Superconducting magnet device

Abstract

To provide a superconducting magnet device which is hardly affected by temperature changes in a device installation environment and can stably maintain the uniformity of a generated magnetic field.SOLUTION: A superconducting magnet device 1 includes: a helium tank 12 which is cylindrically arranged around a central axis CL so as to surround a sample region S including the central axis CL and has a low-temperature region T therein; a winding frame 51H which has a cylindrical shape around the central axis CL and is arranged in the low-temperature region T; a superconducting coil 51 which is composed of a superconducting wire wound around an outer periphery of the winding frame 51H and generates a magnetic field when excited; a shim coil 61 which is arranged in the sample region S and generates a magnetic field when excited; a room-temperature magnetic shim 62 which is arranged in the sample region S and enhances the uniformity of the magnetic field in the sample region S in cooperation with the shim coil 61; and a low-temperature magnetic shim 70 which is held by the winding frame 51H in the low-temperature region T.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a superconducting magnet device and an NMR device and an MRI device equipped with the same. [Background technology]

[0002] Conventionally, NMR (Nuclear Magnetic Resonance) devices capable of learning the bonding state between molecules have been widely used in the chemical, medical, agricultural, and industrial fields. Since a strong magnetic field is desirable for such NMR measurements, the NMR devices include superconducting magnet devices. The superconducting magnet devices use superconducting coils made of superconducting materials. For example, since metallic superconductors transition to a superconducting state at extremely low temperatures, superconducting coils using metallic superconductors are often kept continuously cold by immersing them in extremely low-temperature liquid helium stored in a container. In addition, a method of conductively cooling superconducting coils using a cryogenic refrigerator without using liquid helium has also been put to practical use.

[0003] Patent Document 1 discloses a technology in which a magnetic shim is attached to the inner wall of the wall on the measurement space side of a liquid helium container. Such a magnetic shim can improve the homogeneity of the magnetic field formed in the measurement space by the superconducting coil. Also, compared to a case in which the magnetic shim is placed exclusively in the measurement space at room temperature, it can prevent the magnetic field homogeneity in the measurement space from being disturbed by the influence of temperature changes in the room in which the device is installed. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 63-272335 Summary of the Invention [Problem to be solved by the invention]

[0005] In the technology described in Patent Document 1, the magnetic shim is exposed to liquid helium and is therefore less susceptible to the temperature changes. However, there is a problem in that it is difficult to adjust the relative position of the magnetic shim and the superconducting coil when manufacturing the device, and as a result, it is difficult to stably maintain the uniformity of the magnetic field in the measurement space.

[0006] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a superconducting magnet device that is less susceptible to temperature changes in the environment in which the device is installed and can stably maintain the uniformity of the magnetic field it generates. [Means for solving the problem]

[0007] A superconducting magnet device according to one aspect of the present invention comprises a cryogenic vessel having a low-temperature region inside and arranged in a cylindrical shape around a central axis so as to surround a sample region including the central axis, a reel having a cylindrical shape centered on the central axis and arranged in the low-temperature region, a superconducting coil made of superconducting wire wound around the outer periphery of the reel and generating a magnetic field when excited, a shim coil arranged in the sample region and generating a magnetic field when excited, a sample region magnetic shim arranged in the sample region and cooperating with the shim coil to increase the uniformity of the magnetic field in the sample region, and a low-temperature magnetic shim held by the reel in the low-temperature region and increasing the uniformity of the magnetic field in the sample region.

[0008] According to this configuration, the magnetic field in the sample region, which functions as a measurement region, can be made stable and uniform. Also, in addition to its original function of winding a superconducting wire, the reel can be given the function of holding a low-temperature magnetic shim. Therefore, the reel, which is the structural foundation of the superconducting magnet device, can hold the low-temperature magnetic shim in the low-temperature region, which is stable against temperature changes and electromagnetic forces. As a result, a dedicated holding member for holding the low-temperature magnetic shim is not required, and the superconducting magnet device can be configured with a simple structure, and the superconducting magnet device can be made more compact.

[0009] In the above configuration, it is preferable that the low-temperature magnetic shim is held by the reel so as to be sandwiched between the reel and the superconducting wire.

[0010] According to this configuration, the low-temperature magnetic shim is firmly sandwiched between the bobbin and the superconducting wire of the superconducting coil. Therefore, the position of the low-temperature magnetic shim is stably maintained in both the radial and axial directions of the bobbin even during cooling and coil excitation. In addition, because the low-temperature magnetic shim is held by the bobbin with high rigidity, it has high vibration isolation against external vibration transmission and is expected to have sufficient earthquake resistance.

[0011] In the above configuration, it is preferable that the bobbin has an engagement portion that engages with at least a portion of the low-temperature magnetic shim.

[0012] According to this configuration, when the low-temperature magnetic shim is held on the bobbin, the engaging portion can have a function of positioning the low-temperature magnetic shim and the bobbin. Also, since the centers of the superconducting coil and the low-temperature magnetic shim can be aligned with high precision, the low-temperature magnetic shim is less likely to cause magnetic errors.

[0013] In the above configuration, it is preferable that the engagement portion is a recess formed on the outer periphery of the bobbin and capable of receiving at least a portion of the low-temperature magnetic shim.

[0014] According to this configuration, the low-temperature magnetic shim is partially or entirely housed in the groove-shaped recess, so that the position of the low-temperature magnetic shim relative to the superconducting coil can be stably maintained. Also, because the low-temperature magnetic shim is fitted into the recess, the low-temperature magnetic shim can be prevented from moving due to the electromagnetic force between the low-temperature magnetic shim and the superconducting coil.

[0015] In the above configuration, it is preferable that at least a portion of the superconducting wire is made of an oxide superconducting wire.

[0016] According to this configuration, a stable magnetic field can be generated and maintained even if the temperature of the sample region changes.

[0017] In the above configuration, it is desirable for the low-temperature magnetic shim to include at least a first low-temperature magnetic shim that homogenizes the magnetic field component parallel to the central axis of the coil magnetic field formed in the sample region by the superconducting coil, and a second low-temperature magnetic shim that homogenizes the magnetic field component along the circumferential direction in a cross section perpendicular to the central axis of the coil magnetic field.

[0018] According to this configuration, a stable and uniform magnetic field can be formed in both the axial and radial directions in the sample region, thereby enabling the functions of the device in which the superconducting magnet device is installed to be exerted stably and accurately. Effect of the Invention

[0019] According to the present invention, a superconducting magnet device is provided which is less susceptible to temperature changes in the environment in which the device is installed and which is capable of stably maintaining the uniformity of the magnetic field it generates. [Brief description of the drawings]

[0020] [Figure 1] 1 is a schematic cross-sectional view of a superconducting magnet device according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic cross-sectional view showing an enlarged portion of a superconducting magnet device according to one embodiment of the present invention, illustrating the shapes of the magnetic fields that are formed. [Diagram 3] 2 is an enlarged cross-sectional view of a portion of a superconducting magnet apparatus according to an embodiment of the present invention. FIG. [Figure 4] FIG. 11 is an enlarged cross-sectional view of a portion of a superconducting magnet apparatus according to a modified embodiment of the present invention. [Diagram 5] 4 is a graph showing the transition of room temperature and the Z1 component of the magnetic field after excitation of a superconducting magnet device in an embodiment of the present invention. [Figure 6] 1 is a graph showing changes in room temperature and the Z1 component of the magnetic field after excitation in a superconducting magnet device in a comparative example compared to an embodiment of the present invention. [Figure 7]4 is a graph showing the magnitude of non-uniform components of each magnetic field component with and without a magnetic shim in a superconducting magnet device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] The present invention relates to a superconducting magnet device 1, which is a main component of an NMR (Nuclear Magnetic Resonance) device and generates a static magnetic field to be applied to a measured object. NMR devices are used to measure the bonding state between molecules in the chemical field, as well as in the medical and agricultural chemical fields and the industrial field. As an example, the NMR device includes a sample holder (also called a probe, including an NMR signal transmission and reception antenna), an NMR signal transmitter and receiver, an NMR signal analyzer, an automatic sample exchange device with sample temperature adjustment, an automatic coolant supply device, and the like, in addition to the superconducting magnet device 1. The present invention relates to a superconducting magnet device 1 equipped with a magnetic shim (magnetic piece, shim) for adjusting the magnetic field uniformity of the main magnetic field. Hereinafter, a superconducting magnet device 1 according to one embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view of the superconducting magnet device 1.

[0022] The superconducting magnet device 1 includes a vacuum vessel 10, a helium vessel 12 (low-temperature vessel), a nitrogen vessel 14, a radiation shield 16, a support structure 18, and a superconducting magnet 50. The inside of the vacuum vessel 10 is evacuated by a vacuum pump (not shown) or the like. In detail, after the inside of the vacuum vessel 10 is evacuated and cooled by a refrigerant, a predetermined vacuum valve is closed to seal off the vacuum, and the vacuum pump is disconnected for operation. As an example, the inner diameter of the vacuum vessel 10 based on the central axis CL is set to 54 mm, the outer diameter is set to 1000 mm, and the height of the vacuum vessel 10 is set to 1500 mm. The helium vessel 12 is sealed so that liquid helium He can be stored therein. The inside of the helium vessel 12 corresponds to the low-temperature region T in the present invention. That is, the helium vessel 12 is arranged cylindrically around the central axis CL so as to surround the sample region S including the central axis CL, and has the low-temperature region T inside.

[0023] The nitrogen tank 14 is sealed so that liquid nitrogen N2 can be stored therein. In Fig. 1, supply ports for supplying each liquid and outlets for vaporized gas of each liquid are simply illustrated at the top of the helium tank 12 and the nitrogen tank 14. In reality, these supply ports and outlets are provided with various valves. Examples of materials for the vacuum vessel 10, the helium tank 12, and the nitrogen tank 14 include aluminum and stainless steel.

[0024] The helium tank 12, the nitrogen tank 14, and the vacuum vessel 10 form a multi-layered three-dimensional annular shape and constitute a cryostat (a cryogenic thermostat) that surrounds and keeps the superconducting magnet 50 cool. In this embodiment, these structures are arranged coaxially around the central axis CL of the superconducting magnet 50. The superconducting magnet 50 generates a magnetic field whose direction is parallel to the central axis CL. In this embodiment, a sample P (object to be measured) (see FIG. 2) can be placed in a sample region S (measurement space) at room temperature located inside the superconducting magnet 50, more specifically, inside the vacuum vessel 10 (near the central axis CL). The sample region S is not limited to room temperature. For example, a temperature-variable sample holder may be inserted into the sample region S in the superconducting magnet to lower or raise the temperature of the sample region S.

[0025] The radiation shield 16 is a shield container cooled by the cold energy of helium gas in order to prevent the cold energy from escaping. The radiation shield 16 may be forcedly cooled by a refrigerator (not shown). Examples of materials for the radiation shield 16 include aluminum and copper.

[0026] The superconducting magnet 50 generates a strong magnetic field for measurement in the superconducting magnet device 1. For this purpose, the superconducting magnet 50 is cooled to an extremely low temperature state and maintained in a superconducting state. The superconducting magnet 50 is accommodated in the helium tank 12 so as to be immersed in the liquid helium in the helium tank 12. The helium tank 12 containing the superconducting magnet 50 in this manner is accommodated in a vacuum vessel 10 and is vacuum insulated. As a result, evaporation of the liquid helium, which has a boiling point of 4.2 K at atmospheric pressure, is suppressed.

[0027] In a superconducting magnet device 1 used in an NMR device or the like, it is required that the magnetic field uniformity in the measurement space is extremely high, that is, the magnetic flux density is uniform and has no gradient, and the spatial change of the magnetic flux density is extremely small. In order to realize such a high uniformity of the magnetic field, the coil shape and current density of the superconducting magnet that generates the main magnetic field are devised at the design stage. However, there are cases where the desired magnetic field uniformity cannot be obtained due to the fact that the manufacturing precision as designed cannot be obtained or the influence of ferromagnetic materials that cause disturbances, such as rebars in a reinforced concrete building, present at the installation site of the device. For this reason, superconducting magnet devices have conventionally been equipped with magnetic shims for magnetic field correction to correct the non-uniformity of the main magnetic field caused by the superconducting magnet and obtain a high magnetic field uniformity.

[0028] The inventors of the present invention first placed a magnetic shim on the inner wall of helium tank 12, placed a superconducting magnet inside helium tank 12, filled helium tank 12 with liquefied helium, and thoroughly evaluated the magnetic field uniformity. However, they discovered that it was difficult to reproduce the relative positions of the magnetic shim and the superconducting magnet as desired, and furthermore, that there was a limit to how much the magnetic field of the superconducting magnet can be corrected by a magnetic shim positioned outside it.

[0029] In order to solve the above problems, the structure of the superconducting magnet device 1 according to the present invention, which was conceived based on a new idea, will be described in further detail. Fig. 2 is a schematic cross-sectional view of an enlarged portion of the superconducting magnet device 1 according to this embodiment, illustrating the shapes of the magnetic fields that are formed. Note that the actual device has a shape obtained by rotating the structure on the right side of the central axis CL in Fig. 2 once around the central axis CL.

[0030] <Structure of superconducting magnet device> In the superconducting magnet device 1, a coil using an oxide superconductor and a coil using a low-temperature superconductor (main coil and correction coil) are concentrically arranged, and as a whole generate a desired magnetic field in the sample region S. In this case, since the magnetic field that the wire is subjected to becomes stronger the closer to the center of the coil (the closer to the central axis), it is necessary to use a material that can hold a current density according to that magnetic field. For example, an oxide superconductor is used at the highest magnetic field, and Nb 3 For example, oxide superconductors are used in magnetic fields of 18 T or more, and NbTi is used in magnetic fields of 9 T or more. 3 Sn is used for magnetic fields of 100 T or less, and NbTi is used for magnetic fields of 9 T or less. Generally, the cost of superconductors decreases in this order of the three, so it is desirable to use NbTi, which has a low unit price, in weak magnetic fields. Of course, oxide superconductors can be used in any magnetic field condition. Furthermore, oxide superconductors have the advantage that they can handle a high current density, making the overall size of the magnet smaller. In some cases, the same current value is passed through each of the above coils, while in other cases, currents of different values ​​are passed through them.

[0031] The superconducting magnet device 1 will be described in more detail with reference to Fig. 2. The above-mentioned superconducting magnet 50 has an oxide superconducting coil 51 and a metal-based superconducting coil 52. The superconducting magnet device 1 further includes a metal-based superconducting shim coil 55, a pair of upper and lower metal-based auxiliary coils 56, a support 60, a room-temperature shim coil 61, a room-temperature iron shim 62, and a low-temperature iron shim 70.

[0032] The oxide superconducting coil 51 has a cylindrical shape centered on a central axis CL. The oxide superconducting coil 51 is constructed by winding a superconducting wire made of an oxide superconductor around a predetermined winding frame. In order for the oxide superconducting coil 51 to function as a high-temperature superconducting coil, the oxide superconductor is a known bismuth-based oxide, Bi 2 Sr 2 CaCu 2 Ox(Bi-2212) and Bi 2 Sr 2 Ca 2 Cu3 Oy(Bi-2223), and furthermore, REBCO(REBa 2 Cu 3 Oy and Re are rare earth elements. When a predetermined driving current is applied to the oxide superconducting coil 51 and the oxide superconducting coil 51 is excited, the oxide superconducting coil 51 generates a magnetic field in the sample region S. The detailed structure of the oxide superconducting coil 51 will be described later together with the low-temperature iron shim 70.

[0033] The metal-based superconducting coil 52 is disposed so as to surround the oxide superconducting coil 51, and has a cylindrical shape centered on the central axis CL. The metal-based superconducting coil 52 is constructed by winding a metal-based superconducting wire around a predetermined winding frame. In order for the metal-based superconducting coil 52 to function as a low-temperature superconducting coil, the metal for the conductor wire is niobium tin (Nb 3 For example, a superconducting coil made of a material selected from the group consisting of niobium (Sn) and niobium titanium (NbTi) can be used. Like the oxide superconducting coil 51, the metal-based superconducting coil 52 also generates a magnetic field in the sample region S when excited. Note that, instead of the metal-based superconducting coil 52, a superconducting coil similar to the oxide superconducting coil 51 may be disposed at the position of the metal-based superconducting coil 52.

[0034] The metal-based superconducting shim coil 55 is disposed so as to surround the metal-based superconducting coil 52 from the radial outside, and has a cylindrical shape centered on the central axis CL. The metal-based superconducting shim coil 55 has a thinner layer shape compared to the metal-based superconducting coil 52, and is configured as a low-temperature superconducting coil by winding a metal-based superconducting wire around a predetermined bobbin. The metal-based superconducting shim coil 55 also generates a magnetic field in the sample region S when excited, similar to the oxide superconducting coil 51. As an example, the inner diameter of the metal-based superconducting shim coil 55 based on the central axis CL is set to 600 mm.

[0035] There are two types of shim coils: one that is wound like the main coil to adjust the axial component (axial shim coil), and one that is pre-wound in a rectangular shape and then attached in a saddle shape to the wound axial shim and fixed in place (radial shim coil).

[0036] A pair of upper and lower metal-based auxiliary coils 56 are disposed between the metal-based superconducting coil 52 and the metal-based superconducting shim coil 55 in the radial direction. Each metal-based auxiliary coil 56 has a cylindrical shape centered on the central axis CL, and is disposed opposite the upper end and the lower end of the metal-based superconducting coil 52, respectively. Each metal-based auxiliary coil 56 is also configured by winding a metal-based superconducting wire, for example, NbTi, around a predetermined winding frame, and generates a magnetic field in the sample region S when excited, similar to the oxide superconducting coil 51 (low-temperature superconducting coil). Note that, although a pair of upper and lower metal-based auxiliary coils 56 is shown in FIG. 2, the metal-based auxiliary coils 56 may be two pairs, or a configuration in which one coil is added to the pair of metal-based auxiliary coils 56, for example, a main coil made smaller, is placed at the center in the axial direction.

[0037] The support 60 is disposed in the sample region S. The support 60 has a cylindrical portion centered on the central axis CL and a disk portion connected to the lower end of the cylindrical portion. The outer periphery of the disk portion is fixed to the bottom surface of the vacuum vessel 10.

[0038] The room temperature shim coil 61 (shim coil) is a cylindrical coil provided on the support 60 so as to be placed in the sample region S. The room temperature shim coil 61 is also formed by winding a metal-based superconducting wire, for example, NbTi, around a predetermined spool, and generates a magnetic field in the sample region S when excited, similar to the oxide superconducting coil 51. As an example, in this embodiment, the room temperature shim coil 61 is made of a copper coil. Also, the inner diameter of the room temperature shim coil 61 based on the central axis CL is set to 44 mm. Note that the name "room temperature" of the room temperature shim coil 61 in this embodiment is used as an example for the purpose of explanation, and does not limit the present invention. The same applies to the names of other members hereinafter.

[0039] The room temperature iron shim 62 (sample region magnetic shim) is fixed to the support 60 so as to be disposed on the outer periphery side of the room temperature shim coil 61. The room temperature iron shim 62 may be attached to a separate winding frame (pipe) other than the one fixed to the support 60. The room temperature iron shim 62 is made of magnetic soft iron, but may be made of pure iron. In another embodiment, the room temperature iron shim 62 may be made of a metal mainly composed of a ferromagnetic material other than iron, such as nickel or cobalt. No current flows through the room temperature iron shim 62. As a magnetic material, the room temperature iron shim 62 has a function of correcting (adjusting) the magnetic field formed in the sample region S, and cooperates with the room temperature shim coil 61 to increase the uniformity of the magnetic field in the sample region S. Although one room temperature iron shim 62 is illustrated in FIG. 2, in reality, a plurality of room temperature iron shims 62 are arranged around the room temperature shim coil 61 according to the shape of the magnetic field. In particular, as described below, the room-temperature iron shim 62 has a function of correcting low-order radial components of the magnetic field formed in the sample region S. Although the main function of the room-temperature iron shim 62 is to correct low-order radial components, it may also correct axial components and higher-order radial components.

[0040] The low-temperature iron shim 70 is placed in a low-temperature region T formed by liquid helium. Particularly in this embodiment, the low-temperature iron shim 70 is held by the winding form 51H (FIG. 3) of the oxide superconducting coil 51. The low-temperature iron shim 70 is made of electromagnetic soft iron like the room-temperature iron shim 62, but may be a magnetic shim made of other materials. The low-temperature iron shim 70 has a function of particularly correcting the Z2 component of the magnetic field formed in the sample region S, as described below.

[0041] As shown in Fig. 2, the superconducting magnet 50 (oxide superconducting coil 51, metal-based superconducting coil 52), metal-based superconducting shim coil 55, metal-based auxiliary coil 56, room temperature shim coil 61 and low temperature iron shim 70 are arranged symmetrically (approximately symmetrically) above and below the horizontal reference line RL passing through the portion of the sample region S where the sample P is placed. These members are not limited to being arranged symmetrically. For example, if another current path is arranged above the coil and the influence of the magnetic field caused by it is large, the correction coils may be arranged asymmetrically to correct the magnetic field components generated by the current path.

[0042] <About the magnetic field of the superconducting magnet device> As mentioned above, in the superconducting magnet device 1, it is required that the magnetic field uniformity in the sample region S, which is the measurement space, is extremely high, that is, that the magnetic flux density is uniform without gradient and the spatial change in the magnetic flux density is extremely small. The inventor has newly discovered that the magnetic field in the superconducting magnet device 1 shown in Fig. 2 can be homogenized as follows. Note that the graphs shown at each M in Fig. 2 are schematic diagrams showing the magnitude and distribution of the magnetic field formed on the central axis CL.

[0043] A first magnetic field M1 is formed on the central axis CL by the superconducting magnet 50 provided in the low-temperature region T. Although the first magnetic field M1 is disposed substantially symmetrically above and below the reference line RL, a flat region is unlikely to be formed at the top of the first magnetic field M1. For this reason, a pair of upper and lower metallic auxiliary coils 56 are disposed outside the superconducting magnet 50 in the low-temperature region T, thereby forming a pair of second magnetic fields M2 on the central axis CL. It is expected that a third magnetic field M3 in which the top of the first magnetic field M1 is flattened will be formed by the magnetic fields of the pair of second magnetic fields M2 acting on the first magnetic field M1.

[0044] However, a shielding current is generated in the oxide superconducting coil 51 made of an oxide superconductor, and a fourth magnetic field M4 is formed as a shielding magnetic field. In this case, the effect of the pair of second magnetic fields M2 is weakened, and it becomes difficult to form a flat magnetic field such as the third magnetic field M3. Therefore, in this embodiment, a low-temperature iron shim 70 is disposed inside the oxide superconducting coil 51 to form a fifth magnetic field M5 that cancels out the fourth magnetic field M4, making it possible to form a uniform third magnetic field M3.

[0045] In particular, in this embodiment, the low-temperature iron shim 70 can greatly improve the uniformity of the magnetic field in the direction parallel to the central axis CL. Furthermore, the room-temperature iron shims 62 arranged around the room-temperature shim coil 61 are positioned so as to improve the uniformity of the magnetic field in the circumferential direction when viewed in a cross section perpendicular to the central axis CL. In other words, by arranging multiple room-temperature iron shims 62 around the room-temperature shim coil 61, the magnetic field distribution in the cross section perpendicular to the central axis CL can be made closer to a perfect circle.

[0046] Next, the functions of the low-temperature iron shim 70 and the room-temperature shim coil 61 will be further explained using a known functional expansion formula for the magnetic field. If the coordinate system in the sample region S is represented by r, θ, and φ, the functional expansion of the magnetic field can be expressed as the following formula 1. Note that r represents the distance from the center, and θ and φ represent the direction from the origin as angles.

[0047]

number

[0048] Equation 1 can be rewritten as Equation 2 below.

[0049]

number

[0050] Furthermore, the lower-order terms of Equation 2 can be expressed as in Equation 3 below. Note that in Equation 3 below and subsequent equations, terms with lower orders are omitted.

[0051]

number

[0052] If we rewrite Equation 3 into the X, Y, and Z coordinate system, it can be expressed as Equation 4 below.

[0053]

number

[0054] Equation 4 can be rewritten in symbolic form as Equation 5 below.

[0055]

number

[0056] The terms on the right side of Equation 5 are called, from the left, a constant term, a Z1 term, an X term, a Y term, a Z2 term, a ZX term, a ZY term, a C2 term, and an S2 term. In Equation 4, the fifth term on the right side corresponds to the axial component, and the terms X, Y, ZX, ZY, C2, and S2 in Equation 5 correspond to the radial components. The radial component can be said to be a term in Equation 5 that includes elements other than Z. Here, the axial component has a characteristic that it is easy to predict in advance by calculation how much it will generate. On the other hand, the radial component has a characteristic that it is relatively difficult to predict in advance by calculation, and its influence is difficult to understand unless the superconducting magnet device 1 is manufactured, immersed in the helium tank 12, and the magnetic field is actually measured. Based on the characteristics of the axial component and the radial component, the present inventors came up with the idea of ​​improving the magnetic field uniformity by using the room temperature iron shim 62 and the low temperature iron shim 70 described above.

[0057] That is, since the low-temperature iron shim 70 is disposed in the low-temperature region T, even if the room temperature of the sample region S changes, the relative position with respect to the oxide superconducting coil 51 does not change, and the magnetic field components are stable. However, since it is necessary to disassemble the superconducting magnet device 1 to adjust the degree of influence of the low-temperature iron shim 70, adjustment after manufacture is difficult.

[0058] On the other hand, the room-temperature iron shim 62 can correct the magnetic field for the generated magnetic field nonuniformity components by appropriately arranging the room-temperature iron shim 62 on the support 60 even after the superconducting magnet device 1 is manufactured, and the magnetic field uniformity can be further improved by repeating trial and error. However, the relative position between the room-temperature iron shim 62 and the oxide superconducting coil 51 may be shifted due to temperature changes in the sample region S. This relative position shift is caused by the difference in expansion and contraction between the room-temperature iron shim 62 and the low-temperature iron shim 70, particularly in the Z direction (the axial direction of the central axis CL), due to the difference in temperature changes between the sample region S and the low-temperature region T. As described above, when the relative positional relationship between the room-temperature iron shim 62 and the oxide superconducting coil 51 is shifted, there is a problem that the magnetic field components (particularly the Z1 component and the Z2 component) are affected and tend to vary over time. This problem can be solved by the low-temperature iron shim 70 as described above.

[0059] From the above, the inventors have discovered that it is preferable to correct the large axial component contained in the magnetic field formed in the sample region S using the low-temperature iron shim 70, while correcting the radial component using the room-temperature iron shim 62.

[0060] In other words, for the superconducting magnet device 1 shown in FIG. 2, the Z1 component, which is difficult to predict in advance, can be corrected by the metallic superconducting shim coil 55. Then, the low-temperature iron shim 70 corrects most (80% or more) of the Z2 non-uniform component, which can be predicted by calculation. Furthermore, the remaining Z2 non-uniform component can be completely corrected by the room-temperature shim coil 61. Also, part of the radial non-uniform components (especially low-order terms such as X, Y, ZX, and ZY), which are difficult to predict in advance, are corrected by the room-temperature iron shim 62 arranged on the outer circumferential surface of the room-temperature shim coil 61. Then, the remaining radial non-uniform components are completely corrected by the room-temperature shim.

[0061] With the above-mentioned configuration, the superconducting magnet device 1 is less susceptible to temperature changes in the installation environment, and the uniformity of the generated magnetic field can be stably maintained. As described above, in this embodiment, the large axial component is corrected by the low-temperature iron shim 70, but the low-temperature iron shim 70 may also include a function for correcting the radial component. In this case, the configuration is premised on the fact that the amount of correction can be calculated in advance, or that the purpose is to correct an approximate value.

[0062] <Structure of oxide superconducting coil> 3 is an enlarged cross-sectional view of a superconducting magnet 50 (part of the superconducting magnet device 1) according to this embodiment. In FIG. 3, the size in the axial direction of the central axis CL is reduced compared to FIG. 2. The superconducting magnet device 1 has a reel 51H for supporting the oxide superconducting coil 51. The reel 51H has a cylindrical shape centered on the central axis CL, and is made of stainless steel as a non-magnetic material, for example. The reel 51H is placed in a low temperature region T.

[0063] As described above, the oxide superconducting coil 51 is made of a superconducting wire wound around the outer periphery of the reel 51H, and generates a magnetic field when excited. As shown in FIG. 3, the outer diameter of the reel 51H is partially reduced on its outer periphery to provide a recess (engagement portion) capable of receiving the low-temperature iron shim 70. The low-temperature iron shim 70 (low-temperature magnetic shim) is placed in this recess, and is thereby held by the reel 51H in the low-temperature region T. That is, the recess has a function of engaging with at least a portion of the low-temperature iron shim 70. As a result, the low-temperature iron shim 70 is held by the reel 51H so as to be sandwiched between the reel 51H and the oxide superconducting coil 51 (superconductor wire).

[0064] The low-temperature iron shim 70 has a first shim 71, a second shim 72, and a third shim 73. All of these shims are made of iron foil. The first shim 71 is wound around the reel 51H so as to fit into a recess formed in the reel 51H. Furthermore, the second shim 72 is wound around the outer circumferential surface of the first shim 71, and the third shim 73 is wound around the outer circumferential surface of the second shim 72. As will be described in detail in the embodiment below, the axial widths and thicknesses of the first shim 71, the second shim 72, and the third shim 73 are set to be smaller in this order. The three shims are aligned so that their centers coincide with each other. The axial width of the first shim 71 is set to correspond to the width of the recess formed in the reel 51H.

[0065] Furthermore, since the second shim 72 and the third shim 73 are smaller in axial size than the first shim 71, spaces are formed on both sides of the second shim 72 and the third shim 73. For this reason, in this embodiment, a pair of spacers 81 are arranged to fill these spaces. Note that the thickness of each shim is set so that the surface of the third shim 73 is flush with the surface of the winding frame 51H in Fig. 3. Furthermore, an insulating sheet 82 is wound around the low-temperature iron shim 70 so as to cover it from the outside, and a superconducting wire is wound around the insulating sheet 82 to form the oxide superconducting coil 51.

[0066] On the other hand, Fig. 4 is an enlarged cross-sectional view of a superconducting magnet 50 according to a modified embodiment of the present invention. In this example, the thickness relationship between the first shim 71, the second shim 72, and the third shim 73 is set differently from that in the example of Fig. 3. Also, the axial width of the second shim 72 is set to correspond to the width of the recess formed in the reel 51H. The axial width of the first shim 71 is set smaller than that of the second shim 72, and the axial width of the third shim 73 is set smaller than that of the second shim 72 and larger than that of the first shim 71.

[0067] In this modified embodiment, spacers 81 are disposed in spaces formed on both sides of the first shim 71 and on both sides of the third shim 73. The other structure is similar to that shown in FIG.

[0068] As described above, in each embodiment of the present invention, the superconducting magnet device 1 includes at least the helium tank 12, the reel 51H, the oxide superconducting coil 51, the room temperature iron shim 62, and the low temperature iron shim 70. With this configuration, the magnetic field in the portion of the sample region S where the sample P is placed can be stabilized and uniformed. In addition to the original function of the reel 51H, which is the function of winding the superconducting wire, the reel 51H can be given the function of holding the low temperature iron shim 70. Therefore, the reel 51H, which is the structural foundation of the superconducting magnet device 1, can hold the low temperature iron shim 70, which is stable against temperature changes and electromagnetic forces, in the low temperature region T. As a result, a dedicated holding member for holding the low temperature iron shim 70 is not required, and the superconducting magnet device 1 can be configured with a simple structure and the superconducting magnet device 1 can be made space-saving.

[0069] Furthermore, by using such a superconducting magnet device 1 in an NMR device, the measurement function of the NMR device can be stably realized.

[0070] Furthermore, in the above embodiment, the low-temperature iron shim 70 is held by the reel 51H so as to be sandwiched between the reel 51H and the oxide superconducting coil 51.

[0071] With this configuration, the low-temperature iron shim 70 is firmly sandwiched between the winding frame 51H and the superconducting wire of the oxide superconducting coil 51. Therefore, even during cooling or coil excitation, the position of the low-temperature iron shim 70 is stably maintained in both the radial and axial directions of the winding frame 51H. In addition, because the low-temperature iron shim 70 is held by the winding frame 51H, which has high rigidity, it is highly vibration-proof against external vibration transmission and is expected to have sufficient earthquake resistance.

[0072] In realizing the above-mentioned magnetic field uniformity, if the contribution rate of the low-temperature iron shim 70 is greater than the contribution rates of the metal-based superconducting shim coil 55, the room-temperature shim coil 61, and the room-temperature iron shim 62, then stably maintaining the position of the low-temperature iron shim 70 is beneficial in utilizing the above-mentioned magnetic field. Also, since a fixing jig for the low-temperature iron shim 70 is not manufactured separately, and the low-temperature iron shim 70 is integrated into the winding form 51H of the oxide superconducting coil 51, temperature distribution in the low-temperature iron shim 70 is unlikely to occur, and magnetic field correction can be performed accurately.

[0073] If the low-temperature iron shim 70 is fixed to another fragile winding frame, external vibrations may be transmitted and natural vibrations may be induced. In this case, sidebands may occur in the NMR signal of the NMR device. Furthermore, in the event of an earthquake, the NMR device may be destroyed by the natural vibrations. The NMR device including the superconducting magnet device 1 according to this embodiment can reduce the occurrence of such problems.

[0074] Also, in the above embodiment, the winding frame 51H has an engagement portion that engages with at least a portion of the low-temperature iron shim 70. This engagement portion is appropriately set at a location where the low-temperature iron shim 70 can efficiently correct magnetic field errors. With this configuration, when the low-temperature iron shim 70 is held on the winding frame 51H, the engagement portion can have a positioning function for the low-temperature iron shim 70 and the winding frame 51H. In particular, since the centers of the oxide superconducting coil 51 and the low-temperature iron shim 70 can be aligned with high precision, the low-temperature iron shim 70 is less likely to generate magnetic errors.

[0075] Furthermore, in the above embodiment, the engagement portion is a recess formed on the outer periphery of the winding frame 51H and capable of receiving at least a part of the low-temperature iron shim 70. By accommodating a part or all of the low-temperature iron shim 70 in such a groove-shaped recess, the position of the low-temperature iron shim 70 relative to the oxide superconducting coil 51 can be stably maintained. Also, because the low-temperature iron shim 70 is fitted into the recess, movement of the low-temperature iron shim 70 due to the electromagnetic force between the low-temperature iron shim 70 and the oxide superconducting coil 51 can be suppressed.

[0076] Furthermore, in the above configuration, at least a portion of the superconducting wire of the oxide superconducting coil 51 is made of an oxide superconductor, so that a stable magnetic field can be generated and maintained even if the temperature of the sample area S changes.

[0077] The low-temperature iron shim 70 may include a first low-temperature magnetic shim and a second low-temperature magnetic shim. The former homogenizes the magnetic field components parallel to the central axis CL of the coil magnetic field formed in the sample region S by at least the oxide superconducting coil 51. On the other hand, the latter homogenizes the magnetic field components along the circumferential direction in a cross section perpendicular to the central axis CL of the coil magnetic field. In other words, the first low-temperature magnetic shim is an axial iron shim that corrects the axial component, and the second low-temperature magnetic shim corresponds to a radial iron shim that corrects the radial component.

[0078] According to this configuration, a stable and uniform magnetic field can be formed in both the axial and radial directions in the sample region S, so that the measurement function of the NMR device can be realized stably and accurately. EXAMPLES

[0079] Next, the superconducting magnet device 1 according to the present invention will be further described based on examples, but the present invention is not limited to the following examples.

[0080] <Evaluation of low-temperature magnetic shims> 3 and 4 were fabricated, and the superconducting magnet device 1 was excited to evaluate each component of the magnetic field formed on the central axis CL of the sample region S. Table 1 shows the parameters of the fabricated low-temperature iron shim 70.

[0081] [Table 1]

[0082] Example 1 corresponds to the embodiment in Fig. 3, and Examples 2 and 3 correspond to the embodiment in Fig. 4. In Table 1, No. 1 corresponds to the first shim 71, No. 2 corresponds to the second shim 72, and No. 3 corresponds to the third shim 73. The inner diameter and outer diameter are the inner diameter and outer diameter of each cylindrical shim centered on the central axis CL, the width is the width in the direction parallel to the central axis CL, and the thickness corresponds to half the difference between the inner diameter and the outer diameter. In each example, a recess is formed in the winding frame 51H to a depth corresponding to the total thickness of the shims.

[0083] Table 2 shows the magnitudes of the magnetic field components Z4, Z6, Z8, and Z10 and the sums of their absolute values ​​in each of Examples 1, 2, and 3. The numbers Z4 to Z10 correspond to the orders of Z in Equation 4.

[0084] [Table 2]

[0085] As shown in Table 2, in all of the examples, the sum of the absolute values ​​of the Z4 to Z10 magnetic field components was kept less than 10, while the Z2 component was kept at 27.9 ppm (=25.1 KHz / cm 2 It was confirmed that it is possible to perform design calculations to generate approximately

[0086] <Time stability of magnetic field components> Fig. 5 is a graph showing the transition of room temperature and the Z1 component of the magnetic field after excitation of the superconducting magnet device 1 in the embodiment of the present invention. Fig. 6 is a graph showing the transition of room temperature and the Z1 component of the magnetic field after excitation of the superconducting magnet device in a comparative example compared to the embodiment of the present invention.

[0087] In this experiment, the relationship between temperature and the Z1 component was evaluated by changing the room temperature of the environment in which the NMR device was installed, with and without the low-temperature iron shim 70 (low-temperature magnetic shim) in Figure 2. Note that in Figures 5 and 6, the temperature graphs represent the surface temperature of the vacuum vessel 10 (cryostat), with a change of 1 on the vertical axis corresponding to a temperature change of 3 degrees. Also, in the graph of the Z1 component, a change of 1 on the vertical axis corresponds to a change in the magnetic field component of -500Hz / cm.

[0088] At the reference point of the comparative example in FIG. 6, when the temperature changes by +1.8 degrees (0.6×3 degrees), the Z1 component changes by -225 Hz / cm. On the other hand, at the reference point of the embodiment in FIG. 5, when the temperature changes by +1.8 degrees (0.6×3 degrees), the Z1 component changes by only +38 Hz / cm. In this way, the low-temperature iron shim 70 was able to suppress the change in the Z1 component to about one-sixth. As a result, the magnetic field component was stabilized, making it possible to perform NMR measurements for a long period of time.

[0089] <Correction using low-temperature magnetic shims and room-temperature magnetic shims> FIG. 7 is a graph showing the magnitude (absolute value) of the non-uniform component (variation amount) of each magnetic field component with and without magnetic shims (room-temperature iron shim 62, low-temperature iron shim 70) in the superconducting magnet device 1 according to one embodiment of the present invention. In this experiment, the influence of the magnetic shims on the Z2 component, X component, and ZY component of the magnetic field described above was evaluated. The graphs on the left side of each magnetic field component in FIG. 7 correspond to the case where no magnetic shim is provided. On the other hand, the graphs on the right side of each magnetic field component correspond to the case where the room-temperature iron shim 62 and the low-temperature iron shim 70 are provided. It was confirmed that the non-uniform component of the Z2 component can be significantly reduced by the effect of the low-temperature iron shim 70, and the non-uniform components of the X and ZY components can be significantly reduced by the effect of the room-temperature iron shim 62. Note that the non-uniformity of each magnetic field component remaining after reduction can be sufficiently corrected by the room-temperature shim coil 61.

[0090] Although the superconducting magnet device 1 according to the present invention has been described above, the present invention is not limited to these embodiments, and the following modified embodiments are possible.

[0091] (1) In the above embodiment, the superconducting magnet device 1 is applied to an NMR device, but the present invention is not limited to this. The superconducting magnet device 1 may be applied to an MRI (Magnetic Resonance Imaging) device.

[0092] (2) In the above embodiment, the low-temperature iron shim 70 is held by the reel 51H on the outer periphery side of the reel 51H, but the low-temperature iron shim 70 may be held by the reel 51H on the inner periphery side of the reel 51H. The low-temperature iron shim 70 can be fixed to the reel 51H by various fixing methods such as adhesion or screw fastening.

[0093] (3) In the above embodiment, the nitrogen tank 14 is disposed to surround the helium tank 12. However, an argon layer may be disposed in place of the nitrogen tank 14, and the liquid argon may prevent heat from entering the helium tank 12. [Explanation of symbols]

[0094] 1 NMR device 10 Vacuum container 100 Superconducting magnet device 12 Helium tank (low temperature container) 14 Nitrogen tank 16 Radiation Shield 18 Support structure 50 Superconducting magnet 51 Oxide superconducting coil (superconducting coil) 51H Winding frame 52 Metallic superconducting coil 55 Metallic superconducting shim coil 56 Metallic auxiliary coil 60 Support 61 Room temperature shim coil 62 Room temperature iron shim (sample area magnetic shim) 70 Low temperature iron shim (low temperature magnetic shim) 71 1st Sim 72 2nd Sim 73 3rd Sim 81 Spacer 82 Insulation sheet CL center axis M1 1st magnetic field M2 2nd magnetic field M3 3rd magnetic field M4 4th magnetic field M5 5th magnetic field P sample RL reference line S sample area T low-temperature area

Claims

1. a cryocontainer having a low-temperature region therein, the cryocontainer being arranged cylindrically around a central axis so as to surround a sample region including the central axis; a winding frame having a cylindrical shape centered on the central axis and disposed in the low temperature region; a superconducting coil that is made of a superconducting wire wound around the outer periphery of the bobbin and generates a magnetic field when excited; a shim coil disposed in the sample region and configured to generate a magnetic field when excited; a sample region magnetic shim disposed in the sample region and cooperating with the shim coil to increase the uniformity of the magnetic field in the sample region; a low-temperature magnetic shim held by the former in the low-temperature region to enhance the uniformity of the magnetic field in the sample region; A superconducting magnet device comprising:

2. 2. The superconducting magnet apparatus according to claim 1, wherein the low-temperature magnetic shim is held by the former so as to be sandwiched between the former and the superconducting wire.

3. 、 3. The superconducting magnet apparatus according to claim 1, wherein the bobbin has an engagement portion that engages with at least a portion of the low-temperature magnetic shim.

4. 4. The superconducting magnet apparatus according to claim 3, wherein the engagement portion is a recess formed on an outer periphery of the bobbin and capable of receiving at least a portion of the low-temperature magnetic shim.

5. 3. The superconducting magnet apparatus according to claim 1, wherein at least a portion of the superconducting wire is made of an oxide superconductor.

6. The low temperature magnetic shim is a first low-temperature magnetic shim for homogenizing at least a magnetic field component parallel to the central axis of a coil magnetic field formed in the sample region by the superconducting coil; A second low-temperature magnetic shim that homogenizes a magnetic field component along a circumferential direction in a cross section perpendicular to the central axis, among the magnetic field of the coil; 3. The superconducting magnet device according to claim 1 or 2, further comprising:

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