Superconductivity - Part 13: AC loss measurements - Magnetometer methods for hysteresis loss in superconducting multifilamentary composites

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".

Supraconductivité - Partie 13: Mesure des pertes en courant alternatif - Méthodes de mesure par magnétomètre des pertes par hystérésis dans les composites multifilamentaires supraconducteurs

La CEI 61788-13:2012 décrit des éléments nécessaires pour mesurer les pertes par hystérésis dans les composites multifilamentaires de Cu/Nb-Ti au moyen d'un magnétomètre à courant continu ou à faible vitesse de rampe. La présente norme internationale spécifie une méthode de mesure des pertes par hystérésis dans les conducteurs composites multifilamentaires de Cu/Nb-Ti. On suppose que les mesures sont effectuées sur des fils ronds à des températures égales ou proches de 4,2 K. La magnétométrie en courant continu ou à faible vitesse de rampe sera effectuée au moyen d'un interféromètre quantique supraconducteur ou d'un magnétomètre à échantillon vibrant. L'extension à la mesure des supraconducteurs en général est donnée en Annexe. Cette deuxième édition annule et remplace la première édition parue en 2003. Cette édition constitue une révision technique. Les modifications apportées à la deuxième édition sont une extension à la mesure des supraconducteurs en général, de tailles et formes d'échantillons diverses et à des températures différentes de 4,2 K, et le remplacement par le mot "incertitude" pour toutes les expressions statistiques quantitatives utilisant les termes "précision" et "exactitude".

General Information

Status
Published
Publication Date
24-Jul-2012
Technical Committee
Current Stage
PPUB - Publication issued
Start Date
25-Jul-2012
Completion Date
25-Jul-2012
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IEC 61788-13
Edition 2.0 2012-07
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Superconductivity –
Part 13: AC loss measurements – Magnetometer methods for hysteresis loss in
superconducting multifilamentary composites
Supraconductivité –
Partie 13: Mesure des pertes en courant alternatif – Méthodes de mesure par
magnétomètre des pertes par hystérésis dans les composites multifilamentaires
supraconducteurs
IEC 61788-13:2012
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC 61788-13
Edition 2.0 2012-07
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Superconductivity –
Part 13: AC loss measurements – Magnetometer methods for hysteresis loss in
superconducting multifilamentary composites
Supraconductivité –
Partie 13: Mesure des pertes en courant alternatif – Méthodes de mesure par
magnétomètre des pertes par hystérésis dans les composites multifilamentaires
supraconducteurs
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX T
ICS 17.220, 29.050 ISBN 978-2-83220-292-0

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: 3 ----------------------
– 2 – 61788-13 © IEC:2012
CONTENTS

FOREWORD ........................................................................................................................... 3

INTRODUCTION ..................................................................................................................... 5

1 Scope ............................................................................................................................... 6

2 Normative references ....................................................................................................... 6

3 Terms and definitions ....................................................................................................... 6

4 General specifications ...................................................................................................... 8

4.1 Target uncertainty ................................................................................................... 8

4.2 Uncertainty and uniformity of the applied field ......................................................... 8

4.3 VSM calibration ....................................................................................................... 8

4.4 Temperature ............................................................................................................ 9

4.5 Specimen length ...................................................................................................... 9

4.6 Specimen orientation and demagnetization effects .................................................. 9

4.7 Normalization volume .............................................................................................. 9

4.8 Mode of field cycling or sweeping ............................................................................ 9

5 The VSM method of measurement .................................................................................. 10

5.1 General ................................................................................................................. 10

5.2 VSM measurement principle .................................................................................. 10

5.3 VSM specimen preparation .................................................................................... 10

5.4 VSM measurement conditions and calibration ....................................................... 12

5.4.1 Field amplitude .......................................................................................... 12

5.4.2 Direction of applied field ............................................................................ 12

5.4.3 Rate of change of the applied field (sweep rate) ........................................ 12

5.4.4 Waveform of the field change .................................................................... 12

5.4.5 Specimen size and shape correction .......................................................... 12

5.4.6 Allowance for addendum (background subtraction) .................................... 13

5.4.7 Data point density ...................................................................................... 13

6 Test report ...................................................................................................................... 13

6.1 General ................................................................................................................. 13

6.2 Initiation of the test ................................................................................................ 13

6.3 Technical details ................................................................................................... 13

Annex A (informative) The SQUID method of measurement ................................................. 15

Annex B (normative) Extension of the standard to the measurement of

superconductors in general ................................................................................................... 16

Annex C (informative) Uncertainty considerations ................................................................ 18

Bibliography .......................................................................................................................... 23

Figure 1 – A typical experimental setup of VSM measurement .............................................. 11

Figure 2 – Three alternative specimen configurations for the VSM measurement .................. 11

Table C.1 – Output signals from two nominally identical extensometers ................................ 19

Table C.2 – Mean values of two output signals ..................................................................... 19

Table C.3 – Experimental standard deviations of two output signals ..................................... 19

Table C.4 – Standard uncertainties of two output signals ...................................................... 20

Table C.5 – Coefficient of variations of two output signals .................................................... 20

---------------------- Page: 4 ----------------------
61788-13 © IEC:2012 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
______________
SUPERCONDUCTIVITY –
Part 13: AC loss measurements –
Magnetometer methods for hysteresis loss
in superconducting multifilamentary composites
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

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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 61788-13 has been prepared by IEC technical committee 90:

Superconductivity.

This second edition cancels and replaces the first edition published in 2003. It constitutes a

technical revision.
Modifications made to the second edition are

– to extend to the measurement of superconductors in general, in various sample sizes and

shapes, and at temperatures other than 4,2 K,

– to use the word “uncertainty” for all quantitative (associated with a number) statistical

expressions and eliminate the quantitative use of “precision” and “accuracy” in accordance

with the decision at the June 2006 IEC/TC90 meeting in Kyoto.
---------------------- Page: 5 ----------------------
– 4 – 61788-13 © IEC:2012
The text of this standard is based on the following documents:
FDIS Report on voting
90/302/FDIS 90/306/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 stability 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: 6 ----------------------
61788-13 © IEC:2012 – 5 –
INTRODUCTION

IEC Technical Committee 90 proposes magnetometer and pickup coil methods for measuring

the AC losses of Cu/Nb-Ti composite superconducting wires in transverse time-varying

magnetic fields. These represent initial steps in standardization of methods for measuring the

various contributions to AC loss in transverse fields, the most frequently encountered

configuration.

It was decided to split the initial proposal mentioned above into two documents covering two

standard methods. One of them describes the magnetometer method for hysteresis loss and

low frequency (or sweep rate) total AC loss measurement in a slowly varying magnetic field,

and the other describes the pickup coil method for total AC loss measurement in higher

frequency (or sweep rate) magnetic fields. The frequency range is 0 Hz – 0,06 Hz for the

magnetometer method and 0,005 Hz – 60 Hz for the pickup-coil method. The overlap between

0,005 Hz and 0,06 Hz is a complementary frequency range for the two methods.
This standard deals with the magnetometer method.
---------------------- Page: 7 ----------------------
– 6 – 61788-13 © IEC:2012
SUPERCONDUCTIVITY –
Part 13: AC loss measurements –
Magnetometer methods for hysteresis loss
in superconducting multifilamentary composites
1 Scope

This part of IEC 61788 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 (SQUID
magnetometer, See Annex A.) or a vibrating-sample magnetometer (VSM). In case

differences between the calibrated magnetometer results are noted, the VSM results,

extrapolated to zero ramp rate, will be taken as definitive. Extension to the measurement of

superconductors in general is given in Annex B.
2 Normative references

The following documents, in whole or in part, are normatively referenced in this document and

are indispensable for its application. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60050 (all parts), International Electrotechnical Vocabulary (available at

IEC 61788-5, Superconductivity – Part 5: Matrix to superconductor volume ratio measurement

– Copper to superconductor volume ratio of Cu/Nb-Ti composite superconductors
3 Terms and definitions

For the purposes of this part of IEC 61788, the terms and definitions given in IEC 60050-815,

together with the following terms and definitions, apply.
3.1
AC loss

power dissipated in a composite superconductor due to application of a time-varying magnetic

field or electric current

Note 1 to entry: The AC loss per magnetic field cycle is designated Q. Although all such loss is inevitably

"hysteretic" in the general sense, the AC loss in a superconducting composite is assumed to be separable into

"hysteresis-", "eddy-current-", and "coupling-" loss components, as defined below (see Note 1 and Note 2 of

IEC 60050-815:2000, 815-04-54).

[SOURCE: IEC 60050-815:2000, 815-04-54, modified – The original two notes have been

replaced by a new note to entry.]
---------------------- Page: 8 ----------------------
61788-13 © IEC:2012 – 7 –
3.2
hysteresis loss

loss of the type whose value per cycle is independent of frequency arising in a super-

conductor under a varying magnetic field

Note 1 to entry: This loss is caused by the irreversible magnetic properties of the superconducting material due to

pinning of flux lines.

Note 2 to entry: Hysteresis loss is that which takes place only within the superconducting regions of the Cu/Nb-Ti

composite, and hence which would be present even in the absence of the matrix. The hysteresis loss per cycle,

designated Q , is associated with the area of the magnetization vs. field (M-H) hysteresis loop; the associated M is

occasionally referred to as the "persistent-current magnetization".

[SOURCE: IEC 60050-815:2000, 815-04-55, modified – A new note to entry has been added.]

3.3
eddy current loss

loss arising in the normal matrix of a superconductor or the structural material when exposed

to a varying magnetic field, either from an applied field or from a self-field
Note 1 to entry: The eddy current loss per cycle is designated Q .

[SOURCE: IEC 60050-815:2000, 815-04-56, modified – A new note to entry has been added. ]

3.4
coupling loss

loss arising in multi-filamentary superconducting wires with a normal matrix due to coupling

current
Note 1 to entry: The coupling loss per cycle is designated Q

[SOURCE: IEC 60050-815:2000, 815-04-59, modified – A new note to entry has been added. ]

3.5
proximity effect coupling loss

loss stemming from currents that circulate along the filaments of a superconducting composite

and across the intervening matrix rendered superconducting by proximity effect (PE)

Note 1 to entry: By so doing, the PE currents compete for the same paths as the coupling currents. Since the PE

entire current path is superconductive, P is a persistent-current effect and when it is present serves to augment

P Proximity effect can be expected in Cu/NbTi composites when the interfilamentary spacing drops below about

1 µm. The PE loss per cycle is designated Q .
3.6
demagnetization

phenomenon in which the specimen’s magnetization reduces the applied magnetic field

sensed by the superconductor

Note 1 to entry: It depends on the strength of that magnetization as well as sample geometry and applied field

orientation. It is usually negligible for multifilamentary Cu/Nb-Ti composites at 4,2 K in large magnetic fields.

3.7
flux creep

thermally activated flux motion in which fluxons move from one pinning centre to another

Note 1 to entry: Flux creep refers to the logarithmic time dependence of decay (at fixed applied field strength and

sample temperature) of a superconductor's persistent-current magnetization. A significant level of flux creep will

---------------------- Page: 9 ----------------------
– 8 – 61788-13 © IEC:2012

contribute a frequency dependence to the hysteretic loss. The effect is negligible for Cu/Nb-Ti composites, except

when proximity effect coupling is present.

[SOURCE: IEC 60050-815:2000, 815-03-20, modified – The original note has been replaced

by a new note to entry.]
3.8
flux jump

cooperative and transitional movements of pinned fluxons as a result of a magnetic instability

initiated by mechanical, thermal, or electrical disturbances

Note 1 to entry: A flux jump manifests itself as a sudden drop in magnetization of the superconductor.

3.9
filamentary volume
total volume of the filaments within a given sample
3.10
composite volume
total specimen volume including both superconductor and matrix
3.11
sweep amplitude
max
maximum value of the applied field
3.12
magnetization loop

trace of specimen magnetization as function of applied magnetic field strength as the field is

varied around a complete cycle starting and ending at +H
max

Note 1 to entry: The area of the loop, Q, is the "energy loss per cycle". As indicated above, by analogy with the

components of power dissipation, Q can be regarded as having the components Q , Q , Q , and Q .

h e c pe
4 General specifications
4.1 Target uncertainty

The target uncertainty of this method is defined as coefficient of variation (COV; standard

deviation divided by the average). The COV shall not exceed 5 %.

Important variables and elements affecting the uncertainty of the results are specified as

follows. Introduction to the uncertainty is given in Annex C.
4.2 Uncertainty and uniformity of the applied field

An applied magnetic field system shall provide the magnetic field with a relative standard

uncertainty not to exceed 0,5 %. The applied field shall have a uniformity of 0,1 % over the

volume of the specimen.
4.3 VSM calibration

The goal of VSM calibration is to ensure that the specimen's moment is measured with a

relative combined standard uncertainty not to exceed 1 %. Calibration shall be performed with

all cryostats and any other metal parts in place (as they would be in an actual measurement).

The magnetometer shall be calibrated using a small Ni sphere whose calibration is traceable

to the National Institute of Standards and Technology (N.I.S.T., U.S.A.)’s standard reference

material 772a. This is a Ni sphere 2,383 mm in diameter prepared from high purity Ni wire.

---------------------- Page: 10 ----------------------
61788-13 © IEC:2012 – 9 –

The certified value of its magnetic moment, m, is (3,47 ± 0,01) mA m at 298 K, in a field, H,

of 398 kA/m (µ H = 0,5 T). In calibration against this sphere, field and temperature corrections

are made according to
m = 3,47 [1 + 0,0026 ln(H/398)][1 – 0,00047(T−298)] (mA m )

with H in kA/m (1 kA/m = 12,56 Oe) and T in K. For convenience, a calibration field of about

400 kA/m is recommended.
4.4 Temperature

Measurements shall be made at or near 4,2 K, the normal boiling point of liquid helium and

the actual temperature of measurement reported to a combined standard uncertainty not

exceeding 0,05 K.

At temperatures other than 4,2 K, the temperature shall be known with a relative standard

uncertainty not exceeding 1,2 %, which corresponds to the above combined standard

uncertainty at 4,2 K.
4.5 Specimen length

Several magnetization components are functions of specimen length, L. Length dependence

needs to be eliminated or appropriately allowed for.

a) In relatively short samples, critical current density anisotropy in the longitudinal and

transverse directions will lead to a measurable "end effect" and hence to a length

dependence in Q . To avert this possibility, specimens shall be prepared whose

superconducting components (filaments) have a length/diameter ratio of more than 20.

b) Proximity effect can be expected to be present in Cu/Nb-Ti multifilamentary composites

only if the filament spacing, d , is less than about 1 µm. Under this condition, the resulting

PE contribution to magnetization will depend on sample length, L, and twist pitch, L .

Under this condition, these lengths will need to be taken into account in the following way

when reporting the results:

– for d < about 1 µm and the filaments are untwisted, Q shall be measured as function

s h
of L and the results extrapolated to zero L;

– for d < about 1 µm and the filaments are twisted, Q shall be measured at L > 5 L .

s h p
4.6 Specimen orientation and demagnetization effects

Loss measurements shall be made on strand specimens in a transverse magnetic field. For

the fully penetrated fine filaments of a multifilamentary Cu/Nb-Ti strand, demagnetization is

negligible. By the same token, it is negligible for round-, flat-, or square-cross-sectioned

bundles of such strands. However, for the sake of completeness in reporting the results, the

specimen configuration shall be reported.
4.7 Normalization volume

It may be desirable to report hysteretic loss in terms of the superconductor volume. To pursue

this route, it is necessary to invoke a standard procedure for determining the matrix

(Cu)/superconductor volume ratio (see IEC 61788-5). For the purposes of this standard, these

steps are eliminated, and AC loss is to be reported in terms of total composite volume.

Volume should be measured with a relative combined standard uncertainty not to exceed

0,5 %.
4.8 Mode of field cycling or sweeping

The applied field may be changed point-by-point over the field cycle starting and ending at

H . SQUID magnetometry is restricted to this mode of field change, and it is optional for the

max

VSM to be operated in point-by-point mode. The VSM may also be operated semicontinuously,

the M-H loop being constructed from 200 or so (M,H) data-pairs.
---------------------- Page: 11 ----------------------
– 10 – 61788-13 © IEC:2012
5 The VSM method of measurement
5.1 General

For a full description of the application of VSM technique, the paper by Collings et al. [1 ] is

recommended.
5.2 VSM measurement principle

The basic principle of the Foner [2] VSM is as follows. The specimen to be measured is

located in a uniform magnetic field, which causes it to become magnetized. The specimen is

mechanically oscillated near a set of pickup coils. The oscillating magnetic moment causes an

oscillation in the magnetic field linking the pickup coils, thereby inducing an AC voltage which

is then detected and converted into a magnetic moment value by electronic circuitry. The

magnetometer is a "substitution" rather than "absolute" device and its output signal requires

calibration against a reference. Custom-made (hand-made) VSMs do exist, but increasingly,

commercial versions of this machine are used. In general, they share the following

characteristics. The specimen to be measured is typically mounted on a vertical rod which

vibrates longitudinally (vertically) with a position amplitude of about 1 mm and at a suitably

low frequency.

The magnetic field may be supplied by either a horizontally mounted iron-core electromagnet

(EM) or a vertically mounted superconducting solenoid (SCS) – the conventional attitudes in

each case – causing the vibration direction of the sample to be perpendicular or parallel,

respectively, to the field direction. The pickup coils are appropriately located and connected in

...

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