JPH06267700A - Alpha-undulator - Google Patents

Abstract

PURPOSE:To provide a simple structural undulator for emitting radiation light by deflecting electron beams in a short cycle. CONSTITUTION:Magnetic fields B1 and B2 having the same magnetic flux direction and located perpendicular to the traveling direction of electron beams are generated at the locations, d apart from each other, by positioning a magnet 1 and a magnet 2 in parallel. Under this state, an electron e<-> enters the first magnetic field B1 at an incident angle of theta to deflect the electron e<-> by (180-theta) deg. degrees at this point. The deflected electron e enters the second magnetic field B2 to the deflect the electron e<-> by (180+2theta) deg. degrees at this point. The electron e<-> again enters the first magnetic field B1 at an angle of theta. Repeating this process forms an electron movement locus as shown in the diagram to reduce a wave pitch (cyclic length) lambdaw. Small size and simplified structure are available due to the low number of used magnets. theta is freely changed. Thus, advantages such as variable lambdaw are available.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an .alpha.-undulator for deflecting an electron beam into a state in which its locus of movement is .alpha.

[0002]

2. Description of the Related Art A conventional undulator generates an alternating magnetic field on the path of an electron beam, and the alternating magnetic field causes undulations in the movement of electrons to generate an electromagnetic wave.
As a specific example of such an undulator, for example,
Monthly Physics Vo11.4 No. 5, 1983 has a detailed description of undulators for free electron lasers.

The undulator shown in this document is shown in FIG. As shown in FIG. 7A, when the magnets M having different polarities are alternately arranged in the upper and lower two stages, the magnetic fields generated between the upper and lower opposed magnetic pole faces are alternately reversed, and as shown in FIG. In addition, the electron e ⁻ swings in the direction of the X axis in a plane perpendicular to the Y axis (see FIG. 8A) and meanders, and synchrotron radiation is generated in the same reason as the synchrotron orbital radiation.

The principle of the undulator is basically the same as that of FIG. 8 at present. For example, the one proposed by the present applicant in Japanese Patent Application No. 4-207917 also employs a method of waving an electron beam using an alternating magnetic field.

[0005]

In the conventional undulator, magnets of opposite polarities are alternately arranged at a constant pitch on the path of the electron beam in order to create an alternating magnetic field, as shown in FIG. Therefore, there is a physical limit to shortening the electron wave pitch λ ₀ [FIG. 8 (b)], and there is a problem that λ ₀ is fixed to the same value as the magnet arrangement pitch. It was

Further, since a large number of magnets are used, the structure for holding the magnets is very complicated. An object of the present invention is to eliminate these problems.

[0007]

In order to solve the above-mentioned problems, in the present invention, the directions of magnetic flux are the same between two sets of opposed magnetic pole faces, and both are perpendicular to the traveling direction of the electron beam. To generate a first magnetic field and a second magnetic field. Then, the electron beam that has entered the first magnetic field at the incident angle θ is
In the magnetic field, it is deflected by (180-2) ° toward the second magnetic field, and the electron beam entering this second magnetic field at an angle of θ is deflected by (180 + 2θ) ° to the first magnetic field one before. The first magnetic field is re-entered at an angle of θ at a position λw away from the entry point, and the operation is repeated to extract the emitted light.

The two sets of opposing magnetic pole surfaces in this α undulator may be formed separately for each magnet by using two sets of magnets, or may be formed integrally with one magnet. In the case of forming one magnet, a magnetic shield material having an electron beam path is arranged between a pair of opposed magnetic pole surfaces, and a part of the opposed magnetic pole surface is projected to the left and right of this magnetic shield material. It can also be created by the method of making.

The α undulator of the present invention is the second
A configuration in which the amount of separation of the magnetic field from the first magnetic field at the electron beam incident point is changed stepwise can also be considered. The stepwise change is that when the first magnetic field is generated by the former and the second magnetic field is generated by the latter by using the first and second magnets, the second magnet is divided into a plurality of paths in the direction of the electron beam. Therefore, it is possible to change the amount of change by attaching a position adjusting mechanism to the split magnet.

In addition, the magnet used in the present invention may be either a permanent magnet or an electromagnet.

[0011]

Operation: The electron beam is (180-2θ) in the first magnetic field.
Deflection is performed by (180-2θ) ° in the second magnetic field, and the total deflection angle of one cycle becomes 180 °. Therefore, the flight trajectory of the electron becomes a shape in which the character of α is repeatedly drawn, which realizes a short-cycle undulator.

Further, if either the distance between the first and second magnetic fields or the incident angle of the electron beam with respect to the magnetic field is changed, the incident pitch (= period length) λw changes, so that the overall period length also becomes variable.

Further, when the amount of separation d from the first magnetic field at the electron beam incident point of the second magnetic field is changed stepwise,
The period length partially changes within the same undulator, so it is possible to say that undulators with different specifications can be made without significantly changing the basic design.

In addition, since the number of magnets used is smaller than that of the conventional one, it is possible to avoid complication of the holding mechanism and the like. The details of the operation will be described in the section of Examples.

[0015]

1 to 5 show an embodiment of an .alpha. Undulator of the present invention.

In the undulator of FIG. 1, two sets of magnets 1 and 2 having a C-shaped cross section are opposed to each other in parallel as shown in the figure, and are separated from each other in the X-axis direction by a coordinate system in the figure and screwed to a base 3. is doing. The magnets 1 and 2 are magnetized in the Y-axis direction and have the same polarity. The strengths of the magnetic fields generated by the magnets 1 and 2 do not have to be the same.

This α undulator is a magnet 1 here.
Generate a first magnetic field, so that the electron e ⁻ extracted from the accelerator such as a linac is injected as shown in the figure. θ indicates the angle of electron incidence on the first magnetic field with reference to the central axis C. Although the electrons actually fly in the vacuum duct, the duct is omitted in the figure.

The α undulator of FIG. 2 is obtained by replacing the magnets 1 and 2 having the C-shaped cross section of FIG. 1 with two magnets 4 and 5 having the rectangular cross section, respectively, and the function is the same as that of FIG. Is.

The α undulator shown in FIG. 3 shows that the distance d between the magnets 1 and 2 (= the distance between the first and second magnetic fields) d is changed stepwise. Here, the distance d ₁ in the middle of the longitudinal direction is (d + a). With this configuration, an effect different from that of the undulator of FIGS.

The change amount a of the distance d can be fixed or variable. Here, an insertion hole (not shown) of a fixing bolt provided on the base 3 is an elongated hole in the X-axis direction, and the magnets 2 divided into 3 within the allowable range of the elongated hole can be moved and fixed in the X-axis direction. ing. In FIG. 3, only the central split magnet is moved by a, but the value of d may be set to gradually change from the electron inlet side to the electron outlet side. When fixing the variation amount a to one value,
Of course, the variable adjustment mechanism is unnecessary, and dividing the magnet itself is not essential.

The α-undulator of FIG. 2 can also change the separation amount d in a stepwise manner in the same manner.

In the α undulator of FIG. 4, the opposing magnetic pole surface for producing the first magnetic field and the opposing magnetic pole surface for producing the second magnetic field are integrally formed in one magnet 6. In this undulator, the magnet can be easily held and the parallelism of the first and second magnetic fields can be easily obtained.

Similarly, the α-undulator of FIG. 5 also produces the first and second magnetic fields by one magnet.
The magnet 7 has a pair of wide opposing magnetic pole surfaces and generates a uniform magnetic field in the space between the magnetic pole surfaces. When the magnetic shield material 8 is inserted between the opposed magnetic pole surfaces as shown in FIG. 5, the magnetic shield material 8 is inserted between the opposed magnetic pole surfaces protruding to the left and right of the magnetic shield material as shown in FIG.
A first magnetic field B1 and a second magnetic field B2 shown in are generated. The magnetic shield material 8 is made of a magnetic material, and a through hole 8a extending in the two axial directions of X and Z is formed in the body as shown in FIG. 5 (b) in a plane perpendicular to the Y axis. ing.

The through hole 8a is used as a passage for the electron beam, and a magnetic field is not formed in the hole due to the function of the magnetic shield material 8. That is, as shown in FIG. 5C, when the magnetic shield material 8 is inserted between the opposing magnetic pole faces, the magnetic flux indicated by the arrow flows inside the magnetic shield material, so that the inside of the through hole 8a is in the magnet 1 of FIG. Like the space between the two, the space has a magnetic field of 0. Therefore, the electrons can go straight through the through hole 8a, and the undulator has substantially no difference from that in FIG.

The magnets used in the illustrated α undulator are all permanent magnets, but they may be replaced by electromagnets.

The operation of the α undulator of the present invention will be described in detail below. FIG. 6 shows the movement of electrons flying in the X and Z axis directions on a plane perpendicular to the Y axis in the α undulator of FIG. Here, it is assumed that the magnets 1 and 2 generate magnetic fields B1 and B2, respectively. Electronic e ^-
The deflection radius is determined by the strength B of the magnetic field and the energy E of the electron, and between them, E (GeV) = 0.3B (T) ×
There is a relationship of r (m). Therefore, now, the deflection radius of the magnet 1 is r ₁ and that of the magnet 2 is r ₂ .

The electron e ⁻ extracted from an accelerator such as a linac first enters the first magnetic field B1 at an angle θ from the left side of the figure, and in the same magnetic field, the radius of r ₁ is (180−2θ) °.
Biased. Then, after exiting the first magnetic field at an angle θ, it flies linearly in the space between the magnets 1 and 2 toward the second magnetic field B2. Since the magnets 1 and 2 are parallel to each other, they also enter the second magnetic field B2 at the angle θ. In this second magnetic field B2, r
Deflection of (180 + 2θ) ° is performed with a radius of ₂ . After that, it exits the second magnetic field at an angle θ toward the first magnetic field B1,
Re-enter the first magnetic field B1 at an angle θ. By repeating this operation, in the first magnetic field B1, electrons are incident to the right in the figure at the pitch λw, and the deflection is repeated many times under the same condition.

When the electrons are deflected, they emit light tangentially. Of the emitted light, the light generated at point A in the figure is B
It overlaps with the light generated at the point and becomes the same state as the conventional undulator. In the second magnetic field B2, a state similar to that of an undulator in which electrons are undulated with a period of λw to the left and travels is generated.
In 2, the direction of generation of emitted light is different from the general direction of travel of electrons, and the states of acceleration and deceleration of electrons do not match those on the side of the first magnetic field, and therefore cannot be interpreted as the same physical phenomenon.

Wave cycle length (pitch) of this undulator
λw is expressed by the following equation when r ₁ = r ₂ , that is, when the strengths of the magnetic fields B1 and B2 are the same.

Λw = 2 × (r ₁ = r) cos θ + 2d × tan (90−θ) ... = 2d × tan (90−θ) Thus, the period length λw of the wave is mainly the distance d between the magnetic fields. , Depends on the incident angle θ of the electron. Of these, in particular, the incident angle θ
Are not subject to change restrictions due to magnet shape or the like. That is, FIG.
Even after the distance d between the magnets is determined, the period length λw of the wave is
It can be freely changed and set to any value by changing.

Next, the effect of the undulator having the configuration of FIG. 3, that is, the separation distance d of the magnet 2 from the magnet 1 is changed stepwise will be described.

FIG. 7 shows the movement of electrons flying in the X and Y axis directions in a plane perpendicular to the Y axis. Here, the separation distance d at the position where the electron e ⁻ first enters the second magnetic field B2,
The separation distance at the next incident position is gradually increased to d ₁ , and the separation distance at the next incident position is gradually increased to d ₂ , and accordingly, the period length λw of the wave in the first magnetic field B1 is also 2 dtan.
(90−θ) → 2d ₁ tan (90−θ) → 2d ₂ tan
It can be seen that the value gradually increases to (90−θ). This utilizes the fact that λw also depends on d in the above equation, and by utilizing this function, the optical klystron can also be formed without significantly changing the overall shape.

The α undulators of FIGS. 2, 4 and 5 are also
Since the magnetic field distribution is the same as in FIG. 1, the same operation as described in FIG. 6 is performed. Further, these α undulators can also obtain the effect of changing the cycle length described in FIG. 7 by partially changing d.

The range in which the incident angle θ can be freely changed when d is changed stepwise is narrower than when d is not changed. The α undulator of FIG. 5 also has a limitation due to the size of the through hole 8a, so that the range of freely changing the incident angle θ becomes narrow.

[0035]

As described above, according to the present invention,
A first magnetic field and a second magnetic field, which have the same magnetic flux direction and are both perpendicular to the traveling direction of the electron beam, are generated in parallel positions, and the two magnetic fields generate electrons with a deflection angle of one cycle of 1
Since the emitted light is extracted in the first magnetic field by deflecting it to 80 °, the physical limit in shortening the wave pitch is different from the conventional undulator in which electrons are meandered using an alternating magnetic field. Is eliminated, and a short cycle undulator can be realized.

The second magnet for the first magnet (first magnetic field)
When the separation distance of the magnet (second magnetic field) is changed, an undulator with a partially changed period can be obtained in the same undulator, and the degree of freedom in designing and changing specifications can be increased.

Furthermore, since the undulator having a variable total cycle length, which has not existed in the past, can be changed only by changing the angle of incidence of electrons with respect to the magnetic field, the degree of freedom in usage can be increased.

In addition, since it is not necessary to use a large number of magnets and the period can be shortened, the overall size can be reduced and the overall structure can be simplified.

[Brief description of drawings]

FIG. 1 is a perspective view showing an example of an α undulator of the present invention.

FIG. 2 is a perspective view of a second embodiment.

FIG. 3 is a perspective view of a third embodiment.

FIG. 4 is a perspective view of a fourth embodiment.

5A is a perspective view of a fifth embodiment. FIG. 5B is a perspective view showing details of the magnetic shield material. FIG. 5C is a perspective view showing the function of the magnetic shield material.

FIG. 6 is a diagram showing a magnet array of the α undulator of the present invention.

FIG. 7 is a diagram showing how the wave period changes with a stepwise distance change between magnetic fields.

8A is a diagram showing a magnet array of a conventional undulator. FIG. 8B is a diagram showing an electron wave due to an alternating magnetic field.

[Explanation of symbols]

 1, 2 C-shaped cross-section magnets 3 units 4, 5 rectangular-section cross-section magnets 6 2 magnets with 2 pairs of opposing magnetic pole surfaces 7 magnets with 1 pair of opposing magnetic pole surfaces 8 magnetic shield material 8a through hole B1 first magnetic field B2 2 magnetic fields

Claims (5)

[Claims] 1. A first magnetic field and a second magnetic field which have the same magnetic flux direction and are both perpendicular to the traveling direction of the electron beam.
Two sets of magnets that generate a magnetic field between the opposing magnetic pole faces are arranged in parallel and separated from each other, and the first magnetic field created by the first magnet has an incident angle θ.
The electron beam that entered at (180-2
θ) ° is deflected to the second magnetic field created by the second magnet, and the electron beam entering this second magnetic field at an angle of θ is deflected (180 + 2θ) ° to the first magnetic field one before. An α undulator that re-enters the first magnetic field at an angle of θ at a position λw away from the entry point and repeats this operation to take out emitted light. 2. The α undulator according to claim 1, wherein the separation amount d at the point of incidence of the electron beam on the second magnetic field of the second magnet with respect to the first magnet is changed stepwise. 3. The α undulator according to claim 2, wherein the second magnet is divided into a plurality of pieces in the traveling direction of the electron beam, and the divided magnets are provided with a variable adjustment mechanism for the separation amount d. 4. An α undulator in which two sets of opposing magnetic pole faces for generating the first and second magnetic fields are formed into one magnet, and the magnets are replaced with the two sets of magnets according to claim 1. 5. A magnetic shield material having a passage of an electron beam is arranged between the opposing magnetic pole surfaces of one magnet, and a first magnetic field and a second magnetic field are provided between the opposing magnetic pole surfaces of the magnetic shield material which are extended to the left and right. An α undulator that is generated to extract emitted light by the same action as the α undulator according to claim 1.