Gradient coil system and nuclear magnetic resonance equipment

Abstract

The embodiment of the utility model discloses a gradient coil system and nuclear magnetic resonance equipment, the gradient coil system is suitable for a Halbach magnet, and the gradient coil system comprises a gradient coil, a cooling sleeve and a circulating cooler; the gradient coil is used for generating a gradient magnetic field, and the direction of the gradient magnetic field is the same as that of a static magnetic field of the Halbach magnet; the cooling sleeve is of an annular hollow shell structure, a cooling cavity is formed in the hollow part of the cooling sleeve, and the cooling cavity is used for containing the gradient coil; the circulating cooler is communicated with the cooling cavity and used for feeding cooling liquid into the cooling cavity so as to soak and cool the gradient coil. The gradient coil system and the nuclear magnetic resonance equipment have the advantages of being high in cooling efficiency, compact in structure, high in safety coefficient and the like.

Description

Technical Field

[0001] The present application relates to the field of porous medium NMR analysis and detection instruments, and in particular to a gradient coil system and a nuclear magnetic resonance device. Background Art

[0002] Nondestructive measurement of one-dimensional spatial distribution of pore fluid is an important research object for porous media samples such as geotechnical and energy exploration. Nuclear magnetic resonance (NMR) technology has been rapidly developed and maturely applied in the field of energy and geotechnical porous media measurement due to its characteristics of rapidity, nondestructiveness, nontoxicity, and sensitivity only to hydrogen-containing pore fluids.

[0003] Spatial positioning nuclear magnetic resonance technology has been developed from the field of medical nuclear magnetic resonance imaging. The hardware condition for spatial positioning is the gradient coil, and the software condition is the pulse gradient imaging sequence and Fourier transform. With the promotion and cheapening of nuclear magnetic resonance imaging hardware and software technology, the technology has been introduced into the energy and geotechnical porous media fields for the measurement of one-dimensional spatial distribution of pore fluids, and for cutting-edge research such as water seepage and dynamic experimental process monitoring.

[0004] Energy, Geotechnical Porous Media One-dimensional Space Selected T2 Spectrum Measurement was first conducted using a derivative method of medical nuclear magnetic resonance imaging technology. The sequence diagram used is as follows: Figure 1 The response signal expression of the frequency-coded one-dimensional space layer selection T2 test is shown in formula (1):

[0005]

[0006] Where S(N·TE,t) is the sampling signal; TE is the echo interval, N is the echo number; z is the slice selection direction, G is the gradient value in the slice selection direction, t is the gradient encoding time; T2 is the relaxation time; γ is the H nuclear gyromagnetic ratio.

[0007] Perform inverse Fourier transform on each echo signal S(N·TE,t) to obtain echo signals at different positions. All echo signals are combined to obtain echo attenuation signals M(N·TE,z) at different positions, as shown in formula (2):

[0008]

[0009] The one-dimensional space selected layer T2 spectrum f(T2,z) can be obtained by decomposing M(N·TE,z) using T2 inversion algorithms such as BRD.

[0010] The frequency-encoded one-dimensional space selected T2 test method uses a mature pulse gradient space encoding method, which has the advantages of fast imaging speed and flexible parameter adjustment; the disadvantage is that pulse gradient encoding requires echo time TE. Therefore, the echo interval TE of this method is generally ≥2ms. The longer TE has little effect on the human body with long T2 relaxation time characteristics, but has a great impact on porous media with small and medium T2 relaxation time components, resulting in poor measurement accuracy (the core problem is the loss of signals of small and medium relaxation time components, especially components with T2<10ms). Therefore, the frequency-encoded one-dimensional space selected T2 test method is only suitable for loose porous medium samples with medium and long T2 relaxation time characteristics, and is not suitable for dense porous medium samples with small and medium T2 relaxation time characteristics.

[0011] In the field of nuclear magnetic resonance logging, Figure 2 As shown, due to the special positional relationship between the instrument and the test area "Inside-Outside", the main magnetic field of this type of NMR instrument itself has a gradient (that is, the main magnetic field is not a uniform field, but a gradient magnetic field).

[0012] The gradient field of the gradient type main magnetic field always exists, and the gradient value remains unchanged (that is, the gradient value is a fixed value). The gradient encoding is implemented by the limited bandwidth of the radio frequency pulse to select the layer. The calculation formula is shown in formula (3):

[0013]

[0014] Where △H is the thickness of the selected layer in the gradient direction, in m; γ is the H nuclear gyromagnetic ratio, which is equal to 42.58MHz / T; G constant is the gradient value of the gradient field, in T / m; P180 is the 180° RF pulse width of the CPMG sequence, in us.

[0015] The fixed gradient field and pulse gradient field gradient encoding methods are completely different, so the echo acquisition parameter TE is not limited by the gradient encoding parameter, and the minimum value allowed by the instrument hardware can be used to acquire the CPMG sequence echo signal. Since only the samples at the selected spatial position are excited by the radio frequency energy, the samples at other positions are in a non-resonant state (that is, they do not contribute to the nuclear magnetic resonance signal), the response signal expression of the constant gradient encoding one-dimensional space selected layer T2 test is shown in formula (4):

[0016]

[0017] Where S(N·TE,z) is the sampling signal; TE is the echo interval, N is the echo number; z is the spatial position in the layer selection direction. The constant gradient encoding method is selective excitation sampling. The one-dimensional space layer selection T2 spectrum f(T2,z) can be obtained by directly inverting the echo signal S(N·TE,z) at different positions.

[0018] From formula (3), we can see that in the layer thickness parameter △H of the constant gradient method, since γ is a constant, G constant It is a hardware-fixed value, and only the RF pulse width P180 can adjust the size of △H. Increasing P180 can reduce △H, but since nuclear magnetic RF hardware generally has the constraint of TE≥M*P180 (M is generally 2-6), increasing P180 also increases the minimum TE value of the system, which is not conducive to the NMR signal acquisition of porous medium samples. Therefore, the measurement parameter △H of the one-dimensional space selected layer T2 spectrum technology of the gradient main magnetic field is generally not adjustable, and is usually a fixed value. The fixed △H makes this method less adaptable to different samples.

[0019] In view of this, the industry has integrated the advantages of adjustable gradient value of nuclear magnetic imaging gradient coil and constant gradient field mode TE not constrained by gradient encoding, and launched a constant gradient mode one-dimensional space selected layer T2 spectrum testing technology based on pulse gradient hardware structure (that is, using gradient coil to generate gradient field), which has been successfully applied and promoted on the most commonly used flat magnet structure NMR instruments. [1-2] ([1] Wu Fei, Yang Peiqiang, Zhou Xiaolong, et al. One-dimensional space selected T2 spectrum testing method based on pulse gradient hardware structure [P]. Chinese Patent: CN202010347963.4, 2020.04.28. [2] Wu G, Tian H, Yan R, et al. Fast-nondestructive measurement of axial slice water content and water distribution with NMR SFG-MSCPMG sequence [J]. Magnetic Resonance Imaging, 2024, 105: 1-9.).

[0020] The core of the one-dimensional space selected layer T2 spectrum test technology in the constant gradient mode of the gradient coil structure is that the gradient coil generates a gradient magnetic field through the current, so the gradient value can be changed by the gradient current. Therefore, the layer thickness calculation formula of this method is shown in formula (5):

[0021]

[0022] In the formula, G eff is the gradient coil efficiency, in T / m / A; I exp It is the output current of the DC power supply for the gradient coil, in A.

[0023] Compared with formula (3), formula (5) only needs to adjust the gradient coil power supply current to adjust the layer thickness △H, without adjusting P180 (affecting the key acquisition parameter TE). Therefore, the one-dimensional space selected layer T2 spectrum testing technology in the constant gradient mode of the gradient coil structure has stronger adaptability, and the key parameter △H can be freely adjusted according to the measurement needs without affecting the acquisition parameter TE.

[0024] Although the one-dimensional space selected layer T2 spectrum testing technology of the constant gradient mode of the gradient coil structure combines the advantages of the two types of technologies, it is different from the pulse gradient working mode in that the acquisition period of the selected layer CPMG sequence echo signal lasts for a long time (a single acquisition generally lasts for hundreds of milliseconds to 2 seconds) and the gradient current is large, which leads to a large amount of ohmic heat generated during the signal acquisition period. Therefore, it is necessary to additionally configure a cooling module for the gradient coil. The heat generated during its operation is removed by a circulating cooler through the cooling plate attached to the gradient coil plate to protect the safe operation of the gradient coil.

[0025] In order to carry heat efficiently, the cooling plate needs to fit tightly to the gradient coil plate, and cooling plates are added on both sides of the gradient plate. Therefore, a larger static space inside the magnet is required to install the gradient coil plate and its cooling plate. When encountering a long T2 relaxation sample, the gradient duration is long, and the gradient coil continues to heat up due to insufficient cooling efficiency, the heating efficiency and cooling efficiency can be balanced by increasing the waiting time (during this period, the gradient coil can be unpowered and stop generating heat), but the additional waiting time TW will reduce the measurement efficiency. In view of this, for indoor NMR measurement instruments with small constraints on magnet size, dimensions and weight, the one-dimensional space selected layer T2 spectrum test technology of the gradient coil structure constant gradient mode generally selects a flat structure magnet with sufficient net space inside the magnet ([2] Wu G, Tian H, Yan R, et al. Fast-nondestructive measurement of axial slice water content and water distribution with NMR SFG-MSCPMG sequence[J]. Magnetic Resonance Imaging, 2024, 105: 1-9.).

[0026] Halbach array is a new type of permanent magnet structure proposed by K. Halbach of Lawrence Berkeley National Laboratory in the United States in 1979. Its characteristic is that the magnetization direction of the magnet is arranged in an orderly manner according to a specific rule, so that the magnetic field on one side of the magnet array is enhanced and the magnetic field on the other side is weakened. Figure 3 As shown, Figure 3 (a) is the theoretical model, Figure 3(b) is a discrete model. This magnetic field concentration effect can reduce the magnetic flux leakage around the magnet, thereby achieving the goal of obtaining a high magnetic field strength and magnetic field uniformity in a small volume magnet. It is currently the preferred magnet structure for miniaturization and lightweighting of NMR analyzer magnets.

[0027] With the maturity and commercialization of Halbach magnet technology, this type of magnet is becoming increasingly popular on mobile vehicle-mounted measurement platforms ([3] Gilgisov, Hou Xueli, Murzakayev. Application of mobile full-diameter core nuclear magnetic resonance measuring instrument in Russian ultra-heavy oil formation evaluation [J]. Well Logging Technology, 2017, 41(5): 506-511.). Figure 4 As shown, 10 is a cylindrical Halbach magnet, 20 is a core conveying device, 30 is an electronic circuit and control computer module, and 40 is a power module. The device fully utilizes the lightweight and miniaturized advantages of the Halbach magnet and does not use a classic flat-plate structure magnet (for samples of the same size, the weight of the flat-plate magnet is about 1.5 to 3 times that of the Halbach magnet).

[0028] Depend on Figure 3 As can be seen from the schematic diagram, the internal space of the Halbach magnet is compact. First, it needs to accommodate the RF coil for collecting signals. If a gradient coil system with a constant gradient mode is added, and if the contact cooling structure used in the flat magnet is adopted, three problems will be faced: (1) The circular gradient coil and the cooling plate have high requirements for processing and assembly processes in order to fully fit them. (2) If a double-sided cooling plate is used to improve the cooling efficiency, additional static space inside the magnet will need to be added, which will increase the size and weight of the magnet. (3) The cooling efficiency of the contact cooling structure is low. If the gradient heat generation is large, the measurement efficiency needs to be sacrificed to ensure the safety of the equipment.

[0029] In view of this, in response to the constant gradient layer selection test requirements of Halbach magnets, the industry proposed a solution using a Halbach magnet with a gradient main magnetic field ([4] Liu Huabing, Wang Zhengduo, Sun Zhe, et al. A magnet system structure and measurement method capable of forming a variable gradient static magnetic field [P]. Chinese patent: CN201710254930.3, 2017.04.25.), such as Figure 5 As shown, 1 is the Halbach outer ring magnet, 2 is the Halbach inner ring magnet, and 3 is the Halbach magnet adjustment part. However, the gradient direction of this solution is axial, which is not the sample length direction most commonly used in the industry, and the adjustable range of the gradient value is also small. Therefore, this solution has not been commercially applied and promoted.

[0030] In order to meet the most commonly used gradient field direction in the application field, the industry has proposed a Halbach magnet solution with a gradient field direction in the length direction ([5] Liu Huabing, Li Zeri, Chen Xi, et al. A nuclear magnetic resonance imaging device and method for rapid on-site detection [P]. Chinese patent: CN202211641074.4, 2022.12.19.), such as Figure 6 As shown in the figure, although this structure has the advantages of small size, simple structure, and no ohmic heat, as described in formula (3), the disadvantage of this structure is that the gradient value cannot be adjusted. Even if the gradient value is changed by replacing the outer magnetic ring (generating a gradient field), there are problems such as increased complexity and inability to continuously change the gradient value. Therefore, the key measurement parameter of this scheme, the layer thickness △H, cannot be adjusted. This feature limits the practicality and adaptability of the gradient main magnetic field Halbach magnet scheme.

[0031] In summary, in the field of NMR analysis and detection instruments, for the one-dimensional space selected layer T2 spectrum testing technology in the constant gradient mode of the gradient coil structure, the industry has not yet seen a gradient coil system for Halbach magnets with practical features such as continuously adjustable gradient value, high cooling efficiency, compact structure, and small space occupancy.

[0032] Therefore, there is an urgent need to provide a new gradient coil system suitable for the Halbach magnet to solve the above problems. Utility Model Content

[0033] The utility model aims to solve at least one of the technical problems existing in the prior art. To this end, the utility model provides a gradient coil system and a nuclear magnetic resonance device, which have the advantages of high cooling efficiency, compact structure, high safety factor and the like.

[0034] In a first aspect, the present application provides a gradient coil system, the gradient coil system being applicable to a Halbach magnet, the gradient coil system comprising a gradient coil, a cooling sleeve and a circulating cooler;

[0035] The gradient coil is used to generate a gradient magnetic field, and the direction of the gradient magnetic field is the same as the direction of the static magnetic field of the Halbach magnet;

[0036] The cooling sleeve is an annular hollow shell structure, and the hollow portion of the cooling sleeve forms a cooling chamber, and the cooling chamber is used to accommodate the gradient coil;

[0037] The circulating cooler is in communication with the cooling chamber, and is used for sending cooling liquid into the cooling chamber to soak and cool the gradient coil.

[0038] Furthermore, the gradient coil system further comprises a gradient coil power supply constant current source, and the gradient coil power supply constant current source is used to continuously provide direct current with a maximum duty cycle ≥ 70% to the gradient coil.

[0039] Furthermore, the cooling sleeve includes an outer cylinder and an inner cylinder, the outer cylinder and the inner cylinder are connected to form the hollow shell structure, the first end of the outer cylinder is provided with a first mounting portion, the second end of the outer cylinder is provided with a second mounting portion, the first end of the inner cylinder is provided with a third mounting portion, the second end of the inner cylinder is provided with a fourth mounting portion, the first mounting portion and the third mounting portion are connected and fixed, the second mounting portion and the fourth mounting portion are connected and fixed, a first sealing unit is provided between the first mounting portion and the third mounting portion, a second sealing unit is provided between the second mounting portion and the fourth mounting portion, and the first sealing unit and the second sealing unit are used to seal the cooling chamber.

[0040] Furthermore, a fixed frame is provided on the end surface of the cooling sleeve, and an introduction position for a gradient coil introduction line and a lead-out position for a gradient coil lead-out line are respectively provided on the cooling sleeve, and the gradient coil introduction line and the gradient coil lead-out line are respectively connected to the power supply line of the gradient coil power supply constant current source, and a first insulating pressure cap and a third sealing unit are sequentially provided along the introduction direction of the gradient coil introduction line, and a fourth sealing unit and a second insulating pressure cap are sequentially provided along the lead-out direction of the gradient coil lead-out line, and the first insulating pressure cap and the second insulating pressure cap are used to prevent the gradient coil introduction line and the gradient coil lead-out line from being electrically conductive with the fixed frame, and the third sealing unit and the fourth sealing unit are used to seal the lead-out position and the introduction position to seal the cooling chamber.

[0041] Furthermore, a copper block and an insulating pad are provided on the fixed frame, one side of the insulating pad is connected to the fixed frame, and the other side of the insulating pad is connected to the copper block. The copper block is fixed to the fixed frame through the insulating pad, and an insulating stopper is provided on the periphery of the copper block.

[0042] Furthermore, the gradient coil includes a skeleton and an insulated wire. A groove is provided on the outer wall of the skeleton. A first fixing layer is provided in the groove. A second fixing layer is provided on the surface of the insulated wire. The insulated wire is fixed in the groove through the first fixing layer and the second fixing layer.

[0043] Furthermore, the gradient coil system also includes a temperature monitoring module, which is used to obtain at least one of the Halbach magnet temperature, the outer cylinder temperature of the cooling sleeve, the liquid outlet temperature of the circulating cooler, and the liquid return temperature of the circulating cooler.

[0044] Furthermore, the gap of the cooling chamber is 1-1.5 mm.

[0045] In a second aspect, the present application further provides a nuclear magnetic resonance device, which includes a Halbach magnet and the gradient coil system in the first aspect.

[0046] One or more of the above embodiments of the present invention have at least one or more of the following beneficial effects:

[0047] The utility model provides a gradient coil system and nuclear magnetic resonance equipment, which give full play to the lightweight and miniaturized advantages of Halbach magnets, and propose a high-efficiency heat conduction and heat exchange immersion gradient coil system adapted to Halbach magnets. Combined with a circulating cooler, efficient cooling of the gradient coil in a constant gradient output working mode is achieved, thereby achieving thermal balance during the operation of the system. Specifically, the gradient coil is set in a cooling sleeve, and a coolant is passed into the cooling sleeve. The coolant can take away the heat generated by the gradient coil during operation, thereby achieving efficient cooling of the gradient coil in a constant gradient output working mode. In addition, the system has a compact structure and occupies little space. It has unique technical advantages and promotion value in the fields of indoor rock physics experiments in the field of porous media, vehicle-mounted mobile on-site core testing, and other fields.

[0048] Furthermore, insulating caps and sealing units are designed at the lead-in and lead-out positions of the gradient coil, respectively. The cooling sleeve can be better sealed by the extrusion sealing method of the insulating cap and the sealing ring to ensure the sealing effect of the cooling chamber. The lead-in and lead-out lines of the gradient coil are connected to the power supply line of the gradient coil power supply constant current source through a copper block, an insulating pad is added between the copper block and the frame, and an insulating block is arranged on the periphery of the copper block. The design of the copper block, the insulating pad and the insulating block can fully ensure the working safety of large current when the gradient coil is powered.

[0049] Furthermore, the present application utilizes temperature data to actively determine the real-time status of the system's thermal balance, and designs corresponding judgment logic to determine the system's working status in real time in the NMR acquisition control software, and actively stops measurement when the system's thermal balance is unbalanced, thereby avoiding safety risks and fully ensuring the safe operation of the system.

[0050] Additional aspects and advantages of the present invention will be given in part in the following description and in part will become apparent from the following description or will be learned through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] The disclosure of the present invention will become easier to understand with reference to the accompanying drawings. It is easy for those skilled in the art to understand that these drawings are only for illustrative purposes and are not intended to limit the scope of protection of the present invention. In addition, similar numbers in the drawings are used to represent similar components, among which:

[0052] Figure 1 It is a frequency-coded one-dimensional space layer selection T2 test sequence diagram provided by the background technology of this application;

[0053] Figure 2 It is a schematic cross-sectional view of an NMR logging tool provided in the background technology of this application;

[0054] Figure 3 It is the theoretical model and discrete model of the Halbach array provided in the background technology of this application;

[0055] Figure 4 This is a schematic diagram of the appearance and structure of a mobile full-diameter core nuclear magnetic resonance measuring instrument provided by the background technology of this application;

[0056] Figure 5 It is a schematic diagram of the Halbach magnet structure with the gradient field direction being axial provided in the background technology of this application;

[0057] Figure 6 It is a schematic diagram of the Halbach magnet structure provided by the background technology of this application, in which the gradient field direction is the length direction;

[0058] Figure 7 is a schematic diagram of the overall structure of the gradient coil system provided in an embodiment of the present application;

[0059] Figure 8 is a schematic cross-sectional structure diagram of a gradient coil system provided in an embodiment of the present application;

[0060] Fig. 9 is a partial structural schematic diagram of a gradient coil system provided in an embodiment of the present application;

[0061] Fig.10 is a physical picture of the gradient coil skeleton provided in the embodiment of the present application;

[0062] Fig.11 is a physical diagram of a gradient coil provided in an embodiment of the present application;

[0063] Fig.12 is a design diagram of a gradient coil winding skeleton provided in an embodiment of the present application;

[0064] Fig.13 is a physical picture of the gradient coil and cooling sleeve provided in the embodiment of the present application;

[0065] Fig.14is a perspective view of a gradient coil provided in an embodiment of the present application disposed in a cooling sleeve;

[0066] Fig.15 is a connection diagram of a gradient coil system provided in an embodiment of the present application;

[0067] Fig.16 is a three-dimensional diagram of the overall structure of a nuclear magnetic resonance device provided in an embodiment of the present application;

[0068] Fig.17 It is a front view of the overall structure of the nuclear magnetic resonance device provided in an embodiment of the present application;

[0069] Fig.18 It is a partial structural stereogram of a nuclear magnetic resonance device provided in an embodiment of the present application;

[0070] Fig.19 It is a partial structural front view of a nuclear magnetic resonance device provided in an embodiment of the present application;

[0071] Fig. 20 This is a physical picture of the mobile NMR core measuring instrument provided in the embodiment of the present application;

[0072] Fig.21 It is a graph showing changes in the outer cylinder temperature of the cooling sleeve, the liquid outlet pipe temperature of the circulating cooler, and the liquid return pipe temperature of the circulating cooler in the constant gradient working mode of the gradient coil provided in an embodiment of the present application;

[0073] Fig. 22 This is a graph showing changes in nuclear magnetic signal quantity in a constant gradient working mode of a gradient coil provided in an embodiment of the present application;

[0074] Fig.23 This is a graph showing changes in magnet resonance frequency in a gradient coil constant gradient working mode provided in an embodiment of the present application.

[0075] Description of Reference Numerals

[0076] Halbach outer ring magnet 1, Halbach inner ring magnet 2, Halbach magnet adjustment part 3, cylindrical Halbach magnet 10, core conveying device 20, electronic circuit and control computer module 30, power module 40, gradient coil 100, skeleton 110, insulated wire 120, groove 130, cooling sleeve 200, outer cylinder 210, first mounting part 211, first mounting groove 212, inner cylinder 220, third mounting part 221, second mounting groove 222, fixing frame 230, first insulating pressure cap 240, third sealing unit 25 0, fourth sealing unit 260, second insulating pressure cap 270, copper block 280, insulating pad 290, insulating block 291, coolant inlet 292, coolant outlet 293, circulating cooler 300, liquid outlet pipe 310 of circulating cooler, liquid return pipe 320 of circulating cooler, temperature monitoring module 400, first temperature measuring point 410, second temperature measuring point 420, third temperature measuring point 430, gradient coil power supply constant current source 500, power supply line 510, radio frequency coil 600, Halbach magnet 700, NMR spectrometer 800, NMR acquisition control computer 900. DETAILED DESCRIPTION

[0077] Some embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are only used to explain the technical principles of the present invention and are not intended to limit the protection scope of the present invention.

[0078] As shown in the background technology, the gradient field is the core condition for achieving spatial positioning measurement in the nuclear magnetic resonance method. The pulsed gradient field in the field of medical nuclear magnetic resonance imaging is not suitable for T2 short relaxation porous medium samples. The static gradient field technology in the field of nuclear magnetic resonance logging has problems such as fixed excitation parameters and unadjustable layer thickness. In recent years, the fusion technology based on pulsed gradient field hardware and using a constant gradient field working mode has emerged, giving full play to the advantages of the two technologies and has been successfully applied in NMR equipment with a flat magnet structure. Halbach magnets, which have the advantages of lightweight and miniaturization, are becoming increasingly mature and popular in mobile NMR equipment. Traditional cooling structures cannot meet application requirements in terms of space and cooling efficiency.

[0079] In this regard, the present application provides a gradient coil system and a nuclear magnetic resonance device, which have the advantages of compact structure, high cooling efficiency, good sealing, high insulation, and high safety factor. It realizes the high-efficiency, layer-thickness adjustable constant gradient layer selection T2 spectrum measurement function of the Halbach magnet NMR instrument, and has unique technical advantages and promotion value in the fields of indoor rock physics experiments in the porous medium field, vehicle-mounted mobile on-site core testing, and other fields.

[0080] The following are optional technical solutions for this application, but are not intended to limit the technical solutions provided in this application. Through the following optional technical solutions, the technical objectives and beneficial effects of this application can be better achieved and realized.

[0081] The present application provides a gradient coil system, which is suitable for a Halbach magnet, such as Figure 7-9 As shown, the gradient coil system includes a gradient coil 100 , a cooling sleeve 200 , a circulating cooler 300 and a temperature monitoring module 400 .

[0082] The gradient coil 100 is used to generate a gradient magnetic field. The gradient magnetic field direction of the gradient coil 100 is the same as the static magnetic field direction of the matched Halbach magnet 700. The gradient magnetic field direction of the gradient coil 100 is also the same as the length direction of the sample (i.e., the radial direction of the Halbach magnet 700). In addition, the gradient coil 100 provided in the present application has the advantage that the gradient value can be adjusted continuously and flexibly, which improves the adaptability and application effect of the one-dimensional space selected layer T2 test in the constant gradient mode of the gradient coil 100.

[0083] like Figure 10-11 As shown, the gradient coil 100 includes a skeleton 110 and an insulated wire 120. A groove 130 is provided on the outer wall of the skeleton 110, and the insulated wire 120 is fixed in the groove 130. In order to ensure the insulation and service life of the gradient coil 100, the skeleton 110 is made of a high-strength, high-insulation non-metallic material. Preferably, the skeleton 110 is made of glass fiber and processed by a high-precision four-axis CNC machine tool. The insulated wire 120 is an enameled wire with a shielding layer. Preferably, the insulated wire 120 is a copper wire with a shielding layer.

[0084] Since the insulated wire 120 is relatively long, in order to prevent the insulated wire 120 from popping out of the groove 130 due to winding stress, the present application provides a first fixing layer in the groove 130. The fixing effect of the first fixing layer on the insulated wire 120 can prevent the insulated wire 120 from popping out of the groove 130 due to winding stress. In addition, in order to prevent the insulated wire 120 from loosening due to the Lorentz force in the magnetic field when the gradient current is applied, a second fixing layer is provided on the surface of the insulated wire 120 after the winding of the insulated wire 120 is completed. Through the combined effect of the first fixing layer and the second fixing layer, the insulated wire 120 can be firmly fixed in the groove 130.

[0085] In a specific embodiment, the first fixing layer and the second fixing layer are epoxy resin glue. In specific implementation, glue is applied in the groove 130 to prevent the insulated wire 120 from popping out of the groove 130 due to winding stress. After the insulated wire 120 is wound, epoxy resin glue is evenly applied on the surface of the insulated wire 120 to tightly fix the insulated wire 120 in the groove 130, thereby preventing the insulated wire 120 from loosening due to the Lorentz force in the magnetic field when the gradient current is applied.

[0086] like Fig.12 As shown in FIG. 1 , the target field method is generally used in the design of gradient coil winding to determine key parameters such as the main magnetic field direction, the gradient field direction, the effective inner diameter of the gradient coil 100 (the reserved installation space for the RF coil 600), the volume of the gradient linear region and the linearity, and to simulate different winding models. Under the principle of effectively balancing the gradient efficiency, the cross-sectional area of ​​the winding copper wire corresponding to the maximum current, the ohmic thermal efficiency, the winding spacing and other factors, a reasonable gradient current distribution is selected, and then the design scheme of the gradient coil skeleton is determined.

[0087] In a specific embodiment, the gradient efficiency of the gradient coil 100 is 0.1Gs / cm / A, the copper wire diameter is 2.5mm, the internal resistance is 0.5Ω, the maximum carrying current is 100A, the gradient linear region volume is diameter 110mm*length 100mm, the linearity is 2.5%, the gradient direction is the length direction of the sample (the length direction of the sample in this application is the X direction), and the main magnetic field is the Z direction.

[0088] After the outer dimensions of the frame 110 of the gradient coil 100 are finalized, the cooling sleeve 200 of the gradient coil 100 is designed according to the reserved effective inner diameter of the gradient coil 100 and an immersion cooling structure is adopted. The function of the cooling sleeve 200 is to provide sealing and insulation conditions for cooling the gradient coil 100, such as Figure 7 , 8 , 13 and 14, the cooling sleeve 200 is an annular hollow shell structure, and the cooling sleeve 200 includes an outer cylinder 210 and an inner cylinder 220, and the outer cylinder 210 and the inner cylinder 220 are connected to form a hollow shell structure, and the hollow part of the cooling sleeve 200 forms a cooling chamber. The cooling chamber is used to accommodate the gradient coil 100, and a coolant inlet 292 and a coolant outlet 293 are provided on the cooling sleeve 200. The circulating cooler 300 is connected to the cooling chamber. Specifically, the circulating cooler 300 is connected to the coolant inlet 292 and the coolant outlet 293 respectively, and the circulating cooler 300 is used to send the coolant into the cooling chamber to soak and cool the gradient coil 100.

[0089] In a specific embodiment, the coolant inlet 292 and the coolant outlet 293 are respectively arranged on the two end surfaces of the cooling sleeve 200. The number of the coolant inlet 292 and the coolant outlet 293 can be multiple, and the multiple coolant inlets 292 and the coolant outlet 293 are distributed circumferentially on the two end surfaces of the cooling sleeve 200. Such a design can improve the cooling efficiency of the coolant on the gradient coil 100.

[0090] In the present application, the gradient coil 100 is disposed in a cooling sleeve 200, and a coolant is passed into the cooling sleeve 200. The coolant can take away the heat generated by the gradient coil 100 during operation, thereby achieving efficient cooling of the gradient coil 100 in a constant gradient output working mode, and further achieving thermal balance during the operation of the system.

[0091] The present application uses non-magnetic metal screws to lock the gradient coil 100 and the cooling sleeve 200 to prevent the position of the gradient coil 100 from changing the magnetic field and the gradient field direction. After the gradient coil 100 and the cooling sleeve 200 are assembled, an ohmmeter is used to measure the resistance between the copper wire in the gradient coil 100 and the outer shell of the cooling sleeve 200. If there is continuity, it means that the insulation position of the gradient coil 100 and the cooling sleeve 200 is damaged, and it is necessary to disassemble and check to eliminate the problem until the two are no longer conductive.

[0092] Further, the first end of the outer cylinder 210 is provided with a first mounting portion 211, the second end of the outer cylinder 210 is provided with a second mounting portion, the first end of the inner cylinder 220 is provided with a third mounting portion 221, the second end of the inner cylinder 220 is provided with a fourth mounting portion, the first mounting portion 211 and the third mounting portion 221 are connected and fixed, and the second mounting portion and the fourth mounting portion are connected and fixed. As a mere illustrative example, rather than a limitation on the scope of protection, the first mounting portion 211 can be a protruding block, and the third mounting portion 221 can be a slot. Similarly, the third mounting portion 221 can be a protruding block, and the fourth mounting portion can be a slot. The block is inserted into the slot to form a fixed connection between the outer cylinder 210 and the inner cylinder 220.

[0093] Furthermore, a first sealing unit is provided between the first mounting portion 211 and the third mounting portion 221, and a second sealing unit is provided between the second mounting portion and the fourth mounting portion, and the first sealing unit and the second sealing unit are used to seal the cooling chamber. Specifically, a first mounting groove 212 is provided on the first mounting portion 211, and the first sealing unit is placed in the first mounting groove 212, and a second mounting groove 222 is provided on the third mounting portion 221, and the second sealing unit is placed in the second mounting groove 222.

[0094] In the embodiment of the present application, the first sealing unit and the second sealing unit are preferably O-rings, and the number of the first mounting groove 212 and the second mounting groove 222 can be multiple, for example, the number of the first mounting groove 212 and the second mounting groove 222 can be two respectively, the number of the first sealing unit and the number of the first mounting groove 212 are equal and one-to-one corresponding, and the number of the second sealing unit and the number of the second mounting groove 222 are equal and one-to-one corresponding. Multiple O-rings are passed on both sides between the outer cylinder 210 and the inner cylinder 220 to squeeze and seal the cooling chamber by structure, so as to achieve the purpose of preventing the coolant in the cooling chamber from leaking.

[0095] The space of the cooling chamber in the cooling sleeve 200 needs to be reasonably selected. A small space in the cooling chamber will result in less coolant and reduce the cooling efficiency, while a large space in the cooling chamber will cause the outer diameter of the cooling sleeve 200 to expand and increase the size and weight of the magnet. After simulation and practice, the gap of the cooling chamber is 1-1.5mm. It should be noted here that the gap of the cooling chamber is the distance between the side wall of the outer cylinder 210 and the side wall of the inner cylinder 220 facing the cooling chamber respectively.

[0096] The cooling sleeve 200 is made of non-magnetic metal material, such as titanium alloy or stainless steel 316. The sleeve material will produce weak magnetism due to cutting action during machine tool processing. Because the cooling sleeve 200 is installed inside the magnet, its magnetism will affect the magnetic field uniformity of the main magnetic field. Therefore, the cooling sleeve 200 needs to be demagnetized after processing.

[0097] The gradient coil system also includes a gradient coil power supply constant current source 500. The function of the gradient coil power supply constant current source 500 is to provide a stable, high duty cycle direct current for the gradient coil 100. It is the power supply of the gradient coil 100. A commercial constant current source can be used or customized according to the gradient coil system. The core requirement is that the high duty cycle is continuously and stably output and can work continuously (that is, it requires good heat dissipation performance). Specifically, the required maximum power supply current value can be calculated according to the minimum selected layer thickness and gradient efficiency using formula (5). The maximum operating current of the gradient coil power supply constant current source 500 is ≥ 1.5 to 2 times the maximum current value; at 50% output amplitude, the maximum duration of the output current pulse of the gradient coil power supply constant current source 500 is not less than 3 seconds, and the maximum duty cycle of the gradient coil power supply constant current source 500 is ≥ 70%.

[0098] A fixed frame 230 is also provided on the end surface of the cooling sleeve 200, and the fixed frame 230 is used to fix the cooling sleeve 200 on the Halbach magnet 700. The cooling sleeve 200 is provided with an introduction position for the gradient coil introduction line and an extraction position for the gradient coil extraction line, respectively. The gradient coil introduction line and the gradient coil extraction line pass through the introduction position and the extraction position respectively and are connected to the power supply line 510 of the gradient coil power supply constant current source 500. In order to ensure the sealing effect of the cooling chamber, it is necessary to do a good job of sealing the introduction position and the extraction position. Specifically, a first insulating pressure cap 240 and a third sealing unit 250 are sequentially arranged along the introduction direction of the gradient coil introduction line, and a fourth sealing unit 260 and a second insulating pressure cap 270 are sequentially arranged along the extraction direction of the gradient coil extraction line. The first insulating cap 240 and the second insulating cap 270 are used to prevent the gradient coil lead-in wire and the gradient coil lead-out wire from being electrically connected to the fixed frame 230. Preferably, the first insulating cap 240 and the second insulating cap 270 are made of non-metallic hard plastic material, such as PEEK. The third sealing unit 250 and the fourth sealing unit 260 are used to seal the lead-out position and the lead-in position to ultimately achieve the purpose of sealing the cooling chamber. As a preferred embodiment, the third sealing unit 250 and the fourth sealing unit 260 are preferably sealing rings. The extrusion sealing method of the insulating cap and the sealing ring used in the present application can better ensure the sealing effect of the cooling chamber.

[0099] A copper block 280 is provided on the fixed frame 230, and the gradient coil lead-in wire, the gradient coil lead-out wire and the power supply wire 510 of the gradient coil power supply constant current source 500 are connected through the copper block 280. In order to prevent the copper block 280 from being electrically conductive with the fixed frame 230, an insulating pad 290 is also provided on the fixed frame 230. Specifically, one side of the insulating pad 290 is connected to the fixed frame 230, and the other side of the insulating pad 290 is connected to the copper block 280. The copper block 280 is fixed to the fixed frame 230 through the insulating pad 290. The locking screw hole of the copper block 280 and the installation position needs to be filled with an insulating non-metallic ring sleeve to avoid the risk of the locking screw connecting the copper block 280 to the entire machine housing. After the gradient coil lead-in wire, the gradient coil lead-out wire and the power supply wire 510 of the gradient coil power supply constant current source 500 are connected, the resistance between the copper block 280 and the metal housing of the magnet is measured with an ohmmeter. If the two are conductive, the cause needs to be checked until the two are not conductive.

[0100] Furthermore, an insulating block 291 is provided on the outer periphery of the copper block 280. The insulating block 291 can not only prevent the copper block 280 from contacting with external devices, but also prevent external impurities from sputtering onto the copper block 280, thereby achieving the purpose of protecting the copper block 280. In addition, the provision of the insulating block 291 can also prevent the operator from touching the copper block 280 and causing electric shock, thereby fully ensuring the working safety of the high current when the gradient coil 100 is powered.

[0101] The function of the circulating cooler 300 is to control the temperature of the coolant using the principle of electric refrigeration, and to continuously circulate the coolant using its own turbine pump to cool the gradient coil 100. A mature commercial circulating cooler can be used. When selecting, it is necessary to meet the following requirements: it has a constant temperature function, and the temperature control range is 5 to 40°C; the pump pressure of the circulating pump is adjustable; the cooling power is not less than 2 times the ohmic thermal efficiency under the conditions of the maximum current and the highest duty cycle of the gradient coil 100. Industrial fluorinated liquid is recommended as the coolant, and silicone oil or water is not recommended, because fluorinated liquid has no NMR signal and is not conductive. When the cooling sleeve 200 leaks and needs to be repaired, it will not contaminate the RF coil 600 and the magnet.

[0102] The temperature monitoring module 400 is used to obtain the temperature of the Halbach magnet 700, the temperature of the outer cylinder 210 of the cooling sleeve 200, the liquid outlet temperature of the circulating cooler, and the liquid return temperature of the circulating cooler, and upload the measured values ​​to the NMR acquisition control system in real time, so that the NMR acquisition control system can judge whether the measurement parameters are safe and whether the circulating cooling function works normally. It is a real-time monitoring module for judging the working state of the gradient coil system. Among them, the liquid outlet temperature of the circulating cooler can be obtained by the temperature of the liquid outlet pipe 310 of the circulating cooler, and the liquid return temperature of the circulating cooler can be obtained by the temperature of the liquid return pipe 320 of the circulating cooler. Whether the measurement parameters are safe can be evaluated by the temperature of the Halbach magnet 700 and the gradient coil 100. Since the gradient coil 100 is arranged in the cooling sleeve 200, the coolant in the cooling sleeve 200 cools down the gradient coil 100. When the measurement parameters are not appropriate, the gradient coil 100 will generate severe heat, resulting in the heating efficiency of the gradient coil 100 being greater than the cooling efficiency of the coolant, which will cause the outer cylinder temperature of the cooling sleeve 200 to increase. Therefore, it is possible to indirectly judge whether the gradient coil 100 is working normally through the outer cylinder temperature of the cooling sleeve 200.

[0103] The connection diagram of the gradient coil system designed in this application is as follows Fig.15As shown, the Halbach magnet 700 is connected and fixed to the cooling sleeve 200 as a whole, the cooling liquid inlet 292 and the cooling liquid outlet 293 on the cooling sleeve 200 are respectively connected to the liquid outlet pipe 310 and the liquid return pipe 320 of the circulating cooler, the gradient coil power supply constant current source 500 is connected to the lead-in wire and the lead-out wire of the gradient coil 100 through the power supply line 510, the gradient coil power supply constant current source 500 is connected to the NMR spectrometer 800, and the NMR spectrometer 800 is connected to the NMR acquisition A control computer 900 is connected, and its four temperature measuring points are respectively a first temperature measuring point 410, a second temperature measuring point 420, a third temperature measuring point 430, and a fourth temperature measuring point (not shown). The first temperature measuring point 410 corresponds to the temperature of the outer cylinder 210 of the cooling sleeve 200, the second temperature measuring point 420 corresponds to the temperature of the liquid outlet pipe 310 of the circulating cooler, the third temperature measuring point 430 corresponds to the temperature of the liquid return pipe 320 of the circulating cooler, and the fourth temperature measuring point (not shown) corresponds to the temperature of the Halbach magnet 700.

[0104] As a preferred implementation, the temperature monitoring module 400 is a PT100 temperature probe or an optical fiber temperature probe, with at least 4 detection channels, and the corresponding 4 temperature measurement points are the outer cylinder 210 of the cooling sleeve 200, the liquid outlet pipe 310 of the circulating cooler, the liquid return pipe 320 of the circulating cooler, and the Halbach magnet 700. The temperature monitoring module 400 does not need a digital display screen, and directly uploads the NMR data acquisition control computer via a communication line. The core function of the temperature monitoring module 400 is to monitor the thermal equilibrium state of the gradient coil system in real time. When a fault occurs and the gradient coil heats up, the NMR acquisition control software directly stops the acquisition to avoid the risk of high temperature of the equipment (such as the gradient coil melting, the magnet magnetic field demagnetization and other serious consequences), and is an active protection switch for the safe operation of the gradient coil system.

[0105] The present application also provides a nuclear magnetic resonance device, such as Figure 16-19 As shown, the apparatus includes a Halbach magnet 700, a radio frequency coil 600, an NMR spectrometer 800 and the above-mentioned gradient coil system.

[0106] The Halbach magnet 700 is used to generate the main magnetic field, the radio frequency coil 600 is used to transmit radio frequency pulses, and the NMR spectrometer 800 is used to control the radio frequency coil 600 to collect the nuclear magnetic resonance signal of the sample to be tested. The Halbach magnet 700, the radio frequency coil 600, the gradient coil 100, and the cooling sleeve 200 are all annular cylindrical structures, and the four are basically coaxial. The spatial positions of the four are: the radio frequency coil 600 is in the innermost layer, the gradient coil 100 is arranged in the cooling chamber of the cooling sleeve 200, the cooling sleeve 200 is in the outer layer of the radio frequency coil 600, and the Halbach magnet 700 is in the outer layer of the cooling sleeve 200.

[0107] The present application also provides a method for detecting the working state of the above-mentioned gradient coil system, the method comprising:

[0108] At least one of the temperature of the Halbach magnet 700, the temperature of the outer cylinder 210 of the cooling sleeve 200, the outlet temperature of the circulating cooler 300, and the return temperature of the circulating cooler 300 is obtained; based on at least one of the temperature of the Halbach magnet 700, the temperature of the outer cylinder 210 of the cooling sleeve 200, the outlet temperature of the circulating cooler 300, and the return temperature of the circulating cooler 300, it is determined by using preset conditions whether the gradient coil and / or the circulating cooler are operating normally.

[0109] It should be noted that the outlet liquid temperature of the circulating cooler can be obtained by the temperature of the outlet liquid pipe 310 of the circulating cooler, and the return liquid temperature of the circulating cooler can be obtained by the temperature of the return liquid pipe 320 of the circulating cooler. Whether the gradient coil 100 is working normally can be indirectly judged by the outer cylinder temperature of the cooling sleeve 200.

[0110] In the present application, the temperature of the Halbach magnet 700, the temperature of the outer cylinder 210 of the cooling sleeve 200, the temperature of the liquid outlet pipe 310 of the circulating cooler, and the temperature of the liquid return pipe 320 of the circulating cooler are measured by the temperature monitoring module 400, and the temperature is directly uploaded to the NMR acquisition control computer 900 through the communication line. Based on at least one of the above temperatures, the preset conditions are used to determine whether the gradient coil 100 and / or the circulating cooler are working properly and thus determine the working status of the system.

[0111] Specifically, the logic of using the preset conditions to determine whether the gradient coil and / or the circulating cooler 300 is working properly and then determining the working state of the system is as follows:

[0112] 1) When the temperature of the liquid outlet pipe 310 of the circulating cooler = the set temperature of the circulating cooler 300, the temperature of the liquid return pipe 320 of the circulating cooler ≥ the temperature of the liquid outlet pipe 310 of the circulating cooler, the temperature of the outer cylinder 210 of the cooling sleeve 200 ≤ the maximum safe operating temperature allowed by the gradient coil system, and the temperature of the Halbach magnet 700 = the set temperature of the Halbach magnet 700, it is determined that the working state of the gradient coil system is normal.

[0113] 2) When the temperature of the outer cylinder 210 of the cooling sleeve 200 is greater than the maximum safe working temperature allowed by the gradient coil system, and the temperature of the return pipe 320 of the circulating cooler is greater than or equal to the temperature of the outlet pipe 310 of the circulating cooler, it is determined that the heating efficiency of the gradient coil 100 is greater than the cooling efficiency of the gradient coil 100. At this time, the NMR acquisition control software needs to stop sampling, and can only re-measure when the temperature of the outer cylinder 210 of the cooling sleeve 200 is less than or equal to the maximum safe working temperature allowed by the gradient coil system, and the measurement parameters need to be adjusted to reduce the accumulation of heat (generally, the waiting time TW is increased).

[0114] 3) When the temperature of the liquid outlet pipe 310 of the circulating cooler is greater than the set temperature of the circulating cooler 300, it is determined that the refrigeration function of the circulating cooler 300 is abnormal, and it is necessary to stop measuring and repair the circulating cooler.

[0115] 4) When the temperature of the outer cylinder 210 of the cooling sleeve 200 is greater than the maximum safe operating temperature allowed by the gradient coil system, and the temperature of the return pipe 320 of the circulating cooler is equal to the temperature of the outlet pipe 310 of the circulating cooler, it is judged that the circulation pump of the circulating cooler 300 is abnormal, and it is necessary to stop measuring and repair the circulating cooler.

[0116] This application uses temperature data to actively determine the real-time status of the system's thermal balance, and designs corresponding judgment logic to determine the system's working status in real time in the NMR acquisition control software, and actively stops measurement when the system's thermal balance is unbalanced, avoiding safety risks and fully ensuring the safe operation of the system.

[0117] Using the above detailed design, a mobile NMR core measuring instrument equipped with the gradient coil system provided by the present application is manufactured, such as Fig.13 In order to test the cooling efficiency of the gradient coil system designed in this application, the continuous measurement acquisition parameters are designed as shown in Table 1, where the temperature real-time monitoring and NMR related data under parameter No. 6 are as follows: Figure 21-23 The temperature of the magnet in this system is set to 32°C, and the temperature of the circulating cooler is set to 25°C. Fig.21 As shown, the gradient coil system designed in this application works continuously and stably. The gradient coil 100 generates heat due to the constant gradient mode, and the temperature rises continuously at the beginning, but after thermal equilibrium, the system temperature reaches stability. The maximum temperature of the outer cylinder 210 of the cooling sleeve 200 of the gradient coil 100 is less than the set temperature of the magnet, which is within the safe working range. Fig. 22 As shown in the figure, during the continuous operation of the gradient coil system, the nuclear magnetic signal is stable, indicating that the gradient efficiency of the gradient coil and the stability of the constant current source of the power supply meet the design requirements. Fig.23As shown, during the continuous operation of the gradient coil system, the extreme difference of the magnet frequency is 664.9 Hz, and the absolute standard deviation is 234.83 Hz. Compared with the main frequency of 6.1513 MHz, the ratios are 0.011% and 0.004% respectively, which meets the design indicator of the ratio of frequency change to main frequency <1%.

[0118] All the measurement parameters in Table 1 were measured in practice, and the measured effect data of different acquisition parameters were summarized as shown in Table 2. As can be seen from Table 2, judging from the relative standard deviation of the nuclear magnetic signal, the relative standard deviation of the magnet resonance frequency, the maximum temperature of the gradient coil and other data, the gradient coil system designed in this application is stable during continuous measurement and has excellent performance, and realizes the one-dimensional space selected layer T2 spectrum continuous measurement function in the constant gradient mode of the gradient coil structure for the Halbach magnet.

[0119] Table 1 Continuous acquisition parameter design of gradient coil system

[0120]

[0121] Table 2 Summary of evaluation data under different acquisition parameters of gradient coil system

[0122]

[0123] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the utility model. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0124] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present utility model, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0125] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations of the present invention. Ordinary technicians in the field can change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A gradient coil system, characterized in that: The gradient coil system is suitable for a Halbach magnet, and the gradient coil system comprises a gradient coil, a cooling sleeve and a circulating cooler; The gradient coil is used to generate a gradient magnetic field, and the direction of the gradient magnetic field is the same as the direction of the static magnetic field of the Halbach magnet; The cooling sleeve is an annular hollow shell structure, and the hollow portion of the cooling sleeve forms a cooling chamber, and the cooling chamber is used to accommodate the gradient coil; The circulating cooler is in communication with the cooling chamber, and is used for sending cooling liquid into the cooling chamber to soak and cool the gradient coil.

2. The gradient coil system according to claim 1, characterized in that The gradient coil system further comprises a gradient coil power supply constant current source, and the gradient coil power supply constant current source is used to continuously provide direct current with a maximum duty cycle of ≥70% to the gradient coil.

3. The gradient coil system according to claim 2, characterized in that: The cooling sleeve includes an outer cylinder and an inner cylinder, the outer cylinder and the inner cylinder are connected to form the hollow shell structure, the first end of the outer cylinder is provided with a first mounting portion, the second end of the outer cylinder is provided with a second mounting portion, the first end of the inner cylinder is provided with a third mounting portion, the second end of the inner cylinder is provided with a fourth mounting portion, the first mounting portion and the third mounting portion are connected and fixed, the second mounting portion and the fourth mounting portion are connected and fixed, a first sealing unit is provided between the first mounting portion and the third mounting portion, a second sealing unit is provided between the second mounting portion and the fourth mounting portion, and the first sealing unit and the second sealing unit are used to seal the cooling chamber.

4. The gradient coil system according to claim 2, characterized in that A fixed frame is also arranged on the end surface of the cooling sleeve, and an introduction position of a gradient coil introduction line and a lead-out position of a gradient coil lead-out line are respectively opened on the cooling sleeve, and the gradient coil introduction line and the gradient coil lead-out line are respectively connected to the power supply line of the gradient coil power supply constant current source, and a first insulating pressure cap and a third sealing unit are sequentially arranged along the introduction direction of the gradient coil introduction line, and a fourth sealing unit and a second insulating pressure cap are sequentially arranged along the lead-out direction of the gradient coil lead-out line, and the first insulating pressure cap and the second insulating pressure cap are used to prevent the gradient coil introduction line and the gradient coil lead-out line from being electrically connected to the fixed frame, and the third sealing unit and the fourth sealing unit are used to seal the lead-out position and the introduction position to seal the cooling chamber.

5. The gradient coil system according to claim 4, characterized in that A copper block and an insulating pad are arranged on the fixed frame, one side of the insulating pad is connected to the fixed frame, and the other side of the insulating pad is connected to the copper block. The copper block is fixed to the fixed frame through the insulating pad, and an insulating stopper is arranged on the periphery of the copper block.

6. The gradient coil system according to claim 1, characterized in that: The gradient coil comprises a frame and an insulated wire. A groove is arranged on the outer wall of the frame. A first fixing layer is arranged in the groove. A second fixing layer is arranged on the surface of the insulated wire. The insulated wire is fixed in the groove through the first fixing layer and the second fixing layer.

7. The gradient coil system according to claim 3, characterized in that: The gradient coil system further comprises a temperature monitoring module, which is used to obtain at least one of the temperature of the Halbach magnet, the outer cylinder temperature of the cooling sleeve, the outlet temperature of the circulating cooler, and the return temperature of the circulating cooler.

8. The gradient coil system according to any one of claims 1 to 7, characterized in that: The gap of the cooling chamber is 1-1.5 mm.

9. A nuclear magnetic resonance device, characterized in that: The device comprises a Halbach magnet and a gradient coil system according to any one of claims 1 to 8.

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