IEC 61788-13:2012

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
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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
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX T
ICS 17.220, 29.050 ISBN 978-2-83220-292-0

– 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

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.

– 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.
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.

– 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
P
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.]

61788-13 © IEC:2012 – 7 –
3.2
hysteresis loss
P
h
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
h
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
P
e
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 .
e
[SOURCE: IEC 60050-815:2000, 815-04-56, modified – A new note to entry has been added. ]
3.4
coupling loss
P
c
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
c.
[SOURCE: IEC 60050-815:2000, 815-04-59, modified – A new note to entry has been added. ]
3.5
proximity effect coupling loss

P
pe
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
pe
P Proximity effect can be expected in Cu/NbTi composites when the interfilamentary spacing drops below about
h.
1 µm. The PE loss per cycle is designated Q .
pe
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

– 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
H
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.

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

– 10 – 61788-13 © IEC:2012
5 The VSM method of measurement
5.1 General
1)
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
pairs such that any external field oscillations (magnetic noise) are cancelled and only the
specimen-generated field oscillations are detected. A typical experimental setup of VSM
measurement is given in Figure 1.
The loss is determined from the numerically integrated area of the full M-H loop.
The specimen is positioned at the "sweet spot", a small region of the pickup coil space within
which the detected signal changes only slightly with variation of vertical or horizontal
positioning of the specimen. Using a small calibrating specimen of, for example Ni, the
specimen space is to be explored and the sweet spot determined as the volume within which
the response does not change more than 2 %. Suppose Z to be the vertical direction, Y the
direction along the magnet-pole axis, and X the direction normal to the magnet-pole axis, then
the center of the sweet spot is located by a procedure known as "saddling", viz seeking the
maximum signal along Z combined with the maximum along X and the minimum along Y.
5.3 VSM specimen preparation
The size of the sweet spot in the typical VSM restricts specimen volume to less than about
30 mm . For the VSM measurement of Cu/Nb-Ti multifilamentary composite wires, it is
permissible to use one of three alternative specimen configurations as shown in Figure 2.
a) Short straight specimen: This consists of one or more straight pieces of strand (the size of
the bundle depending on the signal strength required) up to about 1 cm in length. The
ends of the strand pieces are to be finely ground flat (see for example [1]).
b) Multiturn coil: If long lengths of fine wire are to be measured, they may be wound for
measurement into a multiturn coil (see for example [3]). For EM-VSM measurement, the
coil may be oval in shape and mounted with its long axis vertically (parallel to the vibration
axis). The plane of the coil will be normal to the field direction. For SCS-VSM
measurement, the multiturn coil should be round and mounted with its plane perpendicular
to the vibration axis.
___________
1)
Numbers in square brackets refer to the Bibliography.

61788-13 © IEC:2012 – 11 –
To minimize the possibility of interstrand coupling, the strands of the short straight bundle
and the multiturn coil are to be insulated by varnish, or by potting, or otherwise be
electrically separated.
c) Helical coil: Lying between the short straight sample and the multiturn coil is the helical
coil. As recommended by Goldfarb et al. [4], this consists of a single length of strand
wound along the grooves of a screw thread. The axis of the helix is parallel to the field
direction which can then be regarded as transverse to the specimen axis if the pitch angle
°
is less than 8 . Using the helical technique, a relatively long piece of moderately thick
strand can be accommodated for measurement.

Vibration unit
Power
Oscillator
amplifier
Lock-in
Specimen holder
amplifier
Magnet
CPU
Amplifier
Hall sensor
Amplifier
Pickup coil Specimen
IEC  1545/12
Cryostat
Figure 1 – A typical experimental setup of VSM measurement

a) Short sample b) Helical coil c) Multiturn coil
IEC  1546/12
Figure 2 – Three alternative specimen configurations for the VSM measurement

– 12 – 61788-13 © IEC:2012
5.4 VSM measurement conditions and calibration
5.4.1 Field amplitude
The measuring field amplitude, to be determined by the application, shall be specified (see
Clause 6).
5.4.2 Direction of applied field
The field shall be applied transversely to the strand axis. Thus, the applied field will be normal
to the axis of the short straight specimen, normal to the plane of the multiturn coil, or parallel
to the axis of the helical coil.
5.4.3 Rate of change of the applied field (sweep rate)
5.4.3.1 Effect of coupling
The sweep rate of the applied field should be sufficiently low as to render negligible any
coupling contribution, P , to the AC loss. But in very low sweep rate, including point-by-point
c
measurement, the effect of strong coupling will re-appear in the form of eddy current decay
(exponential creep), the effect of which will then need to be taken into account. If detectable
coupling is encountered in measurements made at typical VSM sweep rates, Q shall be
h
determined by extrapolation to zero dH/dt, it having been previously determined that the Q
measured is linear in dH/dt. For specimens with a low n value in the voltage-current relation at
higher temperatures, Q shall be also determined by a similar extrapolation.
h
5.4.3.2 Proximity effect
In fine filament composites the measurer shall be alert to the possibility of a proximity effect
(PE) contribution to the hysteretic loss. The PE contribution enhances the hysteretic loss
beyond that expected for (a bundle of) individual filaments. It is a valid contribution to the total
hysteric loss and should therefore be included.
5.4.3.3 Flux jump
In thick filament composite the measurer shall be also alert to the possibility of a flux jump,
which disturbs to measure the intrinsic magnetization. The report shall include a note on flux
jump (6.3 d)).
5.4.4 Waveform of the field change
The field sweep rate shall be linear between the end-points ±H , see 3.11 and 4.7 above.
max
5.4.5 Specimen size and shape correction
Calibration shall be performed as directed above under 4.2. Furthermore, consideration shall
be given to the size and shape of the specimen with respect to those of the calibration sample.
The specimen shall be centered on the sweet spot.
For specimens smaller than the calibration sample, no size correction need be applied.
For specimens larger than the calibration sample, one of two size corrections are allowed:
a) a replica of the specimen will be fabricated from Ni and used as a secondary standard;
b) the sweet spot will be mapped out and a size and shape correction will be generated
based on the measured response.

61788-13 © IEC:2012 – 13 –
5.4.6 Allowance for addendum (background subtraction)
The measurer shall be alert to the possibility that the specimen holder and associated parts
(for example temperature sensor) may make a significant contribution to the loss. Whenever
this turns out to be the case, a correction shall be applied.
5.4.7 Data point density
In modern computer-controlled VSM measurements, it is possible to select, from a broad
range, the number of data-pairs that make up the M-H loop. If fine structure is present (for
example those describing the various features of PE magnetization), a high point density is
necessary. If point-by-point measurements are made, the M-H loop shall consist of no less
than 100 data pairs.
6 Test report
6.1 General
The report of the results of the AC loss testing shall include at least the following
specifications. The reason for any missing information shall be explained.
6.2 Initiation of the test
– Name of the laboratory performing the test
– Names of groups or persons requesting the test
– Other details concerning sponsorship of the test
6.3 Technical details
a) The superconducting composite strand – details when available
– Manufacturer and strand identification code
– Strand materials
– Strand design, for example number of re-stacks
– Cu/superconductor volume ratio within filamentary bundle and overall
– Matrix residual resistance ratio, RRR
– Twist pitch
– Filament count
– Filament diameter
b) The specimen – the strand as prepared for measurement
– Form of the specimen (bundle or coil)
• Dimensions of bundle, number of wires in bundle
• Length of the bundle
– Dimensions of coil
– Total length of strand in sample
– Sample mounting – orientation with respect to the applied field
c) Test facilities – apparatus and conditions
– Magnetometer calibration procedure and related details
– Uncertainty of field determination and calibration procedure
– Uncertainty of temperature determination and procedure used

– 14 – 61788-13 © IEC:2012
– Specify whether point-by-point or continuous applied field change and, in the latter
case, the field ramp rates used
– Number of data points taken in constructing the four segments of the M-H loop
d) Results – final report and analysis
– The measured hysteretic loss, Q , per unit volume of strand corrected to 4,2 K if
h
necessary
– Field sweep amplitude
– Temperature of measurement
– A set of typical M-H loops
– State whether proximity effect is noted
– State whether flux jumping is noted
– Discuss the dH/dt dependence of loss and if extrapolation to zero dH/dt was needed to
determine the static Q
h
– Discuss if creep-effect corrections to the low ramp-rate loss were needed

61788-13 © IEC:2012 – 15 –
Annex A
(informative)
The SQUID method of measurement

A.1 SQUID measurement principle
A SQUID basically consists of a superconducting ring, which is broken by one (r.f. SQUID) or
two (d.c. SQUID) “weak links”, where the superconductivity is strongly suppressed. These
devices exhibit a macroscopically observable quantum interference effect, which is strongly
correlated to the magnetic flux inside the ring. With suitable electronic circuitry, the quantum
interference effect can be exploited to obtain extremely accurate measurements of this
magnetic flux. Superconducting flux transformers are used to couple the total magnetic flux of
complex external superconducting pick-up coil configurations into the ring of the SQUID
sensor. A detailed treatment of the underlying physics, electronic circuits and general error
sources using SQUID sensors can be found in [5].
In SQUID magnetometers, the magnetic moment of a specimen is derived from the magnetic
flux it creates in a pick-up coil, and which can be measured accurately using the SQUID
sensor. As in the VSM measurement, the results depend on a proper calibration of the
instrument. Generally, this calibration is based on the interpretation of the measured magnetic
flux as being caused by a magnetic dipole moment. In order to suppress magnetic flux noise
and the large background flux of the applied field, the pick-up coil is replaced by a pick-up
system forming a first or second order gradiometer. The specimen is moved in the pick-up coil
system, and its magnetic moment is calculated from the output voltage of the SQUID sensor
as a function of the specimen’s position in the gradiometer coils. A periodic movement of the
sample allows changes in the magnetic moment to be monitored over a longer time scale and
avoids drift effects in the detection electronics.
In typical commercial SQUID systems, the pick-up coil diameter is a few centimeters,
comparable to the separation between the pick-up coils. In order to obtain the maximum
signal amplitude, the specimen movement also extends over a range of a few centimeters,
although it may be significantly reduced in some newer commercial models. The magnetic
field used to magnetize the specimen is created by superconducting magnets with the axis
parallel to the direction of the specimen movement.
A.2 Specimen preparation
Typical size and specimen configurations are described in 5.3. A recalibration of the
instrument (see 4.2) for the specimen geometry (see 5.4.5) is necessary if the specimen’s
dimension perpendicular to the axis of the pick-up coils is larger than typically 5 mm
(depending on the design of the pick-up coils in the specific instrument).
A.3 Specific SQUID measurement conditions and calibration
All specifications from 5.4 apply, with the exception that the point-by-point measuring mode is
necessary in SQUID magnetometers, which automatically leads to longer measuring times
and a significant reduction of the point density. Due to the low speed of the SQUID’s data
acquisition, a full magnetization loop shall consist of not less than 50 data points. Many more
than 50 may be needed in order to resolve any fine structure in the hysteresis loop.
A.4 Test report
See Clause 6.
– 16 – 61788-13 © IEC:2012
Annex B
(normative)
Extension of the standard to the measurement
of superconductors in general
B.1 Overview
The standard magnetization procedure for measuring low frequency AC loss of Cu/Nb-Ti
superconducting composites is extended to the measurement of superconductors in general
and at temperatures other than 4,2 K.
B.2 Superconductors in general
The methods described in IEC 61788-13 are extended to the measurement of unstabilized
Nb-Ti, i.e. Nb-Ti without Cu, or the Cu/Nb-Ti composite in which the Cu has been removed by
etching. In the latter case the resulting filamentary bundle may be supported by resin
impregnation.
The methods described in IEC 61788-13 are extended to the measurement of other classes of
stabilized or unstabilized superconductors in the form of round wire such as:
Sn (as processed by the
a) the low-temperature superconductors (LTSC) Nb-Ti-Ta, Nb
bronze route, the powder-in-tube route, the internal-tin route, etc), Nb Al
b) the intermediate-temperature superconductor MgB
c) the high temperature superconductors (HTSC) Bi-2212, Bi-2223, YBCO
B.3 Sample shape
All classes of wire may be measured in the form of a “short straight specimen”. Ductile wires
may also be measured as a “helical coil” or “multiturn coil”.
B.4 Sample size
The sample should be of such a size that it lies fully within the sweet spot. If a larger sample
needs to be measured a correction will have to be applied. There are two ways of applying the
correction:
a) numerically, after exploring the sample space both inside and outside the sweet spot
using a small standard calibrating sample (small Ni sphere);
b) by recalibrating the magnetometer using a standard sample (Ni) of the same shape as the
sample to be measured.
B.5 Measurement at temperatures other than 4,2 K
B.5.1 Measurement temperature
Measurements with the vibrating sample magnetometer may be performed over a wide range
of temperatures:
a) at 4,2 K, the normal boiling point of liquid He;
b) below 4,2 K by pumping on liquid He;

61788-13 © IEC:2012 – 17 –
c) above 4,2 K by a temperature-controlled stream of He gas (e.g. a needle-valve/heater
arrangement);
d) the refrigeration may be based either on liquid He itself or through the use of a cryocooler.
B.5.2 Calibration
All the measuring components of the VSM are located outside the cooled space, thereby
enabling a machine calibrated at room temperature using a standard Ni sample to perform
measurements at any temperatur
...