JPH04361526A - Superconducting magnet device for crystal pullingup device - Google Patents

Abstract

PURPOSE:To collectively operate by electrically and thermally connecting two superconducting magnets which are provided on the superconducting magnet device used for a single crystal pulling-up device in such a manner that fused raw material is pinched by them. CONSTITUTION:The opposing two superconducting magnets 1 and 1 are connected by an interconnecting tube 30 of heat-insulating structure so that the liquid helium in a liquid helium vessel and evaporated gas 2 can go back and forth between the two superconducting magnets. Also, a superconducting conductor and a normal conducting conductor are passed through the interconnecting tube 30, the two superconducting magnets 1 and 1 are electrically connected, and they can be operated collectively. Besides, the thermal shield of the two superconducting magnets 1 and 1 are thermally connected by the interconnecting tube 30, and by the shield refrigerator 3 provided on one superconducting magnet, other superconducting magnet can also be cooled.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting magnet device for use in a crystal pulling device used for pulling up single crystal silicon rods, which are used as materials for semiconductor silicon wafers, for example.

0002

[Prior Art] When a silicon single crystal is grown and pulled from a silicon raw material melted at high temperature to produce a single crystal silicon rod, when a uniform strong static magnetic field is applied to the melted silicon raw material, the melting vessel Convection, which causes impurities to be eluted and diffused, is suppressed, and a high-quality single crystal silicon rod can be obtained. This was shown in the "Crystal Growth Method" (Japanese Patent Application No. 55-8578) filed earlier by the present applicant, and N
It is called the CZ method and is widely used.

The present invention relates to a superconducting magnet device for applying a uniform strong static magnetic field to the molten silicon raw material, and FIGS. 7 to 10 show a conventional superconducting magnet device for a single crystal pulling device. In Fig. 7, 1 is a pair of superconducting magnets facing each other, and 2 is a service that connects current leads for excitation and demagnetization of the superconducting magnet 1, supplying liquid helium, and piping for exhausting evaporated helium gas. Port 3 is a shield refrigerator to suppress evaporative consumption of liquid helium, 4
Reference numeral 6 indicates a frame of the superconducting magnet 1, 6 indicates a magnetic pole of a magnetic material provided in the opening of the superconducting magnet, and 7 indicates a magnetic yoke that connects the magnetic poles 6 and circulates magnetic flux. 8 is a space in which a melting container is placed between two superconducting magnets 1, and indicates a space that requires a uniform, unidirectional, strong static magnetic field. 9 indicates the direction of the static magnetic field in the space 8. Reference numeral 10 denotes a fixture for positioning and fixing the superconducting magnet 1 and the magnetic yoke 7.

FIG. 8 is a diagram showing a vertical cross section including the service port 2, and in the figure, reference numerals 1, 2, 6, 7, 8,
9 shows the same part as FIG. Reference numerals 11 to 15 indicate the configuration of the superconducting magnet 1, and 11 is a vacuum chamber;
12 is a first heat shield, 13 is a second heat shield, 14 is a liquid helium tank, 15 is a solenoid-shaped superconducting coil kept at an extremely low temperature by liquid helium, and 16 is liquid helium.

FIG. 9 is a diagram showing a diagonal cross section including the shield refrigerator 3, and in the figure, reference numerals 1, 11, 12
, 13, 14, 15, 16, 3, 6, 7, 8, 9 are shown in Figure 7
and shows the same parts as FIG. Reference numerals 51 and 52 indicate cooling parts (cold heads) of the shield refrigerator 3 having different temperatures, and the cooling part 52 has a lower temperature than the cooling part 51. Cold heads 51 and 52 are heat shields 12 and 13, respectively.
The structure is thermally coupled to the

FIG. 10 shows an electric circuit diagram of a superconducting magnet. In the figure, 15 is a solenoid-shaped superconducting coil, and 21 is a normal conductor that connects an external power source and the superconducting coil 15 when excitation and demagnetization of the superconducting coil 15 is performed. 23 is a persistent current switch that short-circuits or releases both ends of the superconducting coil 15 in a superconducting state, 24 is a control lead of a normal conductor for turning on and off the persistent current switch 23, and 25 is a control lead of a normal conductor in case the superconducting coil 15 A low-resistance short-circuit protection element 26 is provided to suppress the voltage generated when the normal conduction transition occurs. A heater is used to heat the coil 15 to bring it into normal conduction state and attenuate the current. Reference numeral 14 indicates a liquid helium bath in which the circuit is housed.

Next, the operation will be explained. First, normal excitation and demagnetization of the superconducting magnet 1 will be explained. The superconducting coil 15 and persistent current switch 23 housed in the liquid helium tank 14 are energized by the liquid helium 16 injected into the liquid helium tank 14 from the service port 2.
It is maintained at an extremely low temperature of 2K and is in a superconducting state. Now, the on/off control lead 2 of the persistent current switch 23
4, the persistent current switch 23 is opened, and a predetermined current is supplied to the superconducting coil 15 from the excitation lead 21 of the superconducting coil 15. After that, the current in the control lead 24 is cut off, the persistent current switch 23 is closed, and both ends of the superconducting coil 15 are short-circuited. After that, the excitation lead 21
When the current in the superconducting coil 15 is set to zero, a persistent current loop is formed in which the current in the superconducting coil 15 flows through the persistent current switch 23 without decreasing, and the magnetic field continues to be generated without being supplied with current from the power source. This is called persistent current mode operation. In this conventional device, if the excitation rates of the two superconducting magnets 1 are different, the magnetic field output of the two superconducting magnets 1 will be different and the magnetic field uniformity in the space 8 will be poor, so the output of the excitation power source is adjusted so that the same current is excited. It is necessary to adjust and excite. Note that the above procedure is performed in reverse for normal demagnetization work for superconducting magnets.

Second, emergency demagnetization of the superconducting magnet 1 will be explained. When it is necessary to urgently demagnetize the superconducting magnet 1 due to an accident of adsorption of iron objects, etc., the heater 26 installed close to the superconducting coil 15 is energized to heat the superconducting coil 15 and cause it to transition to normal conductivity. The resistor attenuates the current confined within the persistent current loop. In this conventional device, when there is a time difference in the heater energization for emergency demagnetization of two superconducting magnets 1, the current attenuation of the superconducting magnet 1 that was demagnetized first causes an induced current in the other superconducting magnet 1. is induced, the current passing through the superconducting coil increases, and a magnetic attraction force greater than that during normal operation is generated between the superconducting yoke and the radial electromagnetic force of the coil increases, which may damage the coil itself. To prevent this, emergency demagnetization is performed by simultaneously applying heater current.

Thirdly, protection of the superconducting coil 15 in the event of a normal conduction transition failure will be explained. If the superconducting coil 15 fails due to a normal conduction transition due to some reason, such as heat generation when it stops slightly, the current flowing through the persistent current loop will rapidly increase due to the generation of resistance in the part where the normal conduction transition has occurred and the expansion of the normal conduction part. This causes significant current attenuation. This rapid current attenuation causes an induced voltage L of several hundreds of volts in the superconducting coil 15, for example.
・di/dt is generated (L is the inductance of the superconducting coil, and di/dt is the degree of current attenuation). In response to the generation of such voltage, any two points are short-circuited using a low resistance protection element 25 to suppress the generation of high voltage, thereby preventing dielectric breakdown. The turn-on voltage of the protection element 25 in FIG. 10 is several tens of V at a temperature of 4.2 K in liquid helium, and excitation and demagnetization are performed without turning on with the inductance voltage generated at the current increase/decrease rate of normal excitation and demagnetization. When a transfer failure occurs, it is turned on and performs the above protective operation.

Fourth, the supply of liquid helium and the exhaust of evaporated gas will be explained. The supply of liquid helium and the exhaust of evaporated gas are performed by piping that connects the outside and the liquid helium tank 14 provided at the service port 2 . Although the detailed structure was not shown in the illustration of the conventional device, if outside air enters the liquid helium tank 14, the oxygen and nitrogen in the air may freeze and clog the pipes, so liquid helium is usually The supply pipe and the evaporative gas exhaust pipe are separate pipes, and the supply pipe is sealed except when liquid helium is being supplied. In addition, a check valve is installed in the evaporative gas exhaust piping in the normal evaporative gas exhaust path to prevent atmospheric air from entering. In order to prevent the internal pressure of the liquid helium tank 14 from rising to a pressure that would destroy the liquid helium tank, an exhaust path having a pressure relief device for exhausting evaporated gas is arranged in parallel with the normal exhaust path having the above-mentioned check valve. It is installed to exhaust gas generated in the event of a failure.

Fifth, the reduction in liquid helium evaporation consumption of the shield refrigerator 3 will be explained. The shield refrigerator 3 attached to each of the two superconducting magnets 1 performs an endothermic cycle (
The heat shields 12 and 13 of the superconducting magnet 1 are endothermically cooled using a Gifford-McMahon cycle, etc.). As a result, heat intrusion from the outside into the liquid helium tank 14 is reduced, and evaporative consumption of the liquid helium 16 is suppressed.

0012

[Problems to be Solved by the Invention] Since the conventional superconducting magnet device for a crystal pulling device is constructed as described above, firstly, in excitation, two superconducting magnets must be excited with exactly the same current. First, when excitation/demagnetization is performed using two excitation power supplies, it is necessary to adjust the output of the two excitation power supplies, and when excitation is performed in parallel or in series with one excitation power supply and the current is set at the same time, it is necessary to adjust the output of the two excitation power supplies. However, this method is complicated in that it is necessary to make an external connection between the two superconducting magnets.

Second, during emergency degaussing, it is necessary to energize the emergency degaussing heater between two superconducting magnets at the same time, and when two heater power supplies are used, the coordination between the two heater power supplies is difficult. Furthermore, when power is supplied in series or in parallel using one heater power source, it is necessary to make external connections between the superconducting magnets, which is complicated.

Thirdly, when a normal conduction transition failure occurs in the superconducting coil of one of the two superconducting magnets, the superconducting coil that has the normal conduction transition failure short-circuits the protective element due to the generation of resistance. The current attenuates quickly. An induced current is induced in the superconducting coil of the other superconducting magnet due to the current attenuation due to the above-mentioned normal conduction transition fault, and the coil current increases, and the accompanying rise in the magnetic field causes a gap between this superconducting coil and the adjacent magnetic yoke. Magnetic attraction increases. Therefore, there was a problem in that the coil support structure needed to be strengthened. Furthermore, since the radial electromagnetic force of the coil also increases, there is a problem in that it is necessary to wind and reinforce the coil with binding wire or the like to prevent the coil from being damaged.

Fourthly, since each of the two superconducting magnets has a helium tank, it is complicated to perform the liquid injection work independently.

Fifth, even if the magnet is designed to be completely symmetrical with respect to the vertical plane passing through the center of the space 8 where the static magnetic field of the two superconducting magnets is required, the characteristics of the material used to manufacture the magnet, e.g. Differences in thermal insulation properties occur due to differences in thermal emissivity due to differences in surface conditions, slight differences in the length of heat transfer paths due to variations in manufacturing dimensions, and differences in the degree of vacuum of the vacuum chamber. Therefore, even if liquid helium is supplied to two superconducting magnets at the same time up to the upper limit of the liquid helium tank, the evaporation consumption per unit time is different for each magnet, so the subsequent supply cycle is different for the two magnets, and each magnet There was the complexity of supplying liquid helium on different days.

The present invention was made to solve the above-mentioned problems. First, two superconducting coils can be connected in parallel without connecting them in series and parallel outside the superconducting magnet.
It is possible to excite the same current using the same power supply. Second
Furthermore, when energizing the emergency degaussing heater, it is possible to simultaneously energize the two heaters using one power source, without having to connect serial and parallel result lines outside the superconducting magnet, as in the excitation and demagnetization described above. Third, even if a normal conduction transition failure occurs in either one of the two superconducting coils, the coil current in the other superconducting coil will not increase, and the magnetic attraction force and electromagnetic force of the coil will not increase. do. Fourth, even if two superconducting magnets have different evaporation and consumption characteristics of liquid helium, a superconducting material for crystal pulling equipment that has a function of supplying liquid helium in one supply cycle, etc. The purpose is to obtain a magnet device.

[0018]

[Means for Solving the Problems] A superconducting magnet device for a single crystal pulling device according to the present invention connects liquid helium tanks of two superconducting magnets sandwiching a molten raw material through two communicating pipes having a heat-insulating structure. Each of the heat insulating structures of the communicating tube is thermally connected to the corresponding heat insulating structure of the superconducting magnet, and liquid helium and evaporated gas of the liquid helium can flow through the communicating tube.

Further, the two superconducting magnets are electrically connected by a superconducting conductor or a normal conducting conductor passing through the communication pipe.

[0020]

[Operation] In this invention, the communication pipe that communicates between the two superconducting magnets allows liquid helium and liquid helium evaporated gas to flow between the two superconducting magnets. It can also be performed all at once, even if there is a difference in the evaporation consumption characteristics of liquid helium between two superconducting magnets.
Liquid helium can be supplied in one injection period.

[0021] Furthermore, a communication pipe is provided that connects the liquid helium baths of the two superconducting magnets, and the two superconducting magnets are electrically connected through this communication pipe, so that the superconducting coils of each magnet are powered by one excitation power source. Excited by the same current. Further, in the case of emergency demagnetization, when one of the two superconducting magnets is demagnetized, the other magnet is also demagnetized at the same time.

Furthermore, a short circuit by a protection element against a normal conduction transition fault is formed by connecting the symmetrical points of the superconducting coils of each of the two superconducting magnets through the communication tube. Therefore, when a normal conduction transition fault occurs, there is no concentration of current due to induction from the magnet where the conduction transition fault has occurred to the other magnet, and there is no increase in the magnetic attraction force and coil radial electromagnetic force acting between the magnetic yokes.

[0023]

[Example] Example 1. An embodiment of this invention is shown below in Figure 1.
~ Figure 4 will be explained. In FIG. 1, symbols 1, 2,
3, 6, 7, 8, and 9 indicate the same parts as in FIG. 30 is 2
These are two upper and lower communication pipes that communicate the liquid helium tanks of the two superconducting magnets 1. 31 is a flexible portion provided in the communication pipe 30. In addition, in this figure, two superconducting magnets 1 are electrically and thermally connected by a communication tube 30, so
The service port and shield refrigerator of one superconducting magnet 1 are integrated in the other superconducting magnet.

FIG. 2 shows a cross-sectional view of the service port 2 and the communication pipe 30 on the same plane, with reference numerals 1, 2, 6, 7, 8, 9, and 11.
, 12, 13, 14, and 15 indicate the same parts as in FIG. Reference numeral 31 indicates a flexible portion provided in the communication pipe 30. Communication pipe 3
0, 32 is a vacuum chamber, 33 is the first heat shield, 34 is the second
The heat shield 35 is a liquid helium tank, which are the vacuum tank 11 of the superconducting magnet 1 and the first heat shield 1, respectively.
2. It is connected to the second heat shield 13 and the liquid helium tank 14. Inside the liquid helium tank 35, liquid helium 16 and evaporated gas of liquid helium flow, and although not shown in this figure, a lead electrically connects the two superconducting magnets.

FIG. 3 shows a cross-sectional view of the shield refrigerator 3 and the communication pipe 30 on the same plane, and the symbols 1, 3, 6, 7, 8, 9, 11
, 12, 13, 14, 15, 16, 51, and 52 indicate the same parts as in FIG. Also, codes 30, 31, 32, 33,
34 and 35 indicate the same parts as shown in FIG. In the figure, cold heads 51 and 52 are one of the superconducting magnets 1
This heat shield is connected to the heat shield of the other superconducting magnet 1 via the heat shields 33 and 34 of the communication tube 30.

FIG. 4 shows an electric circuit diagram of a superconducting magnet, and in the figure, reference numerals 14, 15, 21,
23, 24, 25, and 26 indicate the same parts as in FIG. In addition, 35 is a communication pipe 3 that communicates the two superconducting magnets.
0 is a liquid helium tank, 41 is a superconducting lead connecting the superconducting coils 15 of two superconducting magnets 1 in series,
42 connects two superconducting magnets 1 to a persistent current switch 2
3 indicates a superconducting lead for short-circuiting, 43 indicates a connection point of the superconducting lead, and the superconducting lead 43 is connected to the liquid helium tank 1.
It passes through a communication pipe installed at a position lower than the lower limit height of the liquid helium level in No. 4. The protection element 25 against a normal conduction transition fault connects the symmetrical points of the superconducting coils 15 of two superconducting magnets using a normal conductive lead 44, and the connecting lead 44 is located at a position near or above the upper limit of the liquid helium level in the liquid helium tank 14. It passes through a communication pipe installed in the One heater 26 for emergency demagnetization is provided in each closed loop formed by the protection element 25 and including the superconducting coil 15 .

Next, the operation will be explained. First, normal excitation and demagnetization of a superconducting magnet will be explained. Two superconducting coils 15 housed in liquid helium baths 14 of two superconducting magnets 1 are connected in series with superconducting leads 41, and both ends of the two superconducting coils 15 are connected to a persistent current switch 23 and a superconducting lead 43 to form a superconducting loop. It is designed to be short-circuited and open-circuited. Therefore, first, a necessary current is applied to the on/off control lead 24 of the persistent current switch 23, and the persistent current switch 23 is opened. Next, a predetermined current is supplied to the two superconducting coils 15 from the excitation leads 21 of the superconducting coils 15 . At this time, since the two superconducting coils 15 are connected in series by the superconducting leads 41, the two superconducting coils 15 are excited with the same current without making an external connection between the two superconducting magnets 1 with one excitation power source. be done. Next, the current in the control lead 24 is cut off, the persistent current switch 23 is closed, and the two superconducting coils 1
5 are superconducting short-circuited via superconducting leads 42. Thereafter, when the current in the excitation lead 21 is set to zero, the current in the superconducting coil 15 does not decrease, forming a persistent current loop that flows in series through the two superconducting coils 15 via the persistent current switch 23 and the superconducting leads 41 and 42. ,
The magnetic field continues to be generated without receiving current from the power source. Further, for the demagnetization procedure, the above excitation procedure is performed in reverse.

Regarding the connection of the two superconducting magnets 1 using the superconducting leads 41 and 42, the superconducting conductors are connected to each other by crimping, spot welding, or the like so that the superconducting properties are not lost at the connection point 43. However, at the connection point 43, under conditions of a strong environmental magnetic field, the superconducting lead undergoes deterioration in its characteristics such that it undergoes a normal conduction transition at a lower current than the superconducting conductor of the superconducting lead. Therefore, the connection point 43 is placed in the communicating tube where the magnetic field is relatively low, avoiding the vicinity of the superconducting coil 15 where the magnetic field is strong, to prevent normal conduction transition.

[0029] Furthermore, the leads 41 and 42 of the superconducting conductor are
During normal operation, the liquid helium is passed through a communication pipe installed below the lower limit of the liquid helium level to prevent it from rising above the surface of the liquid helium and causing a rise in temperature and normal conduction transition. Furthermore, by arranging the connection point 43 within the communication pipe 35, each heat-insulating container can be manufactured independently at the time of manufacturing the magnet device, making it easy to assemble the two superconducting magnets 1, adjust their relative positions, etc. It can be carried out.

Second, emergency demagnetization of a superconducting magnet will be explained. The basic method of demagnetizing the superconducting magnet 1 in an emergency is the same as in the conventional example, in which the heater 26 provided close to the superconducting coil 15 is energized to heat the superconducting coil 15 and make it transition to normal conductivity. However, in the past, during emergency demagnetization, due to the time difference between the emergency demagnetization of the two superconducting magnets 1, the heaters 26 of each of the two superconducting magnets were simultaneously turned off to prevent damage to the coils due to excessive magnetic attraction force or electromagnetic force. Care was taken to ensure that electricity could be supplied. However, in this embodiment, the two superconducting magnets 1 are connected to the helium tank 3 of the communication pipe 30 as shown in FIG.
The leads 41, 42, and 44 passing through the superconducting coil 5 constitute a closed circuit group including symmetrical parts of the two superconducting coils 15. For this reason, one heater 26 is provided for each part of the superconducting coil 15 constituting each closed circuit of one superconducting magnet 1.
To urgently attenuate the current flowing through two superconducting magnets 1 at the same time without making an external connection between the two superconducting magnets using one power source by arranging them in close proximity, connecting them in series or in parallel, and energizing them. Can be done.

Thirdly, protection of superconducting coils in case of normal conduction transition failure will be explained. As described in the above explanation of emergency demagnetization, the two superconducting magnets 1 are connected to the superconducting conductor leads 41 and 42 that are energized during normal persistent current mode operation and pass through the helium bath 35 of the communication tube 30, as shown in FIG. The protection element 25 and the lead 44 constitute a closed circuit group including symmetrical parts of the two superconducting coils 15. Since the lead 44 is a normal conductor and does not form a persistent current loop, it can be placed in a communication pipe provided near the upper limit of the liquid helium level or higher. As mentioned above, since it has a closed circuit group configuration, the superconducting persistent current mode operation in the closed circuit consisting of the superconducting coils 15 of the two superconducting magnets 1, the persistent current switch 23, and the leads 41 and 42 of the superconducting conductors. Even if a normal conduction transition fault occurs in any part and any of the protective elements 25 is short-circuited, the currents in the symmetrical parts of the two superconducting coils 15 are equally attenuated. Therefore, one superconducting magnet 1
The normal conduction transition fault induces an induced current in the other superconducting magnet 1, and the current in that superconducting coil becomes excessive, and the magnetic attraction between this superconducting coil and the adjacent magnetic yoke does not increase.

Fourth, the supply of liquid helium and the exhaust of evaporated gas will be explained. The supply of liquid helium and the exhaust of evaporated gas are performed by a supply pipe in a service port 2 provided in one superconducting magnet 1 and an exhaust pipe for evaporated gas. The configuration of the supply piping and evaporative gas exhaust pipe is basically the same as the conventional one. Here, since the two superconducting magnets 1 communicate with each other through the liquid helium tank 35 of the communication pipe 30, the liquid helium injected from the service port 2 provided in one superconducting magnet 1 also flows into the other superconducting magnet 1. The liquid helium flows into the two superconducting magnets, and the liquid helium levels become equal. Furthermore, even if the evaporation and consumption characteristics of liquid helium are different between the two superconducting magnets, the liquid helium flows back and forth through the communication pipe 30, so the liquid level height of the liquid helium in the two superconducting magnets 1 is maintained in detail. At this time, one of the two communication pipes 30 is located at a position lower than the lower limit height of the liquid helium level in the liquid helium tank, and the other one is located above the upper limit of the liquid helium level, so it is necessary to have the service port 2. The gas generated due to liquid helium evaporation and consumption of the superconducting magnet 1 that does not accumulate in the superconducting magnet 1 does not push down the liquid level, and the gas generated from the communication pipe 30 that is near the upper limit of the liquid helium level is transferred to the other superconducting magnet. 1 and is exhausted through the service port.

The communication pipe 30 whose liquid helium level is below the lower limit is always filled with liquid helium during normal operation of the superconducting magnet 1, and if there is a difference in the liquid helium evaporation consumption characteristics of the two superconducting magnets 1. However, it serves as a pipe that supplies liquid helium from the side with the lowest consumption to the side with the highest consumption by the difference in consumption.

Fifth, the reduction of the amount of liquid helium evaporation in the shield refrigerator will be explained. Two superconducting magnets 1
A shield refrigerator 3 attached to one side of the superconducting magnet 1 endothermically cools the heat shields 12 and 13 of the superconducting magnet 1. The two superconducting magnets 1 are connected by a communication tube 30, and the heat shields 33 and 34 of the communication tube 30 are thermally connected to the heat shields 12 and 13 of the two superconducting magnets 1, respectively. Therefore, the shield refrigerator 3 attached to one superconducting magnet 1 can also absorb heat and cool the heat shield of the other superconducting magnet 1, and the number of shield refrigerators can be reduced.

In addition, the two superconducting magnets 1 are attached to one pedestal 40 having a position adjustment tool that can be independently adjusted, and the two superconducting magnets 1 are connected to the communication pipe 3.
The structure is such that it can be transported with the 0 installed and assembled. In addition, the communication tube 30 has a flexible portion 31, which is effective for absorbing thermal contraction caused by the initial cooling of the superconducting magnet 1 and for absorbing errors in machining when connecting two superconducting magnets 1 with the communication tube 30. to work.

Example 2. In the first embodiment, the service port 2 and the shield refrigerator 3 are attached to the same superconducting magnet 1, but they may be attached to different superconducting magnets 1 as shown in FIG.

Example 3. Alternatively, a superconducting magnet as shown in FIG. 6 may be used, which does not have a persistent current switch and is used while connected to an excitation power source that is not operated in persistent current mode.

[0038]

[Effects of the Invention] As described above, according to the present invention, the first
In addition, since liquid helium and liquid helium evaporated gas can freely flow back and forth between the two superconducting magnets using the current-carrying tube, a service port used for supplying liquid helium and exhausting evaporated gas only needs to be provided on one superconducting magnet. Furthermore, since the two superconducting magnets are thermally connected to each other via the heat shield of the communication tube, the shield refrigerator only needs to be attached to one of the superconducting magnets.

Second, two superconducting magnets are excited by the same current using one excitation power source without making any external connection between the two superconducting magnets, and a highly uniform magnetic field can be obtained.

Third, during emergency demagnetization, two superconducting magnets can be simultaneously demagnetized by energizing the heater provided in one of the superconducting magnets, without considering energizing the emergency degaussing heater for each superconducting magnet at the same time. can.

Fourth, when a normal conduction transition failure occurs in one superconducting magnet, a protection circuit is formed that connects the lines of symmetry of the two superconducting coils, so an increase in induced current is not generated in the other superconducting magnet. First, an increase in the magnetic attraction force between the magnetic yoke and the magnetic yoke does not occur. As described above, it is possible to obtain a highly reliable and inexpensive device with a simple structure and good magnetic field uniformity characteristics.

[Brief explanation of drawings]

FIG. 1 is a perspective view of Embodiment 1 of the present invention.

FIG. 2 is a sectional view of the one in FIG. 1 in a plane along the service port and the communication pipe;

FIG. 3 is a cross-sectional view of the shield refrigerator of FIG. 1 and a plane along a communicating pipe.

FIG. 4 is an electrical circuit diagram of that of FIG. 1;

FIG. 5 is a perspective view of a second embodiment of the invention.

FIG. 6 is an electrical circuit diagram of a third embodiment of the present invention.

FIG. 7 is a perspective view of a conventional superconducting magnet device for a crystal pulling device.

8 is a sectional view of the one in FIG. 7 in a plane along the service port; FIG.

FIG. 9 is a cross-sectional view of the one in FIG. 7 taken along a plane along the shield refrigerator.

FIG. 10 is an electrical circuit diagram of that of FIG. 7;

[Explanation of symbols]

1 Superconducting magnet 2 Service port 3 Shield refrigerator 8 Space 11 where the melting container is placed Vacuum chambers 12, 13 First and second heat shields 14
Liquid helium tank 15 Superconducting coil 16 Liquid helium 21 Excitation lead 23 Persistent current switch 24 Control lead 25 Protective element 26 Heater 30 Communication tube 31 Flexible part 32 Vacuum chambers 33, 34 First and second heat shields 35
Liquid helium tank 40 Frame 41, 42 Superconducting lead 43 Superconducting lead connection point 44 Normal conducting lead

Claims (9)

[Claims] Claim 1: When pulling and refining a crystallized material from a molten raw material in order to produce a single crystal material such as silicon, a static magnetic field is applied to the raw material by sandwiching the molten raw material between at least two superconducting magnets. A superconducting magnet device for a single crystal pulling device, comprising at least one communication pipe that communicates the liquid helium tanks of the at least two superconducting magnets with each other, and the communication pipe has a heat insulating structure having a vacuum tank and a heat shield. Become,
A superconducting magnet device for a single crystal pulling device, characterized in that the superconducting magnet body and the heat shield are connected to each other. 2. The superconducting magnet device for a single crystal pulling apparatus according to claim 1, wherein at least two superconducting magnets sandwiching the molten raw material are electrically connected by a lead passing through a communicating tube. 3. The single crystal pulling apparatus according to claim 2, wherein the magnetic field generating superconducting coils of at least two superconducting magnets sandwiching the molten raw material are connected in series by superconducting leads passing through a communicating tube. Superconducting magnet device. 4. The superconductor for a single crystal pulling apparatus according to claim 3, wherein both ends of the superconducting coils connected in series can be short-circuited in a superconducting state by a persistent current switch using superconducting leads passing through a communication tube. magnet device. 5. The superconducting magnet device for a single crystal pulling device according to claim 3, wherein the connection point of the superconducting lead is arranged in a communicating pipe. [Claim 6] When symmetrical points of the superconducting coils of at least two superconducting magnets are connected by a protection element such as a resistor or a diode connected in anti-parallel, the connecting lead is a lead passing through a communication pipe. The superconducting magnet device for a single crystal pulling device according to claim 3, characterized in that: 7. In order to urgently demagnetize a superconducting magnet, when a heater is provided near a superconducting coil to cause the superconducting coil to transition to normal conductivity, a 7. The superconducting magnet device for a single crystal pulling device according to claim 6, wherein at least one of the heaters is provided. 8. There are at least two communication pipes, at least one of which is located at a position lower than the lower limit height of the liquid helium level in the liquid helium tank of the superconducting magnet, and the other one is located at a position lower than the lower limit height of the liquid helium level in the liquid helium tank of the superconducting magnet. The superconducting magnet device for a single crystal pulling device according to claim 1, wherein the superconducting magnet device is located at a position near or above the upper limit of helium level. 9. Claim 2, characterized in that the superconducting lead is arranged in the communicating pipe at a position below the lower limit of the liquid helium level of the liquid helium tank, and the normal conducting lead is arranged in the communicating pipe at a position near the upper limit or higher. Or a superconducting magnet device for a single crystal pulling device according to 8.