JP2000082599A - Electromagnet for circular accelerator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To generate an intense magnetic field, by providing a main coil for generating a magnetic field for deflecting a beam and causing it to orbit on a beam orbital surface, alternately disposing acceleration cavities and magnetic poles along the orbiting direction of the beam, and inserting a correction coil between the periphery of the magnetic poles and the main coil. SOLUTION: A correction coil 17 is also inserted between the magnetic-pole periphery 11 of magnetic poles 3 and a main coil 5, and magnetic fields generated by the correction coil 17 and by pole-face correction coils are increased as a whole, and therefore it is not necessary to increase the coil diameter of the pole-face correction coils. Because the correction coil 17 disposed near the main coil 5 or superconducting coil is easy to cool, it can be made up of a normal conduction coil, but if a large magnetic field is wanted, it can be made up of a superconducting coil. In general, the correction coil 17 is made up by disposing a pair of coils symmetrically about a mid-plane 14. If an asymmetric magnetic field running along a Z-axis is to be corrected, the correction coil 17 can be disposed asymmetrically about the mid-plane 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnet for a circular accelerator for extracting charged particles for irradiating an affected part.

[0002]

2. Description of the Related Art As a conventional electromagnet for a circular accelerator, Pr
oposal for a Manufacturin
g Prototype SUPERCONDUCTI
NGCYCLOTRON for Advanced
Cancer Therapy, MSUC-874
L, Ferbruary, 1993, p2, FIG.
1 is known.

FIG. 12 is a perspective view showing the overall structure of a conventional electromagnet for a circular accelerator. In the figure, 1 is an electromagnet, 2
Is a center of the electromagnet 1, 3 is a magnetic pole, 5 is a main coil (a superconducting coil in the illustrated example), 6 is a Z axis, and is a central axis of the electromagnet for a circular accelerator. 7 is an acceleration cavity, 9 is a yoke top plate, 1
0 is a yoke, 11 is a magnetic pole outer peripheral part, and 12 is a correction iron plate.

The magnetic pole 3 is usually made of iron. Since a large attractive electromagnetic force acts in the Z-axis direction between the magnetic poles 3 arranged symmetrically along the Z-axis, the magnetic poles 3 are supported by the yoke top plate 9 and the yoke 10 made of thick iron. Therefore, the total weight of the yoke top plate 9 and the yoke 10 is generally several tens tons.

FIG. 13 shows another electromagnet for a circular accelerator shown in FIGS. 11-76 of Experimental Physics Course 28, Accelerator (Kyoritsu Shuppan), Chapter 11, p. 448. In the figure, 13 is a magnetic pole surface correction coil, and 15 is an acceleration cavity correction coil.

FIG. 14 is a diagram schematically showing a sectional view of the magnetic pole 3 and the magnetic pole surface correction coil 13 in the electromagnet for a circular accelerator shown in FIG. Z of electromagnet for circular accelerator
The midpoint of the axis is called a midplane 14, and the magnetic pole surface correction coil 13 has a coil winding disposed on the magnetic pole surface between the magnetic pole 3 and the midplane 14. The midplane 14 is a surface around which a beam to be accelerated circulates, and is also called a beam orbit plane. Note that the R axis is in the radial direction.

FIG. 15 is a diagram schematically showing a sectional view of the accelerating cavity 7 and the accelerating cavity correcting coils 15 and 16 in the circular accelerator electromagnet shown in FIG.
The acceleration cavity correction coil 15 inserts a coil winding between the acceleration cavity 7 and the midplane 14, and the acceleration cavity correction coil 16 inserts a coil winding between the acceleration cavity 7 and the yoke top plate 9.

FIG. 16 is a schematic sectional view of the magnetic pole 3 and the correction iron plate 12 of the electromagnet for a circular accelerator shown in FIG. Next, the operation of the circular accelerator electromagnet will be described mainly using the circular accelerator electromagnet shown in FIG. FIG.
In the second example, the main coil 5 for generating a magnetic field for deflecting the beam is a superconducting coil, and is formed by a pair of solenoid coils.

The beam incident on the center 2 of the electromagnet is deflected by the magnetic field generated by the main coil 5 and travels on the beam orbit surface 14 shown in FIG. ) Is accelerated in the beam traveling direction (radial direction R). In the range from the vicinity of the center 2 of the electromagnet to immediately before the outer peripheral portion 11 of the magnetic pole, the beam is accelerated and the energy of the beam increases each time the beam passes through the acceleration cavity 7. As the energy of the beam increases, the orbit radius of the beam increases. That is, the trajectory increases while drawing a spiral.

When the orbital radius of the beam is near the magnetic pole outer peripheral portion 11, the beam is not accelerated because the accelerating cavity 7 disappears. Further, since the magnetic pole 3 is eliminated, the magnetic field decreases rapidly. Thereby, the beam travels substantially straight without being deflected and is taken out of the electromagnet. The position where the magnetic field starts to decrease rapidly is hereinafter referred to as a beam extraction radius. This beam extraction radius is substantially equal to the radius of the magnetic pole outer peripheral portion 11. In the examples of FIGS. 12 and 13, the acceleration cavities 7 and the magnetic poles 3 are alternately arranged in the circumferential direction. In the examples shown in these figures, the acceleration cavities 7 and the magnetic poles 3 are alternately arranged three times symmetrically with respect to the Z axis.

Next, the AVF cyclotron will be described. In this type of circular accelerator, the frequency of the acceleration cavity 7 is kept constant. This makes it possible to increase the Q value of the acceleration cavity and obtain a large acceleration electric field. To keep the frequency of the accelerating cavity constant, it is necessary to keep the orbital frequency of the beam constant. The following relationship is established between the orbital frequency w of the beam and the magnetic field in the Z-axis direction (magnetic field averaged in the circumferential direction) Bz (r).

W = qBz (r) / m

Here, q is the charge of the charged particle, and m is the mass of the beam. The mass m of the beam increases with an increase in the energy of the beam, that is, with an increase in the radius r of the orbit of the beam. In order to keep the orbital frequency w of the beam constant, Bz is also r
It is necessary to make the magnetic field distribution increase with the increase. This magnetic field is called an isochronous magnetic field. The actual magnetic field averaged in the circumferential direction must exactly match this magnetic field.

One of the purposes of the magnetic pole 3 shown in FIG. 12 is to create the above isochronous magnetic field. Therefore, as r increases, the gap between the magnetic pole 3 and the beam orbit plane is reduced, and the width of the magnetic pole 3 is increased with r. In particular, in the vicinity of the magnetic pole outer peripheral portion 11, which is the beam extraction radius, the gap is a small gap of several tens mm.

In order to obtain a magnetic field that increases strictly with the radial direction, the accuracy of the current three-dimensional magnetic field calculation code is insufficient. Therefore, it is necessary to correct the magnetic field distribution based on the actual measurement of the magnetic field measurement.

As described above, it has been described that correction is necessary to bring the magnetic field Bz (r) closer to the isochronous magnetic field. Next, another magnetic field that needs to be corrected will be described. In a magnetic field distribution Bz (θ) in the circumferential direction at a position where the radial radius is constant, C
The magnetic field that changes with OSθ or SINθ is called the primary harmonic magnetic field. In the presence of this magnetic field, beam resonance occurs and the charged particle diameter increases and charged particles are lost.

In particular, this primary harmonic magnetic field needs to be small near the beam extraction radius. This magnetic field also needs to be corrected to a certain specification (usually about 1 to 2 Gauss). The maximum magnetic field near the extraction radius is
In the case of a superconducting electromagnet, the maximum value is about 4T, so this value is a very severe value. For this reason, correction based on magnetic field measurement is required as in the case of isochronous magnetic field generation.

The means for correcting these magnetic fields will be described below with reference to FIGS. FIG. 13 shows various coils for isochronous magnetic field correction. First, 1
Reference numeral 3 denotes a magnetic pole surface correction coil arranged on the magnetic pole surface. FIG. 14 schematically shows a cross section of the magnetic pole surface correction coil 13.
It is. The magnetic pole surface correction coil 13 can generate a magnetic field in the Z direction. By arranging a large number of coils with different currents, various magnetic field distributions varying along the radial direction can be generated, and the above isochronous magnetic field can be generated.

Next, FIG. 13 shows an acceleration cavity correction coil 1.
There are five. The accelerating cavity correction coil 15 is disposed in a vacant space near the accelerating cavity. FIG. 15 schematically shows a cross section of the acceleration cavity correction coil 15. In FIG. 15, the accelerating cavity correction coil 15 has a coil winding between the midplane 14 and the accelerating cavity 7, and although not shown in FIG. Arrange the windings.

However, the acceleration cavity correction coils 15, 16
Since magnetic poles generally exist in the circumferential direction, they cannot be arranged entirely along the circumferential direction. In the example of FIG. Similarly to the magnetic pole surface correction coil 13, these coils can be arranged with a large number of coils and change the current value of each coil to correct the isochronous magnetic field.

By the way, in the example of FIG. 13, the main coil 5 is a normal conductive magnet, and the magnetic field intensity is at most about 2T. In this case, the correction is performed by the acceleration cavity correction coils 15 and 16.
But it was enough. However, in the case of a superconducting coil as shown in FIG. 12, the magnetic field intensity becomes close to 4T, and the magnetic field intensity for correction needs to be increased.

[0022]

As described above, FIG.
In the case of a superconducting coil as indicated by a circle, when the magnetic field strength approaches 4T, the magnetic field strength may not be sufficient with the accelerating cavity correction coil shown in FIG. That is, as shown in FIG. 14, in the magnetic pole surface correction coil 13, the coil winding is arranged in the gap between the magnetic pole 3 and the midplane 14, but this gap is as small as several tens mm at the take-out radius position as described above.

Since the magnetic pole is normally at room temperature, the magnetic pole surface correction coil is a normal conducting coil.
Large cross-sectional areas are required. Therefore, there is a problem that a magnetic pole surface correction coil having a large cross-sectional area cannot be inserted into the gap and a large magnetic field intensity cannot be obtained. A similar problem occurs in the case of the acceleration cavity correction coil 15 shown in FIG.

Further, in the case of the accelerating cavity correction coil 16 shown in FIG. 15, since there is a large gap between the accelerating cavity 7 and the yoke top plate 9, a coil having a large sectional area can be arranged. However, since the location of the accelerating cavity correction coil 16 is far from the beam orbital surface 14, a large magnetomotive force is required to generate a magnetic field of a certain magnitude on the beam orbital surface 14. was there.

As described above, since there is a limit to the correction of the harmonic magnetic field in the normal conducting coil, in the electromagnet for a circular accelerator shown in FIG. I was FIG. 16 schematically shows this state. Outer peripheral portion 1 of magnetic pole 3
1 shows how the correction iron plate 12 is attached. The correction iron plate 12 is particularly effective for correcting the primary harmonic magnetic field, and can correct the error magnetic field by asymmetrically attaching iron in the circumferential direction.

However, as shown in FIG.
Are supported by a yoke top plate 9, and the yoke top plate 9 is supported by a yoke 10. In order to correct the error magnetic field by correcting the magnetic field distribution with the correction iron plate 12, the yoke top plate 9 is disassembled from the yoke 10 as shown in FIG. 12, and the correction iron plate 12 is manually moved to the surface of the outer peripheral portion 11 of the magnetic pole 3. Must be attached to However, the yoke top plate 9 and the magnetic pole 3 generally have a very large weight of several tens of tons, and disassembly of the yoke top plate 9 requires a great deal of trouble.
1 cannot be stuck on the surface.

The present invention has been made in order to solve the above-mentioned problems, and in particular, has a correction coil capable of generating a magnetic field having sufficient strength to correct a magnetic field near a beam extraction radius. It is intended to obtain an electromagnet for a circular accelerator.

[0028]

According to a first aspect of the present invention, there is provided an electromagnet for a circular accelerator, comprising: a main coil for generating a magnetic field for deflecting a beam injected into the center of the electromagnet to orbit around a beam orbital surface; An accelerating cavity for applying an electric field to the beam during orbiting on the orbital surface and accelerating in the beam traveling direction; and magnetic poles alternately arranged with the accelerating cavity along the orbital direction of the beam, the outer periphery of the magnetic pole And a correction coil inserted between the main coil and the main coil.

In the electromagnet for a circular accelerator according to a second aspect of the present invention, the correction coil is divided into a plurality of pieces along the circumferential direction of the magnetic poles and inserted. Is different.

According to a third aspect of the present invention, there is provided an electromagnet for a circular accelerator, wherein a circling surface of a beam is a symmetric surface, and a first correction coil group and a second correction coil group which are opposed to each other via the symmetric surface. And a correction coil having the same current value is connected in series to the current source.

In the electromagnet for a circular accelerator according to a fourth aspect of the present invention, the correction coil is formed by winding a coil winding around a cylindrical winding frame and then inserting a magnetic pole into the cylinder.

According to a fifth aspect of the present invention, there is provided an electromagnet for a circular accelerator, wherein the electromagnet includes a control means for changing a current value of a correction coil according to a rotation angle of the rotating gantry when the electromagnet is mounted on the rotating gantry. .

In the electromagnet for a circular accelerator according to the present invention, the correction coil is disposed between the magnetic pole and the beam orbit plane.

In the electromagnet for a circular accelerator according to the present invention, the correction coil is arranged near the surface of the acceleration cavity.

[0035]

Embodiment 1 Hereinafter, Embodiment 1 of the present invention will be described with reference to the drawings.
FIG. 1 is a sectional view of an electromagnet for a circular accelerator according to the present embodiment. In the drawings, the same reference numerals as those in FIGS. 14 to 16 indicate the same or corresponding parts. In the present embodiment, a correction coil 17 is inserted between the outer peripheral surface 11 of the magnetic pole 3 and the main coil 5. Conventionally, the magnetic pole surface correction coil 13 is provided between the plane portion of the magnetic pole 3 and the mid plate 14 as shown in FIG. 14, or as shown in FIG. Or the acceleration cavity correction coil 16 is inserted between the acceleration cavity 7 and the yoke ceiling 9.

In this embodiment, in addition to the conventional position shown in FIG. 14, the correction coil 17 is inserted between the outer peripheral surface 11 of the magnetic pole 3 and the main coil 5. Thereby, each correction coil 1
It is possible to increase the total magnetic field generated by 3,17. This eliminates the need to increase the diameter of the magnetic pole surface correction coil 3. The correction iron plate 1 shown in FIG.
It is not necessary to use 2.

In the example of FIG. 1, the correction coil 17 is an example of a solenoid type coil. Since the correction coil 17 is located at a different position from the main coil 5, it has a different distribution.
Therefore, by adjusting the value of the current flowing through the correction coil 17,
Correction to an isochronous magnetic field is possible.

The correction coil 17 is arranged in the vicinity of the main coil 5 which is a superconducting coil and can be easily cooled, and may be constituted by a normal conducting coil. However, if a larger magnetic field is to be obtained, a superconducting coil may be used. When the main coil 5 is composed of a superconducting coil, the magnetic pole 3 is in a completely saturated state of about 4T. Therefore, the magnetic field distribution of the correction coil 17 can be handled almost similarly to the air-core coil.

Although only one pair of correction coils 17 is shown in the example of FIG. 1, two or more pairs of correction coils may be used. Further, the correction coil 17 generally includes a pair of coils,
4 and symmetrically arranged.

When correcting an asymmetric magnetic field along the Z axis, the correction coil 17 may be arranged asymmetrically with respect to the midplane 14.

Embodiment 2 FIG. 2A shows that the correction coil 17 shown in FIG. 1 is divided into 21 to 26 and 27 to 32 in a circumferential direction 20 around the Z axis.
The state where it is symmetrically arranged with respect to the midplate 14 is shown. Here, the divided coils 21 to 26 are respectively placed in the first
Correction coils to the sixth correction coil, and coils 27 to 32 to the seventh correction coil 7 to the twelfth correction coil 12, respectively.
Call.

In FIG. 2B, reference numeral 33 denotes a wall surface of a cryostat for accommodating the main coil 5 which is a superconducting coil.

In the first embodiment, an example of the correction to the isochronous magnetic field by the correction coil 17 has been described. In the present embodiment, correction of the primary harmonic magnetic field near the extraction radius by the correction coil 17 will be described.

The correction coils 17 shown in FIG. 2A are arranged symmetrically with respect to the midplane 14, and are divided along the circumferential direction and arranged in the first to sixth correction coils 26 to 26. 7th correction coil 27 to twelfth correction coil 3
2 The current is supplied to each of the first to sixth correction coils 21 to 26 and the seventh to twelfth correction coils 32 symmetrically arranged with respect to the midplane 14, as shown in FIG. In the same direction with the same size. The return of the current flowing through these correction coils is at a position farther from the midplane 14 as shown in FIG. As is apparent from the cross-sectional view of the coil winding arrangement shown in FIG. 2B, a magnetic field in the Z direction can be generated near the magnetic field extraction radius.

Since the main coil 5 is shown as a superconducting coil in FIG. 2B, reference numeral 33 denotes a wall surface of a cryostat for accommodating the superconducting coil.
However, the main coil 5 may be a normal conducting coil. Although the magnetic pole 3 exists, as described in the first embodiment, the main coil 5 has a magnetic field close to 4T and is in a completely saturated state, so that the correction coil 17 can generate a magnetic field substantially close to the air-core coil. .

Further, a first correction coil 21 to a sixth correction coil 26, a seventh correction coil 27 to
The twelfth correction coil 32 changes the current as shown in FIG. In particular, the correction coils at the 180-degree rotationally symmetric position with respect to the Z axis, for example, the first correction coil 21 and the fourth correction coil 24 have the same magnitude of the current, but reverse the direction of the current. Due to this current distribution, COS
A magnetic field that varies with θ can be generated. A diagram showing the generated magnetic field is a diagram shown by a cosine curve in FIG. C in the θ direction
It can be seen that it changes with OSθ.

This magnetic field is called a primary harmonic magnetic field 35. When this magnetic field is generated due to a manufacturing error of the magnetic pole 3 or the like, the first correction coil 21 to the twelfth correction coil 32 are changed in the circumferential direction as described above so that a magnetic field in the opposite direction to this magnetic field is generated. If you excite with the current distribution
The error magnetic field can be corrected. Also, because it is a coil,
By sequentially changing the current of each coil, the primary harmonic error magnetic field can be corrected without providing the correction iron plate 12 irrespective of the phase and intensity of the primary harmonic magnetic field.

The example in which the correction coil 17 is divided into six parts in the circumferential direction has been described.
The phase of the next harmonic magnetic field is controllable. Further, if the correction coil 17 is further divided finely and the current of the coil is made to flow in the circumferential direction so as to be proportional to COS (2θ),
As shown in the lower diagram of FIG. 3, it is possible to generate a magnetic field varying in the circumferential direction by COS (2θ) and a secondary harmonic magnetic field. Thereby, it is possible to correct a secondary harmonic error magnetic field generated due to a manufacturing error of the magnetic pole or the like. Hereinafter, higher-order magnetic fields can be generated by increasing the number of coil divisions.

When a current in the same direction is applied to each coil in addition to the above-described current, a magnetic field that is uniform in the circumferential direction and changes in the radial direction can be applied, and correction to the isochronous magnetic field can be performed. Available. In the example of FIG. 2A, the coil windings of the first to sixth correction coils 21 to 26 and the coil windings of the seventh to twelfth correction coils 32 have the Z axis. Although present continuously at the center along the entire circumference in the circumferential direction, it may be present intermittently.

Embodiment 3 When a magnetic field is generated by applying a current to the correction coil 17, as the number of divisions of the correction coil 17 increases, the number of power supplies for supplying a current to each correction coil increases, which causes a cost increase. . In the present embodiment, a method of installing a power supply that reduces the number of power supplies regardless of the increase in the number of divisions of the correction coil 17 will be described. FIG. 4 is a diagram showing a method of connecting the power supply and the correction coil 17 in the present embodiment. In the figure, 40
Is a power supply for supplying a current for generating a magnetic field to the correction coil.

In the second embodiment, according to FIG.
The direction of the coil current of the correction coil 17 that generates the next harmonic magnetic field has been described. In summary, there are two types of current arrangements as follows. As shown in FIG. 2C, a correction coil at a position symmetrical by 180 degrees with respect to the Z axis, for example, a first correction coil 21 and a fourth correction coil 21
And the magnitude of the current is the same as that of the correction coil 24,
The direction of the current is opposite. As shown in FIG. 2A, currents of the first to sixth correction coils 21 to 26 and currents of the seventh to twelfth correction coils 32 are arranged symmetrically with respect to the midplane 14. Are arranged to flow in the same direction with the same size. Therefore, in both cases, the magnitude of the current is the same. Therefore, the power supply 40 can be shared. FIG. 4 shows this state. As a result, if the power supply 40 is connected in series to the coil, the number of power supplies 40 can be reduced. Furthermore,
Since the currents are the same in the upper and lower diagrams of FIG. 4, they can be connected in series. . That is, four coils can be connected in series, and the number of power supplies can be reduced to 1/4 of the number of coils.

Embodiment 4 The correction coil 17 has a complicated structure as shown in FIG.
Winding work through the wall of the fixed cryostat is not easy. In the present embodiment, a method of manufacturing a correction coil by an easy winding operation will be described.

FIGS. 5A to 5C are diagrams for explaining a method of winding a correction coil in the present embodiment. In the figure, 42 is a winding frame, and 44 is a coil winding constituting the correction coil 17. When manufacturing the correction coil 17, a coil winding 44 is first wound around a winding frame 42 as shown in FIG.
In this case, if the winding frame 42 is provided with a groove or a projection for winding the coil winding 44, the winding is easy. The first to twelfth correction coils 3 to 3
Alternatively, the coil windings 44 may be separately manufactured for each 2 and the coil windings 44 may be attached to the winding frame 42 by screws or the like.

After the coil winding 44 is wound around the winding frame 42 to form the correction coil 17, as shown in FIG. 5B, the winding frame 42 to which the correction coil 17 is attached is inserted into the electromagnet, and then
The magnetic pole 3 and the yoke top plate 10 may be inserted. The completed electromagnet is shown in the lower left diagram of FIG.

Embodiment 5 FIG. 6 is a perspective view showing the entire structure of a rotating gantry on which an electromagnet for a circular accelerator is mounted. In the figure, reference numeral 50 denotes a rotating gantry, and 52 denotes a rotating angle θg of the rotating gantry, which is an angle from a horizontal plane. Numeral 54 denotes a beam transport system, and numeral 56 denotes a patient irradiating a beam.

FIG. 7 is a view for explaining a primary harmonic magnetic field generated when an electromagnet for a circular accelerator is mounted on a rotating gantry. In the figure, 58 is the center Z axis of the electromagnet for a circular accelerator, 60 is the center Z axis of the main coil 5, and 62 is the deviation δ between the center Z axis of the electromagnet for a circular accelerator and the center Z axis of the main coil.

Next, the rotating gantry will be outlined.
The beam extracted from the electromagnet 1 for a circular accelerator passes through a beam transport system 54 and is irradiated to a cancer patient 56. In order to irradiate the beam intensively on the affected part, the beam needs to be rotated and irradiated. For this reason, the rotating gantry 50
is necessary. The rotating gantry 50 has a beam irradiation system 54.
Need to be rotated to be large.

In order to reduce the size, the example of FIG. 6 adopts a structure in which the electromagnet 1 for a circular accelerator is mounted on the rotating gantry 50. In addition, since the electromagnet 1 for circular accelerators is mounted on the rotating gantry 50, the Z axis of the electromagnet 1 for circular accelerators is oriented in the horizontal direction.

When the electromagnet 1 for a circular accelerator is mounted on the rotating gantry 50 and the main coil 5 is a superconducting coil, a primary harmonic magnetic field is newly generated. The reason for this occurrence will be described with reference to FIG. The support portion for supporting the main coil (superconducting coil) 5 in the room temperature space is made as thin as possible to reduce heat penetration.
For this reason, the support portion bends in the radial direction due to gravity. Therefore, in FIG. 7, Z which is the central axis of the electromagnet 1 for a circular accelerator is used.
The axis is oriented in the horizontal direction, and the radial direction is the vertical direction.

On the other hand, the magnetic pole 3 is composed of the yoke top plate 9 and the yoke 10
It is fixed to. Since the yoke top plate 9 is made of thick iron as described in the conventional example, the deflection due to gravity can be ignored. That is, the center Z axis 5 of the circular accelerator electromagnet 1
8 coincides with the central axis of the magnetic pole 3.

As a result, the central axis 60 of the main coil and the central Z axis 58 of the electromagnet 1 for a circular accelerator are shifted by δ as shown in FIG.
Will shift. When, for example, the distribution of one round in the circumferential direction at the take-out radius is evaluated with reference to the center Z axis of the electromagnet 1 for a circular accelerator, a primary harmonic magnetic field 35 is generated as shown in the lower diagram of FIG. I do.

If the rotating gantry 50 does not rotate, the correction may be performed by the correction coil 17 as it is, but the rotating gantry 50 actually rotates. Therefore, the main coil 5 appears to rotate with respect to the left Z axis with reference to the center Z axis 58 of the electromagnet 1 for a circular accelerator. That is, it appears that the phase of the primary harmonic magnetic field is shifted every rotation. For this reason, it is impossible to correct the primary harmonic magnetic field with the correction iron plate.
Active correction must be made according to the rotation angle of the rotating gantry.

To perform such correction, the control device shown in FIG. 8 is used. In the figure, reference numeral 64 denotes a device for detecting the rotation angle θg of the rotating gantry 50 (52 in FIG. 6), such as an encoder. 66 determines the current value of the correction coil 68 based on the rotation angle θg of the rotating gantry 50;
A control unit for controlling the current output from the power supply 40, 68 is a correction coil.

The magnitude of the primary harmonic magnetic field is grasped in advance by magnetic field measurement or the like corresponding to the rotation angle θg of the rotating gantry 50. Thereby, the current value of the correction coil 68 is also determined. The control unit 66 determines the power supply current value from the rotation angle θg of the rotating gantry 50, and controls the output current value from the power supply 40. In the above example, the rotation angle is measured by an encoder or the like. However, the rotation angle may be a set value instead of an actually measured value.

Embodiment 6 FIG. 9 shows the rotation angle θ of the rotating gantry 50 of the correction coil 17.
FIG. 9 is a diagram showing a current corresponding to g. Embodiment 5
Has described that the current value of the correction coil 68 is actively changed according to the rotation angle θg of the rotating gantry 50. If the correction coil 68 is the coil 17 disposed between the main coil 5 and the magnetic pole 3, a magnetic field particularly near the extraction radius can be generated, so that the position can be easily corrected.

Since the Z axis of the electromagnet for the circular accelerator is oriented in the horizontal direction, the Z axis of the correction coil 17 is also oriented in the horizontal direction as shown in FIG. FIG. 9 (b) shows the coil 2
The current change according to the rotation angle θg of the rotating gantry 50 in the correction coil divided into 1, 22, 23, and 27, 28, and 29 is also shown. The primary harmonic magnetic field corresponding to the rotation angle θg of the rotating gantry 50 can be generated by the coil current shown in FIG.

Embodiment 7 FIG. 10 is a partial cross-sectional view of a circular accelerator electromagnet provided with a magnetic pole surface correction coil. In the figure, reference numeral 80 denotes a magnetic pole surface correction coil disposed between the magnetic pole 3 and the midplane 14. In the fifth embodiment, the correction coil disposed between the main coil 5 and the magnetic pole 3 has been described. In the fifth embodiment, a correction coil using a coil having another shape will be described. FIG.
The first-order harmonic magnetic field can also be generated by the magnetic pole surface correction coil 80 shown in FIG. This magnetic pole surface correction coil 80
The winding method is different from that of the correction coil 13 on the magnetic pole surface shown in FIGS. For example, the correction coil 13 on the magnetic pole surface shown in FIG. 14 is for correcting an isochronous magnetic field, and the current does not change in the circumferential direction.

However, the pole surface coil 80 shown in FIG.
As in the case of the correction coil 17 shown in FIG. 2, the coil is divided in the circumferential direction, and the coil current is supplied so that the current changes in the circumferential direction. Thereby, a primary harmonic magnetic field can be generated. Further, the current value of each coil divided in the circumferential direction is changed for each rotation angle θg of the rotating gantry 50. Thereby, the primary harmonic magnetic field generated when the rotating gantry 50 rotates can be actively corrected.

Eighth Embodiment FIG. 11 is a diagram showing an acceleration cavity surface correction coil according to the present embodiment. Reference numeral 82 denotes an acceleration cavity surface coil disposed between the yoke top plate 9 and the acceleration cavity 7, and reference numeral 84 denotes an acceleration cavity surface coil disposed between the midplane 14 and the acceleration cavity 7.

In this embodiment, a coil having a different shape from the above embodiments will be described. As shown in FIG. 11, an acceleration cavity surface coil 8 arranged near the acceleration cavity 7
2 and 84 can also generate a primary harmonic magnetic field. This coil is divided so that the current changes in the circumferential direction, similarly to the magnetic pole surface coil 80 shown in FIG.
(See (a)), and the coil current is supplied. As a result, a primary harmonic magnetic field can be generated on the midplane 14.

Further, the coil current value divided in the circumferential direction is changed for each rotation angle θg of the rotating gantry 50. Thus, the primary harmonic magnetic field generated when the rotating gantry 50 rotates is actively corrected as in the embodiment.

[0072]

According to the first aspect of the present invention, a main coil for deflecting a beam injected into the center of an electromagnet to generate a magnetic field for orbiting on a beam orbital plane, and a beam during orbiting on the beam orbital plane. An accelerating cavity for applying an electric field to the beam and accelerating in the beam traveling direction, and magnetic poles alternately arranged with the accelerating cavity along the circling direction of the beam, and between the outer periphery of the magnetic pole and the main coil. Since the correction coil is inserted to form the electromagnet for the circular accelerator, there is an effect that a magnetic field having a sufficient strength for correcting the magnetic field can be generated near the beam extraction radius.

According to the second aspect of the present invention, the correction coil is divided into a plurality of pieces along the circumferential direction of the magnetic pole and inserted, and the current value or the current direction is made different in at least a part of the divided correction coils. Therefore, there is an effect that the primary harmonic error magnetic field can be easily corrected.

According to the third aspect of the present invention, the circling surface of the beam is set as the target surface, and the first surface opposed to the target surface via the target surface is disposed.
The correction coils having the same current value are connected in series to the current sources in the correction coils between the correction coil group and the second correction coil group, so that the number of current sources can be reduced regardless of the increase of the correction coils. There is an effect that can be.

According to the fourth aspect of the present invention, the correction coil is formed by winding a coil winding around a cylindrical winding frame and then magnetic poles are inserted into the cylinder to incorporate the correction coil into the electromagnetic for the circular accelerator. This has the effect of making it easier.

According to the fifth aspect of the present invention, since the control means for changing the current value of the correction coil in accordance with the rotation angle of the rotating gantry when mounted on the rotating gantry is provided, the rotation angle of the rotating gantry is provided. There is an effect that the primary harmonic magnetic field according to the above can be actively corrected.

According to the sixth aspect of the present invention, since the correction coil is disposed between the magnetic pole and the beam orbit plane, the primary harmonic magnetic field corresponding to the rotation angle of the rotating gantry can be actively corrected. is there.

According to the seventh aspect of the present invention, by disposing the correction coil near the surface of the acceleration cavity, there is an effect that the primary harmonic magnetic field corresponding to the rotation angle of the rotating gantry can be actively corrected.

[Brief description of the drawings]

FIG. 1 is a sectional view of an electromagnet for a circular accelerator according to claim 1 of the present invention.

FIG. 2 is a diagram of a correction coil according to claim 2 of the present invention.

FIG. 3 shows a magnetic field generated by a correction coil according to claim 2 of the present invention.

FIG. 4 is a connection diagram of a correction coil according to a third embodiment of the present invention with a power supply.

FIG. 5 is an illustration of a method of assembling a correction coil according to claim 4 of the present invention.

FIG. 6 is a perspective view of an electromagnet for a circular accelerator according to claim 5 of the present invention.

FIG. 7 is an explanatory diagram of generation of an error magnetic field according to claim 5 of the present invention.

FIG. 8 is a configuration diagram according to claim 5 of the present invention.

FIG. 9 is a diagram showing a correction coil according to claim 6 of the present invention and a waveform of a current flowing through the correction coil.

FIG. 10 is a sectional view of an electromagnet for a circular accelerator according to claim 7 of the present invention.

FIG. 11 is a sectional view of an electromagnet for a circular accelerator according to claim 8 of the present invention.

FIG. 12 is a perspective view of a conventional electromagnet for a circular accelerator according to the present invention.

FIG. 13 is a cross-sectional view of a conventional electromagnet for a circular accelerator.

FIG. 14 is a cross-sectional view of a conventional electromagnet for a circular accelerator according to the invention.

FIG. 15 is a perspective view of a conventional electromagnet for a circular accelerator.

FIG. 16 is a perspective view of a conventional electromagnet for a circular accelerator according to the present invention.

[Explanation of symbols]

1 electromagnet, 3 magnetic poles, 5 main coil, 6 Z axis, 7
Acceleration cavity, 11 magnetic pole outer periphery, 13 magnetic pole surface correction coil, 14 midplane, 15 acceleration cavity correction coil (1), 16 acceleration cavity correction coil (2), 17
Correction coil, 20 circumferential direction, 35 primary harmonic magnetic field, 36 secondary harmonic magnetic field, 42 winding frame, 44 coil winding, 50 rotation gantry, 52 rotation gantry rotation angle θg.

Claims (7)

[Claims] 1. A main coil for deflecting a beam injected into the center of an electromagnet to generate a magnetic field for orbiting on a beam orbital surface, and applying an electric field to the beam while orbiting on the beam orbital surface to advance the beam. An acceleration cavity for accelerating in the direction, and a magnetic pole alternately arranged with the acceleration cavity along the circling direction of the beam, wherein a correction coil is inserted between the outer periphery of the magnetic pole and the main coil. Electromagnets for circular accelerators. 2. The method according to claim 1, wherein the correction coil is divided into a plurality of parts along the circumferential direction of the magnetic pole and inserted, and a current value or a current direction is made different in at least a part of the divided correction coils. 2. The electromagnet for a circular accelerator according to 1. 3. A circulating plane of a beam is defined as a symmetric plane, and a correction coil having the same current value is supplied to a first correction coil group and a second correction coil group disposed opposite each other via the symmetric plane. 3. The electromagnet for a circular accelerator according to claim 1, wherein the electromagnet is connected in series to a source. 4. The circular accelerator according to claim 1, wherein the correction coil is formed by winding a coil winding around a cylindrical winding frame and then inserting a magnetic pole into the cylinder. electromagnet. 5. The apparatus according to claim 1, further comprising control means for varying a current value of a correction coil according to a rotation angle of said rotating gantry when mounted on the rotating gantry. An electromagnet for a circular accelerator as described in the above. 6. The electromagnet for a circular accelerator according to claim 5, wherein the correction coil is disposed between the magnetic pole surface and the beam orbit surface. 7. The electromagnet for a circular accelerator according to claim 5, wherein the correction coil is arranged near the surface of the acceleration cavity.