GB2326527A

GB2326527A - Superconducting magnet

Info

Publication number: GB2326527A
Application number: GB9811685A
Authority: GB
Inventors: Takashi Sasaki; Koji Ito; Masanori Arata; Masamichi Kawai; Takahiro Tuschihashi; Yoshihiro Koguchi
Original assignee: Toshiba Corp
Current assignee: Toshiba Corp
Priority date: 1997-05-30
Filing date: 1998-05-29
Publication date: 1998-12-23
Anticipated expiration: 2018-05-29
Also published as: GB2326527B; TW460635B; KR100282562B1; GB9811685D0; CN1201843A; CN1138876C; KR19980087523A

Description

SUPERCONDUCTING MAGNET APPARATUS The present invention relates to a superconducting magnet apparatus used for a pull-up device of a semiconductor single crystal, and more particularly, to a repulsive force supporting mechanism of a superconducting coil generating a cusped magnetic field with a controlled distribution of the magnetic field.

Conventionally, there is a known superconducting magnetic apparatus which is mainly used for a pull-up device of a semiconductor single crystal and which is designed in a manner such that electrically connected two annular superconducting coils in series are disposed so as to oppose to each other on an axis, and a magnetic field, called cusped type, is generated by magnetizing the coils at opposite polarities. One of such examples is shown in Fig. 13.

In a superconducting magnet apparatus shown in Fig. 13, electrically connected two annular superconducting coils in series (called merely coils, hereinafter) 101a and 101b are disposed so as to oppose to each other at upper and lower locations in the axial direction AX of an opening OP on an annular vacuum vessel or container 102, and electric current is supplied from an external exciting power source (not shown) to the coils 101a and 101b.

At that time, since the same current flows to both the coils 101a and 101b, a magnetic field which is symmetric with respect to a neutral line Al between both the coils 101a and 101b, i.e., a cusped type magnetic field as shown with magnetic lines of force B1 ... B1 in Fig. 13, is generated in a magnet, and repulsive forces F1 and F1 acting in opposite directions are applied to both the coils 101a and 101b associated with the symmetric magnetic field distribution. Such repulsive force F1 is increased as the magnet becomes larger, for example, tens to hundreds tons.

Thereupon, in an apparatus for generating cusped magnetic field, a supporting mechanism for supporting the repulsive forces acting on both the coils is generally provided in the vacuum vessel. One of such examples is shown in Fig. 14.

In a superconducting magnetic apparatus including both the coils 101a and 101b in the vacuum vessel 102 shown in Fig. 14 which is similar to that described above, annular helium vessels or containers 103a and 103b for liquid helium passages are disposed around both the coils 101a and 101b, supports (support members) 104a and 104b are disposed outside and inside of the helium vessels 103a and 103b, and the repulsive forces acting on both the coils 101a and 101b are supported by utilizing compression strength of both the supports 104a and 104b.

In the case of the magnet apparatus including the support mechanism, a heat outside the vacuum vessel 102 is transferred to interiors of the helium containers 103a and 103b through the support 104a. Therefore, in generally, in the apparatus of this type, a cryogenic refrigerator 110 is provided outside the vacuum vessel 102, and double radiation shields 105a and 105b thermally connected to the cryogenic refrigerator 110 are disposed around the helium vessel 103a, the radiation shields 105a and 105b being thermally connected to the support 104a so that a portion of the heat transferred through the support 104a from the contacted portions is absorbed by the radiation shields 105a and 105b.

In the above described conventional superconducting magnet apparatus of the cusped type magnetic field, however, since the repulsive forces of the coils are supported by utilizing the compression strength of the support, in order to support a stronger repulsive forces due to upsizing of the apparatus, there is a limitation that a cross section of the support must be increased so as not to be buckled by the compression force.

Therefore, in this case, since the cross section of the support is increased, the heat transferred from outside to the support becomes increased and therefore, the evaporation amount of the liquid helium is increased, the number of charging of the liquid helium and maintenance cost are also increased, and it is necessary to increase the number of cryogenic refrigerator which cool the radiation shield or to increase the apparatus in size so as to improve the performance thereof. As a result, there are problems that the entire magnet apparatus is increased in weight and size, and its cost is also increased.

The present invention seeks to substantially eliminate defects or drawbacks encountered in the prior art described above and to provide a superconducting magnet apparatus having a simple and compact support structure for supporting the repulsive force which is to be received by the superconducting coil and manufacturing the same with relatively low price.

According to the present invention, there is provided a superconducting apparatus comprising: a vacuum vessel; two annular superconducting coils opposed to each other in an axial direction of the vacuum vessel; and a support structure for supporting the two superconducting coils, the support structure comprising a coil connecting body for connecting the two superconducting coils in the axial direction of the vacuum vessel and a support body for integrally supporting the two superconducting coils connected by the coil connecting body, the two superconducting coils being disposed to the vacuum vessel through the support body.

In preferred embodiments, the coil connecting member comprises an annular member disposed around the two superconducting coils in a circumferential direction thereof. The annular member is composed of a winding frame for winding the two superconducting coils.

The coil connecting member comprises a plurality of arc-shaped members disposed around the two superconducting coils in the circumferential direction thereof at constant distances from one another. The coil connecting body comprises connecting members for sandwiching and connecting the two superconducting coils in the axial direction thereof and a position keeping member for keeping an axial distance between the two superconducting coils connected by the connecting members. Each of the connecting members comprises a base portion extending in the axial direction along at least one of radially inner and outer sides of the two superconducting coils and shoulder portions extending from axially opposing ends of the base portion so as to bend toward an axially outer side of the two superconducting coils. The base portion and the shoulder portion are integrally formed. The shoulder portion comprises two end plates disposed so as to abut against the axially outer side of the two superconducting coils, respectively, and the base body comprises a fastening member for fastening the two end plates in the axial direction.

The connecting member is circumferentially provided with a slit for reducing eddy current, and the connecting member is formed of a material having high thermal conductivity or a compound made of a material having high thermal conductivity and a material having high strength.

The position keeping member comprises a mechanism for freely adjusting a length of a clearance in the axial direction of the superconducting coils in accordance with an axial thermal expansion between the two superconducting coils and the connecting member.

The central distance of conductor in the axial direction of the two superconducting coils and a radius of the center of the conductor in the diametral direction are equal to each other.

At least one of the two superconducting coils is provided with an auxiliary annular superconducting coil in the radial direction, or in the axial direction, of the superconducting coil in a manner coaxial therewith.

There may be further disposed a member for exciting the superconducting coils so as to generate magnetic fields different from each other.

At least one of the two superconducting coils is provided at its axially outer side with an auxiliary annular coil for generating a magnetic field in opposite direction between the superconducting coils.

There may be further disposed an annular helium container surrounding the two superconducting coils and a double annular radiation shield surrounding the annular helium container.

Cryogenic refrigerator may be disposed at symmetric equiangular positions with respect to a center axis of the vacuum vessel.

According to the present invention of the characters mentioned above, since it is possible to separate the repulsive force acting to the two superconducting coils from the support body which is in contact with the vacuum vessel and to support such repulsive force only by the coil connecting body, it is possible to substantially get rid of a limitation of design for increasing the strength such as an increase in cross section of the support as countermeasure for repulsive force and also possible to largely suppress the heat transfer from outside of the vacuum vessel to low temperature portion.

If the winding frame is used, it is possible to assemble the apparatus as it is without removing the coil from the winding frame, and there is a merit that a relatively low cost apparatus can be provided while reducing the number of manufacturing days.

Further, in order to reduce eddy current generated when the superconducting coil stops the exciting, it is preferable that the connecting member is circumferentially provided with a slit for reducing eddy current.

As one mode of the position keeping member, it comprises a mechanism for freely adjusting a length of a clearance in the axial direction of the superconducting coils in accordance with an axial thermal expansion between the two superconducting coils and the connecting member.

As other modes of the present invention, the following structures may be employed.

A distance of center of conductor in the axial direction of the two superconducting coils and a radius of the center of the conductor in the radial direction are equal to each other. In this case, there is a merit that since it is possible to generate a magnetic field distribution most effectively, a length of the conductor can be minimized.

At least one of the two superconducting coils is coaxially provided with an auxiliary annular superconducting coil in the radial direction of the superconducting coil. In this case, it is possible to control the magnetic field distribution, for example, by exciting the auxiliary coil using a power source separate from that of the superconducting coil. Therefore, by exciting or not exciting the auxiliary coil, it is possible to move (in a vertical direction) the axis of symmetry of the magnetic field to any position in the axial direction of the coil with respect to the coil, and a large-scaled mechanism for moving the entire magnet (or including "crucible" in the case of the pull-up device of single crystal) is not required.

This merit can also be obtained even when at least one of the two superconducting coils is coaxially provided with an auxiliary annular superconducting coil in the axial direction of the superconducting coil.

A member for exciting the two superconducting coils such that magnetic fields generated in the coils are varied from each other is further provided. As one mode of this member, the two coils are excited by a different power source, and electric current of both the power sources are varied, so that a position in which the magnetic field becomes maximum or minimum is set at arbitrary position in the axial direction of the coil.

At least one of the two superconducting coils is provided at its axially outer side with an auxiliary annular coil for generating a magnetic field in opposed direction between the superconducting coils. In this case, it is possible to reduce the leakage of the magnetic flux to outside by the auxiliary annular coil, thereby further reducing the weight of the apparatus.

The nature and further characteristic features of the present invention will be made more clear from the following descriptions made with reference to the accompanying drawings.

In the accompanying drawings: Fig. 1 is a schematic sectional view, taken along the line I-I in Fig. 12 latter mentioned, showing a structure of a superconducting magnet apparatus according to the present invention; Fig. 2 is a schematic sectional view showing a structure of the apparatus using a winding frame; Fig. 3 is a schematic sectional view showing a structure of connecting member using an end plate and a connecting bar; Fig. 4 is a schematic sectional view showing a structure of a position keeping member using a spring; Fig. 5 is a view showing a conception of an essential portion of a superconducting magnet apparatus according to a second embodiment; Fig. 6 is a view showing a conception of an essential portion of a superconducting magnet apparatus according to a third embodiment; Fig. 7 is a view showing a conception of an essential portion of a superconducting magnet apparatus according to a fourth embodiment; Fig. 8 is a schematic block diagram for explaining a case using a plurality of power sources; Fig. 9 is a schematic block diagram for explaining another case using a plurality of power sources; Fig. 10 is a view showing a conception of a superconducting magnet apparatus according to a fifth embodiment; Fig. 11 is a plan view showing a conception of a superconducting magnet apparatus according to a sixth embodiment; Fig. 12 is a perspective view of a superconducting magnet apparatus according to the present invention; Fig. 13 is a view showing a conception for explaining cusped magnetic field distribution when a conventional superconducting magnet apparatus is used; and Fig. 14 is a schematic sectional view showing a structure of the conventional superconducting magnet apparatus; Preferred embodiments of a superconducting magnet apparatus according to the present invention will be described hereunder with reference to the accompanying drawings.

Fig. 12 shows a perspective view of the super conducting magnet apparatus of the present invention to which the following various embodiments will be applicable.

In Fig. 12, a superconducting magnet apparatus 100 has an annular cylindrical outer appearance which comprises an annular vacuum vessel 101 in which annular superconducting coils mentioned hereinlater are disposed. A refrigerator mount 102 is mounted on an upper wall portion of the vacuum vessel 101, and the refrigerator mount 102 includes a cryogenic refrigerator 103 and a current lead 104. An eye-bolt mount 105 and a connector for instrumentation 106 are also mounted to the wall portion of the vacuum vessel 101. An exhaust port 107 may be formed to a side wall portion thereof.

(First Embodiment) Fig. 1 shows a superconducting magnet apparatus 1 having an outer appearance of Fig. 12 and including two annular superconducting coils (which will be referred to as "coil" hereinafter) 2a and 2b disposed at upper and lower positions, respectively, as viewed in Fig. 1, separated in the axial direction of opening of an annular vacuum vessel or container 1. The two coils 2a and 2b are integrally surrounded by an annular helium vessel or container 3, which is covered with double annular radiation shields 4a and 4b. Each of the radiation shields 4a and 4b is thermally connected to a cryogenic refrigerator (Fig. 12) disposed outside the vacuum vessel 1.

In this magnet apparatus, a plurality of connecting members 10 as coil connecting members of the present invention each made of non-magnetic material (such as stainless steel) for sandwiching both the coils 2a and 2b in the axial direction, and a plurality of position keeping members 20 each for keeping an axial distance between the coils 2a and 2b are disposed in a circumferential direction of the coils in the helium container 3 at a distance from one another. A helium container support 30 as a supporting member of the present invention for supporting the helium vessel 3 is disposed in the vacuum vessel 1.

The connecting member 10 is integrally provided to have U-shaped cross section with a base portion (ring portion) 11 extending in the axial direction at least at one of outer peripheral side or inner peripheral side of the coils 2a and 2b (in the drawing, outer peripheral side), and shoulder portions (end plate portions) 12 and 12 extending so as to bend toward outer sides of the coils 2a and 2b in the axial direction AX from opposite ends of the base portion 11. The connecting member 10 supports repulsive force due to the cusped magnetic field of each of the coils 2a and 2b.

The position keeping members 20 includes an extension mechanism such as a turnbuckle and is constructed such that two extruded bars 21 and 21 are connected to each other by a nut 22, and stiffening plates 23 and 23 are mechanically or metallurgically mounted to opposite ends of the connected extruded bars 21 and 21, the stiffening plates 23 and 23 being abutted against opposed surfaces of the coils 2a and 2b, respectively. By rotating the nut 22, the extruded bars 21 and 21 are extended and contracted, and the appropriate axial distance between the coils 2a and 2b is kept by the opposite stiffening plates 23 and 23.

A size of the helium vessel support 30 is set so as to be inserted between the opposed helium vessel 3 and the radiation shield 4a in the axial direction. The helium vessel support 30 extends in the axial direction between the outer peripheral surface of the helium vessel 3 and the upper inner peripheral surface of the vacuum vessel 1 and comprises a hang-down member such as a bar capable of hanging down the helium vessel 3. The support 30 is thermally connected to each of the radiation shields 4a and 4b for preventing a heat of the vacuum vessel 1 from being transferred to the helium vessel 3.

The apparatus of this first embodiment will operate as follows.

When the apparatus is actuated, the connection member 10, the keeping members 20 and both the coils 2a and 2b are kept equally at a cryogenic temperature by liquid helium in the helium vessel 3, electric current is supplied from an exciting power source (not shown), and the cusped magnetic field is generated in the apparatus.

Repulsive force acting on the coils 2a and 2b due to the generated cusped magnetic field is strongly supported by the connection member 10 in the helium vessel 3.

Therefore, according to this magnet apparatus, since repulsive force acting on both the coils 2a and 2b is supported in the helium vessel 3, it is unnecessary to mount a structure for supporting the strong repulsive force from a room temperature side of the vacuum vessel 1 as in the conventional repulsive force support. In other words, since it is unnecessary to provided a structure for supporting the repulsive force of the coils 2a and 2b in spaces of the vacuum vessel 1 and the helium vessel 3, it is possible to enhance the flexibility in design of the support 30.

That is, a strength required for the support 30 is sufficient if it could support at least a deadweight of the entire helium vessel (e.g., some hundreds kg to some tons) irrespective of the magnitude of the repulsive force of the coils 2a and 2b. Therefore, a cross section of the support can be reduced in diameter, and as a result, it is possible to design the support 30 so as to be inserted into the clearance between the helium vessel 3 and the radiation shield 4a, and therefore, a sufficient length of the support can be secured.

If the thin and long support 30 is employed in this manner, since it is possible to largely reduce the transfer of the heat from the room temperature side, outside the vacuum vessel 1, to the cryogenic temperature side (helium vessel) which is inside of the vacuum vessel, evaporation amount of the liquid helium can be suppressed to reduce its consumption amount. It is unnecessary to increase the number of the cryogenic refrigerators, and it is hence possible to provide an apparatus structure capable of reducing its size and weight at a low price with a low maintenance cost.

The following modification and application may be employed for the connecting member.

For example, as a method for reducing eddy current generated in the connecting member when the magnet starts the exciting or stops the exciting, at least one slit may be formed in a ring portion of the connecting member 10 in its circumferential direction. In this case, there are merits that the eddy current generated when the magnet starts the exciting or stops the exciting is suppressed more effectively through the slit, thus further reducing the heat generated by the eddy current and reducing the evaporation amount of the liquid helium.

Further, as a constituent material of the connecting member, a material having an excellent thermal conductivity such as aluminum, copper and the like is usable. In this case, there is a merit that even if the level of the liquid helium in the helium vessel is lowered and the superconducting coil is exposed from the liquid, such exposed portion of the coil can be cooled by the connecting member. Further, if a compound material comprising such high thermal conductivity material and a relatively strong material such as stainless steel is used, it is possible to provide a connecting member having an excellent strength in addition to an excellent thermal conductivity.

As the connecting member, a winding frame 10a for winding both the coils 2a and 2b as shown in Fig. 2 may be employed. If the winding frame 10a is used, it can also function as the position keeping member. Therefore, if the winding frame 10a around which the coils 2a and 2b are wound is incorporated in the helium vessel 3 as it is, the connecting member and the position keeping member are not required, and the producing process can further be simplified, thus being advantageous.

Further, as the connecting member, it is possible to employ a structure member 10b as shown in Fig. 3 in which end plates 12b and 12b are used as the two shoulders, and connecting bars llb and llb as base portions are integrally mounted to opposite sides of the end plates 12b and 12b. In this case, a plurality of sets of the two end plates 12b and 12b may be disposed in a circumferential direction of the coil at distance from one another, or they may be integrally formed into a doughnut-like disc.

Although the extension mechanism using the extruded bars and nut as the position keeping member is employed in this embodiment, the present invention should not be limited to this mechanism.

For example, as the position keeping member, it is possible to employ a member 20a made of stainless steel or the like as shown in Fig. 4 in which the two interval bars 21a and 21a are connected to each other through a spring 24, and an adjusting nut 22a is provided at the connected portion for adjusting the distance between the coils.

In this case, a difference in thermal shrinkage between the position keeping member 20a made of, e.g., stainless steel, and the connecting member 10 made of the above-mentioned aluminum can be absorbed by the spring 24.

Therefore, a stress due to the thermal shrinkage generated between the members 20a and 10 and between the members 20a, 10 and coils 2a, 2a can be suppressed more effectively.

Although a plurality of the connecting members and the position keeping members are disposed in the circumferential direction of the coil, the present -invention is not necessarily limited to this arrangement, and they may be integrally formed into a ring-shaped member in the circumferential direction of the coil, for example.

(Second Embodiment) In a superconducting magnet apparatus shown in Fig. 5, in addition to the structure described above, each of the coils 2a and 2b is wound in a preset center radius R1, and the coils 2a and 2b are disposed to upper and lower portions with a preset coil center distance L1. The radius R1 and the distance L1 are set to provide an equal length.

According to this magnetic apparatus, in addition to the effect of the first embodiment, since magnetic flux density at a position in the axial direction AX of the coil and magnetic flux density at a position parallel to axis Al of symmetry of the cusped magnetic field (neutral point of space magnetic field between both the coils) are substantially equal to each other, the cusped magnetic field having the most efficient magnetic field distribution can be generated, and a driving stability of the superconducting coil can be secured more appropriately, thus being advantageous. The same merits can be obtained even though the conventional support is used.

(Third Embodiment) In a superconducting magnet apparatus shown in Fig. 6, in addition to the structure described above, the lower coil 2b is provided at its outer periphery with an auxiliary coil 40 which is connected to a power source (not shown) separate from that of the upper and lower main coils 2a and 2b. Arbitrary magnetic field is generated only by the auxiliary coil 40 in addition to the cusped magnetic field generated by the main coils 2a and 2b.

In this case, in addition to the effect of the previous embodiments, it is possible to freely move spatially, in a vertical direction, the cusped magnetic field symmetry axis with respect to the coil by generating a cusped magnetic field by using upper and lower main coils and generating another magnetic field by using the auxiliary coil in the same or opposite direction as the former magnetic field.

Such merits are exhibited to the utmost when the superconducting magnet apparatus is applied to a pull-up device of a semiconductor single crystal.

In the case of a conventional pull-up device, only the same magnetic forces can be generated in both the coils, and a position of the axis of symmetry of the space magnetic field is always fixed at the neutral point between the coils, and a liquid level of the crystal material melted in a crucible is gradually lowered due to the pulling up operation. Therefore, the position of the molten liquid level is always varied with respect to the fixed magnetic field and as a result, there is a problem that a quality of the single crystal is not stable.

According to this embodiment, since it is possible to freely move the axis of symmetry of the cusped magnetic field with respect to the coil in a vertical direction spatially in accordance with a variation in the liquid level of the molten single crystal, it is possible to always generate the optimal magnetic field in accordance with the molten liquid level even if a mechanism for relatively vertically moving the crucible or the entire magnet be not used. Therefore, it is possible to improve the stability in quality of the obtained single crystal.

This merit is also exhibited when the conventional support is used.

Although the auxiliary coil is disposed on the lower coil in this embodiment, the present invention should not be limited to this arrangement, and the same effect can be exhibited even though the auxiliary coil is disposed on the upper coil side. If the auxiliary coil is disposed on each of the upper and lower coil sides, it is possible to control the magnetic field distribution accurately in a wider range. If a plurality of auxiliary coils are disposed, a variation of magnetic field can be controlled more accurately.

Although the auxiliary coils is disposed on the outer periphery of the main coil (lower or upper coil) in this embodiment, the present invention should not be limited to this arrangement, and the same effect can be obtained even if the auxiliary coil is disposed on an inner periphery of the main coil.

(Fourth Embodiment) In a superconducting magnetic apparatus as shown in Fig. 7, in addition to the structure described above, auxiliary coils 41a and 41b are provided at axially outer sides of the coils 2a and 2b, and the exciting state is controlled to be varied such that a total exciting magnetic field of the upper main coil 2a and the auxiliary coil 41a and a total exciting magnetic field of the lower main coil 2b and the auxiliary coil 41b become equal to each other, thereby vertically moving the position of the axis of symmetry AX of the cusped magnetic field spatially with respect to both the coils 2a and 2b.

For example, during a normal operation, the auxiliary coils 41a and 41b are not excited and only the main coils 2a and 2b are excited at 100 %, thus keeping the position of the axis of symmetry AX of the cusped magnetic field at the neutral point between the upper and lower coils 2a and 2b.

In this state, when the axis of symmetry AX is moved upward from the neutral point, the upper coil 2a is not excited and the upper auxiliary coil 41a is excited at 100%, and when the axis of symmetry AX is moved downward from the neutral point, the lower coil 2b is demagnetized and the lower auxiliary coil 41b is magnetized at 100%.

Therefore, according to this embodiment, when the axis of symmetry of the cusped magnetic field is vertically moved spatially, its position can continuously be varied, and the symmetry between the upper and lower magnetic fields sandwiching the axis of symmetry can always be secured independent from variation in position of the axis of symmetry of the cusped magnetic field. This merit can also be exhibited even when the conventional support is used.

Although each of the upper and lower main coils is provided with one auxiliary coil in this embodiment, the present invention should not be limited to this arrangement. If each of the upper and lower main coils is provided with a plurality of auxiliary coils, it is possible to further increase the moving amount of the axis of symmetry of the cusped magnetic field.

In the above third and fourth embodiments, although the position of the axis of symmetry of the cusped magnetic field is moved spatially in the vertical direction, the present invention should not be limited to this arrangement. One example of such a state is shown in Figs. 8 and 9.

In a superconducting magnet apparatus shown in Fig. 8, the upper and lower coils 2a and 2b are respectively connected to current leads 50... 50 for supplying electric current and power sources 51 and 51. By supplying electric current from the sources 51 and 51 to the coils 2a and 2b individually, the coils 2a and 2b are separately excited to generate the magnetomotive forces.

In this case, if a control is conducted so as to make constant the generated magnetic field of one of the upper and lower main coils and to vary the generated magnetic field of the other main coils, it is possible to vertically move the axis of symmetry Al of the cusped magnetic field. Therefore, even if the above mentioned auxiliary coil is not used, it is possible to control the vertical movement of the axis of symmetry with relatively simple structure.

In a superconducting magnet apparatus shown in Fig. 9, a main power source 51 is connected to each of the upper and lower coils 2a and 2b in series through current leads 50 and 50, and another auxiliary power source 52 is connected to only the lower coil 2b through another current lead 50.

In this case, electric current from the main power source 51 is supplied to both the coils 2a and 2b, and electric current from the auxiliary power source 52 is supplied only to the lower coil 2b, so that exciting magnetic force higher than that of the upper coil 2a is generated in the lower coil 2b, thereby vertically varying the position of the axis of symmetry Al of the cusped magnetic field.

In this case, as compared with the above case, since three current leads suffice, a heat transfer from the current leads to low temperature portion can be suppressed, and the consumption of the liquid helium is reduced. The auxiliary power source may be connected to the upper coil only.

(Fifth Embodiment) In a superconducting magnet apparatus shown in Fig. 10, in addition to the structure described above, auxiliary coils 42a and 42b are provided at an outer side of the upper and lower main coils 2a and 2b in the axial direction AX, and magnetizing state is controlled such that magnetic fields of the auxiliary coils 42a and 42b are generated in opposite direction to those of the main coils 2a and 2b.

According to this embodiment, since the magnetic fields are generated in the auxiliary coils in the opposite direction to the magnetic filed generated in the upper coil, it is possible to effectively reduce the leakage of magnetic field in an upper and outer direction of the magnet. Since the same effect can be obtained for the lower coil and the auxiliary coil, the entire leakage of the magnetic field can largely be reduced.

Here, as a method for reducing the leakage of magnetic field, a magnetic material such as an iron may be used. In this case, however, this is not a good method because there is a disadvantage that the entire apparatus is increased in size. Comparing with this method, if the above described auxiliary coil is used, it is possible to provide a superconducting magnet apparatus of a structure which is more simple and is capable of reducing the apparatus in both the size and weight, and therefore, an influence of the magnetic field exerted on the magnetic material and electronic equipment around the magnet can greatly be reduced, thus being advantageous. This merit can also be obtained even if the conventional support is used.

(Sixth Embodiment) In a superconducting magnet apparatus shown in Fig. 11, in addition to the structure described above, two cryogenic refrigerator 60 and 60 are disposed at 1800 symmetric positions (equiangular positions) with respect to a center axis of the vacuum vessel 1. By driving each of the cryogenic refrigerator 60 and 60, it is possible to equally cool the radiation shield and the like (not shown) in the vacuum vessel 1.

According to this embodiment, since it is possible to substantially avoid a situation that non-cooled portion locally exists in low temperature side within the vacuum vessel, in the case of a cooling type magnet which directly cools the coil by the cryogenic refrigerator, the coil is uniformly cooled by the cryogenic refrigerators disposed on the equiangular positions, and when a plurality of cryogenic refrigerators are thermally connected, commonly instead of individually, to a plurality of coils, there is a merit that if a performance of one of the cryogenic refrigerators is varied, other cryogenic refrigerators can cool the coils, which further improve a reliability of the apparatus. The same merit can be obtained even if the conventional support is used.

The number of cryogenic refrigerators should not be limited to two, and three or more cryogenic refrigerators may be used. In this case, it is preferable to dispose them on the equiangular positions.

It is to be noted that the present invention is not limited to the described embodiments and many other changes and modifications may be made without departing from the scopes of the appended claims.

As described above, according to the present invention, since coil connecting member is used for connecting the superconducting coils to each other, it is possible to provide a simple support structure for supporting repulsive force acting on the superconducting coils. Even if a cross section of the support structure which is to be mounted to the vacuum vessel for example, it is possible to largely reduce an amount of heat transferring from an outside of the vacuum vessel through the support structure and as a result, it is possible to provide, at relatively low cost, an apparatus structure suitable for reducing in size and weight.

Claims

1. A superconducting magnet apparatus comprising: a vacuum vessel; two annular superconducting coils opposed to each other in an axial direction of the vacuum vessel; and a support structure for supporting the two superconducting coils, said support structure comprising a coil connecting body for connecting the two superconducting coils in the axial direction of the vacuum vessel and a support body for integrally supporting the two superconducting coils connected by the coil connecting body, said two superconducting coils being disposed to the vacuum vessel through said support body.

2. A superconducting magnet apparatus according to claim 1, wherein said coil connecting body comprises an annular member disposed around the two superconducting coils in a circumferential direction thereof.

3. A superconducting magnet apparatus according to claim 2, wherein said annular member is composed of a winding frame for winding the two superconducting coils.

4. A superconducting magnet apparatus according to claim 1, wherein said coil connecting body comprises a plurality of arc-shaped members disposed around said two superconducting coils in the circumferential direction thereof at constant distances from one another.

5. A superconducting magnet apparatus according to claim 1, wherein said coil connecting body comprises connecting members for sandwiching and connecting said two superconducting coils in the axial direction thereof and an position keeping member for keeping an axial position between said two superconducting coils connected by said connecting members.

6. A superconducting magnet apparatus according to claim 5, wherein each of said connecting members comprises a base portion extending in the axial direction along at least one of radially inner and outer sides of the two superconducting coils and shoulder portions extending from axially opposing ends of the base portion so as to bend toward an axially outer side of the two superconducting coils.

7. A superconducting magnet apparatus according to claim 6, wherein said base portion and said shoulder portion are integrally formed.

8. A superconducting magnet apparatus according to claim 6, wherein said shoulder portion comprises two end plates disposed so as to abut against the axially outer side of the two superconducting coils, respectively, said base body comprising a fastening member for fastening the two end plates in the axial direction.

9. A superconducting magnet apparatus according to one of claims 5-8, wherein said connecting member is circumferentially provided with a slit for reducing eddy current.

10. A superconducting magnet apparatus according to one of claims~iT,wherein said connecting member is formed of a material having high thermal conductivity or a compound made of material having high thermal conductivity and a material having high strength.

11. A superconducting magnet apparatus according to one d clsvs 910,wherein said position keeping member comprises a mechanism for freely adjusting a length of a clearance in the axial direction of the superconducting coils in accordance with an axial thermal expansion between the two superconducting coils and the connecting member.

12. A superconducting magnet apparatus according to any preceding claim, wherein a central distance of conductor in the axial direction of the two superconducting coils and a radius of the center of the conductor in the diametral direction are equal to each other.

13. A superconducting magnet apparatus according to any preceding claim, wherein at least one of said two superconducting coils is provided with an auxiliary annular superconducting coil in the radial direction of the superconducting coil in a manner coaxial therewith.

14. A superconducting magnet apparatus according to one of claims 1-12, wherein at least one of said two superconducting coils is provided with an auxiliary annular superconducting coil in the axial direction of the superconducting coil in a manner coaxial therewith.

15. A superconducting magnet apparatus according to any preceding claim, further comprising means for exciting said two superconducting coils so as to generate magnetic fields of the superconducting coils different from each other.

16. A superconducting magnet apparatus according to any preceding clXim,wherein at least one of said two superconducting coils is provided at an axially outer side thereof with an auxiliary annular coil for generating a magnetic field in opposite direction between said superconducting coils.

17. A superconducting magnet apparatus according toany preceding claim, further comprising an annular helium vessel surrounding the two superconducting coils and a double annular radiation shield surrounding said annular helium vessel.

18. A superconducting magnet apparatus according to claim 17, wherein cryogenic refrigerators are disposed at symmetric equiangular positions with respect to a center axis of the vacuum container.

19. A superconducting magnet apparatus according to any preceding claim, wherein said coil connecting member is formed of a non-magnetic material.

20. A superconducting magnet apparatus substantially as herein described, with reference to Figures 1-12 of the accompanying drawings.