Ion sources, accelerators and particle therapy systems

Abstract

To enhance the maintainability.SOLUTION: An ion source 3 that extracts an extraction beam 15 from an acceleration cavity A in a magnetic pole 1 includes a chimney 22, at least one cathode 23, a high-frequency acceleration electrode 8, and a dummy electrode 9. The chimney is fixed to the acceleration cavity. At least one cathode is disposed so as to be able to be inserted into the chimney. The cathode is one of a pair of cathodes inserted from both sides of the chimney and disposed to face each other. The high-frequency acceleration electrode accelerates the extraction beam. The dummy electrode is disposed opposite to or in parallel to the high-frequency acceleration electrode. The chimney is electrically connected to the dummy electrode through a contact piece C.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to an ion source, an accelerator, and a particle beam therapy system. [Background technology]

[0002] As background art in this technical field, for example, Patent Document 1 is disclosed. The synchrocyclotron in Patent Document 1 includes a magnetic structure that provides a magnetic field to a cavity, a particle source that provides a plasma column to the cavity, and a voltage source that provides a radio frequency (RF) voltage to the cavity to accelerate particles from the plasma column in an acceleration region. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2011-505670 Summary of the Invention [Problem to be solved by the invention]

[0004] The ion source described in Patent Document 1 includes a housing for holding a plasma column. The housing is interrupted by an acceleration region to expose the plasma column. A voltage source is configured to apply a radio frequency (RF) voltage to the cavity to accelerate particles from the plasma column in the acceleration region.

[0005] However, the structure described in Patent Document 1 has problems such as divergence of the extracted ion beam and a decrease in beam current due to disturbances in the electric field caused by insufficient positional accuracy of the separated plasma columns and disturbances in the beam extraction electric field caused by the column space generated by the separation. For this reason, when replacing a damaged cathode, it is necessary to adjust the position while extracting the beam, which takes time for the ion source replacement and position adjustment work, resulting in a problem of reduced device availability.

[0006] The present invention has been made in view of the above problems, and an object of the present invention is to provide a technique for improving maintainability. [Means for solving the problem]

[0007] In order to achieve the above object, the present invention provides an ion source that extracts an ion beam from an acceleration cavity in a magnetic pole, the ion source comprising: a chimney fixed to the acceleration cavity; and at least one cathode that is insertably arranged within the chimney. [Effects of the Invention]

[0008] According to the present invention, it is possible to improve maintainability. Problems, configurations, and effects other than those described above will become apparent from the following description of the embodiments. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a diagram showing the overall configuration of a particle beam therapy system according to a first embodiment. [Figure 2] FIG. 1 is a longitudinal sectional view of a circular accelerator according to a first embodiment. [Figure 3] FIG. 1 is a cross-sectional view of a circular accelerator according to a first embodiment. [Figure 4] FIG. 2 is a schematic cross-sectional view of the ion source and its surroundings before a cathode is inserted according to the first embodiment. [Figure 5] FIG. 2 is a schematic cross-sectional view of the ion source and its surroundings after a cathode is inserted according to the first embodiment. [Figure 6] FIG. 6 is a schematic cross-sectional view showing the alignment structure of the ion source of FIG. 5. [Figure 7] FIG. 10 is a schematic cross-sectional view of the ion source and its surroundings before a cathode is inserted according to the second embodiment. [Figure 8] FIG. 10 is a schematic cross-sectional view of the ion source and its surroundings after a cathode is inserted according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, specific examples of an ion source, an accelerator, and a particle beam therapy system according to embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the examples, but is defined by the claims. [Example]

[0011] An ion source, an accelerator, and a particle beam therapy system according to a first embodiment of the present invention will be described below with reference to Figures 1 to 6. First, the overall configuration of the particle beam therapy system and the configuration of related devices will be described with reference to Figure 1.

[0012] FIG. 1 is a diagram illustrating the overall configuration of a particle therapy system according to a first embodiment.

[0013] In FIG. 1, a particle beam therapy system 100 includes a circular accelerator 50 as an example of a cyclotron-type “accelerator”, a beam transport system 52, an irradiation device 54, a treatment table 40, and a control device 56.

[0014] In the particle beam therapy system 100, ions generated in the ion source 3 are accelerated by a circular accelerator 50 to form an ion beam. The accelerated ion beam is extracted from the circular accelerator 50 and transported to an irradiation device 54 by a beam transport system 52. The transported ion beam is shaped by the irradiation device 54 to match the shape of the affected area, and a predetermined amount of ion is irradiated onto the target, a patient 45 lying on the treatment couch 40. The operation of each device and instrument in the particle beam therapy system 100, including the circular accelerator 50, is controlled by a control device 56.

[0015] Next, the structure of the circular accelerator 50 will be described with reference to FIGS.

[0016] 2 is a longitudinal sectional view of the circular accelerator according to the first embodiment of FIG. 1, and FIG. 3 is a transverse sectional view of the circular accelerator according to the first embodiment of FIG.

[0017] As shown in FIGS. 2 and 3, the cyclotron-type circular accelerator 50 includes a pair of main magnetic poles 1 as an example of “magnetic poles”, a circular coil 2, a vacuum vessel 6, a radio frequency acceleration electrode 8, an ion source 3, and a dummy electrode 9.

[0018] A pair of main magnetic poles 1 are made of a magnetic material, such as iron, and are arranged to face each other. A magnetic pole 10 is provided between the opposing magnetic poles of the main magnetic pole 1 to generate a circular orbit 12 for the ion beam, generating a magnetic field between the magnetic poles. The main magnetic pole 1 generates a magnetic field B using the magnetic pole 10, and also forms a gradient magnetic field from the center of the orbit of the magnetic pole 10 outward, thereby generating a focusing force for the orbiting ion beam and achieving stable orbit. The opposing upper and lower surfaces of the main magnetic pole 1, in the magnetic pole gap where the magnetic field B is generated, are symmetrical. Alternatively, the upper and lower surfaces may be shaped to have a magnetic pole shape with irregularities in the direction of ion beam propagation, thereby adding a focusing effect.

[0019] The vacuum vessel 6 is sandwiched between the main poles 1, forming a single vacuum vessel with the magnetic poles 10 as its inner surface. The vacuum vessel 6 is made of a non-magnetic material. A separate vacuum vessel may be provided in the gap between the magnetic poles, without the magnetic poles 10 as its inner surface.

[0020] The toroidal coil 2 is installed closer to the atmosphere than the vacuum vessel 6, and generates a magnetic field B between the pair of upper and lower main poles 1. The toroidal coil 2 can generate a magnetic field whether it is a coil made of a normal conducting material or a coil made of a superconducting material. The toroidal coil 2 may be installed inside the vacuum vessel 6, and is not particularly limited.

[0021] The ion source 3 is inserted into the magnetic pole 10 from above or below and fixed in the acceleration cavity A within the magnetic pole 10. The ion source 3 may be inserted laterally into the magnetic pole 10; the insertion direction is not particularly limited. When a high-frequency power supply 20 supplies high-frequency power, the ion source 3 and the dummy electrode 9 are at the same potential. When plasma is generated in the ion source 3 and high-frequency power is supplied from the high-frequency power supply 20, an extraction beam 15, an example of an "ion beam," is formed by a high-frequency electric field generated between the high-frequency electrode 8 and the ion source 3 and between the high-frequency electrode 8 and the dummy electrode 9. The extracted beam 15 is accelerated by the magnetic field B of the magnetic pole 10 and the electric field generated in the gap 7 between the high-frequency acceleration electrode 8 and the dummy electrode 9, and moves around in a spiral orbit 12. The extraction beam 15 is accelerated each time it passes through the gap 7, increasing its energy until it reaches a predetermined energy level, after which it is extracted from the main magnetic pole 1 by the extraction device 17. The extraction device 17 deflects the trajectory by using magnetic and electric fields.

[0022] Next, the ion source 3 will be described in detail with reference to FIGS.

[0023] FIG. 4 is a schematic cross-sectional view of the ion source and its surroundings according to the first embodiment before a cathode is inserted, FIG. 5 is a schematic cross-sectional view of the ion source and its surroundings according to the first embodiment after a cathode is inserted, and FIG. 6 is a schematic cross-sectional view showing an alignment structure of the ion source of FIG. 5.

[0024] Fig. 4 shows an example in which the ion source 3 is formed by fixing the chimney 22 to the dummy electrode 9 and inserting the cathode 23 and cathode holder 28 into the chimney 22 from above and below. Fig. 6 shows an example in which the structure of the cathode fixture 24 has a tapered structure for positioning the cathode holder 28 when it is inserted and for insulating support from the chimney 22. The cathode 23 and cathode holder 28 at the top of Fig. 4 show the state before insertion, and after insertion, they will be in the state of the cathode 23 and cathode holder 28 at the bottom of Fig. 4. The upper and lower cathodes 23 may have the same shape or different shapes.

[0025] 4 is an example of a PIG (Penning Ionization Gauge) type ion source including a pair of cathodes 23 that generate electrons, a chimney 22, and a pair of discharge power supplies 21 a, 21 b. The pair of discharge power supplies 21 a, 21 b may use separate power supplies or may share a single power supply, and this is not a limitation.

[0026] The dummy electrode 9 is placed opposite or parallel to the RF acceleration electrode 8 .

[0027] The chimney 22 is formed in a cylindrical shape. An extraction hole 29 for extracting the extracted beam 15 is provided on the peripheral wall of the chimney 22 on the side of the RF acceleration electrode 8. A bulge 30 that bulges out toward the extraction hole 29 is formed on the inner peripheral surface of the chimney 22 facing the extraction hole 29.

[0028] The chimney 22 is fixed to the dummy electrode 9 via a contact C. The contact C electrically connects the chimney 22 to the dummy electrode 9. The distance between the chimney 22 and the high-frequency electrode 8 is set so as to form an accelerating electric field that reduces the divergence of the extracted beam 15.

[0029] One end of the cathode 23 is held by a cathode holder 28. When the pair of cathodes 23 held by the pair of cathode holders 28 are inserted into the chimney 22 from openings on both sides of the chimney 22 along the insertion direction I, the cathodes 23 are arranged facing each other. The tip ends of the cathodes 23 inserted into the chimney 22 overlap with the bulging portions 30 in the insertion direction I of the cathodes 23.

[0030] The cathode holder 28 is supported by a cathode fixture 24 that is fixed to the chimney 22. The cathode fixture 24 positions the cathode holder 28 inserted into the chimney 22 and provides insulation from the chimney 22. Furthermore, the cathode holder 28 has a cooling structure to prevent abnormal damage due to overheating of the cathode.

[0031] The chimney 22 has the role of confining the plasma and forming an accelerating electric field, and plasma is generated by discharge between the cathode 23 and the chimney 22. For this reason, the chimney 22 is sometimes called an anode.

[0032] The cathode 23 is made of a material that easily emits electrons, such as tungsten (W) and lanthanum hexaboride (LaB6). However, the material of the cathode 23 is not particularly limited. Furthermore, the cathode 23 may be a cold cathode that is not heated, or a hot cathode that is forcibly heated by passing a current through it to emit electrons. However, the life of the cathode 23 is longer in a cold cathode. The chimney 22 is made of a heat-resistant material, and tantalum (Ta) or copper (Cu), which has good thermal conductivity, is preferred. However, the material of the chimney 22 is not particularly limited.

[0033] The cathode fixture 24 is made of an insulating material such as alumina (Al2O3) and boron nitride (BN), but the material of the cathode fixture 24 is not particularly limited as long as it can withstand high temperatures and has high insulating properties.

[0034] The ion source 3 emits electrons from the cathode 23. The cathode 23 is damaged by the generated plasma and discharge with the chimney 22. A damaged cathode 23 makes stable plasma generation difficult. For this reason, the cathode 23 must be replaced periodically. If the entire ion source 3, including the chimney 22, is replaced, the position of the chimney 22 and the RF electrode 8 must be adjusted after the replacement, and the adjustment time affects the system's operating rate. Based on previous test results, it was determined that the chimney 22 is not as damaged as the cathode 23 and does not need to be replaced at the same intervals as the cathode 23. Therefore, it is possible to replace only the cathode 23. Furthermore, because the position of the cathode 23 does not affect the distance between the chimney 22 and the RF electrode 8, installation accuracy is assured and the divergence of the extracted beam 15 is not affected. This facilitates readjustment after the cathode 23 is replaced during maintenance.

[0035] FIG. 6 is a schematic cross-sectional view showing the alignment structure of the ion source of FIG.

[0036] The structure of the cathode holder 28 and the cathode fixture 24, which have a tapered structure for positioning the cathode holder 28 and the chimney 22 and for insulating and supporting them, will be described below.

[0037] The cathode fixture 24 has an insertion hole 31 into which the cathode 23 is inserted. A tapered surface 32 is formed on the opening edge of the insertion hole 31, the diameter of which increases in the direction opposite to the insertion direction I of the cathode 23. A tapered surface 33 is formed on the base of the cathode holder 28, which faces the tapered surface 32 when the cathode 23 is inserted into the insertion hole 31. This tapered structure allows the tapered surfaces 32, 33 to come into contact with each other when the cathode 23 is inserted into the chimney 22, allowing the cathode 23 to be accurately positioned in a specified position in the chimney 22. Note that positioning can also be achieved by limiting the hole diameter of the insertion hole 31, even without providing a tapered structure. The tapered structure also acts as a guide when the cathode 23 is inserted into the chimney 22.

[0038] The ion source 3 operates as follows to generate plasma, which is the source of an ion beam. First, a voltage is applied between the cathode 23 and the chimney 22 by the discharge power supplies 21a and 21b. By setting the cathode 23 at a negative potential with respect to the chimney 22, electrons are emitted toward the chimney 22. A gas inlet pipe 27 is connected to the chimney 22, and a sample gas 25 is supplied into the chimney 22 through the gas inlet pipe 27. Plasma is generated by the emitted electrons and the sample gas 25, and an extraction beam 15 is formed from an extraction hole 29 for extracting the ion beam, which is provided in the peripheral wall of the chimney 22, by an accelerating electric field generated between the high-frequency electrode 8 and the chimney 22. At this time, the magnetic field B generated by the magnetic pole 10 causes the electrons to perform a spiral motion, extending their residence time in the chimney 22 and further increasing the plasma generation efficiency.

[0039] Next, the effects of this embodiment will be described. The ion source 3 of this embodiment described above is an ion source 3 that extracts an extraction beam from the acceleration cavity A in the main magnetic pole 1. The ion source 3 includes a chimney 22 and a pair of cathodes 23. The chimney 22 is fixed to the acceleration cavity A. The pair of cathodes 23 are inserted from both sides of the chimney 22 and arranged opposite to each other.

[0040] This allows only the cathode 23 to be replaced when the cathode 23 is damaged, thereby improving the ease of maintenance of the ion source 3.

[0041] Furthermore, the system includes a radio-frequency acceleration electrode 8 for accelerating the extraction beam 15 and a dummy electrode 9 arranged opposite or parallel to the radio-frequency acceleration electrode 8, and the chimney 22 is electrically connected to the dummy electrode 9 via a contact C. As a result, even when the cathode 23 in the ion source 3 for generating plasma is replaced, the chimney 22 and the radio-frequency electrode 8 are not reassembled, so there is no change in the electrode spacing and it is not necessary to adjust the position of the chimney 22 to readjust the trajectory of the extraction beam 15.

[0042] Furthermore, the chimney 22 is formed in a cylindrical shape, and an extraction hole 29 for extracting the extracted beam 15 is provided on the side of the RF acceleration electrode 8 on the peripheral wall of the chimney 33.As a result, the chimney 22 is not divided on the orbit, so that the acceleration electric field is less likely to be disturbed, current loss of the orbiting beam is reduced, and the utilization efficiency of the extracted ion beam 15 can be improved.

[0043] Furthermore, a bulging portion 31 that bulges toward the extraction hole 29 is formed on the inner peripheral surface of the chimney 22 facing the extraction hole 29, and the tip of the cathode 23 overlaps with the bulging portion 31 in the insertion direction I of the cathode 23. This brings the bulging portion 31 closer to the extraction hole 29, thereby increasing the current value.

[0044] Furthermore, the chimney 22 is formed in a cylindrical shape, and a pair of cathodes 23 are inserted from openings on both sides. As a result, the chimney 22 is not separated in the orbit, which makes it difficult for the accelerating electric field to be disturbed, reduces current loss in the orbiting beam, and improves the utilization efficiency of the ion beam.

[0045] The ion source further includes a cathode holder 28 that holds one end of the cathode 23, and a cathode fixture 24 that has an insertion hole 31 into which the cathode 23 is inserted and supports the cathode holder 28 when the cathode 23 is inserted into the insertion hole 31, and a tapered surface 32 that expands in diameter toward the side opposite the insertion direction I is formed at the opening of the insertion hole 31 opposite to the cathode insertion direction I. This allows the cathode 23 to be inserted into the chimney 22 while being guided by the tapered surface 32, and can improve the positional accuracy of the cathode 23 inserted into the chimney 22. Furthermore, because the structure of the cathode holder 28 can be simplified, replacement of the cathode 23 is easier than in conventional internal ion sources such as those described in Patent Document 1, and reassembly is easier, assembly time can be shortened, and the availability rate of the device can be improved.

[0046] Furthermore, the cathode holder 28 is formed with a tapered surface 33 opposite the tapered surface 32, which allows for improved insertion guidance and positioning accuracy of the cathode 23.

[0047] The circular accelerator 50 includes an ion source 3. This allows the device to be started up in a short time, making it possible to provide a circular accelerator that can improve the availability of the device. [Example]

[0048] Example 2 shows an example of an ion source 63 having a structure in which a cathode holder 28, a cathode 23, a cathode fixing device 24, and an anode electrode 64 are inserted as a unit into a chimney 22. In the following description, the same components as those in Example 1 are denoted by the same reference numerals, and the description thereof will be simplified.

[0049] FIG. 7 is a schematic cross-sectional view of the ion source and its surroundings according to the second embodiment before the cathode is inserted, and FIG. 8 is a schematic cross-sectional view of the ion source and its surroundings according to the second embodiment after the cathode is inserted.

[0050] The ion source 63 includes an anode electrode 64 as an example of an "anode." The anode electrode 64 is attached to the outer periphery of the cathode 23 via the cathode holder 24. The anode electrode 64 has a cylindrical portion 65 that is inserted into the chimney 22 and a flange portion 66 that extends outward from one end of the cylindrical portion. The anode electrode 64 has the same potential as the chimney 22. Furthermore, the anode electrode 64 is made of the same material as the chimney 22, such as tantalum (Ta) or copper (Cu).

[0051] The end of the chimney 22, into which the integrated structure of the cathode holder 28, cathode 23, cathode fixture 24, and anode electrode 64 is inserted, may be provided with a tapered structure for positioning, similar to the cathode fixture 24. That is, a tapered surface that expands in diameter in the direction opposite to the insertion direction I of the cathode 23 may be formed on the opening edge of the chimney 22. This allows the cathode holder 28, cathode 23, cathode fixture 24, and anode electrode 64 to be inserted into the chimney 22 as a unit while being guided by the tapered surface, and also increases the positional accuracy of the cathode 23 inserted into the chimney 22. Furthermore, the anode electrode 64 may be formed with a tapered surface that faces the tapered surface of the chimney 22 when inserted into the chimney 22. This makes it possible to improve the insertion guidance and positioning accuracy of the cathode holder 28, the cathode 23, the cathode fixing device 24, and the anode electrode 64 as a single unit.

[0052] By providing the anode electrode 64 in a part of the chimney 22 that is easily damaged, damage to the chimney 22 can be further reduced. The easily damaged anode electrode 64 can be replaced together with the cathode 23. However, since the anode electrode 64 is separated from the chimney 22, the positions of the chimney 22 and the radio-frequency electrode 8 are not changed. Therefore, since the accelerating electric field is not affected, readjustment of the extraction beam 15 after replacing the cathode 23 is not required. The rest of the structure and operation are the same as those described using Figures 4 and 5, and will not be described here.

[0053] The present invention is not limited to the above-described embodiments and includes various modifications. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment with other configurations.

[0054] 4 to 8 show the same structure on both the top and bottom. Furthermore, Examples 1 and 2 are examples in which the cathodes 23 are inserted from the top and bottom of the main pole 1, respectively. However, the cathodes 23 can operate in the same way even if they are inserted from the sides of the main pole 1. Furthermore, the chimney 22 may be configured so that at least one cathode 23 can be inserted therein.

[0055] Furthermore, the circular accelerator 50 may be a cyclotron type accelerator having a magnetic pole with unevenness on the magnetic pole 10, or a synchrocyclotron type accelerator having a magnetic pole tilted from the center of the magnetic pole 10 and modulating the frequency of the high-frequency acceleration, with similar effects.

[0056] A synchrocyclotron accelerator is a type of accelerator that is an improved version of a cyclotron. It repeatedly accelerates charged particles moving circularly between large magnetic poles by applying a frequency-modulated radio-frequency electric field. At the speed of light, the mass of the accelerated particles increases due to relativistic effects, and the period of the circular motion of the charged particles in the magnetic field increases in proportion to the mass. The resulting periodic discrepancy with the radio-frequency voltage is eliminated by modulating the frequency.

[0057] Since the synchrocyclotron accelerator has the same configuration as the cyclotron accelerator, the ion source 3 can be disposed inside the main magnetic pole 1, and similar effects can be obtained. [Explanation of symbols]

[0058] 1...main magnetic pole, 3...ion source, 8...radio frequency acceleration electrode, 9...dummy electrode, 15...extraction beam, 22...chimney, 23...cathode, 24...cathode fixture, 28...cathode holder, 29...extraction hole, 30...bulge, 31...insertion hole, 32...tapered surface, 33...tapered surface, 43...ion source, 44...anode, 50...circular accelerator, 52...beam transport system, 54...irradiation device, 63...ion source, 64...anode electrode, 100...particle beam therapy system, A...acceleration cavity, C...contact, I...insertion direction

Claims

1. An ion source extracting an ion beam from an acceleration cavity in a magnetic pole, a chimney fixed to the acceleration cavity; At least one cathode insertably disposed within the chimney; a radio frequency acceleration electrode for accelerating the ion beam; and a dummy electrode disposed opposite or parallel to the radio frequency acceleration electrode, the chimney is electrically connected to the dummy electrode; Ion source.

2. The cathode is A pair of cathodes inserted from both sides of the chimney and arranged opposite each other, The ion source of claim 1 .

3. The chimney is electrically connected to the dummy electrode via a contact. The ion source of claim 1 .

4. The chimney is formed in a cylindrical shape, an extraction hole for extracting the ion beam is provided on the peripheral wall of the chimney on the side of the radio frequency acceleration electrode; The ion source of claim 1 .

5. a bulging portion that bulges toward the extraction hole is formed on an inner peripheral surface of the chimney that faces the extraction hole, The tip of the cathode is overlapped with the bulge in the insertion direction of the cathode.

5. The ion source of claim 4.

6. The chimney is formed in a cylindrical shape, and the pair of cathodes are inserted from openings on both sides, respectively.

3. The ion source of claim 2.

7. An ion source extracting an ion beam from an acceleration cavity within a magnetic pole, comprising: a chimney fixed to the acceleration cavity; At least one cathode insertably disposed within the chimney; a cathode holder that holds one end of the cathode; a cathode fixing device that is provided with an insertion hole into which the cathode is inserted and that supports the cathode holder when the cathode is inserted into the insertion hole, an opening of the insertion hole on the opposite side to the insertion direction of the cathode, the opening having a tapered surface whose diameter increases in the opposite direction to the insertion direction; Ion source.

8. The cathode holder has a tapered surface formed thereon that faces the tapered surface.

8. The ion source of claim 7.

9. An ion source extracting an ion beam from an acceleration cavity within a magnetic pole, comprising: a chimney fixed to the acceleration cavity; At least one cathode insertably disposed within the chimney; The cathode is a pair of cathodes inserted from both sides of the chimney and arranged opposite to each other; an anode is attached to each of the pair of cathodes; The cathode and the anode are each inserted into the chimney. Ion source.

10. a tapered surface whose diameter increases in the direction opposite to the insertion direction of the cathode is formed on the opening edge of the chimney; 10. The ion source of claim 9.

11. The anode has a tapered surface formed thereon that faces the tapered surface when the chimney is inserted. The ion source of claim 10.

12. An accelerator comprising an ion source according to any one of claims 1 to 11.

13. A particle beam therapy system comprising the accelerator according to claim 12, a beam transport system, an irradiation device, and a treatment table.

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