JP2002043097A - Accelerator and charged particle accelerating method using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control instability of a beam by reducing a flat top voltage in an accelerator center region part. SOLUTION: In an accelerator provided with an accelerating cavity 22, where an accelerating voltage of a designated frequency is applied to accelerate electrically charged particles 8 and a flat top(FT) cavity 24, where a flat top(FT) voltage of n times of the frequency of the accelerating voltage (n is an odd number of 3 or larger) is applied to level an accelerating electric field, in parallel between counterposing magnetic poles 10, an accelerator center side tip 24A of the FT cavity 24 is shorted to a ground plate 11 of the magnetic pole 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an accelerator and a method for accelerating charged particles using the same. More particularly, the present invention relates to an accelerating voltage of a predetermined frequency for accelerating charged particles between opposing magnetic poles. The accelerating cavity to be applied and the flat-top cavity to which a flat-top voltage having a frequency of n times (n is an odd number of 3 or more) the accelerating voltage is applied in order to flatten the accelerating electric field are arranged side by side. The present invention relates to an accelerator and a method for accelerating charged particles using the accelerator.

[0002]

2. Description of the Related Art One of accelerators for accelerating charged particles is an AVF (Azimuthal) having an angularly changing magnetic field.
Varied Field) type cyclotron. This is, for example, as shown in FIG.
In the meantime, the gap 12 of the magnetic pole is changed to converge the charged particles 8 to form the peak 12 and the valley 14 (AVF).
Principle).

As a means for accelerating, as shown in FIG. 2, an electric field is concentrated between a dee electrode 16 for generating a high-frequency electric field and a dummy dee electrode 18 grounded to the ground, and the dee and the dummy dee are connected to each other. When passing through the gap, the charged particles 8 are accelerated.

Further, as shown in a plan view of FIG. 3, a flat top (FT) cavity 24 to which a flat top (FT) voltage having a frequency three times the acceleration voltage is applied is provided, and as shown in FIG. There is one in which the peak of the combined voltage Vc is flattened by combining the voltage Va and an FT voltage Vft having, for example, a frequency three times that of the voltage Va.
Thereby, the acceptance of the acceleration phase of the cyclotron is broadened, and the intensity of the accelerated particles can be increased to about 3 to 5 times.

[0005] However, the conventional FT cavities are mainly single-gap FT cavities employed in PSI in Switzerland and cyclotrons in Osaka University, and all of these cyclotrons are SSC (Separated Sector Cyclotr).
on), a separate-sector cyclotron called
In an AVF cyclotron with a single circular magnetic pole, the FT
Cavities are difficult to implement and are rarely employed.

That is, in the conventional FT cavity, as shown in FIG. 5 (perspective view) and FIG.
Are connected to each other and open to the magnetic pole, so that a voltage is generated at the tip 24A of the FT cavity as shown in a measurement example in FIG. In the figure, 26 is an electrode, 30 is a coaxial resonator for generating harmonics, 32 is its inner cylinder, 34 is
The outer cylinder 36 is a movable short plate for adjusting the resonance frequency.

[0007]

However, when an FT voltage is generated at the tip 24A of the FT cavity 24, the rotating particles 8 receive a high voltage at the center of the orbit. Also, A
In the VF cyclotron, as shown in FIG. 8, near the center, there is a portion where the magnetic field transitions from the bump magnetic field to the isochronous magnetic field, and there is a flat portion of the magnetic field. In this part, it is known that the betatron frequency νr = 1, and if the beam is accelerated / decelerated by an asymmetric electric field, the beam becomes unstable and cannot be accelerated. In particular, when the accelerating particles having low energy become unstable, the FT cavity 24 cannot be arranged at a symmetric position with respect to the center of the accelerator due to the arrangement of the equipment, and must be arranged at an asymmetric position. Then, as shown in FIG.
There is a problem that a phenomenon that the center of the beam is shifted easily occurs. Particularly in a cyclotron, the asymmetric accelerating electric field generated by the FT cavity may cause a fatal resonance phenomenon.

In the FT cavity 24, the movable short plate 36 is used to generate a harmonic three times the acceleration frequency.
However, the conventional FT cavity has a problem that the position of the movable short plate 36 is near the center, and it is difficult to manufacture mechanically.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems. Even if the FT cavities are arranged asymmetrically, the asymmetry due to the FT voltage is prevented from being generated in the central region. A first object is to provide an accelerator that can generate a sufficient FT voltage in an acceleration region and can obtain an ideal acceleration voltage distribution.

A second object of the present invention is to provide a method for accelerating charged particles using the accelerator.

[0011]

SUMMARY OF THE INVENTION According to the present invention, there is provided an accelerating cavity for applying an accelerating voltage of a predetermined frequency for accelerating charged particles between opposing magnetic pole poles, and for accelerating an accelerating electric field. In an accelerator provided with a flat top cavity to which a flat top voltage having a frequency of n times (n is an odd number of 3 or more) of the acceleration voltage is applied, a tip of the flat top cavity on the center side of the accelerator is a magnetic pole pole. The first problem has been solved by short-circuiting.

In addition, a movable short plate for making the frequency of the flat top voltage variable is disposed in a coaxial resonator outside the flat top cavity.

The present invention also solves the second problem by accelerating charged particles using the accelerator.

[0014]

Embodiments of the present invention will be described below in detail with reference to the drawings.

In the accelerator according to this embodiment, FIG.
As shown in FIG. 0 (a perspective view of the FT cavity) and FIG. 11 (a cross-sectional view of the tip of the FT cavity), in an accelerator similar to the conventional example,
Without opening the accelerator center-side tip 24A of the FT cavity 24,
The ground plate 11 of the magnetic pole 10 is electrically short-circuited, and the voltage generated there is reduced to zero.

The span angle of the FT cavity 24 is, for example,
The span angle is set to １ ／ of the span angle of the acceleration cavity 22.

According to this embodiment, when the tip is opened, the voltage of the electrode 26 of the FT cavity, which is indicated by the broken line A in FIG. At the outermost periphery from which the maximum voltage is generated, an ideal voltage distribution can be obtained.

Further, by grounding the tip, the position of the frequency-variable short plate 36 moves outward as is apparent from the measurement example shown in FIG. 13 and is located at a position that can be mechanically realized. be able to.

The present invention is particularly effective when the FT cavities are asymmetrically arranged. However, even when the FT cavities are symmetrically arranged, the position of the short plate can be extended outward. So effective.

In the above embodiment, the present invention
Although the present invention has been applied to the AVF cyclotron, the application target of the present invention is not limited to this. The frequency of the FT voltage is not limited to three times the acceleration voltage, and may be an odd number of 5 or more.

[0021]

According to the present invention, by short-circuiting the tip of the FT cavity, the FT voltage in the central region can be reduced, and the instability of the beam can be suppressed.

Further, since the short plate position for obtaining the required high frequency is located on the outside, the structure can be realized mechanically.

[Brief description of the drawings]

FIG. 1 is a plan view showing a principle configuration of an AVF cyclotron as an example to which the present invention is applied;

FIG. 2 is an explanatory diagram showing an acceleration method when there is no FT cavity.

FIG. 3 is a plan view showing an arrangement example of an acceleration cavity and an FT cavity of an AVF cyclotron.

FIG. 4 is a diagram showing an example of a combined state of an acceleration voltage and an FT voltage in the AVF cyclotron.

FIG. 5 is a partially cutaway perspective view showing the entire configuration of a conventional FT cavity.

FIG. 6 is a cross-sectional view of the same tip.

FIG. 7 is a diagram showing a measurement example of a voltage distribution in the FT cavity of FIG. 6;

FIG. 8 is a diagram showing the distribution of the average magnetic field intensity formed by the FT cavity of FIG. 6;

FIG. 9 is a plan view for explaining a conventional problem.

FIG. 10 is a partially cutaway perspective view showing the entire configuration of the FT cavity according to the embodiment of the present invention.

FIG. 11 is a cross-sectional view of the same tip.

FIG. 12 is a diagram showing a comparison between a voltage distribution of an FT cavity in a conventional example and an embodiment of the present invention.

FIG. 13 is a diagram showing a measurement example of a voltage distribution of the FT cavity in the embodiment.

[Explanation of symbols]

 Reference Signs List 8 charged particle 10 magnetic pole 11 ground plate 22 accelerating cavity 24 flat top (FT) cavity 24A tip 30 coaxial resonator 36 movable short plate

Claims (3)

[Claims] An accelerating cavity for applying an accelerating voltage of a predetermined frequency for accelerating charged particles between opposing magnetic pole poles and an n of said accelerating voltage for flattening an accelerating electric field.
In an accelerator provided with a flat-top cavity having a frequency of twice (n is an odd number of 3 or more) to which a flat-top voltage is applied, an accelerator center-side tip of the flat-top cavity is short-circuited to a magnetic pole. A featured accelerator. 2. The accelerator according to claim 1, wherein a movable short plate for changing the frequency of the flat top voltage is provided in a coaxial resonator outside the flat top cavity. 3. An accelerator according to claim 1 or 2,
A method for accelerating charged particles, comprising accelerating charged particles.