Superconductivity - Part 4: Residual resistance ratio measurement - Residual resistance ratio of Nb-Ti and Nb<sub>3</sub>Sn composite superconductors

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.

Supraconductivité - Partie 4: Mesurage du rapport de résistance résiduelle - Rapport de résistance résiduelle des composites supraconducteurs de Nb-Ti et de Nb<sub>3</sub>Sn

IEC 61788-4:2020 est disponible sous forme de IEC 61788-4:2020 RLV qui contient la Norme internationale et sa version Redline, illustrant les modifications du contenu technique depuis l'édition précédente.
IEC 61788-4:2020 spécifie une méthode d'essai pour la détermination du rapport de résistance résiduelle (RRR) des composites supraconducteurs de Nb-Ti et de Nb3Sn avec une matrice de Cu, Cu-Ni, Cu/Cu-Ni et Al dans une condition sans contrainte et dans un champ magnétique externe nul. Cette méthode est destinée à être utilisée avec des éprouvettes de supraconducteurs présentant une structure monolithique avec une section rectangulaire ou circulaire, un RRR de valeur inférieure à 350 et une surface de section inférieure à 3 mm2. Dans le cas de Nb3Sn, les éprouvettes ont subi un traitement thermique de réaction. Cette cinquième édition annule et remplace la quatrième édition parue en 2016. Cette édition constitue une révision technique. Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
a) modification de la distance adéquate des prises de tension sur les éprouvettes pour un mesurage fiable,
b) nouveau rapport du résultat de l’essai interlaboratoire du rapport de résistance résiduelle des supraconducteurs Nb3Sn qui atteste de la validité de la méthode de mesure utilisée dans la présente norme,
c) révision des définitions prêtant à confusion concernant le rapport entre le cuivre et la fraction de cuivre.

General Information

Status
Published
Publication Date
19-Mar-2020
Technical Committee
Current Stage
PPUB - Publication issued
Completion Date
20-Mar-2020
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IEC 61788-4:2020 - Superconductivity - Part 4: Residual resistance ratio measurement - Residual resistance ratio of Nb-Ti and Nb<sub>3</sub>Sn composite superconductors
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IEC 61788-4
Edition 5.0 2020-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Superconductivity –
Part 4: Residual resistance ratio measurement – Residual resistance ratio of
Nb‑Ti and Nb Sn composite superconductors
Supraconductivité –
Partie 4: Mesurage du rapport de résistance résiduelle – Rapport de résistance
résiduelle des composites supraconducteurs de Nb-Ti et de Nb Sn
IEC 61788-4:2020-03(en-fr)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC 61788-4
Edition 5.0 2020-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Superconductivity –
Part 4: Residual resistance ratio measurement – Residual resistance ratio of
Nb‑Ti and Nb Sn composite superconductors
Supraconductivité –
Partie 4: Mesurage du rapport de résistance résiduelle – Rapport de résistance
résiduelle des composites supraconducteurs de Nb-Ti et de Nb Sn
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 17.220.20; 29.050 ISBN 978-2-8322-7916-8

Warning! Make sure that you obtained this publication from an authorized distributor.

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® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
---------------------- Page: 3 ----------------------
– 2 – IEC 61788-4:2020 © IEC 2020
CONTENTS

FOREWORD ........................................................................................................................... 4

INTRODUCTION ..................................................................................................................... 6

1 Scope .............................................................................................................................. 7

2 Normative references ...................................................................................................... 7

3 Terms and definitions ...................................................................................................... 7

4 Principle .......................................................................................................................... 8

5 Apparatus ........................................................................................................................ 8

5.1 Material of measurement mandrel or of measurement base plate ............................ 8

5.2 Diameter of the measurement mandrel and length of the measurement base

plate ....................................................................................................................... 9

5.3 Cryostat for the resistance ( ) measurement ........................................................ 9

6 Specimen preparation ...................................................................................................... 9

7 Data acquisition and analysis .......................................................................................... 9

7.1 Resistance ( R ) at room temperature ...................................................................... 9

7.2 Resistance ( R or R ) just above the superconducting transition ......................... 10

2 2

7.2.1 Correction of strain effect .............................................................................. 10

7.2.2 Data acquisition of cryogenic resistance ........................................................ 10

7.2.3 Optional acquisition methods ......................................................................... 12

7.3 Correction on measured R of Nb-Ti composite superconductor for bending

strain .................................................................................................................... 12

7.4 Residual resistance ratio (RRR) ............................................................................ 12

8 Uncertainty and stability of the test method ................................................................... 13

8.1 Temperature ......................................................................................................... 13

8.2 Voltage ................................................................................................................. 13

8.3 Current ................................................................................................................. 13

8.4 Dimension ............................................................................................................. 13

9 Test report ..................................................................................................................... 13

9.1 RRR value ............................................................................................................ 13

9.2 Specimen .............................................................................................................. 14

9.3 Test conditions ..................................................................................................... 14

9.3.1 Measurements of R and R ........................................................................ 14

1 2

9.3.2 Measurement of R ....................................................................................... 15

9.3.3 Measurement of R ....................................................................................... 15

Annex A (informative) Additional information relating to the measurement of RRR .............. 16

A.1 Recommendation on specimen mounting orientation ............................................. 16

A.2 Alternative methods for increasing temperature of specimen above

superconducting transition temperature ................................................................ 16

A.3 Alternative measurement methods of R or R .................................................... 16

2 2

A.4 Bending strain dependency of RRR for Nb-Ti composite superconductor .............. 19

A.5 Procedure of correction of bending strain effect .................................................... 22

Annex B (informative) Uncertainty considerations ............................................................... 24

B.1 Overview............................................................................................................... 24

B.2 Definitions............................................................................................................. 24

---------------------- Page: 4 ----------------------
IEC 61788-4:2020 © IEC 2020 – 3 –

B.3 Consideration of the uncertainty concept .............................................................. 24

B.4 Uncertainty evaluation example for IEC TC 90 standards ...................................... 26

Annex C (informative) Uncertainty evaluation in test method of RRR for Nb-Ti and

Nb Sn composite superconductors ....................................................................................... 28

C.1 Evaluation of uncertainty ....................................................................................... 28

C.2 Summary of round robin test of RRR of a Nb-Ti composite superconductor ........... 31

C.3 Reason for large COV value in the intercomparison test on Nb Sn composite

superconductor ..................................................................................................... 32

Bibliography .......................................................................................................................... 34

Figure 1 – Relationship between temperature and resistance.................................................. 8

Figure 2 – Voltage versus temperature curves and definitions of each voltage ...................... 11

Figure A.1 – Definition of voltages ........................................................................................ 18

Figure A.2 – Bending strain dependency of RRR value for pure Cu matrix of Nb-Ti
composite superconductors (comparison between measured values and calculated

values) .................................................................................................................................. 20

Figure A.3 – Bending strain dependency of RRR value for round Cu wires ............................ 20

Figure A.4 – Bending strain dependency of normalized RRR value for round Cu wires .......... 21

Figure A.5 – Bending strain dependency of RRR value for rectangular Cu wires ................... 21

Figure A.6 – Bending strain dependency of normalized RRR value for rectangular Cu

wires ..................................................................................................................................... 22

Figure C.1 – Distribution of observed r of Cu/Nb-Ti composite superconductor ............... 32

RRR

Table A.1 – Minimum diameter of the measurement mandrel for round wires ........................ 22

Table A.2 – Minimum diameter of the measurement mandrel for rectangular wires................ 22

Table B.1 – Output signals from two nominally identical extensometers ................................ 25

Table B.2 – Mean values of two output signals ..................................................................... 25

Table B.3 – Experimental standard deviations of two output signals ...................................... 25

Table B.4 – Standard uncertainties of two output signals ...................................................... 26

Table B.5 – COV values of two output signals ....................................................................... 26

Table C.1 – Uncertainty of each measurement ...................................................................... 31

Table C.2 – Obtained values of RRR for six Nb Sn specimens ............................................. 32

Table C.3 – Average, standard deviation and coefficient of variation for six specimens ......... 33

---------------------- Page: 5 ----------------------
– 4 – IEC 61788-4:2020 © IEC 2020
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SUPERCONDUCTIVITY –
Part 4: Residual resistance ratio measurement –
Residual resistance ratio of Nb-Ti and Nb Sn
composite superconductors
FOREWORD

1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising

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9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent

rights. IEC shall not be held responsible for identifying any or all such patent rights.

International Standard IEC 61788-4 has been prepared by IEC technical committee 90:

Superconductivity.

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 Nb

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.

---------------------- Page: 6 ----------------------
IEC 61788-4:2020 © IEC 2020 – 5 –
The text of this standard is based on the following documents:
FDIS Report on voting
90/448/FDIS 90/451/RVD

Full information on the voting for the approval of this standard can be found in the report on

voting indicated in the above table.

This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

A list of all parts of the IEC 61788 series, published under the general title Superconductivity,

can be found on the IEC website.

The committee has decided that the contents of this publication will remain unchanged until the

stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to

the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.

IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates

that it contains colours which are considered to be useful for the correct understanding

of its contents. Users should therefore print this document using a colour printer.

---------------------- Page: 7 ----------------------
– 6 – IEC 61788-4:2020 © IEC 2020
INTRODUCTION

Copper, Cu/Cu-Ni or aluminium is used as matrix material in Ni-Ti and Nb Sn composite

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 and AC losses 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.

This document specifies the test method for residual resistance ratio of Nb-Ti and Nb Sn

composite superconductors. The curve method is employed for the measurement of the

resistance just above the superconducting transition. Other methods are described in

Clause A.3.
---------------------- Page: 8 ----------------------
IEC 61788-4:2020 © IEC 2020 – 7 –
SUPERCONDUCTIVITY –
Part 4: Residual resistance ratio measurement –
Residual resistance ratio of Nb-Ti and Nb Sn
composite superconductors
1 Scope

This part of IEC 61788 specifies a test method for the determination of the residual resistance

ratio (RRR) of Nb-Ti and Nb Sn 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 mm . In the case

of Nb Sn, the specimens have received a reaction heat-treatment.
2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies.

For undated references, the latest edition of the referenced document (including any

amendments) applies.

IEC 60050-815, International Electrotechnical Vocabulary (IEV) – Part 815: Superconductivity

(available at: www.electropedia.org)
3 Terms and definitions

For the purposes of this document, the terms and definitions given in IEC 60050-815 and the

following apply.

ISO and IEC maintain terminological databases for use in standardization at the following

addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
residual resistance ratio
RRR

ratio of resistance at room temperature to the resistance just above the superconducting

transition
Note 1 to entry: This note applies to the French language only.

Note 2 to entry: In this document for Nb-Ti and Nb Sn composite superconductors, the room temperature is defined

as 293 K (20 °C), and the residual resistance ratio is obtained in Formula (1), where the resistance ( R ) at 293 K is

divided by the resistance ( R ) just above the superconducting transition.
r = (1)
RRR
---------------------- Page: 9 ----------------------
– 8 – IEC 61788-4:2020 © IEC 2020

Here r is a value of the residual resistance ratio, R is a value of the resistance measured in a strain-free

RRR
condition and zero external magnetic field.

Figure 1 shows schematically a resistance versus temperature curve acquired on a specimen while measuring the

cryogenic resistance.

The cryogenic resistance, R , is determined by the intersection, A, of two straight lines (a) and (b) at

temperature T* .
Figure 1 – Relationship between temperature and resistance
4 Principle

The resistance measurement both at room and cryogenic temperatures shall be performed with

the four-terminal technique. All measurements are done without an applied magnetic field.

The target relative combined standard uncertainty of this method is defined as an expanded

uncertainty ( k= 2 ) not to exceed 5 %.

The maximum bending strain induced during mounting and cooling the Nb-Ti specimen shall

not exceed 2 %. The measurement shall be conducted in a strain-free condition or in a condition

with allowable thermal strain for the Nb Sn specimen.
5 Apparatus
5.1 Material of measurement mandrel or of measurement base plate

Material of the measurement mandrel for a coiled Nb-Ti specimen or of the measurement base

plate for a straight Nb-Ti or Nb Sn specimen shall be copper, aluminium, silver, or the like

whose thermal conductivity is equal to or better than 100 W/(m·K) at liquid helium temperature

(4,2 K). The surface of the material shall be covered with an insulating layer (tape or a layer

made of polyethylene terephthalate, polyester, polytetrafluoroethylene, etc.) whose thickness

is 0,1 mm or less.
---------------------- Page: 10 ----------------------
IEC 61788-4:2020 © IEC 2020 – 9 –
5.2 Diameter of the measurement mandrel and length of the measurement base plate

The diameter of the measurement mandrel shall be large enough to keep the bending strain of

the specimen less than or equal to 2 % for the Nb-Ti specimen. The Nb Sn specimen on a base

plate shall be measured in a strain-free condition or a condition with allowable thermal strain.

The measurement base plate shall be at least 30 mm long in one dimension.
5.3 Cryostat for the resistance ( R ) measurement

The cryostat shall include a specimen support structure and a liquid helium reservoir for

measurement of the resistance R . The specimen support structure shall allow the specimen,

which is mounted on a measurement mandrel or a measurement base plate, to be lowered into

and raised out of a liquid helium bath. In addition, the specimen support structure shall be made

so that a current can flow through the specimen and the resulting voltage generated along the

specimen can be measured.
6 Specimen preparation

The test specimen shall have no joints or splices with a length of 30 mm or longer. The specimen

shall be instrumented with current contacts near each of its ends and a pair of voltage contacts

over its central portion. The distance between two voltage taps ( L ) shall be 15 mm or longer.

A thermometer for measuring cryogenic temperature shall be attached near the specimen.

Some mechanical method shall be used to hold the specimen against the insulated layer of the

measurement mandrel or base plate. Special care should be taken during instrumentation and

installation of the specimen on the measurement mandrel or base plate so that no excessive

force, which may cause undesired bending strain or tensile strain, would be applied to the

specimen. Ideally, the Nb Sn specimen is intended to be as straight as possible; however, this

is not always the case, thus care should be taken to measure the specimen in its as received

condition.

The specimen shall be mounted on a measurement mandrel or on a measurement base plate

for these measurements. Both resistance measurements, R and R , shall be made on the

1 2
same specimen and the same mounting.
7 Data acquisition and analysis
7.1 Resistance ( R ) at room temperature

The mounted specimen shall be measured at room temperature ( T (K)), where T satisfies

m m

the following condition: 273 K ≤ T ≤ 308 K. A specimen current ( I (A)) shall be applied so that

m 1
2 2

the current density is in the range of 0,1 A/mm to 2 A/mm based on the total wire cross-

(V)), and shall be recorded. Formula (2)
sectional area, and the resulting voltage ( U I T
1 1 m

below shall be used to calculate the resistance ( R ) at room temperature. The resistance ( R )

m 1

at 293 K (20 °C ) shall be calculated using Formula (3) for a wire with Cu matrix. For wires that

do not contain a pure Cu component, the value of R shall be set equal to R , without any

1 m
temperature correction.
R = (2)
---------------------- Page: 11 ----------------------
– 10 – IEC 61788-4:2020 © IEC 2020
R = (3)
1+ 0,00393×−T 293
( )
 
7.2 Resistance ( R or R ) just above the superconducting transition
2 2
7.2.1 Correction of strain effect

Under a strained condition of the Nb-Ti specimen, the measured cryogenic resistance, R , is

not a correct value for R . The corresponding correction of the strain effect is described in 7.3.

7.2.2 Data acquisition of cryogenic resistance

The specimen, which is still mounted as it was for the room temperature measurement, shall

be placed in the cryostat for electrical measurement specified in 5.3. Horizontal mounting of the

specimen is recommended in Clause A.1. Alternative cryostats that employ a heating element

to sweep the specimen temperature are described in Clause A.2. The specimen shall be slowly

lowered into the liquid helium bath and cooled to liquid helium temperature over a time period

of at least 5 min.

During the acquisition phases of the low-temperature R measurements, a specimen current

2 2

( I ) shall be applied so that the current density is in the range 0,1 A/mm to 10 A/mm based

on the total wire cross-sectional area, and the resulting voltage ( U (V)), I (A), and specimen

temperature ( T (K)) shall be recorded. In order to keep the ratio of signal to noise high enough,

the measurement shall be carried out under the condition that the absolute value of the resulting

voltage above the superconducting transition exceeds 10 μV. An illustration of the data to be

acquired and its analysis is shown in Figure 2.
NOTE Voltages
...

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