JPH05129100A - Undulator apparatus - Google Patents

Abstract

PURPOSE:To obtain a small-sized and low-priced device by arranging a plurality of horizontal magnetic field generating electromagnets and vertical magnetic field generating electromagnets alternately along the axis of an electron beam to allow the electron beam to meander. CONSTITUTION:Horizontal/vertical magnetic field generating electromagnets 19, 20 including an electrode 15, a yoke 16 and an excitation coil 17 are arranged at the same intervals on a frame 6. The electromagnets 19, 20 are electrically connected in such a manner that the exciting direction thereof turns intermittently by 90 deg. along an electron beam axis. The deflection capacities of electromagnets 18c, 18b on end parts are set to halves of those of electromagnets 19, 20. According to this constitution, it is possible to vary K value by increasing/decreasing exciting current even without varying the length of magnetic pole cavity and no magnetic field may be generated if magnetization process is stopped even though the apparatus is not removed from above the trajectory of the electron beam. Therefore, a drive mechanism can be eliminated so as to realize a small size and low price of the apparatus.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an undulator device which is a light source device for synchrotron radiation.

[0002]

2. Description of the Related Art Synchrotron radiation, if the energy of electrons is sufficiently high, has a spectrum showing a continuous distribution extending from the vacuum ultraviolet region to the X-ray region, and is a general-purpose light source in that wavelength region. 3 (a) and 3 (b) are conceptual diagrams of the undulator device described in "Future of Synchrotron Radiation" on pages 45 to 64 of "Accelerator Science Vol. 1, No. 4, 1986-6", for example. ) And (b) are perspective views showing a configuration example of a magnetic circuit of a conventional undulator device, respectively. FIG. 5 is a side view showing an example of manufacturing a conventional device. For example, in FIGS. 3, 4 and 5, 1 is a magnetic field generator, 2 is a trajectory of an electron beam, 3 is a permanent magnet, 4 is a pole member, 7 is a guide,
8 is a support arm, 9 is a servo motor, 10 is an encoder, 11 is a ball screw, 12 is a pedestal, 13 is a dolly, 14
Is a rail.

Next, the operation will be described. As shown in FIG. 3, in the undulator device, the magnetic field generation device 1 is configured to generate a magnetic field that changes periodically by combining permanent magnets 3 and the like, and the incident electron beam is orthogonal to the magnetic field due to the Lorentz force. A force is applied in the direction, and the orbit 2 also meanders periodically. At this time, the electrons receive acceleration and emit synchrotron radiation.

For example, if the periodic magnetic field B _y is B _y = B ₀ sin (2πz / λ _u ) (1), the maximum inclination Ψ _{0 of the} electron orbit with respect to the z axis and the Lorentz factor γ ^-1 are obtained. The ratio K of the magnetic field strength B ₀ (Tesla) and the period length λ _u (cm) is expressed as K = Ψ ₀ / γ ⁻¹ = 0.934B ₀ (Tesla) λ _u (cm) (2) To be done. However, when the electron energy is E (GeV), γ = 1957 · E (3). Also, the fundamental wavelength λ ₁ of this synchrotron radiation
_{Is, λ 1 = λ u (1} + K 2/2) / 2λ 2 ...... (4) next, K becomes large value, i.e. the higher the longer magnetic field period length, or more fundamental wave is low energy electron beam It can be seen that the wavelength of becomes longer. Further, the harmonic characteristic strongly depends on this K value, and when K << 1, the spectrum is only the fundamental wave. On the other hand, in the case of K >> 1, it becomes a train of harmonics much like the synchrotron radiation in a circular orbit, and becomes broadband continuous spectrum light. Radiation with K <3 is called undulator radiation, and radiation with K> 3 is called wiggler radiation. In particular, the undulator radiation has a brightness 10 ³ to 10 ⁴ times higher than that of synchrotron radiation in a circular orbit, becomes tunable quasi-monochromatic light, and becomes linearly polarized light having an electric vector parallel to the meandering surface of the electron beam. This characteristic is of extremely high practical value.

FIGS. 4 (a) and 4 (b) respectively show examples of the construction of a conventional magnetic circuit, in which the magnetic field generator 1 is composed of a permanent magnet 3 such as a rare earth magnet having a high coercive force and a residual magnetic field. Also, as shown in FIG. 4 (b), there is also one in which the magnetic field strength of each magnetic pole can be adjusted by taking in and out the magnetic pole material 4 made of a material having a high saturation magnetic flux density. The black arrow indicates the magnetic field direction in the permanent magnet 3 and the open arrow indicates the magnetic field direction in the air gap between the permanent magnets.

FIG. 5 shows an actual manufacturing example. In order to adjust the magnetic field strength of each magnetic pole as described above, the servo motor 9, the encoder 10 and the ball screw 11 are shown.
Then, the permanent magnet 3 fixed to the support arm 8 is moved up and down along the guide 7 attached to the frame 6 so that the magnetic pole gap distance can be made variable. Further, in order to completely remove the influence of these magnetic fields, the pedestal 12 to which the device is fixed is placed on the carriage 13 and moved on the rail 14,
It can also be detached from the electron beam track 2. In this case, the cycle length λ _u is 7.4 (cm),
When used in an electron storage ring with electron energy of 0.8 (GeV), if γ = 1566 from equation (3) and the magnetic field strength B ₀ is 0.36 (tesla) from equation (1), then K ~
It becomes 2.5, and it can be seen from Equation (4) that the undulator radiation fundamental wavelength is about 6182 (nm).

[0007]

Since the conventional undulator device is constructed as described above, it is necessary to control the beam energy or the K value (parameter) in order to select the wavelength, as can be seen from the equation (3). is there. Since the beam energy of the electron storage ring to which the undulator device is attached is usually fixed for a long period of time, it is routinely performed by making the K value variable. Further, since it is difficult to make the cycle length variable, the gap length between magnetic poles is changed to increase or decrease the magnetic field.
In addition, it is necessary to remove the entire apparatus from the electron beam trajectory 2 in order to completely eliminate the influence of the magnetic field. The driving mechanism for these is very large, and there is a problem that it takes time for driving.

The above is a description of the case where the magnetic field is simply generated in the vertical direction. However, when the magnetic field is generated in the horizontal direction, that is, when the electron beam is meandered in the vertical direction and the polarization direction of the undulator radiation is changed. The device shown in FIG. 5 must be rotated by 90 ° before installation. Furthermore, in order to obtain circularly polarized undulator radiation, it is necessary to combine these to generate a vertical and horizontal periodic magnetic field at the same location on the orbit, and thus cause the electron beam to meander in a spiral shape. However, the above method has a problem that it is more difficult to construct such a device.

The present invention has been made to solve the above problems, and generates or removes a periodic magnetic field in the horizontal method and in the vertical direction at the same position on the orbit of an electron beam, or changes the intensity. It is an object of the present invention to obtain an undulator device that does not require a drive mechanism for.

The undulator device according to the present invention is
Many same electromagnets, each magnetic pole direction is 90 °
They are arranged along the orbit of the electron beam in the adjacent positional relationship of rotating each.

[0011]

In the undulator device according to the present invention, the deflection magnetic field (bipolar magnetic field) generated by the electromagnet is rotated by 90 ° along the electron beam axis so that the phases thereof are deviated from each other by 90 ° on the electron beam axis. The horizontal and vertical periodic magnetic fields can be generated, and as a result, the electron beam can be spirally meandered and circularly polarized undulator radiation can be obtained.

[0012]

EXAMPLES Example 1. An embodiment of the present invention will be described below with reference to the drawings. In FIGS. 1 and 2, 15 is a magnetic pole, 16 is a yoke, 17 is an exciting coil, 18 is an end electromagnet, and 19 and 20 are for generating a horizontal magnetic field composed of the magnetic pole 15, the yoke 16 and the exciting coil 17. An electromagnet and an electromagnet for generating a vertical magnetic field. FIG. 1 shows a front view of the apparatus. A magnetic circuit is constituted by the electrode 15, yoke 16 and exciting coil 17, and a deflection magnetic field can be generated between the magnetic poles 15 by passing a current through the exciting coil 17. FIG. 2 is a side view showing a state in which the electromagnets 19 and 20 are arranged on the frame 6 at equal intervals. These electromagnets 19, 20
The excitation direction is electrically connected so as to rotate by 90 ° along the electron beam axis. Actually, of these electromagnets 19 and 20, the two electromagnets 18 at the ends are
It is necessary that a and 18b have a deflection capability that is half that of the internal electromagnets, and the electromagnets 18a and 18b at the ends have the number of turns of the excitation coil 17 so that all the electromagnets 18 and 19 can be excited in series. Adjust it by reducing it or by reducing the exciting current as a separate power source at the end.

For example, when the period length (corresponding to four electromagnets) λ _{u at} which the electromagnets 18 and 19 can be arranged as described above is 60 (cm), the electron energy is 6 (GeV).
When used for the electron storage ring of
1742 and K = 2.5, the magnetic field strength B is calculated from the equation (1).
_{If 0} is 0.0446 (Tesla), it can be seen from the formula (4) that the undulator radiation fundamental wavelength is about 900 (nm).

As described above, the undulator device using the electromagnets 18 and 19 has a cycle length about one digit larger than that of the conventional device, but the electron energy of the electron storage ring is about 6 to 8 (GeV). If it is large, it is possible to obtain the same performance as a conventional undulator device,
Even if the magnetic pole gap length is not changed, the K value can be changed by increasing or decreasing the exciting current, and even if the device is not removed from the electron beam trajectory, the magnetic field is not generated if the excitation is stopped. Also, increase or decrease of such magnetic field or ON
The time required for turning on / off can be significantly reduced, and the utilization efficiency of the undulator radiation light is improved.

Example 2. In the above embodiment, when all the electromagnets 18 and 19 except the both ends are excited in series,
That is, the case of generating a spiral magnetic field has been described, but an electromagnet for generating a horizontal magnetic field and a horizontal magnetic field is
It may be one in which every other magnetic field is excited in series so that the horizontal magnetic field and the vertical magnetic field can be independently increased / decreased or turned ON / OFF.

Further, even if the number of cycles is increased or decreased, the same effect as in the above embodiment can be obtained.

[0017]

As described above, according to the present invention, the magnetic field generator generates magnetic poles for generating a deflection magnetic field, an exciting coil, and electromagnets made of yokes are rotated at regular intervals by 90 ° in the direction of the magnetic poles. Since they are arranged, the generation of a periodic magnetic field in a spiral shape, a horizontal direction, or a vertical direction, increase / decrease of the magnetic field, or ON / OFF can be simplified, and the speed can be increased. As a result, the drive mechanism etc. can be omitted, the device can be made inexpensive,
It also has the effect of saving space.

[Brief description of drawings]

FIG. 1 is a front view of an electromagnet for an undulator device according to an embodiment of the present invention.

FIG. 2 is a side view of an undulator device according to an embodiment of the present invention.

FIG. 3 is a conceptual diagram of a conventional undulator device.

FIG. 4 is a cross-sectional view showing a configuration example of a magnetic circuit of a conventional undulator device.

FIG. 5 is a side view showing a manufacturing example of a conventional undulator device.

[Explanation of symbols]

 15 Magnetic poles 16 Yoke 17 Excitation coils 18a, 18b End electromagnets 19 Horizontal magnetic field generation electromagnets 20 Vertical magnetic field generation electromagnets

Claims (1)

[Claims] 1. A plurality of horizontal magnetic field generating electromagnets in which a magnetic field is generated in the horizontal direction and vertical magnetic field generating electromagnets in which a magnetic field is generated in the vertical direction are alternately arranged along an electron beam axis.
An undulator device characterized by causing the electron beam to meander.