MCZ superconducting magnet with active shielding function

Abstract

The utility model 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 utility model relates to the technical field of superconducting magnets, in particular to an 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 monocrystalline silicon market is expanding rapidly. By improving the crystal composition through the magnetron Czochralski (MCZ) method, the impurity content and distribution in monocrystalline silicon can be reduced, thereby improving its quality.

[0003] The core equipment of the magnetron Czochralski method is the addition of a magnet to the existing Czochralski single crystal furnace. This magnet generates the magnetic field required for crystal pulling, assisting in controlling the process. Traditionally, permanent magnets generate magnetic fields, but these are inefficient for large single crystal furnaces. Besides not being able to generate sufficient magnetic field strength, they are also very expensive. Electromagnets were once an option, but even slightly higher magnetic fields present challenges for them. Besides high energy consumption, achieving effective cooling is challenging and expensive. With the development of superconducting technology, superconducting magnets have become particularly prominent due to their small size, light weight, stable magnetic field, and low energy consumption. Existing single crystal magnets used in magnetic pulling utilize superconducting magnets.

[0004] The MCZ single crystal furnace is a production device whose magnets and furnace body work together, requiring manual operation and equipment assistance. When the magnetic field is on, the proper functioning of the crystal pulling furnace and the safety of workers are crucial, placing high demands on the magnet's stray field. This is particularly important in factory planning. Lowering the stray field can increase the volume ratio per unit area, allowing for more equipment to be installed within the same factory, improving plant utilization and output.

[0005] Superconducting magnets, such as Xi'an Juneng Superconducting Magnet Technology Co., Ltd.'s patented "A Superconducting Magnet, Magnetically Controlled Single Crystal Pulling Equipment, and Control Method" (CN116798724A), utilize two superconducting coils. Passive shielding is employed to reduce stray fields. This method primarily involves using ferromagnetic material with relatively high magnetic permeability to form a ring around the magnet, which absorbs the magnetic lines of force and diffuses them outward, thereby reducing stray fields outside the magnet. This method is somewhat effective, but its performance is relatively limited. To achieve this, the thickness of the ferromagnetic material must be further increased, significantly increasing the weight of the magnet. This change significantly impacts transportation, installation, and cost. Summary of the Invention

[0006] In order to overcome the deficiencies of the prior art, the utility model 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 stability of the single crystal furnace operation, improving the safety of the staff, and also increasing the volume ratio of the factory.

[0007] To achieve the above objectives, an MCZ superconducting magnet with active shielding function is designed, comprising a skeleton, a superconducting magnet coil, and a dewar structure. The dewar structure comprises 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 respectively by 50K pull rods.

[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 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 outside 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 utility model 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 adding materials to the furnace, opening, removing crystal rods, and removing crucibles. 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 This is a schematic structural diagram of the utility model.

[0017] Figure 2 This is a schematic diagram of the internal structure of the utility model.

[0018] Figure 3 This is a schematic diagram of the specific structural connection of the utility model.

[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-level cold head, 13 is the second-level 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. The superconducting magnet main coil 1 is wound around the middle of the skeleton 2, and the upper and lower sides of the skeleton 2 are respectively wound with an upper shielding coil 8 and a lower shielding coil 9; 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 4K pull rods 14; the upper and lower ends of the 50K structure 4 are respectively suspended in the 300K structure 5 by 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 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] The MCZ superconducting magnet generates horizontal and vertical magnetic fields.

[0028] Superconducting magnet coils and coil bobbins. The superconducting magnet coils are designed as a three-coil structure with active shielding. This structure minimizes space occupancy and magnet height, enabling the design of a thin and lightweight 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 to a position close to the superconducting magnet to achieve a shielding effect.

[0030] The coil skeleton 2 is made of metal or non-metallic materials, and is used to support the superconducting coil designed according to the target magnetic field, and to assist in forming and fixing 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 consists of, from the inside out, the 4K structure 3, the 50K structure 4, and the 300K structure 5. The 4K structure 3 is the core of the superconducting magnet, connecting all components required for superconductivity. The 50K structure 4 is a thermal barrier, primarily used to shield heat from external conduction / radiation entering the 4K structure 3. The 300K structure 5 is the outer shell of the magnet, supporting all components and enclosing a vacuum chamber within it.

[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 design a cooling link to establish a thermal connection channel for all parts that need to enter the superconducting state, which can efficiently remove 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 structure to maximize the stability and uniformity of heat conduction; if a liquid helium immersion method is used, the 4k structure 3 mainly constructs 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 sufficient liquid helium, most of the coil will be immersed in the liquid helium, so that the coil is kept at the liquid helium temperature to achieve a superconducting state.

[0033] A 50K structure 4 is required outside the 4K structure 3 to isolate the internal 4K structure 3 from heat radiation from the magnet's exterior. This structure, often called a cold shield, is typically made of high-purity aluminum. This shield effectively resists thermal shock from the magnet's exterior and ensures consistent thermal radiation to the 4K structure 3 within the magnet. The cold shield is often covered with multiple layers of polymer insulation film to reflect external heat radiation, effectively reducing the amount of heat radiated from the magnet's exterior to the interior.

[0034] The 300K structure 5 is a commonly used support structure for magnets. At the same time, a vacuum cavity is constructed for the 4K structure 3 and the 50K structure 4. In actual operation, the vacuum state inside the magnet is ensured, effectively suppressing 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 minimizes heat conduction between the layers and requires the proper placement and orientation of the rods to minimize stress on them and conserve space for the magnets. Because 300K structure 5 has the highest mechanical strength, both 4K structure 3 and 50K structure 4 are suspended from 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, 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 the cryogenic cooling mechanism for the entire magnet. The cold head container 11 supports the connection of the cold head 10 to the magnet, connects to the Dewar structure, and encloses the entire cold head 10. The cold head container 11 and the 300K structure 5 are made of stainless steel, connecting the superconducting magnet and the cold head 10 and ensuring 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 is well thermally connected to the 50K structure 4 , and the secondary cold head 13 is well thermally connected to the 4K structure 3 .

[0040] like Figure 3 The figure shows the structure of an embodiment of the present invention. The superconducting magnet main coil 1 is wound on a frame 2 according to certain requirements and connected to a 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 as much as possible.

[0042] Cold head 10 is located in cold head container 11, which is sealed to 300K structure 5 and covers the entire primary cold head 12 and secondary cold head 13. The primary cold head 12 is thermally connected to the 50K structure 4, while the secondary cold head 13 is thermally connected to the 4K structure 3. This magnet design uses two cold heads to ensure sufficient cooling capacity. Alternatively, a single cold head can be used, with the other cold head container 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 active shielding magnet structure is more compact and requires less space.

[0045] This new magnet utilizes superconducting coils to generate the magnetic field required to assist in crystal pulling. The superconducting coils also provide active shielding, reducing stray fields outside the magnet. This improves the stability of the single crystal furnace, enhances worker safety, and increases the factory's capacity utilization. Furthermore, this magnet boasts a more compact structure and smaller size, making it extremely easy to use. The height of the magnet does not affect crystal pulling operations such as furnace loading, opening, removing ingots, and removing the crucible. The generated magnetic field effectively controls the flow of silicon liquid in the crucible and the concentration of impurities, resulting in 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 includes a 4K structure, a 50K structure, and a 300K structure, and is characterized in that: The superconducting magnet main coil (1) is wound around the middle of the skeleton (2), and the upper shielding coil (8) and the lower shielding coil (9) are wound around the upper and lower sides of the skeleton (2) respectively; the skeleton (2), the superconducting magnet main coil (1), the upper shielding coil (8) and the lower shielding coil (9) 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 suspended in the 300K structure (5) by using 4K pull rods (14); the upper and lower ends of the 50K structure (4) are suspended in the 300K structure (5) by using 50K pull 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), wherein 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 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 horizontal and vertical magnetic fields.

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