Ion source and neutron generator

Abstract

A nuclear reaction generator includes a chamber configured to contain a gas and to contain a target. The nuclear reaction generator also includes a filament disposed 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 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 is configured such that a nuclear reaction occurs when the positive ions interact with the target.

Description

[0001] This application is a divisional application of the patent application for invention titled "Ion Source and Neutron Generator" with the application number CN201980096485.X, the filing date of September 6, 2019.

[0002] Cross - Reference to Related Applications

[0003] This application claims the benefit of priority of U.S. Provisional Patent Application No. 62 / 836,481, filed on April 19, 2019, the entire content of which is incorporated herein by reference. Technical Field

[0004] The present technology generally relates to an ion source and an accelerator sharing 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 to produce a nuclear reaction that results in neutron production. Accordingly, the present technology may also relate to systems and methods for using the ion source to generate nuclear reactions. Background Art

[0005] This section is intended to provide background or context for the present invention as claimed in the claims. The descriptions herein may include concepts that may be practicable, but are not necessarily concepts that have been previously conceived or practiced. Thus, unless otherwise indicated herein, the materials described in this section are not prior art to the descriptions and claims in this application and are not admitted to be prior art merely by virtue of their inclusion in this section.

[0006] Ion sources typically include a chamber in which ionization occurs, a gas disposed in the chamber, and an ionization energy source. Conventional high-current ion generation methods are generally limited to generating a plasma by 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 for generating a plasma generally require a relatively high gas pressure 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 are generated.

[0007] Ions generated by an ion source can be used for a variety of applications, including but not limited to particle accelerators for mass spectrometry, medical devices and diagnostics, and semiconductor manufacturing. The ions generated by the ion source can be accelerated towards a target and used to produce nuclear reactions, including nuclear reactions that produce neutrons. Conventional neutron sources use discrete devices for the ionization of ionizing material, acceleration, and target fusion. These neutron sources can incorporate the application of various ion generation methods, as well as functions specific to particle accelerators, 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 non-destructive testing and evaluation of materials. These devices have many drawbacks, either limiting their available ion current, resulting in a neutron yield insufficient for many applications, or being very complex and thus difficult and expensive to build, maintain, and operate.

[0008] In one example, neutrons can be generated by the steps of: generating 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:

[0009] D + T → n + 4 He E n = 14.1 MeV (1)

[0010] D + D → n + 3 He E n = 2.5 MeV (2)

[0011] Neutron sources based on reactions (1) and (2) are typically single-beam, linear electrostatic devices that introduce significant ion losses during transmission, resulting in overheating and reduced neutron yield.

[0012] Improved techniques related to ion sources and methods for producing high ion generation rates at low background pressures are needed, which will allow for increased ion yield and long-term continuous operation without substantial maintenance or support equipment. Summary of the Invention

[0013] In one aspect, an ion source includes a chamber containing a gas; a filament disposed near the center of the chamber; an acceleration 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 acceleration 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 the first positive voltage (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 the region between the filament and the acceleration 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 circulating electron trap where electrons oscillate back and forth at the center of the device, resulting in ionization of the 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 can be less than 1 millitorr. In other embodiments, the pressure in the chamber can be less than 0.1 millitorr.

[0014] 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 stated, voltages herein are applied / reference / measured / etc. relative to the chamber, 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 the region between the filament and the acceleration 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 circulating electron trap where electrons oscillate back and forth at the center of the device, resulting in ionization of the 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. The suppression grid will prevent secondary electrons generated from ion-wall collisions from being accelerated toward the center of the device - this effect would consume power and reduce efficiency.

[0015] In a third aspect, a method for generating ions includes disposing a filament and an acceleration grid in a chamber containing a gas, the acceleration 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 acceleration 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 acceleration grid. The thermions may be trapped in the ionization region.

[0016] In a fourth aspect, a method for generating neutrons includes disposing a filament, an acceleration grid, a suppression 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 acceleration 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 acceleration grid. In the fourth aspect, the acceleration grid is concentric with the filament and surrounded by the filament, the suppression grid is concentric with the filament and surrounds the filament, and the target is concentric with the suppression grid and surrounds the suppression grid. The method may further include applying a negative voltage to the suppression grid. The method may even further include impinging the positive ions passing through the suppression grid on the target. The impinging positive ions are implanted into the target or impinge on previously implanted ions to produce fusion neutrons. Additionally, secondary electrons may be emitted from the target due to the impinging ions impinging on previously implanted ions. Due to the potential difference between the filament and the acceleration grid, the thermions may be trapped between them. Due to the potential difference between the target and the suppression grid to which the negative voltage is applied, secondary electrons may be reflected from the suppression grid toward the target.

[0017] Additional features, advantages, and embodiments of the present disclosure may be set forth from a consideration of the following detailed description, the drawings, and the claims. Further, it is to be understood that both the foregoing summary of the present disclosure and the following detailed description are exemplary and are intended to provide further explanation without limiting the scope of the claimed present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present disclosure will be more fully understood from the following detailed description in conjunction with the accompanying drawings, in which:

[0019] Figure 1 A schematic diagram of an ion source and a neutron generator is shown.

[0020] Figure 2A showing a Figure 1Cross-sectional view of the ion source and the neutron generator.

[0021] Figure 2B Shows Figure 1 Stereoscopic cross-sectional view of the ion source and the neutron generator.

[0022] Figure 3 Shows Figure 1 Exploded contour view of the ion source.

[0023] Figure 4 Shows a control system for Figure 1 the ion source, wherein the control system includes a controller and a voltage source. Detailed Description

[0024] Before turning to the drawings that illustrate 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 terms are for descriptive purposes only and should not be considered limiting.

[0025] In one aspect, the ion source includes a chamber in which a filament 2, an acceleration grid 3, and a gas are disposed. In another aspect, the neutron generator includes a chamber in which a filament 2, an acceleration grid 3, a suppression grid 4, a target 5, and a gas are disposed. That is, the target 5 (and, in some embodiments, the 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 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 systems disclosed herein can also be described as an ion source and a divergence accelerator or a fusion reactor.

[0026] In one example of the ion source, the filament 2 is composed of tungsten or a tungsten alloy and the acceleration grid 3 is composed of tungsten or a tungsten alloy. In one example of the neutron source, the filament 2 is composed of tungsten or a tungsten alloy and the acceleration grid 3 is composed of tungsten or a tungsten alloy, the suppression grid 4 is composed of tungsten or a tungsten alloy and the target 5 is composed of titanium or a titanium alloy (and optionally backfilled with a low hydrogen solubility metal such as stainless steel). Various other materials and preferred properties of the materials are provided in detail below.

[0027] As Figure 1 and 2A shown, the chamber of the ion source and / or the neutron generator has a circular cross-section (i.e., the chamber can be cylindrical or spherical). Figure 2BShows a perspective cross-sectional view of an ion source and / or neutron generator in an embodiment having a cylindrical shape (i.e., in an embodiment where the filament 2, acceleration grid 3, suppression grid 4, and / or target 5 are each formed in a cylindrical shape). However, in other embodiments, the geometry of the chamber is not limited in this regard. However, in other instances (not shown), the chamber may have the shape of a cube, cuboid, pyramid, cone, etc. The geometry of the chamber can be customized to suit the particular application in which the ion source is used. In some instances, the chamber may be symmetric about its central axis. In other instances, the chamber may not be symmetric about its central axis. Compared with conventional ion sources, the ion source 10 is easy to construct and easy to replace.

[0028] filament

[0029] 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 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 minimum energy required for electrons to overcome the attraction holding the electrons on the filament 2, thereby causing the release of electrons (thermions) from the filament 2. The minimum energy (i.e., work function) is defined as the minimum thermodynamic work required to move an electron from the solid surface (i.e., the filament 2) to a point immediately outside the filament 2 in the chamber. The work function is a characteristic of the material of the filament 2 and the state of contamination 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 electrons without melting. Preferably, the filament 2 is made of a material having a low work function so that a large number of thermoelectrons are emitted. For example, the filament 2 can be made of a metal (e.g., tungsten or tungsten alloy). In various embodiments, the material of the filament 2 is characterized by a 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, thorium tungsten, barium aluminate, or a mixture of any two or more thereof.

[0030] Reference Figure 2A - 2B, in some examples of ion sources and / or neutron generators, the filament 2 can optionally be disposed within one or more filament guides 2a configured to maintain filament spacing and provide mechanical support to suspend the filament 2 above the length of the device. In one example, the filament guide 2a can include a plurality of holes 2b (e.g., holes, slots, etc.), the plurality of holes being configured to receive a portion of the filament 2 therein (e.g., threading the filament 2 into and out of the holes). In this example, the holes 2b can be spaced evenly or unevenly along the filament guide 2a having the holes, and the filament 2 can be received within all or a subset of the holes 2b. The filament guide 2a having the holes 2b can be made of a non-conductive refractory material. In some embodiments, the non-conductive refractory material can be ceramic. Exemplary ceramics include glass, clay, and metal oxides. In a particular example, the filament 2 can be made of tungsten or a tungsten alloy and the filament guide can be made of ceramic.

[0031] In some examples, the ion source 10 includes one and only one filament 2. In other examples, the ion source 10 can include a plurality of filaments 2 spaced along and supported by the filament guide. In other embodiments, other methods and / or structures for emitting electrons in a chamber can be used and the systems and methods herein can be modified accordingly.

[0032] Acceleration grid

[0033] The acceleration grid 3 is at least partially surrounded by the filament 2. The filament 2 and the acceleration grid 3 can be concentric, although this is not required. In some examples, the acceleration grid 3 can be a solid material that includes a plurality of holes (i.e., holes, slots, etc.) spaced along its length. In other examples, the acceleration grid 3 can be a frame or grid that includes a first set of parallel bars or lines of material extending in a first direction (e.g., along the length of the chamber) and a second set of bars or lines of material that intersect and cross the first set of parallel bars, thereby defining holes therebetween. The holes 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 to be collected (ion source) or accelerated towards the suppression grid 4 and the target 5 (neutron generator).

[0034] 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 is made of a conductive material and can resist ion damage. The acceleration 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.

[0035] The accelerating grid 3 is connected to a voltage source 20 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 can be +100100 V, while the predetermined voltage applied to the filament 2 can be +100000 V. Due to the potential difference (voltage bias), the thermoelectrons 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 limits the high-energy thermoelectrons (electrons) generated by thermoelectron emission through the filament 2. The thermoelectrons can be reabsorbed by the filament 2, but the thermoelectrons with sufficient energy will be trapped (confined between the filament 2 and the accelerating grid 3). The trapped high-energy thermoelectrons circulate in the ionization region for a long enough time to strike the low-density neutral gas molecules according to the following reaction:

[0036] M + e - → M +· + 2e – (3)

[0037] where M is a gas molecule and e - is an electron (thermoelectron) that interacts with the gas molecule and transfers energy greater than the ionization energy of the molecule, causing the electron to be ejected from the gas molecule (electron ionization).

[0038] 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 multiple thermions are generated. The second positive voltage is greater than the first positive voltage (more positive than the first positive voltage). The multiple thermions are configured to ionize the gas to generate positive ions in the ionization region in the chamber, including the region located between the filament and the accelerating grid. The first positive voltage and the second positive voltage are substantially maintained above the voltage at the wall of the chamber, which can be maintained at ground potential. This creates a circulating electron trap where electrons oscillate back and forth in the center of the device, resulting in the ionization of the low-pressure background gas. Due to the electric field configuration, the ions generated in the region will be accelerated outward toward the wall of the structure.

[0039] Gaseous molecules (e.g., hydrogen) ionized by collision with high-energy hot electrons in the ionization region contribute positive charge to the ionization region, thereby reducing the negative potential of the accumulated electron space charge generated by the thermionic current. The vacuum level within the acceleration grid 3 is generated by an external vacuum source and maintained at a level that reduces the likelihood of collision with neutral particles within the ionization region. For example, the gas pressure within the ionization region can be less than or equal to 10 mTorr, e.g., less than or equal to 5 mTorr or less than or equal to 1 mTorr. The low gas pressure within the ionization region increases the ion yield or neutron yield because the likelihood of ions colliding with gas molecules before collection or before striking the target 5 to generate neutrons is reduced.

[0040] Suppression grid

[0041] In the neutron generator, the 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 instances, the suppression grid 4 can be a solid material that includes a plurality of holes (i.e., holes, slots, etc.) spaced along its length. In other instances, the suppression grid 4 can be a frame or grid that includes a first set of parallel bars or lines of material extending in a first direction (e.g., along the length of the chamber) and a second set of bars or lines of material that intersect and cross the first set of parallel bars, thereby defining holes between the first and second sets. The positions of the holes in the suppression grid 4 correspond to the positions of the holes in the acceleration grid 3. The holes 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 be accelerated toward the target 5.

[0042] The suppression grid 4 is connected to a voltage source 20 configured to apply a negative predetermined voltage to the suppression grid 4 (discussed in more detail below). When positive ions within 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 an effect similar to that provided by the suppression grid 4.

[0043] The suppression grid 4 is made of a conductive material and can resist ion damage, such as a 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.

[0044] Target

[0045] 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 can be made of a solid metal hydride forming material. The material of the target 5 can be selected such that when fully loaded, there is a ratio of 1:1 to 2:1 between the hydrogen set on the target 5 and the material used to fabricate the target 5. The material of the target 5 can be a conductive metal or semimetal having a hydrogen absorption affinity, preferably a low-mass material with a very small nuclear interaction cross-section. For example, the target 5 can be made of carbon, aluminum, titanium, magnesium, zirconium, yttrium, scandium, erbium, or a mixture or alloy of any two or more thereof.

[0046] In some instances, the target 5 is the wall of the chamber itself (or is integrated into the wall). In other instances, the target 5 is a layer disposed on the inner surface or the outer surface of the chamber. In instances where the target 5 is a layer, the target 5 can optionally be backed by a low-hydrogen solubility metal, or the low-hydrogen solubility metal can form the wall of the chamber itself. The low-hydrogen solubility metal can be stainless steel.

[0047] The target 5 is not connected to the voltage source 20 and is maintained at ground potential (substantially 0V). 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 strike the target 5. The impinging ions are either implanted into the target 5 or strike previously implanted ions to generate fusion neutrons. In an example of a neutron generator where the positive ions generated at ionization energy are hydrogen isotopes, a hydrogen concentration accumulates on the target 5 such that the hydrogen isotopes have the opportunity to collide with another hydrogen isotope on the target 5 to generate neutrons according to the above reactions (1) and (2).

[0048] When high-energy ions strike the target 5, the surface of the target 5 emits approximately 2 - 3 secondary electrons, which are held at a potential slightly higher than that 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 unwanted electron currents in the ionization region disposed 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.

[0049] Voltage Source and Controller

[0050] The voltage source 20 is disposed outside the chamber. The voltage source 20 can be any known voltage source. The controller 30 can be set 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 can change the voltage supplied to each of the filament 2, the acceleration grid 3, and the suppression grid 4 to adjust the system or change the ion or neutron yield. A control panel or display can be provided to allow a user to select individual, different voltages to be supplied to each of the filament 2, the acceleration grid 3, and the suppression grid 4.

[0051] As described above, the target 5 is held at ground potential, while the suppression grid 4 is held at a voltage slightly negative with respect to the ground potential. The acceleration grid 3 is held at a high positive voltage with respect to the ground potential, and the filament 2 is held at a voltage slightly positive with respect to the voltage of the acceleration grid 3. This electron arrangement reduces the likelihood of unwanted arc discharges and protects the filament 2 from damage by arcs or high-energy electron currents.

[0052] In an example of a neutron generator in which the chamber is cylindrical, a cylindrical neutron generator of a predetermined length (determined according to a particular application) is configured to produce an axially aligned, uniform, and isotropic neutron flux. The cylindrical arrangement of the components allows the neutron generator to produce a high ion current density without being limited by space charge.

[0053] As shown in the various exemplary embodiments, the construction and arrangement of the ion source and / or neutron generator are merely illustrative. Although only a few embodiments are described in detail in this disclosure, many modifications are possible without materially departing from the novel teachings and advantages of the described subject matter (e.g., changes in the size, dimensions, structure, shape and proportions, parameter values, mounting arrangements, use of materials, colors, orientations, image processing and segmentation algorithms, etc. of the various elements). Elements shown as integrally formed can be composed of multiple parts or elements, the positions of the elements can be reversed or otherwise changed, and the nature or number of discrete elements or positions can be altered or changed. According to alternative embodiments, the order or sequence of any process, logical algorithm, or method step can be changed or reordered. Other alternatives, modifications, changes, and omissions can also be made in the design, operating conditions, and arrangements of the various exemplary embodiments without departing from the scope of the present invention.

[0054] As used herein, the terms “about,” “approximately,” “substantially,” and similar terms are intended to have a broad meaning consistent with the 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 reviewing this disclosure will understand that these terms are intended to allow for the description of certain features described and claimed without restricting the scope of these features to the precise numerical ranges provided. Accordingly, these terms should be interpreted to indicate that non-substantive or immaterial modifications or alterations to the described and claimed subject matter are considered to be within the scope of the invention as set forth in the appended claims.

[0055] As used herein, the terms “coupled,” “connected,” etc. mean that two components are directly or indirectly connected to each other. Such an engagement may be fixed (e.g., permanent) or movable (e.g., removable or releasable). Such an engagement may be achieved by integrally forming two components or two components and any additional intermediate components with each other into a single unitary body, or by attaching two components or two components or any additional intermediate components to each other.

[0056] References herein to the position of elements (e.g., “top,” “bottom,” “above,” “below,” etc.) are for purposes of describing the orientation of the respective elements in the drawings only. It should be noted that, depending on other exemplary embodiments, the orientation of the respective elements may be different, and such variations are intended to be covered by this disclosure.

[0057] Regarding the use of substantially any plural and / or singular terms herein, those of ordinary skill in the art may convert the plural to the singular and / or the singular to the plural, as appropriate, based on the circumstances and / or application. For clarity, various singular / plural conversions may be set forth herein explicitly.

[0058] Embodiments of the subject matter and the operations described in this specification, e.g., voltage control, may be implemented in digital circuitry, or in computer software embodied in a tangible medium, firmware, or hardware (including the structures disclosed in this specification and their structural equivalents), or in a combination of one or more of them. Embodiments of the subject matter described in this specification may 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 apparatus. Alternatively or additionally, the program instructions may be encoded on an artificially generated propagated signal, e.g., a machine-generated electrical, optical, or electromagnetic signal, that is generated to encode information for transmission to a suitable receiver apparatus for execution by the data processing apparatus. A computer storage medium may be, or be included 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 of them. Moreover, while a computer storage medium is not a propagated signal, a computer storage medium may be a source or destination of computer program instructions encoded in an artificially generated propagated signal. The computer storage medium may also be or be included 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.

[0059] 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. A method for generating ions, the method comprises: providing a filament in a chamber containing a gas; applying a first positive voltage to the filament relative to the chamber to heat the filament to a temperature at which thermionic emission occurs and a plurality of thermions are generated; and ionizing the gas to generate positive ions in an ionization region of the chamber.

2. The method according to claim 1, which comprises: providing an acceleration grid in the chamber, the acceleration grid being surrounded by the filament; applying a second positive voltage to the acceleration grid relative to the chamber, the second positive voltage being greater than the first positive voltage.

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

4. The method according to any one of claims 1 - 3, which comprises maintaining the pressure in the chamber at less than 1 millitorr.

5. The method according to any one of claims 1 - 4, which comprises maintaining the pressure in the chamber at less than 0.1 millitorr.

6. A method for generating a nuclear reaction, the method comprises: providing a filament in a chamber containing a gas and providing a target at the chamber, the target surrounding the filament; applying a first positive voltage to the filament relative to the chamber to heat the filament to a temperature at which thermionic emission occurs and a plurality of thermions are generated; and ionizing the gas to generate positive ions in an ionization region of the chamber.

7. The method according to claim 6, which comprises: providing an acceleration grid in the chamber, the acceleration grid being surrounded by the filament; applying a second positive voltage to the acceleration grid relative to the chamber, the second positive voltage being greater than the first positive voltage.

8. The method according to claim 7, wherein the step of applying the first positive voltage and the step of applying the second positive voltage are simultaneous.

9. The method according to claim 7 or 8, which further comprises: applying a negative voltage to a suppression grid positioned between the acceleration grid and the target relative to the chamber.

10. The method according to claim 9, wherein the step of applying the first positive voltage, the step of applying the second positive voltage, and the step of applying the negative voltage are simultaneous.

11. The method according to claim 9 or 10, wherein the acceleration grid and the suppression grid each comprise a plurality of holes configured to allow positive ions to pass through, and the method further comprises: using the potential difference between the acceleration grid and the suppression grid to accelerate the positive ions passing through the acceleration grid towards the suppression grid.

12. The method according to any one of claims 4 - 9, which further comprises: impinging the positive ions on the target, wherein the impinging positive ions are implanted into the target or impinge on previously implanted ions to generate fusion neutrons.

13. The method according to claim 10, which further comprises emitting secondary electrons from the target due to the impinging ions impinging on previously implanted ions.

14. The method according to claim 10 or 11, which includes reflecting the secondary electrons from the suppression gate towards the target due to the negative voltage applied to the suppression gate.

15. The method according to any one of claims 6 - 14, which includes maintaining the pressure in the chamber at less than 1 millitorr.

16. The method according to any one of claims 6 - 15, which includes maintaining the pressure in the chamber at less than 0.1 millitorr.

17. The method according to claim 2 or 7, wherein: the chamber includes a first end and a second end; the filament is one of a plurality of filaments provided in the chamber and is oriented along a first direction extending between the first end and the second end; the plurality of filaments are spaced apart around the circumference of the acceleration gate such that the plurality of filaments surround the acceleration gate; the method includes applying a first positive voltage to the plurality of filaments; the acceleration gate surrounds an open central region of the chamber, includes a plurality of holes spaced apart around the open central region of the chamber, and extends along the first direction; and the plurality of holes allow positive ions to pass through the acceleration gate and the open central region of the chamber.

18. The method according to claim 2 or 7, wherein: the acceleration gate surrounds the open central region of the chamber; the acceleration gate includes a plurality of holes spaced apart around the open central region of the chamber; and the plurality of holes allow positive ions to pass through the acceleration gate and the open central region of the chamber.

19. The method according to claim 18, which includes generating a circulating electron trap by applying a second positive voltage to the acceleration gate, wherein electrons oscillate back and forth in the open central region of the chamber, and the circulating electron trap causes ionization of the gas in the open central region.

Images