JPH0311604A - Superconductive magnet - Google Patents

Abstract

PURPOSE:To increase a critical conduction density while decreasing the leakage rate of a trapped magnetic flux even in a high magnetic field and thereby to enable generation of the high magnetic field by a method wherein a crystal of an oxide superconductor shaped in a flat-plate ring is stacked vertically to the face of a flat plate. CONSTITUTION:A molded body formed by molding an oxide superconductor in the shape of a cylinder, or a body obtained by sintering this molded body, is melted by a band melting method in a furnace having a temperature gradient in a direction vertical to the central axis of the cylinder. Thereby a plate-shaped crystal is precipitated vertically to the central axis and solidified under the temperature gradient, so that a structure of stacked plate-shaped crystals be formed. The structure is so formed that the plate-shaped crystal has a part of being continuous in the shape of a ring as a single crystal even when it is inclined a little to the axis of the cylinder. According to this method, the structure has characteristics that a critical conduction density is high and the leakage rate of a trapped magnetic flux is low even under a high magnetic field.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a superconducting magnet.

[Prior Art] Conventionally, superconducting magnets that operate at liquid helium temperatures have been constructed by forming a wire made of an intermetallic superconducting material into a coil shape. Attempts have also been made to manufacture superconducting magnets using oxide superconductors that operate at liquid nitrogen temperatures by winding sintered oxide superconductors into wires or tapes into coils.

[Problems to be Solved by the Invention] A superconducting magnet requires a superconducting material that has a high critical current density in a high magnetic field and has a low leakage rate of trapped magnetic flux. A superconducting magnet constructed from a sintered body is
It was not possible to generate a high magnetic field mainly because the critical current density in the magnetic field was low due to weak coupling between grains, and the leakage rate of the trapped magnetic flux was large.

[Means for Solving the Problems] The present invention provides a superconducting magnet in which flat ring-shaped crystals of an oxide superconductor are stacked perpendicularly to the plane of the flat plate.

The superconducting magnet of the present invention has a structure in which a single crystal ring is formed and the rings are stacked, so that it has a high critical current density even under a high magnetic field and a low leakage rate of trapped magnetic flux.

In the superconducting magnet of the present invention, each of the flat ring-shaped crystals only needs to be continuous as a single crystal, and cracks may exist between the crystals. Moreover, it is preferable that an oxide containing at least one of the metal elements constituting the oxide superconductor exists between the crystals, and binds the ring-shaped crystals.

The oxide superconductor of the present invention is not particularly limited in composition and can be applied to various oxide superconductors. For example, it can be preferably applied to materials containing rare earth elements, alkaline earth metals, and copper.

Examples of the method for manufacturing the superconducting magnet of the present invention include the following.

For example, a cylindrical molded body of oxide superconductor, or a sintered product of the oxide superconductor, is processed perpendicular to the central axis using the zone melting method in a furnace with a temperature gradient perpendicular to the central axis of the cylinder. The superconducting magnet of the present invention can be obtained by precipitating plate-like crystals. When an oxide superconductor is solidified under a temperature gradient, a structure in which plate-shaped crystals are stacked can be obtained relatively easily. The plate-shaped crystal does not need to be exactly perpendicular to the axis of the cylinder; even if it is slightly inclined, it suffices as long as it has a continuous ring-shaped portion as a single crystal.

The superconducting magnet of the present invention can also be obtained by molding an oxide superconductor in which plate crystals are oriented and stacked, which is obtained by a directional solidification method or the like.

When the superconducting magnet of the present invention is excited by applying a high magnetic field from the outside, it becomes a good superconducting magnet in which a high magnetic field is maintained within the cylinder even after the external magnetic field is removed.

[Example] Y2O3, BaCO5, CuO in atomic ratio Y:Ba:
After weighing and mixing Cu = 1:2:3, 90
It was baked at 0°C for 12 hours. The obtained powder was pressed into a cylindrical shape with an outer diameter of 20 mm, an inner diameter of 8 mm, and a height of 10 mm using a mold, and then fired at 920° C. to obtain a cylindrical sintered body. This is because the temperature in the center is high (maximum temperature 1050℃)
In a vertical tubular electric furnace where the temperature is low at the top and bottom, the cylinder is moved gradually from the bottom to the top, with the axis of the cylinder being horizontal.
Directional solidification by zone melting was performed. Furthermore, 400℃,
Annealing was performed in oxygen for 80 hours. The obtained material has a structure as shown in Figure 1, with a flat ring-shaped YBa2
Cua07 crystals were stacked, and although cracks were observed between them due to anisotropy of thermal contraction, YJaCuO5 particles precipitated during directional solidification bound the tabular crystals.

When the critical temperature of this material was measured using the AC magnetic susceptibility method, T
The onset of c was at 92. The critical current density determined by measuring the magnetization curve at liquid nitrogen temperature was 9200 A/cm2 under a single magnetic field. Further, after this cylinder was cooled to liquid nitrogen temperature in the external magnetic field of IT, the central magnetic field of the cylinder was 0.2 T after the external magnetic field was removed.

[Effects of the Invention] The superconducting magnet of the present invention has a high critical conductivity density even in a high magnetic field. Furthermore, the leakage rate of the captured magnetic flux is low, and a high magnetic field can be generated.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the structure of a superconducting magnet obtained in an example of the present invention. FIG. 2 is a partially enlarged view of FIG. 1.

Claims (3)

[Claims] (1) A superconducting magnet in which flat ring-shaped crystals of oxide superconductor are stacked perpendicularly to the plane of the flat plate. (2) The superconducting magnet according to claim 1, wherein the flat ring-shaped crystals are bonded by an oxide containing at least one of the metal elements constituting the oxide superconductor. (3) The superconducting magnet according to claim 1 or 2, wherein the oxide superconductor contains a rare earth element, an alkaline earth metal, and copper.