SUPERCONDUCTING APPARATUS

Abstract: Disclosed is a superconducting apparatus comprising a su­ perconducting coil (1) and a cooling apparatus (2) for cooling this superconducting coil (1). The cooling apparatus (2) is con­ stituted by a cooling medium circulating path for subjecting a cooling medium to a vaporization/liquefication cycle, and a temperature equalizing plate (11) for effecting a uniform cool­ ing of the superconducting coil (1) by the cooling medium. The cooling medium circulating path is constituted by a pair of flow­ ing-down parts (21) trhough which a liquid cooling medium flows downwards by gravity, and a pair of vaporization parts (22) through which the liquid cooling medium flows upwards while it is being vaporized. The temperature-equalizing plate (11) covers the peripheral surface making one entire round of the superconducting coil (1) around the axis of the coil (1). It is divided into at least two parts at its lower end, which are elec­ trically insulated from each other.

Description: The present invention relates to a superconducting apparatus capable of being miniaturized and, more particularly, to a cooling apparatus for a superconducting coil of the superconducting apparatus. In a superconducting apparatus, it is necessary to cool a superconducting coil thereof down to a temperature which is as low as, for example, 4 K. Hitherto, as disclosed in IEEE Transactions on Magnetics, Vol. MAG-15, No. 1, January 1979, pages 46-48, the cooling of a superconducting coil has been performed through immersing this coil itself in a liquid helium reservoir. This method, however, has drawbacks in that; a large space for the liquid helium reservoir is necessary, a large quantity of liquid helium must be stored, the process steps of making the liquid helium reservoir are complicated, etc. Another method of cooling the superconducting coil by forcedly circulating a coolant such as, for example, liquid helium through a coolant circulating path connected to the superconducting coil, said coolant circulating path being connected to said superconducting coil in such a manner that heat transfer can be effected therebetween, has also been proposed, in a paper by H. Ohgume et al entitled "Development of the Experimental Apparatus to Study Internally Cooled Superconductors Property", given in the Proceedings of the Ninth International Cryogenic Engineering Conference. In this second method, however, since it is necessary to provide a means of subjecting the coolant to forced circulation, it is difficult to apply this method to a small-sized superconducting coil and obtain a small-sized superconducting apparatus. Copending EP-A-0144873, which forms part of the state of the art under Article 54(3) EPC only, discloses superconducting apparatus comprising a superconducting coil cooled by liquid helium circulated from a tank over the surface of the coil. The helium from the tank first flows through a pipe to the base of the coil, where the pipe branches into several parallel loops, each of which surrounds the entire periphery of the coil and is coaxial therewith. This cooling system operates under gravity flow, without the need for forced circulation, but suffers from internal heat generation from electrical resistance in the circulation pipes when electric current is induced by the energizing or de-energizing of the superconducting magnet. This problem can be compounded by the presence of a cylindrical, metallic, coil winding form in which the loops of the circulation path are embedded. The object of the present invention is to provide a superconducting apparatus capable of being miniaturized, in which a superconducting coil can be cooled with uniformity. A superconducting apparatus in accordance with the present invention comprises a superconducting coil and a cooling apparatus for cooling said superconducting coil, said cooling apparatus being characterized in that it is constituted by a cooling medium circulating path for subjecting a cooling medium to a vaporization/liquefaction cycle, and a temperature equalizing plate for effecting a uniform cooling of said superconducting coil by said cooling medium, said cooling medium circulating path comprising a pair of flowing-down parts through which a liquid cooling medium flows downwards by gravity, each connected to a vaporization part through which said liquid cooling medium flows upwards while it is being vaporized, such that no section of the circulating path follows an entire turn of the superconducting coil around its axis, said temperature-equalizing plate covering the peripheral surface of said superconducting coil 3 following one entire turn of said superconducting coil around the axis of the coil and comprising at least at its lower region an electrically insulating insert (12), so that its cross-section does not form an electrically conductive closed loop. In the above-mentioned superconducting apparatus, the cooling medium circulating path may be constituted by cooling pipes. In this case, the flowing-down part may be constituted by a single pipe which is straight or bent along its temperature-equalizing plate. Further, the vaporization part may be constituted by a pipe which is curved or bent in a zigzag manner. Or alternatively, it may be constituted by a plurality of pipes or zigzag pipes whose upper and lower ends are connected to common headers, respectively. The temperature-equalizing plate can be constituted by a plurality of, e.g., a pair of arched plates which are arranged to have a cylindrical shape as a whole. These arched plates are electrically insulated from each other to thereby prevent an eddy current from being produced in the temperature-equalizing plate. As a result, the induction heating of the same is prevented. In the superconducting apparatus of the invention, the cooling medium is circulated due to the density difference produced by its vaporization, so that the cooling of the superconducting coil is effected with an extremely high uniformity. This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: Fig. 1 is a perspective view of a superconducting coil according to an embodiment of the invention; and, Fig. 2 is a perspective view of a superconducting apparatus according to another embodiment of the invention. Preferred embodiments of the invention will now be described with reference to the drawings. Fig. 1 shows a superconducting apparatus according to a first embodiment of the invention. In Fig. 1, a superconducting coil 1 which is made in the form of an annular ring is cooled to a very low temperature by a cooling apparatus 2 covering the entire outer peripheral surface of that coil 1. The cooling apparatus 2 is constituted by a cooling assembly 16 and a temperature-equalizing plate 11 which covers the entire outer peripheral surface of the cylindrical superconducting coil 1. The temperature-equalizing plate 11 is constituted by a pair of arched plates 11a and 11b each formed of a material having high heat conductivity such as, for example, copper. The ends of each arched plate 11a or 11b are bent in the radially outward direction of the coil 1, respectively, to thereby form a rib. Of these ribs, two opposed ribs are joined together by insulating bolts 13 with an insulating plate 12 interposed therebetween, thereby constituting the temperature-equalizing plate 11. By insulating one of the arched plates 11a and 11b from the other as mentioned above, it is possible to prevent the induction heating of the temperature-equalizing plate due to the excitation of the superconducting coil 1. In order to increase the efficiency of heat transfer between the temperature-equalizing plate 11 and the superconducting coil 1, both are made integral by means of an epoxy resin 14 having substantially the same heat expansion coefficiency as that of copper and having a high heat conductivity. In this case, the temperature-equalizing plate 11 is formed with a plurality of bores 15 via which the temperature-equalizing plate 11 is made integral with the epoxy resin 14. Accordingly, the temperature-equalizing plate 11 and the epoxy resin 14 are thermally shrunk in a state wherein both are integrated together. The superconducting coil 1 is cooled via the temperature-equalizing plate 11 by a cooling assembly 16 of gravity-drop circulating system. The cooling assembly 16 is constituted by a liquid helium tank 17 installed above the coil 1, and a cooling pipe unit 18 for circulating a cooling medium from a bottom portion of said tank 17 to a side portion thereof by way of a specified arrangement of passages. The liquid helium tank 17 is intended to store therein a liquid helium P. The cooling pipe unit 18 has two systems of pipes, on the outer surfaces of the paired arched plates 11a and 11b constituting the temperature-equalizing plate 11. In Fig. 1, however, only the pipe system on the outer surface of the arched plate 11a is shown. Each system of pipe is constituted by a flowing-down part 21 which extends downwards along the outer surface of the temperature-equalizing plate 11 from the bottom portion of the liquid helium tank 17, and a vaporization part 22 which extends upwards from a lower end of the flowing-down part 21 while it zigzags up along the outer surface of the temperature-equalizing plate 11, to reach a position above a free liquid surface of the liquid helium tank 17. The flowing-down part 21 is fixed to the temperature-equalizing plate 11 via a heat insulating spacer 23 having low heat conductivity and thus is heat-insulated therefrom by means of the heat insulating spacer 23. The vaporization part 22 is fixed, by, for example, soldering, to the temperature-equalizing plate 11 at its specified portions or over its entire length in a state of having been cohered thereto. Further, the vaporization part 22 is embedded in the epoxy resin 14. The superconducting coil 1 and the cooling apparatus 2 are enveloped by a radiation shield 24 having a temperature of, for example, approximately 50 to 80K and, further, are received as a whole in a vacuum container 25, to thereby prevent the entry thereinto of heat from outside. In the superconducting apparatus having the foregoing construction, the superconducting coil 1 is cooled as follows. That is, the liquid helium P stored in the liquid helium tank 17 flows downwards by gravity from the bottom portion of the liquid helium tank 17 through the flowing-down part 21 of the cooling pipe unit 18. Since the flowing-down part 21 is thermally insulated from the temperature-equalizing plate 11, the liquid helium P reaches the lowermost end of that flowing-down part 21 while its temperature is kept as it is. Subsequently, the liquid helium P reaches the lowermost portion of the vaporization part 22. Since the vaporization part 22 is connected to the temperature-equalizing plate 11 in such a manner that heat transfer between the two is effected, heat exchange between the liquid helium P and the superconducting coil 1 is effected at the vaporization part 22 via the temperature-equalizing plate 11, said liquid helium P thus being vaporized. The helium thus vaporized rises through the vaporization part 22 which is curved in a zigzag manner to return to the position above the free liquid surface of the liquid helium tank 17. The liquid helium in tank 17 thus returned is liquefied by a liquefying apparatus not shown and is again circulated through the cooling pipe unit 18 from the tank 17, in the above-mentioned manner. In the refrigeration cycle which has been explained above, a difference of density is created between the cooling medium in the flowing-down part 21 of the cooling pipe unit 18 and the cooling medium in the vaporization part 22 thereof and this density difference produces a power for circulating the cooling medium. The above-mentioned cooling apparatus, therefore, does not require the use of a means for circulating the cooling medium. As stated above, in the superconducting apparatus shown in Fig. 1, it is possible to circulate the cooling medium without using any means for forced circulation of the same. For this reason, it is possible to miniaturize and simplify the superconducting apparatus as a whole. Fig. 2 shows a superconducting apparatus according to a second embodiment of the invention. This superconducting apparatus differs from that which is shown in Fig. 1 in respect of the construction of the vaporization part 22 of the cooling pipe unit 18. That is, in the superconducting apparatus of Fig. 2, each vaporization part 22 is constituted by a plurality of circumferentially extending branched pipes 31 which are cohered on the outer surface of the temperature-equalizing plate 11, and headers 32 and 33 each of which connects the corresponding ends, at one side, of the associated branched pipes 31. Accordingly, the liquid helium P flows downwards from the liquid helium tank 17 into the flowing-down part 21 of the cooling pipe unit 18 to reach the header 33 connected to the lower end thereof and, thereafter, flows upwards from the header 33 through the associated branched pipes 31. In this process of upward flow, heat exchange is effected between the liquid helium P and the superconducting coil 1, so that the liquid helium P is vaporized. The vaporized helium flows are joined together in the header 32 connected to the upper ends of the branched pipes 31. The resultant helium gas passes through a return pipe 34 into the liquid helium tank 17. In the construction shown in Fig. 2, the manufacture of the vaporization part 22 of the cooling pipe 18 is easier than in the construction shown in Fig. 1, and it is possible to increase the rate of circulation of the cooling medium, so that the cooling efficiency can be greater, than in the construction shown in Fig. 1. The present invention is not limited to the above-mentioned embodiments. For example, in the superconducting apparatus of Fig. 2, the branched pipes 31 may be curved in a zigzag manner. By so doing, it is possible to further enhance the cooling efficiency. Even in this case, no particular difficulty is caused in manufacturing the branched pipes 31.

Claims: A superconducting apparatus comprising a superconducting coil (1) and a cooling apparatus (2) for cooling said superconducting coil (1), said cooling apparatus (2) being characterized in that it is constituted by a cooling medium circulating path for subjecting a cooling medium to a vaporization/liquefaction cycle, and a temperature equalizing plate (11) for effecting a uniform cooling of said superconducting coil (1) by said cooling medium, said cooling medium circulating path comprising a pair of flowing-down parts (21) through which a liquid cooling medium flows downwards by gravity, each connected to a vaporization part (22) through which said liquid cooling medium flows upwards while it is being vaporized, such that no section of the circulating path follows an entire turn of the superconducting coil (1) around its axis, said temperature-equalizing plate (11) covering the peripheral surface of said superconducting coil (1) following one entire turn of said superconducting coil (1) around the axis of the coil (1) and being divided into two parts at least at its lower end, so that its cross-section does not form an electrically conductive closed loop. A superconducting apparatus as set forth in claim 1, characterized in that said cooling medium circulating path consists of a cooling pipe unit (18) through which said cooling medium flows. A superconducting apparatus as set forth in claim 1 or 2, characterized in that said flowing-down part (21) is heat-insulated from said temperature-equalizing plate (11); and said vaporization part (22) is thermally connected to said temperature-equalizing plate (11) so as to enable heat transfer between them. A superconducting apparatus as set forth in claim 3, characterized in that said flowing-down part (21) consists of a single pipe which is straight or bent along the temperature-equalizing plate. A superconducting apparatus as set forth in claim 4, characterized in that said vaporization part consists of a pipe curved in a zigzag manner. A superconducting apparatus as set forth in claim 4, characterized in that said vaporization part (22) consists of a pipe array which consists of a plurality of pipes (31) having their mutually corresponding ends commonly connected with headers (32, 33). A superconducting apparatus as set forth in claim 6, characterized in that said vaporization part (22) consists of a pipe array which consists of a plurality of zigzag curved pipes having their mutually corresponding ends commonly connected with corresponding headers. A superconducting apparatus as set forth in any preceding claim, characterized in that said temperature-equalizing plate (11) consists of a plurality of divided arched plate members (11a, 11b) which are electrically insulated from each other. A superconducting apparatus as set forth in any preceding claim, characterized in that said superconducting coil (1) and said temperature-equalizing plate (11) are made integral with each other by organic resin. A superconducting apparatus as set forth in claim 9, characterized in that said temperature-equalizing plate (11) is formed with a plurality of bores (15).

Inventors: GOMEI, YOSHIO C/O PATENT DIVISION, NAKAGOME, HIDEKI C/O PATENT DIVISION, OHGUMA, HIROTSUGU C/O PATENT DIVISION, TAKANO, ICHIRO C/O PATENT DIVISION
Applicants: KABUSHIKI KAISHA TOSHIBA
Application year: 1985
Main classification: H01F7
IPC codes: H01L39, F25B23, H01F6