Deflection electromagnet and particle beam radiation device

Abstract

To provide a deflection electromagnet which satisfies the requirements for deflecting charge particle beams and also can reduce the winding time of a wire rod, and a technique related to the deflection electromagnet.SOLUTION: In a three-dimensional coil 11 provided in a deflection electromagnet, when a coordinate system is defined by the direction of applying a magnetic field denoted by Y and the direction of the orbit of a charge particle beam denoted by Z, in an X-Y cross-sectional coordinate formed by the radial direction X of the arc orbit of a charge particle beam deflected by a magnetic field and the application direction Y, coil conductors 12 (12a, 12b), in which the excitation current flows in the same direction, are wound with a relatively lower space factor in the range where the angle formed with the radial direction X satisfies 30°<|θ|, compared to other ranges.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] An embodiment of the present invention relates to a bending electromagnet that deflects a charged particle beam and related techniques. [Background technology]

[0002] In order to deflect a charged particle beam, a bending electromagnet is required to generate a magnetic field of the required strength uniformly throughout the entire passing area, and a wire arrangement that satisfies the necessary conditions for deflecting the charged particle beam is determined by theoretical calculation. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2013-206635 A Summary of the Invention [Problem to be solved by the invention]

[0004] In conventional technology, in order to improve uniformity while maintaining the required magnetic field strength, a multi-stage winding coil with multiple layers is required, which increases the winding time for the wire depending on the number of layers, resulting in high costs for the bending electromagnets.

[0005] The embodiments of the present invention have been made in consideration of the above circumstances, and have an object to provide a bending electromagnet and related technologies that reduce the winding time of the wire while satisfying the necessary conditions for deflecting a charged particle beam. [Means for solving the problem]

[0006] In the bending electromagnet according to the embodiment, when a coordinate system is defined by a magnetic field application direction Y and a trajectory direction Z of the charged particle beam, in an XY cross-sectional coordinate system formed by a radial direction X of the arcuate trajectory of the charged particle beam deflected by the magnetic field and the magnetic field application direction Y, the bending electromagnet is provided with a three-dimensional coil wound with a space factor that is relatively lower in the range of 30°<|θ|, where the angle formed by the coil wire with the same direction of excitation current and the radial direction X is lower than in other ranges. Effect of the Invention

[0007] According to an embodiment of the present invention, a bending electromagnet and related techniques are provided that reduce the winding time of wire while satisfying the necessary conditions for deflecting a charged particle beam. [Brief description of the drawings]

[0008] [Figure 1] 1 is a perspective view showing a three-dimensional coil applied to a bending electromagnet according to a first embodiment of the present invention. [Diagram 2] The XY cross-sectional coordinates of the three-dimensional coil perpendicular to the Z-direction of the charged particle beam. [Diagram 3] 5 is a graph showing the space factor of the coil wire at an angle θ in the circumferential direction of the three-dimensional coil in the first embodiment. [Figure 4] (A) Planar development of the three-dimensional coil in a plane coordinate system with the circumferential angle θ and the particle beam trajectory direction Z. (B) Cross-sectional view of the three-dimensional coil in a linear coordinate system with the circumferential angle θ. [Diagram 5] FIG. 13 is a cross-sectional view showing a widely adopted cosθ-type three-dimensional coil as a comparative example. [Figure 6] 1 is a graph showing the space factor of the coil wire at angle θ in the circumferential direction of a cosθ-type three-dimensional coil (comparison example). [Figure 7] (A) A diagram showing the strength of the dipole component of the magnetic field generated by an excited cosθ-type three-dimensional coil (comparison example), and (B) a diagram showing the sum of the strengths of the same and other multipole components (4-pole component, 6-pole component, ... 2n-pole component). [Figure 8] FIG. 11 is a cross-sectional view showing an example of a three-dimensional coil applied to a bending electromagnet according to the second embodiment. [Figure 9]13 is a graph showing the space factor of the coil wire at an angle θ in the circumferential direction of the three-dimensional coil in the second embodiment. [Figure 10] FIG. 11 is a cross-sectional view of a bending electromagnet according to a third embodiment. [Figure 11] FIG. 2 is a cross-sectional view of a gantry-type particle beam irradiation device in which a bending electromagnet according to each embodiment is mounted. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] (First embodiment) Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. Fig. 1 is a perspective view showing a three-dimensional coil 11 applied to a bending electromagnet 10A (10) according to a first embodiment of the present invention. Fig. 2 shows the XY cross-sectional coordinates of the three-dimensional coil 11 perpendicular to the trajectory direction Z of the charged particle beam. As shown in Fig. 1, the three-dimensional coil 11 has a curved shape so that its central axis coincides with the trajectory direction Z of the charged particle beam. At least the entire inside of the three-dimensional coil 11 forms a vacuum magnetic field space 13 through which the charged particle beam passes.

[0010] As shown in Fig. 1, the three-dimensional coil 11 provided in the deflection electromagnet 10 has a coordinate system defined by the magnetic field application direction Y and the trajectory direction Z of the charged particle beam. As shown in Fig. 2, attention is paid to the XY cross-sectional coordinates formed by the radial direction X of the arc trajectory of the charged particle beam deflected by the magnetic field and the application direction Y. In this case, the coil wires 12 (12a, 12b) having the same excitation current direction are wound with a relatively lower space factor in the range of the angle formed with the radial direction X of 30°<|θ| (θ<-30°, 30°<θ) than in other ranges. Note that in the XY cross-sectional coordinates, the coil wires 12 (12a, 12b) are wound symmetrically with respect to the application direction Y.

[0011] When an excitation current is applied to the helically wound coil wire 12 (12a, 12b), a magnetic field is applied along the winding axis (Y-axis) according to Ampere's law. The magnetic fields formed at both ends of the winding axis (Y-axis) of the three-dimensional coil 11 are distorted, but a uniform magnetic field is formed in the center of the cross section of the three-dimensional coil 11.

[0012] A charged particle beam passing in a direction (Z-axis) perpendicular to the direction in which the magnetic field is applied (Y-axis) is subjected to a Lorentz force in a direction along the X-axis perpendicular to the Y-axis and Z-axis. The charged particle beam is deflected by the Lorentz force as a centripetal force, and describes an arcuate trajectory. The excitation current flowing through the coil wire 12 (12a, 12b) is adjusted so that the arcuate trajectory of the charged particle beam coincides with the central axis Z of the deflection electromagnet 10.

[0013] Fig. 3 is a graph showing the space factor of the coil wire 12 at angle θ in the circumferential direction of the three-dimensional coil 11. In Fig. 3, the range of 50°<θ<+75° indicates a state in which the coil wire 12 is not wound (space factor = 0). The space factor increases rapidly at the boundaries of θ<+50° and +75°<θ, and becomes a constant value in the range of 0<θ<+40° (the graph shows the space factor at this constant value = 1). Furthermore, in the open region 15 and the gap region 16, the space factor = 0.

[0014] The space factor can be adjusted by changing the winding spacing of the wound coil wire 12. Note that the spirally wound coil wire 12 can be wound with a relatively lower space factor when the angle it forms with the radial direction X of the magnetic field is in the range of 30°<|θ|, and further in the range of 45°<|θ|, than in other ranges. Note that the above explanation is for the first quadrant of the XY coordinate system, but the same applies to the other second to fourth quadrants because the wiring of the coil wire 12 is symmetrical.

[0015] Fig. 4(A) is a planar development of the three-dimensional coil 11 in a plane coordinate system with the circumferential angle θ and the particle beam trajectory direction Z. Fig. 4(B) is a cross-sectional view of the three-dimensional coil 11 in a linear coordinate system with the circumferential angle θ. Note that when developing Fig. 4(A) in a plane, the three-dimensional coil 11 is partially stretched and expanded so that the trajectory direction Z of the charged particle beam becomes a straight line.

[0016] In this way, the three-dimensional coil 11 has the coil wire 12 wound around an opening region 15 formed so that the magnetic field application direction Y passes through on one side, and a gap region 16 is formed so that the magnetic field application direction Y passes through on the other side. Then, of the wound coil wire 12, both ends 17a, 17b along the trajectory direction Z face each other with a gap therebetween (see FIG. 1), and both ends 19a, 19b of the wound coil wire 12 perpendicular to the trajectory direction Z form passage openings 18a, 18b for passing the charged particle beam, respectively.

[0017] By forming the three-dimensional coil 11 in this manner, two coils can be combined to face each other from a single continuous coil wire 12. This improves the degree of freedom in setting the space factor of the coil wire 12 at the angle θ in the circumferential direction of the three-dimensional coil 11. Furthermore, the winding time of the coil wire 12 can be reduced, thereby reducing the manufacturing cost of the bending electromagnet 10.

[0018] (Comparative Example) Fig. 5 is a cross-sectional view showing a widely adopted cosθ-type three-dimensional coil as a comparative example. Fig. 6 is a graph showing the space factor of the coil wire at the circumferential angle θ of this cosθ-type three-dimensional coil. Fig. 7(A) is a diagram showing the strength of the dipole component of the magnetic field generated by an excited cosθ-type three-dimensional coil (comparative example). Fig. 7(B) is a diagram showing the sum of the strengths of other multipole components (4-pole component, 6-pole component, ... 2n-pole component) of the magnetic field generated by an excited cosθ-type three-dimensional coil (comparative example).

[0019] In this way, the magnetic field generated by the three-dimensional coil can be decomposed into multipole components (dipole components, quadrupole components, hexapole components, ... 2n-pole components). Here, the dipole components contribute to the generation of the centripetal force necessary for the charged particle beam to trace an arc trajectory, and the others (quadrupole components, hexapole components, ...) are unnecessary components that reduce the uniformity of the magnetic field that contributes to the generation of the centripetal force.

[0020] 7, the dipole, quadrupole, and hexapole components of the magnetic field all have strong positive components near the circumferential angle θ = 0°. Therefore, while the coil of the comparative example efficiently generates dipole components, the quadrupole and hexapole components are also large, which deteriorates the uniformity of the magnetic field that contributes to the centripetal force of the arc orbit.

[0021] Therefore, in the case of the cosθ-type three-dimensional coil shown as a comparative example, in order to improve uniformity while maintaining the required magnetic field strength, a multi-stage winding coil spanning multiple layers is required. Furthermore, the winding time increases according to the number of layers of the winding coil, making the bending electromagnets expensive.

[0022] Second embodiment Next, a second embodiment of the present invention will be described with reference to Fig. 8. Fig. 8 is a cross-sectional view showing an example of a three-dimensional coil 11 (11a, 11b) applied to a deflection electromagnet 10B (10) according to the second embodiment. Fig. 9 is a graph showing the space factor of the coil wire at an angle θ in the circumferential direction of the three-dimensional coil 11 in the second embodiment (the broken line is an overlay of the space factor of the single-layer three-dimensional coil shown in Fig. 3). In Fig. 8, parts having the same configuration or function as Fig. 2 are indicated by the same reference numerals, and duplicated explanations will be omitted.

[0023] The deflection electromagnet 10B (10) of the second embodiment has a plurality of (two are illustrated in the figure) three-dimensional coils 11 (11a, 11b) stacked concentrically. An outer ring coil 21 is wound concentrically and has a higher space factor than the three-dimensional coils 11 (11a, 11b) in the range of 30°<|θ|.

[0024] In this way, the space factor can be increased on the outside of the radial direction X in the range of 30°<|θ|. It is also possible to layer only the three-dimensional coil 11 without using such an outer ring coil 21, and to provide a gradient in the space factor so that the outside is higher than the inside in the radial direction X. The three-dimensional coil 11 may also be configured to be layered concentrically so that the open regions 15 and the gap regions 16 alternate.

[0025] 8 and 9, the space factor of the wound coil wire 12 is 0.75 in the range of 0°<θ<+45°. The space factor then drops sharply when the angle exceeds +45°<θ, and becomes 0.2 when the angle is +60°<θ<+80°. Furthermore, the space factor starts to increase when the angle is +80°<θ.

[0026] Furthermore, compared to the cosθ-type three-dimensional coil shown as a comparative example in Figure 6, in the embodiment, the space factor is high on the inner diameter side in the range of 0°<θ<+45°, the space factor is low in the range of +45°<θ<+80°, and the space factor is high in the range of +80°<θ<+90°.

[0027] In this way, by making the bending electromagnet 10 multi-layered with multiple three-dimensional coils 11, it is possible to improve the strength of the dipole component contributing to the Y-direction magnetic field while suppressing the quadrupole component, hexapole component, ... that contribute to the non-uniformity of the Y-direction magnetic field. The principle behind this is explained below.

[0028] In order to make the charged particle beam trace an ideal arcuate trajectory, it is necessary to arrange the coil wire 12 so that the dipole component of the generated magnetic field is kept at a certain level or higher while the sum of the other multipole components (quadrupole component, hexapole component, etc.) approaches zero.

[0029] As shown in Figure 7(A), the bipole component weakens as the circumferential angle θ increases, and at the same angle θ, it is stronger on the inside in the radial direction than on the outside. On the other hand, as shown in Figure 7(B), when the circumferential angle is 0°<θ<+30°, a positive multipole component occurs, and when it is +30°<θ, a negative multipole component occurs. Also, at the same angle, both the positive and negative multipole components are stronger on the inside in the radial direction than on the outside. Furthermore, near a circumferential angle of +45°<θ, the multipole component has a stronger negative component, and the bipole component has a weaker positive component. Furthermore, the negative multipole component is stronger on the inside in the radial direction than on the outside.

[0030] As a result, the three-dimensional coil can efficiently eliminate the deterioration of magnetic field uniformity in the Y direction by winding with a relatively lower space factor in the angle range of +45°<θ than in other ranges. Also, the strength of the two-pole component that is reduced by lowering the space factor in this range of +45°<θ can be compensated for by increasing the space factor in other ranges.

[0031] Also, by winding with a higher space factor on the outside of the radial direction X than on the inside in the range of 45°<|θ|, the strength of the dipole component can be compensated for while suppressing deterioration of the magnetic field uniformity. Therefore, multi-layering the outside of the three-dimensional coil 11 with the outer ring coil 21 contributes to relatively improving the strength of the dipole component that contributes to the Y-direction magnetic field, compared to the quadrupole component, hexapole component, ... that contribute to the nonuniformity of the Y-direction magnetic field.

[0032] In the case of the embodiment, the necessary conditions for deflecting a charged particle beam can be met with a smaller number of layers of winding coils than in the cosθ-type three-dimensional coil shown as the comparative example (four layers in the comparative example in Figure 5, and three layers in the embodiment in Figure 8).

[0033] Third embodiment Next, a second embodiment of the present invention will be described with reference to Fig. 10. Fig. 10 is a cross-sectional view of a deflection electromagnet 10C(10) according to a third embodiment. As described above, the deflection electromagnet 10 includes a ferromagnetic yoke material 25 that is concentrically arranged outside the three-dimensional coil 11 and further induces the magnetic field. An example of the ferromagnetic yoke material 25 is made of iron. The three-dimensional coil 11 and the ferromagnetic yoke material 25 are housed inside a vacuum duct 26 having a similar curved shape, with their respective central axes aligned with the Z-axis, and are held in a vacuum space together with the magnetic field space 13.

[0034] The coil wire 12 wound around the bending electromagnet 10 may be one exhibiting normal conductivity or superconductivity. As a cooling method for turning the coil wire 12 into a superconducting state, a method of immersing the three-dimensional coil 11 in a refrigerant such as liquid helium, or a thermal conduction cooling method using a cryogenic refrigerator can be used.

[0035] (Particle beam irradiation device) 11 is a cross-sectional view of a gantry-type particle beam irradiation device 30 (hereinafter referred to as "irradiation device") equipped with a bending electromagnet 10 according to the embodiment. The irradiation device 30 treats cancer or the like by irradiating a patient 35 with a charged particle beam 33 such as protons or carbon ions accelerated to a high energy of several hundred MeV.

[0036] This gantry-type irradiation device 30 includes a gantry 32 having an internal treatment space 38 and rotated around a rotation axis 31 by a rotation drive unit (not shown), a bending electromagnet 10 fixed to the gantry 32 and rotatably mounted via a joint 39 at the end of a beam transport system (not shown), an irradiation nozzle 34 that irradiates the treatment space 38 with the charged particle beam 33 transported by the bending electromagnet 10 from the radial direction of the gantry 32, and a movement control unit 37 that moves a bed 36 on which a patient 35 is placed, and sets its position and direction in the treatment space 38.

[0037] By configuring the irradiation device 30 in this manner, it becomes possible to bend the trajectory of the charged particle beam 33 input along the rotation axis 31 of the gantry 32 by 90° and irradiate the patient 35 with the charged particle beam 33 from any direction perpendicular to the rotation axis 31. By employing the bending electromagnet 10 of each embodiment in the irradiation device 30, it is possible to reduce the load on the gantry 32 that is rotated and displaced, and improve the irradiation accuracy of the charged particle beam 33.

[0038] According to at least one of the embodiments of the deflection electromagnet described above, the space factor of the coil wire is wound in the range of 30°<|θ| so that it is relatively lower than in other ranges, thereby making it possible to reduce the winding time of the wire while satisfying the necessary conditions for deflecting a charged particle beam.

[0039] Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, modifications, and combinations can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope of the invention and its equivalents described in the claims, as well as in the scope and spirit of the invention. [Explanation of symbols]

[0040] 10 (10A, 10B, 10C)... bending electromagnet, 11... three-dimensional coil, 12... coil wire, 13... magnetic field space, 15... opening region, 16... spacing region, 17a, 17b... ends of spacing region, 18a, 18b... passage port, 19a, 19b... ends of passage port, 21... outer ring coil, 25... yoke material, 26... vacuum duct, 30... particle beam irradiation device, 31... rotating shaft, 32... gantry, 33... charged particle beam, 34... irradiation nozzle, 35... patient, 36... bed, 37... movement control unit, 38... treatment space, 39... joint.

Claims

1. When the coordinate system is defined by the direction of magnetic field application Y and the direction of the trajectory of the charged particle beam Z, In the XY cross-sectional coordinate system formed by the radial direction X of the arcuate trajectory of the charged particle beam deflected by the magnetic field and the application direction Y, A deflection electromagnet comprising a three-dimensional coil in which coil wires having the same direction of excitation current are wound with a space factor relatively lower in the range of an angle of 30°<|θ| with respect to the radial direction X than in other ranges.

2. 2. The bending electromagnet according to claim 1, wherein the three-dimensional coil comprises: The ends of the wound coil wire on both sides along the orbital direction Z face each other with a gap therebetween, A bending electromagnet in which both ends of the wound coil wire perpendicular to the trajectory direction Z form passage openings for passing the charged particle beam.

3. 3. The bending electromagnet according to claim 1, A bending electromagnet in which a plurality of the three-dimensional coils are concentrically stacked, and the outer side in the radial direction X in the range of 30°<|θ| is wound with a higher space factor than the inner side.

4. 4. The bending electromagnet according to claim 3, A bending electromagnet is disposed concentrically outside the volume coil and includes a ferromagnetic yoke material for further inducing the magnetic field.

5. 3. The bending electromagnet according to claim 1, wherein the three-dimensional coil comprises: The three-dimensional coil is a bending electromagnet wound with a space factor that is relatively lower in the range of an angle between the three-dimensional coil and the radial direction X and that is 45°<|θ| than in other ranges.

6. 3. The bending electromagnet according to claim 1, The coil wire is a bending electromagnet that exhibits superconductivity.

7. The bending electromagnet according to claim 4, A particle beam irradiation device mounted on a rotating gantry.

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