SUPER-CONDUCTING MAGNET DEVICE FOR GENERATING HORIZONTAL MAGNETIC FIELD USING CURVED ANNULAR OR ELLIPTICAL SHAPED COILS TECHNICAL FIELD The present invention relates to a configuration of suitable coils to apply to a system which requires a horizontal magnetic field such as a single-crystal growing device, particularly a configuration of super-conducting coils for improving the generation of a horizontal magnetic field. There are several configurations of super-conducting coils, such as a saddle-type or solenoid type which are commonly used to generate a horizontal magnetic field. It is known that the most effective coil configuration for reducing the loss of magnetic field is the saddle-type super-conducting coil. However, the saddle-type super-conducting coil has a disadvantage in the aspect of the magnetic force and manufacturing difficulty. On the other hand, though the solenoid type super-conducting coil is easy to manufacture, it has the disadvantage of easily losing the magnetic field.

Due to the characteristics of the super-conducting coil, super-conducting coils must be placed in a cryostat. In the case of the solenoid type super-conducting coil, it has the disadvantage of requiring a larger cryostat. The present invention is intended to compensate for these two disadvantages.

BACKGROUND ART There are many technologies available to deploy a super-conducting coil for generating a horizontal magnetic field. Among them, a typical one is the single crystal growing technology. In the case of applying an eight (8) inch single crystal growing device a magnetic field is not needed. But, in the case of applying a twelve (12) inch single crystal growing device, a magnetic field is necessary. That is, in order to restrain the movement of the single-crystal oxygen erupted from the surface of the crucible, the super-conducting magnet is essential in the twelve inch single crystal growing device. It is lcnown that the horizontal magnetic field is the most effective orientation of the magnetic field in the single crystal growing device.

Referring to Figs. 1 through 5, the conventional technology such as a single crystal growing device for generating a horizontal magnetic field is explained in detail.

Fig. 1 is a cross sectional view of single-crystal growing device for generating a horizontal magnetic field according to the first conventional technology. Fig. 2 is a

super-conducting magnet device using a solenoid coil for generating a horizontal magnetic field according to the second conventional technology. Fig. 3 is a super- conducting magnet device using a saddle-type coil for generating a horizontal magnetic field according to the third conventional technology. Fig. 4 is a super-conducting magnet device using one or more pairs of solenoid coils for generating a horizontal magnetic field according to the fourth conventional technology. Fig. 5 is a plan view of a super- conducting magnet device employing two pairs of solenoid coils in a cryostat according to the fourth conventional technology.

Regarding the first conventional technology for generating a horizontal magnetic field, Japanese Patent Unexamined Publication No. 10-139599, entitled"Super- Conducting Magnet For Single Crystal Pulling Up Device"discloses that a magnet device is capable of easily varying the bore dimension, center of magnetic field, and transverse and longitudinal magnetic field strength. As shown in Fig. 1, the magnet device comprises: a super-conducting magnet installed outside of a growing furnace (1), and a crucible (2) installed inside of the growing furnace (1) for melting a single crystal semiconductor material (4) such as silicon by a heater (3). The magnetic field is applied by the super-conducting magnet for growing a single crystal from the molten single crystal semiconductor material (4). Each superconducting coil (6a, 6b) submerged in the liquid refrigerant is installed in a separate cryostat (5a, 5b) disposed opposite each other.

The magnetic field direction generated by each superconducting coil is traversed against the growing direction (8) of the growing furnace. Each cryostat is supported by a pair of supports (7) to adjust the installation space.

Regarding the second conventional technology as shown in Fig. 2, a single cryostat with an annular shape is used instead of separate cryostats. The annular shaped single cryostat (21) consists of an upper plate (21a), lower plate (21b) and a hollow center column (22) which penetrates the container perpendicularly. The annular shaped container and hollow center column are welded and sealed along the peripheries of both plates to form a vacuum container with a strong magnetic field space (S) at room temperature. There is a pair of solenoid type superconducting coils (C, C') installed inside of the cryostat (21) around the strong magnetic field space (S).

The solenoid type superconducting coil used in the first and second conventional technology has the advantage of easy manufacturing, but the disadvantage of low magnetic field generating efficiency. Accordingly, to obtain the predetermined magnetic field, a larger size of solenoid coil should be used, so that it has the disadvantage of

increasing the size of the cryostat.

To solve the aforementioned problems, a saddle type superconducting coil (D, D') of the third conventional technology is introduced as shown in Fig. 3. It has the advantage of improving the efficiency of the magnetic field within the required space and minimizing the size of the cryostat. However, it has the disadvantage of difficult manufacturingbecause it generates a strong magnetic force that acts on the wire of superconducting coil. If the super-conducting wire experiences minor movement due to the action of the electromagnetic force, the coil temperature is raised by the frictional heat, so that the condition of superconductivity is disturbed, leading to a normal state.

There is another problem raised due to the lowered critical current values at the bent potion (A) of the coil. Because the superconducting magnet must be maintained at the temperature of-269°C (4°K), a movement of 1 u, m can cause a serious problem.

To overcome the above problem, Japanese Patent Unexamined Publication No.

2001-203106 has suggested the fourth conventional technology as shown in Fig. 4. The cryostat (21) includes a hollow center column (22) oriented vertically to provide a magnetic field space (S). It also contains at least two pairs of the solenoid superconducting coils (C, C', C1, C2, C3, C1', C2', C3') installed on opposite sides of the cryostat (21) around the hollow center column (22). Even though this conventional technology solves the problems on a certain level, it still does not solve the fundamental problems that solenoid type superconducting coils have.

Particularly, the solenoid type superconducting coils occupy a larger space, therefore the weight of the superconducting magnet device is increased due to the large outer diameter of the shield.

DISCLOSURE OF THE INVENTION The present invention is introduced to achieve the aforementioned objectives of easy manufacturing, generating horizontal magnetic field and effectively distributing the magnetic force. It also provides a superconducting coil which effectively generates a magnetic field without increasing the size of the cryostat.

An object of the present invention is to provide a super-conducting magnetic device for generating a horizontal magnetic field comprising one or more pair of super- conducting coils arranged on opposite sides of a cryostat. A magnetic field use space (S) is provided at the center of the cryostat for the horizontal magnetic field. A

curved annular or elliptical shaped super-conducting coil (E ; El, El', E2, E2', E3, E3') is employed for improving the characteristics of the horizontal magnetic field in the magnetic field use space (S).

Preferably, more than one pair of curved annular or elliptical shaped super- conducting coils (E1, E1', E2, E2'or E1, El', E2, E2', E3, E3') are arranged on opposite sides of the cryostat around the magnetic field use space (S).

BRIEF DESCRIPTION OF DRAWINGS Fig. 1 is a cross sectional view of single-crystal growing device for generating a horizontal magnetic field according to the first conventional technology.

Fig. 2 is a super-conducting magnet device using a solenoid coil for generating a horizontal magnetic field according to the second conventional technology.

Fig. 3 is a super-conducting magnet device using a saddle-type coil for generating a horizontal magnetic field according to the third conventional technology.

Fig. 4 is a super-conducting magnet device using one or more pairs of solenoid coils for generating a horizontal magnetic field according to the fourth conventional technology.

Fig. 5 is a plan view of a super-conducting magnet device employing two pairs of solenoid coils in a cryostat according to the fourth conventional technology.

Fig. 6 is a configuration of the curved annular or elliptical shaped super- conducting coils according to the present invention.

Fig. 7 is a plan view illustrating two pairs of curved annular or elliptical shaped super-conducting coils arranged in a cryostat according to the present invention.

Fig. 8 is a perspective drawing illustrating two pairs of curved annular or elliptical shaped super-conducting coils arranged in a cryostat according to the present invention.

Fig. 9 is a perspective drawing illustrating three pairs of curved annular or elliptical shaped super-conducting coils arranged in a cryostat according to the present invention.

Fig. 10 is an explanatory model for comparing the magnetic effect of the super- conducting coils of the present invention with that of the fourth conventional technology.

Fig. 11 is a magnetic field distribution of the solenoid type super-conducting coils in the explanatory model of the fourth conventional technology.

Fig. 12 is a magnetic field distribution of the curved type super-conducting coils in the explanatory model of the present invention.

TERMINOLOGY OF IMPORTANT PARTS: 1: growing device 2: furnace 3: heater 4: semi-conductor material 5a, 5b : cryostat 6a, 6b: super-conducting coils 7: support 8: growing orientation 9: single crystal 21: cryostat 21 a : upper plate 21b : lower plate 22: hollow container 23,24 : vacuum space C, C', C1, C2, C3, C1', C2', C3' : solenoid type super-conducting coils D, D' : saddle-type super-conducting coils E, E', E1, E2, E3, E1', E2', E3' : curved annular or elliptical shaped super-conducting coils S: magnetic field use space L: occupied width or space for the solenoid type super-conducting coils L' : occupied width or space for the curved type super-conducting coils DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the implementing examples of the present invention are described in detail referring to Figs. 5 through 9.

Fig. 5 is a plan view of a super-conducting magnet device employing two pairs of solenoid coils in a cryostat according to the fourth conventional technology. Fig. 6 is a configuration of the curved annular or elliptical shaped super-conducting coils according to the present invention. Fig. 7 is a plan view illustrating two pairs of curved annular or elliptical shaped super-conducting coils arranged in a cryostat according to the present invention. Fig. 8 is a perspective drawing illustrating two pairs of curved annular or elliptical shaped super-conducting coils arranged in a cryostat according to the present invention. Fig. 9 is a perspective drawing illustrating three pairs of curved annular or elliptical shaped super-conducting coils arranged in a cryostat according to the present invention.

As shown in Figs. 6 and 7, the front view of the superconducting coils (E; E1, E2 ; E1', E2') is an annular or elliptical shape. However, the top view of the

superconducting coils (E; E1, E2; E1', E2') is a segment of curvature having a smaller radius than that of the cryostat, as shown in Fig. 7. This new configuration of superconducting coil does not suffer from the disadvantages inherent to the saddle type coils of the third conventional technology and the solenoid type superconducting coils of the fourth conventional technology.

Herein, a ratio of horizontal axis (a) to vertical axis (b), i. e. alb is preferred to be <BR> <BR> 0. 6-1. 4 considering the various factors. When the rate (a/b) is 1, i. e. , a circular shape, it is the most stable in the aspect of force. If one wants to reduce the height of the cryostat, a coil having the ratio (a/b) less than 1 could be applied. If one wants to arrange as many superconducting coils as possible in the cryostat, the coil having the rate (a/b) larger than 1 could be applied.

Furthermore, the curvature of the superconducting coils is determined based on the inner and outer radii of the cryostat. Less curvature of the superconducting coils is more stable in the aspect of magnetic force. However, the curved superconducting coils are concentric with cryostat to minimize the size of the cryostat.

As shown in Fig. 6, the curved annular or elliptical shaped superconducting coils of the present invention are produced as follows: first, a center magnetic field and inner and outer radii of the cryostat are determined (for example: approximately 5, 000-6, OOOG with 1600mm diameter for a 12-inch wafer single crystal growing device). When the inner diameter of the cryostat is determined, the curvature of superconducting coils is decided. When the center the magnetic field is determined, the height and inner diameter of the superconducting coils are decided using a magnet analysis program. With the determined dimensions of height, inner diameter and curvature radius of the superconducting coils, a wire winding frame is produced. Then, the super-conducting wire is wound on the wire winding frame to produce the curved annular or elliptical shaped superconducting coils of the present invention.

As shown in Figs. 7 and 8, two pairs of curved annular or elliptical shaped superconducting coils (E1, E2; El', E2') are arranged on opposite sides of the cryostat.

As shown in Fig. 9, three pairs of curved annular or elliptical shaped superconducting coils (E1, El', E2, E2', E3, E3') are arranged on opposite sides of the cryostat. However, it has proved that the arrangement of a pair of curved annular or elliptical shaped superconducting coils is superior to that of a conventional arrangement.

Particularly, the superconducting coils of the present invention are arranged on opposite sides with respect to the center of the cryostat. The magnetic field use

space (S) is provided within the hollow center column in the cryostat. The magnetic field direction is perpendicular to the magnet field use space. Along with the magnet device of the present invention, the curved annular or elliptical shaped superconducting coils arranged on opposite sides of the cryostat generate magnetic fields from opposite directions through the magnetic field use space (S). That is, the magnetic force is activated to the opposite side of the paired curved coils to form the horizontal magnetic field because the curved coils are arranged at the opposite side of the cryostat, through the magnetic field use space (S). The magnetic field of the single crystal growing device is moved perpendicular to the direction of horizontal magnetic field.

As shown in Fig. 7, the cryostat (21) forms an annular shape with a hollow column or cylindrical shape of the magnetic field use space (S). A pair of inner and outer vacuum cylindrical chambers (23,24) isolates the cryostat (21) to provide a space for installing the superconducting coils.

Referring to Fig. 5, the solenoid type superconducting coil of the fourth conventional technology has a thickness of 80mm and diameter of 1000mm. In this case, the inner diameter of the magnetic field use space (S) must be 1600mm diameter for a 12-inch wafer single crystal growing device. Comparing the space clearance (L) of the cryostat for the solenoid type superconducting coils with that of the curved annular or elliptical shaped superconducting coils, under the same conditions of the magnetic field center and the inner diameter of the cryostat, the space clearance (L) for the solenoid type coils is 178. 83mm and the space clearance (L) for the curved annular or elliptical shaped superconducting coils is 80mm.

In the case of the saddle-type coil of the third conventional technology, the magnetic force acts outward the coils. Thus, the saddle-type coil has the tendency to concentrate the magnetic force at a certain location (location B in Fig. 3). As a result a phenomenon of quenching, wherein the superconducting space turns to normal state, can easily occur at the weak portion, so that it is impossible to obtain the required strength of the magnetic field. In the aspect of hardware, where a curved portion is changed to a straight portion (location A in Fig. 3) without a transition part, it is difficult to smoothly wind the wires.

Comparing with the above conventional coils, the present invention of curved annular or elliptical shaped superconducting coils has the advantages that the magnetic force is uniformly distributed and the wires can be easily wound due to the smooth curvatures.

As aforementioned in the solenoid type coils of the second and fourth conventional technology, the solenoid type coil does not effectively distribute the magnetic field due to the dispersion of the magnetic field. Generally, the cryostat has a cylindrical shape for arranging the superconducting coils to obtain the horizontal magnetic field. The solenoid type superconducting coils (C1, C2, C1', C2') occupy a wide space. Thus, the overall size of the cryostat grows larger due to the requirement of a wide space clearance (L) as referenced to Fig. 5.

On the contrary, using the curved annular or elliptical shaped superconducting coils of the present invention as shown in Fig. 7, it is possible to reduce the dispersion of the magnetic flux and to minimize the size of the cryostat. For manufacturing the superconducting coils which generate the same magnetic flux density at a center, the space clearance (L) of the solenoid type coil is twice as large as that of the curved annular or elliptical shaped superconducting coil.

The efficiency of magnetic field generation is proportional to the amount of wire length for winding. The total weight of wire length for winding is measured for calculating the strength density of the central magnetic field per meter of wire length for winding. When the coil specification is determined for an operating current of 200A, and a central magnetic flux density of 3, 691Gauss, the solenoid type conventional coils require 13. 87Km of wire length for winding. Thus, the efficiency of magnetic field generation will be 0.266 Gauss/m.

Contrary with this data, the curved annular or elliptical shaped superconducting coils of the present invention require 12. 23Km of wire length for winding. Thus, the efficiency of magnetic field generation will be 0.301 Gauss/m.

Referring to Figs. 10 through 12, the magnetic field distribution is represented to show how uniformly the magnetic field is distributed in a certain space. This uniform magnetic field is a very important factor for single crystal growing devices.

Fig. 10 is an explanatory model for comparing the magnetic effect of the super- conducting coils of the present invention with that of the fourth conventional technology.

Fig. 11 is a magnetic field distribution of the solenoid type super-conducting coils in the explanatory model of the fourth conventional technology. Fig. 12 is a magnetic field distribution of the curved type super-conducting coils in the explanatory model of the present invention.

As shown in Fig. 10, two pairs of superconducting coil are applied to measure horizontal magnetic field along the X-axis and Y-axis. Comparing the graphs shown in

Figs. 11 and 12, there are no significant differences in the magnetic field in the Z-axis.

Referring to Figs. 11 and 12, the homogeneity, the difference of the magnet flux density, for the superconducting coils of the present invention is compared with that of the conventional coils at the central magnetic field value of 0.45 Tesla. The superconducting coils of the present invention in Fig. 12 have a size and number of turns different from those of the conventional coils in Fig. 11. For the purposes of comparison, a 12-inch wafer single crystal growing device having a diameter of 880mm is used. The magnet flux density is measured at a position of 400mm. It is assumed that the specifications of both coils, such as the length and number of wire windings, are the same and that the <BR> <BR> magnetic field at the center (i. e. , 0 position) is 0.45 Tesla. Because the magnet flux density of both coils is almost uniformly distributed in the Y-axis and Z-axis, the magnet flux density in the X-axis will be discussed and compared. The uniformity of magnetic field is measured from the center (0 position) of the magnetic field with a flux density of 0.45 Tesla. Comparing the values of magnetic field at a position 400mm from the center, the conventional solenoid type coil is 0.55 Tesla and the curved annular or elliptical shaped superconducting coils of the present invention is 0.49 Tesla. The uniformity of the magnetic field is represented as the ratio of central magnetic flux density (a) to the magnetic flux density at the 400mm position (b). The conventional solenoid type coil has a/b=0. 818 and the curved annular or elliptical shaped superconducting coil has a/b=0. 918.

The ideal case has the value of a/b=l.

Comparing the graphs with the values of X-axis and Y-axis, the conventional solenoid type coil deviates widely along the X-, Y-axes from the center. However, the curved annular or elliptical shaped superconducting coil of the present invention deviates relatively less along the X-, Y-axes from the center. This means that the curved annular or elliptical shaped superconducting coil distributes the magnetic field more uniformly than conventional coils. For example, the magnet flux density is indicated by the arrows in Figs. 11 and 12 for the 12-inch wafer single crystal growing device at the position of 440mm (0.44m) from the center. The difference between the X-axis and Y-axis indicated by the arrows is the dispersion of the magnetic field for the conventional solenoid type coil (Fig. 11) and the curved annular or elliptical shaped superconducting coil (Fig. 12).

The narrow gap between the X-axis and Y-axis indicated by the arrows means that the curved annular or elliptical shaped superconducting coil has better uniformity of magnetic field.

Finally, the weight of the magnet shield and cryostat is compared between

the conventional solenoid type coil and the curved annular or elliptical shaped superconducting coil. The weight of the vacuum cylindrical chambers is neglected for this comparison because both coil types employ similar cylindrical chambers.

Furthermore, the weight difference between the two types of coil is negligible compared with that of the magnet shield. Therefore, the weight of the magnet shield and cryostat only will be considered for comparison, hereinafter. When a magnet shield is made of iron with 50t upward and 120t around, the weight of the magnet shield for the conventional solenoid type coil is 13.21 tons and for the curved annular or elliptical shaped superconducting coils is 11.69 tons.

While the present invention has been described in detail with its preferred embodiments, it will be understood that further modifications are possible. The present application is therefore intended to cover any variations, uses or adaptations of the invention following the general principles thereof, and includes such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains within the limits of the appended claims.

INDUSTRIAL APPLICABILITY Accordingly, the present invention of the curved annular or elliptical shaped super-conducting coils more effectively generates and distributes the magnetic forces than the saddle type or solenoid type superconducting coils. It also has the advantage of being more easily and quickly produced than the conventional superconducting coils. It has the effect of improving magnetic field density by 15% with the same wire length for windings compared to the solenoid type super-conducting coils.