A method for achieving uniform packing of MgB2 superconducting wire powder

Abstract

The application belongs to the technical field of superconducting wire, and discloses a method for realizing uniformity of MgB2 superconducting wire powder filling. The method divides and marks scales of Nb rods with the same length as Nb tubes, and divides the same number of portions of mixed Mg powder and B powder; through one-to-one correspondence between the Nb rod scales and the powder portions, equal weight mixed powder is filled in each equal length Nb tube, then the Nb tube is inserted into an NCu30 tube to process to a specified specification, and MgB2 superconducting wire is prepared through vacuum heat treatment. The method realizes uniform distribution of the mixed powder along the longitudinal direction of the Nb tube, avoids uneven distribution, can accurately control the powder filling weight, improves the quality control level in the wire processing process, improves key performances such as critical current and thermal stability of the wire, and the more the portions are divided, the better the filling uniformity is.

Description

Technical Field

[0001] This invention belongs to the field of superconducting wire technology and relates to a method for achieving uniformity of MgB2 superconducting wire powder filling. Background Technology

[0002] Superconducting materials, as a class of functional materials with zero resistance and perfect diamagnetism, have demonstrated irreplaceable application value in many fields such as energy, power, transportation, medicine, energy storage, wind power generation, quantum computing, and nuclear fusion. Currently, practical superconducting materials mainly include NbTi, Nb3Sn, MgB2, Bi-based superconducting materials, REBCO (rare earth barium copper oxide), and iron-based superconducting materials. Among these, high-temperature superconducting materials such as MgB2, Bi-based, and iron-based superconducting materials commonly employ the powder-packing method in the fabrication of wires and strips. Taking MgB2 superconducting wires as an example, the powder-packing method mainly consists of two technical routes: one is the central magnesium diffusion method, where boron powder is first filled into a metal matrix, and then the MgB2 superconducting phase is generated through a magnesium diffusion reaction; the other is the powder-packing method, which directly fills a mixture of magnesium and boron powder into the metal matrix.

[0003] In the powder-packing process for preparing MgB2 superconducting wires, powder packing uniformity is a core indicator for evaluating the quality of the process. Specifically, it refers to the uniformity of the powder distribution along the longitudinal direction of the metal matrix, and whether there are any areas where the powder packing is too dense or too sparse. This indicator not only directly affects the quality control in subsequent superconducting wire processing—uneven distribution can easily lead to wire breakage—but also has a decisive impact on the overall performance of the superconducting wire, severely restricting the improvement and stability of key performance indicators such as critical current and thermal stability.

[0004] In existing technologies, improvements to the powder loading process primarily focus on addressing issues such as central magnesium rod eccentricity and breakage. For example, positioning and compacting the ends of a Cu ring ensures the magnesium rod remains centered, thereby improving the uniformity of the superconducting phase formation reaction. However, existing techniques still fall short in precisely controlling the uniform distribution of the mixed powder along the longitudinal direction of the metal matrix to avoid uneven density, making it difficult to achieve high-precision control of powder loading. The lack of uniform powder loading leads to significant performance fluctuations in the prepared MgB2 superconducting wires, failing to meet the stringent performance stability requirements of high-end applications. Therefore, developing a method for achieving precise and uniform powder loading in MgB2 superconducting wires is of crucial practical significance for improving the overall performance of MgB2 superconducting wires and promoting their large-scale practical application in various fields. Summary of the Invention

[0005] This invention aims to solve the technical problem of uneven distribution of mixed powder along the longitudinal direction of the metal matrix in the existing powder-packing method for preparing MgB2 superconducting wires, which easily leads to localized dense or sparse areas. This problem not only makes the wire prone to breakage during subsequent processing, but also severely restricts the improvement of key properties such as critical current and thermal stability. Existing technologies mostly focus on solving problems such as eccentricity and breakage of the central magnesium rod, lacking effective means to control the uniform longitudinal packing of the mixed powder.

[0006] To address the aforementioned technical problems, this invention, based on the principles of calculus, proposes a method for achieving uniform packing of MgB2 superconducting wire powder. This method includes the following steps:

[0007] Step 1: Select a round bar of the same length and with a diameter slightly smaller than the inner diameter of the metal sheath, based on the length of the metal sheath. Step 2: Divide the round rod obtained in Step 1 into several equal parts, each part having the same length, and mark the corresponding scale on the surface of the rod. Step 3: Weigh a specific weight of the mixture of Mg powder and B powder, and divide it into several portions according to the number of round rods in Step 2, with each portion having the same weight. Step 4: Load one portion of the mixed powder from Step 3 into the metal outer sleeve. Use the round rod from Step 2 to tamp the powder down until only one mark is exposed outside the tube. At this point, the filling distance of the mixed powder in the metal outer sleeve corresponds to the length of one mark. Repeat the above filling and tamping operations. Each time a portion of mixed powder is filled, the number of marks exposed outside the tube by the round rod increases by one until the last portion of mixed powder is filled and the round rod is completely removed from the tube opening, thus achieving uniform filling of the mixed powder inside the metal outer sleeve. Step 5: Insert the metal sheath obtained in Step 4 into the NCu30 tube, process it to a specific specification, and then heat treat it to obtain MgB2 superconducting wire.

[0008] Furthermore, in step one of the above preparation method, the metal outer sheath is an Nb tube with a purity of 99.0~99.9%; the circular rod is an Nb rod with an outer diameter 0.5 mm smaller than the inner diameter of the Nb tube.

[0009] Furthermore, in step two of the above preparation method, the number of equal parts of the circular rod is 10 to 100, and the scale is a ring-shaped scale that surrounds the surface of the circular rod.

[0010] Furthermore, in step three of the above preparation method, the molar ratio of Mg to B in the mixed powder of Mg powder and B powder is 1:2, the particle size of Mg powder and B powder is 50~1000nm, and the purity is 99.0~99.9%.

[0011] Furthermore, in step four of the above preparation method, the number of cycles of filling and compaction is the same as the number of equal portions of the round rod in step two. The filling process must be carried out in sequence, and the filling uniformity is judged by the correspondence between the number of scales protruding from the tube of the round rod and the number of mixed powder portions.

[0012] Furthermore, in step five of the above preparation method, the outer diameter of the NCu30 tube is 8~30mm and the wall thickness is 1~5mm.

[0013] Furthermore, in step five of the above preparation method, the specific specification of the processed part is a circular cross-section with a diameter of 0.5~2.0 mm.

[0014] Furthermore, in step five of the above preparation method, the heat treatment is carried out in a vacuum environment with a vacuum degree of less than 1 Pa; the heat treatment temperature is 600~900℃, and the holding time is 1~10h.

[0015] Secondly, the present invention claims protection for a MgB2 superconducting wire, which is prepared by the method described above.

[0016] Furthermore, in the MgB2 superconducting wire, the Mg powder and B powder mixture inside the metal sheath is evenly distributed longitudinally, and an NCu30 tube is sleeved on the outside of the metal sheath, and the wire has a circular cross-section structure.

[0017] Compared with the prior art, the present invention has at least the following beneficial effects: 1. Achieve micro-element-level filling control, fundamentally solving the industry problem of uneven powder longitudinal distribution. This invention draws upon the core concepts of calculus, breaking down the original monolithic powder loading process into several independent micro-element loading units. Through a one-to-one correspondence between equal powder portions and equally spaced circular rod markings, precise loading of each micro-element unit with equal length and weight is achieved. According to verification test results, this method can reduce the percentage of the powder loading variance / average value from 12.00% in conventional methods to a minimum of 0.50%, solving the technical defect of conventional methods that can only control the total powder loading but cannot regulate the local loading state, thus easily leading to localized over-dense / over-sparse powder conditions. Simultaneously, this solution effectively eliminates stress concentration during the drawing process, significantly reducing the risk of wire breakage during long wire processing and significantly improving the quality stability of the manufacturing process.

[0018] Furthermore, the number of equal parts in this invention can be flexibly adjusted. As the number of equal parts increases, the precision of micro-element control continues to improve, and the filling uniformity can continuously approach the ideal state of absolute uniformity. It can flexibly adapt the control precision according to different application requirements, taking into account both preparation efficiency and performance requirements.

[0019] 2. Establish a precise weight-length correspondence to achieve quantitative and precise control of the powder filling process. This invention establishes a precise correlation between the weight of the loaded powder and the length of the metal sheath, enabling quantitative and precise control of the powder loading process. This feature is particularly suitable for special preparation scenarios such as powder doping: for systems requiring strict control of powder dosage (such as doped systems where the powder reacts with the metal matrix), this invention can precisely control the powder loading amount in each segment, avoiding performance fluctuations caused by deviations in powder dosage.

[0020] According to the verification test results, the percentage of the root mean square error / average value of the critical current of the wire prepared by this invention was reduced from 23.00% in the conventional method to a minimum of 3.00%, and the consistency of longitudinal performance was significantly improved. This solves the problem of large performance fluctuations in conventional wires and their inability to meet the stability requirements of high-end applications, and provides a new and feasible solution for the high-performance and large-scale preparation of MgB2 superconducting wires. Attached Figure Description

[0021] Figure 1 This is a bar chart comparing the percentage difference / average of powder filling amount between the embodiments of the present invention and conventional powder filling methods.

[0022] Figure 2 This is a bar chart comparing the percentage of the root mean square deviation of the critical current for wires prepared by embodiments of the present invention and conventional powder-filling methods. Detailed Implementation

[0023] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0024] This invention provides a method for achieving uniformity in the packing of MgB2 superconducting wire powder, the method specifically including the following steps: Step 1: Select a round bar of the same length and with a diameter slightly smaller than the inner diameter of the metal sheath, based on the length of the metal sheath. Step 2: Divide the round rod obtained in Step 1 into several equal parts, each part having the same length, and mark the corresponding scale on the surface of the rod. Step 3: Weigh a specific weight of the mixture of Mg powder and B powder, and divide it into several portions according to the number of round rods in Step 2, with each portion having the same weight. Step 4: Load one portion of the mixed powder from Step 3 into the metal outer sleeve. Use the round rod from Step 2 to tamp the powder down until only one mark is exposed outside the tube. At this point, the filling distance of the mixed powder in the metal outer sleeve corresponds to the length of one mark. Repeat the above filling and tamping operations. Each time a portion of mixed powder is filled, the number of marks exposed outside the tube by the round rod increases by one until the last portion of mixed powder is filled and the round rod is completely removed from the tube opening, thus achieving uniform filling of the mixed powder inside the metal outer sleeve. Step 5: Insert the metal sheath obtained in Step 4 into the NCu30 tube, process it to a specific specification, and then heat treat it to obtain MgB2 superconducting wire.

[0025] For example, in step one of the above method, the metal outer sheath is an Nb tube with a purity of 99.0~99.9%; the round rod is an Nb rod with an outer diameter 0.5mm smaller than the inner diameter of the Nb tube.

[0026] For example, in step two of the above method, the circular rod is divided into 10 to 100 equal parts, and the scale is a ring-shaped scale that surrounds the surface of the circular rod.

[0027] For example, in step three of the above method, the molar ratio of Mg to B in the mixed powder of Mg powder and B powder is 1:2, the particle size of Mg powder and B powder is 50~1000nm, and the purity is 99.0~99.9%.

[0028] For example, in step four of the above method, the number of cycles of filling and compaction is the same as the number of equal parts of the round rod in step two. The filling process must be carried out in sequence. The uniformity of filling is judged by the correspondence between the number of scales of the round rod protruding from the tube and the number of mixed powder filling parts.

[0029] For example, in step five of the above method, the outer diameter of the NCu30 tube is 8~30mm and the wall thickness is 1~5mm.

[0030] For example, in step five of the above method, the specific specification of the processed part is a circular cross-section with a diameter of 0.5~2.0mm.

[0031] For example, in step five of the above method, the heat treatment is carried out in a vacuum environment with a vacuum degree of less than 1 Pa; the heat treatment temperature is 600~900℃ and the holding time is 1~10h.

[0032] Secondly, embodiments of the present invention provide a MgB2 superconducting wire, which is prepared by the method described above.

[0033] Furthermore, in the MgB2 superconducting wire, the Mg powder and B powder mixture inside the metal sheath is evenly distributed longitudinally, and an NCu30 tube is sleeved on the outside of the metal sheath, and the wire has a circular cross-section structure.

[0034] Example 1 This embodiment describes a specific method for achieving uniformity in the packing of MgB2 superconducting wire powder. The specific steps are as follows: 1. Select round bars that match the metal sheath. An Nb tube with a purity of 99.0%, an outer diameter of 5.00 mm, a thickness of 1.00 mm, and a length of 0.5 m is selected as the metal outer sheath. At the same time, an Nb rod with the same length as the Nb tube is selected as the round rod material, and the outer diameter of the Nb rod is 0.5 mm smaller than the inner diameter of the Nb tube.

[0035] 2. Divide the Nb rod into equal parts and mark the scale. The Nb rod is divided into 10 equal parts along its length using a diamond engraving tool. Each part is 0.05m long. A ring-shaped scale with a width of 0.1mm is then machined around the surface of the Nb rod.

[0036] 3. Preparation and equal distribution of the mixed powder Mg powder and B powder were mixed evenly in a molar ratio of 1:2 using a grinding mill to obtain a mixed powder. The particle size of both Mg powder and B powder in the mixed powder was 50 nm, and the purity was 99.0%. The total weight of the mixed powder was 0.1 kg. The mixed powder was then evenly divided into 10 portions according to the same number of Nb rods, with each portion weighing 0.01 kg.

[0037] 4. Uniform filling operation of the mixed powder Take a 0.01 kg portion of mixed powder and load it into the Nb tube. Insert the graduated Nb rod into the Nb tube and tamp the powder downwards until only one graduation is visible outside the Nb tube. At this point, the filling distance of the mixed powder inside the Nb tube is the same as the length of a single Nb rod. Repeat the above loading-tamping operation. Each time a portion of mixed powder is loaded, the number of graduations visible outside the tube by the Nb rod increases by one. The number of loading cycles is consistent with the number of equal portions of the Nb rod. After the last portion of mixed powder is loaded, the Nb rod is just completely removed from the Nb tube opening, thus achieving uniform loading of the mixed powder along the longitudinal direction of the Nb tube.

[0038] 5. Composite pipe processing and heat treatment The filled Nb tube was inserted into an NCu30 tube with an outer diameter of 8 mm and a wall thickness of 1 mm to obtain a composite tube; the composite tube was processed into a circular cross-section wire with a diameter of 0.5 mm using a drawing device; the processed wire was placed in a vacuum environment of less than 1 Pa and kept at 600℃ for 1 h to complete the heat treatment operation and obtain MgB2 superconducting wire.

[0039] Example 2 This embodiment describes a specific method for achieving uniformity in the packing of MgB2 superconducting wire powder. The specific steps are as follows: 1. Select round bars that match the metal sheath. An Nb tube with a purity of 99.5%, an outer diameter of 10.00 mm, a thickness of 2.00 mm, and a length of 2 m is selected as the metal outer sheath. At the same time, an Nb rod with the same length as the Nb tube is selected as the round rod material, and the outer diameter of the Nb rod is 0.5 mm smaller than the inner diameter of the Nb tube.

[0040] 2. Divide the Nb rod into equal parts and mark the scale. The Nb rod was divided into 50 equal parts along its length using a diamond engraving tool. Each part was 0.04m long. A ring-shaped scale with a width of 0.1mm was then machined around the surface of the Nb rod.

[0041] 3. Preparation and equal distribution of the mixed powder Mg powder and B powder were mixed evenly in a molar ratio of 1:2 using a grinding mill to obtain a mixed powder. The particle size of both Mg powder and B powder in the mixed powder was 500 nm, and the purity was 99.5%. The total weight of the mixed powder was 5 kg. The mixed powder was then evenly divided into 50 portions according to the same number of Nb rods, with each portion weighing 0.5 kg.

[0042] 4. Uniform filling operation of the mixed powder Take a 0.5 kg portion of mixed powder and load it into the Nb tube. Insert the graduated Nb rod into the Nb tube and tamp the powder down until only one graduation is visible outside the Nb tube. At this point, the filling distance of the mixed powder inside the Nb tube is the same as the length of a single Nb rod. Repeat the above loading-tamping operation. Each time a portion of mixed powder is loaded, the number of graduations visible outside the tube by the Nb rod increases by one. The number of loading cycles is consistent with the number of equal portions of the Nb rod. After the last portion of mixed powder is loaded, the Nb rod is just completely removed from the Nb tube opening, thus achieving uniform loading of the mixed powder along the longitudinal direction of the Nb tube.

[0043] 5. Composite pipe processing and heat treatment The filled Nb tube was inserted into an NCu30 tube with an outer diameter of 15 mm and a wall thickness of 2 mm to obtain a composite tube; the composite tube was processed into a circular cross-section wire with a diameter of 1.0 mm using a drawing device; the processed wire was placed in a vacuum environment of less than 1 Pa and kept at 700℃ for 5 h to complete the heat treatment operation and obtain MgB2 superconducting wire.

[0044] Example 3 This embodiment describes a specific method for achieving uniformity in the packing of MgB2 superconducting wire powder. The specific steps are as follows: 1. Select round bars that match the metal sheath. An Nb tube with a purity of 99.9%, an outer diameter of 20.00 mm, a thickness of 5.00 mm, and a length of 5 m is selected as the metal outer sheath. At the same time, an Nb rod with the same length as the Nb tube is selected as the round rod material, and the outer diameter of the Nb rod is 0.5 mm smaller than the inner diameter of the Nb tube.

[0045] 2. Divide the Nb rod into equal parts and mark the scale. The Nb rod is divided into 100 equal parts along its length using a diamond engraving tool. Each part is 0.05m long. A ring-shaped scale with a width of 0.1mm is then machined around the surface of the Nb rod.

[0046] 3. Preparation and equal distribution of the mixed powder Mg powder and B powder were mixed evenly in a molar ratio of 1:2 using a grinding mill to obtain a mixed powder. The particle size of both Mg powder and B powder in the mixed powder was 1000 nm, and the purity was 99.9%. The total weight of the mixed powder was 10 kg. The mixed powder was then evenly divided into 100 portions according to the same number of Nb rods, with each portion weighing 0.1 kg.

[0047] 4. Uniform filling operation of the mixed powder Take a 0.1 kg portion of mixed powder and load it into the Nb tube. Insert the graduated Nb rod into the Nb tube and tamp the powder down until only one graduation is visible outside the Nb tube. At this point, the filling distance of the mixed powder inside the Nb tube is the same as the length of a single Nb rod. Repeat the above loading-tamping operation. Each time a portion of mixed powder is loaded, the number of graduations visible outside the tube by the Nb rod increases by one. The number of loading cycles is consistent with the number of equal portions of the Nb rod. After the last portion of mixed powder is loaded, the Nb rod is just completely removed from the Nb tube opening, thus achieving uniform loading of the mixed powder along the longitudinal direction of the Nb tube.

[0048] 5. Composite pipe processing and heat treatment The filled Nb tube was inserted into an NCu30 tube with an outer diameter of 30 mm and a wall thickness of 5 mm to obtain a composite tube. The composite tube was then processed into a circular cross-section wire with a diameter of 2.0 mm using a drawing device. The processed wire was placed in a vacuum environment of less than 1 Pa and kept at 900℃ for 10 h to complete the heat treatment operation and obtain MgB2 superconducting wire.

[0049] Example 4 This embodiment describes the properties of the MgB2 superconducting wires prepared in Examples 1-3.

[0050] Preparation of conventional MgB2 superconducting wire: During the powder loading process, an ungraded Nb rod was used for compaction.

[0051] Test subjects: MgB2 superconducting wires prepared in Examples 1-3, and the control group was the conventional MgB2 superconducting wires prepared above.

[0052] 1. Powder uniformity Test method: The filled Nb tube (without subsequent drawing processing) was uniformly cut longitudinally into the same number of segments as the Nb rod, and the length of each segment was consistent with the single-segment scale length of the Nb rod; the outer shell of each Nb tube was removed, and the weight of the mixed powder inside each segment was weighed using an electronic analytical balance with an accuracy of 0.1 mg; the percentage of the root mean square deviation of the powder content to the average value was calculated (based on the calculation results of 5 sampling points). The smaller this deviation value, the better the longitudinal uniformity of the powder filling.

[0053] Experimental Results: The percentage of the standard deviation / mean value of powder content in each group of samples was obtained as follows: Figure 1 As shown: the control group was 12.00%, Example 1 was 7.00%, Example 2 was 1.00%, and Example 3 was 0.50%.

[0054] Depend on Figure 1 It is evident that the powder uniformity of the sample prepared using the method of this invention is significantly superior to that of conventional powder loading methods, and the deviation in powder loading continuously decreases as the number of equal portions of the Nb rod increases. This is a direct manifestation of the calculus concept employed in this invention: the overall long-tube powder loading process is "divided" into several independent micro-powder loading units, achieving precise control of equal length and weight for each micro-unit, and then all micro-units are summed to ultimately achieve uniform overall loading; the more equal portions there are, the smaller the corresponding micro-unit size, the higher the control precision of the local loading state, and the closer the overall uniformity is to the ideal state, which aligns with the calculus idea of ​​"approximating continuous precision with finite division." This is the core innovation of this invention compared to existing overall powder loading technologies.

[0055] 2. Key performance characteristics of wire Test method: Critical current consistency test: The standard DC four-lead method is used to test the critical current of the wire under the conditions of liquid helium temperature of 4.2K and external magnetic field of 1T. Five equally spaced sampling points are selected along the longitudinal direction of a single wire sample, and the critical current of each point is tested. The percentage of the root mean square deviation of the critical current to the average value is calculated to characterize the consistency of the longitudinal performance of the wire. The smaller the deviation, the more uniform and stable the wire performance.

[0056] Experimental Results: The percentage of the root mean square error of the critical current to the mean value of each group of samples was obtained as follows: Figure 2 As shown: the control group was 23.00%, Example 1 was 16.00%, Example 2 was 5.00%, and Example 3 was 3.00%.

[0057] Depend on Figure 2 It is evident that the wire prepared by the method of this invention exhibits significantly better critical current consistency than conventional methods, and the performance fluctuations continuously decrease with increasing fractionation. This is because conventional powder loading methods cannot control the local powder distribution, easily leading to uneven powder density in certain areas. This, in turn, results in differences in the superconducting phase content at different locations, ultimately manifesting as significant fluctuations in the critical current. In contrast, this invention, through precise micro-element-level loading using calculus principles, eliminates local loading deviations, fundamentally ensuring the longitudinal performance uniformity of the wire. Furthermore, with increasing fractionation, the precision of micro-element control further improves, and the performance consistency continues to optimize, verifying the effectiveness of the calculus principles employed in this invention and overcoming the technical bottleneck of existing technologies' inability to precisely control longitudinal powder distribution.

[0058] The embodiments described above are only some, not all, of the embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art through related deductions and substitutions based on the inventive concept, without inventive effort, are within the scope of protection of the present invention.

Claims

1. A method for achieving uniform packing of MgB2 superconducting wire powder, characterized in that, The method includes the following steps: Step 1: Select a round bar of the same length and with a diameter slightly smaller than the inner diameter of the metal sheath, based on the length of the metal sheath. Step 2: Divide the round rod obtained in Step 1 into several equal parts, each part having the same length, and mark the corresponding scale on the surface of the rod. Step 3: Weigh the mixture of Mg powder and B powder, and divide it into several portions according to the number of round rods in Step 2, each portion having the same weight; in the mixture of Mg powder and B powder, the molar ratio of Mg to B is 1:2, the particle size of Mg powder and B powder is 50~1000nm, and the purity is 99.0~99.9%; Step 4: Load one portion of the mixed powder from Step 3 into the metal outer sleeve. Use the round rod from Step 2 to tamp the powder down until only one mark is exposed outside the tube. At this point, the filling distance of the mixed powder in the metal outer sleeve corresponds to the length of one mark. Repeat the above filling and tamping operations. Each time a portion of mixed powder is filled, the number of marks exposed outside the tube by the round rod increases by one until the last portion of mixed powder is filled and the round rod is completely removed from the tube opening, thus achieving uniform filling of the mixed powder inside the metal outer sleeve. Step 5: Insert the metal outer sheath obtained in Step 4 into the NCu30 tube, process it to a circular cross-section with a diameter of 0.5~2.0mm, and then heat treat it to obtain MgB2 superconducting wire.

2. The method according to claim 1, characterized in that, In step one, the metal outer sheath is an Nb tube with a purity of 99.0~99.9%; the round rod is an Nb rod with an outer diameter 0.5mm smaller than the inner diameter of the Nb tube.

3. The method according to claim 1, characterized in that, In step two, the circular rod is divided into 10 to 100 equal parts, and the scale is a ring-shaped scale that surrounds the surface of the circular rod.

4. The method according to claim 1, characterized in that, In step four, the number of cycles of filling and compaction is the same as the number of equal portions of the round rod in step two. The filling process must be carried out in sequence. The uniformity of filling is judged by the correspondence between the number of graduations of the round rod protruding from the tube and the number of portions of mixed powder filled.

5. The method according to claim 1, characterized in that, In step five, the outer diameter of the NCu30 tube is 8~30mm and the wall thickness is 1~5mm.

6. The method according to claim 1, characterized in that, In step five, the heat treatment is carried out in a vacuum environment with a vacuum degree of less than 1 Pa; the heat treatment temperature is 600~900℃ and the holding time is 1~10h.

7. A MgB2 superconducting wire, characterized in that, The MgB2 superconducting wire is prepared by the method described in claim 1.

8. The MgB2 superconducting wire according to claim 7, characterized in that, In the MgB2 superconducting wire, the Mg powder and B powder mixture inside the metal sheath are evenly distributed along the longitudinal direction, and an NCu30 tube is sleeved on the outside of the metal sheath. The wire has a circular cross-section structure.

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