JPH0896998A - Undulator, and method for oscillating free electron laser - Google Patents

Abstract

PURPOSE: To improve the oscillating efficiency of free electron laser. CONSTITUTION: An accelerating tube 4 having a static voltage electrode 5 arranged therein is inserted into the magnetic field of an undulator 1 using an electromagnet 2, and a charged beam 3 is incident thereto. A static voltage is applied to the static voltage electrode, the energy of the charged beam consumed by the oscillation of a free electron laser is compensated by the acceleration and focusing of the charged beam, and the energy is kept in the oscillating level of the free electron laser. The generating efficiency of the free electron laser which was as small as about 1% in the past can be improved several times by the stable oscillation of the free electron laser. The economical efficiency and operability of the free electron laser can be enhanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an undulator used for causing a charged beam to meander, a free electron laser device using the undulator, and an oscillation method. INDUSTRIAL APPLICABILITY Since the present invention can obtain a stable-sustaining free electron laser with a high gain, it can be widely used in various industrial fields requiring a laser.

[0002]

2. Description of the Prior Art A reduction in the energy level of a charged beam in an undulator can result in a large efficiency loss in a device using the undulator, even if it is not very large. For example, when used in a free electron laser device, when the charged beam introduced into the undulator from the high frequency accelerator causes energy loss of 1%, the energy level usually does not reach a predetermined threshold value and the free electron laser oscillation condition is satisfied. Is broken, oscillation does not occur, and free electron laser generation efficiency is extremely reduced. One of the means to solve this kind of problem is to supplement the charged beam with energy in some way and continue to maintain the oscillation conditions.

Therefore, J. F. Schmerge et al.
We have developed a high-efficiency free-electron laser device that employs an undulator structure that causes the charged beam to meander in the electrodes of the radio frequency accelerator and supplements the charging energy lost by the meandering with microwave power (JF Schmerge et al., Nucl. Instru. Meth. .
A341 (1994) p335-340). Specifically, a rectangular parallelepiped acceleration tube made of stainless steel is used, and electrostatic electrodes made of vacuum-melted iron are arranged above and below the inner surface thereof so as to be alternately shifted in the traveling direction of the charged beam. By alternately shifting the upper and lower electrodes to the left and right, the electric field generated between the upper and lower electrodes causes the charged beam to meander and be accelerated. At this time, the energy lost by meandering is supplemented by the microwave power applied to the electrostatic voltage electrode.

[0004]

However, since the electrode structure of the high frequency accelerator is limited by the frequency of the high frequency to be used, J. F. The method of Schmerge et al. Cannot have an arbitrary meandering period length in the undulator. Therefore, the range of variable wavelength, which is an advantage of the free electron laser device, is limited. Also, since the charged beam is accelerated even when the free electron laser is not oscillating,
Another problem is that it is difficult to adjust the oscillation conditions. The present invention
It was completed as a result of research aimed at a free electron laser device which can be easily adjusted and has high generation efficiency without narrowing the advantages of a highly efficient undulator, especially a free electron laser.

[0005]

The present invention will be described with reference to the drawings. In order to achieve the above object, the present invention provides an undulator 1 using an electromagnet 2 in which an electrostatic tube 5 for accelerating a traveling charged beam 3 in a magnetic field formed by the electromagnet is arranged. 4 provides an undulator characterized in that 4 is inserted. Also,
An undulator 1 in which an electron accelerator 14 for injecting a charged beam into the undulator 1 and an accelerating tube 4 in which electrostatic voltage electrodes for accelerating the charged beam 3 are arranged are inserted in a magnetic field formed by using an electromagnet 2. And a set of optical resonators 9 sandwiching the undulator 1 are provided. Further, using an electron accelerator, an undulator in which an accelerating tube having electrostatic voltage electrodes for accelerating a charged beam traveling in a magnetic field is inserted, and a set of optical resonators, the charged beam from the electron accelerator to the accelerating tube is used. The incident electron beam is caused to meander by a magnetic field to emit spontaneous emission light, and the spontaneous emission light is reciprocated between optical resonators to oscillate a free electron laser in synchronization with the subsequent charged beam and the oscillated free electron laser A free electron laser oscillation method is provided, wherein the electrostatic voltage applied to the electrostatic voltage electrode is controlled in accordance with the above.

[0006]

Actions and Embodiments The present invention will be described more specifically with reference to the drawings. FIG. 1 is a schematic view of an example of an embodiment of the undulator of the present invention used for free electron laser oscillation. 2A and 2B are diagrams showing an embodiment of the electrode used in the present invention, FIG. 2A is a front view from the upstream side in the traveling direction of the charged beam, and FIG. 2B is a sectional view taken along line AA ′.

In the present invention, in the undulator 1, a means for accelerating the charged beam 3 is used to supplement the energy consumed by the charged beam 3. Specifically, the electrostatic voltage electrode 5 is placed in the magnetic field formed by the electromagnet 2 of the undulator 1.
The accelerating tube 4 in which is arranged is inserted, and the charged beam 3 is injected into the accelerating tube 4. The electrostatic voltage electrode 5 has a function of accelerating the charged beam 3 traveling in the accelerating tube 4 and focusing it if necessary. There is no particular limitation on the type of the accelerating tube 4, but normally, a vacuum sealing type is used, and the number and arrangement pitch of the electrostatic voltage electrodes 5
Specifications such as the diameter of the electrode hole 6 which becomes the passage of the charged beam 3 are as follows.
It is determined by the size of the charged beam, the amount of energy to be replenished, and the like. However, in order to keep the magnetic field strength of the undulator 1 at or above a predetermined value, it is desirable to make the outer diameter of the acceleration tube 4 as small as possible. The arrangement pitch of the electrostatic voltage electrodes 5 can be determined based on the required inter-electrode electric field. Further, the electrostatic voltage electrode 5 may be of the same type as that used in the high frequency accelerator. Since the electrostatic voltage electrode plate 5 forms an electrostatic field suitable for focusing the charged beam, as shown in FIG. 2B, the electrode plate 6 is surrounded by the electrode hole 6 with respect to the incident direction of the charged beam. It is desirable to make the diameter of the protrusion narrow while projecting. Reference numeral 13 is an insulator. When the inside of the accelerating tube 4 is used under high vacuum, the material of the electrostatic voltage electrode 5 is preferably oxygen-free copper or stainless steel.

On the other hand, the arrangement of the electromagnets 2 may be in conformity with a normal undulator, but the arrangement pitch is preferably about 2 to 3 times the outer diameter of the acceleration tube 4. The iron core 7 of the electromagnet 2 may have a structure in which the tip is narrowed toward the magnetic field to be formed so that a strong magnetic field is easily generated in the charged beam orbit. An example embodiment of the magnetic poles is shown in FIG. (A) is a plan view orthogonal to the charged beam trajectory, (b) is a sectional view taken along the line BB 'of (a), and 15 is a coil.

The present invention will be described by taking free electron laser oscillation as an example. A charged beam 3 emitted from an electron accelerator 14 such as an electron linac, a synchrotron or a microtron is an accelerating tube 4 inserted in an undulator 1 of the present invention.
And is meandered with a predetermined cycle length by the magnetic field formed by the electromagnet 5. Spontaneous radiation 8 emitted by the serpentine is synchronized with a subsequent pulse of the charged beam 3 while reciprocating between a set of optical cavities 9, for example a pair of mirrors adjusted by a precision alignment system, A certain energy level, that is, a threshold value is reached and the free electron laser is oscillated. The oscillated free electron laser is extracted and used as the output 10. The charged beam 11 oscillating the free electron laser is the beam catcher 1
Guided to 2.

By the way, in the conventional undulator, the charged beam consumes energy due to the oscillation of the free electron laser, the energy level does not reach the threshold value in a short time, the oscillation of the free electron laser stops, and the oscillation is sustained and stable. I can't get it. In the undulator 1 of the present invention, since the charged beam 3 is incident on the accelerating tube 4, it oscillates a free electron laser in the accelerating tube 4 and consumes energy. To maintain a constant energy level. By controlling the voltage applied to the electrostatic voltage electrode 5 according to the oscillation of the free electron laser, the energy level of the charged beam 3 can be kept constant. For example, a free electron laser 1
The output of 0 is continuously measured using a photon detector, and the applied voltage of the electrostatic voltage electrode 5 is controlled according to the output of the detector. Since the charged beam can maintain the oscillation condition of the free electron laser, the output of the free electron laser is maintained and the generation efficiency of the free electron laser can be improved.

[0011]

Since the undulator of the present invention can easily maintain the charged beam at a predetermined energy level, it can be stably operated, and the prospect of its use in various fields has been opened up. For example, when used in a free electron laser device,
The generation efficiency of the free electron laser, which was only about 1% because the charged beam loses energy and cannot sustain the oscillation state, can be improved several times by maintaining the stable oscillation state. In many cases, the energy required for electrostatic acceleration is not so large, the energy to be supplemented by the electrostatic voltage electrode is about 10% of the energy of the charged beam, and the adjustment is easy. The present invention greatly improves the economical efficiency and operability of a free electron laser, and has a great effect on the practical application of the free electron laser in a wide field such as industry, medicine, and research.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an undulator of the present invention.

FIG. 2 is a diagram showing an example of an embodiment of an electrode used in the present invention. (A): Front view from the upstream side of the charged beam. (B): AA 'sectional drawing of (a).

FIG. 3 is a diagram showing an example of an embodiment of a magnetic pole. (A): A plan view orthogonal to the charged beam trajectory. (B): A BB 'sectional view of (a).

[Explanation of symbols]

1: Undulator 2: Electromagnet 3: Charged beam 4: Accelerating tube 5: Electrostatic voltage electrode 6: Electrode hole 7:
Iron core 8: Spontaneous emission light 9: Optical resonator 10: Output free electron laser 11: Charged beam oscillating free electron laser 12:
Beam catcher 13: Insulator 14: Electron accelerator 15: Coil

Claims (3)

[Claims] 1. An undulator 1 using an electromagnet 2, wherein an electromagnet has an accelerating tube 4 in which a static voltage electrode 5 is arranged for accelerating a charged beam 3 in a magnetic field. Undulator. 2. An electron accelerator 14 for injecting a charged beam into an undulator 1 and an accelerating tube 4 in which electrostatic voltage electrodes for accelerating a charged beam 3 are arranged in a magnetic field formed by using an electromagnet 2. Undulator 1 which is being used,
A set of optical resonators 9 sandwiching the undulator 1
And a free electron laser device. 3. An electron accelerator, an undulator in which an accelerating tube having electrostatic voltage electrodes for accelerating a charged beam traveling in a magnetic field is inserted, and a set of optical resonators are used.
A charged beam is made incident on an accelerating tube from an electron accelerator, the charged beam is meandered by a magnetic field to emit spontaneous emission light, and the spontaneous emission light is reciprocated between optical resonators and synchronized with the subsequent charged beam to produce a free electron laser. Is oscillated, and the electrostatic voltage applied to the electrostatic voltage electrode is controlled according to the oscillated free electron laser.