JP2013165055A - Method of controlling septum electromagnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a septum electromagnet and a particle beam radiotherapy device that facilitate maintenance and can accurately control a track of a particle beam.SOLUTION: There is provided a method of controlling a septum electromagnet 1 provided with an auxiliary coil 5 such that current in mutually opposite circumferential directions flow at parts corresponding to a first part 3u and a second part 3d of a septum coil 3, the method including a step S10 of measuring a beam state including change in at least one of a beam width and a position of a particle beam passing downstream from a vacuum duct 2, a step S20 of calculating a kick angle or magnetic field intensity of an unnecessary magnetic field produced in the vacuum duct 2 on the basis of the beam state, and a step S30 of calculating a value of current made to flow to the auxiliary coil 5 so as to cancel the calculated kick angle or magnetic field intensity on the basis of a magnetic field measurement result or an electric field analysis result when the current is made to flow to the auxiliary coil 5.

Description

  The present invention relates to a method for controlling a septum electromagnet provided in a radiation source such as a circular particle accelerator or a storage ring device and used for supplying or taking out a particle beam.

  A septum electromagnet moves a particle beam in a duct onto a circular orbit by generating a magnetic field in a duct provided so as to share a tangent with the circular orbit of the particle beam. It is a device that takes in the duct. In a basic septum electromagnet, the C-shaped cross section has an open portion on the outer peripheral side, and the arc extending duct has an arc extending duct between the outer peripheral septum coil and the inner peripheral return coil. It arrange | positions in a space | gap part so that it may be pinched | interposed between them. The septum coil and the return coil are connected in series so that currents of the same magnitude flow in opposite directions in the circumferential direction. Thereby, the magnetic field perpendicular | vertical to the circumferential direction and radial direction which are the advancing direction of a particle beam can be generated in a duct, and a particle beam can be deflected to radial direction.

  On the other hand, the septum coil and the return coil are formed by connecting copper pipes into a coil shape because of the necessity of cooling, and have high rigidity unlike a general winding coil. The septum electromagnet is configured so that a strong force is applied to the coil during operation, so that the yoke can be separated into the upper part and the lower part in the axial direction, that is, the vertical direction in the installed state, for convenience of maintenance. At that time, it is necessary that the highly rigid septum coil and return coil can be divided into the upper part and the lower part together with the yoke. In this case, the upper septum coil and the upper return coil are fixed to the upper yoke, and the lower septum coil and the lower return coil are fixed to the lower yoke. Therefore, when the radial position is shifted between the upper coil and the lower coil, an unnecessary radial magnetic field (skew magnetic field) is generated.

  Thus, for example, it is conceivable to suppress the skew magnetic field by applying a technique (for example, see Patent Documents 1 to 4) in which an auxiliary coil is provided in the vicinity of a region where the distribution of the magnetic field is desired to be improved.

JP 63-224230 A (page 3, FIGS. 1 to 3) JP-A-1-209700 (2 pages, FIG. 1 and FIG. 2) JP-A-6-151096 (0011-0021, FIGS. 1-6) JP 2001-43998 A (0010 to 0021, FIGS. 1 to 3)

  However, the disclosed technique controls the arrangement of the auxiliary coil and the magnitude of the current in order to improve the magnetic field distribution on a predetermined line in the cross section perpendicular to the traveling direction of the particle beam, It was difficult to improve the magnetic field distribution in the cross section. For this reason, even when applied to a septum electromagnet having a particle beam widely distributed in the cross section, a region where the unnecessary magnetic field is not suppressed is generated, and the trajectory of the particle beam traveling in the region cannot be accurately controlled. Therefore, it has been difficult to use a septum electromagnet that can be easily maintained and can accurately control the trajectory of the particle beam, for example, a device that requires precise particle beam control such as a particle beam therapy device. .

  The present invention has been made to solve the above problems, and an object of the present invention is to provide a septum electromagnet and a particle beam therapy apparatus that can be easily maintained and can accurately control the trajectory of the particle beam.

  In the method for controlling a septum electromagnet according to the present invention, a septum coil and a return coil are disposed so as to sandwich a vacuum duct extending in an arc shape, and the septum coil and the return coil are arranged in a central portion in the axial direction together with a yoke and a first portion. The second portion is configured to be separable, and between the septum coil and the vacuum duct, the portions corresponding to the first portion and the second portion of the septum coil are opposite to each other in the circumferential direction. A method for controlling a septum electromagnet provided with an auxiliary coil through which a current flows, measuring a beam state including at least one of a beam width and a position variation of a particle beam passing downstream of the vacuum duct; A step for calculating a kick angle or magnetic field strength of an unnecessary magnetic field generated in the vacuum duct based on the beam state. And calculating a current value to be passed through the auxiliary coil for canceling the calculated kick angle or magnetic field strength based on a magnetic field measurement result or an electromagnetic field analysis result when a current is passed through the auxiliary coil. It is characterized by that.

  According to the method for controlling a septum electromagnet of the present invention, a septum electromagnet and a particle beam that can be easily maintained and can accurately control the trajectory of the particle beam by efficiently suppressing the skew magnetic field caused by the shift in the septum coil. A therapeutic device can be obtained.

It is a top view for explaining composition of a septum electromagnet concerning Embodiment 1 of the present invention, a sectional view, and a sectional view showing parts which can be separated at the time of maintenance. It is a wiring diagram of each coil and drive power supply for demonstrating the structure of the septum electromagnet concerning Embodiment 1 of this invention. It is a cross-sectional schematic diagram which shows the magnetic field component in the surface perpendicular | vertical to the track | orbit of the particle beam in a vacuum duct for demonstrating operation | movement of the septum electromagnet concerning Embodiment 1 of this invention. It is a cross-sectional schematic diagram which shows magnetic field distribution in the surface perpendicular | vertical to the track | orbit of the particle beam in a vacuum duct for demonstrating operation | movement of the septum electromagnet concerning Embodiment 1 of this invention. It is a cross-sectional schematic diagram of the circumferential direction which shows the track | orbit of the particle beam in a vacuum duct for demonstrating operation | movement of the septum electromagnet concerning Embodiment 1 of this invention. It is a figure which shows the structure of the particle beam therapy apparatus using the septum electromagnet concerning Embodiment 1 of this invention. It is a flowchart for demonstrating the 1st control method of the septum electromagnet concerning Embodiment 1 of this invention. It is a flowchart for demonstrating the 2nd control method of the septum electromagnet concerning Embodiment 1 of this invention. It is a flowchart for demonstrating the 3rd control method of the septum electromagnet concerning Embodiment 1 of this invention.

Embodiment 1 FIG.
Hereinafter, the configuration and operation of the septum electromagnet according to Embodiment 1 of the present invention and the particle beam therapy system using the same will be described. FIGS. 1-9 is for demonstrating the structure and operation | movement of a septum electromagnet concerning Embodiment 1 of this invention, and the structure of the particle beam therapy apparatus using a septum electromagnet, FIGS. ) Is a side view (a) showing the configuration of the septum electromagnet, a cross-sectional view (b) in which the description in the depth direction is omitted, and a main part of the septum electromagnet, of the cut surface along the line AA in the side view. Among these, it is sectional drawing of the part corresponding to (b) for showing the relationship of the coil isolate | separated at the time of a maintenance. FIG. 2 is a wiring diagram of a coil constituting the septum electromagnet and its driving power source, and FIG. 3 shows a magnetic field component in a plane perpendicular to the diameter and height direction in the vacuum duct, that is, perpendicular to the particle beam trajectory. 4A and 4B show a magnetic field distribution in a plane perpendicular to the particle beam trajectory in the vacuum duct when the upper and lower septum electromagnets are displaced. a) shows when the auxiliary coil is not operated, and (b) shows when it is operated. FIG. 5 is a schematic cross-sectional view in the circumferential direction showing the trajectory of the particle beam in the vacuum duct. 1 (b), (c), FIG. 3, and FIG. 4, a cylindrical coordinate system (r, h, c (orthogonal coordinate system is used in the circumferential direction) consisting of a radial position, an axial height, and a circumferential position. Corresponding to the moving coordinate system to be moved to (1)), and in FIG. 5, it is described in the orthogonal coordinate system (X, Y, Z (stationary coordinate system)).

  Moreover, FIG. 6 is a figure which shows the structure of the particle beam therapy apparatus using the septum electromagnet concerning Embodiment 1 of this invention. FIGS. 7 to 9 illustrate first to third control methods for adjusting the current value of the auxiliary coil as control methods for the septum electromagnet according to the first embodiment of the present invention. It is a flowchart of.

First, the configuration of the septum electromagnet according to the first embodiment will be described based on FIGS. 1 and 2.
The septum electromagnet 10 has an arc shape and is arranged so as to share a tangent to a circular accelerator 100 described later and a duct 11 forming a part of a circular orbit path of the storage ring. By providing the gap 1s extending in the direction (c), the yoke 1 having a C-shaped cross section (r, h plane) perpendicular to the extending direction as shown in FIG. The magnetic shield 6 addressed to the magnetic field 6, the septum coil 3 that is installed outside the radial direction (r) in the air gap 1 s and the current flows in the circumferential direction, and the septum coil 3 is installed inside the radial direction so as to face the septum coil 3. And a return coil 4 through which a current opposite to that of the septum coil 3 flows, and a vacuum duct 2 sandwiched between the septum coil 3 and the return coil 4 and extending in the circumferential direction. With a typical structure , Between the septum coil 3 and the vacuum duct 2, in which an auxiliary coil 5 for suppressing unnecessary magnetic field (skew field) in the vacuum duct 2.

  The height of the septum coil 3 and the return coil 4 is set so as to cover the rectangular opening of the yoke 1 in the axial direction (h: perpendicular to the radial direction r and the circumferential direction c), that is, in the vertical direction in the installed state. Yes. The auxiliary coil 5 is sized so as to be the same height as the septum coil 3, but the upper half and the lower half are configured such that currents in opposite directions flow in the circumferential direction (c). ing.

  In order to facilitate maintenance, the septum electromagnet 10 according to the first exemplary embodiment, as shown in FIG. 1 (c), the yoke 1 is separated from the yoke 1u and the lower yoke with the center in the axial direction (h) as a boundary. It can be separated into 1d. The septum coil 3 can be separated into an upper septum coil 3u that is positioned and fixed with respect to the upper yoke 1u and a lower septum coil 3d that is positioned and fixed with respect to the lower yoke 1d. Similarly, the return coil 4 can also be separated into an upper return coil 4u that is positioned and fixed with respect to the upper yoke 1u and a lower return coil 4d that is positioned and fixed with respect to the lower yoke 1d. On the other hand, the auxiliary coil 5 is also installed on the upper side, and consists of an upper auxiliary coil 5u that flows in one direction and a lower auxiliary coil 5d that is installed on the lower side and flows in a direction opposite to that of the upper auxiliary coil 5u. Both the 5u and the lower auxiliary coil 5d are positioned and fixed with respect to the vacuum duct 2.

  As shown in FIG. 2, the septum coil 3 and the return coil 4 are connected in series to the drive power supply 9M for the main coil, the auxiliary coil 5 is connected to the drive power supply 9S for the auxiliary coil, and the drive power supply 9M and the drive power supply. 9S is connected to the control part 60 which outputs the control signal for controlling drive, respectively. As a result, a current having the same adjusted current value can be supplied to the septum coil 3 and the return coil 4, and a current having a separately adjusted current value can be supplied to the auxiliary coil 5.

Next, the operation will be described with reference to FIGS.
When the drive power supply 9M is driven, a current in the opposite direction flows in the septum coil 3 and the return coil 4, which are the main coils of the septum electromagnet 10, in the circumferential direction. At this time, for example, if a current in the negative direction in the circumferential direction (c) (frontward in the drawing) flows through the septum coil 3 and a positive current in the circumferential direction (c) (backward in the drawing) flows through the return coil 4, In the cross-section (r, h) plane perpendicular to the circumferential direction of FIG. 3, as shown in FIG. A downward main magnetic field B is generated in the direction. Thereby, the particle beam moving in the positive direction of the c direction along the circumferential direction (c) in the vacuum duct 2 is deflected toward the septum coil 3 side (positive direction of the r direction), whereby the vacuum duct. It moves from the 2 side to the duct 11 side (for example, the orbit of the accelerator). Alternatively, the particle beam moving in the negative direction of the c direction in the duct 11 is deflected toward the return coil 4 side (the negative direction of the r direction), so that from the duct 11 (for example, the orbit of the accelerator). Move to vacuum duct 2.

  At this time, as described above, if the yoke 1 can be separated into the upper yoke 1u and the lower yoke 1d, the upper septum coil 3u and the lower septum coil 3d are not limited to the initial installation, but are always opened and closed for maintenance. An installation error (misalignment) in the horizontal direction (r, c direction) may occur. In this case, as shown in FIG. 3B, a magnetic field Bw having a skew magnetic field that is an unnecessary magnetic field component (r direction) other than the main magnetic field B (h direction) is generated on the midplane Pm. At this time, as shown in FIG. 4 (a), the closer to the coil, the higher the magnetic flux density. Therefore, as shown in FIG. 3 (b), the magnetic field Bw whose absolute value of the skew magnetic field component increases as it approaches the coil. It tends to increase.

  However, in the septum electromagnet 10 according to the first exemplary embodiment, unnecessary magnetic field components can be suppressed by adjusting the current flowing through the correction coil 5. As described above, the septum coil 3 and the return coil 4 that generate the main magnetic field B are installed so that coils of the same height face each other at regular intervals, and the current flowing through the septum coil 3 passes through the return coil 4. Return to power. On the other hand, the auxiliary coil 5 is configured so that the same current flows in the opposite direction up and down. However, since the auxiliary coil 5 is positioned and fixed to the vacuum duct 2, there is no positional deviation between the upper auxiliary coil 5u and the lower auxiliary coil 5d. Moreover, they are formed so as to be the same height as the septum coil 3 when they are vertically aligned. Therefore, the direction of the magnetic field generated by the auxiliary coil 5 is a direction orthogonal to the main magnetic field B. In addition, as described above, there is no deviation between the upper and lower coils 5u-5d, and the upper and lower coils 5u-5d are arranged so that they are aligned at the same height as the septum coil 3. Thus, the spatial dependence of the magnetic field generated by the auxiliary coil 5 can be approximated to the spatial dependence of the unnecessary magnetic field generated by. Therefore, regardless of the coordinates on the midplane pm, the magnetic field distribution can be formed evenly in the vertical direction as shown in FIG.

Here, the beam trajectory in the vacuum duct 2 of the septum electromagnet 10 will be described.
FIG. 5 shows a Z-direction 300 mm corresponding to a quarter in the circumferential direction (c) of a cross section (XZ plane: corresponding to the rc plane) perpendicular to the Z-axis (corresponding to h in cylindrical coordinates) of the vacuum duct 2. It shows the orbit of the particle beam of the minute. In the figure, the horizontal axis is the Z direction length in the orthogonal coordinate system (X, Y, Z), and corresponds to the circumferential length (c) in the cylindrical coordinate system used in FIGS. The X direction length corresponds to the radial length (r). As shown in the drawing, the particle beam passes between the duct aperture DPi on the inner side (return coil 4 side) and the duct aperture DPx on the outer side (septum coil 3 side) of the vacuum duct 2. The passage region is a region having a predetermined width that is biased toward the septum coil 3 side from the inner track Oi in the substantially middle portion of the duct aperture to the outer track Ox in the vicinity of the outer duct aperture DPx.

  That is, the influence of the unnecessary magnetic field Bw is larger in the region close to the septum coil 3 than in the region close to the return coil 4 in the region in the vacuum duct 2. On the other hand, due to the nature of the septum electromagnet 10, the dimension constraint on the septum coil 3 side is larger than that on the return coil 4 side. Therefore, it is easier to install the auxiliary coil 5 on the return coil 4 side where the thickness restriction is smaller than on the septum coil 3 side that needs to be thinly finished. Alternatively, it is conceivable to provide auxiliary coils on the upper and lower surfaces of the vacuum duct 2. However, as shown in FIG. 4, the state of the unnecessary magnetic field varies depending on the region, so that the particle beam passing with a width receives an unnecessary magnetic field that varies depending on the region. Therefore, even if the unnecessary magnetic field is simply suppressed for a narrow area with the midplane Pm, the effect of suppressing the influence of the unnecessary magnetic field is low, and it is necessary to suppress the unnecessary magnetic field in the entire particle beam passage area.

  Therefore, by providing the auxiliary coil 5 between the septum coil 3 and the vacuum duct 2 as in the present embodiment, the spatial dependence of the magnetic field created by the auxiliary coil 5 at least in the region affecting the orbit is reduced. By approaching the space dependence, the unnecessary magnetic field Bw that affects the trajectory control can be efficiently suppressed. In order to finish the auxiliary coil 5 thin, it is difficult to cool the auxiliary coil 5 by flowing water into the tube (hollow conductor) like the septum coil 3. In that case, for example, it may be in close contact with the vacuum duct 2 in an electrically insulated state to form a heat conduction path and be cooled.

  The unnecessary magnetic field becomes stronger as the deviation between the upper and lower coils increases. For example, the amount of deviation in the radial direction (r) of the upper and lower septum coils 3u, 3d (the return coil 4 is also displaced in the same manner, but because the deviation of the septum coil 3 is problematic as described above). 4 is 0.5 mm, the unnecessary magnetic field component is distributed from the septum coil 3 side to the central portion of the midplane Pm as shown in FIG. However, by passing a main coil current, that is, a current about 1/20 of the current flowing through the septum coil 3, to the auxiliary coil 5 having the above-described configuration, a spatially dependent magnetic field close to the spatial dependency of the unnecessary magnetic field is generated. It is possible to generate unnecessary magnetic fields. Similarly, if the deviation amount is 0.3 mm, a current that is approximately 1/65 of the current flowing through the septum coil 3 is caused to flow through the auxiliary coil 5 to generate a spatially dependent magnetic field that is close to the spatial dependence of the unnecessary magnetic field. Unnecessary magnetic field can be suppressed.

  In addition, if the positioning target of the auxiliary coil 5 is the upper and lower yokes 1u and 1d as in the case of the septum coil 3 and the return coil 4, the distance between the septum coil 3 and the auxiliary coil 5 is made equal in the vertical direction regardless of the installation situation. Can keep. However, it is more important to reduce the installation error between the upper and lower auxiliary coils 5u and 5d in order to bring the spatial dependence of the magnetic field generated by the auxiliary coil 5 closer to the spatial dependence of the unnecessary magnetic field. As shown in the above, it is desirable to set the vacuum duct 2 that does not separate the auxiliary coil 5 in the vertical direction as a positioning target.

Next, the configuration of the particle beam therapy system including the septum electromagnet 10 according to the first exemplary embodiment of the present invention will be described with reference to FIG.
In the figure, the particle beam therapy system includes a circular accelerator 100 (hereinafter simply referred to as an accelerator) that is a synchrotron as a particle beam supply source, a transport system 30 that transports a particle beam supplied from the accelerator 100, and a transport. The irradiation apparatus 40 which irradiates the patient K with the particle beam conveyed by the system | strain 30 and the treatment room 50 provided with the irradiation apparatus 40 are provided. The septum electromagnet 10 includes an incident device 10A for taking the particle beam emitted from the pre-accelerator 20 into the accelerator 100, and an emitting device 10B for emitting the particle beam accelerated in the accelerator 100 to the transport system 30. It is provided in the accelerator 100.

<Accelerator>
The accelerator 100 includes a vacuum duct 11 serving as an orbital path around which the particle beam circulates, an incident device 10A for allowing the particle beam supplied from the front stage accelerator 20 to enter the orbit, and the particle beam into the orbit in the vacuum duct 11. Bending electromagnets 13a, 13b, 13c, 13d (collectively referred to as 13) for deflecting the particle beam trajectory so as to circulate along, and a converging electromagnet for converging so that the particle beam formed on the circular trajectory does not diverge. 14 a, 14 b, 14 c, 14 d (collectively referred to as 14), a high-frequency acceleration cavity 15 that accelerates by applying a high-frequency voltage synchronized with a circulating particle beam, and a particle beam accelerated inside the accelerator 100 is taken out of the accelerator 100, An exit device 10B for exiting to the transport system 30, and a hexapole electrode that excites resonance in the orbit of the particle beam in order to emit the particle beam from the exit device 10B. It is equipped with a stone 17.

  2, the driving of the septum electromagnet 10 is described with reference to FIG. 2, the deflection electromagnet 13 includes a deflection electromagnet controller that controls the excitation current of the deflection electromagnet 13, and the high-frequency acceleration cavity 15 includes a high-frequency acceleration cavity 15. There are devices (not shown) for controlling each part, such as a high-frequency source for supplying a high-frequency voltage to the device and a high-frequency control device for controlling the high-frequency source, a deflection electromagnet control device, a high-frequency control device and a convergence device. The control unit 60 also includes an accelerator controller that controls other components such as the electromagnet 14 to control the entire accelerator 100.

  In addition, the front accelerator 20 is illustrated as a single device in the figure for the sake of simplicity, but in reality, an ion source (ion) that generates charged particles (ions) such as protons and carbon (heavy particles) ( Ion beam generator) and a linear accelerator system for initial acceleration of the generated charged particles. The charged particles incident on the accelerator 100 from the pre-stage accelerator 20 are accelerated by a high frequency electric field and accelerated to about 70 to 80% of the speed of light while being bent by a magnet.

<Transport system>
The particle beam accelerated by the accelerator 100 is emitted to a transport system 30 called a HEBT (High Energy Beam Transport) system. The transport system 30 includes a vacuum duct 31 that serves as a particle beam transport path, a switching electromagnet 32 that is a switching device that switches the beam trajectory of the particle beam, and a deflection electromagnet 33 that deflects the particle beam to a predetermined angle. Then, the particle beam that is sufficiently energized by the accelerator 100 and is emitted from the extraction device 10B and traveling through the vacuum duct 31 is transported by the switching electromagnet 32 as needed (for the treatment room 50A transport path 30A and 50B). The transport route 30B, ... 50N transport route 30N) is changed and guided to the irradiation device 40 provided for each designated treatment room 50.

<Irradiation device>
The irradiation device 40 is a device that shapes the particle beam supplied from the transport system 30 into an irradiation field corresponding to the size and depth of the affected area of the patient K to be irradiated and irradiates the affected area. There are a plurality of methods for forming the irradiation field. For example, in the scanning irradiation method in which the irradiation field is formed by scanning the particle beam, the accuracy of the irradiation field is greatly affected by the accuracy of the orbit when it is incident. Therefore, by using the septum electromagnet 10 according to the first embodiment, the influence of the unnecessary magnetic field is suppressed and the particle beam is supplied in the set orbit, so that the irradiation field can be formed as set, Effective treatment can be performed with minimal influence on surrounding tissues.

<Treatment room>
The treatment room 50 is a room for performing treatment by actually irradiating the patient K with a particle beam, and basically includes the irradiation device described above for each treatment room. In the figure, in the treatment room 50A, the entire irradiation apparatus 40A rotates from the deflection electromagnet 33 portion around the patient K (treatment table), and the rotation irradiation room (the irradiation angle of the particle beam to the patient K can be freely set) An example of a rotating gantry is also shown. Usually, for one accelerator 100, for example, a horizontal irradiation chamber for irradiating a particle beam in a horizontal direction from an irradiation device to a patient fixed on a treatment table whose angle and position can be freely set, and other types There are several different treatment rooms.

<Control system>
As a control system of a system having a plurality of subsystems (the accelerator 100, the transport system 30, the irradiation device 40 for each treatment room 50, etc.) as described above, the sub-controller that controls each subsystem exclusively and the entire system are commanded. In many cases, a hierarchical control system including a main controller for controlling the system is used. The control unit 60 of the particle beam therapy system according to the first embodiment of the present invention also employs the configurations of the main controller and the sub controller. Functions that can be controlled in the subsystem are sub-controllers, and operations that control a plurality of systems in cooperation are controlled by the main controller.

  On the other hand, in the particle beam therapy system, it is common to use a workstation or a computer for the control unit 60. Therefore, functions such as the main controller and the sub controller of the control unit 60 are expressed by software or the like, and do not always fit in specific hardware. Therefore, although they are collectively described as the control unit 60 in the drawing, this does not mean that the control unit 60 physically exists as a single piece of hardware.

In such a particle beam therapy system, how to control the current value flowing through the auxiliary coil 5 described above will be described with reference to the flowcharts shown in FIGS.
First, the deviation of the septum coil 3 is not uniform in the A cross section, the B cross section, and the C cross section shown in FIG. However, the distortion of the beam profile downstream of the septum electromagnet 10 is determined by an integration amount obtained by integrating unnecessary magnetic field components (skew magnetic fields) in each section in the circumferential direction. Therefore, the current flowing through the correction coil 5 can be calculated as a value corresponding to the integral value of the deviation amount as follows. These controls are executed via the control unit 60 described above.

First control example.
In the first control example, by monitoring the downstream beam profile (beam width, position fluctuation), the current value of the correction coil 5 (current value corresponding to the current value flowing through the septum coil 3; the same applies hereinafter). To decide. A first control example will be described with reference to FIG.
First, as the downstream beam state, the beam width or position variation downstream of the septum electromagnet 10 is measured (step S10), and the kick angle by the skew magnetic field or the skew magnetic field strength is calculated from the measured downstream beam state by beam calculation. (Step S20).

  Then, based on the electromagnetic field analysis result or the magnetic field measurement result when the current is actually passed through the correction coil 5, the current value (provisional value) passed through the correction coil 5 for canceling the calculated kick angle and skew magnetic field is calculated. Calculate (step S30). The current value of the correction coil 5 is adjusted to the calculated provisional value (step S40).

  The downstream beam state is measured with the current adjusted to the provisional value flowing through the correction coil 5 (step S50). Thereby, if the fluctuation amount with respect to the setting value of the downstream beam state is equal to or less than the reference value (“Y” in step S60), the provisional value is ended as the setting value. On the other hand, if the fluctuation amount with respect to the setting value of the downstream beam state exceeds the reference value (“N” in step S60), the process proceeds to step S20 and readjustment is performed.

Second control example.
In the second control example, the skew magnetic field component is measured using a magnetic field sensor, and the current value of the correction coil 5 is determined from the integral value in the circumferential direction. A second control example will be described with reference to FIG.
First, using a magnetic field sensor such as a Hall element, the skew magnetic field in the vacuum duct 2 is measured at several points in the circumferential direction (step S12), and an integral value is calculated from the measured skew magnetic field or a long pickup coil or the like. (Step S22).

  Then, based on the electromagnetic field analysis result or the magnetic field measurement result when the current is actually passed through the correction coil 5, a current value (provisional value) passed through the correction coil 5 for canceling the calculated skew magnetic field is calculated ( Step S30). The current value of the correction coil 5 is adjusted to the calculated provisional value (step S40).

  A skew magnetic field is measured in a state where a current adjusted to a provisional value is supplied to the correction coil 5 (step S52). As a result, if the skew magnetic field intensity is equal to or less than the reference value (“Y” in step S62), the provisional value is set as the set value, and the process ends. On the other hand, if the intensity of the skew magnetic field exceeds the reference value (“N” in step S62), the process proceeds to step S22 and readjustment is performed.

Third control example.
In the third control example, the deviation of the upper and lower coils is measured, the skew magnetic field is calculated from the deviation amount, and the current value of the correction coil 5 is determined from the integral value in the circumferential direction. A third control example will be described with reference to FIG.
First, the amount of deviation of the upper and lower coil positions is measured using a device that measures the position and dimensions of a laser displacement system or the like (step S13), and the skew magnetic field strength is calculated from the measured deviation by electromagnetic field analysis (step S23). ).

  Then, based on the electromagnetic field analysis result or the magnetic field measurement result when the current is actually passed through the correction coil 5, a current value (provisional value) passed through the correction coil 5 for canceling the calculated skew magnetic field is calculated ( Step S33). The current value of the correction coil 5 is adjusted to the calculated provisional value (step S40).

  A skew magnetic field is measured in a state where a current adjusted to a provisional value is supplied to the correction coil 5 (step S53). Thus, if the skew magnetic field strength is equal to or lower than the reference value (“Y” in step S63), the provisional value is set as the set value, and the process ends. On the other hand, if the intensity of the skew magnetic field exceeds the reference value (“N” in step S63), the process proceeds to step S33 and readjustment is performed. At this time, in step S33, the correction amount of the current value is recalculated based on the intensity of the adjusted skew magnetic field.

  In the third adjustment example, the example in which the skew magnetic field is measured in step S53 has been described. However, for example, as in steps S50 and S60 in the first adjustment example, the downstream beam state is provisionally measured. It may be determined whether or not the value is suitable.

  Such an adjustment is performed every time maintenance is performed, and an unnecessary magnetic field is generated by storing the current value flowing through the correction coil 5 in a table, for example, for each current value flowing through the septum coil 3. This makes it possible to extract the beam with an accurate trajectory.

  As described above, according to the septum electromagnet 10 according to the first embodiment, the septum electromagnet 10 has an arc shape, has the gap 1s that opens to the outer peripheral side and extends in the circumferential direction (c), and in the axial direction (h). A yoke 1 configured to be separable at a substantially central portion, a septum coil 3 installed on the outer side in the radial direction (r) in the gap 1 s and through which current flows in one direction in the circumferential direction, a septum coil 3 and a predetermined Installed between the septum coil 3 and the return coil 4, the return coil 4 that is installed inside the gap 1 s in the radial direction so as to be opposed to each other with a space therebetween, and a current in the direction opposite to that of the septum coil 3 flows. The septum coil 3 is formed so as to be separable into an upper part 3u as a first part and a lower part 3d as a second part corresponding to the division of the yoke 1. Between the septum coil 3 and the vacuum duct 2, there is provided an auxiliary coil 5 through which currents in opposite directions in the circumferential direction flow in the portions (5u, 5d) corresponding to the upper portion 3u and the lower portion 3d of the septum coil 3. Therefore, even if the upper and lower septum coils 3u and 3d are displaced during installation and maintenance, a magnetic field having a distribution similar to that of the skew magnetic field generated due to the displacement is corrected coil 5. The skew magnetic field can be efficiently suppressed by generating at. Therefore, it is possible to obtain a septum electromagnet and a particle beam therapy device that can be easily maintained and can accurately control the trajectory of the particle beam.

  In particular, since the auxiliary coil 5 is formed so that the dimension in the axial direction (h) is the same as that of the septum coil 3, the magnetic field to be generated can be made closer to the distribution of the skew magnetic field, and the skew magnetic field can be more efficiently performed. Can be suppressed.

  Further, since the auxiliary coil 5 is integrated with the vacuum duct 2 and positioned with respect to the vacuum duct 2, there is no positional deviation between the upper auxiliary coil 5u and the lower auxiliary coil 5d, and the generated magnetic field is further skewed. The skew magnetic field can be suppressed more efficiently.

  Further, the particle beam therapy system according to the first embodiment includes an accelerator 100 that uses at least the septum electromagnet 10 according to the first embodiment for the particle beam extraction device 10B, and the particle beam emitted from the emission device 10B. Since the transport system 30 for transporting and the irradiation device 40 for forming and irradiating the particle beam supplied via the transport system 30 in a predetermined irradiation field are provided, the particle beam whose emission position and orbit are accurate is irradiated. Since it can supply to the apparatus 40, it can irradiate with an exact irradiation field.

1: Yoke (1u: upper yoke, 1d: lower yoke, 1s: gap),
2: Vacuum duct,
3: Septum coil (3u: upper septum coil (first part), 3d: lower septum coil (second part)),
4: Return coil (4u: upper return coil, 4d: lower return coil),
5: auxiliary coil (5u: upper auxiliary coil (part corresponding to the first part), 5d: lower auxiliary coil (part corresponding to the second part)),
6: Magnetic shield,
9: Drive power supply (9M: for main coil, 9S: for auxiliary coil),
10: Septum electromagnet, 11: Duct (circular orbit path)
20: front accelerator, 30: transport system, 40: irradiation device, 50: treatment room, 60: control unit,
100 accelerator.

Claims (1)

A septum coil and a return coil are arranged so as to sandwich a vacuum duct extending in an arc shape, and the septum coil and the return coil can be divided into a first portion and a second portion together with a yoke at a central portion in the axial direction. In addition, an auxiliary coil is provided between the septum coil and the vacuum duct to allow currents in opposite directions to flow in the circumferential direction at portions corresponding to the first portion and the second portion of the septum coil. A method for controlling a septum electromagnet,
Measuring a beam state including at least one of a beam width and a position variation of a particle beam passing downstream of the vacuum duct;
Calculating a kick angle or magnetic field strength of an unnecessary magnetic field generated in the vacuum duct based on the beam state;
Calculating a current value to be passed through the auxiliary coil for canceling the calculated kick angle or magnetic field strength based on a magnetic field measurement result or electromagnetic field analysis result when a current is passed through the auxiliary coil;
A control method for a septum electromagnet, comprising:

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