JPS581487B2 - Manufacturing method of superconducting coaxial cable - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing superconducting coaxial cables, and in particular aims at reducing transmission losses due to periodic variations in the inner diameter of the outer conductor.

As shown in Figure 1, a superconducting coaxial cable consists of a central conductor 1 (superconductor or composite metal with superconductor on the outside) coated with an insulator 2, and a tape-shaped outer conductor 3 coated on top of the insulator 2. (Superconductor or composite metal with superconductor inside) is attached vertically, and then passed through a die and formed to a predetermined outer diameter.

As shown in FIG. 2, the tape 30 used for the outer conductor 3 is rolled with a rolling roll 4 to a desired thickness.

At this time, due to deformation of the bearing of the roll 4 or the roll 4 itself, periodic thickness fluctuations occur in the length direction of the table 30 with a pitch corresponding to the circumferential length of the roll 4.

Figures 3a and 3b illustrate this situation.

"Fig. 3a" is a plan view, where solid lines 31 indicate mountain portions and dotted lines 32 indicate valley portions.

"Figure 3b" is an exaggerated depiction of the variation in thickness corresponding to Figure 3a.

When such a tape 30 is placed vertically on the insulator 2 and pulled out with a die, the outer diameter of the outer conductor 3 becomes constant as shown in "Figure 4a", and the variation in thickness becomes the variation in the inner diameter. appears.

Note that ``Figure 4b'' and ``Figure 4c'' on the left respectively show cross sections taken along lines B--B and c--c in Figure 4a.

The characteristic impedance Zc of the coaxial cable is expressed by the following formula.

Here, ε: relative dielectric constant dl: inner diameter of the outer conductor d2: outer diameter of the inner conductor When the inner diameter of the inner conductor changes periodically as described above, the characteristic impedance Zc also changes periodically.

When the coaxial tube wavelength becomes equal to the pitch of the inner diameter variation (for example, when the roll circumference is 400 mm and the frequency is 250 MHz), the reflected waves due to the periodic uneven characteristic impedance increase, and the transmission The loss will be huge.

This transmission loss is almost negligible in standard coaxial cables.

However, in superconducting coaxial cables, the transmission loss is originally very small, so its influence is very large.

The present invention aims to solve the above problem, and the present invention aims to solve the above problem.
Mountain portion 31 and valley portion 32 due to thickness variation of 0
(As mentioned above, the inner diameter fluctuations do not appear periodically at right angles to the tube axis direction, but appear continuously in a spiral shape, thereby eliminating the periodicity of the inner diameter fluctuation.)

The next K embodiment will be explained.

In the present invention, as shown in "Fig. 5", the tape 3
0 so that the mountain portions 31 and the valley portions 32 appear inclined with respect to the length direction.

How to do this is shown in "Figure 6a" and "Figure 6b"
Shown below.

5 is an open type, narrow and elongated, and has a flat pressure surface.

A tape 30 is fed between the upper and lower molds 5 at a constant speed in a constant direction.

The mold 5 is installed obliquely to the direction of flow of the tape 30, and is vibrated up and down (electromagnetic or mechanical, etc.) to freely forge the tape 30 and drop it to the desired thickness. .

Ideally, the thickness of the processed tape 30 would be completely uniform throughout, but this is not possible.

However, even if there is a variation in thickness, it appears parallel to the direction in which the mold 5 hits.

That is, as shown in FIG. 5, the peaks 31 and valleys 32 are oblique.

When this tape 30 is placed vertically on the insulator 2 and formed,
As shown in "Figures 7a to 7f".

Note that 7b, 7c...Tf diagrams are respectively 7th
Cross sections taken along lines BB, CC, . . . FF in figure a are shown.

At this time, it is important that the peak portions 31 and valley portions 32 of the tape 30 match at the butt line (FIG. 8).

In other words, if we take the case of the mountain portion 31 in Fig. 5 as an example, S
It is important that 1 and R2 match at the butt line of the tape 30 to form a continuous spiral.

In this way, periodic inequalities in characteristic impedance due to periodic fluctuations in the inner diameter of the outer conductor 3 do not appear.

Therefore, an increase in conduction loss due to multiple reflections at a specific frequency does not occur.

In addition, in the case of Fig. 5 and Fig. 8, one mountain part 31
Or, the spiral of the valley part 32 was formed, but "
As shown in FIG. 9, two spirals may be created when the tape 30 is attached vertically.

Furthermore, the number of spirals may be increased by making the distance between the mountain portion 31 and the valley portion 320 closer.

In the present invention, the tape 30 is fed in a certain direction at a certain speed, and an elongated open mold 5 with a flat pressure surface is installed obliquely to the feeding direction and vibrates up and down.
Since the tape 30 is continuously freely forged to a desired thickness, even if the thickness of the tape 30 is not completely uniform, the peak portions 31 and valley portions 32 appear diagonally.

Then, such a tape 30 is vertically spliced and molded so that the peak portions 31 and the valley portions 32 coincide with each other at the tape abutting portions, so that they form a spiral shape that continues in the tube axis direction.

Therefore, periodic non-uniformity in characteristic impedance due to periodic variations in the inner diameter of the outer conductor 3 does not occur as described above, and therefore no increase in transmission loss due to multiple reflections at a specific frequency occurs.

[Brief explanation of the drawing]

Fig. 1 is a general explanatory diagram of the structure of a superconducting coaxial cable, Fig. 2 is an explanatory diagram of a conventional processing method for the tape 30 for the outer conductor 3, and Figs. 3a and 3b are processed by the conventional method. Fig. 4a is a cross-sectional view of a conventional superconducting coaxial cable, and Figs. 4b and 4c are respectively B--B in Fig. 4a.
The cross-sectional views taken along lines B and CC, FIG. 5 and the following are related to embodiments of the present invention.
6a is a schematic plan view of the processing method for the tape 30, FIG. 6b is a side view of the same side, and FIG. Figure 7a is an explanatory diagram of the cross section, and Figures 7b to 7f are the seventh diagram, respectively.
The cross-sectional view taken along B-B-F-F in Figure a, and Figure 8, are for the outer conductor 3.
FIG. 9 is an explanatory diagram showing that the peak portion 31 and the valley portion 32 are spiral-shaped in the tape 30.
1 and a valley portion 32 are formed more densely. FIG. 1... Center conductor, 2... Insulator, 3...
...outer conductor, 4...rolling roll, 5.
...Type, 30...Tape for external conductor, 3
1...Mountain part, 32...Valley part.

Claims (1)

[Claims] 1. The material is fed in a certain direction at a certain speed, and is continuously free-forged into the desired shape using a long and narrow open die 5 with a flat pressure surface, which is installed obliquely to the feeding direction and vibrates up and down. The tape 30 dropped to a thickness of A method for manufacturing a superconducting coaxial cable, characterized by: