ECR ion source and method
Patent Information
- Application Number
- JP2025064337
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2025-04-09
- Publication Date
- 2026-10-22
Smart Images
Figure 2026170661000001_ABST
Abstract
Description
[Technical Field]
[0001] The present invention relates to an ECR ion source and method. [Background technology]
[0002] Conventionally, ECR (Electron Cyclotron Resonance) has been used to generate ions using the electron cyclotron resonance phenomenon. Ctron (Cyclotron Resonance) ion sources are known (for example, Patent Document 1, Patent Document 2). [Patent Document 1] Japanese Patent Publication No. 2003-257329 [Patent Document 2] Japanese Patent Publication No. 2004-281202 [Overview of the Initiative] [Problems that the invention aims to solve]
[0003] To provide a miniaturizable ECR ion source. [Means for solving the problem]
[0004] In a first aspect of the present invention, there is provided an ECR ion source for ionizing an element to be ionized. The ECR ion source may comprise a vacuum chamber. The ECR ion source may comprise an ionization source supply unit. The ionization source supply unit may supply an ionization source into the vacuum chamber. The ECR ion source may comprise a magnetic field forming unit. The magnetic field forming unit may form a predetermined magnetic field in the vacuum chamber, the magnitude of which is equal to or greater than a resonance magnetic field. The ECR ion source may comprise an electromagnetic wave source. The electromagnetic wave source may supply an electromagnetic wave into the vacuum chamber so as to satisfy the resonance condition of a TE mode (Transverse Electric Mode), which is a mode in which the electromagnetic wave propagates in the vacuum chamber, to generate a standing wave in the vacuum chamber. The ECR ion source may comprise a material supply unit. The material supply unit may supply a material containing the element to be ionized into the vacuum chamber. The ECR ion source may comprise an extraction unit. The extraction unit may extract the ionized element to be ionized. The ionization source supply unit increases the electron density in the vacuum chamber by supplying the ionization source, and the relative permittivity ε under the resonance condition of the TE mode r may be varied.
[0005] Relative permittivity ε r is defined such that the plasma frequency of electrons in the vacuum chamber is ω pe , the angular frequency of the electromagnetic wave supplied by the electromagnetic wave source is ω, and the cyclotron angular frequency of electrons in the vacuum chamber is ω ce , and the following expression may hold. TIFF2026170661000002.tif15168
[0006] The vacuum chamber may have a cylindrical shape. The resonance condition of the TE mode is defined such that the resonance frequency of the standing wave is ω mnp , the relative permeability is μ r , the zero point of the derivative of the Bessel function is j' mn (m and n are positive integers), the inner radius in the direction perpendicular to the axial direction of the vacuum chamber is R, the axial length of the vacuum chamber is d, and p is a positive integer, and the following expression may hold. TIFF2026170661000003.tif20170
[0007] The ionization source can be electrons.
[0008] The ionization source supply unit may be a filament that supplies electrons.
[0009] The ionization source supply unit may be an electron gun that supplies electrons.
[0010] The ionization source supply unit may be a bias disk that supplies electrons.
[0011] The ECR ion source may include an electromagnetic wave supply unit. The electromagnetic wave supply unit may receive electromagnetic waves from an electromagnetic wave source. The electromagnetic wave supply unit may supply electromagnetic waves from the electromagnetic wave source to a vacuum chamber.
[0012] The frequency of the electromagnetic waves supplied into the vacuum chamber may be 2.00 GHz or higher. The inner radius R may be 20 mm or less. The length d may be 20.6 mm or less.
[0013] A second aspect of the present invention provides a method for ionizing an element to be ionized. The method may include an ionization source supply step. In the ionization source supply step, an ionization source may be supplied into a vacuum chamber. The method may include a magnetic field formation step. In the magnetic field formation step, a predetermined magnetic field may be formed in the vacuum chamber, having a magnitude equal to or greater than the resonance magnetic field. The method may include an electromagnetic wave supply step. In the electromagnetic wave supply step, electromagnetic waves may be supplied into the vacuum chamber to satisfy the resonance conditions of the TE mode (Transverse Electric Mode), which is a mode in which electromagnetic waves propagate in the vacuum chamber, thereby generating standing waves in the vacuum chamber. The method may include a material supply step. In the material supply step, a material containing the element to be ionized may be supplied into the vacuum chamber. The method may include an extraction step. In the extraction step, the ionized element to be ionized may be extracted. In the ionization source supply step, the electron density in the vacuum chamber is increased by supplying an ionization source, and the relative permittivity ε at the TE mode resonance conditions is increased. rYou may change it. [Brief explanation of the drawing]
[0014] [Figure 1] This diagram shows the principle of an example of a conventional ECR ion source. [Figure 2] This figure shows an example of the principle of an ECR ion source. [Figure 3] This figure shows an example of simulation results for the magnetic field in 10GHz and 2.45GHz operating modes. [Figure 4] This is an example of a standing wave formed inside the vacuum chamber 10. [Figure 5] This graph shows the relationship between the cyclotron angular frequency ωce, the ratio of the electromagnetic wave angular frequency ω, and the relative permittivity εr. [Figure 6] This figure shows an example of the configuration of the ECR ion source 200 according to one embodiment of the present invention. [Figure 7] This is an example flowchart of a method for ionizing an element to be ionized using the ECR ion source 200. [Figure 8] This figure shows an example of simulation results for standing waves in a vacuum chamber when the electron density inside the vacuum chamber is made non-uniform. [Figure 9] This figure shows an example of simulation results of standing waves in a vacuum chamber when the relative permittivity εr is varied. [Figure 10] This figure shows an example of simulation results for standing waves in a vacuum chamber with an inner radius R = 20 mm and a length d = 20.6 mm. [Modes for carrying out the invention]
[0015] The present invention will be described below through embodiments, but these embodiments are not intended to limit the invention as defined in the claims. Furthermore, not all combinations of features described in the embodiments are necessarily essential to the solution of the invention.
[0016] Figure 1 shows the principle of an example of a conventional ECR ion source. In this specification, "axial direction" refers to the direction parallel to the longitudinal direction (Z-axis direction) of the ECR ion source 100 (or vacuum chamber 10), and in Figure 1, it means the left-right direction on the plane of the paper. Also, in this specification, "radial direction" refers to the direction perpendicular to the axial direction and forming the cross-section of the vacuum chamber 10, and in Figure 1, it means, for example, the up-down direction on the plane of the paper (Y-axis direction). "Circumferential direction" refers to the direction that circles around the "axial direction".
[0017] An example of a conventional ECR ion source is the ECR ion source 100, which comprises a vacuum chamber 10, a magnetic field forming unit 20, an electromagnetic wave source 30, a material supply unit 40, and an extraction unit 50. The ECR ion source 100 may also have other components. The ECR ion source 100 may also be referred to as an ECR ionization system.
[0018] The vacuum chamber 10 is a sealed container capable of maintaining a vacuum inside. While the vacuum chamber 10 can be cylindrical, as in conventional designs, it is not limited to this and can be of various shapes. Furthermore, conventionally known methods can be used to maintain the vacuum inside the vacuum chamber 10. The vacuum chamber 10 may also be a plasma chamber. The inner surface of the vacuum chamber 10 may be lined with alumina. By lining the surface with alumina, secondary electrons are generated inside the vacuum chamber 10, thereby maintaining the electron density.
[0019] The magnetic field forming unit 20 forms a predetermined magnetic field within the vacuum chamber. In this example, the magnetic field forming unit 20 is provided with multiple coils. The coils used in the magnetic field forming unit 20 can be general-purpose wire coils (solenoid coils), but they may be made of a superconducting material with a high critical temperature for cooling purposes. For example, it is preferable to use coils made of MgB2 wire for the magnetic field forming unit 20. The magnetic field forming unit 20 may also include permanent magnets.
[0020] The coils may be wound so as to cover the vacuum chamber 10 from the outside. In Figure 1, multiple coils are wound axially so as to cover the vacuum chamber 10 from the outside. Alternatively, the coils may be wound so as not to cover the vacuum chamber 10 from the outside. In Figure 1, six coils are wound circumferentially so as not to cover the vacuum chamber 10 from the outside.
[0021] The electromagnetic wave source 30 supplies electromagnetic waves into the vacuum chamber 10. In this example, the electromagnetic wave source 30 supplies electromagnetic waves into the vacuum chamber 10 in the axial direction of the vacuum chamber 10. The electromagnetic wave source 30 may also supply electromagnetic waves into the vacuum chamber 10 in the radial direction of the vacuum chamber 10. The electromagnetic wave source 30 may supply electromagnetic waves in the microwave wavelength range. For example, a general-purpose electromagnetic wave source 30 capable of oscillating high-frequency electromagnetic waves in the range of 2.00 GHz to 100 GHz can be used. The frequencies of the electromagnetic waves oscillated by the electromagnetic wave source 30 are, for example, 2.00 GHz, 2.45 GHz, 8.00 GHz, 10.00 GHz, 12.00 GHz, 14.00 GHz, 18.00 GHz, and 28.00 GHz, but are not limited to these. In order to supply electromagnetic waves into the vacuum chamber 10, a waveguide for propagating electromagnetic waves may be provided adjacent to the vacuum chamber 10.
[0022] The material supply unit 40 may supply a material containing the element to be ionized into the vacuum chamber 10. The material may be, for example, a gas, a solid, or a liquid metal. In the case where the material is a gas, the ECR ion source 100 may be provided with a gas inlet pipe (not shown) for supplying the material gas. From the gas inlet pipe, a material gas such as methane or helium is supplied into the vacuum chamber 10. When the material gas supplied from the gas inlet pipe is supplied into the vacuum chamber 10, electrons in the material gas are ionized within the vacuum chamber 10. The ionized electrons are accelerated as described later.
[0023] The extraction unit 50 extracts the ionized target element. The extraction unit 50 is, for example, an extraction electrode. The extraction unit 50 is provided near the outlet of the vacuum chamber 10. By providing the extraction unit 50, the ECR ion source 100 can be supplied to an accelerator (particle beam accelerator), etc.
[0024] Here, the principle of a conventional ECR ion source will be explained. Figure 2 shows an example of the principle of an ECR ion source. In the ECR ion source 100, electromagnetic waves are input into the vacuum chamber 10, and electrons are periodically accelerated using a high-frequency standing wave electric field generated in a plane perpendicular to the central axis of the vacuum chamber 10. Using the magnetic field generated in the axial and radial directions of the vacuum chamber 10 by the magnetic field forming unit 20, the accelerated electrons are made to move in a cyclotron motion, and the rotational angular frequency (cyclotron angular frequency) is matched with the angular frequency of the electromagnetic wave to induce electron cyclotron resonance (ECR resonance), gradually increasing the energy of the electrons and ionizing gas molecules and vaporized metal / solid atoms. While confining the electrons with increased energy by the Miller effect of the magnetic field, the acceleration of electrons and the ionization of atoms by ionization are repeated to form a high-density plasma state. Then, a high voltage is applied to the vacuum chamber 10, and an electric field for ion extraction is formed by the extraction unit 50, and ions are extracted from the plasma near the outlet to generate an ion beam.
[0025] The charged particle beams generated by ion sources are widely used in various fields, including nuclear and elementary particle physics experiments, particle beam cancer therapy, and the production of radioisotopes (RI) for medical and industrial use. They serve as ion beam sources for accelerators, as well as in ion implantation devices for semiconductors and ion engines for rockets. To implement ion accelerators in the medical and industrial fields, miniaturization and weight reduction of ion sources and accelerator bodies, simplification of equipment configuration and operation control, and increased intensity and quality of ion beams are required. In particular, the intensity and quality of the beam output from the accelerator depend on the intensity and quality of the beam supplied from the ion source, making high-performance ion sources extremely important.
[0026] Next, the magnetic field generated by the magnetic field forming unit 20 will be described. In order to efficiently accelerate electrons and impart energy using the high-frequency electric field formed by the input electromagnetic wave, it is necessary to adjust the magnetic field so that ECR resonance is achieved such that the angular frequency of the electromagnetic wave matches the cyclotron angular frequency. Specifically, the magnetic field is adjusted so that the following Equation 1 holds (the magnetic field at this time is defined as the resonance magnetic field). Here, B ECR is the magnetic flux density of the resonance magnetic field (unit: T (tesla)), and f is the frequency of the input electromagnetic wave (unit: GHz (gigahertz)). [Equation 1] TIFF2026170661000004.tif16168
[0027] FIG. 3 is a diagram showing an example of simulation results of a magnetic field when operating at 10 GHz (hereinafter referred to as 10 GHz operation mode magnetic field) and a magnetic field when operating at 2.45 GHz (hereinafter referred to as 2.45 GHz operation mode magnetic field). Under all simulation conditions, magnetic field peaks are formed on the positive side of the horizontal axis (Z) and the negative side of the horizontal axis (Z). By providing the peaks, heavy ions can be confined when generating heavy ions. In FIG. 3, the horizontal axis represents the position in the axial direction (Z-axis direction) of the vacuum chamber 10. In FIG. 3, the vertical axis represents the magnitude of the axial magnetic field of the vacuum chamber 10. According to the simulation of the 10 GHz operation mode magnetic field, B ECR =357 mT is the resonance magnetic field. According to the simulation of the 2.45 GHz operation mode magnetic field, B ECR =87.5 mT is the resonance magnetic field. Since the energy obtained by electrons is inversely proportional to the magnetic field gradient, and the magnetic field gradient is approximately zero at the position where the magnetic field reaches its minimum value, the energy reaches its maximum at the position where the magnetic field reaches its minimum value in each of the 10 GHz operation mode magnetic field and the 2.45 GHz operation mode magnetic field, and the magnetic flux density at the position where the minimum value is reached is defined as B ECRIn this case, the electron density inside the vacuum chamber will be equivalent to or greater than the critical electron density of the 2.45 GHz operating mode magnetic field. In this example, the frequency of the electromagnetic waves supplied into the vacuum chamber is 2.45 GHz, but it is not limited to this, and the frequency of the electromagnetic waves supplied into the vacuum chamber may be 2.00 GHz or higher.
[0028] Next, we will explain the high-frequency standing waves formed inside the vacuum chamber 10. The energy gained by electrons through ECR electron heating is proportional to the square of the electric field strength of the electromagnetic wave and inversely proportional to the magnetic field gradient. In order to increase the electric field strength in the plasma region by inputting electromagnetic waves into the vacuum chamber 10, it is necessary to form standing waves inside the vacuum chamber 10 to locally maximize the electric field strength. The dimensions of the vacuum chamber 10 (inner radius and axial length) are determined so as to maximize the electric field strength of the standing waves, taking into consideration impedance matching between the waveguide and the vacuum chamber 10.
[0029] Figure 4 shows an example of a standing wave formed inside the vacuum chamber 10. The electric field strength of the standing wave formed inside the vacuum chamber 10 by electromagnetic waves depends on the internal dimensions of the vacuum chamber 10, and the electric field strength can be maximized by optimizing the internal diameter and axial length of the vacuum chamber 10. Here, in order to create the standing wave shown in Figure 4, it is necessary to satisfy the resonance conditions of the TE mode (Transverse Electric Mode), which is the mode in which electromagnetic waves propagate inside the vacuum chamber 10. The resonance conditions of the TE mode are that, when the vacuum chamber 10 has a cylindrical shape, the angular frequency (resonance frequency or operating frequency) of the standing wave is ω mnp , the relative permeability is μ r The zeros of the derivative of the Bessel function are j' mn (where m and n are positive integers), R is the inner radius of the vacuum chamber 10 in the direction perpendicular to the axial direction (see Figure 1), d is the axial length of the vacuum chamber 10 (see Figure 1), and p is a positive integer. Then the following equation 2 holds. [Formula 2] TIFF2026170661000005.tif20170
[0030] In Equation 2, when the angular frequency of the standing wave (resonance frequency or operating frequency) is lowered, the inner radius R and length d must be increased. In other words, when the angular frequency of the standing wave (resonance frequency or operating frequency) is lowered, a large vacuum chamber 10 must be prepared. On the other hand, when the vacuum chamber 10 is reduced by decreasing the inner radius R and length d, the angular frequency of the standing wave (resonance frequency or operating frequency) must be increased. In this case, the angular frequency of the standing wave (resonance frequency or operating frequency) and the frequency of the input electromagnetic wave become equal, so the frequency of the input electromagnetic wave also increases (i.e., the wavelength of the input electromagnetic wave becomes shorter). Therefore, from Equation 1, the magnetic flux density B of the resonant magnetic field ECR It needs to be made larger.
[0031] Magnetic flux density B of the resonant magnetic field ECR To increase the size of the facility, electromagnetic waves above 18 GHz are required to generate multivalent heavy ions, necessitating superconducting electromagnets. This would require large-scale cryostats to house the superconducting coils, electromagnetic power supplies, and refrigeration systems, necessitating a significant amount of space. Furthermore, construction costs could increase.
[0032] Furthermore, in order to generate a high-intensity beam of multivalent ions, the magnetic field in the center of the vacuum chamber 10 is reduced, and a magnetic field distribution (mirror field) is created in which the magnetic fields on the upstream and downstream sides are increased, thereby confining electrons and increasing the electron density in the plasma. This promotes ionization by accelerated electrons in multiple ways, increasing the amount of multivalent ions generated. If the size of the vacuum chamber 10 is large, the size of the superconducting solenoid coil (mirror coil) also increases, and the region close to the ECR magnetic field formed inside the vacuum chamber 10 expands, resulting in a larger volume of generated plasma. Therefore, it becomes more difficult to extract the ion beam from the outlet opening, and in conventional technology, measures such as multi-holes with multiple openings are used to increase beam intensity, but this also increases the beam size, which degrades the beam quality.
[0033] As described above, in order to increase the intensity of a multivalent ion beam, it is necessary to increase the energy of electrons (electron heating) to strip electrons with a high ionization potential from atoms. Therefore, a high electromagnetic wave frequency is required to generate multivalent ions, and in conjunction with this, a magnetic field distribution with a large ECR magnetic field and a large mirror field ratio must be formed, which requires a large superconducting electromagnet system, and thus the entire ion source becomes large. Furthermore, if the size of the vacuum chamber 10 is reduced to avoid increasing the size of the superconducting coil, the electromagnetic wave frequency increases, requiring a superconducting coil that generates an even higher magnetic field, which again makes the system large. If the ECR magnetic field strength is reduced to reduce the size of the electromagnet, the electromagnetic wave frequency also decreases (wavelength increases), and the size of the vacuum chamber 10 also increases, creating a contradiction. The electric field strength of the standing wave formed in the vacuum chamber 10 depends on the size of the vacuum chamber 10, as shown in equation 2 above. Therefore, the dimensions of the vacuum chamber 10 that can generate the maximum electric field strength according to the electromagnetic wave frequency are fixed and cannot be adjusted later. As the vacuum chamber 10 increases in size, the volume of plasma generated inside also increases. As mentioned above, increasing the intensity of the ion beam extracted from the plasma results in a larger beam size and a decrease in beam quality. Therefore, the challenge is to simultaneously achieve high intensity and high quality of the ion beam, as well as miniaturization and weight reduction.
[0034] Next, the principle of the present invention will be explained. Electromagnetic waves (microwaves) can be decomposed into four fundamental waves—L-waves, R-waves, O-waves, and X-waves—within a magnetized plasma. Of these four fundamental waves, only the R-wave contributes to electron acceleration (i.e., electron heating) using the electron cyclotron resonance phenomenon in the plasma. The effect of electron heating depends on factors such as electron density and magnetic field strength.
[0035] Here, the wavenumber k of the R wave. r Then the following equation 3 holds true. Here, k0 is the wavenumber of the electromagnetic wave in a vacuum, and ε is the relative permittivity. r The plasma oscillation frequency of electrons in the vacuum chamber 10 is ω peω is the angular frequency of the electromagnetic waves supplied by the electromagnetic wave source 30, and ω is the cyclotron angular frequency of the electrons in the vacuum chamber 10. ce , [Formula 3] TIFF2026170661000006.tif19169
[0036] Plasma frequency ω pe The electron density n in the vacuum chamber 10 is e It is proportional to the square root of . The angular frequency ω of the electromagnetic wave is proportional to the magnetic flux density B of the magnetic field in the vacuum chamber 10. Cyclotron angular frequency ω ce From the formula for cyclotron motion, qB / m (where q is the charge of the electron, m is the mass of the electron, and B is the magnetic flux density generated in the vacuum chamber 10 by the magnetic field generating unit) is given by the cyclotron angular frequency ω ce k is proportional to the magnetic flux density B of the magnetic field in the vacuum chamber 10. Therefore, from equation 3, the wave number k of the R wave is r is the electron density n e , the magnetic flux density B of the magnetic field in the vacuum chamber 10 and the magnetic flux density B of the resonant magnetic field ECR It depends on the electron density n. e , the magnetic flux density B of the magnetic field in the vacuum chamber 10 or the magnetic flux density B of the resonant magnetic field ECR By changing the wave number k of the R wave, r and relative permittivity ε r The electron density n can be changed. e Modify it. Transforming equation 3 results in equation 4. [Equation 4] TIFF2026170661000007.tif28170
[0037] Magnetic flux density B of the magnetic field in the vacuum chamber 10 and magnetic flux density B of the resonant magnetic field ECR The ratio is expressed by the relationship in Equation 5, and from Equation 4, the relative permittivity ε in the resonance condition of the TE mode (Equation 2) is r This is the magnetic flux density B of the magnetic field and the magnetic flux density B of the resonant magnetic field. ECR It changes with the ratio. Plasma frequency ω pe and electron density n eSince this is expressed by the relationship in Equation 6, from Equation 4, the relative permittivity ε in the resonance condition of the TE mode (Equation 2) is r is the plasma frequency ω pe It changes depending on the circumstances. [Formula 5] TIFF2026170661000008.tif16169[Formula 6] TIFF2026170661000009.tif9169
[0038] Figure 5 shows the cyclotron angular frequency ω ce The ratio of the angular frequency ω of the electromagnetic wave to the relative permittivity ε r This graph shows the relationship between the cyclotron angular frequency ω. In Figure 5, the cyclotron angular frequency ω ce The horizontal axis represents the angular frequency ω of the electromagnetic wave, and the horizontal axis represents the relative permittivity ε. r The vertical axis shows this. In Figure 5, the conditions of equation 7 and equation 8 are shown graphically. As shown in Figure 5, the relative permittivity ε is higher under the condition of equation 7 than under the condition of equation 8. r It tends to become large. Therefore, plasma frequency ω pe (That is, electron density n e The larger the relative permittivity ε, the greater the relative permittivity ε. r It tends to grow large. [Equation 7] TIFF2026170661000010.tif16166[Formula 8] TIFF2026170661000011.tif17166
[0039] Therefore, the electron density n e When this value is increased, the relative permittivity ε in the resonance condition of the TE mode (Equation 2) r Therefore, considering equation 2, the angular frequency of the same standing wave mode is ω mnp In contrast, it becomes possible to reduce the inner radius R and length d. In summary, electron density n e By increasing the magnetic field, the magnetic flux density B of the resonant magnetic field is increased. ECR When brought closer to the TE mode, the relative permittivity ε in the resonance conditions rThe inner radius R and length d can be increased, and standing waves can be formed in a small vacuum chamber 10.
[0040] Figure 6 shows an example of the configuration of an ECR ion source 200 according to one embodiment of the present invention. The ECR ion source 200 comprises a vacuum chamber 10, a magnetic field forming unit 20, an electromagnetic wave source 30, a material supply unit 40, an extraction unit 50, an ionization source supply unit 60, and an electromagnetic wave supply unit 70. The ECR ion source 200 may also have other components. The ECR ion source 200 may also be referred to as an ECR ionization system. In the following description, components identical to those of the ECR ion source 100 will not be described.
[0041] The ionization source supply unit 60 supplies an ionization source into the vacuum chamber 10. By supplying an ionization source into the vacuum chamber 10 before plasma generation, the ionization source supply unit 60 increases the electron density within the vacuum chamber 10. The ionization source is, for example, electrons (thermionic electrons). By providing the ionization source supply unit 60, the electron density within the vacuum chamber 10 can be increased before plasma generation, shortening the wavelength of the R wave, reducing the angular frequency of the electromagnetic wave and the ECR magnetic field, and making it possible to form standing waves in a smaller vacuum chamber.
[0042] Therefore, it becomes possible to miniaturize the ECR ion source, and even when inputting electromagnetic waves of the same power as conventional ECR ion sources, a higher energy density can be obtained, thereby increasing the electron density. Furthermore, because the vacuum chamber 10 is small, the plasma volume can be reduced, and more beams can be extracted from a single aperture, making it possible to increase the intensity without degrading the quality of the beam.
[0043] The ionization source supply unit 60 is, for example, a filament. A filament emits thermionic electrons by passing an electric current through a metal with high electrical resistance to raise its temperature. The ionization source supply unit 60 is, for example, an electron gun. The ionization source supply unit 60 may be a thermal cathode electron gun. A thermal cathode electron gun emits thermionic electrons from a cathode heated to a high temperature. The ionization source supply unit 60 may be a photocathode RF electron gun. A photocathode RF electron gun uses the photoelectric effect of a laser. The ionization source supply unit 60 is, for example, a bias disk. A bias disk applies a negative voltage to a metal plate placed in the vacuum chamber 10 to repel electrons leaking from the plasma and supply slow electrons. The examples of the ionization source supply unit 60 are not limited to these.
[0044] The electromagnetic wave supply unit 70 receives electromagnetic waves from the electromagnetic wave source 30. The electromagnetic wave supply unit 70 supplies electromagnetic waves from the electromagnetic wave source 30 to the vacuum chamber 10. The electromagnetic wave supply unit 70 is, for example, an antenna. The example of the electromagnetic wave supply unit 70 is not limited to an antenna. In this invention, the angular frequency of the electromagnetic waves becomes small, so if a waveguide is used, the waveguide becomes large. By providing an antenna, electromagnetic waves from the electromagnetic wave source 30 can be received, and the ECR ion source 200 can be further miniaturized.
[0045] Figure 7 is an example of a flowchart for a method of ionizing an element to be ionized using the ECR ion source 200. The method of ionizing an element to be ionized comprises an ionization source supply step S502, a magnetic field formation step S504, an electromagnetic wave supply step S506, a material supply step S508, and an extraction step S510. The method of ionizing an element to be ionized may also include other steps. In addition, the method of ionizing an element to be ionized may include a step of preparing a small vacuum chamber 10 before the ionization source supply step S502.
[0046] In the ionization source supply step S502, an ionization source is supplied into the prepared small vacuum chamber 10. As described above, the ionization source may be supplied into the vacuum chamber 10 by using a filament, electron gun, bias disk, etc. In the ionization source supply step S502, the electron energy in the vacuum chamber 10 may be low at the initial stage of supplying the ionization source. As the ionization source continues to be supplied, ions begin to be generated in the vacuum chamber 10. Then, the value of equation 9 increases. In this case, the electromagnetic waves supplied by the electromagnetic wave source 30 can enter the inside of the vacuum chamber 10. [Formula 9] TIFF2026170661000012.tif18169
[0047] In the magnetic field formation process S504, a predetermined magnetic field is formed in the vacuum chamber 10, where the magnitude of the magnetic field is greater than or equal to that of the resonant magnetic field. In this case, the magnitude of the magnetic field is brought close to that of the resonant magnetic field at almost all points within the vacuum chamber 10. Then, the value of equation 10 approaches 1. [Formula 10] TIFF2026170661000013.tif17170
[0048] In the electromagnetic wave supply process S506, electromagnetic waves are supplied into the vacuum chamber 10 in the axial direction of the vacuum chamber 10. At this time, electromagnetic waves are supplied into the vacuum chamber 10 in such a way that the resonance conditions for the TE mode (Equation 2) are satisfied, and standing waves are generated in the vacuum chamber 10. Therefore, by providing the ionization source supply process S502, the relative permittivity ε r As the magnetic field becomes larger, standing waves can be formed even in a small vacuum chamber 10, and ions can be generated. Since the denominator of equation 4 is the same as equation 11, there is no limit to the miniaturization of the vacuum chamber 10 by adjusting the magnetic field. As mentioned above, the electromagnetic wave source 30 may also be supplied into the vacuum chamber 10 in the axial direction of the vacuum chamber 10 using the electromagnetic wave supply unit 70. [Formula 11] TIFF2026170661000014.tif14166
[0049] Furthermore, with conventional ion sources, the electromagnetic wave source 30 continuously supplies electromagnetic waves, causing the plasma temperature to rise too high and the beam to become unstable. On the other hand, with the ECR ion source 200, if the plasma temperature rises too high, the electron density becomes too large, and the approximation formula 4 no longer holds. When the approximation formula 4 no longer holds, it becomes impossible to introduce electromagnetic waves from the electromagnetic wave source 30 into the vacuum chamber 10. When it becomes impossible to introduce electromagnetic waves from the electromagnetic wave source 30 into the vacuum chamber 10, the plasma temperature drops, and electromagnetic waves can be introduced again. Therefore, the plasma temperature does not rise too high as with conventional ion sources, and the plasma temperature is stabilized. Consequently, by miniaturizing the vacuum chamber 10, the plasma temperature can be kept constant, and the beam can be stabilized.
[0050] In the material supply process S508, a material containing the element to be ionized is supplied into the vacuum chamber 10. The material supply unit 40 may supply the material containing the element to be ionized into the vacuum chamber 10.
[0051] In extraction process S510, the ionized target element is extracted. The ionized target element is used in ion beams, etc.
[0052] Figure 8 shows an example of simulation results for standing waves in a vacuum chamber when the electron density inside the vacuum chamber is non-uniform. As shown in Figure 8, standing waves are formed even when the electron density inside the vacuum chamber is non-uniform.
[0053] Figure 9 shows the relative permittivity ε r This figure shows an example of simulation results of standing waves in a vacuum chamber when the relative permittivity ε is changed. (a) is the relative permittivity ε r This is a simulation of a standing wave when =ε0 (where ε0 is the relative permittivity in a vacuum). (b) Relative permittivity ε r This is a simulation of standing waves when =100ε0 (where ε0 is the relative permittivity in a vacuum). As shown in Figure 9, standing waves are formed in both (a) and (b).
[0054] Here, the relative permittivity ε r The resonant frequency of the standing wave when ε = 0 (i.e., the resonant frequency in a vacuum) is ω vaccum Let's assume that. From equation 2, the following equation 12 holds. From equation 12, if the relative permittivity is increased 100 times from the relative permittivity in a vacuum, the resonant frequency of the standing wave becomes 1 / 10th. For example, relative permittivity ε r When the resonant frequency of the standing wave is 4.17 GHz in the case where =ε0, the relative permittivity ε r The resonant frequency of the standing wave when = 100ε0 is 0.417GHz. [Formula 12] TIFF2026170661000015.tif18169
[0055] Figure 10 shows an example of simulation results of standing waves in a vacuum chamber with an inner radius R = 20 mm and a length d = 20.6 mm. The vacuum chamber may have an inner radius R of 20 mm or less and a length d of 20.6 mm or less. In Figure 10, a cylindrical vacuum chamber with an inner radius R = 20 mm and a length d = 20.6 mm is subjected to a flat magnetic field of 955 G (Gauss). When the electron density reaches a critical density of 2.45 GHz, the wavelength of the R wave becomes 1 / 3.46, and a standing wave of the TE mode (TE110 mode: m=1, n=1, p=0 in Equation 12) can be formed, enabling ion generation. The vacuum chamber shown in Figure 10 has a volume of 1 / 41 of that of a conventional ion source vacuum chamber. Note that conventional ion sources are... The vacuum chamber shown in Figure 10 has the same radius-to-length ratio, and the input electromagnetic wave is selected at the same 2.45 GHz to form a standing wave in TE110 mode. When 1 joule of energy is stored, the electric field strength is twice that of a conventional ion source.
[0056] As described above, in this embodiment, the wavelength of the R wave is changed by the magnetic field strength and electron density, and a standing wave is formed using only the R wave. Therefore, the geometric limitations of the vacuum chamber due to conventional standing waves are overcome, and the design of the ion source can be made more flexible. Furthermore, by reducing the size of the vacuum chamber and decreasing the total surface area of the vacuum chamber while maintaining the area of the extraction port, the beam intensity can be increased while maintaining beam quality. In addition, the energy density increases as the volume decreases, allowing for more efficient ionization with less power and increasing the beam current value. This makes it possible to simultaneously achieve a lighter ion source, higher beam quality, and higher beam intensity.
[0057] Furthermore, the smaller vacuum chamber allows for a smaller magnet, reducing the required input power. This lowers the manufacturing and operating costs of ion sources, accelerating the adoption of particle beam technology in industrial and medical fields. Both the vacuum chamber and magnet can be reduced to a fraction of their original volume, making palm-sized ion sources feasible. This will advance applications requiring weight reduction, such as ion engines for rockets, contributing to space development. It will also enable further miniaturization of medical accelerators, such as PET accelerators in hospitals. The simultaneous achievement of high quality and high intensity ion beams will increase the production volume of radioisotopes (RIs) for medical and industrial applications. Moreover, it will contribute to the development of particle beam technologies, such as particle beam therapy using short-lived RIs.
[0058] Although the present invention has been described above using embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments. It will be apparent to those skilled in the art that various modifications or improvements can be made to the above embodiments. Furthermore, not all combinations of features described in the embodiments are necessarily essential to the solution of the invention.
[0059] It should be noted that the execution order of operations, procedures, steps, and stages in the apparatus, systems, programs, and methods shown in the claims, specifications, and drawings is not explicitly stated as "before," "prior to," etc., and that these can be implemented in any order unless the output of a previous process is used in a later process. Even if the operation flow in the claims, specifications, and drawings is described using phrases such as "first," "next," etc. for convenience, this does not mean that it is essential to perform the operations in that order. [Explanation of symbols]
[0060] 10. Vacuum chamber, 20. Magnetic field forming unit, 30. Electromagnetic wave source, 40. Material supply unit, 50. Extraction unit, 60. Ionization source supply unit, 70. Electromagnetic wave supply unit, 100. ECR ion source, 200. ECR ion source
Claims
1. An ECR ion source for ionizing the target element, vacuum chamber and An ion source supply unit that supplies an ionization source into the vacuum chamber, A magnetic field forming unit that forms a predetermined magnetic field within the vacuum chamber, the magnetic field having a magnitude greater than or equal to the resonant magnetic field, An electromagnetic wave source that supplies electromagnetic waves into the vacuum chamber to satisfy the resonance conditions of the TE mode (Transverse Electric Mode), which is a mode in which electromagnetic waves propagate within the vacuum chamber, thereby generating standing waves within the vacuum chamber, A material supply unit that supplies a material containing the ionized element into the vacuum chamber, A drawer unit for drawing out the ionized target element and Equipped with, The ionization source supply unit increases the electron density in the vacuum chamber by supplying the ionization source, and the relative permittivity ε in the resonance conditions of the TE mode r Change ECR ion source.
2. The relative permittivity ε r teeth, The plasma oscillation frequency of electrons in the vacuum chamber is ω pe , The frequency of the electromagnetic waves supplied by the aforementioned electromagnetic wave source is ω, The cyclotron frequency of electrons in the vacuum chamber is ω ce , year, The following equation holds true: The ECR ion source according to claim 1.
3. The vacuum chamber has a cylindrical shape, The resonance conditions for the TE mode are: The resonant frequency of the standing wave is ω mnp , Specific permeability μ r , The zeros of the derivative of the Bessel function are defined as j'. mn (m and n are positive integers) The inner radius of the vacuum chamber in the direction perpendicular to the axial direction is R. The axial length of the vacuum chamber is d, Let p be a positive integer. year, The following equation holds true: The ECR ion source according to claim 2.
4. The ionization source is an electron. The ECR ion source according to claim 1.
5. The ionization source supply unit is a filament that supplies electrons. The ECR ion source according to claim 4.
6. The ionization source supply unit is an electron gun that supplies electrons. The ECR ion source according to claim 4.
7. The ionization source supply unit is a bias disk that supplies electrons. The ECR ion source according to claim 4.
8. The system further includes an electromagnetic wave supply unit that receives electromagnetic waves from the electromagnetic wave source and supplies electromagnetic waves from the electromagnetic wave source to the vacuum chamber. The ECR ion source according to claim 1.
9. The frequency of the electromagnetic waves supplied into the vacuum chamber is 2.00 GHz or higher. The aforementioned inner radius R is 20 mm or less. The length d is 20.6 mm or less. The ECR ion source according to claim 3.
10. A method for ionizing an element to be ionized, An ion source supply process for supplying an ionization source into a vacuum chamber, A magnetic field formation step in which a predetermined magnetic field having a magnitude greater than or equal to the resonant magnetic field is formed inside the vacuum chamber, An electromagnetic wave supply step of supplying electromagnetic waves into the vacuum chamber to satisfy the resonance conditions of the TE mode (Transverse Electric Mode), which is a mode in which electromagnetic waves propagate within the vacuum chamber, thereby generating standing waves within the vacuum chamber, A material supply step of supplying a material containing the ionized element into the vacuum chamber, An extraction step to extract the ionized target element and Equipped with, In the ionization source supply step, the electron density in the vacuum chamber is increased by supplying the ionization source, and the relative permittivity ε in the resonance conditions of the TE mode is increased. r Change method.