JP3097993B2 - Magnet structure for superconducting wiggler - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a superconducting wiggler magnet which is inserted into an electron beam accelerator ring or the like to generate radiation, and more particularly to a magnet structure which enables a small superconducting wiggler.

[0002]

2. Description of the Related Art As applied technology of radiation generated by a wiggler inserted in an electron beam accelerator ring or the like has been developed, stronger radiation has been required. Such a demand for radiation having high energy can be met by strengthening the magnetic field acting on the electron beam. However, since it is difficult to obtain a magnetic field strength of 2 T (tesla) or more with a conventional normal conducting coil, a superconducting wiggler using a superconducting coil capable of generating a strong magnetic field has come to be used.

[0003] An electron beam having a relative velocity incident on a wiggler meanders in a magnetic field having a distribution of positive and negative polarities in the length direction to emit radiation. The electron beam is most deflected by a central magnet provided at the center of the wiggler and generates a predetermined radiation light. In order to radiate the emitted light in the same direction as the trajectory of the electron beam and to return the electron beam to the original trajectory position, side magnets are provided before and after the center magnet that generate a magnetic field in a direction different in polarity from the center magnet. . The superconducting wiggler arranged in this order of the upstream side magnet, the center magnet, and the downstream side magnet is called a three-pole superconducting wiggler. In the three-pole superconducting wiggler, the center magnet and the upstream and downstream side magnets need to be housed in a cryostat together with the iron yokes interposed therebetween and cooled in order to maintain the superconductivity of the superconducting coil.

In a three-pole superconducting wiggler, the strength of the magnetic field generated by the central main coil is usually +4 to + 8T (tesla).
The magnetic field of the side coil is-
(程度) 程度 − (１ ／) is often selected.
Here, the sign of +-means the direction of the magnetic field. further,
In order to return the electron beam meandering on the axis to the original coaxial orbit, the excitation of each superconducting coil is controlled to integrate the magnetic field distribution along the orbit of the electron beam (this is defined as the Z-axis direction).
It is necessary to adjust the magnetic field distribution so that BzdZ becomes zero. In a normal three-pole superconducting wiggler, the integral value is made zero mainly by adjusting the excitation of the side coil. As described above, in order to adjust the magnetic field distribution, it is necessary to enable excitation independently for each coil group, and the number of pairs of coils and current leads connected thereto increases. This complicates the heat insulating structure of the cryostat of the superconducting wiggler and is a major factor in increasing the size of the entire wiggler.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a superconducting wiggler economically provided by reducing the size of a cryostat and making it easier to operate.

[0006]

In order to solve the above-mentioned problems, a superconducting wiggler according to the present invention comprises a central magnet and side magnets provided on the incident side and the exit side of the electron beam with the center magnet interposed therebetween. This is a three-pole wiggler arranged to face each other with a superconducting coil used as a center magnet, and a permanent magnet and an electromagnet combined with a side magnet instead of a superconducting coil. Further, the superconducting coil of the central magnet is housed in the cryostat together with the first iron yoke, the second iron yoke is attached to the permanent magnet and the electromagnet of the side magnet, and is disposed outside the cryostat. Is preferably provided so as to be close to the side surface of the second iron yoke so as to form a magnetic circuit that passes a magnetic flux through the superconducting coil and the side magnet and into the electron beam path.

According to the present invention, the magnetic field at the center of the wiggler is 2
Even if it is necessary to use a superconducting coil beyond T,
Focusing on the fact that a superconducting coil may not always be necessary because the absolute value does not reach 2T at the side position where the strength of 1/4 to 1/3 is sufficient,
A simple wiggler is provided by using a superconducting coil for the center magnet and a permanent magnet for the side magnet. For example, if the maximum magnetic field generated by the central coil is about + 5T, the magnetic field of the side coil is-
It is sufficient to use about 1.2T, which indicates that it is not necessary to use a superconducting coil for the side coil. In the superconducting wiggler of the present invention, the superconducting coil of the central magnet and the permanent magnet of the side magnet are designed so that the magnetic field distribution along the electron beam orbit conforms to predetermined conditions, and the electromagnet of the side magnet attached to the electromagnet is used. Therefore, even if there is a design or manufacturing error in the magnet arrangement, it can be easily compensated.

[0008] Further, since the portion to be stored in the cryostat is limited to the superconducting coil of the central magnet and its peripheral devices, the volume required for the cryostat is greatly reduced as compared with the conventional case. Furthermore, since the side magnet used to adjust the magnetic field distribution is not housed in the cryostat, there is no need to draw the current lead that supplies the adjustment current into the cryostat. This has the advantage that the heat insulation structure of the cryostat is simplified. The center magnet and side magnet are separated, and the side magnets are made up of simple permanent magnets and electromagnets. A relatively large amount of standardized manufacturing of side magnets that do not require any technical skills is possible. For this reason, a standardized side magnet to be combined with the central magnet later can be arbitrarily selected, and economical wiggler manufacturing becomes possible.

According to the second superconducting wiggler magnet structure of the present invention, the central magnet and the side magnet are each combined with an iron yoke. Moreover,
Since the side surface of the first iron yoke of the center magnet accommodated in the cryostat is disposed close to the side surface of the second iron yoke of the side magnet disposed outside the cryostat, the upper and lower passages pass through the superconducting coil. The symmetrical magnetic circuit formed so as to penetrate the side magnets does not increase the reluctance so much, and the magnetic field generated in the electron beam path can maintain a sufficiently large intensity. For this reason, the capacity of the magnet corresponding to the required magnetic field strength does not become excessive, and a sufficiently small wiggler can be configured.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The superconducting wiggler magnet structure according to the present invention will be described below in detail with reference to the embodiments shown in the drawings. FIG. 1 is a side sectional view showing an embodiment of a superconducting wiggler magnet configuration of the present invention, FIG. 2 is a drawing showing a magnetic field distribution in this embodiment, and FIG. 3 is an example of a superconducting wiggler using the magnet structure of this embodiment. FIG.

In FIG. 1, a main coil 1, which forms a central magnet in a pair up and down, is a superconducting coil and is housed in a cryostat. The side magnets 3 are arranged in the normal temperature air space on the upstream side and the downstream side of the cryostat. Side magnet 3 is permanent magnet row 5
And a compensating electromagnet 7, and are arranged such that the magnetic field direction by the permanent magnet array 5 is opposite to the magnetic field direction by the main coil 1. These magnet groups are arranged vertically symmetrically with respect to the beam duct 9 through which the electron beam passes, and symmetrically in the longitudinal direction with the main coil 1 interposed therebetween in the axial direction of the beam duct 9.

In order to apply a stronger magnetic field to the electron beam passing through the beam duct 9, it is desirable to minimize the leakage magnetic flux. For this purpose, an iron yoke 11 surrounding the main coil 1 and an iron yoke 13 surrounding the respective side magnets 3 are provided to close between the main coil 1 and the upstream side magnet 3 and between the main coil 1 and the downstream side magnet 3. To form a magnetic circuit 15,
An effective magnetic field is applied to the axis of the beam duct 9. In order to reduce the resistance of the magnetic circuit 15 and apply a more effective magnetic field, it is preferable that the side surface of the iron yoke 11 of the main magnet 1 and the side surface of the side magnet 3 be as close as possible to reduce the gap.

FIG. 2 shows the magnetic field distribution along the axis of the beam duct. The horizontal axis represents the axial distance of the beam duct, and the vertical axis represents the magnetic field intensity at the axial position of the beam duct. In order to return the trajectory of the electron beam after passing through the wiggler to the same position and direction as the original trajectory, the magnetic field distribution is symmetrical and the integral of the positive magnetic field strength and the integral of the negative magnetic field strength cancel each other. It is necessary to do. Although the permanent magnet array 5 of the side magnets 3 is configured to cancel the magnetic field distribution formed by the central main coil 1, the magnetic field intensity generated by the magnetizing / demagnetizing or assembling of the permanent magnet becomes indefinite. In addition, the magnetic field distribution generated by the main magnet 1 may change depending on the operating conditions.
The magnetic field distribution is adjusted by adjusting the excitation of the electromagnet 7 provided in the side magnet 3.

For example, with respect to the magnetic field distribution at the central portion for generating the radiated light, the magnetic field distribution at both side portions formed by the permanent magnet rows 5 of the side magnets 3 is insufficient in intensity, as shown by the dashed line in the figure. In the case of, the electromagnet 7 is appropriately excited in the opposite direction to the main coil 1 so that the integral value of the magnetic field distribution cancels out the positive and negative to become zero. The magnetic field distribution indicated by the solid line in the figure shows the state after compensation by the electromagnet 7. Also, the main coil 1
The pre-installed permanent magnet row 5
If the magnetic field distribution on the side due to is too strong, the electromagnet 7 is excited to generate a magnetic field in the same direction as the main coil 1, and the integral value of the magnetic field distribution along the axis of the beam duct becomes zero. Adjust as follows.

[0015]

FIG. 3 shows an example of a superconducting wiggler using the magnet structure of the present embodiment. The parts having the same functions as the elements shown in FIG. make it easier. In FIG. 3, a main coil 1 having a superconducting coil is provided at the center of the superconducting wiggler apparatus.
And a cryostat 21 for storing the iron yoke 11 and maintaining a very low temperature state, and the side magnet 3 is installed outside the cryostat 21. The side magnet 3 includes a permanent magnet array 5, an electromagnet 7 and an iron yoke 13, and is disposed at a position symmetrical with respect to the central main coil 1.

When viewed along the axis of the beam duct 9 through which the electron beam passes, the main coil 1 and the side magnets 3 are symmetrical in the front-rear direction with respect to the center of the main coil 1 and at the same time, up and down with the beam duct 9 therebetween. It is arranged symmetrically also in the direction. This symmetric relationship is based on the main coil 1, the permanent magnet row 5
The same holds for the arrangement of the iron yokes 11 and 13 surrounding the compensating electromagnet 7. The beam duct 9 passes through the side magnet 3 and the cryostat 21 concentrically with the central axis (Z axis) of the magnetic field formed by the main coil 1 and the side magnet 3, and both ends thereof are connected to a vacuum gut such as an accelerator ring. You. Both the cryostat 21 and the beam duct 9 penetrating the side magnet 3 are installed with a high degree of parallelism to the reference floor surface by adjusting the height by the installation legs 23.

The cryostat 21 for accommodating the main coil 1 and the like has a horizontal cylindrical shape, and has an inner tank 25 filled with liquid helium and a shield tank 2 filled with liquid nitrogen.
7 and an outer tank 29 as a protective outer shell. A multilayer heat insulating material (super insulation) or the like having an improved heat insulating effect is provided by stacking a polyester film on which aluminum is deposited on a vacuum layer between the tanks via a spacer. It has the following structure. Liquid helium is supplied to the inner tank 25 via a liquid helium pipe 31, and liquid nitrogen is supplied to the shield tank 27 via a liquid nitrogen pipe 33. The main coil 1 which is a superconducting coil and the iron yoke 11 surrounding the main coil 1
5 and cooled by liquid helium.

In order to minimize the leakage magnetic flux in the magnetic circuit formed by the iron yoke 11 in the inner tank 25 and the iron yoke 13 outside the tank, it is preferable to reduce the distance between the main coil 1 and the side magnet 3. For this reason, the thickness of the heat insulating layer provided on both end surfaces of the cryostat 21 is formed as thin as possible. In this embodiment, a high-temperature superconducting current lead 35 is used for power supply when the main coil 1 is excited. The high-temperature superconducting current lead 35 is disposed in an adiabatic vacuum layer between the inner tank 25 and the liquid nitrogen shield tank 27. The upper end of the high-temperature superconducting current lead 35 is cooled by heat conduction from the liquid nitrogen shield tank 27, and the lower end is cooled by heat conduction from liquid helium in the inner tank 1.
The connection from the upper end of the high-temperature superconducting current lead 35 to the current introduction terminal 37 of the outer bath 29 is connected by a normal copper braided lead 39, and further connected to the excitation DC power supply 41 via the current terminal 37.

In this embodiment, the material of the permanent magnet 3 of the side magnet 3 is, for example, JIS which is a metal-based cast magnet.
Standard (JISC2502) MCB500, MCG58
0, MCB750 or the like is preferably used, and these permanent magnets can generate a magnetic field of 1.2 to 1.4 T if the magnetic circuit is appropriately adjusted. As described above, the ratio of the peak magnetic field strength between the main coil and the side magnet is -−１.
In this case, the strength of the magnetic field generated by the main coil 1 when the above-described side magnet 3 is used is about 5T, so that a simple superconducting wiggler having a magnetic field strength of about 5T can be designed.

The permanent magnets 5 for side magnets are formed by sticking a plurality of rectangular pieces to the opposing surface of the iron yoke 13 and symmetrically up and down with respect to the beam duct 9 together with the iron yoke 13 and symmetrically with respect to the main coil 1. Assembled.
The compensating electromagnet 7 in the side magnet 3 is formed by winding a normal insulated copper wire around the iron yoke 13 and impregnating and solidifying the resin. The number of windings and the current value are determined by the magnitude of the magnetic field to be compensated and adjusted. Appropriate currents are supplied to the upstream and downstream compensating electromagnets 7 from separate magnetic field adjusting DC power supplies 43 to compensate for the bias of the magnetic field formed by the respective permanent magnet arrays 5 to adjust the conditions of the magnetic field distribution. Can be trimmed.

The beam duct 9 has a double vacuum piping structure having a rectangular cross section. The inner vacuum duct has a beam bore that is exposed to the electron beam. The outer vacuum duct is connected to the outer tank end plate 47 of the cryostat 21 in the area of the side magnet 1 to form an adiabatic vacuum space having the same vacuum as in the outer tank 29, and serves as a cold bore of the inner tank 25 in the area of the cryostat 21. It forms a vacuum-resistant shell. In the area of the cryostat 21, the inner vacuum duct is connected to the thermal anchor 45 from the liquid nitrogen shield tank 27.
Is almost liquid nitrogen temperature (about 80
K), and also serves as a heat shield for the cold bore in the inner tank 25. By increasing the length of the inner vacuum duct in the region of the side magnet 3, conduction heat input from the outside to the thermal anchor 45 is suppressed.

Both ends of the beam duct 9, that is, the ends of the side magnets 3 are connected to the vacuum duct of the accelerator ring by using a flange 49. The main coil 1 and the compensating electromagnets 7 of the side magnets 3 are independently excited in parallel. At this time, the magnitude of the current supplied to the compensating electromagnet 7 with respect to the current supplied to the main coil 1 is adjusted so that the integrated value of the magnetic field distribution along the traveling axis of the electron beam becomes zero, as described above. This current ratio is determined while monitoring the magnetic field distribution with a search coil or the like before passing the electron beam.

In this embodiment, the beam duct has a double vacuum pipe structure. However, it goes without saying that the present invention can be similarly applied to a triple pipe structure. Also, the DC power supply for adjusting the magnetic field is provided independently for the upstream and downstream electromagnets, but it is sufficient to make up for the difference in the amount of compensation required for both, and after both are fed from a common power supply, Can be added to improve the economical efficiency of the device.

[0024]

As described above, by using the magnet structure of the present invention, it is possible to reduce the size of the expensive superconducting magnet portion, and to reduce the size of the cryostat, which generally becomes more expensive as it becomes larger. Further, if the permanent magnet and electromagnet portion, which do not require such a high level of technology, are standardized and manufactured separately from the superconducting magnet and combined with each other, a superconducting wiggler can be manufactured at low cost. The intensity of the emitted light generated by the magnet structure of the present invention is limited,
When the free electron laser can be supplied more economically, the field of application of the free electron laser will expand dramatically, and it will be used in medical, inspection, lithography, and other technical fields that do not require such strong light. Become like

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a superconducting wiggler magnet structure according to the present invention.

2 is a drawing showing a magnetic field distribution in the superconducting wiggler magnet structure of FIG.

FIG. 3 is a partially cutaway sectional view showing a superconducting wiggler using the magnet structure of FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Main coil 3 Side magnet 5 Permanent magnet row 7 Compensation electromagnet 9 Beam duct 11, 13 Iron yoke 21 Cryostat 25 Inner tank 27 Shield tank 29 Outer tank 45 Thermal anchor

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H05H 13/04

Claims (2)

(57) [Claims] 1. A central magnet using a superconducting coil, and side magnets which incorporate a permanent magnet and an electromagnet and are provided on the electron beam incident side and the emission side of the central magnet, respectively, are opposed to each other with an electron beam passage therebetween. Magnet structure in a three-pole type superconducting wiggler. 2. The superconducting coil is housed in a cryostat together with a first iron yoke, a second iron yoke is attached to the permanent magnet and the electromagnet, and a side surface of the first iron yoke is the second iron yoke. 2. The magnet structure according to claim 1, wherein a magnetic circuit is provided so as to be close to a side surface of the magnet and penetrates a magnetic flux into the electron beam path through the superconducting coil and the side magnet.