JPS6041810B2 - superconducting coaxial line - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a superconducting coaxial line structure that makes it possible to control propagation loss.

Superconducting coaxial cables take advantage of the fact that the high-frequency loss of superconductors is about three orders of magnitude lower than that of normal conductors, and have features such as low loss, wide band, low noise, and no crosstalk in principle. There are some that have

Conventionally, as an example of this superconducting coaxial line, the inner diameter of the outer conductor is 1.6-, the diameter of the inner conductor is O, 5Tn1n, lead is used as the superconductor, and FEP is adopted as the dielectric material. A prototype superconducting coaxial line has been produced.

It is known that the attenuation of these superconducting coaxial lines can be typically expressed by the following equation at a liquid helium temperature of 4.2. α■O, 5f+O, 05f2dBIh) (
f: GH2) (1) That is, in 1GH2, O, 6
Low loss of less than dBlkm has been obtained.

In this equation (1), the first term is the leakage attenuation due to the dielectric, and the second term is the resistance attenuation due to the surface resistance of the lead superconductor. However, when the above-mentioned materials are used, the above-mentioned attenuation amount is almost determined as a value unique to the material, so in order to change the attenuation amount, it is necessary to change the material used.

In that case, another inherent loss is obtained, and any value in between cannot be obtained. In the application of superconducting coaxial lines, especially when you want to use them over short distances, the above loss value is too small, and the effects of reflection and impedance imbalance become a problem.Instead, it is necessary to increase the loss to absorb the above negative effects. , a demand arises to realize stable transmission. In this case, it would be convenient if the loss value could be set arbitrarily. In order to cope with the diversity of these applications, the present invention forms a thin normal conductive layer on the surfaces of the inner and outer conductors of a superconducting coaxial line, thereby making it possible to arbitrarily change the loss value within a certain range. The present invention provides a superconducting coaxial line that can be used as a superconducting coaxial line.

Hereinafter, embodiments will be described in detail with reference to the drawings. Figure 1 shows
This figure shows one embodiment of the present invention, where 1 is a superconductor that becomes an internal conductor, and 2 is a metal material for reinforcing and stabilizing the superconductor 1. Copper, which has good workability, is usually used. used.

3 is an external superconductor, and 4 is a metal material for backing and reinforcing it, and copper or the like, which has good workability, is also used.

5 is a dielectric material made into a solid shape, and 6 is a normal conductive thin layer.

The equivalent circuit per unit length of superconducting coaxial line in such a structure can be approximated as shown in FIG. Here, R
, (f) is the surface resistance of the superconductor, RN(f) is the surface resistance of the normal conducting layer, L is the inductance of the line, C is the capacitance, G(f) is the leakage conductance of the dielectric, and 1 is the frequency. It is. The normal conducting thin layer 6 must be formed below the skin depth of the electromagnetic field, and the electromagnetic field penetrates this thin layer 6 and reaches the superconductors 1 and 3. ing. In this case, the attenuation constant α of the coaxial line can be expressed as follows.

Here, A. ．． b is a constant determined by the material of the dielectric and superconductor, respectively, and c is a constant determined by the material and thickness of the normal conductive layer. In addition, n depends on the resistance state of the normal conductive layer at low temperature, but it is 21 when the normal conductive layer has an abnormal skin effect and 112 when the normal skin effect is present.
There is. Normally, 2 or 3 is expected. As explained above, the loss can be increased by adding the third term to equation (2), but the present invention particularly allows the constant c to be controlled by changing the thickness. There is a principle.
This is because the electromagnetic field is attenuated inside the normal conducting layer, and the thicker the layer, the stronger the effect. However, if it is too thick and all the electromagnetic field exists only within the normal conducting layer, there is a risk of losing the low loss property that is the advantage of superconductivity. Therefore,
Design the thickness to give the desired loss value. As a guideline for the depth δ of the skin effect into which the electromagnetic field penetrates, an example of estimation will be shown in a state where the abnormal skin effect is occurring.

δ is, for example, JOUrIlalOfAppliedPh
ySlCS magazine ■o1-39, NO. Legend PP2592 (
1968), m (electron mass) = 9.1 × 10-31 (K9), e (
Electron charge) = 1.6 x 10-19 (C), μo (vacuum permeability) = 4π x 10'-9 (Hlm), and as an example, the physical property value of lead at a temperature of 4.2 K. Using, ■F (Fermi velocity) = 2.43 × 1σ (7TL1
S), Nn (density of normal conduction electrons in two-fluid model)
=5.25×lσ7(7n-3), and from these δ
=0.36 μm is obtained.

Therefore, a normal conductive layer that is sufficiently thinner than this δ is additionally formed on the superconductor layer (for example, about 10 PWL) by means of vapor deposition, sputtering, plating, or the like. Of course,
The actual forming method, thickness, etc. are determined through experiments, but from the manufacturing standpoint, the above values are sufficiently realistic values as a guide. The above effect has been demonstrated by forming a thin carbon layer on the lead surface of the superconducting coaxial line made of the above-mentioned lead superconductor and FEP dielectric. For example, IEICE Transactions Vol. 63-13, NO. 7.PP. 7l5-72
2 (1980) Study of transmission characteristics of superconducting coaxial lines
As exemplified in , α=0.55f+0 as an example of equation (2) indicating the loss value due to the presence of the carbon layer.
．． 52f2+0.3f213(DBI-)...
・(4) has been actually measured in a superconducting coaxial line of 1 Tsumugi.

That is, in this case, C in equation (2) is 0.3. Also,
This can also be achieved with thin layers such as aluminum. Further, as can be seen from the above explanation, the range in which the loss can be set is the range in which the conductor resistance loss is almost determined by the normal conductor layer loss from the inherent loss values of the superconductor and the dielectric. Note that the effect of the normal conductive layer 6 occurs independently on the surface of the inner conductor 1 and the inner surface of the outer conductor 3, and therefore depends on the degree of loss setting,
Either one may be used depending on conditions such as ease of manufacture.

As explained above, according to the present invention, the characteristics of superconducting coaxial lines are low loss, low noise, and electromagnetic field shielding (no crosstalk).
It has the advantage of being able to set the loss value arbitrarily within a certain range without damaging the signal, and has the effect of absorbing reflections at terminal stations and connection points, as well as deterioration of frequency characteristics due to uneven impedance, especially over short distances. In addition to being considered effective in the case of use, it also has the effect of relaxing the tolerance range of processing dimensional accuracy, which is a factor of impedance unevenness, within the necessary loss.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of one embodiment of the superconducting coaxial line of the present invention, and FIG. 2 is a diagram for explaining the present invention in detail.

Claims (1)

[Claims] 1. In a superconducting coaxial line in which the surface of the inner conductor and the inner surface of the outer conductor are made of superconductors, a normal conducting thin layer with a thickness equal to or less than the depth of the skin effect where the electromagnetic field penetrates is formed on the surface of the inner and outer conductors. A superconducting coaxial line, characterized in that the electromagnetic field is formed such that the electromagnetic field undergoes loss through the normal conducting thin layer.