JP3310074B2 - Superconducting magnet device - 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 device, and more particularly to a superconducting magnet device operated in a permanent current mode.

[0002]

2. Description of the Related Art In a NMR spectrometer and a semiconductor crystal pulling apparatus for physicochemical analysis, a superconducting magnet apparatus operated in a permanent current mode is used as a magnetic field supply source. A superconducting magnet device operated in a persistent current mode usually immerses a superconducting coil having a persistent current switch connected between both ends into liquid helium in a cryostat and selectively connects both ends of the superconducting coil to a power supply outside the cryostat. It is configured to be connectable. In the permanent current switch, an electric heater is attached to a superconducting wire, and the attached portion is molded with a heat insulating material such as fiber reinforced plastic.

In order to actually switch to the permanent current mode, first, the electric heater of the permanent current switch is energized to turn off the permanent current switch, and in this state, the current is supplied from the external power supply to the superconducting coil at a predetermined increasing rate. Shed. Then, when the current flowing through the superconducting coil reaches the target value, the power supply to the electric heater is stopped, and the permanent current switch is turned on. Thereafter, the output current of the power supply is reduced, and the supply path from the power supply is finally cut off.

In the superconducting magnet device operated as described above, a current flows through the permanent current switch at the time of excitation and demagnetization, and heat is generated. In order to suppress the consumption of liquid helium due to this heat generation, the resistance when off is usually 20 to 200 (Ω)
Permanent current switch is used. Further, in this type of superconducting magnet device, as described above, a method of completely disconnecting the current supply circuit after excitation is adopted. Therefore, assuming that the permanent current switch is quenched during operation,
In general, a protection resistor is connected between both ends of the superconducting coil, and the protection resistor is arranged in liquid helium. Encouragement
Since a current flows through the protection resistor at the time of demagnetization, the higher the value of the protection resistor is, the better the consumption of liquid helium is suppressed. However, in order to prevent dielectric breakdown from occurring in a helium gas portion having a low withstand voltage due to a voltage across the protection resistor at the time of quench, a protection resistor of about several Ω is usually used.

However, in the superconducting magnet device configured as described above, it is necessary to use a protection resistor having a small resistance value, which not only leads to an increase in size and weight of the device, but also causes an increase in excitation and demagnetization. However, there is a problem that a large amount of heat is generated by the protection resistor in the above, and an efficient device cannot be configured.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a small, lightweight, and efficient superconducting magnet device in which a permanent current switch can also serve as a protective resistor.

[0007]

In order to achieve the above object, a superconducting magnet device according to the present invention comprises a superconducting coil disposed in a vacuum atmosphere and cooled below a critical temperature through a solid heat conduction path. It is electrically connected to both ends of the superconducting coil and is always cooled to a critical temperature or lower through the solid heat conduction path. When the coil quenches itself, the heat transmitted through the solid heat conduction path causes the superconductivity to decrease. A permanent current switch is also provided that quench the coil and quench itself with the heat transmitted through the solid heat conduction path when the superconducting coil quenches.

[0008]

When one of the superconducting coil and the permanent current switch is quenched, the other is automatically quenched. Therefore, at the time of quenching, the energy stored is consumed by the heat capacity of the superconducting coil and the heat capacity of the permanent current switch, and if it is set in advance so that appropriate consumption sharing can be obtained by weight distribution of the wire, etc. Energy can be consumed without burning or the like.
That is, since the permanent current switch can also serve as the protection resistor, the protection resistor as in the conventional device can be omitted. Therefore, the size and weight of the device can be reduced. At the moment when the permanent current switch is quenched, a voltage corresponding to the product of the current and the resistance value is generated at both ends of the permanent current switch, but all elements are provided in a vacuum atmosphere having a high dielectric strength. Therefore, even if the voltage between both ends becomes, for example, 600 V or more, the dielectric breakdown does not occur. This means that the resistance value when the permanent current switch is off can be set high. Therefore, heat generated by the permanent current switch at the time of excitation / demagnetization can be suppressed, and efficiency can be improved.

[0009]

Embodiments will be described below with reference to the drawings.

FIG. 1 is a schematic structural view of a superconducting magnet device according to one embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes a vacuum container whose inside is evacuated. In the vacuum vessel 1, a heat shield plate 3 for preventing heat from entering by radiation is arranged so as to form a closed vacuum space 2.

A superconducting coil 4 is arranged in a vacuum space 2 surrounded by a heat shield plate 3. The superconducting coils 4, the critical temperature is winding a compound superconducting wire of an alloy-based superconducting wire or Nb ₃ Sn, such as more than NbTi 10K, it is formed by impregnating a resin.

A permanent current switch 5 is connected to both ends of the superconducting coil 4. This permanent current switch 5
Is formed of, for example, a superconducting wire using Cu-Ni as a matrix, and is specifically formed in a weight relationship described later.

Both ends of the superconducting coil 4 have a critical temperature of 100K.
The above oxide-based superconducting leads 6a, 6b and copper lead 7
The connection terminals are connected to connection terminals 8a and 8b attached to the wall of the vacuum vessel 1 via a and 7b. This connection terminal 8a,
8b is connected to a current source 9 provided outside the vacuum vessel 1 via a detachable lead wire. On the other hand, the superconducting coil 4
The permanent current switch 5 is thermally connected to a solid heat conduction path, in this example, a heat conduction member 10 formed of a copper material while maintaining electrical insulation. The heat conduction member 10 is thermally connected to a cooling stage of the refrigerator 11.

In this example, the refrigerator 11 is constituted by a Gilead McMahon refrigerator (hereinafter abbreviated as a GM refrigerator). The GM refrigerator 11 includes a first cooling stage 12 cooled to about 70K and a second cooling stage 13 cooled to a 4K level (for example, the refrigerating capacity is 1 W). It is mounted using a mounting hole (not shown) provided on the upper wall of the vacuum container 1 so as to be located in the container 1. Then, the second cooling stage 13 is thermally and mechanically connected to the heat conducting member 10. Further, the first cooling stage 12 is thermally and mechanically connected to the heat shield plate 3.

Here, the relationship among the three elements of the heat conducting member 10, the superconducting coil 4, and the permanent current switch 5 will be described in further detail. That is, the distance between the portion where the superconducting coil 4 is thermally connected and the portion where the persistent current switch 5 is connected is set to a small value on the heat conducting member 10. Is set to 100 A / mm ² or more. In particular,
With reference to the position where the persistent current switch 5 is connected, when the persistent current switch 5 itself is quenched, the superconducting coil 4 is also quenched by the heat transmitted through the heat conducting member 10, and when the superconducting coil 4 is quenched, The permanent current switch 5 is also provided so as to obtain a heat conduction relationship in which the heat is transmitted through the conductive member 10 to quench the permanent current switch 5. The permanent current switch 5 absorbs 1/3 of the energy stored in the superconducting coil 4 at the time of quenching.
The weight of the wire is set so that the temperature rises from 4K to 200K. Further, when the current flowing through superconducting coil 4 is, for example, 130 A, permanent current switch 5
(Ω) is set so as to obtain an off-resistance.

With such a configuration, in order to switch to the permanent current mode, first, the electric heater of the permanent current switch 5 is energized so that the permanent current switch 5 is turned off.
In this state, a current flows from the current source 9 to the superconducting coil 4 at a predetermined increase rate. At this time, the excitation voltage is set so that the heat generated by the permanent current switch 5 is suppressed to 0.5 W or less. Then, when the current flowing through the superconducting coil 4 reaches the target value, the power supply to the electric heater is stopped and the permanent current switch 5 may be switched on.

In the case of this example, when one of the superconducting coil 4 and the permanent current switch 5 is quenched during the operation in the permanent current mode, the other automatically becomes the quench state. Therefore, at the time of quenching, the stored energy is consumed by the heat capacity of the superconducting coil 4 and the heat capacity of the permanent current switch 5, and it is set in advance so that appropriate consumption sharing can be obtained by weight distribution of the wire and the like. With this arrangement, energy can be consumed without causing burnout or the like. As described above, since the permanent current switch 5 can also serve as a protective resistor, the size and weight of the device can be reduced. At the moment when the persistent current switch 5 is quenched, a voltage corresponding to the product of the current and the resistance is generated at both ends of the permanent current switch 5, but all elements are provided in a vacuum atmosphere having a high dielectric strength. Therefore, even if the voltage between both ends becomes, for example, 600 V or more, the dielectric breakdown does not occur. Therefore, the resistance value of the permanent current switch 5 when the permanent current switch 5 is off can be set high.
Heat generated in the permanent current switch 5 during demagnetization can be suppressed, and efficiency can be improved.

FIG. 2 is a schematic configuration diagram of a superconducting magnet device according to another embodiment of the present invention. In this figure, the same parts as those in FIG. 1 are indicated by the same reference numerals. Therefore, a detailed description of the overlapping part will be omitted.

In this embodiment, a protection diode 14 is connected between both ends of the superconducting coil 4 with the polarity shown in the figure, and this diode 14 is connected to the superconducting coil 4 by using an extension 10 ′ of the heat conducting member 10.
Cooling down to 4K level.

The forward blocking voltage of the diode 14 cooled below 10K is about 20V. Therefore, no current flows through the diode 14 during demagnetization as well as during excitation, and there is no heat generation at all. When the superconducting coil 4 or the permanent current switch 5 is quenched, the diode 14 conducts and functions as a protection element. In this case, the permanent current switch 5 is protected by the diode 14, so that it can be as small as possible. That is, in this case, the stored energy is consumed by the heat capacity of the superconducting coil 4.

[0022]

As described above, according to the present invention, the overall size and weight can be reduced, and the efficiency during excitation and demagnetization can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a superconducting magnet device according to one embodiment of the present invention.

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

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Vacuum container 3 ... Heat shield plate 4 ... Superconducting coil 5 ... Permanent current switch 10 ... Heat conduction member 11 ... Refrigerator 12 ... 1st stage cooling stage 13 ... 2nd stage cooling stage 14 ... Diode

Claims (1)

(57) [Claims] A superconducting coil disposed in a vacuum atmosphere and cooled to a critical temperature or lower through a solid heat conducting path, and electrically connected to both ends of the superconducting coil and connected through the solid heat conducting path. Is always cooled below the critical temperature,
A permanent current switch that quench the superconducting coil with heat transmitted through the solid heat conduction path when quenched itself, and quench itself with heat transmitted through the solid heat conduction path when the superconducting coil quench. A superconducting magnet device comprising: