Magnetic field measurement device for accelerator and particle beam therapy system

Abstract

To provide a magnetic field measurement device of an accelerator and a particle beam therapy system capable of measuring a magnetic field in a magnetic channel having a curved part.SOLUTION: A magnetic field measurement device 2000 for measuring a magnetic field in a predetermined region 1019 of an accelerator 1004 includes a magnetic sensor and at least one sensor head 2400 for supporting the magnetic sensor on the tip side. The sensor head has a curved shape corresponding to the predetermined region.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a magnetic field measuring device for an accelerator and a particle beam therapy system. [Background technology]

[0002] Patent Document 1 describes that in a circular accelerator that accelerates a charged particle beam while increasing the orbital radius by applying high frequency waves in a main magnetic field, the charged particle beam is emitted by applying high frequency waves to the charged particle beam that have a different frequency from the high frequency waves used for acceleration.

[0003] Patent document 2 discloses a magnetic field measurement method in which a measurement reference laser is incident parallel to the central axis of a magnet that has a measurement reference in space, and the magnetic measurement device is positioned using the laser as a reference to measure the magnetic distribution within the magnet. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-133745 [Patent Document 2] Japanese Patent Application Publication No. 5-223909 Summary of the Invention [Problem to be solved by the invention]

[0005] Particle therapy is a type of radiation therapy that destroys cancer cells by irradiating tumors with charged particle beams (hereinafter referred to as "beams") such as proton beams or carbon beams. A particle therapy system for administering particle therapy includes, for example, an ion source that generates ions, a particle accelerator (hereinafter referred to as "accelerator") that accelerates a large number of ions to form a beam, a beam transport system (hereinafter referred to as "transport system") that transports the beam from the accelerator to the treatment room, a rotating gantry that changes the direction of beam irradiation toward the tumor, an irradiation system that irradiates the tumor with the beam from the rotating gantry, and a control system that controls these components.

[0006] Particle therapy systems use circular accelerators such as synchrotrons, cyclotrons, and synchrocyclotrons. In recent years, development has progressed to miniaturize these circular accelerators in order to reduce the size of particle therapy systems.

[0007] A promising way to reduce the size of an accelerator is to increase the main magnetic field that circulates the beam inside the accelerator, and a promising way to increase the main magnetic field is to use a superconducting magnet for the main electromagnet that generates the main magnetic field. From the perspective of applying superconducting magnets, cyclotrons and synchrocyclotrons, which use a static main magnetic field, are more promising options than synchrotrons, which dynamically adjust the magnitude of the main magnetic field.

[0008] In circular accelerators with a static main magnetic field, such as cyclotrons and synchrocyclotrons, the energy of the beam extracted outside the accelerator is generally fixed to one type, and the energy is adjusted by attenuating the beam outside the accelerator using an energy absorber called a degrader.

[0009] One of the challenges is to reduce the amount of unnecessary radiation generated by this energy adjustment. Therefore, Patent Document 1 discloses the configuration of an accelerator (hereinafter referred to as a variable energy beam accelerator) in which the energy of the beam extracted outside the accelerator is variable, even though the main magnetic field is a static circular accelerator.

[0010] The circular accelerator described in Patent Document 1 accelerates a beam circulating within the accelerator (hereinafter referred to as the circulating beam) to a desired energy, and then applies a radio-frequency electric field to the circulating beam in a direction (hereinafter referred to as the horizontal direction) perpendicular to the beam propagation direction and the magnetic pole gap direction (hereinafter referred to as the vertical direction). The horizontal amplitude of the oscillations (hereinafter referred to as betatron oscillations) of the beam particles centered around the central orbit to which the radio-frequency electric field is applied gradually increases. The beam passes through a magnetic field region called a peeler and a regenerator, which generate resonance of betatron oscillations around the central orbit. The horizontal amplitude of the betatron oscillations of the beam passing through the peeler and the regenerator increases rapidly, and the beam reaches a septum coil located on the outer periphery of the main magnetic pole. The trajectory of the beam passing through the septum coil is significantly deflected by the magnetic field generated by the septum coil, and the beam is extracted outside the accelerator. Patent Document 1 also discloses that the septum coil can be replaced with a passive structure (magnetic channel) using a magnetic material.

[0011] When a septum coil is used for beam extraction in a variable energy beam accelerator, the magnetic field along the beam extraction path can be easily adjusted by adjusting the current in the septum coil. In addition, if a shielding coil is combined with the septum coil, the leakage magnetic field generated by the septum coil in the beam circulation region can be suppressed to a virtually negligible level.

[0012] On the other hand, if the septum coil is replaced with a magnetic channel, a coil power supply and a configuration for running cooling water through the coil are not required. However, this makes it difficult to adjust the magnetic field.

[0013] The magnetic field generated by the magnetic channel is determined by the surrounding magnetic environment. Furthermore, because the magnetic material inside the superconducting magnet is nearly magnetically saturated due to the strong magnetic field, the magnetic field of the magnetic channel cannot be shielded by magnetic material. Therefore, the magnetic field in the beam orbital region must be generated taking into account the leakage magnetic field from the magnetic channel into the beam orbital region, and therefore the position of the magnetic channel cannot be easily shifted to adjust the magnetic field on the beam extraction path.

[0014] However, to ensure beam extraction efficiency, a means for adjusting the magnetic field on the beam extraction path is essential. In particular, in variable energy beam accelerators, it is necessary to adjust the magnetic field on the beam extraction trajectory, which differs for each energy, so that the beam reaches the transport system outside the accelerator at the subsequent stage.

[0015] In order for the accelerator to achieve the desired performance, it is necessary to accurately measure the magnetic field distribution of the magnetic channel in advance. However, since the magnetic channel is not a simple linear shape but has curved parts, it is not possible to position it using a laser beam as described in Patent Document 2.

[0016] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a magnetic field measuring device for an accelerator and a particle beam therapy system that are capable of measuring the magnetic field inside a magnetic channel having a curved portion. [Means for solving the problem]

[0017] In order to solve the above problem, a magnetic field measuring device according to one aspect of the present invention is a magnetic field measuring device that measures the magnetic field of a specified region of an accelerator, and includes a magnetic sensor and at least one sensor head portion that supports the magnetic sensor at its tip side, and the sensor head portion has a curved shape that corresponds to the specified region. [Effects of the Invention]

[0018] According to the present invention, the magnetic field in a predetermined region can be measured by using a sensor head portion having a curved shape corresponding to the predetermined region. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a configuration diagram of a particle beam therapy system. [Figure 2] FIG. 2 is a perspective view of a main field magnet that generates the main magnetic field in the accelerator. [Figure 3] FIG. 1 is a longitudinal cross-sectional view of a main field magnet in an accelerator along a vertical plane. [Figure 4] FIG. 1 is a longitudinal cross-sectional view of a main field magnet including a regenerator in an accelerator. [Figure 5] FIG. 1 is a cross-sectional view along the mid-plane of a main field magnet in an accelerator. [Figure 6] FIG. 1 is a diagram showing the magnetic field distribution on the center line of the main magnetic field in an accelerator. [Figure 7] FIG. 2 is a diagram for explaining the circular orbit of an ion beam in an accelerator. [Figure 8] FIG. 2 is a schematic diagram showing the magnetic field distribution on the mid-plane of the magnetic field in an accelerator. [Figure 9] FIG. 1 shows the radial distribution of the magnetic field on the mid-plane at the periphery of the magnetic pole in the accelerator. [Figure 10] FIG. 1 is a schematic diagram of a beam extraction path in an accelerator. [Figure 11] FIG. 1 is a cross-sectional schematic diagram of the entrance to a magnetic channel in an accelerator. [Figure 12] FIG. 1 is a cross-sectional view at the mid-plane showing an enlarged view of the beam exit trajectory and magnetic channel. [Figure 13] FIG. 1 is a perspective view of a magnetic field measuring device. [Figure 14] FIG. 2 is a plan view of a first sensor head. [Figure 15] FIG. 2 is a side view of the first sensor head. [Figure 16] FIG. 4 is a plan view of a second sensor head. [Figure 17] FIG. 10 is a plan view of a third sensor head. [Figure 18] FIG. 2 is an explanatory diagram showing a magnetic field measurable region within the magnetic channel of each sensor head. [Figure 19] 1 is a flowchart showing a magnetic field measurement method. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In this embodiment, as will be described later, the magnetic field inside a magnetic channel (magnet) incorporated in an accelerator is measured multiple times at different positions to determine the magnetic field distribution. The accelerator of this embodiment can change the energy of the extracted beam, and since the beam trajectory also changes depending on the energy, a curved portion is formed in the magnetic channel. In this embodiment, the magnetic field inside the magnetic channel with the curved portion is measured from outside the magnetic channel.

[0021] The accelerator 1004 and the particle beam therapy system 1001 including the accelerator 1004 will be described below, followed by a magnetic field measuring device 2000 for measuring the magnetic field of the magnetic channel 1019 of the accelerator 1004. [Example]

[0022] A particle beam therapy system according to Example 1 will be described with reference to Figures 1 to 19. In the drawings used in this specification, identical or corresponding components are denoted by identical or similar reference numerals, and repeated description of these components may be omitted.

[0023] First, the overall configuration of a particle therapy system will be described with reference to Fig. 1. Fig. 1 is a diagram showing the overall configuration of a particle therapy system 1001 according to an embodiment of the present disclosure.

[0024] 1 is a system that irradiates a subject PE with an ion beam formed by accelerating ions in an accelerator 1004 (described later). The accelerator 1004 in this embodiment is a variable energy accelerator that accelerates an ion beam using hydrogen ions, i.e., protons, to any energy within a predetermined range and emits the ion beam.

[0025] In this embodiment, the predetermined range of the accelerated ion beam is explained as an example of a range from 70 MeV to 235 MeV. The ion beam may be a heavy particle ion beam using helium, carbon, or the like, and the extraction energy, which is the energy of the extracted ion beam, is not limited to the range from 70 MeV to 235 MeV.

[0026] The particle therapy system 1001 is installed on the floor of a building (not shown). The particle therapy system 1001 includes, for example, an ion beam generator 1002, a beam transport system 1005, a rotating gantry 1006, an irradiation device 1007, a treatment planning device 1008, and a control system 1009. The ion beam generator 1002 includes an ion source 1003 and an accelerator 1004.

[0027] The ion source 1003 is an ion introduction device that supplies ions to the accelerator 1004. The accelerator 1004 accelerates the ions supplied from the ion source 1003 to form an ion beam, and emits the ion beam.

[0028] The accelerator 1004 is connected to a radio frequency power supply 1036, which is the power supply for the radio frequency accelerating cavity 1037, and a coil excitation power supply 1057. The accelerator 1004 is connected to an ion beam current measuring device 1098, which measures the current of the ion beam. This ion beam current measuring device 1098 includes a moving device 1017 and a position detector 1039. A more detailed description of the configuration of the accelerator 1004 will be given later. As will be described later, the magnetic field distribution in a predetermined region of the accelerator 1004 is measured by a magnetic field measuring device 2000.

[0029] The beam transport system 1005 is a transport system that transports the ion beam extracted from the accelerator 1004 to the irradiation device 1007, and has an ion beam path 1048 through which the ion beam passes. The ion beam path 1048 is connected to a magnetic channel 1019 for extracting the ion beam from the accelerator 1004 and the irradiation device 1007. The ion beam path 1048 is provided with electromagnets for transporting the ion beam from the accelerator 1004 to the irradiation device 1007. For example, a plurality of quadrupole electromagnets 1046, a bending electromagnet 1041, a plurality of quadrupole electromagnets 1047, a bending electromagnet 1042, a quadrupole electromagnet 1049, a quadrupole electromagnet 1050, a bending electromagnet 1043, and a bending electromagnet 1044 are arranged in this order.

[0030] The rotating gantry 1006 is configured to be rotatable around a rotation axis 1045, and is a rotating device that rotates the irradiation device 1007 around the rotation axis 1045. A part of an ion beam path 1048 is installed in the rotating gantry 1006. Of the electromagnets for transporting the ion beam, the bending electromagnet 1042, quadrupole electromagnets 1049 and 1050, and bending electromagnets 1043 and 1044 are installed in the rotating gantry 1006.

[0031] The irradiation device 1007 is attached to the rotating gantry 1006 and is connected to the ion beam path 1048 downstream of the bending electromagnet 1044 .

[0032] The irradiation device 1007 has scanning magnets 1051 and 1052, a beam position monitor 1053, and a dose monitor 1054. The scanning magnets 1051 and 1052, the beam position monitor 1053, and the dose monitor 1054 are arranged in a casing (not shown) of the irradiation device 1007. The scanning magnets 1051 and 1052, the beam position monitor 1053, and the dose monitor 1054 are arranged along the central axis of the irradiation device 1007, i.e., the beam axis of the ion beam.

[0033] The scanning magnets 1051 and 1052 each deflect the ion beam and constitute a scanning system that scans the ion beam in directions approximately perpendicular to each other within a plane approximately perpendicular to the central axis of the irradiation device 1007. A beam position monitor 1053 and a dose monitor 1054 are disposed downstream of the scanning magnets 1051 and 1052. The beam position monitor 1053 measures the passing position of the ion beam. The dose monitor 1054 measures the dose of the ion beam.

[0034] A treatment table 1055 on which a patient PE, who is an object to be examined, lies is arranged downstream of the irradiation device 1007 so as to face the irradiation device 1007.

[0035] The treatment planning device 1008 generates details of ion beam irradiation for the patient PE as a treatment plan and notifies the control system 1009. The irradiation details include, for example, the ion beam irradiation area, irradiation energy, irradiation angle, and number of irradiations.

[0036] The control system 1009 is a control unit that controls the ion beam generator 1002, the beam transport system 1005, the rotating gantry 1006, and the irradiation device 1007 in accordance with the treatment plan notified from the treatment planning device 1008, and irradiates the patient PE with the ion beam.

[0037] The control system 1009 includes a central control unit 1066 , an accelerator / transport system control unit 1069 , a scan control unit 1070 , a rotation control unit 1071 , and a database 1072 .

[0038] The central control device 1066 controls the ion beam generator 1002, the beam transport system 1005, the rotating gantry 1006 and the irradiation device 1007 via the accelerator / transport system control device 1069, the scan control device 1070 and the rotation control device 1071 in accordance with the treatment plan notified from the treatment planning device 1008, and irradiates the ion beam to the patient PE.

[0039] The accelerator / transport system control device 1069 controls the ion beam generator 1002 and the beam transport system 1005. The scan control device 1070 controls the irradiation device 1007. The scan control device 1070 controls the scanning magnets 1051 and 1052 based on the measurement results of the beam position monitor 1053 and the dose monitor 1054, and scans the ion beam. The rotation control device 1071 controls the rotating gantry 1006. The database 1072 stores the treatment plan notified from the treatment planning device 1008. The database 1072 may store various information used by the central control device 1066.

[0040] The central control device 1066 has a CPU (Central Processing Unit) 1067, which is a central processing device, and a memory 1068 connected to the CPU 1067. A database 1072, an accelerator / transport system control device 1069, a scan control device 1070, and a rotation control device 1071 are electrically connected to the CPU 1067 in the central control device 1066.

[0041] The CPU 1067 reads a computer program that controls each device that constitutes the particle beam therapy system 1001 in accordance with the treatment plan stored in the database 1072, executes the read computer program, and performs control processing to control each device in the particle beam therapy system 1001.

[0042] The CPU 1067 controls each device by outputting commands to each device via the accelerator / transport system control device 1069, the scan control device 1070, and the rotation control device 1071, and irradiates the affected area of ​​the patient PE with an ion beam according to the treatment plan. The memory 1068 is used as a work area for computer programs and stores various data used and generated in the processing of the CPU 1067.

[0043] The computer program executed by CPU 1067 may be a single computer program or may be divided into multiple computer programs. Part or all of the processing by a computer program may be realized by dedicated hardware. The computer program may be installed into central control device 1066 from database 1072, or may be installed into central control device 1066 from a program distribution server or external storage medium (not shown). Each device in control system 1009 may be configured in a form in which two or more devices are connected by wire or wirelessly.

[0044] The lower part of Fig. 1 shows an apparatus 2000 for measuring the magnetic field in a magnetic channel 1019 as a predetermined region of the accelerator 1004. Details of the magnetic field measuring apparatus 2000 will be described later, but Fig. 1 shows a frame 2100, a position adjustment unit 2200, a rod 2300, a sensor head 2400, and a control unit 2500. Details of the magnetic field measuring apparatus 2000 will be described later.

[0045] <Accelerator 1004> The accelerator 1004 of the ion beam generator 1002 will now be described in detail. Fig. 2 is a perspective view of the accelerator 1004. Fig. 3 is a longitudinal sectional view of the accelerator 1004 taken along a vertical plane 3. Fig. 4 is a longitudinal sectional view including a regenerator. Fig. 5 is a transverse sectional view of the accelerator 1004 taken along a mid-plane 2.

[0046] (Main field magnet 1) The accelerator 1004 is a device that accelerates an ion beam while making it circulate using a main magnetic field and an accelerating high frequency electric field, and has a main magnetic field magnet 1 as shown in FIGS.

[0047] The main magnetic field magnet 1 is a main magnetic field generating device that generates a main magnetic field for circulating the ion beam. As shown in Fig. 2, the main magnetic field magnet 1 has an upper return yoke 4 and a lower return yoke 5, each of which has a substantially disk-like shape when viewed vertically.

[0048] The upper return yoke 4 and the lower return yoke 5 have shapes that are approximately plane-symmetrical to each other with respect to the mid-plane 2. The mid-plane 2 passes roughly through the vertical center of the main field magnet 1 and approximately coincides with the orbital plane of the ion beam accelerated within the accelerator 1004.

[0049] The upper return yoke 4 and the lower return yoke 5 are approximately perpendicular to the intermediate plane 2 and have shapes that are approximately symmetrical with respect to a vertical plane 3, which is a plane that passes through roughly the center of the main magnetic field magnet 1 on the intermediate plane 2. In Fig. 2, the intersection of the intermediate plane 2 with the main magnetic field magnet 1 is indicated by a dashed line, and the intersection of the vertical plane 3 with the main magnetic field magnet 1 is indicated by a broken line.

[0050] As shown in FIG. 3 , two coils 6 are arranged in a space surrounded by the upper return yoke 4 and the lower return yoke 5, approximately symmetrically with respect to the midplane 2. The coils 6 are superconducting coils, and are made of superconducting wires using a superconductor such as niobium titanium. The coils 6 are installed inside a cryostat (not shown), which is a cooling mechanism for cooling the coils 6, and are cooled to below the superconducting transition temperature by the cryostat. The coils 6 are led out of the main field magnet 1 by the coil lead-out wiring 1022 shown in FIG. 1 and connected to a coil excitation power supply 1057. The coil excitation power supply 1057 is a power supply that supplies power to the coils 6, and is controlled by an accelerator / transport system control device 1069.

[0051] A vacuum vessel 7 is provided inside the coil 6 in the space surrounded by the upper return yoke 4 and the lower return yoke 5. The vacuum vessel 7 is a vessel for maintaining a vacuum state inside, and is made of, for example, stainless steel. Inside the vacuum vessel 7, an upper magnetic pole 8 and a lower magnetic pole 9 are arranged symmetrically across the mid-plane 2, and are respectively connected to the upper return yoke 4 and the lower return yoke 5. The upper return yoke 4, the lower return yoke 5, the upper magnetic pole 8, and the lower magnetic pole 9 are made of, for example, pure iron or low-carbon steel with reduced impurity concentrations.

[0052] Main field magnet 1 having the above configuration forms a main magnetic field that applies a magnetic field in the vertical direction to internal acceleration space 20 (space sandwiched between upper magnetic pole 8 and lower magnetic pole 9) centered on midplane 2.

[0053] The distribution of the main magnetic field is designed so that ions supplied from the ion source 1003 circulate stably as an ion beam within the acceleration space 20 according to the principle of weak focusing. The principle of weak focusing indicates that ions circulate stably as an ion beam when the main magnetic field monotonically decreases as it approaches the periphery and the gradient is between a predetermined upper limit and a predetermined lower limit.

[0054] 4 is a longitudinal cross-sectional view of accelerator 1004 taken along a vertical plane passing through regenerator region 32, showing gap distance G32 at a position sandwiching regenerator region 32 and gap distance G33 at a position sandwiching substantially flat region 33. As shown in FIG. 4, gap distance G32 is designed to be narrower than gap distance G33.

[0055] 6 is a diagram showing the intensity distribution on the center line of the main magnetic field. The center line is the intersection line between the intermediate plane 2 and the vertical plane 3. In this embodiment, the direction along this intersection line is the Y-axis direction, and the direction perpendicular to the Y-axis direction on the intermediate plane 2 is the X-axis direction.

[0056] 6, the strength of the main magnetic field is greatest at a predetermined position O1 shifted in the Y-axis direction from the magnetic pole center position O2, which is the center of the upper magnetic pole 8 and the lower magnetic pole 9 in the direction of the mid-plane 2, and gradually decreases as it approaches the outer periphery of the upper magnetic pole 8 and the lower magnetic pole 9. Note that, hereinafter, position O1 may also be referred to as the center of the main magnetic field distribution.

[0057] (Ion source 1003) In the example of FIG. 2, the ion source 1003 is installed above the main magnetic field magnet 1. The upper return yoke 4 and the upper magnetic pole 8 are provided with a through-hole 24 for guiding ions from the ion source 1003 to position O1 in the acceleration space 20. A central axis (ion injection axis) 12 of the through-hole 24 is approximately perpendicular to the mid-plane 2 and passes through to position O1. The ion source 1003 is arranged above the through-hole 24 and introduces ions through the through-hole 24 into position O1 in the acceleration space 20. The ion source 1003 may be installed inside the main magnetic field magnet 1. In this case, the through-hole 24 is not necessary.

[0058] (Magnetic Channel 1019) 2 to 5, the accelerator 1004 has a magnetic channel 1019 that extracts an ion beam and sends it to the beam transport system 1005. The magnetic channel 1019 is an example of a "predetermined region of the accelerator."

[0059] The magnetic channel 1019 is a section that extracts an ion beam from inside the main magnetic field magnet 1 to outside the main magnetic field magnet 1, and is arranged outside the acceleration space 20, for example, on the outer periphery closer to the position O1 of the center of the main magnetic field distribution on the Y axis of the upper magnetic pole 8 and the lower magnetic pole 9. The magnetic channel 1019 has a magnetic channel inlet 1019a that opens near the Y axis, and takes in an ion beam of desired energy from the magnetic channel inlet 1019a and extracts it to the outside of the accelerator 1004 through through-holes 18 provided in the upper return yoke 4 and the lower return yoke 5. The tip of the beam transport system 1005 is installed in the through-hole 18, and the extracted ion beam is guided to the irradiation device 1007 via the beam transport system 1005.

[0060] (RF Acceleration Cavity 1037) The accelerator 1004 has a radio frequency acceleration cavity 1037. The radio frequency acceleration cavity 1037 is a device for accelerating ions injected into the acceleration space 20 to form an ion beam. The radio frequency acceleration cavity 1037 includes a pair of dee electrodes 1037a arranged on either side of an intermediate plane 2. The dee electrode 1037a has a fan-shaped shape when viewed vertically. The apex (center) of the fan-shaped electrode 1037a is located near position O1, which is the center of the main magnetic field distribution, and is arranged so as to cover a portion of the ion beam trajectory including position O2, the magnetic pole center.

[0061] A ground electrode (not shown) is arranged opposite the radial end face of the dee electrode 1037a, and an accelerating electric field, which is an accelerating high-frequency electric field for accelerating the ion beam, is formed between the radial end face of the dee electrode 1037a and the ground electrode.

[0062] Since the Dee electrode 1037a is formed in a fan shape with the position O1 as the apex, the accelerating electric field can be applied so that the direction of travel of the circulating ion beam is parallel to the accelerating electric field, that is, at a position where an axis parallel to the X axis passing through the center of each orbit around which the ion beam orbits intersects with each orbit.

[0063] The RF accelerating cavity 1037 is drawn out to the outside of the main field magnet 1 through a through-hole 16 provided along the Y-axis direction between the upper return yoke 4 and the lower return yoke 5, and is connected to a waveguide 1010 at its exterior. A RF power supply 1036 is connected to the waveguide 1010. The RF power supply 1036 is a power supply that supplies power to the RF accelerating cavity 1037 through the waveguide 1010, and is controlled by an accelerator / transport system control device 1069. The power supplied from the RF power supply 1036 excites a RF electric field as an accelerating electric field between the Dee electrode 1037a and the ground electrode. A vacuum is drawn through the through-hole 15, and the interior is maintained in a vacuum state.

[0064] The radius of the circular orbit, which is the orbit of the ion beam circulating within the acceleration space 20, gradually increases as the ion beam accelerates, as described below. To properly accelerate the ion beam, the accelerating electric field must be synchronized with the ion beam. To achieve this, the resonant frequency of the radio frequency acceleration cavity 1037 must be modulated according to the energy of the ion beam. The resonant frequency can be modulated, for example, by adjusting the inductance or capacitance of the radio frequency acceleration cavity 1037. Known methods can be used to adjust the inductance or capacitance of the radio frequency acceleration cavity 1037. For example, when adjusting the capacitance, the resonant frequency is modulated by controlling the capacitance of a variable capacitor connected to the radio frequency acceleration cavity 1037.

[0065] (Density of orbit) FIG. 7 is a diagram for explaining the orbits of the ion beams circulating in the acceleration space 20, and shows the orbits of ion beams with different energies.

[0066] Ions introduced from the ion source 1003 into the acceleration space 20 are formed into an ion beam by a radio frequency electric field, which is an acceleration electric field, and circulate within the acceleration space 20. As shown in Fig. 6, the main magnetic field in the acceleration space 20 is maximum at a position O1 shifted from the position O2 of the magnetic pole center, and gradually decreases as it approaches the outer periphery of the upper magnetic pole 8 and the lower magnetic pole 9. In this case, the low-energy ion beam circulates along an orbit centered on position O1.

[0067] As the ion beam is accelerated by the radio frequency electric field, the radius of the orbit increases and the center of the orbit gradually approaches position O2 of the central axis 13 of the upper magnetic pole 8 and the lower magnetic pole 9. The circular orbit 127 of the ion beam having the maximum energy shown in Fig. 5 has a shape that roughly follows the outer periphery of the upper magnetic pole 8 and the lower magnetic pole 9, and its center roughly coincides with position O2.

[0068] Therefore, as shown in Figure 7, the ion beam's orbit becomes dense between position O1 and position Y1 at the end of acceleration space 20 in the Y-axis direction, and becomes sparse between position O1 and position Y2 at the end in the Y-axis direction on the opposite side across position O2, the center of upper magnetic pole 8 and lower magnetic pole 9.

[0069] 5, the center of the orbit 127 of the maximum energy beam, which has the maximum energy (235 MeV) among the extractable ion beams, roughly coincides with the position O2 of the magnetic pole center. The center O3 of the orbit 126 of the minimum energy beam, which has the minimum energy among the extractable ion beams, is on the line connecting the position O2 of the magnetic pole center and the position O1 of the center of the main magnetic field distribution.

[0070] (Ion beam extraction) As shown in FIG. 8, the accelerator 1004 has a high-frequency kicker 40, a peeler region 31, a regenerator region 32, and a substantially flat region 33 as a mechanism for guiding the ion beam circulating in the acceleration space 20 to the magnetic channel 1019, and extracts an ion beam having a predetermined range of energy by utilizing the density of the circulating orbit.

[0071] The radio frequency kicker 40 is a displacement unit that displaces the ion beam circulating in the main magnetic field region where the main magnetic field is excited in the acceleration space 20, to the outside of the main magnetic field region. The radio frequency kicker 40 increases the amplitude of the betatron oscillation of the ion beam, for example, by applying a horizontal radio frequency electric field to the ion beam. As a result, the ion beam is displaced so as to pass through the peeler region 31, the regenerator region 32, and the approximately flat region 33. The peeler region 31, the regenerator region 32, and the approximately flat region 33 constitute a disturbance magnetic field region that disturbs the ion beam displaced by the radio frequency kicker 40 and excites a magnetic field that guides the ion beam to the magnetic channel 1019.

[0072] In this embodiment, the radio frequency kicker 40 is used as the "displacement unit" for displacing the ion beam circulating in the main magnetic field region to the outside of the main magnetic field region, but a bump coil can also be used as the displacement unit instead of the radio frequency kicker 40. When a bump coil is used as the displacement unit, the bump coil excites a magnetic field to deflect the circulating ion beam and displace it from the inside to the outside of the main magnetic field region.

[0073] FIG. 8 is a diagram for explaining the arrangement of the peeler region 31, the regenerator region 32, and the substantially flat region 33, and shows the magnetic field distribution on the intermediate plane 2 around which the ion beam circulates.

[0074] 6 is formed in the main magnetic field region 30 shown in Fig. 8. A peeler region 31, a regenerator region 32, and a substantially flat region 33 are formed on the outer periphery of the magnetic pole of the main magnetic field region 30. The peeler region 31 and the regenerator region 32 are provided on the outer periphery of the dense region where the ion beam orbits are dense in the main magnetic field region 30, and are parts that disturb the ion beam displaced outward by the radio frequency kicker 40, thereby exciting a magnetic field that guides the ion beam to the magnetic channel 1019.

[0075] 9 is a diagram showing the radial distribution of the magnetic field in the peeler region 31, the regenerator region 32, and the substantially flat region 33. The magnetic field distribution in the peeler region 31 corresponds to the magnetic field distribution along line A-Aa in FIG. 8. The magnetic field distribution in the regenerator region 32 corresponds to the magnetic field distribution along line B-Ba in FIG. 8. The magnetic field distribution in the substantially flat region 33 corresponds to the magnetic field distribution along line C-Ca in FIG. 8.

[0076] The magnetic fields at the innermost positions (positions A, B, C) of the peeler region 31, the regenerator region 32, and the substantially flat region 33 are substantially the same.

[0077] The peeler region 31 is the first region where the magnetic field strength decreases relatively greatly outward (from A to Aa).

[0078] The regenerator region 32 is a second region where there is a relatively large increase in magnetic field strength outward (from B to Ba).

[0079] The substantially flat region 33 is a third region where the magnetic field is substantially constant. In this embodiment, the magnetic field in the substantially flat region 33 decreases slightly and more gradually than the magnetic field in the peeler region 31 as it moves outward (from C to Ca).

[0080] Therefore, at the outer periphery of each region, the magnetic field in the peeler region 31 is the smallest, the magnetic field in the regenerator region 32 is the largest, and the magnetic field in the approximately flat region 33 is between the magnetic fields in the peeler region 31 and the regenerator region 32.

[0081] The operation of extracting an ion beam having a desired energy from the accelerator 1004 will now be described.

[0082] In response to commands from the central controller 1066, the accelerator and transport system controller 1069 generates ions in the ion source 1003 and introduces the ions through the through-hole 24 to position O1 in the acceleration space 20 within the main field magnet 1. The accelerator and transport system controller 1069 uses the radio frequency acceleration cavity 1037 to generate an acceleration electric field in the acceleration space 20, accelerating the ions to form an ion beam. The formed ion beam increases its energy as it orbits.

[0083] When the ion beam reaches the desired energy, the accelerator and transport system control device 1069 turns off the power supplied to the RF accelerating cavity 1037 and turns on the RF kicker 40. This applies a RF electric field to the ion beam superimposed on the main magnetic field. As a result, the circular orbit 126 of the ion beam is displaced in the radial direction (toward position Y1). For example, as shown in FIG. 8, when the ion beam is the lowest energy beam, the circular orbit 126 is displaced in the radial direction as shown by circular orbit 126a, and when the ion beam is the highest energy beam, the circular orbit 127 is displaced in the negative direction of the Y axis as shown by circular orbit 127a.

[0084] As a result, the ion beam passes through the peeler region 31 and the regenerator region 32. This causes a horizontal betatron oscillation resonance called "2 / 2 resonance," causing the ion beam to diverge in the radial direction and reach the magnetic channel entrance 1019a. The ion beam completely leaves the circular orbit by the magnetic channel 1019, and is extracted to the outside of the accelerator 1004 through the through-hole 18.

[0085] In the accelerator 1004 of this embodiment, the energy of the extracted ion beam is variable, so that the peeler region 31 and the regenerator region 32 are formed in the region through which not only the maximum energy beam but also the minimum energy beam passes.

[0086] In order to properly induce resonance due to betatron oscillation, the product of the magnitude of the magnetic field gradient and the length through which the ion beam passes through the region having the magnetic field gradient is important. As shown in Fig. 8, the length through which the ion beam passes through the peeler region 31 and the regenerator region 32 becomes shorter as the energy of the ion beam decreases. Therefore, in order to induce resonance in a low-energy ion beam, it is preferable to increase the magnetic field gradient so as to compensate for the short length through which the ion beam passes through the peeler region 31 and the regenerator region 32.

[0087] An ion beam having higher energy than the lowest energy beam passes through the same peeler region 31 and regenerator region 32 as the lowest energy beam. For this reason, in this embodiment, the peeler region 31 is limited to a narrow range, and the peripheral portion of the magnetic pole excluding the peeler region 31 and regenerator region 32 becomes a substantially flat region 33 having a substantially constant magnetic field as shown in Fig. 8. This keeps the product of the magnitude of the magnetic field gradient and the length of the region having the magnetic field gradient at an appropriate size without becoming excessively large for a high energy beam.

[0088] In addition, since it is natural for the magnetic field to decrease in magnitude at the periphery of the magnetic pole and the ion beam is stabilized due to the principle of weak convergence, in this embodiment, the magnetic field in the approximately flat region 33 has a slight decreasing gradient.

[0089] (Beam exit trajectory and intersection area) The beam extraction path will now be described. Similar to Fig. 5, Fig. 10 is a cross-sectional view of the accelerator 1004, and the internal equipment is not shown in order to explain the beam extraction trajectory.

[0090] The high-energy beam extraction trajectory 301 passes from the magnetic channel entrance 1019a through the through-hole 18 of the return yoke and is extracted to the outside of the accelerator 1004. Similar to the high-energy beam extraction trajectory 301, the low-energy beam extraction trajectory 302 also passes from the magnetic channel entrance 1019a through the through-hole 18 of the return yoke and is extracted to the outside of the accelerator 1004. If the traveling direction of low-energy beam extraction trajectory 302 is directed outward from high-energy beam extraction trajectory 301 at magnetic channel entrance 1019a and the low-energy beam extraction trajectory 302 is attempted to pass through narrow through-hole 18, an intersection region 304 will be generated where high-energy beam extraction trajectory 301 and low-energy beam extraction trajectory 302 intersect between the magnetic channel entrance 1019a and the through-hole 18 (i.e., inside main magnetic field magnet 1, particularly within magnetic channel 1019). Then, the low-energy beam passes near boundary surface 18a on the positive side of the Y-axis of through-hole 18, and the high-energy beam passes near boundary surface 18b on the negative side of the Y-axis of through-hole 18.

[0091] (Details of Magnetic Channel 1019) 11 is a cross-sectional view of the magnetic channel inlet 1019a. The magnetic channel 1019 includes a septum 51 (first septum) located on the inside in the radial direction and an antiseptum 52 (second septum) located on the outside in the radial direction, sandwiching a passage region for the displaced ion beam, and the extracted beam passes through a beam passage region 530. The septum 51 and the antiseptum 52 are made of a magnetic material.

[0092] In this embodiment, antiseptum 52 is divided into upper and lower halves with respect to the midplane and arranged opposite to each other with a gap, while septum 51 is not divided into upper and lower halves. Therefore, the magnetic field generated by magnetic channel 1019 in beam passing region 530 has a magnetic field distribution in which the magnetic field in the opposite direction to the main magnetic field becomes stronger as it goes radially inward and the magnetic field in the opposite direction to the main magnetic field becomes weaker as it goes radially outward.

[0093] This is because, as shown in Figure 11, on the radially inner side, magnetic flux passing through the septum 51 in the same direction as the main magnetic field returns in the opposite direction, while on the radially outer side, magnetic flux flowing in the same direction as the main magnetic field leaks through the antiseptum 52, which is divided into upper and lower parts.

[0094] 12 is an enlarged cross-sectional view at the mid-plane of the beam extraction trajectory and the magnetic channel 1019. The magnetic channel entrance 1019a is located in the space between the magnetic poles, and the tips of the septum 51 and antiseptum 52 also extend into the space between the magnetic poles. A curved portion 1019c is formed midway through the magnetic channel 1019. Although not shown in Fig. 12, reference position members that serve as reference surfaces for measuring the magnetic field are provided at the entrance 1019a and the exit 1019b of the magnetic channel 1019.

[0095] (Magnetic field measuring device) In the accelerator 1004 configured as described above, the magnetic field in the magnetic channel 1019 is measured using a magnetic field measuring device 2000 shown in FIG. 13 during manufacturing or maintenance and inspection, and the magnetic field in the beam extraction region is adjusted.

[0096] First, the magnetic field on the beam extraction path is measured. The magnetic field on the beam extraction path can be measured by inserting a rod (arm member) with a sensor head 2400 fixed to its tip through the through-hole 18 or the through-hole 15. After adjusting the magnetic field, the beam is adjusted. Details of these will be omitted.

[0097] 13 includes, for example, a support frame 2100, a position adjustment unit 2200, a rod 2300, a sensor head 2400, and a control unit 2500. The support frame 2100 and the sensor head 2400 can also be called the support frame unit 2100 and the sensor head unit 2400.

[0098] The support frame 2100 is movably provided on the floor (not shown) of a building that houses the accelerator, and supports the position adjustment unit 2200, the rod 2300, and the sensor head 2400 from below. The support frame 2100 may also support the control unit 2500. The control unit 2500 may be provided in a location separate from the support frame 2100.

[0099] The support frame 2100 includes, for example, a flat lower plate portion 2110 provided on the lower side, a flat upper plate portion 2120 provided on the upper side, and multiple legs 2130 erected between the lower plate portion 2110 and the upper plate portion 2120.

[0100] The position adjustment unit 2200 is a device that adjusts the position of the sensor head 2400. The position adjustment unit 2200 includes, for example, a longitudinal direction adjustment unit 2210, a lateral direction adjustment unit 2220, a vertical direction adjustment unit 2230, and a rod fixing unit 2240 provided on the vertical direction adjustment unit 2230. Here, the longitudinal direction is a direction parallel to the longitudinal direction of the sensor head 2400. The lateral direction is a direction perpendicular to the longitudinal direction in the same plane. The vertical direction is a direction perpendicular to the longitudinal direction and the lateral direction.

[0101] The longitudinal direction adjustment unit 2210 adjusts the position of the sensor head 2400 in the longitudinal direction (the direction of insertion into the magnetic channel 1019). The lateral direction adjustment unit 2220 adjusts the lateral direction position of the sensor head 2400. The vertical direction adjustment unit 2230 adjusts the vertical direction position of the sensor head 2400.

[0102] Since the longitudinal direction adjustment unit 2210 is formed as a single device over the entire longitudinal direction, the sensor head 2400 and the rod 2300 can be moved more smoothly than if multiple short-side direction adjustment units 2220 were arranged in the longitudinal direction, rotated 90 degrees on the same plane.

[0103] The control unit 2500 continuously moves the longitudinal direction adjustment unit 2210 and intermittently moves the lateral direction adjustment unit 2220. This makes it possible to reduce vibrations occurring in the sensor head 2400.

[0104] The configuration of the support frame 2100 is not limited to the above example, as long as it functions as the support frame 2100. The function of the support frame 2100 is, for example, to support the sensor head 2400 without vibrating it. Similarly, the configuration of the position adjustment unit 2200 is not limited to the above example, as long as it functions as the position adjustment unit 2200. The function of the position adjustment unit 2200 is, for example, to adjust the position of the tip of the sensor head 2400 within the measurement coordinate system with a predetermined accuracy. Therefore, the support frame 2100 and the position adjustment unit 2200 may be formed, for example, like a three-axis robot arm. As described below, the magnetic field measurement device 2000 switches between and uses multiple sensor heads 2400 depending on the position within the magnetic channel 1019 to be measured.

[0105] The rod 2300 is a member that supports the sensor head 2400, and can also be called an arm. The rod 2300 includes, for example, a large diameter portion 2310 and a small diameter portion 2320 provided on the tip side of the large diameter portion 2310. A tapered portion connecting the large diameter portion 2310 and the small diameter portion 2320 may be provided.

[0106] The reason why rod 2300 is composed of large diameter portion 2310 on the base end side and small diameter portion 2320 on the tip end side is to reduce the weight of the tip end side of rod 2300 and reduce vibrations occurring in sensor head 2400. Instead of forming rod 2300 into a stepped rod shape from large diameter portion 2310 and small diameter portion 2320, rod 2300 may be formed into a substantially conical shape whose diameter gradually decreases from the base end side toward the tip end side.

[0107] The rod 2300 is formed into the above-described shape from a non-magnetic and conductive material such as CFRP (Carbon Fiber Reinforced Plastics). The rod 2300 is conductive, allowing electrical signals from a magnetic sensor 2420 and a position sensor 2430 (described later) to be guided to the base end of the rod 2300 and input to the control unit 2500. This eliminates the need for signal lines for transmitting signals from the sensors 2420 and 2430, thereby reducing the number of components of the sensor head 2400 and simplifying it. However, the sensor head 2400 of this embodiment may also include signal lines for transmitting electrical signals from the sensors 2420 and 2430. In this case, the rod 2300 only needs to be non-magnetic and does not need to be conductive.

[0108] The control unit 2500 can have, for example, a function of controlling the position adjustment unit 2200 based on a signal from the position sensor 2430 and a function of receiving the magnetic field detected by the magnetic sensor 2420. A magnetic field distribution creation unit (not shown) that creates a magnetic field distribution may be provided within the control unit 2500. The control unit 2500 has an operation unit (not shown) and controls the position adjustment unit 2200 in response to an operation from the user of the magnetic field measuring device 2000.

[0109] Fig. 14 is a plan view of a first sensor head 2400(1) as an example of a "sensor head portion formed in a linear shape." Fig. 15 is a side view of the first sensor head 2400(1). The first sensor head 2400(1) can also be called, for example, a "linear sensor head."

[0110] The sensor head main body 2410(1) is formed in a thin, flat plate shape from a non-magnetic, conductive material such as CFRP, and is generally linear, with a magnetic sensor 2420 and a position sensor 2430 provided on its tip side (upper side in FIG. 14). Formed in a linear shape means that there are no curved or bent portions, unlike the other sensor heads 2400(2), 2400(2) described below.

[0111] The magnetic sensor 2420 is a device that detects magnetism, and is, for example, a probe that can measure magnetic flux density, a Hall probe with a Hall sensor, an NMR (Nuclear Magnetic Resonance) probe, a search coil, etc. Any type of device can be used as long as it can detect magnetism (magnetic field).

[0112] The position sensor 2430 is a device that detects the position of the magnetic sensor 2420. Since the difference between the position detected by the position sensor 2430 and the installation position of the magnetic sensor 2420 is known, the magnetic field measurement position by the magnetic sensor 2420 can be calculated from the position detected by the position sensor 2430.

[0113] The position sensor 2430 is, for example, a contact sensor. When the position sensor 2430 comes into contact with a wall portion in the magnetic channel 1019, it outputs an electrical signal indicating the contact, for example, as a change in resistance, current, or voltage.

[0114] The attachment position of the position sensor 2430 in the sensor head 2400 is known, and the position of the sensor head 2400 in the magnetic channel 1019 can be detected by the position adjustment unit 2200, so it is possible to know the position of the magnetic sensor 2420 at the time of receiving a detection signal from the position sensor 2430. Instead of a contact sensor, a non-contact position sensor such as a capacitance displacement meter or an optical fiber displacement meter may be used.

[0115] The position sensor 2430 has three sensing points 2431. When an object (such as the magnetic channel 1019 or the wall of the accelerator 1004) is detected at any of the sensing points 2431, a detection signal is output to the control unit 2500. In this embodiment, sensing points are set at three locations: the tip of the sensor head 2400(1) in the longitudinal direction, and both the left and right sides of the tip.

[0116] Because each sensing point 2431 is located outside the magnetic sensor 2420, it is possible to detect an object before the magnetic sensor 2420 comes into contact with the object and immediately stop the sensor head 2400(1). This makes it possible to prevent the magnetic sensor 2420 from coming into contact with an object and being damaged. Furthermore, because multiple sensing points 2431 are located outside the magnetic sensor 2420 and provided around the magnetic sensor 2420, it is possible to further prevent the magnetic sensor 2420 from coming into contact with surrounding objects.

[0117] 16 is a plan view of a second sensor head 2400(2) as an example of a "sensor head having a curved shape corresponding to a predetermined region." The second sensor head 2400(2) can also be called, for example, a "curved sensor head."

[0118] The second sensor head 2400(2) includes, for example, a sensor head main body 2410(2), a magnetic sensor 2420, and a position sensor 2430. A curved portion 2411(2) is formed midway (for example, approximately at the middle) of the sensor head main body 2410(2). The curved portion 2411(2) is curved at an obtuse angle θ2. The curved portion 2411(2) corresponds to the curved portion 1019c of the magnetic channel 1019 shown in FIG. 12. In other words, the angle θ2 and the like are set so that the magnetic sensor 2420 can reach the curved portion 1019c of the magnetic channel 1019 when the second sensor head 2400(2) is inserted into the magnetic channel 1019 from the magnetic channel outlet 1019b.

[0119] 17 shows an example of a third sensor head 2400(3), which is an example of a "sensor head having a portion that is more bent than a curved portion." The third sensor head 2400(3) can also be called, for example, a "right-angle sensor head."

[0120] The third sensor head 2400(3) includes, for example, a sensor head main body 2410(3), a magnetic sensor 2420, and a position sensor 2430. A right-angled portion 2411(3), which is an example of a "portion that is more bent than a curved portion," is formed midway (for example, approximately at the middle) of the sensor head main body 2410(3). The right-angled portion 2411(3) is bent at an angle θ3, which is approximately a right angle. The angle θ3 is larger than the angle θ2 of the second sensor head 2400(2) (θ3>θ2). The angle θ3 is a right angle or approximately a right angle.

[0121] The curved portion 2411(3) is set at an angle θ3, etc., so that when the tip of the third sensor head 2400(3) is inserted into the entrance 1019a of the magnetic channel 1019 through the through hole 15 shown in Figure 5, the magnetic sensor 2420 can reach the entrance 1019a of the magnetic channel 1019.

[0122] Because the through-hole 15 is located on the lower side in FIG. 5 (the 6 o'clock direction of a clock), it can also be called, for example, a lower through-hole 15 or a 6 o'clock direction through-hole 15.

[0123] 18 is an explanatory diagram showing the magnetic field measurable area within the magnetic channel of each head. The dashed-dotted line O2400(1) in the figure indicates the longitudinal axis when the first sensor head 2400(1) is inserted from the exit 1019b of the magnetic channel 1019 up to position P2400(1) where the position sensor 2430 at the tip of the first sensor head 2400(1) contacts the antiseptum 52.

[0124] A reference position member 2610 for the exit port is provided near the outlet 1019b of the magnetic channel 1019. Before inserting the first sensor head 2400(1) into the magnetic channel 1019, the magnetic field measuring device 2000 brings the position sensor 2430 at the tip of the first sensor head 2400(1) into contact with the reference position member 2610, thereby aligning the coordinate system based on the accelerator 1004 with the coordinate system based on the magnetic field measuring device 2000.

[0125] After aligning the coordinate systems, the magnetic field measuring device 2000 shifts the first sensor head 2400(1) slightly to the exit 1019b and causes it to enter the magnetic channel 1019. The magnetic field measuring device 2000 measures the magnetic field while changing the position of the magnetic sensor 2420 using the position adjustment unit 2200.

[0126] The reference position members 2610 and 2611 may be integrally formed with the magnetic channel 1019 or with a member (not shown) that supports the magnetic channel 1019.

[0127] 18, the hatched area with horizontal lines indicates an area A1 where the magnetic field can be measured by the first sensor head 2400(1). The first sensor head 2400(1) can measure the magnetic field within a range from the outlet 1019b of the magnetic channel 1019 to the contact position P2400(1).

[0128] 18, the hatched area indicates an area A2 where the magnetic field can be measured by the second sensor head 2400(2), which is slightly curved halfway. The second sensor head 2400(2) is also positioned by the reference position member 2610 (after the respective coordinate systems are aligned), and then inserted into the magnetic channel 1019 from the exit 1019b. The magnetic field measuring device 2000 measures the magnetic field with the magnetic sensor 2420 while the second sensor head 2400(2) enters the magnetic channel 1019.

[0129] In FIG. 18, the hatched area with vertical lines indicates an area A3 where the magnetic field can be measured by the third sensor head 2400(3). The third sensor head 2400(3) is inserted into the accelerator 1004 through the through-hole 15. The magnetic field measurement device 2000 brings the position sensor 2430 of the third sensor head 2400(3) into contact with another reference position member 2611 provided near the entrance 1019a of the magnetic channel 1019, thereby aligning the above-mentioned coordinate systems. Then, the magnetic field measurement device 2000 uses the position adjustment unit 2200 to move the third sensor head 2400(3) away from the reference position member 2611 and cause it to enter the entrance 1019a. The magnetic field measurement device 2000 measures the magnetic field with the magnetic sensor 2420 while causing the third sensor head 2400(3) to enter near the entrance 1019a of the magnetic channel 1019.

[0130] 19 is a flowchart showing a magnetic field measurement method. The magnetic field measurement device 200 is brought close to the accelerator 1004 and initial settings are performed (S1). A linear first sensor head 2400(1) is attached to the magnetic field measurement device 2000 (S2). The magnetic field measurement device 2000 brings the position sensor 2430 of the first sensor head 2400(1) into contact with the reference position member 2610 to align the coordinate systems (S3).

[0131] The magnetic field measuring device 2000 places the first sensor head 2400(1) at a predetermined position and causes the magnetic sensor 2420 to measure the magnetic field (S4). The measured magnetic field data is sent to the control unit 2500 and recorded. The first sensor head 2400(1) measures the magnetic field while advancing by a predetermined amount until the first sensor head 2400(1) completes the magnetic field measurement of the area A1 shown in FIG. 18 (S5).

[0132] When the magnetic field measurement by the first sensor head 2400(1) is completed (S5: YES), the second sensor head 2400(2) is attached to the magnetic field measurement device 2000 in place of the first sensor head 2400(1) (S6), and the coordinate system is aligned by the reference position member 2610 (S7). Note that the rod to which the first sensor head 2400(1) is attached may be replaced with another rod to which the second sensor head 2400(2) is attached.

[0133] The magnetic field measuring device 2000 places the second sensor head 2400(2) at a predetermined position and causes the magnetic sensor 2420 to measure the magnetic field (S8). The measured magnetic field data is sent to the control unit 2500 and recorded. The second sensor head 2400(2) measures the magnetic field while advancing by a predetermined amount until the second sensor head 2400(2) completes the magnetic field measurement of the area A2 shown in FIG. 18 (S9).

[0134] When the magnetic field measurement by the second sensor head 2400(2) is completed (S9: YES), the magnetic field measurement device 2000 moves to the side of the through-hole 15 (S10). A third sensor head 2400(3) is attached to the magnetic field measurement device 2000 in place of the second sensor head 2400(2) (S11). The magnetic field measurement device 2000 advances the third sensor head 2400(3) from the through-hole 15 toward the entrance 1019a of the magnetic channel 1019, and aligns the coordinate systems using a reference position member 2611 provided near the entrance 1019a (S12). Note that the rod to which the second sensor head 2400(2) is attached may be replaced with another rod to which the third sensor head 2400(3) is attached.

[0135] The magnetic field measuring device 2000 places the third sensor head 2400(3) at a predetermined position and causes the magnetic sensor 2420 to measure the magnetic field (S13). The measured magnetic field data is sent to the control unit 2500 and recorded. The third sensor head 2400(3) measures the magnetic field while advancing by a predetermined amount until the third sensor head 2400(3) completes the magnetic field measurement of the area A3 shown in FIG. 18 (S14).

[0136] When the magnetic field measurement by the third sensor head 2400(3) is completed, the magnetic field measurement by the magnetic field measurement device 2000 is completed. Based on the measurement results of the magnetic field (magnetic field distribution) by the magnetic field measurement device 2000, the user adjusts various parts of the accelerator 1004.

[0137] According to this embodiment configured as described above, the magnetic field of the magnetic channel 1019 of the accelerator 1004, which has a different trajectory depending on the extracted beam energy, can be accurately measured by inserting the sensor head 2400 into the magnetic channel 1019 from outside the accelerator 1004.

[0138] The magnetic channel 1019 has a curved portion 1019c to accommodate beams with different trajectories. Therefore, the linear sensor head 2400(1) alone cannot measure the magnetic field over the entire range of the magnetic channel 1019, which is curved in the middle. This is because the tip of the sensor head 2400(1) comes into contact with the curved portion 1019c whether the sensor head 2400(1) is inserted from the exit 1019b of the magnetic channel 1019 or from the entrance 1019a of the magnetic channel 1019.

[0139] In contrast, the magnetic field measuring device 2000 of this embodiment is equipped with not only a linear sensor head 2400(1) but also a curved sensor head 2400(2), so that the sensor head inserted from the exit 1019b can reach further inside to measure the magnetic field.

[0140] Furthermore, in this embodiment, the substantially rectangular sensor head 2400(3) can be inserted into the accelerator 1004 from the through-hole 15 near the entrance 1019a of the magnetic channel 1019 to measure the magnetic field near the entrance 1019a.

[0141] In this way, the magnetic field measurement device 2000 of this embodiment is provided with a plurality of sensor heads 2400(1) to 2400(3) according to the magnetic channel 1019 having the curved portion 1019c, which is not simply linear, and switches between the plurality of sensor heads 2400(1) to 2400(3) according to the measurement target regions A1 to A3 of the magnetic channel 1019. Therefore, in this embodiment, the magnetic field in the magnetic channel 1019 having the curved portion 1019c can be measured by inserting the sensor head 2400 from outside the magnetic channel 1019 (outside the accelerator 1004).

[0142] In this embodiment, the position sensor 2430 is brought into contact with the reference position members 2610 and 2611 to establish a reference for magnetic field measurement, so that the magnetic field can be measured while calculating the exact position within the magnetic channel 1019, and an accurate magnetic field distribution can be determined.

[0143] Although a method of detecting the position of the magnetic sensor 2420 in the magnetic channel 1019 using a laser beam is also conceivable, the magnetic channel 1019 corresponding to the beams with different trajectories depending on the extracted beam energy has a curved portion 1019c, so that the magnetic sensor 2420 located beyond the curved portion 1019c cannot be detected using a laser beam.

[0144] It should be noted that the present invention is not limited to the above-described embodiment, and includes various modifications. The above-described embodiment has been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to an embodiment having all of the described configurations.

[0145] It is also 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.It is also possible to add, delete, or replace part of the configuration of each embodiment with the configuration of another embodiment.

[0146] It is clear that the present disclosure describes the following configuration to such an extent that a person skilled in the art can implement it.

[0147] (Configuration 1) A magnetic field measuring device for measuring the magnetic field of a predetermined area, comprising a magnetic sensor and at least one sensor head unit supporting the magnetic sensor, wherein the sensor head unit is formed from a non-magnetic material and has a curved shape corresponding to the predetermined area, and the sensor head unit is attached to the tip of a rod, and the rod is inserted into the predetermined area to measure the magnetic field.

[0148] (Configuration 2) The magnetic field measuring device according to configuration 1, further comprising a position sensor provided closer to the tip of the sensor head than the magnetic sensor, for detecting a magnetic field measurement position by the magnetic sensor.

[0149] (Configuration 3) The magnetic field measuring device according to configuration 2, wherein the sensor head unit is provided in plurality, and one of the plurality of sensor head units is formed linearly.

[0150] (Configuration 4) A magnetic field measuring device according to configuration 2, wherein the sensor head unit is multiple, and one of the multiple sensor head units has a shape portion that is more bent than the curved shape portion.

[0151] (Configuration 5) A magnetic field measuring device according to configuration 2, wherein the sensor head units are multiple, and the multiple sensor head units include a sensor head unit formed in the linear shape and a sensor head unit having a shape that is more bent than the curved shape, and the multiple sensor head units can be used depending on the location within the specified region where the magnetic field is to be measured.

[0152] (Configuration 6) The magnetic field measuring device according to any one of configurations 2 to 5, wherein the position sensor is made of a non-magnetic material.

[0153] (Configuration 7) The magnetic field measuring device according to any one of configurations 2 to 6, wherein the position sensor detects the magnetic field measurement position of the magnetic sensor from a plurality of directions.

[0154] (Configuration 8) A magnetic field measuring device according to any one of configurations 2 to 7, wherein the position sensor detects a reference position member indicating a reference position, and the reference position member is provided inside or outside, or both inside and outside, the specified area.

[0155] (Configuration 9) A magnetic field measuring device according to any one of configurations 2 to 8, further comprising a position adjustment unit that controls the position of the sensor head unit, wherein the sensor head unit is moved by the position adjustment unit continuously in a direction approximately parallel to the direction in which the rod is inserted and intermittently in a direction approximately perpendicular to the direction in which the rod is inserted.

[0156] (Configuration 10) A magnetic field measuring device according to any one of configurations 1 to 9, wherein the predetermined region is the inside of an accelerator, the accelerator being an accelerator that accelerates an ion beam while causing it to circulate using a main magnetic field and an accelerating high-frequency electric field, the magnetic field measuring device comprising: a main magnetic field magnet having a plurality of magnetic poles arranged opposite each other, that excites the main magnetic field in a space sandwiched between each magnetic pole; a displacement unit that displaces the ion beam circulating in the main magnetic field region in which the main magnetic field is excited to the outside of the main magnetic field region; and a magnetic channel that extracts the displaced ion beam from inside the main magnetic field magnet to the outside.

[0157] (Configuration 11) A particle beam therapy system including an accelerator whose magnetic field is measured by the magnetic field measurement device according to any one of configurations 1 to 10. [Explanation of symbols]

[0158] 1...Main field magnet 11…Intermediate plane 12…Vertical plane 6...Coil 7...Vacuum container 8…Top magnetic pole 9...Lower magnetic pole 15, 16, 18, 24...Through holes 18a,18b…Boundary surface 20...Acceleration space 30...Main magnetic field area 31...Pila area 32...Regenerator region 33...approximately flat area 40...High frequency kicker 51...Septum 51a, 51b, 51c...Septum 52...Antiseptum 52a, 52b, 52c...Antiseptum 126, 126a, 127, 127a...orbit 301...High energy beam extraction orbit 302...Low energy beam extraction orbit 304...Intersection area 305...Magnetic field distribution 306...Radial spacing 530...Beam passing area 1001...Particle beam therapy system 1002...Ion beam generator 1003...Ion source 1004…Accelerator 1005...Beam transport system 1006...Rotating gantry 1007…Irradiation device 1008...Treatment planning device 1009...Control system 1010...Waveguide 1017...Mobile device 1019...Magnetic channel 1019a...Magnetic channel entrance 1019b...Magnetic channel exit 1019c...Bend 1022...Coil lead wiring 1036…High frequency power supply 1037...Radio frequency acceleration cavity 1037a...Dee electrode 1039...Position detector 1041,1042,1043,1044...bending electromagnet 1045...Rotation axis 1046,1047,1049,1050...quadrupole electromagnet 1048...Ion beam path 1051, 1052...Scanning electromagnets 1053...Beam position monitor 1054...Dose monitor 1055...Treatment table 1057...Coil excitation power supply 1066...Central control unit 1067...CPU 1068...Memory 1069...Accelerator and transport system control device 1070...Scanning control device 1071...Rotation control device 1072...Database 1098...Ion beam current measuring device 2000…Magnetic field measuring device 2100…Support frame 2200...Position adjustment section 2300...Rod 2400...Sensor head 2420...Magnetic sensor 2430...Position sensor 2500...Control unit 2610, 2611...Reference position members

Claims

1. A magnetic field measuring device for measuring a magnetic field in a predetermined area, A magnetic sensor; a sensor head portion supporting the magnetic sensor; Equipped with The sensor head is made of a non-magnetic material and has a curved shape corresponding to the predetermined area, and the sensor head is inserted into the predetermined area to measure a magnetic field. Magnetic field measuring device.

2. The magnetic field measuring device according to claim 1, The sensor head further includes a position sensor that detects the position of the sensor head within the predetermined area. Magnetic field measuring device.

3. The magnetic field measuring device according to claim 2, The sensor head portion is provided in plurality, and one of the plurality of sensor head portions is formed in a linear shape. Magnetic field measuring device.

4. The magnetic field measuring device according to claim 2, The sensor head portion is provided in plurality, and one of the plurality of sensor head portions has a shape portion that is more bent than the curved shape. Magnetic field measuring device.

5. The magnetic field measuring device according to claim 2, a plurality of the sensor heads are present, and the plurality of sensor heads include a sensor head formed in a linear shape and a sensor head having a shape that is more bent than the curved shape; The plurality of sensor heads are used depending on the location in the predetermined area where the magnetic field is to be measured. Magnetic field measuring device.

6. The magnetic field measuring device according to any one of claims 2 to 5, The position sensor is a magnetic field measuring device formed from a non-magnetic material. 。

7. The magnetic field measuring device according to any one of claims 2 to 6, The position sensor is a magnetic field measuring device that detects the magnetic field measurement position of the magnetic sensor from multiple directions.

8. The magnetic field measuring device according to any one of claims 2 to 7, The position sensor detects a reference position member that indicates a reference position, and the reference position member is provided inside or outside the predetermined area, or both inside and outside the predetermined area.

9. The magnetic field measuring device according to any one of claims 2 to 8, a position adjustment unit that controls the position of the sensor head unit; The sensor head is attached to the tip of a rod, A magnetic field measuring device in which the sensor head unit is moved by the position adjustment unit continuously in a direction approximately parallel to the direction in which the rod is inserted and intermittently in a direction approximately perpendicular to the direction in which the rod is inserted.

10. The magnetic field measuring device according to any one of claims 1 to 9, The specified region is the inside of an accelerator, and the accelerator is an accelerator that accelerates an ion beam while causing it to circulate using a main magnetic field and an accelerating high-frequency electric field, and is a magnetic field measurement device comprising: a main magnetic field magnet having a plurality of magnetic poles arranged opposite each other and exciting the main magnetic field in a space sandwiched between each magnetic pole; a displacement unit that displaces the ion beam circulating in the main magnetic field region where the main magnetic field is excited to the outside of the main magnetic field region; and a magnetic channel that extracts the displaced ion beam from inside the main magnetic field magnet to the outside.

11. A particle beam therapy system comprising an accelerator whose magnetic field is measured by the magnetic field measurement device according to any one of claims 1 to 10.

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