JPH01307198A - Septum magnet - Google Patents

Abstract

PURPOSE:To reduce any irradiation damage due to a synchrotron radiation beam, by splitting a septum into upper and lower parts while making the distance between respective faces of the split septum parts larger than the height of the gap between iron cores. CONSTITUTION:Each septum coil made up of a septum 1 and a return conductor 3, and having an iron core 8 so as to cover each septum coil, is allowed to generate a bipolar magnetic field for deflecting charged particles to a beam opening 2. Hereupon the septum 1 is split into the number of parts of not less than two, so symmetrical mutually to the upper and lower parts as to remove the portion facing the opening 2 so that the distance between the split septum coils 1, 1 is formed to be made larger than a gap between iron cores 8. One portion of each septum is thus kept small in thickness with a leakage magnetic field also made small, so that the septum magnet in the title can be prevented from any irradiation damage due to a synchrotron radiation beam generated together with the charged particle beam as well as its orbital deflection.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a septum magnet, and more particularly to a septum magnet suitable for an injection device for a small storage ring for lithography.

[Conventional technology]

Generally, charged particles are accelerated using a combination of multi-stage accelerators. The accelerators are connected by a beam line, and the trajectory of the charged particles is deflected from the beam line by a septum magnet, which is an injection device, and the charged particles enter the next stage accelerator. Conventional equipment is IE, Transaction on Nuclear Science, Volume Nnis-32 Number 5 October 1985 No. 36
Pages 28 to 3630 (IEEE, Tran-sa
tions on Nuclear 5science
, vo Q, NS-32.

Na50ctober 1985 pp3628-3
It had a structure as described in 630). A conventional example will be described below with reference to FIGS. 2 and 3.

First, the orbits of charged particles will be explained. The trajectory of the charged particle is bent by the deflection magnetic field created by the septum magnet, and the charged particle enters the next stage accelerator, and the trajectory of the charged particle at this time is the incident trajectory 10. The incident charged particle is further corrected to its orbit by a perturbator magnet (not shown), and takes the final number: center orbit 11.

Next, the structure of the septum magnet will be explained. The septum magnet includes a septum 1, a return conductor 3, a septum coil consisting of a transition portion 9 connecting the septum 1 and the return conductor 3, and an iron core 8 surrounding the septum coil to form a bipolar magnet. Further, a support plate 4 for supporting the septum 1 is provided on the outside of the septum 1, and fixing spacers 6 are placed above and below the support plate 4. Furthermore, if a leakage magnetic field is generated from the septum magnet, it will have an adverse effect on the charged particles on the center orbit 11, so a magnetic shield plate 5 is installed outside the septum 1 to shield this leakage magnetic field. Further, it is necessary for the distance between the incident trajectory 10 and the center trajectory 11 to be small from the viewpoint of controlling the trajectory of the charged particles. Therefore, the septum 1
, magnetic shield plate 5. It is also necessary that the total thickness of the support plate 4 is small.

Furthermore, septum magnets for small accelerators have a large deflection angle, which increases the gap magnetic flux density.In order to keep the magnetomotive force of the excitation coil small, the gap between the iron cores needs to be small. is installed in a vacuum duct. Therefore, the septum magnet is used in a vacuum, and the outer circumference of the septum magnet The conventional example described above has a structure in which the septum is disposed on the side of the opening 2 through which charged particles pass.

Therefore, there is a problem in that the conductor or insulator of the septum 1 is damaged by some of the charged particles that have deviated from their orbits and by synchrotron radiation light that is generated when the orbits of the charged particles are deflected.

SUMMARY OF THE INVENTION An object of the present invention is to provide a septum magnet which has a structure in which the thickness of the septum portion is kept small, the leakage magnetic field is also reduced, and the magnet is not damaged by the above-mentioned charged particles.

The above object is achieved by vertically symmetrically dividing the septum into at least two parts, excluding the portion facing the opening, and by making the distance between the divided septum coils larger than the gap between the iron cores.

[Effect]

By separately arranging the septum coil as described above, it is possible to prevent damage caused by charged particles and irradiation of synchrotron radiation light that occurs due to orbital deflection of charged particles.

Further, as shown in FIG. 1, the relationship between the height h of the septum cross section and the leakage magnetic flux density will be explained using FIG. 4. The positive direction of the magnetic flux density is the direction of the deflection magnetic field generated at the septum magnet opening. The horizontal axis indicates the vertical center of the septum cross section, and the origin is the end face of the magnetic shield surface, and indicates the leakage magnetic flux density distribution toward the center orbit. If the height h of the septum cross section is smaller than a certain height ho, the direction of the magnetic flux density will be negative, while if one is larger than hO, the direction of the magnetic flux density will be positive, so if h = ho, the leakage magnetic flux density will be The absolute value becomes smaller at the extremes. In addition, the height h of the septum cross section
FIG. 6 shows the change in leakage magnetic flux density on the center orbit side when the ratio h/W to the width W of the septum portion is changed. From this, when h/W is 5 to 8, the leakage magnetic flux density becomes extremely small. Therefore, the above object can be achieved by the means described above.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. As shown in the figure, the septum coil consists of a septum 1 and a return conductor 3. An iron core 8 is present so as to cover the septum coil, and generates a dipole magnetic field for deflecting charged particles at the beam aperture 2. Further, a magnetic shield plate 5 is provided on the side surface of the septum 1 so that the dipole magnetic field does not leak into the center orbit of the accelerator.

In this embodiment, the septum 1 is vertically symmetrically divided into at least two parts, and the distance between the septa 1 facing each other is made larger than the gap between the iron cores 8. Then, due to the geometrical arrangement, the probability of being irradiated by the charged particle itself or synchrotron radiation due to orbital deflection becomes extremely small.

Further, by setting the height h of the septum cross section to the above-mentioned ho, the leakage magnetic field is reduced.

According to this embodiment, damage to the septum due to irradiation with charged particles or synchrotron radiation light is prevented.

It is possible to prevent deterioration of the vacuum due to damage.

In addition, the leakage magnetic field can be reduced. Furthermore, in this embodiment, since the return conductor 3 has a divided structure similar to the septum 1, there is an effect that the winding work is easy.

In other embodiments, the return conductor 3 may have an integrated structure as shown in FIG. According to this embodiment, as in the previous embodiment, damage to the septum 1 caused by charged particles and synchrotron radiation can be prevented, and the leakage magnetic field can be reduced. Furthermore, in this embodiment, since the return conductor 3 has an integrated structure, the return conductor has a simple structure and is easy to support.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to reduce irradiation damage to the septum by charged particles or synchrotron radiation light generated by the charged particles, and also to reduce the leakage magnetic field.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of an embodiment of the septum magnet of the present invention, FIG. 2 is a partially cutaway plan view of a conventional septum magnet, and FIG. 3 is a cross-sectional view of a conventional septum magnet. FIG. 4 is a leakage flux density distribution diagram, FIG. 5 is a cross-sectional view of another embodiment of the present invention, and FIG. 6 is a characteristic diagram showing the relationship between the leakage magnetic field and septum shape. DESCRIPTION OF SYMBOLS 1... Septum, 2... Beam opening, 3... Return conductor, 4... Support plate, 5... Magnetic shield plate, 8
... Iron core, 9 ... Transition part, 10 ... Incident trajectory, 1
1... Central orbit. High school 14th year, 2 drawings, 3 drawings, 4 drawings of sweets〉Tsuru 1

Claims (1)

[Claims] 1. Having a beam aperture through which incident charged particles pass;
A septum that generates a deflection magnetic field at the beam aperture, a septum coil consisting of a return conductor, an iron core that covers the septum coil, and a magnetic shield plate placed on the side of the septum on the accelerator side where charged particles are incident. A septum magnet, characterized in that the septum is divided into upper and lower parts, and the distance between the faces of the divided septum is larger than the height of the core gap. 2. The septum magnet according to claim 1, wherein the height of the septum cross section is 5 to 8 times the width of the septum portion.