JP2005166689A - Monitor for detecting beam position - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a beam position detecting monitor to meet a wide range of current amount with simple structure in beam conveyance systems, such as LINACs or synchrotrons. <P>SOLUTION: A screen 3 where a fluorescent board generating fluorescence, when a beam collides and a metal plate (OTR plate) presenting an optical transition radiation (OTR) phenomenon, when a beam collides are adhered, is inserted into a beam orbit in the beam conveyance system. The beam position detecting monitor finds the position of the beam by observing fluorescence, when a beam amount is small, and by observing the transition radiation beam when a beam amount is large. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a beam detection monitor used for confirming a beam position or measuring a beam size in a beam transport system such as a synchrotron such as a linac or storage ring.

  In the linac, the position of the electron beam trajectory and the beam size are important management targets in the synchrotron. Therefore, it is necessary to measure the position of the electron beam at key points during start-up and steady operation. For this reason, in spite of being a destructive detection method in which the beam cannot be maintained when measured, a fluorescent plate such as aluminum oxide is inserted into the beam trajectory, and the fluorescence generated when the beam collides is observed with a CCD camera or the like Is used.

FIG. 5 is a partially sectional elevational view showing an example of a conventional beam position detection monitor.
When detecting the position of the electron beam, a fluorescent plate is inserted into the electron beam trajectory, and the state in which the electron beam strikes these plates and shines is observed from the viewing window. An image acquired by installing a CCD camera or the like outside the viewing window may be displayed on the image display device. Depending on the amount of electron beam current, the fluorescent plate may be replaced with a metal plate for measurement.

  Patent Document 1 discloses a fluorescent screen monitor device used when adjusting the beam of an accelerator of a storage ring. This fluorescent screen monitor device is provided with a plurality of holes in the fluorescent screen to be inserted into the beam path so that a part of the beam passes downstream so that the position of the beam that has circulated around the other ring can be known. It is a thing.

Since such a beam position detection method using fluorescence has high sensitivity, if the current value of the colliding particle beam increases, the amount of emitted light becomes too large, making it difficult to specify the center position of the beam and making the beam contour unclear. There was a drawback, and while the beam current value at the time of start-up was small, there was a problem that even if it served as a monitor, it could not monitor the steady operation state.
In order to know the position of a strong beam, measures such as measuring the afterglow after taking a certain time after the collision of the beam are performed, but it is difficult to obtain an accurate measurement result.

  On the other hand, when a high energy electron beam collides with a metal such as aluminum, light emission called optical transition radiation (OTR) occurs. Although the position of the electron beam can be measured using this light emission phenomenon, it is difficult to detect a relatively small amount of beam when adjusting the accelerator because the light emission efficiency is low.

The α electromagnet in the linac is a component for performing energy analysis and beam bunching of a charged particle beam, and it is important to accurately adjust the incident position and the incident direction of the beam in operation.
FIG. 6 is a view for explaining beam adjustment in the α electromagnet. The accelerated electron beam emitted from the electron gun is incident on the α electromagnet at a predetermined angle. The electron beam is deflected in the magnetic field of the α electromagnet and rotated almost once, followed by an α-shaped trajectory and emitted toward the next accelerating tube with a predetermined angle.

The slower the electron velocity, the smaller the radius of curvature, so it passes the inside of the α orbit, and the faster the electron velocity, the more the outer orbit passes.
When the electron beam is incident on the entrance line of the α electromagnet with an inclination of 40.71 degrees, the electron beams once separated in the α-shaped orbit are collected again and emitted from the same point with an inclination of 40.71 degrees.
In the α electromagnet's magnetic field, the fast component in the electron beam flies over a long distance and the slow component flies over a short distance. Yes.

In order to utilize the shaping action of the α electromagnet, it is necessary that the incident beam and the outgoing beam overlap with an inclination of 40.71 degrees at the entrance line of the α magnet indicated by a broken line in the figure.
For this reason, conventionally, the position is confirmed and adjusted using a beam position monitor separately prepared in the incident tube. In particular, in order to accurately measure the incident angle, two beam position monitors are set apart from each other and calculated using the measurement results of both.

As described above, the low-energy particles pass through the inner side of the beam trajectory that follows the α-electromagnet in the α-character shape. Therefore, the α electromagnet is equipped with a beam slit plate that can be driven in parallel from the outside, and the beam slit plate is applied from the inside of the α-shaped beam trajectory, and the position of this plate is adjusted to achieve an appropriate energy level. Particles that do not reach are removed so that the energy distribution in the beam can be adjusted.
JP-A-5-249248

  Therefore, what is the problem to be solved by the present invention? In a beam transport system such as a linac or synchrotron, a beam detection monitor capable of measuring a beam position capable of handling a wide range of current amounts by a simple mechanism is provided.

  In order to solve the above-described problems, a beam position detection monitor for detecting a beam position by inserting a screen with a fluorescent plate attached into a beam trajectory of a beam transport system according to the present invention is optically applied to a part of the screen with a fluorescent plate attached. By providing a metal plate (OTR plate) exhibiting an optical transition radiation (OTR) phenomenon, the position of the beam is known by observing the fluorescence when the beam amount is small and observing the transition radiation when the beam amount increases. It is characterized by that.

  With the configuration of the present invention, the beam position and beam profile are detected with high sensitivity using the fluorescence phenomenon in the adjustment at the start-up when the amount of current of the beam is small, and the adjustment is performed in the steady operation condition where the amount of current increases. It is possible to accurately measure the beam position and shape by using the optical transition radiation phenomenon.

For this reason, it is preferable to provide a fluorescent plate on one surface of the screen and a metal plate on the back surface.
In this way, measurement is performed using a phosphor screen during adjustment, and when the beam current increases and a clear image cannot be obtained, the screen is rotated so that the beam hits the metal surface on the back, and the correct beam position is set. Can be confirmed.

Furthermore, a rotation introduction terminal for vacuum can be provided, and the screen can be rotated 180 degrees with this rotation introduction terminal to switch the surface irradiated with the beam.
By using the rotation introduction terminal for vacuum, it is not only possible to easily change the measurement sensitivity by rotating the screen, but it is also necessary to stop the operation of the laser device at the time of switching by providing a mechanism for remote operation Therefore, adjustment becomes extremely easy.

Moreover, you may make it provide both the part of a fluorescent plate and the part of a metal plate in the single side | surface of a screen.
By doing this, it is possible to measure beams of different intensities by simply translating without rotating.
Furthermore, a fluorescent plate may be provided on one side with a straight line passing through the beam center irradiation position of the screen, and a metal plate may be provided on the other side.
By separating the fluorescent plate and the OTR plate at the center of the beam in this way, it is possible to measure beams with different intensities by setting them at the same position without adjusting the screen position to a different position. become.

  Furthermore, the beam position detection monitor of the present invention attaches a material that generates light when an incident beam collides with the back surface of a slit used to remove a particle beam with low energy in a beam trajectory in an α electromagnet used for a linac or the like. When the beam position is measured, the beam position and beam size may be monitored by moving the slit to the beam incident position and observing the light emission position. .

In the present invention, the screen of the beam position detection monitor is used together with the back side of the already used beam slit plate, and it is necessary to extend the stroke of the beam slit plate drive mechanism in the conventional apparatus, but a slight improvement is required. In addition, the beam position at the entrance line of the α magnet can be accurately measured.
Note that different levels of beam positions can be measured by placing the screen in the same position with a fluorescent plate on one side and a metal plate on the other side across a straight line passing through the central portion of the rear surface of the slit.

In each of the above beam position detection monitors, the fluorescent plate may be formed of aluminum oxide and the metal plate may be formed of aluminum.
These materials are relatively easily available, generate sufficient fluorescence, and generate relatively strong OTR light.

A free electron laser apparatus according to the present invention incorporates any one of the above-described beam position detection monitors.
Since the improved beam position detection monitor can adjust the beam position and beam shape more easily and more accurately, a free electron laser device capable of saving rise time and operating with high accuracy can be obtained.

Hereinafter, the present invention will be described in detail based on examples with reference to the drawings.
FIG. 1 is a block diagram showing an embodiment of a beam position detection monitor of the present invention, FIG. 2 is a front view and a side view of a screen used in this embodiment, and FIG. 3 is a side view of various screens used in this embodiment. FIG. 4 and FIG. 4 are block diagrams showing a second embodiment of the beam position detection monitor of the present invention.

The beam position detection monitor of this embodiment is provided in a beam chamber of a beam transport system in a free electron laser device to detect the beam position.
In FIG. 1, 1 is a beam chamber, 2 is a monitor mounting nozzle, 3 is a screen, 4 is a screen insertion cylinder, 5 is a bellows, 6 is a rotation introduction terminal, 7 is a viewing window, 8 is a CCD camera, and 9 is an electronic device. It is a beam.

The screen 3 is lifted up by the cylinder 4 during steady operation to avoid the beam path, but when measuring the beam for adjusting the beam position and checking the accuracy, the screen insertion cylinder 4 is driven to move the beam trajectory. Can be inserted in.
The screen 3 can be rotated 180 degrees manually or remotely by a rotation introducing terminal 6.

FIG. 2 is an enlarged view of the screen 3 used in this embodiment. 2A is a front view of the screen as viewed from the upstream side, and FIG. 2B is a side view.
As shown in FIG. 2A, the surface of the screen 3 may be provided with a target pattern that reveals the actual size so that the center position of the electron beam and the shape of the beam contour can be accurately read.
As shown in FIG. 2B, a fluorescent plate 31 made of aluminum oxide or the like that generates fluorescence when it hits electrons is attached to the surface of the screen 3, and an aluminum metal exhibiting an optical transition radiation (OTR) phenomenon or the like on the back surface. The OTR plate 32 is affixed.

Therefore, when a low energy electron beam is used such as position adjustment at the start of operation, the surface on which the aluminum oxide phosphor plate 31 is attached is directed toward the side on which the electron beam is incident, and the state in which the electron beam strikes and shines is observed. Images can be taken by the CCD camera 8 through the window 7.
Since the fluorescence generated when the electron beam strikes is sufficiently strong, even when an electron beam with a small current value collides, it emits light strongly, and the center position of the beam and the cross-sectional shape of the beam can be detected with high sensitivity.
After confirming the electron beam position, the screen 3 is retracted into the monitor mounting nozzle 2 and the operation is continued.

  In the start-up adjustment, the current value of the electron beam increases as the output is gradually increased. When the fluorescent plate 31 is targeted, the portion that has received the electron beam becomes too bright and saturated, and the center position can be clearly specified. Disappear. Further, the outline of the portion where the electron beam collides is not clear. The same phenomenon occurs when trying to observe the state in normal operation.

Therefore, in the present embodiment, when measuring an electron beam with a large amount of current, the screen 3 is rotated and inserted into the electron beam trajectory so that the OTR plate surface 32 with aluminum attached faces in the direction facing the electron beam. The optical transition radiation (OTR) light generated by the collision with the electrons is photographed by the CCD camera 8 through the viewing window 7 and the position and contour shape are confirmed by the display device. Since the OTR light is less sensitive than the light emitted from the fluorescent screen, the center position and contour of the high energy electron beam can be accurately observed.
When the fluorescent plate 31 or the OTR plate 32 is marked with a position confirmation mark such as a target pattern, when the screen 3 is accurately inserted and fixed in a predetermined position with respect to the beam chamber 1, The traveling position of the electron beam can be correctly grasped based on the distribution situation.

As described above, the position of the electron beam in the low energy state and the high energy state can be detected by the single screen 3.
In addition, when an operator approaches the accelerator device in operation, there is a risk of radiation damage. Therefore, when the energy level is changed and the screen is replaced as in the conventional case, it is necessary to stop the operation of the accelerator or the like.
However, in the beam position detection monitor of the present embodiment, the rotation introduction terminal 6 is used to perform switching by remote operation instead of the operator's hand, so that it is not necessary to stop the operation of the accelerator or the like.
Since the operation is not interrupted, the beam position once adjusted is less likely to be distorted, and the driving efficiency is improved.

Instead of separating and attaching the fluorescent plate and the OTR plate to the two front and back surfaces of the screen 3, the fluorescent plate may be attached to one divided surface and the OTR plate attached to the other.
FIGS. 3A, 3B and 3C are side views showing other forms of the screen.
FIG. 3A is a screen formed by covering the lower side of the substrate 33 formed of a fluorescent plate with a metal plate 34 that generates OTR light, and FIG. 3B is a diagram in which one surface of the substrate 35 is divided and the fluorescent plate is divided into one side. 36 shows a screen formed by attaching an OTR plate 37 to the other, and FIG. 3C shows a screen formed by attaching a fluorescent plate 39 to the upper half of the metal plate 38 as a substrate.

In this way, what is provided with two types of light emitting plates on one surface of the screen can be translated instead of rotating even when the light emitting plates are switched in accordance with the increase or decrease in the amount of current of the electron beam. The mechanism becomes simple.
Furthermore, if the butted portions of the two kinds of light emitting plates are aligned with the center of the electron beam, the setting position of the screen 3 at the time of measurement does not change even if the energy of the electron beam changes, and the operation becomes easy.
In the drawing, the fluorescent plate and the OTR plate are arranged side by side in the up-and-down direction, but not limited to the up-and-down direction, it is sufficient that two types of light-emitting plates are arranged in a direction crossing the drive shaft of the screen.

The beam position detection monitor of this embodiment is used in the α electromagnet portion of the linac used in the free electron laser apparatus.
In FIG. 4, 11 is an α electromagnet chamber, 12 is a beam incident nozzle, 13 is a beam emission nozzle, 14 is a slit mounting nozzle, 15 is a beam slit which also serves as a screen, 16 is a slit driving device, 17 is a bellows, 18 Is a viewing window, 19 is a CCD camera, and 20 is an electron beam trajectory.
As shown in FIGS. 3A, 3B, and 3C, a fluorescent plate and an OTR plate are juxtaposed on the back surface of the beam slit 15, that is, on the right side in the drawing.

The accelerated electron beam is incident on the α electromagnet from the beam incident nozzle 12 with a predetermined angle.
The electron beam follows an α-shaped trajectory 20 in the magnetic field of the α electromagnet, and is shaped by the beam slit 15 at the apex position of the α-shaped trajectory, and then emitted from the beam emitting nozzle 13 at a predetermined angle.
The energy distribution state of the emitted electron beam is determined by the position 15 ′ of the beam slit drawn by a dotted line. The position of the beam slit 15 can be adjusted by the slit driving device 16.

The incident position and incident angle are determined with reference to the entrance line of the α electromagnet indicated by the broken line in the figure.
In order to confirm that the electron beam is incident at the correct position, the beam slit 15 is moved to the position of the entrance line of the electromagnet so that the incident electron beam collides with the back surface to which the light emitting plate is attached.
For this reason, the driving device 16 for the beam slit 15 needs to have a longer stroke than the slit driving device in the conventional device.

  When the light-emitting plate of the beam slit 15 is placed on the entrance line of the α electromagnet serving as a reference for the beam incident position, the electron beam collides and shines by being photographed and observed through a viewing window 18 with a CCD camera. The center position and beam cross-sectional shape can be grasped directly and accurately. When the current amount of the electron beam is small, the measurement can be performed with respect to a wide range of energy by measuring at the fluorescent plate portion and when the current amount is large at the metal plate portion.

  As described above, by using the beam detection monitor of the present invention, it is possible to measure the beam position corresponding to a wide range of current amounts with a simple mechanism. Further, even when the energy level changes, it is possible to switch to a light emitting plate having different sensitivities without stopping the operation of the accelerator or the like, so that the operation efficiency of the apparatus such as linac and synchrotron is improved.

It is a block diagram showing one Example of the beam position detection monitor of this invention. It is the front view and side view of a screen which are used for a present Example. It is a side view of the various screens used for a present Example. It is a block diagram which shows the 2nd Example of the beam position detection monitor of this invention. It is a block diagram showing an example of the prior art beam position detection monitor. It is a block diagram showing another example of the prior art beam position detection monitor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Beam chamber 2 Monitor mounting nozzle 3 Screen 31, 33, 36, 39 Fluorescent plate 32, 34, 37, 38 Optical transition radiation (OTR) plate 35 Substrate 4 Cylinder for screen insertion 5 Bellows 6 Rotation introducing terminal 7 Viewing window 8 CCD camera 9 Electron beam 11 α electromagnet chamber 12 Beam entrance nozzle 13 Beam exit nozzle 14 Slit mounting nozzle 15 Beam slit 16 Slit driving device 17 Bellows 18 Viewing window 19 CCD camera 20 Beam trajectory

Claims (4)

A material that generates light when the incident beam collides with the back surface of the slit used to remove the particle beam whose energy has shifted in the beam trajectory in the alpha electromagnet used in an accelerator such as a linac. A beam position detection monitor characterized by monitoring a beam position and a beam size by moving to a position and observing a light emission position. 2. The material according to claim 1, wherein the light generating material is a fluorescent plate and a metal plate, the fluorescent plate is provided on one side across a straight line passing through the central portion of the slit, and the metal plate is provided on the other side. Beam position detection monitor. 3. The beam position detection monitor according to claim 2, wherein the composition of the fluorescent plate is aluminum oxide and the composition of the metal plate is aluminum. A free electron laser apparatus comprising the beam position detection monitor according to claim 1.

Images