JP4302556B2 - Critical current density measuring method and apparatus - Google Patents

Critical current density measuring method and apparatus Download PDF

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JP4302556B2
JP4302556B2 JP2004072223A JP2004072223A JP4302556B2 JP 4302556 B2 JP4302556 B2 JP 4302556B2 JP 2004072223 A JP2004072223 A JP 2004072223A JP 2004072223 A JP2004072223 A JP 2004072223A JP 4302556 B2 JP4302556 B2 JP 4302556B2
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current density
critical current
permanent magnet
repulsive force
thin film
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重利 大嶋
敦 齊藤
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本発明は製造した高温超電導体薄膜の臨界電流密度測定方法及びその装置に関するものであり、より詳細には、超電導薄膜と永久磁石の磁場との相互作用で得られる斥力を荷重センサで測定し、予め磁化特性法や四端子法、誘導法などにより求めておいた臨界電流密度（Ｊｃ）と斥力／超電導薄膜の膜厚（ａ1 ／ｄ）のグラフ（Ｊｃ−ａ1 ／ｄのグラフ）から、前記測定値を使用して非破壊で臨界電流密度を簡便に測定することができる臨界電流密度測定方法及び装置に関するものである。 The present invention relates to a method and apparatus for measuring the critical current density of a manufactured high-temperature superconductor thin film, and more specifically, the repulsive force obtained by the interaction between the superconducting thin film and the magnetic field of a permanent magnet is measured with a load sensor, From the graph (Jc-a 1 / d graph) of critical current density (Jc) and repulsive force / superconducting thin film thickness (a 1 / d) obtained in advance by the magnetization characteristic method, four-terminal method, induction method, etc. The present invention relates to a critical current density measuring method and apparatus capable of easily measuring the critical current density in a non-destructive manner using the measured values.

超電導、特に液体窒素冷却により超電導性（ゼロ抵抗）を示す高温超電導体が発見されてから、輸送用超電導線材の研究開発が進み種々の高性能な超電導線材が開発されている。超電導線材の性能は主に臨界電流密度によって評価され、近年ではＪｃ〜１ＭＡ／ｃｍ2 を超える高臨界電流密度線材が開発され、その長さは１００ｍに達している。今後、さらなる長尺化と低コスト化が課題となっている。 Since the discovery of superconductors, especially high-temperature superconductors that exhibit superconductivity (zero resistance) by cooling with liquid nitrogen, research and development of superconducting wires for transport has progressed, and various high-performance superconducting wires have been developed. The performance of the superconducting wire is mainly evaluated by the critical current density. In recent years, a high critical current density wire exceeding Jc˜1 MA / cm 2 has been developed, and its length has reached 100 m. In the future, further lengthening and cost reduction will become issues.

一方、これまで、幾つかの臨界電流密度の評価方法が提案されており、それぞれが、幾つかの利点・欠点を有している。最も一般的である四端子法は測定精度が高く、他の測定方法の校正手段としても用いられているが、サンプル形状を加工しなければならないといういわゆる破壊測定方法である。
また、サンプルを加工せずに、準非破壊でＪｃを評価する方法として磁化特性法が最近注目されているが、長尺の超電導線材の測定は困難である。
このような背景の中で、現在主流となっている非破壊測定方法は、誘導法（特許文献１）であるが、誘導法は、
（１）高臨界電流密度、厚膜（１μｍ）のＪｃ測定が困難である。
（２）液体窒素を大量に必要とする。
（３）装置が高価である。
という問題があった。 On the other hand, several evaluation methods of critical current density have been proposed so far, and each has several advantages and disadvantages. The most common four-terminal method has high measurement accuracy and is used as a calibration means for other measurement methods, but is a so-called destructive measurement method in which the sample shape must be processed.
Further, as a method for evaluating Jc quasi-non-destructively without processing a sample, the magnetization characteristic method has recently attracted attention, but it is difficult to measure a long superconducting wire.
In such a background, the non-destructive measurement method that is currently mainstream is the induction method (Patent Document 1).
(1) Jc measurement of high critical current density and thick film (1 μm) is difficult.
(2) A large amount of liquid nitrogen is required.
(3) The device is expensive.
There was a problem.

特開２００３−２０７５２６JP 2003-207526 A

このため、高速線材作製とほぼ同時に線材の非破壊性能試験が可能な評価ツールが望まれている。また、線材の長尺化に伴うオンライン評価機構の開発例もないことから、長尺な高品質超電導線材の非破壊診断ツールの確立が課題となっている。   For this reason, an evaluation tool capable of performing a non-destructive performance test of a wire almost simultaneously with the production of a high-speed wire is desired. Moreover, since there is no development example of the online evaluation mechanism accompanying the lengthening of a wire, establishment of the nondestructive diagnostic tool of a long high quality superconducting wire has been a subject.

本発明は、長尺な高品質超電導線材の非破壊測定のために、永久磁石を用いた臨界電流密度の評価方法を用いることを特徴としており、測定原理は、冷却した超電導体に永久磁石を近づけることによる斥力と、遠ざけていく時に生じる引力を荷重測定センサーで測定し、その内の斥力の荷重特性から臨界電流密度の評価を行うものである。   The present invention is characterized by using a critical current density evaluation method using a permanent magnet for nondestructive measurement of a long high-quality superconducting wire. The measurement principle is that a permanent magnet is attached to a cooled superconductor. The repulsive force by approaching and the attractive force generated when moving away are measured by a load measuring sensor, and the critical current density is evaluated from the load characteristics of the repulsive force.

このため、本発明が採用した技術解決手段は、
演算処理手段と、この演算処理手段に接続されたロッド付き荷重測定センサーと、前記ロッドの先端に取り付けた永久磁石と、前記永久磁石に対向して配置される被検査体としての高温超電導薄膜とを備え、前記永久磁石と前記高温超電導体間の斥力を前記荷重測定センサーによって求め、前記演算処理手段により前記斥力と高温超電導体薄膜厚とを基に予め求めておいたマップから前記被検査体の臨界電流密度を測定することを特徴とする臨界電流密度の測定装置である。
また、前記マップは、磁化特性法、四端子法、誘導法の何れかの方法で測定した値を基に作成したことを特徴とする臨界電流密度の測定装置である。
また、前記に記載の臨界電流密度の測定装置を用い、永久磁石と超電導体間の斥力を荷重測定センサーによって求め、この斥力と超電導体膜厚とを基に、予め求めておいたマップから被検査体の臨界電流密度を求めることを特徴とする臨界電流密度の測定方法である。 For this reason, the technical solution means adopted by the present invention is:
Arithmetic processing means, a load measuring sensor with a rod connected to the arithmetic processing means, a permanent magnet attached to the tip of the rod, and a high-temperature superconducting thin film as an object to be inspected disposed opposite to the permanent magnet A repulsive force between the permanent magnet and the high-temperature superconductor is obtained by the load measuring sensor, and the object to be inspected is obtained from a map obtained in advance by the arithmetic processing means based on the repulsive force and the high-temperature superconductor thin film thickness. It is a critical current density measuring device characterized by measuring the critical current density of the above.
Further, the map is a critical current density measuring device created based on a value measured by any one of a magnetization characteristic method, a four-terminal method, and an induction method.
Further, using the critical current density measuring device described above, the repulsive force between the permanent magnet and the superconductor is obtained by a load measuring sensor, and based on this repulsive force and the superconductor film thickness, A critical current density measuring method characterized in that a critical current density of an inspection object is obtained.

本発明によれば、これまで非破壊測定不可能であった高臨界電流密度かつ厚膜線材の測定・評価が可能となる。永久磁石を使うのでＦｅＮｄＢ磁石のような数１０００Ｇａｕｓｓの磁場が作れる強力磁石を使うことにより１０μｍ位の厚さまで計測できる。直流磁場でよい（強力な永久磁石が使用可能）。小さな直径の磁石を使う、純鉄のヨークを磁石に近づけ磁場を絞りこむ等して膜の内面分布の測定分解能を高くできる。また、測定装置の構成も簡便なため、実用化における設備投資費の節減と、線材の低コスト化につながる。さらに、一ヶ所の測定時間が短いことから大量生産ライン用装置への応用も容易に可能となる。   According to the present invention, it is possible to measure and evaluate a high critical current density and thick film wire material, which has been impossible to measure nondestructively until now. Since a permanent magnet is used, it is possible to measure up to a thickness of about 10 μm by using a strong magnet that can generate a magnetic field of several thousand Gauss, such as an FeNdB magnet. A DC magnetic field is sufficient (a strong permanent magnet can be used). The measurement resolution of the inner surface distribution of the film can be increased by using a magnet with a small diameter or by bringing a pure iron yoke closer to the magnet and narrowing the magnetic field. In addition, since the configuration of the measuring apparatus is simple, it leads to a reduction in capital investment costs for practical use and a reduction in the cost of wires. Furthermore, since the measurement time at one place is short, it can be easily applied to an apparatus for mass production lines.

長尺な高品質超電導線材の非破壊測定のために、永久磁石を用いた臨界電流密度の評価方法を用いる。測定原理は、冷却した超電導体に永久磁石を近づけることによる斥力と、遠ざけていく時に生じる引力を荷重測定センサーで測定し、その内の斥力の荷重特性から臨界電流密度の評価を行う。本発明の方法によれば、誘導法では測定不能な厚みの膜も測定でき、永久磁石の磁場を絞り込むことにより面内分布を高い解像度で測定できる等の特長を有する。   A critical current density evaluation method using a permanent magnet is used for nondestructive measurement of long high-quality superconducting wires. The principle of measurement is to measure the repulsive force caused by bringing a permanent magnet closer to a cooled superconductor and the attractive force generated when moving away from it, and evaluate the critical current density from the load characteristics of the repulsive force. According to the method of the present invention, a film having a thickness that cannot be measured by the induction method can be measured, and the in-plane distribution can be measured with high resolution by narrowing down the magnetic field of the permanent magnet.

以下、本発明の実施例を説明すると、図１に装置の概略図を示す。
測定装置は制御用パソコン（演算処理手段）と測定装置本体というシンプルな構成になっており、制御用パソコン１は本体制御用インターフェースボードを内蔵し、ほぼ全ての測定を自動制御可能となっている。本体近傍には、約２リツトル容量の液体窒素槽３がおかれ、被検査物としての高温超電導薄膜８を簡易に冷却することができる。本体下部は各電源と制御用モータ、加重センサー値の表示ユニット２が設置されている。制御用パソコン、モータ、表示ユニットは公知のものを使用しており、さらに測定を自動制御するためのソフトウエアは本発明の特徴ではないので、詳細な説明は省略する。 DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below. FIG. 1 shows a schematic diagram of an apparatus.
The measuring device has a simple configuration consisting of a control personal computer (arithmetic processing means) and a main body of the measuring device, and the control personal computer 1 has a built-in interface board for controlling the main body so that almost all measurements can be automatically controlled. . In the vicinity of the main body, a liquid nitrogen tank 3 having a capacity of about 2 liters is placed, and the high-temperature superconducting thin film 8 as an object to be inspected can be easily cooled. In the lower part of the main body, each power source, a control motor, and a display unit 2 for weighted sensor values are installed. Since control personal computers, motors, and display units use known ones, and software for automatically controlling measurement is not a feature of the present invention, detailed description thereof is omitted.

パソコンには測定装置本体（ロッド付き加重測定センサー）４が接続されており、加重センサーからの出力をパソコン内に取り込むことができるようになっている。ロッド付き加重測定センサー４のロッド５先端には円柱状の永久磁石６（本例ではφ５〜２．６ｍｍ、ｈ＝３ｍｍ）が取り付けられている。この構成により永久磁石６と被検査物（超電導材）８に働く加重を測定することが出来る。加重測定の分解能は、０．０１ｇ重である。また、測定の際は被検査物表面にポリアミド粘着テープ７を貼り薄膜の劣化を防止しているが、このテープは無くてもよい。   The personal computer is connected with a measuring device main body (a weighted measuring sensor with a rod) 4 so that the output from the weighted sensor can be taken into the personal computer. A cylindrical permanent magnet 6 (φ5 to 2.6 mm, h = 3 mm in this example) is attached to the tip of the rod 5 of the load measuring sensor 4 with rod. With this configuration, the load acting on the permanent magnet 6 and the object to be inspected (superconducting material) 8 can be measured. The resolution of the weighted measurement is 0.01 g weight. Further, at the time of measurement, the polyamide adhesive tape 7 is attached to the surface of the object to be inspected to prevent the thin film from being deteriorated.

上記装置による加重測定
ロッド５の先端に取り付けた永久磁石６を被検査体（高温超電導薄膜）８に近づけていく際、超電導薄膜８に流れるシールド電流（マイスナー効果）によりロツド５に取り付けた永久磁石６と被検査体８の間に斥力が生じる（図２（ａ））。さらに磁石６を近づけ、薄膜の下部臨界磁界（Ｈ．１）以上の磁界が印加されると磁束が薄膜内を貫通する（図２（ｂ））。次に被検査体８からロッド５を離していくと、被検査体８に保持されている磁場により先ほどとは逆にロッド５に取り付けた永久磁石６と被検査体８の間に引力が生じる（図２（ｃ））。薄膜の臨界電流密度Ｊｃが大きいほど、これらの力は強くなることから、既知のＪｃを持つ高温超電導薄膜の斥力、引力特性を測定し、その相関を見いだすことにより簡便にＪｃの評価が可能となる。 Weight measurement by the above device When the permanent magnet 6 attached to the tip of the rod 5 is brought close to the object to be inspected (high temperature superconducting thin film) 8, the permanent magnet attached to the rod 5 by the shield current (Meissner effect) flowing in the superconducting thin film 8 A repulsive force is generated between 6 and the inspection object 8 (FIG. 2A). Further, when the magnet 6 is moved closer and a magnetic field higher than the lower critical magnetic field (H.1) of the thin film is applied, the magnetic flux penetrates the thin film (FIG. 2B). Next, when the rod 5 is moved away from the object 8 to be inspected, an attractive force is generated between the permanent magnet 6 attached to the rod 5 and the object 8 to be inspected by the magnetic field held by the object 8 to be inspected. (FIG. 2 (c)). As the critical current density Jc of the thin film increases, these forces become stronger. Therefore, it is possible to easily evaluate Jc by measuring the repulsive and attractive characteristics of a high-temperature superconducting thin film having a known Jc and finding the correlation between them. Become.

具体的には、予め、誘導法により測定した臨界電流密度Ｊｃと、高温超電導薄膜と永久磁石との間の距離Ｌと斥力との関係からａ1 ／ｄを求め、これらの関係を図４に示すようにマップ化しておく。なお、図４は一例としてＹＢＣＯ薄膜の７７ＫにおけるＪｃ−ａ1 ／ｄ特性をしめしている。マグネットはφ５ｍｍを用いた。実験で得られたＪｃはａ1 に正の相関を示し、
Ｊｃ＝３．６×１０-5×（ａ1 ／ｄ）2/3 〔ＭＡ／ｃｍ2 〕
の関係で説明できている。したがって、本測定装置により測定したａ1 と既知の膜厚さｄを用いて後述のようにして薄膜のＪｃを評価できる。なお、図４は薄膜の材料、磁石の大きさ毎の実験を行い簡単に作成することができる。
ところで上記ａ1 は次のように定義される。
図３は簿膜と永久磁石間の測定最小距離Ｌmin を変えて引力・斥力特性を測定した結果を示している。図３から、Ｌmin が０．５から２．０ｍｍの範囲ではＬ＝０の外挿値が全て一致していることがわかる。そこで、実験で得られた荷重と距離の関係から斥力、引力値それぞれの接線とＬ＝０の交点をそれぞれ、ａ1 、ａ2 と定義する。ａ1 の値は、磁石を近づけた際に超電導体内に流れるマイスナー電流に関係し、ａ1 が大きいほど大きなマイスナー電流が流れると考えられる。一方、ａ2 は超電導薄膜内で反転するシールド電流による磁界と、膜中のトラップ磁界によるものである。よって、ａ1 がＪｃと相関をもつことがわかる。ｄは高温超電導薄膜の膜厚である。 Specifically, a 1 / d is obtained in advance from the relationship between the critical current density Jc measured by the induction method, the distance L between the high-temperature superconducting thin film and the permanent magnet, and the repulsive force, and these relationships are shown in FIG. Map as shown. FIG. 4 shows the Jc-a 1 / d characteristic at 77K of the YBCO thin film as an example. The magnet used was 5 mm. Jc obtained in the experiment shows a positive correlation with a 1 ,
Jc = 3.6 × 10 −5 × (a 1 / d) 2/3 [MA / cm 2 ]
It can be explained by the relationship. Therefore, the Jc of the thin film can be evaluated as described later using a 1 measured by this measuring apparatus and the known film thickness d. Note that FIG. 4 can be easily created by conducting experiments for each thin film material and magnet size.
The above a 1 is defined as follows.
FIG. 3 shows the results of measuring the attractive force / repulsive force characteristics by changing the minimum measurement distance Lmin between the book membrane and the permanent magnet. FIG. 3 shows that all the extrapolated values of L = 0 are the same in the range of Lmin from 0.5 to 2.0 mm. Therefore, from the relationship between the load and distance obtained in the experiment, the intersections of the repulsive force and attractive force value and L = 0 are defined as a 1 and a 2 , respectively. The value of a 1 is related to the Meissner current flowing through the superconductor when the closer the magnets are considered to flow a large Meissner current as a 1 is larger. On the other hand, a 2 is due to the magnetic field due to the shield current reversing in the superconducting thin film and the trap magnetic field in the film. Therefore, it can be seen that a 1 has a correlation with Jc. d is the film thickness of the high-temperature superconducting thin film.

上記装置による臨界電流密度Ｊｃの求め方。
先ずロッド付き加重測定センサー４から被検査体８との間の斥力と距離Ｌを求め、その値をもとにパソコン内で、ａ1 を求め、既知の膜厚とからａ1 ／ｄを求め、この値を使用してパソコン内に記憶しているマップ（図４参照）から臨界電流密度Ｊｃを求める。こうすることで膜厚が既知のサンプルの斥力ａ1 を測定することによって容易にＪｃを算出することができる。 How to determine the critical current density Jc using the above device.
First, the repulsive force and distance L between the load measuring sensor 4 with the rod and the object to be inspected 8 are obtained, a 1 is obtained in the personal computer based on the values, and a 1 / d is obtained from the known film thickness. The critical current density Jc is obtained from the map (see FIG. 4) stored in the personal computer using this value. In this way, Jc can be easily calculated by measuring the repulsive force a 1 of a sample having a known film thickness.

以上、本発明に係る高臨界電流密度かつ厚膜線材の渕定・評価について説明をしたが、パソコンの代わりに専用の制御回路を使用してもよい。さらに本発明はその精神または主要な特徴から逸脱することなく、他のいかなる形でも実施できる。そのため、前述の実施例はあらゆる点で単なる例示にすぎず限定的に解釈してはならない。   The determination and evaluation of the high critical current density and thick film wire according to the present invention has been described above, but a dedicated control circuit may be used instead of the personal computer. Furthermore, the present invention may be implemented in any other form without departing from the spirit or main features thereof. For this reason, the above-described embodiment is merely an example in all respects and should not be interpreted in a limited manner.

本発明により、これまで非破壊測定不可能であった高臨界電流密度かつ厚膜線材の測定・評価が可能となる。   According to the present invention, it is possible to measure and evaluate a high critical current density and thick film wire, which has been impossible to measure nondestructively until now.

本装置の概略構成図である。It is a schematic block diagram of this apparatus. 永久磁石を使用した測定原理の説明図である。It is explanatory drawing of the measurement principle using a permanent magnet. 斥力・引力特性のＬmin 依存性を示すグラフである。It is a graph which shows Lmin dependence of a repulsive force / attraction force characteristic. 臨界電流密度（Ｊｃ）と斥力／超電導薄膜の膜厚（ａ1 ／ｄ）の関係図（マップ）である。FIG. 6 is a relationship diagram (map) between critical current density (Jc) and repulsive force / superconducting thin film thickness (a 1 / d).

符号の説明Explanation of symbols

１ 制御用パソコン
２ 表示ユニット
３ 液体窒素槽
４ ロッド付き荷重測定センサ−
５ ロッド
６ 永久磁石
７ ポロアミド粘着テープ
８ 被検査物
９ ベース
１０ 冷却部
1 PC for control 2 Display unit 3 Liquid nitrogen tank 4 Load measuring sensor with rod
5 Rod 6 Permanent magnet 7 Polamide adhesive tape 8 Inspected object 9 Base 10 Cooling section

Claims (3)

演算処理手段と、この演算処理手段に接続されたロッド付き荷重測定センサーと、前記ロッドの先端に取り付けた永久磁石と、前記永久磁石に対向して配置される被検査体としての高温超電導薄膜とを備え、前記永久磁石と前記高温超電導体間の斥力を前記荷重測定センサーによって求め、前記演算処理手段により前記斥力と高温超電導体薄膜厚とを基に予め求めておいたマップから前記被検査体の臨界電流密度を測定することを特徴とする臨界電流密度の測定装置。 Arithmetic processing means, a load measuring sensor with a rod connected to the arithmetic processing means, a permanent magnet attached to the tip of the rod, and a high-temperature superconducting thin film as an object to be inspected disposed opposite to the permanent magnet A repulsive force between the permanent magnet and the high-temperature superconductor is obtained by the load measuring sensor, and the object to be inspected is obtained from a map obtained in advance by the arithmetic processing means based on the repulsive force and the high-temperature superconductor thin film thickness. An apparatus for measuring critical current density, characterized in that it measures the critical current density. また、前記マップは、磁化特性法、四端子法、誘導法の何れかの方法で測定した値を基に作成したことを特徴とする臨界電流密度の測定装置。 In addition, the critical current density measuring device is characterized in that the map is created based on a value measured by any one of a magnetization characteristic method, a four-terminal method, and an induction method. 請求項１または請求項２に記載の臨界電流密度の測定装置を用い、永久磁石と超電導体間の斥力を荷重測定センサーによって求め、この斥力と超電導体膜厚とを基に、予め求めておいたマップから被検査体の臨界電流密度を求めることを特徴とする臨界電流密度の測定方法。 Using the critical current density measuring device according to claim 1 or 2, the repulsive force between the permanent magnet and the superconductor is obtained by a load measuring sensor, and is obtained in advance based on the repulsive force and the superconductor film thickness. A method for measuring a critical current density, characterized in that a critical current density of an object to be inspected is determined from a map that has been obtained.
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