Design method of large current-carrying critical current sample rod
阅读说明：本技术 一种大载流临界电流样品杆的设计方法 (Design method of large current-carrying critical current sample rod ) 是由 高慧贤 王菲菲 董茂胜 王蒙 昌胜红 刘京州 李建峰 刘向宏 冯勇 于 2020-05-21 设计创作，主要内容包括：本发明公开了一种大载流临界电流样品杆的设计方法,具体包括如下步骤：步骤1,计算超导线用量与低温端铜杆的横截面积；步骤2,根据步骤1的计算结果制作低温端超导复合电流引线；步骤3,计算常温端连接杆的横截面积；步骤4,根据步骤3的计算结果制作连接常温端的连接杆；步骤5,将步骤2制作的复合电流引线与步骤4制作的连接杆进行装配。本发明设计的电流样品杆能够最大载流至2500A,能够完成高临界电流超导体的测量。(The invention discloses a design method of a large current-carrying critical current sample rod, which specifically comprises the following steps: step 1, calculating the consumption of the superconducting wire and the cross-sectional area of a copper rod at a low-temperature end; step 2, manufacturing a low-temperature end superconducting composite current lead according to the calculation result of the step 1; step 3, calculating the cross sectional area of the connecting rod at the normal temperature end; step 4, manufacturing a connecting rod connected with the normal temperature end according to the calculation result of the step 3; and 5, assembling the composite current lead manufactured in the step 2 and the connecting rod manufactured in the step 4. The current sample rod designed by the invention can carry current to 2500A at most and can finish the measurement of a high critical current superconductor.)
1. A design method of a large current-carrying critical current sample rod is characterized by comprising the following steps: the method specifically comprises the following steps:
step 1, calculating the consumption of the superconducting wire and the cross-sectional area of a copper rod at a low-temperature end;
step 2, manufacturing a low-temperature end superconducting composite current lead according to the calculation result of the step 1;
step 3, calculating the cross sectional area of the connecting rod at the normal temperature end;
step 4, manufacturing a connecting rod connected with the normal temperature end according to the calculation result of the step 3;
and 5, assembling the composite current lead manufactured in the step 2 and the connecting rod manufactured in the step 4.
2. The design method of a large current-carrying critical current sample rod as claimed in claim 1, wherein: the calculation process of the superconducting wire usage in the step 1 is as follows:
NbTi/Cu and Nb with known current carrying capacity3The number of the Sn/Cu low-temperature composite superconducting wires is n1And n2Setting a safety coefficient gamma in consideration of the quench risk of the wire;
the number n of the NbTi/Cu low-temperature composite superconducting wiresNbTiComprises the following steps:
nNbTi＝n1/γ；
Nb3actual required number n of Sn/Cu low-temperature composite superconducting wiresNb3SnComprises the following steps:
nNb3Sn＝n2/γ；
the cross-sectional area S of the low-temperature end copper rod1The calculation formula is as follows:
S1＝I1/j1
wherein, I1Current carrying expected by the low temperature end copper rod;
j1and the current carrying capacity of the copper rod at the low-temperature end per unit area.
3. The design method of a large current-carrying critical current sample rod as claimed in claim 2, wherein: the copper rod at the low-temperature end in the step 1 comprises a copper rod I, a copper rod II and a copper rod III, a horizontal transverse plate is arranged at the upper end of the copper rod I, the copper rod I is positioned in the center of the horizontal transverse plate, the copper rod II is arranged on the upper side of one end of the horizontal transverse plate in the vertical direction, and an insertion hole I is formed in the other end of the horizontal transverse plate;
the copper rod III is vertically arranged and is parallel to the copper rod II, the bottom of the copper rod III is connected to the supporting block, and the copper rod III is located at one end of the supporting block; an insulating plate is arranged between the supporting block and the horizontal transverse plate;
a jack II is arranged at the center of the supporting block, a jack III is arranged at the center of the insulating plate, and a jack IV is arranged at one end of the insulating plate; the copper rod I sequentially penetrates through the jack III, the jack II and the insulation board from the jack IV to combine the copper rod I, the copper rod II and the copper rod III.
4. The design method of a large current-carrying critical current sample rod as claimed in claim 2, wherein: the specific process of the step 2 is as follows:
grooves are formed in the side walls of the copper rod II and the copper rod III, and n is arranged at the positions, where the grooves are formed, of the copper rod II and the copper rod III respectivelyNbTiNbTi/Cu low-temperature composite superconducting wire and nNb3SnRoot of Nb3Sn/Cu low-temperature composite superconducting wire;
a through hole is arranged at the center of the copper rod I, and n is connectedNbTiNbTi/Cu low-temperature composite superconducting wire and nNb3SnRoot of Nb3Sn/Cu low-temperature composite superconducting wire is arranged in the leadIn the hole;
the cross-sectional areas of the copper rod I, the copper rod II and the copper rod III are S1.
5. The design method of a large current-carrying critical current sample rod as claimed in claim 3, wherein: and in the step 2, the copper rod I, the copper rod II and the copper rod III are compounded by adopting a low-temperature tin soldering method.
6. The design method of a large current-carrying critical current sample rod as claimed in claim 4, wherein: and during welding in the step 2, the solder is selected from one of SnAg solder or SnPb solder.
7. The design method of a large current-carrying critical current sample rod as claimed in claim 3, wherein: the cross sectional area S of the normal temperature connecting rod in the step 32The calculation formula is as follows:
S2＝I2/j2
wherein, I2-current carrying expected to be achieved by the normal temperature connecting rod;
j2current carrying capacity per unit area of the normal temperature connecting rod.
8. The design method of a large current-carrying critical current sample rod as claimed in claim 6, wherein: the normal temperature connecting rods in the step 4 comprise two normal temperature connecting rods, each normal temperature connecting rod comprises an outer copper pipe and an inner copper pipe which are coaxially sleeved, and the cross sectional area of each outer copper pipe is S2；
Exhaust holes are respectively arranged at the upper end and the lower end of the outer copper pipe and the inner copper pipe at the same time; and the exhaust hole is arranged on the side wall of one side of the outer copper pipe and the inner copper pipe.
9. The design method of a large current-carrying critical current sample rod as claimed in claim 7, wherein: the specific process of the step 5 is as follows: and respectively welding two normal-temperature connecting rods at the upper ends of the copper rod II and the copper rod III.
Technical Field
The invention belongs to the technical field of performance measurement of superconducting materials, and relates to a design method of a large-current-carrying critical current sample rod.
Background
NbTi/Cu low-temperature composite superconductors are one of the most widely applied low-temperature superconductors at present. The high-intensity magnetic field magnet and the magnetic confinement nuclear fusion device (Tokamak) for scientific research have wide application in the aspects of Magnetic Resonance Imaging (MRI) and the like. The NbTi/Cu low-temperature composite superconductor is structurally divided into an integrated superconductor (monolithic structure) and a superconductor (Wire In Channel, hereinafter referred to as WIC Wire) which is made by embedding the integrated superconductor In a copper slot Wire.
Critical current (I)c) Refers to the maximum current that a superconductor does not pass at a particular temperature (typically about 4.2K at liquid helium temperature for cryogenic superconductors) and a particular background magnetic field. The monolithic structure wire of the NbTi/Cu low-temperature composite superconductor is widely applied to various strong magnetic field devices such as various magnets for general scientific research, magnetic confinement nuclear fusion devices and the like, the wire diameter of the monolithic structure wire is small, the diameter of the monolithic structure wire is usually less than 1mm, and the critical current of a single strand is generally below 800A (when the background magnetic field is 4T); the WIC wire has a cross section close to a rectangle and a large cross section, and the current carrying capacity can reach about 2000A (4T of a background magnetic field), so that the WIC wire is generally used in a medical nuclear magnetic resonance imager.
With the development of MRI technology, more and more hospitals are equipped with MRI equipment, so the demand of WIC wires is gradually increased, and the initial critical current sample rod uses red copper as a raw material, and is suitable for the measurement of critical current with the current carrying capacity of 1000A or less. When the current larger than 1000A is measured, the liquid helium consumption is greatly increased, the cost is increased suddenly, and the measured microvolt voltage signal is influenced by a large amount of helium generated by boiling liquid helium, becomes extremely unstable and often causes measurement failure.
Disclosure of Invention
The invention aims to provide a design method of a large current-carrying critical current sample rod, the current sample rod designed by the method can carry current to 2500A at maximum, and measurement of a high critical current superconductor can be completed.
The invention adopts the technical scheme that a design method of a large current-carrying critical current sample rod specifically comprises the following steps:
step 4, manufacturing a connecting rod connected with the normal temperature end according to the calculation result of the
and 5, assembling the composite current lead manufactured in the
The present invention is also characterized in that,
the calculation process of the superconducting wire dosage in the
NbTi/Cu and Nb with known current carrying capacity3The number of the Sn/Cu low-temperature composite superconducting wires is n1And n2Setting a safety coefficient gamma in consideration of the quench risk of the wire;
the number n of the NbTi/Cu low-temperature composite superconducting wiresNbTiComprises the following steps:
nNbTi＝n1/γ；
Nb3actual required number n of Sn/Cu low-temperature composite superconducting wiresNb3SnComprises the following steps:
nNb3Sn＝n2/γ；
minimum cross-sectional area S of copper rod at low temperature end1The calculation formula is as follows:
S1＝I1/j1
wherein, I1Current carrying expected by the low temperature end copper rod;
j1and the current carrying capacity of the copper rod at the low-temperature end per unit area.
the copper rod III is vertically arranged and is parallel to the copper rod II, the bottom of the copper rod III is connected to the supporting block, and the copper rod III is located at one end of the supporting block; an insulating plate is arranged between the supporting block and the horizontal transverse plate;
a jack II is arranged at the center of the supporting block, a jack III is arranged at the center of the insulating plate, and a jack IV is arranged at one end of the insulating plate; the copper rod I sequentially penetrates through the jack III, the jack II and the insulation board from the jack IV to combine the copper rod I, the copper rod II and the copper rod III.
The specific process of the
grooves are formed in the side walls of the copper rod II and the copper rod III, and n is arranged at the positions, where the grooves are formed, of the copper rod II and the copper rod III respectivelyNbTiNbTi/Cu low-temperature composite superconducting wire and nNb3SnRoot of Nb3Sn/Cu low-temperature composite superconducting wire;
a through hole is arranged at the center of the copper rod I, and n is connectedNbTiNbTi/Cu low-temperature composite superconducting wire and nNb3SnRoot of Nb3The Sn/Cu low-temperature composite superconducting wire is arranged in the through hole;
the cross sectional areas of the copper rod I, the copper rod II and the copper rod III are respectively more than or equal to S1。
And in the
And 2, selecting one of SnAg solder or SnPb solder during welding in the
Cross-sectional area S of normal temperature connecting rod in
S2＝I2/j2
wherein, I2-current carrying expected to be achieved by the normal temperature connecting rod;
j2current carrying capacity per unit area of the normal temperature connecting rod.
The normal temperature connecting rods in the step 4 comprise two normal temperature connecting rods, each normal temperature connecting rod comprises an outer copper pipe and an inner copper pipe which are coaxially sleeved, and the outer copper pipeCross sectional area S2；
Exhaust holes are respectively arranged at the upper end and the lower end of the outer copper pipe and the inner copper pipe at the same time; and the exhaust hole is arranged on the side wall of one side of the outer copper pipe and the inner copper pipe.
The specific process of the
The sample rod designed by the design method of the high-current-carrying critical current sample rod has the advantages that the loss of a large amount of liquid helium caused by heating of the copper lead when the current carrying is increased is reduced, the measurement cost is reduced, and the measurement precision is improved. The sample rod manufactured by the invention has stable background voltage in a superconducting state, can be conveniently deducted, calculates critical electricity according to the criterion of a detection standard and has high precision.
Drawings
FIG. 1 is a schematic structural diagram of a sample rod designed by the method for designing a sample rod with a large current-carrying critical current according to the present invention;
FIG. 2 is a schematic diagram of a split structure of a low-temperature copper rod in a sample rod designed by the method for designing a high current-carrying critical current sample rod;
FIG. 3 is a schematic view of an assembly structure of a low-temperature copper rod in a sample rod designed by the method for designing a high-current-carrying critical current sample rod according to the present invention;
FIG. 4 is a top view of a sample rod with a copper rod II and a superconducting wire being combined according to the method for designing a sample rod with a high current-carrying critical current;
FIG. 5 is a top view of a sample rod I and a superconducting wire of the sample rod designed by the method for designing a high current-carrying critical current sample rod according to the present invention;
FIG. 6 is a schematic structural diagram of a normal temperature rod of a sample rod designed by the method for designing a large current-carrying critical current sample rod according to the present invention;
FIGS. 7(a), (b) are graphs of measurements on different sample rods;
FIG. 8 is a measured graph of WIC;
FIG. 9 is Nb3Sn/Cu composite superconductor measurement graph.
In the figure, 1, a superconducting wire, 2, a copper rod I, 3, a copper rod II, 4, a copper rod III, 5, a horizontal transverse plate, 7, jacks I, 9, supporting blocks, 10, an insulating plate, 11, jacks II, 12, jacks III, 13, jacks IV, 14, a connecting rod, 15, a sample and 16 exhaust holes.
Detailed Description
The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.
The invention relates to a design method of a large current-carrying critical current sample rod, which specifically comprises the following steps:
NbTi/Cu and Nb with known current carrying capacity3The number of the Sn/Cu low-temperature composite superconducting wires is n1And n2Setting a safety coefficient gamma in consideration of the quench risk of the wire;
the number n of the NbTi/Cu low-temperature composite superconducting wiresNbTiComprises the following steps:
nNbTi＝n1/γ；
Nb3actual required number n of Sn/Cu low-temperature composite superconducting wiresNb3SnComprises the following steps:
nNb3Sn＝n2/γ；
cross-sectional area S of low temperature end copper rod1The calculation formula is as follows:
S1＝I1/j1
wherein, I1Current carrying expected by the low temperature end copper rod;
j1and the current carrying capacity of the copper rod at the low-temperature end per unit area.
At low temperature, the current carrying of the copper rod can reach 10A/mm2～15A/mm2The medium-low temperature end of the liquid helium adopts 15A/mm2The cross-sectional area of the required copper rod is calculated.
Only NbTi/Cu and Nb are calculated under high and low fields respectively3The reasons for the number of Sn/Cu low-temperature composite superconducting wires are as follows: 5T and Nb below3The Sn/Cu composite superconducting wire has the phenomenon of unstable magnetic flux under low field, and the NbTi/Cu composite superconducting wire is more than 8TThe wire has lost its current-carrying capacity and only relies on Nb3Sn/Cu composite superconducting wire.
Referring to fig. 1-3, the low-temperature end copper rod comprises a copper rod I2, a copper rod II3 and a copper rod III4, a horizontal
the device also comprises a vertically arranged copper rod III4, wherein the copper rod III4 and the copper rod II3 are arranged in parallel, the bottom of the copper rod III4 is connected to the supporting
A jack II11 is arranged at the center of the supporting
The horizontal
Grooves are arranged on the side walls of the copper rod II3 and the copper rod III4, and n is arranged at the position where the grooves are arranged on the copper rod II3 and the copper rod III4 respectivelyNbTiNbTi/Cu low-temperature composite superconducting wire and nNb3SnRoot of Nb3Sn/Cu low-temperature composite superconducting wire; NbTi/Cu low-temperature composite superconducting wire and nNb3SnRoot of Nb3The Sn/Cu low-temperature composite superconducting wire is collectively called a superconducting wire.
Referring to fig. 4, a schematic diagram of a structure of mounting a superconducting wire on a copper rod II3 is shown; the structure of mounting
Referring to FIG. 5, a through hole is opened at the center of the copper rod I2, and n isNbTiNbTi/Cu low-temperature composite superconducting wire and nNb3SnRoot of Nb3A
the cross-sectional areas of the copper rod I2, the copper rod II3 and the copper rod III4 are all S1.
The copper rod I2, the copper rod II3 and the copper rod III4 are all compounded by adopting a low-temperature soldering method.
The solder is one of SnAg solder or SnPb solder during soldering.
cross-sectional area S of normal temperature connecting rod in
S2＝I2/j2
wherein, I2-current carrying expected to be achieved by the normal temperature connecting rod;
j2current carrying capacity per unit area of normal temperature connecting rod, here 10A/mm2And (4) calculating.
Step 4, manufacturing a connecting rod connected with the normal temperature end according to the calculation result of the
in step 4, the normal temperature connecting rods 14 comprise two normal temperature connecting rods, each normal temperature connecting rod comprises an outer copper pipe and an inner copper pipe which are coaxially sleeved, and the cross-sectional area of each outer copper pipe is S2(ii) a Exhaust holes 16 are respectively arranged at the upper end and the lower end of the outer copper pipe and the inner copper pipe at the same time; and the exhaust hole 16 is arranged on one side wall of the outer copper pipe and one side wall of the inner copper pipe.
The distribution positions of the exhaust holes 16 on the connecting rod 14 are shown in fig. 6, the aperture of each exhaust hole 16 is 1-3 mm, and the number of the exhaust holes at the upper end and the lower end of each outer copper pipe and each inner copper pipe is 3-5;
the connecting rod 14 is made of red copper materials, in order to increase the cooling area, the design of a double-layer copper pipe is adopted, a layer of thin-wall through pipe with proper thickness is sleeved outside the inner copper pipe, and the area of the designed copper pipe needs to meet the requirement of a theoretical calculation part. The both ends all open the gas pocket (aperture 1mm ~ 3mm, 3 ~ 5 of quantity are suitable) under the top of connecting rod 14, guarantee that cold helium can pass through from each surface of connecting rod smoothly to and the heat that produces when the time takes away heavy current and passes through.
And 5, assembling the composite current lead manufactured in the
The specific process of the
All low temperature joints require argon arc welding and brazing with a brazing wire (hereinafter "brazing"). The brazing and soldering sequence is reasonably arranged, for example, when brazing is carried out after the completion of soldering, attention must be paid to fully cooling a soldered part in the process so as to prevent desoldering.
The design principle of the design method of the large current-carrying critical current sample rod is as follows: firstly, the design principle of a low temperature end is as follows: the low temperature end here refers to the portion of the sample rod immersed in liquid helium. By utilizing the characteristic that the superconducting wire can carry current without resistance at low temperature, the low-temperature superconducting wire NbTi/Cu (generally applied in the range of the magnetic field not exceeding 8T) and Nb are carried3Sn/Cu (generally applied in the range of magnetic field not exceeding 12T) is combined with pure copper to design a measuring rod capable of carrying over 2000A of current in the range of field intensity from zero field to 12T.
Connecting rod design principle: the liquid helium non-soaked sample rod reaches the end part of the room temperature. The part still adopts red copper as the material, but in order to fully utilize the latent heat of cold helium gas to reduce the heat generation of the sample rod, the sample rod is changed into a multi-layer sleeve structure so as to increase the cooling area, and the upper end and the lower end are respectively provided with an air hole to ensure the smoothness of a cold helium gas path.
The design method of the large current-carrying critical current sample rod is successfully used for manufacturing the sample rod for measuring the critical current of the WIC wire, and comprises the following specific operations:
1. calculating the amount of superconducting wire and the cross-sectional area of copper lead
The sample rod is designed to be 2500A, depending on the design current of the WIC superconducting wire. The NbTi/Cu superconducting wire used, which has a diameter of about 0.7mm, is about 400A under a 5T background field. And calculating the safety coefficient gamma to be 0.7 according to a formula to obtain 9 roots. And Nb with a diameter of about 0.8mm is used3The Sn/Cu superconducting wire is about 300A under a 12T background field. And calculating the safety coefficient gamma to be 0.7 according to a formula to obtain 10 roots.
The area of the copper lead part is calculated to be more than 450mm2。
2. Low-temperature end composite current lead manufacturing method
In liquid helium, the sample rod is prevented from being damaged by accidental quench of the superconducting wire, and the cross section of the copper rod at the low-temperature end is calculated to be more than 167mm2The requirement can be met by using a copper rod with the diameter of 15 mm.
According to the designed assembly sequence, part of the parts are brazed first. Embedding the superconducting wire into grooves in the copper rod II3 and the copper rod III4 in a mode of soldering the superconducting wire; the solder is SnAg alloy which is more suitable for low-temperature superconducting measurement. Superconducting wire was then fed into the through hole in the center of the copper rod I2.
3. Current lead manufacturing of connecting rod
Calculated, the sectional area of the connecting rod is more than 250mm2. A copper tube of 12mm external diameter and 6mm internal diameter was used and a thin walled copper tube of 16mm external diameter and 14mm internal diameter was fitted over the outside and each current pole (positive or negative) required a 2-way sleeve of copper tube of the same design, thus requiring a total of 4. Both ends are perforated separately.
4. Assembly
And (4) assembling and welding all the parts to complete the manufacture of the sample rod.
Proof of effectiveness
The sample rod manufactured by the design method of the large current-carrying critical current sample rod is used for measuring the critical current of the sample from the maximum current to about 2500A, and thousands of samples are measured so far. Fig. 7(a) is a graph of measurement using a common copper sample rod. Along with the increase of the current, the sample is influenced by the heating of the sample rod, the back bottom voltage fluctuates greatly when the sample is in a superconducting state, the critical current is difficult to calculate according to the criterion of the detection standard, the experiment fails, and the rod cannot measure the critical current under the current carrying. The sample rod (see fig. 7(b)) manufactured by the method has stable background voltage in a superconducting state, can be conveniently deducted, calculates critical power according to the criterion of a detection standard, and has high precision.