Ion source and neutral particle injection device

Abstract

In the ion source, the distribution of charged particles is appropriately controlled. [Solution] The system comprises a plurality of plasma generation units 140, each having a magnetic flux generating unit 143; an expansion chamber 160 connected to the plurality of plasma generation units 140 and emitting charged particles; and a magnetic path member 150 through which the magnetic flux generated by the magnetic flux generating units 143 passes. The magnetic flux density in the internal space of the expansion chamber 160 is defined as a first magnetic flux density B, and the magnetic flux density in the internal space of the expansion chamber 160 when the magnetic path member 150 is removed is defined as a second magnetic flux density B0. The magnetic path member 150 is formed such that the magnetic flux density ratio B / B0 at the central axis CL-P of the expansion chamber 160 is different from the magnetic flux density ratio B / B0 at the peripheral edge of the expansion chamber 160.

Description

[Technical Field]

[0001] This invention relates to an ion source and a neutral particle injection device. [Background technology]

[0002] Ion source outputs of 100[A] or more are required for neutral beam injection (NBI) devices for nuclear fusion and particle sources for materials research. To achieve this current, the diameter of the ion source is generally increased, and the beam is extracted using multiple holes. To obtain a sufficient current from the extraction holes of the ion source, it is preferable to obtain a sufficiently high density of charged particles near the extraction holes. To obtain a large diameter and high density of charged particles, for example, as shown in Non-Patent Document 1 below, a system is known that comprises multiple drivers for generating plasma and expansion chambers connected to these drivers. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Si-Yu Xing, et al., 3D modeling of a double-driver ion source considering ion magnetization: an investigation of plasma symmetry modulation methods, (Nuclear Fusion, Volume 64, Number 5), [online], [Retrieved September 27, 2024], Internet <URL:https: / / iopscience.iop.org / article / 10.1088 / 1741-4326 / ad34e3> [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] By the way, in the technology described above, there is a desire to control the distribution of charged particles more effectively. This invention has been made in view of the circumstances described above, and aims to provide an ion source and a neutral particle injection device that can appropriately control the distribution of charged particles. [Means for solving the problem]

[0005] To solve the above problems, the ion source of the present invention comprises a plurality of plasma generation units, each having a magnetic flux generating unit; an expansion chamber connected to the plurality of plasma generation units and emitting charged particles; and a magnetic path member through which the magnetic flux generated by the magnetic flux generating units passes. The magnetic flux density in the internal space of the expansion chamber is defined as the first magnetic flux density, the magnetic flux density in the internal space of the expansion chamber when the magnetic path member is removed is defined as the second magnetic flux density, the result of dividing the first magnetic flux density by the second magnetic flux density is defined as the magnetic flux density ratio, and the magnetic path member is formed such that the magnetic flux density ratio at the central axis of the expansion chamber and the magnetic flux density ratio at the peripheral edge of the expansion chamber are different. [Effects of the Invention]

[0006] According to the present invention, the distribution of charged particles can be appropriately controlled. [Brief explanation of the drawing]

[0007] [Figure 1] This is a schematic diagram of an NBI device according to the first embodiment. [Figure 2] This is a schematic diagram of the ion source in the first embodiment. [Figure 3] This is a schematic cross-sectional view of the main part of the ion source in the comparative example. [Figure 4] This figure shows an example of the electron density distribution near the extraction electrode in the expansion chamber. [Figure 5] This figure shows an example of the electron density distribution in the circumferential direction within the expansion chamber. [Figure 6] This is a schematic cross-sectional view of the main part of the ion source in the first embodiment. [Figure 7]It is a diagram showing a characteristic example of magnetic field strength in the first embodiment. [Figure 8] It is a schematic cross-sectional view of an ion source applied to the second embodiment. [Figure 9] It is a diagram showing an example of the electron density distribution and ion density distribution in the vicinity of the extraction electrode in the expansion chamber in the second embodiment. [Figure 10] It is a side view of the main part of the ion source in the third embodiment. [Figure 11] It is a side view of the main part of the ion source in the fourth embodiment. [Mode for Carrying Out the Invention]

[0008] [Outline of Embodiment] Generally, in an ion source including a plurality of drivers and an expansion chamber, the electromagnetic field of the driver may affect the electron distribution in the expansion chamber. When applying the technology of Non-Patent Document 1, it is considered possible to adopt RF-based plasma generation having an external antenna as a driver and place an iron plate as a shield between the driver and the expansion chamber in order to prevent the influence of the motional electromagnetic field caused by the antenna on the expansion chamber. However, it is difficult to appropriately control the electron distribution with a uniform iron plate having no structural difference between the wall side of the expansion chamber of one driver and the side of another adjacent driver. Therefore, in the embodiments described below, in an ion source including an expansion chamber, the electron distribution in the expansion chamber is appropriately controlled.

[0009] [First Embodiment] <Configuration of the First Embodiment> Hereinafter, based on the drawings, a preferred first embodiment of an NBI (Neutral Beam Injection) device will be described. In the first embodiment, as will be described later, by changing the magnetic field leaking from the driver to the expansion chamber, the electron distribution in the expansion chamber is made uniform, and thereby the distribution of hydrogen ions following the electron distribution is made uniform. In the first embodiment, between the plurality of drivers and the expansion chamber, a magnetic path member is provided on the wall side of the expansion chamber of each driver.

[0010] Figure 1 is a schematic diagram of the NBI device 1 (neutral particle injection device) according to the first embodiment. In Figure 1, the NBI device 1 heats the plasma 72 formed inside the fusion device 70 by injecting high-speed neutral particles into it, and comprises an ion source 11, a vacuum chamber 50, a neutralization cell 52, a deflection coil 54, a beam dump 56, a cryopump 62, an auxiliary vacuum exhaust system 64, and a pure water cooling system 66. The vacuum chamber 50 is positioned along the fusion device 70 and houses the neutralization cell 52, the deflection coil 54, and the beam dump 56.

[0011] The ion source 11 generates high-speed charged particles and injects them into the vacuum chamber 50. The neutralization cell 52 converts the injected high-speed charged particles into high-speed neutral particles. The deflection coil 54 is positioned to surround the paths of the high-speed neutral and charged particles within the vacuum chamber 50, deflecting the paths of the charged particles. Of the charged particles generated by the ion source 11, those not neutralized by the neutralization cell 52 are deflected by the deflection coil 54 from the path of neutral particles heading towards the plasma 72 and guided to the beam dump 56.

[0012] When charged particles stop in the beam dump 56, heat is generated. The pure water cooling system 66 supplies cooling water maintained at a temperature of approximately 25°C to the beam dump 56, thereby cooling the beam dump 56. The cryopump 62 and auxiliary vacuum evacuation system 64 are a gas reservoir type vacuum pump and a rotary pump, respectively, which condense and capture gas molecules in the vacuum chamber 50 on a cryogenic surface. As a result, the vacuum level in the vacuum chamber 50 is 10°C. -4 It is maintained at around [Pa].

[0013] Figure 2 is a schematic diagram of the ion source 11 in the first embodiment. The ion source 11 is a device for generating hydrogen plasma and includes microwave sources 136-A and 136-B, coil power supplies 138-A and 138-B, microwave drivers 140-A and 140-B, magnetic path members 150-A and 150-B, an expansion chamber 160, a drawout power supply 124, and a reverse bias power supply 125. In the following description, multiple components, physical quantities, information, etc., having the same or similar function or significance may be represented by adding a hyphen and alphanumeric characters to the same symbol, such as "microwave driver 140-A and 140-B". However, if it is not necessary to distinguish between these multiple components, etc., the hyphen and alphanumeric characters may be omitted, such as "microwave driver 140".

[0014] The microwave source 136 generates microwaves. The microwave driver 140 (plasma generation unit) is a driver that generates plasma using microwaves and a magnetic field, and generates plasma by ECR (Electron Cyclotron Resonance) resonance. The microwave driver 140-A includes a waveguide 141-A, a plasma generation chamber 142-A, a solenoid coil 143-A, a vacuum window 144-A, and a gas inlet 145-A.

[0015] Similarly, the microwave driver 140-B includes a waveguide 141-B, a plasma generation chamber 142-B, a solenoid coil 143-B, a vacuum window 144-B, and a gas inlet 145-B. The central axes of the plasma generation chambers 142-A and 142-B are referred to as CL-A and CL-B.

[0016] The plasma generation chamber 142 is a cylindrical vacuum chamber, one end of which is connected to the waveguide 141 via a vacuum window 144, and the other end is connected to the expansion chamber 160. The solenoid coil 143 (magnetic flux generator) is arranged to surround the middle part of the plasma generation chamber 142. The coil power supply 138 supplies a DC current to the solenoid coil 143. As a result, the solenoid coil 143 generates a magnetic field of about 80 gauss in the central part of the chamber 142 along the central axes CL-A and CL-B.

[0017] Waveguide 141 is a rectangular waveguide connected between microwave source 136 and vacuum window 144. Gas inlet 145 is a gas inlet fitting provided on the side of plasma generation chamber 142, to which a hydrogen gas cylinder (not shown) is connected via a polyvinyl chloride tube. As a result, hydrogen gas is supplied to the plasma generation chamber 142 from the hydrogen gas cylinder through the gas inlet 145.

[0018] The expansion chamber 160 extracts hydrogen ions from the plasma generated by the microwave driver 140 toward the neutralization cell 52, and in this embodiment, it plays a role in homogenizing the plasma generated by the microwave driver 140. The expansion chamber 160 comprises a plasma expansion chamber 161, a plurality of cusp magnetic field magnets 162, an extraction electrode 163, a ground electrode 164, and O-rings 166 and 167. The plasma expansion chamber 161 is a cylindrical vacuum chamber to which drivers 140-A and 140-B are connected, and the plasma generated by each driver 140 flows into it. The central axis of the chamber 161 is called CL-P.

[0019] The plasma expansion chamber 161 is connected to the extraction power supply 124, to which a potential of several tens of kV is applied. The extraction electrode 163 and the ground electrode 164 are laid along the side of the plasma expansion chamber 161 opposite to the side to which the driver 140 is connected. The extraction electrode 163 is a copper plate having approximately 1000 extraction holes (not shown) for extracting hydrogen ions, and is connected to the reverse bias power supply 125, to which a potential of several negative kV is applied.

[0020] The ground electrode 164 is a copper plate having approximately 1000 extraction holes (not shown) for extracting hydrogen ions, and is electrically grounded. The O-rings 166 and 167 are polytetrafluoroethylene (PTFE) O-rings for insulation. O-ring 166 is inserted between the plasma expansion chamber 161 and the extraction electrode 163, and O-ring 167 is inserted between the extraction electrode 163 and the ground electrode 164.

[0021] In this way, by applying a potential difference to the plasma expansion chamber 161, the extraction electrode 163, and the ground electrode 164, hydrogen ions can be drawn into the vacuum chamber 50 (see Figure 1). The cusp magnetic field magnet 162 is a neodymium magnet and generates a magnetic field of about 1 [T].

[0022] The cusp field magnets 162 are arranged to cover the sides of the plasma expansion chamber 161, with the aim of confining the plasma within the expansion chamber 160. A checkerboard arrangement, common for cusp field magnets, is used for the magnetization direction of the cusp field magnets 162. That is, the multiple cusp field magnets 162 are arranged so that north poles and south poles alternate.

[0023] The magnetic path member 150 is a semicircular plate with a thickness of about 10 mm and functions as a shield to block the magnetic field from the solenoid coil 143. The material of the magnetic path member 150 is preferably mainly composed of a soft magnetic material such as mild iron. The inner diameter of the magnetic path member 150 is approximately equal to the outer diameter of the plasma generation chamber 142, and the outer diameter of the magnetic path member 150 is approximately equal to the outer diameter of the solenoid coil 143. The magnetic path members 150-A and 150-B are arranged to protrude in the circumferential direction of the expansion chamber 160 when viewed from their respective microwave drivers 140-A and 140-B. No magnetic path member 150 is provided between adjacent microwave drivers 140-A and 140-B.

[0024] In Figure 2, the coordinate system is defined as follows: the z-axis represents the plasma extraction direction from the expansion chamber 160, the x-axis represents the alignment direction of drivers 140-A and 140-B, and the y-axis represents the direction perpendicular to the x and z axes. The angle θ is the circumferential angle of the expansion chamber 160, indicated by the dashed line LN1. The directions closest to the plasma expansion chamber 161 from the central axes CL-A and CL-B of chambers 142-A and 142-B are called DL-A and DL-B, respectively. The angle θ is the angle when direction DL-A is set to 0°.

[0025] <Comparative Example> Next, in order to clarify the operation and effects of the first embodiment, a comparative NBI apparatus will be described. In the comparative NBI apparatus, the ion source 19 shown in Figure 3 is used instead of the ion source 11 (see Figure 2) of the first embodiment.

[0026] Figure 3 is a schematic cross-sectional view of the main part of the ion source 19 in the comparative example. That is, Figure 3 shows a schematic cross-section of the main part of the ion source 19 in the xz plane. In the ion source 19, the magnetic path members 150-A and 150-B (see Figure 2) are not provided, but the other configurations are the same as those of the ion source 11 in the first embodiment.

[0027] In Figure 3, magnetic fluxes 128-A and 128-B are generated by solenoid coils 143-A and 143-B, respectively, extending from drivers 140-A and 140-B toward the inner wall 161a of the plasma expansion chamber 161 and incident perpendicularly to the inner wall 161a of the chamber 161. Ejection holes 1012 are formed in the extraction electrode 163 and the ground electrode 164.

[0028] Electron 130-A is an electron in the plasma generated by driver 140-A, and its kinetic energy is approximately 10 [eV]. To discuss the motion of electron 130-A, we define coordinate axes corresponding to the magnetic flux. First, the direction parallel to the magnetic flux is defined as the t-axis, and the axes on the plane perpendicular to the magnetic flux are defined as the s-axis and u-axis. Electron 130-A moves according to the equation of motion in [Equation 1], where m is the mass of the electron, T is time, q is the charge of the electron, and B is the mass of the electron. tis the magnetic flux density, c is the speed of light, v u , v s , v t are the velocities of electron 130-A in the u-axis, s-axis, and t-axis directions.

[0029]

Number

[0030] From this, the time change of the position of electron 130-A becomes [Equation 2], and it can be seen that it performs circular motion in the su plane perpendicular to the magnetic field.

[0031]

Number

[0032] In [Equation 2], Ω is the gyro frequency, and "Ω = qB t / m". r g is the gyro radius, and "r g = v su Ω". Here, v su is the initial velocity of electron 130-A in the su plane. φ0, s0, u0 are constants determined in the initial state at T = 0. t0 is the position of electron 130-A on the t-axis at T = 0, and v t0 is the velocity of electron 130-A in the t-axis direction at T = 0.

[0033] On the other hand, according to [Equation 2], since the magnetic field does not affect the motion in the t-axis direction parallel to the magnetic field, electron 130-A proceeds along magnetic flux 128-A at its initial velocity. From the above, it can be seen that the orbit of electron 130-A orbits around magnetic flux 128-A while advancing along the magnetic flux. As a result, electron 130-A proceeds toward the inner wall 161a of chamber 161. When electron 130-A is incident perpendicularly on the inner wall 161a, electron 130-A is lost. On the other hand, when electron 130-A approaches the inner wall 161a at a finite angle, due to the magnetic field by cusp magnetic field magnet 162, electron 130-A is confined and avoids collision with the inner wall 161a, and stagnates near the inner wall 161a.

[0034] Based on the above principle, electrons emitted from drivers 140-A and 140-B travel toward the inner wall 161a of chamber 161 and accumulate near region 240 adjacent to the inner wall 161a. As a result, a density variation occurs in the electron density distribution within chamber 161, with a higher density near the inner wall 161a and a lower density in the central part of chamber 161.

[0035] Here, let r be the shorter of the distances between an arbitrary point P (not shown) on the inner surface of the inner wall 161a and the central axes CL-A and CL-B. The distance r is then compared to the magnetic flux density B near point P. wall The relationship between and is shown in [Equation 3] below. Therefore, the electron density distribution in the circumferential direction of chamber 161, indicated by the dashed line LN1 in Figure 2, is not uniform. That is, electrons are concentrated near region 240, where the inner wall 161a is close to the central axes CL-A and CL-B.

[0036]

number

[0037] Figure 4 shows an example of the electron density distribution near the extraction electrode 163 in the expansion chamber 160. In Figure 4, the distance rc on the horizontal axis is the distance from the central axis CL-P of the chamber 161. The solid line shows the density distribution DS1 according to the first embodiment, and the dashed line shows the density distribution DS2 according to the comparative example. Details of density distribution DS1 will be described later. As shown in density distribution DS2, in the comparative example, electrons are concentrated near the inner wall 161a of the chamber 161 shown in Figure 3.

[0038] Figure 5 shows an example of the electron density distribution in the circumferential direction within the expansion chamber 160. In Figure 5, the angle θ on the horizontal axis is the angle when the direction DL-A shown in Figure 2 is set to 0°. The solid line density distribution DS11 is the density distribution according to the first embodiment, and the dashed line density distribution DS12 is the density distribution according to the comparative example. Details of density distribution DS11 will be described later. As shown in density distribution DS12, in the comparative example, peaks appear at angles θ of 0° and 180°, and it fluctuates significantly depending on the angle θ.

[0039] The hydrogen ions (protons) emitted from drivers 140-A and 140-B also follow the electron density distribution due to the effect of space charge, and therefore have a density distribution similar to that of the electrons described above. In general, in order to draw out charged particles with a large current, it is preferable to ensure a sufficient density of such charged particles near the extraction hole 1012 (see Figure 3). Therefore, the unevenness in the electron density distribution that appears in the comparative example may lead to insufficient extraction current from the extraction hole 1012 in the central part of the expansion chamber 160.

[0040] <Operation of the First Embodiment> Next, the operation of the first embodiment will be described. Figure 6 is a schematic cross-sectional view of the main part of the ion source 11 in the first embodiment. That is, Figure 6 shows a schematic cross-section of the main part of the ion source 11 in the xz plane, similar to Figure 3 described above. As described above, in the first embodiment, the magnetic path members 150-A and 150-B are arranged so as to protrude in the circumferential direction of the expansion chamber 160 when viewed from the microwave drivers 140-A and 140-B. As a result, the magnetic fluxes 128-A and 128-B generated by the solenoid coils 143-A and 143-B are concentrated almost entirely in the center of the plasma expansion chamber 161, and the magnetic flux directed toward the inner wall 161a of the chamber 161 can be reduced. In Figure 6, the significance of the z axis and angle θ is the same as in Figure 2. Also, let r be the distance from the central axis CL-A of the plasma generation chamber 142-A.

[0041] Also, although not shown in the diagrams, the inner diameter of the solenoid coil 143-A is R coil The outer diameter of the magnetic path member 150-A is Rziro The inner diameter of the magnetic path member 150-A is R york In this case, of the magnetic flux 128-A from the solenoid coil 143-A, at the surface of the magnetic path member 150-A, -90° < θ < 90°, r > R york The magnetic flux present in this region is absorbed by the magnetic path member 150-A.

[0042] In the comparative example shown in Figure 3, the magnetic flux density inside the chamber 161 is B0 (second magnetic flux density), and the magnetic flux density in the first embodiment shown in Figure 6 is B (first magnetic flux density). On the surface of the magnetic path member 150-A in the first embodiment, -90°<θ<90°, r>R york In this region, the magnetic flux density ratio B / B0 is approximately "0".

[0043] On the other hand, magnetic flux passing through regions other than those mentioned above is affected by the magnetic path member 150-A and curves, but generally, in the angular range θ1 < θ < θ2, the inner diameter R york When the magnetic path member is installed, the magnetic flux density directed towards the angular range θ1 < θ < θ2 is reduced to approximately the magnetic flux density ratio B / B0 shown in [Equation 4].

[0044]

number

[0045] In this embodiment, by covering the range -90° < θ < 90° with the magnetic path member 150-A, the magnetic flux density B directed toward the inner wall 161a can be reduced. As a result, electrons 130-A emitted from driver 140-A travel by wrapping around the magnetic flux, and therefore hardly move toward the direction of -90° < θ < 90°. Similarly, electrons 130-B emitted from driver 140-B also move within the expansion chamber 160 without hardly moving toward the inner wall 161a, due to a mechanism similar to that of electrons 130-A.

[0046] Figure 7 shows an example of the characteristics of the magnetic field strength Bz in the first embodiment. Specifically, Figure 7 shows the dependence of the magnetic field strength Bz in the z direction within the chamber 161 on the rc direction. In Figure 7, the horizontal axis represents the distance rc from the central axis CL-P of chamber 161, with positive values ​​in the direction from the central axis CL-P toward the central axis CL-A of driver 140-A, and negative values ​​in the direction toward the central axis CL-B of driver 140-B. As shown in Figure 7, the magnetic field strength Bz in the z direction is strong at the center of chamber 161 and weakens toward the periphery. Therefore, a magnetic field gradient in the rc direction is generated in the magnetic field strength Bz in the z direction. Due to this magnetic field gradient, the force F in the θ direction acting on electron 130-A is as shown in [Equation 5].

[0047]

number

[0048] In [Equation 5], the magnetic flux density B is a vector quantity, and "×" is the cross product of vectors. Also, "_θ" indicates the θ component. As a result, electrons 130-A circulate in the θ direction, preventing electrons from accumulating in one place and eliminating unevenness in electron density in the θ direction. Thus, in the first embodiment, in the region 250 near the extraction electrode 163, electrons gather with a uniform density distribution in the θ and rc planes.

[0049] Therefore, in the first embodiment, the electron density in the rc direction near the extraction electrode 163 in the expansion chamber 160 is as shown by the density distribution DS1 in Figure 4. The electron density in the θ direction is as shown by the density distribution DS11 in Figure 5.

[0050] Thus, according to the first embodiment, electrons are less likely to move toward the inner wall 161a, which reduces the loss of electrons due to collisions between electrons and the inner wall 161a, making it possible to confine electrons in the expansion chamber 160 for a longer period of time. This makes it possible to improve the electron density in the expansion chamber 160.

[0051] The hydrogen ions (protons) emitted from the driver 140 also follow the density distribution of electrons due to the effect of space charge, and therefore have a density distribution similar to that of the electrons described above. As described above, in order to draw out charged particles with a large current, it is preferable to ensure a sufficient and uniform density of such charged particles near the extraction hole, and this requirement can be met according to the first embodiment. As a result, a large current output can be achieved in the ion source 11.

[0052] [Second Embodiment] Next, an NBI device according to the second embodiment will be described. In the description of each embodiment, parts corresponding to parts of the other embodiments described above will be denoted by the same reference numerals, and their descriptions may be omitted. Figure 8 is a schematic cross-sectional view of the ion source 12 applied to the NBI apparatus 2 of the second embodiment. In the NBI device 2 according to the second embodiment, the ion source 12 shown in Figure 8 is used instead of the ion source 11 in the first embodiment. Except for this point, the NBI device 2 according to the second embodiment is the same as the NBI device 1 of the first embodiment (see Figure 1). However, the NBI device 2 of the second embodiment differs from that of the first embodiment in that the particles extracted from the ion source 12 are negative hydrogen ions.

[0053] In the ion source 12 of the second embodiment, a converter 2000 is provided inside the plasma expansion chamber 161. The converter 2000 is a tungsten rod coated with Cs (cesium) on its surface, has a curved shape, and is positioned along the inner wall 161a of the plasma expansion chamber 161. When hydrogen ions (protons) generated by drivers 140-A and 140-B come into contact with the surface of the converter 2000, the hydrogen ions are converted into negative hydrogen ions.

[0054] Furthermore, the chamber 161 is connected to the extraction power supply 124 (see Figure 2), similar to the first embodiment. However, in the second embodiment, a negative potential, for example, a potential of minus several hundred kV, is applied to the chamber 161 by the extraction power supply 124. The shapes of the extraction electrode 163 and the ground electrode 164 are the same as in the first embodiment. The ground electrode 164 is grounded, similar to the first embodiment. Also, the extraction electrode 163 is connected to the reverse bias power supply 125 (see Figure 2), similar to the first embodiment. However, in the second embodiment, a positive potential, for example, a potential of several kV, is applied to the extraction electrode 163 by the reverse bias power supply 125. In this way, by creating a potential difference between the plasma expansion chamber 161, the extraction electrode 163, and the ground electrode 164, negative hydrogen ions can be extracted into the vacuum chamber 50 (see Figure 1).

[0055] However, since negative hydrogen ions and electrons have the same charge, electrons may also be drawn out from the ion source 12. Therefore, in order to obtain a high-current negative hydrogen ion beam, it is desirable not only to maintain a sufficiently high negative hydrogen ion density near the extraction electrode 163, but also to minimize the electron density near the extraction electrode 163. Furthermore, collecting the hydrogen ions generated by drivers 140-A and 140-B near the converter 2000 is also important from the viewpoint of improving the conversion efficiency to negative hydrogen ions.

[0056] Furthermore, in the second embodiment, the shapes of the magnetic path members 150-A and 150-B are the same as those in the first embodiment (see Figure 2). However, in the second embodiment, the magnetic path members 150-A and 150-B are arranged to protrude from the chambers 142-A and 142-B in the direction toward the central axis CL-P of the chamber 161.

[0057] Therefore, the magnetic fluxes 128-A and 128-B are directed primarily from the microwave drivers 140-A and 140-B towards the inner wall 161a. Consequently, the hydrogen ions emitted from the drivers 140-A and 140-B are also directed towards the inner wall 161a.

[0058] In Figure 8, the meanings of the z-axis, angle θ, and distance r are the same as in Figure 6. Although not shown in the illustration, the inner diameter of the solenoid coil 143-A is R. coil The outer diameter of the magnetic path member 150-A is R ziro The inner diameter of the magnetic path member 150-A is R york In this case, on the surface of the magnetic path member 150-A, 90° < θ < 270°, r > R york The magnetic flux 128-B present in this region is absorbed by the magnetic path member 150-A.

[0059] On the other hand, magnetic flux passing through regions other than those mentioned above is affected by the magnetic path member 150-A and curves, but the magnetic flux density toward the inner wall 161a is hardly attenuated. As a result, electrons 130-A emitted from driver 140-A travel wrapped around the magnetic flux and hardly travel in the direction of 90° < θ < 270. Consequently, electrons 130-A travel toward the inner wall 161a of the expansion chamber 160.

[0060] Near the inner wall 161a, the magnetic field from the cusp magnetic field magnet 162 causes electrons 130-A to experience a repulsive force directed inward towards the chamber 161. As a result, electrons 130-A avoid collisions with the inner wall 161a and remain stagnant in region 260 near the inner wall 161a, thereby becoming trapped within the chamber 161.

[0061] Figure 9 shows an example of the electron density distribution and ion density distribution near the extraction electrode 163 in the expansion chamber 160 in the second embodiment. In Figure 9, the distance rc on the horizontal axis is the distance from the central axis of the chamber 161. The density distribution DS21 shown by the solid line is the electron density distribution according to the second embodiment, and as shown in the figure, the electron density tends to increase as the distance rc increases.

[0062] The hydrogen ions (protons) emitted from the driver 140 also follow the density distribution of electrons due to the effect of space charge, and therefore have a density distribution similar to that of the electrons described above. This allows hydrogen ions to be concentrated in the vicinity of the converter 2000. Then, the converter 2000 can efficiently convert the hydrogen ions (protons) generated by the driver 140 into negative hydrogen ions.

[0063] On the other hand, since the negatively charged hydrogen ions have the same charge as electrons, a repulsive force acts on them, causing them to accumulate in regions with low electron density. Therefore, the density distribution of negative hydrogen ions is predicted to be as shown in the density distribution DS22 in Figure 9. In other words, in this embodiment, by making the electron distribution within the chamber 161 uneven, the distribution of negative hydrogen ions, which repel the electron distribution, can be concentrated near the extraction hole 1012. This makes it possible to efficiently extract negative hydrogen ions from the extraction hole 1012 of the extraction electrode 163, thereby realizing a high current output from the ion source 12.

[0064] [Third Embodiment] Figure 10 is a side view of the main parts of the ion source 13 applied to the NBI apparatus 3 of the third embodiment. Specifically, Figure 10 shows side views of the plasma generation chamber 142 of the microwave driver 140, the magnetic path member 150, and the expansion chamber 160 of the ion source 13, while other elements are not shown.

[0065] In the NBI device 3 according to the third embodiment, the ion source 13 shown in Figure 10 is used instead of the ion source 11 of the first embodiment. Except for this point, the NBI device 3 according to the third embodiment is the same as the NBI device 1 of the first embodiment (see Figure 1). In the first embodiment, the ion source 11 (see Figure 2) was equipped with two microwave drivers 140-A and 140-B. In contrast, the ion source 13 in the third embodiment differs in that it is equipped with three or more drivers 140.

[0066] The ion source 13 comprises n+1 (where n is 2 or greater) microwave drivers 140-0 to 140-n, n magnetic circuit members 150-1 to 150-n (the first to the nth magnetic circuit members), and an expansion chamber 160. That is, no corresponding magnetic circuit member 150 is provided around the microwave driver 140-0 located in the center (not adjacent to the inner wall 161a). Note that in Figure 10, only a portion of the microwave drivers 140 and magnetic circuit members 150 are shown.

[0067] Although not shown in the diagram, each ion source 13 is equipped with n+1 microwave sources 136 (see Figure 2) and a coil power supply 138. In addition, an extraction power supply 124 and a reverse bias power supply 125 (see Figure 2) are connected to the expansion chamber 160.

[0068] The plasma generation chamber 142-0 of driver 140-0 is positioned so that its central axis CL-0 coincides with the central axis CL-P of the expansion chamber 160. Circle CC1 in the figure is a circle centered on the central axis CL-P of the expansion chamber 160. The plasma generation chambers 142-1 to 142-n of drivers 140-1 to 140-n (the first to nth plasma generation units) are arranged at equal intervals in the circumferential direction so that their central axes CL-1 to CL-n lie on circle CC1.

[0069] The magnetic path members 150-1 to 150-n are provided so as to protrude from each chamber 142-1 to 142-n toward the inner wall 161a of chamber 161. Therefore, there are no magnetic path members 150 inside circle CC1, and only outside circle CC1. In other words, the weight of the magnetic path members 150 outside circle CC1 is greater than the weight of the magnetic path members 150 inside circle CC1.

[0070] Here, we will describe the shape of each magnetic path member 150-k (1≦k≦n). The straight line SL-k is the line connecting the central axis CL-k of chamber 142-k and the shortest distance to the inner wall 161a. For example, the straight line SL-1 is the line connecting the central axis CL-1 of chamber 142-1 and the shortest distance to the inner wall 161a. If Φ is the angle made from the central axis CL-k to the straight line SL-k, then the magnetic path members 150-k are arranged in the angular range "-180° / n < Φ < 180° / n".

[0071] In other words, the magnetic path member 150-k has a shape that forms part of a ring, obtained by subtracting the range of chamber 142-k from a sector with an angular range of "-180° / n < Φ < 180° / n". As a result, if we let B be the magnetic flux density from chamber 142-k toward the inner wall 161a of chamber 161, and B0 be the magnetic flux density when the magnetic path member 150-k is absent, then the magnetic flux density ratio B / B0 is as shown in [Equation 6] below. In [Equation 6], R coil , R ziro , R york Its meaning is the same as that of [Mathematics 4].

[0072]

number

[0073] [Fourth Embodiment] Figure 11 is a side view of the main part of the ion source 14 applied to the NBI device 4 of the fourth embodiment. Specifically, Figure 11 shows a side view of the plasma generation chamber 142, magnetic path member 150, and expansion chamber 160 of the microwave driver 140, which are elements of the ion source 14, while other elements are omitted from the illustration.

[0074] In the NBI device 4 according to the fourth embodiment, the ion source 14 shown in Figure 11 is used instead of the ion source 12 in the second embodiment. Except for this point, the NBI device 4 according to the fourth embodiment is the same as the NBI device 2 of the second embodiment (see Figure 8). The ion source 12 in the NBI device 2 according to the second embodiment was equipped with two microwave drivers 140-A and 140-B. In contrast, the ion source 14 in the fourth embodiment differs in that it is equipped with three or more drivers 140.

[0075] The ion source 14 comprises n+1 (where n is 2 or greater) microwave drivers 140-0 to 140-n, n magnetic circuit members 150-1 to 150-n, and an expansion chamber 160. That is, no corresponding magnetic circuit member 150 is provided around the microwave driver 140-0 located in the center (not adjacent to the inner wall 161a). Note that in Figure 11, only a portion of the microwave drivers 140 and magnetic circuit members 150 are shown.

[0076] Although not shown in the diagram, the ion source 14 is equipped with n+1 microwave sources 136 (see Figure 2) and a coil power supply 138. The extension chamber 160 is connected to an extraction power supply 124 and a reverse bias power supply 125 (see Figure 2). Also, as in the second embodiment, the extension chamber 160 is provided with multiple converters 2000 (see Figure 8). In the fourth embodiment, the placement of the microwave driver 140 is the same as in the third embodiment (see Figure 10).

[0077] The magnetic path members 150-1 to 150-n are provided to protrude from each chamber 142-1 to 142-n toward the central axis CL-P of the expansion chamber 160. As a result, according to the fourth embodiment, the weight of the magnetic path member 150 outside the circle CC1 is greater than the weight of the magnetic path member 150 inside the circle CC1.

[0078] Here, the shape of each magnetic path member 150-k (1≦k≦n) will be described. Similar to the third embodiment described above, the straight line SL-k is defined as the straight line connecting the central axis CL-k of chamber 142-k and the shortest distance to the inner wall 161a. For example, the straight line SL-1 is the straight line connecting the central axis CL-1 of chamber 142-1 and the shortest distance to the inner wall 161a. If the angle made from the central axis CL-k to the straight line SL-k is Φ, then the magnetic path members 150-k are arranged in the angular ranges of "Φ<-180° / n" and "180° / n<Φ". This allows electrons to move toward the inner wall 161a, intentionally creating an uneven distribution of electron density.

[0079] [Differentiation] The present invention is not limited to the embodiments described above, and various modifications are possible. The embodiments described above are illustrative examples provided to facilitate understanding of the present invention, and are not necessarily limited to those comprising all the described configurations. Furthermore, it is possible to replace parts of the configuration of one embodiment with those of another embodiment, and to add configurations from other embodiments to the configuration of one embodiment. It is also possible to delete parts of the configuration of each embodiment, add other configurations, or replace them with other configurations. In addition, the control lines and information lines shown in the figures are those considered necessary for explanation, and do not necessarily represent all control lines and information lines required in the product. In practice, it can be assumed that almost all configurations are interconnected. Possible modifications to the above embodiments are as follows, for example.

[0080] (1) In each of the above embodiments, a microwave-based ECR plasma generation method was applied to the microwave driver 140. However, a driver using a microwave antenna may be applied instead. The electromagnetic field caused by the antenna can also be changed in the same manner as in each of the above embodiments, thereby enabling density control of charged particles.

[0081] (2) In each of the above embodiments, a semi-circular magnetic path member was used as the magnetic path member 150, but various shapes other than semi-circular can be used for the shape of the magnetic path member 150. For example, in the first embodiment, when viewed from the central axes CL-A, CL-B (see Figure 2) of the chamber 142, a magnetic path member with more weight near the inner wall 161a, where the electron density should be high, can be placed compared to the area near the central axis CL-P. Therefore, the shape of the magnetic path member 150 may be a square, a triangle, or the like, or it may be a ring shape with asymmetrical thickness on the expansion chamber wall side and the non-wall side.

[0082] (3) Furthermore, the material of the magnetic path member 150 is not limited to one mainly composed of soft magnetic materials such as mild iron, but may also be mainly composed of magnetic materials such as steel, mu-metal, or magnets.

[0083] (4) In addition, although the microwave driver 140 generated hydrogen plasma in each of the above embodiments, the microwave driver 140 may generate plasma other than hydrogen plasma.

[0084] (5) In the third and fourth embodiments (see Figures 10 and 11), the microwave drivers 140-0 that are not adjacent to the inner wall 161a of the chamber 161 were not provided with corresponding magnetic path members 150. However, the microwave drivers 140-0 may also be provided with magnetic path members 150 having a symmetrical or uniform magnetic path configuration. For example, a general uniform iron plate may be used as the magnetic path member 150, or magnets arranged in a checkerboard pattern may be used as the magnetic path member 150.

[0085] (6) In the third and fourth embodiments (see Figures 10 and 11), the microwave driver 140-0 located in the center may be omitted.

[0086] (7) Furthermore, the NBI devices 1 to 4 of each of the above embodiments can be applied not only to the fusion device 70, but also to various other devices such as particle beam medical devices and non-destructive testing devices.

[0087] [Effects of the Embodiment] As described above, according to each embodiment, the ion source 11 to 14 comprises a plurality of plasma generation units (140), each having a magnetic flux generating unit (143); an expansion chamber 160 connected to the plurality of plasma generation units (140) and emitting charged particles; and a magnetic path member 150 through which the magnetic flux generated by the magnetic flux generating unit (143) passes. The magnetic flux density in the internal space of the expansion chamber 160 is defined as the first magnetic flux density (B), the magnetic flux density in the internal space of the expansion chamber 160 when the magnetic path member 150 is removed is defined as the second magnetic flux density (B0), and the result of dividing the first magnetic flux density (B) by the second magnetic flux density (B0) is defined as the magnetic flux density ratio (B / B0). The magnetic path member 150 is formed such that the magnetic flux density ratio (B / B0) at the central axis CL-P of the expansion chamber 160 and the magnetic flux density ratio (B / B0) at the peripheral edge of the expansion chamber 160 are different. This allows the magnetic flux density ratio (B / B0) inside the expansion chamber 160 to be controlled by the shape of the magnetic path member 150, thereby achieving a first magnetic flux density (B) according to the purpose, and thus enabling appropriate control of the distribution of charged particles.

[0088] Furthermore, it is even more preferable that the magnetic path members 150 are provided so as to protrude from each plasma generation section (140) toward the central axis CL-P of the expansion chamber 160, or in a direction away from the central axis CL-P. This allows the distribution of charged particles to be controlled according to the degree of protrusion of the magnetic path members 150.

[0089] Furthermore, it is even more preferable that the magnetic path member 150 has a semi-circular shape. This makes it possible to reduce the first magnetic flux density (B) in the portion along the semi-circular shape within the internal space of the expansion chamber 160.

[0090] Furthermore, it is even more preferable that the magnetic path member 150 contains a soft magnetic material. This allows the magnetic flux generating unit (143) to flexibly control the first magnetic flux density (B).

[0091] Furthermore, the magnetic path members 150 are provided so as to protrude from each plasma generation section (140) toward the central axis CL-P of the expansion chamber 160, and it is even more preferable for the expansion chamber 160 to be equipped with a converter 2000 that performs charge conversion of charged particles. This allows the converter 2000 to perform charge conversion of charged particles.

[0092] Furthermore, it is even more preferable that the system further includes a microwave source 136 that supplies microwaves to each plasma generation unit (140), the magnetic flux generation unit (143) is a solenoid coil, and the plasma generation unit (140) generates plasma using the supplied microwaves and the magnetic field generated by the magnetic flux generation unit (143). This allows plasma to be generated by microwaves radiated from the microwave source 136.

[0093] Furthermore, as in the ion source 13 of the third embodiment, the plurality of plasma generation units (140) include first to nth plasma generation units (140-1 to 140-n) arranged at equal intervals along the circumferential direction of the expansion chamber 160, where n is a natural number of 2 or more. It is even more preferable that the magnetic path member 150 includes first to nth magnetic path members (150-1 to 150-n) provided to protrude from the respective central axes CL-1 to CL-n of the first to nth plasma generation units (140-1 to 140-n) in a direction away from the central axis CL-P of the expansion chamber 160 within an angular range of "360° / n". This allows for the application of a large number of plasma generation units (140) and increases the current output.

[0094] Furthermore, as in the NBI devices 1 to 4 of each embodiment, it is even more preferable to include ion sources 11 to 14 and a neutralization cell 52 that converts charged particles released from the expansion chamber 160 into neutral particles. This makes it possible to release neutral particles. [Explanation of Symbols]

[0095] 1~4 NBI device (neutral particle injection device) 11-14 Ion source 12 Ion sources 13 Ion Source 14 Ion Sources 52 Neutralizing cells 136 Microwave Source 140 Microwave Driver (Plasma Generation Unit) 140-1~140-n Microwave Driver (1st to nth Plasma Generation Section) 143 Solenoid coil (magnetic flux generating part) 150 Magnetic path member 150-1 to 150-n Magnetic circuit members (1st to nth magnetic circuit members) 160 Expansion Room 2000 Converter B Magnetic flux density (first magnetic flux density) B0 magnetic flux density (second magnetic flux density) B / B0 magnetic flux density ratio CL-P center axis CL-1~CL-n Center axis

Claims

1. Multiple plasma generation units, each equipped with a magnetic flux generating unit, An expansion chamber connected to multiple plasma generation units and emitting charged particles, The system includes a magnetic path member that allows the magnetic flux generated by the magnetic flux generating unit to pass through, The magnetic flux density in the internal space of the expansion chamber is defined as the first magnetic flux density, the magnetic flux density in the internal space of the expansion chamber when the magnetic path member is removed is defined as the second magnetic flux density, the result of dividing the first magnetic flux density by the second magnetic flux density is defined as the magnetic flux density ratio, and the magnetic path member is formed such that the magnetic flux density ratio at the central axis of the expansion chamber and the magnetic flux density ratio at the peripheral edge of the expansion chamber are different. An ion source characterized by the following features.

2. The magnetic path members are provided to protrude from each of the plasma generation sections toward the central axis of the expansion chamber, or toward the direction away from the central axis. The ion source according to feature 1.

3. The magnetic path member has a semicircular shape. The ion source according to feature 2.

4. The magnetic path member includes a soft magnetic material. The ion source according to feature 2.

5. The magnetic path members are provided so as to protrude from each of the plasma generation sections toward the central axis of the expansion chamber, The aforementioned expansion chamber includes a converter that performs charge conversion of charged particles. The ion source according to feature 2.

6. The system further comprises a microwave source that supplies microwaves to each of the aforementioned plasma generation units. The magnetic flux generating unit is a solenoid coil, The plasma generation unit generates plasma using supplied microwaves and the magnetic field generated by the magnetic flux generation unit. The ion source according to feature 2.

7. The plurality of plasma generation units include first to n plasma generation units arranged at equal intervals along the circumferential direction of the expansion chamber, where n is a natural number of 2 or more. The magnetic path members include first to n magnetic path members provided so as to protrude from the central axis of each of the first to n plasma generation sections in a direction away from the central axis of the expansion chamber within an angular range of "360° / n". The ion source according to feature 2.

8. An ion source according to any one of claims 1 to 7, The system comprises a neutralization cell that converts charged particles released from the expansion chamber into neutral particles. A neutral particle injection device characterized by the following features.

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