JP2847323B2 - Magnetic field adjustment method for magnetic circuit for insertion light source - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magnetic field adjustment method for a magnetic circuit for an insertion light source, and more particularly to a magnetic field adjustment method for an undulator (described later).

[Prior Art and Problems] As is well known, when high-energy electrons are moved in a periodic magnetic field, emitted light having high directivity and extremely high brightness can be obtained. An apparatus for obtaining such radiation light is an insertion (type) light source.

The insertion light source is composed of many magnetic poles (usually 20 to 200 poles), and is called a wiggler (strong magnetic field type) or an undulator (weak magnetic field type) depending on the strength of the magnetic field. The name insertion light source comes from the fact that this device is inserted and installed in a straight section in the electron storage ring.

The wiggler uses a superconducting electromagnet to sharply bend the electron orbit to extract short-wavelength radiation. On the other hand, the undulator is composed of a number of permanent magnets arranged periodically with the direction of the magnetic field being alternately reversed.The undulator meanders the electron beam passing between the magnetic poles, and interferes with the light generated between the magnetic poles. This is a device for obtaining a quasi-monochromatic light source by increasing the intensity of light in a narrow specific band by about 100 to 1000 times.

As described above, the present invention relates to a magnetic field adjustment method for an insertion light source (hereinafter, may be simply referred to as an apparatus) classified as an undulator.

The conditions required for the insertion light source are as follows: (a) there is no difference between the direction of incidence of the electron beam on the insertion light source and the direction of emission of the electron beam from the insertion light source; That is, no displacement occurs in the beam.

For this purpose, in the conventional apparatus, permanent magnets or electromagnets for adjusting the magnetic field are provided at the entrance and the exit of the apparatus, and the direction of these magnets or the value of the current flowing through the magnets are adjusted by trial and error to satisfy the above two conditions. Was satisfied.

However, such a conventional trial-and-error adjustment method requires an extremely long time for adjustment.

Furthermore, since there are only two adjustment locations, the entrance and the exit of the device, no displacement occurs at the entrance and the exit, but there is a problem that the peaks and valleys of the orbits of the meandering electrons in the device are not aligned. That is, since the peaks and valleys of the electron orbit are not aligned, the emitted light spreads, and light of a desired wavelength cannot be obtained, or
There was a problem that the luminance was weakened.

Hereinafter, the conventional apparatus will be described in more detail with reference to FIGS.

FIG. 4 is a schematic side view of a conventional undulator (Halbach type), FIG. 5 is a view for explaining an electron trajectory before the magnetic field adjustment in the apparatus of FIG. 4, and FIG. 6 is a view after the magnetic field adjustment in the apparatus of FIG. FIG. 4 is a diagram for explaining the electron orbit of FIG.

In FIG. 4, reference numeral 10 denotes the entire magnetic circuit of the illustrated undulator. A plurality of rectangular parallelepiped segment magnets (permanent magnets) 14a, 14c and 14b (a plurality of magnets provided between 14a and 14c) are fixed to the upper base 12, and the lower base 12
16 includes a plurality of other rectangular parallelepiped segment magnets 18a, 18c and 18
b (a plurality of magnets provided between 18a and 18c) is fixed.

The magnets 14a and 14c are arranged at the respective ends of the upper magnet row arranged in series, and the dimension in the Z-axis direction is half that of the magnet 14b. Similarly, magnets 18a and 18c are arranged at each end of the upper magnet row arranged in series, and the dimension in the Z-axis direction is
Half of 18b. The magnets 14a, 14c, 18a and 18c are
This is to reduce the displacement of the electron beam at the entrance and exit of the magnetic circuit 10, and such an arrangement is a known technique.

At the left side (on the drawing) of the magnetic circuit 10 (that is, at the entrance of the device into which the electron beam is input), a cylindrical permanent magnet 20a for adjusting the magnetic field is provided.
And 22a (shown in cross section or side view in the drawings). Further, at the outlet of the magnetic circuit 10, cylindrical permanent magnets 20b and 22b for adjusting the magnetic field are also provided. By rotating these radially magnetized columnar magnets for adjusting the magnetic field, the magnetic field near the entrance and exit of the apparatus is adjusted.

The arrows shown on each of the plurality of permanent magnets indicate the magnetization directions of the magnets.

In FIG. 4, a is the rectangular parallelepiped segment magnets 14b and 1
8b shows the width of each of the rectangular parallelepiped segment magnets 14a-1
The height of each of 4c and 18a-18c is shown. Further, G indicates the height of the gap specified by the upper and lower magnet rows, and λ indicates the period length in the magnetization direction of the rectangular parallelepiped segment magnet. The electron beam is input from the left side of the magnetic circuit 10 in the positive direction of the Z-axis, meanders in the X-axis direction, and exits from the right side of the magnetic circuit 10.

In the conventional example shown in FIG. 4, a rectangular parallelepiped segment magnet is an Nd-Fe-B magnet, and its magnetic characteristics are represented by Br (residual magnetic flux density) = 11.6KG (average value) (BH) max (maximum energy product) = 32MGOe (Average value) ΔBr / Br (fluctuation in magnetization) = ± 1% Δθ (fluctuation in magnetization direction) = 1 ゜ Magnet size (a × b × c) = 30 × 30 × 120 mm (accuracy ± 0.05 mm) (c is When the magnetic field is not adjusted at the entrance and the exit of the magnetic circuit 10, that is, when the magnets 20a, 20b, 22a, and 22b are not provided, the electron trajectory in the X-axis direction in the device 10 Was as shown in FIG. As shown in FIG. 5, the peaks and valleys of the electron trajectory are not aligned, and the difference (electron displacement) ΔX between the positions of the electrons at the entrance and the exit of the magnetic circuit 10 is quite large.

Next, as a result of adjusting the magnetic field at the entrance and exit of the magnetic circuit 10, the electron trajectory was as shown in FIG. Although the displacement ΔX of the electrons has been considerably reduced by adjusting the magnetic field, the peaks and valleys of the electron orbit are still not aligned. Such a displacement of the electron trajectory is caused by variations in the magnetic properties and magnet dimensions of the magnet. As in the conventional example, the magnetic field adjustment only at the entrance and the exit of the magnetic circuit 10 causes a peak and a valley of the electron trajectory. The irregularity of can not be avoided.

[Object of the Invention] The present invention corrects various errors based on variations in magnetic properties, variations in magnet dimensions, variations in magnet positions during magnet assembly, and the like of a plurality of rectangular parallelepiped segment magnets used in an undulator. Therefore, the position of each rectangular parallelepiped segment magnet is adjusted in the magnet facing direction and the direction perpendicular to this direction, the displacement of the electron trajectory at the entrance and exit of the device is made zero, and the peaks and valleys of the meandering trajectory of the electrons are aligned It is an object of the present invention to provide a method for adjusting a magnetic field of a magnetic circuit for an insertion light source that can obtain extremely good emitted light.

According to the present invention, in a magnetic circuit for an insertion light source in which a plurality of rectangular parallelepiped segment permanent magnets are arranged so as to face each other, each of the plurality of rectangular parallelepiped segment permanent magnets is arranged in a facing direction and A mechanism for independently moving in a direction perpendicular to the facing direction and adjusting a magnetic field of a gap formed between the facing permanent magnets, and obtaining a first value obtained by doubling a value of a predetermined electron position; ,
From the first value, a second value is obtained by subtracting the electron position obtained from the measured value of the current magnetic field and the electron position obtained from the value of the magnetic field when the position of each magnet is moved,
The square of the second value is summed over the trajectory axis of the electron to obtain a third value, the third value is used as an evaluation function, and the moving amount of each magnet is set so that the evaluation function is minimized. Seeking.

Hereinafter, a preferred embodiment of the present invention will be described with reference to FIGS.

FIG. 1 is a schematic side view of an undulator according to the present invention, with a part cut away, FIG. 2 is a view for explaining a magnet adjusting mechanism used in the apparatus of FIG. 1, and FIG. 3 is a magnetic field in the apparatus of FIG. FIG. 4 is a diagram illustrating an adjusted electron trajectory.

Each of the rectangular parallelepiped segment magnets 34b and 38b shown in FIG. 1 is an Nb-Fe-B magnet in the same manner as in the conventional example shown in FIG. 4, and the magnetic characteristics thereof are similar to those in the conventional example shown in FIG. Br (residual magnetic flux density) = 11.6KG (average value) (BH) max (maximum energy product) = 32MGOe (average value) ΔBr / Br (magnetization variation) = ± 1% Δθ (magnetization direction variation) = 1 ゜Magnet dimensions (a x b x c) = 30 x 30 x 120 mm (accuracy ± 0.05 mm) (c is the depth dimension), and the gap (gap) between opposing magnets G = 80 mm Frequency (N) = 26 electron energy = 2.4 GeV.

 Therefore, the total number of magnets is 210.

Rectangular segment magnets 34a, 34b, 34c, 38a, 38b and 3
Each of 8c is adjustably connected to bases 32 and 36 via a position adjusting mechanism 50 (only a part is shown in FIG. 1).

FIG. 2 shows the details of the position adjusting mechanism 50 together with the rectangular parallelepiped segment magnets 38b (34b). Reference numeral 39 is a table for directly mounting a magnet.

FIG. 2A shows a rectangular parallelepiped segment magnet 38b (34b).
FIG. 2B is a side view of the magnet position adjusting mechanism 50 viewed in the X-axis direction, and FIG.
4B is a side view of the magnet position adjusting mechanism 50 as viewed in the Z-axis direction.

As shown in FIGS. 2A and 2B, the position adjusting mechanism 50 can adjust the position in the Y-axis direction (vertical direction) and the X-axis direction (parallel direction (vertical direction in the drawing)). like,
Adjustment screws 52 and 54 are provided.

Next, a method for obtaining the adjustment amount of the magnet position will be described in detail. The electron trajectory in the X-axis direction is taken as an example. The orbital axis of the electron, that is, Y at a predetermined point on the central axis (Z axis) of the magnetic circuit
The axial magnetic field is measured, and this is calculated as HMi (i = 1, 2,.
・, I, ..., n). The position of the electron in the X-axis direction is given by a double integral of the magnetic field in the Y-axis direction.

Where C = 0.2997 / electron energy s = three times the period length (N) (see drawing) L = length of magnetic circuit (see drawing) By = Y-axis component of the magnetic field on the central axis Therefore, actual measurement If the electronic position of is OMi, Becomes

Next, let OIi be an electron position in an ideal case where there is no variation in the magnetic properties and dimensions of the magnet. Further, assuming that the adjustment amount of each magnet is Aj (j is the number of the magnet to be actually adjusted, and j = 1 to m (m ≦ 210)), the integral equation and the like are obtained from the position of the magnet at this time. Then, the value of the magnetic field is obtained, and the electron position OCi (Aj) is further calculated from the equation (1).

Double the calculated value of the ideal electron position OIi, and from this value the electron position OMi obtained from the current magnetic field measurement value
And the square of the value obtained by subtracting the electron position OCi (Aj) calculated from the value of the magnetic field when the position of each magnet is moved is summed over the electron trajectory (on the Z axis). It is defined as an evaluation function W and is shown by the following equation (3). That is, Here, i represents a point on the electron orbit, and i = 1 to n
It is.

The movement amount Aj of each magnet is when the evaluation function W is minimized, and is obtained by solving the following equation (4).

The evaluation function W expressed by the equation (3) is a function of the moving amount Aj of each magnet, and is calculated by the above-described integral equation method and (1)
Equation (4) is obtained analytically by the equation, and equation (4) is also obtained analytically.

The positions (m = 21) of all 210 magnets in the magnetic circuit of FIG.
FIG. 6 shows the electron trajectory when (0) is adjusted by the method of the present invention. There was no change in the entrance and the exit, and the unevenness of the peaks and valleys in the meandering trajectory shown in FIG. The adjustment amount of the magnet was within ± 1 mm.

Although the electron trajectory in the X-axis direction has been described above, the adjustment method is the same for the electron trajectory in the Y-axis direction, except that the adjustment direction is different. That is, the magnetic field Bx in the X-axis direction is measured, and this is substituted into the equations (3) and (4) to determine the amount of movement of the magnet in the parallel direction.

[Effects of the Invention] As described above, according to the present invention, an ideal electron trajectory can be obtained by adjusting the variation in the magnetic properties and dimensions of the magnet and the error in assembling the device. Therefore,
It is extremely effective for obtaining good radiation. Moreover,
Systematic adjustment can be performed without requiring experience and intuition, and the adjustment time can be greatly reduced.

[Brief description of the drawings]

FIG. 1 is a schematic side view of a magnetic circuit according to the present invention, FIG. 2 is a view showing details of a magnet position adjusting mechanism shown in FIG. 1, and FIG.
FIG. 4 is a view for explaining an electron trajectory according to the present invention, FIG. 4 is a schematic side view of a conventional magnetic circuit, and FIGS. 5 and 6 are views showing an electron trajectory according to a conventional example. In the figure, 30: Magnetic circuit 34a to 34c: rectangular parallelepiped segment magnet 38a to 38c: rectangular parallelepiped segment magnet 50: magnet position adjustment mechanism

Claims (1)

(57) [Claims] 1. A magnetic circuit for an insertion light source in which a plurality of rectangular parallelepiped segment permanent magnets are arranged so as to face each other, wherein each of the plurality of rectangular parallelepiped segment permanent magnets is independently moved in a facing direction and a direction perpendicular to the facing direction. A mechanism for adjusting the magnetic field of the air gap formed between the opposing permanent magnets. A first value obtained by doubling the value of the predetermined electron position is obtained. From the first value, the current magnetic field is obtained. A second value is obtained by subtracting the electron position obtained from the measured value and the electron position obtained from the value of the magnetic field when the position of each magnet is moved, and the square of the second value is used as the orbit axis of the electron. A magnetic field adjustment method characterized by obtaining a third value by summing up the above values, using the third value as an evaluation function, and calculating the moving amount of each magnet so that the evaluation function is minimized.