Patent Application
20180033496
The present disclosure generally relates to nuclear fusion, and, more particularly, to fusion by inertial electrostatic confinement using a device with continuous walls.
In embodiments, a continuous electrode (CE) inertial electrostatic confinement (IEC) device employs sidewalls with substantially continuous surfaces radially extending from a central core to define radial particle paths. Electrodes coupled to the sidewalls provide an electric field that varies along each particle path to accelerate ions within the particle paths toward the core. Interaction of the ions within the core can result in nuclear fusion, which may be used for electricity generation or for spacecraft propulsion. The CE-IEC device can include one or more features designed to decrease distances between ions, for example, by compacting ion bunches as they travel along the particle paths and/or neutralizing space charge of ion bunches within the core using a population of electrons captured therein.
In one or more embodiments, a device comprises a central core region, particle paths, sidewalls, electrodes, and a control module. Each particle path can radially extend from the central core region and can have a corresponding particle path aligned therewith on an opposite side of the central core region. The sidewalls can extend in a radial direction. Each particle path can be bounded by a corresponding set of the sidewalls. The electrodes can be coupled to the sidewalls so as to provide an electric field that varies along each particle path from a cathode region proximal to the central core region to an anode region remote from the central core region. The control module can control the electrodes to provide the electric field. Each sidewall can provide a continuous surface radially extending from the cathode region to the anode region.
In one or more embodiments, a fusion method comprises directing ion bunches along particle paths that radially extend from a central core region. Each particle path can be bounded by a corresponding set of radially extending sidewalls and can have a corresponding particle path aligned therewith on an opposite side of the central core region. Each sidewall can provide a continuous surface radially extending from a cathode region proximal to the central core region to an anode region remote from the central core region. The method can further comprise generating an electric field that varies along each particle path from the cathode region to the anode region such that the ion bunches are accelerated toward the central core region, and fusing ions from the ion bunches within the central core region. The method can also comprise allowing fusion products to travel from the central core region to beyond the anode region via the particle paths.
Objects and advantages of embodiments of the disclosed subject matter will become apparent from the following description when considered in conjunction with the accompanying drawings.
Embodiments will hereinafter be described with reference to the accompanying drawings, which have not necessarily been drawn to scale. Where applicable, some features may not be illustrated or otherwise simplified to assist in the illustration and description of underlying features. Throughout the figures, like reference numerals denote like elements.
In embodiments, an inertial electrostatic confinement (IEC) device has radially extending sidewalls that define radial particle paths emanating from a central core. Electrodes can be coupled to these sidewalls in order to provide an electric field that varies along the particle paths, for example, from a radially-outer anode region (remote from the central core) to a radially-inner cathode region (proximal to the central core). As such, embodiments employing continuous sidewalls with coupled electrodes are referred to herein as continuous electrode (CE). Although the sidewalls are referred to as continuous, this does not require that the sidewalls be monolithic or isotropic. Rather, the continuous sidewalls provide a substantially continuous surface from the anode region to the cathode region and can have different properties at different radial or azimuthal locations (e.g., formed of different material segments at different radial locations and/or having a resistivity that varies radially).
The electric field can accelerate ions toward the core, where the ions interact to yield nuclear fusion. Non-reacting ions can pass through the core to an opposite (aligned) particle path, where the electric field therein slows the ions to reverse direction and accelerate back toward the core for further interactions. Unlike conventional IEC devices that employ multiple independent grids of different radii centered on the core to provide an electric field, embodiments of the present disclosure employing continuous sidewalls allow the electric potential to be imposed continuously over the particle path and/or to dynamically adjust the electric potential as ions travel within the particle paths (e.g., to compact traveling ion bunches prior to introduction to the core). The continuous sidewalls can also provide a very high grid transparency (i.e., greater than 70%, for example, ˜85%) as seen from the core without otherwise sacrificing structural rigidity.
The sidewalls also provide real estate for conduits from external to the device toward the central core, for example, to provide electrical connections for power or signal transmission, to provide a magnetic field using permanent magnets, and/or to feed ions into the particle paths. While the sidewalls provide an additional surface area that ions could strike (representing a loss to the system) that multiple independent grids would otherwise lack, such ions would be on non-radial trajectories and thus would likely not contribute to nuclear fusion anyway.
Since the ions interact in the core, fusion products are only generated in the core and leave along predominantly radial paths, e.g., along the radially extending particle paths. In general, the IEC device should be as transparent as possible to these energetic particles. In other words, the construction of the IEC device (e.g., sidewalls) should subtend as little solid angle (as seen by the core) as possible. To that end, any radially outer structure that falls within the “shadow” of radially inner structures, as viewed from the device center, will not diminish the transparency of the system. Thus, in embodiments, structures are arranged to fall within this “shadow” of the innermost structure, which is designed to subtend as little solid angle as possible. In other words, the sidewalls could be considered a radially outward extrusion of the innermost edge (adjacent to the core).
Referring to
The focusing region 110 is where the CE structure (i.e., sidewalls 106) is disposed. The open channels between facing sidewalls 106 in the focusing region 110 form the particle paths 108a-108c, along which ion bunches recirculate as they pass into and out of the core. A radially outer region of the sidewalls 106 can be biased at a relatively higher voltage to form anode region 126, while a radially inner region of the sidewalls 106 can be biased at a relatively lower voltage to form cathode region 124. The resulting electric field in the focusing region 110 causes the ions to accelerate toward the core 112. Since the potential profile is generated solely in the focusing region 110, the ions will drift through the core at a constant speed.
Over time, the traveling ions self-assemble into bunches 120 due to two-stream instability. Moreover, due to cross-talk, the bunches 120 synchronize between different particle paths 108a-108c, as shown in
Low angle scattering between counter-streaming ions, which would normally result in the rapid global thermalization of the ion population, is suppressed by local thermalization within each of the bunches 120 near the anode region 126. Moreover, the low-angle collisions among opposing bunches within the core merely reshuffle the specific radial trajectories among the particle paths 108a-108c that the individual ions will follow to exit the inner core 122. Upon refocusing (in focusing region 110), the velocity distribution in the azimuthal direction 118 within each bunch 120 should be indistinguishable from the start of the previous pass, cancelling any azimuthal momentum growth. Low angle scatters among non-opposing ion bunches can introduce both azimuthal and radial (energy) scattering. However, on average these scattering events will both up-scatter and down-scatter the ions equally. Upon refocusing (in focusing region 110), the net ion energy within each bunch 120 due to low angle ion-ion collisions should remain the same.
High angle scatters are confined to the core where the resulting ion trajectories will still be approximately radial. In other words, if the scattering angle of the ion does not otherwise cause it to collide with the inner edge of a sidewall 106, the ion should simply end up in a different channel (proceeding along a different particle path 108a-108c) rather than being lost. Upon refocusing (in focusing region 110), the ion will be merged into the traveling ion bunch 120. Thus, the electric potential within the particle pathways can help keep scattered ions from being lost.
To increase the density of ion bunches as they pass into the core 112, where the bulk coulomb repulsion of the ions would tend to push them apart, a population of electrons is confined to the core of the device in order to neutralize the space charge of the ions. For example, an electron population can be generated within the core by completely ionizing the fusion fuel (e.g., boron), which may be only singly ionized initially prior to injection. For example, any remaining electrons of the fusion fuel can be stripped, either through collisions with other ions passing through the core or as a result of a nuclear fusion event. Alternatively or additionally, electrons can be injected directly into the core, for example, to replenish those that might be lost over time and that would otherwise not be replenished by further ionizing the fusion fuel.
To help confine the electrons to the core, the sidewalls 106 may further provide another anode region 128 adjacent to the core (i.e., radially between the cathode region 124 and the outer core 112). The resulting electric field can create a reversed potential well for electrons that keeps them from escaping the core along particle pathways. For example,
The ions thus travel from the anode region 126 to the cathode region 124 (see
Unreacted ions 120 and/or fusion products 140 travel along substantially radial paths out of the inner core region 122 to the outer core region 112, where they leave behind the confined electrons before passing back into the focusing region 110 (see
The fusion products 140 can thus continue through focusing region 110 and escape to power conversion region 150 beyond sidewalls 106, where the fusion products 140 can be converted to electricity or otherwise used to generate work (e.g., to propel a spacecraft). The fusion products 140 can enter the power conversion region 150 with a nearly isotropic angular distribution and can arrive in pulses a few nanoseconds long separated by several microseconds. The pulsed output of the fusion products 140 can be converted to electricity using a direct conversion process, for example, Traveling Wave Direct Energy Conversion (TW-DEC) or Standing Wave Direct Energy Conversion (SW-DEC), as described in further detail elsewhere herein.
When the ions leave the outer core 112, their self-charge will still tend to cause the bunches of ions to expand. Thus, as they travel along the particle paths 108a-108c in the focusing region 110, the ions 120 can also be continuously refocused and compressed (due to the electric potential provided by the sidewalls 106 and/or magnetic fields from permanent magnets of the sidewalls 106) to combat this natural spreading due to space charge and/or low angle collisions.
As noted above, embodiments of the CE-IEC device can provide a potential that varies continuously in the focusing region 110.
At each radial location on the sidewall, the resistivity normal to the radial direction can be very low, such that locations on the same sidewall at the same radial distance from the core can be held at substantially the same potential. In other words, portions of the sidewall 106 at the same radii would act as an isopotential conductor. Moreover, portions of different sidewalls 106 (i.e., falling along isopotential line 208 in
The variable resistivity material 200 may be accomplished, for example, by engineering a composite material having strips of different material layers at different radii extending in a direction perpendicular to the radial direction 116. Adjacent strips are electrically coupled to each other along contacting faces perpendicular to the radial direction 116 to provide the radially varying resistivity, while otherwise acting as isopotential conductors in a direction perpendicular to the radial direction. The composition of the material 200 can be customized to achieve any desired radial potential profile. For example, the potential profile can monotonically decrease from the anode region to the cathode region, or can be a complex profile that does not necessarily monotonically decrease). For example, the sidewall material can be formed via 3-D printing.
Alternatively or additionally, a customized potential profile can be achieved using a segmented continuous sidewall structure, as illustrated in
Although shown in
Moreover, the features of
As noted above, embodiments of the CE-IEC device can provide a magnetic field to help confine electrons to the core region 112. Since only enough electrons are needed to neutralize the traveling ions, the magnetic field requirement is relatively low and can be satisfied using permanent magnets (e.g., formed of a rare-earth material, such as neodymium, or other permanent magnetic material). For example, radially polarized permanent magnets may be incorporated into sidewalls 106 with same poles (either north or south) facing the core 112. The resulting magnetic field has field lines 312 extending through the channels formed by the sidewalls 106, e.g., substantially following the particle paths 108a-108c, as shown in
The provision of permanent magnets in the sidewalls 106 allows more material to be used, thereby resulting in a stronger magnetic field, without otherwise compromising transparency to particles exiting the core 112. For example, the permanent magnets 306 can be incorporated into each sidewall 106 between conductive panels 302 thereof, as shown in
Each magnet would have a polar orientation 308 extending radially (i.e., with one pole adjacent to the core 112, and the opposite pole spaced at a radially outer location). Although a particular polar orientation is illustrated in
Although
To avoid such electron losses, additional cusps 414 can be provided within the focusing region 106 along the particle paths 108a-108c, as shown in
Such cusped magnetic fields can be generated by incorporating multiple separate magnets in the sidewalls along the radial direction. For example, radially polarized permanent magnets 402A-402C may be incorporated into sidewalls 106, with polar orientations 404A-404C alternating along the radial direction, as shown in
Each magnet would have a polar orientation 404A-404C extending radially (i.e., with one pole closer to the core 112, and the opposite pole spaced at a radially outer location). The resulting magnetic field lines 312 extend through the channels formed by the sidewalls, but with cusped regions 414 directed toward the sidewalls. Although a particular polar orientation is illustrated in
Moreover, the features of
Although the magnetic field configurations of
Despite the provision of a cusped magnetic field, high-angle scattered ions and/or fusion products can impact the edges of the sidewalls 106 facing the core 112. These impacts can cause undesirable heating of the sidewall 106 and its components (e.g., permanent magnets, embedded electrodes, sensors, etc.). Heating of the permanent magnets is especially undesirable as it may lead to de-magnetization. To avoid damaging the sidewalls 106, protective standoffs 502 (i.e., shields) can be provided at the innermost edge of the sidewalls 106, as shown in
Instead of forming the standoff 502 from the heat-resistant material, the standoff 502 can be coated with a layer of the heat-resistant material. For example, the heat-resistant material could be flowed through a pipe extending along sidewall 106, for example, via expanded channel 604 of
Any heat absorbed by the standoff 502 may be passively radiated away or actively cooled by a separate mechanism (e.g., a heat transfer fluid circulating through the standoff 502). The standoff 502 can also be formed of sufficient thickness (or coated with sufficient thickness) such that any sputtering that does occur would still allow for a sufficient lifetime of operation before failure. For example, if sputtering resulted in loss of approximately 0.013 monolayers/second, a standoff 502 having a 1 cm thick layer of carbon could have a lifetime of several years.
In embodiments, transparency of the CE-IEC device can be maintained by taking advantage of otherwise unused real estate of the sidewall structures for various functions, such as, but not limited to, electrical connections for voltage or signals, supporting permanent magnets, feeding fuel (e.g., ions) for fusion, and coating standoffs. For example, one or more of the vertices 602 between adjacent sidewalls 106 can be expanded into channel 604 to accommodate an electrical feed line 606, as shown in
The channel 604 may accommodate a single electrical feed line 606, for example, to set a potential at a single radial location. For example,
Alternatively or additionally, the channel 604 may accommodate multiple electric feed lines 606 to set potentials on different sidewalls, while also having a permanent magnet therein. For example,
Alternatively or additionally, the channel 604 may accommodate multiple electric feed lines 606, for example, to set potentials at more than one radial location. For example,
The features of
The vertex channels 604 could also be used to provide fuel to the CE-IEC device for fusion. For example, protons and boron ions can be generated at appropriate radial locations within a particle path so that the relative energy matches the fusion cross-section resonance, and so that the center mass of the reaction is stationary at the device core (i.e., zero net momentum). To achieve this, neutral atoms can be fed into the device to an appropriate radius prior to ionization. If the feed tubes were placed within the particle paths, they would be subject to fusion product bombardment. To avoid such bombardment, the feed tubes 804 are placed between the sidewalls 106, for example, at the vertices 602 between adjacent sidewalls, for example, as shown in
The vertex channels 604 could also be used to convey signals to/from locations within the sidewalls 106, for example, to convey sensor signals. As discussed above, the potential may be dynamically controlled to compact ion bunches as they travel along the particle paths. In some embodiments, the potential may be controlled without feedback (i.e., open loop), for example, by establishing a time-varying profile and allowing the traveling ion bunches to synchronize to the profile.
Alternatively, one or more sensors 902, as illustrated in
Referring to
The CE-IEC device 100 can be coupled to a controller 1006 that controls operation thereof. Such control by the controller 1006 can include providing a static potential and/or a dynamic potential (e.g., to compact ion bunches) to the sidewalls 106 using voltage source 1008. Although shown as a single component, voltage source 1008 can include multiple voltage sources and/or be capable of generating multiple independent voltages (for example, as needed for the multiple sidewall segments of
The fusion products 1012 can be directed from the focusing region 110 of the CE-IEC device 100 for subsequent use, for example, directly utilized 1014 (e.g., propulsion of a spacecraft) and/or converted for use 1016 (e.g., converted to electricity using electrostatic deceleration and/or dynamically oscillating potentials). In the latter utility, the kinetic energy of the fusion products can be directly converted into electrical energy. Alternatively or additionally, the fusion products can be used to charge a conducting plate, which resulting charge can be used to drive a high impedance load.
For example,
As the fusion products 140 approach the first electrode 1102 in
For example, the electrodes 1102-1108 can form the capacitive element of a tuned resistor-inductor-capacitor (RLC) circuit 1120, as shown in
The description of
An exemplary configuration of a 3-D SW-DEC is illustrated in the cross-sectional view of
Although a cubic configuration for the CE-IEC device 100 is illustrated in
Indeed, practical embodiments of the disclosed subject matter may employ other configurations with different particle path geometries and/or number of particle paths. To this end, the sidewall structure can be formed by radial extrusion of the edges of any polyhedron, so long as the faces of the polyhedron come in diametrically opposed pairs in order to create the aligned particle paths on opposite sides of the core. For example, the number of particle pathways can be increased and the geometry of the innermost edge 104 and/or outermost edge 102 can be more complex, such as a truncated icosahedron (e.g., soccer ball geometry), as described in further detail below with respect to
An entire family of highly symmetric CE options is provided by the geometry of fullerenes—carbon molecules that form closed polyhedral cages. Fullerenes are labeled as CN, where N is the number of carbon atoms in the molecule. Of particular interest are those of icosahedral (−Ih) symmetry, such as C20, C60, C80, C240, etc., where a necessary condition is that N must be a multiple of 20. For each of these, 12 faces are always pentagons and the rest are always hexagons. A regular truncated icosahedron (RTI) has edges of equal length, but the hexagonal faces have an area that is about 60% larger than the pentagons. This is the geometry of the C60 molecule (and the soccer ball). However, the truncation of the icosahedron can be done in such a way that instead of ending up with the edges all the same length, one can achieve a geometry where the two types of faces can be inscribed by circles having substantially the same area. This makes the resulting particle paths more equivalent.
Embodiments of the CE-IEC device can employ various nuclear fusion fuels. For example, the CE-IEC device can employ the deuterium-tritium (D-T) reaction or the deuterium-deuterium (D-D) reaction. For single species fuel, such as D-D, only two diametrically opposed ion bunches 120 will be present along each particle path at any given time, one bunch on each side of the core. While the burning of D-T has the highest cross-section, it may suffer from the production of highly energetic neutrons, which can be absorbed into the nuclei of other materials and create unstable radioactive isotopes. In addition, scattering of these neutrons can dislocate atoms from their lattices resulting in structural degradation over time.
In another example, the CE-IEC device uses an aneutronic fuel such as p-11B, which is the fusion of a hydrogen atom with the most common isotope of boron. The result of the fusion process is three helium nuclei (alpha particles) with a total energy of about 8.7 MeV. For two-species fuel such as p-11B, four diametrically opposed bunches 120—one pair for each of the two species—will be present along each particle path at any given time, two bunches on each side of the core, separated radially.
Although features of the various figures have been separately illustrated, embodiments of the disclosed subject matter can combine one or more of the separately illustrated features. For example, embodiments can include the sidewall geometry features of
Moreover, although the above description has focused on the use of the CE-IEC device for nuclear fusion, embodiments of the disclosed subject matter are not necessarily limited thereto. Indeed, aspects of the disclosed subject matter may be employed in other applications that have traveling ions.
It will be appreciated that the aspects of the disclosed subject matter can be implemented, fully or partially, in hardware, hardware programmed by software, software instruction stored on a computer readable medium (e.g., a nontransitory computer readable medium) or a combination of the above.
For example, components of the disclosed subject matter, including components such as a controller, processor, or any other feature, can include, but are not limited to, a personal computer or workstation or other such computing system that includes a processor, microprocessor, microcontroller device, or is composed of control logic including integrated circuits such as, for example, an application specific integrated circuit (ASIC).
Features discussed herein can be performed on a single or distributed processor (single and/or multi-core), by components distributed across multiple computers or systems, or by components co-located in a single processor or system. For example, aspects of the disclosed subject matter can be implemented via a programmed general purpose computer, an integrated circuit device (e.g., ASIC), a digital signal processor (DSP), an electronic device programmed with microcode (e.g., a microprocessor or microcontroller), a hard-wired electronic or logic circuit, a programmable logic circuit (e.g., programmable logic device (PLD), programmable logic array (PLA), field-programmable gate array (FPGA), programmable array logic (PAL)), software stored on a computer-readable medium or signal, an optical computing device, a networked system of electronic and/or optical devices, a special purpose computing device, a semiconductor or superconductor chip, a quantum computing chip or device, a software module or object stored on a computer-readable medium or signal.
When implemented in software, functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. The steps of a method or algorithm disclosed herein may be embodied in a processor-executable software module, which may reside on a computer-readable medium. Instructions can be compiled from source code instructions provided in accordance with a programming language. The sequence of programmed instructions and data associated therewith can be stored in a computer-readable medium (e.g., a nontransitory computer readable medium), such as a computer memory or storage device, which can be any suitable memory apparatus, such as, but not limited to quantum-based memory, read-only memory (ROM), programmable read-only memory (PROM), electrically erasable programmable read-only memory (EEPROM), random-access memory (RAM), flash memory, disk drive, etc.
As used herein, computer-readable media includes both computer storage media and communication media, including any medium that facilitates transfer of a computer program from one place to another. Thus, a storage media may be any available media that may be accessed by a computer. By way of example, and not limitation, such computer-readable media may comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, quantum-based storage, or any other medium that may be used to carry or store desired program code in the form of instructions or data structures and that may be accessed by a computer.
Also, any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using a transmission medium (e.g., coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave), then the transmission medium is included in the definition of computer-readable medium. Moreover, the operations of a method or algorithm may reside as one of (or any combination of) or a set of codes and/or instructions on a machine readable medium and/or computer-readable medium, which may be incorporated into a computer program product.
One of ordinary skill in the art will readily appreciate that the above description is not exhaustive, and that aspects of the disclosed subject matter may be implemented other than as specifically disclosed above. Indeed, embodiments of the disclosed subject matter can be implemented in hardware and/or software using any known or later developed systems, structures, devices, and/or software by those of ordinary skill in the applicable art from the functional description provided herein.
In this application, unless specifically stated otherwise, the use of the singular includes the plural, and the separate use of “or” and “and” includes the other, i.e., “and/or.” Furthermore, use of the terms “including” or “having,” as well as other forms such as “includes,” “included,” “has,” or “had,” are intended to have the same effect as “comprising” and thus should not be understood as limiting.
Any range described herein will be understood to include the endpoints and all values between the endpoints. Whenever “substantially,” “approximately,” “essentially,” “near,” or similar language is used in combination with a specific value, variations up to and including 10% of that value are intended, unless explicitly stated otherwise.
It is thus apparent that there is provided in accordance with the present disclosure, systems, methods, and devices for inertial electrostatic confinement. Many alternatives, modifications, and variations are enabled by the present disclosure. While specific examples have been shown and described in detail to illustrate the application of the principles of the present invention, it will be understood that the invention may be embodied otherwise without departing from such principles. For example, disclosed features may be combined, rearranged, omitted, etc. to produce additional embodiments, while certain disclosed features may sometimes be used to advantage without a corresponding use of other features. Accordingly, Applicant intends to embrace all such alternatives, modifications, equivalents, and variations that are within the spirit and scope of the present invention.
The present application claims the benefit of U.S. Provisional Application No. 62/367,410, filed Jul. 27, 2016, which is hereby incorporated by reference herein in its entirety.
This invention was made with government support under NNX13AL44H awarded by the National Aeronautics and Space Administration (NASA). The government has certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 62367410 | Jul 2016 | US |
