High-Energy Plasma Generator Using Radio Frequency and Neutral Beam Power

Abstract

An apparatus for generating high energy plasma uses a low energy neutral beam incident on a magnetic confinement mirror plug to generate plasma ions whose energy is boosted to fusion levels by a well-tuned radio frequency electromagnetic field.

Description

Technical Field

[0001] Statement Regarding Federally Sponsored Research or Development This invention was made with government support under DE-SC0002322 awarded by the U.S. Department of Energy. The U.S. government has certain rights in this invention.

[0002] Cross - Reference to Related Applications This application claims the benefit of U.S. Patent Application No. 16 / 839,780, filed on April 3, 2020, which is incorporated herein by reference.

[0003] The present invention relates to an apparatus for generating a high - energy plasma capable of promoting nuclear fusion, and more particularly to a system that uses magnetic mirror confinement and neutral beam injection, together with additional radio - frequency power injection.

Background Art

[0004] High - temperature plasmas can be confined away from a physical container by a magnetic mirror confinement system, thereby preventing damage to the container and possible plasma quenching. Such a confinement system can provide an axial magnetic field that extends between two ends where 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 accompanying increase in magnetic field strength, and is in the direction away from the convergence. Further, the reflecting force is proportional to the component of the particle motion energy perpendicular to the magnetic field. A similar reflecting force acts on plasma electrons.

[0005] Nuclear fusion can be promoted by generating plasma at sufficiently high energy and density in a magnetic mirror confinement system. In one way to reach this high energy / density state, electrically neutral particles (neutral beams) are passed through a magnetic confinement field and incident on the plasma. At this time, the neutral particles of the neutral beam are ionized (i.e., divided into plasma ions and electrons). Since the initial energy of the neutral beam is higher than the energy required for fusion, the resulting plasma ions retain energy suitable for fusion even with the expected collision losses of plasma ion energy after injection into the plasma. The density and energy of the plasma are determined by the loss rate of the high-speed ions incident by the neutral beam, and since the loss rate decreases as the beam energy increases, high-energy ions are confined better than low-energy ions.

[0006] It is difficult and costly from an energy perspective for a neutral beam to generate a sufficient flux of high-energy particles with enough energy to maintain a high fusion output in a magnetic mirror confinement system. At present, such a method is not practical for net fusion energy generation.

Summary of the Invention

Problems to be Solved by the Invention

[0007] The present invention has been made to solve the problems in the above prior art.

Means for Solving the Problems

[0008] The present invention also injects a neutral beam into magnetic mirror confinement, but what is different from the conventional methods is that it uses a low-energy neutral beam having an energy much smaller than the energy required to directly generate effective fusion. Instead, after the neutral beams are ionized, the energy of the fast ions originating from those neutral beams is boosted within the magnetic confinement volume by using a radio frequency electric field. The difficulty of preferentially transferring the radio frequency energy to the fast neutral beam ions rather than the thermal ions is overcome by controlling the incident angle and energy of the neutral beam so that there is a clearly defined "conversion point" of the fast ions within the magnetic confinement field. By tuning the radio frequency wave to a multiple of the cyclotron frequency (i.e., a harmonic) at the conversion point, these neutral beam incident ions are preferentially activated up to the fusion level, and at that time, the expected wave attenuation effect on the thermal ions is very small.

[0009] Therefore, specifically, in one embodiment, the present invention provides an apparatus for generating a high-energy plasma within a magnetic mirror confinement field, the magnetic mirror confinement field extending axially and providing converging magnetic flux lines at opposite first and second ends of a confinement volume that holds the plasma. A neutral beam generator directs a neutral beam of particles into the confinement volume at a predetermined pitch angle with respect to the magnetic field and within a certain energy range. This is done so that the particles dissociate within the confinement volume into plasma ions having the same pitch angle and having a clearly defined conversion point. At the conversion point, the fast ions have an energy that is completely perpendicular. And a radio frequency generator may be used to generate an electric field for accelerating the ions originating from the beam to an energy sufficient for the fusion of the plasma ions.

[0010] Therefore, one feature of at least one embodiment of the present invention is to provide a system that boosts the energy of the plasma ions after they enter the confinement field, thereby significantly enhancing the efficiency of the neutral beam.

[0011] The frequency of the electric field may depend functionally on the cyclotron frequency at the conversion point of the plasma ions of the neutral beam within the magnetic mirror confinement field.

[0012] Thus, one feature of at least one embodiment of the present invention is to preferentially accumulate energy in plasma ions having a matching cyclotron frequency.

[0013] In one embodiment, the frequency of the electric field may be a harmonic of the cyclotron frequency at the conversion point, which is higher than the cyclotron frequency.

[0014] Thus, one feature of at least one embodiment of the present invention is to utilize the preferential transfer of radio frequency electrical energy to resonant fast ions generated at higher order cyclotron harmonics.

[0015] The energy of the neutral beam is set such that more than 50% of the neutral beam particles are converted into plasma ions.

[0016] Thus, one feature of at least one embodiment of the present invention is to enable the use of low energy neutral beams that are suitable for high particle fluxes and thus can achieve high plasma densities.

[0017] The energy of the neutral beam may be less than 50 keV.

[0018] Thus, one feature of at least one embodiment of the present invention is to enable a trade-off setting regarding high flux velocity rather than high energy in the design of the neutral beam generator to increase the ion fuel injection rate.

[0019] The radio frequency generator may boost the energy of the plasma ions from the neutral beam by more than twice.

[0020] Thus, one feature of at least one embodiment of the present invention is to achieve an effective energy boost of the plasma ions after incidence.

[0021] The radio frequency generator may include an antenna, which is arranged so as to be very close to the reflection limit of the plasma ions and to generate a rotating electric vector perpendicular to the axis of the magnetic mirror confinement field.

[0022] Thus, one feature of at least one embodiment of the present invention is to optimize the antenna with respect to the energy accumulation of the plasma ions.

[0023] The angle of the neutral beam may be between 15° and 80° with respect to the axis.

[0024] Thus, one feature of at least one embodiment of the present invention is to achieve a good trade-off between the energy of the neutral beam and the conversion point that isolates the neutral beam from the thermal ions.

[0025] The device may further include a treatment volume, which surrounds at least a part of the confinement volume to receive high-energy neutrons passing through the confinement volume and includes an element to be elementally converted into another element.

[0026] Thus, one feature of at least one embodiment of the present invention is to provide a system for treating materials with neutrons, which treatment is, for example, creating radiopharmaceuticals or, for example, regenerating spent nuclear fuel.

[0027] The neutral beam may be selected from the group consisting of deuterium and tritium, and in some embodiments, the system may use only deuterium with respect to the neutral beam and the gas in the confinement volume.

[0028] Thus, one feature of at least one embodiment of the present invention is to provide a system that can work with well-understood neutral beam materials and, in some cases, can choose to use deuterium while avoiding the use of tritium.

[0029] In one embodiment, the present invention may be used to create a fusion device having a reaction volume that holds a fusible material within an axially extending first magnetic confinement field. In this embodiment, first and second plasma plugs may sandwich the reaction volume along the axis, and each plasma plug is a device that generates high-energy plasma as described above. Plasma ions escaping from the first and second plasma plugs cause a fusion reaction within the reaction volume.

[0030] Accordingly, one feature of at least one embodiment of the present invention is to provide an improved design of a fusion device that performs element conversion or power generation.

[0031] These specific objectives and advantages may only apply to some embodiments that fall within the scope of the claims, and thus do not define the scope of the present invention.

Brief Description of the Drawings

[0032]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0033] Next, referring 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 axis 14 to receive a reaction gas (e.g., deuterium or tritium) from a pressure tank or the like (not shown) via a valve inlet assembly 13.

[0034] First and second electromagnetic coils 16a and 16b may be disposed near opposite ends of the pressure vessel 12 within the pressure vessel 12, thereby defining a confinement volume 17 having a magnetic confinement field 15 therebetween. The electromagnetic coils 16 are oriented and separated to form a Helmholtz pair aligned along axis 14 to establish an axial B0 field therebetween. In one embodiment, the electromagnetic coils 16 may be pancake coils with a helix centered on axis 14 that are powered from a controllable external DC power supply 18 of a type known in the art.

[0035] A radio frequency antenna 19 (shown in simplified form) is disposed immediately adjacent to one of the electromagnetic coils 16b, between the electromagnetic coils 16. This antenna generates a circularly polarized radio wave field that extends along the axis 14 when driven, for example, by a radio frequency generator 20. As is understood in the art, this polarized radio wave field generates an electric vector 21 perpendicular to the axis 14 that rotates about the axis 14. For details of loop antennas suitable for this purpose, see T.H. Stix, "Fast Wave Heating of a Two-Component Plasma," Nuclear Fusion 15, 737 (1975), and R.W. Harvey, M.G. McCoy, G.D. Kerbel, and S.C. Chiu, "ICRF Fusion Reactivity Enhancements in Tokamaks," Nuclear Fusion 26, 43 (1986), which are incorporated herein by reference.

[0036] A treatment volume 22 may be disposed radially outside the pressure vessel 12. The treatment volume 22 may be in the form of, for example, a concentric outer cylindrical tank and may be filled with an aqueous material for element conversion by high energy neutrons. Such materials are, for example, precursors for medical isotopes 99 Mo (Molybdenum 99), 131 I (Iodine 131), 133 Xe (Xenon 133), and 177 Lu (Lutetium 177), or the treatment volume 22 may support a rack for holding spent nuclear fuel rods that have been reactivated by element conversion with high energy neutrons.

[0037] A neutral beam generator 26 for injecting a beam 28 of neutral particles 29 (non-ionized particles with zero net charge) is disposed at a pitch angle θ toward the confinement 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, atoms of deuterium or tritium, which are introduced through the gas line 24 and are atoms ionized by a local plasma (not shown). These ions are accelerated in an accelerator chamber 27 having a series of consecutive charged plates, as is generally understood in the art. Next, these ions pass through a neutralization gas cell 31 to generate neutral particles 29 by a charge exchange process, producing the neutral particles 29 of the beam 28.

[0038] Referring also to FIG. 2 here, the magnetic flux lines 30 generated by the coil 16 have a “bottle” shape that expands radially from the axis 14 at the midpoint between the coils 16 and contracts radially at the location of the coils 16. As is generally understood in the art, this configuration generates a mirror confinement volume where randomly distributed “hot” plasma ions 32 with a sufficient pitch angle gyrate about the magnetic flux lines 30 between the regions defined by the turning points 34.

[0039] As is understood in the art, these hot plasma ions can be fixed in various ways, for example, by using a radio frequency antenna 19 (although with low efficiency), or by using a separate heating system that generates electron cyclotron resonance heating using high-frequency microwaves.

[0040] The hot plasma ions 32 reverse direction in the region of the turning point 34, which is caused by an increase in the axial component of the magnetic Lorentz force generated by the convergence of the magnetic flux lines 30. The frequency 35 of the helical motion centered on the magnetic flux lines 30 is called the "cyclotron frequency" and is a function of the intensity 37 of the magnetic field along the axis 14. For this reason, the cyclotron frequency 35 generally increases towards the electromagnetic coil 16. When the mass and charge of each ion are equal, the cyclotron frequency is nominally the same at any location along the axis 14, regardless of the velocity or energy of the ions. In contrast, ions 32 with equal mass but different pitch angles usually have different turning points 34.

[0041] The velocity, and thus the energy, of the neutral particles 29 of the neutral beam 28, as well as the pitch angle of the neutral beam 28, are set such that most (e.g., more than 50%) of the particles of the neutral beam 28 are ionized within the confinement volume 17 into plasma ions 36 before exiting the confinement field. These plasma ions 36 at the same pitch angle are now charged and are trapped by the magnetic flux lines 30, increasing the plasma density.

[0042] To facilitate this capture of most of the neutral particles 29 of the neutral beam 28, the energy of the neutral beam 28 is limited such that sufficient flight time is obtained for the neutral particles 29 to be ionized. Generally, the desired energy of the neutral beam 28 for ionization is substantially lower than the kinetic energy required for substantial fusion, typically less than 100 keV, or preferably less than 50 keV, more typically on the order of 15 - 25 keV. This is in contrast to prior art schemes, where neutral particles 29 having an energy exceeding the energy required to promote fusion between plasma ions 36 are required, typically having an energy exceeding 1000 keV in the case of D - D fusion. Limiting the energy of the neutral beam 28 can affect the trade - off in the common neutron beam generator 26 to increase the magnetic flux density of the neutral particles 29 while simultaneously increasing the plasma density.

[0043] Continuing to refer to FIGS. 1 and 2, the pitch angle θ of the neutral beam 28 is selected such that a predetermined conversion 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 conversion point 34'. This cyclotron frequency is used to set the frequency of the radio frequency generator 20, as will be described later.

[0044] Furthermore, the antenna 19 is arranged in the vicinity of one of the conversion points 34' so as to obtain the maximum electric field strength in that region.

[0045] Finally, the energy of the neutral beam 28 is set as high as possible within the range of the energy level of the neutral beam 28 that realizes the desired capture of the neutral particles 29 within the confinement volume 17. This is to make the radius of the orbit (gyro orbit 52) of the plasma ions 36 generated by the neutral beam 28 larger than the average dispersion gyro orbit 52 of the "thermal ions" 32 (which are ions not directly derived from the neutral beam 28).

[0046] The inventors of the present application do not wish to be bound by a specific theory, but the above (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 conversion point 34', (b) boosting the energy of the plasma ions 36 above the average dispersion of the thermal plasma ions 32, and (c) maximizing the electric field strength at the conversion 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 attenuation effect of the thermal plasma ions 32.

[0047] In this regard, by setting the radio frequency generator 20 in accordance with ((a)), a preferential coupling with a plasma ion 36 having a cyclotron frequency 35 that is matched (e.g., in a harmonic relationship) is obtained. This is in contrast to the fact that the thermal plasma ions 32 have various Doppler-shifted cyclotron frequencies in a certain range and the coupling effectiveness is low. This coupling is related to the Bessel function B n-1 (k ⊥ *ν ⊥ / ω ci ) and may be proportional to the square thereof. However, n is the resonance cyclotron harmonic order of the incident wave, k ⊥ is the perpendicular wave number, ω ci is the cyclotron frequency of the resonant ions.

[0048] The quantity k ⊥ / ω ci may be the ~v A (Alfvén velocity) of the ions (see "Fast Wave Heating of a Two-Component Plasma" by T.H. Stix, Nuclear Fusion 15, 737 (1975)). Assuming that the Bessel function depends on v ⊥ , the coupling may be proportional to the power of the perpendicular velocity of the ions and may be adjusted to preferentially attenuate the hot tail ions from the neutral beam and those hot tail ions whose energy has increased by diffusion by the radio frequency wave.

[0049] Furthermore, by setting the frequency of the radio frequency generator 20 according to the cyclotron frequency 35 at the conversion point 34', the influence of the electric field from the radio frequency generator 20 on the plasma ions 36 increases. This is because the dwell time 50 of the plasma ions 36 is extended while the axial velocity of the plasma ions 36 is minimized during the conversion of the plasma ions 36 at the conversion point 34'. This is in contrast to, for example, the thermal plasma ions 32 quickly passing through this zone and moving to another conversion point 34 or not reaching the conversion point 34'.

[0050] As described above, by boosting the energy of the plasma ions 36 (according to (b)) so as to exceed the dispersion of the thermal plasma ions 32, and by setting the RF generator 20 to an RF frequency that is a harmonic of the cyclotron frequency 35 of the plasma ions 36, the plasma ions 36 with a larger radius of the gyro orbit 52 and higher energy preferentially absorb power exceeding that of the thermal plasma ions 32 with a smaller gyro orbit 52. In some embodiments, the RF frequency may be set in the range of 20 - 100 MHz, and / or the harmonic order n may be set to be greater than n = 2, preferably n = 4.

[0051] Generally, higher order harmonics boost the relationship between energy absorption and the gyro orbit 52 according to the higher order Bessel functions associated with those harmonics. Specifically, the energy absorption is proportional to J n-1 (k ⊥ ρ). However, J n-1 is the Bessel coefficient corresponding to a given harmonic order n. ρ is the radius of the gyro orbit 52 of the particle centered on the magnetic flux line 30, which increases with energy as

Equation

[0052] Of course, this effective preferential absorption of energy by the plasma ions 36 self-reinforces as energy is absorbed and the gyro orbits of the plasma ions 36 increase.

[0053] Finally, by placing the maximum electric field strength of the antenna 19 near the conversion point 34', the plasma ions 36 are preferentially affected.

[0054] Generally, the magnetic confinement field 15 tends to lose some of the plasma ions 32 with a small pitch angle through its ends. These particles are said to be within the "loss cone". It is possible to increase the plasma density by boosting the population of plasma ions 36 with a known pitch angle θ outside the loss cone.

[0055] The cyclotron frequency of the plasma ions 36 near the conversion point 34', and thus the desired setting of the frequency of the radio frequency generator 20, is mainly a function of the vacuum magnetic field strength 37, but shifts somewhat as a function of the increasing plasma density / pressure. Accordingly, the present invention contemplates that one or both of the DC power supply 18 or the RF frequency generator 20 may be adjusted during operation to maintain the above relationship that boosts the energy transfer to the plasma ions 36. Specifically, this adjustment may be performed by closed-loop feedback control using a sensor 56 that detects the plasma pressure (for example, using a diamagnetic loop), which measures the decrease in the magnetic field due to an increase in the plasma pressure and aligns the excitation frequency of the RF generator 20 with the actual and dynamic cyclotron frequency 35 at the conversion point 34'. The present invention also assumes that while frequency changes may not be necessary within the range where the cyclotron frequency is determined by the full field (the vacuum field from the coil and plasma diamagnetism), the position of the conversion point approaches the electromagnetic mirror coil.

[0056] Next, referring to FIG. 3, this advantage of the present invention when providing a high plasma density serves as part of a system in which two high-energy plasma systems 10 can act as "plugs" to capture high-energy plasma ions in a larger-scale neutron generator 60 for the purpose of element conversion (described above) or fusion power generation. Such a design may utilize, for example, the tandem mirror scheme, for which, for example, is described in G. Dimov, V. Zakaidakov, and M. Kishinevski, Fiz. Plazmy 2, 597 (1976), [Sov. J. Plasma], Phys 2, 326 (1976), and T.K. Fowler and B.G. Logan, Comments on Plasma Physics and Controlled Fusion 2, 167 (1977), which are incorporated herein by reference.

[0057] More specifically, in such a tandem mirror neutron generator 60, the first and second high-energy plasma systems 10a and 10b are disposed opposite each other across the generator volume 62 along the axis 14. Generally, the high-energy plasma system 10 is on the order of 2 m in axial length, while the generation volume 62 is much larger, for example, on the order of 50 m or more.

[0058] The electromagnetic coils 16 of both high-energy plasma systems 10a and 10b are arranged axially to generate deflections in the same direction 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 and travel 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 surrounding the axis 14 in a circle around the perimeter of the volume 62.

[0059] For this purpose, the electromagnetic coil 16 may be a superconducting magnet, for example, a superconducting magnet as 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), which is also incorporated herein by reference.

[0060] A subset of the hot plasma ions 32 has a uniformly distributed pitch angle and is boosted to high energy by the kinetic transfer from the plasma ions 36, and this subset can promote fusion and the emission of neutrons 64 from the volume 62 by escaping from the high energy plasma system 10 into a volume 62 that contains a reaction gas (e.g., deuterium or tritium). The high pressure of the high energy plasma system 10 blocks the escape of the high energy plasma ions from the volume 62, maintaining a high density for effective fusion.

[0061] The volume 62 may be surrounded by an encompassing volume 22, the encompassing volume 22 may contain a heat exchanger liquid 68, and the heat exchanger liquid 68 receives, for example, a working fluid 70 of a thermodynamic engine (e.g., a turbine, etc.) (e.g., for power generation) through one or more heat exchangers. Alternatively, the encompassing volume 22 may be used for elemental conversion of materials for the production of medical isotopes or the reactivation of spent nuclear fuel, as described above.

[0062] This application 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 element conversion, including the use of neutron multiplier generators and other structural details and mechanisms for generating the above-mentioned neutral beams.

[0063] In this specification, certain terms are used for reference only and are not intended to be limiting. For example, terms such as "upper", "lower", "above", and "below" mean directions in the drawings being referred to. Terms such as "front", "back", "rear", "bottom", and "side" indicate the orientation of each part of a component within a consistent but arbitrary reference system, and these are made clear by referring to the text describing the component in question and the associated drawings. Such terms may include the specifically mentioned words, their derivatives, and synonyms. Similarly, terms referring to structure such as "first", "second", and other such numbered terms do not mean a particular order or sequence unless clearly indicated by the context.

[0064] When introducing elements or features of the present disclosure and exemplary embodiments, the articles "a", "an", "the", and "said" are to be taken to mean that there is one or more of such elements or features. The terms "comprising", "including", and "having" are to be construed as inclusive and mean that there may be additional elements or features other than the specifically recited elements or features. Further, of course, method steps, processes, and operations described herein are not to be construed as necessarily being carried out in the specific order illustrated or described, unless the order of performance is specifically specified. Again, of course, additional or alternative steps may be used.

[0065] Specifically intended is that the present invention is not limited to the embodiments and examples contained herein, and the claims are to be understood as including modified forms of those embodiments, including combinations of elements of a part of the embodiments and separate embodiments, as being included within the scope of the claims set forth below. All published documents described herein, including patent and non-patent publications, are hereby incorporated by reference in their entirety.

Claims

1. An apparatus for generating high-energy plasma, comprising: a magnetic mirror confinement field extending axially and providing converging magnetic flux lines at opposite first and second ends of a confinement volume for holding the plasma; a neutral beam generator for directing a neutral beam of particles into the confinement volume at a predetermined pitch and energy such that the particles dissociate within the confinement volume to become plasma ions; a radio frequency generator for generating an electric field to accelerate the plasma ions to an energy sufficient for fusion of the plasma ions; wherein the frequency of the electric field is functionally dependent on the cyclotron frequency at the conversion point of the plasma ions of the neutral beam within the magnetic mirror confinement field; the apparatus.

2. The apparatus according to claim 1, wherein the frequency is a harmonic of the cyclotron frequency, which is higher than the cyclotron frequency.

3. The apparatus according to claim 1, wherein the energy of the neutral beam is set such that more than 50% of the neutral beam particles are converted into plasma ions.

4. The apparatus according to claim 1, wherein the energy of the neutral beam is less than 50 keV.

5. The apparatus according to claim 1, wherein the radio frequency generator boosts the energy of the plasma ions from the neutral beam by more than twice.

6. The apparatus according to claim 1, wherein the radio frequency generator includes an antenna, and the antenna is arranged to be very close to the reflection limit of the plasma ions and to generate a rotating electric vector perpendicular to the axis of the magnetic mirror confinement field.

7. The apparatus according to claim 6, wherein the pitch is 30 to 60° with respect to the axis.

8. Further comprising a treatment volume, the treatment volume surrounding at least a part of the confinement volume for receiving high-energy neutrons passing through the confinement volume and containing an element to be elementally converted into another element.

9. The element to be transformed is a precursor substance ９９ Mo １３１ I １３３ Xe, and １７７ The device according to claim 8, which is a precursor substance of a medical radioisotope selected from the group consisting of Lu.

10. The apparatus according to claim 8, wherein the element to be elementally converted is spent nuclear fuel.

11. The apparatus according to claim 1, wherein the neutral beam is selected from the group consisting of deuterium and tritium.

12. The apparatus according to claim 1, wherein the neutral beam is deuterium.

13. The apparatus according to claim 1, comprising a pair of magnetic coils for generating the magnetic mirror confinement field, wherein the radio frequency generator comprises an antenna between the magnetic coils, and the confinement volume is accommodated within an airtight chamber.

14. A reaction volume for holding a fusible material within a first axially-extending magnetic confinement field, First and second plasma plugs sandwiching the reaction volume along the axis, each plasma plug comprising: (a) a magnetic mirror confinement field extending axially and providing converging magnetic flux lines at opposing first and second ends of a confinement volume for holding a plasma; (b) a neutral beam generator for directing a neutral beam of particles into the confinement volume at a predetermined pitch and energy such that the particles dissociate within the confinement volume into plasma ions; (c) a radio frequency generator for generating an electric field for accelerating the plasma ions to an energy exceeding the energy of the particles entering the confinement volume; the first and second plasma plugs including; including; whereby plasma ions escaping from the first and second plasma plugs cause a fusion reaction within the reaction volume; the frequency of the electric field being functionally dependent on the cyclotron frequency at the conversion point of the plasma ions of the neutral beam within the magnetic mirror confinement field; a fusion device.

15. The fusion device according to claim 14, wherein the pressure of the plasma ions within the first and second plasma plugs is higher than the pressure of the plasma ions within the reaction volume.

16. The fusion device according to claim 15, further comprising a generator for receiving neutrons from the reaction volume and generating electricity.

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