JPH0936444A - Cooling method for superconducting coil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To sustain an oxide superconducting coil stably at a constant temperature by feeding liquid oxygen into the coil housing and then reducing the pressure through a pressure reduction pump thereby cooling the coil down to the triple point of oxygen. SOLUTION: The cooling system for superconducting coil comprises an oxide superconductor 6, a coil housing 1, and a pressure reduction pump 2. Liquid oxygen 7 is then fed through an upper supply port 5 under the atmospheric pressure of about 1atm and then the cover is closed. Subsequently, a valve 4 is opened and communicated with the pressure reduction pump 2 which regulates the inner pressure and controls the temperature in the range of 90-54.4K. Consequently, the coil can be cooled down to the triple point of oxygen (about 54.4K) and sustained stably at a constant temperature level. With such a method, application of oxygen superconductor can be widened.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for cooling an oxide superconducting magnet or a bulk material.

[0002]

2. Description of the Related Art Superconducting materials show superconducting properties below a critical temperature (Tc), but high-temperature oxide superconductors are expected to be used at a liquid nitrogen temperature of 77K because of their high Tc. There are roughly two means for cooling the superconductor. One is cooling with a refrigerator, and the other is using liquid helium or liquid nitrogen as a refrigerant. For cooling the coil or bulk body, the above-mentioned refrigerant is desirable from the viewpoint of heat transfer and heat transfer efficiency and temperature uniformity. Liquid helium may be decompressed into a superfluid state and used at a temperature of 2.19K or less. Further, in Japanese Patent Laid-Open No. 4-822077, the triple point (63.1 K) of nitrogen and the melting point (6
Cooling at 3.9 K) is described. As described above, the operating temperature of the bulk oxide superconducting material is 2.19K,
4.2K, 77K and about 63K are promising.

[0003]

In cooling with liquid helium (2.19K, 4.2K), helium itself is expensive and inconvenient to handle, so that the critical current density is improved as compared with 77K. However, it is not possible to take advantage of the high critical temperature of oxide high-temperature superconductors. On the other hand, when used at liquid nitrogen temperature (77K), the QMG material currently manufactured by the melting method (Mitou Science and Technology Association, New Superconducting Material Research Group, New Superconducting)
Materials Forum News No. 1
0 p. 15) is about 30,000 A / cm ^{2 in} a magnetic field of 1 T,
The Bi-based silver sheath wire has a Jc of 4000 A / cm ² and is approaching a full-scale practical level. However, in order to promote the practical application of these oxide superconductors, a lower temperature refrigerant that is easy to handle is used, and in order to bring out higher superconducting properties, 77K or less, or about 63K or less.
The following simple and stable cooling method is desired.

Further, it has been reported that a bulk magnet using a QMG material at 77K generated a maximum magnetic flux density of 1.35T (Nikkan Iron and Steel Shimbun, February 7, 1991). It has also been reported that flux creep occurs in this QMG bulk magnet and the magnetic flux decreases with time. As described above, flux creep is not practically desirable, and a measure for preventing it is required.

[0005]

In view of the above problems, the present invention provides a method for cooling and exciting an oxide superconducting bulk body or magnet using oxygen which is inexpensive and relatively easy to handle. The present invention can be roughly classified into the following two. One relates to a means for stably cooling liquid oxygen at the triple point temperature (about 54.4 K) of oxygen by decompressing and cooling the liquid oxygen, and the other relates to means for stably cooling the liquid oxygen at atmospheric pressure between the liquid phase and the solid phase. The present invention relates to means for stably cooling at about 54.8K by utilizing latent heat.

In cooling at the triple point, the oxide superconducting coil cooling device or the oxide superconducting coil having a structure in which the space in which the oxide superconducting coil is housed is connected to a decompression pump and the housing chamber can be depressurized by the pump. An oxide superconducting coil cooling device having a structure in which a preliminary decompression space is connected between the accommodated space and a decompression pump, and the coil accommodation chamber and the preliminary decompression chamber can be decompressed by a pump is used. With this, liquid oxygen is put into the storage room of the oxide superconducting coil, then decompressed by the decompression pump, cooled to the temperature of the triple point of oxygen (about 54.4K), and the coil is stably maintained at a constant temperature to cool the superconducting coil. In addition, liquid oxygen is put into the storage chamber of the oxide superconducting coil and then decompressed by a decompression pump, and the temperature at the triple point of oxygen (about 54.
4K) to stably maintain the coil at a constant temperature, and then, in order to replenish the coil storage chamber with oxygen at a triple point temperature as a refrigerant, liquid oxygen is once put in the preliminary decompression chamber to decompress it. After cooling to the triple point state, this oxygen is replenished in the coil storage chamber, and by repeating this replenishment, the coil is stably maintained at a constant temperature for a long time to cool the superconducting coil.

As a measure for preventing flux creep, in cooling the oxide superconducting coil using liquid oxygen, after adjusting the atmospheric pressure in the coil housing chamber and exciting the oxide superconducting coil at a temperature of about 54.4 K or more. There is a cooling method for the superconducting coil that reduces the atmospheric pressure in the coil housing chamber to about 54.4K to prevent the creep of the magnetic flux of the superconducting coil.

On the other hand, in the case of cooling at a melting point in the atmosphere, there is a cooling part of a refrigerator in a space in which an oxide superconducting coil is housed, and an oxide having a structure capable of cooling oxygen in the housed space. A superconducting coil cooling device or an oxide superconducting coil cooling device having a structure in which a space in which an oxide superconducting coil is housed and a spare cooling space are connected and the coil housing chamber and the precooling chamber can be cooled by a refrigerator is used. As a result, liquid oxygen is put into the storage chamber of the oxide superconducting coil, then cooled by a refrigerator, and the coil is stably maintained at a constant temperature near the melting point of oxygen at atmospheric pressure (about 54.8 K). Or by cooling liquid oxygen into the oxide superconducting coil storage chamber and then cooling with a refrigerator to stabilize the coil at a constant temperature at the melting point of oxygen at atmospheric pressure (about 54.8 K). Keep in
Next, in order to replenish the oxygen in which the solid phase, which is the refrigerant, and the liquid phase coexist in the coil storage chamber, liquid oxygen is first put in the pre-cooling chamber and cooled by a refrigerator, so that the solid phase and the liquid phase coexist. After that, the coil storage chamber is supplemented with oxygen, and by repeating this supplementation, the coil is stably maintained at a constant temperature for a long time to cool the superconducting coil.

As a measure for preventing flux creep, in cooling the oxide superconducting coil using liquid oxygen, the temperature inside the coil housing chamber is adjusted by a refrigerator to excite the oxide superconducting coil at a temperature of about 54.8 K or more. After doing
This is a cooling method for a superconducting coil that lowers the temperature of the coil housing chamber to about 54.8K to prevent the creep of the magnetic flux of the superconducting coil.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The triple point of oxygen is about 54.4 K, and this temperature depressurizes liquid oxygen (to about 1.1 mmHg).
It is obtained by doing. Oxygen at the three points is often in the liquid phase because the solidified oxygen becomes sherbet-like.
The melting point of oxygen at atmospheric pressure is about 54.8 K, and the state in which a solid phase and a liquid phase coexist can be obtained by cooling liquid oxygen with a refrigerator or the like. When there is a solid phase in addition to these liquid phases, there is latent heat associated with the phase change, so it is easy to keep the temperature constant, and the superconductor is in contact with the liquid phase and the cooling efficiency is good. The advantage of the three-point cooling is that it does not require a refrigerator and can be cooled relatively easily by a decompression pump. Further, the advantage of the melting point in the atmosphere is that a decompression container is not required and the structure is relatively simple.

The QMG material is approximately 54.4K (or approximately 5K).
4.8K) has a Jc of about 5 times that of 77K and 1T
Has a high value of about 150,000 A / cm ² , and the generated magnetic field is improved by about 5 times compared to 77K for a bulk magnet. This extends the range of applications.

FIG. 1 shows an oxide superconductor 6 and a coil storage chamber 1.
Further, an apparatus including the decompression pump 2 is shown. The coil storage chamber 1 must have a strength that can withstand decompression. Further, the inside of the coil housing chamber 1 must be insulated to some extent by the heat insulating material 3. After putting liquid oxygen 7 from the upper liquid oxygen supply port 5 in the atmosphere of about 1 atm and closing the lid,
It is possible to control the temperature from 90K to about 54.4K by opening the valve 4 and connecting to the decompression pump 2 to reduce the pressure and adjusting the internal pressure. As described above, the invention of claim 1 is a cooling method at an atmospheric pressure of about 1.1 mmHg (about 54.4 K), and since this triple point is a value peculiar to the substance, the temperature becomes extremely stable.

FIG. 2 shows an apparatus comprising an oxide superconductor 6, a coil housing chamber 1, a decompression pump 2 and a preliminary decompression chamber 8.
The coil storage chamber 1 and the preliminary decompression chamber 8 must have a strength that can withstand decompression. Further, the insides of the coil storage chamber 1 and the preliminary decompression chamber 8 must be insulated to some extent by the heat insulating material 3. After putting liquid oxygen 7 from the upper liquid oxygen supply port 5 in the atmosphere of about 1 atm and closing the lid, open the valve 9 and connect it to the decompression pump 2 to decompress and adjust the internal pressure from 90K to about 54.4K. The temperature can be controlled up to.

For long-term cooling, supplemental oxygen is required. If liquid oxygen at atmospheric pressure is supplied to the coil storage chamber during replenishment, the internal temperature rises, and a stable and constant temperature cannot be maintained. Therefore, once liquid oxygen is introduced into the preliminary decompression chamber 8 from the liquid oxygen supply port 5 and decompressed to reach the same temperature as the coil housing chamber 1, the partition wall 10 is opened and the liquid is supplied to the coil housing chamber. As a result, oxygen can be replenished while the temperature is kept constant, and long-term cooling is possible.
Thus, the invention of claim 2 is a long time (semi-permanent) about 5
It provides a cooling method at 4.4K.

FIG. 3 shows an apparatus comprising an oxide superconductor, a coil storage chamber and a refrigerator. Refrigerator 1 in coil storage chamber 1
There is a second cooling unit 11 to cool the liquid oxygen 7 in the coil storage chamber 1 under atmospheric pressure to a state (melting point) where a solid phase and a liquid phase coexist. In addition, the inside of the coil storage chamber 1 has a heat insulating material 3
Must be insulated to some extent. Liquid oxygen can be introduced from the upper liquid oxygen supply port 5 in the atmosphere of about 1 atm, and the refrigerator can be operated to control the temperature from 90K to about 54.8K. As described above, the invention of claim 3 is a cooling method at the melting point, which enables extremely stable cooling due to the latent heat accompanying the phase change.

FIG. 4 shows an apparatus comprising an oxide superconductor 6, a coil housing chamber 1, a refrigerator 12 and a cooling preliminary chamber 13.
A refrigerator 12 is provided in the coil storage chamber 1 and the precooling chamber 13.
Of the cooling chamber (11 and 11a) for cooling liquid oxygen in the coil housing chamber 1 and the pre-cooling chamber 13 under atmospheric pressure to a state where the solid phase and the liquid phase coexist (melting point). Further, the insides of the coil storage chamber 1 and the precooling chamber 13 must be insulated to some extent by a heat insulating material. Liquid oxygen was introduced from the upper liquid oxygen supply port 5 in the atmosphere of about 1 atm, and the refrigerator 12 was operated from 90 K to about 54.8.
The temperature can be controlled up to K.

For long-term cooling, supplemental oxygen is required. If 90 K of liquid oxygen is supplied to the coil storage chamber 1 during replenishment, the internal temperature rises, and a constant temperature cannot be maintained stably. Then, liquid oxygen is once charged into the pre-cooling chamber 13 to be cooled to the melting point, and when the temperature reaches the same temperature as the coil storage chamber, the valve 14 is opened and the oxygen is supplied to the coil storage chamber 1. As a result, oxygen can be replenished while the temperature is kept constant, and long-term cooling is possible. Thus, the invention of claim 4 provides a long-term (semi-permanent) cooling method at about 54.8K.

The use of oxygen as a refrigerant has the following advantages over the conventional cooling method using nitrogen. (1) It can be cooled stably at a lower temperature (about 54K) than the nitrogen melting point or boiling point (about 63K). (2) The boiling point of oxygen is about 90.2K, and if the oxygen of the refrigerant is left as it is (without being depressurized or cooled), the Tc of the rare earth superconductor typified by the Y system is about 90K. Loss superconductivity. As a result, the coil (especially the bulk material) after use need only be left for demagnetization, and the magnet can be stored easily. (3) Oxygen, unlike nitrogen, has magnetism and therefore adheres to the magnet during the generation of a magnetic field to efficiently function as a refrigerant.

[0019]

【Example】

Example 1 RE of several μm in REBa ₂ Cu ₃ O _7-X phase of single crystal form
₂ Superconducting material with finely dispersed BaCuO ₅ phase (QMG
Material) was used to manufacture the magnet shown in FIG. In FIG. 5, (a) is a perspective view when the coils of each layer are disassembled, and (b) is a perspective view when four layers are stacked and assembled. Since each layer has 7 turns, a superconducting coil with 28 turns is shown. I can see it. In the figure, 22 is the direction of current, 20A is 1
The coil of the second layer, 20B is the coil of the second layer, 20C is the coil of the third layer, and 20D is the coil of the fourth layer.
A, 21B, and 21C are electrode parts. Note that each of these electrode portions is shown as two locations in FIG. 5A, but in the state assembled as shown in FIG. 5B, the same reference numerals are combined to form the same location. This was placed in the coil storage chamber 1 as shown in FIG. After introducing liquid oxygen, the pressure was reduced and the mixture was cooled to 54.4K. Next about 5
While maintaining 4.4K, gradually supply current from the outside and
The superconducting coil was excited by flowing 00A. When the distribution of the generated magnetic flux was examined, it was confirmed that the maximum magnetic flux was 0.32T. At 77K, 350A due to heat generation at the current terminal
Only the magnetic flux was flowed, and only about 0.28T was obtained, and the generated magnetic field was improved.

Example 2 RE of several μm in a single crystalline REBa ₂ Cu ₃ O _7-X phase
₂ Superconducting material with finely dispersed BaCuO ₅ phase (QMG
Material) was used to fabricate a bulk magnet having a thickness of 15 mm and a diameter of 42 mm (this magnet can be regarded as a single-turn superconducting coil). This was placed in the coil storage chamber 1 as shown in FIG. A magnetic field of 2.5 T was applied by a normal conducting magnet, liquid oxygen was added, and then the pressure was reduced to about 54.4 K. Next, the superconducting coil was excited by removing the external magnetic field and keeping the magnetic flux trapped in the bulk magnet while maintaining about 54.4K. When the distribution of the trapped magnetic flux was examined after removing the normal conducting magnet, trapping of a magnetic flux of maximum 2.1T was confirmed after 100 seconds. After 10 hours, a preliminary decompression chamber 8 to replenish oxygen
After adding liquid oxygen to and reducing the pressure to about 54.4K,
It was supplied to the superconducting coil storage room. The generated magnetic field did not change before and after the supply, and liquid oxygen could be supplied while maintaining about 54.4K.

Example 3 RE of several μm in a single crystalline REBa ₂ Cu ₃ O _7-X phase
₂ Superconducting material with finely dispersed BaCuO ₅ phase (QMG
Material) was used to fabricate a bulk magnet having a thickness of 15 mm and a diameter of 42 mm (this magnet can be regarded as a single-turn superconducting coil). This was placed in the coil storage chamber 1 as shown in FIG. After adding liquid oxygen,
The pressure was reduced and the mixture was cooled to about 54.4K. Next about 54.4
While maintaining K, the SmCo type ring-shaped permanent magnet was brought close to 0.8 mm from the superconductor coil. At this time, it was confirmed that a 25 kg levitation force (repulsion force) was acting on the permanent magnet by placing a weight. When the levitation force is working, the superconducting current flows in the superconducting coil,
It can be considered that the superconducting coil is excited.

Example 4 RE of several μm in a single crystal REBa ₂ Cu ₃ O _7-X phase
₂ Superconducting material with finely dispersed BaCuO ₅ phase (QMG
Material) was used to fabricate the magnet shown in FIG. 5 (which can be regarded as a 28-turn superconducting coil).
This was placed in the coil storage chamber 1 as shown in FIG. After introducing liquid oxygen, it was cooled to about 54.8 K by a refrigerator. Next, while maintaining about 54.8 K, a current was gradually supplied from the outside to flow 400 A to excite the superconducting coil. When the distribution of the generated magnetic flux was examined, the maximum was 0.32
It was confirmed that the magnetic flux of T was captured. At 77K, due to the heat generation at the current terminal, only 340A was allowed to flow, and a magnetic flux of only about 0.27T was obtained, thus improving the generated magnetic field.

Example 5 RE of 2 μm in a single crystalline REBa ₂ Cu ₃ O _7-X phase
₂ Superconducting material with finely dispersed BaCuO ₅ phase (QMG
Material) was used to fabricate a bulk magnet having a thickness of 15 mm and a diameter of 42 mm (this magnet can be regarded as a single-turn superconducting coil). This was placed in the coil storage chamber 1 as shown in FIG. A magnetic field of 2.5 T was applied by a normal conducting magnet, liquid oxygen was introduced, and the pressure was reduced by a refrigerator to cool to 54.8K. Next 5
The superconducting coil was excited by removing the external magnetic field and keeping the magnetic flux trapped by the bulk magnet while maintaining 4.4K. When the distribution of the trapped magnetic flux was examined after removing the normal conducting magnet, trapping of a magnetic flux of maximum 2.1T was confirmed after 100 seconds. After 10 hours, liquid oxygen was added to the precooling chamber 13 to replenish the oxygen, and the mixture was cooled to about 54.8.
After changing to K, it was supplied to the superconducting coil storage chamber. The generated magnetic field did not change before and after the supply, and liquid oxygen could be supplied while maintaining about 54.8K.

Example 6 RE of several μm in a single crystalline REBa ₂ Cu ₃ O _7-X phase
₂ Superconducting material with finely dispersed BaCuO ₅ phase (QMG
Material) was used to fabricate a bulk magnet having a thickness of 15 mm and a diameter of 42 mm (this magnet can be regarded as a single-turn superconducting coil). This was placed in the coil storage chamber 1 as shown in FIG. After adding liquid oxygen,
It was cooled to about 54.8K by a refrigerator. Next about 5
While maintaining 4.8K, the SmCo-based ring-shaped permanent magnet was brought close to 0.8 mm from the superconductor coil. At this time, it was confirmed that a 25 kg levitation force (repulsion force) was acting on the permanent magnet by placing a weight. When the levitation force is working, it can be considered that the superconducting current is flowing in the superconducting coil and the superconducting coil is excited.

[0025]

As described in detail above, according to the present invention, there is provided a method capable of easily and stably cooling an oxide superconductor at about 55 K using liquid oxygen, and broadening the range of applications of the oxide superconductor. I was able to. Such a cooling method can be applied in various fields, and a great industrial effect can be expected.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of an apparatus for carrying out the present invention.

FIG. 2 is a diagram showing an example of an apparatus for carrying out the present invention.

FIG. 3 is a diagram showing an example of an apparatus for carrying out the present invention.

FIG. 4 is a diagram showing an example of an apparatus for carrying out the present invention.

FIG. 5 is a perspective view showing one of the bulk magnets used in the embodiment, (a) being an exploded view, and (b).
Shows the assembled state.

[Explanation of symbols]

 1 Coil Storage Chamber 2 Decompression Pump 3 Heat Insulation 4, 9 Valve 5 Liquid Oxygen Inlet 6 Oxide Superconductor 7 Liquid Oxygen 8 Preliminary Decompression Chamber 10 Partition Wall 11, 11a Cooling Part 12 Refrigerator 13 Preliminary Cooling Chamber 14 Valve 20A 1 Coil of the second layer 20B Coil of the second layer 20C Coil of the third layer 20D Coil of the fourth layer 21A, 21B, 21C Electrode part 22 Current direction

Claims (4)

[Claims] 1. An oxide superconducting coil containing chamber is filled with liquid oxygen and then decompressed by a decompression pump to cool to a triple point temperature of oxygen (about 54.4 K) to stably maintain the coil at a constant temperature. A characteristic method for cooling a superconducting coil. 2. An oxide superconducting coil is filled with liquid oxygen, decompressed by a decompression pump, cooled to the triple point temperature of oxygen (about 54.4 K), and the coil is stably maintained at a constant temperature. In order to replenish the oxygen at the triple point, which is a refrigerant, in the coil storage chamber, liquid oxygen is once put in the preliminary decompression chamber to reduce the pressure to cool it to the triple point state, and then the oxygen is supplied to the coil storage chamber. A method for cooling a superconducting coil, characterized in that the coil is stably maintained at a constant temperature for a long time by replenishing and repeating this replenishment. 3. Oxide superconducting coil housing chamber is filled with liquid oxygen and then cooled by a refrigerator to stabilize the coil at a constant temperature near the melting point of oxygen at atmospheric pressure (about 54.8 K). A method for cooling a superconducting coil, which is characterized by keeping the same. 4. A liquid oxygen is put into a storage chamber of the oxide superconducting coil and then cooled by a refrigerator to stably bring the coil to a constant temperature in the vicinity of a melting point of oxygen at atmospheric pressure (about 54.8 K). Next, in order to replenish the oxygen in which the solid phase, which is the refrigerant, and the liquid phase coexist in the coil storage chamber, liquid oxygen is once put in the pre-cooling chamber and cooled by a refrigerator to cool the solid phase and the liquid phase. A method for cooling a superconducting coil, characterized in that the coil storage chamber is replenished with oxygen after the coexistence of the above conditions, and the replenishment is repeated to stably maintain the coil at a constant temperature for a long time.