Preparation method of low-temperature coaxial cable outer conductor NbTi capillary tube

Abstract

The invention discloses a preparation method of an outer conductor NbTi capillary tube of a low-temperature coaxial cable, and relates to the technical field of superconducting composite wire processing, and the preparation method comprises the following steps: carrying out pipe-penetrating assembly on an NbTi hollow ingot and a pure Al rod, and carrying out vacuum welding on the front and rear parts by adopting an NbTi upper cover and an NbTi lower cover to obtain an NbTi / Al composite ingot; carrying out hot extrusion forming to obtain a NbTi / Al composite long rod; straightening and sizing cutting and multi-pass cold drawing are carried out, and an NbTi / Al composite thin rod is obtained; straightening and sizing cutting are carried out, and the NbTi / Al capillary rod is obtained; and hanging in a heat treatment furnace, and carrying out heat treatment to obtain the NbTi capillary tube. According to the NbTi capillary tube manufacturing method, through the combination of the tube penetrating assembling technology, the vacuum welding technology, the hot extrusion technology, the cold drawing technology, the straightening fixed-length cutting technology and the heat treatment technology, the NbTi capillary tube manufacturing cost is reduced, and the manufacturing efficiency and quality are improved.

Description

Technical Field

[0001] The present application relates to the technical field of superconducting composite wire processing, and in particular to a method for preparing a NbTi capillary tube as an outer conductor of a low-temperature coaxial cable. Background Art

[0002] As a physical device for realizing quantum computing, the performance of quantum computers restricts the development of quantum computing research. Quantum computers generally use low-temperature superconducting coaxial cables to transmit microwave signals, which are crucial for the operation and measurement of superconducting quantum bits. Low-temperature superconducting coaxial cables usually consist of an inner conductor, an insulating layer, and an outer conductor. The outer conductor is usually a NbTi capillary. Its existing processing technology is restricted by foreign policies, which makes the capillary extremely difficult to process in China. There will be many problems such as poor quality of the inner and outer surfaces of the capillary, low straightness of the tube, uneven thickness of the capillary caused by turning, and long processing time, which seriously affect the mass production and application of superconducting coaxial cables.

[0003] In the prior art, Chinese patent CN113061792A discloses a low-temperature superconducting Nb-Ti alloy capillary and a preparation method thereof. The alloy capillary comprises Mg, B, La, Ti and the remainder Nb. During the preparation, niobium sheets and titanium sheets are first melted, and then magnesium bars and boron particles are added for smelting to obtain an ingot. The ingot is further melted, and La is added for refining to obtain an electrode rod. The electrode rod is smelted in a vacuum consumable electrode arc furnace to obtain an ingot. The ingot is then heated and forged to obtain a forged rod, which is then peeled to obtain an alloy rod, which is then perforated to obtain a tube blank. Finally, the tube blank is annealed and subjected to multiple diameter reduction forming to obtain a capillary.

[0004] However, the preparation cost of the NbTi capillary in the above-mentioned prior art is high, and the preparation efficiency and quality are poor. Summary of the invention

[0005] The present application provides a method for preparing a NbTi capillary tube as an outer conductor of a low-temperature coaxial cable, so as to solve the problems of high preparation cost, poor preparation efficiency and poor quality of the NbTi capillary tube in the prior art.

[0006] On the one hand, the present application provides a method for preparing a low-temperature coaxial cable outer conductor NbTi capillary, comprising the following steps:

[0007] Step 1: Use NbTi hollow ingots and pure Al rods for tube assembly, and use NbTi upper and lower covers for vacuum welding to obtain NbTi / Al composite ingots.

[0008] Step 2: hot extrusion forming the NbTi / Al composite ingot to obtain a NbTi / Al composite long rod.

[0009] Step three, straightening and cutting the NbTi / Al composite long rod to obtain NbTi / Al composite short rod, and performing multiple cold drawing on the NbTi / Al composite short rod to obtain NbTi / Al composite thin rod.

[0010] Step 4: straighten and cut the NbTi / Al composite thin rod to obtain NbTi / Al capillary rod.

[0011] Step 5: Hang the NbTi / Al capillary rod in a heat treatment furnace, place a crucible directly below, and perform heat treatment to melt the Al core in the NbTi / Al capillary rod to obtain a NbTi capillary tube.

[0012] In a possible implementation, in step 1, the mass ratio of Nb to Ti in the NbTi hollow ingot and the NbTi upper and lower covers is 53%:47%.

[0013] The inner diameter of the NbTi hollow ingot is equal to the diameter of the pure Al rod.

[0014] The NbTi upper and lower covers both adopt an integrated two-layer circular step structure, including a large circular step and a small circular step, wherein the diameter of the small circular step is equal to the inner diameter of the NbTi hollow ingot, and the diameter of the large circular step is equal to the outer diameter of the NbTi hollow ingot.

[0015] In a possible implementation, in step 1, the NbTi hollow ingot is preliminarily subjected to vacuum non-consumable melting and drilling machining.

[0016] The NbTi hollow ingot and the pure Al rod are pickled before being assembled into a tube.

[0017] In a possible implementation, in step 2, before hot extrusion forming the NbTi / Al composite ingot, a lubricant is applied to the surface of the NbTi / Al composite ingot.

[0018] The lubricant includes: asphalt and graphite emulsion.

[0019] In a possible implementation, in step 2, the temperature of the hot extrusion forming is 350-500° C., the speed is 10-80 m / min, and the pressure is 370-500 MPa.

[0020] In a possible implementation, in step three, the processing rate of each drawing of the multiple cold drawing passes is 10%, and annealing treatment is performed between each drawing.

[0021] The annealing treatment was carried out at a temperature of 300° C. and for a time of 2 h.

[0022] In a possible implementation, in step five, the heat treatment temperature is 700-800° C., and the insulation time is 10-15 minutes.

[0023] During the heat treatment process, an inert gas is introduced into the heat treatment furnace.

[0024] The inert gas includes Ar gas.

[0025] In one possible implementation, in step five, after obtaining the NbTi capillary, the NbTi capillary is immersed in 50%-60% by volume nitric acid for 1 hour, and ultrasonically cleaned in anhydrous ethanol for 1-2 hours, and the cleaned NbTi capillary is placed in an oven at a holding temperature of 120°C.

[0026] In a possible implementation, in step five, after obtaining the NbTi capillary, an online eddy current test is performed on the NbTi capillary.

[0027] The preparation method of a low-temperature coaxial cable outer conductor NbTi capillary in the present application has the following advantages:

[0028] By combining tube assembly, vacuum welding, hot extrusion, cold drawing, straightening and cutting to length, and heat treatment techniques, the difference in melting points between NbTi and Al is utilized to melt the Al core in the NbTi / Al capillary rod, thereby reducing the preparation cost of the NbTi capillary and improving the preparation efficiency and quality.

[0029] The proposed NbTi upper and lower covers both adopt an integrated two-layer circular step structure, including a large circular step and a small circular step, wherein the diameter of the small circular step is equal to the inner diameter of the NbTi hollow ingot, and the diameter of the large circular step is equal to the outer diameter of the NbTi hollow ingot, so that the NbTi upper and lower covers can be interlocked with the front and back of the NbTi hollow ingot, preventing the pure Al rod from shaking while avoiding the introduction of impurities.

[0030] It is proposed that lubricant is applied to the surface of the NbTi / Al composite ingot before hot extrusion forming the NbTi / Al composite ingot, so as to improve the temperature stability of hot extrusion and prevent the NbTi / Al composite ingot from sticking to the hot extrusion equipment.

[0031] In the proposed heat treatment process, an inert gas is introduced into the heat treatment furnace, which can promote the dripping of the Al liquid after the Al core is melted, and play the role of a protective gas, avoiding the generation of sparks and carbide inclusions, thereby avoiding contamination of the heat treatment furnace and the NbTi / Al capillary rod. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0033] Figure 1 A schematic flow chart of a method for preparing a low-temperature coaxial cable outer conductor NbTi capillary provided in an embodiment of the present application. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0035] Embodiment 1:

[0036] like Figure 1 As shown, the embodiment of the present application provides a method for preparing a NbTi capillary tube as an outer conductor of a low-temperature coaxial cable, comprising the following steps:

[0037] Step 1: Use NbTi hollow ingots and pure Al rods for tube assembly, and use NbTi upper and lower covers for vacuum welding to obtain NbTi / Al composite ingots.

[0038] Step 2: hot extrusion forming the NbTi / Al composite ingot to obtain a NbTi / Al composite long rod.

[0039] Step three, straightening and cutting the NbTi / Al composite long rod to obtain NbTi / Al composite short rod, and performing multiple cold drawing on the NbTi / Al composite short rod to obtain NbTi / Al composite thin rod.

[0040] Step 4: straighten and cut the NbTi / Al composite thin rod to obtain NbTi / Al capillary rod.

[0041] Step 5: Hang the NbTi / Al capillary rod in a heat treatment furnace, place a crucible directly below, and perform heat treatment to melt the Al core in the NbTi / Al capillary rod to obtain a NbTi capillary tube.

[0042] Exemplarily, in step 1, the mass ratio of Nb to Ti in the NbTi hollow ingot and the NbTi upper and lower covers is 53%:47%.

[0043] The inner diameter of the NbTi hollow ingot is equal to the diameter of the pure Al rod.

[0044] The NbTi upper and lower covers both adopt an integrated two-layer circular step structure, including a large circular step and a small circular step, wherein the diameter of the small circular step is equal to the inner diameter of the NbTi hollow ingot, and the diameter of the large circular step is equal to the outer diameter of the NbTi hollow ingot.

[0045] Specifically, in this embodiment, in step 1, the outer diameter of the NbTi hollow ingot is 90 mm, the thickness is 18 mm, and the length is 60 mm; the diameter of the pure Al rod is 54 mm, and the length is 50 mm; the diameter of the large circular step of the NbTi upper and lower covers is 90 mm, and the length is 5 mm, and the diameter of the small circular step is 54 mm, and the length is 5 mm. The small circular step is used to buckle into the NbTi hollow ingot and contact with the pure Al rod.

[0046] Specifically, in this embodiment, the vacuum welding in step 1 adopts vacuum electron beam welding. The welding current is 200mA, the focusing current is 8000mA, the welding speed is 90° / min, and the vacuum degree needs to be controlled to be maintained at 2.0×10 -6 mbar. The welding process needs to be repeated 4-6 times to ensure that there are no defects in the weld.

[0047] Exemplarily, in step 1, the NbTi hollow ingot is preliminarily subjected to vacuum non-consumable melting and drilling machining.

[0048] The NbTi hollow ingot and the pure Al rod are pickled before being assembled into a tube.

[0049] Specifically, vacuum non-consumable melting and drilling machining are to make the composition and structure of the NbTi hollow ingot uniform and the inner wall smooth, and pickling is to remove surface impurities of the NbTi hollow ingot and the pure Al rod, so as to make the composition and structure of the NbTi / Al composite ingot uniform.

[0050] Exemplarily, in step 2, before hot extrusion forming the NbTi / Al composite ingot, a lubricant is applied to the surface of the NbTi / Al composite ingot.

[0051] The lubricant includes: asphalt and graphite emulsion.

[0052] Specifically, in this embodiment, in step 2, a mixture of asphalt and graphite emulsion is applied on the surface of the NbTi / Al composite ingot.

[0053] Exemplarily, in step 2, the temperature of the hot extrusion forming is 350-500° C., the speed is 10-80 m / min, and the pressure is 370-500 MPa.

[0054] Specifically, in this embodiment, in step 2, the hot extrusion forming temperature is 350°C, the speed is 10m / min, and the pressure is 370MPa. The diameter of the obtained NbTi / Al composite long rod is 25mm. The unqualified areas at the head and tail of the NbTi / Al composite long rod are sawed until the Al core and the NbTi layer can be clearly observed to be uniform concentric circles on the front and rear end surfaces. In this embodiment, the head of the NbTi / Al composite long rod is sawed to a length of about 60mm, and the tail is sawed to a length of about 50mm.

[0055] Exemplarily, in step three, the processing rate of each drawing of the multiple cold drawing passes is 10%, and annealing treatment is performed between each drawing.

[0056] The annealing treatment was carried out at a temperature of 300° C. and for a time of 2 h.

[0057] Specifically, in this embodiment, in step three, the NbTi / Al composite long rod is straightened and cut to size to obtain 23 NbTi / Al composite short rods with a diameter of 25 mm and a length of 30 mm, and then plugs are installed on both sides of the head and tail of the NbTi / Al composite short rods. After a peeling, multiple cold drawing is performed, and the processing rate of each drawing is 10%. Annealing treatment is performed between each drawing, and the annealing temperature is 300°C and the time is 2h.

[0058] Specifically, in this embodiment, in step 4, the NbTi / Al composite thin rods obtained in step 3 are straightened and cut to size to obtain 1400 NbTi / Al capillary rod blanks with a diameter of 2.2 mm and a length of 70 mm, and the uneven parts of 10 mm at the head and tail of the NbTi / Al capillary rod blanks are removed to obtain NbTi / Al capillary rods with a diameter of 2.2 mm and a length of 50 mm.

[0059] Exemplarily, in step five, the heat treatment temperature is 700-800° C., and the holding time is 10-15 min.

[0060] During the heat treatment process, an inert gas is introduced into the heat treatment furnace.

[0061] The inert gas includes Ar gas.

[0062] Specifically, in this embodiment, in step five, the heat treatment temperature is 700° C., the holding time is 10 min, and during the heat treatment, Ar gas is introduced into the heat treatment furnace.

[0063] Exemplarily, in step five, after obtaining the NbTi capillary, the NbTi capillary is immersed in 50%-60% by volume nitric acid for 1 hour, and ultrasonically cleaned in anhydrous ethanol for 1-2 hours, and the cleaned NbTi capillary is placed in an oven at a holding temperature of 120°C.

[0064] Specifically, in this embodiment, in step five, after obtaining the NbTi capillary, the NbTi capillary is immersed in 50% by volume nitric acid for 1 hour, and ultrasonically cleaned in anhydrous ethanol for 1 hour, and the cleaned NbTi capillary is placed in an oven at a holding temperature of 120°C.

[0065] Exemplarily, in step five, after obtaining the NbTi capillary, online eddy current detection is performed on the NbTi capillary.

[0066] In Example 1, the result of online eddy current testing is that the NbTi capillary has no defects.

[0067] Embodiment 2:

[0068] Specifically, in this embodiment, in step 1, the outer diameter of the NbTi hollow ingot is 110 mm, the thickness is 23 mm, and the length is 90 mm; the diameter of the pure Al rod is 64 mm, and the length is 80 mm; the diameter of the large circular step of the NbTi upper and lower covers is 110 mm, and the length is 10 mm, and the diameter of the small circular step is 64 mm, and the length is 5 mm. The small circular step is used to buckle into the NbTi hollow ingot and contact with the pure Al rod.

[0069] Specifically, in this embodiment, in step 2, the hot extrusion forming temperature is 420°C, the speed is 40m / min, and the pressure is 440MPa. The diameter of the obtained NbTi / Al composite long rod is 30mm. The unqualified areas at the head and tail of the NbTi / Al composite long rod are sawed until the Al core and the NbTi layer can be clearly observed to be uniform concentric circles on the front and rear end surfaces. In this embodiment, the head of the NbTi / Al composite long rod is sawed to a length of about 60mm, and the tail is sawed to a length of about 50mm.

[0070] Specifically, in this embodiment, in step three, the NbTi / Al composite long rod is straightened and cut to size to obtain 40 NbTi / Al composite short rods with a diameter of 30 mm and a length of 30 mm, and then plugs are installed on both sides of the head and tail of the NbTi / Al composite short rods. After a peeling, multiple cold drawing is performed, and the processing rate of each drawing is 10%. Annealing treatment is performed between each drawing, and the annealing temperature is 300°C and the time is 2 hours.

[0071] Specifically, in this embodiment, in step 4, the NbTi / Al composite thin rods obtained in step 3 are straightened and cut to size to obtain 3000 NbTi / Al capillary rod blanks with a diameter of 2.0 mm and a length of 70 mm, and the uneven parts of 10 mm at the head and tail of the NbTi / Al capillary rod blanks are removed to obtain NbTi / Al capillary rods with a diameter of 2 mm and a length of 50 mm.

[0072] Specifically, in this embodiment, in step five, the heat treatment temperature is 750° C., the holding time is 12 min, and during the heat treatment, Ar gas is introduced into the heat treatment furnace.

[0073] Specifically, in this embodiment, in step five, after obtaining the NbTi capillary, the NbTi capillary is immersed in 55% by volume nitric acid for 1 hour, and ultrasonically cleaned in anhydrous ethanol for 1.5 hours, and the cleaned NbTi capillary is placed in an oven at a holding temperature of 120°C.

[0074] The other steps and parameters of Example 2 are the same as those of Example 1.

[0075] In Example 2, the result of online eddy current testing is that the NbTi capillary is defect-free.

[0076] Embodiment 3:

[0077] Specifically, in this embodiment, in step 1, the outer diameter of the NbTi hollow ingot is 100 mm, the thickness is 25 mm, and the length is 90 mm; the diameter of the pure Al rod is 50 mm, and the length is 80 mm; the diameter of the large circular step of the NbTi upper and lower covers is 100 mm, and the length is 10 mm, and the diameter of the small circular step is 50 mm, and the length is 5 mm. The small circular step is used to buckle into the NbTi hollow ingot and contact with the pure Al rod.

[0078] Specifically, in this embodiment, in step 2, the hot extrusion forming temperature is 500°C, the speed is 80m / min, and the pressure is 500MPa. The diameter of the obtained NbTi / Al composite long rod is 30mm. The unqualified areas at the head and tail of the NbTi / Al composite long rod are sawed until the Al core and the NbTi layer can be clearly observed to be uniform concentric circles on the front and rear end surfaces. In this embodiment, the head of the NbTi / Al composite long rod is sawed to a length of about 60mm, and the tail is sawed to a length of about 50mm.

[0079] Specifically, in this embodiment, in step three, the NbTi / Al composite long rod is straightened and cut to size to obtain 35 NbTi / Al composite short rods with a diameter of 30 mm and a length of 30 mm, and then plugs are installed on both sides of the head and tail of the NbTi / Al composite short rods. After a peeling, multiple cold drawing is performed, and the processing rate of each drawing is 10%. Annealing treatment is performed between each drawing, and the annealing temperature is 300°C and the time is 2h.

[0080] Specifically, in this embodiment, in step 4, the NbTi / Al composite thin rods obtained in step 3 are straightened and cut to size to obtain 890 NbTi / Al capillary rod blanks with a diameter of 4.0 mm and a length of 70 mm, and the uneven parts of 10 mm at the head and tail of the NbTi / Al capillary rod blanks are removed to obtain NbTi / Al capillary rods with a diameter of 4 mm and a length of 50 mm.

[0081] Specifically, in this embodiment, in step five, the temperature of the heat treatment is 800° C., the holding time is 15 min, and during the heat treatment, Ar gas is introduced into the heat treatment furnace.

[0082] Specifically, in this embodiment, in step five, after obtaining the NbTi capillary, the NbTi capillary is immersed in 60% by volume nitric acid for 1 hour, and ultrasonically cleaned in anhydrous ethanol for 2 hours, and the cleaned NbTi capillary is placed in an oven at a holding temperature of 120°C.

[0083] The other steps and parameters of Example 3 are the same as those of Example 1.

[0084] In Example 3, the result of online eddy current testing is that the NbTi capillary is defect-free.

[0085] The embodiments of the present application combine tube assembly, vacuum welding, hot extrusion, cold drawing, straightening and cutting to size, and heat treatment techniques, and utilize the melting point difference between NbTi and Al to melt the Al core in the NbTi / Al capillary rod, thereby reducing the preparation cost of the NbTi capillary and improving the preparation efficiency and quality.

[0086] The proposed NbTi upper and lower covers both adopt an integrated two-layer circular step structure, including a large circular step and a small circular step, wherein the diameter of the small circular step is equal to the inner diameter of the NbTi hollow ingot, and the diameter of the large circular step is equal to the outer diameter of the NbTi hollow ingot, so that the NbTi upper and lower covers can be interlocked with the front and back of the NbTi hollow ingot, preventing the pure Al rod from shaking while avoiding the introduction of impurities.

[0087] It is proposed that lubricant is applied to the surface of the NbTi / Al composite ingot before hot extrusion forming the NbTi / Al composite ingot, so as to improve the temperature stability of hot extrusion and prevent the NbTi / Al composite ingot from sticking to the hot extrusion equipment.

[0088] In the proposed heat treatment process, an inert gas is introduced into the heat treatment furnace, which can promote the dripping of the Al liquid after the Al core is melted, and play the role of a protective gas, avoiding the generation of sparks and carbide inclusions, thereby avoiding contamination of the heat treatment furnace and the NbTi / Al capillary rod.

[0089] Although the preferred embodiments of the present application have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present application.

[0090] Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is also intended to include these modifications and variations.

Claims

1. A method for preparing a low-temperature coaxial cable outer conductor NbTi capillary, characterized in that: The following steps are involved: Step 1: Use NbTi hollow ingots and pure Al rods to assemble through pipes, and use NbTi upper and lower covers to perform vacuum welding to obtain NbTi / Al composite ingots; Step 2, hot extruding the NbTi / Al composite ingot to obtain a NbTi / Al composite long rod; Step 3, straightening and cutting the NbTi / Al composite long rod to obtain NbTi / Al composite short rod, and performing multiple cold drawing on the NbTi / Al composite short rod to obtain NbTi / Al composite thin rod; Step 4, straightening and cutting the NbTi / Al composite thin rod to obtain a NbTi / Al capillary rod; Step 5: Hang the NbTi / Al capillary rod in a heat treatment furnace, place a crucible directly below, and perform heat treatment to melt the Al core in the NbTi / Al capillary rod to obtain a NbTi capillary tube.

2. The method for preparing a low-temperature coaxial cable outer conductor NbTi capillary according to claim 1, characterized in that: In step 1, the mass ratio of Nb to Ti in the NbTi hollow ingot and the NbTi upper and lower covers is 53%:47%; The inner diameter of the NbTi hollow ingot is equal to the diameter of the pure Al rod; The NbTi upper and lower covers both adopt an integrated two-layer circular step structure, including a large circular step and a small circular step, wherein the diameter of the small circular step is equal to the inner diameter of the NbTi hollow ingot, and the diameter of the large circular step is equal to the outer diameter of the NbTi hollow ingot.

3. The method for preparing a low-temperature coaxial cable outer conductor NbTi capillary according to claim 1, characterized in that: In step 1, the NbTi hollow ingot is preliminarily subjected to vacuum non-consumable smelting and drilling machining; The NbTi hollow ingot and the pure Al rod are pickled before being assembled into a tube.

4. The method for preparing a low-temperature coaxial cable outer conductor NbTi capillary according to claim 1, characterized in that: In step 2, before hot extrusion forming the NbTi / Al composite ingot, a lubricant is applied to the surface of the NbTi / Al composite ingot; The lubricant includes: asphalt and graphite emulsion.

5. The method for preparing a low-temperature coaxial cable outer conductor NbTi capillary according to claim 1, characterized in that: In step 2, the temperature of the hot extrusion forming is 350-500°C, the speed is 10-80m / min, and the pressure is 370-500MPa.

6. The method for preparing a low-temperature coaxial cable outer conductor NbTi capillary according to claim 1, characterized in that: In step 3, the processing rate of each drawing of the multiple cold drawing is 10%, and annealing treatment is performed between each drawing; The annealing treatment was carried out at a temperature of 300° C. and for a time of 2 h.

7. The method for preparing a low-temperature coaxial cable outer conductor NbTi capillary according to claim 1, characterized in that: In step 5, the heat treatment temperature is 700-800°C and the holding time is 10-15min; During the heat treatment process, an inert gas is introduced into the heat treatment furnace; The inert gas includes Ar gas.

8. The method for preparing a low-temperature coaxial cable outer conductor NbTi capillary according to claim 1, characterized in that: In step five, after obtaining the NbTi capillary, the NbTi capillary is immersed in 50%-60% nitric acid by volume for 1 hour, and ultrasonically cleaned in anhydrous ethanol for 1-2 hours, and the cleaned NbTi capillary is placed in an oven at a holding temperature of 120°C.

9. The method for preparing a low-temperature coaxial cable outer conductor NbTi capillary according to claim 1, characterized in that: In step five, after obtaining the NbTi capillary, an online eddy current test is performed on the NbTi capillary.

Images