Cryogenic Connection Enclosure

Abstract

Cold enclosure having a tubular shape, surrounding the conductors of a cryogenic connection, consisting of two layers of composite material, joined together by a metallic connection, an outer cover made of an iron and nickel alloy in which the proportion of nickel comprises between thirty and forty per cent, and an inner layer of copper or aluminum, this inner layer preventing the generating of alternating induced fields in the outer cover, which is magnetic.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention concerns a composite tubular cold container surrounding the conductors of a cryogenic connection, these conductors carrying an alternating current or a direct current comprising a residual wave.

2. Description of the Prior Art

The producing of cryogenic connections in which the conductors are contained in a cold container, this cold container carrying a cooling fluid, is known in the carrying of high electric power. In the case of a cryogenic connection having an invariable length, the conductors can consist of "invariable" cables, and the cold container which surrounds them of an iron and nickel alloy having low relative thermal contraction, comprising 30 to 45 per cent of nickel. This is, for example, the case of an alloy known by its trade name "INVAR", produced and commercialized in France by Messrs. Metallurgy d'Imphy.

The use of conductive casing to reduce losses caused by induced currents in the vicinity of cables is also known. An electric screen common to a cable or to a group of cables can also be adopted in a conventional way.

These various devices undergo a thermal contraction when they are cooled, and must be arranged either in a helical configuration, or in the form of corrugated tubes.

This cold contaIner, whose magnetic permeability is high, is the seat of electromagnetic losses due to induced alternating currents.

The aim of the present invention is to overcome this disadvantage.

SUMMARY OF THE INVENTION

The object of the present invention is a cold container made of a composite material, having a tubular shape, surrounding the conductors of a cryogenic connection, comprising a casing made of an iron and nickel alloy whose nickel concentration is comprised between 30 and 45 per cent, characterized in that a metal screen having a resistivity lower than 3.10.sup.-.sup.8 ohms. meter surrounds the conductors inside said casing.

BRIEF DESCRIPTION OF THE DRAWING

Purely by way of a non-limiting illustration, an example of a cold container according to the invention will be described with a single FIGURE for reference, which is a sectional view thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The FIGURE shows a cold container, having a circular shape, made of composite material.

A layer 1 of iron and nickel alloy, containing 30 to 45 per cent of nickel forms the outer casing of the cold container.

Conductors 4 are arranged on the inside 5 of that container, in which a cryogenic fluid flows. This fluid can be helium, in the case of a superconductive cryogenic connection, or nitrogen in the case of a hyperconductive cryogenic connection. The number of conductors has been limited to four by way of an example:

A metal screen 2 is inserted between the conductors 4 and the casing 1. This screen is metallurgically connected to the inner face of the cold container. It is made of material having a resistivity of less than 3.10.sup.-.sup.8 ohms. meter, for example, aluminum.

The screen and the envelope can be made of a laminated strip comprising a first layer consisting of the above-mentioned iron and nickel alloy, and a second layer covering the first and made of aluminum. This strip is bent then welded at 3 when its two edges are face to face after bending. The strip is bent so that the layer 1 is on the outside.

The thickness of the aluminum layer should be sufficient for the alternating induced fields not to reach the invariable casing. The thickness of that layer depends on the resistivity of the aluminum chosen.

Thus, the alternating fields do not reach the casing, which is magnetic. These losses by induced currents in that casing are considerably reduced.

The two layers forming the cold container are connected together. This composite container is braced at its ends, and arranged in a rectilinear configuration.

When the device is cooled, the casing made of iron and nickel alloy having an invariable length is subjected to longitudinal mechanical stresses limited to about 6 kg/squ.m, consistent with the mechanical properties of that alloy. The thickness of aluminum remaining cemented is then subjected to regularly distributed creeping and to longitudinal mechanical stresses in the vicinity of 3.2 kg/squ.m, which represent the proof stress of aluminum at the temperature of the cryogenic connection. The longitudinal tensile stresses on that composite rectilinear container enable it to be used in cryogenic connections.

The principle of the tensioning of a cylindrical rectilinear container having a great length, made of an alloy having slight thermal contraction such as INVAR has been described in French Patent No. 71,07,609 in the name of the applicant. This principle may be applied to the case of the composite container which has just been described.

This composite cylindrical container makes it possible to provide the advantages connected with containers made of an alloy whose relative thermal contraction is less than 5.10.sup.-.sup.4 :

No expansion bellows;

Possibility of continuous production, on the cryogenic connection laying ground.

On the other hand, the electric screen enables the cancelling of losses by induced currents in containers having high resistivity and more particularly in containers made of INVAR or an alloy having the same technical characteristics.

Claims

What is claimed is:

1. In a cold container made of a composite material, having a tubular shape, surrounding the conductors of a cryogenic connection, comprising a casing made of an iron and nickel alloy in which the concentration of nickel comprises between thirty and forty-five per cent, the improvement wherein: a metal screen made of a material having a resistivity lower than 3.10.sup.-.sup.8 ohms. meter surrounds the conductors inside the said casing.

2. The cold container according to claim 1, wherein: said screen comprises a metal layer covering the inside face of the said casing.

3. The cold container according to claim 2, wherein: said casing and the said screen are made from a laminated and bent strip comprising a first layer forming said envelope and a second layer forming said screen.

4. The cold container according to claim 2, wherein: said material forming the said screen comprises one material chosen from the group consisting of aluminum and copper.