EN 61788-2:2007

Superconductivity - Part 2: Critical current measurement - DC critical current of Nb3Sn composite superconductors

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.

Supraleitfähigkeit - Teil 2: Messen des kritischen Stromes - Kritischer Strom (Gleichstrom) von Nb3Sn-Verbundsupraleitern

Supraconductivité - Partie 2: Mesure du courant critique - Courant critique continu des supraconducteurs composites Nb3Sn

La présente partie de la CEI 61788 traite d'une méthode d'essai pour la détermination du courant critique continu des supraconducteurs composites Nb3Sn qui sont fabriqués soit par le procédé du bronze, soit par le procédé de diffusion interne de l'étain, et dont le rapport cuivre/non-cuivre est supérieur à 0,2. La présente méthode est destinée à être utilisée avec des supraconducteurs caractérisés par des courants critiques inférieurs à 1 000 A et des valeurs n supérieures à 12 dans des conditions d'essai normalisées et avec des champs magnétiques inférieurs ou égaux à 0,7 fois la valeur du champ magnétique critique le plus élevé. Le spécimen d'essai est immergé dans un bain d'hélium liquide à une température mesurée pendant l'essai. Le conducteur d'essai composite Nb3Sn a une structure monolithique avec une surface de section ronde totale inférieure à 2 mm2. Le spécimen utilisé dans la présente méthode d'essai a la forme d'une bobine inductive. La présente norme indique les écarts par rapport à la méthode d'essai permis dans des essais individuels de série et d'autres restrictions spécifiques. Les conducteurs Nb3Sn ayant des courants critiques supérieurs à 1 000 A ou des surfaces de section supérieure à 2 mm2 peuvent être mesurés avec la présente méthode avec une réduction anticipée de précision et un effet de champ induit plus significatif (voir Annexe C). D'autres formes d'essai, plus spécialisées, peuvent être mieux appropriées pour des essais de conducteurs de plus grande taille qui ont été omis dans la présente norme dans un souci de simplicité et de précision. En principe, il convient que la méthode d'essai indiquée dans la présente norme s'applique aux fils composites Nb3Sn fabriqués selon un autre procédé. Cette méthode est également supposée adaptable à d'autres fils supraconducteurs composites après des modifications appropriées.

Superprevodnost - 2. del: Meritve kritičnega toka - Enosmerni kritični tok pri superprevodnikih iz Nb3Sn kompozita (IEC 61788-2:2006)

General Information

• Status: Published
• Publication Date: 28-Feb-2007
• Withdrawal Date: 30-Nov-2009
• ICS: 17.220 - Electricity. Magnetism. Electrical and magnetic measurements
• ICS: 29.050 - Superconductivity and conducting materials
• Technical Committee: CLC/SR 90 - Superconductivity
• Drafting Committee: IEC/TC 90 - IEC_TC_90
• Parallel Committee: IEC/TC 90 - IEC_TC_90
• Current Stage: 6060 - Document made available - Publishing
• Completion Date: 05-Jan-2007
• Ref Project: SIST EN 61788-2:2008 - Superconductivity -- Part 2: Critical current measurement - DC critical current of Nb3Sn composite superconductors

Relations

• Replaces: EN 61788-2:1999 - Superconductivity - Part 2: Critical current measurement - DC critical current of Nb3Sn composite superconductors
• Effective Date: 29-Jan-2023

Standards Content (Sample)

SLOVENSKI STANDARD
SIST EN 61788-2:2008
01-januar-2008
1DGRPHãþD
SIST EN 61788-2:2001
6XSHUSUHYRGQRVWGHO0HULWYHNULWLþQHJDWRND(QRVPHUQLNULWLþQLWRNSUL
VXSHUSUHYRGQLNLKL]1E6QNRPSR]LWD,(&

Superconductivity - Part 2: Critical current measurement - DC critical current of Nb3Sn

composite superconductors

Supraleitfähigkeit - Teil 2: Messen des kritischen Stromes Kritischer Strom (Gleichstrom)

von Nb3Sn-Verbundsupraleitern

Supraconductivité - Partie 2: Mesure du courant critique - Courant critique continu des

supraconducteurs composites Nb3Sn
Ta slovenski standard je istoveten z: EN 61788-2:2007
ICS:
17.220.20 0HUMHQMHHOHNWULþQLKLQ Measurement of electrical
PDJQHWQLKYHOLþLQ and magnetic quantities
29.050 Superprevodnost in prevodni Superconductivity and
materiali conducting materials
SIST EN 61788-2:2008 en,fr,de

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

---------------------- Page: 1 ----------------------
EUROPEAN STANDARD
EN 61788-2
NORME EUROPÉENNE
January 2007
EUROPÄISCHE NORM
ICS 17.220; 29.050 Supersedes EN 61788-2:1999
English version
Superconductivity
Part 2: Critical current measurement -
DC critical current of Nb Sn composite superconductors
(IEC 61788-2:2006)
Supraconductivité Supraleitfähigkeit
Partie 2: Mesure du courant critique - Teil 2: Messen des kritischen Stromes -
Courant critique continu des Kritischer Strom (Gleichstrom)
supraconducteurs composites Nb Sn von Nb Sn-Verbundsupraleitern
3 3
(CEI 61788-2:2006) (IEC 61788-2:2006)

This European Standard was approved by CENELEC on 2006-12-01. 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 Central Secretariat 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 Central Secretariat has the same status as the official versions.

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

Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,

Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,

Sweden, Switzerland and the United Kingdom.
CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
Central Secretariat: rue de Stassart 35, B - 1050 Brussels

© 2007 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.

Ref. No. EN 61788-2:2007 E
---------------------- Page: 2 ----------------------
EN 61788-2:2007 - 2 -
Foreword

The text of document 90/195/FDIS, future edition 2 of IEC 61788-2, prepared by IEC TC 90,

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

EN 61788-2 on 2006-12-01.
This European Standard supersedes EN 61788-2:1999.

Modifications made to EN 61788-2:1999 are mostly wording that essentially includes no technical

changes and an addition of a new annex (normative Annex D) in which the specifications in the

one-mandrel method are described.
The following dates were fixed:
– latest date by which the EN has to be implemented
at national level by publication of an identical
national standard or by endorsement (dop) 2007-09-01
– latest date by which the national standards conflicting
with the EN have to be withdrawn (dow) 2009-12-01
Annex ZA has been added by CENELEC.
__________
Endorsement notice

The text of the International Standard IEC 61788-2:2006 was approved by CENELEC as a European

Standard without any modification.

In the official version, for Bibliography, the following note has to be added for the standard indicated:

IEC 61788-1 NOTE Harmonized as EN 61788-1:2007 (not modified).
__________
---------------------- Page: 3 ----------------------
- 3 - EN 61788-2:2007
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications

The following referenced documents are indispensable for the application 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 When an international publication has been modified by common modifications, indicated by (mod), the relevant EN/HD

applies.
Publication Year Title EN/HD Year
IEC 60050-815 2000 International Electrotechnical Vocabulary - -
(IEV)
Part 815: Superconductivity
---------------------- Page: 4 ----------------------
NORME CEI
INTERNATIONALE
IEC
61788-2
INTERNATIONAL
Deuxième édition
STANDARD
Second edition
2006-11
Supraconductivité –
Partie 2:
Mesure du courant critique –
Courant critique continu des
supraconducteurs composites Nb Sn
Superconductivity –
Part 2:
Critical current measurement –
DC critical current of Nb Sn
composite superconductors
© IEC 2006 Droits de reproduction réservés ⎯ Copyright - all rights reserved

Aucune partie de cette publication ne peut être reproduite ni No part of this publication may be reproduced or utilized in any

utilisée sous quelque forme que ce soit et par aucun procédé, form or by any means, electronic or mechanical, including

électronique ou mécanique, y compris la photocopie et les photocopying and microfilm, without permission in writing from

microfilms, sans l'accord écrit de l'éditeur. the publisher.

International Electrotechnical Commission, 3, rue de Varembé, PO Box 131, CH-1211 Geneva 20, Switzerland

Telephone: [phone] Telefax: [phone] E-mail: [e-mail] Web: www.iec.ch

CODE PRIX
PRICE CODE
Commission Electrotechnique Internationale
International Electrotechnical Commission
МеждународнаяЭлектротехническаяКомиссия
Pour prix, voir catalogue en vigueur
For price, see current catalogue
---------------------- Page: 5 ----------------------
61788-2 © IEC:2006 – 3 –
CONTENTS

FOREWORD...........................................................................................................................7

INTRODUCTION...................................................................................................................11

1 Scope.............................................................................................................................13

2 Normative references .....................................................................................................13

3 Terms and definitions .....................................................................................................15

4 Principle .........................................................................................................................17

5 Requirements .................................................................................................................17

6 Apparatus.......................................................................................................................19

6.1 Reaction mandrel material.....................................................................................19

6.2 Reaction mandrel construction ..............................................................................19

6.3 Measurement mandrel material .............................................................................21

6.4 Measurement mandrel construction .......................................................................21

6.5 Measurement set up..............................................................................................21

7 Specimen preparation.....................................................................................................21

7.1 Specimen mounting for reaction heat treatment.....................................................21

7.2 Reaction heat treatment........................................................................................23

7.3 Specimen mounting for measurement....................................................................23

7.4 Specimen bonding.................................................................................................23

8 Measurement procedure.................................................................................................25

9 Precision and accuracy of the test method......................................................................27

9.1 Critical current.......................................................................................................27

9.2 Temperature..........................................................................................................27

9.3 Magnetic field........................................................................................................27

9.4 Specimen support structure...................................................................................27

9.5 Specimen protection..............................................................................................27

10 Calculation of results ......................................................................................................29

10.1 Critical current criteria ...........................................................................................29

10.2 n-value (optional calculation, refer to A.7.2) ..........................................................31

11 Test report......................................................................................................................31

11.1 Identification of test specimen ...............................................................................31

11.2 Report of I values ................................................................................................31

11.3 Report of test conditions........................................................................................33

Annex A (informative) Additional information relating to Clauses 1 to 10 ..............................35

Annex B (informative) Strain effect of Nb Sn conductors .....................................................59

Annex C (informative) Self-field effect..................................................................................63

Annex D (normative) One-mandrel method ..........................................................................67

Bibliography..........................................................................................................................73

---------------------- Page: 6 ----------------------
61788-2 © IEC:2006 – 5 –

Figure 1 – Intrinsic U-I characteristic ....................................................................................29

Figure 2 – U-I characteristic with a current transfer component.............................................29

Figure A.1 – Instrumentation of specimen with a null voltage tap pair ...................................45

Figure B.1 – Uniaxial (tensile) strain dependence of critical current for a typical Nb Sn

composite wire shown with various magnetic fields [7] ..........................................................61

Table A.1 – Thermal contraction data of Nb Sn superconductor and selected materials .......57

---------------------- Page: 7 ----------------------
61788-2 © IEC:2006 – 7 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
___________
SUPERCONDUCTIVITY –
Part 2: Critical current measurement –
DC critical current of Nb Sn composite 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 provides no marking procedure to indicate its approval and cannot be rendered responsible for any

equipment declared to be in conformity with an IEC Publication.

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.

International Standard IEC 61788-2 has been prepared by IEC technical committee 90:

Superconductivity.

This second edition cancels and replaces the first edition published in 1999. Modifications

made to the second edition are mostly wording that essentially includes no technical changes

and an addition of a new annex (normative Annex D) in which the specifications in the one-

mandrel method are described.
---------------------- Page: 8 ----------------------
61788-2 © IEC:2006 – 9 –
The text of this standard is based on the following documents:
FDIS Report on voting
90/195/FDIS 90/199/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, 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 maintenance result date indicated on the IEC web site 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.
---------------------- Page: 9 ----------------------
61788-2 © IEC:2006 – 11 –
INTRODUCTION

The critical currents of composite superconductors are used to establish design limits for

applications of superconducting wires. The operating conditions of superconductors in these

applications determine much of their behaviour and tests made with the method given in the

present standard may be used to provide part of the information needed to determine the

suitability of a specific superconductor.
Results obtained from this method may also be used for detecting changes in the

superconducting properties of a composite superconductor due to processing variables,

handling, ageing or other applications or environmental conditions. This method is useful for

quality control, acceptance or research testing if the precautions given in this standard are

observed.

The critical current of composite superconductors depends on many variables. These

variables need to be considered in both the testing and the application of these materials.

Test conditions such as magnetic field, temperature and relative orientation of the specimen,

current and magnetic field are determined by the particular application. The test configuration

may be determined by the particular conductor through certain tolerances. The specific critical

current criterion may be determined by the particular application. It may be appropriate to

measure a number of test specimens if there are irregularities in testing.

The test method covered in this standard is based on that for the determination of the critical

current of Cu/Nb-Ti composite superconductors (IEC 61788-1[2] and the VAMAS (Versailles

project on advanced materials and standards) prestandardization work on the critical current

of Nb Sn composite superconductors. The critical current of Nb Sn superconductors is known

3 3

to be highly sensitive to mechanical strain compared to Cu/Nb-Ti superconductors. Hence,

some modifications are made on the test procedures which may affect the strain state of a

test specimen. See Annex B for the background to these modifications.
—————————
Figures in square brackets refer to the Bibliography.
---------------------- Page: 10 ----------------------
61788-2 © IEC:2006 – 13 –
SUPERCONDUCTIVITY –
Part 2: Critical current measurement –
DC critical current of Nb Sn composite superconductors
1 Scope

This part of IEC 61788 covers a test method for the determination of the d.c. critical current of

Nb Sn 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 Nb Sn

composite test conductor has a monolithic structure with a total round-cross-sectional area

that is less than 2 mm . 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.

Nb Sn conductors with critical currents above 1 000 A or total cross-sectional areas greater

than 2 mm 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 Nb Sn composite wires

fabricated by any other process. This method is also expected to apply to other
superconducting composite wires after some appropriate modifications.
2 Normative references

The following referenced document is indispensable for the application 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 60050-815:2000, International Electrotechnical Vocabulary (IEV) – Part 815:
Superconductivity
---------------------- Page: 11 ----------------------
61788-2 © IEC:2006 – 15 –
3 Terms and definitions

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

which are repeated here for convenience, and the following apply:
3.1
critical current
maximum direct current that can be regarded as flowing without resistance
NOTE I is a function of magnetic field strength and temperature.
[IEV 815-03-01]
3.2
critical current criterion
I criterion

criterion to determine the critical current, I , based on the electric field strength, E, or the

resistivity, ρ
-13

NOTE E = 10 μV/m or E = 100 μV/m is often used as the electric field strength criterion, and ρ = 10 Ω·m or

-14
ρ = 10 Ω ·m is often used as the resistivity criterion.
[IEV 815-03-02]
3.3
n-value (of a superconductor)

exponent obtained in a specific range of electric field strength or resistivity when the voltage

(U) – current (I) curve is approximated by the equation U ∝ I
[IEV 815-03-10]
3.4
quench

uncontrollable and irreversible transition of a superconductor or a superconducting device

from the superconducting state to the normal state
NOTE A term usually applied to superconducting magnets.
[IEV 815-03-11]
3.5
Lorentz force (on fluxons)
force applied to fluxons by a current

NOTE 1 The force per unit volume is given by J x B, where J is the current density, and B is the magnetic flux

density.
[IEV 815-03-16]
NOTE 2 "Coulomb-Lorentz force" is defined in IEV 121-11-20 [1].
3.6
stress effect
strain effect

change in superconducting properties upon application of mechanical, thermal or electro-

magnetic stress to the superconductor
[IEV 815-03-14]
---------------------- Page: 12 ----------------------
61788-2 © IEC:2006 – 17 –
3.7
bending strain

strain in percent arising from pure bending defined as ε = 100r/R, where r is a half of the

specimen thickness and R is the bending radius
[IEV 815-08-03]
3.8
current transfer (of composite superconductor)

phenomenon that a d.c. current transfers spatially from filament to filament in a composite

superconductor, resulting in a voltage generation along the conductor

NOTE In the I measurement, this phenomenon appears typically near the current contacts where the injected

current flows along the conductor from periphery to inside until uniform distribution among filaments is

accomplished.
3.9
constant sweep rate method

U-I data acquisition method where a current is swept at a constant rate from zero to a current

above I while frequently and periodically acquiring U-I data
3.10
ramp-and-hold method

U-I data acquisition method where a current is ramped to a number of appropriately

distributed points along the U-I curve and held constant at each one of these points while

acquiring a number of voltages and current readings
4 Principle

The critical current of a composite superconductor is determined from a voltage (U) – current

(I) characteristic measured at a certain value of a static applied magnetic field strength

(magnetic field) at a specified temperature in a liquid helium bath at a constant pressure. To

get a U-I characteristic, a direct current is applied to the superconductor specimen and the

voltage generated along a section of the specimen is measured. The current is increased from

zero and the U-I characteristic generated is recorded. The critical current is determined as the

current at which a specific electric field strength (electric field) criterion (E ) or resistivity

criterion (ρ ) is reached. For either E or ρ , there is a corresponding voltage criterion (U ) for

c c c c
a specified voltage tap separation.
5 Requirements

The specimen shall be wound on a cylindrical reaction mandrel with a helical groove and after

reaction, transferred to a measurement mandrel of the same diameter on which the helical

angle is preserved. An alternate one-mandrel method is given in Annex D.
The specimen shall be longer than 430 mm.

The specimen shall be affixed to the measurement mandrel by tightening the specimen and/or

bonding with a low temperature adhesive.

In this test method, the applied magnetic field shall be parallel to the measurement mandrel

axis.
---------------------- Page: 13 ----------------------
61788-2 © IEC:2006 – 19 –

The target precision of this method is a coefficient of variation (standard deviation divided by

the average of the critical current determinations), that is less than 3 % for the measurement

at 12 T and near 4,2 K.

The use of a common current transfer correction is excluded from this test method.

Furthermore, if a current transfer signature is pronounced in the measurement, then the

measurement shall be considered invalid.

It is the responsibility of the user of this standard to consult and establish appropriate safety

and health practices, and determine the applicability of regulatory limitations prior to use.

Specific precautionary statements are given below.

Hazards exist in this type of measurement. Very large direct currents with very low voltages

do not necessarily provide a direct personal hazard, but accidental shorting of the leads with

another conductor, such as tools or transfer lines, can release significant amounts of energy

and cause arcs or burns. It is imperative to isolate and protect current leads from shorting.

Also, the stored energy in the superconducting magnets commonly used for the background

magnetic field can cause similar large current and/or voltage pulses, or deposit large amounts

of thermal energy in the cryogenic systems causing rapid boil-off or even explosive conditions.

Under rapid boil-off conditions, cryogens can create oxygen-deficient conditions in the

immediate area and additional ventilation may be necessary. The use of cryogenic liquids is

essential to cool the superconductors to allow transition into the superconducting state. Direct

contact of skin with cold liquid transfer lines, storage dewars or apparatus components can

cause immediate freezing, as can direct contact with a spilled cryogen. It is imperative that

safety precautions for handling cryogenic liquids be observed.
6 Apparatus
For the one-mandrel method, continue with Clause D.2.
6.1 Reaction mandrel material

The reaction mandrel shall be made from a heat-resistant material that may or may not have a

treated surface. Suitable reaction mandrel materials are recommended in A.3.1. Any one of

these may be used.
6.2 Reaction mandrel construction

The overall geometry of the reaction mandrel should be matched closely to that of the

measurement mandrel to which the individual specimen is to be transferred.

The reaction mandrel shall have a diameter large enough that the specimen bending strain,

which is introduced into the specimen during winding, is less than 5 %.

The mandrel shall have a helical groove in which the specimen shall be wound. The pitch

angle of the groove shall be less than 7°. The depth of the groove shall be at least half the

wire diameter.
---------------------- Page: 14 ----------------------
61788-2 © IEC:2006 – 21 –
6.3 Measurement mandrel material

The measurement mandrel shall be made from an insulating material, or from a conductive

non-ferromagnetic material that is either covered or not covered with an insulating layer.

The critical current may inevitably depend on the measurement mandrel material due to the

strain induced by the differential thermal contraction between the specimen and the measurement

mandrel.

The total strain induced in the specimen at the measuring temperature shall be minimized to

be within ±0,03 %. If there is an excess strain due to the differential thermal contraction of the

specimen and the mandrel, the critical current shall be noted to be determined under an

excess strain state by identification of the mandrel material.

Suitable measurement mandrel materials are recommended in A.3.3. Any one of these may

be used.

When a conductive material is used without an insulating layer, the leakage current through

the mandrel shall be less than 0,2 % of the total current when the specimen current is at

critical current I (see 9.5).
6.4 Measurement mandrel construction
The mandrel shall have a helical groove in which the specimen shall be wound.

The diameter of the measurement mandrel, the pitch angle of the helical groove and its depth

and shape shall be close to those of the reaction mandrel.

The angle between the specimen axis (portion between the voltage taps) and the magnetic

field shall be (90 ± 7)°. This angle shall be determined with an accuracy of ±2°.

The current contact shall be rigidly fastened to the measurement mandrel to avoid stress

concentration in the region of transition between the mandrel and the current contact.

6.5 Measurement set up
...