JPH0821478B2 - Charged particle device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a charged particle device such as an accelerator or storage ring for a charged particle beam, for example, an electron beam, and particularly to a magnetic field equalization of a deflection electromagnet without enlarging a coil. The present invention relates to an improved charged particle device.

[Prior Art] FIG. 5 shows, for example, Yoshikazu Miyahar published by the Japan Chemical Technology Information Center in September 1984.
a), technical report of ISSP by Koji Takata and Tetsuya Nakanishi (Tec
hnical Report of ISSP) No. 21, “Superconducting Racetrack Electron Storage Ring for Synchrotron Radiation and Coexisting Injector Microtron (Superconducting Race)
track Electron Strage Ring and Coexistent Inje
FIG. 8 is a plan view showing a conventional charged particle device described in “ctor Microtron for Synchrotron Radiation”.

In the figure, (1) is a storage ring as a charged particle device for storing charged particles, and (2) is an incident beam line for guiding charged particles (for example, electrons) into the storage ring (1). (3) is a superconducting deflection electromagnet for deflecting charged particles to form a balanced orbit (4), and is composed of a combination of deflection coils described later.

(5) is a synchrotron radiation beam line for extracting radiant light generated when the charged particles are deflected by the deflecting electromagnet (3). This synchrotron radiation is synchrotron radiation, or SOR
It is called (Synchrotron Orbital Radiation), and is taken out to the outside and used for lithography. Generally, a large number of synchrotron radiation beam lines (5) are provided along the deflection electromagnets (3) in order to enhance the utilization efficiency of the device, but here, only one is provided for each deflection electromagnet (3). Is omitted.

(6) is a quadrupole electromagnet for focusing the charged particles in the storage ring (1), (7) is a sextupole electromagnet for correcting the nonlinear magnetic field or chromaticity of the deflection electromagnet (3), and (8) is a radiation A high frequency cavity for compensating the energy loss of charged particles due to the emission of light and accelerating to a predetermined energy,
(9) is a kicker for shifting the equilibrium orbit (4) when injecting charged particles from the incident beam line (2), and (10) is a vacuum donut that serves as a path for charged particles.
(11) is an inflector for injecting charged particles into the storage ring (1) from the incident part beam line (2), and (1)
Reference numeral 2) is a vacuum pump for maintaining a high vacuum in the vacuum donut (10), which are arranged along the equilibrium orbit (4).

The vacuum donut (10) is made of a stainless material that has high mechanical strength and is easy to bake. Further, the inside of the vacuum donut (10) is kept in an ultra-high vacuum by a vacuum pump (12) to prevent charged particles from colliding with gas molecules and losing energy to shorten the life thereof.

6 to 8 are a perspective view, a plan view and a side view, respectively, showing the deflection electromagnet (3) in FIG. In the figure, (31) and (32) are a pair of superconducting deflection coils forming a deflection electromagnet (3), and (31) is an upper coil.
(32) is a lower coil. The upper and lower coils (31), (3
Since 2) has a high magnetomotive force, it has an air-core structure that does not use an iron core. Arrows m ₁ and m ₂ are the upper and lower coils (31),
The direction of the current flowing in (32), the arrow n, indicates the traveling direction of the electron beam on the equilibrium orbit (4).

Further, as is clear from FIGS. 7 and 8, the equilibrium orbit (4) is composed of a semicircle of radius ρ ₀ on the plane of the polar coordinate Rθ (z = 0) and straight lines connecting before and after the semicircle. Indicated by.
ρ ₁ and ρ ₂ are banana-shaped upper and lower coils (31), (32)
Are the inner and outer radii of.

Next, the operation of the conventional charged particle device shown in FIGS. 5 to 8 will be described.

The charged particles that have entered the storage ring (1) from the incident part beam line (2) are pulsed by the inflector (11) and their trajectories are deviated by the kicker (9). Therefore, the charged particles first orbit the orbit slightly deviated from the equilibrium orbit (4), and after several revolutions, continue to orbit on the equilibrium orbit (4) in the direction of arrow n. This equilibrium orbit (4) is determined by the arrangement of the bending electromagnet (3) and the quadrupole electromagnet (6).

Incidentally, m _1, m vertical coils (31) by _two directions of the current, (3
The main magnetic field generated in 2) is in the -z (-y) direction, and the current flowing in the equilibrium orbit (4) is in the direction opposite to the electron beam direction n. Therefore, the charged particles, that is, the electron beam passing between the upper and lower coils (31) and (32) is subjected to an electromagnetic force in the -R direction according to Fleming's left-hand rule, which causes a radius ρ
_Bent with ₀ curvature. Radius ρ _{0 of} this equilibrium orbit (4)
Is given by the following formula.

ρ ₀ = P / (e · By) where P: electron momentum e: electron charge By: magnetic field generated in the y-axis direction of the upper and lower coils (31) and (32) ) Is parallel to the z-axis, and the x-axis described later is an axis in the same direction as the polar coordinate radius R of the equilibrium orbit (4).

On the other hand, the high frequency cavity (8) accelerates charged particles, and the sextupole electromagnet (7) corrects the non-uniformity of the magnetic field in the radial direction of the deflection electromagnet (3) and corrects the chromaticity.

When the charged particles revolving along the equilibrium orbit (4) are deflected by the magnetic field of the deflection electromagnet (3), electromagnetic waves due to bremsstrahlung are emitted as emitted light from the emitted light beam line (5) to the equilibrium orbit (4). Radiate in the tangential direction of.

By the way, since the electron beam oscillates around the equilibrium orbit (4) in the betatron direction, the electron beam generally surrounds the central orbit in the direction orthogonal to the traveling direction n of the electron beam (mainly the R direction, that is, the x-axis direction). Over a range of several cm or more
A uniform magnetic field distribution (good magnetic field region) of about 10 ^-4 to 10 ^-3 is required. When the magnetic field distributions of the superconducting deflection coils (31) and (32) are non-uniform, the equilibrium orbit (4) of the electron beam deviates from the centers of the upper and lower coils (31) and (32), but this deviation amount is larger than the predetermined value. As the electron beam grows larger, the electron beam becomes a vacuum donut (1
At 0), the electron beam will be lost.

FIG. 9 is a characteristic diagram in which the distribution of the magnetic field By in the deflection electromagnet (3) in the R (x-axis) direction is calculated, and the upper and lower coils (3
When the inner radius ρ ₁ and the outer radius ρ _{2 of} 1) and (32) are respectively ρ ₁ = 315.8 mm ρ ₂ = 675.8 mm and the distance between the upper and lower coils (31) and (32) is 252 mm, (By -By ₀ ) / By ₀ ratio (%) is shown.

However, By ₀ is the magnetic field in the y-axis direction at the center of the equilibrium orbit (4), that is, (x, y) = (0,0). Further, here, ω = 50 mm, and the radial position of the equilibrium orbit (4) of R = ρ ₀ (x = 0) obtained from the equation is ρ ₀ = 495.8 mm.

As is clear from FIG. 9, the position where the magnetic field By peaks is a position where the radius is slightly larger than R = ρ ₀ . Therefore, if the equilibrium orbit (4) is set at the position of R = ρ ₀ + ΔR (x = ΔR) where the magnetic field distribution becomes the extreme value, and the region of width 2ω with this as the center is a good magnetic field region, α = (Bymax-Bymin) / By ₀ where Bymax: highest magnetic field in good magnetic field region (2ω) Bymin: lowest magnetic field in good magnetic field region (2ω) By ₀ : reference magnetic field (usually the magnetic field on the central orbit of the electron beam) The magnetic field homogeneity α defined by) is improved. However, in any case, the magnetic field homogeneity α obtained from the calculation result of the magnetic field distribution is on the order of 10 ^-2 .

[Problems to be Solved by the Invention] As described above, in the conventional charged particle apparatus, the pair of upper and lower coils (31) and (32) are used to balance the electron beam trajectory (4).
However, there is a problem that the magnetic field homogeneity α in the good magnetic field region 2ω around the equilibrium orbit (4) can be obtained only on the order of about 10 ^-2 .

A magnetic field generator in which the upper and lower coils (31) and (32) are provided with a second upper and lower coil is also proposed, as disclosed in Japanese Patent Laid-Open No. 61-188907, for example. Since it is arranged and does not have a sufficiently efficient structure, there is a problem that it becomes large.

The present invention has been made to solve the above-mentioned problems, and a charged particle device capable of improving the magnetic field homogeneity in a good magnetic field region around a balanced orbit without enlarging the coil due to an efficient structure. Aim to get.

[Means for Solving the Problems] In the charged particle device according to the present invention, the second upper and lower coils are provided outside the upper and lower coils disposed above and below the equilibrium orbit, and the inner radius of the second upper and lower coils is provided. Is matched with the inner radius of the upper and lower coils, and the characteristic curve of the magnetic field distribution generated by the upper and lower coils and the second upper and lower coils is defined as one convex upward and the other convex downward in the radial direction of the equilibrium trajectory.
The non-uniform magnetic field component in the magnetic field distribution due to the upper and lower coils,
The current density of the second upper and lower coils is approximately twice the current density of the upper and lower coils so as to cancel out the non-uniform magnetic field components in the magnetic field distribution of the upper and lower coils.

[Operation] In the present invention, the non-uniform magnetic field component in the magnetic field distribution of the upper and lower coils and the non-uniform magnetic field component in the magnetic field distribution of the second upper and lower coils are canceled, and the magnetic field distribution in the good magnetic field region is made uniform. .

Further, by arranging the upper and lower coils and the second upper and lower coils in substantially the same plane, it is possible to integrate the coil winding frames and to prevent the coil from becoming large.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings. 1 and 2 are a plan view and a side view showing an essential part of one embodiment of the present invention, that is, a deflection electromagnet, and (4), (31) and (32) are the same as those of the above-mentioned conventional device. Is. Further, the configuration of the entire charged particle device is the same as that shown in FIG.

(33) is a second upper coil disposed outside the upper coil (31), (34) is a second lower coil disposed outside the lower coil (32), arrows m ₃ , m ₄ Is the second upper and lower coil (33),
It is the direction of the current flowing through (34). In addition, as described above,
The (R, θ, z) coordinate system is used for the upper and lower coils (31) to (34), and the (x, y) coordinate system is used for the equilibrium orbit (4).

The second upper and lower coils (33) and (34) have exactly the same shape as the upper and lower coils (31) and (32), and R
It is arranged at a position symmetrical with respect to the −θ (z = 0) plane. However, the current density of the upper and lower coils (31) and (32) is
While the current density is 101.5 A / mm ² , the current density of the second upper and lower coils (33) and (34) arranged outside is 200 A / mm ² . Furthermore, the area of the second upper and lower coils (33), (34) is
The inner radii of the upper and lower coils (31), (32) are approximately twice that of the upper and lower coils (31), (32), and the inner radii of the second banana-shaped upper and lower coils (33, 34) are the inner radii of the upper and lower coils (31), (32), respectively. It is arranged so as to match with.

Next, referring to the characteristic diagrams of FIG. 3 and FIG. 4 showing the generated magnetic field distribution and the combined magnetic field of the coils (31) to (34), the present invention shown in FIG. 1 and FIG. The operation of one embodiment will be described. The operation of orbiting the electron beam on the equilibrium orbit (4) is the same as the conventional operation described above.

In general, the magnetic field distribution curve in the R direction is convex upward when the coil area is small and downward convex when the coil area is large. In addition, when the current density is large, the rate of change of the curve is large. Therefore, as shown in FIG. 3, the magnetic field distribution generated by the upper and lower coils (31) and (32) is represented by the upwardly convex curve A, and generated by the second upper and lower coils (33) and (34). The magnetic field distribution to be represented is represented by a downwardly convex curve B. In this case, the unit of the magnetic field By (vertical axis) is indicated by T (Tesla). Third
From the figure, it can be seen that by combining the curves A and B, a very flat magnetic field distribution in the R direction, that is, a distribution with a high magnetic field uniformity α can be obtained.

Here, the relationship between the magnetic field distribution of the upper and lower coils and the coil area and the coil current will be specifically described.

Referring to FIGS. 1 and 2, the coil areas of the upper and lower coils (31) and (32) are equal to the coil width (= 2 (ρ ₀ −
almost corresponds to ρ ₁ )). When the coil width is gradually increased from 0, if the coil currents (arrows) flowing through the upper and lower coils (31) and (32) are in the same direction,
The magnetic field distribution created by the upper and lower coils (31) and (32) initially becomes an upwardly convex distribution and gradually becomes flat, and then becomes a downwardly convex distribution.

At this time, if the coil width is extremely narrow, manufacturing problems such as bending of both ends of the coil become difficult, so for example, in the case of a coil of a charged particle device with a deflection radius of about 0.6 m, a parallel trajectory Plus (minus) 20 across (4)
A coil width of about 0 mm is required.

When the arrangement of the first pair of upper and lower coils (31) and (32) is determined in this way, in order to make the magnetic field distribution created by the upper and lower coils highly uniform over a wide range, the second upper and lower coils are arranged as in the embodiment of the present invention. Coils (33) and (34) are arranged.

At this time, the magnetic field distribution created by the second upper and lower coils (33) and (34) also changes by changing the coil width (corresponding to the coil area) as described above, and makes the magnetic field distribution highly uniform over the widest range. In order to do so, it is necessary to set the coil area and coil current density of the second upper and lower coils to about twice (for example, 1.8 to 2.2 times) that of the inner upper and lower coils (31) and (32).

This is because if the coil area of the second upper and lower coils is set smaller than twice, the magnetic field distribution created by the second upper and lower coils will be too flat, and the magnetic field distribution of the inner upper and lower coils (31) and (32) will be flat. This is because it is not possible to generate a magnetic field distribution sufficient to make the magnetic field uniform and it is not possible to obtain a wide range of highly homogenized magnetic field distribution region which is the object of the present invention.

On the contrary, if the coil area of the second upper and lower coils is set to be larger than twice, the coil position from the parallel track portion is too far away and the conductor length required for coil formation becomes long, which is expensive. This is because an attempt to adjust these defects in the magnetic field distribution by the current density requires a remarkably large additional current, which is not industrially advantageous.

In other words, as shown in FIG. 3, the upper and lower coils (31)
The optimum combination condition of the second upper and lower coils (33) and (34) capable of adjusting the magnetic field distribution of (32) and (32) in a wide range is that the coil area is about twice and the current density is about twice. However, the coil cross-sectional areas of the coils (31) to (34) are almost the same as shown in FIG.

Figure 4 is, theta = 90 ° represents the distribution of the combined magnetic field of the four coils in y = 0 (31) ~ ( 34), By 0
Is the magnetic field in the y-axis direction at the center of the equilibrium orbit (4), that is, (x, y) = (0,0). From FIG. ⁴ , the magnetic field homogeneity α of the order of 10 ⁻⁴ is a good magnetic field region 2ω in the range of | x | ≦ 40 mm.
You can see that it can be obtained with. This means that the value of the magnetic field homogeneity α is improved by two depositions as compared with the conventional device.

In the above embodiment, a pair of second upper and lower coils (3
Although 3) and (34) are used to cancel the non-uniform components of the magnetic field distribution of the upper and lower coils (31) and (32), two or more pairs of second upper and lower coils may be used. Also, equilibrium orbit (4)
The position of may be selected regardless of the arrangement of the coils (31) to (34).

Further, the case where the coils (31) and (33) and (32) and (34) are arranged at symmetrical positions with respect to the plane of the balanced orbit (4) has been described, but it is always necessary to maintain symmetry. Needless to say, even if it is asymmetric, it does not cause any trouble.

[Advantages of the Invention] As described above, according to the present invention, the second upper and lower coils are provided outside the upper and lower coils in the deflection electromagnet, respectively.
The inner radii of the upper and lower coils are matched with the inner radii of the upper and lower coils, and the characteristic curves of the magnetic field distributions generated by the upper and lower coils and the second upper and lower coils are Is downwardly convex so that the non-uniform magnetic field component in the magnetic field distribution of the upper and lower coils and the non-uniform magnetic field component in the magnetic field distribution of the second upper and lower coils cancel each other so that the current density of the second upper and lower coils rises and falls. Since the current density of the coil is set to about twice, there is an effect that a charged particle device in which the magnetic field homogeneity in the good magnetic field region is remarkably improved can be obtained without inviting an increase in the size of the coil.

[Brief description of drawings]

FIG. 1 is a plan view showing an essential part of an embodiment of the present invention, and FIG.
FIG. 4 is a side view showing the main part of FIG. 1, FIG. 3 is a characteristic view showing the magnetic fields generated by the upper and lower coils in FIG. 1, and FIG.
FIG. 5 is a plan view showing a conventional charged particle device, FIG. 6 is a perspective view showing the main parts in FIG. 5, and FIG. FIG. 8 is a plan view showing the main part of the figure, FIG. 8 is a side view showing the main part of FIG. 6, and FIG.
It is a characteristic view which shows the magnetic field generated by the upper and lower coils in the figure. (3) …… bending magnet, (4) …… equilibrium orbit (31), (32) …… upper and lower coils (33), (34) …… second upper and lower coils ρ ₀ …… radius of balanced orbit ρ ₁ ...... Inside radius of each coil A ...... Magnetic field of upper and lower coils B ...... Magnetic field of second upper and lower coils In the drawings, the same reference numerals indicate the same or corresponding portions.

Claims (4)

[Claims] 1. A charged particle device comprising a deflection electromagnet composed of a pair of upper and lower coils arranged across an equilibrium orbit around which charged particles circulate, wherein a second upper and lower coil is provided outside the upper and lower coils, respectively. An inner radius of the second upper and lower coils is matched with an inner radius of the upper and lower coils, and a characteristic curve of a magnetic field distribution generated by the upper and lower coils and the second upper and lower coils is related to a radial direction of the balanced orbit, One is convex upward, convex downward, a non-uniform magnetic field component in the magnetic field distribution by the upper and lower coils,
The coil area of the second upper and lower coils is approximately twice the coil area of the upper and lower coils so as to cancel out the non-uniform magnetic field component in the magnetic field distribution of the second upper and lower coils, The charged particle device is characterized in that the current density is about twice the current density of the upper and lower coils. 2. The upper and lower coils and the second upper and lower coils are both banana-shaped.
Charged particle device according to paragraph. 3. The upper and lower coils and the second upper and lower coils have the same shape, and are arranged so as to be plane-symmetric with respect to a balanced orbit. The charged particle device according to item 2 or item 2. 4. The second upper and lower coils are at least a pair or more, and the first to third claims are included.
The charged particle device according to any one of items.