A cryogenic and high temperature superconducting hybrid toroidal field magnet for a thermonuclear fusion device

Abstract

This invention discloses a low-temperature and high-temperature superconducting hybrid toroidal field magnet for thermonuclear fusion devices, relating to the field of magnetic confinement fusion technology. The invention proposes placing second and first toroidal reinforcing support structures between radially graded high-field, mid-field, and low-field windings, respectively. These structures are made of high-strength stainless steel (such as N50, JJ1, JK2LB, or reinforced 316LN) with a yield strength >1000 MPa and permeability <1.05 at extremely low temperatures. This provides an internal rigid framework that effectively resists toroidal compression, significantly reduces shear forces on the insulation material within the coil windings, and increases the design upper limit of the toroidal field magnet. Simultaneously, it allows for a reduction in the thickness of the nose region of the coil housing, saving extremely valuable radial space in the center of the device. This invention, combined with the graded use of superconducting materials, achieves a highly efficient balance between device economy and performance.

Description

Technical Field

[0001] This invention relates to the field of magnetic confinement nuclear fusion technology, and more specifically to a low-temperature and high-temperature superconducting hybrid toroidal field magnet for thermonuclear fusion devices. Background Technology

[0002] In tokamak thermonuclear fusion reactors or fusion experimental devices, it is desirable to maximize the circumferential magnetic field in the plasma region in order to improve fusion power generation or plasma parameters. The circumferential field (TF) coil is a key component for generating this magnetic field.

[0003] As the magnetic field generated by the TF coil increases, the coil as a whole will be subjected to an extremely large centripetal force pointing towards the geometric center of the device. To resist this centripetal force, the inner legs of several (18, 16, or 14) TF coils are usually brought together to form a rigid wedging structure.

[0004] Under the immense centripetal force, adjacent TF coils experience extremely strong circumferential compression in the inner leg region. This macroscopic circumferential compression load is transmitted to the inner leg windings of the TF magnet, causing enormous compression deformation of the insulating material on both sides of the winding, resulting in extremely high shear stress in the insulating material layer. Insulating materials (such as glass fiber reinforced epoxy resin and its composites) have relatively weak shear resistance; this enormous shear stress easily leads to cracking and peeling failure of the insulating layer, subsequently causing short circuits or quench failure in the magnet. The enormous shear force on the insulating material has become the core mechanical bottleneck for further improving the circumferential field strength of fusion devices (i.e., the circumferential field strength of the TF coils).

[0005] Existing technologies typically counteract this circumferential compression by significantly increasing the thickness of the stainless steel in the inner region (Nose region) of the TF magnet's inner leg coil box. However, this occupies extremely valuable and limited radial space in the central region of the fusion device, leading to a reduction in the outer diameter and volt-second rate of the central solenoid (CS), and forcing an increase in the device's large radius, severely reducing the overall economic efficiency and compactness of the fusion device. Furthermore, using only high-temperature superconducting materials for the ultra-high field magnet would be extremely costly; using a single low-temperature superconducting material would not meet the high-field requirements. Summary of the Invention

[0006] To address the problem that existing tokamak TF coils fail under extremely high magnetic fields due to wedge compression caused by centripetal force, resulting in excessive shear force on the internal insulation material of the windings, and to solve the problem of wasted space caused by traditional thickened coil boxes, this invention provides a low-temperature and high-temperature superconducting hybrid toroidal field magnet for thermonuclear fusion devices.

[0007] This invention proposes placing second and first circumferential reinforcing support structures between the radially graded high-field winding (REBCO), medium-field winding (Nb3Sn), and low-field winding (NbTi / Nb3Sn), respectively. These support structures are made of high-strength stainless steel (such as N50, JJ1, JK2LB, or reinforced 316LN) with a yield strength >1000 MPa and permeability <1.05 at extremely low temperatures. This structure can effectively resist circumferential compression as an internal rigid skeleton, significantly reducing the shear force on the insulation material within the coil windings, allowing for a higher magnetic field at the center of the fusion device plasma; simultaneously, it can reduce the thickness of the Nose region of the coil box (the sharpest and most curved protruding tip region on the inner side (high-field side) of the D-shaped plasma cross-section), saving extremely valuable radial space at the center of the device. Combined with the graded use of superconducting materials, a very high balance between device economy and performance is achieved.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A cryogenic and high-temperature superconducting hybrid toroidal field magnet for a thermonuclear fusion device includes a TF magnet inner leg, which forms a wedge-shaped support structure at the center of the thermonuclear fusion device to resist centripetal force. The windings of the TF magnet inner leg, arranged radially inward, sequentially include:

[0010] The high-field winding uses REBCO high-temperature superconducting material;

[0011] The second circumferential reinforced support structure is made of high-strength stainless steel.

[0012] The mid-field winding uses Nb3Sn low-temperature superconducting material;

[0013] The first circumferential reinforced support structure is made of high-strength stainless steel.

[0014] The low-field winding uses NbTi or Nb3Sn low-temperature superconducting materials;

[0015] The high-field winding, mid-field winding, and low-field winding are all covered with a ground insulation layer. The first circumferential reinforcing support structure is placed between the ground insulation layers of the mid-field winding and the low-field winding, and the second circumferential reinforcing support structure is placed between the ground insulation layers of the high-field winding and the mid-field winding.

[0016] Where TF represents the toroidal field.

[0017] Beneficial effects:

[0018] 1. This invention innovatively incorporates a high-strength circumferential reinforcing support structure between the graded windings. When the inner legs of the TF magnet face enormous circumferential compression, these built-in high-strength steel plates act as "load-bearing walls," effectively resisting the circumferential compression, significantly reducing the shear stress transmitted to the fragile insulation material, and preventing insulation failure. This overcomes mechanical limitations, enabling the TF coil to safely generate and withstand higher circumferential fields.

[0019] 2. Because the built-in support structure distributes most of the wedge-shaped compression load, the Nose region of the coil box no longer needs to be designed to be extremely thick. This significantly reduces the valuable radial space occupied by the TF coil in the central region of the device (at the inner diameter of the device), allowing for the accommodation of a larger plasma within the same overall size, or reducing the overall size of the device within the same plasma size, greatly improving the overall economics of the fusion device.

[0020] 3. The winding of this invention adopts a three-level gradient design. In the high magnetic field region (e.g., above 14T), expensive but high-performance REBCO high-temperature superconducting material is used; in the medium magnetic field region (e.g., 6T to 14T), Nb3Sn material is used; and in the low magnetic field region (e.g., below 6T or 7T), low-cost and strain-insensitive NbTi material is used. This design achieves a perfect match between the current-carrying capacity of the superconducting material and the spatial distribution of the magnetic field, achieving an optimal balance between ensuring extremely high magnetic fields and magnet construction costs. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of 16 TF coil boxes of a low-temperature and high-temperature superconducting hybrid toroidal field magnet for a thermonuclear fusion device according to the present invention.

[0022] Figure 2 This is an equatorial cross-sectional view of the equivalent winding of the inner leg of 16 TF magnets in a low-temperature and high-temperature superconducting hybrid toroidal field magnet for a thermonuclear fusion device according to the present invention.

[0023] Figure 3 This is a detailed winding diagram of the inner leg section cross-section of a low-temperature and high-temperature superconducting hybrid toroidal field magnet for a thermonuclear fusion device according to the present invention;

[0024] Figure 4 This is a schematic diagram of the inner leg straight section of a low-temperature and high-temperature superconducting hybrid toroidal field magnet for a thermonuclear fusion device according to the present invention;

[0025] Figure 5 Stress cloud diagram of the conductor armor inside a traditional toroidal field coil winding;

[0026] Figure 6 This is a shear stress cloud diagram of the internal insulation material of a traditional toroidal field coil winding.

[0027] The reference numerals in the attached drawings are as follows: 1-TF magnet inner leg; 2-TF magnet outer leg; 3-high field winding; 4-mid field winding; 5-low field winding; 6-ground insulation layer 6; 7-resin filler; 8-first circumferential reinforcing support structure; 9-second circumferential reinforcing support structure; 10-first part of stainless steel coil box; 11-second part of stainless steel coil box; 12-third part of stainless steel coil box; 13-fourth part of stainless steel coil box; 14-fifth part of stainless steel coil box; 15-sixth part of stainless steel coil box; 16-assembly gap. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0029] like Figure 1 , Figure 2 , Figure 3 As shown, the cryogenic and high-temperature superconducting hybrid toroidal field magnet for a thermonuclear fusion device in this embodiment of the invention is composed of multiple toroidal field magnet units with identical structures arranged along the toroidal direction. Each toroidal field magnet unit includes several (e.g., 18, 16, or 14) TF coils. Based on the distance from the toroidal field magnet unit to the center of the device, it is divided into two parts: TF magnet inner leg 1 and TF magnet outer leg 2, with TF magnet outer leg 2 surrounding the TF magnet inner leg 1. The magnet adopts a graded winding structure in the radial direction; the TF magnet inner leg 1 forms a wedge-shaped support structure at the center of the thermonuclear fusion device to resist the enormous centripetal force it experiences. The windings of the TF magnet inner leg 1, arranged radially inward, sequentially include:

[0030] High-field windings are arranged in the high magnetic field region of the windings and are wound with REBCO high-temperature superconducting material.

[0031] The second circumferential reinforced support structure is made of high-strength stainless steel.

[0032] The mid-field winding, located in the middle magnetic field region of the winding, is made of Nb3Sn low-temperature superconducting material.

[0033] The first circumferential reinforced support structure is made of high-strength stainless steel.

[0034] The low-field winding uses NbTi or Nb3Sn low-temperature superconducting materials.

[0035] The high-field winding, mid-field winding, and low-field winding are all covered with a ground insulation layer. The first circumferential reinforcing support structure is placed between the ground insulation layers of the mid-field winding and the low-field winding, and the second circumferential reinforcing support structure is placed between the ground insulation layers of the high-field winding and the mid-field winding.

[0036] Preferably, the first circumferential reinforcing support structure and the second circumferential reinforcing support structure are configured such that when the TF magnet is subjected to centripetal force and is squeezed against each other at the wedge-shaped support structure, the first circumferential reinforcing support structure and the second circumferential reinforcing support structure serve as internal rigid skeletons to directly bear the load generated by the circumferential compression, thereby reducing the shear stress on the internal insulating materials of the high-field winding, the medium-field winding and the low-field winding.

[0037] Preferably, the first circumferential reinforcing support structure and the second circumferential reinforcing support structure are made of stainless steel with a yield strength greater than 1000 MPa and a magnetic permeability less than 1.05 at low temperatures (e.g., 4.5K).

[0038] Preferably, the stainless steel material includes N50 stainless steel, JJ1 stainless steel, JK2LB stainless steel, or 316LN stainless steel that has undergone strengthening treatment.

[0039] Preferably, the TF magnet further includes a stainless steel coil box covering the outside of the winding; wherein, the wall thickness of the stainless steel coil box in the Nose region of the inner leg coil box of the TF magnet at the center of the device is correspondingly reduced due to the sharing of the circumferential compression load by the first circumferential reinforcing support structure and the second circumferential reinforcing support structure, so as to reduce the radial space at the center of the device occupied by the TF magnet.

[0040] The high-field winding, mid-field winding, low-field winding, first circumferential reinforcing support structure, and second circumferential reinforcing support structure are formed into an integral winding assembly through a vacuum pressure impregnation process.

[0041] Specifically, each circumferential field magnet unit includes a high-field winding 3, a mid-field winding 4, a low-field winding 5, a ground insulation layer 6, resin filling 7, a first circumferential reinforcing support structure 8, a second circumferential reinforcing support structure 9, a first part 10 of a stainless steel coil box, a second part 11 of a stainless steel coil box, a third part 12 of a stainless steel coil box, a fourth part 13 of a stainless steel coil box, a fifth part 14 of a stainless steel coil box, and a sixth part 15 of a stainless steel coil box. Each winding is externally covered with a ground insulation layer 6. The second circumferential reinforcing support structure 9 is inserted between the high-field winding 3 and the mid-field winding 4, and the first circumferential reinforcing support structure 8 is inserted between the mid-field winding 4 and the low-field winding 5. Mechanical connection and force transmission are achieved through these circumferential support structures. An assembly gap 16 is reserved between the high-field winding, the mid-field winding, and the low-field winding. This assembly gap is filled with resin and subjected to a vacuum pressure impregnation process after the windings and support structures are assembled. Figure 3 As shown, the first part 10, the second part 11, the third part 12, the fourth part 13, the fifth part 14, and the sixth part 15 of the stainless steel coil box wrap around the entire winding assembly. One end of the second part 11 and the third part 12 of the stainless steel coil box are connected to the first part 10, and the other end is connected to the fourth part 13 and the fifth part 14, respectively. The other end of the fourth part 13 and the fifth part 14 are both connected to the sixth part 15. The low-field winding 5 is located near the center of the device, the high-field winding 3 is located near the plasma side, and the medium-field winding 4 is located between the high-field winding 3 and the low-field winding 5.

[0042] like Figure 2 As shown, in the toroidal field magnet of this embodiment, the high-field winding 3 is wound with REBCO high-temperature superconducting material, the medium-field winding 4 is wound with high-performance Nb3Sn low-temperature superconducting material, and the low-field winding 5 is wound with Nb3Sn or NbTi low-temperature superconducting material. By arranging different superconducting materials in corresponding magnetic field strength regions, each winding operates within its suitable magnetic field and current density range, thereby improving the operating current and magnetic field performance of the entire toroidal field magnet.

[0043] like Figure 3 As shown in the embodiment of the present invention, the first circumferential reinforcing support structure 8 and the second circumferential reinforcing support structure 9 are made of stainless steel and are used to withstand the electromagnetic force generated during the operation of the circumferential field magnet and to reasonably distribute the force on each winding stage. Through the above structural design, the electromagnetic force is avoided from being concentrated on the internal insulation structure of the winding, thereby effectively preventing the insulation material from undergoing performance degradation or structural failure due to excessive stress.

[0044] like Figure 4 As shown in the embodiment of the invention, the assembly gaps 16 reserved between the high-field winding 3, the medium-field winding 4, and the low-field winding 5 are used to compensate for errors in the winding manufacturing and assembly process. These gaps will eventually be filled with resin. Combining the assembly gaps with the stainless steel support structure improves the assembly reliability and operational stability of the structure while ensuring the overall rigidity of the magnet.

[0045] like Figure 3 As shown, in this embodiment of the invention, the installation process of the winding assembly and the coil box includes the following steps:

[0046] First, the high-field winding 3, the mid-field winding 4, the low-field winding 5, and the first circumferential reinforcing support structure 8 and the second circumferential reinforcing support structure 9 are subjected to vacuum pressure impregnation (VPI) process. After the VPI process is completed, the entire winding assembly (including the high-field winding 3, the mid-field winding 4, the low-field winding 5, the first circumferential reinforcing support structure 8, and the second circumferential reinforcing support structure 9) is assembled into the first part 10 of the stainless steel coil box.

[0047] Subsequently, the second part 11, the third part 12, the fourth part 13, and the fifth part 14 of the stainless steel coil box are welded in sequence. Finally, the sixth part 15 of the stainless steel coil box is welded to the entire assembly, completing the final encapsulation of the coil box. After the coil box is installed, the VPI process is performed again to fill the assembly gaps 16 reserved during the previous assembly process, ensuring that the overall assembled structure is gap-free and has good electrical and mechanical properties. The first part 10 of the stainless steel coil box has a U-shaped structure, while the remaining parts of the coil box are flat.

[0048] like Figure 5 , Figure 6 As shown in the stress cloud diagram of the conductor armor and insulation inside a conventional circumferential field coil, the areas of greater stress on the armor and insulation are located on both sides of the circumference, i.e. Figure 5 , Figure 6 The upper-middle section (the darker colored area experiences greater stress) is due to the 16 TF coils pressing against each other in the circumferential direction after energization, resulting in significant circumferential stress on the armor and insulation at the circumferential junction area of ​​the TF coils. Furthermore, the shear stress on the insulation material in this area is close to or has reached its limit. This phenomenon indicates that the stress state of the insulation material is one of the key factors affecting the upper limit of coil design. To effectively solve this problem, this invention adds a first circumferential reinforcing support structure 8 and a second circumferential reinforcing support structure 9 inside the stainless steel coil box. This effectively disperses the load, thereby reducing stress concentration in the insulation material, improving the overall load-bearing capacity and safety of the coil design, and achieving more uniform stress distribution on the armor.

[0049] Although the illustrative specific embodiments of the present invention have been described above to enable those skilled in the art to understand the invention, it should be understood that the invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes will be obvious as long as they are within the spirit and scope of the invention as defined and determined by the appended claims, and all inventions utilizing the concept of the present invention are protected.

Claims

1. A low-temperature and high-temperature superconducting hybrid toroidal field magnet for a thermonuclear fusion device, comprising a TF magnet inner leg that forms a wedge-shaped support structure at the center of the thermonuclear fusion device to resist centripetal force, characterized in that, The windings of the inner leg of the TF magnet, arranged radially inward, include: The high-field winding uses REBCO high-temperature superconducting material; The second circumferential reinforced support structure is made of high-strength stainless steel. The mid-field winding uses Nb3Sn low-temperature superconducting material; The first circumferential reinforced support structure is made of high-strength stainless steel. The low-field winding uses NbTi or Nb3Sn low-temperature superconducting materials; The high-field winding, mid-field winding, and low-field winding are all covered with a ground insulation layer. The first circumferential reinforcing support structure is placed between the ground insulation layers of the mid-field winding and the low-field winding, and the second circumferential reinforcing support structure is placed between the ground insulation layers of the high-field winding and the mid-field winding. Wherein, TF represents the circumferential field; the first circumferential reinforced support structure and the second circumferential reinforced support structure are made of stainless steel with a yield strength greater than 1000MPa and a magnetic permeability less than 1.05 at low temperatures.

2. The low-temperature and high-temperature superconducting hybrid toroidal field magnet for a thermonuclear fusion device according to claim 1, characterized in that, The first and second circumferential reinforcing support structures are configured such that when the inner legs of the TF magnet are subjected to centripetal force and are squeezed against each other at the wedge-shaped support structure, they act as an internal rigid skeleton to directly bear the load generated by the circumferential compression.

3. The low-temperature and high-temperature superconducting hybrid toroidal field magnet for a thermonuclear fusion device according to claim 1, characterized in that, The stainless steel material includes N50 stainless steel, JJ1 stainless steel, JK2LB stainless steel, or 316LN stainless steel that has undergone strengthening treatment.

4. The low-temperature and high-temperature superconducting hybrid toroidal field magnet for a thermonuclear fusion device according to claim 1, characterized in that, The TF magnet inner leg also includes a stainless steel coil box that covers the outside of the winding.

5. The low-temperature and high-temperature superconducting hybrid toroidal field magnet for a thermonuclear fusion device according to claim 1, characterized in that, An assembly gap is reserved between the high-field winding, the mid-field winding and the low-field winding. The assembly gap is filled with resin after the winding and the wedge-shaped support structure are assembled.

6. The low-temperature and high-temperature superconducting hybrid toroidal field magnet for a thermonuclear fusion device according to claim 4, characterized in that, The high-field winding, mid-field winding, low-field winding, first circumferential reinforcing support structure, and second circumferential reinforcing support structure are formed into an integral winding assembly through a vacuum pressure impregnation process.

7. The cryogenic and high-temperature superconducting hybrid toroidal field magnet for a thermonuclear fusion device according to claim 6, characterized in that, The integral winding assembly is housed within the first part of the stainless steel coil box, and is encapsulated by sequentially welding the second, third, fourth, fifth, and sixth parts of the stainless steel coil box.

8. The low-temperature and high-temperature superconducting hybrid toroidal field magnet for a thermonuclear fusion device according to claim 1, characterized in that, The high-field winding is arranged in the high magnetic field region of the winding, the medium-field winding is arranged in the medium magnetic field region of the winding, and the low-field winding is arranged in the low magnetic field region of the winding.

9. The low-temperature and high-temperature superconducting hybrid toroidal field magnet for a thermonuclear fusion device according to claim 1, characterized in that, The first and second circumferential reinforcing support structures are continuously arranged circumferentially along the low-temperature and high-temperature superconducting hybrid circumferential field magnet.

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