JP2001023800A - Variable polarization insertion light source - Google Patents

Abstract

(57) [Summary] To provide a variable polarization insertion light source capable of switching between left and right circularly polarized light and elliptically polarized light at high speed and effectively using the length of a linear portion. SOLUTION: Three sets of planar undulators are arranged in the horizontal direction, and of two adjacent sets of undulators, three diagonal magnet rows are aligned in phase, and at least a half in the horizontal direction with respect to the remaining three magnet rows. The phase shifts by the period distance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron accelerator or an electron storage ring which can be inserted into a linear portion to generate high-brightness circularly polarized light, elliptically polarized light, and linearly polarized light by phase switching. The present invention relates to a variable polarization insertion light source that can be performed at high speed.

[0002]

2. Description of the Related Art An insertion light source (see FIG. 2A) composed of a permanent magnet or a permanent magnet and a magnetic material (iron or iron-cobalt alloy) is provided with a vacuum chamber in a linear portion of an electron accelerator (or electron storage ring). It is useful as a device that emits strong synchrotron radiation. The insertion light source generates a sinusoidal periodic magnetic field in the gap between the magnet rows (FIG. 2).
(B)). As shown in FIG. 3, the insertion light source that generates the periodic magnetic field includes a hullback type (a) composed of only the permanent magnet 10 and a hybrid type (b) composed of the permanent magnet 10 and the magnetic pole 15. As shown in FIG. 2 (c), the high-speed electrons rotating in the accelerator make a meandering motion by the periodic magnetic field, and emit light from each meandering point (Halbach, Nuclear).
Instruments and Method 187, (1981), 109). There are wiggler mode and undulator mode depending on the degree of meandering. In the wiggler mode, the radiated light generated from each meandering point is superimposed, and radiated light having a power 10 to 1000 times higher than the radiated light from the bending electromagnet is obtained. In the undulator mode, on the other hand, the radiated light generated from each meandering motion interferes, and the fundamental wave and its higher-order light have an additional 10 wiggler light.
A strong light of about 1000 times is obtained. The wiggler mode or the undulator mode can be classified by a parameter called a K value. When the K value is around 1 or less, the undulator is used. When the K value is large, the wiggler is used. In the present invention, both are collectively called an undulator or an insertion light source. As shown in FIGS. 3A and 3B, the insertion light source is roughly classified into two types, a Halbach type and a hybrid type. Both types have substantially the same magnetic field intensity and distribution, and there is no significant difference. However, in general, the hybrid type often uses less magnet weight. In addition, in the early stage of the development of the insertion light source, the variation in the angle and characteristics of the permanent magnet was large, so that the hybrid type was easier to align the magnetic field strength than the Halbach type. In recent years, permanent magnets have small dispersion and uniform characteristics, and a method of rearranging magnet pairs has been introduced and improved, so that almost the same magnetic field distribution can be obtained by either method. The displacement of the electron orbit when the air gap is changed is small because the Halbach type has almost linearity, but the hybrid orbit is non-linear and the electron orbit is likely to be displaced. An insertion light source as shown in FIGS. 3A and 3B is a general type called a plane undulator.

[0003] The radiation generated by the undulator is not limited to linearly polarized light. Undulators capable of generating circularly polarized light and elliptically polarized light have already been proposed, and for example, various undulators as shown in FIG. 4 are known. Among them, the Sasaki-type undulator changes the phase of the diagonal magnet row across the gap with respect to the adjacent magnet row, switching between linearly polarized light, elliptically polarized light, and circularly polarized light to generate polarized light. Yes (Japanese Patent Application 4-110236, Japanese J
ournal of Applied Physics 63, (1992), L1794, Nuclear
Instruments and Methods, A331, (1993), 763). For this reason, it is also called a variable polarization undulator. Onuki type (Nuclear Instruments and
Methods, A246, (1986), 94, Review of Scientic Instrum
ents 60, (1989), 1838) and Kitamura type (Review of Scientic Instruments 66, (1995), 1
937) can also change the polarization of emitted light by phase driving. For circularly polarized light or elliptically polarized light, high-speed switching between left and right polarized light is required. This is a request from an experimental method that can greatly increase the S / N ratio of the signal obtained by frequency modulation. In an attempt to switch between left and right circularly polarized light by mechanical phase shift in the Sasaki type shown in FIG. 5, driving at 0.5 Hz has been confirmed. However, the frequency modulation by the phase drive must be forcibly performed while attraction and repulsion on the order of tons act between adjacent magnet rows. Therefore, although phase driving at 1 Hz or higher is possible in principle, it is very difficult in practice. One answer to this is
As shown in Fig. 6, the undulator is arranged back and forth in clockwise (CW) and counterclockwise (ACW) polarization modes (in Fig. 6, a Sasaki type series arrangement is assumed), and the electron kick magnet is undulatored. It switches between left and right polarizations by placing it at the left, right, and middle positions. Since this can be switched by a change in the magnetic field strength of the electromagnet, high-speed switching is possible. However, since only half the length of the straight portion can be effectively used as the undulator, the luminance of emitted light is reduced.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to realize a variable polarization undulator which can switch between left and right polarization modes at high speed and can effectively use the length of a linear portion.

[0005]

Means for Solving the Problems The present inventor has conducted various studies in order to solve the above problems, and as a result, completed the present invention. That is, the variable polarized light insertion light source of the present invention arranges three sets of planar undulators in the horizontal direction, aligns the phases of three diagonal magnet rows among the two adjacent undulators, and adjusts the remaining three magnet rows for the remaining three magnet rows. In the horizontal direction by a distance of at least a half cycle.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the drawings. FIG. 1 shows an example of the insertion light source of the present invention. The variable polarization undulator of the present invention is based on a Sasaki type undulator and is an improvement thereof. The magnet array shown in FIG. 1 includes three sets of upper and lower planar undulators (AA ′, BB ′, and CC ′). If the phase drive is not performed, three undulators are arranged adjacent to each other. The Sasaki type is composed of two sets of upper and lower planar undulators as shown in FIG. 4, the phases of the diagonal magnet rows are aligned with the air gap therebetween, and the phase is set with respect to the remaining pair of adjacent diagonal magnet rows. The magnetic field intensity ratio in the X direction and the Y direction can be changed. On the other hand, the variable polarization undulator of the present invention shown in FIG. 1 further includes one set of upper and lower magnet rows (C-C 'set) at adjacent positions. The center magnet group (B-B 'group) is shared by the left and right magnet groups (A-A', C-C '). Therefore, instead of arranging two Sasaki types (that is, four magnet rows), three magnet rows (A-
A ', BB', and CC ') can obtain the same magnetic field distribution as the two Sasaki types.

The movement of the magnet array will be described with reference to FIG. A-B'-C magnet row and A'-B-C 'magnet row have the same phase, and A-B'-C magnet row and A'-B-C' magnet row have relative phase in the horizontal direction. By performing the movement, various magnetic field distributions can be generated on the α axis and the β axis (on the Z axis), which are the center of the two gaps and the boundary positions. A feature at this time is that when circularly polarized light or elliptically polarized light is arranged on the α axis and the β axis, the rotation of the magnetic field is reversed on the α axis and the β axis. In other words, undulators that can generate clockwise and counterclockwise polarized light are arranged in parallel. Here, the distance that the phase shifts relatively in the horizontal direction can be realized by various magnetic fields by combining the sine wave magnetic fields in the X direction and the Y direction. At least a half cycle distance is required. The three sets of magnet rows (A-B'-C magnet row and A'-B-C 'magnet row) that move in phase are moved by the same distance at the same speed and in the opposite direction about the center of gravity. If it does, the whole center of gravity shift does not occur.

A steering electromagnet for electronic kick is installed at the entrance (front and rear) of the undulator, and the electron beam is switched between the α axis and the β axis by changing the magnetic field strength of the electromagnet. Can be switched. Fast switching between circularly or elliptically polarized light is possible. The switching speed is determined by the speed at which the magnetic field strength of the electromagnet is changed. Since it is different from mechanical phase drive, switching can be performed at a high speed of 1 Hz or more even in a long undulator of 2 m or more. Further, the moving distance of the electron beam at the time of switching is equivalent to one magnet (between the α-axis and the β-axis), so that it can be reduced.
Which of the α-axis and the β-axis is right-polarized light or left-polarized light can be selected by changing the phase between the magnet rows, and either may be used in use.

By appropriately selecting the phase in the A-B'-C magnet row and the phase in the A'-B-C 'magnet row, for example, the emission light at the α point and the β point Various combinations such as circularly polarized light and linearly polarized light, circularly polarized light and elliptically polarized light, and vertically and horizontally polarized light can be realized, but it is not practically effective, so it is not necessary to select such a combination. Absent.

In the Onuki type undulator, the left and right polarization undulators cannot be arranged in parallel as in the present invention. In the Kitamura type, if the two undulators are arranged on the left and right, the left and right polarization undulators can be arranged in parallel as in the present invention, but in the undulator based on this type, six sets of upper and lower or five sets of upper and lower magnets are arranged. There is a need to. Adjusting the magnetic field by combining six or five sets of magnet arrays is very difficult as a practical operation and is not practical. Further, when switching the electron beam, it is necessary to move the magnet width by a distance corresponding to three or two rows. Therefore, even if the same magnetic field distribution as that of the present invention can be realized in principle, it is difficult to employ it practically.

As described above, according to the present invention, three sets of magnet rows are arranged adjacent to each other, and the phases of the A-B'-C magnet rows and the A'-B-C 'magnet rows are aligned with each other. By performing relative phase motion between the -C magnet row and the A'-B-C 'magnet row, various magnetic field distributions can be generated in parallel on each of the α-axis and β-axis at the center of the gap. By oscillating the electron beam between the α-axis and the β-axis at the center of the gap, it became possible to switch the left-right polarized emitted light at high speed.

[0012]

Next, an embodiment of the present invention will be described. (Example) Three sets of hullback type undulators having a period length of 20 mm and 100 periods were manufactured. The magnet is a NdFeB sintered magnet, N
42 (Shin-Etsu Chemical Co., Ltd. brand name; 42MGOe grade)
Was used to apply an electric Ni plating coating. The magnet shape is 5 mm x 100 mm x 50 mm, and the magnetization directions are 5 mm direction and 50 mm direction, respectively. The residual magnetization and magnetization direction distribution of each magnet were within 1% and 1 °, respectively. Magnetic field adjustment was performed separately for the A-B'-C magnet row and the A'-B-C 'magnet row using the magnet row symbols in FIG. The magnetic field measurement points at the time of magnetic field adjustment measured the α axis and the β axis. The reason why the magnetic field adjustment is performed in two sets is that phase drive is not performed in each set, so that the magnetic field can be adjusted in the same manner as a general plane undulator. However, in each set of the α axis and the β axis, a magnetic field was generated in both directions of the X direction and the Y direction. Therefore, the magnetic field was adjusted by measuring the magnetic field in the two axes. After independently adjusting the magnetic field of each of these sets, the three sets of magnet rows are assembled (see FIG. 1), and α
When the magnetic field distribution on the Z axis of the β axis and the β axis was measured, the single integration value was within 150 Gcm for all phases (0 ° to 180 °).
The multiple integral value was within 4500 Gcm ² . However, the gap was measured at 12 mm. When the electron orbit was obtained from the double integral value, when the α axis was clockwise circularly polarized light, the β axis was counterclockwise circularly polarized light. Also, when switching was performed in combination with a steering electromagnet, it was confirmed that switching could be performed at 10 Hz.

[0013]

According to the present invention, a variable polarization insertion light source capable of switching between left and right circularly polarized light and elliptically polarized light at a high speed of 1 Hz or more and effectively utilizing the length of a linear portion can be realized.

[Brief description of the drawings]

FIG. 1 is a schematic view of an example of a variable polarization insertion light source of the present invention.

FIG. 2A is a schematic view of an undulator.
(B) is the periodic magnetic field of (a). (C) is the electron orbit of (a).

FIG. 3 is a schematic view of a basic magnet arrangement of a planar undulator, wherein (a) is a Halbach type. (B) is a hybrid type.

FIG. 4 is a schematic diagram showing classification of various circularly polarized undulators.

FIG. 5 is a schematic diagram showing a Sasaki-type variable polarization undulator.

FIG. 6 is a schematic view showing a series type left-right polarization undulator (Sasaki type).

[Explanation of symbols]

 A, A ', B, B', C, C '{magnet array 10} permanent magnet 15> magnetic pole

Claims (3)

[Claims] 1. A planar undulator is arranged in three sets in the horizontal direction. Of two adjacent sets of undulators, three diagonal magnet rows are aligned in phase, and at least three horizontal magnet undulators are arranged horizontally with respect to the remaining three magnet rows. A variable polarization insertion light source characterized in that the phase shifts by a distance of a half cycle. 2. The method according to claim 1, wherein the three sets of magnet rows, which move in phase, move by the same distance at the same speed but in the opposite direction about the center of gravity, so that the entire center of gravity does not move. Variable polarization insertion light source. 3. A steering electromagnet provided before and after said insertion light source, so that the trajectory of incident electrons can be switched at high speed between a center of two gaps formed by three magnet rows and a boundary position. The variable polarization insertion light source as described in the above.