Superconductivity - Part 23: Residual resistance ratio measurement - Residual resistance ratio of cavity-grade Nb superconductors (IEC 61788-23:2021)

This part of IEC 61788 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.

Supraleitfähigkeit - Teil 23: Messung des Restwiderstandsverhältnisses - Restwiderstandsverhältnis von hochreinen Nb Supraleitern für Kavitäten (IEC 61788-23:2021)

Supraconductivité - Partie 23: Mesurage du rapport de résistance résiduelle - Rapport de résistance résiduelle des supraconducteurs de Nb à cavités (IEC 61788-23:2021)

Superprevodnost - 23. del: Meritve deleža preostale upornosti - Razmerje preostale upornosti niobijskih superprevodnikov (IEC 61788-23:2021)

General Information

Status
Published
Publication Date
24-Oct-2021
Technical Committee
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
07-Oct-2021
Due Date
12-Dec-2021
Completion Date
25-Oct-2021

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SLOVENSKI STANDARD
SIST EN IEC 61788-23:2021
01-december-2021
Nadomešča:
SIST EN IEC 61788-23:2018
Superprevodnost - 23. del: Meritve deleža preostale upornosti - Razmerje
preostale upornosti niobijskih superprevodnikov (IEC 61788-23:2021)
Superconductivity - Part 23: Residual resistance ratio measurement - Residual
resistance ratio of cavity-grade Nb superconductors (IEC 61788-23:2021)
Supraleitfähigkeit - Teil 23: Messung des Restwiderstandsverhältnisses -

Restwiderstandsverhältnis von hochreinen Nb Supraleitern für Kavitäten (IEC 61788-

23:2021)

Supraconductivité - Partie 23: Mesurage du rapport de résistance résiduelle - Rapport de

résistance résiduelle des supraconducteurs de Nb à cavités (IEC 61788-23:2021)
Ta slovenski standard je istoveten z: EN IEC 61788-23:2021
ICS:
17.220.20 Merjenje električnih in Measurement of electrical
magnetnih veličin and magnetic quantities
29.050 Superprevodnost in prevodni Superconductivity and
materiali conducting materials
SIST EN IEC 61788-23:2021 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
SIST EN IEC 61788-23:2021
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SIST EN IEC 61788-23:2021
EUROPEAN STANDARD EN IEC 61788-23
NORME EUROPÉENNE
EUROPÄISCHE NORM
October 2021
ICS 17.220; 29.050 Supersedes EN IEC 61788-23:2018 and all of its
amendments and corrigenda (if any)
English Version
Superconductivity - Part 23: Residual resistance ratio
measurement - Residual resistance ratio of cavity-grade Nb
superconductors
(IEC 61788-23:2021)

Supraconductivité - Partie 23: Mesurage du rapport de Supraleitfähigkeit - Teil 23: Messung des

résistance résiduelle - Rapport de résistance résiduelle des Restwiderstandsverhältnisses - Restwiderstandsverhältnis

supraconducteurs de Nb à cavités von hochreinen Nb Supraleitern für Kavitäten
(IEC 61788-23:2021) (IEC 61788-23:2021)

This European Standard was approved by CENELEC on 2021-09-27. CENELEC members are bound to comply with the CEN/CENELEC

Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.

Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC

Management Centre or to any CENELEC member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by translation

under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the

same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,

Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the

Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,

Turkey and the United Kingdom.
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels

© 2021 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.

Ref. No. EN IEC 61788-23:2021 E
---------------------- Page: 3 ----------------------
SIST EN IEC 61788-23:2021
EN IEC 61788-23:2021 (E)
European foreword

The text of document 90/478/FDIS, future edition 2 of IEC 61788-23, prepared by IEC/TC 90

"Superconductivity" was submitted to the IEC-CENELEC parallel vote and approved by CENELEC as

EN IEC 61788-23:2021.
The following dates are fixed:

• latest date by which the document has to be implemented at national (dop) 2022-06-27

level by publication of an identical national standard or by endorsement

• latest date by which the national standards conflicting with the (dow) 2024-09-27

document have to be withdrawn

This document supersedes EN IEC 61788-23:2018 and all of its amendments and corrigenda (if any).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

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

Any feedback and questions on this document should be directed to the users’ national committee. A

complete listing of these bodies can be found on the CENELEC website.
Endorsement notice

The text of the International Standard IEC 61788-23:2021 was approved by CENELEC as a European

Standard without any modification.

In the official version, for Bibliography, the following notes have to be added for the standards

indicated:
IEC 61788-4 NOTE Harmonized as EN IEC 61788-4
IEC 61788-10 NOTE Harmonized as EN 61788-10
---------------------- Page: 4 ----------------------
SIST EN IEC 61788-23:2021
EN IEC 61788-23:2021 (E)
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications

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.

NOTE 1 Where an International Publication has been modified by common modifications, indicated by (mod), the relevant

EN/HD applies.

NOTE 2 Up-to-date information on the latest versions of the European Standards listed in this annex is available here:

www.cenelec.eu.
Publication Year Title EN/HD Year
IEC 60050-815 - International Electrotechnical Vocabulary - - -
Part 815: Superconductivity
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SIST EN IEC 61788-23:2021
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SIST EN IEC 61788-23:2021
IEC 61788-23
Edition 2.0 2021-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Superconductivity –
Part 23: Residual resistance ratio measurement – Residual resistance ratio
of cavity-grade Nb superconductors
Supraconductivité –
Partie 23: Mesurage du rapport de résistance résiduelle – Rapport de résistance
résiduelle des supraconducteurs de Nb à cavités
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 17.220; 29.050 ISBN 978-2-8322-1011-5

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

Attention! Veuillez vous assurer que vous avez obtenu cette publication via un distributeur agréé.

® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
---------------------- Page: 7 ----------------------
SIST EN IEC 61788-23:2021
– 2 – IEC 61788-23:2021 © IEC 2021
CONTENTS

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

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

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

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

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

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

5 Measurement apparatus ................................................................................................ 9

5.1 Mandrel or base plate ............................................................................................ 9

5.2 Cryostat and support of mandrel or base plate ....................................................... 9

6 Specimen preparation .................................................................................................. 10

7 Data acquisition and analysis ....................................................................................... 11

7.1 Data acquisition hardware ................................................................................... 11

7.2 Resistance (R ) at room temperature ................................................................... 11

7.3 Residual resistance (R ) just above the superconducting transition ...................... 11

7.4 Validation of the residual resistance measurement ............................................... 13

7.5 Residual resistance ratio ..................................................................................... 13

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

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

9.1 General ............................................................................................................... 13

9.2 Test information .................................................................................................. 13

9.3 Specimen information .......................................................................................... 14

9.4 Test conditions .................................................................................................... 14

9.5 RRR value .......................................................................................................... 14

Annex A (informative) Additional information relating to the measurement of RRR ............... 15

A.1 Considerations for specimens and apparatus ....................................................... 15

A.2 Considerations for specimen mounting orientation ............................................... 16

A.3 Alternative methods for increasing temperature of specimen above

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

A.3.1 General ....................................................................................................... 16

A.3.2 Heater method ............................................................................................. 16

A.3.3 Controlled methods ...................................................................................... 16

A.4 Other test methods .............................................................................................. 16

A.4.1 General ....................................................................................................... 16

A.4.2 Measurement of resistance versus time ........................................................ 17

A.4.3 Comparison of ice point and room temperature ............................................. 17

A.4.4 Extrapolation of the resistance to 4,2 K ........................................................ 17

A.4.5 Use of magnetic field to suppress superconductivity at 4,2 K ......................... 18

A.4.6 AC techniques ............................................................................................. 18

Annex B (informative) Uncertainty considerations ............................................................... 19

B.1 Overview............................................................................................................. 19

B.2 Definitions ........................................................................................................... 19

B.3 Consideration of the uncertainty concept ............................................................. 20

B.4 Uncertainty evaluation example for IEC TC 90 standards ..................................... 22

Annex C (informative) Uncertainty evaluation for resistance ratio measurement of Nb

superconductors ................................................................................................................. 24

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SIST EN IEC 61788-23:2021
IEC 61788-23:2021 © IEC 2021 – 3 –

C.1 Evaluation of uncertainty ..................................................................................... 24

C.1.1 Room temperature measurement uncertainty ................................................ 24

C.1.2 Cryogenic measurement uncertainty ............................................................. 25

C.1.3 Estimation of uncertainty for typical experimental conditions ......................... 27

C.2 Inter-laboratory comparison summary .................................................................. 28

Bibliography ....................................................................................................................... 29

Figure 1 – Relationship between temperature and resistance near the superconducting

transition .............................................................................................................................. 8

Figure A.1 – Determination of the value of R from a resistance versus time plot .................. 17

Figure C.1 – Graphical description of the uncertainty of regression related to the

measurement of R ............................................................................................................. 27

Table B.1 – Output signals from two nominally identical extensometers ............................... 20

Table B.2 – Mean values of two output signals .................................................................... 20

Table B.3 – Experimental standard deviations of two output signals ..................................... 21

Table B.4 – Standard uncertainties of two output signals ..................................................... 21

Table B.5 – Coefficients of variation of two output signals .................................................... 21

Table C.1 – Uncertainty of measured parameters ................................................................ 27

Table C.2 – RRR values obtained by inter-laboratory comparison using liquid helium ........... 28

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SIST EN IEC 61788-23:2021
– 4 – IEC 61788-23:2021 © IEC 2021
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SUPERCONDUCTIVITY –
Part 23: Residual resistance ratio measurement –
Residual resistance ratio of cavity-grade Nb superconductors
FOREWORD

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

all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international

co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and

in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports,

Publicly Available Specifications (PAS) and Guides (hereafter referred to as "IEC Publication(s)"). Their

preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with

may participate in this preparatory work. International, governmental and non-governmental organizations liaising

with the IEC also participate in this preparation. IEC collaborates closely with the International Organization for

Standardization (ISO) in accordance with conditions determined by agreement between the two organizations.

2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international

consensus of opinion on the relevant subjects since each technical committee has representation from all

interested IEC National Committees.

3) IEC Publications have the form of recommendations for international use and are accepted by IEC National

Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC

Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any

misinterpretation by any end user.

4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications

transparently to the maximum extent possible in their national and regional publications. Any divergence between

any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter.

5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity

assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any

services carried out by independent certification bodies.

6) All users should ensure that they have the latest edition of this publication.

7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and

members of its technical committees and IEC National Committees for any personal injury, property damage or

other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and

expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC

Publications.

8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is

indispensable for the correct application of this publication.

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.

IEC 61788-23 has been prepared by IEC technical committee 90: Superconductivity. It is an

International Standard.

This second edition cancels and replaces the first edition published in 2018. This edition

constitutes a technical revision.

This edition includes the following significant technical changes with respect to the previous

edition:

a) The scope of this standard was modified to restrict the range of residual resistance ratio to

that encountered by providers of material for superconducting radio-frequency cavities.

b) The references to technical material were updated and corrected.
---------------------- Page: 10 ----------------------
SIST EN IEC 61788-23:2021
IEC 61788-23:2021 © IEC 2021 – 5 –
The text of this International Standard is based on the following documents:
FDIS Report on voting
90/478/FDIS 90/482/RVD

Full information on the voting for its approval can be found in the report on voting indicated in

the above table.
The language used for the development of this International Standard is English.

This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in

accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available

at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are

described in greater detail at www.iec.ch/standardsdev/publications.

A list of all parts in 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 document will remain unchanged until the

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

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

IMPORTANT – The 'color inside' logo on the cover page of this publication indicates that it

contains colors which are considered to be useful for the correct understanding of its contents.

Users should therefore print this document using a color printer.
---------------------- Page: 11 ----------------------
SIST EN IEC 61788-23:2021
– 6 – IEC 61788-23:2021 © IEC 2021
INTRODUCTION

High-purity niobium is the chief material used to make superconducting radio-frequency cavities.

Similar grades of niobium may be used in the manufacture of superconducting wire.

Procurement of raw materials and quality assurance of delivered products often use the residual

resistance ratio (RRR) to specify or assess the purity of a metal. RRR is defined for non-

superconducting metals as the ratio of electrical resistance measured at room temperature

(293 K) to the resistance measured for the same specimen at low temperature (~4,2 K). The

low-temperature value is often called the residual resistance. Higher purity is associated with

higher values of RRR.

Niobium presents special problems due to its transformation to a superconducting state at ~9 K,

so DC electrical resistance is effectively zero below this temperature. The definition above

would then yield an infinite value for RRR. This document describes a test method to determine

the residual resistance value by using a plot of the resistance to temperature as the test

specimen is gradually warmed through the superconducting transition in the absence of an

applied magnetic field. This results in a determination of the residual resistance at just above

superconducting transition, ~10 K, from which RRR is subsequently determined.

International Standards also exist to determine the RRR of superconducting wires. In contrast

to superconducting wires, which are usually a composite of a superconducting material and a

non-superconducting material and the RRR value is representative of only the non-

superconducting component, here the entire specimen is composed of superconducting niobium.

Frequently, niobium is procured as a sheet, bar, tube, or rod, and not as a wire. For such forms,

test specimens will likely be a few millimetres in the dimensions transverse to electric current

flow. This difference is significant when making electrical resistance measurements, since

niobium samples will likely be much longer than that for the same length-to-diameter ratio as a

wire, and higher electrical current may be required to produce sufficient voltage signals.

Guidance for sample dimensions and electrical connections is provided in Annex A. Test

apparatus should also take into consideration aspects such as the orientation of a test specimen

relative to the liquid helium surface, accessibility through ports on common liquid helium dewars,

design of current contacts, and minimization of thermal gradients over long specimen lengths.

These aspects distinguish this document from similar wire standards.

Other test methods have been used to determine RRR. Some methods use a measurement at

a temperature other than 293 K for the high resistance value. Some methods use extrapolations

at 4,2 K in the absence of an applied magnetic field for the low resistance value. Other methods

use an applied magnetic field to suppress superconductivity at 4,2 K. A comparison between

this document and some other test methods is presented in Annex A. Note that systematic

differences of up to 10 % are produced by these other methods, which is larger than the target

uncertainty of this document. It is therefore important to apply this document or the appropriate

corrections listed in Annex A according to the test method used.

Whenever possible, this test method should be transferred to vendors and collaborators who

also perform RRR measurements. To promote consistency, the results of inter-laboratory

comparisons are described in Clause C.2.
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SIST EN IEC 61788-23:2021
IEC 61788-23:2021 © IEC 2021 – 7 –
SUPERCONDUCTIVITY –
Part 23: Residual resistance ratio measurement –
Residual resistance ratio of cavity-grade Nb superconductors
1 Scope

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

ratio (RRR), r , of cavity-grade niobium. This method is intended for high-purity niobium

RRR

grades with 150 < r < 600. The test method is valid for specimens with rectangular or round

RRR
2 2

cross-section, cross-sectional area greater than 1 mm but less than 20 mm , and a length not

less than 10 nor more than 25 times the width or diameter.
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 – 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
RRR

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

transition
r = R / R
(1)
RRR 1 2
where
R is the resistance at 293 K;
R is the resistance just above the superconducting transition, at ~10 K.
---------------------- Page: 13 ----------------------
SIST EN IEC 61788-23:2021
– 8 – IEC 61788-23:2021 © IEC 2021
Figure 1 – Relationship between temperature and resistance near
the superconducting transition

Note 1 to entry: In this document, the room temperature is defined as 20 °C = 293 K, and r is obtained as

RRR

follows: Figure 1 shows schematically resistance versus temperature data and the graphical procedure used to

determine the value of R . In Figure 1, the region of maximum slope is extrapolated upward in resistance, as shown

by line (a), and the region of minimum slope at temperatures above the transition temperature is extrapolated

downward in temperature, as shown by line (b). The intersection of these extrapolations at point A determines the

value of R as well as a temperature value T .
2 c

Note 2 to entry: The value T is similar to the transition value defined in [1] , and should not be confused with the

value defined at the midpoint of the transition, called T in [2].

Note 3 to entry: Some standards or documented techniques, e.g. [3], [4], [5], [6], define r with the value of R

RRR 1

determined at a temperature other than 293 K, or the value of R determined at a temperature below the

superconducting transition. The user of this document should be alert for such differences in definition.

4 Principle

The 4-point DC electrical resistance technique shall be performed both at room temperature

and at cryogenic temperature. The test may be done either as a function of temperature or as

a function of time with increasing temperature.

The relative combined standard uncertainty of this method is 3 % with coverage factor 2.

Measurements shall have the following attributes.

a) Measuring current is sufficiently high to provide voltage signals of the order of 1 µV. For

electrical safety, maximum current density should never exceed 1 A mm .
___________
Numbers in square brackets refer to the Bibliography.
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SIST EN IEC 61788-23:2021
IEC 61788-23:2021 © IEC 2021 – 9 –

b) Contact resistance for current leads is sufficiently low to avoid excessive heating of the

sample. Typical cryogenic measurement conditions require power dissipation at contacts to

be less than 1 mW.

c) Sample sizes are sufficiently large to minimize effects from cutting and handling damage.

Typical samples are 1 mm to 3 mm in cross-section dimension and > 5 mm in cross-
sectional area.

d) Sample length is at least 10 times and not more than 25 times the width or diameter.

Annex A discusses considerations for sample dimensions and measuring current.
5 Measurement apparatus
5.1 Mandrel or base plate

A straight mandrel or base plate shall be used to support the specimen. Possible materials of

construction include pure copper, pure aluminium, pure silver, electrical grades of Cu-Zr,

Cu-Cr-Zr, Cu-Be, and other copper alloys, electrical grades of Al-Mg, Al-Ag, and other

aluminium alloys, and electrical grades of silver alloys. These provide high thermal conductivity

and serve to remove thermal gradients during measurement. The specimen shall be insulated

from the mandrel. Possible insulating materials include polyethylene terephthalate, polyester,

and polytetrafluoroethylene, which may be applied as foils, tapes, or coatings. Glass-fibre

reinforced epoxy or other composite materials with good thermal conductivity at cryogenic

temperature may also be used.

The base plate should have a clean and smooth surface finish. There should be no burrs, ridges,

seams, or other asperities that may affect the specimen. High-purity niobium specimens are

soft and are susceptible to indentation by surface flaws, and such indentations may alter the

sample and invalidate the resistance measurement.

The mandrel or base plate shall support the entire length and width of the specimen. Mandrel

or base plate geometry should not impose a bending strain of more than 0,2 % on the sample.

A thermometer accurate to 0,1 K is helpful but not required. The mandrel or base plate may

incorporate a mounting for a cryogenic thermometer directly against the body of the mandrel or

base plate and near the centre of the test specimen.
Practical base plates
...

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