CN101446611A - Device for measuring critical current properties of high-temperature superconductor by using variable-cross-section current lead wire - Google Patents

Abstract

The invention relates to a device for measuring critical current properties of a high-temperature superconductor by using a variable-cross-section current lead wire. The straight copper bar variable-cross-section current lead wire used by the device uses the improved gas-cooled current lead wire segmented calculation method to carry out the optimized design of geometric parameters of the variable-cross-section current lead wire; and a mixed lead wire section which is formed by welding a copper stranded wire and a BSCCO tape in parallel is used for connecting the tail end of the straight copper bar variable-cross-section current lead wire with a YBCO tape. The device achieves the purposes of reducing the heat leakage of current and reducing the cooling cost of a system for testing the critical current properties of YBCO through the mixed structure.

Description

A kind of device that uses variable-cross-section current lead wire to measure the high-temperature superconductor critical current properties

Technical field

The present invention relates to a kind of device that uses variable-cross-section current lead wire to measure the high-temperature superconductor critical current properties, belong to the superconductor technology application.

Background technology

The critical characteristic test experiments of high-temperature superconductor is described as one of experiment the most classical on the modern physics history.Critical current properties is one of three critical characteristics of superconductor.The critical current properties experiment of high-temperature superconductor is soaked in belt material of high temperature superconduct in the cryogenic liquid (as liquid nitrogen, liquid helium) usually, records different critical electric current values by changing magnetic field size and magnetic direction.

Current feed plays crucial effect in measuring the critical current properties experiment, be used for connecting room temperature power supply and superconducting tape, and apply electric current to the latter.During this, lead-in wire low temperature end face passes out the evaporation that the heat that comes causes cooling liquid, and the cold air that evaporates continues to cool off current feed again.Under overfreezing liquid nitrogen temperature 64K, yttrium is the critical current density of oxide YBCO superconducting tape even can reaches tens thousand of ampere/square centimeters.Joule heat that high-current leading rises and the conductive heat leakage of bringing owing to the temperature difference at lead-in wire two ends will cause a large amount of evaporations of cooling liquid, thereby increase cooling cost greatly.Therefore the optimal design of current feed just seems extremely important.

Because lead-in wire is in the temperature difference of room temperature and cryogenic liquid, lead-in wire is the closer to the low-temperature end position, thermal conductivity is big more, and resistivity is more little, thereby causes conductive heat leakage bigger, Joule heat is less, the refrigerating gas temperature of bottom of going between simultaneously is minimum, and cooling power is higher, and traditional uniform cross section current feed does not utilize these characteristics that go up current feed, cause the waste of refrigerating gas, increased cooling cost indirectly.The optimal design of current feed geometrical structure parameter is exactly will be by finding the solution of current feed thermal balance equation being realized to the length of current feed and the computation optimization of sectional area size, the heat minimum that feasible lead-in wire low temperature end face spills, reduce the consumption of heat eliminating medium, reduce cooling cost.Publish first piece of relevant superconducting magnet in nearly 50 years with current feed optimal design article from nineteen fifty-nine scientist McFee R. at " Review of Scientific Instruments " magazine, scientific worker and engineering technical personnel that various countries are engaged in superconductor applications research have done a large amount of work on the current feed optimum Design of Parameters, thereby a variety of computing method have appearred, the pure analytic solution of partial differential equation for example, the segmentation computing method are based on numerical computation method of finite element software etc.Some can be common to most GAS-COOLED CURRENT LEAD design in these methods, and some is then only at some special operating modes.Generally speaking these computing method all are to be based upon on the basis that the current feed thermal balance equation is found the solution, in conjunction with concrete operating mode, to some calculating parameters (as the rerum natura of lead material, lead-in wire and the heat exchanger effectiveness of refrigerating gas etc.) do some rational hypothesis, thus obtain one comparatively near the parameters optimization of actual conditions.

Summary of the invention

The objective of the invention is to design a kind of device that uses variable-cross-section current lead wire to measure the high-temperature superconductor critical current properties, the straight copper rod variable-cross-section current lead wire that this device uses uses improved GAS-COOLED CURRENT LEAD segmentation computing method that the variable-cross-section current lead wire geometric parameter has been carried out optimal design; The welding in parallel of copper stranded conductor and bismuth system oxide BSCCO band mix lead segments, being used to connect straight copper rod variable cross section lead terminal and yttrium is oxide YBCO band.By such mixed structure, reached and reduce current feed and leak heat, reduce the purpose of YBCO measuring critical current properties system cools cost.Content of the present invention comprises:

The present invention proposes a kind of device that uses variable-cross-section current lead wire to measure the high-temperature superconductor critical current properties, the indoor temperature end binding post that it is characterized in that straight copper rod variable-cross-section current lead wire is installed on the Dewar flange, the upper end of straight copper rod variable-cross-section current lead wire is welded on the lower end of indoor temperature end binding post, the lower end of straight copper rod variable-cross-section current lead wire is mixed lead segments with BSCCO band and copper stranded conductor and is linked to each other, be that oxide YBCO band links to each other with yttrium more afterwards, yttrium is the strip even air gap that oxide YBCO band places background magnet middle part, and be that oxide YBCO band suspension rod is connected on the Dewar flange by yttrium, the background magnet is placed on the background magnet pallet and by background magnet suspension rod and is connected on the Dewar flange, the end of straight copper rod variable-cross-section current lead wire is in the liquid nitrogen liquid level position, and bismuth system oxide BSCCO band mixes lead segments and is among the liquid nitrogen with copper stranded conductor.

Straight copper rod variable-cross-section current lead wire has the cross section that gradually changes of using the design of GAS-COOLED CURRENT LEAD segmentation computing method described in the device of the present invention.

Description of drawings

Fig. 1 shows the current down-lead structure analysis and calculation model;

Fig. 2 shows current feed segmentation computation model synoptic diagram;

Fig. 3 shows current feed and leaks heat and liquid nitrogen vaporization rate relation curve;

Fig. 4 shows variable cross section GAS-COOLED CURRENT LEAD computing method process flow diagram;

Fig. 5 shows current feed Temperature Distribution simulation result;

Fig. 6 shows current feed design physical dimension parameter, wherein, and 5, straight copper rod variable-cross-section current lead wire; 6, the BSCCO band mixes lead segments with copper stranded conductor;

Fig. 7 shows current feed practical set figure, wherein, and 1, the Dewar flange; 2, indoor temperature end binding post; 3, background magnet suspension rod; 4, YBCO band suspension rod; 5, straight copper rod variable-cross-section current lead wire; 6, the BSCCO band mixes lead segments with copper stranded conductor; 7, YBCO band; 8, background magnet; 9, background magnet pallet.

Embodiment

Be to describe design concept of the present invention in detail, Fig. 1 is the heat flux distribution figure of a typical GAS-COOLED CURRENT LEAD, according to classical thermal conduction study law, can analyze that to obtain the each several part hot-fluid as follows:

(1), can get the heat that passes through in cross section, x place, current feed optional position and be according to Fourier heat equation

$Q=-\mathrm{KA}\frac{\mathrm{dT}}{\mathrm{dx}}---\left(1\right)$

In the formula, Q is a heat flux, refers to pass through in the unit interval heat of a certain area of section, and unit is W; K is coefficient of heat conductivity or thermal conductivity, and the capacity of heat transmission of its reflection object is often recorded by experiment, and unit is W/ (mK); A is the lead-in wire sectional area, and promptly perpendicular to the area of section of heat conduction direction, unit is m ²DT/dx is the thermograde of lead-in wire section; Negative sign represents that the heat transferred direction is opposite with the thermograde direction.

(2) cool off according to newton that formula obtains refrigerating gas and current feed convection heat transfer amount is

$Q=\mathrm{hA\ΔT}=m{C}_p\frac{{\mathrm{dT}}_g}{\mathrm{dx}}---\left(2\right)$

In the formula

It is the absolute value of the difference of lead-in wire wall surface temperature and refrigerating gas temperature; A is the convection heat transfer area; H is a convection transfer rate

The Joule heat size that produces when (3) current feed is by electric current I is

$Q={\mathrm{<figure-callout\; id="2"\; label="I"\; filenames="A200810227184E00123.png"\; state="\{\{state\}\}">I</figure-callout>}}^2\mathrm{\&rho;}\frac{L}{A}---\left(2\right)$

ρ is the resistivity of lead material in the formula, and L is a wire length, and A is the lead-in wire sectional area.

According to law of conservation of energy, it is as follows that we can obtain the thermal balance equation of GAS-COOLED CURRENT LEAD

$\frac{d(k\left(T\right)\mathrm{SdT}/\mathrm{dx})}{\mathrm{dx}}-\mathrm{fm}{C}_P\frac{\mathrm{dT}}{\mathrm{dx}}+\mathrm{\&rho;}\left(T\right){\mathrm{<figure-callout\; id="2"\; label="I"\; filenames="A200810227184E00123.png"\; state="\{\{state\}\}">I</figure-callout>}}^2/S=0---\left(4\right)$

Fig. 2 is a GAS-COOLED CURRENT LEAD segmentation computing method infitesimal analysis synoptic diagram, establishes lead-in wire is divided into the n section, and the temperature difference at every section lead-in wire two ends is all equated, make being Δ T, and it is equal to establish lead-in wire sectional area everywhere, so

$\mathrm{\&Delta;T}=\frac{1}{n}(t-t_{n+1})---\left(5\right)$

If segments is enough big, for the electricalresistivity of each section lead material _i, thermal conductivity k _iSpecific heat C with refrigerating gas _iWhat can be similar to thinks constant.So i section lead-in wire satisfies the differential equation with downstream condition

$\left\{\begin{array}{c}{Q}_{\mathrm{ci}}=k_{i}S\frac{\mathrm{dT}}{\mathrm{dx}}+\frac{I^2}{S}{\mathrm{\&rho;}}_{i}x-\mathrm{fm}{C}_{\mathrm{pi}}(T-t_{n+1})\\ x=X_i,T=t_i,x=X_i+{\mathrm{\&Delta;X}}_i,T=t_{i+1}\end{array}\right.---\left(6\right)$

It is found the solution the Temperature Distribution function that can obtain i section lead-in wire is

$T_i\left(x\right)=e^{\frac{\mathrm{fm}{C}_{\mathrm{Pi}}}{{\mathrm{Sk}}_i}}\{\frac{\mathrm{fm}{C}_{\mathrm{Pi}}}{{\mathrm{Sk}}_i}x[\frac{Q_{\mathrm{ci}}}{{\mathrm{Sk}}_i}-\frac{\mathrm{fm}{C}_{\mathrm{Pi}}{t}_i}{{\mathrm{Sk}}_i}-\frac{{\mathrm{<figure-callout\; id="2"\; label="I"\; filenames="A200810227184E00123.png"\; state="\{\{state\}\}">I</figure-callout>}}^2{\mathrm{\&rho;}}_i}{S^2{k}_i}x]\mathrm{dx}+B\}---\left(7\right)$

Put in order

$T_i\left(x\right)=-\frac{Q_{\mathrm{ci}}}{\mathrm{fm}{C}_{\mathrm{Pi}}}+t_i+\frac{{\mathrm{<figure-callout\; id="2"\; label="I"\; filenames="A200810227184E00123.png"\; state="\{\{state\}\}">I</figure-callout>}}^2\mathrm{\&rho;}}{S{\mathrm{fmC}}_{\mathrm{Pi}}}x+\frac{I^2{k}_i\mathrm{\&rho;}}{f^2{m}^2{C}_{\mathrm{Pi}}^2}+{\mathrm{Be}}^{\frac{\mathrm{fm}{C}_{\mathrm{Pi}}}{{\mathrm{Sk}}_i}x}---\left(8\right)$

Boundary condition is brought into, can be solved

$B=\frac{Q_{\mathrm{Ci}}}{\mathrm{fm}{C}_{\mathrm{Pi}}}-\frac{I^2{k}_i\mathrm{\&rho;}}{f^2{m}^2{\mathrm{<figure-callout\; id="2"\; label="C\; Pi"\; filenames="A200810227184E00123.png"\; state="\{\{state\}\}">C</figure-callout>}}_{\mathrm{Pi}}^{}}$

$t_{i+1}-t_i=(\frac{Q_{\mathrm{Ci}}}{\mathrm{fm}{C}_{\mathrm{Pi}}}-\frac{I^2{k}_i\mathrm{\&rho;}}{f^2{m}^2{C}_{\mathrm{Pi}}^2})(e^{\frac{\mathrm{fm}{C}_{\mathrm{Pi}}{X}_i}{{\mathrm{Sk}}_i}}-1)+\frac{{\mathrm{<figure-callout\; id="2"\; label="I"\; filenames="A200810227184E00123.png"\; state="\{\{state\}\}">I</figure-callout>}}^2{\mathrm{\&rho;}}_i{\mathrm{\&Delta;X}}_i}{\mathrm{fm}{C}_{\mathrm{Pi}}S}---\left(9\right)$

Formula (9) arrangement is obtained from the heat Q of i section lead terminal outflow _Ci

$Q_{\mathrm{ci}}=\frac{\mathrm{fm}{C}_{\mathrm{Pi}}(t_i-t_{i+1})-{\mathrm{<figure-callout\; id="2"\; label="I"\; filenames="A200810227184E00123.png"\; state="\{\{state\}\}">I</figure-callout>}}^2{\mathrm{\&rho;}}_i\frac{{\mathrm{\&Delta;X}}_i}{S}}{e^{\frac{\mathrm{fm}{C}_{\mathrm{pi}}}{k_i}\frac{{\mathrm{\&Delta;X}}_i}{S}}-1}+\frac{I^2{k}_i{\mathrm{\&rho;}}_i}{\mathrm{fm}{C}_{\mathrm{pi}}}---\left(10\right)$

Δ Xi is the length of i section lead-in wire in the formula.In addition, for i section lead-in wire,, establish an equation under should satisfying according to law of conservation of energy

$Q_i=Q_{i-1}+{\mathrm{<figure-callout\; id="2"\; label="I"\; filenames="A200810227184E00123.png"\; state="\{\{state\}\}">I</figure-callout>}}^2{\mathrm{\&rho;}}_i\frac{{\mathrm{\&Delta;X}}_i}{S}-\mathrm{fm}{C}_{\mathrm{pi}}\mathrm{\&Delta;T}---\left(11\right)$

Cancellation Qi, put in order

$[\frac{f^2{m}^2{C}_{\mathrm{pi}}^2}{I^2{k}_i{\mathrm{\&rho;}}_i}(t_i-t_{i+1})-\frac{{\mathrm{fmC}}_p}{k_i}\frac{{\mathrm{\&Delta;X}}_i}{S}+1]\exp \left(\frac{{\mathrm{fmC}}_{\mathrm{pi}}}{k_i}\frac{{\mathrm{\&Delta;X}}_i}{S}\right)-1=0---\left(12\right)$

By the iterative computation that goes between piecemeal, just can be in the hope of the horizontal ratio of the length of each section lead-in wire

$\frac{{\mathrm{\&Delta;X}}_1}{S},\frac{{\mathrm{\&Delta;X}}_2}{S},\frac{{\mathrm{\&Delta;X}}_3}{S},...,\frac{{\mathrm{\&Delta;X}}_n}{S}$

Leakage heat with each section lead-in wire

Q ₁，Q ₂，Q ₃，...，Q _n

Wherein Qn is exactly the minimum heat that flows into Cryo Equipment from the current feed lower end, promptly

Q _min＝Q _n (13)

The long horizontal ratio of the best of whole current feed is that each section lead-in wire is long horizontal than sum, promptly

${\left(\frac{X}{A}\right)}_{\mathrm{opt}}=\underset{i=1}{\overset{n}{\mathrm{\&Sigma;}}}\frac{{\mathrm{\&Delta;X}}_i}{S}---\left(14\right)$

Self cooling variable-cross-section current lead wire computing method are to add a sectional area tapering function in the segmentation of lead-in wire is calculated, and make the sectional area of lead-in wire reduce to reach the purpose that makes up the variable cross section lead-in wire piecemeal.

Want the form factor of calculating optimum lead-in wire, the liquid helium rate of evaporation that causes by the heat of the terminal inflow of current feed low-temperature (low temperature) vessel when at first needing to obtain lead-in wire size the best.Desirable a series of nitrogen flow value is calculated the heat that flows out from lead terminal, then can draw the curve of a Q=f (m) according to these group data.For self cooling current feed, satisfy linear functional relation Q=m*C between liquid nitrogen vaporization rate and the liquid nitrogen latent heat simultaneously _L, can make a curve again, the horizontal ordinate m value of two intersections of complex curve place correspondences is the liquid nitrogen vaporization rate value of self cooling optimization lead-in wire.Fig. 3 this two curves that drawn, intersection point is the liquid nitrogen vaporization rate of being asked.

After trying to achieve the liquid nitrogen vaporization rate value of optimizing lead-in wire, can begin to calculate the Q of each section of sectional leading wires according to the segmentation computing method _iWith Δ X _i/ S.Set a lead-in wire indoor temperature end sectional area radius initial value R simultaneously, lead-in wire sectional area change in radius step delta r, then S _i=π (R-i Δ r) ², S _iWith Δ X _iThe length Δ X that/S multiplies each other and can obtain every section lead-in wire _i, the total length X that addition can be optimized and go between.Fig. 4 is the process flow diagram of computing method.

Use these computing method to the system design of the second generation YBCO measuring critical current properties of high-temperature superconducting tape variable-cross-section current lead wire.Fig. 5 is the Temperature Distribution simulation calculation result of current feed current feed under the 500A rated current for this reason.

In addition, mix lead segments one section of the terminal welding of straight copper rod by what copper stranded conductor and the parallel connection of BSCCO superconducting tape were welded.Among the BSCCO superconducting tape was soaked in liquid nitrogen, when working in superconducting state, electric current will be among BSCCO superconduction band flows into the YBCO band, thereby does not produce Joule heat.Be connected current feed with simple use copper stranded conductor and compare, further reduced the leakage heat of current feed with YBCO band situation.

Optimal design size according to the computation optimization gained has been manufactured variable-cross-section current lead wire, as shown in Figure 6.Current feed practical set figure as shown in Figure 7.Current feed indoor temperature end binding post 2 is installed on the Dewar flange 1, and the upper end of straight copper rod variable-cross-section current lead wire 5 is welded on the lower end of indoor temperature end binding post 2, and its lower end is mixed lead segments 6 with BSCCO band and copper stranded conductor and linked to each other, and links to each other with YBCO band 7 more afterwards.YBCO band 7 places the strip even air gap at background magnet 8 middle parts and is connected on the Dewar flange 1 by YBCO band suspension rod 4.Background magnet 8 is placed on the background magnet pallet 9 and by background magnet suspension rod 3 and is connected on the Dewar flange 1.In the device, the end of straight copper rod variable cross section lead-in wire 5 is in the liquid nitrogen liquid level position, and the BSCCO band mixes lead segments 6 and is among the liquid nitrogen with copper stranded conductor.By such mixed structure, reached and reduce current feed and leak heat, reduce the purpose of YBCO measuring critical current properties system cools cost.

Invention has been described according to specific exemplary embodiment herein.It will be conspicuous carrying out suitable replacement to one skilled in the art or revise under not departing from the scope of the present invention.Exemplary embodiment only is illustrative, rather than to the restriction of scope of the present invention, scope of the present invention is by appended claim definition.

Claims (2)

1, a kind of device that uses variable-cross-section current lead wire to measure the high-temperature superconductor critical current properties, the indoor temperature end binding post (2) that it is characterized in that straight copper rod variable-cross-section current lead wire (5) is installed on the Dewar flange (1), the upper end of straight copper rod variable-cross-section current lead wire (5) is welded on the lower end of indoor temperature end binding post (2), the lower end of lead-in wire (5) is mixed lead segments (6) with bismuth system oxide BSCCO band and copper stranded conductor and is linked to each other, be that oxide YBCO band (7) links to each other with yttrium more afterwards, yttrium is the strip even air gap that oxide YBCO band (7) places background magnet (8) middle part, and be that oxide YBCO band suspension rod (4) is connected on the Dewar flange (1) by yttrium, background magnet (8) is placed on background magnet pallet (9) and goes up and be connected on the Dewar flange (1) by background magnet suspension rod (3), the end of straight copper rod variable-cross-section current lead wire (5) is in the liquid nitrogen liquid level position, and bismuth system oxide BSCCO band mixes lead segments (6) and is among the liquid nitrogen with copper stranded conductor.

2, device as claimed in claim 1 is characterized in that described straight copper rod variable-cross-section current lead wire (5) has the cross section that gradually changes of using the design of GAS-COOLED CURRENT LEAD segmentation computing method.

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