CN104483530B - Method and device for measuring non-uniformity of critical current density of surface layer of high-temperature superconducting bulk material - Google Patents
Method and device for measuring non-uniformity of critical current density of surface layer of high-temperature superconducting bulk material Download PDFInfo
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Abstract
The invention discloses a method and a device for measuring non-uniformity of critical current density of a surface layer of a high-temperature superconducting bulk material and belongs to the technical field of magnetic measurement. The measuring device comprises a magnet exciting coil, a secondary coil, a coil bracket, a to-be-measured sample platform, phase-locked amplifiers, a power amplifier, a precision resistor and an impedance regulation resistor; the measuring method comprises the following steps: firstly, fully cooling the to-be-measured sample platform, the magnet exciting coil, the secondary coil and to-be-measured high-temperature superconducting samples in absence of a magnetic field; then calculating to obtain an exciting current peak value and a tertiary harmonic voltage peak value of the secondary coil under the output voltage of each phase-locked amplifier; calculating critical current density values and transmission depths of the to-be-measured high-temperature superconducting samples under the exciting magnetic field strength and drawing a curve. The device and the method can be used for measuring the non-uniformity of critical current density of the surface layer of the high-temperature superconducting bulk material; the measurement error range is 10%; the voltage signals can be measured; the measurement precision is up to 1nV.
Description
Technical field
The invention belongs to Magnetic Measurement Technology field, can obtain in fields such as superconductor research, kicker magnet design, magnetic suspension
To certain application and extension, and in particular to a kind of high-temperature superconducting block top layer critical current density Inhomogeneity measurement method and
Device.
Background technology
With the development of high temperature superconductor technology, high-temperature superconducting block is gradually strided forward to practical, in super-conductive magnetic suspension
Before the aspects such as train, magnetic suspension bearing, high-intensity magnetic field permanent magnet, superconducting energy storage flywheel and superconducting motor have a wide range of applications
Scape.These depend primarily on the ability of superconductor capture magnetic field using involved performance parameter, and the energy of its capture magnetic field
Power relation proportional to the critical current density of superconductor.Critical current density is the basic of decision high-temperature superconducting block performance
One of characteristic parameter.Rational material selects particularly significant for the reliability of system, therefore needs for different application scenarios
Sign is measured to the critical current density of superconductor.Melt a kind of normal in the preparation method that preparation is high-temperature superconducting block
The method seen, it is possible to obtain the bulk of high critical current densities, has a wide range of applications.A seed nuclei used in the method, for example
NdBCO, the crystal orientation needed for producing.Therefore prepared superconduction block material shows anisotropy vertically, critical electricity
Current density also shows vertically significantly change.This characteristic parameter is significant for superconduction block material performance characterization, right
It is also particularly significant in the improvement of its technology of preparing.The change of critical current density has important reference for superconduction block material application
Value.
The critical current density method for inductive measurement of traditional superconduction block material has two kinds, and a kind of is based on measurement superconductor
The method of susceptibility；A kind of is the method based on measurement third harmonic response.The first is according in being positioned over susceptometer
The mean magnetizing situation of superconduction block material carry out calculating analysis, therefore distance high-temperature superconducting block top layer different depth cannot be obtained
The value of critical current density.Second method is current also to be carried out just for the uniform superconduction block material of critical current density characteristic
Measurement and analysis, do not analyze and characterize during in measurement due to the inhomogeneities of critical current density distribution, therefore,
For the magnetic measurement that the critical current density of superconduction block material surface part is distributed also is reported without correlation technique.
The content of the invention
It is an object of the invention to provide a kind of method and dress for measuring high-temperature superconducting block top layer critical current density
Put.The measurement apparatus include that magnet exciting coil, secondary coil, coil brace, testing sample platform, lock-in amplifier, power are put
Big device, precision resistance and impedance adjust resistance；Described precision resistance and impedance adjusts resistance and is connected on magnet exciting coil multiple twin
On lead-out wire, described magnet exciting coil multiple twin lead-out wire is connected with the outfan of power amplifier, and the two of the lock-in amplifier
Individual input connects respectively precision resistance voltage multiple twin lead-out wire and secondary coil multiple twin lead-out wire, and lock-in amplifier outfan connects
Connect the input of power amplifier；Wherein, magnet exciting coil is wound on coil brace, and secondary coil is wound on magnet exciting coil,
Coil brace is fixed on the central hole of testing sample platform, magnet exciting coil, secondary coil, coil brace, testing sample platform,
High-temperature superconductor sample to be measured is placed in liquid nitrogen container.
Described measuring method comprises the steps：
The first step, places and surveys example platform in liquid nitrogen container, places high-temperature superconductor sample to be measured in testing sample platform
Centre bore top；
Second step, places liquid nitrogen in liquid nitrogen container, makes testing sample platform, magnet exciting coil, secondary coil and height to be measured
Temp. superconductive sample is cooled down completely under without magnetic field state；
3rd step, opens lock-in amplifier and power amplifier working power and preheats；
4th step, connects measurement apparatus lead；
5th step, lock-in amplifier parameter setting；
6th step, sets " OSC OUT " initial value as 0.005V, and according to 1.1 times lock-in amplifier output electricity is incrementally increased
It is pressed with valid value；
7th step, under the output voltage of each lock-in amplifier, reads lock-in amplifier A input terminal voltage values, obtains
The voltage effective value of precision resistance, is designated as VR, i, the third harmonic voltage virtual value of lock-in amplifier B inputs is read, it is designated as
V32res；Exciting current peak value is respectively obtained by calculatingWherein r for precision resistance resistance, r=0.5 Ω, i
=1,2 ... M, M represent pendulous frequency, third harmonic voltage peak value in secondary coil
, M represents pendulous frequency；Stop increasing the output voltage of lock-in amplifier when exciting current reaches 0.6A；
8th step, calculates critical current density level of the high-temperature superconductor sample to be measured under certain excitation field intensity：
9th step, calculates penetration depth；
Tenth step, according to the critical current density level and magnetic penetration depth of high-temperature superconductor sample to be measured to data, obtains
Value of critical current density when apart from top layer different depth, and this change is depicted as into JC, i-diCurve.
The present invention compared with prior art, has the advantage that：
(1) range of error of the principle for adopting of the invention and method is for 10%.
(2) present invention is a kind of method and dress of lossless quick detection amount high-temperature superconducting block top layer critical current density
Put；
(3) can to provide any constant pressures of 0-5V defeated for the lock-in amplifiers of Signal Recovery 7264 of the present invention
Go out, output step-length is 1nV, harmonic inhibition capability -90dB, it is possible to achieve the measurement of voltage signal, its certainty of measurement is up to 1nV；
(4) resistor being connected in magnet exciting coil loop of the present invention (is adjusted including precision resistance and impedance
Resistance) it is thousand-island forest park, its temperature stability is 30ppm.Ensure that in magnet exciting coil by the stability of electric current, from
And produce stable AC magnetic field.
(5) excitation field frequencies range of the present invention is 270Hz, and lock-in amplifier can effectively weaken the friendship of other frequencies
The higher hamonic wave magnetic field in interference magnetic field and other frequency ranges of the varying magnetic field near excitation frequency is in the band interference.
Description of the drawings
Fig. 1 is the overall structure profile of apparatus of the present invention；
Fig. 2 is the V in two sections up and down that measurement obtains same sample in the present invention3-ImCurve, abscissa is not in figure
With the numbering of sample, vertical coordinate represents pcrmeability；
Fig. 3 is the J in two sections up and down that measurement obtains same sample in the present inventionc- d curves.
In figure：
1. magnet exciting coil；2. secondary coil；3. coil brace；4. testing sample platform；
5. high-temperature superconductor sample to be measured；6. precision resistance；7. impedance adjusts resistance；8. secondary coil multiple twin lead-out wire
9. precision resistance voltage multiple twin lead-out wire；10. magnet exciting coil multiple twin lead-out wire；11. lock-in amplifiers；
12. power amplifiers；13. liquid nitrogen containers；
Specific embodiment
Below in conjunction with drawings and Examples, the present invention is described in further detail.
The present invention provides a kind of high-temperature superconducting block top layer critical current density Inhomogeneity measurement method and device, such as schemes
Shown in 1, the measurement apparatus include magnet exciting coil 1, secondary coil 2, coil brace 3, testing sample platform 4, lock-in amplifier
11st, power amplifier 12, precision resistance 6 and impedance adjusts resistance 7.Described precision resistance 6 and impedance adjusts resistance 7 and connects
On magnet exciting coil 1, it is critical that the measuring method and device being previously mentioned in the present invention can be used for measurement high-temperature superconducting block top layer
The inhomogeneities of electric current density.
Wherein, magnet exciting coil 1 is wound on coil brace 3, and secondary coil 2 is wound on magnet exciting coil 1, coil brace 3
It is fixed on the central hole of testing sample platform 4.Coil brace 3 and testing sample platform 4 are for ensuring that treats that pyrometry surpasses
Lead the constant gap of the lower surface of sample 5 and magnet exciting coil 1, it is ensured that magnet exciting coil 1 and the sound construction of secondary coil 2, non-loosening, with
And ensure measurement process in whole device mechanical strength stability.Magnet exciting coil 1, secondary coil 2, coil brace 3, treat test sample
Product platform 4, high-temperature superconductor sample 5 to be measured are placed in liquid nitrogen container 13；Liquid nitrogen container 13 is used to contain liquid nitrogen, keeps liquid nitrogen to hold
The internal temperature of device 13 is in liquid nitrogen temperature.High-temperature superconductor sample 5 to be measured is height of the diameter not less than the diameter of twice magnet exciting coil 1
Temp. superconductive bulk, is positioned at the centre bore of testing sample platform 4 top.Described magnet exciting coil 1, secondary coil 2 and coil
Frame 3 is respectively positioned in the centre bore of testing sample platform 4, and described high-temperature superconductor sample 5 to be measured is covered on described centre bore
Side.
Lock-in amplifier 11 provides driving voltage reference signal, access power amplifier 12, power amplification by OUT outfans
Driving voltage signal afterwards accesses magnet exciting coil loop through magnet exciting coil multiple twin lead-out wire 10.Magnet exciting coil 1 is sharp for producing
Exciting field.The precision resistance 6 on magnet exciting coil 1 is connected on for the electric current in subsidiary magnet exciting coil 1：Concrete grammar be by
The precision resistance voltage multiple twin lead-out wire 9 for being connected on the two ends of precision resistance 6 accesses the A inputs of lock-in amplifier 11, and lock mutually amplifies
Device 11 has the function of voltage measurement, is had by Ohm's law, and the electrical current in magnet exciting coil 1 is measured equal to lock-in amplifier 11
Resistance of the voltage divided by precision resistance 6；The impedance being connected on magnet exciting coil 1 adjusts resistance 7 to be used to adjust magnet exciting coil loop
Overall impedance；When secondary coil 2 is used for detecting excitation field magnetization high-temperature superconductor sample 5 to be measured, high-temperature superconductor sample 5 to be measured
Magnetic responsiveness, concrete grammar is that secondary coil multiple twin lead-out wire 8 is connected to into lock-in amplifier B inputs.Lock-in amplifier 11 is read
Take fundamental voltage signal, the third harmonic voltage signal of B inputs of A inputs.
The high-temperature superconducting block top layer critical current density Inhomogeneity measurement method that the present invention is provided, ultimate principle is such as
Under:
Nearby relation can be calculated magnet exciting coil 1 by following between magnetic field and exciting current.
(ρ, θ, z), zero is in the surface of high-temperature superconductor sample 5 to be measured, high-temperature superconductor sample 5 to be measured to set up cylindrical coordinate
Lower surface is Z apart from the upper surface of magnet exciting coil 11, it is Z apart from the lower surface of magnet exciting coil 12, length Z of magnet exciting coil 12-Z1；Treat
It is I that pyrometry superconducting sample 5 carries out the alternating current that magnetized magnet exciting coil 1 is passed throughmCos ω t, ImFor exciting current peak value, ω
=2 π f are exciting current angular frequency, and f is exciting current frequency.Excitation coil 1 is produced parallel to the table of high-temperature superconductor sample 5 to be measured
Face magnetic field H0(ρ t) can be given by formula (1)：
H0(ρ, t)=- ImF1(ρ)cosωt (1)
F in formula (1)1(ρ) parameter determined for loop construction, is given by formula (2)：
In formula (2), ρ ', θ, z are integration variable, and ρ is function F1(ρ) variable；N is the number of turn of magnet exciting coil 1；R1To encourage
The internal diameter of magnetic coil 1, R2For the external diameter of magnet exciting coil 1, the sectional area S=(R of magnet exciting coil 12-R1)×(Z2-Z1)；By magnet exciting coil
1 dimensional parameters bring formula (2) into and can obtain parameter F1(ρ), by F1(ρ) bringing formula (1) into can obtain high-temperature superconductor sample to be measured
The Surface field H of product 50(ρ, t) with exciting current peak ImRelation, the amplitude of excitation field is on coordinate axess ρ directions in coordinate ρ
=ρ*Place reaches peak value.
Under magnetic field excitation, critical current density J of high-temperature superconductor sample 5 to be measuredcWith exciting current peak Im, magnet exciting coil 1
Interior third harmonic voltage peak value V31Between relation can be calculated by following.
Consider shielding action of the supercurrent to magnetic field in the body of high-temperature superconductor sample 5 to be measured, can be approximate think magnetization
The magnetic line of force of superconductor is oriented parallel to superconduction block material interface direction, i.e., parallel to the magnetic-field component of sample surfaces in excitation field
Play Main Function.For third harmonic response of the high-temperature superconductor sample 5 to be measured under longitudinal magnetic field excitation, there is computing formula
(3), (4) are given：
V31=G3ωIm 2/Jc (3)
The third harmonic voltage peak value V of secondary coil 232With third harmonic voltage peak value V in magnet exciting coil 131Have and there is direct ratio
Relation V32=kV31, k is proportionality coefficient, can be obtained by experiment.Therefore the third harmonic voltage peak value V of magnet exciting coil 131Can pass through
The measurement third harmonic voltage peak value V of secondary coil 232Obtain indirectly.μ0For permeability of vacuum, μ0=4 π × 10-7N/A2。
Any two points in the third harmonic voltage collected by secondary coil 2, can be calculated current magnetic field and swash
Critical current density J under encouragingC, i：
JC, i=G3ω(IM, i+1 2-IM, i 2)/(2.5*(V32, i+1-V32, i)) (5)
During measurement, exciting current such as 2 milliamperes, is started to incrementally increase by smaller current, and is surveyed under each exciting current
Third harmonic voltage peak value V in amount secondary coil voltage signal32, so as to obtain a series of (Im, V32) data point.In excitation
When electric current is less, third harmonic voltage peak value V in secondary coil 232Very little, the fluctuation that there is numerical value.Setting third harmonic voltage
Peak value V32It is i to start exciting current when being incremented by*, exciting current is more than into i*Series of points as valid data, by excitation
Electric current is less than i*Point cast out.By i+1, i-th exciting current amplitude IM, i+1、IM, iAnd corresponding secondary coil three times
Harmonic voltage peak value V32, i+1, V32, iBringing formula (5) into both can obtain in exciting current peak ImHigh-temperature superconductor to be measured under effect
Critical current density level J inside sample 5C, i。
Magnetic penetration depth is estimated by the ideal superconductor model that susceptibility is -1, i.e., in high-temperature superconductor sample 5 to be measured
Magnetic field intensity z-axis durection component Hz=0 at surface, ρ direction of principal axis swarming value H ρ (ρ*)=2H0(ρ*) when penetration depth diValue be：
Can be obtained with magnetic field penetration high-temperature superconductor sample 5 to be measured by formula (5) and (6), resulting is a series of
Change critical current density level, that is, can obtain apart from 5 surface different distance of high-temperature superconductor sample to be measured when critical electricity
Current density value, so as to observe the inhomogeneities of critical current density.
The present invention provides a kind of high-temperature superconducting block top layer critical current density Inhomogeneity measurement method, the measurement side
Method comprises the steps：
The first step, places and surveys example platform 4 in liquid nitrogen container 13, places high-temperature superconductor sample 5 to be measured in testing sample
The centre bore top of platform 4, keeps being in close contact, and the diameter of high-temperature superconductor sample 5 to be measured should be greater than 2 times of magnet exciting coil diameter
(as shown in Figure 1) magnet exciting coil 1, in centre bore, secondary coil 2 and coil brace 3 are all covered by high-temperature superconductor sample 5 to be measured
Lid is internally.
Second step, in liquid nitrogen container 13 liquid nitrogen is placed, and is made testing sample platform 4, magnet exciting coil 1, secondary coil 2 and is treated
Pyrometry superconducting sample 5 is cooled down completely under without magnetic field state.
3rd step, opens lock-in amplifier 11 and the working power of power amplifier 12 and preheats 20 minutes.
4th step, connects measurement apparatus lead；
Concrete steps include：
4.1st, the outfan " OUT " of lock-in amplifier 11 is connected on the input terminal of power amplifier 12；By magnet exciting coil
Multiple twin lead-out wire 10 is connected on the lead-out terminal of power amplifier 12；
4.2nd, the precision resistance voltage multiple twin lead-out wire 9 at the two ends of precision resistance 6 connected in magnet exciting coil loop is connect
Enter to lock-in amplifier A inputs；
4.3rd, secondary coil multiple twin lead-out wire 8 is linked into into lock-in amplifier B inputs.
5th step, the parameter setting of lock-in amplifier 11；
Concrete steps include：
5.1 frequencies f=270Hz for adjusting the output voltage of lock-in amplifier 11；
5.2 adjust the output voltage virtual value of lock-in amplifier 11 for 0V；
5.3 adjust the input phase of lock-in amplifier 11 for 0；
The voltage amplification factor of 5.4 setting power amplifier 12 is 5 times；
6th step, according to 1.1 times the output voltage virtual value of lock-in amplifier 11 is incrementally increased, i.e., set " OSC respectively
OUT " is 0.005V, 0.0055V, and 0.00605V, 0.006655V ... wait magnitude of voltage.
7th step, under the output voltage of each lock-in amplifier 11, reads lock-in amplifier A input terminal voltage values, obtains
To the voltage effective value of precision resistance 6, V is designated asR, i, read the third harmonic voltage virtual value of lock-in amplifier B inputs, note
For V32res.Exciting current peak value is respectively obtained by calculatingWherein r for precision resistance 6 resistance, r=0.5
Ω, i=1,2 ... M, represents pendulous frequency, third harmonic voltage peak value in secondary coil 2 , M represents pendulous frequency.According to coil design parameter, third harmonic voltage amplitude is secondary wire in magnet exciting coil 1
2.5 times of circle 2, i.e. proportionality coefficient k=1/2.5.Stop increasing the output of lock-in amplifier 11 when exciting current reaches 0.6A
Voltage.For the measurement result of two planes of A, B up and down of a sample is drawn in such as Fig. 2, wherein abscissa is
Exciting current peak Im, vertical coordinate is secondary coil third harmonic voltage peak value V32。
8th step, calculates critical current density level J of the high-temperature superconductor sample 5 to be measured under certain excitation field intensityC, i：
Coil parameterN=410,2R1=1.5mm, 2R2=6mm, Z1=0.4mm, Z2=2.9mm, ρ *=
1.9mm.Bring above-mentioned parameter into formula (1), (2), (4), coil parameter F can be obtained1(ρ=1.9mm)=2.6 × 104m-1,
G3=242H/m2.Bring above-mentioned value into formula (5) i.e. JC, i=G3ω(IM, i+1 2-IM, i 2)/(2.5*V32, i+1-V32, in i, can
To obtain critical current density level Jc, i of the high-temperature superconductor sample 5 to be measured under certain excitation field intensity, I in formulaM, i+1、IM, i、
V32, i+1、V32, iDifference i+1 exciting current peak value, i-th exciting current peak value, the triple-frequency harmonics of i+1 secondary coil 2
Voltage peak, i-th third harmonic voltage peak value of secondary coil 2.
9th step, calculates penetration depth.
According to formula (6), i.e.,And the 8th in step
The J for arrivingC, i, the magnetic penetration depth d under each excitation field can be obtainedi。
Tenth step, according to the eight, the nine steps data are obtained, it is possible to obtain critical current density is when apart from top layer different depth
Value, and this change can be depicted as JC, i-diCurve (as shown in Figure 3).Sample A, B both sides are given in accompanying drawing 3
Measurement result.Two curves show the critical current density on A, B both sides top layer with the Changing Pattern apart from case depth, by
Wherein every curve it can be seen that, critical current density non-constant value changes with depth difference, shows uneven
Property.The measurement result of contrast A, B both sides, the critical current density numerical value away from both sides differs the 2-3 order of magnitude, and this is illustrated in sample
The crystallization degree of product c-axis direction (crystal growth direction) diverse location has marked difference, i.e., also show significantly uneven
Property.
Claims (2)
1. high-temperature superconducting block top layer critical current density Inhomogeneity measurement method, it is characterised in that：Described measuring method
Comprise the steps,
The first step, places testing sample platform in liquid nitrogen container, places high-temperature superconductor sample to be measured in testing sample platform
Centre bore top；
Second step, places liquid nitrogen in liquid nitrogen container, makes testing sample platform, magnet exciting coil, secondary coil and treats that pyrometry surpasses
Lead sample to cool down completely under without magnetic field state；
3rd step, opens lock-in amplifier and power amplifier working power and preheats；
4th step, connects measurement apparatus lead；
5th step, lock-in amplifier parameter setting；
6th step, sets " OSC OUT " initial value as 0.005V, and incrementally increasing lock-in amplifier output voltage according to 1.1 times has
Valid value；
7th step, under the output voltage of each lock-in amplifier, reads lock-in amplifier A input terminal voltage values, obtains precision
The voltage effective value of resistance, is designated as VR, i, the third harmonic voltage virtual value of lock-in amplifier B inputs is read, it is designated as V32res；
Exciting current peak value is respectively obtained by calculatingWherein r for precision resistance resistance, r=05 Ω, i=1,
2 ... M, M represent pendulous frequency, third harmonic voltage peak value in secondary coilI=1,2 ... M, M is represented
Pendulous frequency；Stop increasing the output voltage of lock-in amplifier when exciting current reaches 0.6A；
8th step, calculates critical current density level J of the high-temperature superconductor sample to be measured under certain excitation field intensityC, i：
JC, i=G3ω(IM, i+1 2-IM, i 2)/(2.5*(V32, i+1-V32, i)),
Wherein,ρ is zero in the pole of the cylindrical coordinate of high-temperature superconductor sample surfaces to be measured
Radius, F1(ρ) parameter determined for loop construction；μ0For permeability of vacuum, μ0=4 π × 10-7N/A2；IM, i+1、IM, i、V32, i+1、
V32, iDifference i+1 exciting current peak value, i-th exciting current peak value, i+1 secondary coil third harmonic voltage peak
Value, i-th secondary coil third harmonic voltage peak value；ω is exciting current angular frequency；
9th step, calculates penetration depth；
By calculated JC, iBring equation below into：
Wherein, H0m, j(ρ*) and H0m, j+1(ρ*) excitation field that is respectively corresponding to jth, j+1 measurement point, H0m, i*(ρ*) for the
i*Excitation field corresponding to individual measurement point；
Tenth step, according to the critical current density level and magnetic penetration depth data of high-temperature superconductor sample to be measured, obtains critical electricity
Value of current density when apart from top layer different depth, and this change is depicted as into JC, i-diCurve.
2. high-temperature superconducting block top layer critical current density Inhomogeneity measurement method according to claim 1, its feature exists
In：The parameter setting of described lock-in amplifier includes：
5.1 frequencies f=270Hz for adjusting lock-in amplifier output voltage；
5.2 adjust lock-in amplifier output voltage virtual value for 0V；
5.3 adjust lock-in amplifier input phase for 0；
5.4 setting power amplifier voltage amplification factors are 5 times.
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