JP5427235B2 - Insertion light source - Google Patents

Description

  The present invention relates to an insertion light source that is inserted into a linear portion of an electron accelerator or an electron storage ring to generate high-luminance emitted light, and more particularly to an insertion light source applicable to an undulator and a free electron laser.

  An insertion light source composed of a permanent magnet or a permanent magnet and a magnetic material (iron or iron-cobalt alloy) is inserted in a form in which a vacuum chamber is sandwiched in a linear portion of an electron synchrotron accelerator, or in a form in which an electron trajectory is sandwiched in the chamber, It is useful as a device that generates radiated light stronger than the radiated light obtained from a conventional deflection magnet.

  FIG. 9 shows a conceptual diagram of the synchrotron accelerator and the insertion light source 31 introduced therein. The insertion light source 31 generates a sinusoidal periodic magnetic field in a vertical plane in the gap between the magnet rows. As shown in FIGS. 3A to 3C, the insertion light source 31 that generates a periodic magnetic field is a hullback type (FIGS. 3A and 3B) that includes only the cuboid permanent magnet 22, a cuboid permanent magnet 22, and a cuboid magnetic material 26 having magnetic poles. There is a hybrid type (Fig. 3C).

  As shown in FIG. 3A, when electrons travel through the insertion light source, a periodic magnetic field causes a sinusoidal periodic motion in a horizontal plane perpendicular to the magnetic field, and radiated light is generated from each meander point. Reference numeral 1 denotes an electron orbit. There are wiggler mode and undulator mode depending on the degree of meandering. Reference numeral 5 represents the amplitude of the electron orbit.

In the wiggler mode, the radiated light generated from each meander point is superimposed, and the luminance (photons / sec / mm ² / mrad ² /0.1% BW) is higher than that of the radiated light 35 from the deflection electromagnet 36 shown in FIG. 10 to 1000 times larger radiation can be obtained.

  In the undulator mode, the radiated light generated from each meandering motion interferes, and the basic energy and its higher-order light can provide light that is about 10 to 1000 times brighter than the wiggler. In FIG. 9, the code | symbol 30 shows the emitted light from an insertion light source, and the code | symbol 1-1 shows the electron orbit which entered from the injector.

  Other characteristics of undulator mode radiation include laser-like characteristics such as high directivity, quasi-monochromaticity that emits only basic energy (and its harmonics) due to interference effects, and high coherence. The insertion light source is disclosed in Non-Patent Documents 1 to 3, for example.

Halbach, Nucl. Instr. And Meth. 187, 109 (1981) Sasaki et al, Nucl. Instr. And Meth. A347, 83 (1994) Tanaka et al, Rev. Sci. Instrum. 70, 4153 (1999)

  The basic energy of the radiated light from the insertion light source is expressed by the following formula using a practical unit.

Further, the parameter K in the formula (1) is defined by the following formula.

  In equations (1) and (2), ε1 is the fundamental energy of the emitted radiation, E is the kinetic energy of the charged particles passing through the insertion light source (equal to the electron storage energy of the synchrotron radiation synchrotron), λu Is the period length of the magnetic field period, and B0 is the magnetic field intensity received by the electrons and is a function of the magnet array gap value (gap), and can be approximated by the following equation.

D and C are constants that vary depending on the material and shape of the magnet, and x is a gap (gap value between magnet rows; unit mm).

  Whether the insertion light source is in the wiggler mode or the undulator mode is classified according to the K value defined by equation (2). When K = 1 or less, the undulator is selected, and when K >> 1, the wiggler mode is set. The undulator radiation has a maximum brightness around K = 1.

  When energy is swept by undulator radiation of quasi-monochromatic light, the basic energy is swept by usually sweeping the K value of Equation (1). The operation of the K value is performed by the operation of the B0 value as understood from the equations (2) and (3). Specifically, x in the equation (3) is changed, that is, the up and down shown in FIGS. 3A and 3B. The gap value (gap) 3 between the magnet arrays is manipulated to manipulate the value of B0 that is inversely proportional to the gap.

  If the gap is widened, the B0 and K values become smaller, the amplitude 5 of the electron orbit 1 becomes smaller, and the photon energy becomes smaller. If the gap is narrowed, the B0 and K values increase, the amplitude 5 of the electron orbit 1 increases, and the photon energy increases.

  However, if the K value is greater than 1, the insertion light source loses the properties of undulator radiation such as high brightness and quasi-monochromaticity. When K is sufficiently larger than 1, the wiggler mode is entered and the luminance is reduced by about 1 to 3 digits, and the components on the higher photon energy side than the basic energy are increased, so that the thermal load on the optical system and the measurement system is remarkably increased. This thermal load becomes a serious problem in a third generation light source with a small electron emittance, and sometimes destroys an optical system and a measurement system.

  Non-Patent Document 2 discloses a technique that uses two sets of upper and lower two sets of magnet rows instead of one set of upper and lower sets of magnets of the normal undulator shown in FIGS. 3A to 3C. Thereby, horizontal and vertical magnetic field dispersion is generated, and the electron trajectory is vibrated in the horizontal and vertical directions, so that horizontal linearly polarized light, circular deflection, vertical linear deflection, and the like can be generated. At the same time, higher-order light emission on the optical axis is suppressed, and the thermal load on the optical system is reduced.

  Non-Patent Document 3 discloses a technique that uses a total of six magnet rows in three sets of upper and lower. As a result, the electron trajectory, which is a simple horizontal sine wave vibration of a normal insertion light source, is changed to a complex electron trajectory having a vibration component in the vertical direction, and polarization control or thermal load reduction is possible.

  However, in the above prior art, the K value that greatly affects the luminance, quasi-monochromaticity and the like cannot be made constant. This is because in the prior art, the basic energy is swept by changing the K value, that is, changing the gap of the magnet array. However, if the interval between the magnets constituting the magnet array is simply increased in order to change the period length λu of the magnetic field period, the magnetic field distribution deviates greatly from the sine wave, so that it does not function as an insertion electrode.

  An object of the present invention is to provide an insertion light source capable of obtaining high-luminance, quasi-monochromatic undulator radiation even during energy sweeping.

  As an embodiment for achieving the above object, in an insertion light source having a permanent magnet or a first magnet row and a second magnet row provided with a permanent magnet and a magnetic pole material, the first magnet row and the first light source An insertion light source further comprising a mechanism for changing a magnetic field period length of the magnetic field formed by the two magnet arrays, wherein the basic energy of the emitted light is swept by changing the magnetic field period length. And

  The insertion light source for generating radiated light by meandering an electron beam with a periodic magnetic field having a sine waveform further includes a magnetic field period length changing means for changing the period length of the magnetic field period while maintaining the periodic magnetic field of the sine wave. The insertion light source is characterized by this.

  It is possible to provide an insertion light source capable of obtaining high-luminance, quasi-monochromatic undulator radiation even during energy sweeping.

It is a perspective view which shows an example (insertion light source comprised with a trapezoid pillar magnet) of the insertion light source which concerns on a present Example. It is a perspective view which shows an example (insertion light source comprised with a trapezoid pillar magnet and a trapezoid pillar magnetic pole material) concerning the present Example. It is a perspective view which shows the example (insertion light source comprised with a trapezoid column magnet and a parallelogram column magnet) of the other insertion light source which concerns on a present Example. It is a perspective view which shows the example (The insertion light source comprised with a trapezoid pillar magnet and a parallelogram pillar magnetic pole material) of the other insertion light source which concerns on a present Example. It is a perspective view which shows the example (The insertion light source comprised with a rectangular parallelepiped magnet, Fullblock Type) of the conventional insertion light source. It is a perspective view which shows the state which extended the magnet row | line | column gap | interval with the insertion light source of FIG. 3A. It is a perspective view which shows the example (The insertion light source comprised by a rectangular parallelepiped magnet and a rectangular parallelepiped magnetic pole material, Hybrid Type) of the conventional insertion light source. It is a schematic diagram (magnetic field period small) of the magnetic field period change in the insertion light source shown to FIG. 1A. FIG. 1B is a schematic diagram of magnetic field cycle change (large magnetic field cycle) in the insertion light source shown in FIG. 1A. It is a schematic diagram (small magnetic field period) of the magnetic field period change in the insertion light source shown in FIG. 2B. It is a schematic diagram (large magnetic field period) of a magnetic field period change with the insertion light source shown to FIG. 2B. It is a schematic diagram (magnetic field period small) of the magnetic field period change in the other insertion light source (insertion light source consisting of an asymmetric trapezoidal column) according to the present embodiment. It is a schematic diagram (large magnetic field period) of the magnetic field period change with the other insertion light source (insertion light source which consists of an asymmetric trapezoid pillar) which concerns on a present Example. It is a schematic diagram for demonstrating the operation mechanism of the insertion light source which concerns on a present Example. It is a graph which shows the emitted light spectrum of the conventional undulator. It is a graph which shows the emitted light spectrum of the undulator which concerns on a present Example. It is a schematic diagram which shows the synchrotron accelerator and the radiation | emission direction of emitted light.

  This embodiment is characterized in that the radiant light energy that is normally swept by controlling the K value is characterized by sweeping the radiant light energy by changing the period length (λu) of the magnetic field instead of fixing the K value. To do.

  As described above, conventional undulators can sweep energy by operating the gap and changing the K value in both basic and improved types. On the other hand, the insertion light source of the present embodiment realizes that energy can be swept while the K value is fixed by operating the gap and simultaneously changing the magnetic field period and the electron orbit period.

  The simplest mechanism for changing the magnetic field cycle is to open and close the distance between the normal cuboid magnet and the magnetic pole. However, if the distance between the magnets and the magnetic pole is increased too much, magnetic field leakage occurs and the magnetic field distribution becomes a sine wave. It seems that it is not the optimal method because it deviates greatly from.

Therefore, the inventor uses a magnet row / magnetic pole row in which trapezoidal or parallelogram-shaped magnets / magnetic pole materials are arranged instead of a normal rectangular parallelepiped, and changes the arrangement of magnets and magnetic poles in the magnet row / magnetic pole row. We have devised to keep the distance between magnets and magnetic poles constant, to prevent magnetic field leakage and to change the magnetic field period and electron orbital period while maintaining the sine wave.
In order to fix the K value to around 1 or other values during the energy sweep, it is necessary to operate B0 in addition to the change in λu, and the value satisfies the following relationship obtained by modifying equation (2): Change to

  In the insertion light source of the present embodiment, by fixing the K value near 1, the characteristics of undulator radiation such as high luminance and quasi-monochromaticity can be maintained in an ideal state even when the energy is swept. In addition, since the quasi-monochromaticity is maintained, the heat load on the optical system / measurement system due to higher-order light does not increase significantly due to the energy sweep.

  Hereinafter, an example explains.

  Examples will be described with reference to FIGS. 1A to 8. 1A, 1B, 2A, and 2B show an example of an insertion light source according to the present embodiment. In these figures and the following figures, the arrow written in the magnet column indicates the magnetization direction. The x, y, and z axes are defined as shown in the lower left of FIGS. 1A and 1B, and this definition is used except for the plan view. In FIG. 1A, FIG. 1B, FIG. 2A, and FIG. 2B, only two magnetic field periods are shown, but an actual insertion light source is composed of about 20 to 200 periods. In the normal insertion light source shown in FIGS. 3A to 3C, the magnet / magnetic pole material is a rectangular parallelepiped, and the magnetic field cycle cannot be changed.

  In this embodiment, a magnetic pole array in which the trapezoidal column magnet 2 and the trapezoidal column magnetic pole material 6 are arranged as shown in FIGS. 1A and 1B, or the trapezoidal column magnet 2 and the parallelogram column as shown in FIGS. 2A and 2B. A magnetic pole array in which magnets 7 or parallelogram pole magnetic pole materials 8 are arranged is used. It is also possible to use a rhombus column in which the length of each side of the quadrilateral is equal. By combining the permanent magnet and the magnetic pole material, it is possible to reduce the magnetic force deterioration of the permanent magnet.

  Both the trapezoidal column and the parallelogram column are arranged so that the trapezoidal surface or parallelogram surface thereof is parallel to the xz plane (electron orbital plane), and the trapezoidal surface is an isosceles trapezoid for the left and right objects. As shown in FIG. 1A, FIG. 1B, FIG. 2A, and FIG. 2B, the dimensions of all trapezoidal column magnets are the same in the same insertion light source, and the dimensions of parallelogram column magnets and magnetic pole materials are also the same.

  When a parallelogram magnet or magnetic pole material is used, the angle of the hypotenuse of the parallelogram is equal to the angle of the trapezoid hypotenuse of the trapezoidal column to the parallel knitting of the trapezoidal column. Arranged parallel to the hypotenuse.

  As shown in FIGS. 6A and 6B, the trapezoidal pole magnet has a trapezoidal surface that is not an isosceles trapezoid, and this mechanism can be realized by using a general trapezoid that is symmetrical to the right and left. By using a trapezoidal column, magnetic field leakage when changing the period length can be reduced. Furthermore, by using the isosceles trapezoid, the magnetic field around the magnet is highly symmetric, and when sweeping the energy of the radiated light, the deterioration of the sine waveform of the magnetic field period can be prevented or reduced. Therefore, an isosceles trapezoid trapezoidal column is suitable.

  As shown in FIGS. 4A and 4B, trapezoidal columns arranged in a nested structure in which trapezoidal upper and lower bases are alternately replaced, or magnets of trapezoidal columns and parallelogram columns as in FIGS. 5A and 5B The electron orbit period 4 (λu) synchronized with the magnetic field period can be changed by shifting the arrangement of the array and the magnetic pole array in the x direction. At this time, if there is a gap between the magnet arrays (or between the magnet and the magnetic pole material), the magnetic field leaks and the magnetic field distribution deviates from the sine wave, so that the entire magnet array / magnetic pole array is expanded and contracted in the z direction.

  4A, 4B, FIG. 5A, and FIG. 5B conceptually show the lower magnet array arrangement and the electron trajectory of FIG. 1A and FIG. 2B, respectively, and the axis direction is shown in the lower left. . The magnet array and magnetic pole array move so that the electron trajectory is always in the center of the magnet array. As described above, in order to satisfy the relationship of K = 1, it is necessary to change B0 in synchronization with λu so as to satisfy the equation (4). The entire magnetic pole array is moved to simultaneously move the gap 3 in FIGS. 1A and 1B and FIGS. 2A and 2B.

  The K value that is regarded as important in the present embodiment is a value that physically represents the relationship between the electron orbit period 4 and the electron orbit amplitude 5 in FIGS. 1A, 1B, 2A, and 2B. Keeping the K value constant near 1 means that the relationship between the electron orbit period 4 and the electron orbit amplitude 5 is ideally maintained for undulator radiation. The K value near 1 means a range of 0.9 to 1.1, more preferably a range of 0.99 to 1.01.

  The operation mechanism of the insertion light source composed of the trapezoidal column magnet of FIG. 1A will be described. First, as shown in FIG. 4A, two support rods (z-axis drive mechanism) 10 (or a plate-like shape) in which each trapezoidal column magnet 2 is alternately placed in parallel with the x-axis in a symmetrical position. Connect to. To reduce the magnetic field period 4, the x-axis (x-direction) drive mechanism 9 is used to move the support bars (z-axis drive mechanism) 10 in the direction of reducing the distance between them, and to increase the support period (z-axis drive). The mechanism) 10 is moved in a direction that increases the distance between them.

  If this operation is simply performed, the trapezoidal columnar magnets facing each other interfere with each other, and the trapezoidal columnar magnet 2 is moved also in the z-direction in synchronization with the x-direction drive. At this time, it is necessary to move the trapezoidal column magnet 2 farther away from the center of the magnet array, but this can be realized by using a support rod (z-axis drive mechanism) 10 that applies an expansion / contraction mechanism used for a fishing rod or an indicator rod. . 4A is a schematic diagram when the magnetic field period 4 is small, and FIG. 4B is a schematic diagram when the magnetic field period 4 is large.

  In order to keep K = 1, it is necessary to move the y direction (gap) in addition to the x and z directions in synchronism with each other, as shown in FIG. The support rod 10 is fixed to a single rod or plate, and a mechanism (y-axis drive mechanism) 11 that moves the entire magnet array in the y-axis direction using this mechanism can be realized.

  4A, 4B, and 7 illustrate the insertion light source including only the trapezoidal column magnet of FIG. 1A. However, the insertion light source including the trapezoidal column magnet 2 and the trapezoidal column magnetic pole material 6 as illustrated in FIG. Can be achieved.

  5A and 5B, in the insertion light source composed of the trapezoidal column magnet 2 and the parallelogram column magnet 7 or the parallelogram column pole material 8, the parallelogram column pole material or the parallelogram column magnet is moved in the x direction. Although not necessary, it is necessary to add a mechanism that moves in the z direction. At this time, the drive mechanism of the trapezoidal column magnet 2 is the same as that shown in FIGS. 4A and 4B, and the drive of the parallelogram column is added independently from the drive mechanism of the trapezoidal column magnet from the top and bottom (y direction). A way to do this is conceivable.

  As can be seen from FIGS. 4A and 4B, in the case of an insertion light source composed of a trapezoidal column magnet or a trapezoidal column magnetic pole, the electron orbit period 4 is limited to 2 to 4 times the long side of the trapezoidal column magnet 2. If the margin between magnets is not taken into consideration at this time, it is desirable that the ratio of the short side to the long side of the isosceles trapezoidal trapezoidal trapezoid is 1: 2 from the viewpoint of preventing magnetic field leakage. Actually, a margin of about several millimeters is made between the magnets, and the ratio of the long side to the single side changes accordingly.

  Even in the case of an insertion light source composed of a trapezoidal column magnet and a parallelogram column magnet, the variable range of the orbital period becomes the widest after all in the trapezoidal column magnet having a ratio of the short side to the long side of 1: 2 and the trapezoidal short side. In the case of a parallelogram pillar magnet / magnetic pole material having parallel sides of the same length, it is variable between 2 to 4 times the short side.

  For example, in the case of a facility with E = 8 in equation (1), if K = 1 is calculated in equation (2), 16 keV to 7.8 keV at λu = 2.6 to 5.2 cm, and λu = 5.2 to Oscillation with a basic energy of 7.8 keV to 3.9 keV is possible at 10.4 cm. In order to realize this, for example, a trapezoidal column magnet having long and short sides of 1.6 cm and 4.2 cm, and long and single sides of 4.2 cm and 9.4 cm are also used. Such trapezoidal columnar magnets may be arranged as shown in FIGS. 1A and 1B or FIGS. 6A and 6B with a margin of 5 mm on each side. For example, in the case of a facility with E = 3, λu = 6 to 12 cm corresponds to 0.5 to 1.0 keV.

  8A and 8B show graphs as an example of the effects of the present embodiment. FIG. 8A shows the spectrum of the undulator, and compares the results of changing the energy from 10.1 keV to 5.1 keV. In this conventional undulator, the K value is changed from 1 (10.1 keV) to 2 (5.1 keV) in order to change the energy. However, many higher-order light components are generated at K = 2 compared to K = 1. I understand. When these higher-order light components are applied to an optical system such as a mirror spectroscope, they generate a lot of heat and destroy them in the worst case.

  On the other hand, in the case of the undulator of this embodiment shown in FIG. 8B, the condition of K = 1 can be maintained even if the energy is changed from 16 keV to 7.8 keV, and it can be seen that the generation of high-order light is small for either energy. As described above, it is possible to confirm the effect of this embodiment that can maintain the quasi-monochromaticity and reduce the heat load.

  The permanent magnet used for the insertion light source is preferably a rare earth sintered magnet, for example, a samarium cobalt (SmCo) magnet or a neodymium (NdFeB) magnet. This is because these magnets have high magnetic properties and can secure the air gap magnetic field strength even if the cycle length is shortened, and a large number of cycle lengths can be obtained with a straight portion having a certain length. Moreover, even if the gap length is large, it is easy to ensure the magnetic field strength.

  According to the present embodiment, by providing a mechanism for changing the period length of the magnetic field period, it is possible to provide an insertion light source capable of obtaining high-luminance, quasi-monochromatic undulator radiation even during energy sweeping. . Moreover, the insertion light source which can reduce the magnetic field leakage at the time of changing period length can be provided by making the shape of the permanent magnet used for the magnet row | line | column for forming a periodic magnetic field into a trapezoid pillar. In addition, by making the shape of the permanent magnet an isosceles trapezoid, the magnetic field around the magnet is symmetric, there is little disturbance of the magnetic field, and when sweeping the energy of the emitted light, the deterioration of the sine waveform of the magnetic field cycle is prevented or reduced. can do.

  Moreover, the magnetic force degradation of a permanent magnet can be reduced by setting it as the structure which combined the permanent magnet and the magnetic pole material as a magnet row | line | column. Further, by using the insertion light source of this embodiment, an electron synchrotron accelerator suitable for diffraction, spectroscopy, and various structural analyzes can be provided.

DESCRIPTION OF SYMBOLS 1 ... Electron orbit, 1-1 ... Electron orbit from an injector, 2 ... Trapezoidal column magnet, 3 ... Gap value (gap), 4 ... Electron orbit period, 5 ... Electron orbit amplitude, 6 ... Trapezoidal column pole material, 7 ... Parallelogram-shaped column magnets, 8 ... Parallelogram-shaped column pole materials, 9 ... x-direction drive mechanism, 10 ... z-direction drive mechanism, 11 ... y-direction drive mechanism, 22 ... rectangular parallelepiped magnet, 26 ... rectangular parallelepiped pole material, 30 ... Insertion light source radiation, 31... Insertion light source, 35... Deflection magnet radiation, 36.

Claims (4)

An insertion light source including a permanent magnet or a first magnet row and a second magnet row, each of which includes a permanent magnet and a magnetic pole material, is arranged so that the Z direction is long, and is spaced apart from each other in the Y direction. In
The first magnet row and the second magnet row have a structure in which the upper and lower bases of the trapezoidal column permanent magnets are alternately replaced, or the upper and lower trapezoidal column permanent magnets and the magnetic pole material of the trapezoidal column. A structure in which the bottom base is alternately replaced, or a structure in which a trapezoidal column permanent magnet and a parallelogram column permanent magnet are alternately arranged, or a trapezoidal column permanent magnet and a parallelogram column magnetic pole material It is arranged in a nested structure, which is an alternating arrangement ,
The mechanism further includes a mechanism for changing a magnetic field period length of a magnetic field formed by the first magnet array and the second magnet array, and the variable mechanism includes the first magnet array and the second magnet array. A mechanism for moving the permanent magnets or the permanent magnets and the magnetic pole material, which are arranged in a nested structure with each other, in the Z direction of the first magnet row and the second magnet row, respectively. The permanent magnets that constitute one magnet row and the second magnet row, and are arranged in a nested structure, or the permanent magnet and the magnetic pole material are arranged in the X direction of the first magnet row and the second magnet row. The insertion light source is characterized in that the basic energy of the radiated light is swept by changing the period length of the magnetic field. The insertion light source according to claim 1.
A mechanism for moving the first magnet row and the second magnet row in the Y direction;
By simultaneously changing the magnetic field period length and the gap between the first magnet row and the second magnet row,
K = 0.934λuB0,
Here, λu is the period length (cm) of the magnetic field cycle, B0 is the magnetic field intensity received by the electrons,
The insertion light source is characterized in that the basic energy is swept while the value of K represented by the formula is kept constant. The insertion light source according to claim 2,
An insertion light source characterized by being fixed in the vicinity of K = 1 when the energy is swept. The insertion light source according to claim 3,
An insertion light source characterized in that “fixed in the vicinity of K = 1” includes fluctuations in the range of 0.9 to 1.1.

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