JPH0722040B2 - Particle beam accelerator - Google Patents

Description

TECHNICAL FIELD The present invention relates to a particle beam accelerator for accelerating or accumulating a particle beam.

[Conventional technology]

Figure 3 shows, for example, Miyahara Yoshikaz et al;
ge Ring and Coexistent Ingector Microtron for Sync
hrotron Radiation), Technical Report of ISS
It is a schematic diagram of the conventional electron beam accelerator shown by P, No. 21 (September, 1984). In the figure, (1) is an electron beam equilibrium orbit, (2) is a high frequency acceleration cavity (hereinafter referred to as RF acceleration cavity), (3) is a focusing magnet, and (4) is a deflection magnet.

Next, the operation will be described. The electron beam orbits on an equilibrium orbit (1) which is a fixed closed orbit determined by its energy and the magnetic field values of the deflecting magnet (4) and the focusing magnet (3). In the electron storage ring shown in this equilibrium orbit (1), the energy loss due to the synchrotron radiation generated when the electrons are deflected is replenished by the RF accelerating cavity (2), and a constant energy Accumulating electrons.
However, the energy of this electron usually has a certain width (this is called energy dispersion). How the energy dispersion is determined will be described below.

Consider the time when the electron came to the RF acceleration cavity (2) converted to the phase of RF voltage. The phase at which the amount of radiated light per round of the electron, that is, the amount of energy loss and the acceleration by the RF voltage, that is, the amount of replenishment, are equal is φ ₀ . If the electron energy is higher than the reference value for some reason, the electron will pass out of the equilibrium orbit (1). In this case, when the RF accelerating cavity (2) is reached, the phase is slightly behind that of ψ ₀ , and the accelerating voltage becomes smaller than the energy loss due to the emitted light. Therefore, the energy of the electron decreases every rotation. However, when the energy is lower than the reference value, the opposite phenomenon occurs and the energy rises. In this way, the electrons oscillate around ψ ₀ on the phase of the high frequency (synchrotron oscillation). But in reality,
Since the amount of emitted light of particles per rotation is proportional to the square of energy, a kind of damping is applied to the above-mentioned vibrational motion (synchrotron attenuation). Therefore, the energy dispersion of electrons in the ring is determined by the energy fluctuation due to the synchrotron radiation and the balance of the synchrotron attenuation. As a result of this, the energy dispersion is inversely proportional to the square root of the radius of curvature of the deflecting magnet (4).

[Problems to be solved by the invention]

In the conventional particle beam accelerator, the energy dispersion is determined as described above, but the energy dispersion is required to be as small as possible. If the energy dispersion is large, the orbit of the electron beam spreads, resulting in a large beam cross-sectional area, a long beam length, and the like, resulting in a decrease in particle density. This leads to a reduction in the frequency of collisions when conducting particle beam collision experiments. Therefore, it is necessary to store a very large current, which causes problems such as instability of the beam. Further, as the beam diameter increases, it becomes necessary to enlarge the vacuum container (not shown in FIG. 3) through which the beam passes and to expand the effective magnetic field region of the magnet, which leads to an increase in the size of the entire device. There will be problems in cost and occupied area.

The present invention has been made to solve the above problems, and an object of the present invention is to obtain a particle beam accelerating device capable of extremely reducing the energy dispersion of a particle beam.

[Means for solving problems]

In the particle beam accelerator according to the present invention, a high-frequency acceleration cavity for beam cooling that forms a high-frequency magnetic field in the lateral even-order TM mode is provided on the closed orbit of the particle beam, and the dispersion function η of the storage ring in the vicinity thereof is It is a big one.

[Action]

In the present invention, since the high-frequency accelerating cavity for beam cooling excites the high-frequency electromagnetic field in the lateral even-order TM mode to decelerate the high-speed electrons and accelerate the low-speed electrons, the energy dispersion can be made small. That is, it is determined by the balance between beam energy dispersion (δ / E), synchrotron radiation attenuation and radiation excitation in the conventional electron storage ring,
It was about 0.1%. Therefore, in this invention, the beam orbit is the central orbit (equilibrium orbit) due to the difference in beam energy.
Focusing on a slightly different property, by passing the electron beam through a standing wave in the lateral even-order TM mode, for example, TM ₁₀ mode, a decelerating action is given to particles with high energy and an accelerating action is given to particles with small energy. Let it be done. The high frequency accelerating cavity for beam cooling of this invention has a very high high frequency (1 GHz)
However, it is effective, and therefore the device can be made small, and the beam energy dispersion (δ / E) of about 10 ^-5 can be achieved.

〔Example〕

An embodiment of the present invention is shown in FIG. 1 and will be described below. In FIG. 1, (1) to (4) are the same as those of the particle beam accelerator shown in FIG.
(5) is a beam cooling high-frequency acceleration cavity (hereinafter referred to as a cooling RF acceleration cavity) provided in the present invention. Further, FIG. 2 shows a sectional view of the cooling RF acceleration cavity (5), (1a) is the direction of the electron beam equilibrium orbit (1), and (6a) and (6b) are for cooling. RF acceleration cavity (5) is TM
The direction of the high frequency electric field generated in ₂₁₀ mode is shown.
The (6a) side is the inside of the storage ring.

Here, a brief explanation of TM and TE modes is as follows.
Now, consider a three-dimensional space of x, y, and z, and let the z direction be the traveling direction of electromagnetic waves. This time, this direction coincides with the traveling direction of the electron beam. Here, when E is an electric field and H is a magnetic field, E _z ≠ 0, H _z = 0, that is, an electromagnetic wave in which the z direction component H _{z of the} magnetic field is a TM mode, E _z = 0, H _z ≠ 0, that is, An electromagnetic wave in which the z-direction component E _{z of the} electric field is zero is called a TE mode. Next, regarding modes, let us consider the TM mode, for example. The equation of E _z is as follows.

Now consider a TM wave in a rectangular parallelepiped as shown in FIG. E _z
Boundary conditions are: x = 0, a, E _z = 0, y = 0, b, E _z = 0, And solving equation (1) gives Is represented. l, m, n is called the number of modes, and the wave of that mode is called TM _{l, m, n} mode. For example, Fig. 5 (A) shows TM
₁₁₀ mode, FIG. 5 (B) is TM ₂₁₀ mode embodiment, the FIG (C) is TM ₁₂₀ mode, FIG. 5 (D) shows the respective E _z of the TM ₁₁₁ mode. l and n indicate the number of peaks at which E _z is maximum or minimum between 0 and a, b, and c in the x, y, and z directions, respectively. Therefore, for example, in the TM ₃₁₀ mode, E _z increases from 0 to a maximum between 0 and a in the x direction, passes through 0 to a minimum, passes through 0 to a maximum, and reaches 0 at a. It will be like going back.

Therefore, consider the movement of electrons in the storage ring. RF for cooling
In a part of the acceleration cavity (5), high-energy electrons (particles) pass outside the equilibrium orbit (1), and low-energy electrons pass inside. This RF acceleration cavity for cooling (5)
Then, it is assumed that the TM ₂₁₀ mode as shown in FIG. 5 (B) is excited. The phase relationship with the particles is such that the outer particles are decelerated and the inner particles are accelerated as shown in FIG. This RF voltage causes high energy particles to decelerate and low energy particles to accelerate. Therefore, the energy dispersion of the particles has a smaller value.

Although the case of the electron storage ring has been described in the above embodiment, it may be a free electron laser or an ion storage ring, and the same effect as that of the above embodiment can be obtained. Further, although the TM ₂₁₀ mode is used in the above-described embodiment, the same result can be obtained by using the lateral even-order TM mode such as the TM ₄₁₀ mode or the TM ₆₁₀ mode.

〔The invention's effect〕

As described above, according to the present invention, since the conventional particle beam accelerator is equipped with the cooling RF acceleration cavity, a particle beam with a small energy dispersion can be obtained, and the device itself can be inexpensive. To be

[Brief description of drawings]

FIG. 1 is a block diagram of a particle beam accelerator according to an embodiment of the present invention, FIG. 2 is a sectional view of a cooling high-frequency acceleration cavity, and FIG. 3 is a block diagram of a conventional particle beam accelerator, and FIG. And FIGS. 5A to 5D are diagrams for explaining the TM mode. In the figure, (1) is an electron beam equilibrium orbit, (2) is a high frequency acceleration cavity, (3) is a focusing magnet, (4) is a deflection magnet, and (5) is a cooling high frequency acceleration cavity. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (3)

[Claims] 1. A particle beam accelerating device for accelerating, deflecting, and converging a particle beam, wherein a high-frequency acceleration cavity, a deflection magnet, and a converging magnet form a closed orbit of the particle beam to accelerate or store the particle beam. The particle beam accelerator according to claim 1, further comprising a high-frequency accelerating cavity for cooling the beam, which reduces energy dispersion of the particle beam. 2. The particle beam accelerator according to claim 1, wherein the beam cooling high-frequency acceleration cavity forms a high-frequency electromagnetic field in the transverse even-order TM mode with respect to the particle beam. 3. The particle beam accelerator according to claim 1, wherein the beam cooling high-frequency acceleration cavity is arranged at a position where the dispersion function has a maximum in a closed orbit of the particle beam.