JPS6315729B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in superconducting split magnets.

In general, superconducting split magnets consisting of multiple coils are less stable than superconducting magnets consisting of a single coil, and cannot reach the desired magnetic field, and the superconducting state changes to the normal conducting state at low magnetic fields. There were many transitions (called quenches).

FIG. 1 shows a conventional split magnet using a rectangular superconducting wire. FIG. 1 is a sectional view of the upper half of a split magnet in which two coils are arranged side by side in the coil axial direction, taken along the coil axial direction. As shown in Fig. 1, the bobbin 1, 1' consists of a cylindrical body 2, both ends 3, 3', and a flange (side plate) at the middle 3''.The coil portion has the following characteristics from the winding direction: In the left-hand coil 1' of FIG. 1, a superconducting wire 4 is drawn in from the left side and is sequentially wound 4', 4'', 4, . . . while being pressed against the inner surface of the flange 3'. A gap 5 is inevitably created between the intermediate flange 3'' of the bobbin and the last turn of the superconducting wire due to the precision of the width of the superconducting wire.Subsequently, the second layer is pressed against the intermediate flange 3'' and continues to be wound, leaving no gap. 5'. In this way, multiple layers are wound. Further, the same operation as the left coil 1' is performed on the right side coil 1 to wind the superconducting wire. In this case as well, voids will occur alternately in the flanges 3 and 3''.

This will be explained in detail as follows.
That is, when the superconducting wire 4 itself is viewed in the longitudinal direction, there are minute variations in line width and minute meandering, so the first
In the figure, even if the length of the bobbin body 2, that is, the distance between the inner walls of the flange, is made to be an integral multiple of the line width, the distance between the last turn in each winding layer and the inner wall of the flange is always narrower than the line width. Gaps 5, 5', . . . remain. For example, for a superconducting wire with a line width of 1 to 2 mm, the
A void of 30μ or more remains.

The quality of superconducting magnets depends on whether or not current technology can prevent the movement of the wire by tens of microns due to electromagnetic force. When the magnet is excited, an electromagnetic force is generated due to the magnetic field distribution within the coil, and even if each winding receives force and moves slightly, the kinetic energy of the winding turns into heat and causes the temperature of the wire to rise. This temperature rise exceeds the critical temperature, which is a condition for expecting a superconducting state, and the wire changes from a superconducting state to a normal conducting state, and the wire does not exhibit its full potential. Therefore, it is necessary to manufacture the coil so that the spaces between the turns and between the layers are dense and no voids are formed.If voids are created at both ends of the coil as described above,
This gap is filled with a filler such as putty to form a coil that is tightly attached between the turns.

However, even if the gap is to be filled with a filling material, the width of the gap is different for each layer, and it is impossible to fill the gap with a material that requires precision. That is, this is because the width of the superconducting wire is smaller than the width of the superconducting wire, which is several tenths of a millimeter or several millimeters, whereas the performance of the magnet only allows the superconducting wire to move within 10 μm. Therefore, a magnet having a coil structure filled with a material has poor stability and cannot generate a desired magnetic field.

Also, when considering the distribution of electromagnetic force within the coil, it is in the direction shown by the arrow (→) in FIG. Looking at the left and right coils as one unit,
When current flows in the same direction, an attractive force is created between the left and right coils, and when current flows in the opposite direction, a repulsive force is created.

A more detailed explanation is as follows. If there are no adjacent coils, the rightward force and the leftward force in one independent coil are balanced, and as a result, the left and right forces cancel each other out and produce no force. This is because the magnetic field distribution within the coil is symmetrical with respect to the center. on the other hand,
When there are two coils as shown in FIG. 1, the magnetic field distribution changes depending on the adjacent coil, and the forces that cannot be canceled out remain as attractive or repulsive forces that are not symmetrical. Therefore, when currents flow in the same direction through two coils, the left and right forces are not balanced within the cross section of one coil, and the force as a whole is pressed against the intermediate flange 3'' (→). Therefore, it is considered that the accuracy of the filler packed into the voids 5, 5' is insufficient, so that it cannot fully fulfill its role and is unable to prevent the movement of the superconducting wire.

As a result of intensive research in view of the current situation, the present invention was developed by keeping the superconducting wire in close contact with the flange located in the direction in which the overall force acts, thereby leaving no room for the superconducting wire to move. ,
They discovered that it is possible to prevent the superconducting wire from moving any longer. That is, the present invention is characterized in that, in a superconducting split magnet divided in the axial direction of the coil, superconducting windings are closely arranged on the coil side plates in the direction of the electromagnetic force acting on each coil.

An example of the present invention will be explained in detail based on the drawings. FIGS. 2 and 3 also have an axially symmetrical structure as in the case of FIG. 1, so the cross section of the upper half of the axial cross section is shown. Therefore, as shown in FIG. 2, in coils in which current flows in the same direction, superconducting wires 4,
4', 4'', etc. In this way, the windings of each layer are all in close contact with the intermediate flange 3'', and gaps 5,
5', 5'', . In addition, when the current is passed in the opposite direction, the superconducting wires 4, 4,',
4"... should be in close contact with both end flanges 3 and 3', and gaps 5, 5', 5"... may be created near the intermediate flange 3". Also, three or more bobbins may be arranged in the axial direction of the coil. The same applies to split magnets that are used in parallel, and the direction of the electromagnetic force acting between each coil and the other coils in parallel depends on whether it is attractive or repulsive. The winding wire may be wound closely around the coil side plate (flange) located therein so as not to create any gaps.

Next, examples of the present invention will be described. A stainless steel bobbin was fabricated with a body inner diameter of 60 mm, an outer diameter of 70 mm, a flange diameter of 24.6 mm, an intermediate flange thickness of 30 mm, both end flanges thickness of 25 mm, and an inner width of the coil portion of 45 mm.
Mylar foil was pasted on this bobbin only in the area where the coil was wound to provide electrical insulation between the coil and the bobbin. Furthermore, the superconducting wire is an ultrafine multifilamentary wire consisting of an NbTi filament and a copper matrix, and its cross-sectional area ratio is 1:1.52. Its external dimensions are 1mm x 2
Approximately 25μm of formal insulation is applied.

Such a bobbin and superconducting wire are connected to magnet 2.
A comparison was made between the present invention and a conventional superconducting split magnet.

Conventional Example In the left-hand coil shown in FIG. 1, the superconducting wires 4, 4', 4'' were pressed against the left-hand flange 3' and wound so as not to create any gaps or between the superconducting wires. After winding into a turn, a gap 5 of about 2 mm was created between it and the flange 3''. A thin tanzak-shaped glass epoxy plate was inserted in that area. Subsequently, the second layer was wrapped so as to be pressed against the intermediate flange 3'', and a glass epoxy plate was inserted into the gap 5' between the flange 3' and the flange 3' in the same manner as above.Such operations were repeated until 70 minutes. A layered coil (outer diameter of about 220 mm) was produced.A coil was also produced for bobbin 1 on the right side in the same manner as above.

EXAMPLE First of all, the first layer is wound in exactly the same way as the first layer in FIG. Put a wedge between it and the next closest turn to create a gap. As a result, the turn closest to the intermediate flange 3'' will move into close contact with the intermediate flange 3'', and the air gap 5 will instead move into the wedged position. The next turn is also placed in close contact with the turn closest to the intermediate flange by inserting a wedge. By repeating such operations, the gap 5 in FIG. 1 moves and becomes the gap 5 in FIG. 2.
This will occur at the position. The second layer is wound in the same manner as in the conventional example. By repeating these operations, all of the superconducting wires were brought into close contact with the intermediate flange 3'', and wound in 70 layers to obtain an outer diameter of approximately 220 mm.The same operation was also performed on the bobbin 1 on the right side, and the superconducting wires of each layer were wound. All the voids were created in the right flange 3.

The two coils thus obtained were individually immersed in liquid helium, a DC power source was connected to the coils,
X
- Increase the current recorded on the Y recorder, read the magnetic field generated when the superconducting state is broken and the voltage at both ends of the coil rises rapidly, and the current begins to drop. Repeat this operation to excite. The change in the generated magnetic field with respect to the number of times was investigated. The results are shown in FIG. FIG. 4A shows a conventional magnet, and FIG. 4B shows a magnet of the present invention. In FIG. 4A, the generated magnetic field varies greatly and cannot exhibit stable performance. Furthermore, in FIG. 4B, almost stable performance is obtained after the third excitation. In the drawings, the dotted line portion of the curve means that the helium was taken out of the fluid and the temperature was raised to room temperature.

In these measurement results, it is thought that in the conventional magnet, the superconducting wires 4, 4', 4'', etc. move in the direction of the air gap 5 due to electromagnetic force, and the superconductivity is broken by the heat generated at that time, causing the coil to When the temperature is raised to room temperature and then cooled again, the superconducting wires 4, 4', 4'', etc. return to the position close to the initial excitation state due to thermal stress, creating gaps between the superconducting wires and returning to the initial excitation repetition. This is thought to indicate an upward trend in the generated magnetic field in the near future.

On the other hand, in the embodiment of the present invention, since the flange 3'' and the superconducting wire 4 are in close contact with each other, and the superconducting wires are also in close contact with each other, the displacement of the superconducting wires 4, 4', 4'', etc. due to electromagnetic force is extremely small. It is thought that it settles into a stable position after the first few excitations.

As detailed above, according to the magnet of the present invention,
Since there is no need to fill the voids at the ends of the windings of the superconducting wire, the manufacturing method is simple, and it has remarkable effects such as generating a stable magnetic field.

[Brief explanation of the drawing]

Figure 1 is a sectional view showing the upper half of a conventional magnet centered around the shaft, Figures 2 and 3 are sectional views of the upper half of a magnet according to an example of the present invention centered around the shaft, and Figure 4A. 4B is a curve diagram showing the relationship between the number of excitations and the generated magnetic field in the conventional magnet, and FIG. 4B is a diagram showing the relationship between the number of excitations and the generated magnetic field in the magnet of the present invention. 1, 1'...Bobbin, 2...Body, 3, 3', 3''
...Flange, 4,4',4''...Superconducting wire, 5,
5', 5''...Void portion.

Claims (1)

[Claims] 1. A superconducting split magnet divided in the axial direction of the coil, characterized in that a superconducting winding is closely arranged on a coil side plate (flange) in the direction of electromagnetic force acting on each coil.