JPH05258897A - Septum electromagnet - Google Patents

Abstract

PURPOSE:To increase the incidence efficiency to two to three times as compared with a conventional injector using a septum electromagnet. CONSTITUTION:The thickness of a septum coil 3 constituting a septum is locally made thin at the beam outlet vicinity 5 of an electromagnet opening section 2 to make the thickness of the septum thin. A notch 7 is provided on the magnetic pole face 6 of the electromagnet opening section 2 to improve the uniformity of the magnetic field distribution near the septum, and a septum coil having the same width as the height 9 of the opening section 2 is installed at this portion. The incidence beam orbit 10 is designed slantly against the center line 11 of the electromagnet opening section 2 in the horizontal plane to reduce the divergence due to the nonuniform magnetic field distribution near the septum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a septum electromagnet,
In particular, the present invention relates to a septum electromagnet for injecting and emitting a charged particle beam in a circular accelerator.

[0002]

2. Description of the Related Art As a conventional septum electromagnet, the document "Molecular Science Laboratory, Design of UVSOR Storage Ring, U"
VSOR-9, 1982 "p.65, septum electromagnet (inflector) for incidence, and" Research Institute for Molecular Science, Design of synchrotron for incidence, UVSOR-7, 1 ".
981 "p.86, a septum electromagnet (deflector) for emission.

In the conventional septum electromagnet (FIG. 2), the thickness of the exciting coil 3 is constant at the electromagnet opening 2 along the beam trajectory direction. Both magnetic pole surfaces 6 of the electromagnet opening are entirely smooth, and between the exciting coil and both magnetic pole surfaces,
There is a gap of at least the thickness of the coil insulating layer 8. Further, the beam trajectory 10 is designed to lie along the centerline of the electromagnet opening in the horizontal plane.

[0004]

An electron storage ring is promising as a high-intensity X-ray source for industrial and medical purposes. Such an accelerator system (FIG. 5) consists of a storage ring 32 and a pre-stage accelerator 22 which supplies an electron beam to it. For installation in factories and hospitals, it is necessary to downsize the system. If the energy of the electron beam incident on the storage ring can be reduced, the pre-stage accelerator can be downsized and the entire system can be downsized. However, it is impossible to make a large number of injections with a low energy injection of about 30 MeV or less, and it is necessary to inject and accumulate a necessary current with one injection. Therefore, an injection device with high injection efficiency is required.

When a septum electromagnet is adopted in the injector, in order to increase the incident efficiency, the thickness of the partition wall (hereinafter referred to as a septum) separating the incident orbit side and the storage ring side is reduced so that the incident beam can be applied to the partition wall. It must be approached and incident almost parallel to the ring center orbit (Fig. 4). However, in the conventional septum electromagnet, the exciting coil 3 cannot be made sufficiently thin and the septum thickness 20 (hereinafter referred to as the septum thickness) becomes large. Further, in the conventional septum electromagnet, the uniformity of the magnetic field distribution in the vicinity of the septum is lost due to the existence of the gap between the exciting coil and the magnetic pole surfaces of the opening. Therefore, in order to avoid the divergence of the beam due to the non-uniform magnetic field distribution, the incident beam cannot be brought close to the septum, and the beam trajectory is designed along the center line of the electromagnet opening in the horizontal plane.

An object of the present invention is to provide a septum electromagnet having a small septum thickness and good uniformity of magnetic field distribution in the vicinity of the septum, and to realize an injection device with high injection efficiency.

[0007]

In order to reduce the septum thickness, the thickness of an exciting coil (hereinafter referred to as a septum coil) that constitutes the septum is locally thinned near a beam exit 5 of an electromagnet opening (see FIG. 1).

Further, in order to improve the uniformity of the magnetic field distribution in the vicinity of the septum, a notch 7 is provided in the magnetic pole surface of the electromagnet opening, and a septum coil 3 having the same width as the height 9 of the opening is provided at that portion. (Fig. 1).

Further, so that the incident beam 10 passes obliquely to the center line 11 of the electromagnet opening in the horizontal plane,
A septum magnet was installed (Fig. 1).

[0010]

The septum 20 is the vacuum partition 18 and the magnetic shield 2.
1, a septum coil 3, and a coil insulating layer 8 (FIG. 4). Although the septum thickness can be reduced by making the septum coil thin, the strength against heat generation and electromagnetic force due to the increase in current density becomes a problem. Therefore, the above problem can be avoided by thinning the septum coil only near the beam outlet of the electromagnet opening.

If the height 9 of the opening of the electromagnet and the width 34 of the septum coil are different (FIG. 2), the uniformity of the magnetic field distribution in the vicinity of the septum coil is lost. Therefore, by providing a notch in the magnetic pole surface of the electromagnet opening to absorb the thickness of the coil insulating layer, a septum coil having the same width as the height of the opening can be installed.

By designing the incident beam trajectory obliquely with respect to the center line of the electromagnet opening in the horizontal plane, the distance that the incident beam passes near the septum is shortened, and the beam due to the non-uniform magnetic field distribution near the septum is shortened. Can be reduced.

[0013]

1 is a sectional view showing an embodiment of a septum electromagnet according to the present invention. The septum electromagnet is composed of a C-shaped iron core 1 made of a magnetic material and exciting coils 3 and 4 installed in an opening 2 thereof. Note that FIG. 1 shows the case where the exciting coil has one turn. A uniform magnetic field is generated in the electromagnet opening by the current flowing through the exciting coil. The charged particle beam passing through the electromagnet aperture is deflected by its uniform magnetic field.

The exciting coil comprises a septum coil 3 having an outer radius of curvature and a return coil 4 having an inner radius of curvature.
In order to improve the beam incidence efficiency, the septum coil is locally thinned near the beam exit 5. In this embodiment, the outer peripheral side of the septum coil is linearly cut to be thin in a taper shape. As a result, heat generation due to an increase in the current density of the septum coil and deformation due to electromagnetic force can be suppressed while maintaining a 0.5 mm
It can be made as thin as possible. Further, both magnetic pole faces 6 of the electromagnet opening are
A notch 7 is provided in the to absorb the thickness of the coil insulating layer 8 and a septum coil having the same width as the height 9 of the opening is installed. As a result, the change in the magnetic field near the septum coil is reduced to zero.
It can be reduced to about 1%, and the beam can be brought closer to the septum coil and incident on the ring. In this embodiment, the notch is provided only at the position of the septum coil, but when it is necessary to reduce the change in the magnetic field near the return coil, the notch is also provided at the position of the return coil.

Further, the incident beam trajectory 10 is designed to be oblique to the center line 11 of the electromagnet opening in the horizontal plane. That is, the beam enters from the position 12 on the return coil side of the center line of the electromagnet opening and exits from the position 13 close to the septum coil. In the present embodiment, the radius of curvature of the center line of the electromagnet opening is made larger than the radius of curvature of the incident beam orbit to realize it. This allows
It is possible to shorten the distance that the incident beam passes near the septum and reduce the divergence of the beam due to the non-uniform magnetic field distribution near the septum.

FIG. 3 is a plan view showing an embodiment of a charged particle beam injector using a septum electromagnet according to the present invention. The charged particle beam injector is a septum magnet 14
And the vacuum container 15 with the septum electromagnet installed inside.
Consists of. The vacuum container is the beam duct 16 on the storage ring side.
And a vacuum chamber 17 in which a septum electromagnet is installed, and both are blocked by a vacuum partition wall 18. The incident beam is deflected by a septum electromagnet, and an incident window 19 provided on the vacuum partition wall is used.
Is incident on the ring from. The septum electromagnet is installed in the vacuum container so that the incident beam passes obliquely to the center line of the opening in the horizontal plane. The septum electromagnet is in close contact with the vacuum partition near the beam outlet in order to reduce the septum thickness.

FIG. 4 is a detailed view of the vicinity of the incident point. The septum 20 includes a vacuum partition 18, a magnetic shield 21, a septum coil 3, and a coil insulating layer 8. The vacuum partition can be thinned to about 0.5 mm to maintain its strength. The magnetic shield reduces the leakage magnetic field from the septum electromagnet to the ring side. By using a magnetic material having a high magnetic permeability (for example, permalloy), the thickness can be reduced to about 0.5 mm. Since the septum coil can be thinned to about 0.5 mm as described above, the septum thickness 20 can be set to 2 mm or less including the coil insulating layer.

FIG. 5 is an illustration of a circular accelerator in which a septum magnet is used as a charged particle beam injector. The charged particle beam from the pre-accelerator 22 passes through the beam transport system 23, is deflected by the incident device 24, and is incident on the ring.
The bump electromagnet 25 arranged on the ring controls the equilibrium orbit on the ring side at the time of incidence and accumulates the incident beam on the ring. As the pre-stage accelerator, for example, a linear accelerator, a microtron, or a synchrotron is used. Further, the ring has a dipole electromagnet 26 for deflecting and converging the beam.
A quadrupole electromagnet 27 and a high-frequency acceleration cavity 28 for supplying energy to the beam are arranged.

The case where the septum electromagnet according to the present invention is used for the entrance device has been described above, but the same applies to the case where the septum electromagnet is used for the exit device.

FIG. 6 is an explanatory view of a circular accelerator using a septum electromagnet as a charged particle beam emitting device. The charged particle beam accelerated to a predetermined energy by the high frequency acceleration cavity 28 in the ring is subjected to magnetic field deflection by the extraction device 29 and is taken out to the beam transport system 30. The kicker electromagnet 31 arranged on the ring controls the equilibrium trajectory of the ring at the time of emission and kicks the accumulated beam into the opening of the septum electromagnet. The beam transport system 30 is connected to, for example, the circular accelerator 32 of FIG. 5, and the circular accelerator 33 is the former accelerator 2 of FIG.
It is 2 (synchrotron).

[0021]

According to the present invention, the septum coil can be made as thin as about 0.5 mm while suppressing its heat generation and deformation, and even if the thickness of the vacuum partition, the magnetic shield and the coil insulating layer is added,
The septum thickness can be reduced to mm or less.

The magnetic field change near the septum is 0.1%.
It can be reduced to a small degree and the beam can be brought closer to the septum and incident on the ring.

Further, the distance that the incident beam passes near the septum can be shortened, and the divergence of the beam due to the non-uniform magnetic field distribution near the septum can be reduced. For example, even if the magnetic field changes by about 1% due to the installation error of the septum coil, the divergence of the beam can be easily reduced to such an extent that the incidence efficiency is not affected.

In the conventional septum electromagnet, the septum thickness is about 4 mm, and a magnetic field change of about several% exists in the vicinity of 2 mm of the septum. Therefore, the effective septum thickness is about 6 mm. Considering a beam from an ordinary linear accelerator for the electron storage ring pre-accelerator as the incident beam,
With the septum electromagnet according to the present invention, the incidence efficiency can be increased to 2-3 times that of the conventional case.

According to the present invention, a septum electromagnet can be adopted as a high-efficiency injection device required for a low energy injection method of an electron storage ring. Conventionally, as a device for injecting a low-energy electron beam into a circular accelerator, an electrostatic deflection type device that can easily reduce the septum thickness has been adopted. However, the electrostatic deflection type injection device is larger in size than the magnetic field deflection type, and the magnetic field deflection type is more advantageous for downsizing the storage ring.
When the beam energy is 15 MeV and the incident angle to the storage ring is 45 degrees, the device length of the electrostatic deflection type is 1.5 m, while the device length of the magnetic field deflection type using a septum electromagnet is 0.5 m.

In the above, when the septum electromagnet according to the present invention is used in the injector, the effect is described especially in the electron storage ring, but other charged particle circular accelerators have the same effect. Further, even when used in the emitting device, there are effects of improving the beam emitting efficiency and reducing the load on the kicker electromagnet.

[Brief description of drawings]

FIG. 1 is a sectional view showing the structure of an embodiment of a septum electromagnet according to the present invention.

FIG. 2 is a sectional view showing the structure of a conventional septum electromagnet.

FIG. 3 is a plan view showing an embodiment of a charged particle beam entrance / exit device using a septum electromagnet according to the present invention.

FIG. 4 is an explanatory diagram of the vicinity of an incident point / an emission point.

FIG. 5 is an explanatory diagram of a circular accelerator in which a septum magnet is used as a charged particle beam injector.

FIG. 6 is an explanatory view of a circular accelerator in which a septum electromagnet is used as a charged particle beam emitting device.

[Explanation of symbols]

3 ... Septum coil, 5 ... Septum coil near beam exit / entrance, 10 ... Incoming / exiting beam trajectories, 11 ... Center line of electromagnet opening, 14 ... Septum electromagnet.

Claims (4)

[Claims] 1. A septum electromagnet having an iron core portion of a magnetic body and an exciting coil of at least one turn in its opening, wherein a charged particle beam passing through the opening is deflected by a magnetic field. Is locally thinned at least at one location near the entrance of the opening. 2. A septum electromagnet having an iron core of a magnetic material and an exciting coil of at least one turn in its opening, wherein a charged particle beam passing through said opening is deflected by a magnetic field. A septum electromagnet, characterized in that a notch is provided in a magnetic pole surface of the opening in order to install an exciting coil having the same width as the height therein. 3. A charged particle beam deflector comprising a septum electromagnet for deflecting a charged particle beam passing through an opening of a magnetic iron core part by a magnetic field, and a vacuum container in which the septum electromagnet is installed. The charged particle beam deflection apparatus, wherein the septum electromagnet is installed in the vacuum container so that the beam passes obliquely with respect to the center line of the opening in a horizontal plane. 4. A circular accelerator, wherein the charged particle beam deflecting device using the septum electromagnet according to claim 1, 2, or 3 is used as the charged particle beam incident device or emission device.