Ion source and neutron generation device

Abstract

To provide an ion source and an accelerator, as well as a method for generating ions and accelerating those ions in the ion source.SOLUTION: A nuclear reaction generation device includes a chamber configured to contain gas and include a target. The nuclear reaction generation device also includes a filament provided within 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 that causes thermionic emission and generates multiple thermions. The multiple thermions are configured to ionize the gas and generate positive ions in the chamber. The target is configured such that nuclear reactions occur when the positive ions interact with the target.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority to U.S. Provisional Application No. 62 / 836,481, filed April 19, 2019, the contents of which are incorporated herein in their entirety.

[0002] Field The present technology generally relates to an ion source and an accelerator that share the same physical space, and a method for generating ions and accelerating the ions in the ion source. In some embodiments, the ions from the ion source can be accelerated toward a target and undergo a nuclear reaction to generate neutrons. Thus, the present technology can also relate to a system and method for generating a nuclear reaction in an ion source. [Background technology]

[0003] background This section is intended to provide a background or context for the claimed invention. The description herein may include concepts that may be pursued, but not necessarily those that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, nothing in this section is intended to be prior art to the description and claims of this application, and is not admitted to be prior art by inclusion in this section.

[0004] An ion source generally includes a chamber where ionization occurs, a gas supplied within the chamber, and an ionization energy source. Conventional approaches to high-current ion generation are generally limited to plasma generation through the use of 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 approaches to plasma generation generally require relatively high gas pressures within the chamber, which can be problematic when ions generated by the source need to be accelerated within the same spatial volume in which they are generated.

[0005] Ions generated by ion sources can be used in a variety of applications, including, but not limited to, mass spectrometry, medical instruments and diagnostics, and particle accelerators used in semiconductor manufacturing. Ions generated by ion sources can be accelerated toward a target and used to initiate nuclear reactions, including neutron generation. Traditional neutron sources employ separate devices for ionization, acceleration, and target fusion of ionized species. These neutron sources can apply various ion generation approaches and include features unique to particle accelerators, such as ion extraction, ion acceleration, beam focusing, beam steering, and beam stopping. Neutron sources have been developed for a variety of applications, including neutron radiography, materials science, condensed matter physics, and nondestructive testing and evaluation of materials. These devices have many drawbacks, either limiting available ion currents, resulting in insufficient neutron yields for many applications, or being highly complex, making them difficult and expensive to build, maintain, and operate.

[0006] In one example, neutrons can be produced by generating ions of deuterium, tritium, or a combination thereof, and accelerating these ions into a hydride target loaded with deuterium and / or tritium by one of the following reactions: D+T→n+ 4 He E n =14.1 MeV(1) D+D→n+ 3 He E n =2.5MeV(2) Neutron sources based on reactions (1) and (2) are traditionally single-beam linear electrostatic devices that suffer from significant ion losses during transport, resulting in excessive heating and reduced neutron yield.

[0007] Improved ion source technology is needed that allows for increased ion yields and long-term continuous operation without significant maintenance or support equipment, as well as methods for generating high ion yields at low background pressures. Summary of the Invention

[0008] overview In one aspect, the ion source includes 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 that causes thermionic emission and generates a plurality of thermal electrons. The second positive voltage is higher (more positive) than the first positive voltage. The thermal electrons are configured to ionize the gas and generate positive ions anywhere within the chamber, including in an ionization region, e.g., the region between the filament and the accelerating grid. The first and second positive voltages are maintained substantially above the voltage of the chamber walls, which may be held at ground potential. This creates a recirculating electron trap in the center of the device, where electrons oscillate back and forth, causing ionization of the low-pressure background gas. Ions generated in this region are accelerated outward toward the walls of the structure by an electric field configuration. In some embodiments, the pressure within the chamber can be less than 1 milliTorr. In other embodiments, the pressure within the chamber can be less than 0.1 milliTorr.

[0009] In a second aspect, a neutron generator includes a chamber containing a gas, a filament disposed near the center of the chamber, an acceleration grid surrounded by the filament, a suppression 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 acceleration grid, and a third negative voltage to the suppression grid. Unless otherwise specified, voltages herein are applied / referenced / measured relative to the chamber; for example, a voltage applied to the filament (or other structure) refers to the differential voltage between the filament and the chamber. The first positive voltage applied to the filament is configured to heat the filament to a temperature that causes thermionic emission and generates a plurality of thermionic electrons. The second positive voltage is greater than the first positive voltage. The plurality of thermionic electrons is configured to ionize the gas and generate positive ions in an ionization region within the chamber, including the region between the filament and the acceleration grid. The first and second positive voltages are maintained substantially above the voltage of the chamber walls, which may be held at ground potential. This creates a recirculating electron trap in the center of the device, where electrons oscillate back and forth, ionizing the low-pressure background gas. Ions generated in this region are accelerated outward toward the walls of the structure by the electric field configuration. The suppression grid prevents secondary electrons resulting from ion collisions with the chamber walls from accelerating toward the center of the device, a power-consuming and efficiency-reducing effect.

[0010] In a third aspect, a method for generating ions includes providing a chamber containing a gas with a filament and an acceleration grid surrounded by the filament, applying a first positive voltage to the filament to heat the filament to a temperature causing thermionic emission and generating a plurality of thermal electrons, applying a second positive voltage greater than the first positive voltage to the acceleration grid, and ionizing the gas to generate positive ions in an ionization region within the chamber, the second positive voltage including a region between the filament and the acceleration grid. The thermal electrons may be confined to the ionization region.

[0011] In a fourth aspect, a method for generating neutrons includes providing a chamber containing a gas with a filament, an acceleration grid, a suppression grid, and a target; applying a first positive voltage to the filament to heat the filament to a temperature causing thermionic emission and generating a plurality of thermionic electrons; applying a second positive voltage greater than the first positive voltage to the acceleration grid; and ionizing the gas to generate positive ions in an ionization region within the chamber, the region including a region between the filament and the acceleration grid. In the fourth aspect, the acceleration grid is concentric with and surrounded by the filament, the suppression grid is concentric with and surrounds the filament, and the target is concentric with and surrounds the suppression grid. The method may further include applying a negative voltage to the suppression grid. The method may further include causing the positive ions passing through the suppression grid to impinge on the target. The incident positive ions are either implanted in the target or collide with previously implanted ions to generate fusion neutrons. Furthermore, secondary electrons may be emitted from the target as a result of the incident ions colliding with previously implanted ions. The potential difference between the filament and the acceleration grid can trap the thermal electrons therebetween, and the potential difference between the target and the suppression grid to which a negative voltage is applied can reflect secondary electrons from the suppression grid towards the target.

[0012] [The present invention 1001] a chamber configured to contain a gas; a filament disposed within the chamber; a voltage source configured to apply a first positive voltage to the filament relative to the chamber; 1. An ion source comprising: the first positive voltage is configured to heat the filament to a temperature that causes thermionic emission and generates a plurality of thermoelectrons; the plurality of thermoelectrons are configured to ionize the gas to generate positive ions. The ion source. [The present invention 1002] the ion source includes an accelerating grid surrounded by the filament; the voltage source is configured to apply a second positive voltage relative to the chamber to the acceleration grid, the second positive voltage being greater than the first positive voltage; The ion source of the present invention 1001. [The present invention 1003] 1001. The ion source of the present invention, further comprising a filament guide, wherein the filament is configured to be threaded through or wound around the filament guide to maintain filament spacing. [The present invention 1004] 1002. The ion source of the present invention, wherein at least one of the filament or the accelerating grid comprises tungsten or a tungsten alloy, and the filament guide comprises a non-conductive refractory material. [The present invention 1005] The ion source of the present invention 1004, wherein the non-conductive refractory material comprises ceramic. [The present invention 1006] The ion source of any one of 1002 to 1005, further comprising a suppression grid surrounding the filament and the acceleration grid, wherein the voltage source is configured to apply a third negative voltage to the suppression grid. [The present invention 1007] the acceleration grid and the retardation grid each include a plurality of openings configured to allow positive ions to pass therethrough; The ion source of the present invention 1006, configured such that the positive ions passing through the acceleration grid are accelerated towards the suppression grid due to a potential difference between the acceleration grid and the suppression grid. [The present invention 1008] The ion source of any one of 1001 to 1007, wherein the chamber is configured to maintain a pressure of less than 1 mTorr. [The present invention 1009] The ion source of any one of 1001 to 1007, wherein the chamber is configured to maintain a pressure of less than 0.1 milliTorr. [The present invention 1010] a chamber configured to contain a gas and including a target; a filament disposed within the chamber; a voltage source configured to apply a first positive voltage to the filament relative to the chamber; A nuclear reaction generating device comprising: the first positive voltage is configured to heat the filament to a temperature that causes thermionic emission and generates a plurality of thermoelectrons; the plurality of thermoelectrons are configured to ionize the gas to generate positive ions within the chamber. The nuclear reaction generating device. [The present invention 1011] The nuclear reaction generating device of the present invention 1010, wherein the target is configured such that a nuclear reaction occurs when the positive ions interact with the target. [The present invention 1012] The nuclear reaction generating device of the present invention 1010 or 1011, wherein the target is at least one of positioned on the inner wall of the chamber, positioned on the outer wall of the chamber, or integrated into the wall of the chamber. [The present invention 1013] an acceleration grid surrounding the filament; the voltage source is configured to apply a second positive voltage relative to the chamber to an acceleration grid; the second positive voltage is greater than the first positive voltage; A nuclear reaction generating device according to any one of the present inventions 1010 to 1013. [The present invention 1014] a suppression grid concentric with and surrounding said filament and acceleration grid; the voltage source is configured to apply a third negative voltage relative to the chamber to the suppression grid. The nuclear reaction generating device of the present invention 1013. [The present invention 1015] the acceleration grid and the retardation grid each include a plurality of openings configured to allow positive ions to pass therethrough; a potential difference between the acceleration grid and the suppression grid causes the positive ions passing through the acceleration grid from the ionization region to accelerate toward the suppression grid; The nuclear reaction generating device of the present invention 1014. [The present invention 1016] A nuclear reaction generating device according to any one of claims 1010 to 1015, wherein the target is made of a solid metal hydride-forming material. [The present invention 1017] The nuclear reaction generating device of the present invention, wherein the solid metal hydride-forming material is titanium or a titanium alloy. [The present invention 1018] The nuclear reaction generating device of any one of claims 1010 to 1017, wherein the target comprises titanium or a titanium alloy. [The present invention 1019] A nuclear reaction generating device according to any one of claims 1010 to 1018, wherein the target comprises a layer provided on the inner surface of the chamber or on a low hydrogen solubility metal provided on the inner surface of the chamber. [The present invention 1020] 1019. The nuclear reaction generating device of claim 1019, wherein the target comprises titanium or a titanium alloy, and at least one of the interior surface of the chamber or the low hydrogen solubility metal comprises stainless steel. [The present invention 1021] A nuclear reaction generating device according to any one of claims 1010 to 1020, wherein the chamber is configured to maintain a pressure of less than 1 millitorr. [The present invention 1022] A nuclear reaction generating device according to any one of claims 1010 to 1021, wherein the chamber is configured to maintain a pressure of less than 0.1 millitorr. [The present invention 1023] A nuclear reaction generating device according to any one of claims 1010 to 1022, wherein at least one of the filament or the acceleration grid comprises tungsten or a tungsten alloy, and the filament guide comprises a non-conductive refractory material. [The present invention 1024] The nuclear reaction generating device of claim 1023, wherein the non-conductive refractory material comprises ceramic. [The present invention 1025] 1. A method for generating ions, comprising: providing a filament within a chamber containing a gas; applying a first positive voltage to the filament relative to the chamber to heat the filament to a temperature causing thermionic emission and generating a plurality of thermoelectrons; ionizing the gas to generate positive ions in an ionization region of the chamber; The method comprising: [The present invention 1026] providing an acceleration grid within the chamber surrounded by the filament; applying a second positive voltage to the accelerating grid relative to the chamber, the second positive voltage being greater than the first positive voltage; The method of the present invention 1025, comprising: [The present invention 1027] 1027. The method of claim 1026, wherein the steps of applying the first positive voltage and applying the second positive voltage are simultaneous. [The present invention 1028] 1028. The method of any of claims 1025 to 1027, comprising maintaining a pressure in the chamber below 1 mTorr. [The present invention 1029] 1029. The method of any of claims 1025-1028, comprising maintaining a pressure in the chamber below 0.1 millitorr. [The present invention 1030] 1. A method for generating a nuclear reaction, comprising: providing a filament in a chamber containing a gas and a target in the chamber surrounding the filament; applying a first positive voltage to the filament relative to the chamber to heat the filament to a temperature causing thermionic emission and generating a plurality of thermoelectrons; ionizing the gas to generate positive ions in an ionization region of the chamber; The method comprising: [The present invention 1031] providing an acceleration grid within the chamber surrounded by the filament; applying a second positive voltage to the accelerating grid relative to the chamber, the second positive voltage being greater than the first positive voltage; The method of the present invention 1030, comprising: [The present invention 1032] 1032. The method of claim 1031, wherein the steps of applying the first positive voltage and applying the second positive voltage are simultaneous. [The present invention 1033] 1033. The method of claim 1031 or 1032, further comprising applying a negative voltage relative to the chamber to the retarder grid disposed between the acceleration grid and the target. [The present invention 1034] 1034. The method of claim 1033, wherein the steps of applying a first positive voltage, applying a second positive voltage, and applying a negative voltage are simultaneous. [This invention 1035] the acceleration grid and the retardation grid each include a plurality of openings configured to allow positive ions to pass therethrough; The method comprises: using a potential difference between the acceleration grid and the retardation grid to accelerate positive ions through the acceleration grid toward the retardation grid; further comprising: The method of the present invention 1033 or 1034. [The present invention 1036] further comprising incident positive ions on the target; the incident positive ions are implanted into the target or collide with previously implanted ions to generate fusion neutrons; Any of methods 1028 to 1033 of the present invention. [This invention 1037] 1034. The method of claim 1034, further comprising emitting secondary electrons from said target as a result of impinging incident ions on previously implanted ions. [The present invention 1038] 1036. The method of claim 1034 or 1035, comprising reflecting said secondary electrons from said retarder grid towards said target as a result of said negative voltage applied to said retarder grid. [This invention 1039] The method of any of claims 1030-1038, comprising maintaining a pressure in said chamber below 1 mTorr. [The present invention 1040] 1039. The method of any of claims 1030-1039, comprising maintaining a pressure in the chamber below 0.1 millitorr. Further features, advantages, and embodiments of the present disclosure can be learned from a study of the following detailed description, drawings, and claims. Moreover, it is to be understood that both the foregoing summary of the disclosure and the following detailed description are exemplary and intended to provide further explanation without further limiting the scope of the disclosure as claimed. [Brief explanation of the drawings]

[0013] The present disclosure will become more fully apparent from the following detailed description taken in conjunction with the accompanying drawings. [Figure 1] 1 shows a schematic diagram of an ion source and a neutron generator. [Figure 2A] 2 shows a cross-sectional view of the ion source and neutron generator of FIG. 1 including a filament guide. [Figure 2B] 2 shows a trimer cross-sectional view of the ion source and neutron generator of FIG. 1. [Figure 3] 2 shows an exploded cross-sectional view of the ion source of FIG. 1; [Figure 4] 2 shows a control system for the ion source of FIG. 1, the control system including a controller and a voltage source. DETAILED DESCRIPTION OF THE INVENTION

[0014] Detailed Description Before turning to the drawings showing specifically exemplary embodiments, it is to be understood that the present application is not limited to the details or methodology set forth in the specification or drawings, and that the terminology is for the purpose of description only and should not be regarded as limiting.

[0015] In one aspect, the ion source includes a filament 2, an acceleration grid 3, and a chamber supplied with gas. In another aspect, the neutron generator includes a filament 2, an acceleration grid 3, a suppression grid 4, a target 5, and a chamber supplied with gas. That is, a target 5 (and, in some embodiments, a suppression grid 4) can be added to the ion source (i.e., the filament 2 and the acceleration grid 3) to form a neutron generator. Both ion sources and neutron generators are within the scope of the present disclosure. All ion sources described herein can be used in the neutron generators described herein. The systems disclosed herein can also be described as ion sources and divergence accelerators, or as nuclear fusion reactors.

[0016] In one example of an ion source, the filament 2 is made of tungsten or a tungsten alloy, and the acceleration grid 3 is made of tungsten or a tungsten alloy. In one example of a neutron source, the filament 2 is made of tungsten or a tungsten alloy, the acceleration grid 3 is made of tungsten or a tungsten alloy, the suppression grid 4 is made of tungsten or a tungsten alloy, and the target 5 is made of titanium or a titanium alloy (optionally lined with a metal with low hydrogen solubility, such as stainless steel). Various other materials and preferred properties of materials are provided in detail below.

[0017] As shown in FIGS. 1 and 2A, the chamber of the ion source and / or neutron generator has a circular cross-section (i.e., the chamber can be cylindrical or spherical). FIG. 2B shows an oblique cross-section of an ion source and / or neutron generator having a circular shape in an embodiment, i.e., in the embodiment, the filament 2, acceleration grid 3, suppression grid 4, and / or target 5 are each cylindrically shaped. However, the shape of the chamber is not so limited in other embodiments. In other examples (not shown), the chamber may have a shape such as a cube, rectangular parallelepiped, pyramid, or cone. The shape of the chamber may be customized to suit the particular application for 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. The ion source 10 is easy to construct and easier to replace than conventional ion sources.

[0018] filament The filament 2 is located near the center of the chamber of the ion source and / or neutron generator. The filament 2 is connected to a voltage source 20 configured to apply a predetermined positive voltage to the filament 2 (described in more detail below), thereby heating the filament 2. The filament 2 is a high-current thermionic emitter in the illustrated embodiment. In some embodiments, field-induced emission (e.g., uniform field emission) is used in addition to or instead of thermionic emission. In thermionic emission, the filament 2 is heated to provide the minimum energy required to overcome the attractive forces holding the electrons to the filament 2, resulting in the emission of electrons (thermal electrons) from the filament 2. The minimum energy (i.e., work function) is defined as the minimum thermodynamic work required to remove electrons from a solid surface (i.e., the filament 2) to a point within the chamber just outside the filament 2. The work function depends on the material properties of the filament 2 and the contamination state of the surface of the filament 2. The filament 2 can be made of any material that can be heated to provide electrons with minimal energy without melting. Preferably, filament 2 is made of a material with a low work function so that a large number of thermal electrons are emitted. For example, filament 2 can be made of a metal (e.g., tungsten or a tungsten alloy). In various embodiments, the material of filament 2 is characterized by high electron emissivity, low vapor pressure, high melting temperature, and resistance to ablation and sputtering. In various embodiments, filament 2 can be composed of lanthanum hexaboride, cerium hexaboride, thoriated tungsten, barium aluminate, or a mixture of any two or more thereof.

[0019] As shown in FIGS. 2A-2B , in some examples of ion sources and / or neutron generators, the filament 2 is optionally provided in one or more filament guides 2 a configured to maintain filament spacing and provide mechanical support to keep the filament 2 stationary along the entire length of the device. In one example, the filament guide 2 a may include a plurality of openings 2 b (e.g., holes, slots, etc.) configured to receive portions of the filament 2 therein (e.g., the filament 2 threads into and out of the openings). In this example, the openings 2 b may be uniformly or non-uniformly spaced along the opening-equipped filament guide 2 a, and the filament 2 may be received in all or some of the openings 2 b. The opening-equipped filament guide 2 a is made of a non-conductive refractory material. In some embodiments, the non-conductive refractory material may be ceramic. Exemplary glasses include glass, clay, and metal oxides. As a specific example, the filament 2 may be tungsten or a tungsten alloy, and the filament guide may be made of ceramic.

[0020] In some examples, the ion source 10 includes only one filament 2. In other examples, the ion source 10 may include multiple filaments 2 supported at intervals along a filament guide. In other embodiments, other approaches and / or structures for emitting electrons within the chamber may be used, and the systems and methods herein may be adapted accordingly.

[0021] Acceleration Grid An acceleration grid 3 is at least partially surrounded by the filament 2. The filament 2 and acceleration grid 3 may be concentric, but are not required to be. In some examples, the acceleration grid 3 may be a solid material including a plurality of openings (i.e., holes, slots, etc.) spaced along its length. In other examples, the acceleration grid 3 may be a framework or mesh including a first set of parallel strips or threads of material extending in a first direction (e.g., along the length of the chamber) and a second set of strips or threads of material intersecting and crossing the first set of parallel strips such that openings are provided between the first and second sets. The openings are configured to allow positive ions (e.g., hydrogen ions) generated in the ionization region (e.g., between the acceleration grid 3 and the filament 2) to pass through the acceleration grid 3 and be collected (an ion source) or accelerated toward the suppression grid 4 and target 5 (a neutron generator).

[0022] In some examples, the acceleration grid 3 is made of the same material as the filament 2. In other examples, the acceleration grid 3 is made of a different material than the filament 2. The acceleration grid 3 may be made of an electrically conductive material and resistant to ion damage. The acceleration grid 3 may also 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.

[0023] The accelerating grid 3 is connected to a voltage source 20 configured to apply a predetermined positive voltage to the accelerating grid 3. The potential of the accelerating grid 3 is higher (more positive) than the potential of the filament 2. For example, the predetermined voltage applied to the accelerating grid may be +100,100 V, while the predetermined voltage applied to the filament 2 may be +100,000 V. The potential difference (voltage bias) causes the thermoelectrons emitted by the filament 2 to accelerate 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 traps the energetic thermoelectrons (electrons) generated by the thermionic emission of the filament 2. While the thermoelectrons may be reabsorbed by the filament 2, those with sufficient energy are captured (trapped between the filament 2 and the accelerating grid 3). The captured energetic thermoelectrons circulate through the ionization region long enough to collide with low-density neutral gas molecules according to the following reaction: M+e - →M +· +2e - (3) where M is a gas molecule and e - are electrons (thermal electrons) that interact with gas molecules and transfer energy greater than the ionization energy of the molecules such that electrons are ejected from the gas molecules (electron ionization).

[0024] Alternatively, 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, generating multiple thermionic electrons. The second positive voltage is greater (more positive) than the first positive voltage. The multiple thermionic electrons are configured to ionize the gas and generate positive ions in an ionization region within the chamber, including the region between the filament and the accelerating grid. The first and second positive voltages are maintained substantially higher than the voltage of the chamber walls, which may be held at ground potential. This creates a recirculating electron trap in the center of the device, where electrons oscillate back and forth, causing ionization of the low-pressure background gas. The ions generated in this region are accelerated outward toward the walls of the structure by the electric field configuration.

[0025] Gaseous molecules (e.g., hydrogen) ionized by collisions with high-energy thermal electrons in the ionization region impart a positive charge to the ionization region, thereby reducing the negative charge of the accumulated electron space charge generated by the thermal electron current. The vacuum level in the acceleration region 3 is generated by an external vacuum source and maintained at a level that reduces the likelihood of collisions with neutral particles in the ionization region. For example, the gas pressure in the ionization region can be 10 mTorr or less, e.g., 5 mTorr or less, or 1 mTorr or less. A lower gas pressure in the ionization region increases the ion or neutron yield by reducing the likelihood that ions will collide with gas molecules before being collected or before entering the target 5 and generating neutrons.

[0026] Suppression Grid In a neutron generator, the suppression grid 4 at least partially surrounds the filament 2. The suppression grid 4, filament 2, and acceleration grid 3 are concentric. The suppression grid 4 is made of the same material as the acceleration grid 3. Like the acceleration grid 3, in some examples, the suppression grid 4 can be a solid material including a plurality of openings (i.e., holes, slots, etc.) spaced along its length. In other examples, the suppression grid 4 can be a framework or mesh including a first set of parallel strips or threads of material extending in a first direction (e.g., along the length of the chamber) and a second set of strips or threads of material intersecting and crossing the first set of parallel strips such that openings are provided between the first and second sets. The locations of the openings in the suppression grid 4 correspond to the locations of the openings in the acceleration grid 3. The openings in 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 accelerate toward the target 5.

[0027] The suppression grid 4 is connected to a voltage source 20, which is configured to apply a predetermined negative voltage to the suppression grid 4 (described in more detail below). As positive ions in the region between the acceleration grid 3 and the filament 2 drift near 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 can be used to achieve a similar effect to that provided by the suppression grid 4.

[0028] The suppression grid 4 is made of a conductive material that can be resistant to ion damage, such as a high-mass metal. The suppression grid 4 may also 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.

[0029] target In a neutron generator, the target 5 at least partially surrounds the suppression grid 4 (e.g., the target 5 may not surround the regions 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 target 5 material may be selected so that, when fully loaded, there is a 1:1 to 2:1 ratio between the hydrogen provided to the target 5 and the material from which the target 5 is made. The target 5 material may be a conductive metal or metalloid with an affinity for absorbing hydrogen, preferably a low-mass 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.

[0030] In some examples, the target 5 is (or is integrated into) the wall of the chamber itself. In other examples, the target 5 is a layer provided on the interior surface of the chamber or on the exterior surface of the chamber. In examples where the target 5 is a layer, the target 5 may optionally be lined with 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.

[0031] The target 5 is not connected to the voltage source 20 and is held at ground potential (substantially 0 V). After traveling outward through the openings in the acceleration grid 3 and the suppression grid 4, the positive ions enter the region between the suppression grid 4 and the target 5. In this region, the positive ions stop accelerating and travel ballistically until they strike the target 5. The incident ions are either injected into the target 5 or collide with previously injected ions to generate fusion neutrons. In the example of a neutron generator in which the positive ions generated by the ionizing energy are hydrogen isotopes, a hydrogen concentration builds up on the target 5 such that a hydrogen isotope from reactions (1) and (2) above can collide with another hydrogen isotope on the target 5 to generate neutrons.

[0032] When energetic ions strike the target 5, approximately two to three secondary electrons may be emitted from the surface of the target 5, which is held at a potential slightly higher than that of the suppression grid 4. The potential difference between the target 5 and the suppression grid 4 causes the secondary electrons to be reflected back to the target 5, reducing electron heating of the acceleration grid 3 and preventing unwanted electron currents in the ionization region provided between the acceleration grid 3 and the filament 2. In other embodiments, a magnetic field can be used to achieve an effect similar to that provided by the suppression grid 4.

[0033] Voltage Sources and Controllers A voltage source 20 is provided external to the chamber. The voltage source 20 may be any known voltage source. A controller 30 is provided and may be programmed to independently control the voltages supplied to each of the filament 2, acceleration grid 3, and suppression grid 4. The controller 30 may vary the voltages supplied to each of the filament 2, acceleration grid 3, and suppression grid 4 to tune the system or vary the ion or neutron yield. A control panel or display may be provided to allow a user to select different individual voltages supplied to each of the filament 2, acceleration grid 3, and suppression grid 4.

[0034] As described above, the target 5 is held at ground potential, the suppression grid 4 is held at a slightly negative voltage relative to ground, the acceleration grid 3 is held at a high positive voltage relative to ground, and the filament 2 is held at a slightly positive voltage relative to the voltage of the acceleration grid 3. This electronic configuration reduces the possibility of unwanted electrical arcing and protects the filament 2 from damage due to arcing or high-energy electron currents.

[0035] In the example of a neutron generator where the chamber is cylindrical, a cylindrical neutron generator of a given length (determined by the particular application) is configured to generate an axially aligned, uniform, isotropic neutron flux. The cylindrical arrangement of components allows the neutron generator to generate high ion current densities without space charge limitations.

[0036] The configuration of the ion source and / or neutron generator as shown in the various exemplary embodiments is merely exemplary. While only a few embodiments are described in detail in this disclosure, many modifications are possible (e.g., the size, dimensions, structure, shape, and proportions of various elements, parameter values, mounting arrangements, material use, color, orientation, image processing and segmentation algorithms, etc.) without substantially departing from the novel teachings and advantages of the subject matter described herein. Some elements shown as integrally formed may be composed of multiple parts or elements, the location of elements may be reversed or changed, and the nature or number of discrete elements or locations may be modified or varied. The order or sequence of any process, logic algorithm, or method steps may be changed or re-sequenced according to alternative embodiments. Other substitutions, modifications, changes, and omissions may be made in the design, operating conditions, and arrangement of the preferred and other exemplary implementations without departing from the scope of the appended claims.

[0037] As used herein, the terms "approximately," "about," "substantially," and similar terms are intended to have a broad meaning consistent with common and accepted usage by those of ordinary skill in the art to which the subject matter of this disclosure pertains. Those of ordinary skill in the art who consider this disclosure will understand that these terms are intended to enable description of particular features described and claimed without limiting the scope of those features to the precise numerical ranges provided. Accordingly, these terms should be interpreted to indicate that insubstantial or insignificant modifications or variations of the subject matter described and claimed are considered to be within the scope of the invention as set forth in the appended claims.

[0038] As used herein, the terms "coupled" and "connected" mean the joining of two members directly or indirectly to one another. Such joining can be static (e.g., permanent) or movable (e.g., removable or releasable). Such joining can be achieved by the two members, or the two members and any additional intermediate members, being a single unit with one another, or by adhesively bonding the two members, or the two members and any additional intermediate members, to one another.

[0039] References herein to the location of elements (e.g., "top," "bottom," "above," "below," etc.) are merely used to describe the orientation of various elements in the figures. It should be noted that the orientation of various elements may differ according to other exemplary embodiments, and such variations are intended to be included in the present disclosure.

[0040] With respect to the use of virtually any plural and / or singular term herein, those skilled in the art can convert from the plural to the singular and / or from the singular to the plural as appropriate to the context and / or application. For clarity, the various singular / plural permutations may be expressly indicated.

[0041] Embodiments of the subject matter and operations (e.g., voltage control) described herein can be implemented in digital electronic circuitry, or computer software embodied on tangible media, firmware, or hardware, including the structures disclosed herein and their structural equivalents, or one or more combinations thereof. Embodiments of the subject matter described herein can be implemented as one or more computer programs, i.e., one or more modules of computer program instructions encoded on one or more computer storage media for execution by or to control the operation of a data processing device. Alternatively, or in addition, the program instructions can be encoded in an artificially generated propagated signal, e.g., a machine-generated electrical, optical, or electromagnetic signal generated to encode information for transmission to a suitable receiver device for execution by the data processing device. A computer storage medium can be, or can be included in, a computer-readable storage device, a computer-readable storage substrate, a random or serial access memory array or device, or one or more combinations thereof. Furthermore, while a computer storage medium is not a propagated signal, a computer storage medium can be a source or destination of computer program instructions encoded in an artificially generated propagated signal. A computer storage medium may also be, or may be contained in, one or more separate components or media (e.g., multiple CDs, disks, or other storage devices). Thus, a computer storage medium may be tangible and non-transitory.

[0042] The operations described herein may be implemented to be performed by a data processing device or circuitry for processing data stored in one or more computer-readable storage devices or received from other sources.

Claims

1. 1. A method for generating ions, comprising: providing a filament within a chamber containing a gas; applying a first positive voltage to the filament relative to the chamber to heat the filament to a temperature causing thermionic emission and generating a plurality of thermoelectrons; ionizing the gas to generate positive ions in an ionization region of the chamber; allowing the positive ions to pass through an accelerating grid and an open central region of the chamber surrounded by the accelerating grid; The method comprising:

2. providing the acceleration grid within the chamber surrounded by the filament; applying a second positive voltage to the accelerating grid relative to the chamber, the second positive voltage being greater than the first positive voltage; The method of claim 1 , comprising:

3. 3. The method of claim 2, wherein the steps of applying the first positive voltage and applying the second positive voltage are simultaneous.

4. the acceleration grid surrounds the open central region of the chamber and includes a plurality of openings spaced apart about the open central region of the chamber; the method including passing the positive ions through the acceleration grid through the plurality of openings and through the open central region of the chamber. The method of claim 2.

5. The method of claim 1 , comprising maintaining a pressure in the chamber below 1 milliTorr.

6. The method of claim 1 , comprising maintaining a pressure in the chamber below 0.1 millitorr.

7. 1. A method for generating a nuclear reaction, comprising: providing a filament in a chamber containing a gas and a target in the chamber surrounding the filament; applying a first positive voltage to the filament relative to the chamber to heat the filament to a temperature causing thermionic emission and generating a plurality of thermoelectrons; ionizing the gas to generate positive ions in an ionization region of the chamber; allowing the positive ions to pass through an accelerating grid and an open central region of the chamber surrounded by the accelerating grid.

8. providing the acceleration grid within the chamber surrounded by the filament; applying a second positive voltage to the accelerating grid relative to the chamber, the second positive voltage being greater than the first positive voltage; The method of claim 7, comprising:

9. the acceleration grid surrounds the open central region of the chamber and includes a plurality of openings spaced apart about the open central region of the chamber; the method including passing the positive ions through the acceleration grid through the plurality of openings and through the open central region of the chamber. The method of claim 8.

10. applying a second positive voltage to the accelerating grid to form a recirculating electron trap in which electrons oscillate back and forth in the open central region of the chamber; the recycling electron capture causes ionization of the gas within the open central region; 10. The method of claim 9.

11. 9. The method of claim 8, wherein the steps of applying the first positive voltage and applying the second positive voltage are simultaneous.

12. The method of claim 8 , further comprising applying a negative voltage relative to the chamber to a suppression grid disposed between the acceleration grid and the target.

13. 13. The method of claim 12, wherein the steps of applying the first positive voltage, applying the second positive voltage, and applying the negative voltage are simultaneous.

14. the acceleration grid and the retardation grid each include a plurality of openings configured to allow positive ions to pass therethrough; The method comprises: using a potential difference between the acceleration grid and the retardation grid to accelerate the positive ions through the acceleration grid toward the retardation grid; further comprising: The method of claim 12.

15. further comprising incident positive ions on the target; the incident positive ions are implanted into the target or collide with previously implanted ions to generate fusion neutrons; 15. The method of claim 14.

16. 16. The method of claim 15, further comprising emitting secondary electrons from the target as a result of bombarding previously implanted ions with incident positive ions.

17. 17. The method of claim 16, comprising reflecting the secondary electrons from the retarder grid toward the target as a result of the negative voltage applied to the retarder grid.

18. The method of claim 7 , comprising maintaining a pressure in the chamber below 1 milliTorr.

19. The method of claim 7 , comprising maintaining a pressure in the chamber below 0.1 millitorr.

20. providing the filament within the chamber includes arranging the filament to extend along a first direction extending between a first end and a second end of the chamber; The method comprises: providing an acceleration grid within the chamber surrounding the open central region, the acceleration grid including a plurality of openings spaced apart around the open central region of the chamber and extending in the first direction; providing a plurality of additional filaments within the chamber, the plurality of additional filaments oriented along the first direction and oriented such that the filament and the plurality of additional filaments are spaced apart around a periphery of the acceleration grid within the chamber; applying the first positive voltage to the plurality of additional filaments; passing the positive ions through the plurality of openings into the open central region of the chamber at the accelerating grid; The method of claim 7, comprising:

Images