JP2007184383A - Magnetic field forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively reduce the height of a magnetic field forming device, using solenoidal superconducting coils, while securing sufficient magnetic field strength and stable coil installation conditions. <P>SOLUTION: A plurality of solenoidal superconducting coils 10 are arranged on one of sides across a magnetic field utilization space S, both in the horizontal and the vertical directions which are approximately perpendicular to the radial direction of the space S. A plurality of solenoidal superconducting coils 10 are arranged on the other side so as to sandwich, facing the coils 10 arranged on the former side across the space S. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a magnetic field forming apparatus used for pulling up a silicon single crystal, a physical property experiment under a horizontal strong magnetic field, and the like.

  In general, in the process of pulling and growing a large-diameter silicon single crystal from a silicon melt in a crucible, a method of applying a strong magnetic field is often used to suppress convection of the silicon melt in the crucible. As the magnetic field direction, a direction (horizontal direction) orthogonal to the pulling axis of the silicon single crystal is often used.

  Conventionally, as a device for forming a strong horizontal magnetic field, devices in which solenoid type superconducting coils are respectively disposed at positions facing each other across the magnetic field utilization space are known. However, in order to form a sufficiently strong magnetic field in such an apparatus, the winding diameter of the superconducting coil must be considerably increased. The increase in the diameter of such a superconducting coil results in an increase in the size of the entire apparatus. This causes inconveniences such as reduction in magnetic field generation efficiency and increase in leakage magnetic field.

  Therefore, as means for solving such inconvenience, Patent Document 1 discloses an apparatus as shown in FIGS. 10 (a) and 10 (b). In this apparatus, a cryostat 1 having a cylindrical magnetic field utilization space S with its axial direction oriented in the vertical direction in the center has three pieces on one side (left side in FIG. 5B) across the magnetic field utilization space S. Solenoid superconducting coils C1, C2, C3 are arranged side by side in the circumferential direction, and the solenoid type superconducting coils C1, C2, C3 are arranged on the other side (the right side in FIG. 5B) with the magnetic field utilization space S in between. The three solenoid type superconducting coils C1 ′, C2 ′, C3 ′ are arranged so as to face each other.

According to this apparatus, since a plurality of superconducting coils are arranged on both sides of the magnetic field utilization space S, the winding diameter required for each coil is smaller than that in which only a pair of opposing superconducting coils are arranged. Accordingly, the entire magnetic field forming apparatus can be reduced in size.
JP 2001-203106 A

  In the magnetic field forming apparatus, reduction of the height dimension has become a big issue. In particular, when this magnetic field forming apparatus is used for pulling a single crystal from the silicon melt as described above, the reduction in the height dimension of the apparatus greatly contributes to the improvement of crystal production efficiency. In other words, since the crystallization of the silicon melt is performed at a height position near the center of the magnetic field, if the position is kept low, the silicon pulling space above it can be made wider, and the length of the product crystal is increased accordingly. It becomes possible to take a large.

  In this respect, in the conventional apparatus shown in FIGS. 10A and 10B, only a pair of superconducting coils are arranged opposite to each other because a plurality of superconducting coils are arranged on both sides of the magnetic field utilization space S. However, the degree of improvement is limited, and there is a limit to reducing the height dimension of the apparatus while maintaining a sufficient magnetic field strength.

  As a means for ensuring both the magnetic field strength and reducing the required height, it is conceivable to arrange a pair of saddle coils Cs as shown in FIG. When used as a conduction coil, there is a drawback that it is difficult to maintain a stable installation state when a strong magnetic field is generated by passing a large current through the coil. That is, each saddle-shaped coil Cs has a shape in which left and right vertical portions that form a straight line and upper and lower flanges that form an arc shape are combined. Therefore, when the saddle-shaped coil Cs is applied to a superconducting coil. There is a situation that it is difficult to fix the superconducting wire in a stationary state against a large electromagnetic force acting with the generation of the strong magnetic field. If the stationary state collapses and the wire moves, there is a risk of quenching due to frictional heat or the like.

  In view of such circumstances, an object of the present invention is to effectively reduce the height dimension of an apparatus while ensuring a sufficient magnetic field strength while using a solenoid type superconducting coil.

  As a result of repeated studies to solve the above problems, the present inventors have arranged a plurality of solenoid-type superconducting coils not only in the horizontal direction but also in the vertical direction, that is, in the direction parallel to the axial direction of the magnetic field utilization space, It has been found that the required height dimension for superconducting coil arrangement can be reduced while maintaining a sufficient magnetic field strength, as compared with conventional devices.

  The present invention has been made from such a viewpoint, and a plurality of solenoid-type superconducting coils are arranged in a posture in which the central axis is oriented in a substantially horizontal direction around a magnetic field utilization space in which the central axis is oriented in the vertical direction. In the magnetic field forming apparatus in which a magnetic field orthogonal to the axial direction is formed in the magnetic field utilization space by energization of these superconducting coils, a plurality of solenoid type superconducting coils are disposed on one side of the magnetic field utilization space. A plurality of arrays are arranged so as to be aligned in both the horizontal direction and the vertical direction substantially orthogonal to the radial direction of the use space, and the superconducting coils arranged on the one side are sandwiched between the superconducting coil and the magnetic field use space. A plurality of superconducting coils are arranged so as to face each other.

  According to this configuration, while using the solenoid-type superconducting coil that can be easily installed stably, the solenoid-type superconducting coil is not only in the horizontal direction substantially perpendicular to the radial direction of the magnetic field utilization space but also in the vertical direction. Further, by arranging a plurality of devices, it is possible to reduce the height of the device while ensuring the same magnetic field strength as that of the conventional device.

  As a specific coil arrangement, for example, on both sides of the magnetic field utilization space, a planar coil arrangement region perpendicular to the radial direction of the magnetic field utilization space has a circumference perpendicular to both the axial direction and the radial direction. A plurality of solenoid superconducting coils that are set in a plurality of locations arranged in the direction and are arranged in both the horizontal direction and the vertical direction on each coil arrangement region is preferable. According to this configuration, by arranging a plurality of superconducting coils in a planar shape in each coil arrangement region, it is possible to secure sufficient magnetic field strength and reduce the height of the apparatus while facilitating the installation. .

  Specifically, a coil support member parallel to the coil placement region is provided in each coil placement region, and a plurality of solenoid type superconducting coils are arranged in both the horizontal direction and the vertical direction on each coil support member. If it is configured to be fixed in a state where the coils are arranged, each coil can be easily disposed at an appropriate position, and can be held in a stable state at that position.

  As an example of the arrangement, three coil arrangement areas facing each other on both sides of the magnetic field utilization space are set, and six solenoid-type superconducting coils in the horizontal direction and three in the vertical direction on each coil arrangement area. It is preferable that the two are arranged in parallel.

  As another coil arrangement mode, a cylindrical coil arrangement area coaxial with the central axis of the magnetic field utilization space is set on both sides of the magnetic field utilization space, and a plurality of coil arrangement areas are provided on each coil arrangement area. The solenoid-type superconducting coils may be arranged so as to be aligned in both the circumferential direction and the vertical direction of the coil arrangement region. According to this configuration, the diameter of the coil arrangement space can be reduced by unifying the distance of each coil from the central axis of the magnetic field utilization space (distance in the radial direction).

  As described above, according to the present invention, a plurality of solenoid-type superconducting coils are arranged not only in the horizontal direction substantially perpendicular to the radial direction of the magnetic field utilization space but also in the vertical direction, thereby providing the same as in the conventional apparatus. There is an effect that the height dimension of the apparatus can be reduced while ensuring the magnetic field strength.

  A preferred embodiment of the present invention will be described with reference to FIGS.

  Similar to the apparatus shown in FIGS. 10A and 10B, the apparatus according to this embodiment has a cylindrical magnetic field utilization space S in which the axial direction is the vertical direction, as shown in FIG. It is provided in the cryostat 1.

  The cryostat 1 has a donut plate-like top plate 2 and a bottom plate 3, and an inner cylinder 4 and an outer cylinder 5 respectively arranged on the inner side and the outer side in the radial direction. It is joined to the top plates 2 and 3 in an airtight state, and the inner space of the inner cylinder 4 is the magnetic field utilization space S. This magnetic field utilization space S may be open on both sides in the vertical direction, or may be one in which the upper or lower edge thereof is closed by the top plate 2 or the bottom plate 3. . Further, the axial direction of the magnetic field utilization space S may not exactly coincide with the vertical direction, and may be slightly inclined depending on the application.

  In the cryostat 1, a space between the cylinders 4 and 5 is a cooling space, and the magnetic field forming apparatus according to the present invention is introduced into the cooling space. This magnetic field forming apparatus is cooled until it becomes a superconducting state by a known cooling means, for example, immersion in a refrigerant such as liquid helium, or a small GM refrigerator or a pulse tube.

  The magnetic field forming apparatus is configured by arranging a plurality of solenoid type superconducting coils (hereinafter simply referred to as “superconducting coils”) 10. Specifically, the center and three right and left coil arrangement regions R1, R2, and R3 are set on one side across the magnetic field utilization space S, and the coil arrangement regions R1, R2, and R3 are respectively set. Three coil arrangement regions R1 ′, R2 ′, R3 ′ are set on the other side so as to face each other (separate by 180 ° in the circumferential direction), and the superconducting coils 10 are respectively arranged in these coil arrangement regions. A plurality are arranged.

Each of the superconducting coils 10 is configured by winding a suitable superconducting wire (for example, Nb ₃ Sn wire) around a winding frame made of, for example, stainless steel.

  Each of the coil arrangement regions has a planar shape perpendicular to the radial direction of the magnetic field utilization space S (the directions of the central axes X1, X2, and X3 shown in FIG. 2), and the central coil arrangement regions R1, R1. The central axis X2 of the coil arrangement regions R2 and R2 'on the left side and the central axis X3 of the coil arrangement regions R3 and R3' on the right side of the magnetic field utilization space S with respect to the central axis (normal axis) X1 of ' They are distributed in the circumferential direction at a predetermined arrangement angle α (≦ 60 °).

  In each of the coil arrangement regions, a total of six superconducting coils 10 in the horizontal direction (left and right direction in FIG. 3) and three in the vertical direction (up and down direction in FIG. 3) are shown in FIG. Two are arranged side by side. As shown in FIG. 3, each superconducting coil 10 has an annular shape (doughnut shape) having an outer diameter D and an inner diameter d, and is arranged in such a manner that its central axis is oriented substantially in the horizontal direction. Predetermined gaps δ1 and δ2 (FIG. 3) are secured in the horizontal and vertical directions while being electrically insulated from each other. The direction of the winding of the superconducting coil 10 in each coil arrangement region is unified, and a magnetic field parallel to each coil axis is formed by energizing these superconducting coils 10 simultaneously.

  Each of the superconducting coils 10 may be connected in series to a common power source or may be connected in parallel. Alternatively, a dedicated power source may be provided for each area.

  According to such a magnetic field generator, although a plurality of superconducting coils 10 are arranged in the vertical direction, the coil diameter of each superconducting coil 10 required to form a sufficient magnetic field can be reduced. Compared with a conventional apparatus (for example, the apparatus shown in FIGS. 10A and 10B) in which only a single superconducting coil is arranged in the vertical direction, the apparatus height dimension required to form a magnetic field having the same strength as this. Can be reduced. That is, when a single large-diameter coil is installed in the vertical direction as in the prior art, the magnetic field follows the coil shape, but the coil installation gap is large, thereby reducing the magnetic field generation efficiency and increasing the device height. On the other hand, when a plurality of small-diameter coils are arranged vertically and horizontally as shown in FIG. 3, the gap between the coils can be reduced, so that the magnetic field generation efficiency is increased and the height of the apparatus can be reduced.

  In the present invention, the specific number, arrangement, and shape of each superconducting coil 10 are not limited to those illustrated, and can be set as appropriate.

  For example, as shown in FIGS. 4 (a) and 4 (b), cylinders coaxial with the central axis of the magnetic field utilization space S are provided on both sides of the magnetic field utilization space S (upper and lower sides in FIG. 4 (b)). A planar coil arrangement region Rs, Rs ′ is set, and a plurality of solenoid type superconducting coils are arranged in both the circumferential direction and the vertical direction of the coil arrangement region on each coil arrangement region Rs, Rs ′ (example in the figure). 9 may be arranged in the circumferential direction and two in the vertical direction.

  When the required magnetic field is strong, three or more superconducting coils 10 may be arranged in the vertical direction, and the number of arrangement in the horizontal direction can be set as appropriate. Moreover, the total number of coil arrangement | positioning area | regions can also be increased / decreased suitably.

  The shape of each superconducting coil 10 is generally a toroidal shape (donut shape) as shown in the figure, but the shape viewed from the direction parallel to the central axis is a vertically long or horizontally long ellipse or other closed curve shape. Also good. In either case, the wire movement (the minute movement of the superconducting wire) is effectively suppressed by the winding tension acting over the entire circumference of the coil. When the electromagnetic force is large and the wire movement cannot be suppressed only by the winding tension, a well-known means such as winding another bind wire around the outer periphery of the coil or impregnating with an impregnation material made of epoxy resin or wax What is necessary is just to regulate a wire movement using a means.

  Various settings can be made for specific means for holding each superconducting coil 10 at a predetermined position. As an example, FIGS. 5A and 5B show a coil support structure suitable when the arrangement angle α of the coil arrangement region is set to 60 ° in the arrangement shown in FIG.

  The coil support frame 14 shown in FIG. 6A is a hexagonal cylinder shape in which a total of six flat plate portions 11, 12, 13, 11 ', 12', 13 'are joined to each other so as to have a regular hexagonal shape in plan view. A total of six superconducting coils 10 (three in the horizontal direction and two in the vertical direction) are arranged on the outer surface of each of the flat plate portions 11, 12, 13, 11 ', 12', 13 '. It is being fixed to the said each flat plate part with the volt | bolt 16 shown to (b). That is, the flat plate portions 11, 12, 13, 11 ', 12', 13 'are respectively arranged in the coil arrangement regions R1, R2, R3, R1', R2 shown in FIGS. A coil supporting member parallel to ', R3' is formed.

  As the material for the coil support frame 14 and the bolt 16, stainless steel such as SUS316, pure aluminum, aluminum alloy, or the like can be used. Moreover, as fixing means other than the bolt 16, for example, welding is suitable, and fixing with an adhesive is also possible.

  FIG. 6 shows an example in which each superconducting coil 10 held by the coil support frame 14 shown in FIG. 5 and operated at the liquid helium temperature is introduced into the refrigerant cryostat 1.

  The cryostat 1 shown in the figure has a hollow donut-shaped vacuum chamber 30 in which a liquid nitrogen tank 32, a radiation shield plate 33, and a liquid helium tank 34 are accommodated. The liquid nitrogen tank 32 has a hollow donut shape, and liquid nitrogen is accommodated therein. The liquid helium tank 34 is disposed on the radially inner side of the liquid nitrogen tank 32, and the radiation shield plate 33 is disposed so as to cover the liquid helium tank 34 from the upper side, the lower side, and the radially inner side.

  The liquid helium tank 34 contains liquid helium 36 as a coolant, and the coil support frame 14 and a number of superconducting coils 10 held by the coil support frame 14 are immersed in the liquid helium 36. The coil support frame 14 is arranged at a position coaxial with the central axis of the magnetic field utilization space S surrounded by the cryostat 1 in such a posture that the flat plate portions 11, 12, 13, 11 ', 12', 13 'are upright. The lower end thereof is fixed to the bottom wall of the liquid helium tank 34. Thus, the superconducting coils 10 are arranged so as to be arranged in both the horizontal direction and the vertical direction on the coil arrangement regions parallel to the flat plate portions 11, 12, 13, 11 ', 12', 13 ', respectively. And it is in a held state. When these superconducting coils 10 are energized, a strong magnetic field having horizontal magnetic flux lines 38 as shown in FIG. 6 is formed in the magnetic field utilization space S.

  In the illustrated example, all flat plate portions 11, 12, 13, 11 ', 12', 13 'are connected to each other to form a single coil support frame 14, but these flat plate portions are independent of each other. And may be arranged individually.

  In both the comparative example apparatus as shown in FIG. 7 (an apparatus having a single superconducting coil in the vertical direction) and the present invention apparatus as shown in FIGS. The coil design and the layout design for generating the density were performed. The specifications are shown in Table 1 (Comparative Example) and Table 2 (Example 1) below.

  In the comparative example device, as shown in FIG. 7, the center and three superconducting coils 20, 22, and 24 on the left and right sides thereof are arranged on one side (left side of the figure) across the magnetic field utilization space S, while the other The three superconducting coils 20 ′, 22 ′, 24 ′ are arranged on the side of the superconducting coils 20, 22, 24 so as to face each other, and these superconducting coils 20, 22, 24, 20 ′, The layout of 22 'and 24 approximates to the layout of each coil arrangement region R1, R2, R3, R1', R2 ', R3' in the device of the present invention shown in FIGS.

Each of the superconducting coils in the comparative example device and the device of the present invention is configured by winding a superconducting wire made of Nb ₃ Sn around a stainless steel winding frame.

  When Table 1 and Table 2 are compared, the effect of Example 1 is very clear. That is, the winding outer diameter D of the superconducting coil in the comparative example device is 694 mm, and at least the device height dimension equivalent to this is required, whereas each superconducting coil 10 in the device of the first embodiment is required. Since the winding outer diameter D is 268 mm and the distance (gap) δ2 between the coils in the vertical direction is 1 mm, the required height dimension is within 268 mm × 2 + 1 mm = 537 mm. Therefore, in this embodiment, it can be expected that the height dimension is reduced by 694 mm−537 mm = 110 mm as compared with the comparative example.

  Further, FIG. 8 shows a histogram obtained by analyzing the magnetic field distribution in the comparative apparatus (upper part of the figure) and the apparatus of the present example (lower part of the figure). By applying the present invention, the uniformity of the magnetic field can be maintained at a level higher than that of the comparative example while suppressing the height of the apparatus.

  Similar to the first embodiment, in the device of the present invention as shown in FIG. 4, a coil design and a layout design for generating a magnetic flux density of 0.4 T at the center of the magnetic field were performed. The specifications are shown in Table 3 below (Example 2).

  Even when Table 3 is compared with Table 1 above, the effect of Example 2 is very clear. That is, the winding outer diameter D of the superconducting coil in the comparative example apparatus is 694 mm, and at least an apparatus height dimension equivalent to this is required. Similarly, since the winding outer diameter D of each superconducting coil 10 is 268 mm and the distance (gap) δ2 between the coils in the vertical direction is 1 mm, the required height dimension is within 268 mm × 2 + 1 mm = 537 mm. Therefore, it can be expected that the height dimension is reduced by 694 mm−537 mm = 110 mm as compared with the comparative example as in the first embodiment.

  Further, FIG. 9 shows a histogram obtained by analyzing the magnetic field distribution in the apparatus of the second embodiment in the same manner as in FIG. 8. As is clear from comparison between FIG. 9 and the upper diagram of FIG. By applying the present invention, the uniformity of the magnetic field can be maintained at a level higher than that of the comparative example while suppressing the height of the apparatus.

1 is a schematic perspective view of a cryostat in which a magnetic field forming apparatus according to an embodiment of the present invention is introduced. (A) is a perspective view which shows the arrangement | sequence of the superconducting coil in the said magnetic field formation apparatus, (b) is the top view. It is a front view which shows the arrangement | sequence of the superconducting coil in each coil arrangement | positioning area | region of the said magnetic field formation apparatus. (A) is a perspective view which shows the arrangement | sequence of the superconducting coil in the magnetic field formation apparatus based on Embodiment different from FIG. 2, (b) is the top view. It is a perspective view which shows the coil support frame for supporting each superconducting coil by the arrangement | sequence shown by FIG. It is a cross-sectional front view which shows the example in which each said superconducting coil supported by the said coil support frame and this coil support frame was introduce | transduced into the cryostat. It is a top view which shows arrangement | positioning of each superconducting coil in a comparative example. It is a histogram which shows distribution of the magnetic field formed with the apparatus of the said comparative example and Example 1 of this invention. It is a histogram which shows distribution of the magnetic field formed with the apparatus of Example 2 of this invention. (A) is a perspective view which shows the example of arrangement | positioning of the coil in the conventional magnetic field formation apparatus, (b) is the top view. It is a perspective view which shows the example of a saddle type coil.

Explanation of symbols

R1, R2, R3, Rs, R1 ', R2', R3 ', Rs' Coil arrangement area S Magnetic field utilization space X1 to X3 Central axis α Coil arrangement area θ Coil arrangement angle 1 Cryostat 10 Solenoid type Superconducting coil 11, 12, 13, 11 ', 12', 13 'Flat plate (coil support member)
14 Coil support frame

Claims (5)

  A plurality of solenoid-type superconducting coils are arranged around the magnetic field utilization space whose central axis is oriented in the vertical direction, with the central axis oriented in a substantially horizontal direction, and these superconducting coils are energized in the magnetic field utilization space. In the magnetic field forming apparatus in which a magnetic field orthogonal to the axial direction is formed, a plurality of solenoid type superconducting coils on one side across the magnetic field utilization space, a horizontal direction substantially perpendicular to the radial direction of the magnetic field utilization space, and A plurality of superconducting coils are arranged so as to be arranged in both vertical directions, and a plurality of superconducting coils are arranged on the other side so as to face each superconducting coil arranged on the one side across the magnetic field utilization space. Magnetic field forming apparatus characterized by that.   2. The magnetic field forming apparatus according to claim 1, wherein a planar coil array region perpendicular to the radial direction of the magnetic field utilization space is disposed on both sides of the magnetic field utilization space across the axial direction and the radial direction. And a plurality of solenoid type superconducting coils arranged in both the horizontal direction and the vertical direction on each coil arrangement region.   3. The magnetic field forming apparatus according to claim 2, wherein three coil arrangement areas facing each other are set on both sides of the magnetic field utilization space, and six solenoid type superconducting coils are horizontally arranged on each coil arrangement area. An apparatus for forming a magnetic field, wherein two are arranged in a vertical direction.   4. The magnetic field forming apparatus according to claim 2, wherein a coil support member parallel to the coil arrangement region is arranged in each coil arrangement region, and a plurality of solenoid type superconducting coils are horizontally arranged in each coil support member. And a magnetic field forming device fixed in a state of being arranged so as to be aligned in both the vertical direction and the vertical direction.   2. The magnetic field forming apparatus according to claim 1, wherein on both sides of the magnetic field utilization space, a cylindrical coil arrangement region coaxial with the central axis of the magnetic field utilization space is set, and a plurality of coil arrangement regions are provided on each coil arrangement region. A magnetic field forming apparatus characterized in that the solenoid type superconducting coils are arranged so as to be aligned in both the circumferential direction and the vertical direction of the coil arrangement region.

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