JP6588849B2 - Superconducting magnet device for beam transportation, beam transportation system, particle beam therapy system, and superconducting magnet arrangement method for beam transportation - Google Patents

Description

The present invention relates to a superconducting magnet device for beam transportation, a beam transportation system, a particle beam therapy system, and a superconducting magnet arrangement method for beam transportation.

Particle beams (beams) obtained by accelerating charged particles such as electrons and protons are used in various forms in research and medical fields. One of the medical beam applications is proton beam (particle beam) therapy. This is a treatment that drives accelerated protons into the cancer and kills the cancer cells. The dose peak (Bragg peak) position is controlled to concentrate the beam energy at the cancer site. Therefore, compared with treatment methods such as surgery such as surgery, chemotherapy with an anticancer agent, and radiation therapy, it has recently become widespread as a treatment method that places less burden on patients.

In beam utilization, the beam must be properly transported along the path from generation to irradiation utilization. Since the moving charged particles are subjected to Lorentz force by the magnetic field, the flight path can be controlled using a magnet (magnetic field). When a particle with a positive charge moves in an upward magnetic field of a certain size (the magnetic field direction is the direction in which the magnetic field lines are directed from the N-pole to the S-pole of the magnet) Turns with a rightward force against the direction of travel. This constant magnetic field is called a dipole magnetic field, and a magnet that generates this magnetic field is called a deflection magnet. Similarly to the lens in the optical system, there is a magnetic lens for the beam, and the magnetic field corresponding to the convex lens concave lens for converging or diffusing the beam is called a quadrupole magnetic field. A magnetic field that corrects for this is called a hexapole magnetic field. A magnetic field such as a dipole magnetic field, a quadrupole magnetic field, or a hexapolar magnetic field is used for transporting the beam.

Non-Patent Document 1 discloses a proton beam device, which accelerates the generated charged particles and injects the beam into the main accelerator (synchrotron) at the next stage, and accelerates the beam to a predetermined energy. And a rotating gantry for irradiating the patient with a beam. The rotating gantry is configured such that the beam nozzle and the beam transport magnet rotate around the patient so that the beam can be optimally irradiated according to the position and shape of the cancer. The disclosed system has a gantry radius of 4 m and a weight of 100 tons.

Non-Patent Document 1 describes a treatment system that irradiates a proton beam, but an apparatus using a heavy particle beam (carbon ion) that has a further therapeutic effect on radiation-resistant cancer has been developed. In Japan, the National Institute of Radiological Sciences (NIRS) HIMAC (Heavy Ion Medical Accelerator in Chiba) and the like are in operation. Since carbon ions have a larger mass per charge than protons, the radius of curvature of the beam trajectory increases when magnets with the same magnetic field strength are used. Therefore, the accelerator (synchrotron) of HIMAC is larger (eg, ring diameter is about 42 m, circumference is about 130 m) than the proton beam system (eg, ring circumference is about 20 m).

A rotating gantry is desired for heavy particle beams as well as a proton beam therapy apparatus, and development of a rotating gantry is underway. In order to realize a rotating gantry, it is essential to bend the beam with a smaller radius, but superconducting magnets are used to generate a strong magnetic field.

Non-Patent Document 2 discloses the development of a rotating gantry for a heavy particle beam therapy system. In these beam transport magnets, in order to bend the beam trajectory, a deflecting magnet (dipolar magnet) generates a magnetic field having a constant intensity in a region through which the beam passes. As an arrangement method of the magnetomotive force source for generating the constant magnetic field, that is, a coil winding method, cosine theta winding is known. This cosine theta winding generates a vertically upward magnetic field, deflects the beam in a horizontal plane, and in an electromagnet having a round cross section with respect to the cross section through which the beam passes, the arrangement of the current constituting the electromagnet is relative to the angle θ from the horizontal plane. In this method, the current density distribution is cos θ. In an actual electromagnet, the coil winding is shifted so that the current (coil winding) arranged at a position where the angle θ is small does not affect the beam trajectory so that the winding is kept away from the beam passage region at the end of the electromagnet. Wrap it around. In Non-Patent Document 2, in order to realize this cosine theta winding, a deflection magnet for realizing a superconducting rotating gantry is realized by a special winding technique called surface winding.

Shimizu, S. et al., “A Proton Beam Therapy System Dedicated to Spot-Scanning Increases Accuracy with Moving Tumors by Real-Time Imaging and Gating and Reduces Equipment Size”, PLOS ONE, April 2014, vol.9, Issue 4, e94971 Takayama, S. et al., “Magnetic field measurement of the superconducting magnet for rotating-gantry”, Proceedings of the 9th annual meeting of Particle Accelerator Society of Japan, 2012.8.8-11, P247-251

In general, a deflecting magnet for transporting a beam needs to generate a magnetic field having a certain strength in a direction orthogonal to the traveling direction of the beam. Need to be wound so that Moreover, in order to generate a constant magnetic field along the beam trajectory, an electromagnet having a winding method such as a cosine theta winding is required, and thus a complicated three-dimensional winding (coil) is required. . In general, a magnet for transporting a beam requires a highly accurate winding in order to obtain a beam position accuracy. Winding a three-dimensional magnet with high accuracy is technically difficult and requires a dedicated winding device. Therefore, there is a demand for a technique for realizing a deflecting magnet for transporting a beam without using a three-dimensionally shaped coil that is highly technically difficult.

In view of the above points, the present invention has an object of realizing a superconducting magnet for beam transportation using only a flat coil that can be easily mounted.

According to the first solution of the present invention,
A superconducting magnet device for beam transport,
In a coordinate system in which the magnetic field generation direction is the z-axis positive direction and the flight path of the beam is on the xy plane, the beam passes through the beam passing area symmetrical with respect to the xy plane, and the arc has a predetermined radius of curvature. The beam passing region is sandwiched between the xy plane at the upper side in the z direction and the xy plane at the lower side of the beam passing region, or the maximum position of the beam passing region in the z direction and the minimum position x−. When the region sandwiched by the y plane is a low angle region, and the region outside the z axis direction from the low angle region is a high angle region,
At least one pair of first flat coils arranged symmetrically with respect to an xy plane inside the arc of the beam passing region and in the low angle region;
Zy at the coordinate origin that is arranged outside the arc of the beam passing region and symmetrically with respect to the xy plane in the low angle region and that represents the center of the beam passing region in the coil cross section of the zx plane. to the plane, it is disposed on the first flat coil and symmetrical or nearly symmetrical, the direction of current and the first flat coil and the left and right opposite, to generate a magnetic field in the same direction as said first flat coil And at least one pair of second flat coils,
At least one pair of third flat coils arranged symmetrically with respect to an xy plane in the z direction outside the beam passage region and in the high angle region;
With
The arrangement position of the first flat coil is between an angle of 0 degrees to 30 degrees formed from the x-axis direction to the z-axis direction when viewed from the coordinate origin,
The arrangement position of the second flat coil is between an angle of 0 degrees to 30 degrees formed from the x-axis minus direction to the z-axis direction when viewed from the coordinate origin,
The third flat coil is disposed at an angle between 30 degrees and 63 degrees formed from the x-axis direction to the z-axis direction when viewed from the coordinate origin, and from the x-axis minus direction when viewed from the coordinate origin. The angle between the direction is between 30 degrees and 63 degrees,
There is provided a superconducting magnet device for transporting a beam.

According to the second solution of the present invention,
A beam transport system including the superconducting magnet device for beam transport as described above is provided.

According to the third solution of the present invention,
A particle beam therapy system including the superconducting magnet device for beam transportation as described above is provided.

According to the fourth solution of the present invention,
A superconducting magnet arrangement method for beam transportation,
In a coordinate system in which the magnetic field generation direction is the z-axis positive direction and the flight path of the beam is on the xy plane, the beam passes through the beam passing area symmetrical with respect to the xy plane, and the arc has a predetermined radius of curvature. The beam passing region is sandwiched between the xy plane at the upper side in the z direction and the xy plane at the lower side of the beam passing region, or the maximum position of the beam passing region in the z direction and the minimum position x−. When the region sandwiched by the y plane is a low angle region, and the region outside the z axis direction from the low angle region is a high angle region,
At least one pair of first flat coils are arranged symmetrically with respect to the xy plane inside the arc of the beam passing region and in the low angle region;
At least one pair of second flat coils is arranged outside the arc of the beam passing region and symmetrically with respect to the xy plane in the low angle region, and the beam passing through the coil cross section in the zx plane. relative z-y plane at the coordinate origin which represents the center of the area, the first place to the flat coil and the symmetrical or substantially symmetrical to the direction of current and the first flat coil and the left and right opposite, the first At least one pair of second flat coils adapted to generate a magnetic field in the same direction as the flat coils;
At least one pair of third flat coils are arranged outside the beam passing region in the z direction and symmetrically with respect to the xy plane in the high angle region;
The arrangement position of the first flat coil is between an angle of 0 degrees to 30 degrees formed from the x-axis direction to the z-axis direction when viewed from the coordinate origin,
The arrangement position of the second flat coil is between an angle of 0 degrees to 30 degrees formed from the x-axis minus direction to the z-axis direction when viewed from the coordinate origin,
The third flat coil is disposed at an angle of 30 to 63 degrees from the x-axis direction to the z-axis direction when viewed from the coordinate origin, and from the x-axis minus direction to the z-axis when viewed from the coordinate origin. The angle between the direction is between 30 degrees and 63 degrees,
A superconducting magnet arrangement method for beam transportation is provided.

According to the present invention, a superconducting magnet for beam transportation can be realized only by a flat coil that is easy to mount.

It is a conceptual diagram which shows the angular position of the coil arrangement | positioning in the cross section of the magnet of this embodiment. It is a bird's-eye view which shows magnetomotive force source arrangement | positioning of the magnet of this embodiment. It is explanatory drawing about how to take the coordinate system for demonstrating a multipolar component magnetic field. It is explanatory drawing which shows the angular position of the line current in which the absolute value of the magnetic field of the n = 2 order component among multipolar expansion | deployment magnetic fields becomes the maximum value. It is explanatory drawing which shows the angle position of the line current from which the absolute value of the magnetic field of a n = 4th-order component among multipolar expansion | deployment magnetic fields becomes the maximum value. It is explanatory drawing which shows the angular position of the line current from which the absolute value of the magnetic field of the n = 6th-order component among multipolar expansion | deployment magnetic fields becomes the maximum value. It is explanatory drawing for demonstrating the response | compatibility with the coil arrangement | positioning in a cross section, and the area | region which generates n = 4 and a 6th-order multipolar magnetic field. It is a conceptual diagram which shows the coil combination in the case of operating the magnet of this embodiment with two power supplies. It is explanatory drawing which shows an example of the target specification and design value of a magnetic field.

The present embodiment relates to an electromagnet (deflecting magnet) for transporting a beam, and provides a method of configuring a deflecting magnet using a coil having a simple shape. The superconducting magnet for beam transportation according to the present embodiment is, for example, a superconducting magnet that is vertically symmetrical, and is configured by a combination of only coils wound in a flat plate shape. The coil positions are arranged at positions that do not interfere, and the coil positions are arranged at positions that satisfy a specific positional relationship that satisfies a predetermined magnetic field uniformity.

Embodiments according to the present invention will be described below. However, the present invention is not limited to the embodiments taken up here, and can be appropriately combined and improved without departing from the scope of the invention.

FIG. 1 is a conceptual diagram showing the angular position of the coil arrangement in the cross section at the center position of the magnet. FIG. 2 is a conceptual diagram showing the coil arrangement of the magnet according to the present embodiment. To clarify the positional relationship of the magnets, first define the coordinates and direction. The magnetic field generation direction is taken in the z-axis positive direction with respect to the right-handed rectangular coordinate system, and the beam that has been flying in the xy plane is deflected in the xy plane by the magnetic field in the z direction. To do. Further, the magnet is vertically symmetric in the xy plane, and the coil arrangement in the cross section is symmetrical or substantially symmetrical.

The magnet of the present embodiment is a superconducting magnet for transporting a beam for realizing a deflection angle of a predetermined angle (for example, 22.5 degrees) or more, and the beam is bent with a constant curvature radius. The passing beam passing region is provided so as not to interfere with the magnetomotive force source arranged symmetrically with respect to the xy plane, and all the magnetomotive force sources are constituted by flat coils. is there. The flat coil mentioned here is a coil in which a wire is wound substantially parallel to the xy plane so as to generate a magnetic field in the z-axis direction, and the cross-sectional shape of the coil winding is the direction of the winding. When the xy plane is a horizontal plane, the coil has a flat (planar) shape that can be placed parallel to this plane.

The flat coil arranged so as not to interfere with the beam passing region is determined in position and shape so as to achieve a predetermined magnetic field uniformity with respect to the beam passing region. It has the following features.

First, a region sandwiched by planes parallel to the xy plane passing through the z-direction maximum position and minimum position (or the direction upper position and the lower position) of the beam passing area is referred to as a low-angle area, and is outside these planes. This area is named the high angle area. In this case, at least one pair of first flat coils 1a symmetric with respect to the xy plane is disposed in the low-angle region on the radially inner side of the arc of the curved arc-shaped beam passage region, and further on the outer side of the arc. In addition, at least one pair of second flat coils 2a symmetric with respect to the xy plane is arranged in the low angle region, and at least one pair of third flat coils symmetric with respect to the xy plane in the high angle region. 3a pairs are arranged. Further, when the magnet is viewed in a cross section cut along the zx plane, the cross-sectional shape of the winding portion is symmetric or substantially symmetric in the four quadrants of the zx plane, and the first quadrant (the x axis is Taking the horizontal axis and paying attention to x> 0, z> 0), the first flat coil 1a is also connected to the third flat line 1a at the angles of 30 degrees and 63 degrees formed from the x axis to the z axis direction when viewed from the coordinate origin. The flat coil 3a is not applied. In the high angle region where the third flat coil 3a is arranged, a fourth flat coil 4a can be further arranged according to the required magnetic field accuracy. In this case, the fourth flat coil 4a is 63. It is arranged at a higher angle side than the degree line.

The superconducting deflecting magnet of this embodiment is composed only of a flat coil having a simple shape, and is arranged so as not to interfere with the beam passage region. Further, a specific angular position in the cross section, which is a multipole component magnetic field. Are arranged so as to avoid a position where a strongest magnetic field or a magnetic field having a relatively high strength compared to other multipolar components is generated. As a result, it is possible to realize a superconducting magnet for transporting a beam having a predetermined magnetic field uniformity while reducing the number of coils and making the magnet easy.

Hereinafter, the present embodiment will be specifically described with reference to the drawings.

(Specification and design result of superconducting deflection magnet)
As an example of the magnetic field specification of the deflecting electromagnet, consider a magnet that deflects a carbon beam with an energy of 430 MeV / u for heavy particles with a radius of 2.8 m. The beam passage area is 200 mm × 200 mm, and a uniform dipole magnetic field is created in this area. As shown in FIG. 2, the magnet is composed of eight vertically symmetrical coils. The magnet is curved so that the center of the magnet through which the beam passes forms an arc with a radius of curvature of 2.8 m. The energy, the beam radius, the passing region, and the like are merely examples, and the present invention is not limited thereto, and can be set to appropriate values. This magnet is constituted by a coil wound in a flat shape called a flat coil. In this configuration, the coil can be arranged so as not to affect the passage of the beam while using the coil manufactured by a simple winding, and further, the coil is arranged outside the magnet of the coil arranged in the vicinity of the vertical symmetry plane. Therefore, it is possible to provide a lightweight magnet without requiring a large amount of return yoke for reducing the leakage magnetic field.

FIG. 9 is an explanatory diagram showing an example of the target specification and design value of the magnetic field. This is a result of an optimization calculation of the shape and position of the rectangular cross-section coil with severe restrictions imposed on the magnetic field error (error) of the magnet center through which the beam passes and relaxed restrictions on the leakage magnetic field. A solution that satisfies a sufficiently small error magnetic field (multipole magnetic field) and a small leakage magnetic field to transport the beam is obtained.

Here, the coil arrangement in the two-dimensional cross section shown in FIG. 1 will be referred to. In the drawing, only the upper side of the vertically symmetrical coil arrangement is shown. The first flat coil 1a and the second flat coil 2a are arranged so as not to invade the line at an angular position of 30 degrees from the x axis. In order to explain what this coil arrangement means, the magnetic field design will be described next.

(About magnetic field design)
Hereinafter, the expression of the magnetic field and the concept of the magnetic field design will be described with respect to the design of the beam transporting electromagnet. Even for an electromagnet that transports a beam in an arc shape, first, a magnetic field design using an infinite linear magnetomotive force source is performed, and a three-dimensional method is used based on the design. A magnetic field generated by an infinite linear magnetomotive force (current) will be described.

FIG. 3 is an explanatory diagram on how to use a coordinate system for explaining the multipole component magnetic field. Here, a coordinate system as shown in FIG. 3 is considered. It is assumed that the magnetomotive force source is a linear current I, and the current flows from the front to the back perpendicular to the paper surface. The direction of the magnetic field is taken in the z-axis direction. The position of the current is given by the distance from the coordinate origin as f and the angle formed from the z-axis as φ. Similarly, the position of the magnetic field evaluation point is given by r and θ.

と、原点からの距離ｒのべき乗で展開した表式で書くことができる。
ここでｎは展開次数であり、

のように、ｎのそれぞれをｎ次の磁場と呼ぶこととする。ｎ＝０の磁場を２極磁場、ｎ＝１の磁場を４極磁場という呼び方もされるが、これはそれぞれのｎ次に特徴的な磁場分布を形成する磁石の極数に由来している。 At this time, the magnetic field Bz (r, θ) around the origin is

And an expression developed by a power of the distance r from the origin.
Where n is the expansion order,

In this way, each n is referred to as an nth order magnetic field. The magnetic field of n = 0 is called a dipole magnetic field, and the magnetic field of n = 1 is called a quadrupole magnetic field. This is derived from the number of poles of the magnet that forms the characteristic magnetic field distribution of each nth order. Yes.

In order to deflect the beam flight path with a constant curvature, a uniform magnetic field is required. With the deflecting electromagnet, basically only the n = 0th order uniform magnetic field (dipolar magnetic field) is left, and the rest The magnetic field design is performed so that the order magnetic field components (also referred to as multipolar magnetic fields) are zero.

As a coil winding method (current arrangement method) for obtaining a dipole magnetic field, cosine theta winding is often used. This is an arrangement method in which the current intensity (current distribution) is distributed in a cos (Θ) shape with respect to an angle Θ formed from the x-axis in the coordinate system in FIG. Note that θ and φ are taken from the z-axis).

In Equation 3 to be described later, the dependency of the multipole deployed magnetic field strength on the angular position of the current source is a portion of sin [(n + 1) φ], but the integration is performed by providing the distribution of sin (φ) as the current strength distribution. Then, as can be seen from the fact that terms other than n = 0 are zero, only a dipole magnetic field can be obtained in the cosine theta winding. The cosine theta winding can be interpreted as a system having a very high degree of freedom because the current density distribution is continuously changed.

In the present invention and / or the present embodiment, it is intended to realize a deflecting magnet by a system in which rectangular cross-section coils are discretely arranged instead of a distributed winding coil in which the current density distribution of a so-called cosine theta winding changes continuously. Yes. Even in this case, as in the case of the cosine theta winding, the coil arrangement must be such that the multipole component magnetic field other than n = 0 is zero (or a value close to zero, a negligible value, etc.). I must. In the present invention and / or this embodiment, the cosine theta winding is different from the case where the multipole component magnetic field is canceled by integration in principle, but by combining the cross-sectional shapes and positions of the discretized coils appropriately, Cancel the polar component magnetic field. Roughly speaking as a general theory, it is necessary to give the degree of freedom of the magnetic field source (coil arrangement) by the order of the order of canceling the magnetic field component. In order to cancel many orders of magnetic fields, it is essential to increase the number of discrete coils.

As in the present embodiment, when the magnetomotive force sources are arranged in a two-dimensional plane in a left-right antisymmetric manner (with respect to the z-axis) and a vertical symmetry (with respect to the x-axis), n is an odd order due to symmetry. The magnetic field is canceled and becomes zero, which is convenient. Here, the left-right antisymmetric means that the coil cross-sectional shape is symmetric with respect to the z-axis and the direction of the current is opposite. In FIG. 1, only the upper half of the coil arrangement is shown, but a mark with a dot in the center of the circle in the figure indicates that current is flowing from the back of the page toward the front, The mark indicates that the current is flowing toward the back of the page.

となる（左右反対称の対称性を考慮した表式）。さらに上下対称の場合には、式２’に、式２’のφを（π−φ）におきかえたものを加算すると、

が得られる。左右反対称、上下対称の電流配置の場合には、このようにｎが奇数次の多極磁場は０となるので、考慮すべき磁場はｎが偶数次の項のみであり、残すべきｎ＝０の２極磁場以外のｎ＝２の６極磁場、ｎ＝４の１０極磁場、ｎ＝６の１４極磁場、、、等をキャンセルする磁場設計を行なうこととなる。ｎ次の磁場は次数が高いほど（ｒ／ｆ）のｎ乗でその強度は小さくなっていくため、無限に高い次数の磁場までをキャンセルする必要はなく、キャンセルすべき磁場に関しては、ビームが通過する領域において要求される磁場精度によって決定される。本実施形態の磁石においては、一例としてｎ＝６次までをキャンセル（又は、予め定めた値以下まで減少）するようにし、それ以上の高次の多極磁場は強度が大きくならないように制約してコイル配置を決定した。 If the sign of the current I in Expression 2 is inverted and the sign of φ is inverted is added to Expression 2,

(Expression in consideration of left-right anti-symmetric symmetry). Furthermore, in the case of vertical symmetry, adding the value obtained by replacing φ in equation 2 ′ with (π−φ) to equation 2 ′,

Is obtained. In the case of the current arrangement of left-right antisymmetric and vertical symmetry, the n-order odd-order multipolar magnetic field is 0, so the only magnetic field to be considered is n-order terms and n = A magnetic field design that cancels n = 2 hexapole magnetic fields other than 0 dipole magnetic fields, n = 4 10-pole magnetic fields, n = 6 14-pole magnetic fields, and the like is performed. Since the strength of the n-th magnetic field increases with the order of (r / f) to the n-th power, it is not necessary to cancel up to an infinitely high-order magnetic field. It is determined by the magnetic field accuracy required in the passing region. In the magnet of this embodiment, for example, up to n = 6th order is canceled (or reduced to a predetermined value or less), and the higher order multipole magnetic field is restricted so that the strength does not increase. The coil arrangement was determined.

(Principle of coil arrangement)
In this embodiment, since the magnetomotive force system is vertically symmetrical and antisymmetrical, only the even-order magnetic field is the target of design, and the leakage magnetic field was designed to reduce it as an effort target. . As shown in FIG. 9, the number of restricted magnetic fields is 7 at the center of the magnet (9 when a leakage magnetic field is further added). Since the number of magnetic fields to be constrained is large, a reasonable coil arrangement is necessary to obtain a predetermined magnetic field uniformity with a small number of discrete coils. In FIG. 9, as an example, the second, fourth, and sixth orders are canceled to be 0.05, 0.16, and 0.16 gauss or less, and the eighth, tenth, and twelfth orders are 7.0, respectively. , 7.2, 5.3 gauss or less. Further, for the leakage magnetic field, as an example, the intensity of the leakage magnetic field component proportional to −2 to the distance in the vertical direction along the z axis from the coordinate origin (center) is set to 3 m in the vertical direction from the coordinate origin along the z axis. 2 gauss or less (1.5 gauss or less in FIG. 9), and the intensity of the leakage magnetic field component proportional to the fourth power of the distance is 20 gauss at a position 3 m in the vertical direction along the z axis from the coordinate origin. In order to be below (in FIG. 9, 12 gauss or less), it is made as small as possible.

Equation 3 is an expression of an n-order multipolar magnetic field near the center of the magnet, but the portion depending on the angular position of the current is a portion of sin [(n + 1) φ] / f ^{n + 1} . In the following, the concept of magnetic field design of each order will be described according to Equation 3.

[N = 0 order]
Considering the most efficient generation of the n = 0th order dipole magnetic field (deflection magnetic field) while suppressing the multipolar magnetic field, it is clear that the current that generates the reverse magnetic field is not arranged at the center of the magnet. (The return currents of the first and second flat coils 1a and 2a are in the opposite directions, but unavoidably. Further, since the current is far away, the contribution is small). Since the n = 0th order magnetic field has a sin [φ] dependence on the current angular position, the current (coil) is arranged as close to the x axis as possible (that is, at a position of 90 degrees from the z axis). Is efficient.

[N = 2 secondary]
FIG. 4 is an explanatory diagram showing the angular position of the line current at which the absolute value of the magnetic field of the n = second order component of the multipolar developed magnetic field becomes the maximum value. Since the magnetic field of the n = second order component has sin [3φ] dependence on the angular position of the current, the sign of the intensity is +1 at a position of 30 degrees from the z-axis, 0 at a position of 60 degrees, It changes to -1 at a position of 90 degrees (shown in FIG. 4 is an angular position at which the absolute value of sin [3φ] has a maximum value when −π / 2 ≦ φ ≦ π / 2). In order to efficiently generate the n = 0th order magnetic field, it is necessary to draw a current to the side close to 90 degrees (x-axis side). Therefore, in order not to generate the hexapolar magnetic field of n = 2, 60 degrees It is a reasonable arrangement method to arrange the lines (balance the magnetomotive force sources). The return current has a smaller contribution in inverse proportion to the n + 1 = 3rd power of the distance f, and therefore, the contribution of the inner current near the magnet center is large. Since the n = second order magnetic field has only a 60-degree line where the sign of the magnetic field changes, if only a positive current is arranged as a magnetomotive force source (not considering the pair of return currents), it is large. The magnetomotive force source is divided into two by this 60-degree line.

[N = 4, 6th order]
FIG. 5 is an explanatory diagram showing the angular position of the line current at which the absolute value of the magnetic field of the n = 4th order component of the multipolar developed magnetic field becomes the maximum value. Since the magnetic field of the n = 4th order component has a sin [5φ] dependence on the current angular position, the intensity sign is +1 at a position of 18 degrees from the z axis, 0 at a position of 36 degrees, It changes to −1 at 54 °, +0 at 72 °, and 1 at 90 ° (in FIG. 5, the absolute value of sin [5φ] is the maximum when −π / 2 ≦ φ ≦ π / 2. Shows the angular position taken).

FIG. 6 is an explanatory diagram showing the angular position of the line current at which the absolute value of the magnetic field of the n = 6th order component of the multipolar developed magnetic field becomes the maximum value. Since the magnetic field of the n = 6th order component has a sin [7φ] dependency on the angular position of the current, the intensity sign is +1, 25.7 degrees at a position of 12.9 degrees from the z-axis. 0 at the position, -1 at the position of 38.6 degrees, +0 at the position of 51.4 degrees, +1 at the position of 64.3 degrees, 0 at the position of 77.1 degrees, and 1 at the position of 90 degrees. (FIG. 6 shows the angular position at which the absolute value of sin [7φ] takes the maximum value when −π / 2 ≦ φ ≦ π / 2). Since the arrangement of rough magnetomotive force sources is determined in the n = 0th order and the second order, the region in which the magnetic fields of n = 4 and 6 that can be arranged under the influence thereof can be adjusted is limited.

Arranging the coil in a region where the amount of n = 4th and 6th-order multipole magnetic fields is large (a region where the sensitivity is high) is not a good solution because the absolute amount of multipole magnetic fields to be canceled increases. Therefore, most of the first flat coil 1a is disposed in a region having an angle larger than 64.3 degrees (for example, 80% or more), and the third flat coil 3a has 38.6 degrees. Most of them (for example, 80% or more) are arranged in the range of 54 degrees to 54 degrees. Depending on the required specifications of the magnetic field, it is necessary to further arrange an electric current in the high angle region. In this case, the fourth flat coil 4a is arranged to adjust the n = 4, 6th order higher-order multipolar magnetic field. Is done.

[N> = 8th order]
Since n> = 8th order high-order multipole magnetic fields increase the angular position where the sign changes, in order to completely cancel these multipole developed magnetic fields, the coil is divided into small areas and the coils are changed into areas where the sign changes. It is necessary to arrange. However, in the magnet of the present embodiment, priority is given to minimizing the number of discrete coils, so that the strength is not increased by adjusting the cross-sectional shape of the coils (as in the example shown in FIG. 9, 8 Next, for the 10th and 12th orders, 7.0 gauss, 7.2 gauss and 5.3 gauss or less, respectively).

FIG. 7 is an explanatory diagram for explaining the correspondence between the coil arrangement in the cross section and the region in which the n = 4th and 6th order multipolar magnetic fields are generated. As described above, when the magnet is configured with 6 to 8 coils (3 to 4 pairs), φ = 60 to cancel the hexapole magnetic field (n = 2) as shown in FIG. The magnetomotive force source is arranged so as to be roughly divided into two in the degree line, and the generation amount of 10 poles (n = 4) and 14 poles magnetic field (n = 6) is large φ = 38.6 degrees, 54 degrees Therefore, it is necessary to arrange the magnetomotive force source so that the magnetomotive force source does not concentrate at the angular position of 64.3 degrees.

(Magnetic field adjustment by two power source excitation)
FIG. 8 is a conceptual diagram showing a coil combination when the magnet of this embodiment is operated with two power sources. In the case of a magnet composed of discrete coils, it may be assumed that the manufacturing accuracy and position accuracy of the winding becomes stricter than a magnet with a wide current distribution such as a cosine theta winding. When a magnet is manufactured, the magnetic field is always deviated from the design due to manufacturing errors, and means for correcting this deviation is required. In particular, a low-order hexapole magnetic field has a large error magnetic field in principle, and distorts the magnetic field with respect to a wide region of the beam passage region. Therefore, magnetic field correction for this component is essential.

In the magnet according to the present embodiment, by exciting the coils constituting the magnet into two groups, it is possible to correct the hexapole magnetic field without mounting a large correction coil. Although the two coil groups are designed to be excited with the same current, they are operated with slightly different current values according to the actual situation of the actual machine (so as to cancel the hexapole magnetic field caused by manufacturing errors). Since it has two degrees of freedom by operating with two power sources, it is possible to freely change the strength of the hexapole magnetic field while keeping the strength of the deflection magnetic field constant.

The hexapole magnetic field (n = 2) changes the sign of the magnetic field generated when the current crosses the 60-degree line from the z-axis, so the coils are grouped by this 60-degree line (FIG. 7), and the excitation current It is possible to generate a hexapole magnetic field efficiently (with a small current difference) by making a difference between the two. In addition, the multi-polar magnetic field higher than the hexapolar magnetic field has a small influence in principle, and the influence is small because the magnetic field is canceled in each coil group.

Moreover, in the magnet of the system of the present embodiment, a longer magnet length is advantageous for producing a uniform magnetic field. Therefore, the magnet length tends to be long, the accumulated energy of the magnet is increased, and it becomes difficult to protect the magnet at the time of quenching. Magnet protection is facilitated by dividing the power supply circuit. In addition, since the magnetic coil arrangement of the present embodiment makes the magnetic coupling between the two power supply circuits extremely small, the circuit with two power supplies can be regarded as almost independent, and energy exchange by magnetic coupling in the magnet protection process One of the advantages is that there is no need to consider.

(Other effects)
The magnet of this embodiment can be easily manufactured by adopting a flat coil, and it is possible to reduce a leakage magnetic field outside the magnet by using a return current that is arranged outside as a result. . Due to this effect, it is possible to greatly reduce the iron yoke necessary for reducing the leakage magnetic field, and therefore it is possible to reduce the load on the support structure and the rotating structure for the rotating gantry.

(Use of the magnet of the present invention and / or this embodiment)
The superconducting magnet for beam transportation according to the present invention and / or the present embodiment can be applied to a beam transportation application that can be considered normally, but is characterized by being light in weight. Therefore, the weight is a particularly important factor such as a rotating gantry for a particle beam therapy system. It is most suitable for the device to become. In addition, the superconducting magnet for beam transportation according to the present invention and / or the present embodiment can be applied to all apparatuses and systems involving beam transportation such as a research accelerator and a medical accelerator. Since it is characterized by being lightweight, it is particularly suitable for a device in which weight is an important factor, such as a rotating gantry for a particle beam therapy system.

(Appendix)
In addition, this invention is not limited to an above-described Example, Various modifications are included. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Further, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Further, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.
Further, the control lines and information lines indicate what is considered necessary for the explanation, and not all the control lines and information lines on the product are necessarily shown. Actually, it may be considered that almost all the components are connected to each other.

1a, 1b: first flat coils 2a, 2b: second flat coils 3a, 3b: third flat coils 4a, 4b: fourth flat coil 5: beam passage region

Claims (14)

A superconducting magnet device for beam transport,
In a coordinate system in which the magnetic field generation direction is the z-axis positive direction and the flight path of the beam is on the xy plane, the beam passes through the beam passing area symmetrical with respect to the xy plane, and the arc has a predetermined radius of curvature. The beam passing region is sandwiched between the xy plane at the upper side in the z direction and the xy plane at the lower side of the beam passing region, or the maximum position of the beam passing region in the z direction and the minimum position x−. When the region sandwiched by the y plane is a low angle region, and the region outside the z axis direction from the low angle region is a high angle region,
At least one pair of first flat coils arranged symmetrically with respect to an xy plane inside the arc of the beam passing region and in the low angle region;
Zy at a coordinate origin that is arranged outside the arc of the beam passing region and symmetrically with respect to the xy plane in the low angle region and that represents the center of the beam passing region in the coil cross section of the zx plane. to the plane, it is disposed on the first flat coil and symmetrical or nearly symmetrical, the direction of current and the first flat coil and the left and right opposite, to generate a magnetic field in the same direction as said first flat coil And at least one pair of second flat coils,
At least one pair of third flat coils arranged symmetrically with respect to the xy plane in the z direction outside the beam passage region and in the high angle region;
With
The arrangement position of the first flat coil is between an angle of 0 degrees to 30 degrees formed from the x-axis direction to the z-axis direction when viewed from the coordinate origin,
The arrangement position of the second flat coil is between an angle of 0 degrees to 30 degrees formed from the x-axis minus direction to the z-axis direction when viewed from the coordinate origin,
The third flat coil is disposed at an angle of 30 to 63 degrees from the x-axis direction to the z-axis direction when viewed from the coordinate origin, and from the x-axis minus direction to the z-axis when viewed from the coordinate origin. The angle between the direction is between 30 degrees and 63 degrees,
A superconducting magnet device for transporting a beam. In the superconducting magnet apparatus for beam transport according to claim 1,
Two or more pairs of the third flat coils are provided, and at least one of the two or more pairs of the third flat coils has an angle of 30 degrees to 63 degrees formed from the x-axis direction to the z-axis direction when viewed from the coordinate origin. A superconducting magnet apparatus for transporting a beam, characterized in that the angle is between 30 degrees and 63 degrees between the x axis minus direction and the z axis direction when viewed from the coordinate origin. In the superconducting magnet apparatus for beam transport according to claim 1,
In order to adjust a high-order multipolar magnetic field in the high-angle region where the third flat coil is disposed, the x-axis direction is changed from the x-axis direction to the z-axis direction as viewed from the coordinate origin, rather than the 63-degree line. A superconducting magnet device for beam transport, further comprising a pair of fourth flat coils arranged symmetrically with respect to the xy plane on the high angle side of the angle. In the superconducting magnet apparatus for beam transport according to claim 1,
More than 80% or most of the coil cross-sectional areas of the first flat coil, the second flat coil, and the third flat coil in the first quadrant of the zx plane by the coordinate origin are the coordinates. Superconductivity for beam transport, characterized in that it is arranged in a region excluding a region of 18 ° to 38.6 ° and a region of 54 ° to 64.3 ° in the x direction as viewed from the z-axis at the origin. Magnet device. In the superconducting magnet apparatus for beam transport according to claim 1,
The first flat coil, the second flat coil, and the third flat coil are coils in which wires are wound substantially parallel to the xy plane so as to generate a magnetic field along the z-axis direction. The cross-sectional shape of the coil winding has a certain shape along the direction of the winding, and the first flat coil and the second flat coil when the xy plane is a horizontal plane. And the third flat coil is a coil having a flat or planar shape that can be placed in parallel with the horizontal plane, and a superconducting magnet device for beam transportation. In the superconducting magnet device for beam transportation according to claim 5 ,
A superconducting magnet apparatus for beam transportation, wherein the coil winding has a rectangular cross-sectional shape along a winding direction. In the superconducting magnet apparatus for beam transport according to claim 1,
A first excitation circuit for the third flat coil;
A superconducting magnet apparatus for beam transportation, comprising: a first excitation coil for the first flat coil and a second excitation circuit for the second flat coil. In the superconducting magnet apparatus for beam transport according to claim 7 ,
The superconducting magnet apparatus for beam transport, wherein the first excitation circuit and the second excitation circuit supply different current values so as to cancel at least a hexapole magnetic field. In the superconducting magnet apparatus for beam transport according to claim 1,
A superconducting magnet apparatus for beam transport, wherein a leakage magnetic field at a position 3 m in the vertical direction along the z axis from the coordinate origin is less than 20 Gauss. In the superconducting magnet apparatus for beam transport according to claim 1,
The strength of the leakage magnetic field component that is proportional to the −2th power of the vertical distance along the z-axis from the coordinate origin is set to 2 gauss or less at a position of 3 m in the vertical direction along the z-axis from the coordinate origin. A superconducting magnet apparatus for beam transport characterized in that the intensity of a leakage magnetic field component proportional to the fourth power is 20 gauss or less at a position 3 m in the vertical direction along the z axis from the coordinate origin.   A beam transport system comprising the superconducting magnet device for beam transport according to claim 1.   A particle beam therapy system comprising the superconducting magnet device for beam transport according to claim 1. A superconducting magnet arrangement method for beam transportation,
In a coordinate system in which the magnetic field generation direction is the z-axis positive direction and the flight path of the beam is on the xy plane, the beam passes through the beam passing area symmetrical with respect to the xy plane, and the arc has a predetermined radius of curvature. The beam passing region is sandwiched between the xy plane at the upper side in the z direction and the xy plane at the lower side of the beam passing region, or the maximum position of the beam passing region in the z direction and the minimum position x−. When the region sandwiched by the y plane is a low angle region, and the region outside the z axis direction from the low angle region is a high angle region,
At least one pair of first flat coils are arranged symmetrically with respect to the xy plane inside the arc of the beam passing region and in the low angle region;
At least one pair of second flat coils is arranged outside the arc of the beam passing region and symmetrically with respect to the xy plane in the low angle region, and the beam passing through the coil cross section in the zx plane. relative z-y plane at the coordinate origin which represents the center of the area, the first place to the flat coil and the symmetrical or substantially symmetrical to the direction of current and the first flat coil and the left and right opposite, the first Generate a magnetic field in the same direction as the flat coil,
At least one pair of third flat coils are arranged outside the beam passing region in the z direction and symmetrically with respect to the xy plane in the high angle region;
The arrangement position of the first flat coil is between an angle of 0 degrees to 30 degrees formed from the x-axis direction to the z-axis direction when viewed from the coordinate origin,
The arrangement position of the second flat coil is between an angle of 0 degrees to 30 degrees formed from the x-axis minus direction to the z-axis direction when viewed from the coordinate origin,
The third flat coil is disposed at an angle of 30 to 63 degrees from the x-axis direction to the z-axis direction when viewed from the coordinate origin, and from the x-axis minus direction to the z-axis when viewed from the coordinate origin. The angle between the direction is between 30 degrees and 63 degrees,
A superconducting magnet arrangement method for beam transport, characterized in that: In the superconducting magnet arrangement method for beam transportation according to claim 13 ,
With the arrangement of the first flat coil, the second flat coil, and the third flat coil, the development order n representing the magnetic field in the beam passage region is set to an odd-order multipolar magnetic field, and n is an even-order. The n = 0 dipole magnetic field, the n = 2 hexapole magnetic field, the n = 4 10 pole magnetic field, and the n = 6 14 pole magnetic field are canceled. Conductive magnet arrangement method.

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