JP2002208499A - Beam duct for accelerator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a beam duct for an accelerator which mainly improves the incident efficiency of an electron beam and hardly gives the influence of a leaked magnetic field of a septum electromagnet to the electron beam. SOLUTION: For the beam duct 10 installed at a position adjacent to a septum electromagnet 120, on which an electron beam is made incident, in an electron accumulating ring equipped with a deflection electromagnet for deflecting an electron orbit B3 at a desired deflection angle and a septum electromagnet 120 for striking an electron on the surrounding orbit so as to accumulate an electron beam in desired energy in the surrounding orbit B3, a magnetic material is used as a material therefor, thereby reducing the influence of a leaked magnetic field of the septum electromagnet 120 on the accumulated electron beam. In this case, pure iron is used as a material for the beam duct 10, whereby magnetic saturation is hard to occur, an effect of magnetic shield is improved, processing is easy, and production cost can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a beam duct for an accelerator generally used for accelerating charged particles such as electrons and ions, and a magnetic shield method using the beam duct for an accelerator. The present invention relates to an accelerator beam duct adjacent to a septum electromagnet used for electron beam incidence and a magnetic shield method using the accelerator beam duct.

[0002]

BACKGROUND OF THE INVENTION The present invention relates to an accelerator for accelerating charged particles such as electrons and ions (a circular accelerator for accelerating charged particles in a predetermined orbit, and a linear accelerator for accelerating charged particles linearly). The present invention relates to a commonly used beam duct for an accelerator, and particularly, a beam duct for an electron storage ring is assumed. Therefore, in order to facilitate understanding of the present invention, an electron storage ring, a method of causing an electron beam to be incident on the electron storage ring, a septum electromagnet used for the incidence, and a magnetic shield of a conventional septum electromagnet will be described below. The structure will be sequentially described with reference to FIGS.

First, regarding the electron storage ring 100,
Since this is described in detail in Japanese Patent Application No. 2000-083715, it will be simply described with reference to FIG. FIG. 3 is a plan view of a race track type electron storage ring 100 as an example of the electron storage ring. In this type of electron storage ring 100, as shown in FIG.
B is opposed to the beam duct 130 maintained at a high vacuum.
The septum electromagnet 12
The electron beam incident through the zero is stored in the designed orbit in the horizontal plane with the desired energy by the deflecting action of the magnetic field.

[0004] Further, other main components of the electron storage ring 100 include quadrupole electromagnets 150A and 150B for converging the electron beam in a circular orbit, a high-frequency accelerating cavity 180 for supplying energy to the stored electron beam, and an electron. Pulse magnet 16 for forming an incident trajectory when light is incident
0, a beam position monitor 170 for monitoring whether or not the electron beam is accumulated in the orbit in the beam duct 130 as designed.

Next, a method of causing an electron beam to be incident on the electron storage ring 100 will be described with reference to FIG. In the electron storage ring 100, in order to stably store the electron beam, electrons are accelerated to a certain energy by the injector 140 shown in FIG. For example, in the type shown in FIG. 3, an electron pulse beam is accelerated to 150 MeV by an injector 140 called a microtron. On the other hand, since the electrons incident from the injector 140 have a certain angle with respect to the orbit of the electron storage ring 100, the direction of the electron beam is changed to smoothly place the electrons on the orbit. The septum electromagnet 120 is used, and the light is incident on the electron storage ring 100 via the septum electromagnet 120.

Next, the septum electromagnet 120 will be described with reference to FIG. FIG. 4 is a plan view schematically showing the septum electromagnet 120. FIG. 4 illustrates a septum electromagnet 120 of a 90-degree deflection type. The septum electromagnet 120 is a device for reducing the incident angle of the electron beam from the injector 140 as described above,
For this reason, the pulsed electron beam is instantaneously excited by a pulse current in synchronization with the passage of the septum electromagnet 120, and uses the deflection effect of the magnetic field to move the electron beam around the orbit (hereinafter, “design trajectory”). At a position slightly deviated from B3 and parallel to the orbit B3,
1

By the way, in the electron storage ring 100, the electron beam orbits around the orbit B3 while vibrating in a plane perpendicular to the traveling direction. This oscillation is called betatron oscillation. If the electron beam does not take any measures after the incidence due to the betatron oscillation, the electron beam circulates around the orbit B3 a plurality of times and then enters the septum. Returning to the incident trajectory B1 of the electromagnet 120, it collides with the inner wall of the beam duct 130, and the stable orbit B3
Disappears before being accumulated in the.

Therefore, a pulse current is applied to the incident pulse magnet 160 shown in FIG. 3 to excite instantaneously, deflect the electron beam using the falling edge of the pulse, and form a deformed orbit only at the time of incidence. To make the electron beam incident. As a result, even after the incidence, the electrons do not collide with the inner wall of the beam duct 130 and stably orbit on the orbit B3.

However, at the time of incidence, the electron beam has a large betatron oscillation amplitude, passes near the excited septum electromagnet 120, and is deflected under the influence of the leakage magnetic field of the septum electromagnet 120 to be deflected. The orbit may become unstable, or the electron beam may be adversely affected by colliding with the beam duct 130 and disappearing.

For this reason, the conventional septum electromagnet 120 is magnetically shielded with a magnetic shield member made of a magnetic material in order to reduce leakage of magnetic flux.
The magnetic shield structure of the conventional septum electromagnet 120 will be described with reference to FIGS. FIG. 5 is a vertical sectional side view showing the structure of the septum electromagnet 120 and the beam duct 130 adjacent to the septum electromagnet 120.

As shown in FIG. 5, a magnetic shield member 134 made of a magnetic material is mounted between a conventional septum electromagnet 120 and a beam duct 130. In FIG. 5, reference numeral 122 denotes an exciting coil of the septum electromagnet 120, and B1 is also shown in FIG. 4, and the incident trajectory of the electron beam incident on the electron storage ring 100 from the septum electromagnet 120; , The orbit (circular orbit) of the stored electron beam during stable accumulation,
B2 is the trajectory of the stored electron beam immediately after the incidence.

As indicated by B2 in FIG. 5, the stored electron beam immediately after incidence passes through the vicinity of the septum electromagnet 120, and thus is liable to be adversely affected by the leakage magnetic field when the septum electromagnet 120 is excited. Therefore, beam duct 130
A magnetic shield member 134 between the septum electromagnet 120 and
The magnetic shield member 134 reduces the leakage magnetic field of the septum electromagnet 120. In addition, as a material of the conventional beam duct 130, a nonmagnetic material such as aluminum, stainless steel, or copper, which is frequently used as a vacuum material, is used.

The effect produced by using the magnetic shield member 134 will be described with reference to FIGS. FIG. 6 is a side view showing only the upper half surface showing the magnetic flux FL of the septum electromagnet 120 when the magnetic shield member 134 is not used. FIG. 7 shows the magnetic shield member 13.
FIG. 4 is a side view showing only the upper half surface showing the magnetic flux FL of the septum electromagnet 120 when using No. 4; 6 and 7, only the upper half is shown because the magnetic flux and each component are vertically symmetrical.

As is apparent from a comparison between FIGS. 6 and 7, the number of magnetic fluxes FL passing near the septum electromagnet 120 is smaller in the case of FIG. It is understood that the leakage magnetic field is reduced to some extent by using.

[0015]

However, the magnetic shield structure of the conventional septum electromagnet 120 has the following problems. In FIG. 5, the magnetic shield member 1
The total thickness of the thickness 34, the wall thickness of the beam duct 130, and the exciting coil 122 is generally called a septum thickness t1. The conventional magnetic shield structure of the septum electromagnet 120 has a problem that the septum thickness t1 increases, as a matter of course because the magnetic shield member 134 is used.

As indicated by B2 in FIG. 5, the stored electron beam immediately after the incidence passes near the inner wall surface 130a of the beam duct 130 in contact with the magnetic shield member 134. In general, the distance d1 between the incident trajectory B1 and the trajectory B2 immediately after the incidence is referred to as turn separation. If the ratio of the septum thickness t1 to the turn separation becomes large, the incident pulse magnet 160 shown in FIG. In addition, the load on the power supply of the incident pulse magnet 160 is increased, and the amount of electron beams that can be incident by one excitation is reduced, resulting in a problem that the incident efficiency is deteriorated.

The design trajectory B3 and the trajectory B2 immediately after the incidence
When the distance from the beam duct is longer, the turn separation can be designed in a wider range, so that if the septum thickness t1 is small and the trajectory B2 immediately after the incidence can be set to be very close to the inner wall surface 130a of the beam duct, the incidence efficiency is improved. Therefore, if the septum thickness t1 is large, the incidence efficiency is deteriorated.
In the design of the electron storage ring 100, this septum thickness t1
The problem is how to reduce the size.

That is, in order to reduce the septum thickness t1, the thickness of the magnetic shield member 134 and the exciting coil 12
2 and the wall thickness of the beam duct 130 need to be reduced. However, since the inside of the beam duct 130 is maintained at a high vacuum, it is necessary to have a thickness that can withstand the atmospheric pressure, and if the thickness of the magnetic shield member 134 is extremely thin, the magnetic shield member 134 will have magnetic saturation. In order to reduce the effect of the magnetic shield, a certain thickness is required. Further, the thickness of the exciting coil 122 cannot be set to a certain value or less due to electric resistance.

Therefore, in the conventional magnetic shield structure of the septum electromagnet 120, it is necessary to secure a constant septum thickness, and it is difficult to improve the incident efficiency. Also, as shown in FIG.
Although it is possible to reduce the leakage magnetic flux of the septum electromagnet 120 to some extent, it is still difficult to completely eliminate the influence on the electron beam.

The present invention solves the above problems (problems),
It is an object of the present invention to provide an accelerator beam duct that improves the electron beam incidence efficiency and hardly affects the electron beam by the leakage magnetic field of a septum electromagnet.

[0021]

The beam duct for an accelerator according to the present invention is used in an accelerator for accelerating charged particles such as electrons and ions, and the orbit of the charged particles is evacuated to a vacuum. In the beam duct to hold,
The beam duct is made of a magnetic material.

With this configuration, the beam duct made of a magnetic material magnetically shields a leaked magnetic field from an external device or the like, thereby eliminating the adverse effect of the leaked magnetic field on charged particles. The performance and reliability of the accelerator can be improved.

The beam duct for an accelerator according to the present invention is used in an electron synchrotron or an electron circular accelerator such as an electron storage ring for accelerating or accumulating electrons in a desired orbit. In the beam duct for maintaining the orbit of the beam duct in a vacuum, a magnetic material is used as a material of the beam duct.

This configuration is particularly effective for accelerating electrons which are smaller in mass than the charges and are susceptible to the leakage magnetic field. In addition, the electron circular accelerator is particularly effective because electrons at almost the speed of light orbit around the design trajectory enormously many times and are affected many times by the leakage magnetic field.

According to a third aspect of the present invention, there is provided a beam duct for an accelerator, comprising: a bending electromagnet for deflecting an electron trajectory at a desired deflection angle;
An electron storage ring provided with a septum electromagnet for causing electrons to enter a design orbit and storing an electron (including positron) beam at a desired energy in a circular orbit, adjacent to the septum electromagnet and allowing an electron beam to enter The beam duct is mounted at a position, and the influence of the leakage magnetic field of the septum electromagnet on the accumulated electron beam is reduced by using a magnetic material as the material.

With this configuration, the leakage magnetic field of the septum electromagnet can be shielded without attaching a magnetic shield member between the beam duct and the septum electromagnet, so that the septum thickness can be reduced, and as a result, the efficiency of incidence on the electron storage ring can be reduced. Can be improved. Further, since the leakage magnetic field of the septum electromagnet is guided to the beam duct for magnetic shield, the influence on the electron beam accumulated in the beam duct can be greatly reduced.

According to a fourth aspect of the present invention, the beam duct for an accelerator is configured to use pure iron as a material of the beam duct.

With this structure, in addition to the above effects, magnetic saturation is less likely to occur, and the effect of the magnetic shield is improved. In addition, processing is easy, manufacturing costs are reduced, and an accelerator beam duct using a suitable material is used. It can be.

According to a fifth aspect of the present invention, there is provided an accelerator beam duct in which an inner surface of the beam duct is covered with a coating material for preventing outgas such as titanium nitride.

According to this structure, outgas from the inner wall of the beam duct can be suppressed, and the degree of vacuum in the beam duct of the accelerator such as an electron storage ring can be improved.

According to a magnetic shield method using an accelerator beam duct according to a sixth aspect of the present invention, an adverse effect of a stray magnetic field on charged particles such as electrons and ions is obtained by using the accelerator beam duct according to any one of the first to fifth aspects. Was removed.

In this manner, the performance and reliability of the accelerator using the accelerator beam duct can be improved.

[0033]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a beam duct for an accelerator (hereinafter sometimes simply referred to simply as a "beam duct") and a magnetic shielding method of the present invention will be described.
This will be described with reference to FIGS. 1 and 2 and FIGS. FIG. 1 is a sectional view showing an embodiment of the beam duct of the present invention. FIG. 2 is a side view showing only the upper half surface showing the magnetic flux FL of the septum electromagnet 120 when the beam duct of the present invention is used.

In FIG. 2, as in FIGS. 6 and 7, since the magnetic flux and each component are vertically symmetrical, only the upper half is shown. In addition, in FIG. 2, the cross-sectional shape of the beam duct is shown as a rectangular shape because of simple magnetic field calculation, and there is no consistency with that shown in FIG. 1, but there is almost no effect on the calculation result. Please note that.

First, the configuration of the accelerator beam duct of the present invention will be described with reference to FIG. As shown in FIG.
The beam duct 10 of the present embodiment has substantially the same shape as the conventional beam duct 130 shown in FIG. 5, but uses pure iron which is a magnetic material for its constituent material, and has an inner wall surface 10a for the inner wall surface 10a. And titanium nitride (TiN) are coated by a method such as an ion plating method.

When the beam duct for an accelerator according to the present invention is constructed as described above, as shown in FIG.
Although the total amount of the stray magnetic field 20 increases, it is guided to the inside 10b of the wall of the beam duct 10 made of a ferromagnetic material. As a result, when comparing FIG. 2 with FIG. 6 and FIG. 7, it is obvious that the magnetic flux FL is observed in the orbits B2 and B3 in which the electron beam is accumulated, particularly in the orbit B2 immediately after the incidence near the septum electromagnet 120. It is understood that the influence of the leakage magnetic field of the septum electromagnet 120 is greatly reduced.

That is, in the prior art, a non-magnetic material is used for the conventional beam duct 130 simply because it is often used as a vacuum material without considering the influence of a magnetic field. On the other hand, in the beam duct 10 of the present invention, contrary to this conventional technique, a magnetic material is used as a constituent material of the septum electromagnet 120. As a result, although the total amount of the leakage magnetic field of the septum electromagnet 120 increases, the flow of the magnetic flux FL of the leakage magnetic field of the septum electromagnet 120 is guided to the inside 10 b of the wall of the beam duct 10, so that the septum for the accumulated electron beam is reduced. That is, the effect of the leakage magnetic field of the electromagnet 120 is significantly reduced.

In addition to the above theoretical description, in the present embodiment, a magnetic field measurement is actually performed. For example, when a pulse-like excitation current is applied to the septum electromagnet 120 to excite the septum electromagnet 120, the peak intensity of the leakage magnetic field in the orbit B2 when using the magnetic shield member 132 shown in FIG. In the case where the beam duct 10 of the invention is used, it is also 0.6 G, and it has been confirmed that the effect of the magnetic shield is remarkably improved.

Therefore, if magnetic shielding is performed using the beam duct 10 of the present invention, unlike the magnetic shielding structure of the conventional septum electromagnet 120, there is no need to use the magnetic shielding member 134. As a result, the septum thickness t1 (see FIG. 5), which is the sum of the wall thickness of the beam duct 10, the thickness of the magnetic shield member 134, and the coil 122, is changed to the wall thickness of the beam duct 10 as shown in FIG. Since the septum thickness t2, which is the sum of the septum and the coil 122, can be reduced, the incidence trajectory B1 and the trajectory B2 of the electron beam after incidence can be reduced.
And the distance d2 between them becomes smaller.

Thus, the incident pulse magnet 16
0 (see FIG. 3) can reduce the load on the power supply and increase the incident efficiency. Further, since the distance between the design trajectory B3 and the orbital trajectory B2 immediately after the incidence can be increased, the number of electrons that collide with the wall of the beam duct 10 and disappear after the incidence can be significantly reduced. Electron incidence efficiency can be increased.

In the conventional beam duct 130, the thickness of the magnetic shield member 134 was reduced to minimize the thickness of the septum thickness t1 and the shield of the leakage magnetic field was insufficient. In the beam duct 10, the beam duct 10 itself has a role of a magnetic shield. Therefore, the thickness does not need to be so small, and the magnetic shield can be sufficiently performed.

Further, as described above, by using pure iron for the magnetic material of the beam duct 10 of the present embodiment,
Magnetic saturation is less likely to occur, and the effect of the magnetic shield is improved, processing is easy, manufacturing costs are reduced, and a magnetic shield beam duct made of a suitable material can be obtained.

Although pure iron has such excellent characteristics, it has a problem that outgas is generated. When the outgas increases, the degree of vacuum in the beam duct deteriorates, and a problem occurs that the life of the electron beam stored in the electron storage ring 100 is shortened. Therefore, in the beam duct 10 of the present embodiment, as described above, the inner surface 10
a is coated with titanium nitride so as to suppress generation of this outgas.

The accelerator beam duct of the present invention is not limited to the above-described embodiment, but can be variously modified. First,
In the above embodiment, in the electron storage ring, the case of the beam duct adjacent to the septum electromagnet has been described.
This is because the leakage magnetic field has a large effect. However, the accelerator beam duct of the present invention
Of course, the present invention can also be applied to a linear type accelerator or an accelerator for accelerating other charged particles such as ions.
If these are used, the adverse effect of the leakage magnetic field from the external device or the like can be reduced, so that the performance and reliability of the accelerator can be improved.

Further, in the above embodiment, pure iron is used as the magnetic material of the beam duct, but it goes without saying that a beam duct using another magnetic material is also included in the present invention. Furthermore, although the example using titanium nitride as the coating material for coating the inner wall surface of the beam duct has been described, it goes without saying that this may be replaced with another coating material for preventing outgassing. is there.

[0046]

The beam duct for an accelerator and the magnetic shield method according to the present invention have the following excellent effects because they are configured as described above. (1) The beam duct for an accelerator is used in an accelerator for accelerating charged particles such as electrons and ions as described in claim 1, and is a beam duct for maintaining the orbit of the charged particles in a vacuum. Since the magnetic material is used as the material for the material, the magnetic leakage from the outside is magnetically shielded by the beam duct made of magnetic material, and the adverse effect of the magnetic leakage on the charged particles can be removed. The performance and reliability of the accelerator used can be improved.

(2) The beam duct for an accelerator according to claim 2 is used for an electron circular accelerator, and in the beam duct for keeping the orbit of electrons in a vacuum, a magnetic material is used as a material of the beam duct. Therefore, the effect of the magnetic shield is particularly effective when accelerating electrons whose mass is smaller than the electric charge and which is easily affected by the leakage magnetic field. (3) Further, the electron circular accelerator is particularly effective because electrons at almost the speed of light orbit at a design orbit a large number of times and are affected many times by the leakage magnetic field.

(4) The beam duct for an accelerator according to claim 3 is a beam duct which is attached to a position where an electron beam is incident and which is adjacent to a septum electromagnet in an electron storage ring, and is made of a magnetic material. By using this, the effect of the leakage magnetic field of the septum electromagnet on the accumulated electron beam is reduced, so that the leakage magnetic field of the septum electromagnet can be shielded without attaching a magnetic shield member between the beam duct and the septum electromagnet. Can be reduced, and as a result, the efficiency of incidence on the electron storage ring can be improved. (5) Further, since the leakage magnetic field of the septum electromagnet is guided to the magnetic shield beam duct, the influence on the electron beam accumulated in the beam duct can be significantly reduced.

(6) In the beam duct for an accelerator according to the fourth aspect, since pure iron is used as the material of the beam duct, magnetic saturation is less likely to occur, and the effect of the magnetic shield is improved, and processing is easy. Thus, the manufacturing cost can be suppressed, and a beam duct for an accelerator using a suitable material can be obtained.

(7) In the beam duct for an accelerator according to the fifth aspect, since the inner surface of the beam duct is coated with a coating material for preventing outgas such as titanium nitride, outgas from the inner wall of the beam duct is suppressed. The degree of vacuum in the beam duct of the accelerator, such as an electron storage ring, can be improved.

(8) In the magnetic shield method using the accelerator beam duct according to claim 6, the adverse effect of the leakage magnetic field on charged particles such as electrons and ions is eliminated by using the accelerator beam duct of the present invention. As a result, the performance and reliability of the accelerator using the accelerator beam duct can be improved.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional side view showing one embodiment of an accelerator beam duct of the present invention.

FIG. 2 is a side view showing only the upper half surface showing the magnetic flux of the septum electromagnet when the beam duct for an accelerator of the present invention is used.

FIG. 3 is a plan view of a race track type electron storage ring.

FIG. 4 is a plan view schematically showing a conventional septum electromagnet.

FIG. 5 is a vertical sectional side view showing a structure of a septum electromagnet and a beam duct adjacent to the septum electromagnet.

FIG. 6 is a side view showing only the upper half surface showing the magnetic flux of the septum electromagnet when the magnetic shield member is not used.

FIG. 7 is a side view showing only the upper half surface showing the magnetic flux of the septum electromagnet when the magnetic shield member is used.

[Explanation of symbols]

 10: beam duct 10a: inner surface of beam duct 100: electron storage ring 110A, 110B: deflection magnet 120: septum magnet B2, B3: orbit

Claims (6)

[Claims] 1. A beam duct for use in an accelerator for accelerating charged particles such as electrons and ions and for keeping a trajectory of the charged particles in a vacuum, wherein a magnetic material is used as a material of the beam duct. A beam duct for an accelerator. 2. An electron circular accelerator such as an electron synchrotron or an electron storage ring for accelerating or accumulating electrons in a desired orbit, and for maintaining the orbit of the electrons in a vacuum. A beam duct for an accelerator, wherein a magnetic material is used as a material of the beam duct. 3. A deflecting electromagnet for deflecting an electron trajectory at a desired deflection angle, and a septum electromagnet for causing electrons to enter a design trajectory, so that an electron (including positron) beam is accumulated at a desired energy in the orbit. In the electron storage ring, a beam duct adjacent to the septum electromagnet and attached at a position where an electron beam is incident, and by using a magnetic material as its material, a leakage magnetic field of the septum electromagnet gives the stored electron beam to the storage electron beam. An accelerator beam duct characterized in that the influence is reduced. 4. The beam duct for an accelerator according to claim 1, wherein pure iron is used as a material of said beam duct. 5. The beam duct for an accelerator according to claim 1, wherein an inner surface of the beam duct is coated with a coating material for preventing outgas such as titanium nitride. 6. An accelerator beam, wherein an adverse effect of a stray magnetic field on charged particles such as electrons and ions is removed by using the beam duct for an accelerator according to claim 1. Magnetic shielding method by duct.