JPH065419A - Spool of superconducting magnet - Google Patents

Abstract

PURPOSE:To prevent a quench from being generated using a groove as a cooling hole and to increase the replenishing intervals of liquid helium. CONSTITUTION:A spool 1 is constituted into a double structure consisting of a spool 11 on inner diameter side, which is small in heat shrinkage factor and is made of a stainless steel, and a spool 12 on the outer diameter side, which is large in heat conductivity and is made of aluminum, and when a superconducting magnet is cooled to a cryogenic temperature, an inner-direction force necessary for preventing the generation of a quench is ensured by reducing the heat shrinkage of a superconducting coil 3 and even if one part of a superconducting wire 30 is exposed from liquid helium, the quench is hardly generated by improving a cooling effect to the wire 30 by cooling heat which is conducted through the spool 12. As the result, even if the helium is consumed and the liquid level of the helium is lowered to some degree, the lowering can be allowed. Thereby, the intervals between the replenishments of the liquid helium can be made long.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting magnet reel formed by winding a superconducting wire around a reel, such as a superconducting magnet of a nuclear magnetic resonance diagnostic apparatus.

[0002]

2. Description of the Related Art In order for a superconducting magnet to maintain a superconducting state, it is necessary that the temperature, the current and the generated magnetic flux density are smaller than their respective critical values. These critical values are the critical temperature, the critical current and the critical magnetic flux, respectively. It is called density. The superconducting state is maintained only when all of the temperature, the current, and the generated magnetic flux density are below their respective critical values, and even if one exceeds the critical value, the superconducting state transitions to the normal conducting state. Quench occurs. When the quench occurs, the magnetic energy stored in the superconducting magnet is released as Joule heat due to the resistance of the superconducting wire in the normal conducting state, causing a large amount of evaporation of expensive liquid helium as a refrigerant. In addition, the temperature of the superconducting wire forming the superconducting magnet may rise due to the Joule heat described above, and there is a risk of burning. For this reason, it is well known that quench is harmful to superconducting magnets.

As a cause of quenching, an electromagnetic force proportional to the product of the magnetic flux density and the exciting current is generated in the superconducting wire, the superconducting wire is displaced, and the frictional heat at that time heats the superconducting wire to exceed the critical temperature. The first reason is that a local quench is generated and propagates to all superconducting coils. Therefore, in order to prevent the displacement of the superconducting wire due to this electromagnetic force, various measures have been taken, and the tension applied when winding the superconducting wire and the structure of the winding frame for winding the superconducting wire into a superconducting coil. Is also an important factor.

FIG. 5 is a sectional view of a conventional superconducting magnet.
In this figure, the bobbin 100 comprises a cylindrical portion 101, an upper collar 102 and a lower collar 103, and the superconducting wire 30 has the cylindrical portion 101, the collars 102, 10 as shown.
It is wound in the space surrounded by 3. The superconducting wire 30 is wound with a predetermined number of layers and turns while applying tension to form the superconducting coil 3. The distance between the collars 102 and 103 in the vertical direction in the drawing determines the number of turns of one layer, and the radial protrusion size of the collars 101 and 102 determines the number of layers. The number of turns of the superconducting coil 3 is per layer. It is the product of the number of turns and the number of layers.

The superconducting wire 30 is wound while tension is applied as described above, and the inward force Ft shown in the drawing tends to contract the winding frame 100. On the other hand, when a superconducting magnet is excited,
A magnetic flux is generated by the current flowing in the superconducting coil 3, and an electromagnetic force proportional to the product of the magnetic flux density and the current of each superconducting wire 30 is generated in each superconducting wire 30 and the outward force Fe as the total force is shown in the figure. Is applied in the opposite direction to the above-mentioned inward force Ft.

When the outward force Fe becomes larger than the inward force Ft, the superconducting wire 30 is lifted up, so that it becomes unstable and easily displaced, and the above-mentioned quenching easily occurs. Therefore, as one of the means for preventing the quench, the inward force Ft may be increased. The maximum inward force Ftm is the tensile strength of the superconducting wire 3 and the reel 100.
Is determined by the strength of. That is, when a soft superconducting wire is wound with excessive tension, the winding frame 100 bears most of the inward force Ft due to this tension, and the winding frame 100 is deformed, and the distribution of the magnetic field is distorted. There is a problem that there is a risk of not being able to obtain.

The material that can be used as the bobbin 100 is limited to copper, aluminum and its alloys, stainless steel and titanium because of the requirements such as ensuring the required allowable stress at extremely low temperatures and being a non-magnetic material. It Stainless steel is limited to non-magnetic steel. In practice, aluminum and stainless steel are often used because of their strength, workability, and low cost.

Aluminum is a relatively flexible material,
In the reel 100 using this, the maximum inward force Ftm is determined by the mechanical strength of the reel 100 even with a winding tension less than the tensile strength of the superconducting wire 30. Determined by dimensions such as wall thickness. On the other hand, stainless steel is a relatively strong material,
The maximum inward force Ftm is determined by the tensile strength of the superconducting wire 30 because it is easy to manufacture the winding frame 100 that is sufficiently strong.

In consideration of heat shrinkage due to cooling, aluminum generally has a larger shrinkage due to cooling than superconducting wires, and stainless steel generally has a smaller heat shrinkage due to cooling than superconducting wires. That is, when the superconducting magnet is cooled by liquid helium, the inward force Ft tends to decrease due to the difference in thermal contraction when the reel 100 is aluminum, and the inward force Ft increases conversely when the reel 100 is stainless steel. There is a direction to do.

From the above reasons, it can be said that stainless steel is suitable as the material of the reel for the purpose of preventing quenching due to displacement of the superconducting wire 30. By the way, the superconducting magnets used in MRI devices and magnetic levitation trains which have been put into practical use in recent years utilize the feature that the resistance of the superconducting wire at cryogenic temperature is substantially zero, and It is operated in a so-called permanent current mode in which a current is semi-permanently applied in a short-circuited state without applying voltage. The advantage of the persistent current mode is that it does not require energization by a power source as described above, and that a stable high magnetic field can be obtained for a long period of time by periodically replenishing liquid helium as a refrigerant. Therefore, in order to take full advantage of the maintenance-free advantage of the permanent current mode, it is necessary to lengthen the replenishment interval of liquid helium.

In order to lengthen the liquid helium replenishment interval described above, it is of course necessary to accommodate the superconducting coil 3 and minimize the heat penetration into the cryogenic container in which the liquid helium is immersed, and at the same time, the liquid surface It is necessary to secure a large allowable consumption of liquid helium by maintaining stable cooling of the superconducting wire against deterioration. FIG. 6 is a cross-sectional view showing cooling heat flows 51 and 52 when the liquid surface 41 of the liquid helium 4 of the superconducting magnet is lowered and a part of the superconducting magnet is exposed. In this figure, the superconducting wire 30 below the liquid surface 41 is cooled by the liquid helium 4 and kept at 4.2K which is the evaporation temperature of the liquid helium. On the other hand, the temperature of the exposed superconducting wire 30 rises as the liquid level 41 lowers, but the cooling heat 51 due to heat conduction from the lower part of the winding frame 100 through the cylindrical portion 101 and the collar 102 and the unexposed superconducting wire 3 from this to It is cooled by both the flow of the cooling heat 52 which is sequentially transmitted through the adjacent superconducting wires 30 and goes up.

Among the bobbin materials mentioned above, the thermal conductivity of aluminum at 4.2K is 100 times or more that of stainless steel. If the bobbin 100 is made of an aluminum alloy, even if the superconducting wire 30 is exposed, it is wound. If a part of the frame 100 is below the liquid surface, the temperature rise of the exposed part can be suppressed to some extent low. On the other hand, in the case of a stainless steel reel, the reel 1
When 00 is exposed from the liquid surface 41, the temperature of the exposed portion rises because the thermal conductivity is small, and the temperature of the superconducting wire 30 rises regardless of a slight exposure to exceed the critical temperature and induce quenching. That is, when the reel 100 is made of stainless steel, it is necessary to replenish the liquid helium 4 frequently so that the winding is not exposed in order to prevent quenching during energization. Even if the superconducting wire 30 is exposed, stable cooling can be maintained.

From the above reasons, it can be said that aluminum is suitable as the material of the reel 100 for the purpose of increasing the replenishment interval of liquid helium.

[0014]

As described above, when determining the bobbin material of the superconducting magnet, stainless steel is suitable in the sense of preventing quenching due to displacement of the superconducting wire. On the other hand, in order to maintain stable cooling of the superconducting magnet and to lengthen the liquid helium replenishment interval, aluminum is suitable as the reel material, which contradicts each other, prevents quenching, and keeps the liquid helium replenishment interval. There is a problem that there is no suitable reel material to achieve both the purposes of lengthening.

An object of the present invention is to solve the above problems, and to provide a reel of a superconducting magnet capable of preventing quenching and extending the refilling interval of liquid helium.

[0016]

In order to solve the above-mentioned problems, according to the present invention, a bobbin of a superconducting magnet in which a superconducting wire is wound to form a superconducting coil is provided with an inner-diameter side bobbin and an outer-diameter side bobbin. Consisting of a frame, the inner diameter side reel is made of a material having a small heat shrinkage, the outer diameter side reel is made of a material having a high thermal conductivity, the material of the inner diameter side reel is stainless steel, The material of the outer diameter side winding frame is aluminum,
Further, a predetermined number of cooling holes are provided with the surface on the inner diameter side of the outer diameter side winding frame as at least a part of the inner surface, and a groove is formed along the axial direction on the outer diameter surface of the inner diameter side winding frame. The cooling holes are provided to form the cooling holes, and the cooling holes are formed by providing grooves on the inner diameter surface of the outer diameter side winding frame along the axial direction.

[0017]

In the structure of the present invention, the bobbin is composed of the inner diameter side bobbin and the outer diameter side bobbin which are coaxially and closely adhered to each other, and the inner diameter side bobbin is made of a material having a small heat shrinkage ratio to achieve extremely low temperature. When cooled, it suppresses thermal contraction of the superconducting wire and the outer winding frame to secure the inward force of the superconducting wire, and the outer diameter side winding frame is made of a material with high thermal conductivity to reduce liquid refrigerant and superconductivity. Even when a part of the wire is exposed from the liquid refrigerant, the lower part of the outer diameter side winding frame is cooled by the liquid refrigerant and the thermal conductivity is good, so that even the part exposed from the liquid refrigerant maintains a sufficiently low temperature to cool the superconducting wire. Therefore, the exposed superconducting wire is less likely to be quenched. Also, as the material for the inner diameter side reel, stainless steel or titanium is practically used because it is necessary to maintain the required mechanical strength even at extremely low temperatures, but the use of stainless steel makes it cheaper and the outer diameter side reel is Copper or aluminum is practically used as the material, but aluminum is more suitable in terms of workability and weight. In addition, by providing cooling holes for cooling the outer diameter side reel to increase the contact area between the outer diameter side reel and the refrigerant, the portion exposed from the liquid surface of the refrigerant can be sufficiently cooled and fall. Cooling of the superconducting wire exposed from the surface becomes more reliable. As the cooling holes, a groove may be provided on the outer peripheral surface of the inner winding frame along the axial direction, or a groove may be provided on the inner peripheral surface of the outer winding frame along the axial direction. Also, the cooling holes can be easily provided.

[0018]

EXAMPLES The present invention will be described below based on examples.
FIG. 1 is a sectional view of a superconducting magnet showing an embodiment of the present invention. In this figure, the bobbin 1 comprises an inner diameter side bobbin 11 and an outer diameter side bobbin 12, wherein the inner diameter side bobbin 11 is made of stainless steel and the outer diameter side bobbin 12 is made of aluminum.

Stainless steel is characterized by a small thermal conductivity, a large allowable stress, and a small heat shrinkage ratio.
Since the heat shrinkage rate is small when used for the inner diameter side winding frame 11, when the superconducting wire is immersed in liquid helium so as to be in a superconducting state and cooled to an extremely low temperature, the outer diameter side winding frame 12 and the superconducting wire The reduction of the diametrical dimension due to the contraction is suppressed, and for this reason, the pulling force is applied especially to the superconducting wire. Originally, as described above, the superconducting wire has a winding method in which tension is applied to apply an inward force, but due to the reason described above, this inward force is further increased by cooling to an extremely low temperature. . Therefore, in order to obtain the required inward force, the tension at the time of winding may be small. Instead, the inner diameter side bobbin 11 bears the inward force of the outer diameter side bobbin 12 and the superconducting wire 3, and therefore must have a strength sufficient to withstand this. Since stainless steel has a large allowable stress as described above, it is easy to manufacture the outer diameter side winding frame 12 that sufficiently satisfies the need.

Aluminum is characterized by its light weight, high thermal conductivity, and good workability, and is used more as a reel material than copper. In the case of a conventional aluminum reel, it is not high-purity aluminum in order to secure mechanical strength, but has a permissible stress several times larger than this, for example, manganese or magnesium called A5803 in JIS is 1% to several percent. % Aluminum alloy is used. Therefore, although the same aluminum alloy as the conventional one may be used as the outer diameter side winding frame 12, the inner diameter side winding frame 11 bears the inward force, and the outer diameter side winding frame 12 has a larger thermal conductivity. It is also possible to simply use aluminum for reasons such as desirable.

The superconducting magnet is manufactured by the following procedure. The outer diameter side bobbin 12 is fitted into the inner diameter side bobbin 11 to form the reel 1
To form. At this time, the outer diameter dimension of the inner diameter side winding frame 11 and the inner diameter dimension of the outer diameter side winding frame 12 are set so that a gap is generated to such an extent that the fitting work is not difficult. Since they are not fixed to each other as they are, some method of fixing the outer diameter side winding frame 12 to the inner diameter side winding frame 11 is required when mounting the winding frame 1 on the winding machine. Attach the reel 1 to the winding machine. The winding frame 1 is rotated by the winding machine, and the superconducting wire 3 is wound a predetermined number of times while applying tension as described above. The tension at this time is set to an appropriate value in consideration of the inward force applied when cooled to an extremely low temperature as described above. The one in which the winding frame 1 and the superconducting coil 3 wound around this are integrated is removed from the winding machine. It is stored in a cryogenic container (not shown), cooled, and finally immersed in liquid helium. At this time, the outer diameter side reel 1
2 and the superconducting wire 30 shrink more largely than the inner diameter side bobbin 11, so that the gap between the inner diameter side bobbin 11 and the outer diameter side bobbin 12 disappears to be integrated as the bobbin 1.

FIG. 2 is a cross-sectional view of a superconducting magnet showing an embodiment of the present invention different from that of FIG. 1. The difference from FIG. 1 is that the inner diameter side winding frame 11 and the outer diameter side winding frame 12 are connected by bolts 20. This is a fixed point, and the outer diameter side winding frame 12 of FIG. 1 is different from the outer diameter side winding frame 12 of this figure in that a through hole for the bolt 20 is provided, but the same reference numeral is used because no confusion occurs. Similarly, the inner diameter side winding frame 11 is different from the inner diameter side winding frame 11 of FIG. 1 in that bolt holes for the bolts 20 are provided, but in this case as well, the same reference numerals are attached. .

A plurality of bolts 20 are provided equidistantly in the circumferential direction, and by tightening the bolts 20, the inner diameter side winding frame 11 is fixed so as not to idle during the winding operation.
FIG. 3 is a sectional view taken along line AA of FIG. In this figure, six grooves are equidistantly provided on the inner surface of the outer diameter side winding frame 12 to form cooling holes 6, and the liquid helium 6 is filled therein to cool the outer diameter side winding frame 12. It is effective. If these cooling holes 6 are not provided, the upper surface is the liquid level 4 as can be seen in FIGS.
When exposed from 1, the portion of the outer diameter side reel 12 that contacts the liquid helium 4 is only a part of the lower collar 123, and the inner surface of the cylindrical portion 121 is the cylindrical portion 11 of the inner diameter side reel 11.
Since it is covered with 1 and does not contact the liquid helium 4, the flow of the cooling heat 51 shown in FIG. 6 becomes insufficient. The cooling hole 6 solves such a problem.

FIG. 4 is a cross-sectional view showing the structure of the cooling holes different from that of FIG. 3 at the same position as in FIG. 4. The difference from FIG.
This is that the cooling hole 6A is provided on the outer diameter surface of the inner diameter side winding frame 11A, and in this respect, unlike the inner diameter side winding frame 11 of FIG. 3, the outer diameter side winding frame 12A is also not provided with the cooling hole 6. Figure 3 in dots
Is different from the outer diameter side winding frame 12. Figure 3 shows the structure of the cooling holes.
The superiority and inferiority of the configuration of the cooling hole 6 of FIG. 4 and the cooling groove 6A of FIG. The advantage of the configuration of FIG. 3 is that three of the four faces forming the cooling hole 6 are in contact with the outer diameter side winding frame 12 to be cooled, so that the cooling effect is large. There is a drawback that the mechanical strength of the reel 12 is reduced. On the other hand, in the configuration of FIG. 4, one of the four surfaces of the cooling hole 6A is
Since only the surface is in contact with the outer diameter side winding frame 12, the cooling hole 6A
If there are the same number of cooling holes 6 and the same cross-sectional shape, the cooling effect will be one-third, and the mechanical strength of the inner diameter side winding frame 11A will be reduced. In both cases, the decrease in mechanical strength can be dealt with by increasing the wall thickness of the respective cylindrical portion 111 or 121, and is therefore not a serious problem. As described above, the mechanical strength is the inner diameter side bobbin 11
Or, since most of 11A is loaded, the outer diameter side bobbin 1
Since it is not necessary to expect much about the mechanical strength of 2 or 12A, it may be better to provide the cooling holes 6 in the outer diameter side winding frame 12 as shown in FIG. 3, but there is not such a big difference. Instead, the optimum configuration may be adopted for each superconducting magnet.

The cooling hole 6 or 6A is provided on the inner diameter side winding frame 11 or 1.
It is sandwiched between 1A and the outer diameter side winding frame 12 or 12A to form a cooling hole. Alternatively, the through hole may be directly provided in the cross section of the outer diameter side winding frame 12. In this case, the cooling hole has a circular cross section because of workability, but it is easier to work by providing the groove on the inner surface or the outer surface than by providing the through hole. From the viewpoint of workability, it can be said that the workability in FIG. 4 in which the groove is formed on the outer diameter surface is better than that in FIG. As for the method of forming these cooling holes, the optimum one will be selected individually. The fixing with the bolt 20 is temporary, and when the superconducting wire 3 is wound and cooled to an extremely low temperature, the outer diameter side winding frame 12 contracts and comes into close contact with the inner diameter side winding frame 11, so that the bolt is fixed. 20 is optional. Therefore, a structure different from the bolt 20 can be adopted as a temporary fixing method. Further, by using a winding machine that can directly apply a rotational force to the outer diameter side winding frame 12, the fixing to the inner diameter side winding frame 11 can be omitted. Furthermore, as described above, the combination with the inner diameter side bobbin 11 is performed not before the winding operation of the superconducting wire 3 but after the superconducting wire 3 is wound.
It is also possible to adopt a method of combining 1. In this case, the amount of contraction of the outer diameter side winding frame 12 due to the winding of the superconducting wire 3 reduces the added amount of the inward force of the superconducting wire 3, and the degree of close contact with the inner diameter side winding frame 11 is reduced. It is necessary to consider beforehand that it will be reduced.

[0026]

As described above, according to the present invention, the bobbin has the double structure of the inner diameter side winding frame and the outer diameter side winding frame, and the inner diameter side winding frame is made of a material having a small heat shrinkage rate and cooled to an extremely low temperature. When heat is applied, the heat shrinkage of the superconducting wire and the outer winding frame is suppressed to secure the inward force of the superconducting wire, and the outer diameter side winding frame is made of a material with high thermal conductivity. Even when a part of the outer diameter side winding frame is exposed from the liquid surface and the cooling effect is reduced, the lower part of the outer diameter side winding frame is cooled by the liquid refrigerant and the thermal conductivity is good. Since the superconducting wire is cooled, the exposed superconducting wire is less likely to be quenched, and as a result, the allowable consumption of the liquid refrigerant can be increased, and the replenishment amount of the liquid refrigerant per one time is increased to replenish it. The effect of being able to lengthen the intervals of the Obtained. Further, stainless steel is inexpensive as the material of the inner diameter side bobbin and has a high allowable stress, and aluminum is suitable as the material of the outer diameter side bobbin in terms of workability and weight. Further, cooling holes for cooling the outer diameter side winding frame are provided in a circumferential distribution to increase the contact area between the outer diameter side winding frame and the liquid refrigerant so that the portion exposed from the liquid surface is also sufficiently cooled. By doing so, the exposed superconducting wire can be cooled more reliably. As the cooling holes, a groove may be provided on the outer peripheral surface of the inner winding frame along the axial direction, or a groove may be provided on the inner peripheral surface of the outer winding frame along the axial direction. Also, it is easy to form cooling holes.

[Brief description of drawings]

FIG. 1 is a sectional view of a superconducting magnet showing an embodiment of the present invention.

FIG. 2 is a sectional view of a superconducting magnet showing an embodiment of the present invention different from that of FIG.

3 is a sectional view taken along the line AA of FIG.

4 is a cross-sectional view at the same position as in FIG. 4 showing a configuration of cooling holes different from that in FIG.

FIG. 5 is a sectional view of a conventional superconducting magnet.

6 is a cross-sectional view showing the flow of cooling heat when a part of the superconducting magnet shown in FIG. 5 is exposed.

[Explanation of symbols]

 1 reel 11 inner diameter side reel 11A inner diameter side reel 111 cylinder part 112 collar 12 outer diameter side reel 12A outer diameter reel 121 cylinder part 122 collar 123 collar 3 superconducting coil 30 superconducting wire 4 liquid helium (liquid refrigerant) 41 Liquid level 6 Cooling hole 6A Cooling hole

Claims (5)

[Claims] 1. A winding frame of a superconducting magnet, which forms a superconducting coil by winding a superconducting wire, comprises an inner diameter side winding frame and an outer diameter side winding frame, and the inner diameter side winding frame is made of a material having a small heat shrinkage ratio. The outer diameter side reel is made of a material having a high thermal conductivity, and the reel is a superconducting magnet reel. 2. The material of the inner diameter side bobbin is stainless steel,
The superconducting magnet reel according to claim 1, wherein the material of the outer diameter reel is aluminum. 3. The bobbin for a superconducting magnet according to claim 1 or 2, wherein a predetermined number of cooling holes are provided with at least a part of the inner surface of the outer diameter side winding frame being the inner surface. 4. The cooling hole is formed by providing a groove along the axial direction on the outer diameter surface of the inner diameter side winding frame.
Winding frame of the superconducting magnet described. 5. A cooling hole is formed by providing a groove along the axial direction on the inner diameter surface of the outer diameter side winding frame.
Winding frame of the superconducting magnet described.