JP2909385B2 - Inductive bremsstrahlung device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an inductive bremsstrahlung apparatus. For example, the present invention relates to a wiggler for a free electron laser that applies a periodic magnetic field to an electron beam or a positron beam in order to generate laser light or radiation light with a synchrotron or a linear accelerator.

[0002]

2. Description of the Related Art As shown in FIG. 5, when a high-energy electron beam 1 is meandering in a periodic magnetic field between magnets 3, it is known that radiation with high directivity and high brightness can be obtained. Have been. An apparatus for obtaining such radiation light is called a wiggler (strong magnetic field type) or an undulator (weak magnetic field type), depending on the strength of the magnetic field and the application. A beam duct (vacuum container) 7 for creating a vacuum atmosphere may be provided between the opposing magnets 03.

Further, resonators are arranged before and after the wiggler, and the radiated light generated by the wiggler is reflected by the resonator to resonate the successively incident electron beam 1 and the radiated light, thereby generating free electrons. A laser can be oscillated. Here, the propagation of the electron beam 1 between the opposing magnet arrays 3 of the wiggler without interference or scattering is an important technique for oscillating a free electron laser.

At this time, it is extremely difficult to pass the electron beam 1 between the long and narrow magnet rows 3 at a time. In practice, the electron beam 1 is formed at several points along the wiggler beam axis direction. By monitoring the position of the beam and detecting the position of the electron beam incident from the upstream side, the position of the wiggler is aligned little by little, and the electron beam is propagated to the most downstream. In other words, by knowing where in the beam axis direction the electron beam is located in the horizontal direction with respect to the beam axis, the alignment direction and alignment amount of the wiggler can be grasped.

FIG. 3 shows a conventional wiggler monitor. As shown in the figure, a plurality of permanent magnets 3 for generating a periodic magnetic field in a direction perpendicular to the paper are arranged opposite to each other with a space through which the electron beam 1 passes above and below. Held by the magnet holder 4, and
The permanent magnet holder 4 is vertically movably supported by a gap adjusting mechanism 8 via a rod 5. Gap adjusting mechanism 8
Moves the permanent magnet holder 4 and the permanent magnet 3 up and down with the rod 5, respectively, to adjust the space through which the electron beam 1 passes, that is, the gap 15 facing the permanent magnet 3 (hereinafter, this gap is called the gap). It has a function to do.

Here, a vacuum vessel 7 is inserted into the gap 15 between the permanent magnets 3 from a horizontal direction. The vacuum container 7 movably accommodates the fluorescent plate 2 fixed to the fluorescent plate holder 12, and the fluorescent plate holder 12 air-tightly penetrates one end side of the vacuum container 7 through an extendable bellows 13 to form an air cylinder. 14. Therefore, when it is necessary to monitor the position of the electron beam 1, the air cylinder 14 is driven to expand and contract the bellows 13 to push the fluorescent plate 2 and the fluorescent plate holder 12 to the position where the electron beam 1 passes. At the time
The fluorescent plate 2 and the fluorescent plate holder 12 can be retracted from the position where the electron beam 1 passes. When the electron beam 1 collides with the fluorescent plate 2, the fluorescent plate 2 emits light centering on the collision position.

As the fluorescent plate 2, a ceramic (for example, trade name: Demarquest (AF955R) or the like) which emits light when irradiated with the electron beam 1 is used. On the other hand, a vacuum window 9 is attached to the other end side of the vacuum container 7, and the TV camera 1 facing the vacuum window 9
0 is arranged. The TV camera 10 is connected to a monitor 11 that is observed by an observer. Accordingly, when the TV camera 10 detects the light emission of the fluorescent screen 2 through the vacuum window 9, the image is observed by the observer on the monitor 11, and the position of the electron beam 1 is determined.

FIG. 4 shows the relationship between the gap 15 of the wiggler and the period and the K value representing the performance of the wiggler. As shown in the figure, a minimum K value of 0.5 or more required to oscillate a free electron laser is ensured, and free electron energy in the infrared region is oscillated with a low electron beam energy (about 10 MeV). Wiggler period λ _w =
Considering the case of 12 mm, it is understood that the gap 15 (= g) needs to be reduced to about 6 mm. However, FIG. 4 uses an Nd—Fe—B type permanent magnet as the permanent magnet 3, sets the permanent magnet height h = 50 mm, sets the wiggler type to a Halbach type, and uses the following equation. It is a graph of the calculated result.

[0009] _{K = 93.4 · B 0 λ w} B 0 = 2B r [1-exp (-λ w · h)] exp (-k w · g / 2) · si
n (π / M) / ( π / M) k w = 2π / λ w where, lambda _w; wiggler period [mm] h; permanent magnet Height [mm] g; Gap [mm] B _r; magnet residual Magnetic flux density [T] M; number of magnets per cycle M = 4 for Halbach type

[0010]

In the prior art shown in FIG. 3 described above, the size of the fluorescent plate 2 needs to be at least about 10 mm × 10 mm, and if the size of the fluorescent plate holder 12 is included, The size of the gap 15 requires a region of about 20 mm. However, as shown in the graph of FIG. 4, when the minimum K value required to oscillate the free electron laser is 0.5 or more and the wiggler period is 12 mm, the gap 15 is reduced to about 6 mm. It is necessary to narrow it.

Therefore, when the gap 15 is narrowed to this extent, the fluorescent screen 2 and the fluorescent screen holder 12 are moved to the gap 1.
When a wiggler with such a short cycle and a narrow gap 15 is employed, it is impossible to monitor the position of the electron beam, which greatly hinders a free electron laser oscillation experiment, and makes necessary adjustments. The time and cost of the experiment was very high. As described above, according to the prior art, the period is relatively short, and in the wiggler for obtaining a predetermined magnetic field strength and a K value, the gap 1
5 needs to be reduced to about 6 mm, and the fluorescent screen 2 and the fluorescent screen holder 12 are too large, so that the fluorescent screen 2 cannot be inserted into the gap 15.

Therefore, in a free electron laser oscillation experiment using a wiggler having a narrow gap 15, it becomes difficult to monitor the position of the electron beam 1 passing through the wiggler. The problem that the electron beam 1 collides with the head was likely to occur. That is,
Since the magnet surface is wide in the horizontal direction with respect to the gap 15,
Although the propagation of the electron beam 1 is relatively easy, the gap 15 is small in the vertical direction, so that the propagation of the electron beam 1 is difficult and there is a problem of collision.

For this reason, the electron beam 1 cannot be stably propagated in the wiggler, so that a large amount of time is required for experiments and adjustments, and it is impossible to oscillate a free electron laser if necessary. Was. The present invention has been made in view of the above-mentioned conventional technology.Electrons, a wiggler that applies a periodic magnetic field to a particle beam such as a positron to make meandering motion and emits radiation, a free electron laser, and has a relatively short period with an undulator. An object of the present invention is to provide an induced bremsstrahlung apparatus which can easily propagate an electron beam even when it is necessary to reduce a gap between magnets in order to obtain a predetermined magnetic field strength and a K value. I do.

[0014]

In the present invention, instead of inserting the fluorescent plate into the gap between the opposing permanent magnets, the fluorescent plates are mounted on the mutually facing surfaces of the permanent magnets. Since the fluorescent plate emits light when irradiated with an electron beam, the position where the electron beam passes can be detected by monitoring the pattern. Therefore, it is possible to make the gap between the magnets narrower than in the related art in which the fluorescent plate is inserted.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings. 1 and 2 show a wiggler monitor according to an embodiment of the present invention. As shown in both figures, a plurality of permanent magnets 3 are arranged facing each other across a space through which the electron beam 1 passes in a vacuum vessel 17, and these permanent magnets 3 are each held by a permanent magnet holder 4. Is held.

Each permanent magnet holder 4 is connected via a rod 5
The gap adjusting mechanism 8 outside the vacuum vessel 17 is vertically movably supported, and the bellows 6 is hermetically interposed between the gap adjusting mechanism 8 and the vacuum vessel 17. The gap adjusting mechanism 8 is capable of moving the permanent magnet 3 and its holder 4 up and down by expanding and contracting the bellows 6 via the rods 5 respectively, and
That is, it has a function of adjusting the gap 15 between the permanent magnets 3.

As in the present embodiment, the permanent magnet 3 and its holder 4 are housed in the vacuum vessel 17 so that unlike the conventional wiggler in which the vacuum vessel 7 is inserted into the gap 15 of the permanent magnet 3, The gap 15 between the magnets 3 can be made as small as possible, and the central magnetic field can be made as high as possible. On the opposing surfaces of the permanent magnets 3, thin fluorescent plates 22 are respectively adhered by an adhesive. As the fluorescent plate 22, a ceramic or the like that emits fluorescent light when irradiated with an electron beam is used.

The vacuum container 17 is provided with a vacuum window 9 so that the gap 15 between the permanent magnets 3 can be observed from outside. As shown in FIG. 2, the vacuum windows 9 are provided at a plurality of locations (five locations in the drawing) in the beam axis direction. A TV camera 10 facing the vacuum window 9 is arranged outside the vacuum vessel 7.
0 is connected to the monitor 11 observed by the observer. Therefore, when performing a free electron laser oscillation experiment, FIG.
The electron beam 1 incident on the gap 15 from the left side in the middle is
If the alignment is not optimal, the permanent magnet 3
And the fluorescent plate 3 emits light. The state is photographed by the TV camera 10 through the vacuum window 9 and observed by the observer on the monitor 11,
It can be seen that the electron beam 1 has deviated from the gap 15.

The experimenter can determine the alignment direction and the alignment amount of the wiggler based on the observation result. When the electron beam is incident again and collided with the permanent magnet 3 after the alignment, it is confirmed by the TV camera 10 on the right side of the previous time in FIG.
Realignment is performed based on the result. As described above, the electron beam 1 is incident, observed, and the alignment is repeated, so that the electron beam 1 can be finally propagated from the upstream to the downstream of the wiggler without colliding with the permanent magnet 3. Oscillation becomes possible. Since the gap 15 has a magnet width in the horizontal direction, it does not deviate so that the electron beam 1 does not hit the fluorescent screen 22 at all.

[0020]

As described above in detail with reference to the embodiments, according to the present invention, instead of inserting the fluorescent plate in the gap between the opposing permanent magnets, the permanent magnets are Since the fluorescent screen was attached, the electron beam was propagated to a wiggler and undulator with a narrow gap,
In an experiment in which a free electron beam is oscillated, the position of the propagating electron beam can be easily monitored. Therefore, optimal alignment can be performed efficiently without requiring experience or intuition, the adjustment time for achieving free electron laser oscillation can be significantly reduced, and the cost involved in oscillation experiments can be reduced.

[Brief description of the drawings]

FIG. 1 is a front view of a wiggler beam monitor according to an embodiment of the present invention.

FIG. 2 is a sectional view taken along line AA in FIG.

FIG. 3 is a front view showing a conventional wiggler beam monitor.

FIG. 4 is a graph showing a relationship between a gap, a period, and a K value.

FIG. 5 is an external view of a wiggler in which a permanent magnet is arranged outside a vacuum vessel.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electron beam 2, 22 Fluorescent plate 3 Permanent magnet 4 Permanent magnet holder 5 Rod 6 Bellows 7, 17 Vacuum container 8 Gap adjusting mechanism 9 Vacuum window 10 TV camera 11 Monitor 12 Fluorescent plate holder 13 Bellows 14 Air cylinder

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H05H 13/04 G21K 1/093 G21K 5/04 H01S 3/30 G01T 1/29

Claims (1)

(57) [Claims] 1. A plurality of magnets are horizontally arranged in two rows with a predetermined magnetization direction, a periodic magnetic field is generated between the magnet rows, and an electron beam incident between the magnet rows is moved in a meandering manner. In the induced bremsstrahlung apparatus for radiating the electromagnetic wave, a fluorescent plate is mounted on a surface facing the magnet row.