JPH0583162B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to energy saving of superconducting equipment.

[Conventional technology]

FIG. 2 is a front view of a conventional current lead disclosed in, for example, Japanese Utility Model Application Publication No. 62-91463. In the figure, 1 is the copper main body, 2 is the connection terminal for the power supply,
Reference numeral 3 indicates a connection terminal of a superelectric motor, 4 a grading layer made of a superconductor made of NbTi, and 5 a grading layer made of a superconductor made of Nb _{3 So.}

Next, the operation will be explained. Superconducting equipment is generally immersed and cooled in liquid helium. Liquid helium is a cryogenic fluid, and due to the laws of thermodynamics, its production requires large amounts of electrical power. Normally, in order to liquefy liquid helium at a liquefaction rate of 1/h, a refrigerator input of, for example, 350 to 700 ohms is required. On the other hand, the latent heat of liquid helium is very small, and a heat input of 0.7ω evaporates 1/h of helium.

Therefore, the heat input due to conduction from the current leads,
Alternatively, efforts must be made to reduce the heat input due to the heat generated by the unit as much as possible. For this purpose, in the conventional example, a grading layer 4 made of a superconductor of NbTi and a grading layer 5 made of a superconductor of Nb _{3 So} are used at the low-temperature end of the current lead. Since superconductors have zero electrical resistance, there is no Joule heat generation, and superconductors generally have low thermal conductivity, so the heat input to liquid helium is reduced.

[Problem that the invention seeks to solve]

A conventional current lead is constructed as described above. However, the critical temperature of NbTi is about 9K,
The critical temperature of Nb _{3 So} is about 18.2 K, so for example
When the top temperature of Nb _{3 So} rises above 18.2K, superconducting breakdown occurs. When a superconductor breaks down, its electrical resistance is much higher than that of copper, etc., so it generates a large amount of heat, which causes an avalanche of superconducting breakdown, which can lead to accidents such as burnout of current leads. .

This invention was made to solve the above-mentioned problems, and aims to provide a current lead that can stably maintain a superconducting state.

[Means for solving problems]

The current lead according to the present invention has a thermal anchor at the middle part of the current lead at the temperature of liquid nitrogen, and uses a superconductor whose critical temperature is higher than the boiling point of liquid nitrogen in the part below the thermal anchor.

[Effect]

In the current lead of the present invention, the temperature of the superconductor portion is always maintained below its critical temperature, so superconductor breakdown does not occur.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, 1 to 3 are the same as in FIG. 2, and 6 is a superconductor whose critical temperature is higher than the boiling point of liquid nitrogen. Reference numeral 7 denotes a heat exchanger as a thermal anchor, which is soldered to the copper main body 1, for example. 8 is a liquid nitrogen inlet, 9 is a liquid nitrogen outlet,
10a and 10b are insulating joints.

Next, the operation will be explained. Since the high temperature end of the superconductor 6 is maintained at a temperature below the boiling point of liquid nitrogen by the liquid nitrogen heat exchanger 7, superconductivity does not break down. As the superconductor 6, for example, Y-Ba-Cu-
Use O-based oxide.

It has been experimentally confirmed that this substance has a critical temperature of 80K or higher, which is higher than the boiling point of liquid nitrogen, which is 78K.

In the above embodiment, the thermal anchor is at liquid nitrogen temperature and the superconductor is Y-Ba-Cu-O based oxide. However, if the superconductor has a higher critical temperature, the Therefore, a thermal anchor using a refrigerant having a higher boiling point may be used.

〔Effect of the invention〕

As described above, according to the present invention, a thermal anchor is provided in the middle part of the current lead at a temperature of liquid nitrogen, and a superconductor whose critical temperature is higher than liquid nitrogen is provided in the part below the thermal anchor, so that the temperature of the superconductor part is reduced. The temperature is always maintained below the critical temperature, resulting in stable operating characteristics.

[Brief explanation of the drawing]

FIG. 1 is a front view showing a current lead according to an embodiment of the present invention, and FIG. 2 is a front view showing a conventional current lead. In the figure, 7 is a heat exchanger thermal anchor, 8
9 is a liquid nitrogen inlet, and 9 is a liquid nitrogen outlet. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1. In a current lead that supplies current to a superconducting device in liquid helium, the middle part of the current lead is a thermal anchor at the temperature of liquid nitrogen, and the part of the lead below the part of the current lead where the thermal anchor is taken from the liquid nitrogen is kept at the critical temperature. A current lead characterized by using a superconductor whose temperature is higher than the boiling point of liquid nitrogen.