JP2001110626A - Superconducting magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively reduce noise current being generated by an excitation power supply, suppress heat generation of a permanent current switch for quickly carrying out superconducting transistion, and surely make transition to permanent current mode operation in a superconducting magnet device for performing permanent current mode operation. SOLUTION: An inductance (resistance) element 16 is inserted into a current lead 5, that is positioned between a branch point 5a of a superconducting coil group 1 being connected to an excitation power supply 8 in parallel in a cooling container 4 and a permanent current switch 2, and a current-introducing terminal part 9 of the cooling vessel 4, thus reducing the noise current, when excitation and switch to a permanent current mode operation are made.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting magnet device utilizing a permanent current mode operation which is a phenomenon peculiar to superconductivity.

[0002]

2. Description of the Related Art In recent years, use of a superconducting magnet device as a static magnetic field generation source having high strength, high uniformity and stable in time has become popular. In particular, medical tomographic imaging devices (MRI devices)
Are remarkably popular as sources of static magnetic fields. In the magnet for the MRI apparatus, in order to take a dense and good-contrast tomographic image of a human body (patient) at high speed, and to obtain a high-performance image, a magnet in a spherical space (imaging space) having a diameter of 30 to 45 cm at the center of the magnet is used. A magnetic field strength of 0.5 to 2 Tesla, a magnetic field homogeneity of 1 to 10 ppm, and a time stable static magnetic field characteristic of 0.05 ppm / hr are required. And a superconducting magnet device employing a permanent current mode operation peculiar to the superconducting phenomenon and employing a coil arrangement based on a strict magnetic field uniformity design.

Further, a superconducting magnet apparatus which has a track record of more than 20 to 30 years as a static magnetic field generating source having higher strength, higher uniformity, and higher temporal stability than MRI superconducting magnet apparatuses is an NMR apparatus for chemical analysis. . In magnets for NMR equipment, M
The target area is a sphere space with a diameter of about 10 to 20 mm, which is much smaller than the RI apparatus, but the highest possible magnetic field strength (2
0 Tesla or more is prototyped) and 0.05pp
Time-stable characteristics of m / hr are required, and it is natural that these characteristics can be satisfied only by the superconducting coil and the superconducting magnet device employing the permanent current mode operation. Furthermore, a superconducting magnet device for pulling a silicon single crystal that has been rapidly spreading in recent years has been developed. The silicon single crystal pulling superconducting magnet device is a device that applies a static magnetic field in order to prevent convection of molten silicon and control oxygen penetration from a quartz crucible to pull up a high-quality silicon single crystal.
The magnetic field strength, uniformity, and time stability may be lower than those of an MRI apparatus, but a large target space and various magnetic field shapes are required. Permanent current mode operation is also employed in some devices.

On the other hand, as superconducting magnet devices that perform the permanent current mode operation as described above have become widespread and become inexpensive, the excitation power supply used for exciting these superconducting magnet devices has been simplified from experimental use to commercial use. Inexpensive devices and various devices have been simplified accordingly. In other words, the excitation power supply is switched from a transistor dropper type to a switching type power supply. Also, the quench (rapid normal conduction transition phenomenon of the superconducting coil) detector is omitted, the magnet protection element is omitted at the time of quench, and the power cutoff function linked to the quench is provided. Omission, simplification of various display devices, and the like. Of these simplifications, regarding the omission of parts and elements related to the quench phenomenon, it is common to incorporate a protection element in a superconducting magnet device and protect it by itself, and protection technology has been almost established. I have.

FIG. 8 is a schematic circuit diagram of a conventional superconducting magnet device performing a permanent current mode operation. FIG. 8A shows the state during excitation, and FIG. 8B shows the state in permanent current mode operation with the excitation power supply disconnected. In the figure, 1 is a superconducting coil group composed of a plurality of superconducting coils for generating a predetermined static magnetic field, 2 is a thermal permanent current switch, for example, 3 is a protection element when a quench occurs in the superconducting coil group 1, 4
Is a cooling vessel containing a superconducting coil group 1, a permanent current switch 2, a quench protection element 3 and a superconducting current lead 5 for connecting them, and cooling to a temperature at which superconductivity occurs by a refrigerant such as liquid helium; This is a vacuum insulated container that houses the cooling container 4 via the shield tank 7. Reference numeral 8 denotes an excitation power supply arranged outside the vacuum heat insulating container 6 for supplying current to the superconducting coil group 1, and 9 denotes a cooling container for introducing current from the excitation power supply 8 into the cooling container 4.
Current introduction terminal portions provided in the heat shield tank 7 and the vacuum heat insulation container 6 are a heater for a permanent current switch, 11 is a heater power supply for a permanent current switch, and 12 is a load current schematically shown.

Next, the operation will be described. FIG. 8 (a)
During the excitation shown in (1), the current from the excitation power supply 8 is introduced into the cooling container 4 via the current introduction terminal 9 and supplied to the superconducting coil group 1. At this time, the superconducting coil group 1 and the current lead 5 between the current introducing terminal portion 9 and the superconducting coil group 1 are in a superconducting state due to cooling in the cooling container 4.
DC resistance is almost zero. The permanent current switch 2 is composed of a superconductor. However, the power is supplied from the heater power supply 11 to the heater 10 for the permanent current switch, so that the permanent current switch 2 is heated to a temperature higher than the superconducting critical temperature and has a DC resistance of about several Ω. are doing. The superconducting coil group 1 and the permanent current switch 2 are connected in parallel to the exciting power supply 8 in the cooling container 4, and the regular load current 12 supplied from the exciting power supply 8 is slow at about 0.1 A / sec. Since the current rises from 0 to the rated current at the rising speed, most of the current flows through the superconducting coil group 1 to generate a predetermined static magnetic field in a predetermined space.

After the normal load current 12 reaches the rating, the operation is switched to the permanent current mode operation shown in FIG. Specifically, first, the heater power supply 1 for the permanent current switch
1 is turned off, the heating of the permanent current switch 2 is stopped, and the permanent current switch 2 is made superconductive. After this, the excitation power supply 8
As the current flowing through the coil decreases from the rated value, the superconducting coil group 1
The normal load current 12 flowing through the permanent current switch 2 gradually returns to the permanent current switch 2, and when the exciting current of the exciting power supply 8 becomes 0 amperes, the normal load current 12 entirely returns to the permanent current switch 2, The transition to the mode operation is completed. Thereafter, even if the excitation power supply 8 is disconnected from the magnet device as shown in FIG. 8B, the permanent current mode operation is continued.

[0008]

The conventional superconducting magnet apparatus is constructed as described above. For example, the superconducting magnet apparatus which does not perform the permanent current operation with respect to the noise current generated by the excitation power supply 8 of, for example, a switching type. Conventionally, the protection inside the superconducting magnet device has not been sufficiently performed because it does not cause much trouble. The problem related to the noise current will be described below. The noise current 13 generated by the excitation power supply 8 is a harmonic noise current 13 having various sinusoidal frequency components. For this noise current 13, the superconducting coil group 1 is obtained by multiplying the inductance of the coil group 1 by the frequency. The impedance becomes proportionally high, and as a result, FIG.
As shown in (a), most of the noise current 13 flows through the permanent current switch 2. Permanent current switch 2
In general, the inductance of the persistent current switch 2 is about zero, and the DC resistance of the permanent current switch 2 is about The noise current 13 is inversely proportional to the current.

Normal load current 1 supplied from excitation power supply 8
During excitation until 2 reaches the rated current, noise current 13 circulates through excitation power supply 8 and permanent current switch 2. After the permanent load switch 12 stops heating and gradually cools after the rated load current 12 reaches the rating, the DC resistance of about several Ω of the permanent current switch 2 gradually decreases. The noise current 13 increases in inverse proportion to. Excitation power supply 8
Although the noise current 13 does not increase infinitely due to the characteristics described above, the permanent current switch 2 cannot perform the superconducting transition due to the DC loss or heat generated from the AC loss of the superconductor. May not be able to operate in the permanent current mode.

A countermeasure that has been conventionally taken against the above-mentioned problem occurring in the superconducting magnet device operating in the persistent current mode operation is a noise current 13 flowing through the persistent current switch 2.
In order to reduce the heat generation amount by reducing the amount of heat generation, the permanent current switch 2 may be formed by induction winding, a capacitor may be provided near the output terminal of the excitation power supply 8 or near the current introduction terminal 9 of the superconducting magnet device, or FIG. As shown in (1), a filter circuit 14 is inserted between the superconducting magnet device and the excitation power supply 8.
Of these, making the permanent current switch 2 an induction winding is as follows.
At the time of excitation and at the time of switching to the permanent current mode operation, since the noise current 13 is limited by the inductance due to the induction winding, the above-mentioned problem phenomenon is improved. However,
Even during the operation in the permanent current mode, the permanent current switch 2 generates an unnecessary error magnetic field. Particularly, in the superconducting magnet device for MRI and the superconducting magnet device for NMR, the uniformity of the magnetic field in the required space is important, and when the permanent current switch 2 generates an error magnetic field, a great deal of labor is required to compensate for the error magnetic field. become.

Providing a capacitor in the vicinity of the current introducing terminal portion 9 or inserting the filter circuit 14 between the superconducting magnet device and the exciting power supply 8 can reduce the high-frequency noise current 1.
3 has a reducing effect on the commercial frequency or its third
The effect of reducing the noise current 13 having a relatively low frequency of about five harmonics is small. Further, since the excitation power supply 8 is usually rated at several hundred amperes and several volts to several tens of volts, FIG.
Since the inductance element of the filter circuit 14 has a current carrying capacity of several hundred amperes and allows only a voltage drop of several volts, it becomes a large-sized device in which a cable having a large cross-sectional area is wound with a large diameter, and characteristics and dimensions. Lacked practicality.
As described above, the conventional countermeasures have not been sufficient for the problem caused by the noise current 13 when the superconducting magnet device performing the permanent current mode operation is switched from the excitation to the permanent current mode.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and it is possible to reduce the noise current caused by the excitation power supply without causing any adverse effect due to an unnecessary error magnetic field, and by using only a high frequency. To provide a highly reliable superconducting magnet device that effectively performs low-frequency noise at about the commercial frequency, suppresses heat generation from the permanent current switch, causes superconducting transition quickly, and reliably transitions to permanent current mode operation. The purpose is to do.

[0013]

According to a first aspect of the present invention, there is provided a superconducting magnet device comprising a superconducting coil for generating a magnetic field in a target space, a permanent current switch, a superconducting current lead, and a temperature at which a superconducting phenomenon occurs. A housing for storing the superconducting coil, the permanent current switch, and the current lead, the cooling unit being provided with a cooling means for cooling the electric current lead; And the permanent current switch are connected in parallel via the branch point by the current lead, and after excitation by supplying current to the superconducting coil from the excitation power supply,
An apparatus configuration for circulating a current to a closed circuit formed by the superconducting coil and the permanent current switch, wherein an inductance is provided at a position between the branch point and the excitation power supply in the current lead in the storage container. , And one or both of the resistors.

According to a second aspect of the present invention, in the superconducting magnet device according to the first aspect, the element disposed on the current lead in the container is an inductance element using a superconducting wire.

According to a third aspect of the present invention, there is provided a superconducting magnet device according to the first or second aspect, wherein the element disposed on the current lead in the housing container is provided independently of the winding frame of the superconducting coil. Coil.

According to a fourth aspect of the present invention, there is provided a superconducting magnet device according to the third aspect, wherein the element disposed on the current lead in the housing has a winding frame made of a magnetic material or a magnetic material inside the winding frame. The inserted coil.

According to a fifth aspect of the present invention, there is provided a superconducting magnet device according to the first or second aspect, wherein the element disposed on the current lead in the container is wound around an outer peripheral portion of a permanent current switch. It is a coil integrated with the switch.

A superconducting magnet device according to a sixth aspect of the present invention is the superconducting magnet device according to the first or second aspect, wherein the element disposed on the current lead in the container is wound around an outer peripheral portion of the superconducting coil or a winding frame. It is.

A superconducting magnet device according to a seventh aspect of the present invention is the superconducting magnet device according to the sixth aspect, wherein the superconducting coil is constituted by a plurality of coils forming a uniform magnetic field region in a target space, and is disposed on a current lead in the container. Are divided at a symmetrical position separated by a predetermined distance with respect to the uniform magnetic field region so that magnetomotive forces are in opposite directions, or both ends are connected to a second permanent current switch and closed. A current shim coil that forms a circuit and corrects the uniform magnetic field distribution, or a disturbance magnetic field compensation coil that has both ends connected to a third permanent current switch to form a closed circuit and compensates for a disturbance magnetic field that enters from the outside. is there.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a simulation circuit diagram of a superconducting magnet device that performs a permanent current mode operation according to Embodiment 1 of the present invention, and particularly shows a state during excitation. In the figure, 1 is a superconducting coil group composed of a plurality of superconducting coils for generating a predetermined static magnetic field, 2 is, for example, a thermal permanent current switch, 3 is a protection element when a quench occurs in the superconducting coil group 1, and 4 is A housing containing a superconducting coil group 1, a permanent current switch 2, a quench protection element 3, and a superconducting current lead 5 for connecting them, and having a cooling means for cooling to a temperature at which superconductivity occurs by a refrigerant such as liquid helium. A cooling container 6 as a container is a vacuum heat insulating container that stores the cooling container 4 via a heat shield tank 7. Reference numeral 8 denotes an excitation power supply arranged outside the vacuum heat insulating container 6 for supplying current to the superconducting coil group 1, and 9 denotes a cooling container 4 for introducing a current from the excitation power supply 8 into the cooling container 4. Current introducing terminal portions provided in the tank 7 and the vacuum heat insulating container 6, a permanent current switch heater 10, a permanent current switch heater power supply 12,
Is a load current schematically shown. 5a is a branch point between the superconducting coil group 1 and the permanent current switch 2 connected in parallel to the excitation power supply 8 by the current lead 5, and 15 is a harmonic having various sine wave frequency components generated by the excitation power supply 8. The wave noise current 16 is an element made of an inductance or a resistance inserted in the middle of the current lead 5 connecting the current introducing terminal portion 9 and the branch point 5a.

Next, the operation will be described. First, a current from the excitation power supply 8 is introduced into the cooling container 4 via the current introduction terminal 9 and supplied to the superconducting coil group 1 to be excited. At this time, since the superconducting coil group 1 and the current lead 5 between the current introducing terminal 9 and the superconducting coil group 1 are in a superconducting state due to cooling in the cooling vessel 4, the DC resistance is substantially zero. Since the permanent current switch 2 is generally formed as a non-inductive winding in order to avoid generating an unnecessary static magnetic field component, the inductance of the permanent current switch 2 is approximately zero. The permanent current switch 2 is composed of a superconductor. However, the power is supplied from the heater power supply 11 to the heater 10 for the permanent current switch, so that the permanent current switch 2 is heated to a temperature higher than the superconducting critical temperature and has a DC resistance of about several Ω. are doing.

Normal load current 1 supplied from excitation power supply 8
2 is 0 at a slow rise rate of about 0.1 A / sec.
After passing through the inductance (resistance) element 16, most of the current flows through the superconducting coil group 1 to generate a predetermined static magnetic field in a predetermined space. The inductance (resistance) element 16 has a conduction capacity of several hundred amperes and allows a voltage drop of only a few volts in order to flow a normal load current 12 of several hundred amperes. Therefore, it becomes a small element using a cable having a small sectional area. On the other hand, for the harmonic noise current 15 generated by the excitation power supply 8, the superconducting coil group 1 has a high impedance proportional to the product of the inductance of the coil group 1 and the frequency. As a result, as shown in the figure, most of the noise current 15 flows through the permanent current switch 2 after passing through the inductance (resistance) element 16. As described above, during excitation until the normal load current 12 supplied from the excitation power supply 8 reaches the rated current, the noise current 15 returns to the excitation power supply 8, the inductance (resistance) element 16 and the permanent current switch 2 to return the permanent current. It is reduced by the impedance of the sum of the resistance of the switch 2 and the inductance (resistance) element 16.

After the normal load current 12 reaches the rating, the operation is switched to the permanent current mode operation. Specifically, first, the heater power supply 11 for the permanent current switch is turned off to stop heating the permanent current switch 2, and the permanent current switch 2 is made superconductive. When the permanent current switch 2 is turned into a superconducting state by reducing its resistance value by stopping heating, the impedance of the inductance (resistance) element 16 remains, thereby limiting the noise current 15. For this reason, an increase in the noise current 15 due to the reduction in the resistance of the permanent current switch 2 and the resulting heat generation are suppressed, and the superconducting transition of the permanent current switch 2 is ensured. Thereafter, when the energizing current of the exciting power supply 8 is reduced from the rated value, the normal load current 12 flowing through the superconducting coil group 1 gradually returns to the permanent current switch 2 and the energizing current of the exciting power supply 8 becomes zero. When the ampere is reached, all of the normal load current 12 returns to the permanent current switch 2, and the transition to the permanent current mode operation is completed. Even if the excitation power supply 8 is disconnected from the magnet device, the permanent current mode operation is continued (see FIG. 8B).

In the first embodiment, the superconducting coil group 1 connected in parallel to the excitation power supply 8 and the current lead 5 located between the branch point 5a of the permanent current switch 2 and the current introducing terminal 9 Since the inductance (resistance) element 16 is inserted, the noise current 15
Can be effectively reduced not only at a high frequency but also over a wide range of frequency noise, and the heat generation of the permanent current switch 2 can be suppressed, the superconducting transition can be quickly performed, and the operation can be reliably shifted to the permanent current mode operation. At the time of the operation in the permanent current mode, the normal load current 12 flows through the superconducting coil group 1 and the permanent current switch 2, so that no current flows through the inductance (resistance) element 16 and an unnecessary error magnetic field is generated. It does not occur. Therefore, even if a commercially available inexpensive and simple type, such as a switching type, is used for the excitation power supply 8, the superconducting transition of the permanent current switch due to the noise current does not occur, and a highly reliable superconducting magnet device. Is obtained.

The inductance (resistance) element 16
Is inductance, such as superconducting coil and copper wire coil.
The effect described above can be obtained if the element is made of one or both of the resistors. However, when a superconducting coil, that is, a zero-resistance inductance element using a superconducting wire is used, the inductance value can be easily increased and the noise current can be reduced. , And the voltage drop due to the normal load current 12 becomes almost negligible.
This is particularly effective because it is not necessary to change or improve specifications at all.

Embodiment 2 FIG. In the first embodiment, the cooling container 4 also serving as the liquid helium tank is used. However, a superconducting magnet device using a conduction cooling method using a refrigerator will be described with reference to FIG. The conduction cooling method is generally adopted in a superconducting magnet apparatus for a silicon single crystal pulling apparatus in order to make the magnet compact and reduce the running cost (partly employed in a superconducting magnet apparatus for an MRI). As shown in FIG.
In comparison with the above, there is no cooling vessel 4 and the heat shield tank 7
a is simplified to a single layer, and a refrigeration unit 17 and a heat conduction plate 18 attached to the refrigerator stage 17a are newly installed as alternative cooling means. The superconducting coil group 1, the permanent current switch 2, the inductance (resistance) element 16, and the current lead 5 connecting these via the heat conducting plate 18 exhibit superconducting phenomena in the vacuum insulated container 6a serving as a container. Cool to temperature.

The behaviors of the normal load current 12 and the noise current 15 during excitation and when switching to the permanent current mode operation are the same as those in the first embodiment. Because of the insertion, the noise current 15 generated by the excitation power supply 8 can be effectively reduced not only for high frequency but also for a wide range of frequency noise. The transition can be made reliably. At the time of the operation in the permanent current mode,
No current flows through the inductance (resistance) element 16 at all, and no unnecessary static magnetic field (error magnetic field) is generated.

Embodiment 3 A circuit in which the simulation circuit shown in the first embodiment is actually constituted by a superconducting magnet device is shown below. FIG. 3A schematically shows a cross-sectional structure of an MRI superconducting magnet device according to Embodiment 3 of the present invention, and FIG. 3B is a partially enlarged view thereof. The superconducting magnet device for MRI is a medical examination device, and a uniform magnetic field region 19 is formed by generating a high-intensity, high-uniformity and time-stable magnetic field in a predetermined region by the superconducting coil group 1. The patient is inserted into the cylindrical space in the center of the apparatus together with the bed, and examines the affected part.

As shown in FIG. 3A, the superconducting coil group 1 includes six superconducting coils 1a coaxially arranged with substantially the same diameter, and two superconducting coils 1a having a diameter larger than these six coils 1a. It consists of a coil 1b. A permanent current switch 2 having a built-in heater 10, a protection element 3 at the time of quench, and a small coil 16 as an inductance (resistance) element 16.
a is located at the outermost periphery where the magnetic field strength is weak, and is disposed below the liquid helium liquid surface 4a and below the cooling vessel 4 so as to be always immersed in the liquid helium. ) Are connected in series or in parallel. The cooling container 4 accommodates the above-mentioned circuit components and keeps it at a very low temperature, and also serves as a liquid helium storage tank. The vacuum heat insulating container 6 accommodates the cooling container 4 via a heat shield tank (two tanks) 7 and suppresses evaporation of expensive liquid helium by heat insulation. The current introduction terminal section 9 is connected to the cooling vessel 4
And connected to an excitation power supply 8 (both not shown) via a power cable.

As shown in a partially enlarged view of FIG. 3B, an inductance (resistance) element 16 is constituted by a small coil 16a in which a copper wire or a superconducting wire is wound on a small independent element winding frame 20. Then, it is fixed to the superconducting magnet device via the fixing bracket 21. As described in the first embodiment, the small coil 16a reduces the noise current 15 at the time of excitation and at the time of switching to the permanent current mode operation. An unnecessary error magnetic field is not generated at 19. In addition, since it is wound independently on the element winding frame 20, the degree of freedom in installation is large.

The element winding frame 20 of the small coil 16a
Alternatively, a magnetic body may be used, or a magnetic body inserted inside the element winding frame 20 may be used, a desired inductance can be secured with a small number of turns, and downsizing can be achieved.

Embodiment 4 FIG. FIG. 4A schematically shows a cross-sectional structure of an MRI superconducting magnet device according to a fourth embodiment of the present invention, and FIG. 4B is a partially enlarged view thereof. Here, the inductance (resistance) element 1 is formed by a coil 16b wound around the outer periphery of the permanent current switch 2.
6 is constituted. As shown in the partial enlarged view of FIG.
The permanent current switch 2 is non-inductively wound around a permanent current switch winding frame 2a via a permanent current switch heater 10.
Further, a coil 16b in which a copper wire or a superconducting wire is wound around the outer periphery thereof via a spacer 22 is arranged, and the coil 16b is fixed to the superconducting magnet device via a fixing bracket 21. In this embodiment,
Permanent current switch 2 heated to normal conduction state when excited
Heat from the coil 16b is insulated by the spacer 22.
Keep cool. The spacer 22 may be provided with a groove and cooled with liquid helium.

Also in this case, the installation of the coil 16b reduces the noise current 15 at the time of excitation and at the time of switching to the permanent current mode operation, and no current flows during the permanent current mode operation. Does not generate an error magnetic field. Further, since an independent winding frame is not required, the structure can be simplified.

Embodiment 5 Note that the inductance (resistance) element 16 may be wound as a single element around the outer periphery of the coil or the winding frame of the superconducting coil group 1 and has a simple configuration, which is similar to that of the third and fourth embodiments. Similarly, noise current 1 at the time of excitation and at the time of switching to the permanent current mode operation is generated without generating an unnecessary error magnetic field during the permanent current mode operation.
5 can be obtained. In this configuration, the inductance (resistance) element 16 is further divided into two as shown in FIG. 5, and the coil 16c of each divided piece is made uniform by winding around the winding frame (or the outer peripheral portion of the coil) of the superconducting coil group 1. At a symmetrical position as far away from the magnetic field region 19 as possible,
For example, they may be arranged such that the magnetomotive forces are opposite to each other by, for example, reversing the winding directions. in this case,
Even during excitation, unnecessary error magnetic fields created in the uniform magnetic field region 19 can be canceled out and reduced, so that reliability is improved.

Embodiment 6 FIG. By the way, for MRI and NM
In the superconducting magnet device for R, the number of coils of the superconducting coil group 1, the coil arrangement, the magnetomotive force of each coil, and the like are determined based on a strict design so as to generate a highly uniform magnetic field in the uniform magnetic field region 19. However, due to dimensional errors in various manufacturing processes, the actually completed superconducting magnet device has a slightly inhomogeneous magnetic field component. In order to compensate for the non-uniform magnetic field component, a coil group called a current shim coil is arranged, and a current corresponding to the non-uniform magnetic field component is supplied to each current shim coil to generate a static magnetic field, thereby generating the non-uniform magnetic field component. There are ways to offset.

FIG. 6 is a block diagram showing an M-type transmission system according to a sixth embodiment of the present invention.
6A shows a superconducting magnet device for RI, FIG. 6A is a simulated circuit diagram showing a state during excitation, and FIG. 6B is a cross-sectional view schematically showing the structure of the device. As shown in FIG. 6A, both ends of each coil are connected to a permanent current switch 2 for a current shim coil.
3, a current shim coil 24 forming a closed circuit
Is disposed on the current lead 5 located between the current introducing terminal 9 and the branch point 5a of the superconducting coil group 1 and the permanent current switch 2 connected in parallel to the excitation power supply 8, Inductance (resistance) element 1
6 also works. Each current shim coil 24 is also a circuit element through which the normal load current 12 flows, and is connected to the current shim coil excitation power supply 25 as a single element in parallel with the current shim coil permanent current switch 23. The permanent current switch 23 for the current shim coil is a heater 27 for the permanent current switch provided with a heater power supply 26 for the permanent current switch.
Is heated.

Specifically, as shown in FIG. 6B, a plurality of such current shim coils 24 are wound on the same winding frame as the superconducting coil group 1 or on the outer periphery of the superconducting coils 1a and 1b. Are arranged as coils. Hereinafter, the operation of the superconducting magnet device including the current shim coil 24 will be described. First, when the superconducting coil group 1 is excited, the excitation power supply 25 for the current shim coil is cut off, and the heater power supply 26 for the permanent current switch of the current shim coil 24 is turned off.
To the heater 27 for the permanent current switch of each current shim coil 24 from the permanent current switch 2 for the current shim coil.
3 is kept in a normal conducting state by heating. At this time,
The current shim coil 24 operates only as an inductance element for reducing the noise current 15. Normal load current 12
After reaching the rating, the superconducting coil group 1 is switched to the permanent current mode operation. When the heating of the permanent current switch 2 is stopped and the permanent current switch 2 is made superconductive, the noise current 15
And the heat generated thereby is suppressed, and the superconducting transition of the permanent current switch 2 is ensured.

Thereafter, when the energizing current of the excitation power supply 8 is reduced to 0 amperes, all the normal load current 12 returns to the permanent current switch 2, and the transition to the permanent current mode operation is completed. Disconnect from When the superconducting coil group 1 achieves the permanent current mode operation, a non-uniform magnetic field component is determined from the measurement of the magnetic field in the uniform magnetic field region 19, and a current value to be supplied to each current shim coil 24 to compensate for the non-uniform magnetic field component. After this compensation current value is supplied to each current shim coil 24 by the excitation power supply 25, the heater power supply 26 for the permanent current switch of the current shim coil 24 is turned off, and the permanent current switch 23 of the current shim coil 24 is shifted from the normal conduction state to the superconducting state. Then, each current shim coil 24 is set to the permanent current mode operation. The non-uniform magnetic field component is canceled by the static magnetic field generated by the current shim coil 24, and a highly uniform magnetic field region can be formed with high reliability.

In this embodiment, the current shim coil 24 for correcting the uniform magnetic field distribution is used as an inductance element for reducing the noise current 15 at the time of excitation and at the time of switching to the permanent current mode operation. A superconducting magnet device with further improved reliability can be obtained.

Embodiment 7 In the sixth embodiment, the case where the current shim coil 24 also functions as the inductance (resistance) element 16 in the first embodiment has been described, but the coil group for compensating the disturbance magnetic field functions as the inductance (resistance) element 16. The case where they are also used is shown below. MRI
In the superconducting magnet device for use, during the examination of a patient in a hospital, for example, the disturbance of the magnetic field of the uniform magnetic field region 19 due to the movement of the elevator in the hospital or the magnetic disturbance caused by a train or a car running near the hospital. Therefore, there is a method of canceling the disturbance magnetic field component by disposing a disturbance magnetic field compensation coil group and generating a static magnetic field.

FIG. 7 is a block diagram showing an embodiment 7 of the present invention.
7A and 7B show a superconducting magnet device for RI, FIG. 7A is a simulated circuit diagram showing a state during excitation, and FIG. 7B is a cross-sectional view schematically showing the structure of the device. As shown in FIG. 7A, a disturbance magnetic field compensation coil 29 having both ends connected to a disturbance magnetic field compensation coil permanent current switch 28 to form a closed circuit is connected in parallel to the excitation power supply 8. The superconducting coil group 1 and the current lead 5 located between the branch point 5a of the permanent current switch 2 and the current introduction terminal 9 and the inductance (resistance) according to the first embodiment.
Also serves as element 16. Further, the permanent current switch 28 for the disturbance magnetic field compensating coil is heated by a permanent current switch heater 31 provided with a permanent current switch heater power supply 30. Since the disturbance magnetic field compensation coil 29 does not have a current flow like the current shim coil 24 shown in FIG. 6, there is no current introduction from the excitation power supply.

As shown in FIG. 7B, such a disturbance magnetic field compensation coil 29 is wound on the same winding frame as the superconducting coil group 1 or on the outer periphery of the superconducting coils 1a and 1b. It is arranged as a plurality of coils. Hereinafter, the operation of the superconducting magnet device including the disturbance magnetic field compensation coil 29 will be described. First, when the superconducting coil group 1 is excited, a current is supplied from the permanent current switch heater power supply 30 of the disturbance magnetic field compensation coil 29 to the permanent current switch heater 31 of each disturbance magnetic field compensation coil 29, and the permanent magnetic field compensation coil The current switch 28 is kept in a normal conduction state by heating. At this time, the disturbance magnetic field compensation coil 29 operates only as an inductance element for reducing the noise current 15. After the regular load current 12 reaches the rating, the superconducting coil group 1 is switched to the permanent current mode operation. The heating of the permanent current switch 2 is stopped, and the permanent current switch 2 is turned off.
When superconducting is made, the increase of the noise current 15 and the heat generation due to the noise current 15 are suppressed by the inductance of the disturbance magnetic field compensation coil 29, and the superconducting transition of the permanent current switch 2 is ensured.

Thereafter, when the current supplied to the excitation power supply 8 is reduced to 0 amperes, all of the normal load current 12 returns to the permanent current switch 2, and the transition to the permanent current mode operation is completed. Disconnect from When the persistent current mode operation of the superconducting coil group 1 is achieved, the heater power supply 30 for the permanent current switch of the disturbance magnetic field compensation coil 29 is turned off, and the permanent current switch 28 of the disturbance magnetic field compensation coil 29 is changed from the normal conduction state to the superconducting state. Transfer to In this state, when the above-mentioned magnetic disturbance occurs, a compensation current corresponding to the disturbance magnetic field flows through the disturbance magnetic field compensation coil 29 by electromagnetic induction, and the disturbance of the magnetic field inside the uniform magnetic field region 19 is compensated.

In this embodiment, the disturbance magnetic field compensation coil 29 for compensating a disturbance magnetic field that enters from the outside is provided with a noise current 15 at the time of excitation and at the time of switching to the permanent current mode operation.
As a result, the superconducting magnet device having a further improved reliability can be obtained while simplifying the device configuration.

Although the superconducting magnet device for MRI has been described in the third to seventh embodiments, the present invention is not limited to this and can be widely applied to a superconducting magnet operated in a permanent current mode.

[0046]

As described above, the superconducting magnet device according to claim 1 of the present invention comprises a superconducting coil for generating a magnetic field in a target space, a permanent current switch, a superconducting current lead,
A housing for housing the superconducting coil, the permanent current switch and the current lead, provided with cooling means for cooling to a temperature at which a superconducting phenomenon occurs, and an excitation power supply arranged outside the housing, The superconducting coil and the permanent current switch are connected in parallel by way of the current lead via a branch point, and after excitation is performed by supplying current to the superconducting coil from the excitation power source, the superconducting coil and the permanent current switch are connected. An apparatus configuration for circulating current to a closed circuit formed by a current switch, wherein one or both of an inductance and a resistance are provided at a position between the branch point and the excitation power supply in the current lead in the housing container. Since the device is composed of an element consisting of Transition to persistent current mode operation can be performed reliably, the superconducting magnet apparatus having high reliability can be obtained.

In the superconducting magnet device according to a second aspect of the present invention, since the element arranged on the current lead in the container is an inductance element using a superconducting wire in the first aspect, noise current can be easily reduced. And the reliability can be further improved.

According to a third aspect of the present invention, there is provided a superconducting magnet device according to the first or second aspect, wherein the element disposed on the current lead in the housing is provided on a winding frame different from the winding frame of the superconducting coil. Since the coils are wound independently, the degree of freedom in installing the above elements is large, and a highly reliable superconducting magnet device with reduced noise current can be obtained easily and reliably.

The superconducting magnet device according to a fourth aspect of the present invention is the superconducting magnet device according to the third aspect, wherein the element disposed on the current lead in the housing container has a winding frame made of a magnetic material or a magnetic material inside the winding frame. , The size of the element can be reduced, and a highly reliable superconducting magnet device with reduced noise current can be easily and reliably obtained.

According to a fifth aspect of the present invention, there is provided a superconducting magnet apparatus according to the first or second aspect, wherein the element disposed on the current lead in the container is wound around the outer periphery of the permanent current switch. Since the coil is integrated with the current switch, the element configuration is simplified, and a highly reliable superconducting magnet device with reduced noise current can be easily and reliably obtained.

According to a sixth aspect of the present invention, there is provided a superconducting magnet device according to the first or second aspect, wherein the element disposed on the current lead in the container is wound around the outer peripheral portion of the superconducting coil or the bobbin. Since the coil is a coil, a highly reliable superconducting magnet device with reduced noise current can be easily and reliably obtained.

According to a seventh aspect of the present invention, in the superconducting magnet apparatus according to the sixth aspect, the superconducting coil is constituted by a plurality of coils forming a uniform magnetic field region in a target space, and is arranged on a current lead in the container. The elements provided are divided and arranged at symmetrical positions separated by a predetermined distance from the uniform magnetic field region so that the magnetomotive forces are in opposite directions. This can be reduced not only during operation but also during excitation, and the reliability of the superconducting magnet device is further improved. In addition, since the element arranged on the current lead in the container is a current shim coil whose both ends are connected to the second permanent current switch to form a closed circuit and correct the uniform magnetic field distribution, an excitation power supply is generated. A highly reliable superconducting magnet device that can reduce the noise current that occurs, reliably transition to the persistent current mode operation due to the superconducting transition of the persistent current switch, and can form a highly uniform magnetic field region, has a simplified device configuration. Is obtained. In addition, since the element disposed on the current lead in the container is connected to the third permanent current switch at both ends thereof to form a closed circuit, and is a disturbance magnetic field compensation coil for compensating a disturbance magnetic field that enters from the outside, High reliability that reduces the noise current generated by the excitation power supply, ensures the transition to the permanent current mode operation due to the superconducting transition of the permanent current switch, and prevents the adverse influence from the outside to form a stable uniform magnetic field region. A superconducting magnet device is obtained with a simplified device configuration.

[Brief description of the drawings]

FIG. 1 is a schematic circuit diagram of a superconducting magnet device according to Embodiment 1 of the present invention.

FIG. 2 is a schematic circuit diagram of a superconducting magnet device according to a second embodiment of the present invention.

FIG. 3 is a sectional view showing a structure of a superconducting magnet device according to Embodiment 3 of the present invention.

FIG. 4 is a sectional view showing a structure of a superconducting magnet device according to Embodiment 4 of the present invention.

FIG. 5 is a sectional view showing a structure of a superconducting magnet device according to a fifth embodiment of the present invention.

FIG. 6 is a schematic circuit diagram and a sectional structure diagram of a superconducting magnet device according to Embodiment 6 of the present invention.

FIG. 7 is a schematic circuit diagram and a sectional structure diagram of a superconducting magnet device according to Embodiment 7 of the present invention.

FIG. 8 is a simulation circuit diagram of a conventional superconducting magnet device.

FIG. 9 is a simulation circuit diagram of a conventional superconducting magnet device.

[Explanation of symbols]

1 superconducting coil group, 1a, 1b superconducting coil, 2
4 permanent current switch, 4 cooling vessel as a storage vessel provided with cooling means, 5 current lead, 5a branch point, 6a
Vacuum insulated container as storage container, 8 excitation power supply, 16
Inductance (resistance) element, 16a Small coil as inductance (resistance) element, 16b Coil as inductance (resistance) element, 16c Coil as inductance (resistance) element, 17 Refrigeration device as cooling means, 18 as cooling means Heat conduction plate, 19
Uniform magnetic field area, 20 element winding frame, 23 permanent current switch for current shim coil, 24 current shim coil, 28
Permanent current switch for disturbance magnetic field compensation coil, 29 disturbance magnetic field compensation coil.

Claims (7)

[Claims] 1. A superconducting coil for generating a magnetic field in a target space, a permanent current switch, a superconducting current lead, and cooling means for cooling to a temperature at which superconductivity occurs. A housing for accommodating the current lead, and an excitation power supply arranged outside the housing, wherein the superconducting coil and the permanent current switch are arranged in parallel with the excitation power supply via a branch point by the current lead. A superconducting magnet device that is connected to the superconducting coil and is energized by supplying current to the superconducting coil from the excitation power source, and then circulates a current to a closed circuit formed by the superconducting coil and the permanent current switch. At a position between the branch point and the excitation power supply in the current lead, the element consisting of one or both of an inductance and a resistance is provided. A superconducting magnet device characterized by having a sub-element. 2. The superconducting magnet device according to claim 1, wherein the element disposed on the current lead in the container is an inductance element using a superconducting wire. 3. An element disposed on a current lead in a container is a coil independently wound on a winding frame different from a winding frame of a superconducting coil. The superconducting magnet device as described. 4. The superconducting device according to claim 3, wherein the element disposed on the current lead in the container is a coil in which the bobbin is made of a magnetic material or a magnetic body is inserted inside the bobbin. Magnet device. 5. An element arranged on a current lead in a storage container is a coil wound around an outer periphery of a permanent current switch and integrated with the permanent current switch. 3. The superconducting magnet device according to 2. 6. The superconducting magnet device according to claim 1, wherein the element arranged on the current lead in the container is a coil wound around an outer peripheral portion of the superconducting coil or a bobbin. 7. A superconducting coil is constituted by a plurality of coils forming a uniform magnetic field region in a target space, and an element disposed on a current lead in the container is separated from the uniform magnetic field region by a predetermined distance. A current shim coil which is divided and arranged at symmetrical positions so that magnetomotive forces are opposite to each other, or whose both ends are connected to a second permanent current switch to form a closed circuit and correct the uniform magnetic field distribution. 7. A superconducting magnet device according to claim 6, wherein said both ends are connected to a third permanent current switch to form a closed circuit, and a disturbance magnetic field compensating coil for compensating a disturbance magnetic field intruding from the outside. .