Cryogenic vessel for a superconducting apparatus

Abstract: A cryogenic vessel for a superconducting apparatus has an inner vessel 3 which houses a cryogenic medium e.g. He and a winding of a superconducting apparatus. The inner vessel is surrounded by a vacuum insulating vessel 4 which thermally insulates the inner vessel. A connecting pipe 7 connects the inside of the inner vessel with the outside of the vacuum insulating vessel. A cylindrical dividing pipe 21 surrounds the connecting pipe with a radial clearance therebetween, extends into the inner vessel and is connected between the inner end of the connecting pipe and the inner vessel. A gas flow passageway is formed between the inner end and the outer end of the connecting pipe, the passageway bordering on the inner or outer surface of the connecting pipe. During normal operation, gas which is formed by the vaporization of a cryogenic medium contained inside the inner vessel continually passes along the passageway, absorbing heat from the connecting pipe and reducing the amount of heat which penetrates into the inner vessel by conduction along the connecting pipe. A wiring support pipe for the power supply leads is a single, rigid pipe 70 which has one of its ends connected to the inner vessel or the vacuum insulating vessel by a flexible tube 71 which absorbs thermal shrinkage. Since the wiring support pipe is a single, rigid pipe, it undergoes thermal shrinkage by about the same amount as the power supply leads which it supports, and thermal stresses do not develop in the power supply leads.

Description: BACKGROUND OF THE INVENTION This invention relates to a cryogenic vessel for a superconducting apparatus, and more particularly but not exclusively, it relates to a cryogenic vessel for cooling the superconducting magnet of a superconducting apparatus such as a nuclear magnetic resonance diagnosis apparatus. Figure 1 illustrates a portion of a conventional cryogenic vessel as disclosed in Japanese Patent Publication No. 54-43359. As shown in this figure, a superconducting magnet 1 is electrically connected to a power supply 12 by power supply leads 11 which extend from the outside of a vacuum insulating vessel 4 to the inside of an inner vessel 3 with a freezing mixture 2 such as liquid helium. The power supply leads 11 are supported by a wiring support pipe 13 whose outer end is secured to the vacuum insulating vessel 4 and whose inner end is secured to the inner vessel 3. The wiring support pipe 13 is divided into an upper and lower portion which are connected with one another by a flexible tube 14. The flexible tube 14 enables the upper and lower portion to move with respect to one another when thermal shrinkage occurs due to the cooling of the various parts of the vessel, thereby preventing thermal stresses from developing in the wiring support pipe 13. The upper ends of the power supply leads 11 are secured to the wiring support pipe 13 by a flange 15 mounted on its upper end, and the lower ends of the leads 11 are secured to the wiring support pipe 13 by a connector 16 which is mounted on the inner end thereof and which electrically connects the power supply leads 11 to the superconducting magnet 1. The inner vessel 3 is supported by the vacuum insulating vessel 4 through support members 10. While the flexible tube 14 is effective to prevent thermal stresses from developing in the wiring support tube 13, it results in thrmal stresses arising in the power supply leads 11, since the change in dimensions of the power supply leads 11 due to thermal shringkage is much less than that of the wiring support pipe 13 and the flexible tube 14. For this reason, it is very difficult to reliably connect the power supply leads 11 to the connector 16. SUMMARY OF THE INVENTION It is an object of the present invention to provide a cryogenic vessel for a superconducting apparatus which is more compact than a conventional cryogenic vessel having a connecting pipe of the same length. It is another object of the present invention to provide a cryogenic vessel for a superconducting apparatus in which thermal stresses do not develop in its power supply leads. According to the present invention, there is provided a cryogenic vessel for a superconducting apparatus comprising an inner vessel for containing a superconducting winding of a superconducting device and a cryogenic medium, a vacuum insulating vessel which surrounds the inner vessel so as to thermally insulate it, a connecting pipe which extends into the inner vessel whose inner end opens onto the inside of the inner vessel and whose outer end opens onto the outside of the vacuum insulating vessel, and a dividing pipe having its outer end secured to the outer surface of the inner vessel and its inner end extending into the inner vessel, the connecting pipe extending along the inside of the dividing pipe with a radial clearance between the outer surface of the connecting pipe and the inner surface of the dividing pipe, and the inner end of the connecting pipe being connected to the inner end of the dividing pipe, characterised in that a rupture-type safety valve is disposed at one of the ends of the connecting pipe, and the cryogenic vessel comprises either one of: a) a power supply lead for the superconducting winding, a rigid wiring support pipe which surrounds the power supply lead and which penetrates the inner vessel and the vacuum insulating vessel, and a flexible tube, the outer end of the wiring support pipe being connected to the vacuum insulating vessel by the flexible tube and the inner end of the wiring support pipe being rigidly connected to the inner vessel; or b) a power supply lead for the superconducting winding, a rigid wiring support pipe which surrounds and supports the power supply lead and which penetrates the inner vessel and the vacuum insulating vessel, and a flexible tube, the inner end of the wiring support pipe being connected to the inner vessel by the flexible tube and the outer end of the wiring support pipe being rigidly connected to the vacuum insulating vessel. A wiring support pipe for the power supply leads of a cryogenic vessel in an embodiment of the present invention is a single, rigid pipe which has one of its ends connected to an inner vessel or a vacuum insulating vessel by a flexible tube which absorbs thermal shrinkage. Since the wiring support pipe is a single, rigid pipe, it undergoes thermal shrinkage by about the same amount as the power supply leads which it supports, and thermal stresses do not develop in the power supply leads. Embodiments of the present invention may be applied to various types of cooling means for cryogenic vessels as described in copending European Patent Application No. 86300320.8 (published under no. 0 188 389). BRIEF DESCRIPTION OF DRAWINGS Figure 1 is a transverse cross-sectional view of a portion of a conventional cryogenic vessel. Figure 2 is a transverse cross-sectional view of a portion of a first embodiment of a cryogenic vessel. Figure 3 is a transverse cross-sectional view of a portion of a second embodiment of a cryogenic vessel. Figure 4 is a transverse cross-sectional view of a portion of a third embodiment of a cryogenic vessel. Figure 5 is a longitudinal cross-sectional view of a portion of a fourth embodiment of a cryogenic vessel. Figure 6 is a longitudinal cross-sectional view of a portion of a fifth embodiment of a cryogenic vessel. Figure 7 is a longitudinal cross-sectional view of a portion of an sixth embodiment of a cryogenic vessel. In all of the figures, the same reference numerals indicate the same or corresponding parts. DESCRIPTION OF THE PREFERRED EMBODIMENTS A number of preferred embodiments of a cryogenic vessel in accordance with the present invention will now be described while referring to Figures 2 through 7 of the accompanying drawings. Figure 2 illustrates the essential features of a first embodiment of a cryogenic vessel according to the present invention. Those portions of the vessel not shown in this figure can be same as those of any one of the first four embodiments described and illustrated in the copending European Patent Application No 86300320.8 (published under no. 0 188 389). This figure shows the portion of cryogenic vessel which is penetrated by power supply leads 11. The power supply leads 11 are housed inside a wiring support pipe 70 having a flange 15 formed at its upper end to which the upper ends of the power supply leads 11 are secured, and having a connector 16 installed at its bottom end by means of which the power supply leads 11 are electrically connected to a superconducting magnet 1 housed within an inner vessel 3. The inner vessel 3 is supported by a vacuum insulating vessel 4 through supporting members 10. Whereas in the conventional apparatus of Figure 1 the wiring support pipe comprises separate upper and lower portions connected by a flexible tube 14, in the present embodiment, the wiring support pipe 70 is a single, rigid pipe. The wiring support pipe 70 is rigidly secured near its upper end to the outer surface of the vacuum insulating vessel 4. Its midportion is connected to the outer surface of the inner vessel 3 by a flexible tube 71 which projects outwards from the inner vessel 3. With this construction, the inner vessel 3 is able to freely move with respect to the wiring support tube 70 so that when the supporting members 10 or the inner vessel 3 undergoes thermal shrinkage, the change in dimensions of the inner vessel 3 has no effect on the wiring support pipe 70 or the power supply leads 11. When the inside of the cryogenic vessel is cooled, the wiring support pipe 70 and the power supply leads 11 also undergo thermal shrinkage, but as they have approximately the same coefficient of thermal expansion, they undergo approximately the same amount of shrinkage, and no signifcant thermal stresses are induced therein. Accordingly, the present embodiment overcomes the problem of the conventional cryogenic vessel of Figure 1 in which thermal stresses develop in the power supply leads 11, making it difficult to achieve a good connection between the power supply leads 11 and the connector 16. Figure 3 illustrates a second embodiment of the present invention which differs from the previous embodiment only in that the flexible tube 71 is disposed inside the inner vessel 3, extending inwards from the outer surface of the inner vessel 3 and connecting to the wiring support pipe 70 near its inner end. The effects provided by this embodiment are the same as those of the previous embodiment. In the previous two embodiments, the outer end of a rigid wiring support pipe 70 is rigidly secured to the outer surface of a vacuum insulating vessel 4 and the inner end of the wiring support pipe 70 is connected to an inner vessel 3 through a flexible tube 71. Figure 4 illustrates a third embodiment of the present invention in which the manner of connection is reversed. Namely, the inner end of a wiring support pipe 70 is rigidly connected to an inner vessel 3, and the outer end of the wiring support pipe is connected to a vacuum insulating vessel 4 through a flexible tube 71 which projects outwards from the vacuum insulating vessel 4. The effects are identical to those of the previous two embodiments. In each of the previous embodiments, the inner end of a connecting pipe 7 is rigidly secured to an inner vessel 3 through a dividing pipe 21, and the outer end of the connecting pipe 7 is rigidly secured to a vacuum insulating vessel 4. However, as shown in Figures 5 and 6 it is possible to connect the connecting pipe 7 to the inner vessel 3 or the vacuum insulating vessel 4 in an elastic manner so that thermal shrinkage can be compensated for without producing thermal stresses in the connecting pipe 7. Figure 5 shows a fourth embodiment of the present invention in which a flexible tube 80 is provided between the outer end of the dividing pipe 21 and the surface of the inner vessel 3. Furthermore, Figure 6 shows a fifth embodiment of the present invention in which an outward-projecting flexible tube 80 is connected between the outer end of the connecting pipe 7 and the outer surface of the vacuum insulating vessel 4. These two embodiments are otherwise identical to the embodiment of figure 10 of the copending European Patent Application 86300320.8. The same effects as in that embodiment are achieved. In the same manner, a flexible tube 80 can be employed between the dividing pipe 21 and the inner vessel 3, or between the connecting pipe 7 and the vacuum insulating vessel 4 of a cryogenic vessel having the structure of any one of the other previously-described embodiments. Figure 7 shows a sixth embodiment of a cryogenic vessel according to the present invention in which a connecting pipe 7 serves not only as a means for discharging gas into the atmosphere but also as a support for the power supply leads 11 for a superconducting magnet 1. Power supply leads 11 extend from the outer end of the connecting pipe 7, where they are electrically connected to a power supply 12, to the inner end of the connecting pipe 7, where they are connected to a connector 16 which is electrically connected to the superconducting magnet 1. In order to prevent thermal stresses from developing in the power supply leads 11, a dividing pipe 21 is connected to the surface of an inner vessel 3 by a flexible tube 80 which compensates for any thermal shrinkage. Alternatively, the flexible tube 80 can be used to connect the outer surface of the vacuum insulating vessel 4 to the outer end of the connecting pipe 7, in a manner similar to that shown in Figure 6. The structure is otherwise identical to that of the embodiment of Figure 4 of the aforementioned application. By installing the power supply leads 11 inside the connecting pipe 7, a separate wiring support pipe 70 as in Figure 2 is made unnecessary, and the vessel can be made more compact. In each of the previous embodiments, the cryogenic vessel houses a superconducting magnet 1, but the present invention is not limited to use with a magnet, and it can also be used to house the windings of other types of superconducting devices.

Claims: A cryogenic vessel for a superconducting apparatus comprising an inner vessel (3) for containing a superconducting winding of a superconducting device and a cryogenic medium (2), a vacuum insulating vessel (4) which surrounds the inner vessel so as to thermally insulate it, a connecting pipe (7) which extends into the inner vessel whose inner end opens onto the inside of the inner vessel and whose outer end opens onto the outside of the vacuum insulating vessel (4), and a dividing pipe (21) having its outer end secured to the outer surface of the inner vessel (3) and its inner end extends into the inner vessel, the connecting pipe (7) extending along the inside of the dividing pipe with a radial clearance between the outer surface of the connecting pipe and the inner surface of the dividing pipe, and the inner end of the connecting pipe being connected to the inner end of the dividing pipe, characterised in that a rupture-type safety valve (8) is disposed at one of the ends of the connecting pipe, and the cryogenic vessel comprises either one of: a) a power supply lead (11) for the superconducting winding (1), a rigid wiring support pipe (70) which surrounds the power supply lead and which penetrates the inner vessel (3) and the vacuum insulating vessel (4), and a flexible tube (71), the outer end of the wiring support pipe being connected to the vacuum insulating vessel by the flexible tube and the inner end of the wiring support pipe being rigidly connected to the inner vessel; or b) a power supply lead (11) for the superconducting winding (1), a rigid wiring support pipe (70) which surrounds and supports the power supply lead and which penetrates the inner vessel (3) and the vacuum insulating vessel (4), and a flexible tube (71), the inner end of the wiring support pipe (70) being connected to the inner vessel by the flexible tube and the outer end of the wiring support pipe being rigidly connected to the vacuum insulating vessel (4). A cryogenic vessel as claimed in either one of clauses (a) or (b) of claim 1 wherein, the cryogenic vessel comprises either one of: a) a flexible tube (80) which is connected between the dividing pipe (21) and the inner vessel (3) so as to enable the dividing pipe to move in its axial direction; or b) a flexible tube (80) which is connected between the outer end of the connecting pipe (7) and the vacuum insulating vessel (4). A cryogenic vessel as claimed in clause (a) of claim 2, wherein the connecting pipe (7) serves also as a wiring support pipe.

Inventors: MAEKAWA HIROFUMI, MATSUMOTO TAKAHIRO, NISHIO TETSUO, OOTA HISASHI, MAEKAWA, HIROFUMI, MATSUMOTO, TAKAHIRO, NISHIO, TETSUO, OOTA, HISASHI
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1986
Main classification: F17C3
IPC codes: H01F6, F17C3, G01R33, F17C13