MCZ superconducting magnet with active shielding function

Abstract

The invention relates to the technical field of superconducting magnets, in particular to an MCZ superconducting magnet with an active shielding function. An MCZ superconducting magnet with an active shielding function is characterized in that a superconducting magnet main coil is wound in the middle of a framework, and an upper side shielding coil and a lower side shielding coil are wound on the upper side and the lower side of the framework respectively; the framework, the upper side shielding coil and the lower side shielding coil of the superconducting magnet main coil are located in a 4K structure, the 4K structure is located in a 50K structure, and the 50K structure is located in a 300K structure; the upper end and the lower end of the 4K structure are hung in the 300K structure through 4K pull rods respectively. The upper end and the lower end of the 50K structure are hung in the 300K structure through 50K pull rods respectively. Compared with the prior art, the magnet generates a magnetic field required by auxiliary crystal pulling on the basis of the superconducting coil, active shielding is carried out on the basis of the superconducting coil, a stray field outside the magnet is reduced, the working stability of the single crystal furnace is improved, the safety of workers is improved, and the volume fraction of a factory is also improved.

Description

Technical Field

[0001] The invention relates to the technical field of superconducting magnets, in particular to a MCZ superconducting magnet with an active shielding function. Background Art

[0002] With the growing demand for monocrystalline silicon in the semiconductor, photovoltaic and other industries, the market size of monocrystalline silicon is expanding rapidly. By improving the composition of the crystal through the magnetron Czochralski (MCZ) method, the impurity content and distribution in monocrystalline silicon can be reduced, and the quality of monocrystalline silicon can be improved.

[0003] The core equipment of the magnet-controlled Czochralski method is to add a magnet to the original Czochralski single crystal furnace, which can generate the magnetic field required for crystal pulling and assist in controlling the crystal pulling process. The traditional magnetic field is generated by permanent magnets, but for large single crystal furnaces, the efficiency of permanent magnets is very low. In addition to not being able to generate sufficient magnetic field strength, the cost is also very high; electromagnets were once an option, but slightly higher magnetic fields are also a test for electromagnets. Not to mention high energy consumption, achieving effective cooling is a problem, and the price is high; with the development of superconducting technology, superconducting magnets are particularly outstanding in terms of small size, light weight, stable magnetic field, and low energy consumption. Existing magnetic pulling single crystal magnets all use superconducting magnets.

[0004] The MCZ single crystal furnace is a production equipment. The magnet and the furnace body work together. It needs manual operation and equipment assistance. When the magnetic field is turned on, whether the crystal pulling furnace can work normally and whether the workers can operate safely, all of which put forward higher requirements on the stray field of the magnet. This is also particularly important in factory planning. Lower stray fields can increase the volume ratio per unit area. More equipment can be installed in the same factory, which improves the utilization rate and output rate of the factory.

[0005] Superconducting magnets represented by Xi'an Juneng Superconducting Magnet Technology Co., Ltd.'s patent "A Superconducting Magnet, Magnetically Controlled Crystal Pulling Equipment and Control Method" (CN116798724A) use two superconducting coils to reduce stray fields by using passive shielding. The main method is to use ferromagnetic materials with relatively high magnetic permeability to form an encirclement around the magnet to absorb the magnetic lines of force and diffuse outward to reduce the stray fields outside the magnet. This method has a certain effect, but the performance is relatively limited. In order to achieve a certain effect, the thickness of the ferromagnetic material needs to be further increased, and the weight of the magnet increases significantly. This change has a significant impact on transportation, installation, and cost. Summary of the invention

[0006] In order to overcome the shortcomings of the prior art, the present invention provides a MCZ superconducting magnet with active shielding function. This magnet generates the magnetic field required for assisting crystal pulling based on the superconducting coil, and at the same time performs active shielding based on the superconducting coil, thereby reducing the stray field outside the magnet, improving the working stability of the single crystal furnace, improving the safety of the staff, and also improving the volume ratio of the factory.

[0007] To achieve the above purpose, an MCZ superconducting magnet with active shielding function is designed, including a skeleton, a superconducting magnet coil, and a dewar structure. The dewar structure includes a 4K structure, a 50K structure, and a 300K structure, and is characterized in that: a superconducting magnet main coil is wound around the middle of the skeleton, and an upper shielding coil and a lower shielding coil are wound around the upper and lower sides of the skeleton respectively; the skeleton, the upper shielding coil and the lower shielding coil of the superconducting magnet main coil are located in the 4K structure, the 4K structure is located in the 50K structure, and the 50K structure is located in the 300K structure; the upper and lower ends of the 4K structure are suspended in the 300K structure by 4K pull rods respectively; the upper and lower ends of the 50K structure are suspended in the 300K structure by 50K pull rods respectively.

[0008] The 300K structure is connected to a cold head, the cold head is located in a cold head container, and the cold head container is sealed and connected to the 300K structure.

[0009] The cold head includes a primary cold head and a secondary cold head. The primary cold head is connected to the 50K structure, and the secondary cold head is connected to the 4K structure.

[0010] The 300K structure is a vacuum cavity.

[0011] The outer side of the 50K structure is wrapped with a polymer insulation film.

[0012] The 50K pull rod is made of glass fiber, carbon fiber, stainless steel or titanium alloy.

[0013] The MCZ superconducting magnet generates a horizontal magnetic field and a vertical magnetic field.

[0014] Compared with the prior art, the present invention provides an MCZ superconducting magnet with active shielding function. This magnet generates the magnetic field required for assisting crystal pulling based on the superconducting coil, and at the same time performs active shielding based on the superconducting coil, thereby reducing the stray field outside the magnet, improving the working stability of the single crystal furnace, improving the safety of the staff, and also improving the volume ratio of the factory.

[0015] At the same time, this magnet structure is more compact, smaller in size, and very easy to use. The height of the magnet does not affect the crystal pulling operations such as charging, opening, removing the crystal rod, and removing the crucible. The magnetic field generated can well control the flow of silicon liquid in the crucible and the range of impurities to obtain high-quality crystals. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the structure of the present invention.

[0017] Figure 2 It is a schematic diagram of the internal structure of the present invention.

[0018] Figure 3 It is a schematic diagram of the specific structural connection of the present invention.

[0019] See also Figure 2 , Figure 3 , 1 is the main coil of the superconducting magnet, 2 is the skeleton, 3 is the 4K structure, 4 is the 50K structure, 5 is the 300K structure, 6 is the vacuum cavity, 7 is the polymer insulation film, 8 is the upper shielding coil, 9 is the lower shielding coil, 10 is the cold head, 11 is the cold head container, 12 is the first-stage cold head, 13 is the second-stage cold head, 14 is the 4K pull rod, and 15 is the 50K pull rod. DETAILED DESCRIPTION

[0020] The present invention will be further described below with reference to the accompanying drawings.

[0021] like Figure 1 , Figure 2 As shown, an MCZ superconducting magnet with active shielding function includes a skeleton, a superconducting magnet coil, and a dewar structure. The dewar structure includes a 4K structure, a 50K structure, and a 300K structure. A superconducting magnet main coil 1 is wound around the middle of the skeleton 2, and an upper shielding coil 8 and a lower shielding coil 9 are respectively wound around the upper and lower sides of the skeleton 2; the skeleton 2, the upper shielding coil 8 and the lower shielding coil 9 of the superconducting magnet main coil 1 are located in the 4K structure 3, the 4K structure 3 is located in the 50K structure 4, and the 50K structure 4 is located in the 300K structure 5; the upper and lower ends of the 4K structure 3 are respectively suspended in the 300K structure 5 by using 4K pull rods 14; the upper and lower ends of the 50K structure 4 are respectively suspended in the 300K structure 5 by using 50K pull rods 15.

[0022] The 300K structure 5 is connected to a cold head 10 . The cold head 10 is located in a cold head container 11 . The cold head container 11 is sealed and connected to the 300K structure 5 .

[0023] The cold head 10 includes a primary cold head 12 and a secondary cold head 13 . The primary cold head 12 is connected to the 50K structure 4 , and the secondary cold head 13 is connected to the 4K structure 3 .

[0024] The 300K structure 5 is a vacuum chamber 6 .

[0025] The outer side of the 50K structure 4 is wrapped with a polymer thermal insulation film 7 .

[0026] The 50K tie rod 15 is made of glass fiber, carbon fiber, stainless steel or titanium alloy.

[0027] MCZ superconducting magnets generate horizontal and vertical magnetic fields.

[0028] Superconducting magnet coils and coil frames. The superconducting magnet coils are designed as a three-coil structure with active shielding, which has the smallest space occupancy and magnet height, and can design a thin and light superconducting magnet with sufficiently low external stray fields.

[0029] The structure of the three-coil superconducting magnet is as follows Figure 2 As shown, the middle coil is the superconducting magnet main coil 1, and the upper and lower coils are the upper shielding coil 8 and the lower shielding coil 9. The current directions of the upper shielding coil 8 and the lower shielding coil 9 are opposite to those of the superconducting magnet main coil 1. The magnetic field of the superconducting coil is confined as much as possible in a position close to the superconducting magnet to achieve a shielding effect.

[0030] The coil skeleton 2 is made of metal or non-metal material, used to support the superconducting coil designed according to the target magnetic field, and to assist in the forming and fixing of the coil shape to meet the manufacturing process; the coil is wound on the coil skeleton 2, and the design and production of the coil meets the corresponding superconducting magnet requirements.

[0031] The Dewar structure includes: from inside to outside, 4K structure 3, 50K structure 4 and 300K structure 5. Among them, 4K structure 3 is the core part of the superconducting magnet, and all components that need to achieve superconducting performance are connected to 4K structure 3; 50K structure 4 is a thermal cutoff layer, which is mainly used to shield the heat of external conduction / radiation entering the 4K structure 3 in the magnet; 300K structure 5 is the outer shell of the magnet, supporting all parts of the entire magnet and closing a vacuum cavity for each internal part.

[0032] The 4K structure 3 is mainly used to support the wound superconducting magnet coils (i.e., the superconducting magnet main coil 1, the upper shielding coil 8, and the lower shielding coil 9) and the skeleton 2. If a conductive (little or no liquid helium) structure is used, the 4k structure 3 is mainly designed to be a cold-conducting link so that all parts that need to enter the superconducting state can establish a thermal connection channel, which can efficiently take away the heat from the coil and keep the coil in a low-temperature superconducting state. This efficient thermal connection channel requires a full evaluation of the materials and structures to maximize the stability and uniformity of heat conduction; if a liquid helium immersion method is used, the 4k structure 3 is mainly used to construct a liquid helium container for the superconducting part. The container wraps all the superconducting coil parts inside. When the internal space of the container is filled with enough liquid helium, most of the coil will be immersed in liquid helium, so that the coil is kept at the liquid helium temperature to achieve a superconducting state.

[0033] A 50K structure 4 needs to be built outside the 4K structure 3 to isolate the heat radiation from the outside of the magnet to the internal 4K structure 3, so it is often called a cold screen. The cold screen is generally made of high-purity aluminum, which can effectively resist the heat shock from the outside of the magnet to the inside, and ensure the consistency of the heat radiation received by the 4K structure 3 inside the magnet. The cold screen is often covered with multiple layers of polymer insulation film to reflect the heat radiation from the outside of the magnet and effectively reduce the radiated heat from the outside of the magnet to the inside of the magnet.

[0034] The 300K structure 5 is a commonly used support structure for the magnet. At the same time, a vacuum cavity is constructed for the 4K structure 3 and the 50K structure 4 to ensure the vacuum state inside the magnet in actual work and effectively suppress the occurrence of thermal convection. At the same time, there must be no obvious structural deformation under external standard atmospheric pressure.

[0035] The three layers of the Dewar structure are connected by suspension rods. This connection method can minimize the heat conduction between the layers and requires reasonable planning of the position and direction of the rods to minimize the force on the rods and save space for the magnets. Since the 300K structure 5 has the highest mechanical strength, the 4K structure 3 and the 50K structure 4 are both suspended on the 300K structure 5.

[0036] The 50K pull rod 15 is used to suspend the 50K structure 4. Since the 50K structure 4 is relatively light and the 50K heat capacity is relatively large, the material can be glass fiber, carbon fiber or stainless steel or titanium alloy.

[0037] The 4K pull rod 14 needs to suspend a large weight and has extremely high requirements for heat leakage, so carbon fiber is needed to meet both strength and heat leakage requirements, and thermal cutoff must be established.

[0038] The cold head 10 is a low temperature cooling device for the entire magnet, and the cold head container 11 supports the connection of the entire cold head 10 on the magnet, connects the Dewar structure, and is used to wrap the entire cold head 10. The cold head container 11 and the 300K structure 5 are made of stainless steel to achieve the connection between the superconducting magnet and the cold head 10 and ensure the vacuum structure inside the magnet.

[0039] The cold head 10 is divided into a primary cold head 12 and a secondary cold head 13 . When in use, the primary cold head 12 and the 50K structure 4 are well thermally connected, and the secondary cold head 13 and the 4K structure 3 are well thermally connected.

[0040] like Figure 3 The structure of the embodiment of the present invention is shown in FIG. The superconducting magnet main coil 1 is wound on the frame 2 according to certain requirements and connected to the 4K structure 3. The superconducting magnet main coil 1, the upper shielding coil 8 and the lower shielding coil 9 are connected according to the design requirements to form the required magnetic field structure.

[0041] The 4K structure 3 is wrapped with a 50K structure 4 and a 300K structure 5. The 300K structure 5 forms a vacuum cavity 6, which eliminates heat convection in the magnet. The 50K structure 4 wrapped with a polymer insulation film 7 reduces the heat radiation from the 300K structure 5 to the 4K structure 3 to the greatest extent possible.

[0042] The cold head 10 is located in the cold head container 11, which is sealed and connected to the 300K structure 5 and covers the entire first-level cold head 12 and the second-level cold head 13. The first-level cold head 12 is well thermally connected to the 50K structure 4, and the second-level cold head 13 is well thermally connected to the 4K structure 3. The magnet design uses two cold heads to ensure the cold head refrigeration margin. It is also possible to use a single cold head according to actual conditions, and the other cold head container is sealed.

[0043] The 4K structure 3 is suspended in the 300K structure 5 through the 4K tie rod 14, and the 50K structure 4 is suspended in the 300K structure 5 through the 50K tie rod 15. A moderate pre-tightening force is maintained to ensure that the magnet has a certain impact resistance.

[0044] Of course, the shielding of the superconducting magnet can also be achieved through four coils or multiple coil structures, but the three-coil structure magnet is the simplest actively shielded superconducting coil. At the same time, the three-coil actively shielding magnet structure is more compact and requires less space.

[0045] The magnet of the present invention generates the magnetic field required for assisting crystal pulling based on the superconducting coil, and at the same time, performs active shielding based on the superconducting coil, reduces the stray field outside the magnet, improves the stability of the single crystal furnace, improves the safety of the staff, and also improves the volume ratio of the factory. At the same time, the magnet structure is more compact, smaller in size, and very easy to use. The height of the magnet does not affect the crystal pulling operation process such as charging, opening, removing the crystal rod, and removing the crucible of the furnace body. The generated magnetic field can well control the flow of silicon liquid and the range of impurities in the crucible to obtain high-quality crystals.

Claims

1. A MCZ superconducting magnet with active shielding function, comprising a frame, a superconducting magnet coil, and a Dewar structure, wherein the Dewar structure comprises a 4K structure, a 50K structure, and a 300K structure, and is characterized in that: A superconducting magnet main coil (1) is wound around the middle of the frame (2), and an upper shielding coil (8) and a lower shielding coil (9) are respectively wound around the upper and lower sides of the frame (2); the frame (2), the upper shielding coil (8) and the lower shielding coil (9) of the superconducting magnet main coil (1) are located in the 4K structure (3), the 4K structure (3) is located in the 50K structure (4), and the 50K structure (4) is located in the 300K structure (5); the upper and lower ends of the 4K structure (3) are respectively suspended in the 300K structure (5) by using 4K tie rods (14); the upper and lower ends of the 50K structure (4) are respectively suspended in the 300K structure (5) by using 50K tie rods (15).

2. The MCZ superconducting magnet with active shielding function according to claim 1, characterized in that: The 300K structure (5) is connected to a cold head (10), the cold head (10) is located in a cold head container (11), and the cold head container (11) is sealed and connected to the 300K structure (5).

3. The MCZ superconducting magnet with active shielding function according to claim 2, characterized in that: The cold head (10) comprises a primary cold head (12) and a secondary cold head (13); the primary cold head (12) is connected to the 50K structure (4), and the secondary cold head (13) is connected to the 4K structure (3).

4. The MCZ superconducting magnet with active shielding function according to claim 1 or 2, characterized in that: The 300K structure (5) is a vacuum cavity (6).

5. The MCZ superconducting magnet with active shielding function according to claim 1, characterized in that: The outer side of the 50K structure (4) is wrapped with a polymer thermal insulation film (7).

6. The MCZ superconducting magnet with active shielding function according to claim 1, characterized in that: The 50K pull rod (15) is made of glass fiber, carbon fiber, stainless steel or titanium alloy.

7. The MCZ superconducting magnet with active shielding function according to claim 1, characterized in that: The MCZ superconducting magnet generates a horizontal magnetic field and a vertical magnetic field.

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