JPH0536497A - Electron accumulating ring - Google Patents

Abstract

PURPOSE:To extend the life of electron beam using a circular and weak convergent electron storage ring with a small trajectory radius by setting the n value of a magnetic field distribution to be within specified range by a circular weak convergent-type magnet which is built therein. CONSTITUTION:Electron beam moving a circular trajectory of an electron storage ring has a life and extending the life is one of the problem to be solved for an apparatus of this kind. In the case that the n value of the magnetic field generated by a circular and weak convergent-type magnet which is built in is defined as n=(-R/B).(dB/dR), the life (Touschen life) tau of the stored electrons is given based on a formula shown separately. Here, the lower limit of the n value is determined by the allowable error magnetic field and the upper limit of the n value is determined by the effectiveness of this invention and the range is 0.01<n<0.1. Consequently, the apparatus has an effect in the case that electrons with low energy are accumulated in a circular and weak convergent-type electron storage ring with 0.5m or less radius and by specifying the range of the n value, it is proved by theoretically that life can be extended.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to improvements in electron storage rings in synchrotron radiation generators.

[0002]

2. Description of the Related Art Recently, generation of synchrotron radiation by synchrotron radiation in the tangential direction of the orbit by moving charged particles (particularly electrons) along a trajectory having a predetermined curvature at a velocity close to the speed of light. The device is in the spotlight. In addition, there is a demand for miniaturization of this type of device, and a device having an orbit radius of less than 0.5 m has been proposed. FIG. 1 shows a schematic cross section of a small electron storage ring. A magnetic field generator such as a vacuum magnet 12 or a focusing magnet using a superconducting magnet is arranged in a yoke 10 having an annular cross section. An electron beam produced by an injection accelerator (not shown) is introduced into the vacuum container 12 from the introduction part 11 and travels through the magnetic channels 13, 14 and the inflector 15 to form a circular orbit having a curvature determined by the strength of the magnetic field. Draw and move at a speed close to the speed of light. The electron beam is locally concentrated on a circular orbit and moves in a state called a bunch.

By the way, an electron beam moving on a circular orbit has a lifetime, and extending the lifetime is also one of the problems of this type of apparatus. The lifetime of the electrons in the bunch will be described with reference to FIG. There are three processes in which electrons in the bunch are lost (determine the lifetime). In the first process, electrons collide with the residual gas in the vacuum container to bend the traveling direction of the electrons and collide with the vacuum container to be lost (vacuum life). Second
The process of is lost when the electrons collide with each other in the bunch, the kinetic energy changes, and the electron moves out of the stable energy range (Tauschek life). In the third process, light is emitted by synchrotron radiation, and the kinetic energy is lost by that amount, so that the light goes out of the energy range for stable motion and is lost (quantum lifetime).

[0004]

If the traveling direction of the electron is bent by θ at a certain point A on the orbit due to collision with the residual gas, the electron amplitude y at the point B is (the electron is centered around the bunch center). It is expressed by the following formula 1.

[0005]

[Equation 1]

Where β _A is the beta function value at point A, β _B
Is the beta function value at point B. The radius of the beam duct is a
Then, the electrons collide with the beam duct and are lost in the scattering represented by the following formula 2.

[0007]

[Equation 2]

From Equation 2, the smaller the beta function, the more θ
_MAX increases, probability of loss decreases, or life extends. However, if the vacuum life is extended beyond a certain level, the Towsheck life becomes the main factor of the life of accumulated electrons. In particular, the average orbit radius of the storage ring is 0.
Below 5 m, the beta function is much smaller than that of a normal storage ring, and the vacuum life is sufficiently long.
On the other hand, the electron density distribution in the bunch has a Gaussian distribution, and its standard deviation σ is expressed by the following equation. σ = (εβ) ^1/2 where ε is emittance (proportional constant unique to the storage ring) and β is a beta function.

From this equation, if the beta function becomes smaller,
The beam size becomes smaller and the electron density in the bunch becomes higher (actually, the smaller the storage ring, the larger the emittance, so this is alleviated to some extent). As a result, the probability of scattering electrons is increased, and the Towschek life is shortened. In view of such problems, an object of the present invention is to provide an electron storage ring which is a circular weakly focused electron storage ring having a small orbital radius and which is suitable for extending the life of an electron beam.

[0010]

The electron storage ring according to the present invention has an n value (n = [-R / B]. [DB / dR]) of a magnetic field distribution generated by a built-in circular weakly focusing magnet. Defined) is set so that 0.01 <n <0.1.

[0011]

EXAMPLES Examples of the present invention will be described below. The Tauschek life of a circular weakly focused electron storage ring is given by the following equation. ^{_{τ = σ x 'γ 3 (}} ε max / E 0) 2 V B / [π 1/2 r e 2
cNC (ξ)] where V _B = (4π) ^3/2 σ _x σ _y σ _L ξ = [ε _max / (E ₀ γσ _{x ′} )] ² C (ξ) = log (1 / 1.78 · ξ) It is −1.5. ^{_{However, r e = 2.8 × 10 -15}} m: electron classical radius ^{c = 3.0 × 10 8 m /} s: velocity of light N: electron number of the bunch γ = E ₀ / mc ^2: relativistic mass factor (mc ⁽² is the static energy of the electron) E ₀ : Central energy of electron energy distribution in the bunch ε _max : Maximum allowable displacement of the electron kinetic energy from the central energy V _B : Bunch volume σ _x : Horizontal beam divergence σ _{x '} : Standard deviation of horizontal angular spread with respect to the electron beam traveling direction σ _y : Vertical beam divergence σ _L : Beam traveling divergence, or bunch length

When the energy of the electron is large, the function C (ξ) does not change much with respect to the change of σ _{x ′.} Therefore, when the energy is constant, it can be considered as an approximate constant. In case of circular weakly focused storage ring ε _x ⁰ = 3.84 · 10 ⁻¹³ · γ ² / (n · (1-
n) ^1/2 ): Natural emittance ε _x = ε _x ⁰ / (1 + k ² ) k is the coupling coefficient of horizontal and vertical emittance ε _y = ε _x ⁰ k ² / (1 + k ² ) σ _x = (ε _x β _x ) ^1/2・ {1 + [(1 + k ² ) ・ n /
(3-4n)]} ^1/2 σ _{x '} = (ε _x / β _x ) ^1/2 σ _x σ _x' = ε _x · {1 + [(1 + k ² ) n / (3-4
n)]} ^1/2 σ _y = (ε _y · β _y ) ^1/2 β _x = R · (1-n) ^−1/2 β _y = R · n ^−1/2 σ _L is the following mathematical formula It is represented by 3.

[0013]

[Equation 3]

Therefore, it is also expressed by the following equation 4.

[0015]

[Equation 4]

Further, the following relational expression 5 is obtained.

[0017]

[Equation 5]

Therefore, the Towsheck life is approximately expressed by the following equation (6).

[0019]

[Equation 6]

From the above, it can be seen that it is effective to make n small in order to prolong the Tauschek life of the circular weak focusing ring. At this time, β _y also becomes large,
When R is small, β _y can be kept in a range where the vacuum life is sufficiently long.

In the conventional device, the orbital radius R = 0.
5m, electron energy 650MeV, n value is about 0.3 ~
It is about 0.4. On the other hand, the present invention is intended for a storage ring having an electron orbit radius R = 0.15 m and an electron energy of about 250 MeV. The Tawseck life of this storage ring is
It becomes shorter at a ratio of (250/650) ⁷ (about 0.0012). Therefore, n is 1/20 of the conventional value, which is 0.015 to 0.015.
If it is set to 0.02, the Tauschek life can be extended by 20 ^7/4 (about 189 times). The conventional Tauseck life is about 30 hours, while the storage ring targeted by the present invention has a life of about 7 hours.

The lower limit of the n value is determined by the allowable error magnetic field. Four
If R = 10mm and allowable error magnetic field 4B / B is about 10 ^-3 , (1 / B) · (4B / 4R) is about 0.1 (1 / m)
Is. Therefore, if the minimum value of R is about 0.1 m, then 4n = 0.01. Therefore, the lower limit of the n value is set to 0.01.

The upper limit of the n value is determined by the effectiveness of the present invention. The orbital radius of the target storage ring is 0.1-0.5 m,
There is no significant change in the Tauschek life when n = 0.1, and the Tauschek life is extended with respect to electrons having the lowest possible energy. When n = 0.5 and 0.1, the latter is about 10 times the former. Further, for the storage ring with n = 0.25 or more, there is already a design example R = 0.5 m. However, in this example, if n is further reduced, the beam size becomes too large and the required specifications cannot be met. The beam size is not so large because the radius of the orbit of the storage ring of interest is small. Therefore, the upper limit of the n value is set to 0.1.

[0024]

As described above, the present invention is effective in accumulating low-energy electrons in the circular weak-focusing electron storage ring having an orbital radius of 0.5 m or less, and the magnetic field of the focusing electromagnet. It was theoretically confirmed that the tau-seck life is lengthened by setting the n value of the distribution to a predetermined range.

[Brief description of drawings]

FIG. 1 is a cross-sectional view schematically showing the structure of an electron storage ring.

FIG. 2 is a diagram for explaining an electron beam (bunch) moving in an electron storage ring.

[Explanation of symbols]

 10 Yoke 11 Introductory Part 12 Vacuum Container 13 Magnetic Channel 15 Inflector

Claims (1)

Claim: What is claimed is: 1. An electron storage ring for generating synchrotron radiation in a tangential direction of a trajectory by moving charged particles along a trajectory having a predetermined curvature at a velocity close to the speed of light. An electron storage ring, wherein an n value of a magnetic field distribution generated by a built-in circular weakly-focusing magnet is set to be 0.01 <n <0.1.