Abstract:
The accelerator includes a circular vacuum container which contains a circular return yoke. With respect to the central axis of the vacuum container, an incidence electrode is arranged towards the entrance of a beam emission path inside of the return yoke. Inside of the return yoke, electrodes are arranged radially from the incidence electrode in the periphery of the incidence electrode. Recesses are arranged alternately with the electrodes in the circumferential direction of the return yoke. In the vacuum container, an orbit-concentric region is formed in which multiple beam orbits centered on the incidence electrode are present, and, in the periphery of said region, an orbit-eccentric area is formed in which multiple beam orbits eccentric to the incidence electrode are present. In the orbit-eccentric region, the beam orbits between the incidence electrode and the entrance to the beam emission path are denser.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an accelerator and a particle beam irradiation system, particularly, to an accelerator and a particle beam irradiation system suitable for cancer treatment. 
       BACKGROUND ART 
       [0002]    A particle beam irradiation system can be roughly classified into a particle beam irradiation system (for example, refer to PTL 1) including a synchrotron as an accelerator, and a particle beam irradiation system (for example, refer to PTL 2) including a cyclotron as an accelerator. 
         [0003]    A particle beam irradiation system including a synchrotron includes an ion source; a linear accelerator; a synchrotron; a beam transport; a rotating gantry; and an irradiation apparatus. The synchrotron includes an annular beam duct, and the beam duct is provided with multiple bending magnets, multiple quadrupole magnets, a radiofrequency acceleration cavity, an extraction radiofrequency electrode, and an extraction deflector. The ion source is connected to the linear accelerator, and the linear accelerator is connected to the synchrotron. A portion of the beam transport, which is connected to an extraction port of the synchrotron, is installed in the rotating gantry, and communicates with the irradiation apparatus installed in the rotating gantry. 
         [0004]    Ions (for example, protons or carbon ions) extracted from the ion source are accelerated by the linear accelerator. An ion beam generated by the linear accelerator is injected into the annular beam duct of the synchrotron. The ion beam turning through the beam duct is accelerated to a predetermined energy in the radiofrequency acceleration cavity to which a radiofrequency voltage is applied. A radiofrequency voltage is applied from a radiofrequency electrode of the extraction radiofrequency electrode to the ion beam which has turned around and reached the predetermined energy, thereby extracting the ion beam to the beam transport via the extraction deflector. A tumor volume of a patient on a treatment bed is irradiated with the ion beam from the irradiation apparatus. The rotating gantry rotates the irradiation apparatus such that a beam path of the irradiation apparatus coincides with an irradiation direction of the ion beam toward the target volume. 
         [0005]    In a case where the target volume is divided into multiple layers in an irradiation direction of an ion beam, and each layer is scanned with an ion beam, a layer to which an ion beam has to reach is specified by changing the energy of the ion beam. As described above, the energy of an ion beam is adjusted by controlling the pattern of a radiofrequency voltage applied to the radiofrequency acceleration cavity, an excitation pattern of the quadrupole magnets, and an excitation pattern of the bending magnets. The scanning of the inside of each layer with an ion beam is controlled by adjusting an excitation current of an operation magnet provided in the irradiation apparatus. 
         [0006]    A particle beam irradiation system including a cyclotron includes an ion source; a cyclotron; a beam transport; a rotating gantry; and an irradiation apparatus. The cyclotron includes a vacuum chamber formed of a pair of facing iron cores having a circular section; a radiofrequency acceleration apparatus; and an extraction magnet. The beam transport communicates with an extraction portion of the cyclotron in which the extraction magnet is disposed. The beam transport, the rotating gantry, and the irradiation apparatus of the particle beam irradiation system including a cyclotron have substantially the same structures of those of the particle beam irradiation system including a synchrotron. 
         [0007]    In the particle beam irradiation system including a cyclotron, ions (for example, protons or carbon ions) extracted from the ion source are injected to the center of a section of the iron cores of the cyclotron, and are accelerated by the radiofrequency acceleration apparatus. An accelerated ion beam turns in a spiral pattern from the center of the iron cores toward an inner surface of a return yoke, and is extracted to the beam transport by the extraction magnet provided in a peripheral portion of the iron cores. A tumor volume of a patient on a treatment bed is irradiated with the extracted ion beam from the irradiation apparatus via the beam transport. 
         [0008]    As described above, in a case where the target volume is divided into multiple layers, and each layer is scanned with an ion beam using the particle beam irradiation system including a cyclotron, the energy of an ion beam extracted to the beam transport is adjusted by using a degrader provided in the beam transport. The degrader is formed of a single metal plate or a combination of multiple metal plates having different thicknesses. The degrader reduces the energy of an ion beam passing through the degrader, that is, adjusts the energy of an ion beam with which the target volume is irradiated. Since the energy of an ion beam accelerated by the cyclotron typically is constant, the energy of an ion beam is increased to the maximum energy required for cancer treatment by the cyclotron, the energy is dampened and adjusted to a predetermined energy when the ion beam penetrates through a metal plate provided in the degrader. 
         [0009]    PTL 3 discloses a cyclotron that is used in this type of particle beam irradiation system and is capable of improving ion beam extraction efficiency. The cyclotron includes a pair of magnetic poles between which ion beam turning trajectories are formed, which includes multiple protrusions and multiple recessions which are alternately disposed in a circumferential direction, and by which hill regions are formed interposed between the protrusions and valley regions are formed interposed between the recessions along the turning trajectories; dee electrodes which are provided in the valley regions; and an acceleration cavity that is disposed in at least one valley region other than the valley regions in which the dee electrodes are provided, and on an outer circumferential side in a radial direction of the ion beam turning trajectories, and accelerates an ion beam. In the cyclotron in which the acceleration cavity is provided in addition to the dee electrodes so as to accelerate an ion beam, a turn separation is increased by an increase in the amount of energy increase per one turn of an ion beam, and ion beam extraction efficiency is improved. 
         [0010]    PTL 4 discloses a charged particle beam irradiation method in which a tumor volume is divided into multiple layers from a body surface of a patient in an irradiation direction of an ion beam, and multiple irradiation points inside each layer are irradiated with ion beams by scanning the multiple irradiation points with fine ion beams. An ion beam is moved to an adjacent irradiation point inside a layer by controlling a scanning magnet provided in an irradiation apparatus. An ion beam is moved from a distal layer to a proximal layer by changing the energy of an ion beam. A Bragg peak (to be described later) of an ion beam reaches a distal position of a target volume by the extent of the increase in the energy of the ion beam. In a case where the patient is irradiated with an ion beam, a dose distribution illustrated in FIG. 3 of PTL 4 is obtained in a depth direction from the body surface of the patient, a dose reaches the maximum value at a Brigg peak, and the dose distribution is rapidly decreased at a depth at which the Bragg peak is exceed. Cancer treatment via ion beams uses properties in which a dose reaches the maximum value at a Bragg peak and is rapidly decreased at a depth at which the Bragg peak is exceeded. 
         [0011]    In a particle beam irradiation system disclosed in PTL 5, a circular accelerator which extracts ion beams is attached to a rotating frame which rotates in a vertical position, and a beam transport chamber is provided to guide ion beams, which are extracted from the accelerator, to a treatment room. The beam transport chamber is connected to an extraction port of the accelerator. The beam transport chamber extends in a radial direction of the accelerator, is bent toward a horizontal direction, and reaches a position directly above the treatment room, and thereafter, the beam transport chamber is bent downward. A beam delivery system is attached to a tip end portion of the beam transport chamber. The treatment room is formed inside a radiation enclosure, and a patient to be irradiated with ion beams lies on a treatment bed installed inside the treatment room. A side wall of the radiation enclosure is disposed between the accelerator and the treatment room. A target volume of the patient on the treatment bed is irradiated with ion beams which are extracted from the circular accelerator and transported via the beam transport chamber and the beam delivery system. In order to change an irradiation direction of an ion beam, the direction of the beam delivery system is changed by rotating the accelerator via rotation of the rotating frame, and turning the beam transport chamber and the beam delivery system around a rotational center of the accelerator. 
       CITATION LIST 
     Patent Literature 
       [0012]    PTL 1: JP-A-2004-358237 
         [0013]    PTL 2: JP-A-2011-92424 
         [0014]    PTL 3: JP-A-2014-160613 
         [0015]    PTL 4: JP-A-10-118204 
         [0016]    PTL 5: Japanese Patent No. 3472657 
         [0017]    PTL 6: JP-A-2006-239403 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0018]    The particle beam irradiation system using a synchrotron is capable of generating multiple ion beams of different energies in the synchrotron, and changing the energies of the ion beams extracted from the synchrotron. In contrast, the particle beam irradiation system using a synchrotron requires the multiple bending magnets and the multiple quadrupole magnets, it is not easy to reduce the size of the synchrotron to a certain size or smaller. Ion beams are intermittently extracted from a synchrotron, and the amount of extraction of ion beams is small. 
         [0019]    In contrast, a cyclotron is capable of continuously extracting ion beams, and the amount of extraction of ion beams is large. The energy of an ion beam generated in the cyclotron is constant, and the cyclotron is not capable of extracting ion beams of energies lower than the maximum energy. For this reason, in a case where ion beams of low energies are required, for example, in a case where one layer of a target volume is irradiated with ion beams, it is necessary to adjust the energies of ion beams via the degrader provided in the beam transport such that the ion beams reach that layer. The use of the degrader to adjust the energy of an ion beam causes problems such as an increase in the beam size of an ion beam caused by the degrader, a reduction in the number of ions penetrating through the metal plates of the degrader, and an increase in radioactive waste. 
         [0020]    For this reason, a proton beam therapy system is desirable to be able to continuously extract ion beams of different energies and to improve ion beam extraction efficiency. 
         [0021]    An object of the present invention is to provide an accelerator and a particle beam irradiation system which are capable of efficiently extracting ion beams of different energies. 
       Solution to Problem 
       [0022]    According to characteristics of the present invention, in order to achieve this object, an accelerator includes an annular main coil; multiple magnetic poles configured to form isochronous magnetic fields; and an acceleration electrode configured to accelerate ions. An ion injection portion, into which the ions are injected, is disposed at a position that is different from the position of the center of gravity of the main coil in a radial direction. 
         [0023]    Since the ion injection portion is disposed at the position that is different from that of the center of gravity of the main coil in the radial direction, gaps between multiple adjacent annular beam turning trajectories formed at the periphery of the ion injection portion are wide in a region opposite to an inlet of a beam extraction path relative to the ion injection portion compared to those in a region that is closer to the inlet of the beam extraction path than the ion injection portion. For this reason, in the region in which gaps between adjacent beam turning trajectories are wide and which is positioned opposite to the inlet of the beam extraction path, it is possible to easily separate ion beams from respective beam turning trajectories, and to efficiently extract ion beams of different energies which turn along respective annular beam turning trajectories. 
         [0024]    Also, in an accelerator including a pair of iron cores which are installed to face each other and between which isochronous magnetic fields are formed; and an acceleration electrode configured to accelerate injected ions, in which an ion injection portion, into which the ions are injected, is disposed at a position that is different from the position of the center of the iron cores in a radial direction, it is possible to achieve this object. 
         [0025]    Since the ion injection portion is disposed at the position that is different from that of the center of the iron core in the radial direction, gaps between multiple adjacent annular beam turning trajectories formed at the periphery of the ion injection portion are wide in a region opposite to an inlet of a beam extraction path relative to the ion injection portion compared to those in a region that is closer to the inlet of the beam extraction path than the ion injection portion. For this reason, in the region in which gaps between adjacent beam turning trajectories are wide and which is positioned opposite to the inlet of the beam extraction path, it is possible to easily separate ion beams from respective beam turning trajectories, and to efficiently extract ion beams of different energies which turn along respective annular beam turning trajectories. 
         [0026]    Also, in an accelerator including an annular main coil; magnetic poles configured to form isochronous magnetic fields; and multiple acceleration electrodes configured to accelerate ions, in which the multiple acceleration electrodes are installed to extend from the position of an inner surface of the main coil toward the inside of the main coil, and in which a tip end portion of a portion of each of the multiple acceleration electrodes, which extends away from the inner surface of the main coil from the position of the inner surface of the main coil and is positioned inside the main coil, is disposed at a position that is different from the position of the center of gravity of the main coil in a radial direction, it is possible to achieve this object. 
         [0027]    Since the tip end portion of a portion of each of the multiple acceleration electrodes, which extends away from the inner surface of the main coil from the position of the inner surface of the main coil and is positioned inside the main coil, is disposed at the position that is different from the position of the center of gravity of the main coil in the radial direction, gaps between multiple adjacent annular beam turning trajectories, which are formed at the periphery of the position at which the respective tip end portions of the multiple acceleration electrodes are disposed, are wide in a region opposite to an inlet of a beam extraction path relative to the ion injection portion compared to those in a region that is closer to the inlet of the beam extraction path than the ion injection portion. For this reason, in the region in which gaps between adjacent beam turning trajectories are wide and which is positioned opposite to the inlet of the beam extraction path, it is possible to easily separate ion beams from respective beam turning trajectories, and to efficiently extract ion beams of different energies which turn along respective annular beam turning trajectories. 
         [0028]    Also, in an accelerator including a pair of iron cores which are installed to face each other and between which magnetic fields are formed; and an acceleration electrode configured to accelerate ions, in which the iron core forms multiple protrusions, and in which the multiple protrusions are formed in the iron core in such a way as to extend from an outer circumference of the iron core toward a position that is different from the position of the center of gravity of the iron core in a radial direction, it is possible to achieve this object. 
         [0029]    Since the multiple protrusions are installed to extend from the outer circumference of the iron core toward the position that is different from the position of the center of gravity of the iron core in the radial direction, gaps between multiple adjacent annular beam turning trajectories, which are formed at the periphery of the position at which the respective tip end portions of the multiple protrusions are disposed and is different from the center of gravity of the iron core in the radial direction, are wide in a region opposite to an inlet of a beam extraction path relative to the ion injection portion compared to those in a region that is closer to the inlet of the beam extraction path than the ion injection portion. For this reason, in the region in which gaps between adjacent beam turning trajectories are wide and which is positioned opposite to the inlet of the beam extraction path, it is possible to easily separate ion beams from respective beam turning trajectories, and to efficiently extract ion beams of different energies which turn along respective annular beam turning trajectories. 
         [0030]    (A1) Hereinafter, a more preferable configuration of an accelerator, in which an ion injection portion, into which ions are supplied from an ion source, is disposed at a position that is different from that of the center of gravity or a central axis of a main coil in a radial direction, each of a pair of iron cores extends radially from the ion injection portion at the periphery of the ion injection portion, forms multiple magnetic poles, a tip end of each of which faces the ion injection portion, and forms multiple recessions which extend radially from the ion injection portion at the periphery of the ion injection portion, the magnetic poles and the recessions are alternately disposed at the periphery of the ion injection portion, and the main coil surrounds the multiple magnetic poles and the multiple recessions which are disposed inside each of the iron core, will be described. 
         [0031]    (A2) Preferably, according to (A1), in each of the pair of iron cores, in regions which are positioned on a plane perpendicular to a central axis of the main coil and on both sides of a straight line that connects an inlet of a beam extraction path to the central axis of the main coil, each of radiofrequency acceleration electrodes is disposed between magnetic poles which are adjacent to each other in a circumferential direction of the main coil among the multiple magnetic poles disposed on each of both sides of the straight line and on the plane perpendicular to the central axis. Preferably, respective tip ends of the radiofrequency acceleration electrodes face the ion injection portion, and each of the radiofrequency acceleration electrodes has bent points. Preferably, a portion of each of the radiofrequency acceleration electrodes between the bent points of the radiofrequency acceleration electrode and an end surface of the radiofrequency acceleration electrode facing the main coil is bent toward a first recession which is one of recessions positioned between magnetic poles adjacent to each other in the circumferential direction of the main coil and which is present 180° opposite to the inlet of the beam extraction path. 
         [0032]    (A3) Preferably, according to (A1), a beam current measuring apparatus, which is disposed in the first recession, includes a beam current measuring unit that is disposed in the first recession, in a beam turning region formed between the pair of iron cores, and a trajectory plane on which beam turning trajectories are formed and which is perpendicular to the central axis of the main coil; a movement apparatus that moves the beam current measuring unit on the trajectory plane in the radial direction of the main coil; and a position detector that detects the position of the beam current measuring unit to be moved on the trajectory plane. 
         [0033]    (A4) Preferably, according to (A1), the accelerator includes a first control apparatus (for example, a coil current control apparatus) that controls an excitation current supplied to each of trim coils which are respectively attached to the multiple magnetic poles, when a beam turning trajectory, which is measured by the beam current measuring apparatus disposed in the first recession, is not positioned at a predetermined position. 
         [0034]    (B1) Hereinafter, a more preferable configuration of an accelerator, which includes a beam separation apparatus that separates ion beams from respective beam turning trajectories at multiple positions in a radial direction of a main coil, will be described. 
         [0035]    (B2) Preferably, according to (B1), the accelerator further includes a pair of iron cores that are joined together in a state where a beam turning region, on which beam turning trajectories, along which ion beams respectively turn, are formed, is interposed therebetween; main coils which are respectively disposed inside the pair of iron cores; and a beam path that passes through the iron core and is an extraction port of an ion beam, in which an ion injection portion, to which ions are supplied from an ion source and around which the beam turning region is formed, is disposed at a position that is different from the center of the main coil in the radial direction. 
         [0036]    (B3) Preferably, according to (B2), multiple magnetic poles and multiple recessions are formed in each of the pair of iron cores, are alternately disposed to surround the ion injection portion, and a bending magnet apparatus which is a beam separation apparatus is disposed in one recession to face the ion injection portion. 
         [0037]    (B4) Preferably, according to (B3), the bending magnet apparatus is disposed in a first recession which is one of the recessions and is positioned 180° opposite to an inlet of a beam extraction path relative to the ion injection portion. 
         [0038]    (B5) Preferably, according to (B4), a movement apparatus is provided to move the bending magnet apparatus. 
         [0039]    (B6) Preferably, according to (B3), a beam current measuring apparatus, which is disposed in the recession in which the bending magnet apparatus is disposed, includes abeam current measuring unit that is disposed in the recession, in the beam turning region formed between the pair of iron cores, and a trajectory plane on which beam turning trajectories are formed and which is perpendicular to a central axis of the main coil; a movement apparatus that moves the beam current measuring unit on the trajectory plane in the radial direction of the main coil; and a position detector that detects the position of the beam current measuring unit to be moved on the trajectory plane. 
         [0040]    (B7) Hereinafter, a more preferable configuration of a particle beam irradiation system, which includes the accelerator in (B2) and an irradiation apparatus that outputs ion beams extracted from the accelerator, will be described. 
         [0041]    (B8) Preferably, according to (B7), the particle beam irradiation system includes a rotation apparatus that rotates the irradiation apparatus; a first control apparatus (for example, a rotation control apparatus) that controls rotation of the rotation apparatus so as to set a beam axis of the irradiation apparatus to be aligned with an irradiation direction of ion beams to a target for beam irradiation; and a second control apparatus (for example, a massless septum control apparatus) that, in order to irradiate a layer of multiple layers, into which the target for beam irradiation is divided in the irradiation direction, with an ion beam of an energy required to reach the layer, controls the movement apparatus such that a pair of facing magnetic poles of the bending magnet apparatus to be excited are positioned on a beam turning trajectory along which an ion beam of the energy turn, and that controls a power supply such that the pair of magnetic poles to be excited are excited. 
         [0042]    (C1) Hereinafter, a more preferable configuration of an accelerator in which multiple annular beam turning trajectories, which are formed by multiple magnetic poles formed in each iron core of a pair of iron cores and along which ion beams of different energies respectively turn, are densely formed in the vicinity of an inlet of a beam extraction path, will be described. 
         [0043]    (C2) In the accelerator according to (C1), desirably, an eccentric trajectory region is formed at the periphery of an ion injection portion, and in the eccentric trajectory region, the multiple annular beam turning trajectories are formed with the respective centers eccentric with other, the annular beam turning trajectories are densely formed in the vicinity of the beam extraction path between the ion injection portion and the inlet of the beam path, and gaps between annular beam turning trajectories are wide in a direction 180° opposite to the inlet of the beam path relative to the ion injection portion. 
         [0044]    (C3) In the accelerator according to (C2), desirably, a concentric trajectory region, in which multiple annular concentric beam turning trajectories are formed around the ion injection portion, is formed, and the eccentric trajectory region surrounds the concentric trajectory region. 
       Advantageous Effects of Invention 
       [0045]    According to the present invention, it is possible to efficiently extract ion beams of different energies from an accelerator. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0046]      FIG. 1  is a diagram illustrating the configuration of a particle beam irradiation system in Embodiment 1 which is a preferred embodiment of the present invention. 
           [0047]      FIG. 2  is a perspective view of an accelerator of the particle beam irradiation system illustrated in  FIG. 1 . 
           [0048]      FIG. 3  is a cross-sectional view (sectional view taken along line II-II in  FIGS. 5 and 6 ) of the accelerator illustrated in  FIG. 2 . 
           [0049]      FIG. 4  is an enlarged view illustrating the vicinity of an injection electrode of the accelerator illustrated in  FIG. 2 . 
           [0050]      FIG. 5  is a sectional view taken along line V-V in  FIG. 2 . 
           [0051]      FIG. 6  is a sectional view taken along line VI-VI in  FIG. 2 . 
           [0052]      FIG. 7  is a side view of a massless septum illustrated in  FIG. 2 . 
           [0053]      FIG. 8  is a view which is seen in a VIII-VIII direction in  FIG. 7 . 
           [0054]      FIG. 9  is a block diagram illustrating a detailed configuration of a control system illustrated in  FIG. 1 . 
           [0055]      FIG. 10  is a graph illustrating multiple ion beam trajectories, multiple isochronous lines, and a magnetic field distribution formed inside the accelerator illustrated in  FIG. 2 . 
           [0056]      FIG. 11  is a graph illustrating a change in a gap between a magnetic pole  8 E along an isochronous line IL 1  and a median plane illustrated in  FIGS. 3 and 10 . 
           [0057]      FIG. 12  is a graph illustrating a change in a gap between the magnetic pole  8 E along an isochronous line IL 2  and the median plane illustrated in  FIGS. 3 and 10 . 
           [0058]      FIG. 13  is a graph illustrating a change in a gap between the magnetic pole  8 E along an isochronous line IL 3  and the median plane illustrated in  FIGS. 3 and 10 . 
           [0059]      FIG. 14  is a characteristic graph illustrating a relationship between the advance distance of an ion beam and magnetic field strength when the energy of the ion beam is changed. 
           [0060]      FIG. 15  is a characteristic graph illustrating a relationship between the advance distance of an ion beam and an n value when the energy of the ion beam is changed. 
           [0061]      FIG. 16  is a characteristic graph illustrating a change of each of a modulation wave, a double modulation wave, and a triple modulation wave versus the kinetic energy of an ion beam. 
           [0062]      FIG. 17  is a characteristic graph illustrating a change in a betatron oscillation frequency in horizontal and vertical directions versus the kinetic energy of an ion beam. 
           [0063]      FIG. 18  is a characteristic graph illustrating a relationship between the advance distance of an ion beam and a horizontal β function when the energy of the ion beam is changed. 
           [0064]      FIG. 19  is a characteristic graph illustrating a relationship between the advance distance of an ion beam and a vertical β function when the energy of the ion beam is changed. 
           [0065]      FIG. 20  is a graph illustrating the amount of ejection of an extracted ion beam versus the kinetic energy of the ion beam. 
           [0066]      FIG. 21  is a characteristic graph illustrating a relationship between the advance distance of an ion beam and a horizontal displacement of the ion beam from a trajectory until the ion beam ejected by the massless septum reaches an extraction position. 
           [0067]      FIG. 22  is a graph illustrating excitation of a pair of facing magnetic poles of the massless septum illustrated in  FIG. 7 . 
           [0068]      FIG. 23  is a flowchart illustrating a sequence from injection of ions into the accelerator to extraction of ion beams from the accelerator in a particle beam irradiation method of the particle beam irradiation system illustrated in  FIG. 1 . 
           [0069]      FIG. 24  is a graph illustrating a relationship between a position in a radial direction of a vacuum chamber and the number of ion beams (beam current). 
           [0070]      FIG. 25  is graphs illustrating a change of each state quantity of the accelerator of the particle beam irradiation system in operation. 
           [0071]      FIG. 26  is a flowchart illustrating a sequence of irradiating a target volume of a patient with ion beams in the particle beam irradiation method of the particle beam irradiation system illustrated in  FIG. 1 . 
           [0072]      FIG. 27  is a view illustrating beam turning trajectories formed inside an accelerator of a particle beam irradiation system in Embodiment 2 which is another preferred embodiment of the present invention. 
           [0073]      FIG. 28  is a view illustrating the configuration of a particle beam irradiation system in Embodiment 3 which is still another preferred embodiment of the present invention. 
           [0074]      FIG. 29  is a block diagram illustrating the configuration of a particle beam irradiation system in Embodiment 4 which is still another preferred embodiment of the present invention. 
           [0075]      FIG. 30  is a detailed cross-sectional view of an accelerator illustrated in  FIG. 29 . 
           [0076]      FIG. 31  is a block diagram illustrating a detailed configuration of a control system illustrated in  FIG. 29 . 
           [0077]      FIG. 32  is a flowchart illustrating a sequence of irradiating a target volume of a patient with ion beams in a particle beam irradiation method of the particle beam irradiation system illustrated in  FIG. 29 . 
           [0078]      FIG. 33  is a block diagram illustrating the configuration of a particle beam irradiation system in Embodiment 5 which is still another preferred embodiment of the present invention. 
           [0079]      FIG. 34  is a detailed cross-sectional view of an accelerator illustrated in  FIG. 33 . 
           [0080]      FIG. 35  is a flowchart illustrating a sequence of irradiating a target volume of a patient with ion beams in a particle beam irradiation method of the particle beam irradiation system illustrated in  FIG. 33 . 
           [0081]      FIG. 36  is a block diagram illustrating the configuration of a particle beam irradiation system in Embodiment 6 which is still another preferred embodiment of the present invention. 
           [0082]      FIG. 37  is a detailed cross-sectional view (sectional view taken along line B-B in  FIG. 38 ) of an accelerator illustrated in  FIG. 36 . 
           [0083]      FIG. 38  is a sectional view taken along line A-A in  FIG. 37 . 
           [0084]      FIG. 39  is an enlarged view illustrating the vicinity of a massless septum illustrated in  FIG. 38 . 
           [0085]      FIG. 40  is a side view of a beam current measuring apparatus illustrated in  FIG. 39 . 
           [0086]      FIG. 41  is a view which is seen in a D-D direction in  FIG. 40 . 
           [0087]      FIG. 42  is a block diagram illustrating the configuration of a particle beam irradiation system in Embodiment 7 which is still another preferred embodiment of the present invention. 
           [0088]      FIG. 43  is a detailed cross-sectional view of an accelerator illustrated in  FIG. 42 . 
           [0089]      FIG. 44  is a cross-sectional view (sectional view taken along line G-G in  FIGS. 45 and 46 ) illustrating the vicinity of a vacuum chamber of a particle beam irradiation system in Embodiment 8 which is still another preferred embodiment of the present invention. 
           [0090]      FIG. 45  is a sectional view taken along line E-E in  FIG. 44 . 
           [0091]      FIG. 46  is a sectional view taken along line F-F in  FIG. 44 . 
           [0092]      FIG. 47  is a view illustrating another example of disposition of a massless septum. 
           [0093]      FIG. 48  is a cross-sectional view of a particle beam irradiation system in Embodiment 9 which is still another preferred embodiment of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0094]    Inventors have done various studies so as to realize an accelerator that is capable of continuously extracting ion beams like a cyclotron and extracting ion beams of different energies like a synchrotron. 
         [0095]    First, the inventors have paid attention to a concept in which gaps (gaps between beam turning trajectories in a radial direction of a vacuum chamber) between beam turning trajectories of ion beams turning around inside the vacuum chamber of the cyclotron are increased. In a case where the gaps between the beam turning trajectories are increased, that is, turn separations have been increased, the diameter of the vacuum chamber is increased, and the size of the cyclotron is increased. This is contrary to a reduction in the size of the accelerator. In the cyclotron in the related art, concentric circular beam turning trajectories are formed inside the vacuum chamber, and it is not easy to ensure a turn separation at a high energy. Therefore, it is not easy to efficiently extract ion beams of different energies. 
         [0096]    In a synchrotron, a circular vacuum chamber is used, an ion source communicates with the center of the vacuum chamber such that ions are injected to the center of the vacuum chamber. The inventors have considered a concept in which in the cyclotron, the ion source connected to the center of the vacuum chamber is moved to a beam extraction port formed in the vacuum chamber and is connected to the vacuum chamber, and ions from the ion source are not injected to the center of the vacuum chamber, but are injected to a position offset to the beam extraction port inside the vacuum chamber. As a result, gaps between beam turning trajectories formed inside the vacuum chamber are narrow between an ion injection point, to which ions are injected from the ion source, and the beam extraction port, and unlike those between the ion injection point and the beam extraction port, gaps between beam turning trajectories formed inside the vacuum chamber can be increased between the ion injection point and a direction positioned 180° opposite to the beam extraction port in the vacuum chamber. 
         [0097]    The inventors have devised new accelerators capable of efficiently extracting ion beams of different energies by adopting the aforementioned concept regarding the formation of aforementioned beam turning trajectories. 
         [0098]    Embodiments of the present invention, which adopt the accelerators newly devised by the inventors, will be described with reference to the accompanying drawings. 
       Embodiment 1 
       [0099]    Hereinafter, a particle beam irradiation system in Embodiment 1, which is a preferred embodiment of the present invention, will be described with reference to  FIGS. 1 to 8 . 
         [0100]    A particle beam irradiation system  1  in the embodiment is disposed in a building (not illustrated), and is installed on a floor of the building. The particle beam irradiation system  1  includes an ion beam generator  2 ; a beam transport  13 ; a rotating gantry  6 ; an irradiation apparatus  7 ; and a control system  65 . The ion beam generator  2  includes an ion source  3 , and an accelerator  4  connected to the ion source  3 . The accelerator  4  in the embodiment is an energy-variable continuous wave accelerator. 
         [0101]    The beam transport  13  includes a beam path (beam duct) that reaches the irradiation apparatus  7 . The beam transport  13  is configured such that multiple quadrupole magnets  46 , a bending magnet  41 , multiple quadrupole magnets  47 , a bending magnet  42 , quadrupole magnets  49  and  50 , and bending magnets  43  and  44  are disposed on the beam path  48  in the listed sequence from the accelerator  4  toward the irradiation apparatus  7 . A portion of the beam path  48  of the beam transport  13  is installed in the rotating gantry  6 , and the bending magnet  42 , the quadrupole magnets  49  and  50 , and the bending magnets  43  and  44  are also installed in the rotating gantry  6 . The beam path  48  is connected to a beam extraction path  20  (refer to  FIG. 2 ) that is formed in a septum magnet  19  for extraction provided in the accelerator  4 . The rotating gantry  6  is a rotating apparatus that rotates around a rotational shaft  45  so as to turn the irradiation apparatus  7  around the rotational shaft  45 . 
         [0102]    The irradiation apparatus  7  includes two scanning magnets (ion beam scanners)  51  and  52 ; a beam point monitor  53 ; and a dose monitor  54 . The scanning magnets  51  and  52 , the beam point monitor  53 , and the dose monitor  54  are disposed along a central axis, that is, a beam axis of the irradiation apparatus  7 . The scanning magnets  51  and  52 , the beam point monitor  53 , and the dose monitor  54  are disposed inside a casing (not illustrated) of the irradiation apparatus  7 . The beam point monitor  53  and the dose monitor  54  are disposed downstream of the scanning magnets  51  and  52 . The scanning magnet  51  bends ion beams in a plane perpendicular to the central axis of the irradiation apparatus  7 , and scans the ion beams in a y direction. The scanning magnet  52  bends ion beams in the plane, and scans the ion beams in an x direction perpendicular to the y direction. The irradiation apparatus  7  is attached to the rotating gantry  6 , and is disposed downstream of the bending magnet  44 . A treatment bed  55 , on which a patient  56  lies, is disposed to face the irradiation apparatus  7 . 
         [0103]    The control system  65  includes a central control apparatus  66 ; an accelerator and transport control apparatus  69 ; a scanning control apparatus  70 ; a rotation control apparatus  88 ; and a database  72 . The central control apparatus  66  includes a central processing unit (CPU)  67  and a memory  68  connected to the CPU  67 . The accelerator and transport control apparatus  69 , the scanning control apparatus  70 , the rotation control apparatus  88 , and the database  72  are connected to the CPU  67 . A charged particle beam irradiation system  1  includes a treatment planning system  73 . The treatment planning system  73  is connected to the database  72 . 
         [0104]    The control system  65  will be described in detail with reference to  FIG. 9 . The accelerator and transport control apparatus  69  includes an injection magnet control apparatus  83 ; a beam current measuring unit control apparatus  84 ; a magnet control apparatus  85 ; a massless septum control apparatus  86 ; a coil current control apparatus  94 ; a radiofrequency voltage control apparatus  99 ; and a memory  107 . The scanning control apparatus  70  includes an ion beam confirmation apparatus  87 ; an irradiation point control apparatus  89 ; a dose determination apparatus  91 ; a layer determination apparatus  92 ; and a memory  70 . The CPU  67  is connected to the injection magnet control apparatus  83 , the beam current measuring unit control apparatus  84 , the magnet control apparatus  85 , the massless septum control apparatus  86 , the coil current control apparatus  94 , the radiofrequency voltage control apparatus  99 , the memory  107 , the ion beam confirmation apparatus  87 , the irradiation point control apparatus  89 , the dose determination apparatus  91 , the layer determination apparatus  92 , and the memory  70 . The irradiation point control apparatus  89  is connected to the injection magnet control apparatus  83 , the magnet control apparatus  85 , and the massless septum control apparatus  86 . The dose determination apparatus  91  is connected to the injection magnet control apparatus  83 . The layer determination apparatus  92  is connected to the irradiation point control apparatus  89 . The memory  107  is connected to the injection magnet control apparatus  83 , the beam current measuring unit control apparatus  84 , the magnet control apparatus  85 , the massless septum control apparatus  86 . The memory  70  is connected to the irradiation point control apparatus  89 , the dose determination apparatus  91 , and the layer determination apparatus  92 . 
         [0105]    Hereinafter, the configuration of the accelerator  4  will be described in detail with reference to  FIGS. 3, 4, 5 , and  6 . The accelerator  4  includes a vacuum chamber  27  including circular iron cores  14 A and  14 B which face each other. The iron cores  14 A and  14 B are joined together such that the vacuum chamber  27  is formed and an outer shell of the accelerator  4  is formed, which will be described later. The iron core  14 A includes a return yoke  5 A and magnetic poles  7 A to  7 F. The iron core  14 B includes a return yoke  5 B and magnetic poles  7 A to  7 F. A specific configuration of each of the magnetic poles  7 A to  7 F will be described later. The return yoke  5 A includes a circular base portion  74 A having a predetermined thickness, and a cylindrical portion (for example, a circular cylinder-shaped portion)  75 A that extends from a surface of the base portion  74 A in a direction perpendicular to the surface. The return yoke  5 B includes a base portion  74 B, and a cylindrical portion (for example, a circular cylinder-shaped portion)  75 B that extends from a surface of the base portion  74 B in a direction perpendicular to the surface (refer to  FIGS. 5 and 6 ). The base portion  74 A seals one end portion of the cylindrical portion  75 A, and the return yoke  5 A opens in the other end portion. The base portion  74 B seals one end portion of the cylindrical portion  75 B, and the return yoke  5 B opens in the other end portion. Contact surfaces of the cylindrical portions  75 A and  75 B are sealed which are contact surfaces of the iron cores  14 A and  14 B of the vacuum chamber  27 . 
         [0106]    As illustrated in  FIGS. 5 and 6 , the vacuum chamber  27  is configured such that the iron cores  14 A and  14 B, specifically, the return yokes  5 A and  5 B are joined together in a state where open portions of the return yokes  5 A and  5 B are disposed to face each other, that is, the cylindrical portions  75 A and  75 B face each other. In the embodiment, the vacuum chamber  27  is installed on the floor of the building such that the return yoke  5 B is installed at a lower position on the floor and the return yoke  5 A is mounted on the return yoke  5 B (refer to  FIG. 6 ). In the embodiment, the cylindrical portions  75 A and  75 B respectively form side walls of the return yokes  5 A and  5 B, and serve a side wall of the vacuum chamber  27 . An ion injection tube  3 A is connected to the ion source  3  disposed outside the iron core  14 A, is attached to the base portion  74 A of the return yoke  5 A, and passes through the base portion  74 A. 
         [0107]    A median plane  77  (refer to  FIGS. 5 and 6 ) illustrated by the alternate long and short dash line is a plane which is formed inside the vacuum chamber  27  and at a contact position between the return yokes  5 A and  5 B, and a plane on which ion beams accelerate and turn inside the vacuum chamber  27 . Beam turning trajectories, along which respective ion beams of different energies turn, are formed on the median plane  77 , which will be described later. Since ion beams turn in a direction (direction of a central axis C of the vacuum chamber  27 ) perpendicular to the median plane  77  while being subjected to betatron oscillation, the ion beams turn in a beam turning region  76  (refer to  FIGS. 5 and 6 ) having a predetermined width in the direction perpendicular to the median plane  77 . The central axis C of the vacuum chamber  27  also is a central axis of the iron cores  14 A and  14 B. 
         [0108]    A suction tube  26  is disposed on an extension line of a central axis of the ion injection tube  3 A, passes through the base portion  74 B, and is attached to the base portion  74 B. A vacuum pump  25  is attached to an outer surface of the base portion  74 B, and is connected to the suction tube  26 . The suction tube  26  opens in the beam turning region  76 . 
         [0109]    The accelerator  4  includes the magnetic poles  7 A,  7 B,  7 C,  7 D,  7 E, and  7 F; radiofrequency acceleration electrodes  9 A,  9 B,  9 C, and  9 D; annular coils  11 A and  11 B; a massless septum  12 ; a beam current measuring unit  15 ; an injection electrode  18 ; and the septum magnet  19  for extraction. 
         [0110]    The annular coil (preferably, a circular coil)  11 B is disposed inside the cylindrical portion  75 B of the return yoke  5 B along an inner surface of the cylindrical portion  75 B (refer to  FIGS. 3, 5, and 6 ). Two lead-out wirings  22  are connected to the annular coil  11 B, pass through the cylindrical portion  75 B, and reach the outside of the vacuum chamber  27 . 
         [0111]    Similar to the annular coil  11 B, the annular coil  11 A is disposed inside the cylindrical portion  75 A of the return yoke  5 A along an inner surface of the cylindrical portion  75 A (refer to  FIGS. 5 and 6 ). Similar to the annular coil  11 B, two lead-out wirings (not illustrated) are also connected to the annular coil  11 A, and the lead-out wirings pass through the cylindrical portion  75 A, and reach the outside of the vacuum chamber  27 . The central axis C of the vacuum chamber  27  is a central axis of each of the annular coils  11 A and  11 B. The center of gravity of each of the annular coils  11 A and  11 B is positioned on the central axis C. The annular coils  11 A and  11 B are annular main coils. 
         [0112]    The curved septum magnet  19  passes through the cylindrical portions  75 A and  75 B, and is attached to the cylindrical portion  75 B of the return yoke  5 B. One end of the septum magnet  19  is positioned inside the vacuum chamber  27 , and is positioned on the inside the annular coils  11 A and  11 B. The septum magnet  19  forms a beam extraction path  20 . The one end of the septum magnet  19 , and one end, that is, an inlet of the beam extraction path  20  are positioned inside the vacuum chamber  27 , and are positioned close to inner surfaces of the annular coils  11 A and  11 B inside the annular coils  11 A and  11 B. The septum magnet  19  is disposed between the annular coils  11 A and  11 B in the direction of the central axis C of the vacuum chamber  27 . 
         [0113]    The magnetic poles  7 A,  7 B,  7 C,  7 D,  7 E, and  7 F are formed in each of the iron cores  14 A and  14 B. Each of the magnetic poles  7 A,  7 B,  7 C,  7 D,  7 E, and  7 F which are formed in the iron core  14 A protrudes from the base portion  74 A of the return yoke  5 A in an extension direction of the cylindrical portion  75 A. Each of the magnetic poles  7 A,  7 B,  7 C,  7 D,  7 E, and  7 F which are formed in the iron core  14 B protrudes from the base portion  74 B of the return yoke  5 B in an extension direction of the cylindrical portion  75 B (refer to  FIG. 6 ). The radiofrequency acceleration electrodes  9 A,  9 B,  9 C, and  9 D are respectively attached to the cylindrical portions  75 A and  75 B of the return yokes  5 A and  5 B via waveguide tubes  10 A to  10 D. Each of the magnetic poles  7 A,  7 B,  7 C,  7 D,  7 E, and  7 F and the radiofrequency acceleration electrodes  9 A,  9 B,  9 C, and  9 D, which are provided in the return yoke  5 B, is disposed inside the annular coil  11 B (refer to  FIG. 3 ). Similar to the magnetic poles and the radiofrequency acceleration electrodes which are provided in the return yoke  5 B, each of the magnetic poles  7 A,  7 B,  7 C,  7 D,  7 E, and  7 F and the radiofrequency acceleration electrodes  9 A,  9 B,  9 C, and  9 D, which are provided in the return yoke  5 A, is also disposed inside the annular coil  11 A. 
         [0114]    Disposition of each of the magnetic poles  7 A,  7 B,  7 C,  7 D,  7 E, and  7 F and the radiofrequency acceleration electrodes  9 A,  9 B,  9 C, and  9 D, which are provided in the return yoke  5 B, will be described in detail with reference to  FIG. 3 . The magnetic poles  7 A,  7 B,  7 C,  7 D,  7 E, and  7 F of the return yoke  5 A are respectively symmetrical in shape and disposition with the magnetic poles  7 A,  7 B,  7 C,  7 D,  7 E, and  7 F of the return yoke  5 B relative to the median plane  77 . The radiofrequency acceleration electrodes  9 A,  9 B,  9 C, and  9 D of the return yoke  5 A are respectively symmetrical in shape and disposition with the radiofrequency acceleration electrodes  9 A,  9 B,  9 C, and  9 D of the return yoke  5 B relative to the median plane  77 . For this reason, description of each of the magnetic poles and the radiofrequency acceleration electrodes of the return yoke  5 A will be omitted. 
         [0115]    The magnetic poles  7 A,  7 B,  7 C,  7 D,  7 E, and  7 F, which are formed on the base portion  74 B of the return yoke  5 B, are protrusions which protrude from the base portion  74 B (refer to  FIG. 6 ). 
         [0116]    In the return yoke  5 B, the magnetic poles  7 A,  7 B,  7 C,  7 D,  7 E, and  7 F and recessions  29 A to  29 F are alternately disposed in a circumferential direction of the return yoke  5 B. That is, the recession  29 A (a first recession) is formed between the magnetic poles  7 A and  7 B, the recession  29 B is formed between the magnetic poles  7 B and  7 D, and the recession  29 F is formed between the magnetic poles  7 A and  7 C (refer to  FIGS. 3, 4, and 6 ). In the return yoke  5 B, the recession  29 C is formed between the magnetic poles  7 D and  7 F, the recession  29 D (a second recession) is formed between the magnetic poles  7 F and  7 E, and the recession  29 E is formed between the magnetic poles  7 E and  7 C (refer to  FIGS. 3, 4, and 5 ). In the return yoke  5 B, a recession  29 G is formed between the magnetic poles  7 A,  7 B,  7 C,  7 D,  7 E, and  7 F and the cylindrical portion  75 B, and the annular coil  11 B is disposed in side of the recession  29 G (refer to  FIGS. 3 and 6 ). 
         [0117]    A tip end portion of the ion injection tube  3 A is surrounded by tip ends of the magnetic poles  7 A,  7 B,  7 C,  7 D,  7 E, and  7 F formed on the base portion  74 A of the return yoke  5 A. The injection electrode  18  is attached to a tip end of the ion injection tube  3 A, crosses the median plane  77 , and is disposed in the beam turning region  76 . The tip end of the ion injection tube  3 A communicates with the beam turning region  76 . An ion inlet port, which is an ion injection port formed at the tip end of the ion injection tube  3 A, and the injection electrode  18  are disposed on an alternate long and short dash line X that connects the central axis C of the annular coils  11 A and  11 B to the inlet of the beam extraction path  20 . The ion inlet port and the injection electrode  18  are disposed offset toward the inlet of the beam extraction path  20  from the central axis C of the annular coils  11 A and  11 B. That is, the ion inlet port and the injection electrode  18  are disposed at a different position from that of the central axis C, and are disposed at a different position from that of the center of gravity of the annular coils  11 A and  11 B. The ion inlet port and the injection electrode  18  are disposed at a different position from that of the central axis C of the iron cores  14 A and  14 B. The ion inlet port is an ion injection port through which ions are injected to the beam turning region  76 . An ion injection portion  109  (refer to  FIG. 10 ) receives ions from the ion inlet port. The ion injection portion  109  is a region that is formed inside an innermost beam turning trajectory, and specifically is formed at the periphery of the injection electrode  18  in the beam turning region  76 . 
         [0118]    The recession  29 D (the second recession) which is positioned between the injection electrode  18  and the inlet of the beam extraction path  20 , and the recession  29 A (the first recession), which is positioned 180° opposite to the inlet of the beam extraction path  20  relative to the injection electrode  18 , are disposed straight along the alternate long and short dash line X. 
         [0119]    In the accelerator of the embodiment, multiple protrusions (magnetic poles) are formed in the facing iron cores so as to obtain strong convergence by intensifying and weakening a magnetic field along beam turning trajectories. Hereinafter, in the accelerator of the embodiment in which an ion injection point is provided at a position that is on a trajectory plane and is different from that of the center of the circular iron core, the shapes of the protrusions (magnetic poles) required to obtain a magnetic field distribution for forming eccentric beam turning trajectories will be described. The shapes of the iron cores and the recessions (magnetic poles) suitable for forming eccentric beam turning trajectories differ depending on masses or charges of accelerated ion particles, and are not limited to the shapes illustrated in the drawings. The shapes of the magnetic poles illustrated in the drawings and the following description are an example in which protons are used in the present invention. The center of the iron cores are positioned on the central axis of the iron cores. 
         [0120]    The magnetic poles  7 A,  7 B,  7 C,  7 D,  7 E, and  7 F, which are formed on the base portion  74 A of the return yoke  5 B, are radially disposed around the ion injection port, that is, the position of the injection electrode  18 , in a horizontal direction (direction perpendicular to the central axis C). The width of each of the magnetic poles in the circumferential direction of the annular coil  11 B is decreased toward the injection electrode  18 . A tip end of each of the magnetic poles is sharp, and each sharp tip end faces the injection electrode  18 . The width of each of the magnetic poles  7 A,  7 B,  7 C,  7 D,  7 E, and  7 F in the circumferential direction of the annular coil  11 B is increased to the maximum value in a portion of each magnetic pole which faces the annular coil  11 B. 
         [0121]    The magnetic pole  7 A is bent at bent points  24 A and  24 B which are formed on two facing side surfaces of the magnetic pole  7 A. The magnetic pole  7 B is bent at bent points  24 C and  24 D which are formed on two facing side surfaces of the magnetic pole  7 B. The magnetic pole  7 C is bent at bent points  24 E and  24 F which are formed on two facing side surfaces of the magnetic pole  7 C (refer to  FIG. 4 ). The magnetic pole  7 D is bent at bent points  24 G and  24 H which are formed on two facing side surfaces of the magnetic pole  7 D. The magnetic pole  7 E is bent at bent points  241  and  24 J which are formed on two facing side surfaces of the magnetic pole  7 E. The magnetic pole  7 F is bent at bent points  24 K and  24 L which are formed on two facing side surfaces of the magnetic pole  7 F (refer to  FIG. 4 ). 
         [0122]    A portion of each of the magnetic poles  7 A,  7 B,  7 C,  7 D,  7 E, and  7 F between the bent points and an end surface thereof facing the annular coil  11 B is bent toward the recession  29 A. That is, the portion of each of the magnetic poles  7 A,  7 C, and  7 E between the bent points and the end surface thereof facing the annular coil  11 B is bent toward the recession  29 A in a turning direction of ion beams. The portion of each of the magnetic poles  7 B,  7 D, and  7 F between the bent points and the end surface thereof facing the annular coil  11 B is bent toward the recession  29 A in a direction opposite to the turning direction of ion beams. The absolute value of the bending angle of a bending portion of the magnetic pole  7 A is the same as that of the bending angle of a bending portion of the magnetic pole  7 B. The absolute value of the bending angle of a bending portion of the magnetic pole  7 C is the same as that of the bending angle of a bending portion of the magnetic pole  7 D. The absolute value of the bending angle of a bending portion of the magnetic pole  7 E is the same as that of the bending angle of a bending portion of the magnetic pole  7 F. The absolute values of the bending angles of the magnetic poles  7 A,  7 C, and  7 E are increased in the listed sequence. The absolute values of the bending angles of the magnetic poles  7 E and  7 F are the maximum values. 
         [0123]    A portion of the magnetic pole  7 A between the bent points  24 A and  24 B and the tip end thereof, a portion of the magnetic pole  7 B between the bent points  24 C and  24 D and the tip end thereof, a portion of the magnetic pole  7 C between the bent points  24 E and  24 F and the tip end thereof, a portion of the magnetic pole  7 D between the bent points  24 G and  24 H and the tip end thereof, a portion of the magnetic pole  7 E between the bent points  241  and  24 J and the tip end thereof, and a portion of the magnetic pole  7 F between the bent points  24 K and  24 L and the tip end thereof are disposed around the injection electrode  18  at every 60° in the horizontal direction. 
         [0124]    In the embodiment, concentric trajectory region is formed around the injection electrode  18  (the ion inlet port of the ion injection tube  3 A), and eccentric trajectory region is formed to surround the concentric trajectory region. The concentric trajectory region is formed as a predetermined region inside the bending portions of the magnetic poles  7 A to  7 F. As a result, the shape of each magnetic pole formed inside the bent points is similar to that of a radial sector type AVF cyclotron having six sectors. In the concentric trajectory region, the respective centers of the annular beam turning trajectories, which are formed in the concentric trajectory region and along which ion beams of different energies turn, are the same. That is, the magnet poles are formed such that a magnetic field can be intensified and weakened, that is, convergence and dispersion of beams can be obtained at a predetermined periodic timing of a beam turning trajectory or at a predetermined turning angle at which a magnetic pole is radially installed relative to the center of a beam turning trajectory. 
         [0125]    Relative to the alternating long and short dash line X, the magnetic poles  7 A and  7 B are symmetrical in shape with each other, the magnetic poles  7 C and  7 D are symmetrical in shape with each other, the magnetic poles  7 E and  7 F are symmetrical in shape with each other, the recessions  29 F and  29 B are symmetrical in shape with each other, and the recessions  29 E and  29 C are symmetrical in shape with each other. Among six magnetic poles (protrusions)  7 A to  7 F formed in each of the iron cores  14 A and  14 B, the magnetic poles  7 A,  7 C, and  7 E are installed to be respectively reflection-symmetrical to the magnetic poles  7 B,  7 D, and  7 F relative to a straight line that connects the central axis C of the annular coils to the inlet of the beam extraction path  20 . At the same time, in the embodiment, the magnets are installed such that all of the magnets are not rotationally symmetrical in shape with each other relative to the center of the circular iron cores, the center of gravity of the annular coils, the ion injection point. The reason for this is that even if the center of a beam turning trajectory is gradually displaced for each energy, a magnetic field can be intensified and weakened, that is, convergence and dispersion of beams can be obtained at a predetermined periodic timing of each beam turning trajectory, or as a result, at substantially the same turning angle relative to the center of each beam turning trajectory. For this reason, the magnets are reflection-symmetrical in shape with each other relative to a direction in which the centers of the beam turning trajectories are shifted, and the magnets are installed in such a way as to be diagonally inclined toward a direction opposite to the direction in which the centers are shifted. That is, the magnets are shaped such that that the magnets are not rotationally symmetrical in shape with each other. In such shapes of the magnets, the center of gravity of all of the six magnetic poles is displaced from the center of the iron cores toward the direction opposite to the direction in which the centers of the beam turning trajectories are shifted. Therefore, the center of the iron cores and the center of gravity of all of the six magnetic poles are positioned at different coordinates on a horizontal plane. A relationship between the shapes of the magnets and the beam turning trajectories will be described in detail later with reference to  FIG. 10 . 
         [0126]    A trim coil  8 A is installed on the magnetic pole  7 A, and lead-out wirings  21 A and  21 B are respectively connected to both ends of the trim coil  8 A. A trim coil  8 B is installed on the magnetic pole  7 B, and lead-out wirings  21 C and  21 D are respectively connected to both ends of the trim coil  8 B. A trim coil  8 C is installed on the magnetic pole  7 C, and lead-out wirings  21 E and  21 F are respectively connected to both ends of the trim coil  8 C. A trim coil  8 D is installed on the magnetic pole  7 D, and lead-out wirings  21 G and  21 H are respectively connected to both ends of the trim coil  8 D. A trim coil  8 E is installed on the magnetic pole  7 E, and lead-out wirings  211  and  21 J are respectively connected to both ends of the trim coil  8 E. A trim coil  8 F is installed on the magnetic pole  7 F, and lead-out wirings  21 L and  21 K are respectively connected to both ends of the trim coil  8 F. Each of the lead-out wirings  21 A to  21 K passes through a gap between the annular coils  11 A and  11 B, passes through the cylindrical portion  75 B, and is extracted to the outside of the vacuum chamber  27 . 
         [0127]    The trim coils  8 A to  8 F are respectively installed on the magnetic poles  7 A to  7 F so as to generate an isochronous magnetic field which is desired to be generated in the median plane  77 , and thus, a gap between windings of each of the installed trim coils is not constant. In each of the magnetic poles  7 A to  7 F, the gap between windings of each of the installed trim coils is decreased to the extent that the trim coil is closer to the inner surface of each of the annular coils than the injection electrode  18 . The gap between windings of each of the trim coils installed on the magnetic poles  7 A,  7 C, and  7 E is decreased in the listed sequence. The gap between windings of each of the trim coils installed on the magnetic poles  7 B,  7 D, and  7 F is decreased in the listed sequence. Since beam turning trajectories  78  of a wide range of energies are densely formed in a range which is narrow in a radial direction of the annual coils, and in the vicinity of the inlet of the beam extraction path  20 , in each of the magnetic poles  7 E and  7 F adjacent to the inlet of the beam extraction path  20 , the gap between windings of the installed trim coil is decreased on an outer circumferential portion of each of the magnetic poles  7 E and  7 F so as to cope with a required steep magnetic field radial gradient and required high energy beam turning trajectories. 
         [0128]    The disposition of the radiofrequency acceleration electrodes  9 A,  9 B,  9 C, and  9 D in the return yoke  5 B will be described with reference to  FIGS. 3 and 6 . 
         [0129]    The radiofrequency acceleration electrode  9 A is disposed inside the recession  29 F between the magnetic poles  7 A and  7 C, and is connected to the waveguide tube  10 A. The radiofrequency acceleration electrode  9 A inside the recession  29 F is disposed between the bent points  24 B and  24 E and the annular coil  11 B. The radiofrequency acceleration electrode  9 B is disposed inside the recession  29 B between the magnetic poles  7 B and  7 D, and is connected to the waveguide tube  10 B. The radiofrequency acceleration electrode  9 B inside the recession  29 B is disposed between the bent points  24 D and  24 G and the annular coil  11 B. Ion inlet port-side end surfaces of the radiofrequency acceleration electrodes  9 A and  9 B may be respectively positioned at a midpoint between the bent points of the radiofrequency acceleration electrode  9 A and the ion inlet port and at a midpoint between the bent points of the radiofrequency acceleration electrode  9 B and the ion inlet port. The waveguide tubes  10 A and  10 B pass through the gap between the annular coils  11 A and  11 B, pass through the cylindrical portion  75 B, and are extracted to the outside of the vacuum chamber  27 . The width of each of the radiofrequency acceleration electrodes  9 A and  9 B in the circumferential direction of the annular coil  11 B is increased from the injection electrode  18  toward the annular coil  11 B. 
         [0130]    The radiofrequency acceleration electrode  9 C is disposed inside the recession  29 E between the magnetic poles  7 C and  7 E, and is connected to the waveguide tube  10 C. The radiofrequency acceleration electrode  9 C is bent at bent points  24 M and  24 N (refer to  FIG. 4 ) which are formed on two side surfaces thereof. A portion of the radiofrequency acceleration electrode  9 C between the bent points  24 M and  24 N and an end surface thereof facing the annular coil  11 B is bent toward the recession  29 A (the first recession) in the turning direction of ion beams. The width of the radiofrequency acceleration electrode  9 C in the circumferential direction of the annular coil  11 B is decreased from the bending positions of the bent points  24 M and  24 N toward a tip end thereof, and is increased from the bent points toward the end surface facing the annular coil  11 B. The radiofrequency acceleration electrode  9 D is disposed inside the recession  29 C between the magnetic poles  7 D and  7 F, and is connected to the waveguide tube  10 D. The radiofrequency acceleration electrode  9 D is bent at bent points  24 O and  24 P (refer to  FIG. 4 ) which are formed on two side surfaces thereof. A portion of the radiofrequency acceleration electrode  9 D between the bent points  24 O and  24 P and an end surface thereof facing the annular coil  11 B is bent toward the recession  29 A (the first recession) in the direction opposite to the turning direction of ion beams. The width of the radiofrequency acceleration electrode  9 D in the circumferential direction of the annular coil  11 B is decreased from the bending positions of the bent points  24 O and  24 P toward a tip end thereof, and is increased from the bent points toward the end surface facing the annular coil  11 B. The waveguide tubes  10 C and  10 D pass through the gap between the annular coils  11 A and  11 B, pass through the cylindrical portion  75 B, and are extracted to the outside of the vacuum chamber  27 . The tip ends of the radiofrequency acceleration electrodes  9 C and  9 D are positioned close to the injection electrode  18 , and are connected to each other in an ion injection region in which the injection electrode  18  is installed. The injection electrode  18  faces a connection portion between the radiofrequency acceleration electrodes  9 C and  9 D, and is disposed in the beam turning region  76  while being positioned away from the connection portion. 
         [0131]    The recession  29 A, the injection electrode  18 , the recession  29 D are disposed along the alternate long and short dash line X passing through the central axis C of the vacuum chamber  27 . 
         [0132]    As illustrated in  FIG. 6 , each of the magnetic poles  7 A to  7 F, which are formed on the base portion  74 A of the return yoke  5 A, are a protrusion that protrudes from the cylindrical portion  75 A. Similar to the return yoke  5 B, also in the return yoke  5 A, a recession  29 G is formed between the magnetic poles  7 A,  7 B,  7 C,  7 D,  7 E, and  7 F and the cylindrical portion  75 A, and the annular coil  11 A is disposed inside the recession  29 G (refer to  FIG. 6 ). 
         [0133]    In a state where the return yokes  5 A and  5 B are disposed to face each other, and are joined together, the magnetic poles  7 A face each other, the magnetic poles  7 B face each other, the magnetic poles  7 C face each other, the magnetic poles  7 D face each other, the magnetic poles  7 E face each other, and the magnetic poles  7 F face each other. In a state where the return yokes  5 A and  5 B are joined together in such a manner, the recessions  29 A face each other, the recessions  29 B face each other, the recessions  29 C face each other, the recessions  29 D face each other, the recessions  29 E face each other, and the recessions  29 F face each other. 
         [0134]    Relative to the median plane  77 , the magnetic poles  7 A are symmetrical in shape with each other, the magnetic poles  7 B are symmetrical in shape with each other, the magnetic poles  7 C are symmetrical in shape with each other, the magnetic poles  7 D are symmetrical in shape with each other, the magnetic poles  7 E are symmetrical in shape with each other, and the magnetic poles  7 F are symmetrical in shape with each other, all of which are formed in the return yokes  5 A and  5 B. Relative to the median plane  77 , the recessions  29 A are symmetrical in shape with each other, the recessions  29 B are symmetrical in shape with each other, the recessions  29 C are symmetrical in shape with each other, the recessions  29 D are symmetrical in shape with each other, the recessions  29 E are symmetrical in shape with each other, and the recessions  29 F are symmetrical in shape with each other, all of which are formed in the return yokes  5 A and  5 B. 
         [0135]    As illustrated in  FIG. 5 , at the position of the ion injection tube  3 A, a bottom surface  95  of the recession  29 A formed in the return yoke  5 A approaches closest to a bottom surface  95  of the recession  29 A formed in the return yoke  5 B. In the vacuum chamber  27 , the bottom surfaces  95  are surfaces which are inclined in a direction that is 180° opposite to the inlet of the beam extraction path  20  relative to the injection electrode  18 , specifically, are inclined toward the massless septum  12  disposed inside the recession  29 A. A width between the bottom surfaces  95  in a direction of the central axis C is gradually increased from the ion injection tube  3 A toward the massless septum  12 . As for the magnitude of the width formed between the bottom surfaces  95 , the width between the bottom surface  95  of the recession  29 A formed in the return yoke  5 A and the bottom surface  95  of the recession  29 A formed in the return yoke  5 B becomes the maximum value at a position at which the massless septum  12  is disposed. 
         [0136]    As illustrated in  FIG. 5 , at the position of the ion injection tube  3 A, the bottom surface  95  of the recession  29 D formed in the return yoke  5 A approaches closest to the bottom surface  95  of the recession  29 D formed in the return yoke  5 B. In the vacuum chamber  27 , the bottom surfaces  95  are surfaces which are inclined from the position of the ion injection tube  3 A toward the septum magnet  19 . A width between the bottom surfaces  95  in the direction of the central axis C is gradually increased from the ion injection tube  3 A toward the septum magnet  19 . A width between a portion (on which the annular coil  11 A is disposed) of the bottom surface  95  of the recession  29 D formed in the return yoke  5 A and a portion (on which the annular coil  11 A is disposed) of the bottom surface  95  of the recession  29 D formed in the return yoke  5 B is the same as that between a portion (on which the massless septum  12  is disposed) of the bottom surface  95  of the recession  29 A formed in the return yoke  5 A and a portion (on which the massless septum  12  is disposed) of the bottom surface  95  of the recession  29 A formed in the return yoke  5 B. 
         [0137]    The magnetic poles  7 A,  7 B,  7 C,  7 D,  7 E, and  7 F, the base portion  74 A, and the cylindrical portion  75 A are integrally formed into the iron core  14 A. The magnetic poles  7 A,  7 B,  7 C,  7 D,  7 E, and  7 F, the base portion  74 B, and the cylindrical portion  75 B are integrally formed into the iron core  14 B. 
         [0138]    As illustrated in  FIG. 6 , a gap  28 A is formed between the magnetic pole  7 A of the return yoke  5 A and the facing magnetic pole  7 A of the return yoke  5 B, a gap  28 B is formed between the magnetic poles  7 B which face each other in an axial direction of the vacuum chamber  27 , a gap  28 C is formed between the magnetic pole  7 C of the return yoke  5 A and the facing magnetic pole  7 C of the return yoke  5 B, and a gap  28 D is formed between the magnetic pole  7 D of the return yoke  5 A and the facing magnetic pole  7 D of the return yoke  5 B. In addition, gaps are respectively formed between the magnetic pole  7 E of the return yoke  5 A and the facing magnetic pole  7 E of the return yoke  5 B and between the magnetic pole  7 F of the return yoke  5 A and the facing magnetic pole  7 F of the return yoke  5 B, which is not illustrated. A gap is also formed between the radiofrequency acceleration electrode  9 A of the return yoke  5 A and the facing radiofrequency acceleration electrode  9 A of the return yoke  5 B. A gap is also formed between the radiofrequency acceleration electrode  9 B of the return yoke  5 A and the facing radiofrequency acceleration electrode  9 B of the return yoke  5 B. Similarly, a gap is also formed between the radiofrequency acceleration electrode  9 C of the return yoke  5 A and the facing radiofrequency acceleration electrode  9 C of the return yoke  5 B, and a gap is also formed between the radiofrequency acceleration electrode  9 D of the return yoke  5 A and the facing radiofrequency acceleration electrode  9 D of the return yoke  5 B, which is not illustrated. 
         [0139]    All of the gaps formed between the magnetic poles and the gaps formed between the radiofrequency acceleration electrodes contain the median plane  77 , and form the beam turning region  76  in which ion beams turn in the horizontal direction. 
         [0140]    The massless septum  12  is disposed inside the recessions  29 A formed in the return yokes  5 A and  5 B (refer to  FIG. 5 ), and is positioned between the magnetic poles  7 A and  7 B. The massless septum  12  will be described in detail with reference to  FIGS. 7 and 8 . Each of the massless septum  12  and an energy absorber  62  (to be described later) is a beam separation apparatus that deviates an ion beam from a beam turning trajectory along which the ion beam turns. 
         [0141]    The massless septum  12  includes an iron core member  30  and coils  33 A and  33 B. The iron core member  30  includes iron core portions  31 A and  31 B made of steel and a connection portion  31 C made of steel. The flat plate-like iron core portion  31 A and the flat plate-like iron core portion  31 B are disposed while being parallel to and facing each other. One end portion of the iron core portion  31 A is connected to one end portion of the iron core portion  31 B via the connection portion  31 C. Multiple (for example, 28) magnetic poles  32 A which are protrusions are formed on a surface of the iron core portion  31 A which faces the iron core portion  31 B. The magnetic poles  32 A are disposed in a row in a longitudinal direction of the iron core portion  31 A, with a predetermined gap therebetween. The coil  33 A is separately wrapped around each of the magnetic poles  32 A. Multiple (for example, 28) magnetic poles  32 B which are protrusions are formed on a surface of the iron core portion  31 B which faces the iron core portion  31 A. The magnetic poles  32 B are disposed in a row in a longitudinal direction of the iron core portion  31 B, with a predetermined gap therebetween. The coil  33 B is separately wrapped around each of the magnetic poles  32 B. 
         [0142]    Wirings  23 A are respectively connected to both ends of each of the coils  33 A. As illustrated in  FIG. 8 , multiple wirings  23 A are bundled, one bundle of the wirings  23 A is attached to one side surface of the iron core portion  31 A, and the other bundle of the wirings  23 A is attached to the other side surface of the iron core portion  31 A. Wirings  23 B are respectively connected to both ends of each of the coils  33 B. As illustrated in  FIG. 8 , multiple wirings  23 B are bundled, one bundle of the wirings  23 B is attached to one side surface of the iron core portion  31 B, and the other bundle of the wirings  23 B is attached to the other side surface of the iron core portion  31 B. 
         [0143]    The multiple magnetic poles  32 A which are formed in the iron core portion  31 A, and the multiple magnetic poles  32 B, which are formed in the iron core portion  31 B, are disposed such that each one of the magnetic poles  32 A faces each one of the magnetic poles  32 B. A beam passage  35  is formed between the magnetic poles  32 A and the magnetic poles  32 B, and is a gap through which turning ion beams pass. The beam passage  35  contains a portion of the median plane  77 . 
         [0144]    One end portion of a bar-shaped operation member  16  is attached to the connection portion  31 C in which a through hole  31 D of the massless septum  12  is formed. The operation member  16  is a support member for the massless septum  12 , and is connected to a piston of a movement apparatus  17  including the piston and a cylinder (refer to  FIG. 3 ). A position detector  38  is attached to the movement apparatus  17 , and detects the position of the massless septum  12  inside the vacuum chamber  27  (refer to  FIG. 1 ). The operation member  16  is disposed between the annular coils  11 A and  11 B, and is slidably attached to the cylindrical portion  75 B in a state where the operation member  16  has passed through the cylindrical portion  75 B of the return yoke  5 B. The movement apparatus  17  may be a motor. In a case where a motor is used as the movement apparatus  17 , an encoder is used as the position detector  38 , and is connected to a rotational shaft of the motor. 
         [0145]    The massless septum  12  is a bending magnet apparatus that bends ion beams at different positions in the radial direction of the annular coils disposed inside the return yokes. 
         [0146]    A beam current measuring apparatus  98  includes a beam current measuring unit  15 ; a movement apparatus  17 A; and a position detector  39 . The beam current measuring unit  15  is disposed at the position of the recession  29 A on the median plane  77  inside the vacuum chamber  27 , and on the alternate long and short dash line X which passes through the central axis C of the vacuum chamber  27  and the injection electrode (refer to  FIG. 3 ). A bar-shaped operation member  16 A connected to the beam current measuring unit  15  passes through the vacuum chamber  27 , and extends to the outside of the vacuum chamber  27 . The operation member  16 A is a support member for the beam current measuring unit  15 . On the outside of the vacuum chamber  27 , the operation member  16 A is connected to a piston of the movement apparatus  17 A including the piston and a cylinder. The operation member  16 A is disposed between the annular coils  11 A and  11 B, and is slidably attached to the cylindrical portion  75 B in a state where the operation member  16 A has passed through the cylindrical portion  75 B of the return yoke  5 B. A position detector  39  is attached to the movement apparatus  17 A, and detects the position of the beam current measuring unit  15  inside the vacuum chamber  27  (refer to  FIG. 1 ). The movement apparatus  17 A may be a motor. In a case where a motor is used as the movement apparatus  17 A, an encoder is used as the position detector  39 , and is connected to a rotational shaft of the motor. 
         [0147]    The operation member  16 A is inserted into the beam passage  35  formed between the multiple magnetic poles  32 A and the multiple magnetic poles  32 B of the massless septum  12  through the through hole  31 D that is formed in the connection portion  31 C (refer to  FIG. 5 ). For this reason, when the operation member  16 A is moved in a radial direction of the vacuum chamber  27  along the alternate long and short dash line X, the beam current measuring unit  15  is moved on the median plane  77  inside the beam passage  35 . Since gaps between the beam turning trajectories  78  are wide at the position of the recession  29 A on the alternate long and short dash line X along end surfaces of the magnetic poles  32 A of the massless septum  12 , it is possible to easily measure a beam current of each of the beam turning trajectories  78  by moving the beam current measuring unit  15  on the alternate long and short dash line X in the radial direction of the annular coils and performing measurement. 
         [0148]    A radiofrequency power supply  36  is connected to the waveguide tube  10 D that is connected to the radiofrequency acceleration electrode  9 D (refer to  FIG. 1 ). The waveguide tubes  10 A,  10 B, and  10 C, which are respectively connected to the other radiofrequency acceleration electrodes  9 A,  9 B, and  9 C, are respectively connected to radiofrequency power supplies  36  which are respectively provided for the radiofrequency acceleration electrodes, which is not illustrated. A power supply  37  is connected to the lead-out wirings  21 C and  21 D which are respectively connected to both the ends of the trim coil  8 B provided on the magnetic pole  7 B (refer to  FIG. 1 ). The lead-out wirings, which are respectively connected to both the ends of the trim coil  8 A and  8 C to  8 F provided on the other magnetic poles  7 A and  7 C to  7 F, are respectively connected to power supplies  37  which are respectively provided for the magnetic poles, which are not illustrated. The radiofrequency power supplies and the magnetic poles are present inside the return yoke  5 B. In the return yoke  5 A, the radiofrequency acceleration electrodes  9 A,  9 B,  9 C, and  9 D are respectively connected to separate radiofrequency power supplies  36 , and the magnetic poles  7 A,  7 B,  7 C,  7 D,  7 E, and  7 F are respectively connected to separate power supplies  37 . The injection power supply  18  is connected to a power supply  82  via a wiring  81  (refer to  FIG. 1 ). 
         [0149]    A power supply  57  is connected to the two lead-out wirings  22  which are connected to the annular coil  11 B provided in the return yoke  5 B (refer to  FIG. 1 ). The power supply  57  is connected to the two lead-out wirings  22  which are connected to the annular coil  11 A provided in the return yoke  5 A. One power supply  40  is connected to the wirings  23 A and the wirings  23 B which are respectively connected to the coils  33 A and the coils  33 B which are respectively wrapped around the magnetic poles  32 A and the magnetic poles  32 B of the massless septum  12  (refer to  FIG. 1 ). 
         [0150]    An excitation current is supplied from the power supply  57  to the annular coils  11 A and  11 B via the respective lead-out wirings  22 . The iron cores  14 A and  14 B are magnetized due to action of the excitation current. An excitation current is supplied from the power supplies  37  to the respective trim coils  8 A to  8 F, which are provided on the magnetic poles  7 A to  7 F, via the lead-out wiring  21 A, the lead-out wiring  21 C, the lead-out wiring  21 E, the lead-out wiring  21 G, the lead-out wiring  21 G, the lead-out wiring  21 I, the lead-out wiring  21 K. As a result, the magnetic poles  7 A to  7 F are excited. The ion source  3  is started. A radiofrequency voltage is applied to the radiofrequency acceleration electrodes  9 A to  9 D from the respective radiofrequency power supplies  36  via the respective waveguide tubes  10 A to  10 D. A voltage is applied to the injection electrode  18  from the power supply  82 . 
         [0151]    Due to magnetization of the iron cores  14 A and  14 B, a magnetic circuit is formed by a closed loop from each of the magnetic poles  7 A to  7 F formed in the return yoke  5 B, each of the magnetic poles  7 A to  7 F formed in the return yoke  5 A, the base portion  74 A of the return yoke  5 A, the cylindrical portion  75 A of the return yoke  5 A, the cylindrical portion  75 B of the return yoke  5 B, the base portion  74 B of the return yoke  5 B, and each of the magnetic poles  7 A to  7 F formed in the return yoke  5 B. At this time, magnetic lines of force are generated from the bottom surfaces  95  of the recessions  29 A to  29 F of the return yoke  5 B toward the facing bottom surfaces  95  of the recessions  29 A to  29 F of the return yoke  5 A. Magnetic lines of force generated between facing bottom surfaces  95  are less than magnetic lines of force generated between facing magnetic poles. A magnetic field formed between facing magnetic poles (protrusions) is higher than a magnetic field formed between facing recessions. 
         [0152]    As a result, a magnetic field distribution illustrated in  FIG. 10  is formed on the median plane  77  inside the vacuum chamber  27 . This magnetic field distribution represents the distribution of isochronous magnetic fields. An isochronous magnetic field represents a magnetic field in which, even if the radius of a beam turning trajectory, along which an ion beam turn, is increased due to an increase in the energy of the accelerated ion beam, the length of time required for one turn of the ion beam is not changed. The isochronous magnetic fields are formed by the magnetic poles  7 A to  7 F. In  FIG. 10 , “high” represents a high magnetic field strength region, and “low” represents a low magnetic field strength region. High magnetic field strength regions and low magnetic field strength regions are alternately formed at the periphery of the ion inlet port, that is, the injection electrode  18 . For example, in a high magnetic field strength region, the highest magnetic field strength is 2.2 T, and in a low magnetic field strength region, the lowest magnetic field strength is 0.84 T. In the embodiment, there are six high magnetic field strength regions and six low magnetic field strength regions. When  FIGS. 3 and 10  overlap each other such that the positions of the injection electrodes  18  coincide with each other and the positions of the septum magnets (in  FIG. 10  a point (concentration point) at which beam turning trajectories  78  are offset toward the septum magnet  19 , and the multiple beam turning trajectories  78  are concentrated)  19  coincide with each other, the six high magnetic field strength regions respectively overlap the magnetic poles  7 A to  7 F illustrated in  FIG. 3 . That is, the magnetic poles are respectively disposed in the high magnetic field strength regions. The six low magnetic field strength regions respectively overlap the recessions  29 A to  29 F illustrated in  FIG. 3 . That is, the recessions are respectively disposed in the low magnetic field strength regions. 
         [0153]    Ions (for example, protons (H + )) released from the ion source  3 A are injected into the beam turning region  76  via the ion injection tube  3 A, and an advance direction of the ions is bent toward the horizontal direction in the beam turning region  76  due to action of the injection electrode  18  to which a voltage is applied. The injected protons are accelerated by the radiofrequency acceleration electrodes  9 A to  9 D in a state where the magnetic poles  7 A to  7 F and the annular coils  11 A and  11 B are excited. The protons are accelerated in the vicinity of the injection electrode  18  by the radiofrequency acceleration electrodes  9 C and  9 D, and are accelerated in the vicinity of the annular coils  11 A and  11 B by the radiofrequency acceleration electrodes  9 A to  9 D. The accelerated protons form a proton ion beam (hereinafter, simply referred to as an ion beam), and the proton ion beam turns on the median plane  77  along beam turning trajectories formed at the periphery of the injection electrode  18 . Specifically, since the ion beam is subjected to betatron oscillation in the direction perpendicular to the median plane  77 , the ion beam turns in the beam turning region  76  having a predetermined width with the median plane  77  as a center in the direction perpendicular thereto. 
         [0154]      FIG. 10  illustrates the beam turning trajectories  78  and magnetic field strength distributions on the median plane  77  inside the annular coil  11 B, and illustrates multiple isochronous lines  79 . An isochronous line represents a line that connects together the positions of turning ions (for example, protons) which are present at the same time. Each of the isochronous lines  79  illustrated by the dotted lines in  FIG. 10  extends radially from the injection electrode  18 , and is bent in the middle of the line (at the position of a beam turning trajectory of an ion beam of 35 MeV). Side surfaces of the magnetic poles  7 A to  7 F provided on each of the return yokes  5 A and  5 B respectively coincide with the corresponding isochronous lines  79  illustrated in  FIG. 10 . 
         [0155]    As illustrated in  FIG. 10 , in the accelerator  4 , multiple beam turning trajectories  78  are formed in the beam turning region  76 . In  FIG. 10 , in an ion beam energy range of 250 MeV or less, the beam turning trajectory  78  is illustrated for every 0.25 MeV of energy in an energy region having an energy of 0.5 MeV or less, for every 0.5 MeV of energy in an energy region having an energy range exceeding 0.5 MeV and less than or equal to 1 MeV, for every 1 MeV of energy in an energy region having an energy range exceeding 1 MeV and less than or equal to 10 MeV or less, for every 5 MeV of energy in an energy region having an energy range exceeding 10 MeV and less than or equal to 50 MeV, for every 10 MeV of energy in an energy region having an energy range exceeding 50 MeV and less than or equal to 100 MeV, for every 20 MeV of energy in an energy region having an energy range exceeding 100 MeV and less than or equal to 220 MeV, and for every 15 MeV of energy in an energy region having an energy range exceeding 220 MeV and less than or equal to 250 MeV. 
         [0156]    The beam turning trajectories  78 , along which ion beams of an energy of 35 MeV or less respectively turn, are annular beam turning trajectories centered around the injection electrode  18 . The beam turning trajectories  78 , along which ion beams of an energy exceeding 35 MeV respectively turn, are annular beam turning trajectories which are eccentric from the injection electrode  18 . As a result, between the injection electrode  18  and the septum magnet  19 , the centers of the beam turning trajectories  78  of ion beams of an energy exceeding 35 MeV are offset away from the inlet of the beam extraction path  20 , and gaps between the beam turning trajectories  78  are narrow on an inlet side of the beam extraction path  20 . Particularly, the beam turning trajectories  78  of ion beams of an energy exceeding 60 MeV are concentrated in a predetermined range on the inlet side of the beam extraction path  20 . In a region that is positioned 180° opposite to the inlet of the beam extraction path  20  relative to the injection electrode  18 , gaps between the beam turning trajectories  78  of ion beams of an energy exceeding 35 MeV are increased to the extent that the gaps between the beam turning trajectories  78  are decreased between the injection electrode  18  and the inlet of the beam extraction path  20 . 
         [0157]    The protons, which have passed through the ion injection tube  3 A and have been bent toward the horizontal direction in the beam turning region  76  by the injection electrode  18 , form an ion beam of a low energy, and the ion beam turns along a beam turning trajectory along which an ion beam of a low energy turns. The ion beam is accelerated in the portion of the radiofrequency acceleration electrode  9 C (to which a radiofrequency voltage has been applied) between the bent points  24 M and  24 N and the tip end, and in the portion of the radiofrequency acceleration electrode  9 D (to which a radiofrequency voltage has been applied) between the bent points  24 O and  24 P and the tip end. The accelerated ion beam moves to one of the beam turning trajectories  78  positioned outside the aforementioned beam turning trajectory. For example, an ion beam of 10 MeV turning along the beam turning trajectory  78  of an ion beam of 10 MeV is accelerated in the aforementioned portions of the radiofrequency acceleration electrodes  9 C and  9 D. The accelerated ion beam moves to the beam turning trajectory  78  of an ion beam of 11 MeV, and turns along the beam turning trajectory  8 . In this manner, the turning ion beam is accelerated and sequentially moves to the outside beam turning trajectories  78 , for example, moves to the beam turning trajectory  78  of an ion beam of 119 MeV. An ion beam of 119 MeV turning along this beam turning trajectory is accelerated by the radiofrequency acceleration electrodes  9 A to  9 D, and moves to the outside beam turning trajectory  78  of an ion beam of 220 MeV. 
         [0158]    An ion beam of 220 MeV turning along the beam turning trajectory  78  of an ion beam of 220 MeV is ejected from the beam turning trajectory  78  by the massless septum  12 , that is, is separated from the beam turning trajectory  78 , and then the ion beam of 220 MeV is extracted to the beam path  48  of the beam transport  13  through the beam extraction path  20  formed in the septum magnet  19 . An ion beam of 140 MeV turning along the beam turning trajectory  78  of an ion beam of 140 MeV is ejected therefrom by the massless septum  12 , and then the ion beam of 140 MeV is extracted to the beam path  48  through the beam extraction path  20 . As such, the accelerator  4  of the ion beam generator  2  is capable of extracting ion beams of different energies. The beam turning trajectories  78  are offset toward the inlet of the beam extraction path  20  and the gaps between the beam turning trajectories  78  are narrow between the injection electrode  18  and the inlet of the beam extraction path  20 . The gaps between the beam turning trajectories  78  are wide in the region that is positioned 180° opposite to the inlet of the beam extraction path  20  relative to the injection electrode  18 . As a result, the aforementioned extraction of ion beams can be realized. Particularly, in the eccentric trajectory region (to be described later), concentration of multiple beam turning trajectories  78  (along which ion beams of different energies turn) on the inlet side of the beam extraction path  20  contributes to extraction of the ion beams of different energies. The function of the massless septum  12  will be described in detail later. 
         [0159]    In the accelerator  4  of the embodiment, the following trajectory regions are formed on the median plane  77  on which the beam turning trajectories  78  are formed in the beam turning region  76 : the concentric trajectory region (for example, as illustrated in  FIG. 10 , a region that contains the beam turning trajectory  78  along which an ion beam of 35 MeV turns, and is positioned inside the beam turning trajectory  78 ) in which multiple concentric annular beam turning trajectories are formed around the injection electrode  18  (the ion inlet port of the ion injection tube  3 A); and the eccentric trajectory region (for example, as illustrated in  FIG. 10 , a region that is positioned outside the beam turning trajectory  78  along which an ion beam of 35 MeV turns) which surrounds the concentric trajectory region and in which multiple annular beam turning trajectories having the respective eccentric centers are formed, gaps between the annular beam turning trajectories are narrow between the injection electrode  18  and the inlet of the beam extraction path  20 , and the gaps between the annular beam turning trajectories are wide in the region that is positioned 180° opposite to the inlet of the beam extraction path  20  relative to the injection electrode  18 . 
         [0160]    The bent points  24 M to  24 P, which are formed in the radiofrequency acceleration electrodes  9 C and  9 D disposed inside the vacuum chamber  27 , are positioned at the position of the beam turning trajectory  78  along which an ion beam of 35 MeV turns illustrated in  FIG. 10 . 
         [0161]    In the accelerator  4 , a change in the gap between the magnetic pole  7 E of the return yoke  5 A and the facing magnetic pole  7 E of the return yoke  5 B along an isochronous line IL 1  is illustrated in  FIG. 11 , a change in the gap between the magnetic pole  7 C of the return yoke  5 A and the facing magnetic pole  7 C of the return yoke  5 B along an isochronous line IL 2  is illustrated in  FIG. 12 , and a change in the gap between the magnetic pole  7 A of the return yoke  5 A and the facing magnetic pole  7 A of the return yoke  5 B along an isochronous line IL 3  is illustrated in  FIG. 13 . Gaps illustrated in  FIGS. 11, 12 , and  13  respectively represent half the gap between the facing magnetic poles  7 E, half the gap between the facing magnetic poles  7 C, and half the gap between the facing magnetic poles  7 A. These gaps are respectively equivalent to a gap between the magnetic pole  7 E and the median plane  77 , a gap between the magnetic pole  7 C and the median plane  77 , and a gap between the magnetic pole  7 A and the median plane  77 . The isochronous lines IL 2 , IL 2 , and IL 3  are illustrated in  FIGS. 3 and 10 . The isochronous lines IL 2 , IL 2 , and IL 3  are respectively equivalent to the center lines of the magnetic poles  7 E,  7 C, and  7 A. 
         [0162]    As illustrated in  FIG. 11 , the gap between the magnetic pole  7 E and the median plane  77  becomes the minimum value when the gap is positioned from the tip end of the magnetic pole  7 E in a preferable range of 93.0% to 96.0% of the length between the tip end (facing the injection electrode  18 ) of the magnetic pole  7 E and the end surface (facing the inner surface of the annular coil  11 B) of the magnetic pole  7 E along the isochronous line IL 2 . This implies that the center line height (the height of the magnetic pole  7 E from the bottom surface  95  of each of the recessions  29 D and  29 E) of the magnetic pole  7 E in the direction of the central axis C becomes the maximum value at a position in this range. Similar to the magnetic pole  7 E, the center line height (the height of the magnetic pole  7 F from the bottom surface  95  of each of the recessions  29 C and  29 D) of the magnetic pole  7 F disposed symmetrical with the magnetic pole  7 E relative to the alternate long and short dash line X) in the direction of the central axis C becomes the maximum value when a portion of the magnetic poles  7 F is positioned from the tip end facing the injection electrode  18  in the aforementioned range relative to the center line length of the magnetic pole  7 F. 
         [0163]    As illustrated in  FIG. 12 , the gap between the magnetic pole  7 C and the median plane  77  becomes the minimum value when the gap is positioned from the tip end of the magnetic pole  7 C in a preferable range of 86.2% to 89.2% of the length between the tip end (facing the injection electrode  18 ) of the magnetic pole  7 C and the end surface (facing the inner surface of the annular coil  11 B) of the magnetic pole  7 C along the isochronous line IL 2 . This implies that the center line height (the height of the magnetic pole  7 C from the bottom surface  95  of each of the recessions  29 E and  29 F) of the magnetic pole  7 C in the direction of the central axis C becomes the maximum value at a position in this range. Similar to the magnetic pole  7 C, the center line height (the height of the magnetic pole  7 B from the bottom surface  95  of each of the recessions  29 B and  29 C) of the magnetic pole  7 D (disposed symmetrical with the magnetic pole  7 C relative to the alternate long and short dash line X) in the direction of the central axis C becomes the maximum value when a portion of the magnetic poles  7 D is positioned from the tip end facing the injection electrode  18  in the aforementioned range relative to the center line length of the magnetic pole  7 D. 
         [0164]    As illustrated in  FIG. 13 , the gap between the magnetic pole  7 A and the median plane  77  becomes the minimum value when the gap is positioned from the tip end of the magnetic pole  7 A in a preferable range of 88.7% to 91.7% of the length between the tip end (facing the injection electrode  18 ) of the magnetic pole  7 A and the end surface (facing the inner surface of the annular coil  11 B) of the magnetic pole A along the isochronous line IL 3 . This implies that the center line height (the height of the magnetic pole  7 A from the bottom surface  95  of each of the recessions  29 A and  29 F) of the magnetic pole  7 A in the direction of the central axis C becomes the maximum value at a position in this range. Similar to the magnetic pole  7 A, the center line height (the height of the magnetic pole  7 B from the bottom surface  95  of each of the recessions  29 A and  29 B) of the magnetic pole  7 B (disposed symmetrical with the magnetic pole  7 A relative to the alternate long and short dash line X) in the direction of the central axis C becomes the maximum value when a portion of the magnetic poles  7 B is positioned from the tip end facing the injection electrode  18  in the aforementioned range relative to the center line length of the magnetic pole  7 B. The position of the bottom surface  95  of the recession  29 E in the direction of the central axis C is the same as that of the bottom surface  95  of each of the recessions  29 A to  29 C and  29 F in the direction of the central axis C, which is not illustrated. 
         [0165]    In the return yoke  5 A, the center line height of each of the magnetic poles  7 E and  7 F in the direction of the central axis C becomes the maximum value at a position in the aforementioned range of the magnetic poles  7 E and  7 F of the return yoke  5 B. In the return yoke  5 A, the center line height of each of the magnetic poles  7 C and  7 D in the direction of the central axis C becomes the maximum value at a position in the aforementioned range of the magnetic poles  7 C and  7 D of the return yoke  5 B. In the return yoke  5 A, the center line height of each of the magnetic poles  7 A and  7 B in the direction of the central axis C becomes the maximum value at a position in the aforementioned range of the magnetic poles  7 A and  7 B of the return yoke  5 B. 
         [0166]    As a result, as illustrated in  FIG. 10 , in the magnetic field strength distribution on the median plane  77  between the return yokes  5 B and  5 A, magnetic field strength between the magnetic poles  7 E and  7 F of the return yoke  5 B and the facing magnetic poles  7 E and  7 F of the return yoke  5 A becomes the maximum value of 2.2 T at a position in the aforementioned range, magnetic field strength between the magnetic poles  7 C and  7 D of the return yoke  5 B and the facing magnetic poles  7 C and  7 D of the return yoke  5 A becomes the maximum value of 2.2 T at a position in the aforementioned range, and magnetic field strength between the magnetic poles  7 A and  7 B of the return yoke  5 B and the facing magnetic poles  7 A and  7 B of the return yoke  5 A becomes the maximum value of 2.2 T at a position in the aforementioned range. Accordingly, as illustrated in  FIG. 10 , magnetic field strength on the median plane  77  becomes the maximum value at the position of each of the beam turning trajectories  78  of ion beams of 200 MeV and 180 MeV in a region in which the magnetic poles  7 A to  7 F are disposed and which is positioned inside the inner surfaces of the annular coils  11 A and  11 B. Due to such a magnetic field strength distribution, a convergence force can be applied in a direction perpendicular to the beam turning trajectories, and ion beams are capable of stably turning along the beam turning trajectories  78 . 
         [0167]    In the accelerator  4  of the embodiment, the magnetic field distribution on the median plane  77  is not uniform, and thus, the formed beam turning trajectories  78  have an annular shape, and do not have a perfect circular shape. As described above, in the iron cores  14 A and  14 B, magnetic field strength at the positions of the magnetic poles (protrusions)  7 A to  7 F is higher than that at the positions of the recessions  29 A to  29 F, and thus, the curvatures of beam turning trajectories between facing magnetic poles respectively formed in the iron cores  14 A and  14 B are increased. Six pairs of the facing magnetic poles are disposed for one turn of the beam turning trajectory  78 . For this reason, each of the beam turning trajectories has a shape in which corners of a substantially hexagonal shape are positioned on the beam turning trajectory. In  FIG. 14 , this tendency becomes stronger by the extent of the increase in the amplitude of magnetic field strength along a beam turning trajectory. In a case the amplitudes of magnetic field strength are the same, this tendency becomes strong because bending of an ion beam becomes easier by the extent of the decrease in the energy of a beam turning trajectory. The center of a beam turning trajectory which does not have a perfect circular shape is the center of gravity of the shape of the trajectory, and is an arithmetic mean point of coordinates of the trajectory. 
         [0168]    In a typical cyclotron, to the extent that beam turning trajectories are present close to the outer circumference, bending of ion beams becomes difficult as the energies of the ion beams are increased, and dense formation of the ion beams becomes difficult. For this reason, it is necessary to increase the amplitudes of magnetic field strength along the beam turning trajectories illustrated in  FIG. 14 . That is, typically, the accelerator is designed such that radial magnetic field strength along the center line of each of the magnets becomes the maximum value on a beam turning trajectory (the outermost circumferential beam turning trajectory) of the maximum energy. 
         [0169]    Characteristics of the accelerator  4  in the embodiment will be described with reference to  FIGS. 14 to 21 . Hereinafter, unless specified, the direction perpendicular to the central axis C is referred to as a “horizontal direction”, and the direction of the central axis C, that is, the direction perpendicular to the median plane  77  is referred to as a “vertical direction”. 
         [0170]      FIG. 14  illustrates magnetic field strength distributions along four beam turning trajectories  78  along which an ion beam of 0.5 MeV, an ion beam of 70 MeV, an ion beam of 160 MeV, and an ion beam of 235 MeV respectively turn. A position for an advance distance of “0” represents the position of an intersection between each of the beam turning trajectories  78  and the straight line (the alternate long and short dash line X) (connecting the inlet of the beam extraction path  20  to the central axis C) in the vicinity of the inlet (extraction port of the accelerator  4 ) of the beam extraction path  20  formed in the septum magnet  19 . The position for an advance distance of “1” represents a half turn position of an ion beam which is away from the extraction port of the accelerator  4  along the beam turning trajectory  78 . Since magnetic field strength along the beam turning trajectory  78  for each of the beam turning trajectories  78  is changed as illustrated in  FIG. 14 , a convergence force (amplitude) can be ensured, and ion beams of energies are capable of stably turning along the respective beam turning trajectories  78 . For the beam turning trajectory  78  along which an ion beam of 235 MeV turns, a convergence force is ensured in a magnetic field strength distribution which is not a simple sinusoidal wave, and the ion beam is capable of stably turning along the beam turning trajectory. Specifically, a magnetic field is formed on the beam turning trajectory of an ion beam of 235 MeV such that, among six maximum peaks of the strength of the magnetic field through which the ion beam passes during one turn, maximum peaks positioned second and fifth from the position for an advance distance of 0 are lower than others, and the values of minimum peaks on both sides of the maximum peaks are higher than others. For this reason, a change in the amplitude of the magnetic field strength along the beam turning trajectory of an ion beam of 235 MeV is smaller than that of the beam turning trajectory of an ion beam of 160 MeV. 
         [0171]      FIG. 15  illustrates changes in the gradients of normalized magnetic fields along the respective beam turning trajectories  78 . A normalized magnetic field represents an n value in Expression (1). 
         [0000]    
       
         
           
             
               
                 
                   n 
                   = 
                   
                     
                       
                         B 
                          
                         
                             
                         
                          
                         ρ 
                       
                       
                         B 
                         2 
                       
                     
                      
                     
                       
                         ∂ 
                         
                           B 
                           z 
                         
                       
                       
                         ∂ 
                         r 
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
         [0172]    B represents magnetic field strength, Bρ represents magnetic rigidity of an ion beam, and B z  represents a vertical component of a magnetic field. r represents a vertical position coordinate with respect to a beam turning trajectory on a trajectory plane which is the median plane  77 , and an outward direction is considered to be positive. When n is less than one, an ion beam turning along a beam turning trajectory converges in the horizontal direction, and when n is greater than zero, an ion beam turning along a beam turning trajectory converges in the vertical direction. 
         [0173]    In three beam turning trajectories  78  along which an ion beam of 70 MeV, an ion beam of 160 MeV, and an ion beam of 235 MeV respectively turn, an n value at the position (half turn position from each intersection which will be described later) for an advance distance of “1” is a small value. In contrast, the absolute value of an n value is increased in the vicinity of positions for an advance distance of “0” on the beam turning trajectories  78 , which are the positions of the intersections between the beam turning trajectories  78  and the straight line (the alternate long and short dash line X) (connecting the inlet of the beam extraction path  20  to the central axis C) in the vicinity of the inlet (extraction port of the accelerator  4 ) of the beam extraction path  20 . As described above, at the position for an advance distance of “0”, the beam turning trajectories are concentrated, and gaps between adjacent beam turning trajectories are small. As a result, a magnetic field gradient, that is, the absolute value of an n value is increased. In contrast, the absolute value of a magnetic field gradient is decreased at the position (half turn position) for an advance distance of “1” at which gaps between adjacent beam turning trajectories are large. As such, a horizontal convergent action and a vertical convergent action are alternately exerted on ion beams turning along the respective beam turning trajectories, and thus, the ion beams are capable of stably turning in the horizontal and vertical directions. 
         [0174]    The characteristics illustrated in  FIG. 15  imply the following concept. The integrated absolute value of an n value (represented in Expression (2)) for a semicircle (the sum of a ¼ circle formed in a clockwise direction starting from the position for an advance distance of “1” and a ¼ circle formed in a counter-clockwise direction starting from the position for an advance distance of “1”) of each of the annular beam turning trajectories  78 , the midpoint of which is a position (position for an advance distance of “1”) 180° opposite to the inlet of the beam extraction path  20  with respect to the central axis C, is less than the integrated absolute value of an n value for a semicircle (the sum of a ¼ circle formed in the clockwise direction starting from the position for an advance distance of “0” and a ¼ circle formed in the counter-clockwise direction starting from the position for an advance distance of “0”) of the annular beam turning trajectory  78 , the midpoint of which is the intersection (position for an advance distance of “0”) on the inlet side of the beam extraction path  20 . 
         [0175]    The integrated absolute value of an n value (represented in Expression (1)) for a semicircle of an annular beam turning trajectory, the midpoint of which is the position 180° opposite to the inlet of the beam extraction path, is less than the integrated absolute value of an n value for a semicircle of the beam turning trajectory, the midpoint of which is the inlet of the beam extraction path. As a result, it is possible to efficiently extract ion beams of different energies, and in a case where beam turning trajectories of different energies are densely formed on the inlet side of the beam extraction path while being eccentric with each other, the dense formation allows a reduction in the gradients of magnetic fields generated on the inlet side of the beam extraction path. 
         [0176]    Hereinafter, a magnetic field distribution will be described in detail. Magnetic field strength B (L 1 ) at a position on a beam turning trajectory  78  is represented by Expression (2). 
         [0000]        B ( L   1 )= B   0   +B   1  cos(2π L   1   /L   2 )+ B   2  cos(4π L   1   /L   2 )+ B   3  cos(6π L   1   /L   2 )  (2)
 
         [0000]    B represents magnetic field strength, L 1  represents the advance distance of an ion beam along the beam turning trajectory, L 2  represents the length of a semicircle of the beam turning trajectory, B 0  represents a median value (average magnetic field strength exerted on the ion beam) of the magnetic field strength, and B 1 , B 2 , and B 3  represent Fourier expansion coefficients of the magnetic field strength of the beam turning trajectories  78  of energies. When the length of the semicircle of the beam turning trajectory is taken as a reference wavelength, B 1  represents a radiofrequency amplitude, B 2  represents a double radiofrequency amplitude, and B 3  represent a triple radiofrequency amplitude. 
         [0177]    In the embodiment, as illustrated in  FIG. 16 , in a case where the kinetic energy of an ion beam is approximately 180 MeV or higher, the triple radiofrequency magnetic field component B 3  is increased, and, at the same time, the double radiofrequency magnetic field component B 2  is decreased. For this reason, on the beam turning trajectory  78  along which an ion beam of an energy of 180 MeV or higher, it is possible to ensure a convergence force of the ion beam without increasing the maximum magnetic field. The triple radiofrequency magnetic field component B 3  is decreased to −0.5 T in a range from 0 MeV to 35 MeV which is the concentric trajectory region. 
         [0178]      FIG. 16  illustrates the fact that the absolute value of a change rate of the triple radiofrequency magnetic field component in the magnetic field strength distribution along the annular beam turning trajectory  78 , which is caused by the energy of an ion beam turning along the beam turning trajectory, is decreased at transition of the ion beam from the concentric trajectory region to the eccentric trajectory region.  FIG. 16  illustrates the fact that the value of the triple radiofrequency magnetic field component is decreased in the concentric trajectory region by the extent of the increase in the energy of an ion beam. 
         [0179]    The absolute value of a change rate of a triple radiofrequency magnetic field component in a magnetic field strength distribution along an annular beam turning trajectory, which is caused by the energy of an ion beam turning along the beam turning trajectory, is decreased at transition of the ion beam from the concentric trajectory region to the eccentric trajectory region surrounding the concentric trajectory region. As a result, it is possible to efficiently extract ion beams of different energies, and to stably accelerate ion beams. 
         [0180]      FIG. 17  illustrates a change in a betatron oscillation frequency in the horizontal and vertical directions versus the kinetic energy of an ion beam. The betatron oscillation frequency is substantially simply increased in the horizontal direction as the kinetic energy of the ion beam is increased. The change magnitude of the betatron oscillation frequency is 0.6 or less in a kinetic energy range of 0 MeV to 250 MeV. A beam turning trajectory is biased in the vertical direction in the vicinity of a kinetic energy of 50 MeV, and even if the kinetic energy is increased, the betatron oscillation frequency converges to 0.5 or less in the vertical direction. For this reason, ion beams are capable of stably turning in the beam turning region  76  that is formed between facing magnetic poles and between facing radiofrequency acceleration electrodes illustrated in  FIG. 6 . Ion beams are capable of stably passing though the beam passage  35  formed in the massless septum  12  illustrated in  FIG. 7 . 
         [0181]      FIG. 18  illustrates a change in a horizontal β function along each of the beam turning trajectories  78  for a half turn (advance distance of an ion beam: 1) from an intersection (advance distance of an ion beam: 0) between the straight line straight line (the alternate long and short dash line X) (connecting the central axis C to the inlet of the beam extraction path  20 ) and each of the beam turning trajectories  78  (along which ion beams of 0.5 MeV, 70 MeV, 160 MeV, and 235 MeV respectively turn) in the vicinity of the inlet of the beam extraction path  20 . A β function represents the amount of a spatial extent of an ion beam. The massless septum  12  is disposed at the position at which the advance distance of an ion beam is 1. 
         [0182]    In  FIG. 18 , the horizontal β function is 10 m or less at the position at which the massless septum  12  is disposed. As a result, it is possible to separate the beam turning trajectories  78  from each other along which the ion beams of 0.5 MeV, 70 MeV, 160 MeV, and 235 MeV respectively turn. For this reason, it is possible to separately eject the ion beams of the energies via the massless septum  12 , and to extract the ion beams from the accelerator  4  into the beam transport  13 . 
         [0183]      FIG. 19  illustrates a change in a vertical β function along each of the beam turning trajectories  78  for a half turn (advance distance of an ion beam: 1) from an extraction port (advance distance of an ion beam: 0) of each of the beam turning trajectories  78  along which ion beams of 0.5 MeV, 70 MeV, 160 MeV, and 235 MeV respectively turn. The vertical β function of each of the ion beams of 70 MeV, 160 MeV, and 235 MeV extracted from the accelerator  4  is 3 m or less at the position at which the massless septum  12  is disposed and the advance distance of each ion beam is 1. As a result, the ion beams of the energies are capable of easily passing through the beam passage  35  of the massless septum  12 . The vertical β function between the extraction port of each of the beam turning trajectories  78  and the half turn position is 100 m or less which is a limit in which the ion beams do not collide with the magnetic poles inside the accelerator  4 . As a result, the ion beams are capable of stably turning in the beam turning region  76  formed between facing magnetic poles and between facing radiofrequency acceleration electrodes without colliding the magnetic poles and the radiofrequency acceleration electrodes. 
         [0184]      FIG. 20  illustrates the amount of ejection (caused by excitation of the magnetic poles of the massless septum  12 ) of each ion beam turning along the beam turning trajectory  78  versus the kinetic energy of the turning ion beam when the ion beam is extracted from the accelerator  4 . In  FIG. 10 , the inlet of the beam extraction path  20  formed in the septum magnet  19  is positioned −720 mm from the center of a beam turning trajectory of the minimum energy. The energy of each ion beam extracted from the accelerator  4  is 70 MeV or higher. A “trajectory position” illustrated in  FIG. 20  represents the position of the beam turning trajectory  78  through which each ion beam, which has not been ejected by the massless septum  12 , passes, which is closest to the inlet of the beam extraction path  20 , and is present in the vicinity of the inlet of the beam extraction path  20 . The amount of offset between the trajectory position illustrated in  FIG. 20  and the inlet of the beam extraction path  20  represents the amount of trajectory displacement caused by ejection of a turning ion beam from the beam turning trajectory  78  via the massless septum  12 . The amount of ejection of a turning ion beam is increased by the extent of the decrease in the energy of the ion beam. An excitation current supplied to the coils  33 A and  33 B, which are respectively provided on a pair of the corresponding magnetic poles  32 A and  32 B of the massless septum  12 , is adjusted according to the amount of ejection. 
         [0185]    A pair of the magnetic poles  32 A and  32 B of the massless septum  12  generates magnetic lines of force (magnetic lines of force from the magnetic pole  32 B toward the magnetic pole  32 A) in the same direction as a direction of magnetic lines of force generated in the recessions  29 A of the return yokes  5 A and  5 B in which the massless septum  12  is disposed, and the pair of magnetic poles  32 A and  32 B is excited to intensify a magnetic field. A magnetic field peak illustrated in  FIG. 22  is formed at a predetermined position which is present in the beam passage  35  formed in the massless septum  12  and on the median plane  77  in the radial direction of the vacuum chamber  27 . The position of the magnetic field peak corresponds to the position of any one of the 28 pairs of magnetic poles  32 A and  32 B which are formed in the massless septum  12  and can be selectively excited. The curvature of an ion beam, which passes through a region in the beam passage  35  in which a magnetic field is locally intensified and which is formed by exciting the pair of magnetic poles  32 A and  32 B of the massless septum  12 , is increased compared to the curvature of the beam turning trajectory  78 . For this reason, betatron oscillation of the ion beam in the horizontal direction is amplified by the extent of the excitation amount and the width of the massless septum  12 , and the ion beam is ejected inward from the beam turning trajectory  78  along which the ion beam turns, and is separated from the beam turning trajectory  78 . Since it is possible to adjust the position of a pair of the magnetic poles  32 A and  32 B to be excited in the radial direction by moving the massless septum  12  in the radial direction via the movement apparatus  17 , similar to a case in which 28 or more pairs of the magnetic poles  32 A and  32 B are provided in the massless septum  12 , it is possible to accurately adjust the position of occurrence of the peak of magnetic field strength in the beam passage  35 . 
         [0186]      FIG. 21  illustrates a horizontal displacement of each of an ejected ion beam of 70 MeV, an ejected ion beam of 160 MeV, and an ejected ion beam of 235 MeV from the respective beam turning trajectories in the beam turning region  76  from when the ion beams of the energies are ejected by the massless septum  12  until the ion beams of the energies ejected from the massless septum  12  reach the inlet of the beam extraction path  20  formed in the septum magnet  19 . Unlike other drawings, in  FIG. 21 , the massless septum  12  is disposed at the position at which the advance distance of an ion beam is “0”, and the inlet (ion beam extraction position) of the beam extraction path  20  is positioned at the position (half turn position from the massless septum  12 ) at which the advance distance of an ion beam is “1”. A positive horizontal displacement value implies that an ejected ion beam is displaced toward the outside of the beam turning trajectory  78 , and a negative horizontal displacement (displacement on the median plane  77 ) value implies that an ejected ion beam is displaced toward the inside of the beam turning trajectory  78 . An ion beam, which has been ejected toward the inside of a beam turning trajectory by the massless septum  12 , is displaced inward to some extent, and then, is greatly displaced toward the outside of the beam turning trajectory according to betatron oscillation in the horizontal direction. The massless septum  12  is controlled such that the absolute value of a horizontal displacement of an ejected ion beam is increased to the extent that the energy of a turning ion beam is decreased. An outward displacement of the beam turning trajectory is increased at the ion beam extraction position. As illustrated in  FIG. 21 , the reason distances between the inlet of the beam extraction path  20  and the beam turning trajectories  78 , along which ion beams of different energies respectively turn, are different from each other is that distances between the septum magnet  19  and the beam turning trajectories  78  of the ion beams of the energies are different from each other as illustrated in  FIG. 20 . 
         [0187]    Due to the characteristics illustrated in  FIGS. 14 to 21 , the accelerator  4 , in which the concentric trajectory region and the eccentric trajectory region are formed, is capable of stably turning ion beams of energies along the respective beam turning trajectories  78 , and is capable of continuously extracting ion beams of different energies with which layers, into which a target volume (with which ion beams are irradiated) is divided and which are positioned at different depths, can be irradiated. 
         [0188]    A particle beam irradiation method of the particle beam irradiation system will be described with reference to  FIGS. 23 to 26 . 
         [0189]    Before a target volume of the patient  56  is irradiated with ion beams and is treated, treatment planning data is prepared for the patient  56  using treatment planning system  73 . The treatment planning data contains data regarding a patient identification number, the number of layers into which a target volume is divided from the body surface of the patient in a depth direction, the energy of an ion beam with which each layer is irradiated, an irradiation direction of an ion beam, an irradiation point (spot point) inside each layer, an ion beam dose for the irradiation point inside each layer, and the like. The treatment planning data prepared by the treatment planning system  73  is stored in the database  72  which is a storage apparatus. 
         [0190]    The CPU  67  reads the treatment planning data regarding the patient  56  to be treated here from the database  72  based on input patient identification information, and stores the treatment planning data in the memory  68 . The memory  68  stores the value of an excitation current which is supplied to the quadrupole magnets  46 ,  47 ,  49 , and  50  of the beam transport  13  and the bending magnets  41  to  44  to correspond to the energies (for example, 70 MeV to 235 MeV) of irradiating ion beams; position information regarding beam turning trajectories, along which the ion beams of energies respectively turn, on the median plane  77  inside the accelerator  4 ; and the value of an excitation current which is supplied to the coils  33 A and  33 B, which are respectively wrapped around the magnetic poles  32 A and  32 B of the massless septum  12 , when the ion beams turning along the beam turning trajectories are ejected. 
         [0191]    In order to treat the target volume of the patient  56 , the CPU  67 , which is a control information preparation apparatus, prepares control command information used to control the magnets of the beam transport  13  and the massless septum  12  based on the treatment planning data, the value of the excitation current supplied to the magnets of the beam transport  13 , the position information regarding the beam turning trajectories, and the value of the excitation current supplied to the coils  33 A and  33 B of the massless septum  12 . 
         [0192]    The memory  68  stores the sequence of steps illustrated in  FIG. 23 . The CPU  67  outputs the control command information to control apparatuses included in each of accelerator and transport control apparatus  69  and the scanning control apparatus  70 , based on the sequence. 
         [0193]    An excitation current is supplied to the annular coils and the trim coils (Step S 1 ). The coil current control apparatus  94  receives the control command information from the CPU  67 , and controls the power supplies  37  and the power supply  57  so as to execute Step S 1 . As described above, an excitation current is supplied from the power supplies  37  to the respective trim coils  8 A to  8 F, and the magnetic poles  7 A t  7 F are excited. An excitation current is supplied from the power supply  57  to the annular coils  11 A and  11 B, and the iron cores  14 A and  14 B are excited. As a result, magnetic lines of force are generated in the iron cores  14 A and  14 B. An annular coil current and a trim coil current illustrated in  FIG. 25  respectively flow through the annular coils  11 A and  11 B and the trim coils  8 A to  8 F. The vacuum pump  25  is driven all the time such that air inside the vacuum chamber  27  is discharged via the suction tube  26  and a vacuum state inside the vacuum chamber  27  is maintained. Through portions of the return yokes  5 A and  5 B of the vacuum chamber  27  for the waveguide tubes, the lead-out wirings, and the operation members  16  and  16 A are sealed with sealing members such that sealability is maintained. 
         [0194]    The ion source is started (Step S 2 ). The accelerator and transport control apparatus  69  receives the control command information from the CPU  67 , and starts and controls the ion source  3 . 
         [0195]    A radiofrequency voltage is supplied to the radiofrequency acceleration electrodes (Step S 3 ). In order to execute Step S 3 , the radiofrequency voltage control apparatus  99  adjust a radiofrequency voltage applied to the radiofrequency acceleration electrodes  9 A to  9 D by controlling the radiofrequency power supplies  36  based on the control command information from the CPU  67 . As a result, as described above, a radiofrequency voltage is applied to the radiofrequency acceleration electrodes  9 A to  9 D. A radiofrequency voltage having a frequency illustrated in  FIG. 25  is applied to the radiofrequency acceleration electrodes  9 A to  9 D. 
         [0196]    A voltage is applied to the injection electrode (Step S 4 ). In order to execute Step S 4 , the injection magnet control apparatus  83  applies a voltage to the injection electrode  18  by controlling the power supply  80  based on the control command information from the CPU  67 . Due to the application of a voltage to the injection electrode  18 , the ion source  3  injects ions (protons) into the ion injection portion  109  (formed in the beam turning region  76 ) through the ion inlet port formed at the tip end of the ion injection tube  3 A. The injected ions are bent toward the horizontal direction by the injection electrode  18 , are accelerated in the connection portion between the radiofrequency acceleration electrodes  9 C and  9 D which are positioned close to the ion injection portion  109 , and are started to turn in a counter-clockwise direction. 
         [0197]    An ion beam turns inside the accelerator until the energy of the ion beam is increased to a set energy (Step S 5 ). The injected ions form an ion beam, and in a state where the magnetic poles  7 A to  7 F and the annular coils  11 A and  11 B are excited, first, the ion beam is accelerated to an energy of 70 MeV by the radiofrequency acceleration electrodes  9 C and  9 D to which radiofrequency voltage have been applied. The ion beam is accelerated four times by the two radiofrequency acceleration electrodes during one turn of each of beam turning trajectories of energies of 70 MeV or less. In a region having an energy exceeding 70 MeV, the radiofrequency acceleration electrodes  9 A and  9 B, to which a radiofrequency voltage has been applied, also contribute to acceleration of the ion beam. As a result, the ion beam is accelerated to an energy of 220 MeV by the radiofrequency acceleration electrodes  9 A to  9 D. The ion beam is accelerated eight times by the four radiofrequency acceleration electrodes during one turn of each of beam turning trajectories of energies exceeding 70 MeV. The accelerated ion beam turns along the beam turning trajectories  78  on the median plane  77  inside the accelerator  4 , and the energy of the ion beam is increased to the set energy (for example, 250 MeV). At a position at which the massless septum  12  is disposed, the ion beams turning along the beam turning trajectories  78  for ion beams of 70 MeV to 250 MeV illustrated in  FIG. 10  pass through the beam passage  35  formed between facing magnetic poles  32 A and  32 B of the massless septum  12 . 
         [0198]    The target volume of the patient  56  is irradiated with an ion beam having an energy of 70 MeV or higher for treatment. The ion beam having an energy of 70 MeV or higher is an ion beam having the minimum energy among ion beams with which the target volume, which is a target for irradiation, is irradiated. 
         [0199]    Ion beams turning along the beam turning trajectories are measured (Step S 6 ). In order to execute Step S 6 , the beam current measuring unit control apparatus  84  controls the movement apparatus  17 A based on the control command information from the CPU  67 . The movement apparatus  17 A is driven by this control such that the operation member  16 A is moved. Typically, the beam current measuring unit  15 , which is pulled out to a position between the annular coils  11 A and  11 B, reaches the inside of the beam passage  35  through the through hole  31 D of the connection portion  31 C due to the movement of the operation member  16 A, and is moved toward the injection electrode  18  along the alternate long and short dash line X on the median plane  77 . While being moved toward the injection electrode  18 , the beam current measuring unit  15  measures a beam current of an ion beam turning along each of the beam turning trajectories (for example, as illustrated in  FIG. 10 , from the beam turning trajectory  78  along which an ion beam of 250 MeV turns to the beam turning trajectory  78  along which an ion beam of 70 MeV turns) for each of the beam turning trajectories  78 . The beam current values measured by the beam current measuring unit  15  are respectively equivalent to the energies of the ion beams turning along the beam turning trajectories  78 . Energy information items corresponding to the measured beam current values are sent to the beam current measuring unit control apparatus  84 . The position of the beam current measuring unit  15  toward the injection electrode  18  for each of the beam turning trajectories  78  is detected by the position detector  39 . Position information regarding the beam current measuring unit  15  detected by the position detector  39 , that is, position information items regarding the positions of the beam turning trajectories  78  in the radial direction of the annular coils is sent to the beam current measuring unit control apparatus  84 . The beam current measuring unit control apparatus  84  stores the energy information items corresponding to the measured beam current values and the position information items regarding the beam turning trajectories  78  in the memory  107  of the accelerator and transport control apparatus  69  in a state where the energy information items are respectively associated with the position information items.  FIG. 24  illustrates an example of information in which the energy information items are respectively associated with the beam turning trajectories  78 . 
         [0200]    It is determined whether the beam turning trajectories are respectively formed at predetermined positions (Step S 23 ). The coil current control apparatus  94  determines whether the beam turning trajectories  78  are respectively formed on the median plane  77  at the predetermined positions, based on the position information items regarding the beam turning trajectories  78  which are read from the memory  107 . 
         [0201]    The excitation current supplied to the trim coils is adjusted (Step S 24 ). When at least one beam turning trajectory  78  among the beam turning trajectories  78  is offset from the predetermined position, the determination result of Step S 23  is considered to be “No”. In this case, in order for the beam turning trajectory  78  (has been offset from the predetermined position) to be formed at the predetermined position, the coil current control apparatus  94  adjusts the excitation current supplied to the trim coils  8 A to  8 F by controlling the power supplies  37  which are respectively connected to the trim coils  8 A to  8 F installed on the magnetic poles  7 A to  7 F. The position of a beam turning trajectory is corrected by adjusting an excitation current. 
         [0202]    Thereafter, each of Steps S 6  and S 23  is executed. When the determination result of Step S 23  is considered to be “No”, each of Steps S 24 , S 6 , and S 23  is repeated until the determination result of Step S 23  becomes “Yes”. When all of the beam turning trajectories  78  are respectively formed on the median plane  77  at the predetermined positions, the determination result of Step S 23  becomes “Yes”, and Step S 7  is executed. 
         [0203]    Excitation amounts of the septum magnet and each magnet of the beam transport are adjusted (Step S 7 ). In order to execute Step S 7 , the magnet control apparatus  85  adjusts the excitation current, which is supplied to the septum magnet  19 , to an excitation current corresponding to the energy (for example, 250 MeV) of an ion beam to be extracted by controlling the power supply  82  based on the control command information from the CPU  67 . The septum magnet  19  is excited by the excitation current. The magnet control apparatus  85  adjusts the excitation current, which is supplied to the quadrupole magnets  46 ,  47 ,  49 , and  50  and the bending magnets  41  to  44  of the beam transport  13 , to an excitation current corresponding to an energy (for example, 250 MeV) of an ion beam to be extracted by controlling the separate power supplies (not illustrated) based on the control command information. The quadrupole magnets and the bending magnets are excited by the excitation current. The septum magnet  19  and each magnet provided in the beam transport  13  are excited such that the ion beam of 250 MeV can be transported to the extraction system  7 . 
         [0204]    The positions of the magnetic poles of the massless septum are adjusted (Step S 8 ). In order to execute Step S 8 , based on the control command information from the CPU  67 , the massless septum control apparatus  86  controls the movement apparatus  17  such that the movement apparatus  17  moves the operation member  16 . As a result, the massless septum  12  is moved toward the injection electrode  18  along the alternate long and short dash line X in the radial direction of the vacuum chamber  27  from a position that is 180° opposite to the inlet of the beam extraction path  20  relative to the central axis C of the vacuum chamber  27 . The massless septum  12  can be moved approximately 10 mm by the movement apparatus  17 . The massless septum  12  is moved this distance so as to finely perform adjustment of the positioning of a pair of facing magnetic poles  32 A and  32 B. Due to the movement of the massless septum  12 , in a region in which gaps between adjacent beam turning trajectories  78  (positioned 180° opposite to the inlet of the beam extraction path  20  relative to the central axis C) are wide, in a state where the massless septum  12  is aligned with the beam turning trajectory  78  along which the ion beam of 250 MeV turns, an injection electrode  18  side corner of each of the pair of magnetic poles  32 A and  32 B to be excited is aligned with the beam turning trajectory  78 . In this case, the position of the massless septum  12  inside the vacuum chamber  27  is a leftmost position of the massless septum  12  illustrated in  FIG. 25 . 
         [0205]    The magnetic poles of the massless septum are excited (Step S 9 ). After the pair of magnetic poles  32 A and  32 B are aligned with the beam turning trajectory  78  along which the ion beam of 250 MeV turns, in order to execute Step S 9 , the massless septum control apparatus  86  controls the power supply  40  based on the control command information from the CPU  67 . The massless septum control apparatus  86  controls a switch such that the power supply  40  is connected to the wirings  23 A and  23 B which are respectively connected to the coils  33 A and  33 B wrapped around the magnetic poles  32 A and  32 B to be excited. An excitation current is supplied from the power supply  40  to each of the coils  33 A and  33 B, and the pair of facing magnetic poles  32 A and  32 B to be excited are excited. Due to the excitation, magnetic lines of force are generated in a magnetic circuit formed by a closed loop from the excited magnetic poles  32 A and  32 B, to the iron core portion  31 B, to the connection portion  31 C, to the iron core portion  31 A, and to the magnetic pole  32 A. Magnetic lines of force from the magnetic pole  32 A toward the magnetic pole  32 B cross the beam path  35  which is formed between the magnetic poles and through which ion beams pass. Due to action of the magnetic lines of force, the ion beam of 250 MeV is ejected and separated from the beam turning trajectory  78  along which the ion beam turns, and the ion beam of 250 MeV moves toward the inlet of the beam extraction path  20  formed in the septum magnet  19 . 
         [0206]    Shortly, due to action of the excited septum magnet  19 , the ejected ion beam of 250 MeV is extracted to the beam path  48  of the beam transport  13  through the beam extraction path  20 . The ion beam is guided to the irradiation apparatus  7  through the beam path  48 , and is extracted from the irradiation apparatus  7 . At this time, the patient  56  does not lie on the treatment bed  55 . 
         [0207]    It is confirmed whether the ion beam is extracted from the accelerator (Step S 10 ). The beam point monitor  53  provided in the irradiation apparatus  7  detects the point of the ion beam passing through the irradiation apparatus  7 . Detected position information regarding the ion beam is input from the beam point monitor  53  to the ion beam confirmation apparatus  87 . When the ion beam confirmation apparatus  87  receives the position information regarding the ion beam, the ion beam confirmation apparatus  87  determines that the ion beam have been extracted from the accelerator  4 , and the ion beam confirmation apparatus  87  outputs the determination result to a display apparatus (not illustrated). An operator confirms extraction of the ion beam by observing the determination result displayed on the display apparatus. 
         [0208]    The aforementioned description of each of the step of extracting an ion beam from the accelerator is ended. 
         [0209]    Hereinafter, in the particle beam irradiation method, each of steps of irradiating layers of a target volume of a patient with ion beams of different energies will be described according to the sequence illustrated in  FIG. 26 . 
         [0210]    After the patient  56  lies on the treatment bed  55 , the treatment bed  55  is moved and a target volume is positioned on an extension line of the beam axis of the irradiation apparatus  7 . 
         [0211]    The rotating gantry is rotated such that the beam axis of the irradiation system is set to be aligned with an irradiation direction of an ion beam toward the target volume (target for beam irradiation) (Step S 11 ). The target volume of the patient  56 , on which treatment is performed by irradiating ion beams, is a target for beam irradiation. In order to execute Step S 11 , the rotation control apparatus  88  controls a rotation apparatus (not illustrated) of the rotating gantry  6  based on the control command information from the CPU  67 . The rotation apparatus is driven, and until the beam axis of the irradiation apparatus  7 , through which ion beams pass, is set to be aligned with the irradiation direction, the rotating gantry  6  is rotated around the rotational shaft  45  based on the information regarding the irradiation direction of an ion beam which is contained in the treatment planning data. When the beam axis of the irradiation apparatus  7  coincides with the irradiation direction, the rotation of the rotating gantry  6  is stopped. 
         [0212]    One inner layer of the target for beam irradiation, which is irradiated with an ion beam, is set (Step S 12 ). The irradiation point control apparatus  89  sets one inner layer of the target volume which is irradiated with an ion beam, based on the control command information from the CPU  67 . The irradiation point control apparatus  89  sets a layer at the most distal position as the one layer based on information regarding multiple divided layers of the target volume contained in the treatment planning data stored in the memory  70 . The irradiation point control apparatus  89  retrieves energy information (for example, 220 MeV) regarding an ion beam, with which the set layer is irradiated, from the memory  70 . The irradiation point control apparatus  89  outputs the retrieved energy information regarding the ion beam to the massless septum control apparatus  86 . 
         [0213]    The magnetic poles of the massless septum are positioned (Step S 13 ). Among the multiple magnetic poles  32 A and  32 B formed in the massless septum  12 , one pair of magnetic poles  32 A and  32   b , which are positioned on the beam turning trajectory  78  of an ion beam of 220 MeV corresponding to the energy (for example, 220 MeV) of the ion beam with which the set layer is irradiated, are positioned closer to the injection electrode  18  than another pair of facing magnetic poles  32 A and  32 B which have been positioned on the beam trajectory  78 , along which the ion beam of 250 MeV turns, in Step S 8 . The massless septum control apparatus  86  receives information regarding the layer, which has been set by the irradiation point control apparatus  89 , from the irradiation point control apparatus  89 . Among multiple pairs of magnetic poles  32 A and  32 B of the massless septum  12 , the massless septum control apparatus  86  specifies the pair of magnetic poles  32 A and  32 B which are positioned on the beam turning trajectory  78  of the ion beam of 220 MeV and are excited, based on the information regarding the energy (220 MeV) of the ion beam (with which the set layer is irradiated) input from the irradiation point control apparatus  89 , and the position information (position information regarding the beam current measuring unit  15  which is detected by the position detector  39 ) regarding the beam turning trajectory  78  which is stored in the memory  107  while being associated with energies. The massless septum control apparatus  86  obtains the amount of movement of the massless septum  12  in the radial direction of the annular coils which is required to position an injection electrode  18  side corner of each of the pair of magnetic poles  32 A and  32 B, which have been specified based on the position information regarding the beam turning trajectory  78  stored in the memory  107 , on the beam trajectory  78  of the ion beam of 220 MeV. 
         [0214]    The massless septum control apparatus  86  moves the massless septum  12  toward the injection electrode  18  by controlling the movement apparatus  17  based on the obtained amount of movement of the massless septum  12 . Due to this movement, in the region in which gaps between adjacent beam turning trajectories  78  (positioned 180° opposite to the inlet of the beam extraction path  20  relative to the central axis C) are wide, the injection electrode  18  side corner of each of the specified magnetic poles  32 A and  32 B to be excited is positioned on the beam turning trajectory  78  along which the ion beam of 220 MeV turns. It is possible to confirm the amount of movement of the massless septum  12  when the specified pair of magnetic poles  32 A and  32 B are positioned, based on position data regarding the massless septum  12  measured by the position detector  38 . Step S 13  is substantially the same as Step S 8 . 
         [0215]    The magnetic poles of the massless septum are excited (Step S 14 ). After the positioning of the magnetic poles in Step S 13  is ended, based on information regarding the specified pair of magnetic poles  32 A and  32   b , the massless septum control apparatus  86  controls the switch such that the power supply is connected to the wirings  23 A and  23 B which are respectively connected to the coils  33 A and  33 B wrapped around the one pair of magnetic poles  32 A and  32 B to be excited which are positioned in Step S 13 . The massless septum control apparatus  86  controls the power supply  40  based on the control command information from the CPU  67 , such that the power supply  40  outputs an excitation current to obtain the amount of ejection required to inject the ion beam of 220 MeV illustrated in  FIG. 20  into the inlet of the beam extraction path  20 . The excitation current is supplied to each of the coils  33 A and  33 B which are respectively wrapped around a pair of facing magnetic poles  32 A and  32 B to be excited which have been positioned as described above, and the pair of magnetic poles  32 A and  32 B to be excited are excited. Step S 13  is substantially the same as Step S 8 . 
         [0216]    The excitation amount of each of the septum magnet and the magnets of the beam transport is adjusted (Step S 7 ). The magnet control apparatus  85  receives the information regarding the layer, which has been set by the irradiation point control apparatus  89 , from the irradiation point control apparatus  89 . As described above, based on the energy information (for example, 220 MeV) regarding the ion beam with which the set layer is irradiated, the magnet control apparatus  85  controls the power supply  82  such that the septum magnet  19  is excited by an excitation current corresponding to 220 MeV of the extracted ion beam. As described above, the quadrupole magnets  46 ,  47 ,  49 , and  50  and the bending magnets  41  to  44  of the beam transport  13  are also excited by an excitation current corresponding to 220 MeV. At this time, the excitation amount of each of the septum magnet  19  and the magnets provided in the beam transport  13  becomes equal to an excitation amount illustrated by the second step from the left in the lowest characteristic graph of  FIG. 25 . 
         [0217]    The scanning magnets are controlled such that the irradiation point of an ion beam inside the set layer is set (Step S 15 ). When the irradiation point control apparatus  89  receives a signal indicating the end of adjustment of the excitation amount of each magnet from the magnet control apparatus  85 , based on information regarding an irradiation point inside the set layer contained in the treatment planning data, the irradiation point control apparatus  89  controls an excitation current supplied to each of the scanning magnets  51  and  52  to generate a bending magnetic field in each of the scanning magnets  51  and  52  such that the irradiation point, which is an ion beam target, is irradiated. The bending magnetic field generated in the scanning magnet  51  controls the point of an ion beam in the y direction, which is extracted from the accelerator  4  in Step S 16  (to be described later). The bending magnetic field generated in the scanning magnet  52  controls the point of the ion beam in the x direction perpendicular to the y direction, which is extracted from the accelerator  4 . 
         [0218]    When it is determined that the excitation current supplied to each of the scanning magnets  51  and  52  is controlled for the ion beam to reach the irradiation point which is an ion beam target in Step S 15 , the irradiation point control apparatus  89  outputs a beam irradiation start signal. 
         [0219]    A voltage is applied to the injection electrode (Step S 16 ). Similar to Step S 4 , when the injection electrode control apparatus  83  receives a beam irradiation start signal from the irradiation point control apparatus  89 , the injection electrode control apparatus  83  controls the power supply  80  such that a voltage is applied to the injection electrode  18 . Ions, which have been injected into the beam turning region  76  from the ion source  3  via the ion injection tube  3 A, are bent toward the horizontal direction by the injection electrode  18 , turn on the median plane  77 , and are accelerated by the radiofrequency acceleration electrodes  9 A to  9 D to a radiofrequency voltage is applied. An ion beam turning along the beam turning trajectory  78 , along which an ion beam of 220 MeV turns, enters the beam passage  35  formed between the pair of magnetic poles  32 A and  32 B which have been excited in Step S 14 . The ion beam entering the beam passage  35  is ejected from the beam turning trajectory  78 , along which the ion beam turns, due to action of the pair of excited magnetic poles  32 A and  32 B. That is, the ion beam is separated from the beam turning trajectory  78 . Thereafter, the ion beam is separated from the beam turning trajectory  78 , and moves toward the inlet of the beam extraction path  20 . Due to action of the septum magnet  19 , the ion beam is extracted from the accelerator  4  to the beam path  48  through the beam extraction path  20 . The ion beam reaches the irradiation apparatus  7 , and a target irradiation point inside the set layer is irradiated with the ion beam due to action of the scanning magnets  51  and  52 . 
         [0220]    The point of the ion beam, with which the target irradiation point is irradiated, is measured by the beam monitor  53 , and based on the measured point, it is confirmed whether the target irradiation point is irradiated with the ion beam. 
         [0221]    It is determined whether an irradiation dose applied to the irradiation point coincides with a target dose (Step S 17 ). An irradiation does applied to the target irradiation point is measured by the dose monitor  54 . The measured irradiation does is input to the dose determination apparatus  91 . The dose determination apparatus  91  determines whether the irradiation dose, with which the target irradiation point has been irradiated and which has been measured, reaches the target irradiation dose. When the measured irradiation dose does not coincide with the target irradiation dose, the determination of Step S 17  becomes “No”. Each of Steps  16  and  17  is repeatedly executed, and until the measured irradiation dose coincides with the target irradiation dose, the target irradiation point is continuously irradiated with an ion beam. When the measured irradiation dose coincides with the target irradiation dose (When the determination of Step S 17  is “Yes”), the dose determination apparatus  91  outputs a beam extraction stop signal to the injection electrode control apparatus  83 . 
         [0222]    The application of a voltage to the injection electrode is stopped (Step S 18 ). When the injection electrode control apparatus  83  receives a beam extraction stop signal from the dose determination apparatus  91 , the injection electrode control apparatus  83  controls the power supply  80  such that the power supply  80  stops applying a voltage to the injection electrode  18 . As a result, injection of protons into the beam turning region  76  from the ion source  3  is stopped, and extraction of an ion beam to the beam path  48  from the accelerator  4  is stopped. That is, the irradiation of the target volume with an ion beam is stopped. 
         [0223]    It is determined whether irradiation of the inside of the set layer with an ion beam is ended (Step S 19 ). When irradiation of an irradiation point with an ion beam is ended, the layer determination apparatus  92  determines that the irradiation of the irradiation point inside the set layer with the ion beam is ended. When the determination result is “No”, that is, when the irradiation of the irradiation point inside the set layer with the ion beam is not ended, each of Steps S 15  to S 19  is repeatedly executed. In repeated Step S 15 , an excitation current supplied to each of the scanning magnets  51  and  52  is controlled such that another target irradiation point inside the set layer is irradiated with an ion beam. 
         [0224]    When the other irradiation point is irradiated with an ion beam in Step S 16 , and the determination of Step S 17  becomes “Yes”, application of a voltage to the injection electrode  18  is stopped in Step S 17 . 
         [0225]    When the determination of Step S 19  becomes “Yes”, it is determined whether irradiation of all of the layers with ion beams is ended (Step S 20 ). The layer determination apparatus  92  determines whether irradiation of all of the layers with ion beams is ended. Since there remains a layer which has not been irradiated with an ion beam, the determination of Step S 20  becomes “No”, and Steps S 12  to S 14 , S 7 , and S 15  to S 20  are repeatedly executed in the listed sequence. In Step S 12 , a layer at a second distal position is set. An energy required by an ion beam, with which the layer is irradiated, is 219 MeV. 
         [0226]    In repeated Step S 13 , similar to Step S 13 , the injection electrode  18  side corner of each of the one pair of magnetic poles  32 A and  32 B, which have been aligned with the beam turning trajectory  78  along which the ion beam of 220 MeV moves, is positioned on the beam turning trajectory  78  of an ion beam of 219 MeV. The amount of movement of the massless septum  12  in this case becomes greater than that when the magnetic poles  32 A and  32 B are positioned on the beam turning trajectory  78  along which the ion beam of 220 MeV moves. The one pair of magnetic poles  32 A and  32 B are excited in Step S 14 . 
         [0227]    In Steps S 15  and S 16 , when a voltage is applied to the injection electrode  18 , the ion beam turns along the beam turning trajectory  78 , and due to action of the one pair of excited magnetic poles  32 A and  32 B, the ion beam of 219 MeV is ejected from the beam turning trajectory  78  along which the ion beam of 219 MeV turns. The irradiation apparatus  7  irradiates an irradiation point inside a second distal layer of the target volume with the ejected ion beam. When the determination of Step S 17  becomes “Yes”, Step S 18  is executed, and the irradiation of the irradiation point with the ion beam is stopped. 
         [0228]    When the determination of Step S 19  becomes “No”, each of Steps S 15  to S 19  is repeated until the determination of Step S 19  becomes “Yes”. When the determination of Step S 19  becomes “No”, Steps S 12  to S 14 , S 7 , and S 15  to S 20  are repeatedly executed in the listed sequence until the determination of Step S 20  becomes “Yes”. When each of Steps S 12  to S 14 , S 7 , and S 15  to S 20  is repeated, in Step S 12 , a more proximal layer is set, and the energy of an ion beam reaching the layer is gradually decreased (for example, energy is decreased in a scale of 1 MeV from 220 MeV). In Steps S 13  and S 14 , a pair of facing magnetic poles  32 A and  32 B of the massless septum  12  are positioned on the beam turning trajectory  78  along which an ion beam of a low energy turns, and thereafter, the magnetic poles are excited. When an ion beam of 180 MeV and an ion beam of 160 MeV are extracted from the accelerator  4 , in Step S 14 , another pair of magnetic poles  32 A and  32 B, which are positioned adjacent to an injection electrode  18  side of a pair of magnetic poles  32 A and  32 B that are excited when an ion beam of 220 MeV and an ion beam of 200 MeV are extracted, is excited. In a case where the ion beam of 160 MeV is extracted, the amount of movement of the massless septum  12  when the magnetic poles are positioned in Step  13  becomes greater than that in a case where the ion beam of 180 MeV is extracted. 
         [0229]    When the determination of Step S 20  becomes “Yes”, irradiation of the target volume with ion beams is ended (Step S 21 ). 
         [0230]    The ion beam irradiation treatment of the target volume of the patient  56  is ended. 
         [0231]    In the embodiment, the iron cores  14 A and  14 B have a circular shape suitable for forming an outermost circumferential beam turning trajectory on the median plane  77 , however, may have another shape. The annular coils  11 A and  11 B also have a circular shape, however, may have another shape, for example, a clover shape in which the annular coils  11 A and  11 B surround the magnetic poles formed on the base portions of the return yokes. 
         [0232]    In a typical cyclotron, ion beams can be extracted only from a beam turning trajectory of an ion beam of the highest energy, which is formed at the outermost circumference. In contrast, in the embodiment, it is possible to densely form the multiple beam trajectories  78  of different energies in the vicinity of the septum magnet  19  and the inlet of the beam extraction path  20  by forming the eccentric beam trajectory region in an outer circumferential portion of the accelerator in which gaps between the beam trajectories are narrow. Therefore, at any time, it is possible to selectively extract ion beams of different energies not only from the beam trajectory  78  which is positioned at the outermost circumference and along which an ion beam of the highest energy turns, but also from multiple beam turning trajectories  78  formed inside the beam turning trajectory  76 . For this reason, in the embodiment, ion beams of different energies can be efficiently extracted from the accelerator  4 . 
         [0233]    In the embodiment, in the eccentric trajectory region, the multiple annular beam turning trajectories  78  having the respective eccentric centers are densely formed between the injection electrode  18 , the ion inlet port, or the ion injection portion  109  and the inlet of the beam extraction path  20  and the gaps between the annular beam turning trajectories  78  are wide in the direction that is 180° opposite to the inlet of the beam extraction path  20  relative to the injection electrode  18 . The eccentric trajectory region is present at the periphery of the injection electrode  18  (or the ion inlet port or the ion injection portion  109 ) in the beam turning region  76 , and is formed on the median plane  77  on which the beam turning trajectories  78  are formed. Therefore, in the eccentric beam turning trajectory region, the gaps between the beam turning trajectories  78  of ion beams of different energies are wide in the direction that is 180° opposite to the inlet of the beam extraction path  20  relative to the injection electrode  18 . It is possible to efficiently separate ion beams of different energies from the respective beam turning trajectories  78 . For this reason, it is possible to efficiently extract ion beams of different energies to the beam path  48  of the beam transport  13  through the beam extraction path  20  formed in the septum magnet  19  of the accelerator  4 . In the embodiment, it is possible to continuously extract ion beams of different energies from the accelerator  4 . 
         [0234]    In the embodiment, the concentric trajectory region, in which the multiple annular beam turning trajectories  78  are formed concentric around the injection electrode  18 , is formed inside the eccentric trajectory region on the median plane  77 . Therefore, the degree of concentration of the beam turning trajectories  78  is reduced in the vicinity of the inlet of the beam extraction path  20  through which ion beams are extracted. As a result, a magnetic field gradient in the vicinity of the inlet is further decreased. Ion beams of different energies are capable of more stably turning along the respective beam turning trajectories  78 . 
         [0235]    Since the ion injection portion  109  (or the injection electrode  18  or the ion inlet port) is disposed at the position that is different from that of the center of gravity of the annular coils in the radial direction, the gaps between the multiple adjacent annular beam turning trajectories  78  (formed at the periphery of the ion injection portion (or the injection electrode  18  or the ion inlet port)) are wide in the region positioned opposite to the inlet of the beam extraction path  20  with reference to the ion injection portion (or the injection electrode  18  or the ion inlet port) compared to that in a region closer to the inlet of the beam extraction path  20  than the ion injection portion  109  (or the injection electrode  18  or the ion inlet port). For this reason, in the region in which gaps between adjacent beam turning trajectories  78  are wide and which is positioned opposite to the inlet of the beam extraction path  20 , it is possible to easily separate ion beams from the respective beam turning trajectories  78 , and it is possible to efficiently extract ion beams of different energies turning along the respective annular beam turning trajectories  78 . 
         [0236]    Since the ion injection portion  109  (or the injection electrode  18  or the ion inlet port) is disposed at the position that is different from that of the center of the iron cores in the radial direction, the gaps between the multiple adjacent annular beam turning trajectories  78  (formed at the periphery of the ion injection portion  109  (or the injection electrode  18  or the ion inlet port)) are wide in the region positioned opposite to the inlet of the beam extraction path  20  with reference to the ion injection portion  109  (or the injection electrode  18  or the ion inlet port) compared to that in the region closer to the inlet of the beam extraction path than the ion injection portion  109  (or the injection electrode  18  or the ion inlet port). For this reason, in the region in which gaps between adjacent beam turning trajectories  78  are wide and which is positioned opposite to the inlet of the beam extraction path  20 , it is possible to easily separate ion beams from the respective beam turning trajectories  78 , and it is possible to efficiently extract ion beams of different energies turning along the respective annular beam turning trajectories  78 . 
         [0237]    Since tip end portions of portions (extending toward the inside of the annular coil from the positions of inner surfaces of the radiofrequency acceleration electrodes  9 C and  9 D) of the radiofrequency acceleration electrodes  9 C and  9 D are respectively disposed at positions which are different from that of the center of gravity of the annular coil in the radial direction, the gaps between the multiple adjacent annular beam turning trajectories  78  (formed at the periphery of the positions at which the tip end portions of the radiofrequency acceleration electrodes  9 C and  9 D are respectively disposed) are wide in the region positioned opposite to the inlet of the beam extraction path  20  with reference to the ion injection portion  109  (or the injection electrode  18  or the ion inlet port) compared to that in the region closer to the inlet of the beam extraction path  20  than the ion injection portion  109  (or the injection electrode  18  or the ion inlet port). For this reason, in the region in which gaps between adjacent beam turning trajectories  78  are wide and which is positioned opposite to the inlet of the beam extraction path  20 , it is possible to easily separate ion beams from the respective beam turning trajectories  78 , and it is possible to efficiently extract ion beams of different energies turning along the respective annular beam turning trajectories  78 . 
         [0238]    Since the magnetic poles (protrusions)  7 A to  7 F are installed in such a way as to extend radially inward from the outer circumference of the iron core toward the position that is different from that of the center of gravity of the iron core in the radial direction, the gaps between the multiple adjacent annular beam turning trajectories  78  (formed at the periphery of the position at which respective tip end portions of the magnetic poles  7 A to  7 F are disposed and which is different from that of the center of gravity of the iron core in the radial direction) are wide in the region positioned opposite to the inlet of the beam extraction path  20  with reference to the ion injection portion  109  (or the injection electrode  18  or the ion inlet port) compared to that in the region closer to the inlet of the beam extraction path  20  than the ion injection portion  109  (or the injection electrode  18  or the ion inlet port). For this reason, in the region in which gaps between adjacent beam turning trajectories  78  are wide and which is positioned opposite to the inlet of the beam extraction path  2 , it is possible to easily separate ion beams from the respective beam turning trajectories  78 , and it is possible to efficiently extract ion beams of different energies turning along the respective annular beam turning trajectories  78 . 
         [0239]    In the embodiment, the multiple beam turning trajectories  78  are densely formed in the vicinity of the inlet of the beam extraction path  20 , and thus, ion beams of different energies separated from the respective beam turning trajectories  78  can be easily injected into the inlet of the beam extraction path  20 , and it is possible to efficiently extract ion beams of different energies. 
         [0240]    In the embodiment, the position of the center of the annular beam turning trajectories  78  formed by the magnetic poles  7 A to  7 F is different from that of the center of gravity of the annular coils, and thus, the gaps between the multiple adjacent annular beam turning trajectories  78 , which are formed at the periphery of the ion injection portion  109  (or the injection electrode  18  or the ion inlet port), are wide in a region close to the center of the annular beam turning trajectories  78  compared to that in the region close to the inlet of the beam extraction path  20 . For this reason, in the region in which gaps between adjacent beam turning trajectories  78  are wide and which is positioned close to the center of the beam turning trajectories  78 , it is possible to easily separate ion beams from the respective beam turning trajectories  78 , and it is possible to efficiently extract ion beams of different energies turning along the respective annular beam turning trajectories  78 . 
         [0241]    In the embodiment, a region having the highest magnetic field strength on the median plane  77  is formed closer to the ion injection portion  109  (or the injection electrode  18  or the ion inlet port) than an outermost circumferential beam turning trajectory  78  in a first magnetic field region, and thus, it is possible to efficiently extract ion beams of different energies, and to improve stability of an ion beam turning along a beam turning trajectory that is positioned in the outer circumferential portion among the multiple annular beam turning trajectories  78  formed on the median plane  77 . 
         [0242]    In the embodiment, in the pair of iron cores  14 A and  14 B, the magnetic poles  7 A to  7 F are formed at the periphery of the ion injection portion  109  (or the injection electrode  18  or the ion inlet port) such that the magnetic poles  7 A to  7 F extend radially from the ion injection portion  109  (or the injection electrode  18  or the ion inlet port) and the respective tip ends of the magnetic poles  7 A to  7 F face the ion injection portion  109  (or the injection electrode  18  or the ion inlet port), the recessions  29 A to  29 F are formed at the periphery of the ion injection portion  109  (or the injection electrode  18  or the ion inlet port) in such a way as to extend radially from the ion injection portion  109  (or the injection electrode  18  or the ion inlet port), the magnetic poles and the recessions are alternately disposed at the periphery of the ion injection portion  109  (or the injection electrode  18  or the ion inlet port), and the annular coils  11 A and  11 B surround the respective magnetic poles  7 A to  7 F and the respective recessions  29 A to  29 F which are respectively disposed inside the iron cores  14 A and  14 B. As a result, it is possible to stably inject ions into the beam turning region  76  via the ion injection tube  3 A. 
         [0243]    In the embodiment, the inlet of the beam extraction path  20  opens in the recessions (the second recession)  29 D, and thus, ion beams separated from the respective annular beam turning trajectories  78  can be easily injected into the inlet of the beam extraction path  20 , and it is possible to efficiently extract ion beams of different energies turning along the respective annular beam turning trajectories  78 . The reason for this is that the annular beam turning trajectories  78  formed in the eccentric trajectory region are densely formed in the recession  29 A on the inlet side of the beam extraction path  20 . 
         [0244]    In the embodiment, each of the magnetic poles  7 A to  7 F has the bent points, and the portion of each of the magnetic poles  7 A to  7 F between the bent points and the end surface thereof facing the inner surface of the annular coil is bent toward the recession  29 A. As a result, an eccentric beam region, in which there are the multiple eccentric beam turning trajectories  78 , is formed, gaps between beam turning trajectories are wide, and it is possible to efficiently extract ion beams of different energies turning along the respective annular beam turning trajectories  78 . 
         [0245]    In the embodiment, beam current measuring apparatus  98  is disposed in the recession  29 A, and thus, it is possible to obtain energy information items regarding ion beams turning along the respective beam turning trajectories  78  and position information items regarding the positions of the beam turning trajectories  78  in the radial direction of the annular coils by performing measurement via the beam current measuring apparatus  98 . It is possible to obtain position information regarding the beam turning trajectory  78  corresponding to the energy of an ion beam with which a set layer contained a target volume is irradiated, based on the energy information items regarding the ion beams and the position information items regarding the beam turning trajectories  78 . It is possible to specify a pair of facing magnetic poles  32 A and  32 B to be excited of the massless septum  12  based on the position information. It is possible to accurately position the pair of facing magnetic poles  32 A and  32  to be excited on the beam turning trajectory  78  along which the ion beam of an energy (with which the set layer is irradiated) turns. 
         [0246]    Since the beam current measuring unit  15  of the beam current measuring apparatus  98  can be moved inside the recession  29 A toward the ion injection portion  109  (or the injection electrode  18  or the ion inlet port) along the median plane  77  by the movement apparatus  17 A, it is possible to obtain a wide range of energy information regarding ion beams for the respective beam turning trajectories  78  and a wide range position information regarding the beam turning trajectories  78 . 
         [0247]    When the position of the beam turning trajectory  78 , which is measured by the beam current measuring apparatus  98  disposed in the recession  29 A, does not coincide with a predetermined position, an excitation current, which is supplied to the trim coils  8 A to  8 F attached to the respective magnetic poles  7 A to  7 F, is adjusted by the coil current control apparatus  94 . As a result, even if the beam turning trajectory  78 , which is not present at the predetermined position, is formed, it is possible to form the beam turning trajectory  78  at the predetermined position. 
         [0248]    In the embodiment, as described above, in each of the pair of iron cores  14 A and  14 B, in regions which are positioned on a plane perpendicular to the central axis C and on both sides of the alternate long and short dash line X, the radiofrequency acceleration electrode  9 C with the tip end facing the injection electrode  18  is disposed between the magnetic poles  7 C and  7 E adjacent to each other in the circumferential direction of the vacuum chamber  27 , the radiofrequency acceleration electrode  9 D with the tip end facing the injection electrode  18  is disposed between the magnet  7 D and the magnetic pole  7 F adjacent to each other in the circumferential direction of the vacuum chamber  27 , the portion of the radiofrequency acceleration electrode  9 C between the bent points  24 M and  24 N and the end surface of the radiofrequency acceleration electrodes  9 C facing the annular coil  11 A or  11 B is bent toward the recession  29 A, the portion of the radiofrequency acceleration electrode  9 C between the bent points  24 M and  24 N and the end surface of the radiofrequency acceleration electrode  9 C facing either the annular coil  11 A or the annular coil  11 B is bent toward the recession  29 A. As a result, it is possible to easily accelerate ion beams turning along the respective beam turning trajectories  78  which are present between the beam turning trajectory  78  close to the injection electrode  18  and the beam turning trajectory  78  close to the annular coil  11 A or  11 B. In the embodiment, the radiofrequency acceleration electrodes  9 A and  9 B are respectively disposed between the magnetic poles  7 A and  7 C and between the magnetic poles  7 B and  7 D, and are respectively disposed between the bent points of the respective magnetic poles and the end surfaces thereof facing either the annular coil  11 A or the annular coil  11 B. As a result, it is possible to easily accelerate ion beams turning along the respective beam turning trajectories  78  of ion beams of high energies. 
         [0249]    In the embodiment, the beam current measuring unit  15  is disposed in the recession  29 A and on the median plane  77 , and is moved on the median plane  77  along the alternate long and short dash line X by the movement apparatus  17 , and the position of the moving beam current measuring unit  15  on the median plane  77  is detected by the position detector  39 . As a result, as described above, it is possible to accurately detect a beam current value of each of the beam turning trajectories  78  and the position of each of the beam turning trajectories  78 . 
         [0250]    Since the massless septum  12  is disposed in the respective recessions  29 A of the pair of iron cores  14 A and  14 B, it is possible to easily dispose the massless septum  12  between the iron cores  14 A and  14 B. 
         [0251]    Since the massless septum  12  is disposed in the recessions  29 A, the massless septum  12  is positioned in a portion of the eccentric beam turning trajectory region in which gaps between the beam turning trajectories  78  are wide, and it is possible to efficiently separate ion beams of different energies from the respective beam turning trajectories  78  via the massless septum  12 . As a result, it is possible to efficiently extract ion beams of different energies from the accelerator  4 . 
         [0252]    Since the massless septum  12  includes the multiple pairs of facing magnetic poles  32 A and  32 B, it is possible to position the massless septum  12  on the beam turning trajectory  78  based on the energy of an ion beam with which a set layer of a target volume is irradiated, and to easily specify a pair of the magnetic poles  32 A and  32 B to be excited. 
         [0253]    Since the movement apparatus  17  is provided to move the massless septum  12  in the radial direction of the annular coils, it is possible to perform adjustment of the positioning of a pair of the magnetic poles  32 A and  32 B to be excited of the massless septum  12  on the beam turning trajectory  78  along which an ion beam of energy (with which a set layer of a target volume is to be irradiated) turns. For this reason, it is possible to accurately position a pair of the magnetic poles  32 A and  32 B on the corresponding beam turning trajectory  78 . 
         [0254]    In a particle beam irradiation system using a cyclotron, a degrader including multiple metal plates of different thicknesses is provided in a beam transport to change the energy of an ion beam with which a target volume is irradiated. In contrast, as described above, in the particle beam irradiation system  1  of the embodiment, ion beams of different energies can be extracted from the accelerator  4 , and a degrader is not required. Alternatively, it is possible to considerably reduce the use of the deflector. For this reason, in the particle beam irradiation system  1 , it is possible to prevent an increase in the beam size of an ion beam caused by the degrader, a reduction in the number of ions caused by scattering of a portion of ions when the ions penetrate through metal plates of the degrader, and an increase in radioactive waste caused by radioactivation of the degrader. 
         [0255]    In the embodiment, in order to maintain a vacuum state of the beam turning region  76  in which ion beams turn, the vacuum chamber  27  is formed such that the pair of iron cores  14 A and  14 B are disposed to face each other and are joined together. For this reason, it is possible to further reduce the size of the accelerator  4  in the embodiment compared to that of an accelerator in which a vacuum chamber is disposed between facing iron cores  14  and  14 B in Embodiments 8 and 9 which will be described later. 
         [0256]    In the embodiment, as described above, on the beam turning trajectory  78  along which an ion beam of a low energy (ion beam of 70 MeV or less) turns, an ion beam is accelerated by two radiofrequency acceleration electrodes  9 C and  9 D. Since the beam turning trajectories  78  are eccentric with each other, on the beam turning trajectory  78  along which an ion beam of a high energy (ion beam of an energy exceeding 70 MeV) which requires stable and fine trajectory control and requires a high radiofrequency acceleration voltage or a long acceleration time for a higher acceleration due to a high energy, an ion beam is accelerated by four radiofrequency acceleration electrodes  9 A to  9 D. 
         [0257]    Even if one or three or more radiofrequency acceleration electrodes, which are disposed between the bent points of the magnetic poles and the inner surface of the annular coil and extend from the ion inlet port to the inner surface of the annular coil, may be provided, the aforementioned functions can be demonstrated. In order to form the eccentric trajectory region is formed on the median plane  77  which is a trajectory plane in the beam turning region  76 , among the radiofrequency acceleration electrodes  9 A to  9 D, the radiofrequency acceleration electrodes  9 A and  9 C are respectively symmetrical in shape and disposition with the radiofrequency acceleration electrodes  9 B and  9 D relative to a straight line (the alternate long and short dash line X) that connects the central axis C to the inlet of the beam extraction path  20 . As a result, it is possible to easily obtain stability of turning ion beams. 
         [0258]    The iron cores  14 A and  14 B have a circular shape in the horizontal direction, and typically, the center of the iron cores  14 A and  14 B represents the structural center of the accelerator  4 . The annular coils  11 A and  11 B are circular main coils, and typically, similarly, the center and the center of gravity of the annular coils  11 A and  11 B represent the structural center of the accelerator  4 . In the accelerator  4  of the embodiment, the ion injection portion is installed at a different position from that of the center of the iron cores and the center of gravity of the annular coils. The ion injection portion is provided at a position offset toward the inlet of the beam extraction path  20 . 
         [0259]    In a typical cyclotron, beam turning trajectories are concentrically formed around the structural center of an accelerator, and thus, ions are injected to the structural center of the accelerator. Strictly speaking, ions are not injected to the central point, but are injected into an innermost beam turning trajectory. In a case where ions are injected and guided to the innermost beam turning trajectory, and a region inside of the innermost beam turning trajectory is defined as an ion injection portion, in a typical cyclotron, the ion injection portion is positioned at the structural center of the accelerator. In contrast, in the accelerator  4  of the embodiment, the ion injection portion is installed at a different position from that of the center of the iron cores and the center of gravity of the annular coils. The ion injection portion is disposed at a position offset toward the inlet of the beam extraction path  20 . 
       Embodiment 2 
       [0260]    Hereinafter, a particle beam irradiation system in Embodiment 2, which is another preferred embodiment of the present invention, will be described with reference to  FIG. 27 . 
         [0261]    A particle beam irradiation system  1 A in the embodiment includes an accelerator  4 A, and has a configuration obtained by replacing the accelerator  4  in the particle beam irradiation system  1  of Embodiment 1 with the accelerator  4 A. The rest of the configuration of the particle beam irradiation system  1 A is the same as that of the particle beam irradiation system  1 . 
         [0262]    The accelerator  4 A includes the vacuum chamber  27  including the return yokes  5 A and  5 B. The return yokes  5 A and  5 B are substantially the same as the return yokes  5 A and  5 B in Embodiment 1. The return yoke  5 B of the accelerator  4 A will be described. The return yoke  5 B includes six magnetic poles  7 A to  7 F and four radiofrequency acceleration electrodes  9 A to  9 D, and six recessions  29 A to  29 F are formed in the return yoke  5 B. The magnetic poles  7 A to  7 F and the radiofrequency acceleration electrodes  9 A to  9 D are disposed inside the annular coil  11 B. Similar to the accelerator  4 , the recessions  29 A to  29 F are respectively disposed between the magnetic poles  7 A to  7 F. The radiofrequency acceleration electrodes  9 A to  9 D of the accelerator  4 A are disposed in the same manner in which the radiofrequency acceleration electrodes  9 A to  9 D are disposed in the accelerator  4 . 
         [0263]    An ion inlet port and the injection electrode  18  are disposed in the accelerator  4 A in a state where the ion inlet port and the injection electrode  18  are moved closer to the inlet of the beam extraction path  20  than in the return yoke  5 B of the accelerator  4 . The ion injection tube  3 A is installed in the return yoke  5 A in a state where the ion injection tube  3 A is also moved to the position of the injection electrode  18  by the extent of the movement of the injection electrode  18  to the inlet of the beam extraction path  20 . The suction tube  26  formed in the return yoke  5 B of the accelerator  4 A is attached to the return yoke  5 B of the accelerator  4 A on an extension line of the ion injection tube  3 A. 
         [0264]    The respective bent points  24 A to  24 P of the magnetic poles  7 A to  7 F and the radiofrequency acceleration electrodes  9 C and  9 D are disposed further inward than in the accelerator  4 , and are disposed on the beam turning trajectory  78  which is formed at the periphery of the injection electrode  18  and along which an ion beam of 10 MeV turns. The respective tip ends of the magnetic poles  7 A to  7 F and the radiofrequency acceleration electrodes  9 C and  9 D are sharp and face the injection electrode  18 . Similar to the shapes illustrated in  FIG. 3 , the magnetic poles  7 A to  7 F and the radiofrequency acceleration electrodes  9 C to  9 D are tapered toward the respective tip ends from the respective bent points. Portions of the magnetic poles  7 A to  7 F and the radiofrequency acceleration electrodes  9 C and  9 D between the respective bent points and the respective end surface thereof facing the inner surface of the annular coil  11 B respectively have lengths greater than those in the return yoke  5 B of the accelerator  4  in Embodiment 1. The radiofrequency acceleration electrodes  9 A and  9 B, which are disposed closer to the inner surface of the annular coil  11 B than the respective bent points of the magnetic poles  7 A to  7 D, respectively have lengths little longer than those of the radiofrequency acceleration electrodes  9 A and  9 B of the accelerator  4 . 
         [0265]    For this reason, a concentric trajectory region formed around the injection electrode  18  inside the return yoke  5 B of the accelerator  4 A is smaller than that region in the accelerator  4 . In contrast, an eccentric trajectory region formed at the periphery of the concentric trajectory region becomes larger than that region in the accelerator  4 . 
         [0266]    The return yoke  5 A of the accelerator  4 A also includes the magnetic poles  7 A to  7 F and the radiofrequency acceleration electrodes  9 A to  9 D having the same shapes as those in the return yoke  5 B of the accelerator  4 A. The accelerator  4 A has the same configuration as that of the accelerator  4  including the massless septum  12  except for the respective shapes of the magnetic poles  7 A to  7 F and the radiofrequency acceleration electrodes  9 A to  9 D and the positions at which the injection electrode  18 , the ion injection tube  3 A, and the suction tube  26  are respectively disposed. 
         [0267]    The particle beam irradiation system  1 A in the embodiment also irradiates a target volume of the patient  56  on the treatment bed  55  with ion beams by executing each of Steps S 1  to S 6 , S 23 , S 24 , S 7  to S 14 , S 7 , and S 15  to S 21  executed by the particle beam irradiation system  1 . 
         [0268]    In the embodiment, it is possible to obtain the same effects as in Embodiment 1. 
       Embodiment 3 
       [0269]    Hereinafter, a particle beam irradiation system in Embodiment 3, which is still another preferred embodiment of the present invention, will be described with reference to  FIG. 28 . 
         [0270]    A beam transport and a rotating apparatus of the accelerator  4  of a particle beam irradiation system  1 B in the embodiment are different from those of the particle beam irradiation system  1  in Embodiment 1. The accelerator  4 , the irradiation apparatus  7 , and the control system  65  of the particle beam irradiation system  1 B are the same as those of the particle beam irradiation system  1 . 
         [0271]    In Embodiments 1 and 2, the accelerators  4  and  4 A are horizontally disposed, and the lower surface of the return yoke  5 B of the vacuum chamber  27  is installed such that the lower surface of the return yoke  5 B is placed on a floor of a building. The particle beam irradiation system  1 B in the embodiment includes a rotating frame that is rotatably installed on the floor. The accelerator  4  disposed vertically is attached to the rotating frame. The rotating frame has the same configuration as that of a rotating frame disclosed in PTL 5, and is supported by rotating rollers that are provided in a support apparatus installed on the floor of the building. The support apparatus is the same as a support apparatus (refer to PTL 6) including multiple rollers which supports a rotating gantry provided in a particle beam irradiation system including a synchrotron in the related art. At least one of the rollers provided in the support apparatus is rotated by the rotating apparatus (for example, a motor). The rotating frame is rotated via rotation of the rollers, and the accelerator  4  is rotated around the central axis C of the vacuum chamber  27 . Since the accelerator  4  is vertically disposed, the median plane  77  formed inside the vacuum chamber  27  is perpendicular to the floor. 
         [0272]    A treatment room is surrounded by a radiation shielding wall (not illustrated), and the radiation shielding wall has the same structure as that of a radiation enclosure disclosed in PTL 5. A portion of the radiation shielding wall is a side wall, and is disposed between the accelerator  4  attached to the rotating frame and the treatment room. The treatment bed  55 , on which the patient  56  to be treated lies, is installed inside the treatment room. 
         [0273]    The beam path  48  of a beam transport  13 B, that is connected to the beam extraction path  20  formed inside the septum magnet  19  provided in the vacuum chamber  27 , extends on the outside of the vacuum chamber  27  in the radial direction of the vacuum chamber  27 , is bent in the horizontal direction, and extends to a position directly above the treatment room along the radiation shielding wall which is a ceiling portion of the treatment room. The beam path  48  is bent toward the treatment room from the position directly above the treatment room. Bending magnets  95  and  96  are respectively disposed in bent portions of the beam path  48 , and multiple quadrupole magnets  97  are provided on the beam path  48 . The irradiation apparatus  7  is attached to a tip end portion of the beam path  48 . Similar to the particle beam irradiation system  1  in Embodiment 1, two scanning magnets  51  and  52 , the beam point monitor  53 , and the dose monitor  54  are attached to the irradiation apparatus  7 . 
         [0274]    When a target volume is treated by irradiating a tumor volume of the patient  56 , who lies on the treatment bed  55  inside the treatment room, with ion beams, the proton beam therapy system  1 B executes each of Steps S 1  to S 6 , S 23 , S 24 , S 7  to S 14 , S 7 , and S 15  to S 21  executed in Embodiment 1. Particularly, in a case where the proton beam therapy system  1 B is used, the rotating frame is rotated such that the accelerator  4  is rotated in Step S 11 . At this time, the beam transport  13 B and the irradiation apparatus  7  are turned around the center of rotation (the central axis C) of the accelerator  4 . The beam axis of the irradiation apparatus  7  becomes aligned with an irradiation direction of ion beams to the target volume via turning of the irradiation apparatus  7 . In this case, the target volume of the patient  56  on the treatment bed  55  is positioned on an extension line of the center of rotation of the accelerator  4 . 
         [0275]    The target volume is irradiated with ion beams and is treated by executing each of Steps S 11  to S 14 , S 7 , and S 15  to S 21 . 
         [0276]    In the embodiment, it is possible to obtain the same effects as in Embodiment 1. In the embodiment, the accelerator  4  is vertically disposed, and is rotated by the rotating frame, and thus, the size of the particle beam irradiation system  1 B becomes smaller than that of the particle beam irradiation system  1  in Embodiment 1. 
       Embodiment 4 
       [0277]    Hereinafter, a particle beam irradiation system in Embodiment 4, which is still another preferred embodiment of the present invention, will be described with reference to  FIGS. 29 and 30 . 
         [0278]    A particle beam irradiation system  1 C in the embodiment has a configuration obtained by replacing the ion beam generator  2  in the particle beam irradiation system  1  with an ion beam generator  2 A. The ion beam generator  2 A has a configuration obtained by replacing the accelerator  4  in the ion beam generator  2  with an accelerator  4 B. The accelerator  4 B has a configuration obtained by omitting the massless septum  12 , the movement apparatus  17 , and the power supply  40  from the accelerator  4  and adding the energy absorber  62  and a movement apparatus  60  to the accelerator  4 . A control system  65 A of the particle beam irradiation system  1 C has a configuration obtained by replacing the accelerator and transport control apparatus  69  in the control system  65  with an accelerator and transport control apparatus  69 A. The accelerator and transport control apparatus  69 A has a configuration obtained by replacing the massless septum control apparatus  86  in the accelerator and transport control apparatus  69  with an energy absorber control apparatus  93 . The energy absorber control apparatus  93  is connected to the CPU  67 , the memory  107 , and the irradiation point control apparatus  89 . The rest of the configuration of the accelerator and transport control apparatus  69 A is the same as that of the accelerator and transport control apparatus  69 . The rest of the configuration of the particle beam irradiation system  1 C is the same as that of the particle beam irradiation system  1 . The beam current measuring apparatus  98 , which is used in the particle beam irradiation system  1  and includes the beam current measuring unit  15 , the operation member  16 A, the movement apparatus  17 , and the position detector  39 , is also used in the particle beam irradiation system  1 C, which is not illustrated in  FIGS. 29 and 30 . Similar to the particle beam irradiation system  1 , the beam current measuring apparatus  98  is attached to the vacuum chamber  27 . The beam current measuring unit  15  and the operation member  16 A are disposed in the recession  29 A and on the median plane  77 . 
         [0279]    The energy absorber  62  is disposed inside the vacuum chamber  27  and between the magnetic pole  7 A of the return yoke  5 A and the magnetic pole  7 A of the return yoke  5 B which faces the magnet  7 A of the return yoke  5 A. The energy absorber  62  is attached to a tip end portion of a bar-shaped operation member  63 . The energy absorber  62  is a thin aluminum plate, and is disposed to be perpendicular to the beam turning trajectories  78 . The energy absorber  62  may be formed of non-magnetic metallic materials such as tungsten, copper, and titanium, or non-metallic materials. The width of the energy absorber  62  in the direction perpendicular to the median plane  77  is smaller than a gap between the magnetic pole  7 A of the return yoke  5 A and the magnetic pole  7 A of the return yoke  5 B. 
         [0280]    The operation member  63  attached to the energy absorber  62  passes through the vacuum chamber  27 , and extends to the outside of the vacuum chamber  27 . The operation member  63  is a support member for the energy absorber  62 , and is connected to a piston of the movement apparatus  60  including the piston and a cylinder on the outside of the vacuum chamber  27 . The operation member  63  is disposed between the facing magnetic poles  29 A and between the annular coils  11 A and  11 B. For example, the operation member  63  is slidably attached to the cylindrical portion  75 B in a state where the operation member  63  has passed through the cylindrical portion  75 B of the return yoke  5 B. A position detector  61  is attached to the movement apparatus  60 , and detects the position of the energy absorber  62  inside the vacuum chamber  27  (refer to  FIG. 29 ). The movement apparatus  60  may be a motor. In a case where a motor is used as the movement apparatus  60 , an encoder is used as the position detector  38 , and is connected to a rotational shaft of the motor. The energy absorber  62 , the operation member  63 , the movement apparatus  60 , and the position detector  61  form an extraction adjustment apparatus which is a type of beam separation apparatus. 
         [0281]    Among Steps S 1  to S 6 , S 23 , S 24 , and S 7  to S 10  illustrated in Embodiment 1, the particle beam irradiation system  1 C also executes steps except for Steps S 8  and S 9 . Step S 22  (refer to  FIG. 32 ) (to be described later) is executed between Steps S 7  and S 10 , instead of Steps S 8  and S 9 . Step S 22  will be described in detail later. 
         [0282]    In a case where a target volume of the patient  56  on the treatment bed  55  is treated by irradiating the target volume with ion beams, each of Steps S 11 , S 12 , S 22 , S 7 , and S 15  to S 21  illustrated in  FIG. 32  is executed. Steps other than Step S 22  are executed similar to Embodiment 1. Hereinafter, Step S 22  will be described. 
         [0283]    The energy absorber is positioned (Step S 22 ). In order to execute Step S 22 , based on control command information from the CPU  67 , the energy absorber control apparatus  93  controls the movement apparatus  60  such that the movement apparatus  60  moves the operation member  63 . As a result, the energy absorber  62  is moved on the median plane  77  toward the central axis C of the vacuum chamber  27 . Due to such a movement of the energy absorber  62 , the energy absorber  62  is capable of crossing at least the beam turning trajectories  78  along which ion beams of 70 MeV to 250 MeV respectively turn. 
         [0284]    The energy absorber control apparatus  93  specifies the position of the beam turning trajectory  78  of an ion beam of an energy slightly higher than the energy of an ion beam with which a layer set in Step S 12  is to be irradiated, based on energy information regarding the ion beam with which the layer is irradiated, which is input from the irradiation point control apparatus  89 , the degree of energy dampening performed by the energy absorber  62 , and position information regarding the beam turning trajectories  78  which is measured by the position detector  39  and is stored in the memory  107  while being associated with energies. The energy absorber control apparatus  93  moves the energy absorber  62  to the position of the specified beam turning trajectory  78  and positions the energy absorber  62  on the beam turning trajectory  78  by controlling the specified movement apparatus  60 . 
         [0285]    The position of the energy absorber  62  in the radial direction of the median plane  77  (position inside the vacuum chamber  27  in the radial direction) is measured by the position detector  61 . Position information regarding the energy absorber  62  measured by the position detector  61  is input to the energy absorber control apparatus  93 . The energy absorber control apparatus  93  determines whether the measured position information regarding the energy absorber  62  coincides with the specified position of the beam turning trajectory  78 . In a case where there is no coincidence therebetween, the energy absorber control apparatus  93  controls the movement apparatus  60  such that the energy absorber  62  is moved to the position of the beam turning trajectory. In a case where the measured position information regarding the energy absorber  62  coincides with the position of the beam turning trajectory, the energy absorber control apparatus  93  stops driving of the movement apparatus  60 . 
         [0286]    In a case where the energy absorber  62  is positioned at the specified position of the beam turning trajectory  78  through control of the movement apparatus  60  via the energy absorber control apparatus  93 , after ions are injected into the beam turning region  76  in Step S 16 , an ion beam turning along the beam turning trajectory  78  at the specified position is dampened when passing through the energy absorber  62 . As a result, the ion beam of a dampened energy is positioned outside of an equilibrium trajectory. The beam is subjected to betatron oscillation while moving to the recession  29 D in which the beam extraction path  20  is positioned, and moves toward the inlet of the beam extraction path  20 . As a result, the ion beam, which has passed through the energy absorber  62 , is extracted to the beam path  48  of the beam transport  13  from the accelerator  4 B through the beam extraction path  20 . 
         [0287]    In a case where the energy of an ion beam, with which a layer of the target volume is irradiated, is determined to be 200 MeV based on treatment planning data, an ion beam of 200 MeV is required to be extracted from the accelerator  4 B into the beam path  48 . The energy of an ion beam, which has passed through the energy absorber  62 , is required to be 200 MeV. In this case, energy dampening by the energy absorber  62  is taken into consideration, and thus, an ion beam of an energy of 205 MeV is required to penetrate through the energy absorber  62 . In this case, the energy absorber  62  is positioned on a beam turning trajectory along which an ion beam of 205 MeV turns. 
         [0288]    When the determination of Step S 20  is “No”, each of Steps S 11 , S 12 , S 22 , S 7 , and S 15  to S 20  is repeatedly executed until the determination of Step S 20  becomes “Yes”. During repletion, the aforementioned positioning of the energy absorber  62  is performed in Step S 22 . 
         [0289]    In the embodiment, among the effects obtained in Embodiment 1, it is possible to obtain the remaining effects except for an effect obtained by the massless septum  12 . In the embodiment, the massless septum  12  with a complicated structure and the power supply  40  are not required, and thus, the structure of the particle beam irradiation system  1 C can be simplified. 
         [0290]    Since the movement apparatus  17 A is provided to move the energy absorber  62  in the radial direction of the annular coils, it is possible to perform adjustment of the positioning of the energy absorber  62  on the beam turning trajectory  78  along which an ion beam of energy (with which a set layer of the target volume is to be irradiated) turns. For this reason, it is possible to accurately position the energy absorber  62  on the beam turning trajectory  78 . 
       Embodiment 5 
       [0291]    Hereinafter, a particle beam irradiation system in Embodiment 5, which is another preferred embodiment of the present invention, will be described with reference to  FIGS. 33 and 34 . 
         [0292]    A particle beam irradiation system  1 D in the embodiment has a configuration obtained by replacing the accelerator  4  in the particle beam irradiation system  1  with an accelerator  4 C. The accelerator  4 C has a configuration obtained by adding the energy absorber  62 , the operation member  63 , and the movement apparatus  60  to the configuration of the accelerator  4 . The rest of the configuration of the particle beam irradiation system  1 C is the same as that of the particle beam irradiation system  1 . The accelerator and transport control apparatus  69  in the embodiment includes the energy absorber control apparatus  93  in addition to the massless septum control apparatus  86 . Since the massless septum  12  is used, the thickness of the energy absorber  62  in the embodiment can be reduced to a thickness smaller than that of the energy absorber  62  in Embodiment 4. 
         [0293]    The particle beam irradiation system  1 D executes each of Steps S 1  to S 6 , S 23 , S 24 , and S 7  to S 10  illustrated in Embodiment 1. In a case where a target volume of the patient  56  on the treatment bed  55  is treated by irradiating the target volume with ion beams via the particle beam irradiation system  1 D, each of Steps S 11 , S 12 , S 22 , S 13 , S 14 , S 7 , and S 15  to S 21  illustrated in  FIG. 35  is executed. Step S 22  is the same step as that executed in Embodiment 4. 
         [0294]    In the embodiment, extraction of ion beams in Step S 16  is different from that in Embodiments 1 and 4 due to use of the massless septum  12  and the energy absorber  62 , and thus, Step S 16  will be described in detail. 
         [0295]    The energy absorber  62  is disposed upstream of the massless septum  12  in a turning direction of ion beams. For this reason, after the energy of an ion beam is dampened by the energy absorber  62 , the ion beam of a dampened energy is ejected by the massless septum  12 . The ion beam of an energy dampened by the energy absorber  62  moves inward from a beam turning trajectory along which the ion beam turns before the energy of the ion beam is dampened. Since the amount of movement of the ion beam has been already known, when electrodes of the massless septum  12  are positioned in Step S 13 , as described above, with the amount of movement taken into consideration, the movement apparatus  17  positions a pair of the facing magnetic poles  32 A and  32 B (positioned inside of the beam turning trajectory along which the ion beam turns before the energy thereof is dampened) at the position of an ion beam which has penetrated the energy absorber  62 . 
         [0296]    For this reason, in Step S 16 , the energy absorber  62  is disposed on the beam turning trajectory along which the ion beam (formed by ions injected into the beam turning region  76 ) turns, and thus, the energy of the ion beam, which has passed through the energy absorber  62 , is dampened and becomes equal to the energy of an ion beam with which a layer of the target volume is irradiated. The ion beam which has passed through the energy absorber  62  is ejected by the pair of excited magnetic poles  32 A and  32 B of the massless septum  12  which is positioned in advance. The ejected ion beam is injected into the beam extraction path  20 , and is extracted to the beam path  48  of the beam transport  13 . 
         [0297]    In the embodiment, it is possible to obtain the same effects as in Embodiments 1 and 4. In the embodiment, the massless septum  12  is used with the energy absorber  62 , the thickness of the energy absorber  62  can be reduced to a thickness smaller than that of the energy absorber  62  in Embodiment 4. For this reason, scattering of ion beams by the energy absorber  62  is decreased, and to that extent, ion beams extracted from the accelerator  4 C into the beam transport  13  are increased. Ion beam utilization efficiency in treatment of the patient  56  is increased. 
       Embodiment 6 
       [0298]    Hereinafter, a particle beam irradiation system in Embodiment 6, which is another preferred embodiment of the present invention, will be described with reference to  FIGS. 36, 37, and 38 . 
         [0299]    A particle beam irradiation system  1 E in the embodiment has a configuration obtained by replacing the beam current measuring apparatus  98  in the particle beam irradiation system  1  of Embodiment 1 with a beam current measuring apparatus  98 A. The rest of the configuration of the particle beam irradiation system  1 E is the same as that of the particle beam irradiation system  1 . 
         [0300]    As illustrated in  FIGS. 40 and 41 , the beam current measuring apparatus  98 A includes a monitor housing  101 ; multiple monitor electrodes  103 A; and multiple monitor electrodes  103 B. The monitor housing  101  includes housing body portions  102 A and  102 B which face each other and are disposed parallel with each other, and a connection portion  102 C. The monitor electrodes  103 A are disposed in a row with a predetermined gap therebetween. Each of the monitor electrodes  103 A is attached to one surface of the housing body portion  102 A, which faces the housing body portion  102 B, via multiple (for example, four) insulators  104 . The monitor electrodes  103 B are disposed in a row with a predetermined gap therebetween. Each of the monitor electrodes  103 B is attached to one surface of the housing body portion  102 B, which faces the housing body portion  102 A, via multiple (for example, four) insulators  104 . Respective end portions of the housing body portions  102 A and  102 B are joined together via the connection portion  102 C. The monitor electrodes  103 A are disposed to respectively face the monitor electrodes  103 B. 
         [0301]    An electrode lead wire  106  is connected to each of the monitor electrodes  103 A, and another electrode lead wire  106  is also connected to each of the monitor electrodes  103 B. The electrode lead wires  106  respectively connected to the monitor electrodes  103 A are bundled together and are covered with an electrode lead cover  105 A so as to prevent damage to the electrode lead wires  106  caused by degassing and electrical discharge in a vacuum state of the vacuum chamber  27 . The electrode lead cover  105 A is attached to a top surface of the housing body portion  102 A along the top surface. The electrode lead wires  106  respectively connected to the monitor electrodes  103 B are also bundled together and are covered with an electrode lead cover  105 B so as to prevent damage to the electrode lead wires  106  caused by degassing and electrical discharge in a vacuum state of the vacuum chamber  27 . The electrode lead cover  105 B is attached to a top surface of the housing body portion  102 B along the top surface. The electrode lead wires  106  respectively connected to the monitor electrodes  103 A and the electrode lead wires  106  respectively connected to the monitor electrodes  103 B are bundled together at the position of the connection portion  102 C, and pass through the cylindrical portion  75 B of the return yoke  5 B and are extracted to the outside of the vacuum chamber  27  while being covered with an electrode lead cover (not illustrated). The electrode lead wires  106  are connected to the beam current measuring unit control apparatus  84 . 
         [0302]    As illustrated in  FIGS. 38 and 39 , the beam current measuring apparatus  98 A is disposed between the magnetic poles  32 A and the magnetic poles  32 B facing the magnetic poles  32 A of the massless septum  12 , and is attached to the massless septum  12 . In the embodiment, the massless septum  12  is also disposed in the recessions  29 A which are respectively formed in the facing return yokes  5 A and  5 B. For this reason, the beam current measuring apparatus  98 A is also disposed in the recessions  29 A. The beam passage  35  is formed between the monitor electrodes  103 A and the monitor electrodes  103 B, and is a gap through which turning ion beams pass. The beam passage  35  contains a portion of the median plane  77 . The monitor electrodes  103 A and  103 B face each other with the median plane  77  interposed therebetween. The monitor housing  101  has a length larger than that of the massless septum  12 . The multiple monitor electrodes  103 A and the multiple monitor electrodes  103 B are provided in the monitor housing  101  so as to be capable of measuring beam currents in a range from the beam turning trajectory  78  of an ion beam of 35 MeV to the beam turning trajectory  78  of an ion beam of 250 MeV. 
         [0303]    The particle beam irradiation system  1 E in the embodiment irradiates a target volume of the patient  56  on the treatment bed  55  with ion beams by executing each of Steps S 1  to S 6 , S 23 , S 24 , S 7  to S 14 , S 7 , and S 15  to S 21  executed by the particle beam irradiation system  1 . Among these steps, Step S 6  (measurement of ion beams) executed in the embodiment will be described in detail. In the embodiment, Step S 6  is executed by the beam current measuring apparatus  98 A. After each of Steps S 1  to S 5  is executed, the movement apparatus  17  adjusts the position of the massless septum  12  such that the monitor electrodes  103 A and the monitor electrodes  103 B of the beam current measuring apparatus  98 A are respectively disposed at predetermined positions along the alternate long and short dash line X. An ion beam turning along each of the beam turning trajectories  78  passes through the beam passage  35 . When an ion beam passes through gaps between the facing monitor electrodes  103 A and the monitor electrodes  103 B, a voltage occurring between the electrodes is measured. Measured voltage information equivalent to a beam current is converted into a beam current, and energy information corresponding to the beam current is stored in the memory  107  while being associated with position information regarding the positions of the monitor electrodes on the alternate long and short dash line X in the radial direction of the annular coils, that is, position information regarding the position of the beam turning trajectory  78  in the radial direction. 
         [0304]    In Step S 13 , the massless septum control apparatus  86  positions the massless septum  12  on the beam turning trajectory  78 , and specifies a pair of the magnetic poles  32 A and  32 B based on energy information regarding an ion beam with which a set layer is irradiated, and the position information regarding the beam turning trajectory  78  which stored in the memory  107  while being associated with the energy (voltage information). Similar to Step S 13  in Embodiment 1, the amount of movement of the massless septum  12  is obtained. The massless septum control apparatus  86  moves the massless septum  12  toward the injection electrode  18 , and positions the specified magnetic poles  32 A and  32 B on the beam turning trajectory  78  by controlling the movement apparatus  17  based on the amount of movement. In Step S 14 , the specified pair of magnetic poles  32 A and  32 B is excited. 
         [0305]    In the embodiment, it is possible to obtain the same effects as in Embodiment 1. 
         [0306]    The beam current measuring apparatus  98  in Embodiment 1 detects a beam current by causing a turning ion beam to collide with the beam current measuring unit  15 . For this reason, the movement apparatus  17 A to move the beam current measuring unit  15  is required to perform measurement via destruction of a turning ion beam. In order to measure a beam current of an ion beam turning along the beam turning trajectory  78  positioned at the outermost circumference, the beam current measuring unit  15  is required to be pulled out to the vicinity of the inner surfaces of the annular coils  11 A and  11 B, and the length of the operation member  16 A may have to be increased. Accordingly, an increase in the size of the beam current measuring apparatus  98  becomes a problem. 
         [0307]    When the beam current measuring apparatus  98 A measures a voltage equivalent to a beam current of a turning ion beam via the facing monitor electrodes  103 A and  103 B, the beam current measuring apparatus  98 A in the embodiment is capable of measuring the voltage and obtaining the beam current corresponding to the voltage without destroying the turning ion beam. Since the movement apparatus  17  of the massless septum  12  can be used to finely adjust the position of the monitor electrodes  103 A and  103 B, the size of the beam current measuring apparatus  98 A can be further reduced than that of the beam current measuring apparatus  98 . 
         [0308]    As illustrated later in Embodiment 7, the beam current measuring apparatus  98 A disposed inside the massless septum  12  may be fixed to the cylindrical body  75 B of the return yoke  5 B via a bar-shaped support member  108 . In this case, the support member  108  attached to the beam current measuring apparatus  98 A reaches the outside of the massless septum  12  through the through hole  31 D formed in the connection portion  31  of the massless septum  12 . 
       Embodiment 7 
       [0309]    Hereinafter, a particle beam irradiation system in Embodiment 7, which is another preferred embodiment of the present invention, will be described with reference to  FIGS. 42 and 43 . 
         [0310]    A particle beam irradiation system  1 F in the embodiment has a configuration obtained by replacing the beam current measuring apparatus  98  in the particle beam irradiation system  1 C of Embodiment 4 with beam current measuring apparatus  98 A. The rest of the configuration of the particle beam irradiation system  1 F is the same as that of the particle beam irradiation system  1 C. In the particle beam irradiation system  1 F, the beam current measuring apparatus  98 A is disposed in the recessions  29 A, which are respectively formed in the return yokes  5 A and  5 B, along the alternate long and short dash line X that passes through the central axis C and is perpendicular to the central axis C. The beam current measuring apparatus  98 A is attached to the cylindrical portion  75 B of the return yoke  5 B via the bar-shaped support member  108 . A portion of the median plane  77 , on which the beam turning trajectories  78  are formed, is present inside the beam passage  35  formed in the beam current measuring apparatus  98 A. The monitor electrodes  103 A and the monitor electrodes  103 B face each other with the median plane  77  interposed therebetween. 
         [0311]    In the embodiment, similar to Embodiment 4, among Steps S 1  to S 6 , S 23 , S 24 , and S 7  to S 10  illustrated in Embodiment 1, steps except for Steps S 8  and S 9  are executed. Each of Steps S 11 , S 12 , S 22 , S 7 , and S 15  to S 21  illustrated in  FIG. 35  is executed. 
         [0312]    In the embodiment, similar to Embodiment 6, in Step S 6 , during turning of ion beams, the beam current measuring apparatus  98 A measures a voltage between the monitor electrodes  103 A and the monitor electrodes  103 B facing each other. In Step S 22 , the position of the beam turning trajectory  78  of an ion beam of an energy slightly higher than the energy of an ion beam, with which a set layer is to be irradiated, is specified based on energy information regarding the ion beam with which the layer is irradiated, the degree of energy dampening performed by the energy absorber  62 , and position information which is stored in the memory  107  while being associated with voltage information that is beam current information. The energy absorber control apparatus  93  controls the movement apparatus  60  such that the energy absorber  62  is moved to the position of the specified beam turning trajectory  78 . 
         [0313]    In the embodiment, it is possible to obtain the same effects as in Embodiment 4. In the embodiment, it is also possible to obtain the same effects as those of the beam current measuring apparatus  98 A in Embodiment 6. 
       Embodiment 8 
       [0314]    Hereinafter, a particle beam irradiation system in Embodiment 8, which is another preferred embodiment of the present invention, will be described with reference to  FIGS. 44, 45, and 46 . 
         [0315]    In the particle beam irradiation systems such as the particle beam irradiation systems  1  described in Embodiments 1 to 7, each accelerator includes the vacuum chamber  27  formed of the iron cores  14 A and  14 B. In contrast, in a particle beam irradiation system  1 G of the embodiment, an accelerator  4 D includes the iron cores  14 A and  14 B, and further includes a vacuum chamber  27 A disposed between the iron cores  14 A and  14 B. The vacuum chamber  27 A is made of non-magnetic material (for example, stainless steel). The iron core  14 A is disposed above the vacuum chamber  27 A, and the iron core  14 B is disposed below the vacuum chamber  27 A. The massless septum  12  and the beam current measuring unit  15  of the beam current measuring apparatus  98  are disposed inside the vacuum chamber  27 A. The median plane  77 , on which the beam turning trajectories  78  are formed, is formed inside the vacuum chamber  27 A in such a way as to be perpendicular to the central axis C of the vacuum chamber  27  and the annular coils  11 A and  11 B. The ion injection tube  3 A passes through the base portion  74 A of the return yoke  5 A included in the iron core  14 A, and reaches the inside of the vacuum chamber  27 A. The ion inlet port formed at the tip end of the ion injection tube  3 A opens inside the vacuum chamber  27 A. The suction tube  26 , which is disposed on the extension line of the central axis of the ion injection tube  3 A, is attached to the base portion  74 B in a state where the suction tube  26  has passed through the base portion  74 B of the return yoke  5 B. The suction tube  26  is connected to the vacuum chamber  27 A, and opens inside the vacuum chamber  27 A. The injection electrode  18  is attached to the tip end of the ion inlet tube  3 A. 
         [0316]    The rest of the configuration of the particle beam irradiation system  1 G including the iron cores  14 A and  14 B is the same as that of the particle beam irradiation system  1 . 
         [0317]    The operation member  16  attached to the massless septum  12  and the operation member  16 A attached to the beam current measuring unit  15  pass through the vacuum chamber  27 A and the cylindrical portion  75 B of the return yoke  5 B, and reach the outside of the return yoke  5 B. On the outside of the return yoke  5 B, the operation members  16  and  16 A are respectively connected to the movement apparatuses  17  and  17 A. The septum magnet  19  is attached to the vacuum chamber  27 A and the cylindrical portion  75 B. The beam extraction path  20  formed in the septum magnet  19  communicates with the beam path  48  of the beam transport  13 . The inlet of the beam extraction path  20  is positioned inside the vacuum chamber  27 A. 
         [0318]    The concentric trajectory region and the eccentric trajectory region surrounding the concentric trajectory region are formed on the median plane  77  inside the vacuum chamber  27 A. The concentric trajectory region and the concentric trajectory region surround the injection electrode  18 . Similar to the embodiments, the beam turning trajectories  78  formed in the concentric trajectory region are concentrated on the inlet side of the beam extraction path  20 . In the embodiment, the positions of the injection electrode  18  and the ion inlet port are offset toward the inlet of the beam extraction path  20  from the central axis C of the annular coils, that is, the center of gravity of the annular coils which is positioned on the central axis C. The injection electrode  18  and the ion inlet port are positioned at a position that is different from that of the center of gravity of the annular coils in a radial direction of the accelerator  4 D. Similar to Embodiment 1, the magnetic poles  7 A to  7 F formed in each of the iron cores  14 A and  14 B are disposed to surround the position of the ion inlet port, and extend radially from the position of the ion inlet port. In addition, similar to Embodiment 1, the recessions  29 A to  29 F formed in each of the iron cores  14 A and  14 B are disposed to surround the position of the ion inlet port, and extend radially from the position of the ion inlet port. 
         [0319]    In the embodiment, similar to Embodiment 1, a magnetic field distribution illustrated in  FIG. 10  is formed on the median plane  77 . A target volume of the patient  56  on the treatment bed  55  is irradiated with ion beams by executing each of Steps S 1  to S 6 , S 23 , S 24 , S 7  to S 14 , S 7 , and S 15  to S 21 . 
         [0320]    In the embodiment, it is possible to obtain the same effects as in Embodiment 1. In the embodiment, the vacuum chamber  27 A is separately provided, and thus, it is not necessary to seal respective facing surfaces of the cylindrical portion  75 A of the return yoke  5 A and the cylindrical portion  75 B of the return yoke  5 B which face each other as illustrated in Embodiment 1. In contrast, in the embodiment, the vacuum chamber  27 A is disposed between the iron cores  14 A and  14 B, and thus, the size of the accelerator  4 D in the embodiment becomes larger than that of the accelerator  4  in Embodiment 1. 
         [0321]    As illustrated in  FIG. 47 , the massless septum  12  may be disposed outside the vacuum chamber  27 A, and the vacuum chamber  27 A may be disposed between the magnetic poles  32 A and the magnetic poles  32 B facing the magnetic poles  32 A of the massless septum  12 . In this case, the beam current measuring unit  15  is disposed on the median plane  77  inside the vacuum chamber  27 A. It is possible to eject ion beams turning along the beam turning trajectories  78  which are formed on the median plane  77  inside the vacuum chamber  27 A, and to extract the ion beams to the beam transport  13  through the beam extraction path  20 , via the massless septum  12  disposed in this manner. 
       Embodiment 9 
       [0322]    Hereinafter, a particle beam irradiation system in Embodiment 9, which is another preferred embodiment of the present invention, will be described with reference to  FIG. 48 . 
         [0323]    Similar to the particle beam irradiation system  1 E, in a particle beam irradiation system  1 F of the embodiment, the vacuum chamber  27 A is disposed between the iron cores  14 A and  14 B. The particle beam irradiation system  1 F includes an accelerator  4 E including the iron cores  14 A and  14 B, the vacuum chamber  27 A, the beam current measuring unit  15  disposed inside the vacuum chamber  27 A, and the energy absorber  62 . The operation member  16 A attached to the beam current measuring unit  15  and the operation member  62  attached to the energy absorber  62  pass through the vacuum chamber  27 A and the cylindrical portion  75 B of the return yoke  5 B, and reach the outside of the return yoke  5 B. 
         [0324]    In the embodiment, similar to Embodiment 4, a magnetic field distribution illustrated in  FIG. 10  is formed on the median plane  77 . Among Steps S 1  to S 6 , S 23 , S 24 , and S 7  to S 10  illustrated in Embodiment 1, steps except for Steps S 8  and S 9  are executed. Each of Steps S 11 , S 12 , S 22 , S 7 , and S 15  to S 21  illustrated in  FIG. 32  is executed. In the embodiment, a target volume of the patient  56  on the treatment bed  55  is also irradiated with ion beams which are extracted from the vacuum chamber  27 A into the beam transport  13 . 
         [0325]    In the embodiment, it is possible to obtain the same effects as in Embodiment 4. In contrast, in the embodiment, the vacuum chamber  27 A is disposed between the iron cores  14 A and  14 B, and thus, the size of the accelerator  4 D in the embodiment becomes larger than that of the accelerator  4 B in Embodiment 4. 
         [0326]    In the present invention, an ion source which generates carbon ions (C 4+ ) may be used instead of the ion source  3  that generates protons, the carbon ions (C 4+ ) may be converted into carbon ions (C 6+ ) via charge conversion by a charge converter to form a carbon ion beam (C 6+  ion beam) in the accelerator, and the generated carbon ion beam may be extracted from the accelerator and be guided to the irradiation apparatus  7  via the beam transport. In this case, a target volume of the patient  56  on the treatment bed  55  is irradiated with carbon ion beams instead of proton ion beams. An ion source which generates helium ions may be used as the ion source  3 , and helium ion beams may be extracted from the accelerator into the beam transport. 
         [0327]    In this application, a positional relationship between elements, which are not present on the plane perpendicular to the central axis C of the annular coils  11 A and  11 B, represents a positional relationship between the elements on the median plane  77  when the elements are projected onto the median plane  77  in the direction of the central axis C. In Embodiments 8 and 9, examples of a positional relationship between such elements include a positional relationship between the ion inlet port (ion injection port) formed at the tip end of the ion injection tube  3 A, the injection electrode  18 , or the ion injection portion and each of the magnetic poles  7 A to  7 F, the radiofrequency acceleration electrodes  9 A to  9 D, the beam extraction path  20 , and the recessions  29 A to  29 F; and a positional relationship among the magnetic poles  7 A to  7 F, the radiofrequency acceleration electrodes  9 A to  9 D, the beam extraction path  20 , and the recessions  29 A to  29 F; and a positional relationship between the ion inlet port and the inlet of the beam extraction path  20 . 
       REFERENCE SIGNS LIST 
       [0000]    
       
         
           
               1 ,  1 A,  1 B,  1 C,  1 D,  1 E,  1 F: particle beam irradiation system 
               2 ,  2 A,  2 B: ion beam generator 
               3 : ion source 
               3 A: ion injection tube 
               4 ,  4 A,  4 B,  4 C,  4 D,  4 E: accelerator 
               6 : rotating gantry 
               7 : irradiation apparatus 
               7 A to  7 F,  32 A,  32 B: magnetic pole 
               8 A to  8 F: trim coil 
               9 A to  9 D: radiofrequency acceleration electrodes 
               11 A,  11 B: annular coil 
               12 : massless septum 
               13 ,  13 B: beam transport 
               14 A,  14 B: iron core 
               15 : beam current measuring unit 
               17 ,  17 A,  60 : movement apparatus 
               18 : injection electrode 
               19 : septum magnet 
               20 ,  48 : beam path 
               24 A to  24 P: bent point 
               27 ,  27 A: vacuum chamber 
               29 A to  29 F: recession 
               30 ,  30 A,  30 B: iron core member 
               31 A,  31 B: iron core portion 
               31 C: connection portion 
               33 A,  33 B: coil 
               35 : beam passage 
               36 : radiofrequency power supply 
               37 ,  40 ,  57 ,  80 ,  82 : power supply 
               51 ,  52 : scanning magnet 
               53 : beam point monitor 
               54 : dose monitor 
               62 : energy absorber 
               65 : control system 
               66 : central control apparatus 
               69 ,  69 A,  69 B: accelerator and transport control apparatus 
               70 : scanning control apparatus 
               76 : beam turning region 
               77 : median plane 
               83 : injection electrode control apparatus 
               84 : beam current measuring unit control apparatus 
               85 : magnet control apparatus 
               86 : massless septum control apparatus 
               88 : rotation control apparatus 
               89 : irradiation point control apparatus 
               91 : dose determination apparatus 
               92 : layer determination apparatus 
               93 : energy absorber control apparatus 
               94 : coil current control apparatus 
               98 ,  98 A: beam current measuring apparatus 
               99 : radiofrequency voltage control apparatus 
               101 : monitor housing 
               103 : monitor electrode