JP2718636B2 - Periodic magnetic field generator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a periodic magnetic field generator for efficiently generating short-wavelength coherent radiation with a free electron laser oscillator.

[0002]

2. Description of the Related Art A free electron laser oscillating device generally comprises three main components: an electron accelerator, a periodic electromagnetic field forming means called a wiggler or an undulator, and an optical resonator. Electrons accelerated by an electron accelerator are wiggled. When electrons at speeds nearing the speed of light through the varying magnetic field spatially periodically when introduced into the magnetic field is accelerated motion, radiation from the electron electrons travels while meandering by interaction with the periodic electromagnetic field A so-called free electron laser (hereinafter, referred to as FEL) having superimposed light and having a uniform phase is emitted by stimulated emission.

The FEL has various features due to its structural principle, such as continuously changing the frequency and obtaining a short-wavelength powerful laser beam, and has a wide variety of uses as a light source for lithography and various laser processing. Expected.

As a method for shortening the wavelength of laser light generated by such an FEL, Japanese Patent Application Laid-Open No. 5-48216 discloses a method for generating harmonics of free electron laser light. In this harmonic generation method, a magnet or an electric wire through which a current flows is arranged in a periodic configuration to form a magnetic field that changes spatially and periodically, and a magnetic field deforming means is arranged along the magnet or the electric wire in a predetermined pattern or shape, respectively. In this method, a higher-order vibration wave is superimposed by applying a deformation to a periodically changing magnetic field, and a higher-order vibration wave component is generated in the motion of electrons to obtain a harmonic laser light.

[0005] The wiggler used in this method is composed of a plurality of pairs of magnets having different polarities such that the direction of the magnetic field is opposite for each pair adjacent to each other. What is formed in the shape is used. In the former, a large relative permeability or a diamagnetic metal piece is used as the magnetic field deforming means on the opposing surface of each pair of magnets, and in the latter, a helical electric wire is provided with another electric current flowing therethrough. .

[0006]

By the way, an iron piece used as a magnetic field deforming means in a wiggler using a magnet pair used in the method of generating harmonics of laser light disclosed in the above-mentioned publication is a magnetic field. It is used to correct and modulate the shape of. This small piece of iron is commonly called a shim. Although the description of the related art is omitted, the state of the magnetic field can also be changed by changing the shape of the magnet or changing the magnitude of the current flowing through the electric wire.

However, the change in the magnetic field obtained by such a conventional method has a small range, and is not sufficient when used for a wide range of applications.

The ratio between the fundamental wave and the harmonics of the radiation light or the free electron laser light emitted by bending the charged particle beam by the magnetic field is determined by the strength and shape of the field provided by the magnetic pole. To compensate for this,
In the invention of the above publication, small pieces of iron or the like are attached to the magnetic pole, or the shape of the magnetic pole is changed, but the control is not possible due to the saturation effect of a strong magnetic field.

Further, in the above-mentioned conventional method, the position and the trajectory of the electron beam are simultaneously controlled by attaching an iron piece or the like to the magnetic pole or changing the shape of the magnetic pole.
However, when the energy of the electron beam changes, in order to obtain the same effect, the method using a small piece of iron called a shim is not sufficient due to its saturation effect, or the shape of the magnetic pole needs to be greatly changed. There is.

In the present invention, the magnetic field deforming means is provided inside the magnetic field generated by the conventional periodic magnetic field generator, taking into account the various problems of the above-described conventional periodic magnetic field generator used in the FEL. It is possible to increase the harmonic components of the free electron laser light, increase the magnetic field strength, or make the magnetic field uniform, and also add the correction of the trajectory or position of the electron beam with a simple and economical means. An object of the present invention is to provide a periodic magnetic field generator that can be obtained.

[0011]

According to the present invention, as a means for solving the above-mentioned problems, a magnetic pole member comprising a magnet or an electric wire through which an electric current flows is periodically arranged so as to form a magnetic field which periodically changes spatially. The line of magnetic force from the magnetic pole member is adjacent to the magnetic pole member without contact with the magnetic pole member inside the periodic magnetic field.
To prevent the magnetic flux from flowing into the magnetic field due to other magnetic pole members
The magnetic field deforming means with high magnetic permeability at predetermined intervals
Thus, a periodic magnetic field generator was constructed and arranged in a shape or shape .

As an embodiment of such a magnetic field generator,
The magnetic pole member is provided by disposing a plurality of pairs of magnet pairs in which magnets having different polarities are opposed to each other such that the magnetic field directions of the adjacent pairs are alternately opposite to each other along the traveling direction of the electrons. As a means, a small metal piece having high magnetic permeability can be provided.

In this case, it is preferable that the small metal pieces of the magnetic field deforming means are provided on one or both of the inner and outer surfaces of the vacuum duct for electron beam transmission.

[0014]

[0015]

In the apparatus according to the first aspect of the present invention, the magnetic pole members are periodically arranged and provided in a predetermined pattern or shape by independent magnetic field deformation means inside a magnetic field formed by the magnetic pole members. And The magnetic field deforming means is arranged so as to suppress the line of magnetic force from the magnetic pole member from flowing out to the magnetic field of another adjacent magnetic pole member.

Therefore, by appropriately adjusting and designing the pattern, shape or arrangement interval of the magnetic field deforming means, it is possible to control the enhancement or reduction of the higher spatial frequency components of the magnetic field and to control the harmonics of the emitted light or the free electron laser. Limit or increase the generation of wave components.

The magnetic field deformation means changes the distribution shape of the magnetic field by changing its shape or pattern to be wider or narrower, and variously changes the oscillation waveform caused by the meandering of the electron beam from the sinusoidal basic waveform. It is possible to improve the uniformity of the magnetic field, taper or reverse taper the magnetic field, and change the mode of the periodic change.

Further, the change in the shape or pattern can change the convergence or divergence of the magnetic flux density of the magnetic field,
This makes it possible to correct the trajectory or position of the electron beam.

As a reference, looking at the deformation ratio of the magnetic field strength, the degree of deformation due to the conventional shim is 5 times that of the basic waveform.
It has been confirmed by experiments that the magnetic field deformation means of the present invention has a dramatic effect of contributing to an increase in the magnetic field strength of about 30% as compared with about 30%.

In the second invention, a plate-shaped wiggler magnet is used as the magnetic pole member, and a small metal piece having a high magnetic permeability is provided as a magnetic field deforming means at an intermediate position of the inner circumference of the magnetic field. Therefore, the first invention is carried out by variously changing the shape and pattern of the metal piece.

In this case, as described in the third invention, when there is a vacuum duct for transmitting an electron beam, the above-mentioned small metal piece depends on which of the various functions of the first invention is emphasized. Provided on one or both of its inner and outer surfaces.

Of course, there may be no vacuum duct, and in such a case, the small metal piece may be fixed to an intermediate position inside the basic magnetic field by an appropriate fixing means.

[0023]

[0024]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an overall schematic configuration diagram of a free electron laser oscillation device using the periodic magnetic field generator of the embodiment. This oscillation device includes an electron linear accelerator 1 for accelerating an electron beam to a speed close to the speed of light, a bending electromagnet 2 for bending the trajectory of the electron beam, and accelerating the electron beam at an inner periphery of a magnetic field that periodically changes.
A wiggler magnet 3 that decelerates and stimulates the emission of laser light,
The system includes an optical co-vibrator 4, 4 'for reciprocating the generated laser light many times and accumulating the laser light, a beam damper 5 for decelerating the used electron beam, and the like.

In FIG. 1 and FIGS. 2 and 3, which will be described later, the wiggler magnet 3 is shown as a vertical section (including some side surfaces) near the center of the trajectory of the electron beam.

The wiggler magnet 3 is made of N as in the prior art.
A plurality of pairs of magnet pairs having poles and S poles opposed to each other are arranged so that the direction of the magnetic field of each adjacent magnet pair changes periodically by 180 degrees. It is of the form called.

FIG. 2A shows the details of the magnetic field deformation means 6 provided inside the magnetic field formed by the wiggler magnet 3. Although not shown in FIG. 1, a vacuum duct 7 is provided between each pair of magnets of the wiggler magnet 3 in a track portion through which the electron beam B passes. Are provided with metal pieces 6a or 6b having high magnetic permeability at the pitch of the opposed magnets.

The electron beam B emitted from the accelerator 1 is deflected by the deflection electromagnet 2 and is incident between the optical resonators 4 and 4 ′. The electron beam B travels in the magnetic field of the wiggler magnet 3 while meandering and vibrates. It interacts to generate monochromatic electromagnetic waves (laser light) by stimulated radiation. During the meandering movement, the electrons basically move in a periodic sine wave shape due to the wiggler magnetic field, and due to the meandering movement, the traveling speed becomes slower than the electromagnetic wave, so that the electromagnetic wave is strengthened and stimulated radiation is performed.

In emitting laser light by the above-mentioned stimulated emission, in this embodiment, the magnetic field is deformed by the high permeability metal pieces 6a and 6b provided in the magnetic field of the wiggler magnet 3.

In FIG. 2A, the metal pieces 6a and 6b are arranged to face each other, and the magnetic lines of force are arranged at intervals corresponding to each pair of magnets facing the magnet on the opposite side, and the magnetic lines of force are directed from one to the other magnet. The flow (shown by a solid arrow in the drawing) is provided in such a size and shape that the flow does not flow out to another pair of adjacent magnetic lines.

FIG. 2B shows a vibration waveform of the electron beam caused by the magnetic field of this embodiment. The sine waveform of the solid line in the figure shows the basic waveform when the metal pieces 6a and 6b are not provided,
The dotted waveform is a vibration waveform in which the magnetic field strength is increased when the metal pieces 6a and 6b are provided.

In this embodiment, the concentration (convergence) of the magnetic force lines indicated by the solid line in FIG. 2A occurs, so that the leakage of the magnetic force lines to other magnetic fields as indicated by the dotted line in FIG. 2A is reduced (suppressed). ,
Therefore, the magnetic field intensity naturally increases.

FIG. 3 shows details of the magnetic field deformation means 6 of the second embodiment. In this embodiment, as shown in FIG.
The outer metal piece 6a of the vacuum duct is the same as that of the first embodiment, except that two inner metal pieces 6b are provided at predetermined intervals corresponding to one outer metal piece 6a. Is different. Other configurations are the same as those of the first embodiment.

In this embodiment, as shown in (b), a vibration waveform including a high-frequency component (twice in the illustrated example) is obtained at the same time as the magnetic field intensity is increased with respect to the original sine waveform.

FIG. 4 shows another metal piece 6a or 6b.
Is shown. (A) shows the case where only the metal piece 6b is provided inside the dat, and (b) shows the case where only the metal piece 6b inside the duct is widened in the case of FIG.

FIG. 5 shows various changes in the shapes of the metal pieces 6a and 6b. (A) is normal, (b), (c),
(E) and (f) have a beam converging effect, and (d) has a beam diverging effect.

FIG. 5 is a diagram showing only the metal pieces 6a (or 6b) attached to the vacuum duct as viewed from above the duct.

As a method of obtaining the action by the magnetic field deformation means shown in FIG.
Nstruments and Methods in
Physics Research A304 "(N
ortho-HollandPhysics Public
shing) (1991, P753-758), “Focusing permanent mag.
Among those presented under the title of "net undulator", there is shown one in which the cross-sectional shape of the wiggler magnet itself is modified.

In such a conventional example, the beam convergence / divergence effect can be obtained by deforming the shape of the wiggler magnet itself, while using the various deforming means shown in FIG. 5 without changing the shape of the magnet. By converting iron pieces, similar functions and effects can be obtained at extremely economical cost. This indicates that the method of the present invention is extremely useful.

FIG. 6 shows a modification of the shape of the metal pieces 6a and 6b when the sectional shape of the vacuum duct 7 is circular or square. (A), (b), (c), (d), (e), (f)
Is a type for controlling beam convergence / divergence and position.

FIG. 7 shows an example in which there is no vacuum duct between the wiggler magnets 3 and the entire wiggler magnet is installed in a vacuum space. In the case of (a), the inner and outer metal pieces 6
An example in which a holder 8 that partially supports b and 6a with the same cross section as the duct 7 and a short length is used. In the case of (b), a holder 9 that simply supports the inner and outer metal pieces 6b and 6a is used. This is an example.

FIG. 8 shows that the shape of each of the metal pieces 6a, 6a,... In the traveling direction of the electron beam is reduced with respect to a plurality of wiggler magnets, and the magnetic field strength is reduced (tapered) or increased in the length direction. An example is shown in which the taper (reverse taper) can occur. It can also be used to generate harmonics by repeating this periodically and adding a long-period component.

As a method for obtaining the same effect as the function of the magnetic field deformation means as shown in FIG.
ear Instruments and Metho
dsin Phsysics Research A29
6 (1990, pp. 579-587).
gggler error reduction thr
Among the ones announced under the title of "ooh shim tuning", the above-mentioned shim (correction magnetic piece)
Is attached to the surface of a wiggler magnet.

However, in this method, the degree of magnetic field deformation is small, so that it is insufficient to obtain an effective deformed magnetic field. On the other hand, according to the method shown in FIG. 8, a sufficient deformation magnetic field can be formed. That is, it is extremely easy to improve the uniformity of the shape of the magnetic field, to improve the convergence of the beam by creating a tilt, and to prevent the divergence of the beam by creating quadrupole and hexapole components. Can be.

[0045]

[0046]

[0047]

[0048]

FIGS. 9 to 12 show experiments performed by two different experimental methods and the results thereof. Type A: (a) in FIG. 9, referred to as type B and (b). Fig. 10 shows type A
If a 9 distance D = 40 mm in FIG. 11 D of type A
FIG. 12 shows experimental data in the case of type B and D = 28 mm. The solid line is the basic sine wave,
Indicates a deformed waveform. FIGS. 10 to 12A show the magnetic flux (m).
(a) and (b) are relative intensities (re).
5 shows the Latency Intensity (au.).

It will be understood from these experimental data that the magnetic field deformation means largely contributes to the magnetic field deformation.

[0051]

[Effect] As described above in detail, the periodic magnetic field generation device of the first invention of this application is a magnetic field that varies spatially periodic magnetic pole member, the non-close to the middle position of the magnetic field inside
Providing a magnetically deformable means of high magnetic permeability tactilely , its pattern,
Since the shape is predetermined and the spacing is set to suppress the influence of magnetic flux on adjacent magnetic fields, the method of changing the shape of the magnet, approaching or deforming the position of the adhesive shim or magnetic pole as in the past As compared with, the magnetic field can be guided without escaping to the magnetic field generated by other adjacent magnetic poles, so that a strong magnetic field strength can be obtained.

The shape, pattern (size, thickness, position, gap), interval, etc. of the magnetic field deforming means can be changed without changing the shape of the magnet or the like to deform, correct, taper or reverse taper the magnetic field shape. Or convergent scattering and position control. The various effects described above can be made inexpensive by simply adding a substance having a high magnetic permeability, and can be easily changed, so that versatility is possible, and high-order high-frequency generation with respect to SR light and free electron laser oscillation is also possible. It becomes possible and leads to a wider band of generated light.

[0053] Second, as in the third invention, when generating a periodic magnetic field by wiggler magnets, the magnetic field deforming means can change variously the result field deformation metal small piece of high permeability, these magnetic field deforming means Is much cheaper than replacing the wiggler magnet itself and ensures that various magnetic field deformations can be realized at economical cost.

[Brief description of the drawings]

FIG. 1 is an overall schematic diagram of a free electron laser oscillator using a periodic magnetic field generator according to an embodiment.

FIG. 2 is a partially enlarged view and an operation explanatory view of the periodic magnetic field generator of the above.

FIG. 3 is a partially enlarged view and operation explanatory view of a periodic magnetic field generator according to a second embodiment.

FIG. 4 is a partially enlarged view and operation explanatory view of a periodic magnetic field generator according to a third embodiment.

FIG. 5 is a partially enlarged view of a periodic magnetic field generator according to a fourth embodiment.

FIG. 6 is a partially enlarged view of a periodic magnetic field generator according to a fifth embodiment.

FIG. 7 is a partially enlarged view of a periodic magnetic field generator according to a sixth embodiment.

FIG. 8 is a partially enlarged view and operation explanatory view of a periodic magnetic field generator according to a seventh embodiment.

FIG. 9 shows the arrangement and spacing of wiggler magnets used in the experiment .
Diagram shown

FIG. 10: Experimental data for type A, GAP 40 mm
Graph of

FIG. 11: Experimental data for type A, GAP 44 mm
Graph of

FIG. 12: Experimental data for type B, GAP 28 mm
Graph of

[Explanation of symbols]

 Reference Signs List 1 electron linear accelerator 2 deflection electromagnet 3 wiggler magnet 3 'helical wiggler magnet 4, 4' optical resonator mirror 5 beam damper 6 magnetic field deforming means 6a, 6b metal piece 7 vacuum duct 8, 9 holder

Claims (3)

(57) [Claims] 1. A magnetic pole member comprising a magnet or an electric wire through which an electric current flows is periodically arranged so as to form a magnetic field which changes spatially periodically, and said magnetic pole member and said magnetic pole member are arranged inside said periodic magnetic field.
Magnetic field lines from magnetic pole members are adjacent between magnetic pole members without contact
Between arrangements that suppress the outflow to the magnetic field by other magnetic pole members
The magnetic field deforming means with high magnetic permeability at predetermined intervals
Or, a periodic magnetic field generator configured and arranged in a shape . 2. The magnetic pole member according to claim 1, wherein a plurality of pairs of magnets having magnets having different polarities are opposed to each other so that the directions of the magnetic fields of adjacent pairs are alternately opposite to each other along the traveling direction of electrons. The periodic magnetic field generator according to claim 1, wherein a small metal piece having a high magnetic permeability is provided as the magnetic field deforming means. 3. The periodic magnetic field generator according to claim 2, wherein the small metal pieces of the magnetic field deforming means are provided on one or both of the inner and outer surfaces of the vacuum duct for electron beam transmission.