JP2020141944A - Scanning electromagnet - Google Patents

Abstract

A scanning electromagnet capable of reducing a gap between magnetic pole portions is provided. A vacuum structure (100) is configured to place gap forming surfaces (70a, 70a) in a vacuum. In this case, the gap GP itself formed between the gap forming surfaces 70a, 70a becomes a vacuum space. Therefore, since it is not necessary to dispose the vacuum forming duct 200 (see FIG. 6) in the gap GP, the gap GP can be made smaller. [Selection drawing] Fig. 5

Description

The present invention relates to a scanning electromagnet.

Conventionally, a charged particle beam therapy device that treats an affected part of a patient by irradiating it with a charged particle beam is known. In the charged particle beam therapy device, the charged particle beam emitted from the accelerator is irradiated to the affected area while being scanned by the scanning electromagnet. As a scanning electromagnet used in such a charged particle beam therapy apparatus, the one described in Patent Document 1 is known. In this scanning electromagnet, a duct is arranged in a gap formed between the magnetic poles so that the charged particle beam does not diverge, and the charged particle beam passes through the duct.

Japanese Unexamined Patent Publication No. 2012-254138

Here, when the gap between the magnetic poles is large, various problems occur such that a large magnetomotive force is required to output the same magnetic flux density and a large power source is required. Therefore, it is required to reduce the gap between the magnetic poles. On the other hand, in the scanning electromagnet as described above, since the duct is arranged in the gap between the magnetic poles, there is a problem that the gap between the magnetic poles cannot be reduced.

Therefore, an object of the present invention is to provide a scanning electromagnet capable of reducing the gap between the magnetic pole portions.

In order to solve the above problems, the scanning electromagnet according to the present invention is a scanning electromagnet that scans a charged particle beam in a charged particle beam therapy apparatus, and is wound around a reference axis and in an axial direction in which the reference axis extends. A vacuum formed by a pair of coils facing each other and a magnetic member, supporting the pair of coils on the inner peripheral side, and having a pair of magnetic poles facing each other in the axial direction and a vacuum at which a charged particle beam passes through. Each of the pair of magnetic poles has a structure and a gap forming surface for forming a gap through which a charged particle beam passes by facing each other in the axial direction, and the vacuum structure has a pair of gap forming surfaces. Is configured to be placed in a vacuum.

In the scanning electromagnet, each of the pair of magnetic pole portions has a gap forming surface that forms a gap through which charged particle beams pass by facing each other at a distance from each other in the axial direction. On the other hand, the vacuum structure is configured to arrange a pair of gap forming surfaces in a vacuum. In this case, the gap itself formed between the pair of gap forming surfaces becomes a vacuum space. Therefore, it is not necessary to arrange a duct or the like for forming a vacuum in the gap, so that the gap can be reduced.

The vacuum structure may be configured to place a pair of coils in a vacuum. In this case, since it is not necessary to change the structure around the coil, the winding mode when winding the coil around the magnetic pole portion can be the same as before.

According to the present invention, it is possible to provide a scanning electromagnet capable of reducing the gap between the magnetic pole portions.

It is a schematic block diagram which shows the charged particle beam therapy apparatus which adopts the scanning electromagnet which concerns on one Embodiment of this invention. It is a schematic block diagram near the irradiation part of the charged particle beam therapy apparatus of FIG. It is a figure which shows the layer set for a tumor. It is a perspective view of the scanning electromagnet which concerns on embodiment of this invention. 5 (a) is a schematic cross-sectional view taken along the line Va-Va shown in FIG. 4, and FIG. 5 (b) is a schematic cross-sectional view taken along the line Vb-Vb shown in FIG. It is the schematic sectional drawing which shows the scanning electromagnet which concerns on a comparative example. It is the schematic sectional drawing which shows the scanning electromagnet which concerns on the modification.

Hereinafter, the scanning electromagnet according to the embodiment of the present invention will be described with reference to the accompanying drawings. In the description of the drawings, the same elements are designated by the same reference numerals, and duplicate description will be omitted.

FIG. 1 is a schematic configuration diagram showing a charged particle beam therapy device 1 in which a scanning electromagnet according to an embodiment of the present invention is adopted. The charged particle beam therapy device 1 is a device used for cancer treatment or the like by radiotherapy. The charged particle beam therapy device 1 is emitted from an accelerator 3 that accelerates a charged particle generated by an ion source device and emits it as a charged particle beam, an irradiation unit 2 that irradiates an irradiated object with the charged particle beam, and an accelerator 3. A beam transport line 21 for transporting the charged particle beam to the irradiation unit 2 is provided. The irradiation unit 2 is attached to a rotating gantry 5 provided so as to surround the treatment table 4. The irradiation unit 2 is made rotatable around the treatment table 4 by the rotating gantry 5.

FIG. 2 is a schematic configuration diagram of the vicinity of the irradiation portion of the charged particle beam therapy apparatus of FIG. In the following description, the terms "X-axis direction", "Y-axis direction", and "Z-axis direction" will be used. The "Z-axis direction" is a direction in which the base axis AX of the charged particle beam B extends, and is a depth direction of irradiation of the charged particle beam B. The "base axis AX" is the irradiation axis of the charged particle beam B when it is not deflected by the scanning electromagnet 50 described later. FIG. 2 shows how the charged particle beam B is irradiated along the base axis AX. The "X-axis direction" is one direction in a plane orthogonal to the Z-axis direction. The "Y-axis direction" is a direction orthogonal to the X-axis direction in a plane orthogonal to the Z-axis direction.

First, with reference to FIG. 2, a schematic configuration of the charged particle beam therapy apparatus 1 according to the present embodiment will be described. The charged particle beam therapy device 1 is an irradiation device according to a scanning method. The scanning method is not particularly limited, and line scanning, raster scanning, spot scanning, or the like may be adopted. As shown in FIG. 2, the charged particle beam therapy device 1 includes an accelerator 3, an irradiation unit 2, a beam transport line 21, and a control unit 7.

The accelerator 3 is a device that accelerates a charged particle and emits a charged particle beam B having a preset energy. Examples of the accelerator 3 include a cyclotron, a synchrocyclotron, and a linac. When a cyclotron that emits a charged particle beam B having a predetermined energy is adopted as the accelerator 3, the energy of the charged particle beam sent to the irradiation unit 2 can be obtained by adopting the energy adjusting unit 20 (see FIG. 1). It is possible to adjust (decrease). The accelerator 3 is connected to the control unit 7, and the supplied current is controlled. The charged particle beam B generated by the accelerator 3 is transported to the irradiation unit 2 by the beam transport line 21. The beam transport line 21 connects the accelerator 3, the energy adjusting unit 20, and the irradiation unit 2, and transports the charged particle beam emitted from the accelerator 3 to the irradiation unit 2.

The irradiation unit 2 irradiates the tumor (irradiated body) 14 in the body of the patient 15 with the charged particle beam B. The charged particle beam B is a high-speed acceleration of a charged particle, and examples thereof include a proton beam, a heavy particle (heavy ion) beam, and an electron beam. Specifically, the irradiation unit 2 is a device that irradiates the tumor 14 with a charged particle beam B emitted from an accelerator 3 that accelerates charged particles generated by an ion source (not shown) and transported by a beam transport line 21. .. The irradiation unit 2 includes a scanning electromagnet 50, a quadrupole electromagnet 8, a profile monitor 11, a dose monitor 12, position monitors 13a and 13b, a collimator 40, and a degrader 30. The scanning electromagnet 50, each monitor 11, 12, 13a, 13b, the quadrupole electromagnet 8, and the degrader 30 are housed in an irradiation nozzle 9 as an accommodating body. In this way, the irradiation unit 2 is configured by accommodating each main component in the irradiation nozzle 9. The quadrupole electromagnet 8, the profile monitor 11, the dose monitor 12, the position monitors 13a and 13b, and the degrader 30 may be omitted.

As the scanning electromagnet 50, an X-axis direction scanning electromagnet 50A and a Y-axis direction scanning electromagnet 50B are used. The X-axis direction scanning electromagnet 50A and the Y-axis direction scanning electromagnet 50B are each composed of a pair of electromagnets, change the magnetic field between the pair of electromagnets according to the current supplied from the control unit 7, and pass between the electromagnets. The charged particle beam B is scanned. The X-axis direction scanning electromagnet 50A scans the charged particle beam B in the X-axis direction, and the Y-axis direction scanning electromagnet 50B scans the charged particle beam B in the Y-axis direction. These scanning electromagnets 50 are arranged on the base axis AX in this order on the downstream side of the charged particle beam B with respect to the accelerator 3. The scanning electromagnet 50 scans the charged particle beam B so that the charged particle beam B is irradiated by the scanning path planned in advance by the treatment planning device 90. The detailed structure of the scanning electromagnet 50 will be described later.

The quadrupole electromagnet 8 includes an X-axis direction quadrupole electromagnet 8a and a Y-axis direction quadrupole electromagnet 8b. The X-axis direction quadrupole electromagnet 8a and the Y-axis direction quadrupole electromagnet 8b narrow and converge the charged particle beam B according to the current supplied from the control unit 7. The X-axis quadrupole electromagnet 8a converges the charged particle beam B in the X-axis direction, and the Y-axis quadrupole electromagnet 8b converges the charged particle beam B in the Y-axis direction. The beam size of the charged particle beam B can be changed by changing the current supplied to the quadrupole electromagnet 8 to change the aperture amount (convergence amount). The quadrupole electromagnet 8 is arranged on the base axis AX between the accelerator 3 and the scanning electromagnet 50 in this order. The beam size is the size of the charged particle beam B in the XY plane. The beam shape is the shape of the charged particle beam B in the XY plane.

The profile monitor 11 detects the beam shape and position of the charged particle beam B for alignment at the time of initial setting. The profile monitor 11 is arranged on the base axis AX between the quadrupole electromagnet 8 and the scanning electromagnet 50. The dose monitor 12 detects the dose of the charged particle beam B. The dose monitor 12 is arranged on the base axis AX and downstream of the scanning electromagnet 50. The position monitors 13a and 13b detect and monitor the beam shape and position of the charged particle beam B. The position monitors 13a and 13b are arranged on the base axis AX and on the downstream side of the charged particle beam B with respect to the dose monitor 12. Each of the monitors 11, 12, 13a and 13b outputs the detected detection result to the control unit 7.

The degrader 30 reduces the energy of the passing charged particle beam B to fine-tune the energy of the charged particle beam B. In the present embodiment, the degrader 30 is provided at the tip 9a of the irradiation nozzle 9. The tip 9a of the irradiation nozzle 9 is the downstream end of the charged particle beam B.

The collimator 40 is a member provided at least on the downstream side of the charged particle beam B with respect to the scanning electromagnet 50, and shields a part of the charged particle beam B and allows a part of the charged particle beam B to pass through. Here, the collimator 40 is provided on the downstream side of the position monitors 13a and 13b. The collimator 40 is connected to a collimator drive unit 41 that moves the collimator 40.

The control unit 7 is composed of, for example, a CPU, a ROM, a RAM, and the like. The control unit 7 controls the accelerator 3, the scanning electromagnet 50, the quadrupole electromagnet 8, and the collimator drive unit 51 based on the detection results output from the monitors 11, 12, 13a, and 13b.

Further, the control unit 7 of the charged particle beam therapy device 1 is connected to a treatment planning device 90 that performs a treatment plan for the charged particle beam therapy. The treatment planning device 90 measures the tumor 14 of the patient 15 by CT or the like before the treatment, and plans the dose distribution (the dose distribution of the charged particle beam to be irradiated) at each position of the tumor 14. Specifically, the treatment planning device 90 creates a treatment planning map for the tumor 14. The treatment planning device 90 transmits the created treatment planning map to the control unit 7. In the treatment planning map created by the treatment planning apparatus 90, what kind of scanning path the charged particle beam B draws is planned.

When irradiating a charged particle beam by the scanning method, the tumor 14 is virtually divided into a plurality of layers in the Z-axis direction, and the charged particle beam is scanned in one layer so as to follow the scanning path defined in the treatment plan. Irradiate. Then, after the irradiation of the charged particle beam in the one layer is completed, the irradiation of the charged particle beam B in the adjacent next layer is performed.

When the charged particle beam therapy device 1 shown in FIG. 2 irradiates the charged particle beam B by the scanning method, the quadrupole electromagnet 8 is set to the operating state (ON) so that the passing charged particle beam B converges.

Subsequently, the charged particle beam B is emitted from the accelerator 3. The emitted charged particle beam B is scanned so as to follow the scanning path defined in the treatment plan under the control of the scanning electromagnet 50. As a result, the charged particle beam B is irradiated to the tumor 14 while being scanned within the irradiation range in one layer set in the Z-axis direction. When the irradiation of one layer is completed, the charged particle beam B is irradiated to the next layer.

The charged particle beam irradiation image of the scanning electromagnet 50 under the control of the control unit 7 will be described with reference to FIGS. 3A and 3B. FIG. 3 (a) shows an irradiated body virtually sliced into a plurality of layers in the depth direction, and FIG. 3 (b) shows a scanned image of a charged particle beam in one layer viewed from the depth direction. , Each is shown.

As shown in FIG. 3A, the irradiated body is virtually sliced into a plurality of layers in the irradiation depth direction, and in this example, from a deep layer (the flight of the charged particle beam B is long). In order, the layers L ₁ , the layer L ₂ , ... the layer L _n-1 , the layer L _{n 1} , the layer L _{n + 1} , ... the layer L _N-1 , and the layers L _N and N are virtually sliced. Further, as shown in FIG. 3 (b), the charged particle beam B while drawing a beam trajectory along the scan path TL, the scan path TL layer L _n for continuous illumination (line scanning or raster scanning) along which are successively irradiated, in the case of spot scanning is irradiated to a plurality of irradiation spots of the layer L _n. The charged particle beam B is irradiated along the scanning path TL1 extending in the X-axis direction, slightly shifted in the Y-axis direction along the scanning path TL2, and irradiated along the adjacent scanning path TL1. In this way, the charged particle beam B emitted from the irradiation unit 2 controlled by the control unit 7 moves on the scanning path TL.

Next, the configuration of the scanning electromagnet 50 will be described in detail with reference to FIGS. 4 and 5. FIG. 4 is a perspective view of the scanning electromagnet 50 according to the embodiment of the present invention. In FIG. 4, a part of the structure is broken to show the internal structure. FIG. 5A is a schematic cross-sectional view taken along the Va-Va line shown in FIG. FIG. 5B is a schematic cross-sectional view taken along the line Vb-Vb shown in FIG. However, FIG. 5 shows the structure deformed as compared with FIG. 4 in order to understand the structure.

The reference axis CL for winding the coils 60A and 60B is set, and the direction in which the reference axis CL extends is defined as the "axial direction D1". Further, among the directions orthogonal to the axial direction D1, the direction orthogonal to the basic axis AX of the charged particle beam B is defined as the "width direction D2". Further, the direction in which the base axis AX of the charged particle beam B extends is defined as the "length direction D3". Further, although the terms "inside" and "outside" may be used for each direction, the side near the center position of the scanning electromagnet 50 in each direction is "inside", and the side far from the center position is "outside". Shall be.

As shown in FIGS. 4 and 5, the scanning electromagnet 50 includes coils 60A and 60B, magnetic pole portions 70A and 70B, a yoke 80, and a vacuum structure 100.

The coils 60A and 60B are configured by winding the coil conductor around the reference axis CL. In this embodiment, the coils 60A and 60B are wound in a rectangular ring shape (see FIG. 5). The coils 60A and 60B are arranged so as to face each other and are separated from each other in the axial direction D1. Further, the coils 60A and 60B are arranged so as to overlap each other when viewed from the axial direction D1. The coil 60A has a pair of side portions 61, 61 extending in the length direction D3 and a pair of side portions 62, 62 extending in the width direction D2 (see FIG. 4). The coil 60B also has a pair of side portions 61, 61 and a pair of side portions 62, 62.

The magnetic pole portions 70A and 70B are portions formed by a magnetic member and support the coils 60A and 60B on the inner peripheral side, respectively. The magnetic pole portions 70A and 70B are arranged so as to face each other and are separated from each other in the axial direction D1. The magnetic pole portions 70A and 70B each have gap forming surfaces 70a and 70a forming a gap GP through which the charged particle beam B is passed by facing each other in the axial direction D1 so as to be separated from each other. The gap forming surfaces 70a and 70a are planes parallel to the width direction D2 and the length direction D3. The gap forming surfaces 70a and 70a have a shape corresponding to the shape on the inner peripheral side of the coils 60A and 60B when viewed from the axial direction D1.

The yoke 80 is formed of a magnetic member, and is formed so as to surround the coils 60A and 60B from the outer peripheral side when viewed from the length direction D3 (see FIG. 5A). The yoke 80 has wall portions 81 and 81 extending in the axial direction D1 outside the width direction D2 with respect to the coils 60A and 60B, and wall portions 82 and 82 extending in the width direction D2 outside the axial direction D1 with respect to the coils 60A and 60B. Has. In FIG. 5A, since the yoke 80 and the magnetic pole portions 70A and 70B are made of magnetic members, they have the same hatching. This magnetic member may be configured as a separate piece by setting a boundary surface at an arbitrary position for the sake of assembly and the like.

The yoke 80 is formed to have substantially the same length as the magnetic pole portions 70A and 70B in the length direction D3. Therefore, the sides 62 and 62 of the coils 60A and 60B are exposed from the yoke 80 on one side of the length direction D3, and the sides 62 and 62 of the coils 60A and 60B are exposed from the yoke 80 on the other side of the length direction D3. To do.

The vacuum structure 100 is a structure for setting the passing position of the charged particle beam B to a vacuum. In the present embodiment, the vacuum structure 100 is configured to arrange the gap forming surfaces 70a and 70a in a vacuum. Further, the vacuum structure 100 is configured to arrange the coils 60A and 60B in a vacuum. The vacuum structure 100 is configured to arrange the gap forming surfaces 71A and 71B and the coils 60A and 60B in a vacuum by combining the vacuum container 110 and the yoke 80.

Specifically, the vacuum structure 100 is configured by attaching the vacuum containers 110A and 110B to the yoke 80. The vacuum vessel 110A has wall portions 111, 111, 112, 112 surrounding the coils 60A and 60B from all sides when viewed from the length direction D3, and wall portions 113 facing the yoke 80 and the length direction D3. .. The wall portions 111 and 111 are arranged outside the coils 60A and 60B in the width direction D2 and extend in the axial direction D1. The wall portions 112 and 112 are arranged outside the coils 60A and 60B in the axial direction D1 and extend in the width direction D2. The wall portions 111, 111, 112, 112 are connected so that there is no gap between the end portions. The wall portion 113 closes the opening formed by the outer end portion of each wall portion 111, 111, 112, 112 in the length direction D3.

The vacuum vessel 110A is fixed to the one end surface 80a of the yoke 80 in the length direction D3 at the inner end of each wall portion 111, 111, 112, 112 in the length direction D3. The vacuum container 110A is fixed at the flange portion 114 in a state where airtightness is sufficiently secured with respect to the end face 80a. The wall portion 113 is formed with an opening 113a at a position through which the charged particle beam B passes. The opening 113a is provided with a film or the like that allows the passage of the charged particle beam B while ensuring the vacuum inside the vacuum container 110A.

The vacuum vessel 110B has the same configuration as the vacuum vessel 110A except that the orientation in the length direction D3 is different. The vacuum vessel 110B is fixed to the other end surface 80a of the yoke 80 in the length direction D3. The space inside the vacuum containers 110A and 110B is kept in a vacuum by a vacuum pump or the like (not shown).

From the above, as shown in FIG. 5B, when viewed from the length direction D3, the entire gap forming surfaces 70a, 70a, the gap GP, and the coils 60A, 60B are the wall portions 111, 111, 112, 112 and Surrounded by the yoke 80 all around. Further, the end portion of the vacuum structure 100 is sealed with wall portions 113 and 113 on both sides in the length direction D3. Therefore, in the vacuum structure 100, the entire gap forming surfaces 70a and 70a, the gap GP, and the coils 60A and 60B can be arranged in a vacuum.

Next, the action / effect of the scanning electromagnet 50 according to the present embodiment will be described.

First, the scanning electromagnet 250 according to the comparative example will be described with reference to FIG. The scanning electromagnet 250 has a duct 200 for forming a vacuum in the gap GP between the gap forming surfaces 70a and 70a. In such a configuration, even if the gap GP is reduced, the gap forming surfaces 70a and 70a interfere with the duct 200. Further, when a metal is placed in an electromagnet that is excited at a high cycle such as the scanning electromagnet 250, there arises a problem that heat generation is increased due to the effect of eddy current. Therefore, as the material of the duct 200, plastic or ceramic is used. However, since these materials have lower strength than metal, it is necessary to increase the thickness of the wall of the duct 200. This makes it necessary to further increase the gap GP. From the above, the scanning electromagnet 250 according to the comparative example has a problem that the gap GP cannot be reduced.

On the other hand, in the scanning electromagnet 50 according to the present embodiment, the magnetic pole portions 70A and 70B are separated from each other in the axial direction D1 and face each other to form a gap GP through which the charged particle beam B is passed. Each has. On the other hand, the vacuum structure 100 is configured to arrange the gap forming surfaces 70a and 70a in a vacuum. In this case, the gap GP itself formed between the gap forming surfaces 70a and 70a becomes a vacuum space. Therefore, since it is not necessary to arrange the vacuum forming duct 200 (see FIG. 6) in the gap GP, the gap GP can be reduced.

When the same magnetic flux density is output, if the gap GP is small, the output can be obtained with a small magnetomotive force. Therefore, by adopting the structure of the present embodiment and reducing the gap GP, the power supply can be made compact. Further, when the required flatness of the magnetic flux density is obtained, the required flat region can be secured even if the magnetic pole width is reduced because the gap GP is small. Therefore, the size of the scanning electromagnet 50 as a whole can be reduced. Further, since the magnetomotive force can be reduced and the magnetic pole area can be reduced, the inductance can be reduced. Therefore, it is possible to speed up the response.

The vacuum structure 100 is configured to arrange the coils 60A and 60B in a vacuum. In this case, unlike the structures shown in FIGS. 7B and 7C described later, it is not necessary to change the structure around the coils 60A and 60B. Therefore, when the coils 60A and 60B are wound around the magnetic poles 70A and 70B. The winding mode of is the same as before.

The present invention is not limited to the above-described embodiment.

The above-mentioned vacuum structure 100 is only an example, and any structure may be adopted as long as the gap forming surfaces 70a and 70a can be arranged in a vacuum.

For example, the scanning electromagnet 350 as shown in FIG. 7A may be adopted. The vacuum structure 300 of the scanning electromagnet 350 includes coils 60A and 60B, magnetic poles 70A and 70B, and a vacuum vessel 310 capable of accommodating the entire yoke 80. As a result, the coils 60A and 60B and the gap forming surfaces 70a and 70a can be arranged in a vacuum.

Further, a scanning electromagnet 450 as shown in FIG. 7B may be adopted. In the vacuum structure 400 of the scanning electromagnet 450, the gap forming surfaces 70a and 70a are arranged in a vacuum by evacuating only the vicinity of the magnetic pole portions 70A and 70B. The vacuum structure 400 is arranged on the inner peripheral side of the coils 60A and 60B, and has a wall member 410 that surrounds all four side surfaces of the magnetic pole portions 70A and 70B. The wall member 410 extends upward while surrounding the four side surfaces of the magnetic pole portion 70A, passes around the gap GP, and surrounds the four side surfaces of the magnetic pole portion 70B. The wall member 410 has a pair of wall portions facing the width direction D2 and a pair of wall portions (not shown) facing the length direction D3. The wall portion facing the length direction D3 is formed with an opening through which the charged particle beam B passes while the internal vacuum is secured. Further, the slight gap between the wall member 410 and the magnetic pole portions 70A and 70B is filled with a vacuum sealing material or the like.

Further, a scanning electromagnet 550 as shown in FIG. 7C may be adopted. In the vacuum structure 500 of the scanning electromagnet 550, the magnetic pole portions 70A and 70B are separated from the yoke 80 and housed in the vacuum container 510. With such a configuration, the gap forming surfaces 70a and 70a are housed in the vacuum vessel 510, so that the gap forming surfaces 70a and 70a are arranged in the vacuum. In the vacuum vessel 510, the wall member 410 includes a pair of wall portions facing the width direction D2, a pair of wall portions facing the length direction D3 (not shown), and a pair of wall portions facing the axial direction. Has.

1 ... Charged particle beam therapy device, 50, 350, 450, 550 ... Scanning electromagnet, 60A, 60B ... Coil, 70A, 70B ... Magnetic pole, 70a ... Gap forming surface, 100, 300, 400, 500 ... Vacuum structure.

Claims (2)

A scanning electromagnet that scans a charged particle beam in a charged particle beam therapy device.
A pair of coils that are wound around the reference axis and face each other in the axial direction in which the reference axis extends.
A pair of magnetic poles formed of a magnetic member, supporting the pair of coils on the inner peripheral side, and facing each other in the axial direction,
It is provided with a vacuum structure in which the passing position of the charged particle beam is a vacuum.
Each of the pair of magnetic pole portions has a gap forming surface that forms a gap through which the charged particle beam passes by facing each other at a distance from each other in the axial direction.
The vacuum structure is a scanning electromagnet configured to arrange the pair of gap forming surfaces in a vacuum. The scanning electromagnet according to claim 1, wherein the vacuum structure is configured to arrange the pair of the coils in a vacuum.