Through hole cold wall vector magnet structure and high-intensity magnetic field terahertz near-field measurement system

Abstract

The invention discloses a through hole cold wall vector magnet structure and a strong magnetic field terahertz near field measurement system, the through hole cold wall vector magnet structure comprises a vector magnet, the vector magnet is provided with a magnet through hole penetrating through the top and the bottom of the vector magnet, the vector magnet comprises multiple layers of shells which are sequentially spaced from outside to inside and coaxially sleeved, and the multiple layers of shells are all coaxial with the axis of the magnet through hole; an outer vacuum interlayer, a liquid nitrogen interlayer, a first vacuum interlayer and a second vacuum interlayer are sequentially formed among the multiple layers of shells. According to the invention, the through hole is formed in the vector magnet, enough space is provided for the internal unit of the sample cavity, the outer vacuum interlayer, the liquid nitrogen interlayer, the first vacuum interlayer, the second vacuum interlayer and the liquid helium cavity are arranged, and a multi-layer cold shield is formed by vacuumizing and liquid nitrogen injection, so that a cold wall is formed on the inner wall of the through hole of the magnet; therefore, a low-temperature basis is provided for an optical coupling scanning probe test system under multi-field regulation and control.

Description

Technical Field

[0001] The present invention relates to the technical fields of cryogenic high magnetic field equipment and near-field imaging, and more particularly to a through-hole cold-wall vector magnet structure and a high magnetic field terahertz near-field measurement system. Background Art

[0002] Scanning tunneling microscope measurement under cryogenic high magnetic fields has irreplaceable advantages in condensed matter physics. It can reveal key physical phenomena such as the quantum state, topological order, and magnetoelectric coupling of materials under extreme conditions, providing a unique experimental means for understanding strongly correlated electron systems, topological states, and quantum phase transitions. The vector magnetic field, because it can apply magnetic fields in different directions, can be used to study the electronic behavior of anisotropic materials (such as superconductors, topological insulators, magnetic materials, etc.) in different directions, can perform spin and orbital degree of freedom control, and can help explore new quantum phenomena.

[0003] Cryogenic inserts are widely used for non-ultra-high vacuum systems. They are used to load the sample to be measured into a cryogenic environment and connect the measurement device electrode wires at the room temperature end to the sample. They are commonly used equipment in the field of cryogenic high magnetic field measurement. It is crucial for the sample to obtain a cryogenic environment and be able to maintain such a cryogenic environment for a long time.

[0004] Terahertz waves (0.1–10 THz) have become a key tool for probing the microscopic dynamics of quantum materials because their energy scale (meV) highly matches the low-energy excitations (such as superconducting energy gaps, magnons, plasmons) of the condensed matter system. Through time-domain spectroscopy, strongly correlated phenomena such as superfluid density and pseudogap can be directly analyzed, making up for the limitations of traditional methods; strong-field terahertz pulses can also instantaneously regulate the electronic energy band through Floquet engineering, inducing superconducting or Mott phase transitions and promoting the research of non-equilibrium physics; terahertz near-field scanning microscopy technology has achieved real-space dynamic imaging of the microscopic quantum behavior of the condensed matter system by breaking through the optical diffraction limit (sub-micron to nano-scale resolution); this technology can accurately detect nano-scale phenomena such as exciton diffusion in two-dimensional materials, local modes of plasmons such as graphene, surface states of topological materials, and charge density wave domain structures, revealing the spatial distribution characteristics of electronic correlations and collective excitations that cannot be captured by traditional far-field spectroscopy; combined with ultrafast terahertz pump-probe, it can also track the evolution of transient electron order in the non-equilibrium state, providing a key experimental means for studying the microscopic mechanism of strongly correlated systems and quantum phase transitions.

[0005] The patent document with the patent publication number CN116146885A discloses a telescopic liquid helium dewar using a single-layer optical window, which discloses that the bottom of the first dewar assembly is connected to the second dewar assembly, and the bottom inside the first dewar assembly is a sample chamber; the second dewar assembly includes a telescopic tube assembly, a radiation protection assembly, and a single-layer optical window; the top of the telescopic tube assembly is connected to the bottom of the first dewar assembly, the single-layer optical window is connected to the bottom of the telescopic tube assembly, the radiation protection assembly is located inside the telescopic tube assembly and is coaxially arranged, and the top of the radiation protection assembly extends into the sample chamber after the telescopic tube assembly is compressed. During the use of this solution, the radiation protection assembly can achieve good heat conduction and temperature control, the single-layer optical window can ensure sealing and transmission efficiency, and the sample is vertically sent into the sample chamber by the insert, providing a solution for the application of the scanning probe microscope in a narrow and restricted environment.

[0006] However, in order to vertically send the test device into the sample chamber, it is necessary to greatly compress the bellows. Multiple operators need to crowd under the device to provide sufficient force, which poses a great safety hazard. Due to the limited accuracy of the angle-adjustable bellows, the pipes used as metal waveguides and free spaces will deviate from the angle of the tunnel junction. Moreover, since the internal space of the sample chamber cannot be monitored directly, the process of optical alignment and coupling of the device is a "blind adjustment", while the angle of the tunnel junction is extremely precise. Compressing the bellows is not a fine adjustment, and the test device cannot be truly vertically loaded, with too large a deviation angle, making it impossible to achieve free transmission of laser inside the pipeline. The sample chamber space of this device is not yet sufficient to accommodate enough components to achieve near-field optical measurement. Expanding the space will inevitably result in a higher thermal load. In fact, the lowest test temperature provided by this device is 15K.

[0007] Secondly, due to the strong absorption of traditional quartz optical fibers in the terahertz band (0.1–10 THz), or due to dispersion and nonlinear effects, the original terahertz signal is damaged, and there is no effective fiber to couple terahertz for near-field measurement of scanning probe microscopes. Therefore, introducing a fiber method based on this device cannot solve the design difficulties of the compatibility of terahertz light, low temperature, and strong magnetic field.

[0008] Using a corrugated tube to connect the heat transfer channels between the room temperature region and the low temperature region can not only extend the solid heat conduction length, reduce the temperature gradient, but also reduce the heat exchange interface area, thus significantly reducing the heat leakage of the sample chamber. The patent document with the patent publication number CN117168954A discloses a Dewar with double corrugated tubes and low heat leakage and a rapid sample replacement measurement device. The device includes a vacuum chamber, a refrigeration system and a sample chamber. The vacuum chamber includes a first flange, a first top cover, a second flange, a first cylinder and a first tail pipe. The first and second flanges are symmetrically distributed on both sides of the center line of the first top cover. The refrigeration system includes a refrigerator, a second cylinder, a second top cover, a second tail pipe and a second-stage cold head heat conduction plate. The second-stage cold head of the refrigerator is rigidly connected to the second-stage cold head heat conduction plate. The sample chamber includes a first corrugated tube, a second corrugated tube and a third tail pipe. One end of the first corrugated tube is fixed to the first flange, and the other end is fixed to the second top cover. One end of the second corrugated tube is fixed to the second top cover, and the other end and the third tail pipe are respectively fixed to the upper and lower sides of the second-stage cold head heat conduction plate, and the first, second corrugated tubes and the third tail pipe are coaxial. The first, second and third tail pipes are coaxially arranged from outside to inside. The advantage of this solution is that the structure is compact, and while reducing costs, the heat leakage is greatly reduced.

[0009] However, the structure of this Dewar determines that a dry refrigerator with extremely large vibration must be used, which is difficult to be used in extremely precise measurement processes such as scanning tunneling microscopy imaging. This Dewar cannot provide a magnetic field for the test device alone, and the Dewar itself is not provided with an optical window, and it has not been and is difficult to realize physical property measurements with various forms of optical coupling.

[0010] Current scientific researchers hope to apply the imaging measurement of terahertz optical coupling scanning tunneling microscope in narrow and confined spaces: such as applying it in a magnet with a small aperture to achieve the purpose of studying the interaction between light and matter under magnetic field control. However, when combining terahertz light and a scanning probe microscope, the existing terahertz generation optical path and focusing optical path are both relatively complex, and it is not suitable to apply this combination method in a narrow space. If a low-temperature environment for testing is required at the same time, it is required that the sealing performance is good, the heat leakage of the system is low, and the single-layer optical window can work normally to obtain a high transmission efficiency; at the same time, in a low-temperature environment, the shock absorption of the system is crucial for the stability of imaging. The external shock absorption of the system is greatly interfered by the site and facilities, and the design of internal shock absorption plays an irreplaceable role. At present, the near-field imaging system is only applied in low-temperature equipment and requires a three-dimensional piezoelectric device to achieve precise alignment of light and the probe. There is no report on realizing a terahertz near-field measurement system in a magnetic field.

[0011] The vector magnetic field can naturally adjust the collective alignment direction of spins in materials. By studying anisotropic materials and combining pump-probe techniques, the microscopic mechanisms of spin flipping and domain wall motion can be analyzed. However, for current vector magnets, under the condition of a maximum magnetic field of 9 T along the z-axis, the maximum magnetic field along the x-axis is 3 T. Moreover, most of them use dry refrigerators to cool the magnet coils, resulting in relatively large vibrations of the system itself, which is not suitable for application in scanning probe microscopes, especially in the field of terahertz near-field measurement. On the other hand, the central apertures of most current magnets are relatively small, and the functions that can be achieved in them are relatively single, which is not conducive to the future development of multi-field controlled scanning probe microscope near-field imaging systems. Finally, on the premise of facilitating optical coupling and future realization of ultra-high vacuum compatibility, a vector magnet structure with a central through-hole is required. However, the inner walls of the central through-holes of current magnets are all at room temperature during operation. If low-temperature measurements are required, a closed space that can accommodate the cold head and the insertion of the cold head needs to be provided. However, this will reduce the magnet aperture, and the magnet with limited space combined with a liquid helium cryostat has a small liquid helium capacity and a short low-temperature maintenance time, and it is even difficult to reach the target temperature we need. Another method is to use a piezoelectric motor to rotate the sample to change the relative orientation between the magnetic field direction and the sample plane, so as to construct a vector magnetic field. However, this is naturally contradictory to the optically coupled scanning tunneling microscope.

[0012] The patent document with the patent publication number CN109695985A discloses a low-loss liquid helium dewar with an independent and detachable sample chamber for a confined space. Different from the magnet, this liquid helium dewar can only provide a low-temperature environment and cannot provide a magnetic field. When building a multi-field controlled near-field measurement system that requires low-temperature measurements, a closed space that can accommodate the cold head and the insertion of the cold head needs to be provided for the dewar. The thin-neck structure of this dewar needs to extend to the center of the magnet, which is very difficult to achieve, and the cooling effect provided by the cold quantity is difficult to meet the expectations. This dewar itself includes an optical window and can perform optical coupling tests. However, when inserted into the magnet aperture, the window will be blocked and optical coupling tests cannot be realized.

[0013] The information disclosed in this background art section is only intended to enhance the overall understanding of the present invention and should not be regarded as an admission or any form of implication that this information constitutes prior art known to those of ordinary skill in the art. Summary of the Invention

[0014] The technical problem to be solved by the present invention is how to provide a vector magnet that can build a multi-field controlled near-field measurement system under limited space conditions.

[0015] The present invention achieves the solution to the above technical problems through the following technical means: A through-hole cold-wall vector magnet structure, including a vector magnet, the vector magnet is provided with a magnet through-hole penetrating its top and bottom, the vector magnet includes multiple layers of shells that are sequentially spaced and coaxially sleeved from outside to inside, and the multiple layers of shells are all coaxial with the axis of the magnet through-hole. An outer vacuum interlayer, a liquid nitrogen interlayer, a first vacuum interlayer, and a second vacuum interlayer are sequentially formed between the multiple layers of shells. A liquid helium cavity is also provided between the second vacuum interlayer and the magnet through-hole. The outer vacuum interlayer, the liquid nitrogen interlayer, the first vacuum interlayer, the second vacuum interlayer, and the liquid helium cavity all cover the magnet through-hole and can form a cold wall on the inner wall of the magnet through-hole.

[0016] As a preferred technical solution, the multiple layers of shells include a first shell, a second shell, a third shell, a fourth shell, and a fifth shell that are sequentially sleeved. An outer vacuum interlayer is formed between the first shell and the second shell, a liquid nitrogen interlayer is formed between the second shell and the third shell, a first vacuum interlayer is formed between the third shell and the fourth shell, a second vacuum interlayer is formed between the fourth shell and the fifth shell, and a liquid helium cavity is formed between the fifth shell and the magnet through-hole.

[0017] As a preferred technical solution, the coil of the vector magnet is completely or partially immersed in the liquid helium in the liquid helium cavity. Part of the inner side wall of the liquid helium cavity forms the outer wall of the middle part of the magnet through-hole. A plurality of sections of bellows connected in sequence are provided on the inner wall of the lower part of the magnet through-hole along its axis direction. The bellows provided at the bottom of the magnet through-hole are hermetically fixed to the bottom of the magnet tube perforation, and a seal is provided at the top of the magnet through-hole to seal the top of the magnet tube perforation.

[0018] As a preferred technical solution, it includes an upper plug-in and a lower plug-in. One end of the upper plug-in vertically inserts into the magnet through-hole from the top of the magnet through-hole, and the other end of the upper plug-in is hermetically fixed to the top of the vector magnet. One end of the lower plug-in vertically inserts into the magnet through-hole from the bottom of the magnet through-hole, and the other end of the lower plug-in is hermetically fixed to the bottom of the vector magnet. A liquid nitrogen dewar is provided at one end of the upper plug-in facing the lower plug-in, and a section of bowl-shaped radiation shield is provided on both the upper plug-in and the lower plug-in.

[0019] As a preferred technical solution, each section of the bowl-shaped radiation shield includes a plurality of bowl-shaped radiation shields arranged alternately along the axial direction of the magnet through-hole. The bowl-shaped radiation shield includes a circular sheet and a circular tube with a diameter equal to that of the circular sheet that are fixedly connected. The circular sheet and the circular tube are welded and fixed to form a bowl-shaped structure.

[0020] The present invention also provides a strong magnetic field terahertz near-field measurement system including the above-mentioned through-hole cold-wall vector magnet structure, further including a sample chamber, the sample chamber is connected to one end of the lower plug facing the upper plug, the upper plug further includes a magnet through-hole upper cover plate, the magnet through-hole upper cover plate, the bowl-shaped radiation shield, and the liquid nitrogen dewar are fixedly connected in sequence along the axial direction of the magnet through-hole, the liquid helium dewar is located at the top of the sample chamber, a vacuum chamber is provided in the sample chamber, the lower plug includes a pipeline outer shell, the sample chamber, the bowl-shaped radiation shield, and the pipeline outer shell are fixedly connected in sequence along the axial direction of the magnet through-hole, and a terahertz optical path pipeline, a femtosecond optical path pipeline, and a reserved optical pipeline are provided in the pipeline outer shell.

[0021] As a preferred technical solution, a sample chamber test unit is provided in the sample chamber, the sample chamber test unit is located in the vacuum chamber, the sample chamber test unit includes a sample holder and a scanning tunneling microscope, a lens body base, a lens body clamp, a spring clamp, and a spring fixed on the sample holder. The sample holder includes an upper cover plate of the holder, a support pillar of the holder, and a lower cover plate of the holder. The upper cover plate of the holder is fixedly connected to the lower cover plate of the holder through multiple support pillars of the holder. The spring clamp is sleeved on the support pillar of the holder, the spring clamp can slide axially along the support pillar of the holder, and can also rotate with the axis of the support pillar of the holder as the rotation axis. The spring clamp is elastically connected to the lens body base through a spring, and a scanning tunneling microscope is connected to the lens body base. The pipeline of the terahertz optical path pipeline can be shot to the tunneling area between the tungsten tip on the scanning tunneling microscope and the sample.

[0022] As a preferred technical solution, a light receiving tube, a light guiding tube, and a light hole clamp are fixed on the sample holder. The light guiding tube is detachably coaxially fixed to the light receiving tube through the light hole clamp. The light receiving tube, the light guiding tube, and the light hole clamp are all polished and gold-plated. The projection of the outlet of the light receiving tube can cover or completely cover the tunneling area. A circular groove is formed circumferentially on the lens body base, and a gap is left between the lens body base and the support pillar of the holder.

[0023] As a preferred technical solution, a bent pipe is also fixedly connected to the sample holder. One end of the femtosecond optical path pipeline extends to form a femtosecond optical path hole at the lower cover plate of the holder. One end of the femtosecond optical path hole is connected to the bent pipe, and the other end is arranged facing the tunneling area.

[0024] The present invention also provides a strong magnetic field terahertz near-field measurement system including the above-mentioned through-hole cold-wall vector magnet structure, including a rotating insert. A plug-in sample chamber is provided in the rotating insert. A rotating sample rod is rotatably connected in the plug-in sample chamber. A gate valve is provided in the plug-in sample chamber. The rotating insert is hermetically fixed to the rotating sample rod through a dynamic seal outer nut. A test device is installed at the bottom of the rotating sample rod, and the test device includes a scanning magnetic force microscope.

[0025] The beneficial effects of the present invention are as follows:

[0026] (1) In the present invention, by providing a through-hole in the vector magnet, sufficient space is provided for the internal units of the sample chamber. Through the settings of the outer vacuum interlayer, liquid nitrogen interlayer, first vacuum interlayer, second vacuum interlayer, and liquid helium chamber, and by means of vacuum pumping and injecting liquid nitrogen, a multi-layer cold shield is formed, so that the inner wall of the magnet through-hole forms a cold wall, which can not only provide a magnetic field, but also provide a low-temperature basis for the optical coupling scanning probe test system under multi-field regulation.

[0027] (2) In the present invention, by using the upper plug-in and lower plug-in and integrating the sample chamber on the lower plug-in, and forming a way of inserting from the lower part of the magnet through-hole, it replaces the defect that the position of the sample chamber is inaccurate due to compressing the bellows in the prior art, and avoids the dangerous operation of the operator relying on the compressed bellows for optical coupling purposes; large magnets are generally installed in pits, and various optical paths are assembled at the bottom of the pit. The operator operates the magnet above, which will not interfere with or damage the precision optical path. During the operation of the device, there is no need for an operator under the magnet, and there is enough space to integrate multiple light sources, broadening the application range.

[0028] (3) In the present invention, the liquid helium chamber of the vector magnet is directly in contact with the magnet through-hole, directly providing a low-temperature environment for the sample chamber. Through the design of extending the temperature gradient by the bellows, the heat leakage path is reduced in terms of conduction heat leakage. The upper plug-in and lower plug-in are outside the radiation shield. Through the setting of the bowl-shaped radiation shield, both radiation heat leakage and convective heat leakage are suppressed, reducing the loss of cold quantity.

[0029] (4) In the present invention, by adopting the design of the light-receiving hole and light-guiding hole, the light spot is efficiently converged to the tunnel area, improving the efficiency of optical coupling. The spring clamp realizes the adjustment of the position and pose of the tunnel area. Through the optical path pipeline, the terahertz generation and transmission device are directly connected to the bracket, and the scanning probe microscope is fixed to the bracket, so that the whole device is integrated. On the basis of ensuring the firmness of the overall structure of the device, the optical path deviation phenomenon caused by vibration and the like is reduced. Brief Description of the Drawings

[0030] Figure 1 It is a schematic cross-sectional structure diagram of the low-temperature insert inserted into the vector magnet provided by Embodiment 1 of the present invention;

[0031] Figure 2 It is a schematic cross-sectional structure diagram of the low-temperature insert assembled to the vector magnet provided by Embodiment 1 of the present invention;

[0032] Figure 3 It is a schematic top view structure diagram provided by Embodiment 1 of the present invention;

[0033] Figure 4 It is provided by Embodiment 1 of the present invention Figure 2 Schematic enlarged structure diagram of part A;

[0034] Figure 5 Schematic diagram of the upper plug-in structure provided in Embodiment 1 of the present invention;

[0035] Figure 6 Schematic diagram of the lower plug-in structure provided in Embodiment 1 of the present invention;

[0036] Figure 7 Bottom view schematic diagram of the lower plug-in provided in Embodiment 1 of the present invention;

[0037] Figure 8 Provided in Embodiment 2 of the present invention Figure 2 Schematic diagram of the enlarged partial structure of B in

[0038] Figure 9 Explosion diagram of the sample cavity provided in Embodiment 2 of the present invention;

[0039] Figure 10 Isometric view schematic diagram of the sample cavity provided in Embodiment 2 of the present invention;

[0040] Figure 11 Top view schematic diagram of the sample cavity provided in Embodiment 2 of the present invention;

[0041] Figure 12 Schematic diagram of the magnet center structure provided in Embodiment 1 of the present invention;

[0042] Figure 13 Schematic diagram of the sample cavity structure provided in Embodiment 3 of the present invention;

[0043] Figure 14 Schematic diagram of the rotating insert inserted into the vector magnet structure provided in Embodiment 4 of the present invention;

[0044] Figure 15 Provided in Embodiment 4 of the present invention Figure 14 Schematic diagram of the enlarged partial structure of C of

[0045] Figure 16 Temperature curve graph of the temperature reduction of the cryogenic strong magnetic field terahertz near-field measurement system provided in Embodiment 2 of the present invention;

[0046] Figure 17 Schematic diagram of the driven graphite atom imaging of terahertz obtained by the cryogenic strong magnetic field terahertz near-field measurement system provided in Embodiment 2 of the present invention;

[0047] Figure 18 Schematic diagram of the driven graphite atom imaging of terahertz obtained by the cryogenic strong magnetic field terahertz near-field measurement system provided in Embodiment 2 of the present invention; It should be noted that Figure 18 is the image along the Figure 17 dotted line in Figure 17The region of the medium switch for terahertz light corresponds one-to-one, which is used to prove that the signal source is indeed excited by terahertz light.

[0048] Reference numerals in the drawings: 1. Outer vacuum interlayer; 2. Liquid nitrogen interlayer; 3. Liquid helium chamber; 4. Magnet through-hole; 5. Cryogenic cold shield; 6. Upper plug-in; 11. Lower plug-in; 7. Bowl-shaped radiation shield; 8. Liquid helium dewar; 9. Sample chamber; 10. Vacuum pumping port for magnet through-hole; 12. Terahertz optical path pipeline; 13. Z-axis magnetic field electrode lead; 14. Vacuum interlayer pumping port; 15. 24-hole lead interface; 16. 2-hole lead interface; 17. Suspension point; 18. Liquid nitrogen safety valve; 19. X-axis magnetic field electrode lead; 20. Grounding point; 21. Liquid nitrogen infusion port; 22. Liquid helium level gauge; 23. Liquid helium infusion port; 24. Liquid helium safety valve; 25. Helium recovery port; 26. Femtosecond optical path pipeline; 27. Sample chamber vacuum pipeline; 28. Lower cover plate of magnet through-hole; 29. Upper cover plate of magnet through-hole; 30. Rubber O-ring; 31. Bellows; 311. Bellows 1; 312. Bellows 2; 313. Bellows 3; 32. Light collection tube; 33. Light guiding tube; 34. Optical hole clamp; 35. Upper cover plate of bracket; 36. Bracket pillar; 37. Lower cover plate of bracket; 38. Scanning tunneling microscope; 39. Mirror body base; 40. Mirror body clamp; 41. Spring clamp; 42. Spring; 43. Mirror body counterweight; 44. Femtosecond optical path hole; 45. Tungsten tip; 46. Window assembly; 47. Reserved optical pipeline; 48. Magnet center; 50. Plug-in sample chamber; 51. Rotating sample rod; 52. Gate valve; 53. Dynamic seal outer nut; 54. First housing; 55. Second housing; 56. Third housing; 57. Fourth housing; 58. Fifth housing; 59. Indium metal. Detailed implementation manners

[0049] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0050] Embodiment 1

[0051] Refer to Figure 1 、 Figure 2, a through-hole cold-wall vector magnet structure, comprising a vector magnet, an upper plug 6, and a lower plug 11. The axes of the vector magnet, the upper plug 6, and the lower plug 11 are coaxial. A magnet through-hole 4 is provided in the vector magnet, and this magnet through-hole 4 penetrates through the top and bottom of the vector magnet. One end of the upper plug 6 is vertically inserted into the magnet through-hole 4 from the top of the magnet through-hole 4, and the other end of the upper plug 6 is fixedly connected to the top of the vector magnet, thereby sealing the top opening of the magnet through-hole 4. One end of the lower plug 11 is vertically inserted into the magnet through-hole 4 from the bottom of the magnet through-hole 4, and the other end of the lower plug 11 is fixedly connected to the bottom of the vector magnet, thereby sealing the bottom opening of the magnet through-hole 4.

[0052] The vector magnet includes a multi-layer shell structure that is sequentially spaced and coaxially sleeved from the outside to the inside. In this embodiment, five shells are taken as an example, namely the first shell 54, the second shell 55, the third shell 56, the fourth shell 57, and the fifth shell 58. Of course, it can also be six, seven, or other numbers of shells. The magnet through-hole 4 is provided at the center of the vector magnet. The spaced and coaxially sleeved in this embodiment means that the adjacent shells are sleeved and connected, and there is a gap between the adjacent shells. The first shell 54, the second shell 55, the third shell 56, the fourth shell 57, and the fifth shell 58 are five cylinders with increasing diameters. The axes of the five cylinders are coaxial and are sleeved together. The magnet through-hole 4 penetrates through the centers of the first shell 54, the second shell 55, the third shell 56, the fourth shell 57, and the fifth shell 58. Among them, an outer vacuum interlayer 1 is formed between the first shell 54 and the second shell 55. Refer to Figure 3 , the outer vacuum interlayer 1 is contained inside the first shell. There is a vacuum interlayer extraction port 14 on one side of the top of the first shell 54. The outer vacuum interlayer 1 is connected to a pump group through the vacuum interlayer extraction port 14 to provide a vacuum environment better than 10 -5 Pa, providing an adiabatic vacuum condition for the cryogenic system.

[0053] A liquid nitrogen interlayer 2 is formed between the second shell 55 and the third shell 56. The tops of the second shell 55 and the third shell 56 are coplanar, and the bottoms of the second shell 55 and the third shell 56 are coplanar. A first vacuum interlayer is formed between the third shell 56 and the fourth shell 57. The fourth shell 57 and the first vacuum interlayer together form a cryogenic cold shield 5. A second vacuum interlayer is formed between the fourth shell 57 and the fifth shell 58. A liquid helium cavity 3 is formed between the fifth shell 58 and the outer wall of the magnet through-hole 4. Liquid nitrogen is filled in the liquid nitrogen interlayer 2 to form a liquid nitrogen cold shield, thereby adiabatically containing the first vacuum interlayer, the second vacuum interlayer, and the liquid helium cavity 3 inside it. Activated carbon adsorbents are provided inside the outer vacuum interlayer 1 and the second vacuum interlayer.

[0054] It should be noted that the outer vacuum interlayer 1, the first vacuum interlayer, and the second vacuum interlayer can also be interconnected through pipelines or by opening through-holes in the shells.

[0055] Refer to Figure 1 and Figure 3 , a thin-walled stainless steel pipe is connected to the second housing 55. One end of the thin-walled stainless steel pipe is fixedly connected to the first housing 54 and extends to the inner wall of the top of the first housing 54, thereby providing fixation for the second housing 55. The other end is communicated with the liquid nitrogen interlayer 2, and the connection port with the liquid nitrogen interlayer 2 is located in the area between the tops of the second housing 55 and the third housing 56. The thin-walled stainless steel pipe forms the structural support of the liquid nitrogen interlayer 2. One end of the thin-walled stainless steel pipe extending out of the first housing 54 forms a liquid nitrogen infusion port 21. A liquid nitrogen safety valve 18 is also connected to the thin-walled stainless steel pipe. The thin-walled stainless steel pipe simultaneously serves as the input pipeline for liquid nitrogen, and liquid nitrogen can be poured into the thin-walled stainless steel pipe and the liquid nitrogen interlayer 2 through the liquid nitrogen infusion port 21. The maximum volume of the liquid nitrogen interlayer 2 is 150L, and the outer surface of the liquid nitrogen interlayer 2 is alternately covered with multiple layers of aluminum films and vacuum insulating fiber papers.

[0056] Refer to Figure 2 and Figure 3 , the liquid helium chamber 3 provides a low-temperature environment for the operation of the entire vector magnet and the device test. The center of the vector magnet is set at a position 700 mm from the bottom surface of the magnet through the center of the magnet through-hole 4. The liquid helium chamber 3 is connected with a liquid helium pipeline (not shown in the figure). One end of the liquid helium pipeline extending out of the top of the first housing 54 forms a liquid helium infusion port 23. A liquid helium level gauge 22 is also provided on the liquid helium pipeline. Liquid helium can be poured into the liquid helium chamber 3 through the liquid helium infusion port 23. The maximum volume of the liquid helium chamber 3 is 230L, and the liquid helium can be stored for more than 10 days. This is because the outer vacuum interlayer 1 has good heat insulation effect, and liquid nitrogen is needed to pre-cool the vector magnet. A helium gas recovery pipeline (not shown in the figure) is fixedly connected to the liquid helium chamber 3. One end of the helium gas recovery pipeline extends out of the interface on the outside of the first housing 54 to form a helium gas recovery port 25, and the other end is communicated with the liquid helium chamber 3. The helium gas discharged from the liquid helium chamber 3 through the helium gas recovery pipeline can be recovered through the helium gas recovery port 25. The helium gas recovery port 25 is connected to a vacuum pump group and a nitrogen gas cylinder, and the liquid helium chamber 3 is repeatedly cleaned with dry nitrogen. Due to the huge heat load of the cryogenic strong magnetic field terahertz near-field measurement system, three symmetrically distributed liquid helium safety valves 24 are provided in this embodiment. The liquid helium safety valves 24 are communicated with the liquid helium chamber 3 to provide quench protection.

[0057] The vector magnet is also provided with a Z-axis magnetic field electrode lead wire 13, a 24-hole lead wire interface 15, a 2-hole lead wire interface 16, an X-axis magnetic field electrode lead wire 19, and a ground point 20. The top of the first housing 54 is fixedly connected with the 24-hole lead wire interface 15, the 2-hole lead wire interface 16, the X-axis magnetic field electrode lead wire 19, and the ground point 20. The 24-hole lead wire interface 15 and the 2-hole lead wire interface 16 are used to connect sensor devices to monitor parameters such as the liquid helium cavity, the liquid nitrogen interlayer, and the coil temperature. One end of the Z-axis magnetic field electrode lead wire 13 and the X-axis magnetic field electrode lead wire 19 is electrically connected to the controller, and the other end is connected to the coil inside the vector magnet. The controller inputs current into the coil inside the vector magnet through the Z-axis magnetic field electrode lead wire 13 and the X-axis magnetic field electrode lead wire 19 to generate a magnetic field. The ground point 20 is a screw hole. A copper wire is led from the outside and pressed tightly on the top of the first housing 54 of the vector magnet with a screw, so as to conduct the static charge on the vector magnet to the ground.

[0058] The cryogenic cold shield 5 absorbs the cold provided by the cold helium gas after the liquid helium volatilizes in the helium recovery pipeline. The second housing 55 forms a 77K cold shield, which can significantly reduce the heat leakage between the 77K cold shield and the liquid helium cavity 3. The helium recovery pipeline is a thin-walled stainless steel neck tube, which provides structural support for the liquid helium cavity 3.

[0059] See Figure 4 , at the lower end of the magnet through hole 4, there are three sections of bellows 31, which are respectively called bellows one 311, bellows two 312, and bellows three 313. The bellows one 311, bellows two 312, and bellows three 313 are fixedly connected in sequence. The adjacent bellows 31 are sealed with a rubber O-ring 30. The bellows one 311 and bellows two 312 are used to isolate the magnet through hole 4 from the external outer vacuum interlayer 1. The bellows three 313 is used to isolate the magnet through hole 4, the external outer vacuum interlayer 1, and the external environment. The connection between the end of the bellows one 311 facing away from the bellows two 312 and the magnet through hole 4 is sealed with indium metal 59. There is a rubber O-ring 30 at the connection between the bellows three 313 and the bottom surface of the vector magnet, that is, the bottom of the first housing 54.

[0060] The middle part of the magnet through hole 4 is in direct contact with the liquid helium cavity 3 to provide a low-temperature environment for testing.

[0061] The three sections of bellows 31 serve as a heat transfer channel between the room temperature and the low-temperature region. The structure of the bellows 31 significantly extends the solid heat conduction length, reduces the temperature gradient, and at the same time reduces the heat exchange interface area, thereby reducing the heat leakage of the sample cavity.

[0062] See Figure 1 , Figure 12, in this embodiment, the inner diameter of the magnet through-hole 4 is 130 mm. This large-diameter design facilitates the integration of cryogenic inserts and is the world's first large-diameter through-hole cold-wall vector magnet structure. The magnet center 48 of the vector magnet is located at the center of the magnet coil of the vector magnet. In this embodiment, the magnet center 48 is the central position in the coil where the magnetic field is the largest, most concentrated, and has the best magnetic field uniformity for electromagnetic induction. The designed distance between the magnet center 48 of the vector magnet and the vector magnet surface is 1.7 m. For this part of the inner wall of the magnet through-hole 4, only a traditional thin-walled neck tube structure is required, which greatly reduces heat leakage while ensuring structural stability.

[0063] Refer to Figure 5 , the upper plug-in 6 includes a magnet through-hole upper cover plate 29, at least one bowl-shaped radiation shield 7, and a liquid helium dewar 8 that are fixedly connected in sequence. After the upper plug-in 6 is vertically inserted into the magnet through-hole 4 as a whole, the magnet through-hole upper cover plate 29 is fixedly connected to the top plane of the vector magnet, that is, the top of the first housing 54, so as to seal the top opening of the magnet through-hole 4. In this embodiment, five bowl-shaped radiation shields 7 are taken as an example, but the number is not limited to this, and it can also be one, two, three, four, etc. The five bowl-shaped radiation shields 7 are arranged alternately along the axis of the upper plug-in 6, extending from the room temperature end to the liquid helium temperature end, that is, from the magnet through-hole upper cover plate 29 end of the upper plug-in 6 to the end of the upper plug-in 6 where the liquid helium dewar 8 is provided. The advantage of the axial alternating arrangement is that it can block the exchange gas in the magnet through-hole 4 and effectively reduce the heat leakage caused by convective conduction. The bowl-shaped radiation shield 7 includes a thin circular sheet and a circular tube with the same diameter as the circular sheet. The thin circular sheet and the circular tube are welded and fixed to form a bowl-shaped structure, and the surfaces of the circular sheet and the circular tube are polished.

[0064] Refer to Figure 6 , Figure 7 , the lower plug-in 11 includes a sample cavity 9, a bowl-shaped radiation shield 7, a magnet through-hole vacuum pumping port 10, a terahertz optical path pipeline 12, a femtosecond optical path pipeline 26, a sample cavity vacuum pipeline 27, a reserved optical pipeline 47, and a magnet through-hole lower cover plate 28. The magnet through-hole 4 can be evacuated and filled with exchange gas through the magnet through-hole vacuum pumping port 10. One end of the sample cavity 9 facing away from the upper plug-in 6 is fixedly connected to one end of the bowl-shaped radiation shield 7, and the other end of the bowl-shaped radiation shield 7 is connected to a pipeline housing. Inside the pipeline housing, there are a magnet through-hole vacuum pipeline, a terahertz optical path pipeline 12, a femtosecond optical path pipeline 26, and a sample cavity vacuum pipeline 27. The outer wall of the pipeline housing is fixedly connected to the magnet through-hole lower cover plate 28. Refer to Figure 1, after the lower insert 11 is vertically inserted into the magnet through-hole 4 from the bottom of the magnet through-hole 4, it is fixedly connected to the bottom of the vector magnet, i.e., the bottom of the first housing 54, through the lower cover plate 28 of the magnet through-hole, thereby sealing the bottom opening of the magnet through-hole 4. The bottom of the pipeline housing is fixedly connected with a window assembly 46, and all optical pipeline ports, vacuum pumping ports, and electrode access ports are welded to its end face, and it can be replaced as a whole to change the orientation of the bottom pipeline ports; in this embodiment, the terahertz optical path pipeline 12, the femtosecond optical path pipeline 26, the sample chamber vacuum pipeline 27, and the reserved optical pipeline 47 are fixed on the window assembly 46.

[0065] The sample chamber vacuum pipeline 27 is used to introduce gas and connect electrodes. One end of the terahertz optical path pipeline 12 is coaxially assembled with a TPX window (not shown in the figure), and one end of the femtosecond optical path pipeline 26 is coaxially assembled with a quartz window (not shown in the figure). The inner walls of the magnet through-hole vacuum pipeline (not shown in the figure), the terahertz optical path pipeline 12, the femtosecond optical path pipeline 26, and the sample chamber vacuum pipeline 27 are polished for optical transmission. In this embodiment, the terahertz optical path pipeline 12 is connected to a terahertz generating device, which is located 1 cm below the TPX window. Using a large-area gallium arsenide antenna, it is excited by a femtosecond laser with a pulse width of 35 fs to generate terahertz laser, which directly passes through the TPX window and enters the terahertz optical path pipeline 12.

[0066] After the lower insert 11 is fixed to the lower cover plate 28 of the magnet through-hole, the lower insert 11 does not completely extend into the magnet through-hole 4. This is to extend the distance from the low-temperature end to room temperature and also to protect optical windows such as the TPX window and the quartz window from water condensation.

[0067] During the assembly of the upper and lower inserts and the vector magnet, the displacement of the vector magnet itself or the entire cryogenic strong magnetic field terahertz near-field measurement system can be achieved through the suspension point 17 (not shown in the figure), so that the upper and lower inserts can be smoothly inserted into the central aperture of the magnet, avoiding damage and improper metal-to-metal contact.

[0068] It should be noted that the innovative points of this embodiment compared with the prior art are the structural design of the through-hole cold-wall vector magnet, the assembly work of the cryogenic insert and the vector magnet, the acquisition and maintenance of the cryogenic environment, the optical path transmission and the coupling of optics and scanning probe microscopy in the narrow environment of the vector magnet, and the internal shock absorption of the cryogenic strong magnetic field terahertz near-field measurement system.

[0069] This solution is the first in the world to achieve a liquid helium superconducting vector magnet with a maximum X-axis magnetic field strength of 5 T, where the maximum Z-axis magnetic field strength is 9 T. At the same time, it is also the first vector magnet in the world with the inner wall of the magnet through-hole 4 at liquid helium temperature, and the through-hole has a large aperture of 130 mm. These advantageous conditions are conducive to the construction of our near-field measurement system, but the acquisition and maintenance of its cryogenic environment are very difficult.

[0070] It should be noted that the cooling of large-aperture magnets consumes a large amount of liquid helium, and the subsequent heat load is huge. There is no successful precedent for the two-axis magnet coil with a maximum X-axis magnetic field strength of 5T and a maximum Z-axis magnetic field strength of 9T. The heat load during the cooling and stabilization of the coil adds difficulty to the maintenance of the low-temperature test environment. However, in order to perform optical coupling measurements, a series of pipelines themselves and the huge magnet aperture become inevitable sources of heat leakage.

[0071] Working principle: The outer vacuum interlayer 1 is connected to the pump group through the vacuum interlayer suction port 14, providing better than 10 -5 Pa interlayer vacuum environment; then, the helium recovery port 25 is connected to the vacuum pump group and the nitrogen cylinder, and the liquid helium cavity 3 is repeatedly cleaned with dry nitrogen; liquid nitrogen is poured into the liquid helium cavity 3 through the liquid helium infusion port 23 to pre-cool the vector magnet; when the measurement value of the Z-axis magnetic field electrode lead 13 shows that the coil reaches below 100K, dry nitrogen can be blown into the liquid helium cavity 3 through the helium recovery port 25 to force the pre-cooled liquid nitrogen to be discharged; in order to save time and liquid nitrogen cryogenic liquid, the discharged liquid nitrogen can be directly poured into the liquid nitrogen interlayer 2 through the liquid nitrogen infusion port 21; when the liquid nitrogen is completely discharged, the helium recovery port 25 is connected to the vacuum pump group and the helium cylinder, and the cavity is repeatedly cleaned with dry helium, Subsequently, liquid helium can be infused into the liquid helium chamber 3 through the liquid helium infusion port 23 until the characteristic value of the Z-axis magnetic field electrode lead 13 indicates that the liquid helium temperature has been reached, so that the temperature in the sample chamber 9 can reach below 10 Kelvin. The magnet through-hole vacuum port 10 is connected to the magnet through-hole 4, and dry helium is introduced into the magnet through-hole 4 through the magnet through-hole vacuum port 10 and the soft rubber tube. The volume of helium can be 3 cm of the length of the soft rubber tube. After the amount of helium discharged through the helium recovery port 25 is stabilized again, dry helium is introduced into the sample chamber 9 through the sample chamber vacuum pipe 27 and the soft rubber tube. The volume of helium can be 1 cm of the length of the soft rubber tube.

[0072] The temperature curve of the entire cooling process is recorded as Figure 16 As shown, when only liquid helium is perfused into the liquid nitrogen jacket, the central area of the magnet can reach 80K. After perfusing liquid helium and using exchange gas to transfer cold, the central area of the magnet can reach a low temperature of 10K.

[0073] Example 2

[0074] The difference between this embodiment and embodiment 1 is that a sample cavity internal unit is provided in the sample cavity 9;

[0075] See also Figure 8 , Figure 9, in this embodiment, a low-temperature strong magnetic field terahertz near-field measurement system is provided. This system includes the vector magnet structure in Embodiment 1 and the internal unit of the sample chamber. The internal unit of the sample chamber includes a sample holder and a light receiving tube 32, a light guiding tube 33, an aperture clamp 34, a scanning tunneling microscope 38, a lens body base 39, a lens body clamp 40, a spring clamp 41, a spring 42, and a lens body counterweight 43 fixed on the sample holder; the sample holder includes an upper cover plate 35 of the holder, support columns 36 of the holder, and a lower cover plate 37 of the holder. The upper cover plate 35 of the holder is fixedly connected to the lower cover plate 37 of the holder through four support columns 36 of the holder. One end of the support column 36 of the holder is fixedly connected to the upper cover plate 35 of the holder, and the other end is fixedly connected to the lower cover plate 37 of the holder. The spring clamp 41 is sleeved on the support column 36 of the holder. The spring clamp 41 can freely slide up and down along the axis of the support column 36, can also rotate with the axis of the support column 36 as the rotation axis, and the spring clamp 41 can be tightened and fixed. The spring clamp 41 is elastically connected to the lens body base 39 through the spring 42. In this embodiment, springs 42 are provided at the four corners of the lens body base 39. One end of the four springs 42 is fixedly connected to the spring clamp 41, and the other end is fixedly connected to the lens body base 39, jointly suspending the lens body base 39. A lens body counterweight 43 is detachably fixed at the bottom of the lens body base 39. The lens body counterweight 43 and the lens body base 39 are in threaded fit. Both the lens body counterweight 43 and the lens body base 39 are made of highly thermally conductive oxygen-free copper, and their own masses are also relatively high, which can reduce the resonance frequency of the system. Circular grooves are machined around the lens body base 39. A circular groove is provided at each of the four corners of the lens body base 39. The lens body base 39 does not come into contact with the four support columns 36. A circular groove is also provided in the area at the top of the light receiving tube 32, constituting a limit for the position of the tunneling area.

[0076] Refer to Figure 10 , Figure 11 , the lens body clamp 40 is used to limit the position of the scanning tunneling microscope 38. The lens body clamp 40 is fixedly connected to the lens body base 39 through bolts. The head of the bolt is clamped with the top plane of the lens body clamp 40, and the rod part of the bolt passes through the lens body clamp 40 and is threadedly connected to the lens body base 39. By rotating the bolt, the scanning tunneling microscope 38 can be pressed against the groove provided on the lens body base 39 that is adapted to the scanning tunneling microscope 38. The scanning tunneling microscope 38 can be the inertial piezoelectric motor device using multi-zone drive in the patent publication number CN103986365A. The multi-zone drive inertial piezoelectric motor not only serves as a thrust output device but also serves as a piezoelectric scanning head, and is made into the scanning tunneling microscope 38. A tungsten tip 45 and a sample are provided on the scanning tunneling microscope 38. When the two are close enough to generate a tunneling current, that is, they enter the tunneling area, it is required to adjust the spring clamp 41 to place the tunneling area 1 - 2 cm above the center of the upper end of the light receiving tube 32.

[0077] The light guide tube 33 is coaxially installed with the terahertz optical path tube 12, and the inner diameter of the light guide tube 33 is slightly larger than that of the terahertz optical path tube 12 to ensure no light loss. The light guide tube 33 is detachably and coaxially fixed to the light receiving tube 32 through a light hole clamp 34. The materials of the three are all stainless steel polished and gold-plated. The projection of the outlet of the light receiving tube 32 can cover or completely cover the area where the tungsten tip 45 is located. The light receiving tube 32 is integrally processed into an upper and a lower section. The lower section is a circular ring, and the upper section is a tapered circular ring. The opening area of the circular ring is the same as the lower opening area of the upper section, and the upper opening area of the tapered circular ring is much smaller than the lower opening area. There are multiple light receiving tubes 32, which respectively have different upper opening areas for replacement. There is an additional optical path tube and a similar light guiding and light receiving structure inside it. For example, one end of the femtosecond optical path tube 26 extending to the lower cover plate 37 of the bracket forms a femtosecond optical path hole 44.

[0078] Refer to Figure 10 , adjust the position and angle of the spring clamp 41 so that the tunneling area is placed 1 - 2 cm above the center of the light receiving tube 32, and, then at this time, it just partially surrounds the bracket support 36 but does not touch each other, constituting a limit to the position of the tunneling area. The tunneling area here refers to the area of the tip of the tungsten tip 45 - gap - sample surface after the distance between the tip of the tungsten tip 45 and the sample is within the distance at which the tunneling effect can occur.

[0079] Working principle:

[0080] The internal unit of the sample chamber is fixed in the sample chamber 9 according to the above - mentioned assembly orientation. The terahertz optical path tube 12 included in the lower plug - in 6 has a polished inner wall. Its room - temperature end is coaxially assembled with the TPX window. Our terahertz generating device is located 1 cm below the TPX window. Using a large - area gallium arsenide antenna, it is excited by a femtosecond laser with a pulse width of 35 fs to generate terahertz laser, which directly passes through the TPX window and enters the terahertz optical path tube 12, irradiating the tungsten tip 45 and the sample to ensure the highest transmission efficiency after assembly.

[0081] During the measurement, the tunneling area is just on the same horizontal plane as the indication line of the magnet center 48. Through the scanning tunneling microscope 38 device, terahertz near - field imaging is completed. The comparison before and after turning on and off the terahertz is recorded in Figure 17 , Figure 18 to prove the source of the tunneling current. During the image acquisition process, the vector magnet software can be connected to the controller for communication to apply a magnetic field, and the temperature of the sample area can be measured at temperature change points within 7 - 300 K with the help of a temperature controller.

[0082] Example 3

[0083] Refer to Figure 13 , the difference between this example and Example 2 is that an elbow 49 and a reserved optical pipeline 47 are added;

[0084] The material of the bent pipe 49 is stainless steel, which is gold-plated after polishing. One end of the bent pipe 49 is fixed in the femtosecond optical path hole 44, and the circular hole end face of the other end is aligned with the tungsten tip 45 and the sample area. The reserved optical pipeline 47 also provides an additional optional light source access. Such a bent pipe coupling method has been proven to have a certain transmission efficiency for optical transmission.

[0085] The liquid helium immersion cooling magnet coil has the advantages of good stability and large refrigeration power. The overall vibration of the system is small, which is convenient for providing a low-temperature test environment and is beneficial to the operation of the scanning tunneling microscope 38. However, in the early debugging stage of the system, the main focus is on whether the structure and design are reasonable and whether there are any fundamental problems. However, helium is a non-renewable strategic reserve resource, and there have always been restrictions on its extraction. The price of liquid helium is high, and the operating cost remains high. Pouring liquid nitrogen into the liquid helium cavity 3 through the liquid helium infusion port 23 can stabilize the temperature of the internal unit of the sample cavity below 80 Kelvin, verify the system performance at low temperature, and carry out a series of scientific research tests.

[0086] Example 4

[0087] The difference between this example and Example 1 is that a rotation insert test system including the vector magnet in Example 1 is provided; it includes a rotation insert and the vector magnet with the magnet through hole 4 opened in Example 1, but does not include the upper insert 6 and the lower insert 11 in Example 1;

[0088] Refer to Figure 14 、 Figure 15 , a plug-in sample cavity 50 is opened in the rotation insert. A rotation sample rod 51 is rotatably connected in the plug-in sample cavity 50. A gate valve 52 is provided in the plug-in sample cavity 50. The gate valve 52 can divide the plug-in sample cavity 50. The rotation insert is hermetically fixed to the rotation sample rod 51 through a dynamic seal outer nut 53. An upper sealing plate is provided on the outer shell inside the rotation insert, and the upper sealing plate is hermetically fixed to the top plane of the first housing 54 of the vector magnet.

[0089] The plug-in sample cavity 50 is kept vertical. Inside the magnet through hole 4, the rotation sample rod 51 is kept vertical. Inside the plug-in sample cavity 50, the magnet through hole 4 of the vector magnet, the plug-in sample cavity 50, and the rotation sample rod 51 are coaxially arranged.

[0090] The plug-in sample cavity 50 is coaxial with the magnet through-hole 4. The plug-in sample cavity 50 is inserted into the magnet through-hole 4 to seal the magnet through-hole 4. A testing device, such as a scanning magnetic force microscope, etc., is installed at the bottom of the rotating sample rod 51. Subsequently, the rotating sample rod 51 is coaxial with the plug-in sample cavity 50. The gate valve 52 is opened, and the rotating sample rod 51 is inserted into the plug-in sample cavity 50. External threads and an elastic fluororubber ring are preset on the rotating sample rod 51. By rotating the dynamic sealing external nut 53 to engage with the external threads, the fluororubber ring can be squeezed to fix the rotating sample rod 51 and maintain an independent vacuum state.

[0091] In this embodiment, the vector magnet is equipped with a two-axis magnet coil, which can apply magnetic fields to the Z-axis and the X-axis. (In this embodiment, the axial direction of the magnet through-hole 4 is the Z-axis, the X-axis is perpendicular to the Z-axis. According to the vector synthesis rule, the magnetic field direction can be rotated 360 degrees in the plane. In this example, dry helium gas can be introduced into the plug-in sample cavity 50 in advance. Subsequently, by loosening the dynamic sealing external nut 53, the rotating sample rod 51 can be rotated at any angle in the horizontal plane, that is, the x-axis magnetic field direction itself can be rotated at any angle in the horizontal plane perpendicular to the z-axis, thus realizing the full-space variability of the vector magnetic field direction. After obtaining a suitable magnetic field direction, the dynamic sealing external nut 53 needs to be tightened again. A micrometer protractor can be installed on the rotating sample rod 51 itself to stabilize the mechanical structure, continuously adjust the angle without a pole and accurately position.

[0092] After the test is completed, dry helium gas is introduced into the plug-in sample cavity 50, the dynamic sealing external nut 53 is loosened, and the rotating sample rod 51 is vertically pulled out of the plug-in sample cavity 50 until the rotating sample rod 51 is higher than the gate valve 52. The gate valve 52 needs to be closed, and then the sample and the testing device can be taken out.

[0093] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A through-hole cold-wall vector magnet structure, characterized in that It includes a vector magnet. The vector magnet is provided with a magnet through-hole penetrating its top and bottom. The vector magnet includes multiple layers of shells that are sequentially spaced apart and coaxially sleeved from the outside to the inside. The multiple layers of shells are all coaxial with the axis of the magnet through-hole. An outer vacuum interlayer, a liquid nitrogen interlayer, a first vacuum interlayer, and a second vacuum interlayer are sequentially formed between the multiple layers of shells. A liquid helium cavity is also provided between the second vacuum interlayer and the magnet through-hole. The outer vacuum interlayer, the liquid nitrogen interlayer, the first vacuum interlayer, the second vacuum interlayer, and the liquid helium cavity all cover the magnet through-hole and can form a cold wall on the inner wall of the magnet through-hole.

2. The through-hole cold-wall vector magnet structure according to claim 1, characterized in that, The multiple layers of shells include a first shell, a second shell, a third shell, a fourth shell, and a fifth shell that are sequentially sleeved. An outer vacuum interlayer is formed between the first shell and the second shell, a liquid nitrogen interlayer is formed between the second shell and the third shell, a first vacuum interlayer is formed between the third shell and the fourth shell, a second vacuum interlayer is formed between the fourth shell and the fifth shell, and a liquid helium cavity is formed between the fifth shell and the magnet through-hole.

3. The through-hole cold-wall vector magnet structure according to claim 1, characterized in that, The coil of the vector magnet is completely or partially immersed in the liquid helium in the liquid helium cavity. Part of the inner cavity wall of the liquid helium cavity forms the outer wall of the middle part of the magnet through-hole. A plurality of sections of bellows connected in sequence are provided on the inner wall of the lower part of the magnet through-hole along its axis direction. The bellows provided at the bottom of the magnet through-hole is hermetically fixed to the bottom of the magnet tube perforation. A seal is provided at the top of the magnet through-hole to seal the top of the magnet tube perforation.

4. The through-hole cold-wall vector magnet structure according to claim 1, characterized in that, It includes an upper plug-in and a lower plug-in. One end of the upper plug-in is vertically inserted into the magnet through-hole from the top of the magnet through-hole, and the other end of the upper plug-in is hermetically fixed to the top of the vector magnet. One end of the lower plug-in is vertically inserted into the magnet through-hole from the bottom of the magnet through-hole, and the other end of the lower plug-in is hermetically fixed to the bottom of the vector magnet. A liquid nitrogen dewar is provided at one end of the upper plug-in facing the lower plug-in. A section of bowl-shaped radiation shield is provided on both the upper plug-in and the lower plug-in.

5. A through-hole cold-wall vector magnet structure according to claim 4, characterized in that Each section of the bowl-shaped radiation shield includes multiple bowl-shaped radiation shields arranged alternately along the axial direction of the magnet through-hole. The bowl-shaped radiation shield includes a circular sheet and a circular tube with a diameter equal to that of the circular sheet that are fixedly connected. The circular sheet and the circular tube are welded and fixed to form a bowl-shaped structure.

6. A strong magnetic field terahertz near-field measurement system comprising the through-hole cold-wall vector magnet structure as described in claim 4 or 5, characterized in that, It also includes a sample cavity. The sample cavity is connected to one end of the lower plug-in facing the upper plug-in. The upper plug-in also includes an upper cover plate of the magnet through-hole. The upper cover plate of the magnet through-hole, the bowl-shaped radiation shield, and the liquid nitrogen dewar are sequentially fixedly connected along the axial direction of the magnet through-hole. The liquid helium dewar is located at the top of the sample cavity. A vacuum cavity is provided in the sample cavity. The lower plug-in includes a pipeline outer shell. The sample cavity, the bowl-shaped radiation shield, and the pipeline outer shell are sequentially fixedly connected along the axial direction of the magnet through-hole. A terahertz optical path pipeline, a femtosecond optical path pipeline, and a reserved optical pipeline are provided in the pipeline outer shell.

7. The terahertz near-field measurement system with strong magnetic field according to claim 6, characterized in that, A sample cavity test unit is provided in the sample cavity. The sample cavity test unit is located within the vacuum cavity. The sample cavity test unit includes a sample holder and a scanning tunneling microscope, a lens body base, a lens body clamp, a spring clamp, and a spring fixed on the sample holder. The sample holder includes an upper cover plate of the holder, support columns of the holder, and a lower cover plate of the holder. The upper cover plate of the holder is fixedly connected to the lower cover plate of the holder through multiple support columns of the holder. The spring clamp is sleeved on the support columns of the holder. The spring clamp can slide axially along the support columns of the holder and can also rotate with the axis of the support columns of the holder as the rotation axis. The spring clamp is elastically connected to the lens body base through a spring. A scanning tunneling microscope is connected to the lens body base. The pipeline of the terahertz optical path can be projected onto the tunneling area between the tungsten tip on the scanning tunneling microscope and the sample.

8. A strong magnetic field terahertz near-field measurement system according to claim 7, characterized in that, A light collecting tube, a light guiding tube, and a light hole clamp are fixed on the sample holder. The light guiding tube is detachably and coaxially fixed to the light collecting tube through the light hole clamp. The light collecting tube, the light guiding tube, and the light hole clamp are all polished and gold-plated. The projection of the outlet of the light collecting tube can cover or completely cover the tunneling area. A circular groove is formed circumferentially on the lens body base, and a gap is left between the lens body base and the support columns of the holder.

9. The terahertz near-field measurement system with strong magnetic field according to claim 7, characterized in that A bent pipe is also fixedly connected to the sample holder. One end of the femtosecond optical path pipeline extends to form a femtosecond optical path hole on the lower cover plate of the holder. One end of the femtosecond optical path hole is connected to the bent pipe, and the other end is arranged towards the tunneling area.

10. A strong magnetic field terahertz near-field measurement system comprising a through-hole cold-wall vector magnet structure according to any one of claims 1-3, characterized in that, It further includes a rotating insert. A plug-in sample cavity is provided inside the rotating insert. A rotating sample rod is rotatably connected inside the plug-in sample cavity. A gate valve is provided inside the plug-in sample cavity. The rotating insert is hermetically fixed to the rotating sample rod through a dynamic seal external nut. A testing device is installed at the bottom of the rotating sample rod. The testing device includes a scanning magnetic force microscope.

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