JPS63285809A - Superconductive coaxial wire - Google Patents

Abstract

PURPOSE:To reduce the unevenness of characteristic impedance and the like and to make the frequency property of loss excellent by using a molten quartz type glass as a dielectric and an oxide superconductor as a superconductive inner conductor and a superconductive outer conductor. CONSTITUTION:As the material of a dielectric 3, a molten quartz type glass whose dielectric loss is small in a normal temperature and melting point is high is used. As the superconductor, an oxide superconductor which is an R-M-Cu type oxide (R:La or Y, M:Ba or Sr) is used. Such a superconductor can be made into a thin membrane in a spattering, the MBE method, or a spread-and-heat-treatment method. In such a way, a superconductive outer conductor 4 is formed as a thin membrane directly over the molten quartz glass whose outer diameter production accuracy is good, and the outer diameter accuracy of the outer conductor can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a superconducting coaxial line that is extremely fine and has good transmission characteristics.

[Conventional technology]

Superconducting coaxial lines have been studied as extremely low-loss, broadband transmission lines. It also has the feature of being able to transmit electric power.

Coaxial line loss α is generally expressed by the following equation.

α=αg+αr (dB,/Km)
[: ], ]a, = 'Z 2 X / 0''εr
' f ''-δ (dB/Km) [2) αr=
fir &X/06(Rs(f)/,?Zo)(/
/7td/+/7'rdj) (dVKIn) [3] Here, αg is dielectric loss, α1 is conductor loss, and ε
1 is the relative dielectric constant, f is the frequency (in GH2 units), Rs (f
is the surface resistance W) of the conductor, zO is the characteristic impedance (Ω) of the line, and d/, d2 are the diameters of the inner and outer conductors of the coaxial line (in units of snow layer). Dielectric loss is proportional to f, and superconductor conductor loss is approximately r2 due to the frequency dependence of Rs.
It is known that the absolute value of each loss is extremely small compared to the value at room temperature.

Until now, lead has been used as a superconductor, and the dielectric material is Teflon-based F.
In a superconducting coaxial line with an outer diameter of 6 x m using KP, the following experimental results have been obtained as the loss of formula [1].

α=0.6f×0.0tafz (dn, Ab)
...[4] That is, at /GHz, 0. J-,! Low loss of r dB/KlI+,
/ G) It can be seen that below Iz, dielectric loss is the main factor. However, the operating temperature is determined by the liquid helium temperature (lA2
K) had low practicality due to the high cost of the cooling system, including the heat insulating jacket that creates the operating environment, and the difficulty of handling and maintenance.

However, recently, the critical temperature Tc has changed to liquid nitrogen temperature (7
A superconductor with a temperature exceeding 7 K) has been discovered, and the situation has reached a point where the development of room-temperature superconductors is well within reach.

When a high Tc superconductor is applied to a coaxial line, the problem of the cooling system mentioned above can be eliminated, and the original low loss property can be utilized.

[Problem that the invention seeks to solve]

The problems with coaxial lines using high Tc superconductors are:
In commonly used low-loss glass, the dielectric loss increases as the temperature rises compared to the case of cryogenic operation, and increases by about two orders of magnitude near room temperature. ■For application of high Tc superconductors, there is a possibility of deteriorating the dielectric layer. ■
It is thought that characteristic impedance inequalities will increase due to ultra-fine center-to-center shafts, which will deteriorate transmission characteristics.

In the dielectric loss of (2), for example, in polyethylene, which is a low-loss plastic, at a liquid helium temperature of 442, / around GHz, -δ = (37 to 7.0) ×
/(Y6, but at room temperature -δ=, 2./X#)-'
It has been reported that the number increases by two orders of magnitude. The same applies to Teflon and similar materials. ■Currently known oxide superconducting materials require heat treatment at around 1000°C, so the material must be able to withstand such high temperatures, which is considered to be quite difficult with plastic materials. . The problem in ■ is as follows. If the superconducting coaxial line is used in a frequency band where conductor loss is not a problem, the loss will be determined only by the dielectric loss, regardless of the coaxial line diameter, and ultra-fine cores will be possible. If careful attention is paid, the variation in the wire diameter in the length direction (the variation ratio with respect to the diameter) will generally increase, causing problems in transmission characteristics due to variation in characteristic impedance. That is, because the resistance is extremely small, multiple reflections remain unattenuated, resulting in residual pulsations in the time domain, and large excessive loss pulsations in the loss frequency characteristics. However, in the case of ultra-fine conductors, as shown in Figure 3, which is an example of the method for manufacturing the outer conductor of a conventional superconducting fine coaxial line, a superconductor such as lead is rolled onto the surface of an outer conductor base such as copper ≠ O. Dielectric material 3
With the method of coating the outer periphery of /, it was difficult to keep the variation in outer diameter small.

[Means for solving problems]

Therefore, the present invention solves the above problems (1) and (2) by applying a material that (1) has low dielectric loss at room temperature, and (2) has a high melting point and is compatible with superconductors. Typically, fused silica glass is used as the dielectric material. Literature = American engineering n5tituto
Physics Handbook, 3rd, e
6 > j −/31. McGraw-Hill (1
According to 5i'7.2), -δ of fused silica at room temperature
As, 2X/0-5 (10MHz).

/ X / () −' (/ ()OMHz) +
Examples of values have been reported for IX/0-5 (/OG Hz). This value of quartz is smaller than that of polyethylene, and it also tends to have lower loss in high frequency bands.

Regarding (2), the present invention uses a method such as sputtering, vapor deposition, vapor growth, or coating heat treatment to directly form a superconducting external conductor on the outer circumferential surface of the dielectric material with high precision in manufacturing the outer diameter. This problem is solved by forming the outer conductor as a thin film and improving the accuracy of the outer diameter of the outer conductor. In particular, when fused silica glass is used as the dielectric material, its outer diameter and surface quality can be formed with extremely high precision using current optical fiber manufacturing technology.

As superconductors, oxide superconductors that operate at temperatures exceeding liquid nitrogen temperature (77K) have recently been discovered.

R-M-Ou-based oxide (R: La or Y.

The effect of the present invention is greater as a material having a higher critical temperature Tc is used in the oxide superconductor represented by M: Ba or Sr. It is also known that these superconducting materials can be made into thin films and wires by sputtering, MBK, and coating heat treatment methods. In this case, it is important that the superconductor can be formed with good adhesion to the underlying dielectric material, and the fused silica material of the present invention is suitable. According to conventional theory, the surface resistance of a superconductor is exp (-βTc/T), where Tc is the critical temperature and T is the operating temperature.
(β is a constant), and as Tc is high, TO/T can be increased, so conductor loss can be reduced to a negligible level. From this point of view as well, it is advantageous to use oxide superconductors with high critical temperatures, including the above-mentioned types, as superconductors.

〔Example〕

FIG. 1 shows a cross-sectional structure of an embodiment of a superconducting coaxial line according to the present invention. / is a coaxial core wire base made of copper, 2 is a superconducting internal conductor formed on the surface of l, 3 is a dielectric made of quartz glass, ≠ is a thin film formed on the outer periphery of dielectric 3 with good adhesion. It is a superconductor outer conductor, and the outer layer is a protective coating for coaxial lines.

The structure shown in Figure 1 is disassembled in the order of the manufacturing process and shown in Figure 2.
It is a diagram. (a) shows a configuration state in which the outer periphery of the superconducting inner conductor is coated with a dielectric material 3 with well controlled outer diameter. In this case, the dielectric material 3 made of quartz glass is applied with outer diameter control technology cultivated in optical fiber manufacturing technology, and the outer diameter variation can be controlled with extremely high accuracy by ±01! We were able to manufacture it to a size smaller than μm. The outer diameter value is 200 pm, which is similar to that of optical fiber.
This ensures flexibility as a cable. (b) shows a structure in which the above-mentioned superconducting external conductor is formed as a thin film on the outer periphery of structure (eL) using a sputtering method. Here, superconductors C and G are oxide superconductors of yttrium, barium, and copper. In this case, the dielectric fused silica has the advantage that it is a material that can withstand heat treatment of around 10OσC necessary for forming the oxide superconductor, and is compatible with the base material. (c) shows the configuration of (b) with a protective outer cover applied.

Generally, the main loss in superconducting coaxial lines is dielectric loss. According to the above data at room temperature, the frequency f =
/ GHz, in fused silica -δ=ri×1o-5
(interpolation estimation), and from equation [2], αg=/OdB/KIn is obtained with εr=3.7. Almost similar values were obtained in this example as well.

Of course, this value is large compared to the superconducting coaxial line that operates at extremely low temperatures (lAjK), and is suitable for short-distance cables that take shared power transmission into consideration, or broadband wiring cables, rather than long-distance, high-capacity cables. It would be effective as On the other hand, if low-loss polyethylene is used, -δ=2. /
×/(Y', so ε1=23 and αg = , 2
It is twice as high as ydB/-. Regarding the characteristic impedance non-uniformity, according to the above example of the superconducting coaxial line using lead with a diameter of /, l ffa, it is 0. The allowable amount of variation in the diameter of the inner conductor, outer conductor, and dielectric to give an uneven characteristic impedance of /Ω is /, 2.2J.

72μm, characteristic impedance variation ±O1,2Ω
It has been reported that if uniformity within this range is achieved, smooth damping characteristics can be obtained. In the coaxial line of the present invention, the outer conductor diameter and the dielectric diameter are equal, and the allowable outer diameter variation of the dielectric that gives a characteristic impedance variation of 0.2 Ω is approximately 7.3 μm for a diameter of 200 μm.
m. This can be fully achieved by controlling the outer diameter of the optical fiber to within ±0.4-μm. Using the superconducting coaxial line configured as described above, we were able to create an extremely fine signal transmission line with low loss and good frequency characteristics.

〔Effect of the invention〕

As explained above, the superconducting coaxial line of the present invention uses a fused silica dielectric material that has sufficiently low loss even at liquid nitrogen temperatures and is compatible with the formation of oxide superconductors that become superconducting. However, since the manufacturing precision of the outer diameter of the dielectric material is good, the characteristic impedance non-uniformity is reduced by J, and a superconducting coaxial line with excellent loss frequency characteristics can be obtained with good reproducibility.

[Brief explanation of drawings]

Figure 1 is a structural diagram of the superconducting coaxial line of the present invention, and Figure 2 is:
FIG. 3 is a diagram showing the structure disassembled in the order of manufacturing steps.
FIG. 2 is a diagram showing an example of a conventional method for forming an outer conductor of a fine coaxial line. /... Core wire base, 2... Superconducting internal conductor, 3, 3
/...dielectric material, ri, ri/...hui conductive outer conductor,!・
...Outer cover, ≠O...Outer conductor base. Ina 1 Figure (α) (b) (Riga Z diagram v3 diagram

Claims (2)

[Claims] (1) In a superconducting coaxial line consisting of a linear superconducting inner conductor, a dielectric material surrounding it, and a superconducting outer conductor surrounding it, fused silica glass is used as the dielectric material, and the superconducting inner conductor and superconducting A superconducting coaxial line characterized by using an oxide superconductor as an outer conductor. (2) The oxide superconductor is R-M-Cu based oxide (R:L
The superconducting coaxial line according to claim 1, wherein the superconducting coaxial line is: a or Y, M: Ba or Sr).