JPH0878200A - Method and device for controlling magnetic field made by eddy current - Google Patents

Abstract

PURPOSE: To control a magnetic field made by an eddy current generated in a conductive structure set in a fluctuating magnetic field with a simple structure by arranging a conductive auxiliary structure different from a main structure within the fluctuating magnetic field. CONSTITUTION: A deflecting electromagnet is formed by a vacuum duct 1 arranged between magnetic poles 3 of the deflecting magnet and an auxiliary structure (auxiliary coil) 2 consisting of four linear closed circuits. The magnetic field distribution formed in the duct 1 is determined by the eddy current of the vacuum duct wall and the current carried on the side closer to a charged particle beam orbit of the four coils 2. Since the magnetic field made by the eddy current of the duct 1 is canceled by the structure 2 different from the duct 1, the magnetic field in the duct 1 can be flattened even when the time change of intensity of the deflecting magnetic field is large. Further, since the magnetic field in the duct 1 is not sensitive to the setting position of the structure 2 or the form of the duel 1, the maintenance after set of the structure 2 is not required, and the structure 2 can be easily mounted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device used in a fluctuating magnetic field, and more particularly to a device used between magnetic poles of an electromagnet of an accelerator.

[0002]

2. Description of the Related Art Conventionally, equipment used in a fluctuating magnetic field, which is affected by the magnetic field generated by eddy currents, has a problem of suppressing self-confidence by using a material having low conductivity. I was dealing with it. For example, in a fast cycle synchrotron, in order to suppress the eddy current on the wall of the vacuum duct, the vacuum duct is made of a non-conductive material such as organic resin or ceramic, or the wall is accordion-shaped to increase the resistance value and increase the vortex current. Methods have been taken to reduce the current.

[0003]

Generally, when a conductive substance is present in a fluctuating magnetic field, an eddy current flows by inducing an electric field in the substance as the magnetic field changes with time. Eddy currents generate new magnetic fields.

For example, in a synchrotron, since the magnetic field strength of the deflection electromagnet increases with the acceleration of the beam, an electric field is induced between the magnetic poles of the deflection electromagnet with the time change of the magnetic field. There is a vacuum duct covering the track between the magnetic poles, and if it is made of a conductive material, an eddy current is generated in the wall of the vacuum duct. The eddy current generates a new magnetic field inside the vacuum duct and disturbs the magnetic field of the deflecting electromagnet, so that the converged state of the beam changes and the beam is diverged when a large amount of eddy current flows.

The conventional method for producing a vacuum duct from a non-conductive material such as organic resin or ceramic to suppress the generation of eddy current has the following drawbacks. First, organic resins have the drawbacks of being vulnerable to radiation damage and generating a large amount of gas from the wall. Also, when a vacuum duct is made of ceramic, it is technically difficult to bake the ceramic into a tube of about 1 m, which is equivalent to one deflection electromagnet, so it is necessary to connect tubes of several cm. . As a result, in addition to material defects such as chipping and brittleness,
There are problems such as vacuum leakage at pipe joints and high cost. Also, in the method of reducing the amount of eddy current by increasing the resistance value by making the vacuum duct into a bellows shape, using the bellows makes the vacuum duct larger, the distance between the magnetic poles of the electromagnets increases, and the power supply is burdened. become.

A first object of the present invention is to provide a method and apparatus for controlling a magnetic field generated by an eddy current generated in a conductive structure installed in a fluctuating magnetic field with a simple structure. .

A second object is to provide a particle accelerator capable of reducing the beam loss by the above control method and apparatus.

[0008]

[Means for Solving the Problems] Means for achieving the above-mentioned first object are as follows: in a fluctuating magnetic field that changes with the same time as the fluctuating magnetic field of the area where the main structure in which the eddy current is generated is installed, It is a means for installing an auxiliary structure separately from the main structure.

Means for achieving the above second object are as follows:
This is a means for applying the means for achieving the first object, with the device installed between the magnetic poles of the electromagnet of the particle accelerator as the main structure.

[0010]

[Operation] If an auxiliary structure other than the main structure is installed in a variable magnetic field that changes with time as the variable magnetic field in the area where the main structure in which the eddy current is generated is installed, the auxiliary structure flows to the auxiliary structure. The magnetic field created by the eddy current is superimposed on the magnetic field created by the eddy current of the main structure. Since the magnetic field generated by the eddy current flowing in the auxiliary structure can be controlled by appropriately selecting the position, resistance value, etc. of the auxiliary structure, it is possible to control the entire superimposed magnetic field. The auxiliary structure can have a simple structure by selecting an appropriate shape and arrangement. By installing the main structure and the auxiliary structure in a variable magnetic field that changes with the same time, the magnetic fields created by the respective eddy currents are always in the same ratio, and the same magnetic field distribution is always created without external operation. You can

Further, by applying the above means to the device installed between the magnetic poles of the electromagnet of the particle accelerator, it becomes possible to control the distribution of the magnetic field constant even when the magnetic field produced by the electromagnet changes with time. . As a result, it is possible to suppress the change in the converged state of the beam due to the change in the magnetic field distribution and prevent the beam loss.

[0012]

EXAMPLE As a first example of the particle accelerator according to the present invention, the spatial change of the magnetic field due to the eddy current of the vacuum duct installed between the magnetic poles of the bending electromagnet is reduced to flatten the magnetic field distribution. The synchrotron characterized by the following will be explained.

The synchrotron comprises a conductive vacuum duct, a deflection electromagnet for applying a magnetic field in a predetermined direction to the charged particle beam to form a circular orbit, and an accelerating means for accelerating the charged particle beam. As the beam is accelerated, the magnetic field of the deflection electromagnet becomes stronger and eddy current is generated in the vacuum duct between the magnetic poles. In FIG. 1, a racetrack type vacuum duct 1 made of stainless steel, which is installed between the magnetic poles 3 of the electromagnet, and four linear closed-circuit auxiliary structures 2 (hereinafter referred to as auxiliary coils), A bending electromagnet is shown.
The auxiliary coil is fixed to the vacuum duct and the magnetic poles by the stopper 12. The stopper attached to the vacuum duct here may be attached to the magnetic pole side. The auxiliary coil is made of a material that is more conductive than the vacuum duct, such as copper or aluminum, and forms a closed circuit with no power source. Further, an insulating coating is applied to electrically insulate the vacuum duct and magnetic poles. FIG. 2 shows a sectional view of the deflecting electromagnet, and FIG. 3 shows a plan view of the entire deflecting electromagnet of this embodiment. The coil 13 is a coil for creating a deflection magnetic field, and a current necessary for generating a magnetic field is supplied from a power supply. When the magnetic poles are removed and it is drawn in principle, it becomes as shown in FIG. This sectional view is shown in FIG. The deflection magnetic field created by the magnetic poles is assumed to be in the upward direction as shown by arrow 4. Its intensity is spatially uniform.

When the particles are accelerated, the strength of the deflection magnetic field increases,
An eddy current in the direction shown in FIG. 5 flows through the vacuum duct wall. This eddy current generates a new magnetic field in the vacuum duct in the direction of decreasing the deflection magnetic field, as shown by arrow 5. FIG. 6a shows the magnetic field distribution created by the eddy current in the vacuum duct wall. By the way, currents such as those shown in 2a and 2b of FIG. 5 in which eddies are swirled in the same direction as the eddy current of the vacuum duct also flow through the four auxiliary coils. The side 2a of the auxiliary coil farther from the charged particle beam trajectory is arranged outside the magnetic pole as shown in FIG. Then, the magnetic field generated by the current in the portion 2a becomes almost uniform in the magnetic pole gap, so the magnetic field distribution generated inside the vacuum duct is the eddy current of the vacuum duct wall and the charged particle beam trajectories of the four auxiliary coils. It is determined by the current flowing on the side 2b close to. The part of the auxiliary coil and the side 2b close to the charged particle beam orbit are arranged along the flow of the eddy current flowing in the vacuum duct. As a result, the auxiliary coil 2b
The magnetic field created by the part of
The direction is opposite to the magnetic field created by the eddy current flowing in the vacuum duct wall as shown in. The magnitude of the current flowing through the auxiliary coil is determined by the thickness of the auxiliary coil wire and the magnetic flux surrounded by the auxiliary coil. Select the placement. By doing so, the magnetic field distribution inside the vacuum duct can be flattened as shown in FIG.

The current value of the auxiliary coil can be adjusted by making the wire thickness of the auxiliary coil thicker and connecting the variable resistor 7 to the auxiliary coil as shown in FIG. The distribution can be flattened.

Furthermore, as shown in FIG. 8, by connecting the variable inductor 8 together with the variable resistor 7, the time constant of the auxiliary coil can be adjusted.

A similar magnetic field distribution can be obtained by winding the auxiliary coil twice as shown in FIG.

Further, as shown in FIG. 10, four plate-shaped auxiliary structures 9 (hereinafter referred to as auxiliary conductor plates) are installed between the magnetic poles 3 of the bending electromagnet instead of the four auxiliary coils. Also, the magnetic field distribution can be flattened. Figure 11
The distribution of the magnetic field created by the eddy current in the vacuum duct wall is shown in a, and the distribution of the magnetic field when the auxiliary conductor plate is present is shown in b. It can be seen that the spatial change of the magnetic field is canceled and the magnetic field distribution is flattened.

Next, the beam orbit correcting electromagnet of this synchrotron will be described. FIG. 12 is an explanatory view of a stainless racetrack type vacuum duct 1 installed between magnetic poles of a beam trajectory correcting electromagnet and an auxiliary structure 10 (hereinafter referred to as an auxiliary conductor) having two linear closed circuits. Indicates. Since the beam trajectory correcting electromagnet creates a local magnetic field, the eddy current 11 induced by the time variation of the magnetic field is generated.
Become concentric. The portion of the auxiliary conductor near the vacuum duct is shaped to follow this eddy current. Since the current flowing in the auxiliary conductor is in the opposite direction to the eddy current in the vacuum duct wall near the vacuum duct, the magnetic field created by the current in this part has a distribution that cancels the magnetic field created by the eddy current in the vacuum duct wall. Become. The current in the portion of the auxiliary conductor far from the vacuum duct creates a magnetic field with a substantially uniform spatial distribution, so that a flatter magnetic field distribution can be obtained as a whole as compared with the case without the auxiliary conductor.

In the above embodiment, since the present invention is applied to the racetrack type vacuum duct which is vertically and horizontally symmetrical with respect to the beam trajectory, the auxiliary structure is vertically and horizontally symmetrically arranged with respect to the beam trajectory. Therefore, the maximum magnetic field correction effect can be obtained. A magnetic field correction effect can be obtained by arranging a vertically asymmetric auxiliary structure for a vertically asymmetric vacuum duct, and a horizontally asymmetric auxiliary structure for a horizontally asymmetric vacuum duct.

[0021]

Since the magnetic field created by the eddy current in the vacuum duct is canceled by the auxiliary structure different from the vacuum duct, the magnetic field in the vacuum duct is flattened regardless of how the intensity of the deflection magnetic field changes with time. can do. Further, the magnetic field in the vacuum duct is not sensitive to the installation position of the auxiliary structure or the shape of the vacuum duct. That is, the auxiliary structure does not require maintenance after installation and is easy to install.

Further, by making the conductivity of the auxiliary structure higher than that of the vacuum duct, the size of the auxiliary structure can be reduced.

When the auxiliary coil as described in the above embodiment is used as the auxiliary structure, the magnetic field can be controlled more easily by connecting the variable resistor to the auxiliary coil. Also, by connecting a variable inductor and adjusting the time constant of the circuit of the auxiliary coil to match the time constant of the eddy current of the vacuum duct, the response to the external magnetic field can be improved and the time change of the magnetic field can be improved. The magnetic field distribution can always be flattened even in the case of large.

Further, when the auxiliary coils have to be arranged at a position largely deviated from the center of the magnetic poles, the magnetic flux surrounded by the respective auxiliary coils becomes small, and the necessary current cannot be generated. In this case, a necessary current can be generated by using a two-turn auxiliary coil as shown in FIG.

When the auxiliary conductor plate described in the embodiment is used as the auxiliary structure, the vacuum duct and the auxiliary conductor plate can be integrated into a simple structure. Further, as shown in FIG. 11, the magnetic field can be flattened over a wide range.

When the magnetic field distribution is local,
The 6-pole component of the magnetic field generated by the eddy current in the vacuum duct can be canceled by the method of FIG.

As described above, since the magnetic field generated by the eddy current in the vacuum duct wall in the deflecting electromagnet can be flattened, it is possible to realize a particle accelerator with less beam loss during beam acceleration.

Further, by flattening the magnetic field created by the eddy current in the vacuum duct wall of the beam trajectory correcting electromagnet,
It is possible to quickly correct the beam trajectory.

[Brief description of drawings]

FIG. 1 is a perspective view of a conductive vacuum duct installed between magnetic poles of a bending electromagnet of an accelerator of the present invention and an auxiliary coil.

FIG. 2 is a cross-sectional view of the vicinity of magnetic poles of a bending electromagnet provided with a conductive vacuum duct and an auxiliary coil of the accelerator of the present invention.

FIG. 3 is a plan view of a bending electromagnet having an electrically conductive vacuum duct and an auxiliary coil of the accelerator according to the present invention as viewed from above.

FIG. 4 is an explanatory diagram that illustrates the arrangement of a vacuum duct and auxiliary coils in principle.

FIG. 5 is a cross-sectional view illustrating the arrangement of a vacuum duct and an auxiliary coil in principle.

FIG. 6 is a graph showing a magnetic field distribution inside a vacuum duct installed between magnetic poles of a bending electromagnet.

FIG. 7 is a circuit diagram when a variable resistor is connected to the auxiliary coil.

FIG. 8 is a circuit diagram when a variable resistor and a variable inductor are connected to an auxiliary coil.

FIG. 9 is a circuit diagram when the auxiliary coil is wound twice.

FIG. 10 is a perspective view of a conductive vacuum duct and an auxiliary conductor plate installed between the magnetic poles of the bending electromagnet of the accelerator of the present invention.

FIG. 11 is a graph showing a magnetic field distribution inside a vacuum duct installed between magnetic poles of a bending electromagnet.

FIG. 12 is a perspective view of a conductive vacuum duct and an auxiliary coil installed between the magnetic poles of the beam trajectory correcting electromagnet of the accelerator of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Vacuum duct, 2 ... Auxiliary coil, 3 ... Magnetic pole of a bending electromagnet, 12 ... Stopper.

Claims (15)

[Claims] 1. A main structure having a conductive main structure in a fluctuating magnetic field, and when an eddy current is induced to create a new magnetic field, the main structure is in a fluctuating magnetic field changing with the same time as the fluctuating magnetic field. A vortex characterized in that a conductive auxiliary structure different from the above is disposed, and the magnetic field is controlled by superposing the magnetic field generated by the eddy current flowing in the auxiliary structure on the magnetic field generated by the eddy current of the main structure. How to control the magnetic field created by electric current. 2. The magnetic field control method according to claim 1, wherein a part of the auxiliary structure is arranged along the eddy current flow of the main structure. 3. A conductive structure in which a conductive main structure is in a fluctuating magnetic field, and when an eddy current is induced to create a new magnetic field, it is arranged in a fluctuating magnetic field that changes with the same time as the fluctuating magnetic field. A magnetic field control device comprising a conductive substance, wherein the magnetic field generated by the eddy current flowing in the main structure is controlled by the magnetic field generated by the eddy current flowing in the conductive substance. 4. The magnetic field control device according to claim 3, wherein a part of the conductive material is arranged along the eddy current flow of the main structure. 5. A particle accelerator provided with a deflecting electromagnet for applying a magnetic field in a predetermined direction to a charged particle beam in a conductive vacuum duct to form a circular orbit, and an accelerating means for accelerating the charged particle beam, A particle accelerator, wherein a non-conductive material is installed between magnetic poles of the electromagnet when an eddy current is induced in a vacuum duct by a time change of a magnetic field of the electromagnet to create a new magnetic field. 6. The particle accelerator according to claim 5, wherein a part of the non-magnetic material is arranged along the eddy current flow in the vacuum duct. 7. The particle accelerator according to claim 5, wherein the non-magnetic material is made of a material having a conductivity higher than that of a vacuum duct wall material. 8. The particle accelerator according to claim 5, wherein the non-magnetic material is arranged on both sides of an orbit of the charged particle beam. 9. The particle accelerator according to claim 8, wherein the non-magnetic material is arranged symmetrically with respect to the trajectory of the charged particle beam. 10. The particle accelerator according to claim 5, wherein the non-magnetic material is composed of a linear closed circuit. 11. The non-magnetic material according to claim 10, wherein a part of the closed circuit formed by the non-magnetic material is arranged along the flow of the eddy current in the vacuum duct, and the other part is arranged outside the magnetic pole of the electromagnet. Particle accelerator. 12. The particle accelerator according to claim 10, wherein a resistor is connected to the closed circuit. 13. The particle accelerator according to claim 10, wherein an inductor is connected to the closed circuit. 14. The particle accelerator according to claim 5, wherein the non-magnetic material is a plate. 15. The particle accelerator according to claim 5, wherein the non-magnetic material is installed between a plurality of magnetic poles of electromagnets at point-symmetrical positions.