JPH11233334A - Conduction cooling type superconducting electromagnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent Joule heat generation in a cooling pipe by a method, wherein parts having a relation in that both the direction of turns of the pipe and the number of turns of the pipe can cancel out an induced current in the pipe exist in the pipe in a pair. SOLUTION: An electromagnet 1 has a structure, wherein a superconducting wire is wound on a bobbin 28 on a cylinder, and at the same time, the outer periphery of the cylinder is covered with a bobbin cover 29. A cooling pipe 16 is brought into contact with this electromagnet 1 in a state such that the pipe 16 is wound on the electromagnet 1 with a winding method that the pipe 16 is began to be wound on the respective flanges of upper and lower flanges 2 and 3 of the bobbin 28 from the side of the inflow side 5 of a refrigerant and is ended to wind on the side of the outflow side 6 of the refrigerant. Here, the numbers of turns of the pipe 16 on the respective flanges of the upper and lower flanges 2 and 3 are made equal and the directions of turns of the pipe 16 are set so as to become opposite to each other. Moreover, the inflow side 5 is spirally wound on the inner peripheral surface of the bobbin 28 and is wound spirally on the outer peripheral surface of the bobbin cover 29, in such a way as to fold back from the inner peripheral surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cooling technique in a superconducting magnet apparatus, and more particularly to a cooling technique of a conduction cooling type in which a cooling pipe through which a coolant flows is brought into thermal contact with an electromagnet to perform cooling.

[0002]

2. Description of the Related Art For example, in a nuclear magnetic resonance diagnostic apparatus, a thermophysical property measuring apparatus, an electron accelerator, a synchrotron radiation generator, a magnetic separation apparatus, and the like using a superconducting magnet, the temperature of the magnet is extremely low in order to bring the magnet into a superconducting state. Need to be kept.

Generally, liquid helium is used to cool a superconducting magnet to a very low temperature. A typical cooling method for cooling with liquid helium is an immersion method in which a superconducting magnet is immersed in liquid helium and cooled. Although this immersion method has many practical examples, it has problems such as requiring a large amount of expensive liquid helium and requiring advanced technology for handling liquid helium due to immersion. I have. Therefore, recently, a conduction cooling system has been proposed in which a cooling device is brought into thermal contact with a superconducting magnet to perform cooling.

As one of the conduction cooling methods, there is a technique described in, for example, Japanese Patent Application Laid-Open No. Hei 6-132567. In this technique, a superconducting state of the electromagnet is maintained by cooling a copper block integrated with the bobbin of the electromagnet with a two-stage Gifford McMahon refrigerator. by the way,
The Gifford-McMahon type refrigerator generally has a small refrigerating capacity of about 1 W, and consumes more power than the refrigerating capacity. Therefore, this technique is not suitable for cooling relatively large electromagnets. In this technique, since only a part of the copper block is cooled, the size of the copper block must be increased in order to keep the temperature difference in the electromagnet small in the case of an electromagnet having a large bore diameter. However, enlarging the copper block requires that a large eddy current is generated in the copper block when the magnetic flux density changes drastically due to demagnetization or the like, causing quench (superconducting destruction).
In addition, there is a problem that the cooling time increases due to an increase in heat capacity.

[0005] Such a problem can be avoided by a conduction cooling system in which a cooling pipe through which a cryogenic refrigerant flows is brought into contact with an electromagnet to cool the cooling pipe. An example of such a cooling scheme is
For example, JP-A-62-4309 and JP-B-8-120
No. 42 or Nuclear Instruments and Method
s in Physics Research A238 (1985) p18-34.

[0006]

The method of cooling an electromagnet through a cooling pipe as described above has many advantages, but also has a problem. That is, as long as the electromagnet is cooled to a very low temperature below a predetermined temperature, the superconducting state is maintained, and the amount of heat entering the electromagnet is almost constant. However, in addition to this steady heat, if any part of the heat is abnormally penetrated by heat, the superconducting state of that part is destroyed by the rise in temperature, and the superconducting wire has resistance. And the temperature rise is further accelerated by Joule heat generated by this resistance,
In the worst case, the magnets may be damaged.

[0007] A major source of heat causing abnormal intrusion is Joule heat generated by eddy currents and induced currents (hereinafter simply referred to as induced currents) generated in nearby conductors when the electromagnet is excited or demagnetized. There is. The magnitude of the current induced by the demagnetization depends on the speed of the demagnetization. Therefore, by reducing the speed of the excitation and demagnetization, it is possible to reduce the influence of Joule heat due to the induced current to such a level that there is no practical problem. However, it is often not possible to reduce the speed of excitation / demagnetization in general electromagnet device applications. A typical example is a superconducting magnetic separation device used for treating sludge generated in a sewage treatment plant. This device separates the magnetic material for sludge treatment from the sludge by the high magnetic field generated by the electromagnet and the high magnetic field gradient.In order to regenerate the magnetic filter that has adsorbed the magnetic material, it is necessary to turn off the magnetic field once. Therefore, repetition of demagnetization and excitation operations is indispensable. Since the magnetic filter cannot be adsorbed and separated during reproduction of the magnetic filter, it is necessary to regenerate the magnetic filter in as short a time as possible. Therefore, it is desired to enable a high-speed excitation / demagnetization operation as possible.

[0008] By the way, the conductor which may affect the electromagnet due to Joule heat generated by the induced current includes a bobbin constituting the electromagnet, a bobbin cover, a stabilizing material in the superconducting wire, and a contact with the electromagnet. Cooling tubes. When these conductors have a structure surrounding an electromagnet, a large induced current is generated with a change in the magnetic flux density of the magnet. This current value is much larger in a bobbin, a bobbin cover, and a cooling pipe than in a superconducting wire. However, regarding the bobbin and the bobbin cover, by providing an insulating slit or the like in the bobbin and the bobbin cover, it is easy to avoid a structure surrounding the electromagnet as a continuous conductor. That is, it is easy to make the Joule heat due to the induced current to a level that does not affect practically.

What remains is a cooling tube. By making this cooling pipe not to have a structure surrounding the electromagnet, it is possible to reduce the Joule heat due to the induced current to a level that does not affect practically. However, this requires the cooling pipe to be divided into a plurality of systems, which causes a serious problem. One of them is that the structure for cooling is greatly complicated, but what is more problematic is that the cooling becomes uneven and unstable. That is, when there are a plurality of cooling pipe systems, there is a possibility that temperature unevenness occurs between them.
Then, in a system in which the temperature happens to be lower than that of the other systems, the flow resistance in the system is reduced, so that the refrigerant is concentrated. However, this phenomenon accelerates. For this reason, in other systems, the amount of the refrigerant flowing therethrough decreases, and the necessary cooling cannot be performed. Thus, it can be said that it is not practical to divide the cooling pipe into a plurality of systems to deal with the induced current.

The present invention has been made on the basis of the above-described findings, and relates to a conduction cooling type superconducting magnet apparatus for cooling a superconducting electromagnet to a very low temperature through a cooling pipe. In particular, it is a main object of the present invention to effectively solve the problem of Joule heat accompanying it, and in addition to this, to provide more uniform and stable cooling.

[0011]

According to the present invention, one or more electromagnets formed in superconductivity are cooled to a very low temperature by thermal contact with a cooling pipe through which a refrigerant flows. In the conduction cooling type superconducting magnet device, the cooling tube is wound around the electromagnet, and the winding direction of the cooling tube is inconsistent with respect to the generation of the induced current in the cooling tube due to the excitation and demagnetization of the electromagnet. The portions are paired in one continuous cooling tube, and the number of turns in the pair substantially reduces the induced current in the cooling tube associated with the excitation and demagnetization of the electromagnet. The number of turns has a relationship that can be canceled.

As described above, the cooling pipe is brought into contact with the electromagnet in a winding manner, and the winding direction and the number of windings of the winding contact make it possible to cancel the induced current in the cooling pipe. By making the portions exist in pairs, a state in which the induced current is canceled between the paired portions is obtained, and therefore, the problem of Joule heat generation in the cooling pipe can be effectively eliminated.

In such a conduction cooled superconducting magnet device, it is easy to use a single cooling pipe for the cooling pipe,
By doing so, more uniform cooling can be performed more stably.

A typical method of winding the cooling tube around the electromagnet in the conduction cooling type superconducting magnet device according to the present invention as described above is a method of spirally winding the cooling tube around the electromagnet.

When such a spiral winding is applied to an electromagnet formed by winding a superconducting wire around a cylindrical bobbin and covering the superconducting wire with a bobbin cover, the bobbin and the bobbin Preferably, a spiral groove is formed in at least one of the covers, and the cooling pipe is wound around the groove so as to be embedded in the groove.

By doing so, it is possible to prevent the outer diameter of the electromagnet from being increased by the cooling pipe and the effective diameter inside the bobbin from being reduced by the cooling pipe. This means that when compared with the case where the cooling pipe protrudes from the bobbin or bobbin cover and the case where the external dimensions and the effective diameter inside the bobbin are the same,
This leads to a thicker bobbin and bobbin cover. This leads to more uniform cooling. That is, in the electromagnet as described above, the cooling pipe comes into thermal contact with the bobbin and the bobbin cover, but in this case, the thicker the bobbin and the bobbin cover, the larger the heat transfer area, The temperature difference between the part in contact with the cooling pipe and the part not in contact with the cooling pipe can be made smaller, and thus the uniformity of cooling can be improved.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below. FIG. 1 shows a superconducting electromagnet which is a main part of the conduction cooling type superconducting magnet device according to the first embodiment, and FIG. 2 shows the entire configuration thereof. In FIG. 2, the cold generator 21 arranged in the cold generating circuit for pre-cooling is constituted by, for example, a Gifford McMahon expander (GM expander). The high-pressure gas of the helium compressor unit 22 flows into the cold generator 21 and adiabatically expands inside the helium compressor unit 22.
Generates 0K cold. The expanded gas returns to the compressor unit 22 again.

On the other hand, J isolated from the cold generation circuit for pre-cooling
-Compressor unit 23 of T (Joule Thomson) circuit
The high-pressure helium gas pressurized to about 1.6 MPa through the first heat exchanger 26, the second heat exchanger 27,
Third heat exchanger 8, fourth heat exchanger 9, and fifth heat exchanger 10
Sequentially. A first JT valve 12 is provided in the high-pressure flow path after the fifth heat exchanger 10, and the helium gas that has passed through the fifth heat exchanger 10 expands to a pressure of about 0.8 MPa. Thereafter, the helium gas enters the sixth heat exchanger 11, and further expands to about 0.12 MPa at the second JT valve 13 to reach a temperature of about 4.5K.
And flows into the cooling pipe 16 which is in thermal contact with the electromagnet 1.

The electromagnet 1 has a structure in which a superconducting wire (not shown) is wound around a cylindrical bobbin 28 and the outer periphery thereof is covered with a bobbin cover 29. The bobbin 28 is formed of copper or an aluminum alloy, and in some cases, is formed of stainless steel, FRP, or the like. The superconducting wire is NbTi
It is formed by insulating coating around superconducting material such as Nb3Sn and stabilizing material such as copper. The superconducting wire wound around the bobbin 28 is fixed and has a high thermal conductivity by impregnating the gap with an epoxy resin or the like, and has a structure suitable for conduction cooling. The bobbin cover 29 functions to withstand an electromagnetic force (hoop force) that pushes the electromagnet itself outward, and is formed of an aluminum alloy, stainless steel, copper, or the like.

With respect to the electromagnet 1, the cooling pipe 16 starts to be wound on the upper flange 2 and the lower flange 3 of the bobbin 28, for example, from the inlet side 5 of the refrigerant and ends on the outlet side 6 of the refrigerant. They are in contact with each other in such a winding manner. The number of turns of the cooling pipe 16 in each of the upper flange 2 and the lower flange 3 is the same (shown as one turn in the figure), and the winding directions of the upper flange 2 and the lower flange 3 are opposite to each other. It is to be. Therefore, the cooling pipe 16 which is one continuous pipe has a relationship in which the winding directions are opposite and the number of turns is the same, that is, the induced current accompanying the demagnetization of the electromagnet 1 can be substantially canceled. Since the portions are paired, the induced current generated in the cooling pipe 16 due to the demagnetization of the electromagnet 1 is canceled between the paired portions, so that Joule heat can be prevented.

The conductor that can generate an induced current with the excitation and demagnetization of the electromagnet 1 includes, in addition to the cooling pipe 16, the bobbin 2
8. There is a bobbin cover 29 and a stabilizing material in the superconducting wire. However, with respect to the superconducting wire, there is no problem of Joule heat because current flows through the filament having zero resistance. Further, the bobbin cover 29 and the bobbin 28 can avoid Joule heat by blocking the path of the induced current by preventing the bobbin cover 29 from circling the electromagnet 1 as a continuous conductor. Therefore, bobbin cover 2
9 is divided into two parts by a dividing part 4 with an insulator interposed therebetween by FRP or the like, and the bobbin 28 is provided with a plurality of slits 7 filled with an insulating adhesive or the like to be electrically discontinuous. To be.

The cooling pipe 16 is connected to the electromagnet 1 as described above.
The electromagnet 1 is cooled to a very low temperature by a two-phase flow helium of about 4.5 K flowing through the magnet. Through this process, the liquid helium that has been subjected to the heat load due to the heat intrusion from the outside evaporates in the cooling pipe 16, and becomes a low-pressure two-phase flow helium in which the proportion of gas is increased. After the low-pressure two-phase helium enters the low-pressure side flow path of the sixth heat exchanger 11, the fifth heat exchanger 10, the third heat exchanger 8, and the first heat exchanger 26
, And heat exchange with the high-pressure helium gas during this time, so that the temperature becomes almost normal temperature and returns to the compressor unit 23 from the low-pressure side flow path 15.

The inside of the cryostat 18 is vacuum-insulated, and the cryogenic portion is shielded from external radiant heat by a heat shield plate 17 cooled by a liquid nitrogen tank or a first stage 24 of a cold generation circuit. It is. Although not shown in the figure, a laminated heat insulating material is wound around the outside of the heat shield plate 17 so as to further reduce the penetration of radiant heat. Further, an impurity in the helium gas is removed by providing an adsorber in the pipe.

In the present embodiment, the GM
Although the example using the JT refrigerator is shown, the same effect is obtained in the case of a refrigerator having one JT valve, that is, a refrigerator having no first JT valve 12 and sixth heat exchanger. Also GM / JT
The same effect is obtained even when a refrigerator other than the above is used, or when two-phase helium is transported from a liquid helium tank and cooled by the transport pipe. Further, the effect is not limited to the two-phase flow, and the same effect can be obtained when cooling is performed by a cooling pipe through which supercritical helium flows or a cooling pipe through which low-temperature helium gas flows. In the above description, an example is described in which the magnet is made of a low-temperature superconductor such as NbTi or Nb3Sn. However, the same effect is obtained when a magnet made of a high-temperature superconductor such as an oxide superconductor is used. As the refrigerant, nitrogen can be used in addition to helium, and hydrogen, neon, or the like can also be used.

FIG. 3 shows a main part of a conduction cooling type superconducting magnet device according to a second embodiment. In the present embodiment, the cooling pipe 16 is wound around the outer peripheral surface of the bobbin cover 29. The cooling pipe 16 is composed of a left-handed part when the winding is started from the refrigerant inflow side 5 and a right-handed part starting from the end of the left-handed part. . Further, each winding portion is drawn in a zigzag pattern so as to make more efficient thermal contact with the bobbin cover 29 having a large surface. When the cooling tube 16 is brought into contact with the bobbin cover 29 as described above, it is preferable that the bobbin cover 29 be formed of a material having a high thermal conductivity, such as an aluminum alloy or copper.
Also, the space between the bobbin cover 29 and the superconducting wire is filled with an epoxy resin or the like to improve the thermal conductivity. With the structure according to the present embodiment, uniform cooling is possible even with a magnet having a long axial length. Further, the structure according to the present embodiment is more suitable for a magnet having a small width.

FIGS. 4 and 5 show the principal part of a conduction cooling type superconducting magnet device according to a third embodiment. The electromagnet in the present embodiment is, for example, a split type which is divided into an electromagnet 1a and an electromagnet 1b each formed by winding a bobbin 28a, 28b and a bobbin cover 29a, 29b. Split-type electromagnets are used, for example, when it is necessary to work in a uniform magnetic field for MRI (magnetic resonance imaging apparatus) or NMR (nuclear magnetic resonance apparatus), or when it is desired to reduce the burden on a patient by MRI. Or M
When operating other devices in a uniform magnetic field space, such as CZ (magnetic field single crystal pulling device), or when you want to move the filter in the magnetic field space out of the magnetic field space, such as in a continuous magnetic separation device. Used for

Also in the case of such a split type, it is preferable that the cooling system be a single system and the cooling pipe 16 be a single system. That is, the cooling pipe 16 is a single continuous pipe.
Is straddled over the electromagnet 1a and the electromagnet 1b to be brought into contact. By doing so, control becomes easy even if there is a slight difference between the temperatures of the two magnets 1a and 1b. In addition, only one refrigerator is required, and the structure and control system are simplified. Thus, the cooling pipe 16 common to both magnets 1a, 1b
Is contacted with the cooling pipe 16 as shown in FIG.
Of the pair, the winding direction is opposite to each other, and the number of turns in each part of the pair is
6, the problem of Joule heating can be solved if the number of turns is such that the induced current can be canceled. In the example of FIG. 5, the two magnets 1a and 1b have the same size on the concentric axis and the same exciting ability, so that the number of turns of each part is the same. FIG. 5 shows an example in which the directions of the two magnets 1a and 1b are the same. For this reason, the mechanical winding directions of the cooling pipes 16 for the two magnets 1a and 1b are opposite to each other. When the directions of the magnets 1a and 1b are opposite to each other, the mechanical winding direction of the cooling pipe 16 is made the same for both the magnets 1a and 1b. That is, the winding direction of the cooling pipe in the split type is determined by the relationship with the direction of the induced current that can be generated in the cooling pipe.

FIGS. 6 and 7 show the essential parts of a conduction cooling type superconducting magnet device according to a fourth embodiment. In this embodiment,
One continuous cooling pipe 16 is spirally wound around the outer and inner circumferences of the electromagnet. Specifically, assuming that the cooling pipe 16 is wound from the inflow side 5 of the refrigerant, the inflow side 5 is first spirally wound around the inner peripheral surface of the bobbin 28, and then turned back around the outer peripheral surface of the bobbin cover 29. The portion wound around the bobbin 28 and the portion wound around the bobbin cover 29 are wound in opposite directions to each other and have the same number of turns. The spiral of the cooling pipe 16 is arranged in a staggered relationship between the bobbin and the bobbin cover. By doing so, the cooling pipe 1
6, the spacing between the spiral rings can be substantially reduced, and the temperature non-uniformity between the spiral rings can be reduced.

Further, the bobbin 28 and the bobbin cover 29 are provided with a groove 16g of about the outer size of the cooling pipe 16 corresponding to the spiral path of the cooling pipe 16 in a spiral manner.
A cooling pipe 16 is embedded in the cooling pipe. For this reason, the cooling pipe 16 does not protrude from the bobbin 28 or the bobbin cover 29, so that the bobbin 28 and the bobbin cover 29 are provided under the condition that the external dimensions of the electromagnet and the effective diameter inside the bore portion thereof are desired. Can be made thicker. As a result, the heat transfer area of the bobbin 28 and the bobbin cover 29 is increased, and the temperature difference between the portion in contact with the cooling pipe 16 and the portion not in contact with the cooling pipe 16 can be further reduced, and the uniformity of cooling can be improved. The structure of the present embodiment as described above can be similarly applied to the split type described in the third embodiment.

[0030]

As described above, according to the present invention,
The problem of Joule heat generated by the induced current in the cooling pipe can be effectively solved, and it can contribute to the performance improvement of the conduction cooling type superconducting magnet device that cools through the cooling pipe.

[Brief description of the drawings]

FIG. 1 is a simplified perspective view showing an electromagnet which is a main part of a conduction cooling type superconducting magnet device according to a first embodiment.

FIG. 2 is a configuration diagram of a conduction cooling type superconducting magnet device according to the first embodiment.

FIG. 3 is a simplified perspective view showing an electromagnet which is a main part of a conduction cooling type superconducting magnet device according to a second embodiment.

FIG. 4 is a configuration diagram of a conduction-cooled superconducting magnet device according to a third embodiment.

FIG. 5 is a simplified perspective view showing an electromagnet which is a main part of a conduction cooling type superconducting magnet device according to a third embodiment.

FIG. 6 is a simplified perspective view showing an electromagnet which is a main part of a conduction cooling type superconducting magnet device according to a fourth embodiment.

FIG. 7 is an end view in which the electromagnet of FIG. 6 is sectioned in an axial direction.

[Explanation of symbols]

 1 Electromagnet 16 Cooling tube 16g Groove 28, 28a, 28b Bobbin 29, 29a, 29b Bobbin cover

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Minoru Morita 502, Kandachicho, Tsuchiura-shi, Ibaraki Pref.

Claims (4)

[Claims] 1. A conduction cooling type superconducting magnet device comprising one or a plurality of electromagnets formed so as to be brought into thermal contact with a cooling pipe and cooled to a very low temperature, wherein said cooling pipe is wound around said electromagnet. A conduction cooling type superconducting device, wherein the cooling tube is wound around the electromagnet so that the induced voltage is not generated in the cooling tube when the magnetic flux generated by the electromagnet is changed with time. Magnet device. 2. The conduction-cooled superconducting magnet device according to claim 1, wherein said cooling pipe is formed by a single system. 3. The conduction-cooled superconducting magnet device according to claim 1, wherein the cooling pipe is spirally wound around an electromagnet. 4. The electromagnet has a structure in which a superconducting wire is wound around a cylindrical bobbin and the superconducting wire is covered with a bobbin cover, and a spiral groove is formed in at least one of the bobbin and the bobbin cover. 4. The conduction-cooled superconducting magnet device according to claim 3, wherein the cooling tube is wound around the groove so as to be embedded in the groove.