JP2597339B2 - Superconducting magnet manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to a method for manufacturing a superconducting magnet for preventing quench.

(Conventional technology) A superconducting magnet manufactured using a superconducting wire can produce a small and powerful magnet as compared with a normal conducting magnet. However, in the superconducting magnet, the superconducting state of the superconducting wire forming the coil may be broken and quench may occur.

One of the causes of the quench is an electromagnetic force acting on the superconducting wire forming the superconducting magnet when the superconducting magnet is excited. By the action of this electromagnetic force, the superconducting wire forming the coil slips, generating frictional heat. Due to the frictional heat, when the temperature of the wire rises and exceeds the critical temperature, a part of the superconducting wire is changed from a superconducting state to a normal conducting state. The portion in the normal conduction state generates an electric resistance value, and generates Joule heat because it is energized. Due to this heat generation, the region exceeding the critical temperature further increases, and eventually the entire coil becomes a normal conduction state. When such a state occurs, the coil may be damaged due to an increase in temperature or generation of a high voltage.

Conventionally, in order to prevent quenching of a superconducting wire, there is known a stabilized superconducting wire. 3 and 4 are cross-sectional views of the stabilized superconducting wire. As shown in FIG. 3, it is a wire rod in which a superconducting material 5 such as NbTi is embedded in a stabilizing material 6 such as oxygen-free copper. The stabilizing material 6 is excellent in heat conduction and has a large heat capacity.

The stabilizing wire is roughly divided into two types in terms of the ratio of the superconducting material to the stabilizing material. The cross-sectional area of the superconducting material of the stabilizing wire is S _Cu , and the cross-sectional area of the stabilizing material is S _S. The cross-sectional area ratio of the stabilizer / superconducting material: (S _Cu / S _S ) is an amount related to the stability of the superconducting wire. A superconducting wire having this ratio: (S _Cu / S _S ) of 7 or more is referred to as a completely stabilized superconducting wire because of its high stability.

In the above-mentioned fully stabilized superconducting wire, even if the temperature rises in a part of the wire due to disturbance, since the heat capacity of the wire is large compared to the calorific value, the rising temperature is small and the superconducting temperature does not exceed the critical temperature. The state is maintained, and then cooled by the refrigerant, and the temperature can be restored to the initial temperature. Further, in this case, even if the normal conduction state is temporarily established, the state can be recovered. If the coil of the superconducting magnet is formed of such a superconducting wire, a superconducting magnet that is unlikely to quench can be manufactured.

On the other hand, a superconducting wire having a cross-sectional area ratio of stabilizing material / superconducting material: (S _Cu / S _S ) of about 2 to 3 as shown in FIG. 4 is called an incompletely stabilized superconducting wire.

In the superconducting magnet, the place where the quench phenomenon occurs is a place where the electromagnetic force acts most strongly, that is, several layers of the innermost shell of the coil. Conventionally, there is a method of forming a coil of a superconducting magnet by a grading method in order to prevent such a quench phenomenon. The grading method is a method in which the cross-sectional area of the superconducting wire in the superconducting wire forming the inner layer of the coil, in which the magnetic field acts strongly, is increased to reduce the current density of the superconducting wire. FIG. 5 is an explanatory view of the grating method. The superconducting wire used for the coil outer layer is a wire, and the wire used for the coil inner layer is c wire and d wire. Although the diagram showing the wire is a schematic diagram of the cross section of the wire, it does not necessarily show the actual structure of the wire, but expresses the ratio between the superconducting material and the stabilizing material. Sectional area shaded portion of the center of the superconducting material of the circle: the S _Cu, the cross-sectional area of the blank portion is stabilizing material surrounding: shows the S _S. c wire, and cross-sectional area of the superconducting material of the d-line material: S _Cu is larger than the S _Cu of a wire. The difference between the c-wire and the d-wire is the cross-sectional area ratio of the stabilizer / superconductor. c wire ratio: _{(S Cu} / S S) is the ratio of a wire: _{(S Cu} / S S) to equal the d-line material ratio: (S _Cu /
S _S ) is smaller than the ratio of a-wire material: (S _Cu / S _S ). The grating method uses an a-wire material for the outer layer and a b-wire material, a c-wire material or an intermediate wire material for the inner layer.

(Problems to be Solved by the Invention) In the above-mentioned grating method, the cross-sectional area ratio of the stabilizing material / superconducting material of the wire used for the inner layer is about the same as that of the superconducting wire used for the outer layer. Or less, which is insufficient in terms of resistance to quench.

Further, when a coil is formed only of the above-described safety-stabilized superconducting wire, there is a disadvantage that the coil becomes large because the cross-sectional area of the superconducting material is smaller than the entire cross-sectional area.

An object of the present invention is to prevent quenching and to obtain a new method for manufacturing a small superconducting magnet.

[Constitution of the Invention] (Means for Solving the Problems) The above-mentioned grating method is a method of increasing the cross-sectional area of the superconducting material of the superconducting wire in the inner layer of the coil to reduce the current density to prevent quench. On the other hand, the method of the present invention uses a completely stabilized superconducting wire having a large heat capacity as a superconducting wire forming an inner layer of a coil to prevent quench, and a coil layer outside the same is constituted by an incompletely stabilized superconducting wire. It is something to do.

A superconducting wire having a small cross-sectional area ratio of the stabilizing material / superconducting material has a disadvantage that quenching is apt to occur, but there is an advantage that the coil can be miniaturized when manufactured. A superconducting wire having a large cross-sectional area ratio of the stabilizing material / superconducting material is unlikely to cause quench, but requires a large total cross-sectional area, resulting in an increase in size of the coil. Thus, the present invention has been accomplished as a result of careful consideration of the features of these wires and the locations where quench occurs.

FIG. 6 schematically illustrates the method of the present invention.
The difference between the a wire used for the coil outer layer and the b wire used for the coil inner layer is the cross-sectional area ratio of the stabilizing material / superconducting material.
As in FIG. 5, the hatched portion represents the superconducting material, and the surrounding blank portion represents the stabilizing material. Wire a is an incompletely stabilized superconducting wire, and wire b is a completely stabilized superconducting wire. As is clear from this figure, if the coil is formed only with the b wire, the size will be increased.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view of a coil portion of a superconducting magnet of the present invention.
A superconducting wire is wound around the coil winding frame 1 over n layers to form a superconducting coil. The first and second layers on the innermost layer side are formed of the fully stabilized superconducting wire 2. The third or more layers are formed of the incomplete superconducting wire 3.

Electromagnetic force applied to the coil wire at the time of excitation, at both ends of the first layer, it is applied a force F ₂ as shown in FIG. In FIG. 2, showing a coil wire around the center portion of the first layer of the coil, the electromagnetic force F ₁ exerted on該線material. The first layer and the second layer are particularly strongly affected by the electromagnetic force, and the wire slightly moves and slips, but the frictional heat generated thereby causes the first layer and the second layer to be safely stabilized. Absorbed and dispersed by the superconducting wire and collected without quench.

[Effect of the Invention] According to the manufacturing method of the present invention, there is an effect that a high-performance superconducting magnet that is small and hardly causes quench can be manufactured.

[Brief description of the drawings]

1 is a sectional view of a coil of a superconducting magnet according to an embodiment of the present invention, FIG. 2 is an enlarged view of a coil portion, FIG. 3 is a sectional view of a completely stabilized superconducting wire, and FIG. FIG. 5 is an explanatory view of a grating method, and FIG. 6 is an explanatory view of a wire used in the present invention. 1 ... Coil winding frame, 2 ... Fully stabilized superconducting wire, 3 ... Incompletely stabilized superconducting wire, 4 ... Superconducting wire, 5,7 ... Superconducting material, 6,8 ... Stabilizing material

Claims (1)

(57) [Claims] In the manufacture of a superconducting magnet using a superconducting wire, an inner layer of the superconducting coil which is subjected to a strong electromagnetic force is constituted by a completely stabilized superconducting wire, and an outer coil layer is incompletely stabilized. A method for manufacturing a superconducting magnet, comprising a superconducting wire.