JP2020030882A - Accelerator and particle beam irradiation device, and beam extraction method - Google Patents

Abstract

To provide a cyclotron-type accelerator and a particle beam irradiation device comprising the same, and a beam extraction method, capable of successively extracting a predetermined energy beam at predetermined timing.SOLUTION: A cyclotron-type accelerator comprises: an annular coil 13; two main electromagnets, installed so as to face each other, for forming a magnetic field therebetween; high frequency acceleration cavities 21, 22 and a dee electrode for accelerating a beam; a beam extraction path 140 for extracting the beam to the outside; and a beam desorption device composed of built-in coils 28, 28A that are disposed in the dee electrode and generate deflection magnetic fields, at a plurality of positions in a radial direction of the coil 13, for desorbing the beam from a beam orbit and guiding the beam to the beam extraction path 140.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an accelerator for accelerating ions such as protons and carbon, a particle beam irradiation apparatus provided with the accelerator, and a beam extraction method.

  Patent document for the purpose of making it possible to extract accelerated particles having a current amount corresponding to each application for radiotherapy and RI production with one particle accelerator, and as a result, to improve the operation rate easily In order to extract a proton beam for radiation therapy and a proton beam for RI production from the cyclotron, at least two extraction ports are provided in the cyclotron, and negative ions circulating in the cyclotron are guided to the extraction port. And an ion source that supplies negative ions to the cyclotron, and a control device that controls at least one of the amount of advance and retreat of the foil and the amount of negative ions supplied by the ion source to control the amount of current of the proton beam extracted from the extraction port. A particle acceleration system comprising:

JP 2010-287419 A

  Particle beam irradiation apparatuses are roughly classified into a particle beam irradiation apparatus having a synchrotron as an accelerator and a particle beam irradiation apparatus having a cyclotron as an accelerator.

  Among them, the particle beam irradiation device having a cyclotron includes, for example, an ion source, a cyclotron, a beam transport system, a rotating gantry, and an irradiation device. The cyclotron has a vacuum vessel constituted by a pair of opposed iron cores having a circular cross section, a high-frequency accelerator, and an extraction electromagnet. The beam transport system is connected to the exit of the cyclotron where the extraction electromagnet is located.

  In a particle beam irradiation apparatus having a cyclotron, ions emitted from an ion source (for example, cations or heavy ion such as carbon, which is heavier than protons such as carbon) are incident on the center of the cross section of the iron core of the cyclotron, and are subjected to high-frequency acceleration. Accelerated by the device. The accelerated ion beam spirals from the center of the iron core toward the inner side surface of the return yoke, and is emitted to the beam transport system by an extraction electromagnet provided at the periphery of the iron core. The emitted ion beam passes through the beam transport system and is irradiated from the irradiation device to the affected part of the patient's cancer on the treatment table.

  The beam orbiting inside such a cyclotron moves to the outer trajectory as the energy becomes higher, and is taken out of the accelerator when it reaches the maximum energy. Therefore, the energy of the extracted beam generally has a constant value. Therefore, in order to apply a cyclotron to particle beam therapy or the like that requires beams of various energies, a method of reducing the beam energy using a degrader (energy absorber) outside the accelerator has been used.

  However, when a degrader is used for energy adjustment, there is a problem that a beam current is reduced when passing through the degrader, and beam utilization efficiency is reduced. There are also problems such as an increase in beam size due to scattering and an increase in unnecessary secondary particles.

  Further, when a degrader is used or a foil is provided as in the method of Patent Document 1, an extra configuration needs to be provided on the beam trajectory to extract a beam of arbitrary energy, and highly accurate beam energy control is performed. Therefore, there is a problem that it is difficult to extract a beam having a predetermined energy at a predetermined timing.

  The present invention has been made in view of the above points, and its object is to provide a cyclotron-type accelerator, an accelerator capable of continuously extracting a beam of predetermined energy at a predetermined timing, and a particle beam irradiation apparatus including the accelerator. Another object of the present invention is to provide a beam extraction method.

In order to solve the above problem, for example, a configuration described in the claims is adopted.
The present invention includes a plurality of means for solving the above-mentioned problems. For example, an annular main coil, two iron cores installed opposite to each other and forming a magnetic field therebetween, and a beam are provided. An electrode for accelerating the beam, a beam emission path for extracting a beam to the outside, and a beam emission path disposed in the electrode and at a plurality of radial positions of the main coil, the beam is separated from a beam orbit and guided to the beam emission path. And a beam detachment device including a built-in coil for generating a deflection magnetic field.

  ADVANTAGE OF THE INVENTION According to this invention, in a cyclotron type accelerator, a beam of predetermined energy can be continuously extracted at predetermined timing.

It is a figure showing the whole particle beam irradiation device composition of an example of the present invention. It is a figure showing appearance of an accelerator of an example of the present invention. It is a figure showing the internal structure of the accelerator of an example. It is a figure showing the design track of the accelerator of an example. FIG. 4 is a diagram illustrating a magnetic field distribution along a beam trajectory of the accelerator according to the embodiment. FIG. 4 is a diagram illustrating a main magnetic field distribution in an orbit plane of the accelerator according to the embodiment. It is a figure which shows the in-orbit direction of the accelerator of an Example, and the tune of the perpendicular direction orthogonal to it. It is a figure showing the internal structure of the high frequency acceleration cavity of the accelerator of an example. It is a figure showing the section which looked at the Dee electrode side from the beam track surface of the high frequency acceleration cavity of the accelerator of an example. FIG. 9 is a diagram illustrating a cross section taken along line B-B ′ of FIG. 8. It is a figure showing the section which looked at the Dee electrode side from the beam orbit plane of the other high frequency acceleration cavity of the accelerator of an example.

  Embodiments of an accelerator, a particle beam irradiation apparatus, and a beam extraction method according to the present invention will be described with reference to FIGS.

  First, the overall configuration of the particle beam irradiation apparatus and the configuration of a related apparatus will be described with reference to FIG. FIG. 1 is a diagram showing an overall configuration of a particle beam irradiation apparatus according to the present invention.

  In FIG. 1, the particle beam irradiation device 100 includes an accelerator 1, a beam transport system 60, an irradiation device 70, a treatment table 90, and a control device 80.

  In the particle beam irradiation apparatus 100, the ions generated by the ion source 12 are accelerated by the accelerator 1 to form an ion beam. The accelerated ion beam is emitted from the accelerator 1 and transported to the irradiation device 70 by the beam transport system 60. The transported ion beam is shaped by the irradiation device 70 so as to conform to the shape of the affected part, and is irradiated on the target of the patient 95 lying on the treatment table 90 by a predetermined amount.

  The operation of each device and equipment in the particle beam irradiation device 100 including the accelerator 1 is controlled by the control device 80.

  Next, the structure of the accelerator of this embodiment will be described below with reference to FIGS. FIG. 2 shows the appearance of the accelerator of the embodiment.

  The accelerator 1 shown in FIG. 2 is an energy-variable continuous-wave accelerator capable of continuously outputting an energy-variable beam, and converts a charged particle beam circulating at a constant frequency (isochronous) in a constant magnetic field into a high-frequency electric field. Is a circular accelerator that accelerates.

  As shown in FIG. 2, the accelerator 1 is installed to face each other, and its outer shell is formed by a main electromagnet 11 that can be divided into upper and lower portions that form a magnetic field therebetween, and the inside thereof is evacuated. . The main electromagnet 11 is provided with a plurality of through-holes. Among them, there is a through-hole 111 for a take-out beam for taking out an accelerated beam, and a coil connection for drawing out a lead wire of an internal coil 13 (see FIG. 3) to the outside. Through-hole 112 and a through-hole 114 for high-frequency power input are provided on the connection surfaces of the upper and lower main electromagnets 11.

  An ion source 12 is provided above the main electromagnet 11, and a beam enters the accelerator 1 through a beam entrance through hole 115. The position where the beam is incident is located at a position different from the center of gravity of the main electromagnet 11. In addition, the ion source 12 may be arranged in the evacuated internal space 20 inside the main electromagnet 11.

  Next, the internal structure of the accelerator 1 will be described with reference to FIG. FIG. 3 shows a schematic sectional view of the accelerator.

  As shown in FIG. 3, the interior of the accelerator 1 includes a coil (main coil) 13, a return yoke 14, magnetic pole protrusions 121, 122, 123, and 124, an extraction septum electromagnet 40, and a beam extraction path (beam). (Emission path) 140, high-frequency accelerating cavities 21 and 22, and built-in coils 28 and 28A as beam separation devices.

  Inside the main electromagnet 11, there is a cylindrical internal space 20 formed by a cylindrical inner wall. In this internal space 20, an annular coil 13 is installed along the cylindrical inner wall. By passing a current through the coil 13, the main electromagnet 11 is magnetized, and a magnetic field is excited inside the main electromagnet 11 with a predetermined distribution.

  A cylindrical return yoke 14 is provided outside the coil 13.

  The magnetic pole protrusions 121, 122, 123, and 124 are formed inside the coil 13.

  In the accelerator 1, the beam circulates in the internal space 20 of the main electromagnet 11 to accelerate. The energy of the extracted beam ranges from a minimum of 70 MeV to a maximum of 235 MeV, and the orbital frequency of the beam is 19.82 MHz. Four sets of concave and convex magnetic poles are formed along the beam trajectory by the magnetic pole convex portions 121, 122, 123, and 124. The magnetic field acting on the beam is a low magnetic field in a concave portion and a high magnetic field in a convex portion. In this way, the strength of the magnetic field along the beam orbit and the average value of the magnetic field along the orbit are made proportional to the relativistic γ factor of the beam, thereby making the orbiting time of the orbiting beam constant regardless of the energy. The betatron oscillation stably occurs in the orbit plane of the beam and in a direction perpendicular to the orbit plane.

  In the accelerator 1 of the present embodiment, the beam is incident at an energy of about 30 keV from the incident point 130 on the exit side of the beam entrance through-hole 115. The incident beam is accelerated every time it passes through acceleration gaps 23 and 24 (see FIG. 8 and the like) inside the high-frequency acceleration cavities 21 and 22 described later. The accelerator 1 determines the beam trajectory so that the center of the trajectory of the beam moves in one direction on the same plane according to the acceleration of the beam. Accordingly, the magnetic pole shape and the coil arrangement are mirror-symmetric with respect to the center plane so that the in-plane component of the magnetic field becomes zero on the center plane. Further, since the magnetic field distribution needs to be symmetrical with respect to the axis AA ′ in the center plane, as a result, as shown in FIG. The portion 124 has a structure in which the magnetic pole protrusion 122 and the magnetic pole protrusion 123 are bilaterally symmetric. Further, the magnetic pole convex portion 121 and the magnetic pole convex portion 122 have a vertically asymmetric structure, and the magnetic pole convex portion 123 and the magnetic pole convex portion 124 have a vertically asymmetric structure. Due to such a configuration of the magnetic pole convex portions, the beam orbit of the accelerator 1 of the present embodiment is an eccentric orbit in which the orbital center is shifted from the center of the accelerator 1 as shown in FIG.

  The magnetic pole recess (valley) is provided with high-frequency accelerating cavities 21 and 22 for exciting a high-frequency electric field and a septum electromagnet 40 for taking out.

  The hollow high-frequency accelerating cavity 21 is disposed between the magnetic pole convex portion 121 and the magnetic pole convex portion 122, and the hollow high-frequency accelerating cavity 22 is disposed between the magnetic pole convex portion 123 and the magnetic pole convex portion 124. Have been. The high-frequency accelerating cavities 21 and 22 are arranged symmetrically with respect to the axis AA ', and a high frequency power supply (not shown) applies a high frequency from the outside. The high-frequency electrode 3 accelerates the ion beam extracted from the ion source 4 using the electric field generated by the high frequency.

  The high-frequency accelerating cavities 21 and 22 also incorporate the D electrode 25. Further, built-in coils 28 and 28A constituting a massless septum electromagnet are respectively built in the dee electrode 25, and generate a magnetic field in a direction perpendicular to the beam orbit plane in addition to the high-frequency electric field for acceleration. . The built-in coils 28 and 28A constitute a beam separation device that generates a deflection magnetic field for separating the beam from the beam orbit at a plurality of positions in the radial direction of the coil 13 and guiding the beam to the beam extraction path 140.

  Each of the magnetic pole protrusions 121, 122, 123, and 124 is provided with a trim coil (not shown) for fine adjustment of a magnetic field. The trim coil is provided before operation to ensure isochronism and stability of betatron oscillation. Adjust the magnetic field with.

  The extraction septum electromagnet 40 is an electromagnet for giving the beam a deflection necessary for placing the beam on a predetermined design trajectory on the beam extraction path 140. Specifically, the magnetic field is excited in a direction to cancel the magnetic field excited by the main electromagnet 11, and the beam is guided to the beam extraction path 140. Note that, instead of the take-out septum electromagnet 40, an electrostatic septum that deflects a beam with an electric field can be used.

  The beam extraction path 140 is a path for extracting a beam to the outside, and is configured by an extraction beam through hole 111 formed in the main electromagnet 11.

  Next, the configuration of the beam trajectory of the accelerator 1 of the present embodiment will be described. The trajectory of each energy beam is shown in FIG. In FIG. 4, the orbit of the orbit corresponding to 50 energies at a magnetic rigidity of 0.04 Tm from the maximum energy of 235 MeV is indicated by a solid line. The dotted line is a line connecting the same orbital phase of each orbit, and is called an isochronous line. The isochronous line is plotted for each rotation phase π / 18 from the aggregation area.

  As shown in FIG. 4, in the accelerator 1 of the present embodiment, the orbit centered on the vicinity of the ion incidence point in the low energy region of 50 MeV or less, similarly to the conventional AVF (azimuthally varying field) cyclotron. It has become. On the other hand, the orbits of energy larger than 50 MeV are most densely collected near the point of incidence of the extraction septum electromagnet 40. The area where the orbits are densely gathered is called an aggregation area. In the accelerator 1 of the present embodiment, the acceleration gap is set along the isochronous line.

  In order to generate the above-mentioned orbit configuration and stable betatron oscillation around the orbit, the accelerator 1 of the present embodiment uses a magnetic field distribution in which the minimum and maximum of the magnetic field appear four times per revolution along the beam orbit. Has adopted. FIG. 5 shows the magnetic field distribution along the orbit. FIG. 5 shows the magnetic field distribution along the orbits of 235 MeV, 200 MeV, 150 MeV, 70 MeV, and 7.5 MeV, respectively. It is.

  As shown in FIG. 5, while increasing the average magnetic field with respect to energy, by appropriately setting the amplitude, even in an eccentric orbit arrangement such as the accelerator 1 of the present embodiment, a magnetic field that is isochronous and betatron-oscillates A distribution can be realized.

  FIG. 6 shows the magnetic field distribution on the center plane as an isomagnetic field diagram. In FIG. 6, the interval between the maximum magnetic field of 2.2T and the minimum magnetic field of 0.86T is represented by isomagnetic field lines in 32 steps. The circles indicated by broken lines in FIGS. 3, 4 and 6 are circles having a radius of 1494 mm, and contain the orbit of the total energy.

  FIG. 7 shows the results of evaluating the betatron frequency (tune) around the orbit under the above conditions. The tune was calculated based on the magnetic field gradient obtained from the orbital magnetic field and the magnetic field of the energy before and after.

  As shown in FIG. 7, it was found that the horizontal tune was almost 1 at low energy, and increased with acceleration. It was also found that the tune in the direction perpendicular to the orbital plane (vertical tune) is almost 0 at low energy, and exists in the range of 0 or more and less than 0.5 in the entire energy region.

  From these results, especially when the beam has low energy and the horizontal tune is close to 1, the horizontal displacement of the beam at a position 90 degrees away from the position where the beam was kicked, that is, when the beam circulates 1/4 turn, It turns out that it becomes the maximum. Therefore, the built-in coils 28 and 28A constituting the massless septum electromagnet as the beam departure device are arranged inside the high frequency accelerating cavities 21 and 22 which are respectively installed in two valleys 90 degrees away from the converging area where the beam is taken out. Thus, it can be seen that the beam that has been kicked by the deflection magnetic field generated by the built-in coils 28 and 28A is in a state where the maximum displacement can be obtained in the converging region. That is, it is understood that the magnetomotive force required for the massless septum electromagnet can be small.

  Next, the structure of the high-frequency acceleration cavities 21 and 22 will be described with reference to FIGS. FIG. 8 shows the internal structure of the high-frequency acceleration cavity 22.

  By supplying high-frequency power to the high-frequency acceleration cavity 22 from the outside, a high-frequency electric field is formed in the acceleration gaps 23 and 24 formed between the cavity outer wall 29 and the dee electrode 25. A beam through-hole is provided in the cavity outer wall 29 near the acceleration gaps 23 and 24 (not shown). The beam is accelerated by passing through the acceleration gaps 23 and 24 at an appropriate high-frequency electric field phase. The dee electrode 25 is supported by hollow cylindrical stems 26 and 27. The high-frequency acceleration cavity 22 has a vertically symmetric structure with respect to the beam orbit plane.

  The high-frequency acceleration cavity 21 also has a symmetrical structure with respect to the high-frequency acceleration cavity 22, and has a vertically symmetric structure with respect to the beam orbit plane. In the high-frequency accelerating cavity 21 as well, by supplying high-frequency power from the outside, acceleration gaps 23 and 24 are formed between the cavity outer wall 29 and the D electrode 25, and the beam is accelerated.

  FIG. 9 is a cross-sectional view of the high-frequency accelerating cavity 22 when the D-electrode 25 side is viewed from the beam orbit plane. As shown in FIG. 9, a built-in coil 28 is arranged in the dee electrode 25, and is connected to the dee electrode 25 via an insulator.

  The built-in coil 28 installs a plurality of current paths (coils 28a, 28c, 28e, 28g, 28i,...) Formed using, for example, hollow conductors (air-core wires) in a direction substantially parallel to the beam orbit. And a so-called massless septum electromagnet. Although five coils are shown in FIG. 9 for convenience of illustration, the number of provided coils is not limited to five, and a desired number of coils can be provided.

  By passing a current to an arbitrary coil among the plurality of coils 28a, 28c, 28e, 28g, 28i,..., It is possible to locally generate a deflection magnetic field near the beam orbit of the corresponding energy. As a result, the application region of the magnetic field is localized, only the beam of a specific energy is kicked, the beam is shifted from a predetermined design trajectory, and the beam can be efficiently introduced into the extraction septum electromagnet 40.

  FIG. 10 is a sectional view taken along the line B-B 'of FIG. The lead wire 30 of each of the coils 28a, 28c, 28e, 28g, 28i,... Of the built-in coil 28 is guided to the outside of the high-frequency acceleration cavity 22 through the inside of the stems 26, 27, and is connected to a power supply and a water cooling device. . The hollow conductor forming the built-in coil 28 is water-cooled by flowing cooling water therein, so that not only the heat generated by the built-in coil 28 itself but also the heat generated by the D electrode 25 can be cooled.

  As shown in FIG. 11, a plurality of current paths (coils 28b, 28d, 28f, 28h, 28j,...) Formed using hollow conductors inside the dee electrode 25 are also beamed inside the high-frequency acceleration cavity 21. A built-in coil 28A installed in a direction substantially parallel to the track is arranged. The polarity of the deflection magnetic field generated by the built-in coil 28 </ b> A disposed in the high-frequency acceleration cavity 21 is opposite to the polarity of the deflection magnetic field generated by the built-in coil 28 disposed in the high-frequency acceleration cavity 22. As a result, the variation of the BL product from the isochronous magnetic field is offset, and the isochronism is maintained for a longer time. Therefore, even if the intensity of the deflecting magnetic field is weak, the beam can be extracted by kicking after making multiple revolutions in the accelerator 1. FIG. 11 is a cross-sectional view of the high-frequency accelerating cavity 21 when the D electrode 25 is viewed from the beam orbital plane. Although five coils are shown for convenience of illustration, the number of coils provided is not limited to five. Any desired number of coils can be provided.

  The lead wires 30 of the coils 28b, 28d, 28f, 28h, 28j,... Of the built-in coil 28A are also guided to the outside of the high-frequency accelerating cavity 21 through the inside of the stems 26, 27, and a power supply and a water cooling device (both not shown) )It is connected to the. The hollow conductor forming the built-in coil 28A can also simultaneously cool the heat generated in the built-in coil 28A and the D electrode 25 by water-cooling the inside.

  In addition, in the built-in coil 28 shown in FIG. 9 and the built-in coil 28A shown in FIG. 11, the beam trajectory of the corresponding energy may be left-right symmetric, or the coils 28c and 28b may be different from the coils 28e and 28d. The coils 28g and 28f may be left and right asymmetric with the coils 28i and 28h shifted one by one so as to correspond to each other.

  The built-in coils 28 and 28A have an air-core structure so as not to disturb the main magnetic field distribution. In this case, the rise time of the deflecting magnetic field 31 can be shorter than when an iron core is inserted. Suitable for cases where energy switching is required. However, as the rise time of the current flowing through the built-in coils 28 and 28A is shortened, a large eddy current is generated near the skin of the D electrode 25, and there is a concern that the response of the deflection magnetic field 31 is delayed. For this reason, in order to cut off only the eddy current without interrupting the high-frequency current, a slit 25a as shown in FIG. At least one slit 25a can be provided on the surface of the D electrode 25.

  Since the high-frequency electromagnetic field is shielded inside the dee electrode 25 except for the vicinity of the acceleration gaps 23 and 24, the amount of the high-frequency current leaking out of the high-frequency acceleration cavities 21 and 22 through the built-in coils 28 and 28A is small. Usually this is not a problem. However, for the purpose of passing low-frequency coil current but not passing high-frequency waves such as acceleration RF (leakage to the outside), as shown in FIG. 10, between the lead wire 30 of the built-in coils 28 and 28A and the power supply. By additionally providing the high frequency filter 33, the amount of leakage of the high frequency current can be further reduced. The high-frequency filter 33 can be a very common low-pass filter formed by a series inductor or a combination of a series inductor and a parallel capacitor.

  Next, effects of the present embodiment will be described.

  The above-described particle beam irradiation apparatus 100 of the present embodiment includes the accelerator 1 and the irradiation apparatus 70 that irradiates the beam emitted from the accelerator 1. The accelerator 1 faces the annular coil 13 and faces each other. Two main electromagnets 11 that form a magnetic field therebetween, high-frequency accelerating cavities 21 and 22 for accelerating the beam, and a D electrode 25; a beam extraction path 140 for extracting the beam to the outside; And a beam departure device comprising built-in coils 28 and 28A arranged to generate a deflection magnetic field for deviating the beam from the beam orbit at a plurality of positions in the radial direction of the coil 13 and guiding the beam to the beam extraction path 140. Things. Then, a beam of at least one kind of energy is extracted from such an accelerator 1.

  With such a configuration, a beam having a predetermined energy can be continuously extracted by the deflection magnetic field generated by the built-in coils 28 and 28A arranged in the D electrode 25 in the high-frequency acceleration cavities 21 and 22. Therefore, a beam having a predetermined energy can be continuously obtained without providing an extra configuration such as a degrader on the beam trajectory. Therefore, it is possible to obtain the accelerator 1 having no problems such as a reduction in beam use efficiency, an increase in the beam size, an increase in unnecessary two o'clock particles, and an increase in the size of the accelerator 1. Further, since the high-frequency accelerating cavities 21 and 22 have the functions of accelerating and extracting the beam, the effect of contributing to space saving of the accelerator 1 is also achieved.

  Here, as a method of extracting beams of various energies without using a foil as in a degrader or Patent Document 1, a method disclosed in WO 2016/092622 is proposed. The accelerator used in this method is the same as a conventional AVF cyclotron in that it has a main electromagnet magnetic pole having a concavo-convex shape. The main magnetic field distribution is adjusted so that the beam orbit is focused at the entrance of the beam exit path. Then, a bending electromagnet device is installed as a beam departure device in the main electromagnet magnetic pole recess (valley) located on the opposite side of the entrance of the beam emission path by 180 degrees, and control is performed so that the deflection magnetic field acts only on the beam orbit of the specific energy. I have.

  With an accelerator as described in WO 2016/092622, only a beam of that energy is extracted from the beam exit path. Since the beam is extracted from the orbital focusing portion in this way, there is an advantage that the amount of horizontal movement of the beam at the time of extraction is smaller than that of the conventional cyclotron.

  However, in the configuration of WO 2016/092622 described above, the betatron frequency (horizontal tune) in the direction parallel to the beam orbital plane is a value close to 1 particularly in the low energy region, so that the 180 Even if the beam is perturbed at a position on the opposite side, the maximum horizontal movement of the beam is at a position approximately 90 degrees before the entrance of the beam exit path. Therefore, there is a problem that extra magnetic field strength of the bending electromagnet is required because the magnetic field cannot be extracted at a position where the maximum movement amount can be obtained.

  In addition, since the bending electromagnet for extracting a beam needs to be installed in a narrow gap between the main electromagnet poles, it is difficult to increase the size and the magnetic field strength tends to be insufficient. For this reason, it is difficult to extract the beam in half a circle after operating the bending electromagnet. On the other hand, it is easier to take out by kicking a plurality of times with the deflection magnetic field while making multiple rounds, and such measures can be taken. However, if the deflection electromagnet for extracting the beam is installed at one place, the isochronous condition is lost due to the deflection magnetic field. I regret that it will be difficult to obtain.

  However, in the accelerator 1 of the present embodiment, a beam of a predetermined energy is extracted by the built-in coils 28 and 28A disposed in the D electrode 25 in the high-frequency acceleration cavities 21 and 22. Therefore, a deflection magnetic field coil having a small magnetomotive force is used. In addition, the intensity of the deflecting magnetic field for extraction can be kept low, and a beam having a wide range of energy can be continuously extracted with high efficiency while satisfying the isochronous condition.

  Further, since the built-in coils 28 and 28A are massless septum electromagnets using air-core wires, the rise time of the deflecting magnetic field 31 can be shortened as compared with the case where an iron core is inserted without disturbing the main magnetic field distribution. This makes it possible to provide an accelerator suitable for a particle beam irradiation apparatus that requires high-speed energy switching such as scanning irradiation. Further, since the inside can be water-cooled, not only the heat generation of the built-in coil 28 itself but also the heat generation of the D electrode 25 can be cooled, and efficient cooling can be achieved.

  Further, a plurality of built-in coils 28 and 28A are installed inside the dee electrode 25, and lead wires 30 of the built-in coils 28 and 28A are guided to the outside of the high-frequency accelerating cavities 22 and 21 through the insides of the stems 26 and 27 supporting the dee electrode 25. As a result, it is possible to easily and continuously extract a beam having a predetermined energy easily without providing an extra configuration such as a degrader on the beam trajectory while saving space.

  Further, since the orbit of the beam is an eccentric orbit whose center of rotation is deviated from the center of the accelerator 1, the orbits of the orbiting beams are concentrated in the consolidation area. The magnetic field can be deflected to the extraction septum electromagnet 40, and the extraction becomes very easy. In particular, since the interval between the beam orbits in the converging region is narrower than in the past, even when the energy of the ion beam is wide, the magnetic field generated by the built-in coils 28 and 28A allows the ion beam of a predetermined energy to be used. The beam can be stably and easily deflected toward the extraction septum electromagnet 40 on the converging area side.

  In an accelerator, the entrance of a high-frequency accelerating cavity or a beam exit path is generally arranged in a magnetic pole recess (valley) having a sufficient space. Therefore, the high-frequency accelerating cavities 21 and 22 are installed symmetrically by arranging the high-frequency accelerating cavities 22 and 21 at positions 90 degrees ahead and 90 degrees along the beam traveling direction from the entrance of the beam extraction path 140, The orbiting beam can be kicked, and the beam can be extracted at a position where the maximum beam movement is obtained when the horizontal tune is close to 1. Therefore, a beam can be more efficiently extracted even with a smaller deflection magnetic field intensity.

  Further, by reversing the polarity of the deflection magnetic field generated by the built-in coil 28 in the high-frequency acceleration cavity 22 and the polarity of the deflection magnetic field generated by the built-in coil 28A in the high-frequency acceleration cavity 21, the BL from the isochronous magnetic field is reduced. The product fluctuation is canceled, and the isochronism can be kept longer. Therefore, even if the intensity of the deflecting magnetic field is weak, the beam can be extracted by making a plurality of rounds and kicking.

  Further, since the D electrode 25 is provided with the slit 25a in the radial direction of the coil 13, even if an eddy current is generated on the surface of the D electrode 25, it can be cut off. Even if the rise time of the supplied current is shortened, it is possible to suppress a delay in the response of the deflection magnetic field 31.

  Further, by providing a high frequency filter 33 between the power supply of the built-in coils 28 and 28A and the lead wire 30, the amount of the high-frequency current leaking to the outside of the high-frequency acceleration cavities 21 and 22 through the built-in coils 28 and 28A is reduced. It can be further reduced.

  Further, by taking out the beam after rotating the inside of the accelerator 1 a plurality of times after the application of the deflecting magnetic field, it is possible to more easily take out the beam having the predetermined energy even if the deflecting magnetic field intensity is weak.

<Others>
The above embodiment is merely an example, and has been described in detail for easy understanding of the present invention, and is not intended to limit the contents of the invention to the above specific embodiments. The invention itself can be modified into various forms other than the above embodiment.

  For example, in the present embodiment, a case where a total of four magnetic pole protrusions 121, 122, 123, and 124 are used has been described as an example, but there is no limitation as long as the number of magnetic poles is two or more.

  Further, the beam detachment device is arranged in the high-frequency acceleration cavities 21 and 22 for accelerating the beam, but the beam detachment device can be further arranged in the accelerator 1. For example, a massless septum electromagnet can be further disposed in a magnetic pole concave portion between the magnetic pole convex portion 122 and the magnetic pole convex portion 123, and a massless septum electromagnet can be disposed in another place.

DESCRIPTION OF SYMBOLS 1 ... Accelerator 11 ... Main electromagnet 12 ... Ion source 13 ... Coil (main coil)
14 Return yoke 20 Internal spaces 21 and 22 High-frequency accelerating cavities 23 and 24 Acceleration gap 25 Dee electrode 25a Slits 26 and 27 Stems 28 and 28A Built-in coils 28a, 28b, 28c, 28d, 28e, 28f , 28g, 28h, 28i, 28j Coil 29 Cavity outer wall 30 Lead wire 31 Bending magnetic field 33 High frequency filter 40 Extraction septum electromagnet 60 Beam transport system 70 Irradiation device 80 Control device 90 Treatment table 95 ... Patient 100... Particle beam irradiation device 111. Extraction beam penetration 112. Coil connection penetration 114. High-frequency power input penetration 115. Beam incidence penetrations 121, 122, 123, 124. Incident point 140: Beam extraction path (beam emission path)

Claims (11)

An annular main coil,
Two iron cores installed opposite each other and forming a magnetic field between them,
An electrode for accelerating the beam,
A beam exit path for extracting the beam to the outside,
A beam detachment device that is disposed in the electrode and includes a built-in coil that generates a deflection magnetic field for detaching the beam from a beam orbit at a plurality of positions in the radial direction of the main coil and guiding the beam to the beam emission path. An accelerator comprising: The accelerator according to claim 1,
The accelerator according to claim 1, wherein the built-in coil is a massless septum electromagnet using an air-core wire. The accelerator according to claim 2,
The electrode is composed of a high-frequency accelerating cavity and a Dee electrode,
A plurality of the built-in coils are installed inside the dee electrode,
An accelerator, wherein a lead wire of the built-in coil is guided to the outside of the high-frequency acceleration cavity through the inside of a stem supporting the dee electrode. The accelerator according to claim 1,
The beam orbital trajectory is an eccentric orbit in which a circling center is deviated from a center of the accelerator. The accelerator according to claim 1,
The accelerator, wherein the electrode is disposed at a position 90 degrees before and 90 degrees along a beam traveling direction from an entrance of the beam exit path. The accelerator according to claim 5,
The accelerator according to claim 1, wherein the built-in coil in the electrode has a polarity of the deflection magnetic field generated opposite to that of the generated deflection magnetic field. The accelerator according to claim 3,
The accelerator, wherein the dee electrode is provided with a slit in a radial direction of the main coil. The accelerator according to claim 3,
An accelerator, wherein a high-frequency filter is further provided between a power supply of the built-in coil and the lead wire. An accelerator according to claim 1;
And an irradiation device for irradiating the beam emitted from the accelerator. A method for extracting a beam from an accelerator,
A method for extracting a beam, comprising: extracting a beam of at least one kind of energy from the accelerator according to claim 1. The method for extracting a beam according to claim 10,
A method for extracting a beam, comprising: after applying the deflection magnetic field, extracting the beam after orbiting the inside of the accelerator a plurality of times.

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