JPH11102808A - Method of protecting superconducting magnet device against quenching - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for protecting the coils of oxide superconducting lead of a high magnetic field superconducting magnet device against quenching. SOLUTION: A high-magnetic field superconducting magnet device is formed by the combination of superconducting coils of an oxide superconducting lead and superconducting coils of metallic superconducting lead. A heater 5 which is provided outside a coil 1 of oxide superconducting lead is allowed to produce heat at the same time as with production of quenching at superconducting coils 4 of metallic superconducting lead to forcefully have the entire coil 1 of oxide superconducting lead quenched. In this way, the load on the coil 1 of oxide superconducting lead is prevented, and the coil 1 is protected accordingly.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a quench protection method for a high magnetic field superconducting magnet device which prevents a superconducting wire from being damaged by a quench, and more particularly to a high magnetic field suitable for a permanent current superconducting magnet device operated in a permanent current mode. The present invention relates to a quench protection method for a superconducting magnet device.

[0002]

2. Description of the Related Art Generally, nuclear magnetic resonance spectroscopy (hereinafter simply referred to as NMR) using a magnetic field, electron spin resonance (hereinafter simply referred to as ESR), and a measuring device for the de Haas-van Alphen effect, etc. In, the higher the generated magnetic field, the higher the resolution, and the higher the analysis accuracy. In addition, as the generated magnetic field is higher, restrictions on the sample to be analyzed such as the impurity concentration and the sample amount are relaxed. Therefore, these devices tend to have increasingly higher magnetic fields in recent years. In contrast, superconducting magnets commonly used today
The (superconducting magnet), NbTi, which was coiled metal superconducting wire, such as Nb ₃ Sn is used. Critical magnetic field of the metal superconducting wire (maximum magnetic field capable of holding a superconducting) is usually, 11T (tesla) in NbTi, since it is 23T in Nb ₃ Sn, relatively cost is for low field-in said apparatus Inexpensive NbTi superconducting wires are used. For high magnetic fields, Nb ₃ Sn superconducting wires having high superconducting performance and relatively high cost are used in combination with the NbTi superconducting wires. However, for a superconducting magnet operated at 4.2K, the maximum magnetic field is 18T.
It stops, and the generation of 20T is the upper limit even in the superfluid cooling type of about 1.8K.

For this reason, when it is necessary to further increase the magnetic field,
Indicates that the outer and middle layer magnets are NbTi and Nb, respectively. _ThreeSn metal superconducting wire
The inner coil is made of oxide superconducting wire
It has been proposed to make more. Oxide superconductor
The critical magnetic field is usually 100 T or more, and the oxide superconducting wire
A metal superconducting wire with a wound cylindrical superconducting coil inside
Superconducting coil with a cylindrical superconducting coil placed outside
By using a magnet device, a high magnetic field of 20T or more can be obtained.
Can be

In order to put such a superconducting magnet device having a higher magnetic field into practical use, it is necessary to improve the critical current density of the oxide superconducting wire. In addition, since a large current flows under a strong magnetic field, extremely large stress acts on the wire,
It is also important to realize a high-strength oxide superconducting wire that can withstand this stress. Therefore, from such a viewpoint, development of an oxide superconducting wire aiming at a higher critical current density and a higher yield strength has been actively pursued.

On the other hand, in order to put such a high magnetic field superconducting magnet device into practical use, measures to protect the superconducting coil when a quench of the superconducting coil (transition from a superconducting state to a normal conducting state) occurs. Required. That is, the higher the magnetic field of the superconducting magnet device, the greater the energy stored in the magnet. Therefore, for some reason, heat enters the low-temperature stage (cryostat) of the magnet, and the temperature of the entire magnet system rises, the temperature of the superconducting coil also rises, and the quench of the superconducting coil occurs. It is necessary to take measures when the stored energy is released. If there is no quench protection measure for the superconducting coil and this accumulated energy is concentrated in one place of the superconducting coil, there is a possibility that breakage or breakage of the superconducting wire or coil in the concentrated part may occur. . If the superconducting wire coil is damaged, the entire superconducting magnet device suffers fatal damage that cannot be restarted.

Accordingly, conventionally, by the quenching entire superconducting magnet apparatus so as not to suffer a fatal damage, NbTi, protection of the metal superconducting wire coils, such as Nb ₃ Sn have made various. For example, when a quench occurs, the metal superconducting wire coil is divided into small sections in order to disperse the stored energy as much as possible throughout the coil, and a protection resistor is connected to each section, so that power inflow to a specific coil is performed. Prevent concentration. In addition, as shown in FIG. 4, a heater 19 is wound around the outer periphery of the metal superconducting wire coil 4 and fixed with an epoxy resin 21 or the like.On the other hand, the voltage generated at both ends of the metal superconducting wire coil 4 is monitored, and Simultaneously with the occurrence of the overvoltage, the heater 19 is energized to forcibly quench the entire metal superconducting wire coil 4 to prevent concentration of electric power flowing into a specific coil. However,
Both of these methods have a common feature in that after detecting an abnormality of the metal superconducting wire coil, which is the coil in which quench occurs, protection measures for the metal superconducting wire coil are started.

On the other hand, with respect to the quenching countermeasure of the oxide superconducting wire coil, the countermeasure such as the metal superconducting wire coil has not been studied yet. This is because, as described above, the oxide superconducting wire coil is under development with the aim of increasing the critical current density and increasing the yield strength of the oxide superconducting wire, and the oxide superconductor is extremely stable and hardly causes quenching This is because it is considered. That is, in the metal superconducting wire coil, a slight increase in temperature of the metal superconducting wire can trigger quench. However, the temperature margin (temperature difference) from the cryogenic temperature to the critical temperature during use of oxide superconducting wires is considerably larger than that of metal superconducting wires. Is considerably smaller than a metal superconducting wire, and it takes time to generate quench.

[0008]

However, the difficulty of quenching in this oxide superconducting wire coil can be applied only when the oxide superconducting wire coil is used alone. NbT targeted by the present invention
In a high-field superconducting magnet device composed of a combination of a metal superconducting wire coil such as i, Nb ₃ Sn and an oxide superconducting wire coil, when a quench occurs in the metal superconducting wire coil, the Quench propagates through the superconducting wire coil. Then, in this case, as described above, in the conventional quench countermeasure method of starting the protection measure of the coil after detecting the abnormality of the coil where the quench occurs,
It has been found that a large stress may be applied to the oxide superconducting wire coil, causing fatal damage such as breakage of the wire.

That is, when quench occurs in the metal superconducting wire coil, the current in the oxide superconducting wire coil changes due to electromagnetic induction. Next, the quench propagates to the oxide superconducting wire coil, and quench buds occur in a part of the oxide superconducting wire coil. Here, since the critical temperature of the oxide superconducting wire coil is high, it takes time for the temperature of the bud portion to rise and reach the critical temperature. In addition, it takes time for the area around the bud to be heated and the normal conducting portion to spread. For example, the speed at which the normal conducting portion spreads is less than one-hundredth of that of the metal superconducting wire coil.
Therefore, even if the voltage generated at both ends of the oxide superconducting wire coil where quench occurs is monitored as in the conventional technical idea, the normal conducting portion of the oxide superconducting wire coil does not easily spread, Despite the quench already occurring, it is substantially difficult to detect this. If it takes a long time to detect that the quench has occurred in the oxide superconducting wire coil, the induced current increases during that time, and a large stress is applied to the oxide superconducting wire coil, and the wire material becomes It leads to fatal damage such as breaking.

[0010] When this conventional quench protection measure is applied to a high magnetic field superconducting magnet device composed of a combination of a metal superconducting wire coil and an oxide superconducting wire coil, the stress of the oxide superconducting wire coil is determined. Fig. 6 shows the results of a simulation of whether or not to receive this. The conditions and the like in FIG. 6 will be described later in detail in Examples, but as is apparent from FIG. 6, when a quench occurs in the metal superconducting wire coil,
It can be seen that about 2.5 seconds after the occurrence of the quench, a stress of up to about 450 MPa is applied to the oxide superconducting wire coil. The currently achieved maximum strength of the oxide superconducting wire coil is about 210 MPa. Therefore, from Fig. 6, when a quench occurs in the metal superconducting wire coil, a stress greater than the maximum wire strength is applied to the oxide superconducting wire unless a quench protection measure is taken within about 2.5 seconds, and the oxide superconducting wire It can be seen that there is a high possibility that And, as described above, even if the voltage generated at both ends of the oxide superconducting wire coil is monitored as described above, it takes time to detect that the quench occurs in the oxide superconducting wire coil, and this is very difficult. Quench protection measures cannot be implemented within about 2.5 seconds.

Accordingly, the present invention has been made in view of such problems of the prior art, and in a high magnetic field superconducting magnet device constituted by combining a metal superconducting wire coil and an oxide superconducting wire coil, the metal superconducting wire coil is quenched. It is an object of the present invention to provide a quench protection method for a high-field superconducting magnet device that can protect an oxide superconducting wire coil when it occurs.

[0012]

SUMMARY OF THE INVENTION The gist of the present invention for this purpose is that a superconducting coil for generating a main magnetic field is a superconducting magnet device combining an oxide superconducting wire coil and a metal superconducting wire coil. Simultaneously with the quench of the wire coil, the whole oxide superconducting wire coil is forcibly quenched to protect the oxide superconducting wire coil.

As described above, according to the present invention, instead of detecting the quench of the superconducting coil wound with the oxide superconducting wire as in the prior art, the quench of the superconducting coil wound with the metal superconducting wire is detected. Accordingly, the quench occurs in the superconducting coil wound with the metal superconducting wire, and simultaneously, the entire superconducting coil wound with the oxide superconducting wire is forcibly quenched.

The basic concept of the present invention will be described with reference to the circuit diagram of FIG. FIG. 1 shows a circuit diagram of a superconducting magnet device for a nuclear magnetic resonance spectroscopy (NMR) device. In FIG. 1, a superconducting magnet for generating a main magnetic field is accommodated in a cryostat 10 kept at a very low temperature. The superconducting magnet that generates the main magnetic field is composed of an oxide superconducting wire coil 1 wound with an oxide superconducting wire and connected in series with the coil, and an NbTi superconducting wire coil 2 and an Nb ₃ Sn superconducting wire coil 3 connected in series. And a metal superconducting wire coil 4. Reference numeral 11 denotes a magnetic field correction coil around which an NbTi superconducting wire disposed outside the superconducting coil 4 is wound.

Outside the oxide superconducting wire coil 1, a heater 5 connected to a power supply 7 and a circuit 8 which is a feature of the present invention is disposed. In such a circuit configuration,
When quench occurs in the metal superconducting wire coil 4,
The circuit 9 connected to the metal superconducting wire coil 4 uses the circuit 9 of the heater 5 to
To switch 6 in. Then, the switch 6 is operated to make the power source 7 and the heater 5 conductive, and the heater 5 generates heat, thereby forcibly quenching the entire oxide superconducting wire coil 1 in a short time, and The oxide superconducting wire coil 1 is protected by preventing a stress load on the wire coil 1.

In FIG. 1, as a preferred embodiment, a quench protection measure is taken for the metal superconducting wire coil 4 such as NbTi, Nb ₃ Sn or the like. Specifically, when a quench occurs, in order to disperse the stored energy as much as possible throughout the metal superconducting wire coil, a metal superconducting wire coil such as NbTi, Nb ₃ Sn, etc. , Nb ₃ Sn metal superconducting wire coil 3
The, as shown in FIG. 1, a _1, with a plurality of divided into smaller sections of each a _2, a _3, a protective resistor connected in series
22 are connected in parallel for each section to form a protection circuit to prevent concentration of power inflow to a specific coil when a quench occurs.

More specifically, by adopting such a circuit configuration, the current of the quenched portion of the Nb ₃ Sn metal superconducting coil 3 is determined by the electric resistance value of the quenched portion and the quenched portion. Section a containing
(Or b or c) attenuates in accordance with the ratio of the inductances. At this time, the inductance of each of the sections a, b, and c is smaller than the inductance of the entire superconducting magnet 3. Therefore, the superconducting coil 3
The decay of the current value in the quenched part of
Is not divided into the sections, the speed is increased, and damage to the quenched portion can be prevented. Sections b and c other than the quenched section a
However, the electromagnetic energy stored in section a is transferred by electromagnetic induction, and the current values in sections b and c increase. Further, due to the AC loss due to the magnetic field fluctuation during the quench, the temperature in the superconducting state of the sections b and c increases, and the critical current value decreases. As a result, when the current value increased by the induction in the sections b and c exceeds the critical current value reduced by the temperature rise due to the AC loss, quench occurs in the sections b and c, and the current value also increases in the sections b and c. Is attenuated at the same speed as that of the section a, thereby preventing the coil from being damaged.

In this preferred embodiment, a quench protection measure for the metal superconducting wire coil is described, but a similar quench protection measure may be implemented for the oxide superconducting wire coil. As described above, the oxide superconducting wire coil is less likely to be quenched by itself, and thus the necessity of quench protection measures is thinner than that of the metal superconducting wire coil, but as in the present invention, in combination with the metal superconducting wire coil. When used, it may be necessary depending on the configuration of the superconducting magnet device.

Further, in the embodiment shown in FIG.
In addition to connecting 22, the protection resistor 22 and the diode 23 are connected in series as a more preferable embodiment. This is to prevent the Joule heat from being generated by the protection resistor during the excitation of the superconducting wire coil, thereby preventing the evaporation of the cryogen such as liquid helium used for cooling the superconducting magnet device from increasing. More specifically, for example, during the excitation of the Nb ₃ Sn superconducting wire coil 3, at both ends of the sections a _1, a _2, a ₃ were both ends and dividing the superconducting coil 3, a potential difference depending on the excitation of Occurs. As a result, current also flows through the protection resistor 22 and the protection resistor
Joule heating occurs at 22 and evaporation of the cryogen may increase. On the other hand, if the protection resistor 22 and the diode 23 are connected in series, even if a potential difference occurs between both ends of the superconducting wire coil 3 and both ends of the divided sections a ₁ , a ₂ , a ₃ ,
If the potential difference is equal to or less than the ON voltage of the diode 23, no current flows through the protection resistor 22, so that Joule heating of the protection resistor during excitation can be prevented.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described using a high-field superconducting magnet device for an NMR device shown in FIG. Note that the basic configuration of the circuit in FIG. 2 is the same as that in FIG. In FIG. 2, a superconducting magnet for generating a main magnetic field is accommodated in a cryostat 10 kept at a very low temperature. As the superconducting magnet in the cryostat 10, a cylindrical oxide superconducting coil that is arranged inside and generates a main magnetic field wound with a bismuth-based oxide superconducting wire
1 and a cylindrical metal superconducting coil which is arranged outside the oxide superconducting coil 1 and connected in series, and has a Nb ₃ Sn superconducting wire inside and an NbTi superconducting wire wound outside to generate a main magnetic field. 4 A permanent current switch 12 is connected in parallel to the oxide superconducting coil 1, and a heater power supply 15 is connected to the permanent current switch 12.
However, an excitation power supply 14 is connected to the oxide superconducting coil 1 by wirings 13 and 16, respectively.

[0021] As the oxide material of the oxide superconducting _{wire, Bi 2-x Pb x Sr} 2 Ca 2 Cu 3 O y, bismuth oxide such as Bi ₂ Sr ₂ CaCu ₂ O _y being preferred. And also about the manufacturing method of an oxide superconducting wire coil, after sheathing these oxide raw materials with a good conductive metal such as silver, processing the wire into a wire by a known processing method such as drawing, coiling and heat treatment. Known production methods such as the above can be used as appropriate.

It is to be noted that NM which particularly requires uniformity of the magnetic field
In the high-field superconducting magnet device for the R device, in order to guarantee the uniformity of the magnetic field, an NbTi superconducting wire wound around an NbTi superconducting wire, which is placed outside the metal superconducting coil 4 and connected in series, is used. Preferably, a cylindrical coil 11 is provided. In addition, it is easier to compensate for the magnetic field or magnetic flux if the main magnetic field correction coil 11 is disposed outside the superconducting wire coils 1 and 2 for generating the main magnetic field.

In the present invention, the quench occurs in the metal superconducting wire coil 4 and at the same time, the oxide superconducting wire coil 1
The whole is forcibly quenched and the oxide superconducting wire coil
A heater 5 connected to an external power supply 7 and a circuit 8 is disposed outside the oxide superconducting wire coil 1 to protect the coil 1. More specifically, as shown in FIGS. 3 (a) and (b), the heater 5 is provided at a plurality of locations in the circumferential direction of the outer and inner circumferences of the cylindrical oxide superconducting wire coil 1 (FIG. a), four holes 17 and 17 for heater wire penetration are provided in the circumferential direction of the coil 1 and in the axial direction of the coil 1.
8 to surround the oxide superconducting wire coil 1 as a whole. The portion of the heater wire 8 along the outer and inner circumferences of the coil 1 is covered with a heat insulating agent 18 (insulating putty or the like).
It is preferable that the heater wire 8 be covered with heat so that the heat generated by the heater wire 8 is not diffused into the outer and inner spaces of the coil 1.

If the oxide superconducting wire coil 1 is sufficiently small and the entire oxide superconducting wire coil can be forcibly quenched in a short time even with partial heating, the heater wire 8 is not always required, as in this example. , The heater (wire) may be partially provided on the outer periphery of the oxide superconducting wire coil as shown in FIG. However, what matters in the present invention is the time from when quench occurs in the metal superconducting wire coil to when the entire oxide superconducting wire coil can be forcibly quenched. Therefore, in the present invention, regardless of the conditions of the oxide superconducting wire coil, the entire oxide superconducting wire coil is forcibly forced from the occurrence of quenching until a stress (load) exceeding the allowable level is applied to the oxide superconducting wire coil. Need to be quenched.

More specifically, as shown in FIG. 6, after the quench occurs in the metal superconducting wire coil, an extremely short time such as about 2.5 seconds or less can be exceeded for the oxide superconducting wire coil. Stress is applied. Oxide superconducting wire coil,
The maximum strength currently achieved is 210M, as described above.
It is about Pa. Therefore, for example, in the case of FIG. 6, after the quench occurs, the oxide superconducting wire coil has a pressure of 210 MPa.
Unless the entire oxide superconducting coil can be forcibly quenched in a very short time, such as within about 0.9 seconds, until the stress is applied, the oxide superconducting wire may break. In addition, as the size of the oxide superconducting wire coil increases with the size of the high-field superconducting magnet device, the heater (wire) as shown in FIG. , It is difficult to forcibly quench the entire oxide superconducting wire coil. Therefore, in order to shorten the time from when quench occurs in the metal superconducting wire coil until the entire oxide superconducting wire coil can be quenched, and in response to the increase in size of the oxide superconducting wire coil, In order to forcibly quench the entire oxide superconducting wire coil,
As shown in FIGS. 3 (a) and 3 (b), it is preferable that the heater wire is configured so as to surround the oxide superconducting wire coil 1 as a whole in order to achieve or guarantee a quench of the entire coil in a short time.

The oxide superconducting wire coil 1 having such a configuration
Forced quench device in metal superconducting wire coil
At the same time as the quench occurs in the switch 4, the change in current caused by the voltage drop is changed by the wiring 9 connected to the metal superconducting wire coil 4 to the switch 6 in the circuit 8 of the heater 5.
To make the external power supply 7 and the heater wire 8 conductive,
By making the heater wire 8 generate heat by the external power supply 7,
The whole oxide superconducting wire coil 1 is forcibly quenched to protect the oxide superconducting wire coil 1.

Here, NMR in the present invention
The operation of the high magnetic field superconducting magnet device for the device in the permanent current mode will be described below. In the permanent current mode, the excitation of the oxide superconducting coil 1 and the metal superconducting coil 4 is carried out from an external heater power supply 15 to a heater (not shown) of the permanent current switch 12 connected in parallel to the oxide superconducting coil 1. Then, each of the permanent currents is opened. Then, in this state, the oxide superconducting coil 1 is
Apply current to

As described above, when a current is supplied from the external power supply 14 for excitation to the oxide superconducting coil 1, the heater for the permanent current switch 12 is also supplied with electricity from the heater power supply 15, and the heater that generates heat causes the permanent current switch The 12 superconducting wire windings for the switch (not shown) are heated. The heated superconducting wire winding for a switch transitions to a normal conducting state (off state) and has a finite resistance value according to the temperature. Therefore, when a current is supplied from the external power source for excitation 14 to the oxide superconducting coil 1, the permanent current switch 12 is turned off, and the current from the external power source for excitation 14 is supplied to the oxide superconducting coil 1. Flow and its current will increase.

When the current flowing through the oxide superconducting coil 1 reaches a predetermined value and the energization (heating by the heater) of the permanent current switch 12 to the heater is stopped, the permanent current switch 12 is thermally short-circuited with a cooling unit (not shown). The temperature of the switch superconducting wire winding part lowers and transits to the superconducting state (ON state). When the current of the external power supply for excitation 14 is lowered after the winding of the superconducting wire is turned on, the current of the external power supply 14 for excitation remains constant while the current flowing through the oxide superconducting coil 1 remains constant. Permanent current switch 1 to compensate for the drop
The current flows into. That is, the current flows in a loop between the superconducting coil 1 and the superconducting wire winding of the permanent current switch 12. Thereafter, even if the current of the external power supply 14 for excitation is reduced to zero the current supplied to the oxide superconducting coil 1, the current of the oxide superconducting coil 1 flows through the permanent current switch 12 and a predetermined current value Is maintained. Such a state is called operation in the persistent current mode, and the NM shown in FIG.
The high-field superconducting magnet device for the R device is constantly operated in the permanent current mode.

[0030]

EXAMPLE The high-field superconducting magnet device for an NMR device in the permanent current mode shown in FIG. 2 was operated to quench the metal superconducting wire coil and simultaneously forcibly quench the oxide superconducting wire coil. FIGS. 5, 6, and 7 show the results of a simulation of how much stress is applied to the oxide superconducting wire coil over time when the oxide superconducting wire coil is protected. FIG. 5 is similar to FIG. 2 and FIG.
3 shows an example of the invention when the superconducting magnet device and the heater device for the oxide superconducting wire coil shown in FIG. 3 are used, that is, when the entire and compulsory quench device for the oxide superconducting wire coil is used. On the other hand, FIG. 6 shows that the superconducting magnet device and the configuration and the quench generation condition shown in FIG. 2 are the same as those of the invention example, but the overall superconducting force of the oxide superconducting wire coil 1 shown in FIG. No quench device, figure
4 shows a comparative example in which only a partial heater device of the coil of No. 4 is provided. FIG. 7 shows, for further comparison,
Compared to the invention example, the configuration of the NMR system and the quench generation conditions in Fig. 2 were the same, except that the oxide superconducting wire coil did not have a heater device (forcible quench device for the oxide superconducting wire coil), and the metal superconducting wire This shows a conventional example in which the coil is provided with the heater device shown in FIG.

In addition, FIG.
The detailed specifications of the superconducting coil of the superconducting magnet device for NMR equipment are as follows. Oxide that generates main magnetic field Superconducting coil 1; Permanent current Superconducting magnet overall inductance;
1H, rated magnetic field: 2.4T, rated current: 128A, outer diameter: 130mm,
Bore inner diameter: 74mm, winding length: 600mm, wire used: Bi _2-x Pb
_x Sr ₂ Ca ₂ Cu ₃ O _y multifilament. Metal superconducting coil that generates main magnetic field (including superconducting coil for magnetic field uniformity correction); permanent current superconducting magnet whole inductance; 1180H, rated magnetic field; 21.1T, rated current; 350A, bore diameter: 160mm, winding length 890 mm, wire used; multifilament Nb ₃ Sn and NbTi. The quench was generated under the condition that the inner Nb ₃ Sn wire coil of the metal superconducting wire coil was 17.2 T
When the outer NbTi wire coil reached 2.1T, the metal superconducting wire coil was generated.

First, as is apparent from the simulation result of FIG. 7 of the conventional example, in the conventional superconducting magnet apparatus in which the oxide superconducting wire coil is not forcibly quenched, when a quench occurs in the metal superconducting wire coil, Even if the metal superconducting wire coil is forcibly quenched by the heater device, a stress of about 210 MPa of its maximum strength is applied to the oxide superconducting wire coil about 0.6 seconds after the quench occurs, and after about 2.5 seconds, For oxide superconducting wire coils,
It can be seen that a maximum stress of about 450 MPa is applied. Therefore, according to the simulation result of the conventional example shown in FIG. 7, when a quench occurs in the metal superconducting wire coil, it is about 0.6%.
It can be seen that there is a high possibility that the oxide superconducting wire will break within ~ 2.5 seconds.

Further, as is apparent from the simulation result of the comparative example shown in FIG. 6, in the superconducting magnet device in which the oxide superconducting wire coil is partially quenched, the quench occurs in the metal superconducting wire coil and at the same time, the oxide superconducting wire coil is quenched. Although the wire coil is forcibly quenched, the whole oxide superconducting wire coil has not been quenched. As a result, it can be seen that about 0.9 seconds after the occurrence of the quench, the oxide superconducting wire coil is subjected to a stress of about 210 MPa, which is the maximum strength, and about 2.5 seconds, a stress of about 240 MPa is applied. Although this stress is greatly reduced from the stress of about 450 MPa in the conventional superconducting magnet device shown in FIG. 6, the stress is still reduced in view of the currently achieved maximum strength of the oxide superconducting wire coil of 210 MPa. Is not sufficient, and the oxide superconducting wire may be broken.

On the other hand, as is apparent from the simulation result of the embodiment shown in FIG. 5, in the superconducting magnet device of the present invention, the quench occurs in the metal superconducting wire coil, and at the same time, the entire oxide superconducting wire coil is forcibly forced. It can be seen that when quenched, the oxide superconducting wire coil is subjected to only a maximum stress of about 200 MPa after about 2.5 seconds. This stress is significantly reduced compared to the stress in the superconducting magnet device of the comparative example of FIG. 6 and FIG. 7 and the conventional example, and is higher than the currently achieved maximum strength of the oxide superconducting wire coil of 210 MPa. It has been reduced low. Therefore, according to the quench protection method of the present invention, even when a quench occurs in the metal superconducting wire coil of the superconducting magnet device, damage such as breakage of the oxide superconducting wire coil can be prevented.
It can be seen that it can be sufficiently prevented.

In this embodiment, the heater (wire) is partially provided on the outer periphery of the oxide superconducting wire coil (FIG. 6).
This is because the oxide superconducting wire coil of the present example was relatively large, and the coil heating capability of the heater was insufficient. As described above, when the oxide superconducting wire coil is sufficiently small, and even when partially heated, the entire oxide superconducting wire coil can be forcibly quenched, as in the above-described invention example,
Even if the heater wire is not necessarily formed so as to surround the oxide superconducting wire coil, as shown in FIG.
The (wire) may be partially provided on the outer periphery of the oxide superconducting wire coil.

[0036]

As described above, according to the quench protection method of the present invention, when a quench occurs in a metal superconducting wire coil, a high magnetic field capable of protecting not only the metal superconducting wire coil but also the oxide superconducting wire coil. A superconducting magnet device can be provided. Therefore, it has great industrial significance in making a high-field superconducting magnet device capable of obtaining a high magnetic field of 20 T or more practical.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a superconducting magnet device, showing a basic concept of the present invention.

FIG. 2 shows an embodiment of the superconducting magnet device of the present invention.
FIG.

FIG. 3 is an explanatory view showing a forced quench apparatus for an oxide superconducting coil according to the present invention.

FIG. 4 is an explanatory view showing a conventional forced quench apparatus for a metal superconducting coil.

FIG. 5 is an explanatory diagram showing a simulation result of a stress applied to the oxide superconducting coil after the quench of the superconducting coil according to the embodiment of the present invention.

FIG. 6 is an explanatory diagram showing a simulation result of a stress applied to the oxide superconducting coil after the quench of the superconducting coil in the comparative example.

FIG. 7 is an explanatory diagram showing a simulation result of stress applied to an oxide superconducting coil after a quench occurs in the superconducting coil in the conventional example.

[Explanation of symbols]

1: oxide superconducting coil, 2: Nb ₃ Sn superconducting coil,
3: NbTi superconducting coil, 4: Metal superconducting wire coil, 5: Heater, 6: Heater switch, 7: Heater power supply, 8: Heater wiring, 9: Quench detection circuit, 10: Cryostat, 11: Magnetic field correction Superconducting coil, 12: permanent current switch, 13, 16: wiring, 14: excitation power supply, 15: heater power supply,
17: Power supply for excitation, 18: Power supply for excitation, 19: Heater, 20: Heater wire, 21: Epoxy resin, 22: Protection resistor, 23: Diode,

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Osamu Ozaki 1-5-5 Takatsukadai, Nishi-ku, Kobe City, Kobe Steel Works, Kobe Research Institute

Claims (11)

[Claims] 1. A superconducting magnet device in which a superconducting coil for generating a main magnetic field is a combination of an oxide superconducting wire coil and a metal superconducting wire coil. A quench protection method for a superconducting magnet device, comprising: forcibly quenching to protect an oxide superconducting wire coil. 2. The quench protection method for a superconducting magnet device according to claim 1, further comprising means for detecting a quench of the metal superconducting wire coil and means for heating the entire oxide superconducting wire coil. 3. The means for heating the entire oxide superconducting wire coil comprises a heater wire disposed around a superconducting coil around which the oxide superconducting wire is wound, and a means for energizing the heater wire. 4. The quench protection method for a superconducting magnet device according to 4. 4. A superconducting coil for generating the main magnetic field,
A cylindrical superconducting coil in which an oxide superconducting wire is wound is arranged inside, and a cylindrical superconducting coil connected in series with the coil and wound with a metal superconducting wire is arranged outside. Item 4. The quench protection method for a superconducting magnet device according to any one of Items 1 to 3. 5. The coil according to claim 1, wherein the metal superconducting wire coil comprises a coil wound with an Nb ₃ Sn superconducting wire, and a coil wound with an NbTi superconducting wire connected in series with the coil. The quench protection method for a superconducting magnet device according to claim 1. 6. The quench protection method for a superconducting magnet device according to claim 1, wherein the oxide superconducting wire coil comprises a coil formed by winding a bismuth-based oxide superconducting wire. 7. The superconducting magnet device according to claim 1, further comprising a superconducting coil for correcting a main magnetic field.
13. The quench protection method for a superconducting magnet device according to item 13. 8. The superconducting magnet according to claim 1, wherein the metal superconducting wire coil is divided into a plurality of sections, and a protection circuit is provided in which a protection resistor is connected in parallel for each section. How to protect the quench of the device. 9. The quench protection method for a superconducting magnet device according to claim 8, further comprising a protection circuit in which a diode is connected in series with the protection resistor. 10. The superconducting magnet device according to claim 1, wherein the superconducting magnet device is operated in a persistent current mode.
10. The quench protection method for a superconducting magnet device according to any one of claims 9 to 9. 11. The quench protection method for a superconducting magnet device according to claim 1, wherein the superconducting magnet device is for a high magnetic field of 20 T or more.