# TC 90 - Superconductivity

To prepare international standards (IS) related to superconducting materials and devices

## Supraconductivité

Préparer des normes internationales traitant des matériaux et appareils supraconducteurs

### General Information

IEC 61788-22-3:2022 is applicable to the measurement of the dark count rate (DCR, RD) of superconductor strip photon detectors (SSPDs). It specifies terms, definitions, symbols and the measurement method of DCR that depends on the bias current (Ib) and operating temperature (T).

NOTE The data of measurement results in Annex A are based on measurements of one institute only. The standard will be updated after the data of a complete round robin test are available.

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IEC 61788-22-2:2021 is applicable to high-Tc Josephson junctions. It specifies terms, definitions, symbols and the measurement and estimation method for normal state resistance (Rn) and intrinsic critical current (Ici), based on a combination of selecting a data set from measured U–I curves with a geometric mean criterion and fitting a hyperbolic function to that data set.

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IEC 61788-23:2021 is available as IEC 61788-23:2021 RLV which contains the International Standard and its Redline version, showing all changes of the technical content compared to the previous edition.

IEC 61788-23:2021 addresses a test method for the determination of the residual resistance ratio (RRR), rRRR, of cavity-grade niobium. This method is intended for high-purity niobium grades with 150 < rRRR < 600. The test method is valid for specimens with rectangular or round cross-section, cross-sectional area greater than 1 mm2 but less than 20 mm2, and a length not less than 10 nor more than 25 times the width or diameter.

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IEC 61788-17:2021 is available as IEC 61788-17:2021 RLV which contains the International Standard and its Redline version, showing all changes of the technical content compared to the previous edition.

IEC 61788-17:2021 specifies the measurements of the local critical current density (Jc) and its distribution in large-area high-temperature superconducting (HTS) films by an inductive method using third-harmonic voltages. The most important consideration for precise measurements is to determine Jc at liquid nitrogen temperatures by an electric-field criterion and obtain current-voltage characteristics from its frequency dependence. Although it is possible to measure Jc in applied DC magnetic fields [20] [21], the scope of this document is limited to the measurement without DC magnetic fields. This technique intrinsically measures the critical sheet current that is the product of Jc and the film thickness d. The range and measurement resolution for Jcd of HTS films are as follows.

- Jcd: from 200 A/m to 32 kA/m (based on results, not limitation).

- Measurement resolution: 100 A/m (based on results, not limitation).

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IEC 61788-26:2020 specifies a test method for determining the DC critical current of short RE (rare earth)-Ba-Cu-O (REBCO) composite superconductor specimens that have a shape of straight flat tape. This document applies to test specimens shorter than 300 mm and having a rectangular cross section with an area of 0,03 mm2 to 7,2 mm2, which corresponds to tapes with width ranging from 1,0 mm to 12,0 mm and thickness from 0,03 mm to 0,6 mm.

This method is intended for use with superconductor specimens that have critical current less than 300 A and n-values larger than 5 under standard test conditions: the test specimen is immersed in liquid nitrogen bath at ambient pressure without external magnetic field during the testing. Deviations from this test method that are allowed for routine tests and other specific restrictions are given in this document.

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IEC 61788-4:2020 is available as IEC 61788-4:2020 RLV which contains the International Standard and its Redline version, showing all changes of the technical content compared to the previous edition.

IEC 61788-4:2020 specifies a test method for the determination of the residual resistance ratio (RRR) of Nb-Ti and Nb3Sn composite superconductors with Cu, Cu-Ni, Cu/Cu-Ni and Al matrix in a strain-free condition and zero external magnetic field. This method is intended for use with superconductor specimens that have a monolithic structure with rectangular or round cross-section, RRR value less than 350, and cross-sectional area less than 3 mm2. In the case of Nb3Sn, the specimens have received a reaction heat-treatment. This fifth edition cancels and replaces the fourth edition published in 2016. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition:

a) change in the suitable distance of voltage taps on the specimen for reliable measurement,

b) new report on the result of the round robin test of the residual resistance ratio of Nb3Sn superconductors that proves the validity of the measurement method in this standard,

c) revision of the confusing definitions of the copper ratio and copper fraction.

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IEC 61788-7:2020 is available as IEC 61788-7:2020 RLV which contains the International Standard and its Redline version, showing all changes of the technical content compared to the previous edition.

IEC 61788-7:2020 describes measurement of the surface resistance (Rs) of superconductors at microwave frequencies by the standard two-resonator method. The object of measurement is the temperature dependence of Rs at the resonant frequency. The applicable measurement range of Rs for this method is as follows:

- Frequency: 8 GHz - Measurement resolution: 0,01 m Ω at 10 GHz

The Rs data at the measured frequency, and that scaled to 10 GHz, assuming the f 2 rule for comparison, is reported. This third edition cancels and replaces the second edition, published in 2006. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition:

a) informative Annex B, relative combined standard uncertainty for surface resistance measurement has been added;

b) precision and accuracy statements have been converted to uncertainty;

c) reproducibility in surface resistant measurement has been added.

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IEC 61788-25:2018 specifies the test method and procedures for testing tensile mechanical properties of REBCO superconductive composite tapes at room temperature. This test is used to measure the modulus of elasticity and 0,2 % proof strength. The values for elastic limit, fracture strength and percentage elongation after fracture serve only as a reference. This document applies to samples having a rectangular cross-section with an area of 0,12 mm2 to 6,0 mm2 (corresponding to the tapes with width of 2,0 mm to 12,0 mm and thickness of 0,06 mm to 0,5 mm)

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IEC 61788-24:2018 describes a test method for determining the retained critical current after double bending at room temperature of short and straight Ag- and/or Ag alloy-sheathed Bi-2223 superconducting wires that have the shape of a flat or square tape containing mono- or multicores of oxides. The wires can be laminated with copper alloy, stainless steel or Ni alloy tapes.

The test method is intended for use with superconductors that have a critical current less than 300 A and an n-value larger than 5.

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IEC 61788-23:2018 addresses a test method for the determination of the residual resistance ratio (RRR) of cavity-grade niobium. The test method should be valid for specimens with rectangular or round cross-section, cross-sectional area greater than 1 mm2 but less than 20 mm2, and a length not less than 10 nor more than 25 times the width or diameter.

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IEC 61788-22-1:2017 describes general items concerning the specifications for superconducting sensors and detectors, which are the basis for specifications given in other parts of IEC 61788 for various types of sensors and detectors. The sensors and detectors described are basically made of superconducting materials and depend on superconducting phenomena or related phenomena. The objects to be measured (measurands) include magnetic fields, electromagnetic waves, photons of various energies, electrons, ions, a‑particles, and others.

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IEC 60050-815:2015 gives the terms and definitions for the wide area of superconductivity-related technologies, from the physics to their applications representing the present state-of-the-art. The second edition reviews and complements the first edition. This terminology is consistent with the terminology developed in the other specialized parts of the IEV.

It has the status of a horizontal standard in accordance with IEC Guide 108.

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IEC 61788-21:2015 specifies the test methods used for validating the mechanical, electrical, and superconducting properties of practical SC wires.

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IEC TR 61788:2014 which is a technical report, provides general characteristics and guidance on practical superconducting (SC) wires. Particular focus is given to the characteristics that are different from those of ordinary copper and aluminium wires, since practical SC wires have appearance nearly identical to common electrical wires and can be used interchangeably with them. On the other hand, the practical SC wires are typically composite materials consisting of several functional materials. Many forms of SC wires are described in Section 4 of IEC 60050-815, including single core wires, multi-filamentary superconducting wires, composite superconductors and coated conductors. These wires as well as others that might be described as monolithic composite superconducting wires will be the focus in this technical report. A wire is considered as being practical if it can be procured in sufficiently continuous lengths under ordinary commercial transactions to build devices. Conductors made of multiple wires, such as cables, for example, are not included in this scope. Since this report only addresses the characteristics of practical wires, other wires such as prototype, test sample and developmental wires are not included in the scope of this technical report. Key words: superconductivity, supraconductivité

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IEC 61788-19:2013 covers a test method detailing the tensile test procedures to be carried out on reacted Cu/Nb3Sn composite superconducting wires at room temperature. The object of this test is to measure the modulus of elasticity and to determine the proof strength of the composite due to yielding of the copper and the copper tin components from the stress versus strain curve. Furthermore, the elastic limit, the tensile strength, and the elongation after fracture can be determined by means of the present method, but they are treated as optional quantities because the measured quantities of the elastic limit and the elongation after fracture have been reported to be subject to significant uncertainties according to the international round robin test. The sample covered by this test procedure should have a bare round or rectangular cross-section with an area between 0,15 mm2 and 2,0 mm2 and a copper to non-copper volume ratio of 0,2 to 1,5 and should have no insulation. Key words: supraconductivity, mechanical properties

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IEC 61788-18:2013 specifies a test method detailing the tensile test procedures to be carried out on Ag/Bi-2223 and Ag/Bi-2212 superconductive composite wires at room temperature. This test is used to measure the modulus of elasticity and to determine the 0,2 % proof strength. When the 0,2 % proof strength could not be determined due to earlier failure, the stress level at apparent strains of 0,05 %, 0,1 %, 0,15 %, 0,2 %, 0,25 % with increment of 0,05 % is measured. The values for elastic limit, fracture strength, percentage elongation after fracture and the fitted type of 0,2 % proof strength serve only as a reference. The sample covered by this test procedure should have a round or rectangular cross-section with an area of 0,3 mm2 to 2,0 mm2 (corresponding to the tape-shaped wires with width of 2,0 mm to 5,0 mm and thickness of 0,16 mm to 0,4 mm). Key words: superconductivity, mechanical properties measurement

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IEC 61788-12:2013 describes a test method for determining the copper to non-copper volume ratio of Cu/Nb3Sn wires. The test method given hereunder is applicable to Nb3Sn composite superconducting wires with a cross-sectional area of 0,1 mm2 to 3,0 mm2 and a copper to non-copper volume ratio of 0,1 or more. It does not make any reference to the filament diameter; however, it is not applicable to those superconducting wires with their filament, Sn, Cu-Sn alloy, barrier material and other non-copper portions dispersed in the copper matrix or those with the stabilizer dispersed. Furthermore, the copper to non-copper volume ratio can be determined on specimens before or after the Nb3Sn formation heat treatment process. The Cu/Nb3Sn wire has a monolithic structure with a round or rectangular cross-section. Though uncertainty increases, this method may be applicable to the measurement of the copper to non-copper volume ratio of the Cu/Nb3Sn wires whose cross-section and copper to non-copper volume ratio fall outside the specified ranges. This test method may be applied to other composite superconducting wires after some appropriate modifications. This second edition cancels and replaces the first edition published in 2002. It constitutes a technical revision. The main revision is the addition of two new annexes, "Uncertainty considerations" and "Uncertainty evaluation in the test method of the copper to non-copper volume ratio of Nb3Sn composite superconducting wires".

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IEC 61788-5:2013 covers a test method for the determination of copper to superconductor volume ratio of Cu/Nb-Ti composite superconducting wires. This test method and the alternate method in Annex are intended for use with Cu/Nb-Ti composite superconducting wires with a cross-sectional area of 0,1 mm2 to 3 mm2, a diameter of the Nb-Ti filament(s) of 2 micrometers to 200 micrometers, and a copper to superconductor volume ratio of 0,5 or more. The Cu/Nb-Ti composite test conductor discussed in this method has a monolithic structure with a round or rectangular cross-section. This test method is carried out by dissolving the copper with nitric acid. Deviations from this test method that are allowed for routine tests and other specific restrictions are given in this standard. Cu/Nb-Ti composite superconducting wires beyond the limits in the cross-sectional area, the filament diameter and the copper to superconductor volume ratio could be measured with this present method with an anticipated reduction of uncertainty. Other, more specialized, specimen test geometries may be more appropriate for conductors beyond the limits and have been omitted from this present standard for simplicity and to retain low uncertainty. The test method given in this standard is expected to apply to other superconducting composite wires after some appropriate modifications. The copper to superconductor volume ratio of composite superconductors is used mainly to calculate the critical current density of superconducting wires. The test with the method given in this International Standard may be used to provide part of the information needed to determine the suitability of a specific superconductor. Moreover, this method is useful for quality control, acceptance or research testing if the precautions given in this standard are observed. This second edition cancels and replaces the first edition published in 2000. It constitutes a technical revision. The main revisions are the addition of two new annexes, "Uncertainty considerations" (Annex E) and "Uncertainty evaluation in test method of copper to superconductor volume ratio of Cu/Nb-Ti composite superconductors" (Annex F).

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IEC 61788-16:2013 involves describing the standard measurement method of power-dependent surface resistance of superconductors at microwave frequencies by the sapphire resonator method. The measuring item is the power dependence of Rs at the resonant frequency. This method is the applicable for a frequency in the range of 10 GHz, for an input microwave power lower than 37 dBm (5 W). The aim is to report the surface resistance data at the measured frequency and that scaled to 10 GHz. Keyword: superconductivity

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IEC 61788-17:2013 describes the measurements of the local critical current density (Jc) and its distribution in large-area high-temperature superconducting (HTS) films by an inductive method using third-harmonic voltages. The most important consideration for precise measurements is to determine Jc at liquid nitrogen temperatures by an electric-field criterion and obtain current-voltage characteristics from its frequency dependence. Although it is possible to measure Jc in applied DC magnetic fields, the scope of this standard is limited to the measurement without DC magnetic fields. This technique intrinsically measures the critical sheet current that is the product of Jc and the film thickness d. The range and measurement resolution for Jcd of HTS films are from 200 A/m to 32 kA/m, with a measurement resolution of 100 A/m.

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IEC 61788-13:2012 describes considerations for the measurement of hysteretic loss in Cu/Nb-Ti multifilamentary composites using DC- or low-ramp-rate magnetometry. This international standard specifies a method of the measurement of hysteretic loss in multifilamentary Cu/Nb-Ti composite conductors. Measurements are assumed to be on round wires with temperatures at or near 4,2 K. DC or low-ramp-rate magnetometry will be performed using either a superconducting quantum interference device or a vibrating-sample magnetometer. Extension to the measurement of superconductors in general is given in Annex. This second edition cancels and replaces the first edition published in 2003. It constitutes a technical revision. Modifications made to the second edition extend to the measurement of superconductors in general, in various sample sizes and shapes, and at temperatures other than 4,2 K, and use the word "uncertainty" for all quantitative statistical expressions to eliminate the quantitative use of "precision" and "accuracy".

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IEC 61788-15:2011 describes measurements of the intrinsic surface impedance (Zs) of HTS films at microwave frequencies by a modified two-resonance mode dielectric resonator method. The object of measurement is to obtain the temperature dependence of the intrinsic Zs at the resonant frequency f0.

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IEC 61788-4:2011 covers a test method for the determination of the residual resistance ratio (RRR) of composite superconductors comprised of Nb-Ti filaments and Cu, Cu-Ni or Cu/Cu-Ni matrix. This method is intended for use with superconductors that have a monolithic structure with rectangular or round cross-section, RRR less than 350, and cross-sectional area less than 3 mm2. All measurements are done without an applied magnetic field. The method described in the body of this standard is the "reference" method and optional acquisition methods are outlined in Clause A.3. This third edition constitutes a technical revision which adds two new annexes: "Uncertainty considerations" (Annex B) and "Uncertainty evaluation in test method of RRR for NbTi" (Annex C). Copper is used as a matrix material in multifilamentary superconductors and works as an electrical shunt when the superconductivity is interrupted. It also contributes to recovery of the superconductivity by conducting heat generated in the superconductor to the surrounding coolant. The cryogenic-temperature resistivity of copper is an important quantity, which influences the stability of the superconductor. The residual resistance ratio is defined as a ratio of the resistance of the superconductor at room temperature to that just above the superconducting transition.

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IEC 61788-6:2011 covers a test method detailing the tensile test procedures to be carried out on Cu/Nb-Ti superconductive composite wires at room temperature. This test is used to measure modulus of elasticity, 0,2 % proof strength of the composite due to yielding of the copper component, and tensile strength. The value for percentage elongation after fracture and the second type of 0,2 % proof strength due to yielding of the Nb-Ti component serves only as a reference. The sample covered by this test procedure has a round or rectangular cross-section with an area of 0,15 mm2 to 2 mm2 and a copper to superconductor volume ratio of 1,0 to 8,0 and without the insulating coating. This third edition cancels and replaces the second edition published in 2008. It constitutes a technical revision which adds a new Annex C including specific examples of uncertainty estimation related to mechanical tests.

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IEC 61788-8:2010 specifies the measurement method of total AC losses by the pickup coil method in composite superconducting wires exposed to a transverse alternating magnetic field. The losses may contain hysteresis, coupling and eddy current losses. The standard method to measure only the hysteresis loss in DC or low-sweep-rate magnetic field is specified in IEC 61788-13. In metallic and oxide round superconducting wires expected to be mainly used for pulsed coil and AC coil applications, AC loss is generated by the application of time-varying magnetic field and/or current. The contribution of the magnetic field to the AC loss is predominant in usual electromagnetic configurations of the coil applications. For the superconducting wires exposed to a transverse alternating magnetic field, the present method can be generally used in measurements of the total AC loss in a wide range of frequency up to the commercial level, 50/60 Hz, at liquid helium temperature. For the superconducting wires with fine filaments, the AC loss measured with the present method can be divided into the hysteresis loss in the individual filaments, the coupling loss among the filaments and the eddy current loss in the normal conducting parts. In cases where the wires do not have a thick outer normal conducting sheath, the main components are the hysteresis loss and the coupling loss by estimating the former part as an extrapolated level of the AC loss per cycle to zero frequency in the region of lower frequency, where the coupling loss per cycle is proportional to the frequency. This second edition cancels and replaces the first edition published in 2003. This edition constitutes a technical revision. The main changes with respect to the previous edition are listed below:

- extending the applications of the pickup coil method to the a.c. loss measurements in metallic and oxide superconducting wires with a round cross section at liquid helium temperature,

- using the word "uncertainty" for all quantitative (associated with a number) statistical expressions and eliminating the quantitative use of "precision" and "accuracy". Key words: superconductivity, TC90

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IEC 61788-14:2010 provides general requirements for characteristic tests of conventional as well as superconducting current leads to be used for powering superconducting equipment. Current leads are indispensable components of superconducting devices in practical uses such as MRI diagnostic equipment, NMR spectrometers, single crystal growth devices, SMES, particle accelerators such as Tevatron, HERA, RHIC and LHC, experimental test instruments for nuclear fusion reactors, such as ToreSupra, TRIAM, LHD, EAST, KSTAR, W7-X, JT-60SA and ITER, etc., and of advanced superconducting devices in the near future in practical uses such as magnetic levitated trains, superconducting fault current limiters, superconducting transformers, etc. The major functions of current leads are to power high currents into superconducting devices and to minimize the overall heat load, including heat leakage from room temperature to cryogenic temperature and Joule heating through current leads. For this purpose, current leads are dramatically effective for lowering the overall heat load to use the high temperature superconducting component as a part of the current leads. Key words: superconductivity, TC90

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This part of IEC 61788 covers a test method for the determination of the d.c. critical current of either Cu/Nb-Ti composite superconductors that have a copper/superconductor ratio larger than 1 or Cu/Cu-Ni/Nb-Ti wires that have a copper/superconductor ratio larger than 0,9 and a copper alloy (Cu-Ni)/superconductor ratio larger than 0,2, where the diameter of Nb-Ti superconducting filaments is larger than 1 micrometre. The changes for the Cu/Cu-Ni/Nb-Ti are described in Annex C. The Cu-Ni uses all of the main part of the standard with the exceptions listed in Annex C that replace (and in some cases are counter to) some of the steps inthe main text. This method is intended for use with superconductors that have critical currents less than 1 000 A and n-values larger than 12, under standard test conditions and at magnetic fields less than or equal to 0,7 of the upper critical magnetic field. The test specimen is immersed in a liquid helium bath at a known temperature during testing. The test conductor has a monolithic structure with a round or rectangular cross-sectional area that is less than 2 mm2. The specimen geometry used in this test method is an inductively coiled specimen. Deviations from this test method that are allowed for routine tests and other specific restrictions are given in this standard. Test conductors with critical currents above 1 000 A or cross-sectional areas greater than 2 mm2 could be measured with the present method with an anticipated increase in uncertainty and a more significant self-field effect (see Annex B). Other, more specialized, specimen test geometries may be more appropriate for larger conductor testing which have been omitted from this present standard for simplicity and to retain a lower uncertainty. The test method given in this standard is expected to apply to other superconducting composite wires after some appropriate modifications.

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This part of IEC 61788 covers a test method for the determination of the d.c. critical current of Nb3Sn composite superconductors which are fabricated by either the bronze process or the internal tin diffusion process and have a copper/non-copper ratio larger than 0,2. This method is intended for use with superconductors which have critical currents of less than 1 000 A and n-values larger than 12 under standard test conditions and at magnetic fields of less than or equal to 0,7 times the upper critical magnetic field. The test specimen is immersed in a liquid helium bath at a known temperature during testing. The Nb3Sn composite test conductor has a monolithic structure with a total round-cross-sectional area that is less than 2 mm2. The specimen geometry used in this test method is an inductively coiled specimen. Deviations from this test method which are allowed for routine tests and other specific restrictions are given in this standard. Nb3Sn conductors with critical currents above 1 000 A or total cross-sectional areas greater than 2 mm2 can be measured with the present method with an anticipated reduction in precision and a more significant self-field effect (see Annex C). Other, more specialized, specimen test geometries may be more appropriate for larger conductor testing which have been omitted from this present standard for simplicity and to retain precision. The test method given in this standard should in principle apply to Nb3Sn composite wires fabricated by any other process. This method is also expected to apply to other superconducting composite wires after some appropriate modifications.

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This part of IEC 61788 specifies a test method for the resistive determination of the critical temperature of composite superconductors for industrial use. The composite superconductors covered in this standard include Cu/Nb-Ti, Cu/Cu-Ni/Nb-Ti and Cu-Ni/Nb-Ti composite superconductors, Cu/Nb3Sn and Cu/Nb3Al composite superconductors, and metal-sheathed MgB2 composite superconductors, and metal-stabilized Bi-system oxide superconductors and Yttrium- or rare-earth-based coated conductors that have a monolithic structure and a shape of round, flat or square wire containing mono- or multi-cores of superconductors.

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This part of IEC 61788 covers a test method for the determination of the dc critical current of short and straight Ag- and/or Ag alloy-sheathed Bi-2212 and Bi-2223 oxide superconductors that have a monolithic structure and a shape of round wire or flat or square tape containing mono- or multicores of oxides. This method is intended for use with superconductors that have critical currents less than 500 A and n-values larger than 5. The test is carried out with and without an applying external magnetic field. For all tests in a magnetic field, the magnetic field is perpendicular to the length of the specimen. In the test of a tape specimen in a magnetic field, the magnetic field is parallel or perpendicular to the wider tape surface (or one surface if square). The test specimen is immersed either in a liquid helium bath or a liquid nitrogen bath during testing. Deviations from this test method that are allowed for routine tests and other specific restrictions are given in this standard.

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Specifies a test method for the determination of the trapped field (trapped flux density) of bulk high temperature superconductors. This International Standard is applicable to large grain bulk oxide superconductors that have well defined shapes such as round discs, rectangular, and hexagonal pellets. The trapped flux density can be assessed at temperatures from 4,2 K to 90 K. For the purpose of standardization, the trapped flux density will be reported for liquid nitrogen temperature.

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IEC 61788-11:2011 covers a test method for the determination of the residual resistance ratio (RRR) of Nb3Sn composite superconductors. This method is intended for use with superconductor specimens that have a monolithic structure with rectangular or round cross-section, RRR less than 350 and cross-sectional area less than 3 mm2, and have received a reaction heat-treatment. Ideally, it is intended that the specimens be as straight as possible; however, this is not always the case, thus care must be taken to measure the specimen in its as received condition. All measurements are done without an applied magnetic field. The method described in the body of this standard is the "reference" method and optional acquisition methods are outlined in Clause A.3. This second edition cancels and replaces the first edition published in 2003. It constitutes a technical revision. The main revisions are the addition of two new annexes, "Uncertainty considerations" (Annex B) and "Uncertainty evaluation in test method of RRR for Nb3Sn" (Annex C).

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