Beam transport system and method, accelerator equipped with beam transport system, and ion source having the accelerator

Abstract

To provide a beam carrying system and a method for carrying a beam which can efficiently carry a charge particle beam.SOLUTION: A beam carrying system 5 for carrying a charge particle beam includes: a magnetic field generation device 115 provided in a carrying line 12 for carrying a charge particle beam 100 and generating a magnetic field parallel to a central orbit of the charge particle beam; and a beam blocking device 120 provided in a region through which a charge particle beam passes of the inside of the magnetic field generation device, the beam blocking device allowing ones within a predetermined range of the charge particle beams to pass through and stopping the others of the charge particle beams.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a beam transport system and method, an accelerator including the beam transport system, and an ion source including the accelerator. Background Art

[0002] To achieve high-current output from an accelerator, realization of a high-output ion source and low-loss beam acceleration is required. Generally, a beam having an emittance exceeding the acceptance of an accelerator cannot be accelerated and is lost. When beam loss during acceleration is large, not only sufficient output as an accelerator cannot be obtained, but also equipment failure due to heat generation or the like is caused. To prevent this, it is necessary to stop beams outside the acceptance in advance using a collimator to prevent them from entering the accelerator. In the particle sorting method described in Non-Patent Document 1, for a beam extracted from an ion source, an operation of rotating the phase space distribution of particles by a magnetic field and an operation of stopping beam particles located spatially outside by a collimator are alternately repeated. Thereby, in Non-Patent Document 1, particles outside the acceptance of the accelerator are prevented from entering the subsequent-stage accelerator. Prior Art Literature Non-Patent Literature

[0003] Non-Patent Literature 1 J. Pfister, O. Meusel, O. Kester,“COLLIMATION OF HIGH INTENSITY ION BEAMS”,in Proc. International Particle Accelerator Conf 2011.,San Sebastin, Spain , paper WEPC177 Summary of the Invention Problem to be Solved by the Invention

[0004] The technology described in Non-Patent Literature 1 requires the placement of solenoid magnetic fields and collimators in multiple locations, which not only increases the number of devices but also the space required for the beam transport system, thereby increasing manufacturing costs. Furthermore, in the technology of Non-Patent Literature 1, the collimator is installed in a space where there is no solenoid magnetic field, and selection is performed when the beam particles do not have angular momentum in the direction of beam propagation. However, under the above conditions, the beam emittance strongly depends on parameters other than the magnitude of spatial displacement. Therefore, stopping charged particles that are spatially outside with the collimator does not directly lead to the selection of charged particles outside the accelerator acceptance. Consequently, the technology of Non-Patent Literature 1 also stops accelerating charged particles, making it difficult to increase the accelerator output.

[0005] The present invention has been made in view of the above problems, and its object is to provide a beam transport system and method that can efficiently transport charged particle beams, an accelerator equipped with the beam transport system, and an ion source having the accelerator. [Means for solving the problem]

[0006] To solve the above problems, the beam transport system for transporting charged particle beams according to the present invention comprises a magnetic field generator provided in a transport line for transporting charged particle beams and generating a magnetic field parallel to the central trajectory of the charged particle beam, and a beam shielding device provided in the region through which the charged particle beam passes within the magnetic field generator and allowing a predetermined range of charged particle beams to pass while stopping the other charged particle beams. [Effects of the Invention]

[0007] According to the present invention, the charged particle beam can be concentrated in a central orbit by the magnetic field generated by the magnetic field generator and pass through the beam shielding device. Since the charged particle beam outside a predetermined range is stopped by the beam shielding device, the beam can be transported efficiently. [Brief explanation of the drawing]

[0008] [Figure 1] A diagram illustrating the configuration of an accelerator used in particle beam therapy systems. [Figure 2] A longitudinal cross-sectional view showing the structure of the upstream solenoid and collimator. [Figure 3] A diagram illustrating mathematical formulas related to beam transport systems. [Figure 4] An explanatory diagram showing the effect of this embodiment. [Figure 5] An explanatory diagram following Figure 4. [Figure 6] An explanatory diagram following Figure 5. [Figure 7] An explanatory diagram following Figure 6. [Figure 8] An explanatory diagram following Figure 7. [Figure 9] An explanatory diagram showing a comparative example to be compared with this embodiment. [Figure 10] An explanatory diagram following Figure 9. [Figure 11] An explanatory diagram following Figure 10. [Figure 12] A flowchart illustrating the beam transport method. [Figure 13] Configuration diagram of the accelerator according to the second embodiment. [Figure 14] An explanatory diagram showing the relationship between a solenoid-type electromagnet and a collimator, relating to the third embodiment. [Figure 15] A diagram illustrating the relationship between a solenoid-type electromagnet and other collimators, relating to the fourth embodiment. [Figure 16] Plan view of the collimator in Figure 15. [Figure 17] An explanatory diagram illustrating the relationship between a solenoid-type electromagnet, a collimator, and a beam monitor, relating to the fifth embodiment. [Modes for carrying out the invention]

[0009] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In this embodiment, as will be described later, charged particles with large emittance that cannot be accelerated by an accelerator are efficiently stopped, and loss of the charged particle beam in a collimator is reduced. In this embodiment, the correlation <xx’> of the charged particle beam is set to 0, and the charged particle beam is imparted with angular momentum. Thereby, in accordance with the law of conservation of angular momentum for the charged particles of the charged particle beam, the emittance of the charged particle beam becomes a state that depends only on the spatial spread of the charged particle beam. Therefore, in this embodiment, charged particles with different emittances can be sorted with high efficiency, and charged particles with large emittance that cannot be accelerated can be removed. Hereinafter, the charged particle beam may be abbreviated as the beam.

[0010] In the beam transport system according to this embodiment, a converging force and angular momentum are imparted to the charged particle beam by a magnetic field parallel to the traveling direction of the charged particle beam. At this time, a state where there is substantially no correlation <xx’> between the displacement x from the center and the slope x’ in the beam traveling direction can be created, and a state where the emittance depends only on the beam radius can be generated. Therefore, by installing a collimator in a magnetic field parallel to the beam traveling direction, particle sorting utilizing spatial spread can be performed, and particles with different emittances can be sorted.

[0011] According to this embodiment, since the emittance of particles can be sorted based on the magnitude of the spatial spread of the beam, unaccelerable charged particles can be stopped without stopping accelerable charged particles. In this embodiment, beam loss in the collimator portion and inside the accelerator can be minimized, and accelerable beams can be utilized to the maximum extent, thereby realizing a large current of the accelerator. Furthermore, in this embodiment, since beam loss can be reduced, heat generation inside the accelerator can be suppressed, and damage to equipment due to heat can be prevented.

[0012] In this embodiment, for example, the following configurations are disclosed.

[0013] (Expression 1) A beam transport system having a function of sorting charged particle beams, comprising a magnet that generates a magnetic field parallel to the beam orbit on the beam orbit, and a collimator that stops charged particles according to the displacement of the beam particles from the central orbit, wherein arranging the collimator in the magnetic field makes the angular momentum of the charged particle beam≠0, and the Twiss parameter α is in the vicinity of 0 at at least one point on the orbit in the collimator.

[0014] (Expression 2) The beam transport system according to Expression 1, wherein a temperature change of the collimator unit or cooling water passing through the collimator unit is measured, feedback is applied to the solenoid magnetic field intensity according to the temperature change amount, and a state where the Twiss parameter α is in the vicinity of 0 at at least one point on the orbit in the collimator is created.

[0015] (Expression 3) An accelerator according to any one of Expression 1 or Expression 2, comprising the beam transport system, and sorting an accelerated beam based on emittance.

[0016] (Expression 4) An ion source according to any one of Expression 1 or Expression 2, comprising the beam transport system, sorting a beam based on emittance and outputting the sorted beam. [Example]

[0017] A first example will be described with reference to FIGS. 1 to 12. FIG. 1 is a configuration diagram of an accelerator 10. The accelerator 10 forms a part of a particle beam therapy system 1. The particle beam therapy system 1 is disposed across, for example, an accelerator room 2, an accelerator control room 3, and a treatment room (not shown). The particle beam therapy system 1 irradiates a patient (not shown) with a charged particle beam to treat an affected area such as cancer.

[0018] The accelerator room 2 is a space in which the accelerator 10 is installed. The accelerator room 2 is a room whose interior serves as a radiation controlled area. In order to prevent radiation leakage to the outside, the accelerator room 2 is provided with a shielding wall 20 on its outer periphery. Access to the accelerator room 2 by persons is restricted.

[0019] The accelerator room 2 houses the accelerator 10, the lithium target 11, and the beam transport line 12 as components of the particle beam therapy system 1. The beam transport line 12, together with, for example, the solenoid-type electromagnet 115 and collimator 120 described later, constitute the beam transport system 5. More precisely, the temperature measurement section (thermocouple 130 and thermometer 13) and the cooling section (cooling tube 140), described later, can also constitute part of the beam transport system 5.

[0020] The accelerator control room 3 is the room where operator 4 operates the accelerator 10. The accelerator control room 3 is located in a non-radiation controlled area near the accelerator room 2. The accelerator control room 3 is equipped with a thermometer 13, a display device 14, a control device 15, and a speaker 16, which constitute the beam transport line 12. Operator 4, who operates the particle beam therapy system 1 when treating patients, stays in the accelerator control room 3. Operator 4 grasps the state of the charged particle beam based on visual information from the display device 14 and auditory information from the speaker 16, and operates the accelerator 10.

[0021] The accelerator 10 accelerates and emits a charged particle beam. In this embodiment, the accelerator 10 is a proton accelerator that emits a proton beam 100 as a charged particle beam. Hereinafter, the charged particle beam 100 may be referred to as the proton beam 100. For example, the accelerator 10 accelerates the proton beam 100, which has a current of 25 mA and a kinetic energy of 30 keV, until its kinetic energy reaches 2.5 MeV, and emits it into the lithium target 11. Note that the values ​​described below are illustrative examples for explanation purposes, and the beam transport system 5 in this embodiment is not limited to these values.

[0022] The accelerator 10 includes, for example, an ion source 111, a beam transport line 12, and a high-frequency quadrupole linear accelerator 112.

[0023] The ion source 111 is an output unit that generates and emits a proton beam. In the example shown in Figure 1, the ion source 111 is an electron cyclotron resonance (ECR) type ion source. The ion source 111 has a plasma chamber (not shown) inside, and further includes an extraction electrode 113 and a beam extraction power supply 114.

[0024] In the plasma chamber of the ion source 111, hydrogen gas is ionized by a high-frequency voltage to generate a hydrogen plasma. Protons in the hydrogen plasma are extracted to the outside of the plasma chamber by a voltage applied to the extraction electrode 113 and emitted as a proton beam 100 to the low-energy beam transport line 12. The proton beam 100 is a collection of protons that have momentum. In this embodiment, the proton beam 100 extracted from the plasma chamber has a current of 25 mA and a kinetic energy of 30 keV.

[0025] The extraction electrode 113 has two flat plate electrodes positioned opposite each other. When a voltage of 30 kV is applied between these flat plate electrodes, protons in the hydrogen plasma generated in the plasma chamber are accelerated to 30 keV and emitted as a proton beam 100.

[0026] The beam extraction power supply 114 is a high-voltage power supply that applies a high voltage of 30kV to the extraction electrode 113. The voltage applied by the beam extraction power supply 114 is controlled by the control device 15 via cable C1. Cable C1 is, for example, a BNC (Bayonet Neill Concelman) cable.

[0027] The beam transport line 12 is a transport line through which the beam passes, with the interior being evacuated. The beam transport line 12 is equipped with a beam transport system 5. The beam transport system 5 selects and focuses the proton beam 100 emitted from the ion source 111 during the transport process, thereby creating a beam that can be accelerated by the radio frequency quadrupole linear accelerator 112, and injects it into the radio frequency quadrupole linear accelerator 112.

[0028] The high-frequency quadrupole linear accelerator 112 is an accelerator that accelerates a particle beam along a straight line using a high-frequency voltage, which is an acceleration voltage supplied from an acceleration high-frequency source 1055. In this embodiment, the high-frequency quadrupole linear accelerator 112 uses the high-frequency voltage to accelerate the proton beam 100, applying a focusing force, until its kinetic energy reaches 2.5 MeV, and then emits it into the lithium target 11.

[0029] The lithium target 11 is a cone-shaped target mainly composed of lithium (Li), positioned so that its base faces the radio frequency quadrupole linear accelerator 112. The lithium target 11 is equipped with a heat removal function using cooling water. The lithium target 11 generates thermal neutrons by undergoing a 7Li(p,n)7Be reaction with protons in the proton beam 100 supplied from the accelerator 10, and emits this thermal neutron beam towards the patient in the treatment room.

[0030] The beam transport line 12 is a beam transport system through which low-energy beams pass. It transports the proton beam 100 emitted from the ion source 111 from right to left in Figure 1 and into the radio-frequency quadrupole linear accelerator 112.

[0031] The beam transport line 12 consists of solenoid electromagnets 115 and 116, solenoid electromagnet power supplies 117 and 118, a thermometer 13, a display device 14, a recording device 16, a speaker 16, and a beam current measuring device 20. The beam transport line 12 uses solenoid electromagnets 115 and 116 to induce a magnetic field parallel to the direction of propagation of the proton beam 100. The induced magnetic field imparts a focusing force to the proton beam 100. Furthermore, in this embodiment, particles with low emittance are selected by a beam selection mechanism described later. With the above configuration, the beam transport system 5 of this embodiment has the function of shaping the proton beam 100 into a shape that can be accelerated by the high-frequency quadrupole linear accelerator 112.

[0032] The solenoid electromagnets 115 and 116 have wires wound spirally along the direction of propagation of the proton beam 100. When current is supplied to the wires of the solenoid electromagnets from the solenoid electromagnet power supplies 117 and 118, a magnetic field parallel to the direction of propagation of the proton beam 100 is induced.

[0033] The solenoid electromagnet 115 imparts a focusing force and angular momentum to the proton beam 100 with the beam axis as the axis of rotation through the induced magnetic field. Furthermore, the solenoid electromagnet 115 uses a collimator 120 installed inside to stop particles with high emittance. In other words, the solenoid electromagnet 115 has a focusing function that focuses the proton beam towards the central axis and imparts angular momentum, and a selection function that allows only particles with low emittance to pass through and stops particles with high emittance. Through these two functions, the solenoid electromagnet 115 selects beam particles that can be accelerated in the radio frequency quadrupole linear accelerator 112 and transports them toward the radio frequency quadrupole linear accelerator 112. The solenoid electromagnet 116, acting as "another solenoid electromagnet," exerts a focusing force on the proton beam 100 through the magnetic field it induces. As a result, the solenoid electromagnet 116 shapes the beam into a form that can be accelerated by the high-frequency quadrupole linear accelerator 112, and then emits it into the high-frequency quadrupole linear accelerator 112.

[0034] The solenoid electromagnet power supplies 117 and 118 are high-current output power supplies that supply a current in the range of 20A to 100A to the solenoid electromagnets 115 and 116. The current supplied by the solenoid electromagnet power supplies 117 and 118 is controlled by the control device 15 via cables C2 and C3. By changing the current value supplied by the solenoid electromagnet power supplies 117 and 118 to the solenoid electromagnets 115 and 116 over time, the proton beam 100 is shaped into a form that can be accelerated by the high-frequency quadrupole linear accelerator 112. Cables C2 and C3 are, for example, BNC cables.

[0035] Figure 2 shows a cross-sectional view of a solenoid electromagnet 115. The solenoid electromagnet 115 is created, for example, by winding a coil 1151 around the outside of a cylindrical transport line 12. The proton beam 100 enters from the inlet 1151 on the right side of Figure 2 and exits from the outlet 1152 on the left side of Figure 2. The proton beam 100 travels from right to left in Figure 2.

[0036] Inside the solenoid electromagnet 115 are a collimator 120 and a thermocouple 130 acting as a temperature sensor. The collimator 120 is, for example, a ring-shaped copper metal component and includes the thermocouple 130 and a cooling tube 140. The collimator 120 is water-cooled by cooling water (not shown) passing through the cooling tube 140. The solenoid electromagnet 115 induces a magnetic field parallel to the direction of propagation of the proton beam 100. As a result, the proton beam 100 receives a focusing force toward the beam center and undergoes rotational motion with the direction of propagation as the axis of rotation. The beam trajectory center of the proton beam 100 passes through the center of the circular opening 121 of the collimator 120.

[0037] The collimator 120 blocks the propagation of high-emitterance particles 100E as the proton beam 100 passes through the aperture 121, according to the principle described later. The high-emitterance particles 100E collide with the collimator 120, raising its temperature. The temperature of the collimator 120 is measured by the thermocouple 130. The temperature measured by the thermocouple 130 is sent to and displayed on the thermometer 13 shown in Figure 1.

[0038] The thermometer 13 measures the temperature by detecting the current generated by the temperature difference between the two probes (not shown) of the thermocouple 130. The thermocouple 13 sends the measured temperature data to the control device 15 via cable C8. Furthermore, the thermocouple 13 sends the measured temperature data to the display device 14 via cable C7. Cables C7 and C8 are, for example, RJ45 cables. In place of the thermocouple 13, other temperature sensors such as a radiation thermometer may be used. Alternatively, the temperature of the collimator 120 may be measured indirectly by measuring the temperature of the cooling water flowing through the cooling pipe 140.

[0039] The collimator 120 can be installed, for example, in the range (LC / 2) downstream of the direction of travel of the proton 100 from the axial center (longitudinal center) O-O' of the total length LC of the solenoid electromagnet 115. In other words, the collimator 120 can be installed closer to the exit 1152 side where the proton beam 100 is emitted from the solenoid electromagnet 115 than to the inlet 1151 where the proton beam 100 is injected into the solenoid electromagnet 115. This allows the solenoid electromagnet 115 to efficiently realize the function of focusing the proton beam 100 while causing the particles of the proton beam 100 to rotate.

[0040] Returning to Figure 1, the beam current measuring device 20 is a DC Current Transformer (DCCT) that measures the beam current without contacting the beam, and has the function of sequentially measuring fluctuations in the total amount of the proton beam 100 drawn from the ion source 111. The amount of current measured by the beam current measuring device 20 is sent to the control device 15 using a coaxial cable (not shown).

[0041] The control device 15 is a computer system having a memory for recording computer programs and a processor (neither of which is shown) that reads the computer programs recorded in the memory and executes the read computer programs to realize the above functions.

[0042] The control device 15 records the temperature and measurement time measured by the thermometer 13. Furthermore, the control device 15 compares the measured temperature with a specified value, and if the difference between the measured value and the specified value is greater than or equal to a predetermined value, it determines that there is an abnormality in the proton beam 100. When the control device 15 determines that there is an abnormality in the proton beam 100 (detects an abnormality), it issues an alert signal. The alert signal is sent to the display device 14 via cable C6 and displayed. Furthermore, the control device 15 sends the alert signal to the speaker 16 via cable C5, causing the speaker 16 to sound.

[0043] When the control device 15 determines that the proton beam 100 is abnormal, it sends signals to the solenoid electromagnet power supplies 117 and 118 via cables C2 and C3 to adjust the magnetic field. Cables C2 to C5 are, for example, coaxial cables.

[0044] In this embodiment, for example, as shown in Figure 12, the measured value of the beam loss in the collimator 120 and the ratio of that measured value to the total beam are calculated from the temperature rise value measured by the thermometer 13 and the beam current value measured by the beam current measuring device 20 using the procedure described later.

[0045] The control device 15 issues an alert signal if the calculated ratio differs from a specified value by 5%, and sends an instruction signal to increase the output current from the solenoid electromagnet power supply 117 by 0.1% as a magnetic field adjustment signal. Conversely, the control device 15 sends an instruction signal to decrease the output current from the solenoid electromagnet power supply 117 by 0.1% as a magnetic field adjustment signal if the temperature rise value is 5% lower than a specified value.

[0046] The control device 15 may be generated by coordinating a computer having a processor that executes computer programs with a recording device equipped with a recording medium such as a hard disk or magnetic tape.

[0047] The display device 14 is a device that displays various information such as characters, figures, and graphics, and is installed in the accelerator operating room 3. The display device 14 displays the temperature of the collimator 120 measured by the thermometer 13 and whether or not an alert signal has been issued by the control device 15 in real time, and notifies the operator 4.

[0048] Speaker 16 is an audio output device that converts electrical signals into sound and is installed in the accelerator operator's room 3. When speaker 16 determines that the proton beam 100 is abnormal, it outputs an alarm sound corresponding to the alert signal received from the control device 15. Speaker 16 functions as a notification unit that notifies the operator 4 of the alarm (abnormality of the proton beam 100).

[0049] FIG. 4 shows an example of formula 1000 related to a beam transport system. In general, whether beam particles can be accelerated by an accelerator is determined by the magnitude relationship between the accelerator acceptance εacceptance and the Courant-Snyder invariant CSbeam of the particles. Only particles satisfying εacceptance>CSbeam are accelerated, while particles satisfying εacceptance<CSbeam are lost. The average value of the Courant-Snyder invariant CSbeam of particles in a beam is the four-dimensional emittance εbeam of the beam.

[0050] εbeam is expressed as shown in Formula 1 by the variance-covariance matrix Σ and the phase space vector X of beam particles. The phase space vector X is a four-dimensional vector consisting of positions x and y in two mutually different directions intersecting the beam axis direction, and the change amounts x' and y' in the beam orbit direction, and is expressed as X=(x, x', y, y'). The variance-covariance matrix Σbeam is a 4-row 4-column real symmetric matrix that represents the correlation between each element of the phase space vector X, and can be written as shown in Formula 2. The symbol <> in Formula 1 and Formula 2 represents the operation of taking the average of particles in the beam. εbeam represents the volume occupied by the beam in a four-dimensional phase space consisting of positions and momenta in two mutually different directions intersecting the beam axis direction. εbeam is a conserved quantity and does not change during the beam transport process by an electromagnetic field. Generally, the emittance εion of a beam extracted from an ion source is larger than the acceptance of the accelerator. Therefore, in order to avoid beam loss in the accelerator, it is necessary to select beam particles with small emittance and set εbeam<εacceptance when the beam is incident to the accelerator.

[0051] The effect of beam selection by the beam transport system 5 according to the present embodiment will be described with reference to FIGS. 4 to 11. FIGS. 4 to 8 show the beam selection effect of the beam transport system 5 of the present embodiment, and FIGS. 9 to 11 show a comparative example. FIGS. 9 to 11 schematically show phenomena occurring in a beam transport system to which the present embodiment is not applied, and are not prior art.

[0052] First, we will explain the phenomena during beam selection in the comparative example, referring to Figures 9 to 11. Figures 9 to 11 illustrate the positions of particles stopped by the collimator in four-dimensional phase space. Figure 9 shows a part of the beam selection in the comparative example.

[0053] Figure 9 shows the beam distribution in the xy-plane at the point where the beam passes through the collimator. Beam 100R is the distribution of the entire beam passing through the collimator. Beam 101R is a part of beam 100R and is a group of particles that are located outside the inner diameter of the collimator in the xy-plane. In the comparative example, beam 101R is stopped by the collimator. Now, let's focus on beam particle 102R and consider its position in four-dimensional phase space. Beam particle 102R is a part of beam 101R that is cut off by the collimator. Beam particle 102R is a particle with a large displacement in the x-direction and a displacement in the y-direction that is near zero.

[0054] Figure 10 shows the projection of the beam's four-dimensional phase space distribution onto the x,y' plane. In the comparative example, since there is no solenoid electromagnet, the collimator is placed in a space without the magnetic field of the solenoid electromagnet. Therefore, in the comparative example, the beam does not have angular momentum with the direction of propagation as the axis of rotation. This means that there is no correlation between x and y', and the distribution of the beam on the x,y' plane has a shape close to a perfect circle. As a result, the y' of beam particle 102R, which has the largest displacement in the x direction, is near 0.

[0055] Figure 11 shows the projection of the beam's four-dimensional phase space distribution onto the y,y' plane. Since both y and y' are small for beam particle 102R, it is located at the center of the beam on the y,y' plane.

[0056] From the above, in the comparative example, when particles outside the beam on the xy plane are removed by the collimator, the removed particles correspond to the beam center on the y,y' plane. Therefore, in the comparative example, it is not possible to selectively remove particles outside the four-dimensional phase space, and some particles inside the four-dimensional phase space are also removed simultaneously. Furthermore, in the comparative example, it is difficult to stop particles outside the phase space all at once with a single collimator, so it is necessary to install collimators at multiple locations with different phase space distributions of the beam and select them accordingly.

[0057] Next, using Figures 4 to 8, we will explain how the beam transport system 5 of this embodiment solves the problems of the comparative example. In this embodiment, a solenoid magnetic field is used to impart angular momentum to the proton beam 100 as it passes through the collimator, and at the same time, the correlation between x and x' of the proton beam 100 is also addressed.<xx’> This is considered a 0-neighborhood. This solves the problems of the comparative example in this embodiment.

[0058] Figure 4 shows the beam distribution in the xy-plane at the point where the beam passes through the collimator. Beam 100 is the distribution of the entire beam passing through collimator 120. Beam 101 is a part of beam 100, a group of particles located outside the inner diameter of collimator 120 (the diameter of the aperture 121) in the xy-plane. Beam 100 is stopped by collimator 120. Now, let's focus on beam particle 102 and consider its position in four-dimensional phase space. Beam particle 102 is a part of beam 100 that is cut off by the collimator, and is a particle with a large displacement in the x-direction, while its displacement in the y-direction is near zero.

[0059] Figure 5 shows the projection of the four-dimensional phase space distribution of the proton beam 100 onto the x,y' plane. In this embodiment, since the collimator 120 is installed in a space where a magnetic field parallel to the beam propagation direction exists, that is, since the collimator 120 is installed inside the solenoid-type electromagnet 115, the proton beam 100 has angular momentum with the propagation direction as its axis of rotation. Therefore, there is a correlation between x and y', and the distribution of the proton beam on the x,y' plane has a shape like an inclined ellipse. As a result, the y' of beam particles 102 with large displacements in the x direction has a large value.

[0060] Figure 6 shows the projection of the beam's four-dimensional phase space distribution onto the y,y' plane. Since beam particle 102 has a displacement near 0 in the y direction and a large displacement in y', it is located at the edge of the beam distribution on the y,y' plane as well.

[0061] Figure 7 shows the projection of the beam's four-dimensional phase space distribution onto the x',y' plane. Since the y' of beam particle 102 is large, x' takes a value near 0.

[0062] Figure 8 shows the projection of the beam's four-dimensional phase space distribution onto the x,x' plane. In this embodiment, to create a state where there is no correlation between x and x', the beam has a shape close to a perfect circle on the x,x' plane. The displacement of beam particle 102 in the x direction is large, and x' takes a value near 0, so even on the x,x' plane, beam particle 102 is located at the edge of the beam distribution.

[0063] Therefore, in this embodiment, when removing particles outside the beam on the xy plane using the collimator 120, it is possible to selectively remove particles outside the four-dimensional phase space. In this embodiment, by simply placing the collimator 120 in one location within the solenoid-type electromagnet 115, it is possible to select only particles outside the four-dimensional phase space.

[0064] The mechanism of the beam transport system 5 in this embodiment will be explained below using equation 1000 shown in Figure 3. In this embodiment, the four-dimensional emittance εcol when the proton beam 100 passes through the collimator 120 due to the magnetic field generated by the solenoid electromagnet 115 is equal to the square of the beam radius.<r^2> A state that depends solely on col can be created. By stopping particles in the outer part of the beam in the x,y space using the collimator 120, it is possible to reduce the four-dimensional emittance εbeam of the downstream beam. By setting εacceptance > εbeam and selectively removing particles with large emittance, it is possible to prevent unaccelerated particles from entering the high-frequency quadrupole linear accelerator 112 and reduce beam loss.

[0065] In general, when Busch's theorem, a quantum mechanical law of conservation of angular momentum, is applied to a beam with a variance-covariance matrix Σ, the relationship in Equation 3 is derived. The right-hand side of Equation 3 is an invariant quantity in beam transport by electromagnetic fields. ε1 and ε2 in Equation 3 are eigenemitters, and they are related to the four-dimensional emittance ε4d in Equation 4.

[0066] The variance-covariance matrix Σcol when the proton beam 100 passes through the collimator 120 is given by Equation 5. Due to the cylindrical symmetry of the beam distribution,<x^2> col=<y^2> col=<r^2> col,<x’^2> col=<y’^2> col,<yx’> col=-<xy’> col, <xy>col=<x’y’> col = 0.

[0067] Here, since the collimator 120 is installed inside the solenoid electromagnet 115, the proton beam 100 rotates in a plane perpendicular to its orbit due to a magnetic field parallel to the direction of propagation. Therefore, the angular momentum of the rotation corresponds to<yx’> col and the square of the beam orbit radius<r^2> The relationship between col and the solenoid is given by Equation 6. In Equation 6, k is the magnetic flux density B of the solenoid field and the magnetic rigidity Bρ of the beam, and can be written as in Equation 7. In Equation 6, L is the distance on the beam trajectory from the solenoid electromagnet inlet 1151 to the installation position of the collimator 120. Furthermore, by adjusting the current of the solenoid electromagnet 115 through the procedure described later, for example...<xx’> col,<yy’> It is possible to achieve an excitation amount for the solenoid electromagnet 115 such that col is near 0. Therefore, εcol is<r^2> col's function εcol (<r^2> It can be written as shown in equation 8.

[0068] Therefore, the inner diameter Rcol of the collimator 120 is, for example, 3ε(<r^2> ) = εacceptance<r^2> By adopting the square root of ε, it is possible to pass a beam ensemble such that εcol < εacceptance when the proton beam 100 is injected into the radio frequency quadrupole linear accelerator 112. For example, if the distribution of particle displacements within the beam follows a normal distribution, then in this embodiment, approximately 99.7% of the beam injected into the radio frequency quadrupole linear accelerator 112 can be accelerated.

[0069] Next, by adjusting the excitation amount of the solenoid electromagnet 115...<xx’> col,<yy’> This section explains the principles and methods for defining col as a zero-neighbor.

[0070] <xx’>col,<yy’> The Twiss parameters αx and αy are obtained by inverting the sign of col, and these represent the convergence or divergence of the beam in the x and y directions, respectively. When αx, αy > 0, it is a convergent beam, and the beam size decreases as the beam progresses. On the other hand, when αx, αy < 0, it is a divergent beam, and the beam size increases as the beam progresses. The proton beam 100 extracted from the ion source 111 passes through a space without a magnetic field until it reaches the solenoid electromagnet 115. Therefore, when the proton beam 100 reaches the solenoid electromagnet 115, the state is αx, αy < 0, and the beam size tends to increase.

[0071] The solenoid electromagnet 115 has the function of focusing the proton beam 100 in both the x and y directions, and increases the Twiss parameters αx and αy of the proton beam 100. The amount of increase in the Twiss parameters αx and αy depends on the product BL of the magnetic field B produced by the solenoid electromagnet 115 and the distance L from the entrance 1151 of the solenoid electromagnet 115 to the collimator 120. Therefore, by adjusting the excitation amount of the solenoid electromagnet 115, it is possible to change αx and αy when the proton beam 100 passes through the collimator 120.

[0072] The appropriate excitation amount for the solenoid electromagnet 115 can be set by the following mechanism: It can be determined by taking the ratio of the temperature rise dT / dt of the collimator 120 measured by the thermometer 13 to the temperature rise value assuming that the beam current Ibeam measured by the beam current measuring instrument 20 is completely lost.

[0073] When the proton beam 100 passes through the collimator 120, particles with displacements in the xy plane greater than or equal to the inner diameter Rcol of the collimator 120 are stopped. In this embodiment, of the proton beam 100 that reaches the collimator 120 with beam size rcol, particles on the outside of the xy plane are unable to pass through the collimator 120 and are stopped. The ratio of the current amount Iloss of the stopped beam to the beam current value Ibeam measured by the beam current measuring instrument 20 can be written by equation 9. Here, F(r / rcol) is the distribution function of particle displacement in the proton beam 100, which is generally a distribution function that is maximized at r=0. In this embodiment, for example, a second-order chi-squared distribution is used. Therefore, the larger the ratio of the inner diameter Rcol of the collimator 120 to the beam size rcol when the proton beam 100 reaches the collimator 120, the greater the ratio to the beam current amount Ibeam.

[0074] The 30 keV kinetic energy of a particle stopped in collimator 120 is converted into thermal energy, generating a heat quantity W per second as shown in Equation 10. The temperature of collimator 120 rises by ΔT, proportional to the heat quantity W, as shown in Equation 11. Therefore, it can be seen that the larger the ratio between the beam size rcol when the proton beam 100 reaches collimator 120 and the inner diameter Rcol of collimator 120, the greater the temperature rise. In Equation 11, C is the heat capacity of collimator 120, which here is for example 40 J / K.

[0075] The temperature rise ΔTall, which occurs when all of the beam current Ibeam measured by the beam current measuring instrument 20 is assumed to be lost, can be calculated in the same way as in equations 10 and 11. Thus, the ratio of the temperature rises ΔT / ΔTall is expressed in equation 12.

[0076] The relationship between the excitation amount of the solenoid electromagnet 115 and the temperature rise of the collimator 120, as explained by the mechanism described above, is shown in the following three cases.

[0077] Case 1: Assuming the excitation amount of the solenoid electromagnet 115 is appropriate, in this embodiment, the emittance εion of the beam extracted from the ion source 111 is assumed to be three times the acceptance εacceptance of the high-frequency quadrupole linear accelerator 112 described later. In this case, approximately 22% of the extracted proton beam 100 is stopped within the collimator 120. If the beam current Ibeam is 35 mA at this time, 231 J of heat is generated, and the temperature rise ΔTall is 5.1 degrees. Therefore, in the case of an ideal excitation amount, the temperature rise of the collimator should be 1.2 degrees. This temperature rise is defined as the specified value Th.

[0078] Case 2: If αx and αy are less than 0 when the proton beam 100 passes through the collimator 120, it means that the excitation amount of the solenoid electromagnet 115 is insufficient, and the proton beam 100 does not obtain sufficient focusing force. In this case, the beam size when the proton beam 100 passes through the collimator 120 will be larger than the ideal beam size. Therefore, the amount of beam that stops at the collimator 120 will be greater than the amount of beam that stops in the ideal case, and the temperature rise of the collimator 120 will be greater than the specified value Th mentioned above.

[0079] Case 3: When αx and αy are greater than 0 when the proton beam 100 passes through the collimator 120, it means that the excitation amount of the solenoid electromagnet 115 is excessive, and the proton beam 100 is gaining excessive focusing force. In this case, the beam size when the proton beam 100 passes through the collimator 120 will be smaller than the ideal beam size. Therefore, the amount of beam that stops at the collimator 120 will be less than the amount of beam that stops in the ideal case, and the temperature rise of the collimator 120 will be smaller than the specified value Th mentioned above.

[0080] Based on the above relationship, by adjusting the excitation amount of the solenoid electromagnet 115 so that the temperature rise of the collimator 120 approaches the specified value Th, the Twiss parameters αx and αy in the collimator 120 can be set to a vicinity of 0.

[0081] An example of how to operate the beam transport system 5 is explained using Figure 12. The flowchart in Figure 12 shows the procedure for adjusting the twiss parameters αx and αy in the collimator 120 to near 0 in the beam transport line 12 and maintaining this at all times during accelerator 10 operation.

[0082] Step S10: Operator 4 sets the temperature specification value Th of the collimator 120 in the control device 15. In this embodiment, it is assumed that approximately 22% of the extracted beam stops within the collimator 120. In this case, if the beam current Ibeam is 35 mA, the temperature rise of the collimator will be 1.2 degrees under ideal excitation conditions. As described above, this temperature rise value is set as the temperature specification value Th.

[0083] Step S11: Operator 4 turns on the output of the ion source 111. This applies a voltage of 30kV to the extraction electrode 113 of the ion source 111, and the proton beam 100 is output.

[0084] Step S12: The control device 15 obtains the temperature Tc of the collimator 120, which is measured by the thermocouple 130 and the thermometer 13. In Figure 12, the measured temperature of the collimator 120 is represented as temperature Tc.

[0085] Step S13: The control device 15 evaluates the difference between the measured temperature Tc of the collimator 120 measured by the thermometer 13 and the specified temperature Th. The control device 15 determines whether the difference between the measured temperature Tc and the specified value Th is less than 5%. If the difference between the measured temperature Tc and the specified value Th is less than 5% (S13: YES), the control device 15 stores the measured temperature Tc in its memory (S14). Conversely, if the difference between the measured temperature Tc and the specified value Th is 5% or more (S13: NO), the control device 15 proceeds to step S15.

[0086] Step S15: The control device 15 determines the relationship between the specified temperature Th and the measured value Tc. If the measured value Tc is, for example, 5% or more greater than the specified value, the control device 15 proceeds to step S16. If the measured value Tc is, for example, 5% less than the specified value Th, the control device 15 proceeds to step S17.

[0087] Step S16: If the measured temperature Tc is, for example, 5% or more greater than the specified value Th, the magnetic field of the solenoid electromagnet 115 is insufficient, and particles are colliding with the collimator 120 more often than in the ideal state, resulting in an increase in heat. Therefore, the control device 15 outputs an alert signal to the display device 14 and speaker 16, as well as a magnetic field adjustment signal. As the magnetic field adjustment signal, the control device 15 sends an instruction signal to increase the output current from the solenoid electromagnet power supply 117 by 0.1%. This increases the excitation amount of the solenoid electromagnet 115. After this, the process proceeds to step S14, and the control device 15 stores the measured temperature Tc.

[0088] Step S17: The magnetic field generated by the solenoid electromagnet 115 is excessive. Therefore, the control device 15 outputs an alert signal to the display device 14 and the speaker 16, and also sends a signal to reduce the output current from the solenoid electromagnet power supply 117 by 0.1% as a magnetic field adjustment signal. As a result, the excitation amount of the solenoid electromagnet 115 decreases. After this, the control device 15 proceeds to step S14.

[0089] The control device 15 stores the measured temperature Tc and the determination result of step S13 (or the determination result of step S13 and the determination result of S15), and returns to step S12.

[0090] In this embodiment, the emittance of particles can be selected based on the spatial extent of the proton beam 100. Therefore, charged particles that cannot be accelerated can be stopped without stopping the accelerateable charged particles.

[0091] In this embodiment, beam loss in the collimator 120 and accelerator 112 can be minimized, and the accelerating beam can be utilized to its fullest extent, enabling high current operation of the accelerator 10. Furthermore, because beam loss can be reduced in this embodiment, heat generation within the accelerator can be suppressed, preventing equipment damage due to heat. [Examples]

[0092] The second embodiment will be explained using Figure 13. In the following embodiments, including this embodiment, the differences from the first embodiment will be explained in detail. Figure 13 is a diagram of the accelerator 10A used in the particle beam therapy system 1A according to this embodiment.

[0093] In the accelerator 10A of this embodiment, only the solenoid-type electromagnet 115 is provided in the beam transport system 5A, and the downstream solenoid-type electromagnet 116 shown in the first embodiment is not provided.

[0094] This embodiment, configured in this way, produces almost the same effects as the first embodiment. Furthermore, since this embodiment is equipped with only one solenoid-type electromagnet 115, the number of parts can be reduced, thereby lowering manufacturing costs. [Examples]

[0095] A third embodiment will be described using Figure 14. Figure 14 is an explanatory diagram showing the relationship between the solenoid electromagnet 115B and the collimator 120B. In this embodiment, an annular collimator 120B having an opening 121B is provided at approximately the center OO of the axial length LC of the solenoid electromagnet 115B. This embodiment, configured in this way, may have a change in the beam focusing function, but it produces almost the same effects as the first embodiment. [Examples]

[0096] A fourth embodiment will be described using Figures 15 and 16. Figure 15 is a cross-sectional view. Figure 16 is a plan view. In this embodiment, a collimator 120C is provided inside the solenoid electromagnet 115C to stop particles near the center and allow only outer particles to pass through. A small-diameter shielding portion 122C is provided at the center of the collimator 120C, and a plurality of openings 121C are formed outside the shielding portion 122C, spaced apart in the circumferential direction.

[0097] In this configuration, particles at the center of the proton beam 100's direction of travel can be stopped, allowing outer particles to pass through. In other words, this configuration allows for the selection of particles with high emittance and the stopping of particles with low emittance. [Examples]

[0098] A fifth embodiment will be described using Figure 17. Figure 17 is a cross-sectional view showing the relationship between the solenoid electromagnet 115D and the collimator 120D. The collimator 120D has an opening 121D. In this embodiment, a beam monitor 150 is placed on the exit 1152 side of the solenoid electromagnet 115D. In this embodiment, the beam monitor 150 measures the state of the proton beam 100 passing through the solenoid electromagnet 115D. Therefore, in this embodiment, it is not necessary to control the energization of the solenoid electromagnet 115D based on the temperature rise value of the collimator 120D as described in Figure 12. The control device 15 controls the energization of the solenoid electromagnet 115D based on the measurement results from the beam monitor 150.

[0099] The configuration, function, and operation described above are merely examples and are not limited thereto. For example, in this embodiment, the beam transport line transports the beam from the ion source for the particle beam therapy system to the radio frequency quadrupole linear accelerator, but the accelerator that performs beam transport is not limited to this example. For example, it may be an accelerator for nuclear transmutation, an accelerator for nuclear fusion, or an accelerator for particle beam therapy. The accelerators described in each embodiment are linear accelerators, but circular accelerators or the like may be used instead.

[0100] At least one solenoid electromagnet is required between the ion source and the accelerator. While the embodiment shows examples with one or two solenoid electromagnets, three or more solenoid electromagnets may be used. Furthermore, a collimator should be placed in at least one of the three or more solenoid electromagnets. If necessary, collimators may also be placed in multiple or all of the three or more solenoid electromagnets.

[0101] The feedback based on the collimator temperature measurement results is not limited to the current output of the solenoid electromagnet power supply; it may also be the ion source extraction power supply voltage.

[0102] Thus, the present invention is not limited to the embodiments described above. Those skilled in the art can make various additions and modifications within the scope of the present invention. The configuration and processing methods of the embodiments can be changed as appropriate.

[0103] Furthermore, each component of the present invention can be arbitrarily selected or omitted, and an invention comprising the selected configuration is also included in the present invention. Moreover, the configurations described in the claims can be combined in combinations other than those explicitly stated in the claims. [Explanation of symbols]

[0104] 1,1A: Particle beam therapy system, 2: Accelerator room, 3: Accelerator operation room, 4: Operator, 5,5A: Beam transport system, 10,10A: Accelerator, 11: Lithium target, 12: Beam transport line, 13: Thermometer, 14: Display device, 15: Control device, 16: Speaker, 20: Shielding wall, 100: Proton beam, 100E: High emittance beam, 101: Beam located outside the inner diameter of the collimator, 102: Particle (part of the beam abraded by the collimator) ), 111: Ion source, 112: High-frequency quadrupole linear accelerator, 113: Extraction electrode, 114: Beam extraction power supply, 115, 115B, 115C, 115D: Solenoid electromagnet, 116: Other solenoid electromagnet, 117, 118: Solenoid electromagnet power supply, 119: Beam current measuring device, 120, 120B, 120C, 120D: Collimator, 121: Aperture, 130: Thermocouple, 140: Cooling tube, 150: Beam monitor, 1000: Formulas related to the beam transport system< / xy>

Claims

1. A beam transport system for transporting charged particle beams, A magnetic field generator installed in a transport line for transporting a charged particle beam, which generates a magnetic field parallel to the central trajectory of the charged particle beam, A beam shielding device is provided in the region through which the charged particle beam passes within the magnetic field generator, and allows a predetermined range of charged particle beams to pass while stopping the other charged particle beams. Equipped with, The magnetic field generating device is a solenoid-type electromagnet that generates a magnetic field parallel to the central trajectory of a charged particle beam. The beam shielding device is a collimator provided within the solenoid-type electromagnet, which stops charged particles that deviate from the central trajectory of the charged particle beam by a predetermined value or more. At least one point in the central trajectory of the charged particle beam within the collimator, the correlation between the positions x and y in two different directions intersecting the beam axis direction and the changes in the beam trajectory direction x' and y' is adjusted such that the correlation <xx'> and correlation <yy'> are near zero, and the correlation <yx'> is not zero. Beam transport system.

2. Furthermore, it includes a control device for controlling the supply of current to the solenoid-type electromagnet. The beam transport system according to claim 1.

3. The control device controls the energization of the solenoid-type electromagnet based on the temperature of the collimator, thereby adjusting the Twiss parameter α to be near 0 at at least one point in the central trajectory of the charged particle beam within the collimator. The beam transport system according to claim 2.

4. The collimator is provided in the range from the axial center within the solenoid-type electromagnet to the outlet from which the charged particle beam is emitted. The beam transport system according to claim 3.

5. Another solenoid-type electromagnet, different from the one mentioned above, is provided downstream of the solenoid-type electromagnet in the direction of travel of the charged particle beam. The beam transport system according to any one of claims 1 to 4.

6. An accelerator having the beam transport system according to any one of claims 1 to 4.

7. An ion source connected to a beam transport system according to any one of claims 1 to 4.

8. A beam transport method for transporting a charged particle beam using a beam transport system, A collimator is placed inside a solenoid-type electromagnet located in the middle of the transport line that transports the charged particle beam. At least one point in the central trajectory of the charged particle beam within the collimator, the correlation between the positions x and y in two different directions intersecting the beam axis direction and the changes in the beam trajectory direction x' and y' is adjusted such that the correlation <xx'> and correlation <yy'> are near zero, and the correlation <yx'> is not zero. Beam transport method.

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