JP3316984B2 - Particle accelerator beam monitoring method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for monitoring a beam applied to a particle accelerator such as a synchrotron, that is, a method for monitoring an optical axis position of radiation emitted through a beam line.

[0002]

2. Description of the Related Art In recent years, radiation light (abbreviated as synchrotron radiation light, SOR light or SR light) emitted from a particle accelerator such as a synchrotron is taken out and used as a light source, for example, in the manufacture of an ultra-large scale integrated circuit or in the medical field. Diagnosis in
There is a tendency to use it in various fields such as molecular analysis and structural analysis, and facilities for that purpose are being developed.

FIG. 2 shows an outline of a small synchrotron for utilizing synchrotron radiation. In this synchrotron, an electron beam generated by an electron generator 1 such as an electron gun is accelerated to near the light speed by a linear accelerator 2 (linac), deflected by a deflecting electromagnet 3, and then deflected by an inflector 4. 5 is incident. The electron beam incident on the storage ring 5 is converged by the converging electromagnet 7 while being energized by the high-frequency accelerating cavity 6, deflected by the deflection electromagnet 8, and continues to go around the storage ring 5. Then, when the light is deflected by the deflection electromagnet 8, the emitted light is emitted in the tangential direction, and the emitted light is emitted to, for example, an exposure apparatus 10 via a beam line 9 which is a light extraction line, and is used.

A beam monitor for monitoring the radiation passing through the beam line in the particle accelerator to detect the position of the optical axis and the range of expansion, and to perform alignment as necessary. Is provided. As a beam monitor device, a type called a wire monitor is generally adopted. Wire monitor
This is based on the fact that the current value changes due to the photoelectric effect when radiated light is irradiated on a tungsten wire with a current flowing, and the current value changes when a pair of tungsten wires are scanned across the beam line From
The optical axis position and the range of spread of the emitted light are detected.

[0005]

Recently, a large accelerator capable of extracting high-intensity, high-energy radiated light, or an insertion light source such as an undulator or a wiggler has been used in comparison with the above-mentioned small synchrotron. Development of the synchrotron and the like has been promoted. However, when a conventional wire monitor as described above is used as it is as a beam monitor device applied to a particle accelerator for extracting such high-energy radiation, the tungsten wire is overheated and damaged. There was a fear that it would. Therefore, it has been desired to provide an effective means capable of monitoring high-energy radiation light without any trouble and applicable to a large accelerator or an accelerator having an inserted light source.

[0006]

SUMMARY OF THE INVENTION In view of the above circumstances, a beam monitoring method for a particle accelerator according to the present invention is arranged such that, of radiation light, a center light having high brightness is coaxial with the center light and the center light is higher than the center light. Low-brightness harmonics distributed over a wide area
It is characterized in that the intensity of the contained component is detected, and the optical axis position of the entire radiated light is obtained based on the detection result.

[0007]

The present invention focuses on the fact that the radiated light is obtained by superimposing a high-luminance center light and a component including a low-luminance harmonic that is coaxially present around the center light. Instead of directly monitoring the center light, it includes low-intensity harmonics.
It is obtained so as to analogize the position of the optical axis of the entire emitted light by monitoring the outer peripheral edge portion of the free components. That is, when detecting the intensity of the outer peripheral edge portion by using any intensity detecting means, the intensity detecting means can detect the intensity of the low luminance part without receiving the high luminance center light, and the detection result , The position of the optical axis as the entire emitted light is monitored.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a beam monitoring method for a particle accelerator according to the present invention will be described below with reference to FIG. In FIG. 1, reference symbol S indicates emitted light to be monitored. The emitted light S is emitted from the insertion light source with the point 12 as a light emitting point, and is extracted through the beam line while gradually expanding. Such radiation S generally has a plurality of harmonics S1 superimposed around the center light S0. The positions of the optical axis 11 of the center light S0 and the odd-order harmonic S1 are shown in FIG.
As shown in FIG. 2, the intensity distributions are naturally symmetric about the optical axis 11, but the intensity of the harmonic S1 is sufficiently higher than the intensity of the central light S0. It is small. Also, while the intensity distribution of the central light S0 shows a sharp peak at the position of the optical axis 11,
The intensity distribution of the harmonic S1 is gentle, and the range of its spread is wider than that of the central light S0.

The conventional general beam monitoring method directly monitors the center light S0. When monitoring the position of the optical axis of the radiated light S, the above harmonic S1 is used.
Is usually ignored, but in the present method, attention is paid to the harmonic S1, and the radiation S is monitored by monitoring the low-luminance harmonic S1 without monitoring the high-luminance center light S0. The position of the entire optical axis, that is, the position of the optical axis of the central light S0 is determined.

That is, in the present method, for example, a conventional general wire monitor is adopted as a beam monitor device,
By scanning the outer peripheral edge of the harmonic S1 having sufficiently low luminance (that is, the skirt portion in the intensity distribution curve of the harmonic S1), the optical axis position of the harmonic S1 is obtained. The harmonics S thus obtained
Since the first optical axis 11 naturally coincides with the position of the optical axis 11 of the central light S0 as described above, the position of the optical axis 11 can be obtained without directly monitoring the central light S0. is there.

The specific procedure of the method will be described below.
First, the distance L from the light emitting point 12 to the monitor position 14 (the installation position of the wire monitor) is determined in advance. Further, the value of the angular variance σ, which is a parameter indicating the degree of spread of the central light S0, is obtained by calculation based on the following equation (1).

(Equation 1)

Then, the product of L and σ is calculated. This value Lσ indicates the range in which the high-brightness central light S0 spreads at the monitor position as shown in FIG. 1, and the intensity of the central light S0 abruptly and remarkably decreases outside this range. Become. Therefore, the wires 13, 1
The scan range of No. 3 is set outside the range of Lσ obtained above. As a result, the wires 13, 13 do not directly receive the high-brightness center light S0, but receive only the low-brightness harmonic S1. Then, each wire 13 is scanned within the above range, the intensity of the harmonic S1 is detected by the photoelectric effect generated by receiving the harmonic S1, and a point where the detected values of both the wires 13, 13 match is obtained. For example, the midpoint between them becomes the position of the optical axis 11 of the harmonic S1, which is the position of the optical axis 11 of the central light S0.

As described above, in the beam monitoring method of this embodiment, since the low-intensity harmonic S1 is to be monitored, unlike the conventional case in which the high-intensity center light S0 is directly monitored, There is no danger that the wire will be overheated and damaged, and the position of the optical axis 11 of the entire radiated light S can be monitored without any trouble.

In this embodiment, as means for detecting the intensity of the radiated light S, a change in the current in the wire 13 due to the photoelectric effect is detected using a wire monitor. Instead, for example, various means can be used, such as using a beam monitor device having a configuration in which a light receiving plate for receiving the radiation light S is provided and a temperature change when the light receiving plate is scanned is detected by a thermocouple.

[0015]

As described above in detail, in the beam monitoring method of the particle accelerator according to the present invention, since the intensity of the harmonics among the components of the emitted light is detected, for example, any intensity detecting means can be used. When detecting the intensity, the detecting device can detect the intensity without receiving high-luminance central light. Therefore, there is no possibility that the intensity detecting means may be damaged due to overheating, and the optical axis position of the entire radiated light can be monitored without any trouble.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of a beam monitoring method for a particle accelerator according to one embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a conventional general particle accelerator.

[Explanation of symbols]

 S synchrotron radiation S0 center light S1 harmonic component 11 optical axis

Claims (1)

(57) [Claims] 1. A method for monitoring an optical axis of radiation light extracted through a beam line of a particle accelerator, wherein the radiation light is coaxial with the central light around the high-luminance central light and the central light. A beam monitoring method for a particle accelerator, wherein the intensity of a component including a low-luminance harmonic distributed over a wider range is detected, and the optical axis position of the entire radiated light is determined based on the detection result.