Superconducting magnet, particle accelerator, and particle beam therapy device

Abstract

The present application provides a superconducting magnet capable of reducing the influence of coil magnetization magnetic field, a particle accelerator and a particle beam therapy device. In the case where the start current value (Is) is higher than the target current value (If), the control unit (20) performs control to decrease the current value from the start current value (Is) to the target current value (If). In this case, the current value reaches the target current value (If) in the form of decrease. Also, in the case where the start current value (Is) is lower than the target current value (If), the control unit (20) performs control to increase the current value from the start current value (Is) to the format current value (Io) higher than the target current value (If) and then decrease to the target current value (If). In this case, the current value reaches the target current value (If) in the form of decrease. Thus, regardless of the value of the specified current value before the current value is changed, the current value reaches the target current value (If) in the form of decrease. Therefore, the coil magnetization magnetic field at the time of reaching the target current value (If) can be in the same state.

Description

Technical Field

[0001] This application claims priority based on Japanese Patent Application No. 2021-057183, filed on March 30, 2021. The entire contents of that Japanese application are incorporated herein by reference.

[0002] This invention relates to a superconducting magnet, a particle accelerator, and a particle beam therapy device. Background Technology

[0003] The superconducting magnet comprises a coil and a vacuum container. The coil is a ring-shaped component formed by winding superconducting wire. The coil is configured to surround magnetic poles. The superconducting magnet generates a strong magnetic field by passing an electric current through the coil, which is in a superconducting state and cooled by a vacuum chamber, while maintaining a vacuum inside the vacuum container. As a device using such a superconducting magnet, a particle accelerator, for example, described in Patent Document 1, is known.

[0004] Patent Document 1: Japanese Patent Application Publication No. 2020-21901

[0005] Here, if current flows through the coil, a magnetic field is formed around the coil. At this time, the magnetic field formed by the current flow within the coil acts as an external magnetic field, causing the superconductor inside the coil to become magnetized (coil magnetization magnetic field). This coil magnetization magnetic field affects the magnetic field formed around the coil. This coil magnetization magnetic field can sometimes cause problems such as phase shift of the accelerating voltage frequency, for example, in particle accelerators as described above. Therefore, there is a need for a superconducting magnet that can reduce the effects of the coil magnetization magnetic field. Summary of the Invention

[0006] Therefore, the purpose of this invention is to provide a superconducting magnet, a particle accelerator, and a particle beam therapy device that can reduce the influence of the magnetizing magnetic field of a coil.

[0007] One aspect of the present invention relates to a superconducting magnet that generates a magnetic field by allowing current to flow through a coil. The superconducting magnet has a control unit that controls the current value of the coil. When a predetermined current value of the coil is higher than a target current value, the control unit controls the current value to decrease from the predetermined current value to the target current value. When the predetermined current value is lower than the target current value, the control unit controls the current value to increase from the predetermined current value to a predetermined current value higher than the target current value and then decrease to the target current value.

[0008] In superconducting magnets, when the coil current is changed from a predetermined current value to a target current value, differences arise in the coil's magnetizing magnetic field, whether the target current value is reached by decreasing the current or by increasing the current. In contrast, when the predetermined current value is higher than the target current value, the control unit controls the current value to decrease from the predetermined current value to the target current value. In this case, the target current value is reached by decreasing the current. Furthermore, when the predetermined current value is lower than the target current value, the control unit controls the current value to increase from the predetermined current value to a value higher than the target current value and then decrease to the target current value. In this case, the target current value is reached by decreasing the current. Thus, regardless of the predetermined current value before the change, the target current value is reached by decreasing the current. Therefore, the coil's magnetizing magnetic field remains consistent when the target current value is reached, regardless of the predetermined current value before the change. As shown above, the influence of the coil's magnetizing magnetic field can be reduced.

[0009] One aspect of the present invention relates to a superconducting magnet that generates a magnetic field by allowing current to flow through a coil. The superconducting magnet has a control unit that controls the current value of the coil. When a predetermined current value of the coil is lower than a target current value, the control unit controls the current value to increase from the predetermined current value to the target current value. When the predetermined current value is higher than the target current value, the control unit controls the current value to decrease from the predetermined current value to a predetermined current value lower than the target current value and then increase it to the target current value.

[0010] When the specified current value of the coil is lower than the target current value, the control unit controls the current value to increase from the specified current value to the target current value. In this case, the current value reaches the target current value by increasing. Furthermore, when the specified current value is higher than the target current value, the control unit controls the current value to decrease from the specified current value to a value lower than the target current value before increasing to the target current value. In this case, the current value reaches the target current value by increasing. Thus, regardless of the specified current value before the change, the current value will reach the target current value by increasing. Therefore, regardless of the specified current value before the change, the coil magnetization field can be kept in the same state when the target current value is reached. As shown above, the influence of the coil magnetization field can be reduced.

[0011] One aspect of the present invention relates to a superconducting magnet that generates a magnetic field by allowing current to flow through a coil. The magnet has a control unit that controls the current value of the coil. The control unit infers the magnetic field caused by the magnetization of the coil that occurs with the change in the current value, and directs a current value that deviates from the target current value by an amount of magnetic field caused by the magnetization of the coil to flow into the coil.

[0012] The control unit infers the magnetic field generated by the magnetization of the coil as the current value changes, and directs a current value that deviates from the target current value from the magnetic field generated by the coil's magnetization to the coil. In this case, when the current value changes from the specified current value to the target current value, the control unit can control the current value flowing to the coil by pre-feeding control of the coil's magnetization magnetic field. As a result, a magnetic field is formed around the coil in a way that reduces the coil's magnetization magnetic field. As shown above, the influence of the coil's magnetization magnetic field can be reduced.

[0013] The control unit can keep the coil current value constant for a specified period of time. In this case, sufficient time can be ensured for changes in the coil's magnetizing magnetic field.

[0014] During the initial current value scan control, the control unit controls the current value to rise to the maximum current value achievable in subsequent scan controls. Under the initial scan control, the value of the coil's magnetizing magnetic field can vary throughout the entire region of the magnetization curve involved in the initial magnetization process. Therefore, in subsequent scan controls, it is possible to suppress changes in the coil's magnetizing magnetic field value along the magnetization curve involved in the initial magnetization process.

[0015] One aspect of the present invention relates to a particle accelerator that includes the aforementioned superconducting magnet and accelerates particles to generate a particle beam.

[0016] One aspect of the present invention relates to a particle beam therapy apparatus comprising the aforementioned particle accelerator and using a particle beam generated by the particle accelerator for therapy.

[0017] Based on these particle accelerators and particle beam therapy devices, it is possible to achieve the same function and effect as the aforementioned superconducting magnets.

[0018] Invention Effects

[0019] According to the present invention, a superconducting magnet, a particle accelerator, and a particle beam therapy device are provided that can reduce the influence of the magnetic field of coil magnetization. Attached Figure Description

[0020] Figure 1 This is a schematic cross-sectional view showing a particle accelerator equipped with a superconducting magnet according to this embodiment.

[0021] Figure 2This is a schematic cross-sectional view of a particle beam therapy device equipped with a superconducting magnet according to this embodiment.

[0022] Figure 3 This is a schematic diagram used to illustrate the magnetic field used to magnetize a coil.

[0023] Figure 4 It is a graph showing the relationship between the magnetic field formed by the coil when energized and the magnetization magnetic field of the coil.

[0024] Figure 5 It is a diagram showing the relationship between the magnetizing magnetic field of a coil and the current.

[0025] Figure 6 It is a graph that shows how changes in current value correspond to changes in the magnetizing magnetic field of the coil.

[0026] Figure 7 It is a graph that shows how changes in current value correspond to changes in the magnetizing magnetic field of the coil.

[0027] Figure 8 It is a graph that shows how changes in current value correspond to changes in the magnetizing magnetic field of the coil.

[0028] Figure 9 It is a graph that shows how changes in current value correspond to changes in the magnetizing magnetic field of the coil.

[0029] Figure 10 It is a diagram used to illustrate the control content of the magnetization curve involved in the initial magnetization process.

[0030] Figure 11 It is a graph that shows how the current value flows to the coil from the target current value by the amount that deviates from the inferred magnetizing magnetic field of the coil.

[0031] In the diagram: 1-particle accelerator, 3-superconducting magnet, 20-control unit, 30, 30A, 30B-coils, 100-particle beam therapy device. Detailed Implementation

[0032] Hereinafter, various embodiments will be described in detail with reference to the accompanying drawings. Furthermore, in each drawing, the same or corresponding parts are labeled with the same symbols, and repeated descriptions are omitted.

[0033] Figure 1 This is a schematic cross-sectional view showing a particle accelerator equipped with a superconducting magnet according to this embodiment. Figure 1The particle accelerator 1 shown is, for example, a cyclotron, used in neutron capture therapy systems such as those employing boron neutron capture therapy (BNCT) for cancer treatment. It accelerates charged particles supplied from an ion source (not shown) to generate and eject a beam of charged particles. Examples of charged particles include protons, heavy particles (heavy ions), and electrons. Furthermore, particle accelerator 1 can also be used as a cyclotron for PET, a cyclotron for RI manufacturing, and a cyclotron for nuclear experiments. Moreover, particle accelerator 1 can be used in various applications such as... Figure 2 The particle beam therapy device 100 shown is used in this device. Figure 2 The particle beam therapy device 100 shown includes a particle accelerator 1, a delivery line 121, an irradiation unit 102, and a rotating support 105. The irradiation unit 102 emits a particle beam generated by the particle accelerator and delivered by the delivery line 121. The irradiation unit 102 irradiates the patient on the treatment table 104. The irradiation unit 102 is mounted on the rotating support 105, and its irradiation position in the rotational direction is adjusted by the rotating support 105. Furthermore, the particle accelerator 1 is not limited to a cyclotron accelerator and can also be a synchrotron accelerator.

[0034] Return to Figure 1 The particle accelerator 1 has a yoke 2, a superconducting magnet 3, a pair of magnetic poles 4A and 4B, and a vacuum container 5.

[0035] The yoke 2 supports the superconducting magnet 3, a pair of magnetic poles 4A and 4B, and a vacuum container 5. The yoke 2 is a hollow disk-shaped block containing the pair of magnetic poles 4A and 4B, which form the magnetic field required for accelerating charged particles. In a top view, the magnetic poles 4A and 4B are circular and positioned opposite each other across their central plane MP (the acceleration plane for charged particle acceleration). The superconducting magnet 3 is arranged around the magnetic poles 4A and 4B.

[0036] The superconducting magnet 3 includes a pair of coils 30A and 30B, a vacuum container 5, and a control unit 20. Each coil 30A and 30B is ring-shaped and formed by winding superconducting wire. The coils 30A and 30B are arranged around magnetic poles 4A and 4B, respectively. The material of the superconducting wire is not particularly limited and can be NbTi, Nb3Sn, MgB2, Bi-based superconductors (Bi2223, Bi2212, etc.), rare earth superconductors, iron-based superconductors, etc.

[0037] Vacuum container 5 is a container that holds coils 30A and 30B under vacuum. The vacuum container 5 and a refrigerator (not shown) constitute a cryostat that can cool coils 30A and 30B to a superconducting state. For example, a GM (Gifford-McMahon) refrigerator can be used as the refrigerator. However, the type of refrigerator is not limited to a GM refrigerator; for example, a Stirling refrigerator or other refrigerators can also be used.

[0038] In particle accelerator 1, a strong magnetic field is generated by passing an electric current through the coil of a superconducting magnet 3, which is set to a superconducting state by a cooler, while maintaining a vacuum state inside the vacuum container 5. Charged particles supplied from an ion source (not shown) are accelerated by the magnetic field at the midpoint MP of the space between magnetic poles 4A and 4B and are emitted as a charged particle beam.

[0039] The control unit 20 is a device that controls the current values ​​of coils 30A and 30B. Here, to explain the control function of the control unit 20, please refer to... Figure 3 The magnetizing magnetic field of coil 30 will be explained. Unless otherwise specified, coils 30A and 30B will be referred to as "coil 30". When current flows through coil 30, a magnetic field MF is formed around it. At this time, the superconductor inside coil 30 is magnetized (coil magnetizing magnetic field) by using the magnetic field MF as an external magnetic field. This coil magnetizing magnetic field affects the magnetic field formed around coil 30. Figure 3 In the middle, "B error "B" indicates the magnetizing magnetic field of the coil. ext "B is removed from the magnetic field formed by the energized coil 30." error The magnetic field. Here, as... Figure 3 (a) Figure 3 As shown in (b), when the current value is increased to excite the coil 30 and when the current value is decreased to demagnetize the coil 30, the value or behavior of the magnetizing magnetic field of the coil is different due to the influence of the mutual inductance M. Specifically, Figure 4 It is a graph showing the relationship between the magnetic field formed by the coil 30 when energized and the magnetization magnetic field of the coil. Figure 4 The horizontal axis represents the external magnetic field, and the vertical axis represents the magnetization of the superconductor. Additionally, when plotting the relationship between the current value and the magnetization magnetic field of the coil, with the current value as the horizontal axis, it also becomes... Figure 4 They are roughly the same shape. Therefore, Figure 4 The horizontal axis can be considered as the current value. Furthermore, the value of the vertical axis is sometimes simply referred to as the "value of the coil's magnetizing magnetic field." For example... Figure 4As shown, if the current value of coil 30 is increased in the positive region, the value of the coil's magnetizing magnetic field changes on the negative side of the magnetization curve E1. If the current value of coil 30 is decreased in the positive region, the value of the coil's magnetizing magnetic field changes on the positive side of the magnetization curve E2. Thus, the coil's magnetizing magnetic field, caused by the influence of the coil's magnetizing magnetic field, depends on the current scanning mode.

[0040] Figure 5 schematic representation Figure 4 The graph represents the region on the positive side of the horizontal axis. However, the horizontal axis is replaced with the current value relative to coil 30. For example, when the current value of coil 30 is directly changed from the starting current value to the target current value (Ib), the value of the coil's magnetizing magnetic field differs depending on the relationship between the starting current value and the target current value. That is, when the starting current value is "Ia," which is less than "Ib," the value of the coil's magnetizing magnetic field changes on the negative magnetization curve E1. At this time, the value of the coil's magnetizing magnetic field changes from the value at the starting point S1 on the magnetization curve E1 to become the value at the target point F1. When the starting current value is "Ic," which is greater than "Ib," the value of the coil's magnetizing magnetic field changes on the positive magnetization curve E2. At this time, the value of the coil's magnetizing magnetic field changes from the value at the starting point S2 on the magnetization curve E2 to become the value at the target point F2. Thus, although the final target current value is the same as "Ib," the value of the coil's magnetizing magnetic field at target point F1 and the value of the coil's magnetizing magnetic field at target point F2 are different values.

[0041] Therefore, in controlling the change of the current value from a predetermined current value (hereinafter referred to as the starting current value) to a target current value, the control unit 20 performs control regardless of the magnitude of the starting current value, so that the value of the coil magnetizing magnetic field is the same at the target current value. Just before reaching the target current value, the control unit 20 reduces the current value (demagnetizes) to achieve the target current value. In this case, just before reaching the target current value, the control unit 20 controls the current value so that the value of the coil magnetizing magnetic field changes on the positive magnetization curve E2.

[0042] refer to Figure 6 and Figure 7 The control functions of the control unit 20 will be explained. Figure 6 (a) Figure 6 (b) The left-hand curve is a graph showing the relationship between the change in time and the change in current value. Figure 6 (a) Figure 6 The curve on the right side of (b) is a graph showing the relationship between the current value and the value of the magnetizing magnetic field of the coil. Figure 7The same applies thereafter. In the following description, we will use "starting current value Is" and "target current value If". Furthermore, the current value immediately preceding the starting current value Is will be designated as "immediately preceding current value Ip". Immediately preceding the target current value If, ​​the current value used to change the value of the coil's magnetizing magnetic field on the positive magnetization curve E2 will be designated as "format current value Io". Additionally, in the graph representing the current value and the coil's magnetizing magnetic field value, the point corresponding to the starting current value Is will be designated as the starting point S, the point corresponding to the format current value Io will be designated as the format point O, and the point corresponding to the target current value If will be designated as the target point F.

[0043] Figure 6 and Figure 7 This indicates the control content of the control unit 20 when the format current value Io is higher than the target current value If. In this case, regardless of how the value of the coil magnetizing field changes before reaching the format point O, the value of the coil magnetizing field will change on the positive side magnetization curve E2 when reaching the target point F from the format point O.

[0044] Figure 6 This indicates the control content when the starting current value Is is higher than the target current value If and the formatted current value Io. For example... Figure 6 As shown, when the starting current value Is is higher than the target current value If, ​​the control unit 20 controls the current value to decrease from the starting current value Is to the target current value If.

[0045] Figure 6 (a) illustrates the control action when the preceding current value Ip is greater than the starting current value Is. In this case, the control unit 20 decreases the current value to change from the preceding current value Ip to the starting current value Is (left curve), thus the starting point S exists on the positive magnetization curve E2 (right curve). The control unit 20 decreases the current value from the starting current value Is towards the standard current value Io. As a result, the value of the coil's magnetizing field changes from the starting point S towards the standard point O on the positive magnetization curve E2. Furthermore, the control unit 20 decreases the current value from the standard current value Io towards the target current value If. As a result, the value of the coil's magnetizing field changes from the standard point O towards the target point F on the positive magnetization curve E2.

[0046] Figure 6(b) illustrates the control measures when the preceding current value Ip is less than the starting current value Is. In this case, the control unit 20 increases the current value to change from the preceding current value Ip to the starting current value Is (left curve), thus the starting point S exists on the negative magnetization curve E1 (right curve). The control unit 20 increases the current value from the starting current value Is to the target current value Io. At this time, the value of the coil's magnetizing field jumps from the starting point S of the negative magnetization curve E1 to the positive magnetization curve E2, and changes towards the target point O on the positive magnetization curve E2. Furthermore, the control unit 20 decreases the current value from the target current value Io towards the target current value If. Therefore, the value of the coil's magnetizing field changes from the target point O to the target point F on the positive magnetization curve E2.

[0047] Figure 7 This indicates that the starting current value Is is below the target current value If and the format current value Io. For example... Figure 7 As shown, when the starting current value Is is lower than the target current value If, ​​the control unit 20 controls the current value to rise from the starting current value Is to a current value Io that is higher than the target current value If, ​​and then decreases to the target current value If.

[0048] Figure 7 (a) illustrates the control action when the preceding current value Ip is greater than the starting current value Is. In this case, the control unit 20 decreases the current value to change from the preceding current value Ip to the starting current value Is (left curve), thus the starting point S exists on the positive magnetization curve E2 (right curve). The control unit 20 increases the current value from the starting current value Is to the target current value Io. As a result, the value of the coil's magnetizing field jumps from the positive magnetization curve E2 to the negative magnetization curve E1, and changes on the negative magnetization curve E1, changing to the current value corresponding to the target point O. The control unit 20 decreases the current value from the target current value Io to the target current value If. As a result, the value of the coil's magnetizing field jumps from the negative magnetization curve E1 to the positive magnetization curve E2, and changes on the positive magnetization curve E2 from the target point O to the target point F.

[0049] Figure 7(b) illustrates the control parameters when the preceding current value Ip is below the starting current value Is. In this case, the control unit 20 increases the current value to change from the preceding current value Ip to the starting current value Is (left curve), thus the starting point S exists on the negative magnetization curve E1 (right curve). The control unit 20 increases the current value from the starting current value Is to the target current value Io. As a result, the value of the coil's magnetizing field changes from the starting point S on the negative magnetization curve E1 to the position of the current value corresponding to the target point O. The control unit 20 decreases the current value from the target current value Io to the target current value If. As a result, the value of the coil's magnetizing field jumps from the negative magnetization curve E1 to the positive magnetization curve E2, and changes from the target point F on the positive magnetization curve E2.

[0050] The control content based on the control unit 20 is not limited to Figure 6 and Figure 7 The content shown can also be used Figure 8 and Figure 9 The control content shown. Figure 8 and Figure 9 This describes the control settings of the control unit 20 when the format current value Io is lower than the target current value If. In this case, regardless of how the value of the coil's magnetizing field changes before reaching the format point O, it will change on the negative magnetization curve E1 when reaching the target point F from the format point O. That is, just before reaching the target current value, the control unit 20 controls the current value to cause the value of the coil's magnetizing field to change on the negative magnetization curve E1.

[0051] Figure 8 This indicates the control content when the starting current value Is is equal to or greater than the target current value If and the formatted current value Io. For example... Figure 8 As shown, the control unit 20 controls the current value to decrease from the starting current value Is to a current value Io that is lower than the target current value If, ​​and then increases to the target current value If.

[0052] Figure 8 (a) illustrates the control action when the preceding current value Ip is greater than the starting current value Is. In this case, the control unit 20 decreases the current value to change from the preceding current value Ip to the starting current value Is (left curve), thus the starting point S exists on the positive magnetization curve E2 (right curve). The control unit 20 decreases the current value from the starting current value Is to the specified current value Io. As a result, the value of the coil's magnetizing field changes on the positive magnetization curve E2 from the starting point S to the position of the current value corresponding to the specified point O. Furthermore, the control unit 20 decreases the current value from the specified current value Io to the target current value If. As a result, the value of the coil's magnetizing field jumps from the positive magnetization curve E2 to the negative magnetization curve E1, and changes on the negative magnetization curve E1 from the specified point O to the target point F.

[0053] Figure 8 (b) illustrates the control measures when the preceding current value Ip is less than the starting current value Is. In this case, the control unit 20 increases the current value to change from the preceding current value Ip to the starting current value Is (left curve), thus the starting point S exists on the negative magnetization curve E1 (right curve). The control unit 20 increases the current value from the starting current value Is to the target current value Io. At this time, the value of the coil's magnetizing field jumps from the starting point S of the negative magnetization curve E1 to the positive magnetization curve E2, and changes on the positive magnetization curve E2 towards the current value corresponding to the target point O. Furthermore, the control unit 20 decreases the current value from the target current value Io towards the target current value If. Consequently, the value of the coil's magnetizing field jumps from the positive magnetization curve E2 to the negative magnetization curve E1, and changes on the negative magnetization curve E1 from the target point F.

[0054] Figure 9 This indicates the control content when the starting current value Is is lower than the target current value If and the formatted current value Io. For example... Figure 9 As shown, the control unit 20 controls the current value to increase from the starting current value Is to the target current value If.

[0055] Figure 9 (a) illustrates the control action when the preceding current value Ip is greater than the starting current value Is. In this case, the control unit 20 decreases the current value to change from the preceding current value Ip to the starting current value Is (left curve), thus the starting point S exists on the positive magnetization curve E2 (right curve). The control unit 20 increases the current value from the starting current value Is to the target current value Io. As a result, the value of the coil's magnetizing field jumps from the positive magnetization curve E2 to the negative magnetization curve E1, and changes on the negative magnetization curve E1, changing to the target point O. The control unit 20 increases the current value from the target current value Io to the target current value If. As a result, the value of the coil's magnetizing field changes from the target point O to the target point F on the negative magnetization curve E1.

[0056] Figure 9 (b) illustrates the control measures when the preceding current value Ip is less than the starting current value Is. In this case, the control unit 20 increases the current value to change from the preceding current value Ip to the starting current value Is (left curve), thus the starting point S exists on the negative magnetization curve E1 (right curve). The control unit 20 increases the current value from the starting current value Is to the target current value Io. As a result, the value of the coil's magnetizing field changes from the starting point S on the negative magnetization curve F1 to the target point O. The control unit 20 increases the current value from the target current value Io to the target current value If. As a result, the value of the coil's magnetizing field changes from the target point O to the target point F on the negative magnetization curve F1.

[0057] Here, as Figure 10 As shown in (a), the current scanning mode is on the negative side of the coil's magnetizing magnetic field, and has a magnetization curve E3, which is involved in the initial magnetization process, separate from the magnetization curve F1. The magnetization curve E3, involved in the initial magnetization process, is a magnetization curve in which the value of the coil's magnetizing magnetic field changes as the initial rising current value flows through the coil 30. For example, when the current rises from the format current value Io to the target current value If, ​​the value of the coil's magnetizing magnetic field changes on the magnetization curve F1, changing from the format point O to the target point F. However, when the value of the coil's magnetizing magnetic field changes on the magnetization curve E3, the change occurs from a different format point O' to a different target point F'.

[0058] Here, if the value of the magnetizing magnetic field of the coil passes through the magnetization curve E3 involved in the initial magnetization process at least once under a certain current value, then it will change on the magnetization curve F1 in subsequent magnetization processes. Therefore, if... Figure 10 As shown in (c), during the initial current value scan control, the control unit 20 controls the current value to rise to the maximum current value Imax that can be obtained in subsequent scan controls. Thus, as... Figure 10 As shown in (b), the value of the coil's magnetizing magnetic field can vary throughout the entire region of the magnetization curve E3 involved in the initial magnetization process during the initial scan control. Therefore, after this processing ( Figure 10 (c) After time t1), if... Figures 6-9 The process shown allows for control over how the value of the magnetizing magnetic field changes on the magnetization curves F1 and E2.

[0059] Next, the magnitude of the difference between the target current value If and the format current value Io will be explained. This difference ΔI is set according to the following equation (1). μ0 represents the permeability of vacuum, J c The critical current value of a superconductor, r f This represents the filament radius. l0 is any current value, B m This represents the intensity of the strongest magnetic flux density within the coil relative to the current value. Additionally, due to the critical current value J... c Defined by temperature and empirical magnetic field, therefore J c It has an amplitude relative to the applied temperature and empirical magnetic field. For example, as the value of α, the value obtained from equation (2) can be used.

[0060] [Mathematical Expression 1]

[0061] ΔI=αμ0J c rf…(1)

[0062] α=2I0 / B m …(2)

[0063] The control unit 20 keeps the current value of the coil 30 constant at the format current value Io for a predetermined time. This predetermined time is not particularly limited; for example, when the control unit 20 changes the current value from the starting current value Is to the format current value Io, it is sufficient to ensure that the value of the coil's magnetizing magnetic field changes from the starting point to the format point O. For example, the predetermined time can be set to approximately 30 to 600 seconds.

[0064] exist Figures 6-9 In the control described, the control unit 20 controls the current value just before the target current value is reached, so that the value of the coil's magnetizing magnetic field changes on the negative magnetization curve F1 and on the positive magnetization curve E2. Alternatively, as... Figure 11 As shown, in the control of changing the current value of the coil from the starting current value to the target current value, the control unit 20 can infer the magnetizing magnetic field of the coil (the magnetic field caused by the magnetization of the coil 30 that accompanies the change in the current value) and cause the current value that deviates from the target current value from the magnetizing magnetic field of the coil to flow to the coil 30.

[0065] Specifically, the control unit 20 directs a current value that deviates from the predicted value ΔI' relative to the target current value I to the coil 30. For example, as Figure 11 As shown in (a), the control unit 20 directs the current value of "I+ΔI`" to the coil 30. Alternatively, as... Figure 11 As shown in (b), the control unit 20 directs the current value of "I-ΔI`" to the coil 30. ΔI` is set by equation (3). The parameters are the same as those in equation (1) above. α needs to satisfy equation (4). For the magnetic field generated at any point around the coil 30 by the magnetic moment per unit volume of the superconductor, α can be obtained by calculating the sum of the magnetic fields per unit volume.

[0066] [Mathematical Expression 2]

[0067] ΔI′=αμ0J c r f …(3)

[0068]

[0069] Next, the function and effects of the superconducting magnet 3 involved in this embodiment will be explained.

[0070] As described above, in the superconducting magnet 3, the coil 30 uses the magnetic field MF as the external magnetic field, and the superconductor inside the coil 30 is magnetized (coil magnetization magnetic field). Thus, a coil magnetization magnetic field is generated in the coil 30. When a high absolute value of the magnetic field in the coil 30 is required, this coil magnetization magnetic field cannot be ignored. Figure 1As shown, the effects of the coil magnetization field, as described above, can sometimes become problematic in particle accelerator 1. Because of the correlation between the phase shift of the coil magnetization field and the accelerating voltage frequency, the coil magnetization field affects particle acceleration. Therefore, the coil magnetization field, depending on the current scanning mode, may lead to a decrease in the acceleration efficiency of particle accelerator 1. Due to the precision requirements of particle accelerator 1, superconducting magnets capable of reducing the effects of the coil magnetization field are needed.

[0071] Here, in the superconducting magnet 3, when the current value of the coil 30 is changed from the starting current value Is to the target current value If, ​​the target current value If is reached in a decreasing manner and the target current value If is reached in an increasing manner, although the current value is the same, differences will occur in the coil magnetization magnetic field caused by the coil magnetization magnetic field (see reference). Figure 5 In contrast, such as Figure 6 and Figure 7 As shown, when the starting current value Is is higher than the target current value If, ​​the control unit 20 controls the current value to decrease from the starting current value Is to the target current value If. In this case, the current value reaches the target current value If in a decreasing manner. Furthermore, when the starting current value Is is lower than the target current value If, ​​the control unit 20 controls the current value to rise from the starting current value Is to a current value Io higher than the target current value If and then decrease to the target current value If. In this case, the current value reaches the target current value If in a decreasing manner. Thus, regardless of the predetermined current value before the change, the current value will reach the target current value If in a decreasing manner. Therefore, the coil magnetization field can be kept in the same state when the target current value If is reached, regardless of the starting current value Is before the change. As shown above, the influence of the coil magnetization field can be reduced.

[0072] And, as Figure 8 and Figure 9As shown, when the starting current value Is is lower than the target current value If, ​​the control unit 20 controls the current value to rise from the starting current value Is to the target current value If. In this case, the current value reaches the target current value If in an increasing manner. Furthermore, when the specified current value is higher than the target current value If, ​​the control unit 20 controls the current value to decrease from the starting current value Is to a current value Io lower than the target current value If, ​​and then rise to the target current value If. In this case, the current value reaches the target current value If in an increasing manner. Thus, regardless of the starting current value before the current value is changed, the current value will reach the target current value If in an increasing manner. Therefore, regardless of the starting current value Is before the current value is changed, the coil magnetization field can be kept in the same state when the target current value If is reached. As shown above, the influence of the coil magnetization field can be reduced.

[0073] And, as Figure 11 As shown, the control unit 20 infers the magnetic field generated by the magnetization of the coil 30 along with the change in the current value, and causes the current value that deviates from the target current value from the amount of the coil magnetization magnetic field to flow to the coil 30.

[0074] In this case, when the starting current value changes to the target current value, the control unit 20 can control the current flowing to the coil 30 in the form of a pre-feedforward control coil magnetization magnetic field. This creates a magnetic field around the coil 30 that reduces the coil magnetization magnetic field. As shown above, the influence of the coil magnetization magnetic field can be reduced.

[0075] The control unit 20 can keep the current value of the coil 30 constant at a predetermined current value Io for a specified time. In this case, sufficient time can be ensured for changes in the magnetizing magnetic field of the coil.

[0076] In the initial current value scan control, the control unit 20 controls the current value to rise to the maximum current value Imax that can be obtained in subsequent scan controls. Under the initial scan control, the value of the coil's magnetizing magnetic field can change throughout the entire region of the magnetization curve E3 involved in the initial magnetization process. Therefore, in subsequent scan controls, it is possible to suppress changes in the value of the coil's magnetizing magnetic field along the magnetization curve E3 involved in the initial magnetization process.

[0077] The particle accelerator 1 according to this embodiment includes the superconducting magnet 3 described above and accelerates particles to generate a particle beam.

[0078] The particle beam therapy apparatus 100 according to this embodiment includes the particle accelerator 1 described above, and performs therapy using a particle beam generated in the particle accelerator 1.

[0079] According to the particle accelerator 1, by using the superconducting magnet 3 to accelerate charged particles, the influence of the coil magnetization magnetic field caused by the coil magnetization magnetic field can be reduced, thus achieving a particle accelerator with high acceleration efficiency. Furthermore, according to the particle beam therapy device 100, by using the particle accelerator 1 with high acceleration efficiency, the irradiated body can be stably irradiated with a high beam current.

[0080] The present invention is not limited to the embodiments described above.

[0081] For example, superconducting magnets have been used in particle accelerators, but they can also be used in single-crystal silicon pulling devices, etc.

Claims

1. A superconducting magnet that generates a magnetic field by causing a current to flow through a coil, wherein the superconducting magnet has a control section that controls a current value of the coil, the control section performs control that causes the current value to decrease from a prescribed current value to a target current value in a case where the prescribed current value of the coil is higher than the target current value, the control section performs control that causes the current value to increase from the prescribed current value to a format current value that is higher than the target current value and then decrease to the target current value in a case where the prescribed current value is lower than the target current value.

2. A superconducting magnet that generates a magnetic field by causing a current to flow through a coil, wherein the superconducting magnet has a control section that controls a current value of the coil, the control section performs control that causes the current value to increase from a prescribed current value to a target current value in a case where the prescribed current value of the coil is lower than the target current value, the control section performs control that causes the current value to decrease from the prescribed current value to a format current value that is lower than the target current value and then increase to the target current value in a case where the prescribed current value is higher than the target current value.

3. The superconducting magnet according to claim 1 or 2, wherein the control section causes the current value of the coil to be constant for a prescribed time at the format current value.

4. A superconducting magnet that generates a magnetic field by causing a current to flow through a coil, wherein the superconducting magnet has a control section that controls a current value of the coil, the control section estimates a magnetic field caused by magnetization of the coil accompanying a change in the current value, and causes a current value that deviates from a target current value by an amount based on an estimated value of the magnetic field caused by magnetization of the coil to flow to the coil.

5. The superconducting magnet according to any one of claims 1, 2, or 4, wherein the control section performs control that causes the current value to increase to a maximum current value that can be obtained in a second or later scan control in a first current value scan control.

6. A particle accelerator that includes: a magnetic pole; a coil disposed around the magnetic pole; a vacuum container that accommodates the coil; and a control section that controls a current value of the coil, the control section performs control that causes the current value to decrease from a prescribed current value to a target current value in a case where the prescribed current value of the coil is higher than the target current value, the control section performs control that causes the current value to increase from the prescribed current value to a format current value that is higher than the target current value and then decrease to the target current value in a case where the prescribed current value is lower than the target current value, thereby accelerating charged particles to generate a particle beam.

7. A particle beam therapy device that includes a particle accelerator and performs therapy using a particle beam generated by the particle accelerator, the particle accelerator includes: a magnetic pole; a coil disposed around the magnetic pole; a vacuum container that accommodates the coil; and a control section that controls a current value of the coil, the control section performs control that causes the current value to decrease from a prescribed current value to a target current value in a case where the prescribed current value of the coil is higher than the target current value, ​ ​ ​ ​ ​ The particle accelerator performs control to increase the current value from the prescribed current value to a format current value higher than the target current value and then decrease the current value to the target current value, thereby accelerating the charged particles to generate the particle beam, in a case where the prescribed current value is lower than the target current value.

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