JPH08255726A - Manufacture of magnet array and light source using the same - Google Patents

Abstract

PURPOSE: To miniaturize a light source by periodically radiating a rare earth element magnet plate spatially at a predetermined interval with a radioactive ray to demagnetize while applying a reverse magnetic field to the magnet plate unidirectionally magnetized in a thickness direction, and simultaneously applying the reverse magnetic field to invert the magnetization. CONSTITUTION: A permanent magnet magnetic circuit for applying a reverse magnetic field made of a permanent magnet 2 and a yoke 3 is manufactured, and a magnetized rare earth element permanent magnet plate 1 is inserted into an air gap 6. An electron beam 4 is radiated from an upper direction, and radiated to the plate 1 from a gap 5. Thus, a reverse magnetic field is generated in the plate 1 unidirectionally magnetized in the thickness direction, and the magnetization of the radiated site is inverted. Thus, the short period length of the magnet array in which the magnets periodically inverted in the magnetizing direction of the magnets can be realized without forming a thin plate magnet.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a magnet array and an insertion light source using the magnet array.

[0002]

2. Description of the Related Art An insertion light source composed of a permanent magnet or a permanent magnet and a magnetic material (iron or iron-cobalt alloy) is inserted into a linear portion of an electron accelerator (or an electron storage ring) with a vacuum chamber sandwiched between the magnet and the magnet. A sinusoidal periodic magnetic field is generated in the gap between the rows (see FIG. 1). High-speed electrons traveling in the accelerator make a meandering motion by the periodic magnetic field and generate synchrotron radiation from each meandering point (Halbach, Nuclear Instruments and M
ethod 187, (1981), 109).

There are a wiggler mode and an undulator mode depending on the degree of meandering. In the Wiggler mode, the emitted light from each meandering point is superimposed, and the emitted light with a power 10 to 1,000 times higher than that emitted from the deflecting electromagnet is obtained. On the other hand, in the undulator mode, the synchrotron radiation generated by each meandering motion interferes with each other, and the fundamental wave and its higher-order light are 10 to 1,000 times stronger than the Wiggler light. Wiggler mode or undulator mode can be classified by a parameter called K value. K
When the value is around 1 or less, it becomes an undulator, and when it is more than K value, it becomes a wiggler.

Since the emitted light power from the insertion light source is proportional to the number of magnet cycles, it is desirable to use an insertion light source with as many cycles as possible. For that purpose, it is necessary to lengthen the linear portion of the electron accelerator in which the insertion light source is installed. Since it is necessary to make the accelerator large, there is a limit in terms of technology and cost.

In order to reduce the size of the accelerator, it is effective to shorten the cycle length of the inserted light source. However, when shortening the cycle length, the void length must be shortened at the same time.
This is because when the air gap length is large, the magnetic flux emitted from a certain magnetic pole as shown in FIG. 2 does not go to the opposing magnetic pole direction (dotted line in FIG. 2) but flows toward the adjacent magnetic pole (solid line in FIG. 2). .
One measure of the period length and the void length is period length = void length. Therefore, when the cycle length is 5 mm or less, the void length is also 5
It should be less than mm. If the vacuum chamber inserted between the gaps of the insertion light source is narrowed in this way, the impedance becomes high and the required degree of vacuum cannot be achieved,
It takes a long time to evacuate.

In order to realize an insertion light source with a short cycle length, a vacuum sealed insertion light source has been devised (Kitamura; Review
of Scientific Instrument 63 (1), (1992), 400). In the vacuum-sealed type, since the pair of magnet rows is installed in the vacuum chamber, there is no restriction on achieving the degree of vacuum, and the magnet gap length can be shortened. Even in the case of the vacuum-sealed type, it is not possible to shorten the void length to some extent. The obstructing factors include the beam diameter of electrons, the impedance of the vacuum system, the fluttering of the magnetic properties of the magnet, the magnetic field measuring method and the adjusting method, and the factors particularly related to the magnetic properties of the permanent magnet are important.

[0007]

For the insertion light source, a sintered NdFeB magnet of rare earth magnet is often used, and this type of magnet has high magnetic characteristics and is easily magnetized. Therefore,
It is convenient for generating a high magnetic field in the air gap, and since there is little variation in the characteristics between magnets due to magnetization, it is suitable for realizing a precise magnetic field distribution. Therefore, it is generally used as an insertion light source, but a problem arises when an insertion light source with a short period is realized. For example, to realize an insertion light source with a cycle length of 5 mm or less, NdFeB having a thickness of about 1 mm is used.
You need a magnet.

With NdFeB magnets, the manufacture of thin-walled magnets is realized by polishing or cutting, but the processing causes characteristic deterioration. Since the area / volume ratio is small for magnets with a thickness of mm order or more, there is almost no problem of processing deterioration, but the area / volume ratio is large for magnets with a thickness of 1 mm or less, and the surface area is relatively large. The deterioration cannot be ignored.

In particular, in the case where the uniformity of the magnetic characteristics of individual magnets is required as in the insertion light source, in addition to the usual variations in the magnetic characteristics, the variations in the characteristics due to processing deterioration are superposed, which is a serious problem. Is. It has been reported that the heat treatment of the thin NdFeB magnet and the heat treatment of the magnet after the rare earth metal coating are applied to the magnet in order to mitigate the process deterioration, but it is not so effective.

[0010]

In order to realize an insertion light source with a short cycle length, the present invention is to manufacture a magnet array with a short cycle length by improving the magnetizing method without thinning the NdFeB magnet. This is because, in a method of manufacturing a magnet array in which magnets in which the magnetization directions of the individual magnets are periodically reversed are arranged, a reverse magnetic field is applied to a rare earth permanent magnet plate unidirectionally magnetized in the thickness direction. , Periodically irradiating the magnet plate with radiation spatially at regular intervals to demagnetize the irradiation part of the magnet plate,
At the same time, a method of manufacturing a magnet array characterized by applying a reverse magnetic field and reversing the magnetization, and a pair of magnet rows in which magnets in which the magnetization directions of the individual magnets are periodically reversed are arranged to face each other, An insertion light source, in which a gap for passing a particle beam is provided between the magnet rows, is characterized by using the magnet row.

That is, by inserting a rare earth permanent magnet plate unidirectionally magnetized in the thickness direction into a magnetic circuit for generating a reverse magnetic field and irradiating it with radiation, the magnetization of the irradiation site can be reversed. Therefore, it has been found that it is possible to realize a magnet array having a short cycle length in which magnets in which the magnetization directions of the individual magnets are periodically inverted are arranged without machining a thin plate magnet. It was found that an insertion light source with a short period and a high number of cycles can be produced, and by using the insertion light source in a small electron accelerator, strong synchrotron radiation can be generated, and various studies were conducted to complete the present invention.

According to the present invention, a rare earth permanent magnet is processed into a thickness of mm or less, and the insertion light source is not formed by combining the magnets in the same manner as in the prior art. Instead, a large magnet plate corresponding to several cycles or more is produced and reduced. By forming magnetization reversal periodically by magnetizing and reverse magnetic field magnetization, it is possible to form a magnet array in which a large number of small magnets whose magnetization directions are periodically reversed are arranged. Is the main point of the present invention. There are two main points of the technique for realizing the insertion light source having a short cycle length of the present invention. One is a rare earth permanent magnet plate uniformly magnetized in one direction and periodically irradiated with radiation at regular intervals. This is the point of demagnetization, and the other is the point of reversing the magnetization by applying a reverse magnetic field to the demagnetized portion.

First, the demagnetization by irradiation of radiation will be described. It is known that a rare earth magnet is demagnetized by irradiation of some kind of radiation. Especially sintered NdFeB magnets and sintered 1-
Rare earth magnets having a nucleation and growth type coercive force mechanism, such as the 5 type SmCo magnet, are
It is known that it is easy to demagnetize by irradiation with radiation. Demagnetization of this rare earth magnet does not occur by any kind of radiation, it easily occurs by particle beams of protons, electrons, neutrons, etc., and hardly occurs by γ rays or X rays. For example, the present inventors cause by relativistic fast electron beam irradiation.
We reported on the demagnetization of NdFeB magnets [announced at the Japan Radiation Optics Society (1993)].

Regarding the demagnetization effect by electron beam irradiation, it has been clarified that it does not involve a change in the structure of the magnet and is not thermal demagnetization due to temperature rise, but the demagnetization mechanism is not clear. Qualitatively, the demagnetization model shown in FIG. That is, when a magnet magnetized in a certain direction is irradiated with an electron beam, the irradiation site is shown in FIG.
As shown in (enlarged view), they are magnetized in different directions, and it is considered that they are demagnetized by canceling each other. As described above, since the magnet does not undergo permanent deterioration such as tissue change due to electron beam irradiation, the original magnetic flux value is restored by re-magnetization.

When attempting to partially demagnetize a magnetized magnet plate, thermal demagnetization due to application of heat causes diffusion of heat and thermal distortion due to anisotropy of the coefficient of thermal expansion. However, due to the blurring and cracking due to thermal strain, only a magnet plate with a certain thickness or less could be partially demagnetized. On the contrary,
In the case of radiation, especially electron beam irradiation, since demagnetization occurs in a non-thermal process, the boundary between the demagnetized region and the non-demagnetized region is clear, and only the desired region can be demagnetized. Of course, although the temperature rises to some extent by electron beam irradiation, it has been found that only the electron beam irradiation region can be demagnetized by adjusting the irradiation amount and the magnetic characteristics of the magnet plate, especially the coercive force.
This is because the high-speed electrons penetrate into the magnet and the heat does not diffuse from the surface, but heat is generated uniformly at the irradiation site, and the electron beam irradiation is given by repeated irradiation of short-time pulses. This is because the irradiation time is short and the temperature rise does not exceed 80 ° C. Since the position of the electron beam can be precisely controlled by the magnetic field, it is easy to irradiate the electron beam at an interval of about 1 mm required by the insertion light source having a short cycle length.

As described above, the energy intensity of the electron beam required to cause the demagnetization of the magnet may be 1 MeV or more, and preferably 5 to 20 MeV. If this exceeds 20 MeV, there is a problem of activation of the magnet material.

The application of the reverse magnetic field can be performed by a pulsed magnetic field by an electromagnet or an air-core coil or a magnetic circuit using a permanent magnet, but an NdFeB system permanent magnet magnetic circuit that can make the whole compact is desirable. For example, as shown in FIG. 4, the permanent magnet 2 and the yoke 3
A permanent magnet magnetic circuit for applying a reverse magnetic field is manufactured, and the magnetized rare earth permanent magnet plate 1 is inserted into the gap 6. The electron beam 4 is emitted from the upper direction, and the electron beam 4 is emitted to the magnet plate 1 through the gap 5. By moving either the magnet plate or the permanent magnet magnetic circuit, electron beam irradiation can be performed at regular intervals under application of a reverse magnetic field. In a permanent magnet magnetic circuit that applies a reverse magnetic field, the magnetic field strength generated in the air gap 6 is
1 Tesla or more is good. The magnet plate 1 is magnetized in the opposite direction at regular intervals to obtain a magnet array having a constant cycle length. Since demagnetization and temperature rise occur simultaneously during electron beam irradiation, it is considered that the coercive force of the magnet plate falls below the reverse magnetic field at this time and the reverse magnetic field causes magnetization.

Since the reverse magnetic field is applied to the magnet plate magnetized in one direction, magnetization reversal easily occurs due to demagnetization due to electron beam irradiation and accompanying temperature rise, and it is magnetized in the opposite direction. By repeating this at regular intervals, it is possible to manufacture a magnet array in which the magnetization directions are alternately reversed and magnetized in a short period. Since there is no change in the structure of the rare earth permanent magnet due to electron beam irradiation, there is no change in the magnetic characteristics in the inversion region, and there is no problem.
By combining a plurality of magnet arrays manufactured in this way, an insertion light source with a short cycle length can be manufactured.

The rare earth permanent magnet plate used in the present invention is
It is represented by the formula R (FeCo) BT, where R is Y containing La, C
e, Pr, Nd, Sm, Eu, Gd, Tb, Dy, H
One or more rare earth elements selected from o, Er, Tm, Yb and Lu, where T is Al, Si, T
i, V, Cr, Mn, Ni, Cu, Zn, Ga, Zr,
The sintered magnet is mainly composed of NdFeB selected from Nb, Mo, Sn, Hf, Ta and W.

Since the insertion light source of the present invention uses a plurality of magnet arrays produced by the above-mentioned method and has magnetized faces arranged as shown in FIG. 1, particle beams pass between the magnet arrays. It is provided with a void. The length of the straight line portion of this insertion light source is determined by the reversal cycle length of the magnet array, but in the case of the magnet array of the present invention, this cycle length can be set to 5 mm or less, so the insertion light source should be miniaturized. Therefore, it can be used as a vacuum-sealed insertion light source arranged under vacuum.

[0021]

According to the present invention, in a method for manufacturing a magnet array in which magnets whose magnetizing directions are periodically reversed are arranged, a reverse magnetic field is applied to a rare earth permanent magnet plate unidirectionally magnetized in the thickness direction. Meanwhile, a method of manufacturing a magnet array, which comprises periodically irradiating the magnet plate with radiation spatially at regular intervals to demagnetize the irradiation portion of the magnet plate, and at the same time applying a reverse magnetic field to reverse the magnetization, and The gist of the invention is an insertion light source using a magnet array, and according to the present invention, the insertion light source can be miniaturized.

[0022]

EXAMPLES The present invention will be described below with reference to examples. Example 1 A 50 mm wide NdFeB magnet manufactured by the powder sintering method was magnetized. The magnetic characteristics of this NdFeB sintered magnet are Br = 12.5kG,
iHc = 18 kOe and (BH) max = 37.2 MGOe. Next, this magnetized magnet is set in a magnetic circuit for applying a reverse magnetic field having a magnetic field of 11 kG shown in FIG. 4 in the magnetic circuit direction opposite to the magnetic field direction of the magnetic field, and an electron beam with an energy of 10 MeV is emitted from a 1 mm wide irradiation hole for 60 minutes.
When the magnetized portion was irradiated at an interval of mm, a magnet having a magnetization pattern as shown in FIG. 5 and a period length of 2 mm could be obtained.

Example 2 Using eight magnet rows obtained in Example 1, four magnets were made to face each other and the linear portion was 20 cm, the period length was 2 mm, and the period number was 1
00 insertion light source was prepared. It should be noted that with the conventional insertion light source arranged in the atmosphere, a length of 200 to 300 cm was required to realize the number of cycles of 100, so the direct irradiation part of the insertion light source should be
It was possible to make it 10 or less.

[0024]

According to the method of the present invention, a magnet array having a magnetization pattern reversal period of 5 mm or less can be obtained, so that a small insertion light source can be manufactured.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of an insertion light source.

FIG. 2 is a diagram showing a flow of magnetic flux when an insertion light source has a long air gap length.

FIG. 3A is a model diagram showing a demagnetization mechanism by electron beam irradiation. (B) is an enlarged view of an electron beam irradiation site.

FIG. 4 is a model diagram showing a method of manufacturing a magnet array by a reverse magnetic field applying permanent magnet magnetic circuit.

FIG. 5 is a diagram showing an example of a magnetization pattern of a magnet array manufactured by the method of the present invention.

[Explanation of symbols]

 1 ... Rare earth permanent magnet plate 2 ... Permanent magnet 3 ... Yoke 4 ... Electron beam 5 ... Gap 6 ... Void 7 ... Magnetization direction 8 ... Direction of reverse magnetic field

Claims (6)

[Claims] 1. A method of manufacturing a magnet array in which magnets in which the magnetization directions of individual magnets are periodically reversed are arranged, in which a reverse magnetic field is applied to a rare earth permanent magnet plate unidirectionally magnetized in a thickness direction. A method for manufacturing a magnet array, characterized in that the magnet plate is periodically irradiated with radiation at regular intervals to demagnetize an irradiation portion of the magnet plate, and at the same time, a reverse magnetic field is applied to reverse the magnetization. 2. The method for manufacturing a magnet array according to claim 1, wherein the radiation is an electron beam. 3. The method for producing a magnet array according to claim 1, wherein the reverse magnetic field is applied at 1 tesla or more using an NdFeB magnet. 4. An insertion method in which magnet rows in which magnets whose magnetizing directions are periodically reversed are arranged are opposed to each other, and a gap for passing a particle beam is provided between the magnet rows. An insertion light source, comprising a magnet array manufactured by the method according to claim 1 in the light source. 5. The cycle length of reversal of the magnetization direction of the magnet array is 5 mm.
The insertion light source according to claim 4, which is as follows. 6. The insertion light source according to claim 4, wherein the magnet array is arranged under vacuum.