JPS61202407A - Superconductive magnet for nmr-ct - Google Patents

Abstract

PURPOSE:To prevent the deformation of a coil at cooling by reducing a difference in heat shrinkage between the coil and an aluminum bobbin by employing a superconductive wire using aluminum as a stabilizing material. CONSTITUTION:In a cooling medium container 2 surrounded by a room- temperature container 1 of a cryostat, a coil 10 is held and is cooled by liquid helium 3 filling the container 2. A bobbin 6 of the coil 10 is formed of aluminum as a lightweight material. For a superconductive wire 11 forming the coil 10, an aluminum stabilizing superconductive wire in which a superconductive material 13 of filament form is buried in the aluminum 12 is used.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a superconducting magnet for NMR-CT (nuclear magnetic resonance computed tomography) that eliminates the need for training up to rated operation.

[Conventional technology and its problems]

In superconducting magnets for NMR-CT, aluminum is usually used as the bobbin material. This is to reduce the cross-sectional area of the support by reducing the weight of the bobbin, and to minimize heat intrusion from the outside using the support as a heat transfer path.

That is, as shown in FIG. 6, the above-mentioned magnet is housed and held in a refrigerant container 2 surrounded by a room-temperature container 1 of the cryostat.
e) 3, but if the amount of heat entering through the support 4, which is provided in the adiabatic vacuum part to support the container 2, is large, it will be difficult to maintain the superconducting state, so the cross-sectional area of the support is It is desired to make the superconducting magnet 5 as small as possible, and in order to meet this demand, the bobbin 6 of the superconducting magnet 5 is made of aluminum, which is a lightweight material.

By the way, in the conventional superconducting magnet for NMR-CT, a superconducting wire with NbTi filaments buried in stabilized copper is wound thinly around an aluminum bobbin 6 as shown in the figure. The disadvantage is that several training sessions are required to achieve rated operation in order to prevent (transfer to).

In other words, the amount of heat shrinkage of aluminum due to a temperature change from room temperature to 4.2 is 4,300 microns, while that of copper is 33 microns.
00μ/m. On the other hand, there is a general dimensional difference in NMR-mm. Therefore, the magnet is deformed as shown in FIG. Further, when an electromagnetic force is applied, a compressive force in the axial direction is generated, and a compressive strain of about 1000 μ is applied to the coil 7.

This strain acts on the coil, which has become arcuate due to cooling, so the coil buckles as shown by the chain line in the figure and quenches. Traditional magnets require training to avoid this quench, wasting time, power, and cryogen.

[Means for solving problems]

The present invention solves this problem by making the thermal shrinkage rates of the aluminum bobbin and the superconducting wire wound around it similar. That is, NMR-CT that does not require training
A superconducting magnet for use in this field is realized by winding a superconducting wire using aluminum or aluminum and copper as a stabilizing material around an aluminum bobbin. Figure 1 shows its overall structure. This magnet is almost the same as the conventional magnet shown in Fig. 6 except for the superconducting wire forming the coil 10. Therefore, the same parts are given the same reference numerals and the explanation is omitted, and the following is a detailed explanation of the superconducting wire. Describe only the structure.

The superconducting wire 11 shown in FIG. 2 is an aluminum stabilized superconducting wire in which a filament-shaped superconducting material 13 is embedded in aluminum 12. The superconducting wire used in the magnet of the present invention is not limited to this aluminum matrix type wire, but may also be one using a composite material of copper and aluminum as a stabilizing material.

Figures 3 to 5 are examples of wires using the composite stabilizing material, and the wire in Figure 3 is a copper-stabilized superconducting wire in which the superconducting material 13 is coated with copper 14, which is further coated with aluminum 12. It is.

Further, the wire in FIG. 4 is made by twisting a copper-stabilized superconducting wire and a wire made of aluminum 12, while the wire in FIG. It is a collection of coated wires.

Note that the superconducting material 12 is made of NbTi 5Nb3Sn,
Any type such as Nb-Zr may be used.

Further, the superconducting wire shown in FIGS. 4 and 5 may be formed by integrating a copper-stabilized superconducting wire and an aluminum wire or a copper-covered aluminum wire through solder.

Furthermore, when using a composite stabilizer, it is desirable that the cross-sectional area of the aluminum be larger than that of the copper and superconducting material.

In addition, if the stabilized aluminum has a purity of 4N or more, the stability of the magnet will be greatly improved. This is because the electrical resistance is lower than that of electrolytic copper, which delays magnetic flux movement, and improves thermal conductivity and improves cooling performance, which suppresses the so-called flags jump phenomenon in which a large amount of magnetic flux moves suddenly. As described above, in the present invention, by using a superconducting wire made of aluminum as a stabilizing material, the difference in thermal contraction between the coil and the aluminum bobbin is reduced, so that when cooling This prevents the coil from deforming, and the coil undergoes simple compression in the axial direction during excitation, so there is no risk of buckling.

Furthermore, although the coil is deformed by sliding relative to the bobbin due to simple compression, this deformation occurs gradually, and therefore no quench occurs even if training is abolished and rated operation is directly started.

In addition, since the specific gravity of aluminum is approximately 1/3 that of copper, the cross-sectional area of the support can be reduced even if the cross-sectional area of the stabilizing material is made equal to or larger than the conventional one, thereby reducing the amount of external heat intrusion. Since this decreases, the amount of LHe evaporation can also be reduced.

Furthermore, the magnet is cooled in advance to 77.3k with liquid nitrogen, and then cooled to 4.2k with LHe.
The amount of LHe required for cooling from 7.3 k to 4.2 k is 1.421/LICu for copper and 0.5 for aluminum.
91711AI, the consumption of LHe during cooling can also be reduced to about 1/3.

Also, when cooling, the coil and bobbin contract together,
Since there is no complicated deformation, the uniformity of the magnetic field is also increased.

In addition, by using stabilized aluminum with a purity of 4N or higher, the stability is greatly improved as described above.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing the entire superconducting magnet of the present invention, FIGS. 2 to 5 are cross-sectional views showing an example of superconducting wire wound around the magnet, and FIG. 6 is a conventional magnet. The cross-sectional diagram and FIG. 7 are explanatory views of the deformed state of the coil. 1... Room temperature container, 2... Refrigerant container, 3... LHe
14...Support, 5...Superconducting magnet, 6.
... aluminum bobbin, 10 ... coil, 11 ... superconducting wire, 12 ... aluminum, 13 ... superconducting material,
14... Copper patent applicant Sumitomo Electric Industries Co., Ltd. Agent Kama 1) Text 2q)

Claims (3)

[Claims] (1) A superconducting magnet for NMR-CT, characterized in that a superconducting wire using aluminum or aluminum and copper as a stabilizing material is wound around an aluminum bobbin. (2) A superconducting magnet for NMR-CT according to claim (1), wherein the stabilized aluminum has a purity of 4N or higher. (3) The aluminum and copper stabilized superconducting wire has a structure in which a copper stabilized superconducting wire is coated with aluminum, a structure in which a copper stabilized superconducting wire and an aluminum wire are twisted together, or a structure in which a copper stabilized superconducting wire and a copper-coated aluminum wire are twisted together. Claim No. 1 (1) is characterized in that the structure is a collection of lines.
) or (2), the superconducting magnet for NMR-CT.