JP7612495B2 - Magnetic pole forming method, magnetic field adjusting device, accelerator and particle beam therapy system - Google Patents

Description

The present invention relates to a magnetic pole forming method, a magnetic field adjustment device, an accelerator, and a particle beam therapy system, and in particular to a magnetic pole in an electromagnetic device.

Particle beam therapy, in which a particle beam is irradiated onto an affected area, is widely used. Generally, particle beam therapy uses a particle beam therapy system equipped with an accelerator. Ions such as carbon ions, helium ions, and protons are injected into the accelerator, and the ions are accelerated until they have the energy required for treatment. The beam of ions accelerated by the accelerator is directed towards the affected area.

Accelerators use electromagnets that generate a magnetic field. Ions accelerated by an electric field move around the accelerator due to the magnetic field generated by the electromagnet. Generally, when an accelerator is installed in a medical facility or the like, the magnetic field generated by the electromagnet is adjusted. One method of adjusting the magnetic field of an electromagnet (shimming) is passive shimming, in which correction iron is placed around the electromagnet. Correction iron is a magnetic material made of sheet-like iron or the like that is used to adjust the magnetic field distribution. By appropriately placing the correction iron in the area around the electromagnet, the magnetic field distribution in the area of interest can be adjusted.

Patent Document 1 describes a method for adjusting the magnetic field distribution in a region of interest of a magnetic field generating device mounted on a magnetic resonance imaging (MRI) device. This document describes "a method for adjusting the homogeneity of the static magnetic field in the imaging space by calculating, by shimming calculation, the positions of multiple magnetic pieces away from the imaging space generated by a magnetic field generating device, and arranging the multiple magnetic pieces at the positions obtained by the shimming calculation." Specifically, the document describes a method for adjusting the magnetic field by inserting magnetic materials into shim pockets provided around the electromagnets in the magnetic resonance imaging device.

Patent No. 6617135

In the adjustment method described in Patent Document 1, when adjusting the magnetic field distribution of an electromagnet, the size of the correction iron that needs to be handled becomes smaller as the strength of the magnetic field to be adjusted becomes smaller. This can make it difficult to manufacture and handle the correction iron. This can result in limitations on the adjustment precision depending on the size of the correction iron that can be handled.

The object of the present invention is to simplify the adjustment of the magnetic field in an electromagnetic device, or to finely adjust the magnetic field distribution in an electromagnetic device.

The present invention includes the steps of: placing a magnetic field measuring element in an electromagnet device and measuring the magnetic field distribution in the electromagnet device; determining a corrected magnetic material distribution representing the distribution of magnetic material to be modeled relative to a magnetic pole in the electromagnet device based on the magnetic field distribution; and modeling a magnetic material relative to the magnetic pole based on the corrected magnetic material distribution , wherein modeling the magnetic material relative to the magnetic pole includes the steps of removing a modeling substrate from the electromagnet device; a transport device transporting a three-dimensional modeling head together with the magnetic field measuring element within the electromagnet device; a controller controlling the three-dimensional modeling head based on the corrected magnetic material distribution and causing the three-dimensional modeling head to model a magnetic material relative to the magnetic pole; and attaching the modeling substrate on which the magnetic material is modeled to the electromagnet device .

The present invention also provides a three-dimensional modeling head comprising a magnetic field measuring element, a transport device for transporting the magnetic field measuring element within an electromagnet device, a controller for measuring the magnetic field distribution within the electromagnet device using the magnetic field measuring element and calculating a correction magnetic material distribution based on the magnetic field distribution, the correction magnetic material distribution representing the distribution of magnetic material to be added to a magnetic pole in the electromagnet device, and a three-dimensional modeling head, wherein the transport device transports the three-dimensional modeling head together with the magnetic field measuring element within the electromagnet device, and the controller controls the three-dimensional modeling head based on the correction magnetic material distribution and causes the three-dimensional modeling head to model a magnetic material for the magnetic pole .

The present invention is also characterized in that the accelerator for accelerating ions comprises a coil, a magnetic pole that generates a magnetic field within the accelerator together with the coil, and a modeling substrate that is detachable from the magnetic pole and on which a magnetic body is modeled.

The present invention simplifies the adjustment of the magnetic field in an electromagnet device. It also enables fine adjustment of the magnetic field distribution in the electromagnet device.

FIG. FIG. 2 is a cutaway side view of an electromagnetic device and a build substrate. FIG. 2 is a diagram showing a magnetic field measurement setup. 13 is a flowchart of a magnetic field adjustment method. 13 is a flowchart for calculating a corrected magnetic material distribution. FIG. 2 is a side view of an electromagnetic device for a particle beam therapy accelerator. FIG. 2 is a side view of the magnetic field adjusting device. 4 is a flowchart of control executed by a magnetic field adjusting device controller. FIG. 2 is a diagram showing a magnetic field adjusting device. FIG. 2 is a schematic diagram of a shim tray. FIG. 1 illustrates an example of a particle beam therapy system.

Each embodiment of the present invention will be described with reference to the drawings. Identical items shown in multiple drawings will be given the same reference numerals and their description will be omitted.

First Embodiment
An electromagnet device according to a first embodiment of the present invention will be described. As an example of the electromagnet device, the configuration of an H-shaped electromagnet device M100 is shown in FIG. 1. The electromagnet device M100 forms a part of an accelerator that accelerates ions, and generates a magnetic field inside the accelerator. The electromagnet device M100 includes a pair of coils M103 arranged vertically at a predetermined interval, a coil case M102 that houses the coils M103, and a yoke M104 arranged to surround the coil case M102. When the coil M103 is a superconducting coil, the coil M102 functions as a cryostat.

The electromagnet pole M101 (hereinafter, the electromagnet pole M101 will be simply referred to as the pole M101) is located in the inner peripheral region of the upper and lower coils M103 and is fixed to the yoke M104. The space between the upper and lower poles M101 will be referred to as the inter-pole gap M115 below. The pole M101 and yoke M104 that constitute the electromagnet device M100 may be made of a ferromagnetic material such as pure iron or SS400 that has a high magnetization strength per unit volume and can provide uniform magnetization.

In this configuration, a current flows through the coil M103 around the central axis M110 of the electromagnet device M100, which induces a magnetic field in the direction of the electromagnet central axis M110 between the top and bottom of the magnetic pole M101. The distribution of the induced magnetic field is determined by the current flowing through the coil M103, the shape of the magnetic pole M101, the shape of the yoke M104, etc. The magnetic field distribution in the gap M115 between the magnetic poles can be used for various purposes.

In this embodiment, a region of interest M109 is defined in the gap M115 between the magnetic poles. In the following, an example is shown of a method for adjusting the surrounding correction magnetic material distribution and adjusting the magnetic field so that the required magnetic field distribution is generated in the region of interest M109. The correction magnetic material distribution is the spatial distribution of correction magnetic materials such as correction iron.

In the electromagnet device M100 according to this embodiment, in order to generate a desired magnetic field distribution in the region of interest M109, as shown in FIG. 1, a shaping substrate M105 for arranging a correction magnetic body is provided in the interpole gap M115 between the upper and lower magnetic poles M101 of the electromagnet device M100. FIG. 2 shows a cutaway side view of the electromagnet device M100 and the shaping substrate M105.

The shaping substrates M105 are arranged in a pair, one above the other, so as to be symmetrical with respect to a central plane M111, which is a plane perpendicular to the central axis M110. The shaping substrates M105 are configured so as to be freely attached to and detached from the magnetic pole M101 or the yoke M104 by the substrate support mechanism M106. The shaping substrates M105 may be fixed to the magnetic pole M101 or the yoke M104 using bolts and nuts.

The shaping substrate M105 may have upper and lower surfaces parallel to the central plane M111 as shown in FIG. 2, or may be curved to match the magnetic pole surface in order to secure space for placing other equipment in the magnetic pole gap M115. The position coordinates of the upper and lower surfaces of the shaping substrate M105 are measured in advance. Thereafter, when the electromagnet device M100 is actually operated, a magnetic field is excited with the shaping substrate M105 attached.

The magnetic field distribution of the electromagnet device M100 is adjusted by adding a correction magnetic material to the above-mentioned modeling substrate M105 using three-dimensional modeling. The difference between the magnetic field distribution excited in the region of interest M109 of the electromagnet device M100 and the target magnetic field distribution, which is the desired magnetic field distribution to be realized, is obtained, and the correction magnetic material distribution required for magnetic field adjustment is obtained by numerical calculation.

In the present embodiment, the correction magnetic material adjustment is performed by first demagnetizing the electromagnet device M100 by turning off the current flowing through the coil M103. Next, the printing substrate M105 is removed from the electromagnet device M100, and the correction magnetic material is added to the printing substrate M105. The addition of the correction magnetic material to the printing substrate M105 may be performed using a three-dimensional printing device such as a three-dimensional metal printer. The correction magnetic material is added to either or both of the upper and lower surfaces of the printing substrate M105 that are parallel to the central plane M111.

After the desired corrected magnetic distribution calculated in advance is realized using 3D modeling, the modeling substrate M105 is fixed again to the electromagnet device M100. A magnetic field is excited in the electromagnet device M100 by starting up the current in the coil M103, and the magnetic field distribution in the region of interest M109 is measured. The above process is repeated, and the magnetic field is adjusted until the magnetic field distribution measured by the electromagnet device M100 is sufficiently close to the target magnetic field distribution.

Figure 3 shows the magnetic field measurement mechanism M150. In the electromagnet device M100, the two-dimensional distribution of the magnetic field in the central plane M111, which is the geometric center of the electromagnet device M100, is selected as the region of interest M109. The magnetic field measurement mechanism M150 measures the two-dimensional magnetic field distribution in the inter-pole gap M115, which is the region of interest M109 in the electromagnet device M100. The magnetic field measurement mechanism M150 includes a magnetic field measurement element M151, a magnetic field measurement element support rod M153 that supports it, and a linear movement motor M161 and linear movement drive system M162 that move the magnetic field measurement element support rod M153 linearly.

The magnetic field measurement mechanism M150 further includes a measuring element rotation motor M155 and a measuring element rotation drive system M157. The measuring element rotation motor M155 and the measuring element rotation drive system M157 rotate the magnetic field measurement linear movement storage stage M159, which is equipped with the magnetic field measurement element support rod M153, the linear movement motor M161, and the linear movement drive system M162, in an arc. The magnetic field measurement mechanism M150 further includes a controller M171.

For example, a Hall magnetic field sensor having linear response up to the target strong magnetic field region is used as the magnetic field measuring element M151 in order to measure the static magnetic field. In order to shorten the measurement time, multiple magnetic field measuring elements M151 may be provided for one magnetic field measuring element support rod M153. In this case, in order to suppress individual differences between the multiple magnetic field measuring elements M151, the output signal of each magnetic field measuring element M151 may be calibrated in advance using a known NMR sensor or the like.

The magnetic field measuring element support rod M153 may be made of a material that has a length sufficient to enable measurement of the magnetic field in the region of interest M109 and is rigid enough to prevent bending of the measuring element.

The magnetic field measuring element support rod M153 is moved in the longitudinal direction by a linear movement motor M161 and a linear movement drive system M162. The linear movement motor M161 may be, for example, an ultrasonic motor made of a non-magnetic material that can operate even in a magnetic field environment. The torque of the linear movement motor M161 is transmitted to the linear feed mechanism M166 by a belt M165 and a pulley M163. Alternatively, instead of using an ultrasonic motor, the torque generated by the motor at a location sufficiently distant that it is not affected by the electromagnetic force of the electromagnet device M100 may be transmitted by a shaft, belt, or the like.

The linear feed mechanism M166 and the magnetic field measuring element support rod M153 may come into contact with each other through frictional force caused by the interposition of rubber. The linear feed mechanism M166 and the magnetic field measuring element support rod M153 may form a rack-and-pinion mechanism. The linear feed mechanism M166 and the magnetic field measuring element support rod M153 convert the rotational force of the linear movement motor M161 into linear motion, and move the magnetic field measuring element M151 in the forward and backward directions. The magnetic field measurement and linear movement mechanism is configured on the magnetic field measurement linear movement storage stage M159.

The measuring element rotation motor M155 rotates the magnetic field measurement linear movement storage stage M159 in the circumferential direction around the central axis M110 relative to the magnetic field measurement mechanism main stage M167 fixed to the electromagnet device M100. Taking into consideration use in a magnetic field environment, the measuring element rotation motor M155 may be, for example, a non-magnetic ultrasonic motor.

The electrical signal obtained from the magnetic field measuring element M151 is A/D converted by the controller M171, converted to a magnetic field value, and stored. The position information of the magnetic field measuring element M151 is calculated based on the amount of rotation measured by a rotary encoder attached to the non-magnetic ultrasonic motor. The amount of movement of the magnetic field measuring element M151 for each measurement is managed by the controller M171, which controls the amount of rotation of each ultrasonic motor during each movement. This measurement data, control signals, and power for driving the motors are sent and received via the signal/power bus M173.

A flowchart of the magnetic field adjustment method according to the first embodiment is shown in FIG. 4. Of the steps shown in this flowchart, steps S201, S203, and S221 may be performed by a user. The other steps may be executed by the controller M171 in response to user operations, etc.

The controller M171 may include a processor. The processor executes each step by executing a program. This program may be stored in a memory included in the controller M171. The memory may be a storage device such as a hard disk, a USB memory, or an SD card. The memory may be storage on a communication line such as the Internet. One process executed by the controller M171 may be composed of multiple processors that execute distributed processing.

In addition, some or all of the processes executed by the controller M171 may be executed by an external computer. The external computer may be one directly connected to the magnetic field measurement mechanism M150, or one connected to a communication line such as the Internet. One process executed by the controller M171 may be executed by multiple external computers that execute distributed processing.

In this embodiment, the region of interest M109 is in a two-dimensional plane that is the same plane as the central plane M111, and the magnetic field measurement mechanism M150 is attached to the electromagnet device M100 to be adjusted (S201). The shaping substrate M105 to be used for adjustment is attached to the electromagnet device M100 (S203). After the magnetic field measurement mechanism M150 and the shaping substrate M105 are attached, the coil M103 is energized to excite the magnetic field (S205).

The following magnetic field measurement sequence is repeated for all of the preset Nb magnetic field measurement points (S207 to S213). First, the magnetic field sensor is moved to the measurement start position (S207). After the movement, the magnetic field sensor is used to perform magnetic field measurement for about 1 to 2 seconds (S209). The magnetic field data obtained by the measurement is sent to the controller M171 via the signal/power bus M173. At this time, noise elimination, amplification, A/D conversion, data storage, etc. are also performed (S211). It is determined whether the above operations have been performed for all measurement points (S213), and if there are any measurement points that have not been performed (S213: No), the process is performed again from step S207 for those measurement points. If measurements have been completed for all measurement points (S213: Yes), the magnetic field measurement sequence ends (S207 to S213).

Statistics such as the root mean square error (RMSE) are calculated for the measurement points where measurements were performed, and it is confirmed whether the statistics are below a reference value set as the allowable error (S215). If the statistics are below the reference value (S215: Yes), it is determined that the target magnetic field distribution and the magnetic field distribution generated by the electromagnet device M100 are sufficiently close, and the magnetic field adjustment ends (S217). If the statistics are equal to or greater than the reference value (S215: No), processing proceeds to the correction magnetic material adjustment sequence by adding a correction magnetic material to the printing substrate M105 (S219-S225).

In the correction magnetic body adjustment sequence, the electromagnet device M100 is demagnetized (S219), and the printing substrate M105 is removed (S221). At this time, if the electromagnetic force acting between the electromagnet device M100 and the printing substrate M105 is sufficiently weak, the printing substrate M105 may be removed without demagnetizing while the coil M103 is still energized.

If the electromagnetic force is large, the current in the coil M103 is set to zero, the magnetization of the magnetic pole M101 and the yoke M104 is removed, and the electromagnet device M100 is demagnetized. After demagnetization, the printing substrate M105 is removed from the magnetic pole M101 or the yoke M104 (S221). Using the magnetic field distribution measured in the magnetic field measurement sequence, the correction magnetic material distribution required for magnetic field adjustment is calculated (S223). Based on the correction magnetic material distribution obtained here, a correction magnetic material is formed on the printing substrate M105 using 3D printing (S225). In steps S219 to S225, the printing substrate M105 with the correction magnetic material distribution adjusted is attached to the electromagnet device M100 (S203), and the magnetic field measurement sequence (S205-S213) is executed again. By repeating the above, the magnetic field is adjusted until the statistics are less than the reference value.

The right side of Figure 1 shows a schematic mechanism for 3D modeling to form the desired distribution of correction magnetic material. The 3D modeling mechanism is equipped with a head stage P305 that can move two-dimensionally in a horizontal in-plane direction relative to the central plane M111, and a material supply cylinder P304. The 3D modeling head P303 connected to the movable stage ejects correction magnetic material consisting of a magnetic material or a mixture containing magnetic material from the 3D modeling nozzle P301 at the tip of the head. The ejected correction magnetic material adheres to the modeling substrate M105. The correction magnetic material is fixed to the modeling substrate M105 when it is given external stimuli such as heat or light, or when it is dried or solidified over time.

As an example, if the correction magnetic material and the printing substrate M105 are made of iron, it is possible to create a 3D metal printer using directed energy deposition. In this case, a laser is attached to the 3D printing nozzle P301. The laser is irradiated to melt the printing substrate M105 to form a molten area, and magnetic material is ejected from the 3D printing nozzle P301 and supplied to the molten area, thereby adhering the correction magnetic material to the printing substrate M105. By repeating the above process, the desired correction magnetic material distribution is achieved on the printing substrate M105.

The shaping substrate M105 may be made of a magnetic material such as iron, or a non-magnetic material such as stainless steel, aluminum, or CFRP. When a magnetic material is used for the shaping substrate M105, the shaping substrate M105 itself is magnetized, and a magnetic field is generated for the region of interest M109. By arranging the magnetic material near the region of interest M109, the amount of magnetic material used in the entire electromagnet device M100 is reduced, and the magnetic pole gap M115 is effectively utilized.

On the other hand, when a non-magnetic material such as stainless steel, aluminum, or CFRP is used, the main body of the printing substrate M105 is not magnetized. In step S219 of FIG. 4, if the electromagnetic force generated on the printing substrate M105 by the electromagnet device M100 is sufficiently weak, the printing substrate M105 may be removed from the electromagnet device M100 without demagnetization.

Although the above shows an example in which iron is used as the correction magnetic material, the present invention is not limited to a method of constructing the correction magnetic material from a single material. As an example, it is possible to use CFRP as the printing substrate M105 and a mixture of iron and CFRP as the correction magnetic material. The correction magnetic material may be made by melting CFRP filament with a heater and mixing powdered iron with the molten CFRP. The mixture is extruded from the tip of the three-dimensional printing nozzle P301 and applied to the printing substrate M105, thereby achieving the desired distribution of the correction magnetic material.

As another example, a mixture of photocurable resin and iron may be used as the correction magnetic material. In this example, a means similar to 3D printing using the material jet method is used to spray the mixture of photocurable resin and iron from the 3D printing nozzle P301 onto the printing substrate M105. In this example, the 3D printing nozzle P301 may be equipped with an ultraviolet irradiation device, and the mixture applied to the printing substrate M105 may be cured by ultraviolet light. The above means realizes the desired distribution of correction magnetic material on the printing substrate M105.

When a mixture of the above-mentioned magnetic and non-magnetic materials is used as the correction magnetic body, the ratio of magnetic material to non-magnetic material may be set arbitrarily. Since the magnetization strength per unit volume changes depending on the setting, it must be taken into consideration when back-calculating the position or amount of correction magnetic body to be added. For example, if the ratio of iron to non-magnetic material is 1:9, the B-H curve is set as a virtual material with a magnetization strength per unit volume of 1/10 of the magnetic material at the time of back-calculation. The desired correction magnetic body distribution can be obtained by back-analysis using the modified B-H curve.

The use of a mixture of magnetic and non-magnetic materials improves the accuracy of magnetic field adjustment. The limit of adjustment accuracy when using 3D modeling is determined by the resolution of the 3D modeling. For example, when using 3D modeling technology with a limit of 0.1 mm thickness, if only iron is used as the correction magnetic material, the magnetic field strength that 0.1 mm thick iron contributes from the modeling substrate M105 to the region of interest M109 becomes the limit of magnetic field adjustment.

When the above-mentioned mixture of iron and CFRP with a ratio of 1:9 is used as the correction magnetic material, 1/10 of the 0.1 mm thickness limit of 3D modeling, i.e., 0.01 mm of iron material is added. This results in a tenfold increase in the resolution of magnetic field adjustment. For the above reasons, when a mixture is used as the correction magnetic material, the magnetic field distribution can be adjusted with a precision that exceeds the limit of magnetic field adjustment precision by 3D modeling when a single correction magnetic material is used.

Next, the calculation algorithm for the corrected magnetic material distribution in step S223 in FIG. 4 will be described. A flowchart for calculating the corrected magnetic material distribution is shown in FIG. 5. Each step of this flowchart is executed by the controller M171. In this embodiment, as an example considering application to a particle beam therapy system, the region of interest M109 exists in the same plane as the central plane M111, and a vertically symmetrical system is configured.

The correction magnetic material distribution is calculated assuming that the correction magnetic material is magnetized and saturated by the magnetic field generated by the electromagnet device M100, and that the magnetization direction is in the direction of the magnetic field generated between the pole gaps by the electromagnet device M100 (the direction of the central axis M110). The formula for the magnetic field due to magnetic moment is used as the formula for calculating the magnetic field due to saturation magnetization. In general, there are no restrictions on the direction of magnetization or the symmetry of the magnet, and similar calculations can be performed for any direction.

The magnetic field distribution to be generated in the region of interest M109 is called the target magnetic field distribution, and the magnetic field distribution obtained by measurement is called the measured magnetic field distribution. Each distribution is obtained by calculation and measurement, and the difference between the two is calculated. Specifically, from the difference between the two distributions, the minimum and maximum difference values, the average difference value, and the root mean square error (RMSE) of the difference are calculated as evaluation values (S233). These four evaluation values are compared with reference values set in advance as convergence conditions (S235). If the four evaluation values are less than the reference values, it is determined that the measured magnetic field distribution and the target magnetic field distribution are sufficiently consistent, the amount of correction magnetic material to be added is zero, and the calculation ends (S245).

If any of the four evaluation values is equal to or greater than the reference value, a calculation of the corrected magnetic mass is performed. The magnetic field B generated at position r by the magnetic moment of saturation magnetization present at position r' is expressed by (Equation 1).

In (Equation 1), μ is the magnetic permeability, M is the magnetic moment of saturation magnetization, r' represents the position where the correction magnetic body is present, and dr' is its minute amount. In the calculation, the printing substrate M105, which is placed at a height of ±z0 parallel to the central plane M111 shown in FIG. 2, is divided into elements of minute area ΔSi (i=1, 2, 3, ..., Np) (Np is the number of divisions), and the magnetic field generated by the correction magnetic body added to each element is calculated. For element i of minute area ΔSi, the correction height of the correction magnetic body formed on the printing substrate M105 is set to hi. By adding the correction magnetic body to element i by the height increment Δhi, the magnetic field increment Δbi,j generated at point rj (j=1, 2, 3, ..., Nb) (Nb is the total number of magnetic field measurement points) on the region of interest M109 is calculated. In other words, if the magnetic field distribution that element i of the correction height hi creates at point rj of the region of interest M109 is expressed as bi,j(hi), the magnetic field increment Δbi,j can be calculated by the following (Equation 2).

[Equation 2]
Δbi,j=bi,j(hi+Δhi)−bi,j(hi)

(Equation 2) shows the response sensitivity with respect to the increase in magnetic field strength when a correction magnetic material is added to the printing substrate M105. According to (Equation 2), the magnetic field increment Δbi,j is found for each combination of element i and measurement point j (S237). Each magnetic field increment Δbi,j is represented as a response matrix A for i and j and stored (S239). Δbi,j is a function of hi and Δhi, and because magnetization is saturated, linear approximation is appropriate for sufficiently small Δhi.

The total magnetic field increment Δbj at measurement point j is the superposition of the magnetic fields generated by all elements i, and can be expressed as (Equation 3).

[Equation 3]
Δbj = Σ Δbi,j ・Δhi

Σ means the sum of i=1 to i=Np. Using the response matrix A, the relationship between the height increment vector Δh, which combines the height increments Δhi, and the magnetic field increment vector Δb, which combines the magnetic field increments Δbj at each measurement point, is expressed as in (Equation 4).

[Equation 4]
Δb＝A・Δh

The above equation is a simultaneous equation that calculates the magnetic field increment vector Δb from the response matrix A when a correction magnetic material with a height increment vector Δh is added to each point on the printing substrate M105.

By solving (Equation 4), if the magnetic field increment at each measurement point is desired to be Δb, the height increment vector Δh of the correction magnetic body to be added to each element can be obtained (S241). As a simple example, when the total number of magnetic field measurement points Nb is equal to the number of element divisions Np (Np=Nb) and the response matrix A is regular, an inverse matrix of the response matrix A exists, and the height increment vector Δh that satisfies the simultaneous equations expressed above can be obtained.

[Equation 5]
Δh＝A ⁻¹・Δb

If the total number of magnetic field measurement points Nb is not equal to the number of element divisions Np (Np ≠ Nb), generally, there is no single solution. In this case, a least-squares solution is obtained. The value obtained by the following (Equation 6) using the Moore-Penrose generalized inverse matrix A ⁺ of matrix A is the height increment vector Δh that is the least-squares solution.

[Equation 6]
Δh＝A ^＋・Δb

In addition, a truncated singular value decomposition method may be used as an analysis method for the inverse problem of the Nb × Np matrix. The singular value decomposition method is a method of performing singular value decomposition on the response matrix A, and obtaining an inverse matrix using only singular values whose absolute values are greater than a reference value, thereby solving the inverse problem. In this case, the generalized inverse matrix A ⁺ is obtained using the singular value decomposition of the response matrix A.

[Equation 7]
A = U Σ ^VT

In (Equation 7), U denotes a unitary matrix with Nb rows and Nb columns, V ^T denotes a transpose of a unitary matrix V with Np rows and Np columns, and Σ denotes a diagonal matrix.

[Equation 8]
A ⁺ = V Σ ^{+ UT}

In (Equation 8), Σ ⁺ is the reciprocal of each diagonal element of the diagonal matrix Σ. In the truncated singular value decomposition, by using only the diagonal elements of Σ whose absolute values are equal to or greater than a certain threshold, a stable solution can be obtained for the change in the left-hand side Δb when calculating the reciprocal. In this way, the additional amount of each corrective magnetic material is calculated (S241).

After the amount of addition is calculated, the magnetic field distribution after the correction magnetic material is added is evaluated (S243). The magnetic field generated at measurement point j by the correction magnetic material in element i is calculated using the above magnetic moment formula, and added up for all elements i. The magnetic field increment vector Δb at each point may be calculated using the height increment vector Δh calculated as A·Δh=Δb. The above calculation calculates the evaluated magnetic field after the addition of the calculated correction magnetic material, and the target magnetic field and the evaluated magnetic field are compared again using the updated evaluated magnetic field (S233). If the reference value is not met, the amount of addition is calculated again (S237 to S243). These steps S237 to S243 are repeated to calculate the amount of correction magnetic material addition that makes each evaluation value less than the reference value.

During these iterations, in order to suppress oscillations in the solution and improve convergence, and to improve the validity of the linearity of the assumed magnetic field increment and height increment vector Δh, a value obtained by multiplying the calculated addition amount by a relaxation coefficient of about 0.1 to 0.5 may be used as the correction magnetic material addition amount. The relaxation coefficient may be changed for each iteration. For example, a large relaxation coefficient of about 0.5 to 1.0 may be used at the beginning of the iterations to speed up convergence, and then a small relaxation coefficient of about 0.1 to 0.2 may be used to suppress oscillations in the solution and obtain the final solution.

In this embodiment, it is easy to add magnetic material in accordance with the magnetic field distribution, but removing the magnetic material requires a new machining process, which may increase personnel or time costs. Therefore, correction magnetic material may be added to the substrate M105 so that the magnetic field strength is weaker than the desired magnetic field distribution, and the height increment is smaller than the optimal shape of the magnetic pole M101 obtained by calculation.

As a result, the magnetic field is adjusted only by increasing the correction magnetic material, and the number of steps in adjusting the magnetic field is reduced. Note that if the magnetic field distribution exceeds the desired magnetic field distribution and becomes strong, the magnetic field strength can be adjusted by decreasing the current in coil M103 and reducing the magnetomotive force induced in magnetic pole M101, so that all correction magnetic material increments become positive.

In this manner, in this embodiment, a magnetic pole manufacturing method including the following steps (i) to (iii) is carried out.
(i) Placing a magnetic field measuring element M151 in the electromagnetic device M100 and measuring the magnetic field distribution in the electromagnetic device M100.
(ii) calculating a corrected magnetic material distribution representing a distribution of magnetic material to be formed with respect to the magnetic pole M101 in the electromagnet device M100 based on the measured magnetic field distribution. This corrected magnetic material distribution may be calculated, for example, as a height increment vector Δh in each element i.
(iii) shaping magnetic material for magnetic pole M101 based on the corrective magnetic material distribution;

In the above (iii), forming a magnetic body on the magnetic pole M101 may include removing the printing substrate M105 from the electromagnet device M100, printing a magnetic body on the printing substrate M105, and attaching the printing substrate M105 on which the magnetic body has been printed to the electromagnet device M100.

In each of the embodiments described below, a magnetic pole forming method including the above steps (i) to (iii) may be performed.

Second Embodiment
A second embodiment of the present invention will be described with reference to Fig. 6 to Fig. 8. Fig. 6 shows a side view of an electromagnet device M100 for a particle beam therapy accelerator according to the second embodiment. The electromagnet device M100 shown in Fig. 6 includes a magnetic pole M101, a yoke M104, and a coil M103. The magnetic poles M101 face each other across a magnetic pole gap M115 at a fixed interval at the vertical center of the electromagnet device M100, and the upper end or lower end of the magnetic pole M101 is connected to the yoke M104.

The yoke M104 surrounds the magnetic pole M101 and connects the upper and lower magnetic poles M101. This forms a magnetic circuit closed by the magnetic pole M101, the yoke M104, and the inter-pole gap M115. An introduction port M108 is provided in a part of the yoke M104 at the same height as the inter-pole gap M115 as a hole for inserting signal lines, power lines, etc. from the outside. The outside of the introduction port M108 is blocked by a connection flange M112.

A coil slot region M121 exists between the magnetic pole M101 and the yoke M104, and the coil M103 is installed in the coil slot region M121. By passing currents in the same direction through the upper and lower coils M103, a magnetic field is induced in the gap M115 between the magnetic poles, and each coil M103 and each magnetic pole M101 operates as an electromagnet.

The subject of magnetic field adjustment by the magnetic field adjustment device described below is not limited to accelerators for particle beam therapy. The magnetic field adjustment device may be used, for example, to adjust the magnetic field of electromagnet devices such as MRI (Magnetic Resonance Imaging) and research accelerators.

Figure 7 is a side view of the magnetic field adjustment device P300 according to this embodiment. The magnetic field adjustment device P300 is equipped with a correction magnetic material adjustment head P313 equipped with a magnetic field measurement mechanism, and a group of motors and a group of support rails for moving the head to a desired position. The structure of the magnetic field adjustment device P300 is described below.

The correction magnetic material adjustment head P313 is equipped with a three-dimensional modeling head P303, a head position sensor P307, and a magnetic field sensor P309. The three-dimensional modeling head P303, the head position sensor P307, and the magnetic field sensor P309 are installed on the head stage P305. The position of the three-dimensional modeling head P303 is determined from the relative positional relationship between the three-dimensional modeling head P303 and the head position sensor P307, which is obtained using the measurement value of the head position sensor P307. In addition, the spatial coordinates in which the magnetic field sensor P309 exists are determined from the measurement value of the head position sensor P307 and the relative position of the magnetic field sensor P309 and the head position sensor P307.

The correction magnetic material adjustment head P313 moves freely in the space of the magnetic pole gap M115. The correction magnetic material adjustment head P313 is moved using an axial movement motor P315, a radial position adjustment motor P317, a circumferential position adjustment motor P323, and a central position adjustment motor P325, as well as a support rail P311, a support rotation shaft P319, and support rails P320 and P321.

The support rail P311 is installed so as to be parallel to the direction of the central axis M110 of the magnetic pole M101. This allows the correction magnetic material adjustment head P313 to move in the direction of the central axis M110. By moving the correction magnetic material adjustment head P313 in the direction of the central axis M110, the correction magnetic material is added in a state where the magnetic pole M101, which is the target of the correction magnetic material addition, and the correction magnetic material adjustment head P313 are in close proximity, and the spot diameter of the correction magnetic material can be constant.

In addition, the axial position during magnetic field measurement can be adjusted by moving the correction magnetic material adjustment head P313 in the direction of the central axis M110. An axial movement motor P315 is attached to the intersection of the correction magnetic material adjustment head P313 and the support rail P311, and supplies the driving force required to move the correction magnetic material adjustment head P313 along the support rail P311. The rotational torque of the axial movement motor P315 is converted into linear motion using a ball screw mechanism.

The support rail P320 is located in a plane perpendicular to the central axis M110 and is installed so as to be parallel to the radial direction of the magnetic pole M101. The correction magnetic material adjustment head P313 is capable of moving from the center of the magnetic pole M101 to the maximum radial position of the magnetic pole M101. A radial position adjustment motor P317 is attached to the intersection of the support rail P311 and the support rail P320, and the radial position adjustment motor P317 supplies a driving force along the support rail P320. The support rail P320 is equipped with a power transmission mechanism using, for example, a rack and pinion mechanism, and is configured to convert rotational torque into linear motion so that the correction magnetic material adjustment head P313 moves along the support rail P320.

The support rotation shaft P319 is a single-axis support structure that is connected so that the support rail P320 to the correction magnetic material adjustment head P313 can rotate rigidly 360° in the circumferential direction around the central axis M110 of the magnetic pole M101 as a single unit. The support rotation shaft P319 is positioned so that it is coaxial with the central axis M110 of the magnetic pole M101. A circumferential position adjustment motor P323 is attached to supply axial rotation torque to the support rotation shaft P319.

The introduction port M108 provided in the yoke M104 and the connection flange M112 attached to the outside of the introduction port M108 form a fixed structure to which the magnetic field adjustment device P300 is fixed. The support rail P321 connects the connection flange M112 attached to the outside of the introduction port M108 to the support rotation shaft P319. A center position adjustment motor P325 is mounted on the support rail P321. The center position adjustment motor P325 and the support rail P321 adjust the position of the support rotation shaft P319, and the position is adjusted so that the support rotation shaft P319 and the magnetic pole M101 share a central axis. This is achieved by, for example, a ball screw mechanism.

Signals from the head position sensor P307 and the magnetic field sensor P309 are sent to the magnetic field adjustment device controller P333. The signals are sent via the signal/power bus P331. Based on the collected magnetic field distribution information, the magnetic field adjustment device controller P333 calculates the height increment of the correction magnetic material to be added to achieve the target magnetic field distribution. The calculation is performed according to the algorithm shown in Figure 5. The amount of added magnetic material, position information, and motor drive power required when adding the correction magnetic material are sent via the signal/power bus P331 to each of the position adjustment motors P315, P317, P323, and P325 and the 3D modeling head P303.

The correction magnetic material adjustment head P313 used in this embodiment will be described in detail below. The correction magnetic material adjustment head P313 is equipped with a three-dimensional modeling head P303, a head position sensor P307, a magnetic field sensor P309, and a head stage P305 to which these are fixed. The three-dimensional modeling head P303 operates as a three-dimensional modeling machine that can three-dimensionally process magnetic pole material such as iron into a desired shape. As a three-dimensional modeling machine, for example, a three-dimensional metal printer using a directed energy deposition method is used, in which a magnetic material is sprayed as a powder, sintered by laser irradiation, and fixed to the magnetic pole surface.

A 3D metal printer using the directed energy deposition method is equipped with a high-intensity laser for sintering magnetic powder, a nozzle for ejecting the magnetic material, and a transport tube for supplying the magnetic powder. Directed energy deposition may also use a 3D printer that uses powder bed fusion, in which magnetic powder is spread evenly and then sintered by laser irradiation. Compared to powder bed fusion, the directed energy deposition method has the advantage of reducing the amount of iron powder used, suppressing contamination of the vacuum environment due to residual iron powder in the device, and suppressing the induction of error magnetic fields.

In addition, instead of a 3D metal printer, a 3D printer for resin may be used to mix molten resin with iron powder and add the material using a material jet method. Furthermore, while the 3D printing nozzle P301 is in contact with the magnetic pole M101 to which the correction magnetic material is to be added, silicon putty containing iron may be extruded from the tip of the 3D printing nozzle P301 at the tip of the 3D printing head P303. In this way, silicon putty containing iron is added and dries at the magnetic pole M101. Similarly, solder containing iron may be used and applied by contacting the magnetic pole M101 with the solder, and the solder may solidify at the magnetic pole M101.

For example, a three-axis optical displacement sensor is used for the head position sensor P307. The dimensions of the electromagnet are measured in advance, and position information with the center of the electromagnet as the origin is obtained from the distance information to the yoke M104 obtained by the optical displacement sensor. Furthermore, the relative positional relationship on the head stage P305 is measured in advance, and the original position information is converted into accurate position information for the nozzle position of the 3D modeling head P303 and the sensor position of the magnetic field sensor P309.

When the 3D modeling head P303 adds magnetic material and the magnetic field distribution is measured by the magnetic field sensor P309, the above operations are performed by referencing spatial coordinate information obtained by the head position sensor P307. Furthermore, instead of a three-axis optical displacement sensor, a rotary encoder attached to each of the position adjustment motors P315, P317, P323, and P325 may be used as the head position sensor P307. The rotary encoder acquires the number of rotations of the motor, and the amount of displacement caused by each motor is calculated by integrating the number of rotations, thereby controlling the positions of the 3D modeling head P303 and the magnetic field sensor P309. Both the head position sensor P307 and a rotary encoder may be provided and calibrated to each other.

For example, a three-axis Hall sensor is used for the magnetic field sensor P309. Since the magnetic field required for particle beam therapy accelerators is a static magnetic field, the magnetic field components in three directions are measured using a Hall sensor capable of measuring the DC component of the magnetic field. The three-axis Hall sensor is calibrated in advance using a calibrated Hall sensor or an NMR magnetic field sensor and a magnetic field generator such as a Helmholtz coil as a calibration standard. After the Hall sensor arrives at the measurement point, magnetic field data is acquired for one to two seconds per measurement point, and the data with statistical errors removed may be acquired as the magnetic field data at that measurement point.

The Hall voltage output from the Hall sensor is sent as a magnetic field data signal to the magnetic field adjustment device controller P333 via the signal/power bus P331. The magnetic field adjustment device controller P333 uses an RC filter with a time constant of about 0.1 to 1 second and a preamplifier to remove noise from the magnetic field data signal and amplify the signal, converts the magnetic field data signal to a digital signal using an A/D converter, and stores the data. As soon as the signal at one measurement point has been acquired, the signal at the next measurement point is acquired.

This operation is repeated until measurements are completed for all measurement points. Also, instead of a three-axis Hall sensor, an NMR magnetic field sensor may be used as the magnetic field sensor P309. Alternatively, a search coil measurement may be used in which the voltage induced when a pickup coil is moved in a static magnetic field is integrated, or the pickup coil is rotated by a motor and the voltage induced by the magnetic field across the coil is measured.

The position control of the correction magnetic material adjustment head P313 is explained below. The correction magnetic material adjustment head P313 is connected to a connection flange M112 attached to the yoke M104 of the electromagnet device M100 by a support structure including a support rotation shaft P319, support rails P320 and P321. The support rotation shaft P319 and support rails P320 and P321 expand and contract or rotate by the driving forces of the respective motors P315, P317, P323 and P325, and move the correction magnetic material adjustment head P313 to the desired position. In position control, the motors closest to the connection flange M112 operate in order.

First, based on information obtained by the head position sensor P307, the center axis M110 of the magnetic pole M101 and the support rotation axis P319 are aligned. After the rotation axes are aligned, the center position adjustment motor P325 is not operated, the support rail P320 is fixed, and the position of the correction magnetic material adjustment head P313 is adjusted by adjusting the support rotation axis P319, the support rails P320 and P321.

A Cartesian coordinate system (x, y, z) is set with the z-axis in the direction of the central axis M110 of the magnetic pole M101 and the geometric center of the electromagnet device M100 as the origin. The current magnetic field adjustment head position (x0, y0, z0) is sent to the magnetic field adjustment device controller P333 via the signal/power bus P331. The current position coordinates (x0, y0, z0) and destination position information (x, y, z) are converted to the corresponding cylindrical coordinates (r0, θ0, z0) and (r, θ, z), and the movement amount (Δr, Δθ, Δz) = (r-r0, θ-θ0, z-z0) is calculated. An amount equivalent to the circumferential movement amount Δθ is sent to the circumferential position adjustment motor P323, and the motor output is controlled to move the correction magnetic material adjustment head P313.

During the movement, the amount of displacement may be measured using a rotary encoder, and the amount of displacement may be used for control. After the rotation is completed, position information is acquired again using the head position sensor P307, and the rotational position is corrected. After the rotation to the specified angle θ is completed, the correction magnetic material adjustment head P313 is moved to a specified radial position by the radial position adjustment motor P317. In this case, the amount of movement Δr may be controlled using a rotary encoder, and correction may be performed again using the head position sensor P307 after the movement is completed. After the radial position correction is completed, finally, the correction magnetic material adjustment head P313 is moved to a specified z-direction position by the axial movement motor P315. Similarly, the amount of movement Δz is controlled using a rotary encoder, and correction is performed using the head position sensor P307 after the movement is completed.

The control in the magnetic field adjustment device controller P333 in FIG. 7 is described below. FIG. 8 shows a flowchart of the control executed by the magnetic field adjustment device controller P333. Each step may be executed by the magnetic field adjustment device controller P333 as a controller in response to a user operation.

The magnetic field adjustment device controller P333 may include a processor. The processor executes each step by executing a program. This program may be stored in a memory provided in the magnetic field adjustment device controller P333. The memory may be a storage device such as a hard disk, USB memory, or SD card. The memory may be storage on a communication line such as the Internet. One process executed by the magnetic field adjustment device controller P333 may be executed by multiple processors that execute distributed processing.

In addition, some or all of the processing performed by the magnetic field adjustment device controller P333 may be executed by an external computer. The external computer may be one directly connected to the magnetic field adjustment device P300, or one connected to a communication line such as the Internet. One processing performed by the magnetic field adjustment device controller P333 may be executed by multiple external computers that execute distributed processing.

The magnetic field adjustment device P300 according to this embodiment first measures the three magnetic field components (Bx, By, Bz) at all predefined magnetic field measurement points. For measurement, the magnetic field adjustment device P300 moves the magnetic field sensor P309 to the magnetic field measurement point in the same manner as described above (S261). After the movement, the magnetic field adjustment device controller P333 uses the head position sensor P307 to confirm and fine-tune the position of the magnetic field sensor P309 (S263). After the position adjustment is complete, the magnetic field sensor P309 acquires magnetic field data for 1 to 2 seconds (S265).

The acquired magnetic field data is transmitted to the magnetic field adjustment device controller P333 via the signal/power bus P331 and stored (S267). The magnetic field adjustment device controller P333 may suppress noise contained in the signal indicating the magnetic field data or remove noise from the signal indicating the magnetic field data by digital signal processing such as filtering or time averaging before or after storage. After data acquisition is completed, the magnetic field sensor P309 moves to the next magnetic field measurement point and measures the magnetic field. It is determined whether measurements have been made at all magnetic field measurement points (S269), and if measurements have not been made at all magnetic field measurement points, the processing of step S261 is executed, and if measurements have been made at all magnetic field measurement points, the processing of step S271 is executed.

After the magnetic field is measured at all magnetic field measurement points (S269: Yes), the magnetic field adjustment device controller P333 calculates the difference from the target magnetic field distribution and determines whether the difference is within the allowable error at all points (S271).

If the error between the measured magnetic field distribution and the target magnetic field distribution at all magnetic field measurement points is within the tolerance (S271: Yes), the magnetic field adjustment device controller P333 determines that no further calibration is necessary and ends the calibration process (S273). If the error at even one point is greater than the tolerance (S271: No), the magnetic field adjustment device controller P333 adjusts the correction magnetic material distribution by adding magnetic material to the magnetic pole M101.

The magnetic field adjustment device controller P333 calculates the amount of correction magnetic material to be added from the difference between the target magnetic field distribution and the measured magnetic field distribution (S275). The distribution of the correction magnetic material to be added is back-calculated according to the algorithm in FIG. 8. After calculating the correction position of the magnetic pole M101 and the amount of correction magnetic material to be added, the addition of the correction magnetic material begins. The 3D modeling head P303 is moved to a specified position (S277), and the position of the 3D modeling head P303 is fine-tuned based on information from the head position sensor P307 (S279).

After the position adjustment, the 3D modeling head P303 adds a correction magnetic material to the magnetic pole surface (S281), and it is determined whether the correction magnetic material has been added to all magnetic pole adjustment positions (S283). If the correction magnetic material has not been added to all magnetic pole adjustment positions, the process of step S277 is executed, and if the correction magnetic material has been added to all magnetic pole adjustment positions, the process of step S261 is executed. That is, steps S277, S279, and S281 are executed for all magnetic pole adjustment positions (S283). After the operation of adding the magnetic material (S277-S283) is completed, the magnetic field measurement (S261-S269) is performed again. The above magnetic field measurement, calculation of the amount of magnetic material added, and magnetic pole adjustment are repeated, and the above process is continued until the difference between the target magnetic field distribution and the measured magnetic field distribution is within the allowable value.

According to this embodiment, the same effect as the first embodiment can be obtained. Furthermore, since the correction magnetic body is directly added to the magnetic pole M101, the modeling substrate M105 and the shim tray are not required. Here, the shim tray is a substrate for fixing the correction magnetic body, which is divided into areas for each position where the correction magnetic body is placed. The area divided into areas for each position where the correction magnetic body is placed is called a shim pocket. The shim tray may be detachable from the magnetic pole M101. The second embodiment may be used for a system with large spatial constraints regarding the placement of the modeling substrate M105 and the shim tray due to the narrow magnetic pole gap M115 of a particle beam therapy system or the like, coexistence with other elemental equipment such as an RF kicker or an accelerating dee electrode, etc.

In addition, according to this embodiment, the magnetic field of the electromagnet device M100 can be adjusted by inserting the magnetic field adjustment device P300 through the introduction port M108 without disassembling the electromagnet device M100. Generally, accelerators for particle beam therapy systems such as cyclotrons have a structure in which the space of the magnetic pole gap M115 is sealed.

Therefore, disassembly of the electromagnet may be required to attach or detach the printing substrate or shim tray. Accelerators for particle beam therapy systems weigh from several tens to several hundreds of tons, and structural errors caused by reassembly may cause errors in the magnetic field. Therefore, disassembly and reassembly require careful attention and involve personnel costs. According to this embodiment, the disassembly and assembly processes that require personnel costs are omitted, automating magnetic field adjustment becomes easier, and costs are reduced.

Thus, the magnetic field adjustment device P300 according to this embodiment includes a magnetic field sensor P309 as a magnetic field measuring element, a conveyor, and a magnetic field adjustment device controller P333 as a controller. The conveyor includes an axial movement motor P315, a radial position adjustment motor P317, a circumferential position adjustment motor P323, and a central position adjustment motor P325, as well as a support rail P311, a support rotation shaft P319, and support rails P320 and P321. The conveyor is fixed to an introduction port M108, which is a hole provided in a yoke M104 as the housing of the accelerator, and conveys the magnetic field sensor P309 within the accelerator. The magnetic field adjustment device controller P333 measures the magnetic field distribution within the accelerator using the magnetic field sensor P309, and obtains a corrected magnetic material distribution similar to that of the first embodiment based on the magnetic field distribution.

The magnetic field adjustment device P300 according to this embodiment also includes a three-dimensional modeling head P303. The transporter transports the three-dimensional modeling head P303 together with the magnetic field sensor P309 within the accelerator. The transporter transports the magnetic field sensor P309 and the three-dimensional modeling head P303 within a specific plane, i.e., within a plane perpendicular to the central axis M110, and can transport the magnetic field sensor P309 and the three-dimensional modeling head P303 in a direction perpendicular to that plane. The magnetic field adjustment device controller P333 controls the three-dimensional modeling head P303 based on the corrected magnetic material distribution, and causes the three-dimensional modeling head P303 to model a magnetic material at the magnetic pole M101.

Third Embodiment
A magnetic field adjustment device P370 according to the third embodiment will be described with reference to FIG. 9. In the magnetic field adjustment device P370, an articulated robot arm is used as a carrier. The correction magnetic material adjustment head P313 has a three-dimensional modeling head P303, a head position sensor P307, and a magnetic field sensor P309 on a head stage P305, similar to the first embodiment. The control flow is similar to the second embodiment. The support structure and position control method of the correction magnetic material adjustment head P313 are different from those of the second embodiment.

The magnetic field adjustment device P370 is inserted from the outside through an introduction port M108 provided on the yoke M104 of the electromagnet device M100, and is fixed to the electromagnet device M100 by a connection flange M112. The correction magnetic material adjustment head P313 and the connection flange M112 are supported by support arms P345, P349, P359, and P365. The head stage P305 and the support arm P345 are connected by a stage angle adjustment joint P343. The stage angle facing the pole face is adjusted by a stage angle adjustment motor P341.

The support arm P345 and the support arm P349 are connected by a joint P347. The angle between the support arm P345 and the support arm P349 is controlled by an extension mechanism P351 and an arm length adjustment motor P353. The support arm P349 and the support arm P359 are connected by a joint P355. The angle of the joint P355 is controlled by an angle adjustment motor P357. The support arm P359 and the support arm P365 are connected by a joint P361. An angle adjustment motor P363 is attached to the joint P361, and the angle of the entire articulated robot arm perpendicular to the page surface is adjusted by the angle adjustment motor P363.

According to this embodiment, the same effect as the second embodiment can be obtained. Also, in the second embodiment, the head stage P305 is perpendicular to the central axis M110 of the magnetic pole M101, and the correction magnetic material is added sequentially in the direction of the central axis M110. In this embodiment, the head stage P305 may also be in a position that is not perpendicular to the central axis M110. Therefore, the correction magnetic material may be added from the normal direction to each addition location of the magnetic pole M101. This allows processing to be performed even in cases where the magnetic pole M101 has a side that extends in the central axis direction.

Furthermore, by equipping an articulated robot arm with a tool replacement function similar to that of an NC processing machine, nozzles for mixed materials, excavation tools, etc. can be replaced with those stored in a separate location. This makes it possible to use multiple types of correction magnetic material, such as separate correction magnetic materials for coarse adjustment and fine adjustment, or to excavate and remove correction magnetic materials, allowing for more complex magnetic field adjustments.

In the second and third embodiments, the formation of the correction magnetic body for the magnetic pole M101 may be performed when the accelerator is installed. For example, if a hole in which a cavity resonator is provided is provided in the side wall of the yoke M104, this hole may be used as a fixed structure for the magnetic field adjustment device (P300, P370), and the correction magnetic body may be formed in the following process.

First, without the cavity resonator attached, the upper yoke M104 and the lower yoke M104 are joined. At this time, the magnetic field adjustment device (P300, P370) is attached to the accelerator, using the hole for the cavity resonator formed in the yoke M104 as a fixing structure. In this way, without the cavity resonator installed, the correction magnetic body for the magnetic pole M101 is shaped.

After the correction magnetic body is shaped, the upper yoke M104 and the lower yoke M104 are separated, and the magnetic field adjustment device (P300, P370) is removed from the accelerator. After the cavity resonator and other components are attached to the accelerator, the upper yoke M104 and the lower yoke M104 are joined again to complete the installation.

In addition to the above-mentioned process of removing the magnetic field adjustment device (P300, P370) from the accelerator to avoid interference between the cavity resonator and other components (hereinafter referred to as the cavity resonator, etc.) and the magnetic field adjustment device (P300, P370), the following process may be adopted. That is, by shifting the position of the magnetic field adjustment device (P300, P370) and attaching the cavity resonator, etc. to the accelerator, a state in which interference between the cavity resonator, etc. and the magnetic field adjustment device (P300, P370) is avoided may be realized. In this case, the cavity resonator, etc. is attached to the accelerator with the magnetic field adjustment device (P300, P370) attached to the accelerator.

According to the above-mentioned embodiments of the present invention, the size of the correction magnetic material to be handled can be made small, and the correction magnetic material can be arranged with a continuous distribution. This improves the accuracy of magnetic field adjustment. Furthermore, by numerically managing the amount of correction magnetic material, human error during adjustment is reduced, and personnel costs are reduced. In conventional methods using shim trays, etc., it was necessary to prepare correction magnetic materials of various sizes, including surplus materials, which sometimes required costs for production or management. Each embodiment of the present invention reduces the effort required for advance preparation of correction magnetic materials.

Fourth Embodiment
As a fourth embodiment, a magnetic field adjustment method that combines three-dimensional modeling and a shim tray will be described. In this embodiment, the magnetic field is adjusted by placing a magnetic material at a predetermined position, as in the conventional method using a shim tray. In this case, it is necessary to prepare a plurality of correction magnetic bodies for each of various sizes in advance. In this embodiment, the correction magnetic body that realizes the correction magnetic body distribution calculated backward based on the magnetic field measurement results is produced at the adjustment site using, for example, a three-dimensional metal printer, thereby eliminating the need to prepare the correction magnetic body.

Figure 10 shows a schematic diagram of the shim tray M181 used in this embodiment. The shim tray M181 has an arbitrary shape that matches the region of interest M109, and in this embodiment, it is formed in a disk shape to match the electromagnet device M100 in Figure 2. Shim pockets M183 for arranging correction magnetic material are formed at each position of the shim tray M181. The correction magnetic material distribution is adjusted by forming the correction magnetic material in the shim pocket M183 using a three-dimensional modeling machine. The correction magnetic material may be formed by placing a correction magnetic material sheet M185 in the shim pocket M183. In this embodiment, for example, a sheet-shaped magnetic material piece is used as the correction magnetic material sheet M185, and a rectangular groove is used as the shim pocket M183. These may be, for example, circular or spherical, depending on the shape of the shim tray M181 and the region of interest M109.

According to this embodiment, there is no need to prepare correction magnetic bodies of various sizes in advance, and the cost of manufacturing or managing the correction magnetic bodies is reduced. Regarding the amount of correction magnetic body used for fine adjustment, there is no need to substitute the required amount by using multiple correction magnetic bodies (e.g., four pieces) of correction magnetic bodies in units smaller than the required amount of correction magnetic body (e.g., 0.02 cc) than the amount of correction magnetic body (e.g., 0.08 cc), and the number of correction magnetic bodies handled is reduced. Therefore, compared to conventional methods, the occurrence of human error during adjustment is suppressed. Furthermore, according to this embodiment, in addition to adding correction magnetic bodies, it is also easy to remove correction magnetic bodies.

<Application embodiment>
An example of a particle beam therapy system according to an application embodiment is shown in Fig. 11. This particle beam therapy system A500 includes an accelerator A501 for accelerating ions generated by an ion source A503, an extraction channel M107 for extracting the ion beam accelerated by the accelerator A501, and an irradiation device A531 for irradiating the ion beam accelerated by the accelerator A501.

The particle beam therapy system A500 further includes a transport device A533 that transports the ion beam emitted from the accelerator A501 to the irradiation device A531, a support table A521 that supports the treatment subject A523, and a control system A535 that controls the electromagnets and high-frequency power supplies provided in the accelerator A501 and the transport device A533. The accelerator A501 includes an electromagnet device M100 in which a vacuum space is formed, an ion source A503 is connected to a through hole provided in the electromagnet device M100, and ions are sent into the internal space.

The electromagnet device M100 has a structure in which a pair of coils for generating a static magnetic field in the internal space are connected by a yoke, and the magnetic field distribution is adjusted to the desired distribution required for particle acceleration in the orbital plane along which the ion beam is accelerated. Inside the electromagnet device M100, a dee electrode connected to a high-frequency power source for accelerating the ion beam, a kicker magnetic field generating coil for extracting the ion beam from the internal space, and other components are arranged.

The transport device A533 includes a beam pipe A506, several bending electromagnets A509, A513, and A515 arranged around it, and focusing electromagnets A505, A507, and A511. The ion beam traveling inside the beam pipe A506 is deflected in the desired direction by the functions of the bending electromagnets A509, A513, and A515, and can be guided to any desired position by providing several bending electromagnets. In addition, the state of the ion beam is adjusted by the converging or diverging action of the focusing electromagnets. The bending electromagnets and quadrupole electromagnets are configured so that the output of the bending electromagnets and quadrupole electromagnets is adjusted depending on the energy of the ion beam passing through, and this adjustment is performed by the control system A535.

The ion beam transported to the vicinity of the treatment area via the transport device A533 passes through the irradiation device A531 and is irradiated to the affected area of the treatment target placed on the support table A521. There are various mechanisms for irradiating the ion beam to a desired position. For example, the irradiation device A531 and part of the transport device A533 are mounted on a rotating gantry, making it possible to irradiate the ion beam to the treatment target from any angle, and the irradiation device A531 is provided with a scanning magnet that deflects the ion beam. In this embodiment, a known mechanism may be adopted. Furthermore, devices for monitoring the irradiation position and dose may be installed in the particle beam therapy system A500, and information from these monitoring devices may be input to the control system A535, which may control the mechanism for irradiation based on the information.

The particle beam therapy system A500 according to this embodiment employs the electromagnetic device M100 according to each of the above embodiments as the electromagnetic device of the accelerator A501. The accelerator A501 includes a shaping substrate M105 for arranging multiple magnetic material pieces (corrective magnetic bodies) or a magnetic pole M101 with an adjusted distribution of corrective magnetic bodies.

According to the particle beam therapy system A500 of this embodiment, a desired magnetic field distribution is achieved as a static magnetic field in a direction perpendicular to the orbital plane in which the ion beam is accelerated. This reduces the difference between the target acceleration orbit and the actual acceleration orbit.

M100 electromagnet device, M101 magnetic pole, M102 coil case or cryostat, M103 coil, M104 yoke (housing), M105 build substrate, M106 substrate support mechanism, M107 exit channel, M108 inlet port, M109 region of interest, M110 central axis, M111 central plane, M112 connection flange, M115 gap between magnetic poles, M121 coil slot area, M151 magnetic field measuring element, M153 magnetic field measuring element support rod, M155 measuring element rotation motor, M157 measuring element rotation drive system, M159 magnetic field measuring linear movement storage stage, M161 linear movement motor, M162 linear movement drive system, M163 pulley, M165 belt, M166 linear feed mechanism, M167 Magnetic field measurement mechanism main stage, M171 controller, M173, P331 signal/power bus, M181 shim tray, M183 shim pocket, M185 correction magnetic sheet, P300, P370 magnetic field adjustment device, P301 3D modeling nozzle, P303 3D modeling head, P304 material supply cylinder, P305 head stage, P307 head position sensor, P309 magnetic field sensor, P313 correction magnetic adjustment head, P311, P320, P321 support rail, P319 support rotation shaft, P315 axial movement motor, P317 radial position adjustment motor, P323 circumferential position adjustment motor, P325 central position adjustment motor, P333 magnetic field adjustment device controller, P345, P349, P359, P365 Support arm, P341 stage angle adjustment motor, P353 arm length adjustment motor, P357, P363 angle adjustment motor, P343 stage angle adjustment joint, P347, P355, P361 joint, P351 extension mechanism, A500 particle beam therapy system, A501 accelerator, A503 ion source, A504 accelerator support lift, A506 beam pipe, A505, A507, A511 focusing magnet, A509, A513, A515 bending magnet, A521 support table, A523 treatment target, A531 irradiation device, A533 transport device, A535 control system.

Claims (10)

disposing a magnetic field measuring element in an electromagnetic device and measuring a magnetic field distribution in the electromagnetic device;
determining a corrected magnetic material distribution representing a distribution of magnetic materials to be shaped with respect to a magnetic pole in the electromagnet device based on the magnetic field distribution;
forming a magnetic body for the magnetic pole based on the corrective magnetic body distribution;
Including,
Shaping a magnetic body with respect to the magnetic pole includes:
removing the build substrate from the electromagnet device;
a carrier transporting the three-dimensional modeling head together with the magnetic field measuring element within the electromagnetic device;
a controller controls the three-dimensional modeling head based on the corrected magnetic material distribution, and causes the three-dimensional modeling head to model a magnetic material with respect to the magnetic pole;
and attaching the substrate on which the magnetic body is formed to the electromagnet device . A magnetic field measuring element;
A carrier for carrying the magnetic field measuring element within an electromagnetic device;
a controller that measures a magnetic field distribution in the electromagnet device by the magnetic field measuring element, and calculates a correction magnetic material distribution based on the magnetic field distribution, the correction magnetic material distribution representing a distribution of magnetic materials to be added to a magnetic pole in the electromagnet device;
Equipped with a three-dimensional modeling head,
The conveyor includes:
Transporting the three-dimensional modeling head together with the magnetic field measuring element within the electromagnet device;
The controller includes:
A magnetic field adjusting device, comprising : a control unit for controlling the three-dimensional modeling head based on the corrected magnetic material distribution; and causing the three-dimensional modeling head to model a magnetic material with respect to the magnetic pole . The magnetic field adjusting device according to claim 2 ,
The magnetic field adjusting device , wherein the three-dimensional modeling head constitutes a three-dimensional printer . The magnetic field adjusting device according to claim 2,
The three-dimensional modeling head includes:
A magnetic field adjusting device, characterized in that a magnetic body is formed for said magnetic poles by using a mixture of a magnetic material and a non-magnetic material . The magnetic field adjusting device according to claim 2 ,
The electromagnet device includes:
a correction magnetic body fixing substrate disposed relative to the magnetic pole, the correction magnetic body fixing substrate being partitioned for each position at which the correction magnetic body is disposed;
The magnetic field adjusting device , wherein the three-dimensional modeling head models a magnetic body on the substrate for fixing the correction magnetic body . The magnetic field adjusting device according to claim 2 ,
The conveyor includes:
A magnetic field adjustment device, characterized in that the magnetic field measuring element and the three-dimensional modeling head are transported within a specific plane and in a direction perpendicular to the plane . The magnetic field adjusting device according to claim 2 ,
The conveyor includes:
A magnetic field adjustment device comprising an articulated robot arm . In an accelerator for accelerating ions, the accelerator comprises the electromagnet device,
The accelerator comprises:
An accelerator comprising a fixing structure to which the magnetic field adjustment device according to any one of claims 2 to 7 is fixed . 9. The accelerator of claim 8 ,
The fixing structure includes:
a hole formed in the housing of the accelerator;
An accelerator, wherein a cavity resonator is disposed in the hole while avoiding interference with the magnetic field adjustment device . An accelerator according to claim 8 or claim 9 ;
a transport device for transporting the ions accelerated by the accelerator;
an irradiation device that irradiates a patient with the ions transported by the transport device;
A particle beam therapy system comprising :

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