Magnetic circuit device, optical device, and electron beam device

Abstract

To provide a magnetic circuit device, an optical device, and an electron beam device capable of generating a uniform axisymmetric magnetic field.SOLUTION: The magnetic circuit device includes a magnet disposed along a predetermined axis, and a magnetic member covering an outer periphery of the magnet, wherein the magnet is magnetized in a radial direction about the axis, and a ratio between a magnet magnetic path length of the magnet and a gap space magnetic path length of a gap space excluding the magnet and the magnetic member is set to a constant value on a closed magnetic path of magnetic lines of force by the magnet.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a magnetic circuit device, an optical device, and an electron beam device. [Background technology]

[0002] A solenoid coil can be used to generate a uniform, long, axially symmetric magnetic field. However, solenoid coils consume a large amount of power, which may require cooling, and the device configuration becomes large. On the other hand, anisotropic permanent magnets can generate a strong magnetic field without consuming power. Patent Document 1 discloses the structure of a motor with magnets arranged in a Halbach array. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2023-167260 Summary of the Invention [Problem to be solved by the invention]

[0004] Magnets arranged in a Halbach array are effective for generating a strong magnetic field, but are not suitable for generating a long magnetic field distribution such as an axially symmetric magnetic field.

[0005] The present invention has been made in view of the above circumstances, and has as its object to provide a magnetic circuit device, an optical device, and an electron beam device that are capable of generating a uniform, axially symmetric magnetic field. [Means for solving the problem]

[0006] The present application includes multiple means for solving the above-mentioned problems, and one example is a magnetic circuit device comprising a magnet arranged along a predetermined axis and a magnetic material member covering the outer periphery of the magnet, the magnet being magnetized in the radial direction centered on the axis, and in a closed magnetic path of the magnetic field lines formed by the magnet, the ratio of the magnet magnetic path length of the magnet to the gap space magnetic path length of the gap space excluding the magnet and the magnetic material member is set to a constant value. [Effects of the Invention]

[0007] According to the present invention, a uniform, axially symmetric magnetic field can be generated. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a diagram showing a first example of a magnetic circuit device according to an embodiment of the present invention; [Figure 2] FIG. 3 is a diagram showing an example of a distribution of magnetic flux density in the first example of the magnetic circuit device. [Figure 3] FIG. 2 is a diagram illustrating an example of the configuration of a Faraday rotator according to the present embodiment. [Figure 4] FIG. 4 is a diagram showing a second example of the magnetic circuit device of the present embodiment. [Figure 5] FIG. 10 is a diagram showing an example of a distribution of magnetic flux density in the second example of the magnetic circuit device. [Figure 6] FIG. 4 is a diagram showing a third example of the magnetic circuit device of the present embodiment. [Figure 7] FIG. 10 is a diagram showing an example of a distribution of magnetic flux density in the third example of the magnetic circuit device. [Figure 8] FIG. 1 is a diagram illustrating an example of the configuration of a klystron according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] The present invention will be described below with reference to the drawings showing embodiments thereof. Fig. 1 is a diagram showing a first example of a magnetic circuit device 100 according to this embodiment. In Fig. 1, the Z axis is set in the horizontal direction and the R axis is set in the vertical direction, and a cross-sectional view of the magnetic circuit device 100 taken along the ZR plane is shown. Note that the actual magnetic circuit device 100 has an antisymmetric structure centered on the R axis, and an axially symmetric structure centered on the Z axis (axial center 5), but for convenience, the structure of the lower half of the Z axis (-R axis) is omitted.

[0010] The magnetic circuit device 100 includes a magnet 30 and a magnetic member 20. The magnet 30 is a permanent magnet, a cylindrical magnet magnetized in the radial direction and arranged along the Z axis, which is a predetermined axis. For ease of manufacturing, this cylindrical magnet may be constructed by combining multiple sector-shaped magnets. If the number of divisions is large, the sector shape may be approximated by a trapezoid. In this example, the cylindrical magnet is divided into approximately 20 sections. More specifically, the magnetic circuit device 100 has multiple magnets 30 arranged cylindrically around the Z axis. The multiple magnets 30 are also arranged antisymmetrically with respect to the R axis. The cross-sectional shape of each of the multiple magnets 30 on the ZR plane is a pentagon, resembling a rectangle with one corner obliquely cut off. This shape allows the ratio of the magnetic path length of the magnet 30 to the gap space magnetic path length of the gap space excluding the magnet 30 and the magnetic member 20 to be approximately constant (a), as described below, in the closed magnetic path of the magnetic field lines formed by the magnet 30. In addition, on each closed magnetic circuit of the numerous magnetic lines of force, the ratio of the magnet magnetic path length of the magnet 30 to the gap space magnetic path length of the gap space excluding the magnet 30 and the magnetic material member 20 can be set to approximately a constant value a. The cross section of the magnet 30 need only be able to maintain this ratio at an approximately constant value, so it does not have to be pentagonal.

[0011] The magnets 30 are magnetized radially around the Z axis. In the figure, the arrows indicate the magnetization direction. One magnet 30 is magnetized outward in the figure, with the R axis as the boundary, and the other magnet 30 is magnetized inward. In Figure 1, the magnetic field lines of the magnets 30 are shown schematically. Note that the magnetic field lines are shown for convenience and may differ from the actual magnetic field lines. The magnets 30 include, for example, rare earth magnets or ferromagnetic anisotropic ferrite magnets, but are not limited to these.

[0012] The magnetic material member 20 is arranged so as to cover the outer periphery of the magnet 30. More specifically, the magnetic material member 20 is arranged cylindrically around the Z axis along the outer periphery of the magnet 30. The magnetic material member 20 is attached to a cylindrical outer frame 10. The magnetic material member 20 includes, for example, a high-permeability soft magnetic material, but is not limited to this.

[0013] The magnetic circuit device 100 is surrounded by the magnet 30 and includes a space 40 arranged along the Z axis. The space 40 is an area where the axially symmetric magnetic field generated by the magnet 30 is distributed. The magnetic material member 10 is a member that absorbs and shields magnetic flux that leaks to the outside. If the distance to the magnet 30 is too close, more magnetic flux than necessary will be absorbed to the outside, reducing the magnetic flux density at the center, so it is necessary to maintain a distance from the magnet 30 that is approximately the radius of the magnet 30.

[0014] In FIG. 1, consider magnetic field lines passing through the magnet 30 and the magnetic member 20. While multiple such magnetic field lines exist, we will focus on an arbitrary magnetic field line. In the closed magnetic path of the magnetic field lines by the magnet 30, the ratio of the magnet magnetic path length of the magnet 30 (2×Lpm in the example of FIG. 1) to the gap space magnetic path length of the gap space excluding the magnet 30 and the magnetic member 20 (Lgap in the example of FIG. 1) is set to a constant value a. That is, when 2×Lpm = Lpm′, Lpm′ / Lgap = a. Below, we will explain how setting Lpm′ / Lgap = a makes the axially symmetric magnetic field (magnetic flux density Bz) in the Z-axis direction in the space 40 uniform (homogeneous). Note that while there are multiple magnetic field lines passing through the magnet 30, the magnetic member 20, and the gap space excluding the magnet 30 and the magnetic member 20, Lpm′ / Lgap = a is set on each closed magnetic path of the multiple magnetic field lines. In the example of FIG. 1, in a usable region 41 (shown by a broken line) of the space 40, the magnetic flux density Bz in the Z-axis direction can be made uniform.

[0015]

number

[0016] Equation (1) is established from Ampere's law. As the magnet 30 is a permanent magnet, the current j = 0. By considering the path Γ of the closed magnetic circuit, performing a surface integral, and using Stokes' theorem, equation (3) can be obtained from equation (2). By dividing the path Γ of the closed magnetic circuit into the magnetic path length Lpm of the magnet, the magnetic path length Lgap of the gap space, and the magnetic path length Liron of the magnetic material 20, equation (4) is obtained. Assuming that the magnetic field lines are continuous and that the magnetic flux density is uniform and nearly the same in each of the magnet 30, magnetic material 20, and gap space, equation (5) is obtained.

[0017] In equation (5), if we assume that the magnetic permeability μ is sufficiently large, we can ignore the third term in equation (5), and thus obtain equation (6). Meanwhile, within the magnet, if the magnetization of magnet 30 is M, equation (7) holds. Hm is the observed magnetic field. Using equation (8), equation (9) can be obtained from equations (6) and (7).

[0018] Equation (9) shows that when Lpm / Lgap=a is a constant value, the magnetic flux density B is a constant value. In other words, by setting Lpm / Lgap=a, the axially symmetric magnetic field (magnetic flux density Bz) in the Z-axis direction in the space portion 40 can be made uniform (uniform).

[0019] As described above, the magnetic circuit device 100 of this embodiment can generate a uniform, axially symmetric magnetic field.

[0020]

number

[0021] In the cylindrical coordinate system, divB=0 in Maxwell's equations can be written as equation (10). Because it is axially symmetric, the derivative with respect to θ in equation (10) (second term) is zero, and if it is uniform in the axial direction, the derivative with respect to z (third term) is also zero. Therefore, the derivative with respect to r of the first term in equation (10) is also zero. In other words, it becomes uniform. Also, since there is no current, the rotation is also zero, and equation (11) holds. Because it is axially symmetric, the derivative with respect to φ in equation (11) is zero, and Bφ is also zero, leaving only the second term. In other words, equation (12) holds. From equation (12), if there is no change in Br in the Z direction, there will be no change in Bz in the r direction either. Therefore, if Br is uniform in the Z direction, Bz will be uniform in the r direction.

[0022] FIG. 2 is a diagram showing an example of the distribution of magnetic flux density according to the first example of the magnetic circuit device 100. In FIG. 2, the vertical axis represents magnetic flux density, and the horizontal axis represents the Z axis. Although the magnetic flux density is axially symmetric, for ease of measurement, it is measured using Bx, By, and Bz. FIG. 2 also shows magnetic flux densities Bx, By, and Bz in the X, Y, and Z directions, respectively. As shown in FIG. 2, Bx and By are almost zero, and a uniform magnetic field is obtained in the Z axis direction. The magnetic flux density Bz has a value equal to or greater than a predetermined value in the usable region centered around Z=0. The usable region shown in FIG. 2 corresponds to the usable region 41 in FIG. 1. Thus, in the magnetic circuit device 100 of this embodiment, the magnetic flux density Bz in the Z axis direction has a value equal to or greater than a predetermined value in the usable region 41 along the Z axis direction.

[0023] FIG. 3 is a diagram showing an example of the configuration of a Faraday rotator 200 according to this embodiment. The Faraday rotator 200 is an optical device equipped with the magnetic circuit device 100 illustrated in FIG. 1. The Faraday rotator 200 includes a cylindrical magnetic outer cylinder 230, which can be divided into two parts at the center, allowing the device interior to be opened and closed. The magnetic circuit device 100 is incorporated within the Faraday rotator 200. As shown in FIG. 3, multiple magnets 30 are arranged cylindrically within the magnetic outer cylinder 230, and a magnetic member 20 is arranged around the magnets 30. A disk-shaped copper plate 220 is provided in the center of the magnetic outer cylinder 230, and a crystal disk 210 is arranged in the center of the copper plate 220. The copper plate 220 contributes to cooling the crystal. The bore diameter can be, for example, 30 mm, but is not limited thereto.

[0024] The Faraday rotator 200 can be used to configure an optical device (optical isolator) that allows light to pass through only one direction. The optical isolator consists of an input polarizer, a Faraday rotator 200, and an output polarizer. The Faraday rotator 200 is composed of a magnetic circuit device 100 and a crystal disk 210 with a high Verdet constant. When light enters the input polarizer, it exits as linearly polarized light in the direction of the polarizer. By rotating this polarization by 45° within the Faraday rotator 200 and tilting the output polarizer by 45°, the polarization direction of the light can be matched with that of the laser and transmitted. The crystal disk 210 is placed within the axially symmetric magnetic field of the magnetic circuit device 100. The length of the crystal disk 210 and the strength of the magnetic field are adjusted so that the polarization of the light exiting the crystal disk 210 is rotated by 45°, thereby maximizing the intensity of the passing beam. Furthermore, the light waves returning in the opposite direction are polarized by 90 degrees after rotating another 45 degrees from the output polarizer tilted by 45 degrees by the crystal disk 210, and do not pass through the input polarizer, so that the light does not return to the laser side. The Faraday rotator 200 as an optical device includes a magnetic circuit device 100.

[0025] Fig. 4 is a diagram showing a second example of the magnetic circuit device 110 of this embodiment. In Fig. 4, the Z axis is set in the horizontal direction and the R axis is set in the vertical direction, and a cross-sectional view of the magnetic circuit device 110 in the ZR plane is shown. Note that the actual magnetic circuit device 110 has an axisymmetric structure with the Z axis at the center (axial center 5), but for convenience, the structure of the lower half of the Z axis (-R axis) is omitted.

[0026] The magnetic circuit device 110 includes a magnet 30 and a magnetic member 20. The magnet 30 is a permanent magnet, a cylindrical magnet magnetized in the radial direction and arranged along the Z axis, which is a predetermined axis. For ease of manufacturing, this cylindrical magnet may be configured by combining multiple sector-shaped magnets or the like. More specifically, the magnetic circuit device 100 includes multiple cylindrical magnets 30 with different inner diameters arranged along the Z axis (18 magnets in the Z axis direction in the example of FIG. 4). For example, if 20 cylindrical magnets 30 each consisting of a trapezoidal magnet are arranged cylindrically around the Z axis, the magnetic circuit device 110 includes 20 × 18 = 360 trapezoidal magnets. The number of magnets 30 can be set as appropriate.

[0027] The multiple magnets 30 arranged along the Z axis are formed so that the thickness (dimension in the R axis direction or radial direction centered on the Z axis) of the magnets 30 gradually increases with increasing distance from the center of the magnetic circuit device 110 toward the Z axis direction (and the -Z axis direction). The multiple magnets 30 are also arranged antisymmetrically with respect to the R axis. The cross-sectional shape of each of the multiple magnets 30 on the ZR plane is rectangular. By using such a shape, as will be described later, the ratio of the magnet magnetic path length of the magnet 30 to the gap space magnetic path length of the gap space excluding the magnet 30 and the magnetic material member 20 can be approximately constant value a on the closed magnetic path of the magnetic field lines formed by the magnet 30. Note that the ratio of the magnet magnetic path length of the magnet 30 to the gap space magnetic path length of the gap space excluding the magnet 30 and the magnetic material member 20 can be approximately constant value a on each closed magnetic path of the multiple magnetic field lines.

[0028] The multiple magnets 30 are magnetized in the radial direction centered on the Z axis. More specifically, the nine magnets 30 arranged in the Z axis direction from the center of the magnetic circuit device 110 are magnetized, for example, outward in the figure, and the nine magnets 30 arranged in the -Z axis direction from the center of the magnetic circuit device 110 are magnetized inward in the figure. In Figure 4, the magnetic field lines of the multiple magnets 30 are schematically illustrated. Note that the magnetic field lines are illustrated for convenience and may differ from the actual magnetic field lines.

[0029] The magnetic member 20 is disposed so as to cover the outer periphery of the magnet 30. More specifically, the magnetic member 20 is disposed along the outer periphery of the magnet 30 in a cylindrical shape around the Z axis.

[0030] The magnetic circuit device 110 includes a space 40 that is surrounded by the multiple magnets 30 and is arranged along the Z axis. The space 40 is a region in which the axially symmetric magnetic field generated by the multiple magnets 30 is distributed.

[0031] In FIG. 4, consider the magnetic field lines passing through the magnet 30 and the magnetic member 20. Although there are multiple such magnetic field lines, we will focus on an arbitrary magnetic field line. In the closed magnetic path of the magnetic field lines by the magnet 30, the ratio of the magnet magnetic path length of the magnet 30 (2×Lpm in the example of FIG. 4) to the gap space magnetic path length of the gap space excluding the magnet 30 and the magnetic member 20 (Lgap in the example of FIG. 4) is set to a constant value a. In other words, if 2×Lpm=Lpm′, then Lpm′ / Lgap=a. By setting Lpm′ / Lgap=a, the axially symmetric magnetic field (magnetic flux density Bz) in the Z-axis direction in the space portion 40 can be made uniform (uniform), and a uniform axially symmetric magnetic field can be generated.

[0032] As described above, the magnetic circuit device 110 includes a plurality of magnets 30 arranged along the Z axis (a predetermined axis), and each magnet has a constant ratio between the magnetic path length of the magnet and the gap space magnetic path length of the gap space excluding the magnet and the magnetic material member on the closed magnetic path of the magnetic field lines formed by the magnet. This allows for the generation of a uniform, axially symmetric magnetic field.

[0033] FIG. 5 is a diagram showing an example of the distribution of magnetic flux density according to the second example of the magnetic circuit device 110. In FIG. 5, the vertical axis represents the magnetic flux density Bz in the Z-axis direction, and the horizontal axis represents the Z-axis. As shown in FIG. 5, the magnetic flux density Bz in the Z-axis direction is a required value (above a predetermined value) within a required distance range from the center (Z=0) of the magnetic circuit device 110 toward the Z-axis direction. That is, the magnetic flux density Bz has a value above a predetermined value in a usable region centered around Z=0. The usable region shown in FIG. 5 corresponds to the usable region 41 in FIG. 4. Thus, in the magnetic circuit device 110 of this embodiment, the magnetic flux density Bz in the Z-axis direction has a value above a predetermined value in the usable region 41 along the Z-axis direction.

[0034] Note that, since the magnetic flux density Bz is integrated over a closed magnetic circuit to zero, an inverse magnetic field occurs in areas other than the usable area, as shown in Fig. 5. Furthermore, although not shown, the magnetic flux density Bz in the Z-axis direction becomes a required value (above a predetermined value) within a required distance range from the center (Z=0) of the magnetic circuit device 110 toward the -Z-axis direction, resulting in the same magnetic field distribution.

[0035] The magnetic circuit device 110 can be used in beam transport systems, for example, as a magnetic channel for transporting charged particles.

[0036] Fig. 6 is a diagram showing a third example of the magnetic circuit device 120 of this embodiment. In Fig. 6, the Z axis is set in the horizontal direction and the R axis is set in the vertical direction, and a cross-sectional view of the magnetic circuit device 120 taken along the ZR plane is shown. Note that the actual magnetic circuit device 120 has an axisymmetric structure centered on the Z axis, but for convenience, the structure of the lower half of the Z axis (-R axis) is omitted.

[0037] The magnetic circuit device 120 includes a magnet 30 and a magnetic member 20. The magnet 30 is a permanent magnet, a cylindrical magnet magnetized in the radial direction and arranged along the Z axis, which is a predetermined axis. For ease of manufacturing, this cylindrical magnet may be configured by combining multiple sector-shaped magnets, or if the number of divisions is large, the sector shape may be approximated by a trapezoid. Here, the cylindrical magnet is configured by dividing it into approximately 20 parts. More specifically, the magnetic circuit device 120 includes multiple cylindrical magnets 30 arranged along the Z axis (10 in the Z axis direction in the example of FIG. 6). For example, if 20 magnets 30 are arranged cylindrically around the Z axis, the magnetic circuit device 120 includes 20 × 10 = 200 magnets 30. The number of magnets 30 can be set as appropriate.

[0038] The multiple magnets 30 arranged along the Z axis are formed so that the thickness (dimension in the R axis direction or radial direction centered on the Z axis) of the magnets 30 gradually increases with distance from the center of the magnetic circuit device 120 toward the Z axis direction (and the -Z axis direction). The cross-sectional shape of each of the multiple magnets 30 on the ZR plane is preferably a trapezoid with a gradually changing inner diameter, but may also be rectangular because the magnetic field region is away from the magnet end faces. By using such a shape, as will be described later, the ratio of the magnet magnetic path length of the magnet 30 to the gap space magnetic path length of the gap space excluding the magnet 30 and the magnetic material member 20 can be approximately constant (a) in the closed magnetic path of the magnetic field lines formed by the magnet 30. The ratio of the magnet magnetic path length of the magnet 30 to the gap space magnetic path length of the gap space excluding the magnet 30 and the magnetic material member 20 can be approximately constant (a) in each closed magnetic path of the multiple magnetic field lines. Fine adjustment of this ratio can create a gradient in the magnetic field strength.

[0039] The multiple magnets 30 are magnetized in the radial direction centered on the Z axis (indicated by arrows in the figure). More specifically, the five magnets 30 arranged in the Z axis direction from the center of the magnetic circuit device 120 are magnetized outward in the figure, for example, and the five magnets 30 arranged in the −Z axis direction from the center of the magnetic circuit device 120 are magnetized inward in the figure. Note that the five magnets 30 arranged in the Z axis direction from the center of the magnetic circuit device 120 may be magnetized downward in the figure, and the five magnets 30 arranged in the −Z axis direction from the center of the magnetic circuit device 120 may be magnetized outward in the figure. In FIG. 6, the magnetic field lines of the multiple magnets 30 are schematically illustrated. Note that the magnetic field lines are illustrated for convenience and may differ from the actual magnetic field lines.

[0040] The magnetic member 20 is disposed so as to cover the outer periphery of the magnet 30. More specifically, the magnetic member 20 is disposed along the outer periphery of the magnet 30 in a cylindrical shape around the Z axis.

[0041] The magnetic circuit device 120 includes a space 40 that is surrounded by the multiple magnets 30 and is arranged along the Z axis. The space 40 is a region in which the axially symmetric magnetic field generated by the multiple magnets 30 is distributed.

[0042] In FIG. 6, consider the magnetic field lines passing through the magnet 30 and the magnetic member 20. Although there are multiple such magnetic field lines, we will focus on an arbitrary magnetic field line. In the closed magnetic path of the magnetic field lines by the magnet 30, the ratio of the magnet magnetic path length of the magnet 30 (2×Lpm in the example of FIG. 6) to the gap space magnetic path length of the gap space excluding the magnet 30 and the magnetic member 20 (Lgap in the example of FIG. 6) is set to a constant value a. In other words, if 2×Lpm=Lpm′, then Lpm′ / Lgap=a. By setting Lpm′ / Lgap=a, the axially symmetric magnetic field (magnetic flux density Bz) in the Z-axis direction in the space portion 40 can be made uniform (uniform), and a uniform axially symmetric magnetic field can be generated.

[0043] When a gap exists between the magnet 30 and the magnetic member 20 on the closed magnetic path of the magnetic field lines of the magnet 30, the gap may be included in the gap space.

[0044] As described above, the magnetic circuit device 120 includes multiple magnets 30 arranged along the Z axis (a predetermined axis), and each magnet has a constant ratio between the magnetic path length of the magnet and the gap space magnetic path length of the gap space excluding the magnet and the magnetic material member in the closed magnetic path of the magnetic field lines formed by the magnet. This allows for the generation of a substantially uniform, axially symmetric magnetic field. Furthermore, by fine-tuning this ratio, it is possible to create a gradient in the magnetic field strength.

[0045] FIG. 7 is a diagram showing an example of the distribution of magnetic flux density according to the third example of the magnetic circuit device 120. In FIG. 7, the vertical axis represents the magnetic flux density Bz in the Z-axis direction, and the horizontal axis represents the Z-axis. As shown in FIG. 7, the magnetic flux density Bz in the Z-axis direction is equal to or greater than a predetermined value within the usable region of the magnetic circuit device 120 from a predetermined position (Z=50) along the Z-axis direction, and gradually increases as the value of the Z-axis increases. The usable region shown in FIG. 7 corresponds to the usable region 41 in FIG. 6. In this way, the magnetic circuit device 120 of this embodiment has a distribution in which the magnetic flux density Bz in the Z-axis direction is a predetermined value within the usable region 41 along the Z-axis direction.

[0046] Furthermore, by finely adjusting the ratio (Lpm' / Lgap=a) on the closed magnetic circuit, it is possible to impart a gradient to the magnetic flux density Bz (magnetic field strength) in the Z-axis direction, as shown in Fig. 7. In the example of Fig. 7, it is possible to impart a gradient such that the magnetic field strength gradually increases from the position Z=50 to the position Z=400 in the usable region. In other words, the magnetic circuit device 120 includes within the space portion 40 a region in which the magnetic field strength in the axial direction has a gradient according to the value of the ratio.

[0047] 8 is a diagram showing an example of the configuration of a klystron 300 according to this embodiment. Klystron 300, an electron beam device, is an electron tube used to amplify microwaves. Klystron 300 includes an electron gun, a cathode, an input cavity, an intermediate cavity, an output cavity, and a collector. When a low-power radio frequency wave is injected into the cavity under conditions that favor resonance as the electron beam passes through the cavity, resonance occurs between the electron beam and the cavity, enabling high-power radio frequency waves to be extracted from the cavity.

[0048] Electrons emitted from the cathode are accelerated by the anode and enter the input cavity. The electrons are accelerated or decelerated depending on the phase of the microwave introduced into the input cavity. Electrons traveling in the axially symmetric magnetic field generated by the magnetic circuit device 120 in the intermediate cavity are gradually bunched together as accelerated and decelerated electrons. The bunched electrons are gradually strengthened by the high-frequency electric field in the intermediate cavity. When the bunched electron beam passes through the output cavity, a strong AC electric field is induced, and a high-power microwave is output. Klystron 300 as an electron beam device is equipped with magnetic circuit device 120.

[0049] As described above, the magnetic circuit device of this embodiment is configured with multiple magnets 30 (20 in the example described above) arranged in a cylindrical shape around the Z axis. However, the arrangement of the multiple magnets 30 is not limited to a cylindrical arrangement around the Z axis. Depending on the type and structure of the device in which the magnetic circuit device is used, the multiple magnets 30 may be arranged, for example, in an elliptical or polygonal shape around the Z axis. Furthermore, gaps may be present rather than covering all angles. In this case, the higher the symmetry around the Z axis, the better the uniformity (homogeneity) of the magnetic flux density in the Z axis direction. Furthermore, when the multiple magnets 30 are arranged in an elliptical shape around the Z axis, the ratio (Lpm' / Lgap=a) can be kept constant by adjusting the radial thickness of the multiple magnets 30.

[0050] The magnetic circuit device of this embodiment can generate a long, uniform magnetic field in the axial direction, similar to the magnetic field generated by a solenoid coil. Furthermore, since a permanent magnet is used, no power is consumed, so no cooling water is required, and there is no need to worry about water leaks, which can be fatal in high-voltage equipment. Furthermore, no high-power power supply is required, eliminating the need for maintenance and breakdowns.

[0051] Furthermore, the magnetic circuit device of this embodiment does not require a structure for passing current, such as a solenoid coil, and does not pass current, so although an inverse magnetic field is generated on the closed magnetic path of the magnetic field lines generated by the magnet, it is sufficient to avoid using the area where the inverse magnetic field is generated.

[0052] Furthermore, according to the magnetic circuit device of this embodiment, when a uniform magnetic field is generated in the axial direction, the magnetic field in the radial direction around the axis can also be made uniform (even). In a Faraday rotator equipped with the magnetic circuit device of this embodiment, the magnetic field applied to the crystal disk can be made uniform in the radial direction.

[0053] Furthermore, according to the magnetic circuit device of this embodiment, a magnet magnetized in the radial direction around the axis is used, and therefore leakage magnetic flux can be reduced by using a magnetic material (e.g., a high-permeability soft magnetic material) that covers the outer periphery of the magnet.

[0054] In the above-described embodiments, a Faraday rotator was described as an example of an optical device that uses a magnetic circuit device, a klystron was described as an example of an electron beam device, and a beam transport system was described. However, devices that can use the magnetic circuit device of this embodiment are not limited to these, and any device can be used as long as it uses a uniform, axially symmetric magnetic field generated by the magnetic circuit device.

[0055] (Note 1) A magnetic circuit device comprises a magnet arranged along a predetermined axis and a magnetic material member covering the outer periphery of the magnet, the magnet being magnetized in the radial direction centered on the axis, and the ratio of the magnet magnetic path length of the magnet to the gap space magnetic path length of the gap space excluding the magnet and the magnetic material member being a constant value on a closed magnetic path of the magnetic field lines formed by the magnet.

[0056] (Supplementary Note 2) The magnetic circuit device according to Supplementary Note 1 includes a plurality of magnets arranged along the predetermined axis, and each magnet has a constant ratio between the magnet magnetic path length of the magnet and the gap space magnetic path length of the gap space excluding the magnet and the magnetic material member on a closed magnetic path of the magnetic field lines formed by the magnet.

[0057] (Supplementary Note 3) In the magnetic circuit device according to Supplementary Note 1 or Supplementary Note 2, the magnet is arranged cylindrically around the axis.

[0058] (Supplementary Note 4) The magnetic circuit device according to any one of Supplementary Note 1 to Supplementary Note 3 further comprises a space surrounded by the magnet and arranged along the axis.

[0059] (Supplementary Note 5) In the magnetic circuit device according to Supplementary Note 4, the space includes a region in which the magnetic flux density in the axial direction is equal to or greater than a predetermined value.

[0060] (Supplementary Note 6) The magnetic circuit device according to Supplementary Note 4 further includes, within the space, a region having a gradient in magnetic field strength in the axial direction according to the value of the ratio.

[0061] (Supplementary Note 7) In the magnetic circuit device according to any one of Supplementary Note 1 to Supplementary Note 6, the magnet includes a rare earth magnet or a ferromagnetic anisotropic ferrite magnet.

[0062] (Supplementary Note 8) In the magnetic circuit device according to any one of Supplementary Notes 1 to 7, the magnetic material member includes a high-permeability soft magnetic material.

[0063] (Supplementary Note 9) The optical device includes the magnetic circuit device according to any one of Supplementary Note 1 to Supplementary Note 8.

[0064] (Supplementary Note 10) An electron beam device includes a magnetic circuit device according to any one of Supplementary Note 1 to Supplementary Note 8.

[0065] The matters described in each embodiment can be combined with each other. In addition, the independent claims and dependent claims described in the claims can be combined with each other in any combination, regardless of the reference format. Furthermore, although the claims use a format in which a claim references two or more other claims (multiple claim format), this is not limited to this format. A multiple claim (multi-multi claim) that references at least one other multiple claim may also be used. [Explanation of symbols]

[0066] 5 axis center 10 Outer Frame 20 Magnetic materials 30 Magnet 40 Space section 41 Available area 100, 110, 120 Magnetic circuit device 200 Faraday Rotator 210 Crystal Disk 220 Copper plate 230 Magnetic outer cylinder 300 Klystron

Claims

1. a magnet arranged along a predetermined axis; a magnetic member covering the outer periphery of the magnet; Equipped with The magnet is magnetized in a radial direction about the axis, In a closed magnetic path of magnetic lines of force formed by the magnet, the ratio of the magnetic path length of the magnet to the gap space magnetic path length of the gap space excluding the magnet and the magnetic material member is set to a constant value. Magnetic circuit device.

2. a plurality of magnets arranged along the predetermined axis; Each magnet is In a closed magnetic path of the magnetic lines of force formed by the magnets, the ratio of the magnetic path length of each magnet to the gap space magnetic path length of the gap space excluding the magnets and the magnetic material member is set to a constant value. The magnetic circuit device according to claim 1 .

3. The magnet is cylindrically arranged around the axis, The magnetic circuit device according to claim 1 or 2.

4. a space surrounded by the magnet and arranged along the axis; The magnetic circuit device according to claim 1 or 2.

5. The space portion includes a region where the magnetic flux density in the axial direction is equal to or greater than a predetermined value. The magnetic circuit device according to claim 4.

6. The space portion includes a region having a gradient in magnetic field strength in the axial direction according to the value of the ratio. The magnetic circuit device according to claim 4.

7. The magnet includes a rare earth magnet or a ferromagnetic anisotropic ferrite magnet. The magnetic circuit device according to claim 1 or 2.

8. The magnetic member includes a high-permeability soft magnetic material. The magnetic circuit device according to claim 1 or 2.

9. An optical device comprising the magnetic circuit device according to claim 1 or 2.

10. 3. An electron beam device comprising the magnetic circuit device according to claim 1.

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