JP2580370B2 - Periodic magnetic field generator - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a periodic magnetic field generating device used for generating radiation in a radiation generating system using an electron beam, and in particular, to prevent diffusion of an electron beam. Further, the present invention relates to a periodic magnetic field generator such as a wiggler, an undulator, etc., which has been improved to improve the generation of emitted light.

[Conventional technology]

Wiggler is a device that generates a synchrotron radiation from a particle beam accelerated by a particle beam accelerator used for a free electron laser, and is a device that applies a periodic magnetic field to an electron beam. In this device, a plurality of permanent magnet rows are arranged opposite to each other with the electron beam interposed,
The N and S magnetic poles are formed so as to face the electron beam alternately, and it is usual to use several tens of pairs of permanent magnets in the permanent magnet array.

FIG. 3 (a) is a front view of an essential part showing an example of a conventional wiggler magnet device, and FIG. 3 (b) is a view taken along line A- in FIG. 3 (a).
FIG. 3 is a sectional view taken along line A. In both figures, 1 is a permanent magnet,
A plurality of pairs (for example, 100 to 150 pairs) are arranged so that the N and S magnetic poles are opposed to each other via the magnetic gap 2 without being relatively displaced, and different magnetic poles appear adjacent to the flow direction of the electron beam 3. . Reference numeral 4 denotes a yoke, which is formed in a strip shape from a magnetic material such as soft iron, and supports the back side of the permanent magnet 1. The center axis in the flow direction of the electron beam 3 is the z axis, and z
The center line of the NS magnetic pole of the permanent magnet 1 orthogonal to the axis is defined as the y-axis, and the axis orthogonal to the z-axis and the y-axis is defined as the x-axis.

[Problems to be solved by the invention]

A periodic magnetic field is applied to the electron beam 3 in the z-axis direction by the wiggler magnet device having the above-described configuration, and emitted light is generated in the magnetic gap 2. However, the electron beam 3 is diffused at the entrance of the wiggler. There is. If the electron beam 3 is diffused in this way, it is not preferable because it adversely affects the generation of synchrotron radiation. It is recognized that the diffusion of the electron beam 3 as described above is caused by the configuration of the magnetic gap 2 of the permanent magnet 1 near the entrance.

FIG. 4 is a diagram showing the relationship between the axial position near the entrance of the device shown in FIGS. 3 (a) and 3 (b) and the air gap magnetic flux density. In FIG. 4, the origin of the z-axis, that is, the axial position is the entrance of the periodic magnetic field generator, and the air gap magnetic flux density is
This is a value in the y-axis direction in FIG. Note that the maximum value Bg (absolute value) of the air gap magnetic flux degree appears at the position of, for example, the N pole of the permanent magnet 1 in FIG. In the conventional periodic magnetic field generator, as shown in FIG. 4, the maximum value Bg of the air gap magnetic flux density is equal from the entrance to the intermediate portion, and the maximum value is large (for example, 3000 to 5000 G). Therefore, the electrons accelerated while receiving a linear force in the z-axis direction by the magnetic field of the accelerator (not shown) enter the periodic magnetic field generator at the entrance thereof (the z-axis direction).
(See the y-axis direction, see FIG. 3 (b)). Therefore, there is a problem that electrons which have been traveling straight in the z-axis direction are diffused.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the problems existing in the prior art and to provide a periodic magnetic field generator that prevents the diffusion of an electron beam and has an improved convergence function.

[Means for solving the problem]

In order to achieve the above object, in the present invention, a plurality of pairs of permanent magnets are arranged so that NS magnetic poles face each other via a magnetic gap and different magnetic poles appear adjacent to the flow direction of the electron beam. In the periodic magnetic field generator, a technical measure was adopted in which the distance between the magnetic poles facing the magnetic gap was made larger near the entrance than in the middle and gradually decreased along the direction of electron beam travel. .

In the present invention, it is preferable that the envelope connecting the maximum values of the air gap magnetic flux density in the vicinity of the entrance is formed to have a cosine curve.

The permanent magnet in the present invention is preferably formed of R (at least one of rare earth elements such as Nd, Pr, Dy) -Fe-B-based material. The content of the rare earth element R in the R-Fe-B-based material is preferably in the range of 10 to 30 atomic%. If R is less than 10 at%, the magnetic properties (particularly the coercive force) decrease, while if it is more than 30 at%, R-rich is not preferable because the non-magnetic phase increases and the residual magnetic flux density decreases. In this case, rare earth elements such as Nd and Pr are usually used as the rare earth element R, but Nd, which is abundant in resources and relatively inexpensive, is most common. In order to improve the coercive force, a part (about 1 to 30%) of R can be replaced with a heavy rare earth element such as Dy, Ho, or Tb. Further, R is La, Ce, Sm, Gd, Er, Eu,
At least one of Tm, Tb, and Y can be included.

The content of Fe is desirably in the range of 65 to 85 atomic%. Fe is 65
If it is less than atomic%, the residual magnetic flux density decreases, and if it is more than 85 atomic%, the coercive force decreases, which is not preferable.

The content of B is desirably in the range of 2 to 28 atomic%. B is 2
If it is less than atomic%, the coercive force decreases, while if it is more than 28 atomic%, the B-rich nonmagnetic phase increases and the residual magnetic flux density decreases, which is not preferable.

In addition, in addition to the above essential components, impurities inevitably produced (for example, O ₂ ) may be included in some cases. Further, a known additive element (for example, Co, Al, Ti, or the like) may be contained in the R-Fe-B-based material. Such additional elements are described in, for example,
Nos. 162754 and 61-87825.

The permanent magnet according to the present invention can be manufactured, for example, as follows. First, the R-Fe-B-based alloy is dissolved in Ar or in a vacuum by a usual method, but B may be added as ferroboron. Preferably, the rare earth element is charged last. The ingot after melting is coarsely and finely pulverized. The coarse pulverization is performed by a stamp mill, a jaw crusher, a brown mill, a disk mill, or the like, and the fine pulverization is performed by a jet mill, a vibration mill, a ball mill, or the like. Both are performed in a non-oxidizing atmosphere to prevent oxidation, and it is therefore preferable to use an organic solvent or an inert gas. The particle size after pulverization is preferably 2 to 5 μm (FSS). The magnetic powder produced as described above is formed into a molded body of a predetermined shape by a molding apparatus in a magnetic field. This compact is then sintered, and the sintering is performed at 950 to 1150 ° C. in an inert gas such as Ar or He or in a vacuum or in hydrogen.
For 20 minutes to 2 hours. After sintering, heat treatment is performed in an inert gas atmosphere as necessary. Preferred heat treatment conditions are at 500 to 700 ° C. for 30 minutes to 3 hours. Finally, the orientation direction of the magnetic powder (in this case, height or y
(Axial direction) and magnetize. Magnetizing field strength is 20-30kO
The range of e is good.

(Operation)

With the above configuration, the action of the force due to the magnetic field near the entrance of the periodic magnetic field generator can be reduced, the diffusion of the electron beam can be prevented, and the generation of emitted light can be improved.

〔Example〕

FIG. 1 is a front view of an essential part showing an embodiment of the present invention, and FIG. 2 is a diagram showing a relationship between an axial position and an air gap magnetic flux density near an inlet of the apparatus shown in FIG. The directional positions are shown correspondingly. In FIG. 1, the same parts are indicated by the same reference numerals as in FIGS. 3 (a) and 3 (b).
First, in FIG. 1, it faces the magnetic gap 2 of the permanent magnet 1.
The distance 1 between the NS magnetic poles is formed so as to be larger than the distance L at the intermediate portion near the entrance and to gradually decrease along the traveling direction of the electron beam 3. As a result, as shown in FIG. 2, the maximum value of the air gap magnetic flux density gradually increases along the traveling direction of the electron beam 3 (see FIG. 1), that is, in the z-axis direction, and reaches a predetermined value Bg in the middle part. To reach.

With the above configuration, the sudden magnetic field effect on the electron beam 3 shown in FIG. 1 can be reduced, and the diffusion of electrons traveling straight can be prevented.

As shown by the broken line in FIG. 2, more preferable results can be obtained if the envelope connecting the maximum values of the air gap magnetic flux density near the entrance is formed to have a cosine curve.

〔The invention's effect〕

Since the present invention has the configuration and operation as described above, by relaxing the effect of the magnetic field near the entrance, it is possible to prevent the diffusion of the electron beam and to eventually generate the synchrotron radiation efficiently. There is.

[Brief description of the drawings]

FIG. 1 is a front view of an essential part showing an embodiment of the present invention, FIG. 2 is a diagram showing a relationship between an axial position and an air gap magnetic flux density near an inlet of the apparatus shown in FIG. 1, and FIG. FIG. 3 is a front view of a main part showing an example of a conventional wiggler magnet device, FIG. 3 (b) is a sectional view taken along line AA in FIG. 3 (a), and FIG. 4 is FIGS. 3 (a) and 3 (b). FIG. 6 is a diagram showing a relationship between an axial position near an inlet of the device shown in FIG. 1: permanent magnet, 2: magnetic air gap, 3: electron beam.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Nao Maehara 801 Nakahara, Naka-machi, Naka-machi, Naka-gun, Ibaraki Pref. Inside the Japan Atomic Energy Research Institute Naka Laboratory (72) Inventor Yasuaki Kishimoto Naka-hara, Naka-machi, Naka-machi, Naka-gun, Ibaraki 801-1 Inside the Japan Atomic Energy Research Institute Naka Research Laboratory

Claims (2)

(57) [Claims] A periodic magnetic field generator comprising a plurality of pairs of permanent magnets arranged so that NS magnetic poles face each other via a magnetic air gap and different magnetic poles appear adjacent to each other in the electron beam flow direction. A periodic magnetic field generator, wherein a distance between magnetic poles facing an air gap is formed so as to be larger in the vicinity of an entrance than in an intermediate portion and to be gradually reduced along a traveling direction of an electron beam. 2. The periodic magnetic field generator according to claim 1, wherein the envelope connecting the maximum values of the air gap magnetic flux density in the vicinity of the entrance is formed as a cosine curve.