Ion Sources and Neutron Generators

Abstract

A nuclear reaction generator includes a chamber configured to contain a gas and a target material. The nuclear reaction generator also includes a filament disposed in the chamber and a voltage source configured to apply a first positive voltage to the filament relative to the chamber. The first positive voltage is configured to heat the filament to a temperature at which thermionic emission occurs and a plurality of thermions are generated, and the plurality of thermions are configured to ionize the gas to generate positive ions in the chamber. The target material is configured so that a nuclear reaction occurs when the positive ions interact with the target material.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of priority to U.S. Provisional Patent Application No. 62 / 836,481, filed on April 19, 2019, the contents of which are incorporated herein in their entirety. Technical Field

[0003] The present technology generally relates to an ion source and accelerator that share the same physical space and methods for generating ions and accelerating these ions using the ion source. In some aspects, ions from the ion source can be accelerated into a target material to produce a nuclear reaction that results in neutron production. Therefore, the present technology can also relate to systems and methods for generating nuclear reactions using the ion source. Background Art

[0004] This section is intended to provide a background or context for the invention described in the claims. The descriptions herein may contain concepts that may be implemented, but not necessarily concepts that have been previously conceived or implemented. Therefore, unless otherwise indicated herein, the materials described in this section are not prior art to the description and claims in this application and are not admitted to be prior art by inclusion in this section.

[0005] An ion source typically comprises a chamber where ionization occurs, a gas disposed in the chamber, and an ionization energy source. Conventional high current ion generation methods are typically limited to generating plasma using RF excitation, arc discharge, or filament assisted discharge, which require complex electronic, magnetic, and high vacuum arrangements that are difficult to operate and maintain. These methods of generating plasma typically require relatively high gas pressures in the chamber, which can be problematic if the ions generated by the source need to be accelerated within the same volume of space in which they were generated.

[0006] Ions generated by ion sources can be used in a variety of applications, including, but not limited to, particle accelerators for mass spectrometry, medical devices and diagnostics, and semiconductor manufacturing. Ions generated by ion sources can be accelerated toward a target and used to produce nuclear reactions, including nuclear reactions that produce neutrons. Conventional neutron sources use separate devices for ionization, acceleration, and target fusion of ionized matter. These neutron sources can include the use of various ion generation methods, as well as particle accelerator-specific functions such as ion extraction, ion acceleration, beam focusing, beam control, and beam stopping. Neutron sources have been developed for a variety of applications, such as neutron radiography, materials science, condensed matter physics, and nondestructive testing and evaluation of materials. These devices have many disadvantages, either limiting their available ion current, resulting in insufficient neutron yield for many applications, or being very complex, making them difficult and expensive to build, maintain, and operate.

[0007] In one example, neutrons may be generated by producing ions of deuterium, tritium, or a combination thereof, and accelerating these ions into a hydride target loaded with deuterium and / or tritium according to one of the following reactions:

[0008] D + T → n + 4 He E n = 14.1 MeV (1)

[0009] D + D → n + 3 He E n = 2.5 MeV (2)

[0010] Neutron sources based on reactions (1) and (2) are typically single-beam, linear electrostatic devices that introduce significant ion losses during transport, leading to excessive heating and reduced neutron yield.

[0011] Improved technology related to ion sources and methods of producing high ion production rates at low background pressures are needed that would allow for increased ion yields and long periods of continuous operation without extensive maintenance or support equipment. Summary of the invention

[0012] In one aspect, an ion source comprises a chamber containing a gas; a filament disposed near the center of the chamber; an accelerating grid surrounded by the filament; and a voltage source configured to apply a first positive voltage to the filament and a second positive voltage to the accelerating grid. The first positive voltage applied to the filament is configured to heat the filament to a temperature at which thermionic emission occurs and a plurality of thermions are generated. The second positive voltage is greater than (more positive than) the first positive voltage. The plurality of thermions are configured to ionize the gas to generate positive ions in an ionization region, such as anywhere in the chamber, including a region between the filament and the accelerating grid. The first positive voltage and the second positive voltage are maintained substantially above a voltage at the walls of the chamber, which may be maintained at ground potential. This creates a cyclic electron trap where electrons oscillate back and forth in the center of the device, resulting in ionization of a low-pressure background gas. Due to the electric field configuration, ions generated in the region will be accelerated outward toward the walls of the structure. In some embodiments, the pressure in the chamber may be less than 1 mTorr. In other embodiments, the pressure in the chamber may be less than 0.1 mTorr.

[0013] In a second aspect, a neutron generator comprises a chamber containing a gas; a filament disposed near the center of the chamber; an accelerating grid surrounded by the filament; a suppressing grid concentric with and surrounding the filament; a target; and a voltage source configured to apply a first positive voltage to the filament, a second positive voltage to the accelerating grid, and a third negative voltage to the suppressing grid. Unless otherwise specified, voltages herein are applied / referenced / measured / etc. relative to the chamber, e.g., such that the voltage applied to the filament (or other structure) refers to the difference between the filament and the chamber. The first positive voltage applied to the filament is configured to heat the filament to a temperature at which thermionic emission occurs and a plurality of thermions are generated. The second positive voltage is greater than the first positive voltage. The plurality of thermions are configured to ionize the gas to generate positive ions in an ionization region in the chamber, including a region between the filament and the accelerating grid. The first positive voltage and the second positive voltage are maintained substantially above the voltage at the walls of the chamber, which may be maintained at ground potential. This creates a cyclic electron trap where electrons oscillate back and forth in the center of the device, leading to ionization of the low-pressure background gas. Due to the electric field configuration, ions generated in this region will be accelerated outward toward the walls of the structure. The suppression grid will prevent secondary electrons generated by ion collisions with the walls from being accelerated toward the center of the device - an effect that consumes power and reduces efficiency.

[0014] In a third aspect, a method for generating ions includes providing a filament and an accelerating grid in a chamber containing a gas, the accelerating grid being surrounded by the filament; applying a first positive voltage to the filament to heat the filament to a temperature at which thermionic emission occurs and a plurality of thermions are generated; applying a second positive voltage to the accelerating grid, the second positive voltage being greater than the first positive voltage; and ionizing the gas to generate positive ions in an ionization region in the chamber, including a region between the filament and the accelerating grid. The thermal electrons may be trapped in the ionization region.

[0015] In a fourth aspect, a method for generating neutrons includes providing a filament, an accelerating grid, a suppressing grid, and a target in a chamber containing a gas; applying a first positive voltage to the filament to heat the filament to a temperature at which thermionic emission occurs and a plurality of thermions are generated; applying a second positive voltage to the accelerating grid, the second positive voltage being greater than the first positive voltage; and ionizing the gas to generate positive ions in an ionization region in the chamber, including a region between the filament and the accelerating grid. In a fourth aspect, the accelerating grid is concentric with and surrounded by the filament, the suppressing grid is concentric with and surrounds the filament, and the target is concentric with and surrounds the suppressing grid. The method may further include applying a negative voltage to the suppressing grid. The method may even further include impacting positive ions that pass through the suppressing grid onto the target. The impacting positive ions are injected into the target or impact previously injected ions to generate fusion neutrons. In addition, secondary electrons may be emitted from the target because the impacting ions impact previously injected ions. Due to the potential difference between the filament and the accelerating grid, the hot electrons may be trapped therebetween. Due to the potential difference between the target and the suppressing grid to which the negative voltage is applied, the secondary electrons may be reflected from the suppressing grid toward the target.

[0016] According to the consideration of the following detailed description, drawings and claims, other features, advantages and embodiments of the present disclosure can be set forth. In addition, it should be understood that the foregoing overview and the following detailed description of the present disclosure are exemplary and are intended to provide additional explanation without further limiting the scope of the present disclosure claimed. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present disclosure will be more fully understood through the following detailed description made in conjunction with the accompanying drawings, in which:

[0018] Figure 1 A schematic diagram of the ion source and neutron generator is shown.

[0019] Figure 2A The filament guide is shown Figure 1 Cross-sectional view of the ion source and neutron generator.

[0020] Figure 2B Shows Figure 1 A three-dimensional cutaway view of the ion source and neutron generator.

[0021] Figure 3 Shows Figure 1 Exploded outline of the ion source.

[0022] Figure 4 Shown for Figure 1A control system for an ion source, wherein the control system comprises a controller and a voltage source. DETAILED DESCRIPTION

[0023] Before turning to the drawings showing exemplary embodiments in detail, it should be understood that the present application is not limited to the details or methods set forth in the specification or shown in the drawings. It should also be understood that the terminology is used for descriptive purposes only and should not be regarded as limiting.

[0024] In one aspect, the ion source comprises a chamber in which a filament 2, an accelerating grid 3, and a gas are disposed. In another aspect, the neutron generator comprises a chamber in which a filament 2, an accelerating grid 3, a suppressing grid 4, a target 5, and a gas are disposed. That is, the target 5 (and, in some embodiments, the suppressing grid 4) can be added to the ion source (i.e., the filament 2 and the accelerating grid 3) to form a neutron generator. Both the ion source and the neutron generator are within the scope of the present disclosure. Any ion source described herein can be used in the neutron generator described herein. The system disclosed herein can also be described as an ion source and a divergent accelerator or a fusion reactor.

[0025] In one example of an ion source, the filament 2 is composed of tungsten or a tungsten alloy and the accelerating grid 3 is composed of tungsten or a tungsten alloy. In one example of a neutron source, the filament 2 is composed of tungsten or a tungsten alloy and the accelerating grid 3 is composed of tungsten or a tungsten alloy, the suppressor grid 4 is composed of tungsten or a tungsten alloy and the target 5 is composed of titanium or a titanium alloy (and optionally backed by a low hydrogen solubility metal such as stainless steel). Various other materials and preferred properties of the materials are provided in detail below.

[0026] like Figure 1 and 2A As shown, the chamber of the ion source and / or neutron generator has a circular cross-section (ie, the chamber may be cylindrical or spherical). Figure 2B A three-dimensional cross-sectional view of an ion source and / or neutron generator is shown in an embodiment having a cylindrical shape (i.e., in an embodiment in which the filament 2, the accelerating grid 3, the suppressing grid 4, and / or the target 5 are each formed as a cylinder). However, in other embodiments, the geometry of the chamber is not limited in this regard. However, in other examples (not shown), the chamber may have the shape of a cube, a cuboid, a pyramid, a cone, etc. The geometry of the chamber may be customized to suit a specific application in which the ion source is used. In some examples, the chamber may be symmetrical about its central axis. In other examples, the chamber may not be symmetrical about its central axis. Compared to conventional ion sources, the ion source 10 is easy to construct and easy to replace.

[0027] filament

[0028] The filament 2 is disposed near the center of the chamber of the ion source and / or neutron generator. The filament 2 is connected to a voltage source 20, which is configured to apply a positive predetermined voltage (discussed in more detail below) to the filament 2, thereby heating the filament 2. In the illustrated embodiment, the filament 2 is a high current thermionic emitter. In some embodiments, field emission (e.g., even field emission) is used in addition to or instead of thermionic emission. In thermionic emission, the filament 2 is heated to supply the electrons with the minimum energy required to overcome the attraction that holds the electrons on the filament 2, thereby causing the electrons (thermions) to be released from the filament 2. The minimum energy (i.e., work function) is defined as the minimum thermodynamic work required to move electrons from a solid surface (i.e., filament 2) to a point in the chamber immediately outside the filament 2. The work function is a property of the material of the filament 2 and the contamination state on the surface of the filament 2. The filament 2 can be made of any material that can be heated to supply the minimum energy to the electrons without melting. Preferably, the filament 2 is made of a material with a low work function so that a large number of hot electrons are emitted. For example, the filament 2 can be made of metal (e.g., tungsten or a tungsten alloy). In various embodiments, the material of the filament 2 is characterized by high electron emission rate, low vapor pressure, high melting temperature, and resistance to ablation and sputtering. In various embodiments, the filament 2 can be composed of lanthanum hexaboride, cerium hexaboride, thoriated tungsten, barium aluminate, or a mixture of any two or more thereof.

[0029] refer to Figure 2A-2B In some examples of ion sources and / or neutron generators, the filament 2 may optionally be disposed in one or more filament guides 2a configured to maintain filament spacing and provide mechanical support to suspend the filament 2 over the length of the device. In one example, the filament guide 2a may include a plurality of holes 2b (e.g., holes, slots, etc.) configured to receive a portion of the filament 2 therein (e.g., pass the filament 2 in and out of the holes). In this example, the holes 2b may be spaced evenly or unevenly along the filament guide 2a having holes, and the filament 2 may be accommodated in all or a subset of the holes 2b. The filament guide 2a having holes 2b may be made of a non-conductive refractory material. In some embodiments, the non-conductive refractory material may be a ceramic. Exemplary glasses include glass, clay, and metal oxides. In a specific example, the filament 2 may be made of tungsten or a tungsten alloy and the filament guide may be made of ceramic.

[0030] In some examples, the ion source 10 includes one and only one filament 2. In other examples, the ion source 10 may include multiple filaments 2 spaced apart along and supported by a filament guide. In other embodiments, other methods and / or structures for emitting electrons in a chamber may be used, and the systems and methods herein may be modified accordingly.

[0031] Acceleration gate

[0032] The accelerating grid 3 is at least partially surrounded by the filament 2. The filament 2 and the accelerating grid 3 can be concentric, however this is not required. In some examples, the accelerating grid 3 can be a solid material containing a plurality of holes (i.e., holes, slots, etc.) spaced along its length. In other examples, the accelerating grid 3 can be a frame or grid containing a first set of parallel strips or lines of material extending in a first direction (e.g., along the length of the chamber) and a second set of strips or lines of material, the second set of strips or lines intersecting and crossing the first set of parallel strips, thereby providing holes between the first set and the second set. The holes are configured to allow positive ions (e.g., hydrogen ions) generated in the ionization region (e.g., between the accelerating grid 3 and the filament 2) to pass through the accelerating grid 3 to be collected (ion source) or accelerated toward the suppression grid 4 and the target 5 (neutron generator).

[0033] In some examples, the accelerating grid 3 is made of the same material as the filament 2. In other examples, the accelerating grid 3 is made of a different material than the filament 2. The accelerating grid 3 is made of a conductive material and can resist ion damage. The accelerating grid 3 can be made of a refractory metal that is resistant to ablation and sputtering, such as niobium, molybdenum, tantalum, tungsten, rhenium, or a mixture or alloy of any two or more thereof.

[0034] The accelerating grid 3 is connected to a voltage source 20, which is configured to apply a positive predetermined voltage to the accelerating grid 3. The potential of the accelerating grid 3 is greater than the potential of the filament 2 (more positive than the potential of the filament 2). For example, the predetermined voltage applied to the accelerating grid may be +100100V, while the predetermined voltage applied to the filament 2 may be +100000V. Due to the potential difference (voltage bias), the thermal electrons released by the filament 2 are accelerated outward toward the accelerating grid 3. The arrangement and voltage bias of the filament 2 and the accelerating grid 3 create a low potential region that confines high energy thermal electrons (electrons) generated by the thermal electron emission of the filament 2. The thermal electrons can be reabsorbed by the filament 2, but thermal electrons with sufficient energy will be trapped (confined between the filament 2 and the accelerating grid 3). The trapped high energy thermal electrons circulate in the ionization region for a sufficient time to impact low density neutral gas molecules according to the following reaction:

[0035] M + e - → M +· +2e – (3)

[0036] Where M is the gas molecule and e - These are electrons (hot electrons) that interact with gas molecules and transfer energy greater than the ionization energy of the molecules, thereby ejecting electrons from the gas molecules (electron ionization).

[0037] In other words, and as described above, the voltage source can be configured to apply a first positive voltage to the filament and a second positive voltage to the accelerating grid. The first positive voltage applied to the filament is configured to heat the filament to a temperature at which thermionic emission occurs and a plurality of thermions are generated. The second positive voltage is greater than (more positive than) the first positive voltage. The plurality of thermions are configured to ionize the gas to generate positive ions in an ionization region in the chamber, including a region between the filament and the accelerating grid. The first positive voltage and the second positive voltage are maintained substantially above the voltage at the walls of the chamber, which may be maintained at ground potential. This creates a cyclic electron trap with electrons oscillating back and forth in the center of the device, resulting in ionization of a low-pressure background gas. Due to the electric field configuration, ions generated in the region will be accelerated outward toward the walls of the structure.

[0038] Gaseous molecules (e.g., hydrogen) ionized by collision with energetic hot electrons in the ionization region contribute positive charge to the ionization region, thereby reducing the negative potential of accumulated electron space charge generated by the hot ion current. The vacuum level within the accelerating grid 3 is generated by an external vacuum source and maintained at a level that reduces the likelihood of collision with neutral particles in the ionization region. For example, the gas pressure in the ionization region can be less than or equal to 10 mTorr, for example, less than or equal to 5 mTorr or less than or equal to 1 mTorr. The low gas pressure in the ionization region increases the ion yield or neutron yield because the likelihood of ions colliding with gas molecules before being collected or before striking the target 5 to produce neutrons is reduced.

[0039] Suppressor Gate

[0040] In the neutron generator, a suppression grid 4 at least partially surrounds the filament 2. The suppression grid 4, the filament 2, and the acceleration grid 3 are concentric. The suppression grid 4 is made of the same material as the acceleration grid 3. Similar to the acceleration grid 3, in some examples, the suppression grid 4 can be a solid material containing a plurality of holes (i.e., holes, slots, etc.) spaced along its length. In other examples, the suppression grid 4 can be a frame or grid containing a first set of parallel strips or lines of material extending in a first direction (e.g., along the length of the chamber) and a second set of strips or lines of material, the second set of strips or lines intersecting and crossing the first set of parallel strips, thereby providing holes between the first set and the second set. The positions of the holes in the suppression grid 4 correspond to the positions of the holes in the acceleration grid 3. The holes of the suppression grid 4 are configured to allow positive ions passing through the acceleration grid 3 from the ionization region to pass through the suppression grid 4 and be accelerated toward the target material 5.

[0041] The suppression grid 4 is connected to a voltage source 20 configured to apply a negative predetermined voltage (discussed in more detail below) to the suppression grid 4. When positive ions in the region between the acceleration grid 3 and the filament 2 drift into the vicinity of the acceleration grid 3, they are accelerated out of the ionization region by the potential difference between the acceleration grid 3 and the suppression grid 4. In other embodiments, a magnetic field may be used to achieve an effect similar to that provided by the suppression grid 4.

[0042] The suppression grid 4 is made of a conductive material and resistant to ion damage, such as high-quality metal. The suppression grid 4 can be made of a refractory metal that is resistant to ablation and sputtering, such as niobium, molybdenum, tantalum, tungsten, rhenium or a mixture or alloy of any two or more thereof.

[0043] Target

[0044] In the neutron generator, the target 5 at least partially surrounds the suppression grid 4 (for example, the target 5 may not surround the area above and / or below the suppression grid 4). The target 5, the suppression grid 4 and the acceleration grid 3 are concentric. The target 5 may be made of a solid metal hydride forming material. The material of the target 5 may be selected so that when fully loaded, there is a ratio of 1:1 to 2:1 between the hydrogen disposed on the target 5 and the material from which the target 5 is made. The material of the target 5 may be a conductive metal or semimetal with an affinity for hydrogen absorption, preferably a low-quality material with a very small nuclear interaction cross section. For example, the target 5 may be made of carbon, aluminum, titanium, magnesium, zirconium, yttrium, scandium, erbium or a mixture or alloy of any two or more thereof.

[0045] In some examples, the target 5 is the wall of the chamber itself (or is integrated into the wall). In other examples, the target 5 is a layer disposed on the inner surface of the chamber or on the outer surface of the chamber. In examples where the target 5 is a layer, the target 5 may optionally be backed by a low hydrogen solubility metal, or the low hydrogen solubility metal may form the wall of the chamber itself. The low hydrogen solubility metal may be stainless steel.

[0046] The target 5 is not connected to the voltage source 20 and is maintained at ground potential (substantially 0 V). After the positive ions travel outward through the holes in the acceleration grid 3 and the suppression grid 4, they enter the region between the suppression grid 4 and the target 5. In this region, the positive ions stop accelerating and travel ballistically to impact on the target 5. The impacting ions are either injected into the target 5 or impact previously injected ions to produce fusion neutrons. In the example of a neutron generator in which the positive ions generated with ionization energy are hydrogen isotopes, a hydrogen concentration accumulates on the target 5, so that the hydrogen isotope has the opportunity to collide with another hydrogen isotope on the target 5 to produce neutrons according to the above-mentioned reactions (1) and (2).

[0047] When the high energy ions strike the target 5, the surface of the target 5 emits about 2-3 secondary electrons, which are maintained at a potential slightly higher than the potential of the suppression grid 4. Due to the potential difference between the target 5 and the suppression grid 4, the secondary electrons are reflected back into the target 5, which reduces the electron heating of the acceleration grid 3 and prevents the appearance of unwanted electron currents in the ionization region provided between the acceleration grid 3 and the filament 2. In other embodiments, a magnetic field may be used to achieve an effect similar to that provided by the suppression grid 4.

[0048] Voltage Sources and Controllers

[0049] The voltage source 20 is provided outside the chamber. The voltage source 20 may be any known voltage source. The controller 30 may be provided and programmed to independently control the voltage supplied to each of the filament 2, the acceleration grid 3, and the suppression grid 4. The controller 30 may vary the voltage supplied to each of the filament 2, the acceleration grid 3, and the suppression grid 4 to adjust the system or to change the ion or neutron yield. A control panel or display may be provided to allow a user to select a separate, different voltage to be supplied to each of the filament 2, the acceleration grid 3, and the suppression grid 4.

[0050] As described above, the target 5 is held at ground potential, while the suppression grid 4 is held at a voltage slightly negative relative to the ground potential. The accelerating grid 3 is held at a high positive voltage relative to the ground potential, while the filament 2 is held at a voltage slightly positive relative to the voltage of the accelerating grid 3. This electronic arrangement reduces the likelihood of unwanted arcing and protects the filament 2 from damage by arcing or high energy electron currents.

[0051] In the example of a neutron generator having a cylindrical chamber, a cylindrical neutron generator of a predetermined length (determined according to the specific application) is configured to produce an axially aligned, uniform and isotropic neutron flux. The cylindrical arrangement of components allows the neutron generator to produce high ion current density without being limited by space charge.

[0052] As shown in various exemplary embodiments, the construction and arrangement of the ion source and / or neutron generator are illustrative only. Although only a few embodiments are described in detail in the present disclosure, many modifications are possible (e.g., changes in the size, dimensions, structure, shape and proportion of each element, parameter values, mounting arrangements, use of materials, colors, orientations, image processing and segmentation algorithms, etc.) without substantially departing from the novel teachings and advantages of the described subject matter. Elements shown as integrally formed may be composed of multiple parts or elements, the positions of the elements may be reversed or otherwise changed, and the properties or quantities of discrete elements or positions may be altered or changed. According to alternative embodiments, the order or sequence of any process, logic algorithm or method steps may be changed or reordered. Without departing from the scope of the present invention, other substitutions, modifications, changes and omissions may also be made in the design, operating conditions and arrangement of various exemplary embodiments.

[0053] As used herein, the terms "approximately," "about," "substantially," and similar terms are intended to have a broad meaning consistent with the common and recognized usage by those of ordinary skill in the art to which the subject matter of the present disclosure belongs. Those skilled in the art who review the present disclosure should understand that these terms are intended to allow for an explanation of certain features described and claimed without limiting the scope of these features to the precise numerical ranges provided. Therefore, these terms should be interpreted as indicating that insubstantial or inconsequential modifications or changes to the subject matter described and claimed are considered to be within the scope of the present invention as described in the appended claims.

[0054] As used herein, the terms "coupled," "connected," and the like mean that two components are directly or indirectly joined to one another. Such joining may be fixed (e.g., permanent) or movable (e.g., removable or releasable). Such joining may be achieved by the two components, or the two components and any additional intermediate components, being integrally formed as a single, unitary body with one another, or by the two components, or the two components or any additional intermediate components, being attached to one another.

[0055] References to the positions of elements (e.g., "top," "bottom," "above," "below," etc.) herein are only used to describe the orientation of the various elements in the drawings. It should be noted that according to other exemplary embodiments, the orientation of the various elements may be different, and such variations are intended to be covered by the present disclosure.

[0056] Regarding the use of substantially any plural and / or singular terms herein, those skilled in the art can convert the plural to the singular and / or the singular to the plural when appropriate, depending on the circumstances and / or application. For the sake of clarity, various singular / plural conversions may be clearly described herein.

[0057] The subject matter and embodiments of the operations described in this specification (e.g., voltage control) can be implemented in digital circuit systems or in computer software embodied in tangible media, firmware or hardware (including the structures disclosed in this specification and their structural equivalents) or in a combination of one or more of them. The embodiments of the subject matter described in this specification can be implemented as one or more computer programs, that is, one or more modules of computer program instructions encoded on one or more computer storage media for execution by a data processing device or for controlling the operation of a data processing device. Alternatively or in addition, the program instructions can be encoded on an artificially generated propagation signal, such as a machine-generated electrical signal, optical signal, or electromagnetic signal, which is generated to encode information for transmission to a suitable receiver device for execution by a data processing device. The computer storage medium can be or be contained in a computer-readable storage device, a computer-readable storage substrate, a random or serial access memory array or device, or a combination of one or more thereof. Moreover, although the computer storage medium is not a propagation signal, the computer storage medium can be the source or destination of the computer program instructions encoded in the artificially generated propagation signal. The computer storage medium can also be or be contained in one or more separate components or media (e.g., multiple CDs, disks, or other storage devices). Hence, computer storage media may be tangible and non-transitory.

[0058] The operations described in this specification may be implemented as operations performed by a data processing apparatus or processing circuitry on data stored on one or more computer-readable storage devices or received from other sources.

Claims

1. An ion source, comprising: a chamber configured to contain a gas, wherein the chamber includes a first end and a second end; a plurality of filaments disposed in the chamber and oriented along a first direction extending between the first end and the second end; an accelerating grid surrounding an open central region of the chamber, the accelerating grid comprising a plurality of apertures spaced apart around the open central region of the chamber, wherein the accelerating grid extends in the first direction, and wherein the plurality of filaments are spaced apart around a circumference of the accelerating grid such that the plurality of filaments surround the accelerating grid; as well as a voltage source configured to apply a first positive voltage to the plurality of filaments relative to the chamber and a second positive voltage to the accelerating grid; in: The first positive voltage is configured to heat the plurality of filaments to a temperature at which thermionic emission occurs and a plurality of thermions are generated; The plurality of thermal ions are configured to ionize the gas to generate positive ions; and The plurality of apertures allow the positive ions to pass through the accelerating grid and the open central region of the chamber.

2. The ion source of claim 1 , wherein the second positive voltage of the accelerating grid relative to the chamber and the first positive voltage of the plurality of filaments relative to the chamber are configured to produce a cyclic electron trap in which electrons oscillate back and forth in an open central region of the chamber, the cyclic electron trap causing ionization of gas in the open central region. 3 . The ion source of claim 1 , further comprising a filament guide, wherein the plurality of filaments are configured to pass through the filament guide or to be wound around the filament guide to maintain filament spacing. 4 . The ion source of claim 3 , wherein at least one of the plurality of filaments or the accelerating grid comprises tungsten or a tungsten alloy, and the filament guide comprises a non-conductive refractory material.

5. The ion source of claim 4, wherein the non-conductive refractory material comprises ceramic. 6 . The ion source of claim 1 , comprising a suppression grid surrounding the plurality of filaments and the acceleration grid, wherein the voltage source is configured to apply a third negative voltage to the suppression grid.

7. The ion source of claim 6, wherein the suppression grid comprises a plurality of suppression grid apertures configured to allow the positive ions to pass therethrough; and Positive ions passing through the acceleration gate are configured to be accelerated toward the suppression gate due to a potential difference between the acceleration gate and the suppression gate.

8. The ion source of claim 1, wherein the chamber is configured to maintain a pressure of less than 1 mTorr.

9. The ion source of claim 1, wherein the chamber is configured to maintain a pressure of less than 0.1 mTorr.

10. The ion source of claim 1, wherein the accelerating grid comprises a plurality of bars, and the plurality of apertures are disposed between the plurality of bars.

11. The ion source of claim 1, wherein the accelerating grid comprises a solid material and the plurality of holes are disposed in the solid material.

12. The ion source of claim 11, wherein the plurality of apertures are spaced apart along a length of the solid material of the accelerating grid.

13. The ion source of claim 1, wherein the accelerating grid is cylindrical and the plurality of filaments are arranged in a cylindrical shape.

14. The ion source of claim 1, wherein the accelerating grid is concentric with the plurality of filaments.

15. A nuclear reactor generator, comprising: a chamber configured to contain a gas and comprising a first end and a second end; a target material, wherein the target material is disposed in the chamber; an accelerating grid positioned within the chamber, oriented along a first direction extending between the first and second ends of the chamber, surrounding an open central region of the chamber, and comprising a plurality of apertures spaced about the open central region of the chamber; a plurality of filaments disposed in the chamber, oriented along the first direction, and spaced apart around a circumference of the accelerating grid such that the plurality of filaments surround the accelerating grid, and a voltage source configured to apply a first positive voltage to the plurality of filaments relative to the chamber, and applying a second positive voltage to the accelerating gate, in: The first positive voltage is configured to heat the plurality of filaments to a temperature at which thermionic emission occurs and a plurality of thermions are generated; The plurality of thermions are configured to ionize the gas to generate positive ions in the chamber, and The plurality of apertures allow the positive ions to pass through the accelerating grid and the open central region of the chamber.

16. The nuclear reaction generator according to claim 15, wherein the target material is configured such that a nuclear reaction occurs when the positive ions interact with the target material.

17. The nuclear reactor generator of claim 15, wherein the target material is at least one of: positioned on an inner surface of a wall of the chamber, positioned on an outer surface of a wall of the chamber, or integrated into the wall of the chamber.

18. The nuclear reactor generator according to claim 15, wherein: The second positive voltage of the accelerating grid relative to the chamber and the first positive voltage of the plurality of filaments relative to the chamber are configured to produce a cyclic electron trap in which electrons oscillate back and forth in an open central region of the chamber, the cyclic electron trap causing ionization of gas in the open central region.

19. The nuclear reactor generator of claim 18, comprising a suppression grid concentric with and surrounding the plurality of filaments and the acceleration grid, wherein the voltage source is configured to apply a third negative voltage to the suppression grid relative to the chamber.

20. The nuclear reactor generator according to claim 19, wherein: The suppression gate comprises a plurality of suppression gate apertures configured to allow positive ions to pass therethrough; and The positive ions passing through the acceleration gate from the open central region are configured to be accelerated toward the suppression gate due to a potential difference between the acceleration gate and the suppression gate.

21. The nuclear reactor generator according to claim 15, wherein the target material is a conductive metal or semi-metal having an affinity for absorbing hydrogen.

22. The nuclear reactor generator according to claim 21, wherein the target material is selected from carbon, aluminum, titanium, magnesium, zirconium, yttrium, scandium, erbium or a mixture or alloy of any two or more thereof.

23. The nuclear reactor generator of claim 15, wherein the target material comprises titanium or a titanium alloy. 24 . The nuclear reactor generator according to claim 15 , wherein the target material comprises a layer disposed on an inner surface of the chamber or a layer on a metal with low hydrogen solubility disposed on the inner surface of the chamber.

25. The nuclear reactor generator of claim 24, wherein the target material comprises titanium or a titanium alloy; and at least one of the inner surface of the chamber or the low hydrogen solubility metal comprises stainless steel.

26. The nuclear reactor generator of claim 15, wherein the chamber is configured to maintain a pressure of less than 1 mTorr.

27. The nuclear reactor generator of claim 15, wherein the chamber is configured to maintain a pressure of less than 0.1 mTorr.

28. The nuclear reactor generator of claim 15, further comprising a filament guide configured to support the plurality of filaments, wherein at least one of the plurality of filaments or the accelerating grid comprises tungsten or a tungsten alloy, and the filament guide comprises a non-conductive refractory material.

29. The nuclear reactor generator of claim 28, wherein the non-conductive refractory material comprises ceramic.

30. The nuclear reactor generator of claim 15, wherein the accelerating grid comprises a plurality of bars, and the plurality of holes are disposed between the plurality of bars.

31. The nuclear reactor generator of claim 15, wherein the accelerating grid comprises a solid material and the plurality of holes are disposed in the solid material.

32. A nuclear reactor generator according to claim 31, wherein: The plurality of holes are spaced apart along the length of the solid material of the accelerating grid.

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