one embodiment of the present invention is to provide an electron separator that operates without the need for an electrical bias for electron capture, and thus is well suited for secondary use for plasma stability control.

[0024] These specific objects and advantages do not define the scope of the invention, since they may apply only to some embodiments that fall within the scope of the claims. [Brief description of the drawings]

[0025] [Figure 1] FIG. 1 is a cutaway perspective view of a first embodiment of the present invention comprising a magnetic mirror confinement field, a neutral beam generator that directs the beam into the confinement volume, and a radio frequency generator that generates an electric field that acts on plasma ions from the neutron beam generator. [Diagram 2] FIG. 2 is a side elevation view of the magnetic flux lines of the containment volume of FIG. 1 , along with an end view of those magnetic flux lines, both of which show the trajectories of plasma ions of different energies, along with graphs of cyclotron frequency, dwell time, and electric field strength as a function of axial distance. [Diagram 3] FIG. 2 is a simplified cross-sectional elevation view of a nuclear fusion device employing the magnetic mirror confinement field of FIG. 1 as a plug to prevent energetic plasma ions from escaping from a central solenoid magnetic field cell and including a direct energy converter according to the present invention. [Figure 4]4 is a fragmentary and simplified side elevation cross-sectional view of the electron separator plate and ion collector plate of the direct energy converter of FIG. 3, along with an illustration showing the orientation of the cross-section; [Diagram 5] FIG. 5 is an enlarged view of region 5 of FIG. 4 showing the interaction of electrons with the electron separation plate. [Figure 6] FIG. 5 is an enlarged view of region 6 of FIG. 4 showing the interaction of ions with the ion collecting plate. [Figure 7] FIG. 7 is a cutaway perspective view of the electron separation plate and ion collector plate of FIGS. 4, 5, and 6. [Figure 8] FIG. 5 is a schematic diagram of a bias system for the electron separation plate and ion collector plate of FIG. 4. [Figure 9] FIG. 2 is a fragmentary cross-sectional view of an ion collector plate showing internal cooling channels and outer getter material. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] I. Axisymmetric mirror fusion system Referring now to FIG. 1, a high energy plasma system 10 may include a pressure vessel 12 (e.g., in the form of a sealed cylindrical shell such as stainless steel) extending along an axis 14 for receiving a reactant gas (e.g., deuterium or tritium) via a valve inlet assembly 13 from a pressure tank or the like (not shown).

[0027] First and second electromagnetic coils 16a and 16b may be disposed within pressure vessel 12 near opposite ends thereof to define a containment volume 17 therebetween having a magnetic containment field 15. The electromagnetic coils 16 are oriented and spaced apart to form an aligned Helmholtz pair along axis 14 to establish an axial B0 field therebetween. In one embodiment, the electromagnetic coils 16 may be a pancake coil with a helix centered about axis 14 that is powered by a controllable external DC power source 18 of a type known in the art.

[0028] A radio frequency antenna 19 (shown in simplified form) is positioned between the electromagnetic coils 16, proximate to one of the electromagnetic coils 16b, which, when driven by, for example, a radio frequency generator 20, generates a circularly polarized radio wave field that extends along axis 14. As understood in the art, this polarized radio wave field generates an electric vector 21 that rotates about and is perpendicular to axis 14. For details of loop antennas suitable for this purpose, see TH Stix, "Fast Wave Heating of a Two-Component Plasma," Nuclear Fusion 15, 737 (1975), and RW Harvey, MG McCoy, GD Kerbel, and SC Chiu, "ICRF Fusion Reactivity Enhancements in Tokamaks," Nuclear Fusion 26, 43 (1986), which are incorporated herein by reference.

[0029] Radially outwardly of the pressure vessel 12 may be disposed a treatment volume 22, e.g. in the form of a concentric outer cylindrical tank, which may be filled with an aqueous substance for transmutation by high-energy neutrons, such a substance being, e.g., a precursor of a medical isotope. 99 Mo (Molybdenum 99), 131 I (Iodine-131), 133 Xe (Xenon 133), and 177 Lu (lutetium 177), or the treatment volume 22 may support racks holding spent nuclear fuel rods that have been reactivated by transmutation with high-energy neutrons.

[0030] A neutral beam generator 26 that injects a beam 28 of neutral particles 29 (non-ionized particles with zero net charge) is positioned at a pitch angle θ into the containment volume 17. The pitch angle θ is defined as the acute angle between the beam 28 and the axis 14. The neutral particles 29 are, for example, deuterium or tritium atoms that are introduced through a gas line 24 and ionized by a local plasma (not shown). These ions are accelerated in an accelerator chamber 27 that has a series of consecutive charged plates, as is commonly understood in the art. These ions then pass through a neutralizing gas cell 31 to generate neutral particles 29 by a charge exchange process, generating the neutral particles 29 of the beam 28.

[0031] 2, the magnetic flux lines of the magnetic field 30 (B) generated by the coils 16 assume a "bottle" shape, expanding radially from the axis 14 at the midpoint between the coils 16 and contracting radially at the location of the coils 16. As is commonly understood in the art, this configuration creates a mirror confinement volume in which randomly distributed "hot" plasma ions 33 of sufficient pitch angle will spiral about the magnetic flux lines of the magnetic field 30 between the regions defined by turning points 34.

[0032] As is understood in the art, these thermal plasma ions can be anchored in a variety of ways, such as by using a radio frequency antenna 19 (although less efficiently) or by using a separate heating system that uses high frequency microwaves to generate electron cyclotron resonance heating.

[0033] The thermal plasma ions 32 reverse direction in the region of turning points 34, which is caused by the increasing axial component of the magnetic Lorentz force generated by the convergence of the flux lines of the magnetic field 30. The frequency 35 of the spiral motion about the magnetic flux lines 30 is called the "cyclotron frequency" and is a function of the strength of the magnetic field 37 along the axis 14, which is why the cyclotron frequency 35 generally increases toward the electromagnetic coil 16. If each ion has equal mass and charge, the cyclotron frequency will nominally be the same anywhere along the axis 14, regardless of the ion's velocity or energy. In contrast, ions 32 of equal mass but different pitch angles will typically have different turning points 34.

[0034] The velocity, and therefore energy, of the neutral particles 29 of the Neutral Beam 28, as well as the pitch angle of the Neutral Beam 28 are set so that a majority (e.g., greater than 50%) of the particles of the Neutral Beam 28 are ionized into plasma ions 36 within the confinement volume 17 by the time they exit the confinement field. These plasma ions 36, at the same pitch angle, are now electrically charged and are captured by the magnetic flux lines 30, increasing the plasma density.

[0035] To facilitate this capture of most of the neutral particles 29 in the neutral beam 28, the energy of the neutral beam 28 is limited to provide sufficient flight time for the neutral particles 29 to be ionized. In general, the desired energy for ionization of the neutral beam 28 will be well below the kinetic energy required for substantial fusion, typically less than 100,000 eV, or preferably less than 50,000 eV, more typically on the order of 15-25 keV. This is in contrast to prior art approaches, which require neutral particles 29 with energies in excess of the energy required to facilitate fusion between the plasma ions 36, typically greater than 1 million eV for DD fusion. Limiting the energy of the neutral beam 28 may affect the tradeoff between a higher flux density of the neutral particles 29 and simultaneously increased plasma density in a common neutron beam generator 26.

[0036] 1 and 2, the pitch angle θ of the neutral beam 28 is selected so that a predetermined turning point 34′ for the resulting plasma ions 36 is obtained along the axis 14, and thus a corresponding predetermined cyclotron frequency 35 of the plasma ions 36 is obtained at the turning point 34′. This cyclotron frequency is used to set the frequency of the radio frequency generator 20, as described below.

[0037] Additionally, antenna 19 is positioned adjacent one of turning points 34' to obtain maximum field strength in that area.

[0038] Finally, the energy of the Neutral Beam 28 is set as high as possible within the range of Neutral Beam 28 energy levels that achieves the desired trapping of neutral particles 29 within the containment volume 17. This is so that the radius of the orbits (gyro-orbits 52) of the plasma ions 36 created by the Neutral Beam 28 is larger than the average dispersion gyro-orbits 52 of the "thermal ions" 32 (which are ions that do not come directly from the Neutral Beam 28).

[0039] Although the inventors do not wish to be bound by any particular theory, it is believed that the above-mentioned (a) setting the cyclotron frequency of the radio frequency generator 20 to a harmonic of the cyclotron frequency of the plasma ions 36 at the turning point 34', (b) boosting the energy of the plasma ions 36 above the average distribution of the thermal plasma ions 32, and (c) maximizing the electric field strength at the turning point 34' all work together to enable the radio frequency generator 20 to preferentially boost the energy of the plasma ions 36 from the neutral beam 28 regardless of the damping effects of the thermal plasma ions 32.

[0040] In this regard, by setting the radio frequency generator 20 (according to (a)), preferential coupling with plasma ions 36 having a matching (e.g., harmonically related) cyclotron frequency 35 is obtained. This is in contrast to the thermal plasma ions 32, which have a range of different, Doppler-shifted cyclotron frequencies and are less effective at coupling. This coupling is expressed by the Bessel function B n-1 (k ⊥ *ν ⊥ / ω ci ) can be proportional to the square of n is the resonant cyclotron harmonic number of the incident wave, k ⊥ is the vertical wave number, ω ci is the cyclotron frequency of the resonating ion.

[0041] quantity k ⊥ / ω ci is the ion's ~v A (Alfvén velocity) (see TH Stix, "Fast Wave Heating of a Two-Component Plasma", Nuclear Fusion 15, 737 (1975)). If the Bessel function is v ⊥ Dependent on , the coupling is proportional to the power of the ion's vertical velocity and may be adjusted to preferentially attenuate the hot tail ions from the neutral beam as well as those hot tail ions that have been scattered to higher energies by the radio frequency wave.

[0042] Additionally, by setting the frequency of the radio frequency generator 20 according to the cyclotron frequency 35 at the turning point 34', the effect of the electric field from the radio frequency generator 20 on the plasma ions 36 is increased because the dwell time 50 of the plasma ions 36 is lengthened during which the axial velocity of the plasma ions 36 is at a minimum as they turn at the turning point 34'. This is in contrast to, for example, the thermal plasma ions 32 which move quickly through this zone to another turning point 34 or never to the turning point 34'.

[0043] As described above, by boosting the energy of the plasma ions 36 above the dispersion of the thermal plasma ions 32 (according to (b)), and by setting the radio frequency generator 20 to an RF frequency that is a harmonic of the cyclotron frequency 35 of the plasma ions 36, the more energetic plasma ions 36, which have a larger radius of the gyroscopic orbit 52, will preferentially absorb power over the thermal plasma ions 32, which have a smaller gyroscopic orbit 52. In some embodiments, the RF frequency may be set in the range of 20-100 MHz and / or may be set to a harmonic order n greater than n=2, preferably n=4.

[0044] In general, higher harmonics boost the relationship between energy absorption and gyro trajectory 52 according to the higher order Bessel functions associated with those harmonics. Specifically, energy absorption is J n-1 (k ⊥ ρ) where J n-1 is the Bessel coefficient corresponding to a given harmonic order n. ρ is the radius of the particle's gyroscopic orbit 52 around the magnetic flux line 30, which is

number

[0045] Of course, this effective preferential absorption of energy by the plasma ions 36 is self-reinforcing as energy is absorbed and the gyroscopic orbit of the plasma ions 36 increases.

[0046] Finally, by locating the maximum field strength of antenna 19 near turning point 34', plasma ions 36 are preferentially affected.

[0047] In general, the magnetic confinement field 15 tends to lose some plasma ions 32 that have a small pitch angle through its edges. These particles are said to be in the "loss cone." By boosting the population of plasma ions 36 that are outside the loss cone and have a known pitch angle θ, it is possible to increase the plasma density.

[0048] The cyclotron frequency of the plasma ions 36 near the turning point 34', and therefore the desired setting of the frequency of the radio frequency generator 20, is primarily a function of the vacuum field strength of the magnetic field 37, but shifts somewhat as a function of increasing plasma density / pressure. Thus, the present invention contemplates that one or both of the DC power supply 18 and / or the radio frequency generator 20 may be adjusted during operation to maintain the above relationship that boosts energy transfer to the plasma ions 36. Specifically, this adjustment may be made by closed loop feedback control (e.g., using a diamagnetic loop) using a sensor 56 that detects the plasma pressure, which measures the decrease in the magnetic field due to the increase in plasma pressure, and matches the excitation frequency of the radio frequency generator 20 with the actual and dynamic cyclotron frequency 35 at the turning point 34'. The present invention also contemplates that in the range where the cyclotron frequency is determined by the total field (vacuum field from the coil and plasma diamagnetism), no frequency change may be required, but the location of the turning point approaches the electromagnetic mirror coil.

[0049] Referring now to FIG. 3, this advantage of the present invention in providing high plasma density is useful as part of a tandem mirror neutron generator 60 in which two high energy plasma systems 10 can act as a "plug" to capture high energy plasma ions in a larger tandem mirror neutron generator 60 for the purposes of elemental transmutation (as discussed above) or fusion power generation. Such designs may, for example, utilize a tandem mirror approach, as described, for example, in G. Dimov, V. Zakaidakov, and M. Kishinevski, Fiz. Plazmy 2, 597 (1976), [Sov. J. Plasma], Phys 2, 326 (1976), and TK Fowler and BG Logan, Comments on Plasma Physics and Controlled Fusion 2, 167 (1977), which are incorporated herein by reference.

[0050] More specifically, in such a tandem mirror neutron generator 60, first and second high energy plasma systems 10a and 10b are arranged on opposite sides of a generator volume 62 along an axis 14. Typically, the high energy plasma system 10 will have an axial length on the order of 2 meters, whereas the generation volume 62 will be much larger, e.g., on the order of 50 meters or more.

[0051] The electromagnetic coils 16 of both high energy plasma systems 10a and 10b are axially aligned to generate the same directional deflection of the magnetic field along the common axis 14. Thus, the magnetic flux lines 30 of the first high energy plasma system 10a can pass through the volume 62 towards the second high energy plasma system 10b. Within the volume 62, the magnetic flux lines 30 are focused by a solenoid coil 66 that extends axially around the volume 62 in a circle around the axis 14.

[0052] To this end, the electromagnetic coil 16 may be a superconducting magnet, such as that described in D. Whyte, J. Minervini, B. LaBombard, E. Marmar, L. Bromberg, and M. Greenwald, “Smaller and sooner: Exploiting high magnetic fields from new superconductors for a more attractive fusion energy development path,” Journal of Fusion Energy 35, 41 (2016), also incorporated herein by reference.

[0053] A subset of the thermal plasma ions 32, having uniformly distributed pitch angles, are boosted to high energies by kinetic transfer from the plasma ions 36 and are capable of escaping from the high energy plasma system 10 into a volume 62 containing a reactive gas (e.g., deuterium or tritium) to promote nuclear fusion and emission of neutrons 64 from the volume 62. The high pressure of the high energy plasma system 10 prevents the high energy plasma ions from escaping the volume 62, thereby maintaining a high density for effective nuclear fusion.

[0054] Volume 62 may be surrounded by a treatment volume 22, which may contain a heat exchanger liquid 68 that receives, for example, a working fluid 70 of a thermodynamic engine (e.g., a turbine, etc.) (e.g., for generating electricity) through one or more heat exchangers. Alternatively, treatment volume 22 may be used for transmutation of materials, as described above, for the production of medical isotopes, or for the reactivation of spent nuclear fuel.

[0055] A system including the above-mentioned axisymmetric mirror fusion device is disclosed in U.S. Patent No. 10,966,310, entitled "High-energy plasma generator using radio-frequency and neutral beam power," which is assigned to the assignee of the present invention and is incorporated herein by reference. This application also incorporates the disclosures of U.S. Patent Application No. 2019 / 0326029, entitled "Apparatus and Method for Generating Medical Isotopes," and U.S. Patent Application No. 2013 / 0142296, entitled "Apparatus and method for generating medical isotopes," which describe further techniques for managing isotope transmutation, including the use of neutron multiplier generators and other structural details and mechanisms to generate the above-mentioned neutral beams.

[0056] II. Direct Energy Converters 3, direct energy converters 76a and 76b may be disposed along axis 14 outside the generator volume 62 of the first and second high energy plasma systems 10a and 10b, respectively. These direct energy converters 76 are subjected to continuous magnetic flux lines 30 passing through a volume holding a set of axially spaced plate arrays 78 perpendicular to the axial direction. As a non-limiting example, a tandem mirror neutron generator 60 providing a magnetic field of 25 T in the volume 62 may provide a magnetic field of approximately 0.1 T at the leading portion of the plate arrays 78, the reduced magnetic field strength being due to the expanding range and separation of the magnetic flux lines 30.

[0057] The plate array 78 is in communication with a power management circuit 80 controlled by a controller 82 (e.g., a computer), the operation of which is described below. The power management circuit 80 provides an electrical bias to the plate array 78 and extracts power from the plate array 78 for operation of energy consuming components of the general purpose or tandem mirror neutron generator 60, such as the accelerator chamber 27 or other energy consuming devices 83 (including the radio frequency generator 20 or microwave energy input device for maintaining fusion temperatures, as described above).

[0058] 4, the plate array 78 may include an electron separator plate array 84 closest to the generator volume 62, followed by a suppressor grid 85, followed by four ion trapping plate arrays 86a-86c. Each plate array 78 may comprise a set of nested concentric ring vanes extending in a plane generally perpendicular to the axis 14, with each ring vane 90 having radial inner and outer surfaces along the periphery of a frustum of an imaginary cone 93 symmetrical about the axis 14 with an apex pointing towards the volume 62 and a removed base. As the diameter of the ring vanes 90 in the plate array 78 increases, so does the corresponding size of the base of the imaginary cone 93, so that the gaps 91 between adjacent ring vanes 90 are generally aligned with the trajectories 94 of the ions or electrons exiting the high energy plasma system 10 volume. In general, it will be desirable for the trajectories 94 to have tangents between adjacent ring vanes 90 along the conical surfaces defining the ring vanes 90. In this manner, the electron or ion trajectory blocking profile of the ring vanes 90 is substantially minimized relative to the overall area of ​​the plate array 78.

[0059] An exception to this orientation of the ring vanes 90 are the ion-trapping plate arrays 86, which may be oriented at an angle such that ions or electrons along a trajectory 94 cannot intersect and pass between at least one of the ring vanes along their trajectory 94. This exception provides greater assurance that all ions are ultimately trapped by at least one of the ion-trapping plate arrays 86, as described below.

[0060] 5, the ring vanes 90 of the electronic isolation plate array 84 are made of iron or other ferromagnetic material, or a high magnetic permeability μ (e.g., 2.5×10 -2 More than 1×10 -2In one embodiment, the ring vanes 90 of the electron separator plate array 84 act to locally bend the magnetic flux lines 30 to encourage the inward spiraling of electron trajectories 98 onto the surface of the ring vanes 90. Thus, the electron separator plate array 84 is configured to operate in a manner that allows the electrons to move in a direction that is parallel to the magnetic field, without any interference from the magnetic field. e By selectively intercepting electrons having a diameter of 10 mm or less within the magnetic field 30, it is possible to cause a limited deflection of the trajectory 94 that is less likely to promote such collisions. Typically, the Larmor radius of an ion is larger than d1 (the axial length of the vane 90), e.g., by a factor of 2 or more. The radial separation d3 between the vanes 90 and the radial thickness d2 of the vane 90 (the latter representing the blocking profile of the vane 90 along the trajectory 94) may be such that in practice d3 / d2 is 20 or more, reducing the likelihood of direct ion collisions between the ions and the vane 90. This further causes the electron separator plate array 84 to mainly block electrons and not ions.

[0061] Referring now also to FIG. 8 , successive vanes 90 of the electronic separation plate array 84 may be biased with successively increasing voltages by the power management circuitry 80 to establish a radially outward electric field 100 (E), which is represented by a set of idealized, directly connected voltage sources 92. The magnitude of this electric field 100 may be controlled by controller 82 to stabilize the plasma in volume 62 by shear rotation, a general description of which can be found in Beklemishev, AD, Bagryansky, PA, Chaschin, MS, and Soldatkina, EI (2010) "Vortex Confinement of Plasmas in Symmetric Mirror Traps", Fusion Science and Technology, 57:4, pp. 351-360, DOI: 10.13182 / FST10-A9497, as well as Ryutov, DD, Molvik, AW, and Simonen, TC. TC, "Axisymmetric Mirror as a Driver for a Fusion-Fission Hybrid: Physics Issues," J Fusion Energy, 29, p. 548 (2010). Referring now briefly to FIG. 7, for purposes of this biasing, each vane 90 of the electron isolation plate array 84 may be supported by interconnecting insulating struts 89 that extend radially through between successive concentric vanes 90, thereby enabling the desired electric field gradient to be maintained.

[0062] 4 and 8, an electron suppressor grid 85 is positioned after the electron separator plate array 84, which is negatively voltage biased with respect to ring vanes 90 of the electron separator plate array 84. This electron suppressor grid 85 may, but need not, have vanes 90, but may be any type of grid including wires operable to establish an electric field that tends to repel electrons from moving through the electron separator plate array 84 or from the electron separator plate array 84 in an arcing to the nearest ion trapping plate array 86a. For the same purpose of reducing arcing, the edges of all conductive vanes 90 may be rounded to prevent high electric field concentrations.

[0063] 4, 6, and 8, the ion trapping plate arrays 86a-86d following the electron separator plate array 84 and the electron suppressor grid 85 are each given successively higher positive voltages relative to the baseline of the electron separator plate array 84, e.g., 88 kV, 165 kV, and 270 kV, respectively. The ion trapping plate arrays 86 rely on electric fields rather than magnetic fields to trap ions, and use their respective potentials to slow down and trap passing ions. Ions that are not slow enough to be trapped by the first ion trapping plate array 86 can pass through it and encounter the higher potential of the next ion trapping plate array 86b, where they may be trapped. Again, the vanes 90 are angled to allow fast ions (that are not slowed down enough by the potential of the ion trapping plate array 86 there) to move on without hitting the ion trapping plate array 86 at high speed and disproportionately releasing their energy as heat rather than power.

[0064] At each ion trapping plate array 86, ions slowing down enough to be trapped properly will generally pass through that ion trapping plate array 86, be bounced off the bias of the next ion trapping plate array 86, and bend back along a bounce trajectory 105 toward the ion trapping plate array 86 they passed, but because of the angle relative to the trajectory 94, the vanes 90 have a high intercept characteristic (large area perpendicular to the path of the ion's bounce trajectory 105) and a high probability of trapping. Due to the space charge caused by the ion cloud and the angle of incidence of the ion relative to the repulsion of the next ion trapping plate array 86, the ion will tend to be pushed outward in this bounce trajectory 105, thereby favorably increasing the intercept characteristic of the vanes 90. Ions not captured by any of the ion trapping plate arrays 86a-c will strike the ion trapping plate array 86d. Vanes 90 of ion trapping plate array 86d are oriented to intercept ions along trajectories 94 without bouncing, which is meant to be the final trapping point for the ions.

[0065] The power generated by the ion-trapping plate arrays 86 is equal to the current determined by the number of trapped ions in each ion-trapping plate array 86 multiplied by the positive potential of each ion-trapping plate array 86. This power may be applied across any load, or may desirably be used to power the tandem high energy plasma system 10' described above.

[0066] As ions are trapped by the successive ion-trapping plate arrays 86, they recombine with electrons in the metal surfaces of the vanes 90 to release neutral atoms (e.g., lithium fuel), which may be output by a vacuum pump 106 (shown in FIG. 3). Referring now also to FIG. 9, alternatively or additionally, the outer surface (or entirety) of the vanes 90 of each ion-trapping plate array 86 may be coated with a getter material 88 (e.g., tantalum) that can absorb and store neutral particles, thereby preventing them from interfering with the incident ions and / or causing the arcing problems discussed above. In general, the getter material 88 absorbs fuel material (e.g., deuterium) better than it absorbs aluminum or iron.

[0067] The vanes 90 may further include cooling channels 110 in which a coolant such as helium may be circulated by a pump 112 through a heat exchanger 114. The pump 112 may be periodically stopped by a recharge controller 116 (e.g., implemented by the controller 82) to allow the temperature of the vanes 90 to increase due to bombardment by ions (or heating by the heat exchanger 114), thereby expelling trapped deuterium neutrals in preparation for cleaning by the vacuum pump 106. More generally, the vacuum pump may be capable of maintaining a neutral pressure of less than 8 microtorr, as a non-limiting example. Unlike the vanes 90 of the electron separation plate array 84, the vanes of the ion trapping plate array 86 are preferably not ferromagnetic, and may be made of any conductive material with good electrical conductivity, such as aluminum.

[0068] Certain terminology is used herein for reference purposes only and is not intended to be limiting. For example, words such as "upper," "lower," "above," and "below" refer to directions in the drawings to which reference is made. Words such as "front," "back," "rear," "bottom," and "side" refer to the orientation of parts of a component within a consistent, but arbitrary, frame of reference that will become clear with reference to the text and associated drawings that describe the component under discussion.

[0069] Such terms may include the words specifically mentioned above, their derivatives, and synonyms. Similarly, the terms "first," "second," and other such numerical terms referring to structures do not imply a particular sequence or order unless clearly dictated by context. Terms such as "along an axis" or "axially extending" are intended to indicate that a major or greatest extent of a structure is generally aligned, though not necessarily parallel, to an axis, e.g., within 45 degrees of parallel.

[0070] When introducing elements or features of the present disclosure and exemplary embodiments, the articles "a," "an," "the," and "said" are intended to mean that there are one or more of such elements or features. The terms "comprising," "including," and "having" are intended to be inclusive and mean that there may be additional elements or features other than the specifically stated element or feature. It is further understood that the method steps, processes, and operations described herein should not be construed as requiring them to be performed in the particular order described or illustrated, unless specifically identified as such an order of performance. It is also understood that additional or alternative steps may be employed.

[0071] It is specifically intended that the present invention is not limited to the embodiments and examples contained herein, and that the claims be understood to include modifications of those embodiments, including portions of the embodiments, and combinations of elements of the separate embodiments, as falling within the scope of the following claims. All publications mentioned herein, including patent and non-patent publications, are hereby incorporated by reference in their entirety.

Claims

1. 1. An apparatus for generating a high energy plasma, comprising: a magnetic mirror confinement field extending axially and generally radially symmetric about said axis providing converging magnetic flux lines at first and second opposing ends of a confinement volume for holding the plasma; a fuel beam delivery system for injecting fusion fuel into the containment field; a direct energy converter disposed along the axis outside the magnetic mirror confinement field, the direct energy converter comprising a plurality of arrays of radially spaced charged plates separated from one another by gaps that are substantially aligned with the trajectories of ions escaping the magnetic mirror confinement field, the direct energy converter generating electrical power from the ions; An apparatus comprising:

2. The apparatus of claim 1 , wherein the charged plates are faces of frustums of nested cones centered on the axis, with apexes of the cones pointing towards the containment volume.

3. 10. The apparatus of claim 1, wherein the charged plate comprises an outer surface of a getter material for absorbing neutral particles derived from ions of a fuel material.

4. 4. The apparatus of claim 3, wherein the getter material is tantalum.

5. The apparatus of claim 3 , further comprising a cooling channel in thermal communication with said plate for cooling said plate.

6. The apparatus of claim 5 further comprising a coolant controller that controls the flow of the coolant to cyclically heat the plate to expel the neutrals.

7. 2. The apparatus of claim 1, wherein the array is arranged as a set of spaced apart planes along and perpendicular to the axis, and further comprising a power system applying a voltage to the charged plates that increases continuously as a function of distance from the containment volume.

8. 10. The apparatus of claim 1, wherein the fuel beam delivery system comprises an accelerator chamber, the accelerator chamber receiving power from a direct energy converter.

9. 10. The apparatus of claim 1, further comprising an electron separator comprising a set of radially spaced magnetic elements between the charged plate and the containment volume, the magnetic elements having a spacing and axial length adapted to magnetically deflect electrons into the magnetic elements.

10. 10. The apparatus of claim 9, wherein the spaced apart magnetic elements are ferromagnetic and are magnetized by the axially extending magnetic flux lines of the magnetic mirror confinement field.

11. The apparatus of claim 9 , wherein the magnetic element is electrically biased with respect to the charged plate to allow a current to flow between the charged plate and the magnetic element.

12. 10. The apparatus of claim 9, wherein the magnetic elements are further electrically biased with respect to one another by a controller, the controller varying the electrical bias to generate a radially oriented electric field adapted to control the plasma.

13. 10. The apparatus of claim 9, wherein the magnetic elements are vanes, each vane having an axial dimension at least ten times its radial thickness.

14. The apparatus of claim 1 , wherein the magnetic elements are faces of frustums of nested cones centered on the axis, with apexes of the cones pointing towards the containment volume.

15. A direct converter for a nuclear fusion device, comprising: a plurality of arrays of radially spaced charged plates spaced apart from one another along an axis of ion escape from a containment volume of a plasma fusion system and having axially extending gaps, said arrays being electrically biased to trap ions passing along said axis; an electron trap consisting of a set of spaced apart magnetic elements between the charged plate and the containment volume, the magnetic elements having a spacing and an axial length adapted to magnetically deflect electrons into the magnetic elements; A direct converter including

16. 16. The apparatus of claim 15, wherein the spaced magnetic elements are ferromagnetic and adapted to be magnetized by axially extending magnetic flux lines emerging from the containment volume along the axis.

17. 16. The apparatus of claim 15, wherein the magnetic elements are vanes, each vane having an axial length at least 10 times its radial thickness.

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