JP2022176617A - Septum magnet, accelerator, and particle beam therapy system - Google Patents

Abstract

To downsize a septum magnet.SOLUTION: A septum magnet 30 comprises: a septum coil 32 extending along a beam extraction track; and an additional septum coil 36 that is provided in parallel with the septum coil 32 and extends along the beam extraction track. The additional septum coil 36 comprises a plurality of additional septum conductors 38 extending along the beam extraction track. The plurality of additional septum conductors 38 are arranged so as to draw an arc protruding on the side of a circulating track. The plurality of additional septum conductors 38 includes an additional septum conductor 38 that is close to the circulating track and is disposed closer to the circulating track than the septum coil 32 so as to avoid an ion beam track plane 48.SELECTED DRAWING: Figure 2

Description

The present invention relates to septum electromagnets, accelerators and particle beam therapy systems, and more particularly to electromagnets for extracting ion beams from accelerators.

Particle beam therapy is widely used to irradiate an affected area with particle beams. In general, particle beam therapy uses a particle beam therapy system equipped with an accelerator. Ions such as carbon ions, helium ions, and protons are injected into the accelerator and accelerated until they have the energy required for treatment. A beam (ion beam) of ions accelerated by an accelerator is irradiated toward the affected area. A particle beam therapy system adjusts the ion beam energy and spatial spread according to the position and shape of the affected area.

The accelerator uses a septum electromagnet for extracting the ion beam. A septum electromagnet has a septum coil and a return coil. The septum coil and the return coil extend along a beam extracting trajectory along which an ion beam is extracted from inside the accelerator to outside the accelerator, and sandwich the beam extracting trajectory.

An ion beam circulating in the accelerator is guided to a beam extraction trajectory at the beam extraction stage. The septum coil and return coil generate a septum magnetic field that is a magnetic field in the opposite direction to the circulating magnetic field. The ion beam is deflected to the outside of the accelerator by the septum magnetic field and extracted from the accelerator. The extracted ion beam is transported to a predetermined position and used for experiments, RI production (Radio Isotope), particle beam therapy, and the like.

A septum electromagnet is described in Patent Document 1 and Non-Patent Document 1 below. Further, Patent Documents 2 and 3 describe a coil for deflecting an ion beam as a technique related to the present invention. Patent Document 4 describes an accelerator as a technique related to the present invention.

WO2013/121503 WO2015/045017 JP 2013-206635 A Japanese Patent Application Laid-Open No. 2020-202015

Kei Sugita, Ekbert Fischer, "Cosine-theta-type septum magnet and its application to superconductivity", Proceedings of the 13th Annual Meeting of Particle Accelerator Sciety of Japan August 8-10,2016,Chiba,Japan.

In recent years, there is an increasing need to install a particle beam therapy system in a relatively small building, and it is desired to simplify and miniaturize the devices used in the particle beam therapy system.

As a design for miniaturizing the septum electromagnet, it is conceivable to increase the current flowing through the septum coil and shorten the septum electromagnet. However, in order to suppress heat generation and the like in order to increase the current flowing through the septum coil, it may be necessary to widen the cross-section of the conductive wire that constitutes the septum coil. On the other hand, when the cross-section of the conductive wire forming the septum coil is widened, the septum coil may hinder the progress of the ion beam.

An object of the present invention is to miniaturize a septum electromagnet.

The present invention comprises a septum coil extending along a beam extraction trajectory, and an additional septum coil arranged in parallel with the septum coil and extending along the beam extraction trajectory, wherein the additional septum coil extends along the beam extraction trajectory. a plurality of additional septum conductors extending along the track, the plurality of additional septum conductors being arranged to form an arc that bulges toward the loop track.

According to the present invention, the septum electromagnet is miniaturized.

It is a figure which shows the accelerator which concerns on 1st Embodiment. It is a figure which shows the septum electromagnet which concerns on 1st Embodiment. FIG. 11 shows an additional septum coil and an additional return coil; It is a figure which shows the cross-section of each coil conductor. FIG. 10 is a diagram showing a septum electromagnet according to a second embodiment; FIG. 11 shows an additional septum coil and an additional return coil; FIG. 4 is a diagram showing a septum electromagnet in which the septum electromagnet according to the first embodiment and the septum electromagnet according to the second embodiment are cascaded; FIG. 10 is a diagram showing a septum electromagnet according to a third embodiment; FIG. 11 is a diagram showing a septum electromagnet according to a fourth embodiment; FIG. 11 is a diagram showing a septum electromagnet according to a fifth embodiment; FIG. 4 is a diagram showing calculation results of magnetic field distribution inside a septum electromagnet; FIG. 11 is a diagram showing a septum electromagnet according to a sixth embodiment; It is a figure which shows the accelerator which concerns on 7th Embodiment. It is a figure which shows the particle beam therapy system which concerns on 8th Embodiment.

Each embodiment of the present invention will be described with reference to each figure. The same reference numerals are attached to the same components shown in multiple drawings to simplify the description. The terms "top," "bottom," "left," "right," etc. herein refer to directions in the drawing. These directional terms are for convenience of explanation, and do not limit the posture when arranging each component.

FIG. 1 schematically shows the configuration of an accelerator 100 according to the first embodiment of the invention. Accelerator 100 is called a synchrotron. Accelerator 100 includes ion source 10 , injection device 12 , bending magnets 14 - 1 to 14 - 4 , vacuum ducts 16 - 1 to 16 - 4 , acceleration cavity 18 , quadrupole magnet 20 and septum magnet 30 .

Vacuum duct 16-1, bending electromagnet 14-1, vacuum duct 16-2, bending electromagnet 14-2, vacuum duct 16-3, bending electromagnet 14-3, acceleration cavity 18, vacuum duct 16-4 and bending electromagnet 14- 4 are arranged in a ring in this order to form a circular path of the ion beam. The ion source 10 supplies ions to the injection device 12, which injects the ions into the vacuum duct 16-1. Each of the bending electromagnets 14-1 to 14-4 deflects the ion beam to the left by 90°, and the ion beam travels straight through each of the vacuum ducts 16-1 to 16-4.

The ions circulate in the circulating path while being accelerated by the high-frequency electric field in the acceleration cavity 18 . In the acceleration cavity 18, the frequency of the high-frequency electric field is controlled according to the cycle of the ions. A quadrupole electromagnet 20 provided in each vacuum duct 16-1 to 16-4 adjusts the spatial spread of the ion beam.

When the ion beam is accelerated and the energy of the ion beam reaches a predetermined energy, the ion beam is deflected outward along the beam extraction trajectory by the septum electromagnet 30 and extracted from the accelerator 100 .

FIG. 2 shows a cross section that appears when the septum electromagnet 30 is cut along line AA. In FIG. 2, the x-axis is defined with the direction away from the orbit being the positive direction. The x-axis is perpendicular to the beam extraction trajectory. In the following description, the x-axis negative direction side as viewed from the inside of the septum electromagnet 30 is referred to as the orbital side, and the x-axis positive direction side (the side opposite to the orbital side) is referred to as the beam extraction side. Septum electromagnet 30 includes septum coil 32 , return coil 40 , additional septum coil 36 and additional return coil 44 .

The septum coil 32 has a plurality of septum conductors 34 arranged vertically. Each septum conductor 34 extends along a beam extracting track that deflects toward the beam extracting side as it progresses toward the drawing surface in FIG. The return coil 40 and the septum coil 32 are arranged at positions sandwiching the beam extraction trajectory. The return coil 40 has a plurality of return conductors 42 arranged vertically. Each return conductor 42 extends along the beam extraction trajectory.

In the example shown below, the septum coil 32 and return coil 40 are made up of N septum conductors 34 and N return conductors 42, respectively. One end on the near side of each septum conductor 34 and each return conductor 42 is called an incident side end, and one end on the far side is called an outgoing side end. The N septum conductors 34 and the N return conductors 42 may have, for example, the following structure.

The outgoing end of the lowermost septum conductor 34 is one end into which current flows. The incident end of the lowermost septum conductor 34 is connected to the incident end of the lowermost return conductor 42 . The outgoing end of the lowermost return conductor 42 is connected to the outgoing end of the second septum conductor 34 from the bottom. The incident side end of the septum conductor 34 second from the bottom is connected to the incident side end of the return conductor 42 second from the bottom. . . . The output side end of the N-1th return conductor 42 from the bottom is connected to the output side end of the Nth (uppermost) septum conductor 34 from the bottom. The incident side end of the uppermost septum conductor 34 is connected to the incident side end of the uppermost return conductor 42 . The outgoing end of the uppermost return conductor 42 is one end from which current flows.

Thus, the input end of the i-th septum conductor 34 from the bottom is connected to the input end of the i-th return conductor 42 from the bottom, and the output end of the i-th return conductor 42 from the bottom is connected to i+1 from the bottom. It is connected to the outgoing end of the second septum conductor 34 . However, i is any integer from 1 to N−1.

According to such a configuration, the current flowing into the output end of the lowermost septum conductor 34 is transferred to the lowermost septum conductor 34, the lowermost return conductor 42, the second septum conductor 34 from the bottom, The second return conductor 42 from the bottom, the third septum conductor 34 from the bottom, . A current flows through each septum conductor 34 from the exit-side end to the incident-side end, and a current flows through each return conductor 42 from the incident-side end toward the exit-side end.

The structure in which the plurality of septum conductors 34 and the plurality of return conductors 42 are connected is not limited to the structure described above. The plurality of septum conductors 34 and the plurality of return conductors 42 are arranged so that a current flows through each septum conductor 34 from the output side end to the incident side end, and a current flows through each return conductor 42 from the incident side end toward the output side end. Connected. For example, the incident side end of the i-th septum conductor 34 from the top is connected to the incident side end of the i-th return conductor 42 from the top, and the output side end of the i-th return conductor 42 from the top is connected to the (i+1)th septum from the top. It may be connected to the conductor 34 at the outgoing end.

The additional septum coil 36 is arranged closer to the beam extraction side than the septum coil 32 and has a plurality of additional septum conductors 38 . A plurality of additional septum conductors 38 are arranged in the vertical direction so as to draw an arc that bulges toward the loop track.

The additional return coil 44 is arranged closer to the orbit than the return coil 40 and has a plurality of additional return conductors 46 . A plurality of additional return conductors 46 are arranged in the vertical direction so as to draw an arc expanding toward the beam extraction side. That is, the plurality of additional septum conductors 38 and the plurality of additional return conductors 46 cylindrically surround the extraction beam trajectory. Each of the plurality of additional septum conductors 38 and the plurality of additional return conductors 46 may be arranged in an arc with a cross section perpendicular to the beam extraction trajectory.

In the example shown below, the additional septum coil 36 and the additional return coil 44 are configured by M additional septum conductors 38 and M additional return conductors 46, respectively. The M additional septum conductors 38 and the M additional return conductors 46 may have, for example, the following structure.

The outgoing end of the lowermost additional septum conductor 38 becomes one end into which current flows. Similar to the septum coil 32, the incident side end of the j-th additional septum conductor 38 from the bottom is connected to the incident side end of the j-th additional return conductor 46 from the bottom, and the output side end of the j-th additional return conductor 46 from the bottom is connected. is connected to the outgoing end of the j+1-th additional septum conductor 38 from the bottom. The outgoing end of the additional return conductor 46 on the uppermost side is one end from which the current flows. However, j is any integer from 1 to M−1.

According to such a configuration, the current flowing into the output end of the lowermost additional septum conductor 38 is transferred to the lowermost additional septum conductor 38, the lowermost additional return conductor 46, the second lowest additional septum conductor It flows through each conductor in the order of the septum conductor 38, the second additional return conductor 46 from the bottom, the third additional septum conductor 38 from the bottom, and flows out from the outgoing end of the uppermost additional return conductor 46. . A current flows through each additional septum conductor 38 from the output-side end to the incident-side end, and a current flows through each additional return conductor 46 from the incident-side end toward the output-side end.

The structure in which the plurality of additional septum conductors 38 and the plurality of additional return conductors 46 are connected is not limited to the structure described above. In the plurality of additional septum conductors 38 and the plurality of additional return conductors 46, a current flows from the output side end to the incident side end in each additional septum conductor 38, and the current flows in each additional return conductor 46 from the incident side end to the output side end. are fluidly connected. For example, the incident side end of the j-th additional septum conductor 38 from the top is connected to the incident side end of the j-th additional return conductor 46 from the top, and the output side end of the j-th additional return conductor 46 from the top is j+1 from the top. th additional septum conductor 38 may be connected to the outgoing end.

A septum magnetic field for deflecting the ion beam to the beam extraction side is generated in the septum magnetic field region 6 surrounded by the plurality of additional septum conductors 38 and the plurality of additional return conductors 46 .

In FIG. 3, the additional septum coil 36 and the additional return coil 44 are drawn as extracted from the septum electromagnet 30 . In FIG. 3, elevation/depression angles θ and φ viewed from a reference point O defined within the septum magnetic field region 6 are defined. The reference point O may be the centroid of the septum magnetic field region 6 . The elevation/depression angle θ is an elevation/depression angle in which the counterclockwise rotation is positive with respect to the x-axis positive direction, and the elevation/depression angle φ is an elevation/depression angle in which the clockwise rotation is positive with respect to the x-axis negative direction.

A plurality of additional return conductors 46 are arranged such that the spatial distribution of current matches or approximates Q·cos θ, where Q is a constant. That is, the plurality of additional return conductors 46 form a cosine wound coil. The plurality of additional return conductors 46 are arranged densely on the beam extraction side and sparsely on the upper and lower sides.

A plurality of additional septum conductors 38 are arranged such that the spatial distribution of current matches or approximates Q·cos φ. That is, the plurality of additional septum conductors 38 form a coil of cosine turns. However, in the present embodiment, among the plurality of additional septum conductors 38 , the additional septum conductor 38 closer to the loop track is arranged closer to the loop track than the septum coil 32 . In FIG. 3, additional septum conductors 38 closer to the orbit are indicated by two-dot chain lines if these conductors were not arranged closer to the orbit than the septum coil 32 .

In the example shown in FIG. 3 , two additional septum conductors 38 are positioned closer to the orbit than the septum coil 32 . Furthermore, the two additional septum conductors 38 arranged closer to the loop track than the septum coil 32 are arranged above and below the track surface 48 to avoid the track surface 48 . Here, the orbital plane 48 is a virtual plane on which the ion beam draws a circular orbit.

In this way, the plurality of additional septum conductors 38 are densely arranged on the circuit track side and sparse on the upper and lower sides when viewed excluding those arranged on the circuit track side of the septum coil 32 . are placed. The plurality of additional septum conductors 38 are arranged densely on the circuit track side and sparsely on the upper and lower sides, even when those arranged closer to the circuit track side than the septum coil 32 are viewed together. good too.

FIG. 4 shows examples of cross-sectional structures of the septum conductor 34, the additional septum conductor 38, the return conductor 42, and the additional return conductor 46. FIG. These coil conductors comprise coolant lines 26 , conductors 22 and insulators 24 . The refrigerant pipe 26 is formed in a tubular shape. The conductor 22 is cylindrical and covers the refrigerant pipe 26 . The periphery of the conductor 22 is covered with an insulator 24 . A coolant 28 such as water flows through the coolant pipe 26 , and the coolant 28 takes heat from the conductor 22 . The conductor 22 is thereby cooled.

Returning to FIG. 2, the operation of the septum electromagnet 30 will be described. FIG. 2 shows an ion beam 1 on a circular orbit and an ion beam 2 on a beam extraction orbit. Currents flow through the septum coil 32 , the additional septum coil 36 , the return coil 40 and the additional return coil 44 , thereby generating an upward septum magnetic field in the septum magnetic field region 6 . The ions that have orbited the orbit and have a predetermined energy undergo betatron oscillation according to the magnetic field generated by an electromagnet (not shown) for ion beam extraction, and enter the septum electromagnet 30 . Ions incident on the septum electromagnet 30 are deflected to the outside of the circular orbit by the septum magnetic field, travel along the ion extraction orbit, and are extracted from the septum electromagnet 30 to the outside.

The septum electromagnet 30 according to this embodiment is provided with an additional septum coil 36 and an additional return coil 44 in addition to the septum coil 32 and the return coil 40 . Additional septum coil 36 and additional return coil 44 generate a magnetic field with a more uniform x-axis distribution than septum coil 32 and return coil 40 . That is, when viewed along the x-axis direction, the magnetic field generated by the additional septum coil 36 and the additional return coil 44 has a higher effective magnetic flux density than the magnetic field generated by the septum coil 32 and the return coil 40 . This increases the deflection angle of the ion beam per fixed distance and shortens the septum electromagnet 30 compared to when only the septum coil 32 and return coil 40 are used.

Further, in the septum electromagnet 30 according to this embodiment, the septum coil 32 and the return coil 40 are used together with the additional septum coil 36 and the additional return coil 44 . The septum coil 32 and return coil 40 are simpler in construction than the cosine-wound additional septum coil 36 and additional return coil 44 . Therefore, according to the septum electromagnet 30 according to the present embodiment, the structure is simplified as compared with the case where all the coils are cosine-wound coils. That is, the deflection angle of the ion beam per fixed distance is increased while avoiding excessively complicated structure.

Furthermore, in the septum electromagnet 30 according to the present embodiment, the two additional septum conductors 38 arranged closer to the orbital side than the septum coil 32 are arranged above and below the raceway surface 48 so as to avoid the raceway surface 48. are placed. As a result, the thickness of the additional septum coil 36 in the radial direction of the loop track can be reduced while the distribution of the current flowing through the additional septum coil 36 matches or approximates the ideal distribution. Therefore, the possibility of ions deviating from the orbit and impinging on the septum electromagnet 30 from colliding with the additional septum coil 36 is reduced. In addition, the number of ion beams that can be extracted from the accelerator 100 per fixed time increases compared to the case where the additional septum conductor 38 is provided on the orbital surface 48 .

Here, an embodiment is shown in which the additional septum conductor 38 arranged closer to the orbital track side than the septum coil 32 is arranged to avoid the track surface 48 . If the distance between the ion beam 1 on the circular orbit and the ion beam 2 on the extraction orbit is large, the additional septum conductor 38 arranged closer to the circular orbit than the septum coil 32 avoids the orbital surface 48 . may be placed without

FIG. 5 shows a cross section of a septum electromagnet 60 according to a second embodiment of the invention. Septum electromagnet 60 includes septum coil 32 , return coil 40 , additional septum coil 50 and additional return coil 54 .

Additional septum coil 50 includes a plurality of additional septum conductors 52 . Some of the additional septum conductors 52 closer to the loop track are arranged closer to the loop track than the septum coil 32 . The additional septum conductors 52 are arranged in the vertical direction so as to draw an arc that bulges toward the loop track. Additional return coil 54 includes a plurality of additional return conductors 56 . A plurality of additional return conductors 56 are arranged closer to the loop track than the return coil 40 . The additional return conductors 56 are arranged vertically so as to draw an arc that expands toward the beam extraction side. A plurality of additional septum conductors 52 and a plurality of additional return conductors 56 cylindrically surround the extraction beam trajectory. Each of the plurality of additional septum conductors 52 and the plurality of additional return conductors 56 may be arranged in an arc with a cross section perpendicular to the beam extraction trajectory.

The plurality of additional septum conductors 52 and the plurality of additional return conductors 56 are divided into the following four conductor groups. The first conductor group is the left conductor group by the additional septum conductor 52 whose elevation angle φ is -45° or more and less than 45°. The second conductor group is an upper conductor group consisting of an additional septum conductor 52 with an elevation/depression angle φ of 45° or more and less than 90° and an additional return conductor 56 with an elevation/depression angle θ of 45° or more and less than 90°. The third conductor group is a right conductor group with additional return conductors 56 having an elevation angle θ of −45° or more and less than 45°. The fourth conductor group is a lower conductor group consisting of an additional septum conductor 52 whose elevation/depression angle φ is −90° or more and less than −45°, and an additional return conductor 56 whose elevation/depression angle θ is −90° or more and less than −45°. is.

The direction of current flowing through the left conductor group and the direction of current flowing through the right conductor group are the same. Also, the direction of current flowing through the upper conductor group and the direction of current flowing through the lower conductor group are the same. The direction of the current flowing through the left conductor group and the right conductor group is opposite to the direction of the current flowing through the upper conductor group and the lower conductor group.

Each of the plurality of additional septum conductors 52 and each of the plurality of additional return conductors 56 are connected so as to obtain the above relationship for the direction of current flowing through each conductor. Also, either the incident side end or the exit side end of each of the plurality of additional septum conductors 52 may be one end into or out of which the current flows. Either the incident side end or the outgoing side end of each of the plurality of additional return conductors 56 may be one end from which current flows out or in. FIG.

In FIG. 6 , the additional septum coil 50 and the additional return coil 54 are drawn out from the septum electromagnet 60 . A plurality of additional return conductors 56 are arranged such that the spatial distribution of current matches or approximates P·cos2θ. Here, P may be a constant or a variable related to time. That is, the plurality of additional return conductors 56 form a coil of double angle cosine turns. The plurality of additional return conductors 56 are arranged densely on the beam extraction side and sparsely on the beam extraction side and diagonally below the beam extraction side.

A plurality of additional septum conductors 52 are arranged such that the spatial distribution of current matches or approximates P·cos2φ. That is, the plurality of additional septum conductors 52 form a coil of double cosine turns. However, in the present embodiment, among the plurality of additional septum conductors 52 , the additional septum conductor 52 closer to the loop track is arranged closer to the loop track than the septum coil 32 . In the example shown in FIG. 6, two additional septum conductors 52 are positioned closer to the orbit than the septum coil 32 . Furthermore, the two additional septum conductors 52 arranged closer to the orbital track than the septum coil 32 are arranged above and below the track surface 48 and are arranged at positions avoiding the track surface 48 .

In this way, when the plurality of additional septum conductors 52 are viewed from the septum coil 32 excluding those arranged on the loop track side, the loop track side becomes denser, and the plurality of additional septum conductors 52 are arranged diagonally above the loop track side and on the loop track side. They are arranged so that the diagonally lower part becomes sparse. Even when the plurality of additional septum conductors 52 arranged closer to the loop track side than the septum coil 32 are viewed together, the loop track side becomes denser, and the loop track side obliquely above and the loop track side diagonally below becomes denser. They may be arranged so as to be sparse.

Returning to FIG. 5, the operation of septum electromagnet 60 will be described. An upward septum magnetic field is generated in the septum magnetic field region 6 by the current flowing through the septum coil 32 and the return coil 40 . The ions that have traveled around the orbit and have a predetermined energy undergo betatron oscillation in accordance with the magnetic field generated by the electromagnet for extracting the ion beam, and enter the septum electromagnet 60 . Ions incident on the septum electromagnet 60 are deflected to the outside of the circular orbit by the septum magnetic field, travel along the ion extraction orbit, and are extracted from the septum electromagnet 60 to the outside.

The septum electromagnet 60 according to this embodiment is provided with an additional septum coil 50 and an additional return coil 54 in addition to the septum coil 32 and the return coil 40 . An additional septum coil 50 and an additional return coil 54 generate a magnetic field that adjusts the spread of the ion beam, similar to a quadrupole electromagnet. In this embodiment, the additional septum coil 50 and the additional return coil 54 of double angle cosine winding are provided so that the number of quadrupole magnets used for the ion beam extracted from the accelerator can be reduced.

In addition, in the septum electromagnet 60 according to the present embodiment, the two additional septum conductors 52 arranged closer to the orbital side than the septum coil 32 are arranged above and below the raceway surface 48 so as to avoid the raceway surface 48. are placed. As a result, the thickness of the additional septum coil 50 in the radial direction of the loop track can be reduced while the distribution of the current flowing through the additional septum coil 50 matches or approximates the ideal distribution. Therefore, the possibility of ions deviating from the orbit and impinging on the septum electromagnet 60 from colliding with the additional septum coil 50 is reduced. In addition, the number of ion beams that can be extracted from the accelerator per fixed time increases compared to the case where the additional septum conductor 52 is provided on the track surface 48 .

Here, an embodiment is shown in which the additional septum conductor 52 arranged closer to the loop track than the septum coil 32 is arranged to avoid the track surface 48 . When the distance between the ion beam 1 on the circular orbit and the ion beam 2 on the extraction orbit is large, the additional septum conductor 52 arranged closer to the circular orbit than the septum coil 32 avoids the orbital surface 48 . may be placed without

As shown in FIG. 7, a septum electromagnet 200 may be constructed by cascading the septum electromagnet 30 according to the first embodiment and the septum electromagnet 60 according to the second embodiment. That is, septum electromagnets 30 and 60 may be arranged such that the ion beam emitted from septum electromagnet 30 is incident on septum electromagnet 60 .

In this case, the septum coil 32 and the return coil 40 may be provided in common for the septum electromagnet 30 and the septum electromagnet 60 . That is, septum coil 32 and return coil 40 may be arranged to extend from septum electromagnet 30 to septum electromagnet 60 . Also, the septum coil 32 and the return coil 40 may be provided individually for the septum electromagnet 30 and the septum electromagnet 60, respectively.

The plurality of additional septum conductors 38 in the septum electromagnet 30 shown in FIG. 7 are denser on the loop track side when the additional septum conductors 38 arranged closer to the loop track than the septum coil 32 are viewed. forming a first group of conductors arranged in a manner such that: Further, the plurality of additional septum conductors 52 in the septum electromagnet 60 are arranged so as to be dense on the orbital track side when viewed excluding the additional septum conductors 52 arranged closer to the orbital side than the septum coil 32, In addition, the second conductor group is formed so as to be sparsely arranged on the oblique upper side of the circular track side and obliquely on the lower side of the circular track side. These first conductor group and second conductor group are cascaded along the beam extraction track.

FIG. 8 shows a septum electromagnet 62 according to a third embodiment of the invention. The septum electromagnet 62 comprises the septum coil 32 and the return coil 40, and the additional septum coil 36 and the additional return coil 44 of cosine winding, and the additional septum coil 50 and the additional return coil 54 of the double-angle cosine winding arranged in parallel.

An additional septum coil 50 with a double angle cosine winding is arranged adjacent to the septum coil 32 on the beam extraction side. However, of the additional septum conductors 52 that constitute the additional septum coil 50 , a portion closer to the loop track is arranged on the loop track side of the septum coil 32 . An additional septum coil 36 with cosine winding is arranged adjacent to the additional septum coil 50 with double angle cosine winding on the beam extracting side. In FIG. 8 , the double cosine winding additional septum coil 50 is depicted with a solid line that is thicker than the solid line that depicts the septum coil 32 . An additional septum coil 36 of cosine winding is also drawn with a dashed line.

Of the plurality of additional septum conductors 38 constituting the cosine-wound additional septum coil 36 , the two additional septum conductors 38 on the loop track side are arranged above and below the track surface 48 on the loop track side of the septum coil 32 . A face 48 is located at the averted position. Furthermore, among the plurality of additional septum conductors 52 that constitute the double angle cosine winding additional septum coil 50 , the two additional septum conductors 52 on the loop track side are arranged above and below the track surface 48 on the loop track side of the septum coil 32 . , and the raceway surface 48 is located at a position avoided. Two additional septum conductors 52 belonging to the additional septum coil 50 are positioned above and below the two additional septum conductors 38 belonging to the additional septum coil 36 on the orbit side of the septum coil 32 .

An additional return coil 54 with double-angle cosine winding is arranged adjacent to the return coil 40 on the orbit side, and an additional return coil with cosine winding is arranged on the orbit side of the additional return coil 54 with double-angle cosine winding. 44 are arranged adjacently. In FIG. 6 , the double angle cosine winding additional return coil 54 is depicted with a thicker solid line than the solid line that depicts the return coil 40 . An additional return coil 44 with a cosine winding is drawn with a dashed line.

In this way, the plurality of additional septum conductors 38 in this embodiment are arranged so as to be dense on the loop track side when viewed excluding the additional septum conductors 38 arranged closer to the loop track than the septum coil 32. form a first group of conductors. Further, the plurality of additional septum conductors 52 are arranged so as to be dense on the loop track side when the additional septum conductors 52 arranged closer to the loop track than the septum coil 32 are viewed. A second conductor group is formed so as to be sparsely arranged on the obliquely upper side and obliquely on the lower side of the loop track. These first conductor group and second conductor group are arranged side by side along the beam extraction track.

According to such a configuration, the deflection angle of the ion beam per fixed distance is increased and the septum electromagnet 62 is shortened compared to the case where only the septum coil 32 and the return coil 40 are used. Moreover, the structure is simplified as compared with the case where all the coils are cosine wound. That is, the effect of deflecting the ion beam is enhanced while avoiding excessively complicated structure. In addition, the ions are less likely to collide with the cosine-wound additional septum coil 36 and the double-angle cosine-wound additional septum coil 50 before they deviate from the orbit and enter the septum electromagnet 62 . This increases the number of ion beams that can be extracted from the accelerator per given time period compared to each additional septum conductor on the orbital plane 48 .

Here, an embodiment is shown in which the cosine-wound additional septum coil 36 and the additional return coil 44 are provided inside the double-angle cosine-wound additional septum coil 50 and the additional return coil 54 . In addition to such a configuration, the additional cosine winding septum coil 36 and the additional return coil 44 may be provided outside the double angle cosine winding additional septum coil 50 and the additional return coil 54 .

FIG. 9 shows a septum electromagnet 64 according to a fourth embodiment of the invention. A septum electromagnet 64 is obtained by adding a correction coil 72 to the septum electromagnet 30 according to the first embodiment shown in FIG. The correction coil 72 is composed of one or more pairs of correction coil conductors 74 extending along the beam extraction trajectory. The paired two correction coil conductors 74 are arranged above and below the track surface 48 on the circling track side of the septum coil 32 . FIG. 9 shows an example in which two pairs of correction coil conductors 74 are arranged. The pair of correction coil conductors 74 on the right side has a wider vertical arrangement interval than the pair of correction coil conductors 74 on the left side.

Currents in directions opposite to each other flow through the two correction coil conductors 74 forming a pair. This produces a correction magnetic field in the x-axis positive or x-axis negative direction. The septum coil 32, the return coil 40, the additional septum coil 36, and the additional return coil 44 generate a septum magnetic field and a magnetic field in the x-axis direction leaking to the orbit side. Due to this leakage magnetic field, the trajectory of the accelerating ion beam may deviate from the desired trajectory. According to this embodiment, the leakage magnetic field is suppressed by the correction magnetic field emitted from the correction coil 72, and the trajectory of the ion beam during acceleration is brought closer to or coincides with the ideal trajectory.

The correction coil 72 may be added to the septum electromagnet 60 according to the second embodiment and the septum electromagnet 62 according to the third embodiment.

FIG. 10 shows a septum electromagnet 66 according to the fifth embodiment. The septum electromagnet 66 has a plurality of additional septum conductors 52 forming the additional septum coil 51 on the orbit side of the septum coil 32 , and a plurality of additional septum conductors 52 forming the additional return coil 55 on the beam extraction side of the return coil 40 . An additional return conductor 56 is arranged. The beam extraction side of the septum coil 32 and the loop side of the return coil 40 face the septum magnetic field region 6 .

Further, the additional septum conductor 52 above the x-axis and the additional septum conductor 52 below the x-axis may contact at the raceway surface 48 . Similarly, the x-axis upper additional return conductor 56 and the x-axis lower additional return conductor 56 may meet at the track surface 48 .

The plurality of additional septum conductors 52 and the plurality of additional return conductors 56 are divided into the following four conductor groups. The first conductor group is the left conductor group by the additional septum conductor 52 whose elevation angle φ is -45° or more and less than 45°. The second conductor group is an upper conductor group consisting of an additional septum conductor 52 with an elevation/depression angle φ of 45° or more and less than 90° and an additional return conductor 56 with an elevation/depression angle θ of 45° or more and less than 90°. The third conductor group is a right conductor group with additional return conductors 56 having an elevation angle θ of −45° or more and less than 45°. The fourth conductor group is a lower conductor group consisting of an additional septum conductor 52 whose elevation/depression angle φ is −90° or more and less than −45°, and an additional return conductor 56 whose elevation/depression angle θ is −90° or more and less than −45°. is.

The direction of current flowing through the left conductor group and the direction of current flowing through the right conductor group are the same. Also, the direction of current flowing through the upper conductor group and the direction of current flowing through the lower conductor group are the same. The direction of the current flowing through the left conductor group and the right conductor group is opposite to the direction of the current flowing through the upper conductor group and the lower conductor group.

Each of the plurality of additional septum conductors 52 and each of the plurality of additional return conductors 56 are connected so as to obtain the above relationship for the direction of current flowing through each conductor. Also, either the incident side end or the exit side end of each of the plurality of additional septum conductors 52 may be one end into or out of which the current flows. Either the incident side end or the outgoing side end of each of the plurality of additional return conductors 56 may be one end from which current flows out or in. FIG.

The plurality of additional return conductors 56 are arranged densely on the beam extraction side and sparsely on the beam extraction side and diagonally below the beam extraction side. The plurality of additional return conductors 56 may be arranged such that the spatial distribution of current matches or approximates P·cos2θ. That is, the plurality of additional return conductors 56 may form a double angle cosine coil.

The plurality of additional septum conductors 52 are densely arranged on the loop track side and sparsely arranged diagonally above the loop track side and diagonally below the loop track side. A plurality of additional septum conductors 52 may be arranged such that the spatial distribution of current matches or approximates P·cos2φ. That is, the plurality of additional septum conductors 52 may form a coil of double cosine turns.

Compared to the septum magnets 30, 60, 62, and 64 according to the above-described embodiments, the septum magnet 66 according to the present embodiment has a gap between the ion beam 1 on the circular orbit and the ion beam 2 on the extraction orbit. May be used for large distances. According to the arrangement of the plurality of additional return conductors 56 and the arrangement of the plurality of additional septum conductors 52 in the septum electromagnet 66 according to the present embodiment, and the direction of the current flowing through each conductor, the additional septum coil 51 and the additional return coil 55 are quadrupolar. Acts as an electromagnet. Therefore, the number of quadrupole magnets used for the ion beam extracted from the accelerator can be reduced.

FIG. 11 shows the calculation results of the magnetic field distribution inside the septum electromagnet 66 . The horizontal axis indicates the position on the x-axis, and the vertical axis indicates the magnetic field strength. An ideal distribution 400 is an ideal magnetic field distribution, and a calculated distribution 402 is a magnetic field distribution obtained by simulation. In the example shown in FIG. 11, the deviation of the magnetic field distribution from the ideal distribution is 4%. The deviation of the magnetic field distribution from the ideal distribution is preferably less than 1%. That is, by setting the deviation of the magnetic field distribution from the ideal distribution to less than 1%, sufficient performance for converging the ion beam can be obtained.

Also in the above-described first to fourth embodiments, each conductor constituting the septum coil, the return coil, the additional septum coil, and the additional return coil is arranged so that the deviation of the magnetic field distribution from the ideal distribution is less than 1%. to get the same effect.

Here, as a fifth embodiment, a left conductor group (additional septum conductor 52) is provided on the loop track side of the septum coil 32, and a right conductor group (additional return conductor 56) is provided on the beam extraction side of the return coil 40. A septum electromagnet 66 is shown. Instead of such a configuration, a configuration in which the left conductor group is provided on the beam extraction side of the septum coil 32 and the right conductor group is provided on the loop track side of the return coil 40 may be adopted.

FIG. 12 shows a septum electromagnet 70 according to the sixth embodiment. This septum electromagnet 70 is obtained by modifying the structure of the additional septum coil 51 in the septum electromagnet 66 according to the fifth embodiment. That is, in the septum electromagnet 70 , the additional septum conductors 52 closer to the orbital track than the septum coil 32 are arranged above and below the track surface 48 , and are arranged at positions that avoid the track surface 48 .

According to such a configuration, the thickness of the additional septum coil 51 in the radial direction of the loop track can be reduced while the distribution of the current flowing through the additional septum coil 51 matches or approximates the ideal distribution. Therefore, the possibility of ions deviating from the orbit and impinging on the septum electromagnet 70 from colliding with the additional septum coil 51 is reduced.

As in the septum electromagnet 62 shown in FIG. 8, the septum coil 32 and the return coil 40 are provided with the additional septum coil 36 and the additional return coil 44, and the additional septum coil 51 and the additional return coil 55 in the fifth embodiment. They may be arranged side by side. Similarly, the additional septum coil 36 and the additional return coil 44 and the additional septum coil 51 and the additional return coil 55 in the sixth embodiment may be arranged in parallel with the septum coil 32 and the return coil 40 .

FIG. 13 schematically shows an accelerator 102 according to a seventh embodiment of the invention. Accelerator 102 is called a cyclotron. FIG. 10 shows a cross section of the accelerator 102 cut in a horizontal plane. Accelerator 102 includes electromagnet housing 80 , accelerating electrode pair 90 and septum electromagnet 30 .

The electromagnet housing 80 forms a cylindrical beam deflection magnetic field region 82 therein. The electromagnet housing 80 generates a magnetic field in the positive z-axis direction toward the drawing surface in the beam deflection magnetic field region 82 . Acceleration electrode pair 90 is composed of two D electrodes 90A and 90B obtained by cutting a hollow disk-shaped cavity. A high frequency electric field is generated between the D electrode 90A and the D electrode 90B.

Ions are injected into an ion injection point 84 between the D electrodes 90A and 90B. The ions are accelerated by the high-frequency electric field between the D-electrodes 90A and 90B, and draw an orbital trajectory 86 within the accelerating electrode pair 90 in which the orbital radius increases as the energy increases. The ions that have orbited the orbit 86 and have a predetermined energy undergo betatron oscillation in accordance with an electric field generated by a kicker (not shown) and enter the septum electromagnet 30 . Ions incident on the septum electromagnet 30 are deflected to the outside of the circular orbit 86 by the septum magnetic field, travel along the ion extraction orbit, and are extracted outside the septum electromagnet 30 .

The septum electromagnet according to each of the above embodiments may be used in other types of accelerators. For example, as shown in Patent Document 4, the septum electromagnet according to each of the above embodiments may be used in an eccentric accelerator in which ions are injected at a position displaced from the center of the beam deflection magnetic field region. .

FIG. 14 shows a particle beam therapy system 104 according to an eighth embodiment of the invention. The particle beam therapy system 104 includes an accelerator 102 , a rotating gantry 301 , an irradiation device 302 , a treatment table 303 , a treatment control device 304 and an accelerator control device 305 . In addition to the components shown in FIG. 10, the accelerator 102 includes a septum power supply/local controller 306 and a main power supply/local controller 307 as power sources.

An ion beam extracted from the accelerator 102 is incident on the rotating gantry 301 . The rotating gantry 301 operates as a beam transport device that transports the ion beam and changes the traveling direction of the ion beam. The ion beam is transported through rotating gantry 301 to irradiation device 302 . The irradiation device 302 irradiates an ion beam onto a target of a patient 308 lying on a treatment table 303 .

The treatment control device 304 transmits an on/off signal to the accelerator control device 305 to instruct the ion beam extraction or stop of the ion beam extraction. The accelerator controller 305 controls the septum power supply/local controller 306 and the main power supply/local controller 307 according to the on/off signals. The septum power supply/local controller 306 applies current to the septum electromagnet 30 or cuts off the current flowing to the septum electromagnet 30 under the control of the accelerator controller 305 . The main power/local controller 307 applies current to the main parts of the accelerator 102 or cuts off the current flowing to the main parts under the control of the accelerator controller 305 . Note that the main part of the accelerator 102 is other components of the accelerator 102 that do not include the septum electromagnet 30 .

The treatment control device 304 measures the dose of the ion beam irradiated to the patient 308 by the irradiation device 302, and also measures control information indicating the energy required for the ion beam, the dose required for the ion beam, and the like. The result is output to the accelerator control device 305 . Further, the treatment control device 304 outputs control information instructing the irradiation direction to the rotating gantry 301 and outputs control information instructing the irradiation region to the irradiation device 302 .

The accelerator controller 305 transmits necessary information to the septum power supply/local controller 306 and the main power supply/local controller 307 according to the control information output from the treatment controller 304 . The septum power/local controller 306 and the main power/local controller 307 individually control the main parts of the septum electromagnet 30 and the accelerator 102 according to the information transmitted from the accelerator controller 305 .

For example, the accelerator control device 305 and the septum power supply/local control device 306 apply a current of magnitude according to the instruction of the therapy control device 304 to each coil of the septum electromagnet 30 at the timing according to the instruction of the therapy control device 304. Execute control. The timing of following the instruction of the treatment control device 304 includes, for example, the timing of irradiating the patient 308 with an ion beam and the timing of extracting the ion beam from the accelerator 102 . In this way, by performing pulse operation in which the current flowing through each coil of the septum electromagnet 30 is turned on/off in accordance with an instruction from the treatment control device 304, the amount of heat generated by the septum electromagnet 30 is suppressed. Therefore, by applying a current having a large effective value to each coil compared to the case where the current is applied continuously, the deflection angle of the ion beam per fixed distance can be increased and the septum electromagnet 30 can be designed to be shortened. .

Here, a particle beam therapy system 104 using a septum electromagnet 30 is shown. Septum electromagnets 60, 200, 62, 64, 66 and 70 shown in FIGS. 5, 7, 8, 9, 10 and 12, respectively, may be used in the particle beam therapy system.

1 ion beam on circular orbit, 2 ion beam on extraction orbit, 6 septum magnetic field region, 10 ion source, 12 injection device, 14-1 to 14-4 bending electromagnet, 16-1 to 16-4 vacuum duct, 18 acceleration cavity, 20 quadrupole electromagnet, 22 conductor, 24 insulator, 26 refrigerant pipe, 28 refrigerant, 30, 60, 62, 64, 66, 70, 200 septum electromagnet, 32 septum coil, 34 septum conductor, 36, 50, 51 Additional septum coil, 38, 52 Additional septum conductor, 40 Return coil, 42 Return conductor, 44, 54, 55 Additional return coil, 46, 56 Additional return conductor, 48 Track surface, 72 Correction coil, 74 Correction coil conductor, 80 Electromagnet Case, 82 Beam deflection magnetic field region, 84 Ion injection point, 86 Orbital orbit, 90 Acceleration electrode pair, 90A, 90B D electrode, 100, 102 Accelerator, 104 Particle beam therapy system, 301 Rotating gantry, 302 Irradiation device, 303 Treatment Table, 304 therapy controller, 305 accelerator controller, 306 septum power supply and local controller, 307 main power supply and local controller, 400 ideal distribution, 402 calculated distribution.

Claims (14)

a septum coil extending along the beam extraction trajectory;
an additional septum coil arranged in parallel with the septum coil and extending along the beam extraction trajectory;
The additional septum coil is
A septum electromagnet, comprising: a plurality of additional septum conductors extending along the beam extracting orbit, the plurality of additional septum conductors being arranged to draw an arc that swells toward the loop orbit. The septum electromagnet according to claim 1,
A septum electromagnet, wherein among the plurality of additional septum conductors, the additional septum conductor closer to the loop track is arranged closer to the loop track than the septum coil. In the septum electromagnet according to claim 1 or 2,
The plurality of additional septum conductors are
A septum electromagnet, characterized in that the septum electromagnets are arranged densely on the orbital side. In the septum electromagnet according to claim 1 or 2,
The plurality of additional septum conductors are
a first conductor group arranged densely on the circuit track side;
forming a second conductor group arranged so that the oblique upper part of the loop track side and the oblique lower part of the loop track side are sparse;
A septum electromagnet, wherein the first conductor group and the second conductor group are arranged side by side along the beam extraction track. In the septum electromagnet according to claim 2,
A septum electromagnet, wherein the additional septum conductor arranged closer to the orbit than the septum coil is arranged to avoid an ion beam orbital plane. In the septum electromagnet according to claim 5,
The plurality of additional septum conductors are
A septum electromagnet, wherein the septum electromagnet is arranged densely on the circuit track side when viewed with the additional septum conductors arranged on the circuit track side of the septum coil removed. In the septum electromagnet according to claim 5 or 6,
The plurality of additional septum conductors are
a first conductor group arranged densely on the loop track side when viewed excluding the additional septum conductors arranged closer to the loop track than the septum coil;
forming a second conductor group arranged so that the oblique upper part of the loop track side and the oblique lower part of the loop track side are sparse;
A septum electromagnet, wherein the first conductor group and the second conductor group are arranged side by side along the beam extraction track. In the septum electromagnet according to any one of claims 1, 2 and 5,
The plurality of additional septum conductors are
A septum electromagnet, characterized in that the septum electromagnets are arranged so as to be sparse on the oblique upper side of the orbital side and obliquely on the lower side of the orbital side. In the septum electromagnet according to claim 1 or 2,
a correction coil arranged closer to the orbit than the septum coil and extending along the beam extraction orbit;
A septum electromagnet, wherein the correction coil includes a pair or a plurality of pairs of correction coil conductors extending along the beam extraction orbit on the orbit side of the septum coil. In the septum electromagnet according to claim 1 or 2,
a return coil extending along the beam extraction trajectory;
an additional return coil extending along the beam extraction trajectory;
The return coil is
arranged at a position sandwiching the beam extraction trajectory between the septum coil,
The additional return coil is
A septum electromagnet, comprising: a plurality of additional return conductors extending along the beam extraction orbit, the plurality of additional return conductors being arranged to draw an arc that swells toward the side opposite to the loop orbit. In the septum electromagnet according to claim 1 or 2,
A septum electromagnet, wherein the plurality of additional septum conductors are arranged such that the deviation of magnetic field distribution from an ideal distribution in a septum magnetic field region located on the beam extraction side of the septum coil is less than 1%. A septum electromagnet according to claim 1 or claim 2,
An accelerator, wherein an accelerated ion beam is extracted from said beam extraction trajectory. 13. The accelerator of claim 12, wherein
A power supply for applying current to the septum coil and the additional septum coil,
The power source is
An accelerator, wherein a current is passed through the septum coil and the additional septum coil according to the timing at which the ion beam is extracted. an accelerator according to claim 12;
a beam transport device for transporting the ion beam extracted from the accelerator;
an irradiation device that irradiates a patient with the ion beam transported by the beam transport device;
A particle beam therapy system comprising:

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