【発明の詳細な説明】
〔産業上の利用分野〕
本発明は、電流供給源から液体Ｈｅ等で冷却された超電
導マグネット等の超電導素子へ電流を供給する為に用い
られる電流リード用導体に関する．〔従来の技術及びそ
の課題〕
超電導を利用したマグネット、送電ケーブル又はＳＱＵ
ＩＤやジョセフソン素子等を組込んだ電子機器等は液体
Ｈｅ等により冷却して用いられるもので、これら電子機
器等への電流の供給は運転開始又は運転中に外部電源よ
り電流リードを通してなされる．
ところで電流リード用導体には従来、鋼材が用いられて
いるが、超電導マグネット等では大電流を必要とし、依
って電流リード用導体はサイズを太くして、ジュール発
熱の低減や過電流による溶断防止が計られている．しか
しながら電流リード用導体を太くすると外部からの流入
熱量が増加してＨｅ等の冷媒の蒸発量が増え冷却コスト
が増大するという問題があった．
このようなことから、近年液体窒素温度で超電導を示す
酸化物超電導体を電気良伝導体からなる支持体と複合し
た電流リード用導体が提案された（特開昭６３−２４５
９１０）．
この電流リード用導体においては、電流は液体Ｈｅ等で
冷却された超電導素子側では主に酸化物超電導体を通り
、又常温の電流供給源側では金属被覆層を通って供給さ
れるもので、酸化物超電導体は、液体Ｈｅ等で冷却され
た超電導素子側では抵抗ゼロの為通電によるジェール発
熱がなく、又酸化物超電導体は熱伝導性が低い為外部か
らの熱流入が少なく、かくして電流リード用導体として
は優れた特性を有するものである．しかしながら電流リ
ード用導体は長さが数１０ｃｍと短い上、一端が常温、
他端が極低温に冷却され、しかもこの温度間でのヒート
サイクルが何回も繰り返される為に熱歪により酸化物超
電導体内にクラックが生じたり、或いは、酸化物超電導
体と金属被覆層とが剥離したりして通電抵抗が増大して
電流リード用導体が焼損したり、又は性能が経時的に劣
化する等耐久性に劣るというような問題があった．一方
、上記酸化物超電導体は層状ペロブス力イト型結晶構造
の為結晶異方性が強く、電流はＣｕ一〇原子を含むａｂ
面に流れ易く、従って通電方向に対し垂直な方向にＣ軸
を配向させるのが高いＪ，を得るのに必要な要件である
．しかしながら前記の従来の酸化物超電導体は結晶配向
がランダムな為に、十分に高いＪ，値が得られず、電流
供給に長時間を要し、又電流供給を早めるとジュール熱
が発生して液体Ｈｅが大量に蒸発してしまうという問題
があった．
〔課題を解決するための手段〕
本発明はかかる状況に鑑み鋭意研究を進めた結果なされ
たものでその目的とするところは、耐久性に優れ且つ液
体Ｈ ｅ等の冷媒の蒸発量を低減し得る電流リード用導
体を提供することにある。DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a current lead conductor used to supply current from a current supply source to a superconducting element such as a superconducting magnet cooled with liquid He or the like. [Conventional technology and its issues] Magnet, power transmission cable or SQU using superconductivity
Electronic devices incorporating IDs, Josephson elements, etc. are cooled with liquid He, etc., and current is supplied to these electronic devices through current leads from an external power source at the start of operation or during operation. ．． By the way, steel has traditionally been used for current lead conductors, but superconducting magnets require large currents, so current lead conductors are made thicker to reduce Joule heat generation and prevent melting due to overcurrent. is being measured. However, when the current lead conductor is made thicker, there is a problem in that the amount of heat flowing in from the outside increases, the amount of evaporation of refrigerant such as He increases, and the cooling cost increases. For these reasons, in recent years a current lead conductor has been proposed in which an oxide superconductor exhibiting superconductivity at liquid nitrogen temperature is combined with a support made of a good electrical conductor (Japanese Patent Laid-Open No. 63-245
910). In this current lead conductor, current is mainly supplied through the oxide superconductor on the side of the superconducting element cooled with liquid He, etc., and through the metal coating layer on the side of the current supply source at room temperature. Oxide superconductors have zero resistance on the side of the superconducting element cooled with liquid He, etc., so there is no gel heat generation due to energization, and oxide superconductors have low thermal conductivity, so there is little heat inflow from the outside, and thus the current It has excellent properties as a conductor for leads. However, the current lead conductor is short, several tens of centimeters long, and one end is kept at room temperature.
The other end is cooled to an extremely low temperature, and the heat cycle between these temperatures is repeated many times, so cracks may occur in the oxide superconductor due to thermal strain, or the oxide superconductor and metal coating layer may There were problems such as delamination, increased current carrying resistance, burnout of the current lead conductor, and poor durability such as performance deterioration over time. On the other hand, the above-mentioned oxide superconductor has a layered perovskite crystal structure, so it has strong crystal anisotropy, and the current is ab containing 10 Cu atoms.
Therefore, it is necessary to orient the C-axis in a direction perpendicular to the current direction to obtain a high J. However, since the conventional oxide superconductor described above has a random crystal orientation, it is not possible to obtain a sufficiently high J value, it takes a long time to supply current, and Joule heat is generated when the current supply is accelerated. There was a problem that a large amount of liquid He evaporated. [Means for Solving the Problems] The present invention was made as a result of intensive research in view of the above situation, and its purpose is to provide a refrigerant with excellent durability and reduce the amount of evaporation of refrigerant such as liquid He. An object of the present invention is to provide a conductor for a current lead.
即ち本発明は、電流供給源から超電導素子へ電流を供給
する為の電流リード用導体であって、酸化物超電導体と
５〜５０容量％の金属とからなり、その表面の少なくと
も一部が金属で覆われているものであることを特徴とす
るものである。That is, the present invention provides a current lead conductor for supplying current from a current supply source to a superconducting element, which is made of an oxide superconductor and 5 to 50% by volume of metal, and at least a part of its surface is made of metal. It is characterized by being covered with
本発明の電流リード用導体は、液体窒素温度等の比較的
高温で超電導となる酸化物超電導体と金属との複合体か
らなり、その表面の少なくとも一部分が金属で覆われて
いるものである．本発明において酸化物超電導体には叱
界温度（Ｔ，〉が〜９３ＫのＹＢａｘＣｕｓＯｖ−６又
は上記Ｙを他の希土類元素で置換したもの、Ｔｃが９０
〜ｌｌＯＫのＢ ｌ．ｓｒ．ＣａＣｕ．Ｏｓ、ＢｉｇＳ
ｒｚＣａｘＣｕｓＯ＋＊、Ｔｃが１００ 〜１２５Ｋの
Ｔ ｌ ｘ Ｂ ａ ｘ Ｃ ａ Ｃ ｕ ！ Ｏ ｓ
、Ｔ １ ｚ Ｂ ａ ｚ Ｃ ａ ｚ Ｃｕ，Ｏ．、
Ｔｊ！ＢａｔＣａｘＣｕｓＯｍ．ｓ等が用いられ、更に
上記各々の酸化物超電導体をＩＩＩ威する金属元素の一
部をｐｂ、Ｉｎ％ｓｂ、アルカリ金属等で置換したもの
、又はＯの一部をＦで置換したもの等が含まれる．又上
記酸化物超電導体と複合する金属としてはＡｕ，Ａｇ，
Ｃｕ，Ｐｄ，Ｐｔ又はこれらの合金が酸化物超電導体と
非反応性であり又熱及び電気的伝導性に優れていて好ま
しく、又その形状は粉末状、粒子状、塊状等任意の形状
のものが適用される．
本発明において、電流リード用導体の少なくとも一部の
表面を覆う金属としては前記の複合金属の他ＳＵＳ，Ａ
ｌ，Ｆｅ−Ｎｉ合金等が適用される．
而して本発明の電波リ一ド用導体の製造方法としては、
例えば酸化物超電導体又はその前駆物質の粉末に複合す
る金属粉末を所定量配合し混合して、次いでこの混合粉
体にバインダーを添加して混練し、この混線体を棒状に
押出し、この棒材を酸素含有雰囲気中にて所定温度に加
熱して焼結し、更にこの焼結棒材の表面の所定箇所にＡ
ｇ等の金属をろう付け等により複合する方法、又は上記
混合粉体をＡｇ製パイプ等に充填し、これをスエージ中
一等により所定形状に加工する方法等が適用される．
上記加熱焼結工程において、酸化物超電導体にあっては
戒形体の焼結及び上記焼結体への酸素の補給並びに結晶
構造の調整がなされる．又前駆物質にあっては酸化物超
電導体への反応並びに上記と同じ焼結、酸素補給、結晶
構造の調整がなされる．
本発明の電流リード用導体は、その形状を抵抗零の超電
導素子側を細くし、電流供給源側に向けて段階的に又は
テーパー状に太くして、長手方向各部位の抵抗をできる
だけ均一化してジュール発熱を効率的に抑えることが望
ましい．
更に酸化物超電導体と複合させる金属量等は電流リード
用導体の各部位により変化させて抵抗の均一化を計るこ
ともできる．
又本発明の電流リード用導体は、特に超電導素子側を液
体窒素等により冷却して用いることによりその効果が一
層発現されるものである．〔作用〕
本発明の電流リード用導体にあっては、電流は主に、低
温に冷却される超電導素子側では抵抗零の超電導体部分
を流れ、又電流供給源側では複合した金属又は／及び表
面を覆って複合した金属部分を流れる。従って特に超電
導素子側にあってはジュール熱を生じることがない．
又電流リード用導体を介して外部から流入するは電流リ
ード用導体の断面積、ｌは長さ、λは熱伝導率、ｔは温
度．）により示されるが、この式によれば本発明の電流
リード用導体は、超電導素子側では抵抗０の為Ａを小さ
くすることができ、又酸化物超電導体のλは濶の数百分
の１と小さく、従って本発明の電流リード用導体は外部
からの熱流入を極めて小さくし得るものであり、かくし
て液体Ｈｅ等の冷媒の蒸発が低減される．又上記酸化物
超電導体に例えば分散方式などにより複合させた金属は
、酸化物超電導体の靭性又は熱的電気的伝導性の向上に
寄与するもので、その量は５容量％（以下％と略記）未
満では上記作用が十分に得られず、又５０％を超えると
超電導素子側においてジュール熱が生じて冷媒の蒸発が
増大するので５〜５０％に限定する必要があり、特には
１０〜４０％の範囲が好ましい．本発明において電流リ
ード用導体の少なくとも一部の表面に複合する金属は、
電流リード用導体の機械的補強材、外気からの保護材、
電磁気的安定化材、接続端子等としての作用を発現し得
るもので、複合金属の材種、複合部位、複合面積等はそ
の目的に応じて任意に決められる．
〔実施例〕
以下に本発明を実施例により詳細に説明する．実施例ｌ
平均粒径６ｎのＹＢａ＊Ｃｕ３０ｇの仮焼戒粉と平均粒
径ＩＩｔｍのＡｇ粉とを種々比率で配合して混合し、こ
れをＣＩＰ威形後予゜備焼結し、次いでこの予備焼結体
を外径２５ｓｍ一のＡｇ製パイプに充填して真空封止し
た．しかるのちこのＡｇ製パイプをスエージャー及びド
ローベンチで縮径加工し、次いでこれを圧延加工して幅
６ｍ、厚さ０．５閣（内側厚さ０．４ｍ）のテープとな
し、このテープをＯ，気流中で８９０″Ｃ３Ｈ加熱焼結
し、８９０゜Ｃから１．５℃／ｓｉｎの速度で冷却して
電流リード用導体を製造した．
斯くの如くして得られた各々の電流リード用導体を４０
０■長さに切断し、これを１０本Ｔｉテーブで結束しこ
れに長さ２００ｍｓ断面積１００一の銅線を半田付けし
て取付けて電流リードとなした．
而して得られた各々の電流リードに液体Ｈｅ中と室温間
でのヒートサイクルを５０回繰返したのち、これをＮｂ
−Ｔｉ製直流超電導マグネットに配線して４． ２ Ｋ
Ｏ． ８ Ｔ ５ ０ ０ Ａの条件にて運転し、運
転中の液体Ｈｅの蒸発量を測定した．比較の為従来の電
流リードに銅線を用いたものについても同様の測定を行
った．結果１，ｔＡｇ粉の配合量を併記して第１表に示
した．尚液体Ｈｅの蒸発量は電流リードを配線しないと
きの自然蒸発量を差引いて示した．
第１表より明らかなように本発明品（１〜４）を用いた
場合のＨｅ蒸発量は、従来の銅線（７）を用いた場合の
半分以下に留まった．
本発明品のうちＮｏｌ及びＮｏ４のＨｅ蒸発量が他に較
べ多い原因は、前者はＡｇ粉の配合量が少ない為靭性に
劣りヒートサイクル時に一部にクラックが生じたこと、
後者はＡｇ粉が多い為ジュール発熱及び外部からの熱流
入が増えたことによるものである．
一方比較品のＮｏ５はＡ ｇ ＃）が配合していなかっ
た為にヒートサイクル時にクランクが多数発生して臨界
電流密度（Ｊ，）が低下し焼損してしまった．又Ｎｏ６
はＡｇ粉配合量が多すぎた為、ジュール発熱及び外部か
らの熱流入が増大してＨｅが大量に蒸発した．
〔効果）
以上述べたように本発明の電流リード用導体は、耐久性
に優れ且つ液体Ｈｅ等の冷媒の蒸発を少なく抑えること
ができ、工業上顕著な効果を奏するものである．The current lead conductor of the present invention is made of a composite of metal and an oxide superconductor that becomes superconducting at relatively high temperatures such as liquid nitrogen temperature, and at least a portion of its surface is covered with metal. In the present invention, the oxide superconductor is YBaxCusOv-6 with a scolding temperature (T) of ~93K, or one in which the above Y is replaced with another rare earth element, and a Tc of 90K.
~ll OK's B l. sr. CaCu. Os, BigS
rzCaxCusO+*, T l x B a x C a C u with Tc of 100 to 125K! Os
, T 1 z B a z C a z Cu, O. ,
Tj! BatCaxCusOm. s etc. are used, and a part of the metal element that enhances each of the above oxide superconductors is replaced with PB, In% sb, an alkali metal, etc., or a part of O is replaced with F, etc. is included. In addition, the metals to be composited with the oxide superconductor include Au, Ag,
Cu, Pd, Pt, or an alloy thereof is preferable because it is non-reactive with the oxide superconductor and has excellent thermal and electrical conductivity, and it can be in any shape such as powder, particles, or lumps. is applied. In the present invention, the metal covering at least a part of the surface of the current lead conductor includes SUS, A
l, Fe-Ni alloy, etc. are applicable. The method for manufacturing the radio wave read conductor of the present invention is as follows:
For example, a predetermined amount of composite metal powder is mixed with powder of an oxide superconductor or its precursor, then a binder is added to this mixed powder and kneaded, and this mixed wire body is extruded into a rod shape. is heated to a predetermined temperature in an oxygen-containing atmosphere to sinter it, and A
A method of combining metals such as Ag by brazing or the like, or a method of filling an Ag pipe or the like with the above mixed powder and processing it into a predetermined shape by swaging or the like are applied. In the above heating and sintering process, in the case of an oxide superconductor, the sintered body is sintered, oxygen is supplied to the sintered body, and the crystal structure is adjusted. In addition, the precursor material undergoes the reaction to form an oxide superconductor, as well as the same sintering, oxygen supply, and crystal structure adjustment as described above. The current lead conductor of the present invention has a shape that is made thinner on the side of the superconducting element with zero resistance and thickened stepwise or tapered toward the current supply source side, so that the resistance of each part in the longitudinal direction is made as uniform as possible. It is desirable to efficiently suppress Joule heat generation. Furthermore, the resistance can be made uniform by varying the amount of metal combined with the oxide superconductor depending on each part of the current lead conductor. Furthermore, the current lead conductor of the present invention is particularly effective when used after cooling the superconducting element side with liquid nitrogen or the like. [Function] In the current lead conductor of the present invention, current mainly flows through the superconductor portion with zero resistance on the side of the superconducting element that is cooled to a low temperature, and on the side of the current supply source, the current flows mainly through the composite metal or/and Flows through the composite metal parts covering the surface. Therefore, Joule heat is not generated, especially on the superconducting element side. Also, the current flowing from the outside through the current lead conductor is the cross-sectional area of the current lead conductor, l is the length, λ is the thermal conductivity, and t is the temperature. ), but according to this formula, the current lead conductor of the present invention has zero resistance on the superconducting element side, so A can be made small, and λ of the oxide superconductor is several hundredths of A. Therefore, the current lead conductor of the present invention can extremely reduce heat inflow from the outside, thereby reducing evaporation of refrigerant such as liquid He. In addition, the metal compounded with the oxide superconductor by, for example, a dispersion method contributes to improving the toughness or thermal and electrical conductivity of the oxide superconductor, and the amount thereof is 5% by volume (hereinafter abbreviated as %). ), the above effect cannot be obtained sufficiently, and if it exceeds 50%, Joule heat is generated on the superconducting element side and evaporation of the refrigerant increases, so it is necessary to limit it to 5 to 50%, especially 10 to 40%. A range of % is preferred. In the present invention, the metal compounded on at least a part of the surface of the current lead conductor is
Mechanical reinforcing material for current lead conductors, protection material from outside air,
It can act as an electromagnetic stabilizer, a connecting terminal, etc. The type of composite metal, composite part, composite area, etc. can be arbitrarily determined depending on the purpose. [Example] The present invention will be explained in detail below using Examples. Example 1 Calcined powder of 30 g of YBa*Cu with an average particle size of 6n and Ag powder with an average particle size of IItm are blended and mixed in various ratios, and this is pre-sintered after CIP shaping. The preliminary sintered body was filled into an Ag pipe with an outer diameter of 25 sm and vacuum sealed. Afterwards, this Ag pipe was reduced in diameter using a swager and a draw bench, and then rolled into a tape with a width of 6 m and a thickness of 0.5 mm (inside thickness 0.4 m). , 890" C3H heat sintering in an air stream, and cooling from 890°C at a rate of 1.5°C/sin to produce current lead conductors. Each current lead conductor thus obtained 40
The wires were cut into 0.0 mm lengths, tied together with 10 Ti tapes, and a copper wire with a length of 200 ms and a cross-sectional area of 100 mm was soldered and attached to this to form a current lead. Each current lead thus obtained was heat cycled 50 times between liquid He and room temperature, and then heated with Nb.
- Wire to Ti DC superconducting magnet 4. 2K
O. It was operated under conditions of 8 T 500 A, and the amount of evaporation of liquid He during operation was measured. For comparison, similar measurements were performed on a conventional current lead using copper wire. Results 1 and the amount of tAg powder added are shown in Table 1. The amount of evaporation of liquid He is shown by subtracting the amount of natural evaporation when the current lead is not wired. As is clear from Table 1, the amount of He evaporation when using the products of the present invention (1 to 4) remained less than half that when using the conventional copper wire (7). Among the products of the present invention, the reason why No. 1 and No. 4 had a higher amount of He evaporation than the others was that the former had poor toughness due to the small amount of Ag powder blended, and some cracks occurred during the heat cycle.
The latter is due to an increase in Joule heat generation and heat inflow from the outside due to the large amount of Ag powder. On the other hand, comparison product No. 5 did not contain A g #), so many cranks occurred during the heat cycle, the critical current density (J,) decreased, and it burned out. Also No.6
Because the amount of Ag powder blended was too high, Joule heat generation and heat inflow from the outside increased, causing a large amount of He to evaporate. [Effects] As described above, the current lead conductor of the present invention has excellent durability and can suppress evaporation of refrigerant such as liquid He, and has a remarkable industrial effect.