JP3117173B2 - Superconducting magnet device with refrigerator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting magnet apparatus with a refrigerator, and more particularly, to a superconducting magnet apparatus having at least two stages, and cooling the refrigerator stage with a refrigerator to drive a superconducting coil in a permanent current mode. The present invention relates to a superconducting magnet device with a refrigerator.

[0002]

2. Description of the Related Art Known permanent current mode operation superconducting magnet devices used in a magnetic resonance apparatus (MRI), a magnetic levitation train, and the like generally include a superconducting magnet that generates a steady magnetic field and a permanent current flowing through the superconducting magnet. NbTi to flow through the, Nb ₃ a superconducting wire made of a material such as Sn, by filling in liquid helium which functions as a refrigerant cooled to a predetermined low temperature, the persistent current mode based on the cooling conditions It is necessary to use liquid helium as the refrigerant.

[0003] On the other hand, a superconducting magnet device that operates by using only the cooling function of a refrigerator without using liquid helium as a refrigerant is also described in, for example, "The 48th Autumn Meeting of 1992 Autumn Conference on Low Temperature Engineering and Superconductivity," 299 pages to 3rd
It is known as described on page 01. And, this known superconducting magnet device, without using a permanent current switch, in order to allow current to flow through the superconducting magnet and this superconducting magnet, cooling to a predetermined low temperature by the cooling function of the refrigerator, The operation is performed based on the cooling state.

[0004]

The known superconducting magnet device of the permanent current mode operation using liquid helium as a refrigerant is inevitably provided in a vacuum vessel containing a superconducting magnet, a superconducting wire and the like. Since an operation such as injection of liquid helium as a refrigerant is required, a work process for cooling the superconducting magnet, the superconducting wire, and the like becomes complicated. There is a problem that it is difficult for a novice to perform an operation of generating a constant magnetic field including a work process for the operation.

On the other hand, the known superconducting magnet device operating in the persistent current mode, which is operated only by the cooling function of the refrigerator, does not use liquid helium, so that the work process for cooling the superconducting magnet and the superconducting wire is complicated. Although it is not required to be skilled in this work process, since a permanent current switch is not used, always connect a superconducting magnet or superconducting wire with a drive power supply,
It is necessary to energize them, and the maximum value of the generated magnetic field or energizing current in steady operation depends on the amount of heat inflow from the current lead made of copper or the like that constitutes the energizing circuit to the high-temperature refrigeration stage, There is a problem that it is limited by the relationship with the refrigerating capacity of the high-temperature side refrigerating stage of the machine.

However, the maximum value of the generated magnetic field or the energizing current in the steady operation is determined by using a permanent current switch.
If the current lead is not always energized, but is energized only at the start of the permanent current mode operation, the limitation can be eased for the time being, but the known superconducting magnet that works by the cooling function of only the refrigerator. The device does not disclose the use of such a permanent current switch, nor does it disclose the location of the permanent current switch.

Incidentally, Japanese Patent Application Laid-Open No. 55-150513 discloses a means for providing a permanent current switch having fixed and movable electrodes, and for mechanically moving the movable electrode by pressurizing and discharging a working medium such as liquid helium gas. However, if the permanent current switch is operated near 4.2 K, which is the boiling point of 1 atm of liquid helium, a liquefied state occurs when helium gas is injected, which causes a problem in operation.

An object of the present invention is to eliminate the above-mentioned problems, and an object of the present invention is to perform cooling by a refrigerator without using liquid helium as a refrigerant, to improve workability and operational stability, and to reduce power consumption. It is an object of the present invention to provide a superconducting magnet device with a refrigerator in a permanent current mode operation for reducing the amount of power consumption.

[0009]

In order to achieve the above object, the present invention has a refrigerator having two refrigerating stages, the refrigerating stages being cooled by a refrigerating machine, and a superconducting coil being driven in a permanent current mode. In the attached superconducting magnet device, a permanent current switch made of a superconducting material having a critical temperature higher than the operating temperature of the high-temperature refrigeration stage is arranged on the high-temperature refrigeration stage.
A superconducting coil made of a superconducting material having a critical temperature higher than the operating temperature of the low-temperature refrigeration stage is disposed, and a critical temperature higher than the operating temperature of the high-temperature refrigeration stage is provided between the permanent current switch and the superconducting coil. Means for arranging a current lead made of a superconducting material having a high level.

In order to achieve the above object, the present invention provides a superconducting magnet with a refrigerator having at least three refrigeration stages, wherein the refrigeration stages are cooled by the refrigerator and a superconducting coil is driven in a permanent current mode. In the apparatus, a superconducting coil or a permanent current switch made of a superconducting material having a critical temperature higher than the operating temperature of the refrigeration stage is arranged in each refrigeration stage, and the operation of the high-temperature refrigeration stage is provided between adjacent refrigeration stages. A second means provided with a current lead made of a superconducting material having a critical temperature higher than the temperature;

[0011]

According to the first means, in the superconducting magnet device having two stages of refrigeration stages and operating in the permanent current mode, the high-temperature side refrigeration stage has a temperature higher than the operating temperature of the high-temperature side refrigeration stage. High superconducting material, for example, a permanent current switch made of an oxide superconductor or the like is arranged, and between the permanent current switch and the superconducting coil, a superconducting material whose critical temperature is higher than the operating temperature of the high-temperature side refrigeration stage, for example, And a current lead made of an oxide superconductor or the like.

[0012] For this reason, the time stability of the constant magnetic field generated by the superconducting coil can be improved by installing the permanent current switch during the operation in the permanent current mode in the superconducting magnet device with the refrigerator, and the amount of power during operation Can be reduced.

The operating temperature of the permanent current switch is higher than that of a permanent current switch using an NbTi or Nb ₃ Sn superconducting wire which is used based on a known cooling temperature of liquid helium, and the heat capacity is larger. As a result, the temperature of the permanent current switch hardly rises when the same energy is applied, so that it is hard to be quenched by the application of disturbance such as mechanical vibration.

Further, when the permanent current switch is turned off to excite the superconducting magnet through the superconducting current lead, the voltage at the time of excitation is applied to both ends of the permanent current switch, and Joule heat is generated. If a permanent current switch is installed on the high-temperature side refrigeration stage, compared with the case where a permanent current switch is installed on the low-temperature side refrigeration stage, the refrigeration capacity of the high-temperature side refrigeration stage is higher, so cooling of the Joule heat is reduced. It is much easier to do.

In addition, since the superconducting coil is installed on the low-temperature side refrigeration stage and the permanent current switch is installed on the high-temperature side refrigeration stage, the leakage magnetic field of the superconducting coil is permanent. The influence on the current switch can be reduced, and a material whose critical current decreases when a magnetic field is applied can be used for the permanent current switch, and the range of material selection can be widened.

Next, according to the second means, in a superconducting magnet device having three or more refrigerating stages and operating in a persistent current mode, each refrigerating stage is more critical than the operating temperature of the refrigerating stage. A superconducting coil or permanent current switch made of superconducting material with high temperature is arranged,
Current leads made of a superconducting material having a critical temperature higher than the operating temperature of the high-temperature side refrigeration stage are arranged between adjacent refrigeration stages.

Therefore, the effect obtained by the first means can be obtained in a superconducting magnet device having three or more refrigerating stages.

In both of the first and second means, after the current lead disposed between the room temperature part and the high-temperature side refrigeration stage is set to the permanent current mode operation, the operation of the high-temperature side refrigeration stage is started. With a detachable type that can be detached at the mounting portion or in the middle, it is possible to reduce a temperature rise due to heat flowing into the high-temperature side refrigeration stage through the current lead. If the mounting portion of the refrigeration stage is formed of an object having a large heat capacity, such as a copper block, the temperature rise due to the heat flowing into the high-temperature refrigeration stage through the current lead can be further suppressed.

[0019]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view showing the structure of a first embodiment of a superconducting magnet device with a refrigerator according to the present invention.

In FIG. 1, 1 is a GM refrigerator, 2 is a high-temperature refrigeration stage, 3 is a low-temperature refrigeration stage, 4 is a superconducting coil, 5 is a superconducting current lead, 6 is a permanent current switch, 7 is a current lead, 8 Is a mounting part, 9 is a heat shield plate,
10 is a vacuum vessel, 11 is a Wilson seal, and 12 is a compressor.

The GM refrigerator 1 is mounted outside the vacuum vessel 10 and connected to the compressor 12. G
The refrigeration output of the M refrigerator 1 is configured to cool the high-temperature side refrigeration stage 2 and the low-temperature side refrigeration stage 3 disposed in the vacuum vessel 10, and no liquid helium is inserted into the vacuum vessel 10. It is. The superconducting coil 4
It is made of NbTi and is arranged so as to be electrically insulated from the low-temperature refrigeration stage 3 and to make good thermal contact. The permanent current switch 6 is made of a Tl-1223 oxide superconductor, is electrically insulated from the high-temperature side refrigeration stage 2, and is disposed so as to be in good thermal contact. The superconducting current lead 5 is formed by soldering copper electrodes to both ends of a bulk material of the Bi-2223 oxide superconductor, one end of which is soldered to the electrode of the superconducting coil 4 and the other end of which is a permanent current switch. 6 is soldered to the electrodes. In this case, one end is electrically insulated from the low-temperature refrigeration stage 3 and is mechanically firmly fixed to the low-temperature refrigeration stage 3 so as to make good thermal contact. Although it is electrically insulated from the high-temperature side refrigeration stage 2 and is in thermal contact with the refrigeration stage 2 as much as possible, the high-temperature side refrigeration stage 2 is mechanically The structure is not fixed firmly.

A current lead 7 having normal conduction characteristics is connected between the room temperature portion outside the vacuum vessel 10 and the high-temperature side refrigeration stage 2, and is attached to the high-temperature side refrigeration stage 2 side of the current lead 7. A part 8 is provided, and this part is detachable. The mounting portion 8 is made of an object having a high thermal conductivity and a large heat capacity, for example, a block made of copper or the like, so that the temperature of the mounting portion 8 does not easily rise when the current lead 7 is energized. In order to prevent the degree of vacuum of the vacuum vessel 10 from being lowered when the current lead 7 is pulled out from the mounting portion 8, the mounting jig for the flange portion of the current lead 7 is a Wilson seal 11 provided with an O-ring. It consists of.

Further, the superconducting coil 4 is covered with a copper block (not shown), and is configured to quickly reach the refrigeration temperature of the low-temperature refrigeration stage 3 by the fixed conduction of the copper block. The heat shield plate 9 is attached to the high-temperature refrigeration stage 2 and covers the low-temperature refrigeration stage 3, the superconducting coil 4, the superconducting current lead 5, and the permanent current switch 6, respectively, so as to minimize the amount of heat penetration. The inside of the vacuum vessel 10 is kept in a vacuum during operation.

FIG. 2 is a circuit diagram showing an electric circuit according to the first embodiment.

In FIG. 2, 6h is a heater winding, 13 is an excitation power source, 14 is a switch, and other components that are the same as those shown in FIG.

The output of the excitation power supply 13 is supplied to the permanent current switch 6 arranged on the high-temperature refrigeration stage 2 via the current lead 7, and at the same time, the low-temperature refrigeration stage 3 is supplied via the superconducting current lead 5. Is supplied to the superconducting coil 4 arranged in the first position. The heater winding 6h switches the permanent current switch 6 between the superconducting state and the normal conducting state. When the heater winding 6h is not driven, the permanent current switch 6 is switched to the superconducting state. When the line 6h is driven, the permanent current switch 6 is switched to the normal conduction state.

Here, the operation in the first embodiment, that is, its operation procedure will be described as follows.

First, a vacuum exhaust device is attached to the vacuum vessel 10, and the inside of the vacuum vessel 10 is evacuated. Next, when the evacuation is completed, the GM refrigerator 1 is operated to cool the high-temperature refrigeration stage 2 and the low-temperature refrigeration stage 3. During this cooling, the temperature of each part such as the high-temperature side refrigeration stage 2, the low-temperature side refrigeration stage 3, the superconducting coil 4, the current lead 5, the permanent current switch 6, etc. was monitored, and each part was cooled to a predetermined temperature. Make sure that When the completion of cooling of each part is confirmed, the heater winding 6h is driven to turn off the permanent current switch 6. Subsequently, the switch 14 is turned on to supply the output of the exciting power supply 13 to the superconducting coil 4, and when the exciting current flowing through the superconducting coil 4 reaches a predetermined current value, the current value is held. Next, the heater winding 6h is deactivated, and the permanent current switch 6 is turned off.
Is turned on. Next, the output current value of the excitation power supply 13 is reduced from the predetermined current value to zero. Here, when it is confirmed that the output current value of the excitation power supply 13 has become zero, the current lead 7 is pulled out from the mounting portion 8.

Through the above procedure, the superconducting magnet device with a refrigerator cools the high-temperature side refrigerating stage 2 and the low-temperature side refrigerating stage 3 only by the refrigerating capacity based on the operating power of the GM refrigerator 1. Thereby, superconducting coil 4 can be maintained in the permanent current mode.

In this case, the permanent current switch 6 is set to Tl−
In the case of using the 1223 oxide superconductor, it is possible to increase the steady-state conduction current as compared with the case where the permanent current switch 6 is not used.

FIG. 3 is a sectional view showing the construction of a second embodiment of the superconducting magnet device with a refrigerator according to the present invention, and shows an example having three stages of refrigeration stages. is there.

In FIG. 3, reference numeral 15 denotes a lowest-temperature side refrigeration stage, and other components that are the same as those shown in FIG.

In the second embodiment, the lowest-temperature side refrigeration stage 15 is separately disposed inside the superconducting coil 4 disposed on the low-temperature-side refrigeration stage 3. A small superconducting coil 4 which is electrically insulated and arranged in good thermal contact
Is disposed on the lowest-temperature refrigeration stage 15. In this case, the small superconducting coil 4 having a high applied magnetic field on the inner side is cooled by the lowest temperature freezing stage 15, and the outer superconducting coil 4 on the outside thereof is cooled by the low temperature side freezing stage 3.

FIG. 4 is a circuit diagram showing an electric circuit according to the second embodiment.

In FIG. 4, the same components as those shown in FIG. 3 are denoted by the same reference numerals.

The superconducting coil 4 arranged on the low-temperature refrigeration stage 3 and the superconducting coil 4 arranged on the lowest-temperature refrigeration stage 15 are connected in series via a superconducting current lead 5, and here, too, are excited. The output of the power supply 13 is supplied to the permanent current switch 6 disposed on the high-temperature refrigeration stage 2 via the current lead 7 and is disposed on the low-temperature refrigeration stage 3 connected in series via the superconducting current lead 5. The supplied superconducting coil 4 and the superconducting coil 4 arranged on the lowest temperature refrigeration stage 15 are both supplied.

The operation of the second embodiment having the above-described configuration is essentially the same as the operation of the second embodiment. Therefore, the operation of the second embodiment will be described. Omitted.

Next, FIG. 5 is a circuit diagram showing a first example of an electric circuit according to the second embodiment, which has a protection function at the time of quenching.

In FIG. 5, reference numeral 16 denotes a protection resistor, reference numeral 17 denotes a diode, and other components identical to those shown in FIG.

The protection resistor 16 and the diode 17
Are electrically connected in series, and both are arranged on the high-temperature side refrigeration stage 2. The protection resistor 16 and the diode 1
7 are electrically connected in parallel to the permanent current switch 6.

The operation of the first circuit example is as follows.
And the diode 17 in series with the permanent current switch 6
Since the operation is the same as the operation of the circuit configuration diagram shown in FIG. 4 except that protection during quenching can be achieved by connecting in parallel, the operation description of the first circuit example is omitted. .

FIG. 6 is a circuit diagram showing a second circuit example in which two superconducting coils are provided in the electric circuit according to the first embodiment and different currents flow therethrough. .

In FIG. 6, reference numerals 4a and 4b denote first and second superconducting coils, 5a, 5b and 5c denote first, second and third superconducting current leads, and 6a and 6b denote first and second permanent coils. Current switches, 7a, 7b, 7c are first, second, and third current leads; 13a, 13b are first and second excitation power supplies;
4a and 14b are first and second switches, 16a and 16b
Are the first and second protection resistors, and 17a and 17b are the first and second protection resistors.
And the same components as those shown in FIG. 2 are denoted by the same reference numerals.

Then, the first superconducting coil 4a, the first,
Second superconducting current leads 5a, 5b, first permanent current switch 7a, first and second current leads 7a, 7b, first
The first circuit including the excitation power supply 13a, the first switch 14a, the first protection resistor 16a, and the first diode 17a is the same as the electrical circuit of the first embodiment except that the first protection resistor 16a In this case, the first protection resistor 16a and the first diode 17a are electrically connected in series and both are arranged on the high-temperature side refrigeration stage 2, and The series connection circuit has a configuration electrically connected in parallel to the first permanent current switch 6a. Also, the second superconducting coil 4b,
Second and third superconducting current leads 5b and 5c, second permanent current switch 7b, second and third current leads 7b and 7
c, a second excitation power supply 13b, a second switch 14b,
Similarly, the second circuit including the second protection resistor 16b and the second diode 17b is obtained by adding the second protection resistor 16b and the second diode 17b to the electric circuit of the first embodiment. In this case as well, the second protection resistor 1
6b and the second diode 17b are electrically connected in series and arranged together on the high-temperature side refrigeration stage 2, and this series connection circuit electrically connects the second permanent current switch 6b
Are connected in parallel. Further, the first
And the second circuit share the second current lead 7b and the second superconducting current lead 5b and are combined to be electrically coupled to each other.

The operation of the second circuit example having such a configuration is as follows.
When the first switch 14a and the second switch 14b are turned on, the current flowing through the first circuit and the second circuit, that is, the first superconducting coil 4a and the second superconducting coil 4b
That the value of the current flowing through the
The operation differs from the operation of the electric circuit in the first embodiment in that the protection during quenching can be achieved in both the first circuit and the second circuit. The operation is the same as that of the electric circuit in the first embodiment. Since this operation is apparent to those skilled in the art, further description of the operation of the second circuit example will be omitted.

FIG. 7 is a circuit diagram showing a third circuit example in which two superconducting coils are provided in the electric circuit according to the second embodiment and different currents flow therethrough. .

In FIG. 7, 4c and 4d denote first and second superconducting coils, 5d, 5e and 5f denote first, second and third superconducting current leads, and 6c and 6d denote first and second permanent current leads. Current switches, 7d, 7e, 7f are first, second, and third current leads; 13c, 13d are first and second excitation power supplies;
4c and 14d are first and second switches, 16c and 16d
Are first and second protection resistors, and 17c and 17d are first and second protection resistors.
And the same components as those shown in FIG. 4 are denoted by the same reference numerals.

Then, the first superconducting coil 4c, the first,
Second superconducting current leads 5d, 5e, first permanent current switch 7c, first and second current leads 7d, 7e, first
The circuit portion including the excitation power supply 13c, the first switch 14c, the first protection resistor 16c, and the first diode 17c constitutes a first circuit, and the first protection resistor in the first circuit 16c and the first diode 17c are electrically connected in series and arranged together on the high-temperature side refrigeration stage 2, and this series connection circuit is electrically connected in parallel to the first permanent current switch 6c. Has become. The second superconducting coil 4d, the second and third superconducting current leads 5e and 5f, the second permanent current switch 7d, the second and third current leads 7e and 7f, and the second excitation power supply 1
3d, a second switch 14d, a second protection resistor 16d,
The second diode 17d constitutes a second circuit. Similarly, the second protection resistor 16d and the second diode 17d in the second circuit are electrically connected in series and both are connected to the high-temperature refrigeration stage. 2 and the series connection circuit is electrically connected in parallel to the second permanent current switch 6d. Further, the first circuit and the second circuit share a second current lead 7e and a second superconducting current lead 5e and are combined so as to be electrically coupled to each other.

The operation of the third circuit example having such a configuration also includes the first switch 14c and the second switch 14d.
Is applied, the current flowing through the first circuit and the second circuit, that is, the value of the current flowing through the first superconducting coil 4c and the current flowing through the second superconducting coil 4d can be different from each other. The first circuit is characterized in that the protection during quench can be achieved in both the first circuit and the second circuit.
Is different from the operation of the circuit example of FIG.
The operation is the same as that of the circuit example of FIG. Since the operation is obvious to those skilled in the art, further description of the operation of the third circuit example will be omitted.

[0051]

According to the present invention, the time stability of the constant magnetic field generated by the superconducting coil can be improved by installing the permanent current switch during the operation in the permanent current mode in the superconducting magnet device with a refrigerator. There is an effect that the amount of electric power during operation can be reduced.

Also in accordance with the present invention, a persistent current switch is used which operates at a known liquid helium cooling temperature.
As compared with a permanent current switch using a bTi or Nb ₃ Sn superconducting wire, the operating temperature is higher and the heat capacity is larger, and the temperature of the permanent current switch is less likely to rise for the same energy application. Has the effect of being hardly quenched by the application of disturbance such as

Further, according to the present invention, when the permanent current switch is turned off and the superconducting magnet is excited via the superconducting current lead, a voltage at the time of the excitation is applied to both ends of the permanent current switch to generate Joule heat. However, since the permanent current switch is installed on the high-temperature side refrigeration stage of the refrigerator, the refrigeration capacity of the high-temperature side refrigeration stage is higher than when a permanent current switch is installed on the low-temperature side refrigeration stage. There is an effect that cooling for a minute is significantly easier.

In addition, according to the present invention, since the superconducting coils are installed on the low-temperature refrigeration stage and the permanent current switches are installed on the high-temperature refrigeration stage, they are separated from each other. The effect that the leakage magnetic field of the superconducting coil affects the permanent current switch can be reduced, and a material that reduces the critical current when a magnetic field is applied can be used for the permanent current switch, thereby expanding the range of material selection. There is also.

[Brief description of the drawings]

FIG. 1 is a sectional configuration diagram showing a configuration of a first embodiment of a superconducting magnet device with a refrigerator according to the present invention.

FIG. 2 is a circuit configuration diagram showing an electric circuit in the first embodiment shown in FIG.

FIG. 3 is a sectional configuration diagram showing a configuration of a second embodiment of the superconducting magnet device with a refrigerator according to the present invention.

FIG. 4 is a circuit configuration diagram showing an electric circuit in the second embodiment shown in FIG.

FIG. 5 is a circuit configuration diagram showing a first circuit example having a protection function at the time of quench in the electric circuit in the second embodiment shown in FIG. 3;

FIG. 6 is a circuit configuration diagram showing a second circuit example in which different currents flow through two superconducting coils in the electric circuit according to the first embodiment shown in FIG. 2;

FIG. 7 is a circuit configuration diagram showing a third circuit example in which different currents flow through two superconducting coils in the electric circuit according to the second embodiment shown in FIG. 5;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 GM refrigerator 2 High temperature side refrigerating stage 3 Low temperature side refrigerating stage 4 Superconducting coil 4a, 4c First superconducting coil 4b, 4d Second superconducting coil 5 Superconducting current lead 5a, 5d First superconducting current lead 5b, 5e 2 superconducting current lead 5c, 5f third superconducting current lead 6 permanent current switch 6a, 6c first permanent current switch 6b, 6d second permanent current switch 6h heater winding 7 current lead 7a, 7d first current Leads 7b, 7e Second current lead 7c, 7f Third current lead 8 Mounting part 9 Heat shield plate 10 Vacuum container 11 Wilson seal 12 Compressor 13 Excitation power supply 13a, 13c First excitation power supply 13b, 13d Second Excitation power supply 14 Switches 14a, 14c First switches 14b, 14d Second switches Pitch 15 coldest side refrigeration stage 16 protection resistor 16a, 16c first protection resistor 16b, 16d second protection resistor 17 diodes 17a, 17c first diode 17b, 17d second diode

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01F 6/00 ZAA

Claims (6)

(57) [Claims] 1. A superconducting magnet device with a refrigerator having two refrigerating stages, wherein the refrigerating stages are cooled by a refrigerating machine, and a superconducting coil is driven in a permanent current mode. A permanent current switch made of a superconducting material whose critical temperature is higher than the operating temperature of the refrigeration stage is arranged.
A superconducting coil made of a superconducting material having a critical temperature higher than the operating temperature of the low-temperature refrigeration stage is disposed, and a critical temperature higher than the operating temperature of the high-temperature refrigeration stage is provided between the permanent current switch and the superconducting coil. A superconducting magnet device with a refrigerator, wherein a current lead made of a superconducting material having a high weight is arranged. 2. It has at least three freezing stages,
In the superconducting magnet device with a refrigerator, in which these refrigeration stages are cooled by a refrigerator and the superconducting coils are driven in a permanent current mode, each refrigeration stage has a superconducting coil made of a superconducting material having a critical temperature higher than the operating temperature of the refrigeration stage. Alternatively, a permanent current switch is arranged, and a current lead made of a superconducting material having a critical temperature higher than the operating temperature of the high-temperature side refrigeration stage is arranged between adjacent refrigeration stages, wherein the superconducting magnet device with a refrigerator is characterized in that: . 3. The superconducting magnet device with a refrigerator according to claim 1, wherein the current lead is made of an oxide superconductor. 4. A high-temperature refrigeration stage, wherein a series circuit of a protection resistor and a diode is connected in parallel with a superconducting coil disposed on the high-temperature refrigeration stage, and the protection resistor is disposed on the high-temperature refrigeration stage. 4. The superconducting magnet device with a refrigerator according to any one of items 3 to 3. 5. The high-temperature side refrigeration stage has a current lead connected between the high-temperature side refrigeration stage and a room temperature portion, and a connection portion of the current lead to the high-temperature side refrigeration stage is detachable. The superconducting magnet device with a refrigerator according to any one of claims 1 to 4. 6. The superconducting magnet with a refrigerator according to claim 5, wherein a connection portion between the current lead and the high-temperature side refrigeration stage is made of an object having a large heat capacity such as a copper block. apparatus.