Accelerator and charged particle beam therapy device

Abstract

To provide an accelerator having an ion source filament that is highly resistant to Lorentz force, and a charged particle beam therapy device.SOLUTION: A cyclotron 1 is an accelerator having an ion source 2 and accelerating ions generated from the ion source 2, and a filament 11 of the ion source 2 has a loop-shaped tip 29 that is wider than a gap 28 between the upper ends 27q, 27q of legs 27, 27 of the filament 11.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to an accelerator.

Background Art

[0002] Conventionally, as a technical document related to an accelerator, for example, Patent Document 1 is known. Patent Document 1 describes a cyclotron including an ion source having a filament, which accelerates ions generated in the ion source by a magnetic field.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The ion source included in an accelerator may be used in the presence of a strong magnetic field. A Lorentz force acts on the filament of the internal ion source due to the current flowing through the filament and the above magnetic field. The filament is a component that becomes hot due to the above current, and since it receives the Lorentz force in a state where its hardness has decreased at high temperature, it is likely to be deformed. And if such deformation of the filament occurs, maintenance of the ion source may be required. If maintenance is performed frequently, there is a problem that the downtime of the accelerator increases. In view of this problem, an object of the present invention is to provide an accelerator having a filament of an ion source with high resistance to the Lorentz force, and a charged particle beam therapy device.

Means for Solving the Problems

[0005] The gist of the present invention resides in the following [1] to [9].

[0006] [1] An accelerator having an ion source for accelerating ions generated from the ion source, wherein a filament of the ion source has a loop portion having a loop shape.

[0007] [2] The accelerator according to [1], wherein the loop portion extends along a plane orthogonal to the direction of a magnetic field existing at a position of the filament.

[0008] [3] The accelerator according to [1] or [2], wherein a Lorentz force directed toward the inside of the loop shape is generated by a current flowing through the loop portion and the magnetic field.

[0009] [4] The accelerator according to any one of [1] to [3], wherein the loop shape forms an arc.

[0010] [5] The ion source has a mounting seat to which the filament is attached, and the filament includes a pair of leg portions extending from the mounting seat in the direction of the magnetic field and the loop portion connecting the tips of the leg portions, and in the arrangement direction of the leg portions, a width of the loop portion is larger than a distance between the tips of the leg portions. The accelerator according to any one of [1] to [4].

[0011] [6] The accelerator according to any one of [1] to [5], wherein the ion source is an internal ion source disposed within a yoke of the accelerator.

[0012] [7] The accelerator according to any one of [1] to [6], wherein the ion source is a PIG ion source.

[0013] [8] The accelerator according to any one of [1] to [7], wherein the loop portion extends while being wound in a coil shape.

[0014] [9] A charged particle beam therapy apparatus including the accelerator according to any one of [1] to [8].

Advantages of the Invention

[0015] According to the present invention, an accelerator having a filament of an ion source with high resistance to Lorentz force and a charged particle beam therapy apparatus can be provided.

Brief Description of Drawings

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Mode for Carrying Out the Invention

[0017] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

[0018] The charged particle beam therapy apparatus 101 of this embodiment will be described with reference to FIG. 1. As shown in FIG. 1, the charged particle beam therapy apparatus 101 of this embodiment is an apparatus that performs treatment by irradiating a lesion (for example, a tumor or the like) inside a patient 102 with a charged particle beam. Here, the charged particle beam is, for example, a proton beam, a heavy particle beam, or the like. The charged particle beam therapy apparatus 101 includes a cyclotron 1 (accelerator) that accelerates charged particles and emits a charged particle beam, an irradiation unit 103 that irradiates the patient 102 with the charged particle beam, a rotating gantry 113 that rotates the irradiation unit 103 around a horizontal rotation axis A around a treatment table 108 on which the patient 102 lies, and a transport line 107 that connects the cyclotron 1 and the irradiation unit 103 and transports the charged particle beam from the cyclotron 1 to the irradiation unit 103. The transport line 107 has a plurality of quadrupole electromagnets 114 for converging the charged particle beam and a plurality of bending magnets 115 for bending the charged particle beam. Further, the transport line 107 has a plurality of ESSs (not shown) that selectively pass charged particle beams having a desired energy width among the sent charged particle beams.

[0019] The above cyclotron 1 will be described in more detail with reference to FIG. 2. As shown in FIG. 2, the cyclotron 1 is a circular accelerator that accelerates ions supplied from an ion source 2 by a magnetic field and outputs a charged particle beam. Examples of the ions supplied from the ion source 2 include protons, heavy particles (heavy ions), electrons, and the like. In this embodiment, the case where the ions supplied from the ion source 2 are protons (hydrogen ions H + ) will be described as an example.

[0020] The ion source 2 is an internal ion source built into the cyclotron 1 and is disposed inside the yoke 7 of the cyclotron 1. The ion source 2 is located at the center of the disk-shaped cyclotron 1 and is supported by a columnar support 3 extending along the central axis C of the cyclotron 1. The ion source 2 is disposed on the median plane which is the acceleration plane of the charged particle beam.

[0021] The cyclotron 1 includes an annular coil 4 arranged around a central axis C, an RF cavity 5 arranged in the hollow part of the coil 4, a hollow yoke 7, and a control unit (control means) 8. The yoke 7 is a hollow disk-shaped block made of a magnetic metal, and the coil 4 and the RF cavity 5 are arranged inside it.

[0022] The control unit 8 is an electronic control unit composed of a CPU [Central Processing Unit], a ROM [Read Only Memory], a RAM [Random Access Memory], etc. The control unit 8 comprehensively controls the cyclotron 1.

[0023] The cyclotron 1 supplies current to the coil 4 to generate a strong magnetic field (arrow B), thereby accelerating the ions supplied from the ion source 2 in the internal space G of the RF cavity 5 and outputting an ion beam. The strong magnetic field is, for example, a magnetic field of 1 T [tesla] or more. Inside the cyclotron 1, a magnetic field of about 1 T to 3 T is formed, for example.

[0024] Figures 3 and 4 are diagrams for explaining the ion source 2. First, the configuration of the ion source 2 will be described with reference to Fig. 3(a). The ion source 2 is a PIG ion source. As shown in Fig. 3(a), the ion source 2 has a conductive chimney (cylindrical body) 10, a filament 11 and an anti-cathode 12 arranged inside the chimney 10, and an extraction electrode 13 for extracting ions from inside the chimney 10.

[0025] The chimney 10 is a conductive cylindrical member with its upper end closed. An anti-cathode 12 is arranged on the upper end side inside the chimney 10. The lower end side of the chimney 10 is open, and the filament 11 is arranged by being inserted from the lower end side.

[0026] On the side surface of the chimney 10, a slit 10a for extracting hydrogen ions (protons) H + is formed. The hydrogen ions H extracted from the slit 10a +Advances while accelerating along an orbit that rotates around the chimney 10. The chimney 10 has a constricted shape at the middle part where the slit 10a is located according to the rotation orbit of the hydrogen ion H + . Note that the shape of the chimney 10 is not limited to the one described above.

[0027] The filament 11 is a metal member that is disposed in the hollow portion of the chimney 10 and emits electrons (thermoelectrons) e into the chimney 10 by passing an electric current therethrough to generate heat.

[0028] The anticathode 12 is an electrode for maintaining the electrons e in the chimney 10. The anticathode 12 is disposed in the chimney 10 so as to face the filament 11 in the magnetic field direction and is fixed to the chimney 10 via an annular insulator (not shown). The anticathode 12 maintains the electrons e in the chimney 10 by causing the electrons e to reciprocate in the magnetic field direction between the anticathode 12 and the filament 11.

[0029] The extraction electrode 13 is an electrode for extracting the hydrogen ions H + generated in the chimney 10 from the slit 10a. The extraction electrode 13 is provided outside the slit 10a, and by applying an extraction voltage between the extraction electrode 13 and the chimney 10, the hydrogen ions H + are extracted.

[0030] Also, a power source 14 for supplying an electric current to the filament 11 is connected to the ion source 2. The power source 14 is a DC power source and supplies a DC current to the filament 11.

[0031] The power source 14 is controlled by the control unit 8 and supplies an electric current to the filament 11 according to a signal from the control unit 8. The power source 14 is disposed outside the yoke 7. Note that a dedicated power source is provided for the chimney 10.

[0032] In addition, outside the ion source 2, a hydrogen tank 15 for introducing hydrogen gas into the chimney 10 is provided inside the yoke 10 (see Fig. 4(b)). The hydrogen tank 15 is arranged outside the yoke 7, and hydrogen gas is introduced into the chimney 10 through the inside of the support 3.

[0033] Next, the generation of ions in the ion source 2 will be described. Fig. 3(a) is a diagram for explaining the generation of electrons e in the ion source 2. As shown in Fig. 3(a), first, in the ion source 2, the control unit 8 controls the power supply 14 to supply current to the filament 11. The filament 11 generates heat by the supply of current and emits electrons (thermoelectrons) e.

[0034] Fig. 3(b) is a diagram for explaining the movement of electrons e in the ion source 2. The control unit 8 controls the power supply for the chimney 10 to apply a voltage (arc voltage) between the chimney 10 and the filament 11. As a result, the electrons e emitted from the filament 11 are attracted to the chimney 10, but since a strong magnetic field generated by the coil 4 exists inside and outside the ion source 2, the electrons e are trapped by the magnetic field and move while accelerating in the direction of the magnetic field B.

[0035] Fig. 4(a) is a diagram for explaining the collision of electrons e in the ion source 2. As shown in Fig. 4(a), in the ion source 2, when the electrons e moving in the direction of the magnetic field B collide with the anticathode 12, new electrons e are generated from the anticathode 12. The electrons e generated from the anticathode 12 move while accelerating in the direction opposite to the direction of the magnetic field B. In this way, the electrons e reciprocate between the filament 11 and the anticathode 12.

[0036] Fig. 4(b) is a diagram for explaining the generation of hydrogen ions in the ion source. As shown in Fig. 4(b), in the ion source 2, while the electrons e are reciprocating inside the chimney 10, hydrogen gas is introduced from the hydrogen tank 15 into the chimney 10. The control unit 8 also controls the introduction of hydrogen gas. As a result, inside the chimney 10, due to the collision between the electrons e and hydrogen molecules H 2 and, hydrogen ions H +is generated, and a plasma P in which hydrogen ions H + and electrons e are mixed is generated.

[0037] When a draw-out voltage is applied to the draw-out electrode 13, hydrogen ions H + are drawn out from the plasma P in the chimney 10. The hydrogen ions H + are drawn out through the slit 10a and accelerated while rotating around the chimney 10. The cyclotron 1 continuously draws out hydrogen ions H + from inside the chimney 10 by the draw-out electrode 13 and forms an ion beam by accelerating them with a magnetic field and an electric field.

[0038] Subsequently, the detailed configuration of the filament 11 of the ion source 2 will be described with reference to FIGS. 5 and 6. FIG. 5 is a perspective view showing the filament 11 and the mounting seat 30 to which the filament 11 is attached, and FIG. 6 is a plan view of the filament 11. The direction of the magnetic field B at the position of the ion source 2 is parallel to the central axis C (FIG. 2). Hereinafter, the direction of the magnetic field B at the position of the ion source 2 is referred to as "upward", and the terms "up / down" are used.

[0039] Since a current flows through the filament 11 as described above, a Lorentz force is applied to the filament 11 under the influence of a strong magnetic field (for example, a magnetic field of 1 T or more) inside the cyclotron 1. The Lorentz force is applied to the filament 11 as long as the current continues to flow, so the filament 11 gradually deforms. Then, if the deformation exceeds the allowable range as the usage time of the cyclotron 1 becomes longer, maintenance for replacing the filament 11 is required, resulting in downtime of the cyclotron 1 and the charged particle beam therapy apparatus 101 (FIG. 1) using the same. Therefore, in order to reduce this downtime, a configuration of the filament 11 as described below is adopted to enhance the resistance of the ion source 2 to the Lorentz force.

[0040] The filament 11 includes a filament main body portion 21 formed by bending an integral metal material, and a positive electrode portion 23a and a negative electrode portion 23b provided at both ends of the filament main body portion 21. The metal material constituting the filament main body portion 21 may be plate-shaped or wire-shaped. The metal material of the filament main body portion 21 is, for example, Ta (tantalum). The filament main body portion 21 has two legs 27, 27 extending upward in parallel from the electrode portions 23a, 23b, and a tip portion 29 connecting the upper ends 27q, 27q of the legs 27, 27. The direction in which the legs 27, 27 extend from the electrode portions 23a, 23b is a direction parallel to the central axis C (FIG. 2).

[0041] Also, the ion source 2 includes a mounting seat 30 for mounting the filament 11. The mounting seat 30 is located below the chimney 10 (FIG. 3) and includes a high-voltage side electrode 31a and a low-voltage side electrode 31b for supplying current to the filament 11. Threaded holes 24 are formed in the electrode portions 23a, 23b of the filament 11, and by screwing the electrode portions 23a, 23b to the high-voltage side electrode 31a and the low-voltage side electrode 31b, respectively, the filament 11 is fixed at a predetermined position within the hollow portion of the chimney 10.

[0042] The tip portion 29 (loop portion) of the filament main body portion 21 has a loop shape. Here, if the direction in which the upper ends 27q, 27q of the two legs 27, 27 are aligned is defined as the H direction (arrow H in FIG. 6), the above-mentioned "loop shape" means a shape having a wider width in the H direction compared to the gap 28 between the upper ends 27q, 27q. Since the legs 27, 27 are parallel to each other, the direction in which the lower ends 27p, 27p (connection portions with the electrode portions 23a, 23b) of the two legs 27, 27 are aligned is also the H direction. And it can also be said that the above-mentioned "loop shape" is a shape having a wider width in the H direction compared to the gap 28 between the lower ends 27p, 27p.

[0043] In the specific examples shown in FIGS. 5 and 6, the tip 29 has an arc shape (a shape that forms a part of a perfect circle), and the diameter R of the arc is larger than the gap 28. As shown in FIG. 6, the tip 29 protrudes on both sides in the H direction from the positions of the upper ends 27q, 27q. The tip 29 extends along a plane orthogonal to the direction of the magnetic field B. The center of the arc drawn by the tip 29 may be on the central axis of the chimney 10 or on the central axis C. Also, the length of the arc drawn by the tip 29 is 3 / 4 or more of the entire circumference having the same radius as the arc.

[0044] During the operation of the cyclotron 1, current is supplied from the power supply 14 (FIG. 4) to the filament 11 through the high-voltage side electrode 31a and the low-voltage side electrode 31b, and a current D flows through the filament 11 in the direction indicated by the arrow in the figure. Then, due to the action of the current D and the magnetic field B, a Lorentz force F directed radially inward of the arc drawn by the tip 29 is generated at the tip 29 of the filament 11. Note that since the current flowing through the legs 27, 27 of the filament 11 is parallel to the magnetic field B, no Lorentz force is generated on the legs 27, 27.

[0045] As described above, the cyclotron 1 includes an internal ion source 2 disposed within the yoke 7, and accelerates ions generated from the ion source 2 within the magnetic field B. The ion source 2 has a filament 11 through which current is passed to emit electrons e (thermoelectrons). The filament 11 has two legs 27, 27 on the positive and negative sides extending from the mounting seat 30, and a tip 29 connecting between the upper ends 27q, 27q of the legs 27, 27. The tip 29 extends along a plane orthogonal to the direction of the magnetic field B and has an arc shape. The current D flowing through the tip 29 and the magnetic field B generate a Lorentz force F directed inward of the arc.

[0046] The operational effects of the ion source 2 having the filament 11 as described above, the cyclotron 1 having the ion source 2, and the charged particle beam therapy apparatus 101 using the cyclotron 1 will be described.

[0047] As described above, the filament 11 generates heat when energized and becomes hot. Among the filament 11, the heat of the electrode portions 23a and 23b and the leg portions 27 and 27 that are relatively close to the mounting seat 30 easily escapes to the mounting seat 30 side, but the heat of the tip portion 29 hardly escapes to the mounting seat 30 side. Therefore, the tip portion 29 is likely to become relatively hot. Accordingly, the tip portion 29 has a relatively large decrease in hardness due to the high temperature, and since it receives the Lorentz force F in the state where the hardness has decreased, there is a relatively large concern that deformation due to the Lorentz force F will occur.

[0048] On the other hand, according to the filament 11, as described above, a Lorentz force F in a direction toward the inner side in the radial direction of the arc is generated with respect to the tip portion 29 having an arc shape. According to the relationship between the shape of the tip portion 29 and the direction of the Lorentz force F, it can be said that the tip portion 29 has a strong structure against the Lorentz force F. Therefore, it can be said that the filament 11 has high resistance to the Lorentz force F. Thus, the deformation of the filament 11 due to the Lorentz force F is suppressed, the filament 11 has a longer life, and consequently, the frequency of maintenance of the ion source 2 is suppressed. And the downtime of the cyclotron 1 and the charged particle beam therapy apparatus 101 can be reduced.

[0049] Also, as can be understood from the resultant Lorentz force F acting on the tip 29, the bending moment acting on the legs 27, 27 of the filament 11 due to the Lorentz force F depends on the size of the gap 28. That is, the larger the gap 28, the larger the bending moment acting on the legs 27, 27. Therefore, in order to improve the resistance to the Lorentz force F with respect to the legs 27, 27 (particularly, the lower ends 27p, 27p), it is preferable that the gap 28 be smaller. On the other hand, the larger the area of the region surrounded by the filament 11, the more efficiently the electrons e (FIG. 3(a)) are generated. Here, in the filament 11 of the present embodiment, the diameter R of the arc drawn by the tip 29 is larger than the gap 28 (FIG. 5). According to this configuration, the gap 28 can be made smaller while securing the area of the region surrounded by the filament 11 (at the tip 29). Therefore, according to the filament 11, it is possible to improve the resistance to the Lorentz force F while ensuring the generation of the necessary electrons e.

[0050] From this perspective, it is preferable that the gap 28 be relatively small with respect to the diameter R of the above-described arc. For example, in the example described with reference to FIGS. 5 and 6, the length of the arc drawn by the tip 29 is set to be 3 / 4 or more of the entire circumference, but it is more preferably 80% or more of the entire circumference, and even more preferably 90% or more.

[0051] Also, if the area of the region surrounded by the filament 11 (at the tip 29) can be increased, the current of the filament 11 required to emit sufficient electrons e can be decreased. Then, the heat generation of the filament 11 during operation is suppressed, and the decrease in the hardness of the filament 11 is suppressed. As a result, the deformation of the filament 11 can be suppressed.

[0052] The present invention can be implemented in various forms with various changes and improvements based on the knowledge of those skilled in the art, including the above-described embodiments. Also, it is possible to configure the following modification examples by using the technical matters described in the above-described embodiments. The configurations of the respective embodiments and the like may be used in appropriate combination.

[0053] For example, as shown in Fig. 7(a), the tip 29 in Fig. 5 may be changed to be wound in a coil shape. That is, the tip 29 may be, for example, a coil-shaped one extending along a helix centered on the central axis C. In this case, since the current flowing through the tip 29 increases according to the number of turns, electrons e (Fig. 3(a)) are generated more efficiently at the tip 29. The number of turns of the coil-shaped tip 29 is not limited to that illustrated in Fig. 7(a) and may be appropriately designed in consideration of various conditions.

[0054] Also, as shown in Fig. 7(b), the tip 29 may extend in an arc shape along a plane parallel to the direction of the magnetic field B. In this case, the Lorentz force acting on the upper half of the tip 29 and the Lorentz force acting on the lower half are almost the same in magnitude and opposite to each other, and as a result, they are almost canceled out except for the part depending on the gap 28. Therefore, the bending moment acting on the legs 27, 27 is almost the same as in the case of the structure shown in Fig. 5. Also, with the configuration of Fig. 7(b), since the width (diameter R) of the tip 29 is wider than the gap 28 between the upper ends 27q, 27q of the legs 27, 27, the gap 28 can be reduced while securing the area of the region surrounded by the filament 11 (at the tip 29). Therefore, it is possible to improve the resistance to the Lorentz force F while ensuring the generation of the necessary electrons e.

[0055] Also, as shown in Fig. 8, the tip 29 in Fig. 7(b) may be changed to be wound in a coil shape. That is, the tip 29 may be, for example, a coil-shaped one extending along a helix centered on an axis orthogonal to the central axis C. The number of turns of the coil-shaped tip 29 is not limited to that illustrated in Fig. 8 and may be appropriately designed in consideration of various conditions.

Explanation of reference numerals

[0056] 1... Cyclotron (accelerator), 2... Ion source, 7... Yoke, 11... Filament, 27... Leg, 27q... Upper end (tip of the leg), 29... Tip part (loop part), 30... Mounting seat, 101... Charged particle beam therapy device, B... Magnetic field, D... Current, F... Lorentz force.

Claims

1. An accelerator having an ion source and accelerating ions generated from the ion source, An accelerator, wherein the filament of the ion source has a loop portion having a loop shape.

2. The accelerator of claim 1 , wherein the loop portion extends along a plane perpendicular to a direction of a magnetic field present at the location of the filament.

3. The accelerator according to claim 2 , wherein a Lorentz force acting inwardly of the loop shape is generated by the current flowing through the loop portion and the magnetic field.

4. The accelerator of claim 3 , wherein the loop shape defines a circular arc.

5. the ion source has a mounting seat to which the filament is attached; The filament includes a pair of legs extending from the mounting seat in the direction of the magnetic field, and the loop portion connecting the tips of the legs, The accelerator according to claim 4 , wherein a width of the loop portion in an arrangement direction of the legs is greater than a distance between the tips of the legs.

6. The accelerator of claim 5 , wherein the ion source is an internal ion source disposed within a yoke of the accelerator.

7. The accelerator of claim 6 , wherein the ion source is a PIG ion source.

8. The accelerator of claim 1 , wherein the loop portion extends in a coil shape.

9. A charged particle beam therapy system comprising the accelerator according to claim 1.

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