IEC 61788-11:2011

Superconductivity - Part 11: Residual resistance ratio measurement - Residual resistance ratio of Nb3Sn composite superconductors

IEC 61788-11:2011 covers a test method for the determination of the residual resistance ratio (RRR) of Nb3Sn composite superconductors. This method is intended for use with superconductor specimens that have a monolithic structure with rectangular or round cross-section, RRR less than 350 and cross-sectional area less than 3 mm2, and have received a reaction heat-treatment. Ideally, it is intended that the specimens be as straight as possible; however, this is not always the case, thus care must be taken to measure the specimen in its as received condition. All measurements are done without an applied magnetic field. The method described in the body of this standard is the "reference" method and optional acquisition methods are outlined in Clause A.3. This second edition cancels and replaces the first edition published in 2003. It constitutes a technical revision. The main revisions are the addition of two new annexes, "Uncertainty considerations" (Annex B) and "Uncertainty evaluation in test method of RRR for Nb3Sn" (Annex C).

Supraconductivité - Partie 11: Mesure du rapport de résistance résiduelle - Rapport de résistance résiduelle des supraconducteurs composites de Nb3Sn

La CEI 61788-11:2011 spécifie une méthode d'essai pour la détermination du rapport de résistance résiduelle (RRR) des supraconducteurs composites de Nb3Sn. Cette méthode est destinée à être utilisée avec des éprouvettes de supraconducteurs présentant une structure monolithique avec une section rectangulaire ou circulaire, un rapport RRR inférieur à 350 et une surface de section inférieure à 3 mm2, et qui ont reçu un traitement thermique de réaction. Dans l'absolu, il est prévu que les éprouvettes soient aussi droites que possible; cependant, ce n'est pas toujours le cas, c'est pourquoi il faut s'assurer que la mesure est effectuée sur des éprouvettes en l'état de livraison. Toutes les mesures sont effectuées sans appliquer de champ magnétique. La méthode décrite dans le corps de texte de la présente norme est la méthode de "référence" et des méthodes d'acquisition facultatives sont présentées à l'Article A.3. Cette deuxième édition annule et remplace la première édition parue en 2003, dont elle constitue une révision technique. Les principales révisions sont l'ajout de deux nouvelles annexes, "Considérations relatives à l'incertitude" (Annexe B) et "Evaluation de l'incertitude de la méthode d'essai de RRR de Nb3Sn" (Annexe C).

General Information

• Status: Withdrawn
• Publication Date: 10-Jul-2011
• Withdrawal Date: 02-Feb-2016
• ICS: 17.220.20 - Measurement of electrical and magnetic quantities
• ICS: 29.050 - Superconductivity and conducting materials
• Technical Committee: TC 90 - Superconductivity
• Drafting Committee: WG 4 - TC 90/WG 4
• Current Stage: WPUB - Publication withdrawn
• Completion Date: 05-Feb-2016

Standards Content (Sample)

IEC 61788-11
®

Edition 2.0 2011-07
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE


Superconductivity –
Part 11: Residual resistance ratio measurement – Residual resistance ratio of
Nb Sn composite superconductors
3

Supraconductivité –
Partie 11: Mesure du rapport de résistance résiduelle – Rapport de résistance
résiduelle des supraconducteurs composites de Nb Sn
3

IEC 61788-11:2011

---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC 61788-11
®

Edition 2.0 2011-07
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE


Superconductivity –
Part 11: Residual resistance ratio measurement – Residual resistance ratio of
Nb Sn composite superconductors
3

Supraconductivité –
Partie 11: Mesure du rapport de résistance résiduelle – Rapport de résistance
résiduelle des supraconducteurs composites de Nb Sn
3

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX S
ICS 17.220; 29.050 ISBN 978-2-88912-581-4

® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale

---------------------- Page: 3 ----------------------
– 2 – 61788-11  IEC:2011
CONTENTS
FOREWORD . 3
INTRODUCTION . 5
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
4 Requirements . 7
5 Apparatus . 7
5.1 Material of measuring base plate . 7
5.2 Length of the measuring base plate . 7
5.3 Cryostat for the resistance, R , measurement . 7
2
6 Specimen preparation. 8
7 Data acquisition and analysis . 8
7.1 Resistance (R ) at room temperature . 8
1
7.2 Resistance (R ) just above the superconducting transition . 8
2
7.3 Residual resistance ratio (RRR) . 10
8 Uncertainty and stability of the test method . 11
8.1 Temperature . 11
8.2 Voltage measurement. 11
8.3 Current . 11
8.4 Dimension . 11
9 Test report. 11
9.1 RRR value . 11
9.2 Specimen . 11
9.3 Test conditions . 12
Annex A (informative) Additional information relating to the measurement of RRR . 13
Annex B (informative) Uncertainty considerations . 15
Annex C (informative) Uncertainty evaluation in test method of RRR for Nb Sn . 19
3

Figure 1 – Relationship between temperature and resistance  . 7
Figure 2 – Voltage (U) versus temperature (T) curves and definitions of each voltage . 9

Table B.1 – Output signals from two nominally identical extensometers . 16
Table B.2 – Mean values of two output signals . 16
Table B.3 – Experimental standard deviations of two output signals. 16
Table B.4 – Standard uncertainties of two output signals . 17
Table B.5 – Coefficient of variations of two output signals. 17
Table C.1 – Uncertainty of each measurement . 20
Table C.2 – Obtained values of R , R and RRR for three Nb Sn samples. 21
1 2 3

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61788-11  IEC:2011 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________

SUPERCONDUCTIVITY –

Part 11: Residual resistance ratio measurement –
Residual resistance ratio of Nb Sn composite superconductors
3


FOREWORD
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all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
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patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 61788-11 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. The main revisions are the addition of two new annexes, "Uncertainty
considerations" (Annex B) and "Uncertainty evaluation in test method of RRR for Nb Sn"
3
(Annex C).

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– 4 – 61788-11  IEC:2011
The text of this standard is based on the following documents:
FDIS Report on voting
90/268/FDIS 90/279/RVD

Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts of the IEC 61788 series, published under the general title Superconductivity,
can be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC 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.

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61788-11  IEC:2011 – 5 –
INTRODUCTION
Copper or aluminium is used as stabilizer material in multifilamentary Nb Sn superconductors
3
and works as an electrical shunt when the superconductivity is interrupted. It also contributes
to recovery of the superconductivity by conducting the heat generated in the superconductor
to the surrounding coolant. The resistivity of copper used in the composite superconductor in
the cryogenic temperature region is an important quantity which influences the stability of
the superconductor. The residual resistance ratio is defined as a ratio of the resistance of the
superconductor at room temperature to that just above the superconducting transition.
In this International Standard, the test method for the residual resistance ratio of Nb Sn
3
composite superconductors is described. The curve method is employed for the measurement
of the resistance just above the superconducting transition. Other methods are described in
Clause A.3.

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– 6 – 61788-11  IEC:2011
SUPERCONDUCTIVITY –

Part 11: Residual resistance ratio measurement –
Residual resistance ratio of Nb Sn composite superconductors
3



1 Scope
This part of IEC 61788 covers a test method for the determination of the residual resistance
ratio (RRR) of Nb Sn composite superconductors. This method is intended for use with
3
superconductor specimens that have a monolithic structure with rectangular or round cross-
2
section, RRR less than 350 and cross-sectional area less than 3 mm , and have received a
reaction heat-treatment. Ideally, it is intended that the specimens be as straight as possible;
however, this is not always the case, thus care must be taken to measure the specimen in its
as received condition. All measurements are done without an applied magnetic field.
The method described in the body of this standard is the “reference” method and optional
acquisition methods are outlined in Clause A.3.
2 Normative references
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.
IEC 60050-815, International Electrotechnical Vocabulary – Part 815: Superconductivity
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60050-815 and the
following apply.
3.1
residual resistance ratio
RRR
the ratio of resistance at room temperature to the resistance just above the superconducting
transition
NOTE In this standard for Nb Sn composite superconductors, the room temperature is defined as 293 K (20 °C),
3
and the residual resistance ratio is obtained in Equation (1) below, where the resistance (R ) at 293 K is divided by
1
the resistance (R ) just above the superconducting transition.
2
R
1
RRR = (1)
R
2
Figure 1 shows schematically a resistance versus temperature curve acquired on a specimen while measuring
cryogenic resistance. Draw a line in Figure 1 where the resistance sharply increases (a), and draw also a line in
Figure 1 where the resistance increases gradually (b) with temperature. The value of resistance at the intersection
of these two lines at T=T *, A, is defined as resistance (R ) just above the superconducting transition.
c 2

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61788-11  IEC:2011 – 7 –

(b)
A
R
2
(a)
0
Temperature
T *
c
IEC  1603/11

Temperature T * is that at the intersection point.
c
Figure 1 – Relationship between temperature and resistance
4 Requirements
The resistance measurement both at room and cryogenic temperatures shall be performed
with the four-terminal technique.
The target relative combined standard uncertainty of this method is defined as an expanded
uncertainty (k = 2) not to exceed 10 % based on the coefficient of variation (COV) of 5 % in
the intercomparison test (see Clause C.2).
5 Apparatus
5.1 Material of measuring base plate
Material of the measuring base plate shall be copper, aluminum, silver or the like whose
thermal conductivity is equal to or better than 100 W/(m⋅K) at liquid helium temperature
(4,2 K). The surface of the material shall be covered with an insulating layer (tape or a layer
made of polyethylene terephthalate, polyester, polytetrafluoroethylene, etc.) whose thickness
is 0,1 mm or less.
5.2 Length of the measuring base plate
The measuring base plate shall be at least 30 mm long in one dimension.
5.3 Cryostat for the resistance, R , measurement
2
The cryostat shall include a specimen support structure and a liquid helium reservoir for the
resistance, R , measurement. The specimen support structure shall allow the specimen,
2
which is mounted on a measurement base plate, to be lowered and raised into and out of a
liquid helium bath. In addition, the specimen support structure shall be made so that a current

Resistance

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– 8 – 61788-11  IEC:2011
can flow through the specimen and the resulting voltage generated along the specimen can
be measured.
6 Specimen preparation
The test specimen shall have no joints or splices, and shall be 30 mm or longer. The distance
between two voltage taps (L) shall be 25 mm or longer. A thermometer for measuring
cryogenic temperature shall be attached near the specimen.
Some mechanical method shall be used to hold the specimen against the insulated layer of
the measurement base plate. Special care shall be taken during instrumentation and
installation of the specimen on the measurement base plate so that no excessive force, which
may cause undesired bending strain or tensile strain, shall be applied to the specimen.
The specimen shall be instrumented with current contacts near each end of the specimen and
a pair of voltage contacts over a central portion of the specimen. The specimen shall be
mounted on a measurement base plate for these measurements. Both resistance measure-
ments, R and R , shall be made on the same specimen and the same mounting.
1 2
7 Data acquisition and analysis
7.1 Resistance (R ) at room temperature
1
The mounted specimen shall be measured at room temperature (T (K)), where T satisfies
m m
the following condition 273 ≤ T ≤ 308. A specimen current (I (A)) shall be applied so that
m 1
2 2
the current density is in the range of 0,1 A/mm to 1 A/mm based on the total wire
cross-sectional area, and the resulting voltage (U (V)), I and T shall be recorded.
1 1 m
Equation (2) below shall be used to calculate the resistance (R ) at room temperature. The
m
resistance (R ) at 293 K shall be calculated using equation (3) for a wire with Cu stabilizer.
1
The value of R shall be set equal to R , without any temperature correction, for wires that do
1 m
not contain a pure Cu component.
U
1
R = (2)
m
I
1
R
m
R = (3)
1
[1+ 0,00393⋅ (T − 293)]
m
7.2 Resistance (R ) just above the superconducting transition
2
7.2.1 The specimen, which is still mounted as it was for the room temperature measurement,
shall be placed in the cryostat for electrical measurement specified under 5.3. Alternate
cryostats that employ a heating element to sweep the specimen temperature are described in
Clause A.2.
7.2.2 The specimen shall be slowly lowered into the liquid helium bath and cooled to liquid
helium temperature over a time period of at least 5 min.
7.2.3 During the acquisition phases of the low-temperature R measurements, a specimen
2
2
current (I ) shall be applied so that the current density is in the range of 0,1 A/mm to
2
2
10 A/mm based on the total wire cross-sectional area and the resulting voltage (U(V)), I (A),
2
and specimen temperature (T (K)) shall be recorded. In order to keep the ratio of signal to
noise high enough, the measurement shall be carried out under the condition that the

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61788-11  IEC:2011 – 9 –
absolute value of resulting voltage above the superconducting transition exceeds 10 µV. An
illustration of the data to be acquired and its analysis is shown in Figure 2.


U
(b)
U*
2+
A
(a)
U
U
0+
20+
U
U
20–
0rev
0
T
U
0–
U*
2– IEC  1604/11


Voltages with subscripts + and – are those obtained in the first and second measurements under positive and
negative currents, respectively, and U and U are those obtained at zero current. For clarity, U is not
20+ 20– 0rev
shown coincident with U . Voltages U * and U * with asterisk are those at the intersection points.
2+ 2-
0–
Figure 2 – Voltage (U) versus temperature (T) curves
and definitions of each voltage
7.2.4 When the specimen is in superconducting state and test current (I ) is applied, two
2
voltages shall be measured nearly simultaneously: U (the initial voltage recorded with a
0+
positive current polarity) and U (the voltage recorded during a brief change in applied
0rev
current polarity). A valid R measurement requires that excessive interfering voltages are not
2
present and that the specimen is initially in the superconducting state. Thus, the following
condition shall be met for a valid measurement:
|U −U |
0+ 0rev
< 1 % (4)
U
2
where U is the average voltage for the specimen in the normal state at cryogenic
2
temperature, which is defined in 7.2.10.
7.2.5 The specimen shall be gradually warmed so that it changes to the normal state
completely. When the cryostat for the resistance measurement specified under 5.3 is used,
this can be achieved simply by raising the specimen to an appropriate position above the
liquid helium level.

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– 10 – 61788-11  IEC:2011
7.2.6 The specimen voltage versus temperature curve shall be acquired with the rate of
temperature increase maintained between 0,1 K/min and 10 K/min.
7.2.7 The voltage versus temperature curve shall continue to be recorded during the
transition into the normal state, up to a temperature somewhat less than 25 K. Then, the
specimen current shall be decreased to zero and the corresponding voltage, U , shall be
20+
recorded at a temperature below 25 K.
7.2.8 The specimen shall then be slowly lowered into the liquid helium bath and cooled to
the same temperature, within ± 1 K, where the initial voltage signal U was recorded. A
0+
specimen current, I , with the same magnitude but negative polarity (polarity opposite that
2
used for the initial curve) shall be applied and the voltage U shall be recorded at this
0–
temperature. The procedural steps 7.2.5 to 7.2.7 shall be repeated to record the voltage
versus temperature curve with this negative current. In addition, the recording of U shall be
20–
made at the same temperature, within ± 1 K, where U was recorded.
20+
7.2.9 Each of the two voltages versus temperature curves shall be analyzed by drawing a
line (a) through the data where the absolute value of voltage sharply increases with
temperature (see Figure 2) and drawing a second line (b) through the data above the
transition where the voltage is raised gradually and almost linearly with temperature increase.
U * and U * in Figure 2 shall be determined at the intersection of these two lines for the
2+ 2–
positive and negative polarity curves respectively.
7.2.10 The corrected voltages, U and U , shall be calculated using the following
2+ 2–
equations, U = U * – U and U = U * – U . The average voltage, U , shall be defined
2+ 2+ 0+ 2– 2– 0– 2
as
| U −U |
2+ 2
−
 U =   (5)
2
2
7.2.11 A valid R measurement requires that the shift of thermoelectric voltage be within
2
acceptable limits during the measurements of the U and U . Thus, the following condition
2+ 2–
shall be met for a valid measurement,
|∆ −∆ |
+ −
< 3 % (6)
U
2
where ∆ and ∆ are defined as ∆ = U – U and ∆ = U – U If the R measurement
+ – + 20+ 0+ – 20– 0–. 2
does not meet the validity requirements in 7.2.4 and this subclause, then improvement steps
either in hardware or experimental operation shall be taken to meet these requirements
before results are reported.
7.2.12 Equation (7) shall be used to calculate the measured resistance (R ) just above the
2
superconducting transition.
U
2
 R =   (7)
2
I
2
7.3 Residual resistance ratio (RRR)
The RRR shall be calculated using Equation (1).

---------------------- Page: 12 ----------------------
61788-11  IEC:2011 – 11 –
8 Uncertainty and stability of the test method
8.1 Temperature
The room temperature shall be determined with a standard uncertainty not to exceed 0,6 K,
while holding the specimen, which is mounted on the measuring base plate, at room
temperature.
8.2 Voltage measurement
For the resistance measurement, the voltage signal shall be measured with a relative
standard uncertainty not to exceed 0,5 %.
8.3 Current
When the current is directly applied to the specimen with a programmable DC current source,
the specimen test current shall be determined with a standard uncertainty not to exceed 0,3 %.
When the specimen test current is determined from a voltage-current characteristic of a
standard resistor by the four-terminal technique, the standard resistor, with a relative
combined standard uncertainty not to exceed 0,3 %, shall be used .
The fluctuation of d.c. specimen test current, provided by a d.c. power supply, shall be less
than 0,5 % during every resistance measurement.
8.4 Dimension
The distance along the specimen between the two voltage taps, (L), shall be determined with
a relative combined standard uncertainty not to exceed 5 %.
9 Test report
9.1 RRR value
The obtained RRR value shall be reported as
RRR(1±U ) (n = ∙∙∙ ), (8)
re
where U = 2u (k = 2) is the expanded relative uncertainty with u denoting the uncertainty, k
re r r
is a coverage factor and n is the sampling number. It is desired that n be larger than 4 so that
the normal distribution can be assumed for the estimation of the standard deviation. If n is not
sufficiently large, a square distribution shall be assumed. In case of n = 1 the analytic method
–2
described in Annex C shall be used with b/R = 1,46 × 10 estimated from the
2
intercomparison test.
9.2 Specimen
The test report for the result of the measurements shall also include the following items, if
known:
a) manufacturer;
b) classification and/or symbol;
c) shape and area of the cross-section;
d) dimensions of the cross-sectional area;
e) number of filaments;

---------------------- Page: 13 ----------------------
– 12 – 61788-11  IEC:2011
f) diameter of the filaments;
g) Cu to non-copper ratio.
9.3 Test conditions
9.3.1 The following test conditions shall be reported for the measurements of R and R :
1 2
a) total length of the specimen;
b) distance between the voltage taps (L) ;
c) length of the current contacts;
d) transport currents (I and I );
1 2
e) current densities (I an
...